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the problem of reconstructing a multidimensional signal from its projection is uniquely multidimensional, having no 1 - d counterpart. it has applications that range from computer - aided tomography to geophysical signal processing. it is a problem which can be explored from several points of view — as a deconvolution problem, a modeling problem, an estimation problem, or an interpolation problem. = = motivation and applications = = the problem of reconstruction from projections has arisen independently in a large number of scientific fields, since it is widely applied in areas such as medical imaging, geophysical tomography, industrial radiography and so on. for example, by using ct scanner, the lesion information of the patients can be presented in 3d on the computer, which offers a new and accurate approach in diagnosis and thus has vital clinical value. = = problem statement and basics = = a projection is a linear mapping of an m { \ displaystyle m } dimensional signal into an n { \ displaystyle n } dimensional one, where n ≤ m { \ displaystyle n \ leq m }. and the objective of reconstruction is to restore the m { \ displaystyle m } dimensional signal based on the n { \ displaystyle n } dimensional signal. the following case is a 2 - d signal projected into 1d signal. the signal in the original coordinate is denoted as d ( u, v ) { \ displaystyle d ( u, v ) }. now consider a collimated beam of radiation coming from the opposite orientation of v ^ { \ displaystyle { \ hat { v } } }, producing a projection along u ^ { \ displaystyle { \ hat { u } } }. v ^ { \ displaystyle { \ hat { v } } } and u ^ { \ displaystyle { \ hat { u } } } are normal to each other, and the angle between u { \ displaystyle u } and u ^ { \ displaystyle { \ hat { u } } } is theta. the signal obtained along u ^ { \ displaystyle { \ hat { u } } } axis is defined to be p θ ( u ^ ) { \ displaystyle p _ { \ theta } ( { \ hat { u } } ) }. the relationship between the original coordinate and the rotated coordinate is given by [ u ^ v ^ ] = [ cos θ sin θ − sin θ cos θ ] [ u v ] { \ displaystyle { \ begin { bmatrix } {
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the relationship between the original coordinate and the rotated coordinate is given by [ u ^ v ^ ] = [ cos θ sin θ − sin θ cos θ ] [ u v ] { \ displaystyle { \ begin { bmatrix } { \ hat { u } } \ \ { \ hat { v } } \ end { bmatrix } } = { \ begin { bmatrix } \ cos \ theta & \ sin \ theta \ \ - \ sin \ theta & \ cos \ theta \ end { bmatrix } } { \ begin { bmatrix } u \ \ v \ end { bmatrix } } } or inversely, [ u v ] = [ cos θ − sin θ sin θ cos θ ] [ u ^ v ^ ] { \ displaystyle { \ begin { bmatrix } u \ \ v \ end { bmatrix } } = { \ begin { bmatrix } \ cos \ theta & - \ sin \ theta \ \ \ sin \ theta & \ cos \ theta \ end { bmatrix } } { \ begin { bmatrix } { \ hat { u } } \ \ { \ hat { v } } \ end { bmatrix } } } then we have p θ ( u ^ ) = − ∞ ∞ d ( u, v ) d v ^ = − ∞ ∞ d ( u ^ cos ( θ ) − v ^ sin ( θ ), u ^ sin ( θ ) + v ^ cos ( θ ) ) d v ^ { \ displaystyle p _ { \ theta } ( { \ hat { u } } ) = \ int _ { - \ infty } ^ { \ infty } d ( u, v ) \, \ mathrm { d } { \ hat { v } } = \ int _ { - \ infty } ^ { \ infty } d ( { \ hat { u } } \ cos ( \ theta ) - { \ hat { v } } \ sin ( \ theta ), { \ hat { u } } \ sin ( \ theta ) + { \ hat { v } } \ cos ( \ theta ) ) \, \ mathrm { d } { \ hat { v } } } by varying theta, a large number of projections can be obtained. given the projection - slice theorem, d ( ω, θ ) { \ displaystyle d ( \ omega, \ theta )
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##rm { d } { \ hat { v } } } by varying theta, a large number of projections can be obtained. given the projection - slice theorem, d ( ω, θ ) { \ displaystyle d ( \ omega, \ theta ) }, the slice of the fourier transform of d ( u, v ) { \ displaystyle d ( u, v ) } at angle theta, is equivalent to p θ ( ω ) { \ displaystyle p _ { \ theta } ( \ omega ) }, the fourier transform of the projection p θ ( u ^ ) { \ displaystyle p _ { \ theta } ( { \ hat { u } } ) }. therefore, the unknown d ( u, v ) { \ displaystyle d ( u, v ) } can be obtained from its fourier transform by means of the fourier transform inversion integral d ( u, v ) = 1 4 π 2 − ∞ ∞ − ∞ ∞ d ( ω 1, ω 2 ) e j ω 1 u e j ω 2 v d ω 1, ω 2 { \ displaystyle \ mathrm { d } ( u, v ) = { \ frac { 1 } { 4 \ pi ^ { 2 } } } \ int _ { - \ infty } ^ { \ infty } \ int _ { - \ infty } ^ { \ infty } d ( \ omega _ { 1 }, \ omega _ { 2 } ) e ^ { j \ omega _ { 1 } u } e ^ { j \ omega _ { 2 } v } \, \ mathrm { d } \ omega _ { 1 }, \ omega _ { 2 } } = 1 4 π 2 0 ∞ − π π d ( ω, θ ) e j ω u cos ( θ ) e j ω v s i n θ | ω | d ω d θ { \ displaystyle = { \ frac { 1 } { 4 \ pi ^ { 2 } } } \ int _ { 0 } ^ { \ infty } \ int _ { - \ pi } ^ { \ pi } d ( \ omega, \ theta ) e ^ { j \ omega u \ cos ( \ theta ) } e ^ { j \ omega vsin \ theta } { \ begin { vmatrix } \ omega \ end { vmatrix } } \, \ mathrm { d } \ omega \ mathrm { d } \ theta } = 1 4 π 2
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\ omega vsin \ theta } { \ begin { vmatrix } \ omega \ end { vmatrix } } \, \ mathrm { d } \ omega \ mathrm { d } \ theta } = 1 4 π 2 − π π 0 ∞ p θ ( ω ) e j ω ( u cos θ + v sin θ ) | ω | d ω d θ { \ displaystyle = { \ frac { 1 } { 4 \ pi ^ { 2 } } } \ int _ { - \ pi } ^ { \ pi } \ int _ { 0 } ^ { \ infty } p _ { \ theta } ( \ omega ) e ^ { j } \ omega ( u \ cos \ theta + v \ sin \ theta ) { \ begin { vmatrix } \ omega \ end { vmatrix } } \, \ mathrm { d } \ omega \ mathrm { d } \ theta } = 1 4 π 2 0 π ( − ∞ ∞ p θ ( ω ) | ω | { \ displaystyle = { \ frac { 1 } { 4 \ pi ^ { 2 } } } \ int _ { 0 } ^ { \ pi } ( \ int _ { - \ infty } ^ { \ infty } p _ { \ theta } ( \ omega ) { \ begin { vmatrix } \ omega \ end { vmatrix } } } e j ω u ^ d ω ) d θ { \ displaystyle e ^ { j \ omega { \ hat { u } } } \ mathrm { d } \ omega ) \ mathrm { d } \ theta } by taking the inverse fourier transform and assuming g ( u ^ ) = f − 1 ( | ω | 2 ) { \ displaystyle g ( { \ hat { u } } ) = { \ mathcal { f } } ^ { - 1 } ( { { \ begin { vmatrix } \ omega \ end { vmatrix } } ^ { 2 } } ) }, we get d ( u, v ) = i θ i [ p θ ( u ^ ) ∗ g θ i ( u ^ ) ] { \ displaystyle d ( u, v ) = \ sum _ { i } \ vartriangle \ theta _ { i } [ p _ { \ theta } ( { \ hat { u } } ) * g _ { \ theta i } ( { \ hat { u }
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) = \ sum _ { i } \ vartriangle \ theta _ { i } [ p _ { \ theta } ( { \ hat { u } } ) * g _ { \ theta i } ( { \ hat { u } } ) ] } = = approaches = = in practice, there are a wide rarity of methods that are utilized, most of which are reconstruct 3 - d information ( volume ) from 2 - d signals ( image ). typically used methods are ct, mri, pet and spect. and the filtered back projection based on the principles introduced above are commonly applied. = = = computed tomography ( ct ) = = = in ct, a volume is formed by stacking the axial slices. the software cuts the volume in a different plane ( usually orthogonal ). commonly, slice data is generated using an x - ray source that rotates around the object. x - ray sensors are positioned on the opposite side of the circle from the x - ray source. = = = magnetic resonance imaging ( mri ) = = = in mri, energy from an oscillating magnetic field is temporarily applied to the patient at the appropriate resonance frequency. the protons ( hydrogen atoms ) emit a radio frequency signal which is measured by a receiving coil. the radio signal can be made to encode position information by varying the main magnetic field using gradient coils. = = = positron emission tomography ( pet ) = = = the system detects pairs of gamma rays emitted indirectly by a positron - emitting radionuclide ( tracer ), which is introduced into the body on a biologically active molecule. three - dimensional images of tracer concentration within the body are then constructed by computer analysis. in modern pet - ct scanners, three dimensional imaging is often accomplished with the aid of a ct x - ray scan performed on the patient during the same session, in the same machine. = = = single - photon emission computed tomography ( spect ) = = = spect imaging is performed by using a gamma camera to acquire multiple 2 - d images ( projections ) from multiple angles. multiple projections are used to yield a 3 - d data set. this data set may then be manipulated to show thin slices along any chosen axis of the body. spect is similar to pet in its use of radioactive tracer material and detection of gamma rays, while the tracers used in spect emit gamma radiation that is measured more directly. = = see also = = 3d
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axis of the body. spect is similar to pet in its use of radioactive tracer material and detection of gamma rays, while the tracers used in spect emit gamma radiation that is measured more directly. = = see also = = 3d scanner filtered back projection algebraic reconstruction technique 3d data acquisition and object reconstruction = = references = = = = external links = = http : / / www. tecn. upf. es / ~ afrangi / ibi / reconstruction _ color _ 2. pdf http : / / opax. swin. edu. au / ~ dliley / lectures / het408 / backproj. pdf
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archimede construction systems are construction techniques achieving rhombic dodecahedral shapes, a space - filling geometry. in america, most of these systems generate building envelopes made up of as little as two panel shapes and sizes, this feature allowing for maximum industrialization. these panels are generally pressure injected with a rigid structural insulating foam like polyurethane. in europe and asia, post and beam structure often create a dodecahedral shape that is later filled with different cladding materials. although the basic geometry sometimes contains an entire house, most applications of the system are an agglomeration of cells each forming a rhombic dodecahedral living space that can be a room or a larger living area when combined with adjacent dodecahedral modules. = = history = = the peculiar three - dimensional structure of the honey bee comb has intrigued for thousands of years. it is quite possible that some isolated construction project used a scaled - up version of this zonohedron, however a largely visible use of these shapes only appeared in the early 1980s. les systemes archimede inc. of tring junction qc started to produce applying us4462191, a patent owned by j. poirier who also co - founded the manufacturing firm with placide poulin. = = references = = = = external links = = high - tech housing, popular science magazine why rhombic dodecahedral shells are so strong, text and illustrations by j. b. poirier, arch. arctic refuges on stilts, forbes magazine housing industry takes some tips from the bees, the montreal gazette prefabs doing well, the montreal gazette
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sand sheets are flat, gently undulating plots of sand surfaced by grains that may be too large for saltation. they form approximately 40 percent of aeolian depositional surfaces. sand sheets exist where grain size is too large, or wind velocities too low, for dunes to form. = = references = =
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a primary standard in metrology is a standard that is sufficiently accurate such that it is not calibrated by or subordinate to other standards. primary standards are defined via other quantities like length, mass and time. primary standards are used to calibrate other standards referred to as working standards. see hierarchy of standards. = = in chemistry = = standards are used in analytical chemistry. here, a primary standard is typically a reagent which can be weighed easily, and which is so pure that its weight is truly representative of the number of moles of substance contained. features of a primary standard include : high purity stability ( low reactivity ) low hygroscopicity ( to minimize weight changes due to humidity ) high equivalent weight ( to minimize weighing errors ) long lasting molar solution i. e. concentration remains unchanged for long periods of time non - toxicity ready and cheap availability ( the last two are not as essential as the first four. ) some examples of primary standards for titration of solutions, based on their high purity, are provided : arsenic trioxide for making sodium arsenite solution for standardisation of sodium periodate solution ( until ph. eur. 3, appendix 2001 also for iodine and cerium ( iv ) sulfate solutions, since ph. eur. 4, 2002 standardised by sodium thiosulfate ) benzoic acid for standardisation of waterless basic solutions : ethanolic sodium and potassium hydroxide, tbah, and alkali methanolates in methanol, isopropanol, or dmf potassium bromate ( kbro3 ) for standardisation of sodium thiosulfate solutions potassium hydrogen phthalate ( usually called khp ) for standardisation of aqueous base and perchloric acid in acetic acid solutions sodium carbonate for standardisation of aqueous acids : hydrochloric, sulfuric acid and nitric acid solutions ( but not acetic acid ) sodium chloride for standardisation of silver nitrate solutions sulfanilic acid for standardisation of sodium nitrite solutions zinc powder, after being dissolved in sulfuric or hydrochloric acid, for standardization of edta solutions such standards are often used to make standard solutions. these primary standards are used in titration and are essential for determining unknown concentrations or preparing working standards. = = see also = = technical standard = = references = = = = external links = = analytical standards. department of chemistry, university of adelaide, australia.
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corporate jargon ( variously known as corporate speak, corporate lingo, corpo lingo, business speak, business jargon, management speak, workplace jargon, corpospeak, corporatese, or commercialese ) is the jargon often used in large corporations, bureaucracies, and similar workplaces. the language register of the term is generally being presented in a negative light or disapprovingly. it is often considered to be needlessly obscure or, alternatively, used to disguise an absence of information. its use in corporations and other large organisations has been widely noted in media. marketing speak is a related label for wording styles used to promote a product or service. = = coinage and use = = corporate speak is associated with managers of large corporations, business management consultants, and occasionally government. reference to such jargon is typically derogatory, implying the use of long, complicated, or obscure words ; abbreviations ; euphemisms ; and acronyms. for that reason some of its forms may be considered as an argot. some of these words may be neologisms or inventions, designed purely to fit the specialized meaning of a situation or even to " spin " negative situations as positive situations, for example in the practice of greenwashing. although it is pervasive in the education field, its use has been criticized as reflecting a sinister view of students as commodities and schools as retail outlets. = = criticism = = the use of corporate jargon is criticised for its lack of clarity as well as for its tedium, making meaning and intention opaque and understanding difficult. it is also criticized for not only enabling delusional thoughts, but allowing them to be seen as an asset in the workplace. corporate jargon has been criticized as " pompous " and " a tool for making things seem more impressive than they are ". steven poole writes that it is " engineered to deflect blame, complicate simple ideas, obscure problems, and perpetuate power relations ". marketing speak is a related label for wording styles used to promote a product or service to a wide audience by seeking to create the impression that the vendors of the service possess a high level of sophistication, skill, and technical knowledge. such language is often used in marketing press releases, advertising copy, and prepared statements read by executives and politicians. = = examples = = many corporate - jargon terms have straightforward meanings in other contexts ( e. g., leverage in physics, or picked up
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is often used in marketing press releases, advertising copy, and prepared statements read by executives and politicians. = = examples = = many corporate - jargon terms have straightforward meanings in other contexts ( e. g., leverage in physics, or picked up with a well - defined meaning in finance ), but are used more loosely in business speak. for example, a deliverable can become any service or product. the word team had specific meanings in agriculture and in sport before becoming a ubiquitous synonym for a group spanning one or more levels in a corporate organisation. the phrases going forward or moving forward make a confident gesture towards the future, but are generally vague on timing, which usually means they can be removed from a sentence with little or no effect on its overall meaning. in order to obfuscate or distract from unpleasant or unwanted news, filler such as the phrase " at this time " or overly complicated grammatical constructions – e. g. usage of the present progressive – is frequently used at the beginning of a sentence despite its clear redundancy. examples include " at this time, we have decided we are not going to move forward with your application " when " we have decided not to move forward with your application " would suffice. legal terms such as chapter 11 can be used : for example, chapter 11, title 11, united states code is about us bankruptcy. some systems of corporate jargon recycle pop ethics with terms such as responsibility. corporate speak in non - english - speaking countries frequently contains borrowed english acronyms, words, and usages. russian - speakers, for instance, may eschew native constructions and use words such as лидер ( literally : lider for'leader') or adopt forms such as пиарщик ( piarshchik for'pr specialist'). jargon, like other manifestations of language, can change over time ; and management fads may influence management - speak. this changing popularity over time can be seen in the english corpus used by google books ngram viewer. = = see also = = academese buzzword bingo corporate communication corporate identity corporate propaganda doublespeak headlinese journalese legalese military terminology officialese weasel word = = references = = = = further reading = = bryan garner ( 2011 ). dictionary of modern legal usage. oxford university press. isbn 978 - 0195384208., regarded as an authoritative guide to legal language, and aimed at the practicing lawyer. maria fraddosio
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= bryan garner ( 2011 ). dictionary of modern legal usage. oxford university press. isbn 978 - 0195384208., regarded as an authoritative guide to legal language, and aimed at the practicing lawyer. maria fraddosio, new els : english for law students ( naples, edizioni giuridiche simone, 2008 ) is a course book for italian university students. bbci ( 2006 ) " workplace jargon isolates staff " [ 1 ] reef business information ( 2006 ) " managers unable to communicate with staff, " personnel today = = external links = = business terms and business jargon explained archived 2019 - 10 - 10 at the wayback machine corporate gibberish generator corporatepoems. com corporate language rating business buzzword generator example of a generator of random plausible business - speak sentences jargon grader database of over 700 corporate jargon terms business english dictionary for corporate jargon
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there is an established practice of using the electrical conductance of blood ( pv loops ) in heart ventricles to determine the instantaneous volume of the ventricle. this technique involves inserting a tetra - polar catheter into the ventricle and measuring conductance. this measured conductance is a combination of blood and muscle and various techniques are used to identify the blood conductance from the total measured conductance. blood conductance can then be converted to volume using a linear ( baan ) or a non - linear ( wei ) relationship that relates conductance to volume. = = traditional conductance technology = = this approach is based on the idea that the total conductance, g, of a fluid between two electrodes is a function of the fluid's conductivity ( reciprocal of resistivity ) and volume. in cardiology, a tetra - polar catheter is inserted into the ventricle and a constant current ( i ) is applied across the two outer electrodes. this generates an electrical field within the ventricle and the two inner electrodes measure a voltage generated due to the electric field. this measured voltage ( v ) is used to determine conductance through a modified version of ohm's law. conductance ( g ) is the reciprocal of resistance ( r ) which changes the standard ohm's equation from v = ir to v = i / g. conductance is then related to blood volume though baan's equation. when used in cardiology, the electric field generated is not limited to the blood ( the fluid of interest ) but also penetrates the heart wall, giving rise to additional conductance often called " parallel conductance " or " muscle conductance ", gm which must be removed. various techniques have been attempted to remove the gm contribution with varying degrees of success. the most common method is the hypertonic saline technique which involves injecting a bolus of hypertonic saline into the ventricle to alter blood conductivity without affecting the surrounding muscle. another less commonly used technique involves evacuating the ventricle of blood and measuring muscle conductance alone with a conductance catheter. clearly both techniques are unreliable, somewhat invasive and fail to account for the continuous variation in gm over the cardiac cycle. = = improved admittance technology = = the admittance technique is an improvement over the conductance technique for the real - time removal of muscle conductance gm. blood and muscle respond to alternating ( ac ) electrical currents very differently. blood is purely resist
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= = improved admittance technology = = the admittance technique is an improvement over the conductance technique for the real - time removal of muscle conductance gm. blood and muscle respond to alternating ( ac ) electrical currents very differently. blood is purely resistive while muscle has both resistive and capacitive properties. the fixed charges in muscle cells create a significant reactance that causes a phase shift ( time delay ) in the measured signal, relative to the excitation signal. admittance technology uses this phase shift to determine the instantaneous muscle conductance and remove it from the total measured conductance. = = = removal of gm = = = the total admittance ( y ), of the blood filled ventricle is given by y = gb + gm + iωcm where : gb is the measured conductance of the blood ( the desired signal ) gm is the measured conductance of the cardiac muscle ( unwanted signal ) cm is the measured capacitance of the cardiac muscle ω is the angular frequency of the excitation signal the signals gm and cm are both properties of cardiac muscle and vary in a fixed ratio. thus the ratio of gm to cm is equal to the ratio of muscle conductivity ( σ ) to muscle permittivity ( ε ). the ratio σ / ε is the constant of proportionality. although both σ and ε are functions of the health of the heart tissue, they are relatively constant for short periods of time. using this proportionality, one can rewrite the equation for gm as gm = ( σ / ε ) cm note that the imaginary component of y depends only on the amount of muscle in the field of the catheter. this makes it easy to isolate by measuring the phase shift, φ, of the measured signal : cos ( φ ) = ( gb + gm ) / y sin ( φ ) = ωcm / y hence, cm = y. sin ( φ ) / ω also, gm = ( σ / ε ) cm thus, blood conductance is determined as gb = y. cos ( φ ) - gm wei's equations can be applied to this calculated blood conductance gb to obtain blood volume. unlike baan's equation, wei's equation takes into account the non - linear nature of the electrical field and the dynamic nature of the cardiac cycle to give a more accurate representation of the blood volume. = = experimental results = = admittance technique involves the measurement of both phase angle and total conductance in the ventricle. thus, it is possible
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and the dynamic nature of the cardiac cycle to give a more accurate representation of the blood volume. = = experimental results = = admittance technique involves the measurement of both phase angle and total conductance in the ventricle. thus, it is possible to observe how the parallel conductance ( muscle conductance ) varies throughout the cardiac cycle. a plot showing both the blood and muscle contribution are shown in the figure. = = references = = = = further reading = = wei cl, valvano jw, feldman md, nahrendorf m, peshock r, pearce ja ( august 2007 ). " volume catheter parallel conductance varies between end - systole and end - diastole ". ieee trans biomed eng. 54 ( 8 ) : 1480 – 9. doi : 10. 1109 / tbme. 2007. 890732. pmid 17694869. s2cid 15306967. clark je, kottam a, motterlini r, marber ms ( 2009 ). " measuring left ventricular function in the normal, infarcted and corm - 3 - preconditioned mouse heart using complex admittance - derived pressure volume loops ". j pharmacol toxicol methods. 59 ( 2 ) : 94 – 9. doi : 10. 1016 / j. vascn. 2008. 10. 007. pmid 19059354. us 7925335, feldman, marc d. ; pearce, john a. ; valvano, jonathan w. ; wei, chia - ling, " method and apparatus for determining cardiac performance in a patient with a conductance catheter ", published april 12, 2011
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bone segment navigation is a surgical method used to find the anatomical position of displaced bone fragments in fractures, or to position surgically created fragments in craniofacial surgery. such fragments are later fixed in position by osteosynthesis. it has been developed for use in craniofacial and oral and maxillofacial surgery. bone segment navigation is a patented surgical procedure, using a frameless and markerless registration technique. it uses for the first time natural registration surfaces instead of single artificial x - ray visible markers, in order to achieve a higher precision ( 1 mm and better ). previous methods of cutting and watzinger do not meet the criteria of bone segment navigation. after an accident or injury, a fracture can be produced and the resulting bony fragments can be displaced. in the oral and maxillofacial area, such a displacement could have a major effect both on facial aesthetics and organ function : a fracture occurring in a bone that delimits the orbit can lead to diplopia ; a mandibular fracture can induce significant modifications of the dental occlusion ; in the same manner, a skull ( neurocranium ) fracture can produce an increased intracranial pressure. in severe congenital malformations of the facial skeleton surgical creation of usually multiple bone segments is required with precise movement of these segments to produce a more normal face. = = surgical planning and surgical simulation = = an osteotomy is a surgical intervention that consists of cutting through bone and repositioning the resulting fragments in the correct anatomical place. to insure optimal repositioning of the bony structures by osteotomy, the intervention can be planned in advance and simulated. the surgical simulation is a key factor in reducing the actual operating time. often, during this kind of operation, the surgical access to the bone segments is very limited by the presence of the soft tissues : muscles, fat tissue and skin - thus, the correct anatomical repositioning is very difficult to assess, or even impossible. preoperative planning and simulation on models of the bare bony structures can be done. an alternate strategy is to plan the procedure entirely on a ct scan generated model and output the movement specifications purely numerically. = = materials and devices needed for preoperative planning and simulation = = the osteotomies performed in orthognathic surgery are classically planned on cast models of the tooth - bearing jaws, fixed in an articulator. for edentulous patients, the surgical planning may be made by using stereo
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= the osteotomies performed in orthognathic surgery are classically planned on cast models of the tooth - bearing jaws, fixed in an articulator. for edentulous patients, the surgical planning may be made by using stereolithographic models. these tridimensional models are then cut along the planned osteotomy line, slid and fixed in the new position. since the 1990s, modern techniques of presurgical planning were developed – allowing the surgeon to plan and simulate the osteotomy in a virtual environment, based on a preoperative ct or mri ; this procedure reduces the costs and the duration of creating, positioning, cutting, repositioning and refixing the cast models for each patient. = = transferring the preoperative planning to the operating theatre = = the usefulness of the preoperative planning, no matter how accurate, depends on the accuracy of the reproduction of the simulated osteotomy in the surgical field. the transfer of the planning was mainly based on the surgeon's visual skills. different guiding headframes were further developed to mechanically guide bone fragment repositioning. such a headframe is attached to the patient's head, during ct or mri, and surgery. there are certain difficulties in using this device. first, exact reproducibility of the headframe position on the patient's head is needed, both during ct or mri registration, and during surgery. the headframe is relatively uncomfortable to wear, and very difficult or even impossible to use on small children, who can be uncooperative during medical procedures. for this reason headframes have been abandoned in favor of frameless stereotaxy of the mobilized segments with respect to the skull base. intraoperative registration of the patient's anatomy with the computer model is done such that pre - ct placement of fiducial points is not necessary. = = surgical segment navigator = = initial bone fragment positioning efforts using an electro - magnetic system were abandoned due to the need for an environment without ferrous metals. in 1991 taylor at ibm working in collaboration with the craniofacial surgery team at new york university developed a bone fragment tracking system based on an infrared ( ir ) camera and ir transmitters attached to the skull. this system was patented by ibm in 1994. at least three ir transmitters are attached in the neurocranium area to compensate the movements of the patient's head. there are three or more ir transmitters are attached to the bones where the oste
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system was patented by ibm in 1994. at least three ir transmitters are attached in the neurocranium area to compensate the movements of the patient's head. there are three or more ir transmitters are attached to the bones where the osteotomy and bone repositioning is about to be performed onto. the 3d position of each transmitter is measured by the ir camera, using the same principle as in satellite navigation. a computer workstation is constantly visualizing the actual position of the bone fragments, compared with the predetermined position, and also makes real - time spatial determinations of the free - moving bony segments resulting from the osteotomy. thus, fragments can be very accurately positioned into the target position, predetermined by surgical simulation. more recently a similar system, the surgical segment navigator ( ssn ), was developed in 1997 at the university of regensburg, germany, with the support of the carl zeiss company. = = references = =
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in chemistry, molecular symmetry describes the symmetry present in molecules and the classification of these molecules according to their symmetry. molecular symmetry is a fundamental concept in chemistry, as it can be used to predict or explain many of a molecule's chemical properties, such as whether or not it has a dipole moment, as well as its allowed spectroscopic transitions. to do this it is necessary to use group theory. this involves classifying the states of the molecule using the irreducible representations from the character table of the symmetry group of the molecule. symmetry is useful in the study of molecular orbitals, with applications to the huckel method, to ligand field theory, and to the woodward – hoffmann rules. many university level textbooks on physical chemistry, quantum chemistry, spectroscopy and inorganic chemistry discuss symmetry. another framework on a larger scale is the use of crystal systems to describe crystallographic symmetry in bulk materials. there are many techniques for determining the symmetry of a given molecule, including x - ray crystallography and various forms of spectroscopy. spectroscopic notation is based on symmetry considerations. = = point group symmetry concepts = = = = = elements = = = the point group symmetry of a molecule is defined by the presence or absence of 5 types of symmetry element. symmetry axis : an axis around which a rotation by 360 ∘ n { \ displaystyle { \ tfrac { 360 ^ { \ circ } } { n } } } results in a molecule indistinguishable from the original. this is also called an n - fold rotational axis and abbreviated cn. examples are the c2 axis in water and the c3 axis in ammonia. a molecule can have more than one symmetry axis ; the one with the highest n is called the principal axis, and by convention is aligned with the z - axis in a cartesian coordinate system. plane of symmetry : a plane of reflection through which an identical copy of the original molecule is generated. this is also called a mirror plane and abbreviated σ ( sigma = greek " s ", from the german'spiegel'meaning mirror ). water has two of them : one in the plane of the molecule itself and one perpendicular to it. a symmetry plane parallel with the principal axis is dubbed vertical ( σv ) and one perpendicular to it horizontal ( σh ). a third type of symmetry plane exists : if a vertical symmetry plane additionally bisects the angle between two 2 - fold rotation axes perpendicular to the principal axis, the plane is dubbed dihedral ( σd ).
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it horizontal ( σh ). a third type of symmetry plane exists : if a vertical symmetry plane additionally bisects the angle between two 2 - fold rotation axes perpendicular to the principal axis, the plane is dubbed dihedral ( σd ). a symmetry plane can also be identified by its cartesian orientation, e. g., ( xz ) or ( yz ). center of symmetry or inversion center, abbreviated i. a molecule has a center of symmetry when, for any atom in the molecule, an identical atom exists diametrically opposite this center an equal distance from it. in other words, a molecule has a center of symmetry when the points ( x, y, z ) and ( −x, −y, −z ) of the molecule always look identical. for example, whenever there is an oxygen atom in some point ( x, y, z ), then there also has to be an oxygen atom in the point ( −x, −y, −z ). there may or may not be an atom at the inversion center itself. an inversion center is a special case of having a rotation - reflection axis about an angle of 180° through the center. examples are xenon tetrafluoride ( a square planar molecule ), where the inversion center is at the xe atom, and benzene ( c6h6 ) where the inversion center is at the center of the ring. rotation - reflection axis : an axis around which a rotation by 360 ∘ n { \ displaystyle { \ tfrac { 360 ^ { \ circ } } { n } } }, followed by a reflection in a plane perpendicular to it, leaves the molecule unchanged. also called an n - fold improper rotation axis, it is abbreviated sn. examples are present in tetrahedral silicon tetrafluoride, with three s4 axes, and the staggered conformation of ethane with one s6 axis. an s1 axis corresponds to a mirror plane σ and an s2 axis is an inversion center i. a molecule which has no sn axis for any value of n is a chiral molecule. identity, abbreviated to e, from the german'einheit'meaning unity. this symmetry element simply consists of no change : every molecule has this symmetry element, which is equivalent to a c1 proper rotation. it must be included in the list of symmetry elements so that they form a mathematical group, whose definition requires inclusion of the identity element. it is so called because it is analogous
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molecule has this symmetry element, which is equivalent to a c1 proper rotation. it must be included in the list of symmetry elements so that they form a mathematical group, whose definition requires inclusion of the identity element. it is so called because it is analogous to multiplying by one ( unity ). = = = operations = = = the five symmetry elements have associated with them five types of symmetry operation, which leave the geometry of the molecule indistinguishable from the starting geometry. they are sometimes distinguished from symmetry elements by a caret or circumflex. thus, cn is the rotation of a molecule around an axis and e is the identity operation. a symmetry element can have more than one symmetry operation associated with it. for example, the c4 axis of the square xenon tetrafluoride ( xef4 ) molecule is associated with two c4 rotations in opposite directions ( 90° and 270° ), a c2 rotation ( 180° ) and c1 ( 0° or 360° ). because c1 is equivalent to e, s1 to σ and s2 to i, all symmetry operations can be classified as either proper or improper rotations. for linear molecules, either clockwise or counterclockwise rotation about the molecular axis by any angle φ is a symmetry operation. = = symmetry groups = = = = = groups = = = the symmetry operations of a molecule ( or other object ) form a group. in mathematics, a group is a set with a binary operation that satisfies the four properties listed below. in a symmetry group, the group elements are the symmetry operations ( not the symmetry elements ), and the binary combination consists of applying first one symmetry operation and then the other. an example is the sequence of a c4 rotation about the z - axis and a reflection in the xy - plane, denoted σ ( xy ) c4. by convention the order of operations is from right to left. a symmetry group obeys the defining properties of any group. closure property : this means that the group is closed so that combining two elements produces no new elements. symmetry operations have this property because a sequence of two operations will produce a third state indistinguishable from the second and therefore from the first, so that the net effect on the molecule is still a symmetry operation. this may be illustrated by means of a table. for example, the point group c3 contains three symmetry operations : rotation by 120°, c3, rotation by 240°, c32
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the net effect on the molecule is still a symmetry operation. this may be illustrated by means of a table. for example, the point group c3 contains three symmetry operations : rotation by 120°, c3, rotation by 240°, c32 and rotation by 360°, which is equivalent to identity, e. the group c3 is therefore not the same as the operation c3, although the same notation is used. this table also illustrates the following properties associative property : existence of identity property : existence of inverse element : the order of a group is the number of elements in the group. for groups of small orders, the group properties can be easily verified by considering its composition table, a table whose rows and columns correspond to elements of the group and whose entries correspond to their products. = = = point groups = = = the successive application ( or composition ) of one or more symmetry operations of a molecule has an effect equivalent to that of some single symmetry operation of the molecule. for example, a c2 rotation followed by a σv reflection is seen to be a σv'symmetry operation : σv * c2 = σv '. ( " operation a followed by b to form c " is written ba = c ). moreover, the set of all symmetry operations ( including this composition operation ) obeys all the properties of a group, given above. so ( s, * ) is a group, where s is the set of all symmetry operations of some molecule, and * denotes the composition ( repeated application ) of symmetry operations. this group is called the point group of that molecule, because the set of symmetry operations leave at least one point fixed ( though for some symmetries an entire axis or an entire plane remains fixed ). in other words, a point group is a group that summarises all symmetry operations that all molecules in that category have. the symmetry of a crystal, by contrast, is described by a space group of symmetry operations, which includes translations in space. = = = examples of point groups = = = assigning each molecule a point group classifies molecules into categories with similar symmetry properties. for example, pcl3, pof3, xeo3, and nh3 all share identical symmetry operations. they all can undergo the identity operation e, two different c3 rotation operations, and three different σv plane reflections without altering their identities, so they are placed in one point group, c3v, with order 6. similarly, water ( h2o ) and hydrogen sulfide
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e, two different c3 rotation operations, and three different σv plane reflections without altering their identities, so they are placed in one point group, c3v, with order 6. similarly, water ( h2o ) and hydrogen sulfide ( h2s ) also share identical symmetry operations. they both undergo the identity operation e, one c2 rotation, and two σv reflections without altering their identities, so they are both placed in one point group, c2v, with order 4. this classification system helps scientists to study molecules more efficiently, since chemically related molecules in the same point group tend to exhibit similar bonding schemes, molecular bonding diagrams, and spectroscopic properties. point group symmetry describes the symmetry of a molecule when fixed at its equilibrium configuration in a particular electronic state. it does not allow for tunneling between minima nor for the change in shape that can come about from the centrifugal distortion effects of molecular rotation. = = = common point groups = = = the following table lists many of the point groups applicable to molecules, labelled using the schoenflies notation, which is common in chemistry and molecular spectroscopy. the descriptions include common shapes of molecules, which can be explained by the vsepr model. in each row, the descriptions and examples have no higher symmetries, meaning that the named point group captures all of the point symmetries. = = laue classes = = all of the group operations described above and the symbols for crystallographic point groups themselves were first published by arthur schoenflies in 1891 but the groups had been applied by other researchers to the external morphology of crystals much earlier in the 19th century. in 1914 max von laue published the results of experiments using x - ray diffraction to elucidate the internal structures of crystals producing a limited version of the table of " laue classes " shown. when adapted for molecular work this table first divides point groups into three kinds : asymmetric, symmetric and spherical tops. these are categories based on the angular momentum of molecules, having respectively 3, 2 and 1 distinct values of angular momentum, becoming more symmetrical down the table. a further sub - division into systems is defined by the rotational group g in the leftmost column then into rows of laue classes that take the form of cyclic and dihedral groups in the first two categories and tetrahedral and octahedral classes in the third. rotational groups occur in the first column and define the non - rotational groups in their class. the second and third
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take the form of cyclic and dihedral groups in the first two categories and tetrahedral and octahedral classes in the third. rotational groups occur in the first column and define the non - rotational groups in their class. the second and third columns contain non - rotational groups belonging to the same abstract group as that in the first column a fourth column contains groups that are a direct product of their defining rotational group with space inversion ( parity inversion ) and so are of twice the order of other members of the class. groups in this column contain the inversion operation itself as a member. for example, seven groups in the hexagonal system all contain the c6 cyclic system, mostly as physical rotational group but in the third column of the table as an abstract group. so, c6 and c3h are distinct manifestations of the same group while c6h is simply c6 x i. groups d6, c6v and d3h are also example of the same abstract group and d6h is the direct product d6 x i. it is difficult to overstate the importance of the laue class in the applications of point groups to the description of physical properties at the molecular level. since all the point groups of a laue class have the same abstract structure, they also have exactly the same irreducible representations and character tables. any representation of one is automatically a representation of the class and any group in it. one important point is that higher symmetry molecules do not cease to have the lower symmetry of their subgroups. using the hexagonal example again, picture the series of groups c6 of order 6, d6 of order 12 and d6h of order 24, each group being of twice the order of the previous one. once the irreducible representations of a physical example of a cyclic group have been found it is usually a simple process to extend this to the higher order groups. laue found that x - ray diffraction was unable to distinguish between such groups tetrahedral and octahedral point groups have a relationship similar to that between cyclic and dihedral groups and the tetrahedral g occurs in all cubic groups. = = representations and their characters = = a set of matrices that multiply together in a way that mimics the multiplication table of the elements of a group is called a representation of the group. the simplest method of obtaining a representation of molecular group transformations is to trace the movements of atoms in a molecule when symmetry operations are applied. for example, a water molecule belonging
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multiplication table of the elements of a group is called a representation of the group. the simplest method of obtaining a representation of molecular group transformations is to trace the movements of atoms in a molecule when symmetry operations are applied. for example, a water molecule belonging to the c2v point group might have an oxygen atom labelled 1 and two hydrogen atoms labelled 2 and 3 as shown in the right hand column vector below. if the hydrogen atoms are imagined to rotate by 180 degrees about an axis passing through the oxygen atom we have the familiar c2 operation of this point group. the oxygen atom in position number 1 stays in position but the atoms in positions 2 and 3 are moved to positions 3 and 2 in the resulting column vector. the matrix connecting the two provides a 3 x 3 representation for this operation. [ 1 3 2 ] = [ 1 0 0 0 0 1 0 1 0 ] × [ 1 2 3 ] { \ displaystyle { \ begin { bmatrix } 1 \ \ 3 \ \ 2 \ \ \ end { bmatrix } } = { \ begin { bmatrix } 1 & 0 & 0 \ \ 0 & 0 & 1 \ \ 0 & 1 & 0 \ \ \ end { bmatrix } } \ times { \ begin { bmatrix } 1 \ \ 2 \ \ 3 \ \ \ end { bmatrix } } _ { } } this point group only contains four operations and matrices for the other three operations are obtained similarly, including the identity matrix which just contains 1's on the leading diagonal ( top left to bottom right ) and 0's elsewhere. having obtained the representation matrices in this way it is not difficult to show that they multiply out in exactly the same way as the operations themselves. [ 1 0 0 0 0 1 0 1 0 ] c 2 × [ 1 0 0 0 1 0 0 0 1 ] σ v = [ 1 0 0 0 0 1 0 1 0 ] σ v ′ { \ displaystyle \ underbrace { \ begin { bmatrix } 1 & 0 & 0 \ \ 0 & 0 & 1 \ \ 0 & 1 & 0 \ \ \ end { bmatrix } } _ { c _ { 2 } } \ times \ underbrace { \ begin { bmatrix } 1 & 0 & 0 \ \ 0 & 1 & 0 \ \ 0 & 0 & 1 \ \ \ end { bmatrix } } _ { \ sigma _ { \ text { v } } } = \ underbrace {
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##rix } 1 & 0 & 0 \ \ 0 & 1 & 0 \ \ 0 & 0 & 1 \ \ \ end { bmatrix } } _ { \ sigma _ { \ text { v } } } = \ underbrace { \ begin { bmatrix } 1 & 0 & 0 \ \ 0 & 0 & 1 \ \ 0 & 1 & 0 \ \ \ end { bmatrix } } _ { \ sigma'_ { \ text { v } } } } although an infinite number of such representations exist, the irreducible representations ( or " irreps " ) of the group are all that are needed as all other representations of the group can be described as a direct sum of the irreducible representations. the first step in finding the irreps making up a given representation is to sum up the values of the leading diagonals for each matrix so, taking the identity matrix first then the matrices in the order above, one obtains ( 3, 1, 3, 1 ). these values are the traces or characters of the four matrices. asymmetric point groups such as c2v only have 1 - dimensional irreps so the character of an irrep is exactly the same is the irrep itself and the following table can be interpreted as irreps or characters. looking again at the characters obtained for the 3d representation above ( 3, 1, 3, 1 ), we only need simple arithmetic to break this down into irreps. clearly, e = 3 means there are three irreps and a c2 representation sum of 1 means there must be two a and one b irreps so the only combination that adds up to the characters derived is 2a1 + b1 robert mulliken was the first to publish character tables in english and so the notation used to label irreps in the above table is called mulliken notation. for asymmetric groups it consists of letters a and b with subscripts 1 and 2 as above and subscripts g and u as in the c2h example below. ( subscript 3 also appears in d2 ) the irreducible representations are those matrix representations in which the matrices are in their most diagonal form possible and for asymmetric groups this means totally diagonal. one further thing to note about the irrep / character table above is the appearance of polar and axial base vector symbols on the right hand side. this tells us that, for example, cartesian base vector x transforms as irrep b1 under
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one further thing to note about the irrep / character table above is the appearance of polar and axial base vector symbols on the right hand side. this tells us that, for example, cartesian base vector x transforms as irrep b1 under the operations of this group. the same collection of product base vectors is used for all asymmetric groups but symmetric and spherical groups use different sets of product base vectors. point group c2h has the operations { e, c2, i, σh } and the 1, 5 - dibromonapthalene ( c10h6br2 ) shown in the figure belongs to this symmetry group. it is possible to construct four 18 x 18 matrices representing the transformations of atoms during its symmetry operations in the style of the water molecule example above and reduce it to 18 1d irreps. notice however that carbon atom number 1 either stays in place or it is exchanged with carbon atom number 5 and these two atoms can be analysed separately from all the other atoms in the molecule. the transformation matrix for these two atoms alone during the molecular c2 rotation is [ 5 1 ] = [ 0 1 1 0 ] × [ 1 5 ] { \ displaystyle { \ begin { bmatrix } 5 \ \ 1 \ \ \ end { bmatrix } } = { \ begin { bmatrix } 0 & 1 \ \ 1 & 0 \ \ \ end { bmatrix } } \ times { \ begin { bmatrix } 1 \ \ 5 \ \ \ end { bmatrix } } _ { } } with character 0. when this computation is carried out for each of the operations above the characters obtained are ( 2, 0, 0. 2 ) because two operations leave the atoms in place and two move them. the irrep table for this group is below. the first column tells us there are two1d irreps, the second column ( c2 ) that there is one a and one b while columns 3 and 4 reveal that one irrep has subscript g the other has to have subscript u. this means that the irreps resulting from the two atoms are ag + bu. in fact, the 18 atoms in this molecule are paired off in exactly the same way as carbon atoms 1 and 5 so that, from a symmetry perspective, the atom consists of 9 pairs of equivalent atoms related through symmetry. it follows that each pair contributes the same irreps as the pair examined above to give a total 18 dimensional irrep result
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1 and 5 so that, from a symmetry perspective, the atom consists of 9 pairs of equivalent atoms related through symmetry. it follows that each pair contributes the same irreps as the pair examined above to give a total 18 dimensional irrep result of 9 ( ag + bu ). symmetric point group representations symmetric point groups are divided into systems based on the increasing order of the main rotational axis from three to infinity. systems are in turn divided into cyclic and dihedral groups and within a system the order of the dihedral group is twice that of the cyclic group. cyclic groups only have one dimensional representations as shown in the table of irreps and the number of irreps is equal to the order of the group. the irreps shown use standard notation for the rotational group of a class but mulliken sometimes gave different symbols to other members of the same class even though they belong to the same abstract group and therefore have the same irreps. dihedral point groups contain a cyclic group of the same rotational order : so group dn always contains group cn as an index - 2 subgroup. it follows that dihedral irreps are superimposed on cyclic irreps because the cyclic group within a dihedral one does not cease to be a cyclic group. a dihedral group also contains a 2 - fold rotational axis at right angles to the main cyclic axis and this has two consequences. firstly, the a and b cyclic irreps are split into pairs of one dimensional irreps identified by subscripts 1 and 2. secondly, pairs of 1d e−x and e + x cyclic irreps combine to form single ex 2d irreps in the dihedral group because the 2 - fold horizontal rotation makes pairs of rotations equivalent. for example, a 60 degree rotation about the main axis becomes equivalent to a ( 360 − 60 ) degree rotation because the 2 - fold horizontal rotation makes them equivalent. combinations of this kind are said to form a class. infinite order dihedral group irreps sometimes use greek symbol descriptions, σ, π, δ that follow from early linear molecule calculations. taking benzene as a simple example, we have a molecule that belongs to the series of point groups c6, d6 and d6h with increasing orders 6, 12 and 24. the six carbon atoms may be represented by a 6 x 6 matrices which in group c6 have irreps a, b, e + 1, e - 1, e + 2 and e - 2 because n objects in
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, 12 and 24. the six carbon atoms may be represented by a 6 x 6 matrices which in group c6 have irreps a, b, e + 1, e - 1, e + 2 and e - 2 because n objects in an n - fold cyclic group always produce one of each irrep. if these cyclic irreps are promoted to group d6 we obtain a1, bx, e1 and e2 when subscripts are added to the 1d a and b irreps and the others merge to form 2d irreps. a1 is there because the most symmetric irrep has to occur once and only once in the result leaving only the b irrep subscript to be deduced. the character of the 2 - fold horizontal rotation operation is 2 because 2 carbon atoms stay in place during the rotation, char ( c2 ) = 2 telling us that there are two more 1 subscripts than 2 subscripts so the result is a1, b1, e1 and e2. finally, promotion to d6h requires the addition of g and u subscripts. since char ( i ) = 0 there are an equal number of g and u subscripts, and a1g has to be present as the most symmetric group so b1u is mandatory. furthermore, odd and even 2d irreps take u and g subscripts so the final result for the carbon atoms is ( a1g, b1u, e1u, e2g ), but with the hydrogen atoms we get 2 ( a1g, b1u, e1u, e2g ). boric acid and boron trifluoride provide further hexagonal examples in spite of their slightly misleading schoenflies symbols c3h and d3h. taking boric acid first, we have three sets of equivalent atoms : 1 boron, 3 oxygen and 3 hydrogen. obviously the oxygen and hydrogen atoms produce the same irreps so only one has to be deduced. applying the 6 - fold cyclic group to ( say ) the hydrogen atoms produces characters ( 3, 0, 0, 3, 0, 0 ) yielding irreps a + e + 2 + e - 2 doubling up and adding an irrep for the central boron atom produces a + 2 ( a + e + 2 + e - 2 ) in standard laue class notation. unfortunately, mulliken used a different notation for c3h and d3h irreps to that used for
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central boron atom produces a + 2 ( a + e + 2 + e - 2 ) in standard laue class notation. unfortunately, mulliken used a different notation for c3h and d3h irreps to that used for other groups and a conversion table would be needed if that was important. boron trifluoride has a central boron atom with 3 fluorine atoms and belongs to cyclic subgroup c3h and the larger dihedral group d3h. following the above reasoning, the irreps in c3h are a + ( a + e + 2 + e - 2 ) and when promoted to the dihedral group this becomes a1 + ( a1 + e2 ). again, conversion to mulliken notation is required if that is important. spherical point group representations spherical classes are defined by the tetrahedral, octahedral and icosahedral rotational groups t, o and i. the first two of these, t and o, are related in much the same way as cyclic and dihedral groups are related in symmetric groups. both tetrahedral and octahedral molecules are often shown with their atoms inscribed in the apices or faces of cubes and might be considered as a single " cubic " system. every point group in this system contains the simple tetrahedral rotational group as a subgroup. methane ( ch4 ) is often used as an example and, although often described as a tetrahedral molecule because of the very visible rotational symmetry, it really belongs to the octahedral symmetry class. considering methane first as a tetrahedral molecule the 12 operations of group t are { e, 3 x c, 4 x b, 4 x b3 } where c is a 180 degree rotation along x, y and z axes and b is a 120 degree rotation about the apices of a cube. character tables under these four headings exhibit the corresponding four irreps a, e + 1, e - 1 and t and it would it is not difficult to convert the transformations of atoms during the symmetry operations to reducible matrices and thence to molecular irreps but this not necessary. methane has two sets of equivalent atoms that are transformed into each other during operations : a single carbon atom and 4 hydrogen atoms. a single atom can only ever be transformed into itself and therefore always contributes the most symmetrical irrep to the end total irrep count. additionally, there is a rule of group theory that the most symmetrical irrep must occur once and only
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a single atom can only ever be transformed into itself and therefore always contributes the most symmetrical irrep to the end total irrep count. additionally, there is a rule of group theory that the most symmetrical irrep must occur once and only once in the irreps of any equivalent atom set so the five dimensions of irreps being sought contain 2a and three others. the only way of filling the remaining three dimensions is to adopt 3d irrep t so the irreps are 2a + t. ( e irreps have to be taken in pairs in physical molecular applications ). methane sulfur hexafluoride extending this treatment to the octahedral group td requires six 4 - fold roto - inversion operations ( f ) about the main axes and six 2 - fold roto - inversions ( a ), appearing as mirror reflections through opposite edges of the imaginary cube in which methane is placed. so half the operations of this group are rotational and half non - rotational. rotational group t exists within non - rotational group td = { e, 3 x c, 8 x b / b3, 6 x f, 6 x a } t irreps a, e + 1, e - 1 and t are promoted to td irreps a1, a2, e1 and t1 and t2. ( e irreps collapse into one because the 3 - fold irreps become equivalent while a and t expand into two ). reasoning as above we know that the irreps in td must be 2a1 + tx so the last step is to find the 3d subscript. a brief look at the 4 x 4 transformation matrix for the 4 - fold rotation operation f shows character ch ( f ) = 0 and the subscript x has to be 2 to balance the 1 on the a irrep. sulfur hexafluoride can be treated first as a tetrahedral molecule t, then as octahedral o and finally as centred molecule oi. there are two sets of equivalent atoms consisting of a single sulfur atom and six fluorine atoms. transformations of the fluorine atoms generate a six dimensional representation that can only reduce into the direct sum of tetrahedral irreps a, e + 1, e - 1 and t because the direct sum must include the most symmetrical irrep once and only once. a direct sum of 5 can only be made up from a 2 and a 3 - no other combination is possible. these irreps are " promoted "
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and t because the direct sum must include the most symmetrical irrep once and only once. a direct sum of 5 can only be made up from a 2 and a 3 - no other combination is possible. these irreps are " promoted " to 2a1 + e1 + tx in group o. to get the x observe that the 4 - fold rotation in sf6 has character ch ( f ) = 2 because two atoms stay in position and a glance at this column of the table suggests a1 + e1 + t1. finally the inversion operation ( i ) applied go the fluorine atoms has character ch ( i ) = 0 indicating equal numbers of g and u subscripts ( because none of the atoms remains in position ). since the most symmetrical irrep must occur once the only possible result is a1g + e1g + t1u. the single sulfur atom always has the most symmetric irrep to the final reduction of the seven dimensional matrices to a direct sum is 2a1g + e1g + t1u. the following reference of character tables uses symbols zx for abstract cyclic groups cx with a4 and s4 ( alternating and symmetric permutations of 4 objects for t and o. many authors just use c, t and o in two senses, making it clear which is intended. = = historical background = = much of our understanding of quantum theory was developed during the early years of the 20th century, leading up to schrodinger's three dimensional wave equation. e. bright wilson used character tables in 1934 to predict the symmetry of vibrational normal modes. hans bethe used characters of point group operations in his study of ligand field theory in 1929, and eugene wigner used group theory to explain the selection rules of atomic spectroscopy. the first character tables were compiled by laszlo tisza ( 1933 ), in connection to vibrational spectra. the complete set of 32 crystallographic point groups was published in 1936 by rosenthal and murphy = = symmetry of molecular orbitals = = when schrodinger's 3d wave equation is applied to a one - electron atom it provides a number of solutions called wave functions that are then used to label the allowed energy levels in that atom. exact solutions of this kind are usually described by three quantum numbers, n, l and m from which the probable radial and angular distribution of the electron around the atom can be computed. this type of deduction leads to the familiar s, p, d, f,... description of atomic
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three quantum numbers, n, l and m from which the probable radial and angular distribution of the electron around the atom can be computed. this type of deduction leads to the familiar s, p, d, f,... description of atomic orbitals based on the l and m quantum numbers. each solution is a base vector from which more complex structures may be constructed. descriptions of many - electron atoms use the one - electron model to build models that are sometimes pictured as multiple electrons in the simple structure. molecular orbitals then take linear combinations of atomic orbitals ( lcaos ) to explain the distribution of electrons over multiple atoms within a molecule. atomic orbital symmetry follows from the angular part of the wave function which increases in complexity in the series s, p, d, f,... so that s orbitals only have radial symmetry while p orbital base vectors have a symmetry identical to that of the cartesian polar base vectors. consider the example of water ( h2o ), which has the c2v symmetry described above. the 2px orbital of oxygen has, like the x base vector, b1 symmetry. it is oriented perpendicular to the plane of the molecule and switches sign with a c2 and a σv'( yz ) operation, but remains unchanged with the other two operations ( obviously, the character for the identity operation is always + 1 ). this orbital's character set is thus { 1, −1, 1, −1 }, corresponding to the b1 irreducible representation. likewise, the 2pz orbital is seen to have the symmetry of the a1 irreducible representation ( i. e. : none of the symmetry operations change it ), 2py b2, and the 3dxy orbital a2. these assignments are noted in the rightmost columns of the table. each molecular orbital also has the symmetry of one irreducible representation. for example, ethylene ( c2h4 ) has symmetry group d2h, and its highest occupied molecular orbital ( homo ) is the bonding pi orbital which forms a basis for its irreducible representation b1u. = = the molecular symmetry group = = one can determine the symmetry operations of the point group for a particular molecule by considering the geometrical symmetry of its molecular model. however, when one uses a point group to classify molecular states, the operations in it are not to be interpreted in the same way. instead the operations are interpreted as rotating and / or reflecting the vibronic ( vibration - electronic ) coordinates and these operations commute
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one uses a point group to classify molecular states, the operations in it are not to be interpreted in the same way. instead the operations are interpreted as rotating and / or reflecting the vibronic ( vibration - electronic ) coordinates and these operations commute with the vibronic hamiltonian. they are " symmetry operations " for that vibronic hamiltonian. the point group is used to classify by symmetry the vibronic eigenstates of a rigid molecule. the symmetry classification of the rotational levels, the eigenstates of the full ( rotation - vibration - electronic ) hamiltonian, can be achieved through the use of the appropriate permutation - inversion group ( called the molecular symmetry group ), as introduced by longuet - higgins. = = symmetry of vibrational modes = = each normal mode of molecular vibration has a symmetry which forms a basis for one irreducible representation of the molecular symmetry group. for example, the water molecule has three normal modes of vibration : symmetric stretch in which the two o - h bond lengths vary in phase with each other, asymmetric stretch in which they vary out of phase, and bending in which the bond angle varies. the molecular symmetry of water is c2v with four irreducible representations a1, a2, b1 and b2. the symmetric stretching and the bending modes have symmetry a1, while the asymmetric mode has symmetry b2. the overall symmetry of the three vibrational modes is therefore γvib = 2a1 + b2. = = = vibrational modes of ammonia = = = the molecular symmetry of ammonia ( nh3 ) is c3v, with symmetry operations e, c3 and σv. for n = 4 atoms, the number of vibrational modes for a non - linear molecule is 3n - 6 = 6, due to the relative motion of the nitrogen atom and the three hydrogen atoms. all three hydrogen atoms travel symmetrically along the n - h bonds, either in the direction of the nitrogen atom or away from it. this mode is known as symmetric stretch ( v₁ ) and reflects the symmetry in the n - h bond stretching. of the three vibrational modes, this one has the highest frequency. in the bending ( ν₂ ) vibration, the nitrogen atom stays on the axis of symmetry, while the three hydrogen atoms move in different directions from one another, leading to changes in the bond angles. the hydrogen atoms move like an umbrella, so this mode is often referred to as the " umbrella mode ". there is also an asym
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, while the three hydrogen atoms move in different directions from one another, leading to changes in the bond angles. the hydrogen atoms move like an umbrella, so this mode is often referred to as the " umbrella mode ". there is also an asymmetric stretch mode ( ν₃ ) in which one hydrogen atom approaches the nitrogen atom while the other two hydrogens move away. the total number of degrees of freedom for each symmetry species ( or irreducible representation ) can be determined. ammonia has four atoms, and each atom is associated with three vector components. the symmetry group c3v for nh3 has the three symmetry species a1, a2 and e. the modes of vibration include the vibrational, rotational and translational modes. total modes = 3a1 + a2 + 4e. this is a total of 12 modes because each e corresponds to 2 degenerate modes ( at the same energy ). rotational modes = a2 + e ( 3 modes ) translational modes = a1 + e vibrational modes = total modes - rotational modes - translational modes = 3a1 + a2 + 4e - a2 - e - a1 - e = 2a1 + 2e ( 6 modes ). = = = more examples of vibrational symmetry = = = w ( co ) 6 has octahedral geometry. the irreducible representation for the c - o stretching vibration is a1g + eg + t1u. of these, only t1u is ir active. b2h6 ( diborane ) has d2h molecular symmetry. the terminal b - h stretching vibrations which are active in ir are b2u and b3u. fac - mo ( co ) 3 ( ch3ch2cn ) 3, has c3v geometry. the irreducible representation for the c - o stretching vibration is a1 + e. both of which are ir active. = = molecular rotation and molecular nonrigidity = = as discussed above in § the molecular symmetry group, point groups are useful for classifying the vibrational and electronic states of rigid molecules ( sometimes called semi - rigid molecules ) which undergo only small oscillations about a single equilibrium geometry. longuet - higgins introduced the molecular symmetry group ( a more general type of symmetry group ) suitable not only for classifying the vibrational and electronic states of rigid molecules but also for classifying their rotational and nuclear spin states. further, such groups can be used to classify the states of non - rigid ( or fluxional ) molecules that tunnel between equivalent
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only for classifying the vibrational and electronic states of rigid molecules but also for classifying their rotational and nuclear spin states. further, such groups can be used to classify the states of non - rigid ( or fluxional ) molecules that tunnel between equivalent geometries and to allow for the distorting effects of molecular rotation. the symmetry operations in the molecular symmetry group are so - called'feasible'permutations of identical nuclei, or inversion with respect to the center of mass ( the parity operation ), or a combination of the two, so that the group is sometimes called a " permutation - inversion group ". examples of molecular nonrigidity abound. for example, ethane ( c2h6 ) has three equivalent staggered conformations. tunneling between the conformations occurs at ordinary temperatures by internal rotation of one methyl group relative to the other. this is not a rotation of the entire molecule about the c3 axis, although each conformation has d3d symmetry, as in the table above. the molecule 2 - butyne ( dimethylacetylene ) has the same molecular symmetry group ( g36 } as ethane but a very much lower torsional barrier. similarly, ammonia ( nh3 ) has two equivalent pyramidal ( c3v ) conformations which are interconverted by the process known as nitrogen inversion. additionally, the methane molecule ( ch4 ) and trihydrogen cation { h3 + ) have highly symmetric equilibrium structures with td and d3h point group symmetries respectively ; they lack permanent electric dipole moments but they do have very weak pure rotation spectra because of rotational centrifugal distortion. sometimes it is necessary to consider together electronic states having different point group symmetries at equilibrium. for example, in its ground ( n ) electronic state the ethylene molecule c2h4 has d2h point group symmetry whereas in the excited ( v ) state it has d2d symmetry. to treat these two states together it is necessary to allow torsion and to use the double group of the molecular symmetry group g16. = = see also = = parity ( physics ) § molecules irreducible representation § applications in theoretical physics and chemistry woodward – hoffmann rules § correlation diagrams hapticity § hapticity and fluxionality character table crystallographic point group molecular geometry point groups in three dimensions symmetry of diatomic molecules symmetry in quantum mechanics = = references = = = = external links = = the molecular symmetry group [ 3 ] @ the
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##pticity and fluxionality character table crystallographic point group molecular geometry point groups in three dimensions symmetry of diatomic molecules symmetry in quantum mechanics = = references = = = = external links = = the molecular symmetry group [ 3 ] @ the university of western ontario point group symmetry @ newcastle university molecular symmetry @ imperial college london molecular point group symmetry tables character tables for point groups for chemistry molecular symmetry online @ the open university of israel an internet lecture course on molecular symmetry @ bergische universitaet decor – symmetry @ the cambridge crystallographic data centre landskrone kai. libretexts - chemistry. section 2. 2 : point groups
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the socionext milbeaut image / video processors are media processors in multi - processor system on a chip architecture. started by fujitsu with the m - 1 series in 2000 each generation ( 2013 : 7th ) has several variants regarding included modules and processor - cores, built for mobile phones, digital compact cameras, milcs and dslrs like leica m ( typ 240 ) and leica s2, nikon dslrs ( see nikon expeed ), some pentax k mount cameras and for the sigma true - ii processor. = = technology = = multiple fr - v processor cores, with each single processor - core able to compute many instructions / operations in parallel are used for image - and video - processing. storage - and display - interfaces and other modules are added and a digital signal processor ( dsp ) increases the number of simultaneous computations. an on - chip 32 - bit fujitsu fr microcontroller ( 6th generation in 2011 introduced the dual - core arm architecture ) initiates and controls the operation and data transfers of all processors, modules and interfaces and can be seen as the main control unit of the camera. the milbeaut is also used as an application - specific integrated circuit ( asic ) or application - specific standard product ( assp ). the 7th generation uses a 55 nm low - power process ( suvolta ) and arm cortex - a5 microcontroller. = = references = =
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mobile cloud computing ( mcc ) is the combination of cloud computing and mobile computing to bring rich computational resources to mobile users, network operators, as well as cloud computing providers. the ultimate goal of mcc is to enable execution of rich mobile applications on a plethora of mobile devices, with a rich user experience. mcc provides business opportunities for mobile network operators as well as cloud providers. more comprehensively, mcc can be defined as " a rich mobile computing technology that leverages unified elastic resources of varied clouds and network technologies toward unrestricted functionality, storage, and mobility to serve a multitude of mobile devices anywhere, anytime through the channel of ethernet or internet regardless of heterogeneous environments and platforms based on the pay - as - you - use principle. " = = architecture = = mcc uses computational augmentation approaches ( computations are executed remotely instead of on the device ) by which resource - constraint mobile devices can utilize computational resources of varied cloud - based resources. in mcc, there are four types of cloud - based resources, namely distant immobile clouds, proximate immobile computing entities, proximate mobile computing entities, and hybrid ( combination of the other three model ). giant clouds such as amazon ec2 are in the distant immobile groups whereas cloudlet or surrogates are member of proximate immobile computing entities. smartphones, tablets, handheld devices, and wearable computing devices are part of the third group of cloud - based resources which is proximate mobile computing entities. vodafone, orange and verizon have started to offer cloud computing services for companies. = = challenges = = in the mcc landscape, an amalgam of mobile computing, cloud computing, and communication networks ( to augment smartphones ) creates several complex challenges such as mobile computation offloading, seamless connectivity, long wan latency, mobility management, context - processing, energy constraint, vendor / data lock - in, security and privacy, elasticity that hinder mcc success and adoption. = = = open research issues = = = although significant research and development in mcc is available in the literature, efforts in the following domains is still lacking : architectural issues : a reference architecture for heterogeneous mcc environment is a crucial requirement for unleashing the power of mobile computing towards unrestricted ubiquitous computing. energy - efficient transmission : mcc requires frequent transmissions between cloud platform and mobile devices, due to the stochastic nature of wireless networks, the transmission protocol should be carefully designed. context - awareness issues : context - aware
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computing towards unrestricted ubiquitous computing. energy - efficient transmission : mcc requires frequent transmissions between cloud platform and mobile devices, due to the stochastic nature of wireless networks, the transmission protocol should be carefully designed. context - awareness issues : context - aware and socially - aware computing are inseparable traits of contemporary handheld computers. to achieve the vision of mobile computing among heterogeneous converged networks and computing devices, designing resource - efficient environment - aware applications is an essential need. live vm migration issues : executing resource - intensive mobile application via virtual machine ( vm ) migration - based application offloading involves encapsulation of application in vm instance and migrating it to the cloud, which is a challenging task due to additional overhead of deploying and managing vm on mobile devices. mobile communication congestion issues : mobile data traffic is tremendously hiking by ever increasing mobile user demands for exploiting cloud resources which impact on mobile network operators and demand future efforts to enable smooth communication between mobile and cloud endpoints. trust, security, and privacy issues : trust is an essential factor for the success of the burgeoning mcc paradigm. it is because the data along with code / component / application / complete vm is offloaded to the cloud for execution. moreover, just like software and mobile application piracy, the mcc application development models are also affected by the piracy issue. pirax is known to be the first specialized framework for controlling application piracy in mcc requirements = = mcc research groups and activities = = several academic and industrial research groups in mcc have been emerging since last few years. some of the mcc research groups in academia with large number of researchers and publications include : mdc, mobile and distributed computing research group is at faculty of computer and information science, king saud university. mdc research group focuses on architectures, platforms, and protocols for mobile and distributed computing. the group has developed algorithms, tools, and technologies which offer energy efficient, fault tolerant, scalable, secure, and high performance computing on mobile devices. mobcc lab, faculty of computer science and information technology, university malaya. the lab was established in 2010 under the high impact research grant, ministry of higher education, malaysia. it has 17 researchers and has track of 22 published articles in international conference and peer reviewed cs journals. icclab, zurich university of applied sciences has a segment working on mcc. the init cloud computing lab is a research lab within the institute of applied information technology ( init ) of zurich university of applied sciences ( zhaw ). it
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journals. icclab, zurich university of applied sciences has a segment working on mcc. the init cloud computing lab is a research lab within the institute of applied information technology ( init ) of zurich university of applied sciences ( zhaw ). it covers topic areas across the entire cloud computing technology stack. mobile & cloud lab, institute of computer science, university of tartu. mobile & cloud lab conducts research and teaching in the mobile computing and cloud computing domains. the research topics of the group include cloud computing, mobile application development, mobile cloud, mobile web services and migrating scientific computing and enterprise applications to the cloud. smartlab, data management systems laboratory, department of computer science, university of cyprus. smartlab is a first - of - a - kind open cloud of smartphones that enables a new line of systems - oriented mobile computing research. mobile cloud networking : mobile cloud networking ( mcn ) was an eu fp7 large - scale integrating project ( ip, 15m euro ) funded by the european commission. the mcn project was launched in november 2012 for the period of 36 month. the project was coordinated by sap research and the icclab at the zurich university of applied science. in total 19 partners from industry and academia established the first vision of mobile cloud computing. the project was primarily motivated by an ongoing transformation that drives the convergence between the mobile communications and cloud computing industry enabled by the internet and is considered the first pioneer in the area of network function virtualization. = = see also = = cloudlet cloud computing cloud collaboration mobile collaboration crowd computing = = references = =
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fluorescence in situ hybridization ( fish ) is a molecular cytogenetic technique that uses fluorescent probes that bind to only particular parts of a nucleic acid sequence with a high degree of sequence complementarity. it was developed by biomedical researchers in the early 1980s to detect and localize the presence or absence of specific dna sequences on chromosomes. fluorescence microscopy can be used to find out where the fluorescent probe is bound to the chromosomes. fish is often used for finding specific features in dna for use in genetic counseling, medicine, and species identification. fish can also be used to detect and localize specific rna targets ( mrna, lncrna and mirna ) in cells, circulating tumor cells, and tissue samples. in this context, it can help define the spatial - temporal patterns of gene expression within cells and tissues. = = probes – rna and dna = = in biology, a probe is a single strand of dna or rna that is complementary to a nucleotide sequence of interest. rna probes can be designed for any gene or any sequence within a gene for visualization of mrna, lncrna and mirna in tissues and cells. fish is used by examining the cellular reproduction cycle, specifically interphase of the nuclei for any chromosomal abnormalities. fish allows the analysis of a large series of archival cases much easier to identify the pinpointed chromosome by creating a probe with an artificial chromosomal foundation that will attract similar chromosomes. the hybridization signals for each probe when a nucleic abnormality is detected. each probe for the detection of mrna and lncrna is composed of ~ 20 - 50 oligonucleotide pairs, each pair covering a space of 40 – 50 bp. the specifics depend on the specific fish technique used. for mirna detection, the probes use proprietary chemistry for specific detection of mirna and cover the entire mirna sequence. probes are often derived from fragments of dna that were isolated, purified, and amplified for use in the human genome project. the size of the human genome is so large, compared to the length that could be sequenced directly, that it was necessary to divide the genome into fragments. ( in the eventual analysis, these fragments were put into order by digesting a copy of each fragment into still smaller fragments using sequence - specific endonucleases, measuring the size of each small fragment using size - exclusion chromatography, and using that information to determine where the large fragments overlapped one another. ) to preserve the fragments with
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still smaller fragments using sequence - specific endonucleases, measuring the size of each small fragment using size - exclusion chromatography, and using that information to determine where the large fragments overlapped one another. ) to preserve the fragments with their individual dna sequences, the fragments were added into a system of continually replicating bacteria populations. clonal populations of bacteria, each population maintaining a single artificial chromosome, are stored in various laboratories around the world. the artificial chromosomes ( bac ) can be grown, extracted, and labeled, in any lab containing a library. genomic libraries are often named after the institution in which they were developed. an example being the rpci - 11 library, which is named after roswell park comprehensive cancer center ( formerly known as roswell park cancer institute ) in buffalo, new york. these fragments are on the order of 100 thousand base - pairs, and are the basis for most fish probes. = = = preparation and hybridization process – rna = = = the purpose of using rna fish is to detect target mrna transcripts in cells, tissue sections, or even whole - mounts. the process is done in 3 main procedures : tissue preparation ( pre - hybridization ), hybridization, and washing ( post - hybridization ). the tissue preparation starts by collecting the appropriate tissue sections to perform rna fish. first, cells, circulating tumor cells ( ctcs ), formalin - fixed paraffin - embedded ( ffpe ), or frozen tissue sections are fixed. some commonly used fixatives are 4 % formaldehyde or paraformaldehyde ( pfa ) in phosphate buffered saline ( pbs ). fish has also been successfully done on unfixed cells. after fixation, samples are permeabilized to allow the penetration of hybridization reagents. the use of detergents at a 0. 1 % concentration is commonly used to enhance the tissue permeability such as tween - 20 or triton x - 100. it is critical for the hybridization process to have all optimal conditions to have a successful in situ result, including temperature, ph, salt concentration, and time of the hybridization reaction. after checking all the necessary conditions, hybridization steps can be started by first adding a target - specific probe, composed of 20 oligonucleotide pairs, hybridizes to the target rna ( s ). separate but compatible signal amplification systems enable the multiplex assay ( up to two targets per assay ). signal amplification
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probe, composed of 20 oligonucleotide pairs, hybridizes to the target rna ( s ). separate but compatible signal amplification systems enable the multiplex assay ( up to two targets per assay ). signal amplification is achieved via series of sequential hybridization steps. after the hybridization steps, washing steps are performed. these steps aim to remove nonspecific hybrids and get rid of unbound probe molecules from the samples to reduce any background signaling. the use of ethanol washes are typically used at this stage to reduce autofluorescence in tissues or cells. at the end of the assay the tissue samples are visualized under a fluorescence microscope such as the confocal fluorescence microscope and the keyence microscope. = = = preparation and hybridization process – dna = = = first, a probe is constructed. the probe must be large enough to hybridize specifically with its target but not so large as to impede the hybridization process. the probe is tagged directly with fluorophores, with targets for antibodies or with biotin. tagging can be done in various ways, such as nick translation, or polymerase chain reaction using tagged nucleotides. then, an interphase or metaphase chromosome preparation is produced. the chromosomes are firmly attached to a substrate, usually glass. repetitive dna sequences must be blocked by adding short fragments of dna to the sample. the probe is then applied to the chromosome dna and incubated for approximately 12 hours while hybridizing. several wash steps remove all unhybridized or partially hybridized probes. the results are then visualized and quantified using a microscope that is capable of exciting the dye and recording images. if the fluorescent signal is weak, amplification of the signal may be necessary in order to exceed the detection threshold of the microscope. fluorescent signal strength depends on many factors such as probe labeling efficiency, the type of probe, and the type of dye. fluorescently tagged antibodies or streptavidin are bound to the dye molecule. these secondary components are selected so that they have a strong signal. = = variations on probes and analysis = = fish is a very general technique. the differences between the various fish techniques are usually due to variations in the sequence and labeling of the probes ; and how they are used in combination. probes are divided into two generic categories : cellular and acellular. in fluorescent " in situ " hybridization refers to the cellular placement of the probe probe
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in the sequence and labeling of the probes ; and how they are used in combination. probes are divided into two generic categories : cellular and acellular. in fluorescent " in situ " hybridization refers to the cellular placement of the probe probe size is important because shorter probes hybridize less specifically than longer probes, so that long enough strands of dna or rna ( often 10 – 25 nucleotides ) which are complementary to a given target sequence are often used to locate a target. the overlap defines the resolution of detectable features. for example, if the goal of an experiment is to detect the breakpoint of a translocation, then the overlap of the probes — the degree to which one dna sequence is contained in the adjacent probes — defines the minimum window in which the breakpoint may be detected. the mixture of probe sequences determines the type of feature the probe can detect. probes that hybridize along an entire chromosome are used to count the number of a certain chromosome, show translocations, or identify extra - chromosomal fragments of chromatin. this is often called " whole - chromosome painting. " if every possible probe is used, every chromosome, ( the whole genome ) would be marked fluorescently, which would not be particularly useful for determining features of individual sequences. however, it is possible to create a mixture of smaller probes that are specific to a particular region ( locus ) of dna ; these mixtures are used to detect deletion mutations. when combined with a specific color, a locus - specific probe mixture is used to detect very specific translocations. special locus - specific probe mixtures are often used to count chromosomes, by binding to the centromeric regions of chromosomes, which are distinctive enough to identify each chromosome ( with the exception of chromosome 13, 14, 21, 22. ) a variety of other techniques uses mixtures of differently colored probes. a range of colors in mixtures of fluorescent dyes can be detected, so each human chromosome can be identified by a characteristic color using whole - chromosome probe mixtures and a variety of ratios of colors. although there are more chromosomes than easily distinguishable fluorescent dye colors, ratios of probe mixtures can be used to create secondary colors. similar to comparative genomic hybridization, the probe mixture for the secondary colors is created by mixing the correct ratio of two sets of differently colored probes for the same chromosome. this technique is sometimes called m - fish. the same physics that make a variety of colors possible for
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hybridization, the probe mixture for the secondary colors is created by mixing the correct ratio of two sets of differently colored probes for the same chromosome. this technique is sometimes called m - fish. the same physics that make a variety of colors possible for m - fish can be used for the detection of translocations. that is, colors that are adjacent appear to overlap ; a secondary color is observed. some assays are designed so that the secondary color will be present or absent in cases of interest. an example is the detection of bcr / abl translocations, where the secondary color indicates disease. this variation is often called double - fusion fish or d - fish. in the opposite situation — where the absence of the secondary color is pathological — is illustrated by an assay used to investigate translocations where only one of the breakpoints is known or constant. locus - specific probes are made for one side of the breakpoint and the other intact chromosome. in normal cells, the secondary color is observed, but only the primary colors are observed when the translocation occurs. this technique is sometimes called " break - apart fish ". = = = single - molecule rna fish = = = single - molecule rna fish, also known as stellaris® rna fish or smfish, is a method of detecting and quantifying mrna and other long rna molecules in a thin layer of tissue sample. targets can be reliably imaged through the application of multiple short singly labeled oligonucleotide probes. the binding of up to 48 fluorescent labeled oligos to a single molecule of mrna provides sufficient fluorescence to accurately detect and localize each target mrna in a wide - field fluorescent microscopy image. probes not binding to the intended sequence do not achieve sufficient localized fluorescence to be distinguished from background. single - molecule rna fish assays can be performed in simplex or multiplex, and can be used as a follow - up experiment to quantitative pcr, or imaged simultaneously with a fluorescent antibody assay. the technology has potential applications in cancer diagnosis, neuroscience, gene expression analysis, and companion diagnostics. = = = fibre fish = = = in an alternative technique to interphase or metaphase preparations, fiber fish, interphase chromosomes are attached to a slide in such a way that they are stretched out in a straight line, rather than being tightly coiled, as in conventional fish, or adopting a chromosome territory conformation, as in interphase fish. this is
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##phase chromosomes are attached to a slide in such a way that they are stretched out in a straight line, rather than being tightly coiled, as in conventional fish, or adopting a chromosome territory conformation, as in interphase fish. this is accomplished by applying mechanical shear along the length of the slide, either to cells that have been fixed to the slide and then lysed, or to a solution of purified dna. a technique known as chromosome combing is increasingly used for this purpose. the extended conformation of the chromosomes allows dramatically higher resolution – even down to a few kilobases. the preparation of fiber fish samples, although conceptually simple, is a rather skilled art, and only specialized laboratories use the technique routinely. = = = q - fish = = = q - fish combines fish with pnas and computer software to quantify fluorescence intensity. this technique is used routinely in telomere length research. = = = flow - fish = = = flow - fish uses flow cytometry to perform fish automatically using per - cell fluorescence measurements. = = = ma - fish = = = microfluidics - assisted fish ( ma - fish ) uses a microfluidic flow to increase dna hybridization efficiency, decreasing expensive fish probe consumption and reduce the hybridization time. ma - fish is applied for detecting the her2 gene in breast cancer tissues. = = = mar - fish = = = microautoradiography fish is a technique to combine radio - labeled substrates with conventional fish to detect phylogenetic groups and metabolic activities simultaneously. = = = hybrid fusion - fish = = = hybrid fusion fish ( hf - fish ) uses primary additive excitation / emission combination of fluorophores to generate additional spectra through a labeling process known as dynamic optical transmission ( dot ). three primary fluorophores are able to generate a total of 7 readily detectable emission spectra as a result of combinatorial labeling using dot. hybrid fusion fish enables highly multiplexed fish applications that are targeted within clinical oncology panels. the technology offers faster scoring with efficient probesets that can be readily detected with traditional fluorescent microscopes. = = = merfish = = = multiplexed error - robust fluorescence in situ hybridization is a highly multiplexed version of smfish. it uses combinatorial labeling, followed by imaging, and then error - resistant encoding to capture a high number of rna molecules and spatial localization within the cell. the capture of a large number of rna molecules enables elucida
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of smfish. it uses combinatorial labeling, followed by imaging, and then error - resistant encoding to capture a high number of rna molecules and spatial localization within the cell. the capture of a large number of rna molecules enables elucidation of gene regulatory networks, prediction of function of unannotated genes, and identification of rna molecule distribution patterns, which correlate with their associated proteins. = = = starfish = = = starfish is a set of software tools developed in 2019 by a consortium of scientists to analyze data from nine different variations of fish, since all variations produce the same set of data — gene expression values mapped to x and y coordinates in a cell. the software, created for all scientists, not just bioinformaticians, reads a set of images, removes noise, and identifies rna molecules. this approach has set out to define a standard analysis scheme of fish datasets in a similar way to single - cell transcriptomics analysis. = = medical applications = = often parents of children with a developmental disability want to know more about their child's conditions before choosing to have another child. these concerns can be addressed by analysis of the parents'and child's dna. in cases where the child's developmental disability is not understood, the cause of it can potentially be determined using fish and cytogenetic techniques. examples of diseases that are diagnosed using fish include prader - willi syndrome, angelman syndrome, 22q13 deletion syndrome, chronic myelogenous leukemia, acute lymphoblastic leukemia, cri - du - chat, velocardiofacial syndrome, and down syndrome. fish on sperm cells is indicated for men with an abnormal somatic or meiotic karyotype as well as those with oligozoospermia, since approximately 50 % of oligozoospermic men have an increased rate of sperm chromosome abnormalities. the analysis of chromosomes 21, x, and y is enough to identify oligozoospermic individuals at risk. in medicine, fish can be used to form a diagnosis, to evaluate prognosis, or to evaluate remission of a disease, such as cancer. treatment can then be specifically tailored. a traditional exam involving metaphase chromosome analysis is often unable to identify features that distinguish one disease from another, due to subtle chromosomal features ; fish can elucidate these differences. fish can also be used to detect diseased cells more easily than standard cytogenetic methods, which require dividing
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to identify features that distinguish one disease from another, due to subtle chromosomal features ; fish can elucidate these differences. fish can also be used to detect diseased cells more easily than standard cytogenetic methods, which require dividing cells and requires labor and time - intensive manual preparation and analysis of the slides by a technologist. fish, on the other hand, does not require living cells and can be quantified automatically, a computer counts the fluorescent dots present. however, a trained technologist is required to distinguish subtle differences in banding patterns on bent and twisted metaphase chromosomes. fish can be incorporated into lab - on - a - chip microfluidic device. this technology is still in a developmental stage but, like other lab on a chip methods, it may lead to more portable diagnostic techniques. = = = species identification = = = fish has been extensively studied as a diagnostic technique for the identification of pathogens in the field of medical microbiology. although it has been proven to be a useful and applicable technique, it is still not widely applied in diagnostic laboratories. the short time to diagnosis ( less than 2 hours ) has been a major advantage compared with biochemical differentiation, but this advantage is challenged by maldi - tof - ms which allows the identification of a wider range of pathogens compared with biochemical differentiation techniques. using fish for diagnostic purposes has found its purpose when immediate species identification is needed, specifically for the investigation of blood cultures for which fish is a cheap and easy technique for preliminary rapid diagnosis. fish can also be used to compare the genomes of two biological species, to deduce evolutionary relationships. a similar hybridization technique is called a zoo blot. bacterial fish probes are often primers for the 16s rrna region. fish is widely used in the field of microbial ecology, to identify microorganisms. biofilms, for example, are composed of complex ( often ) multi - species bacterial organizations. preparing dna probes for one species and performing fish with this probe allows one to visualize the distribution of this specific species within the biofilm. preparing probes ( in two different colors ) for two species allows researchers to visualize / study co - localization of these two species in the biofilm and can be useful in determining the fine architecture of the biofilm. = = = comparative genomic hybridization = = = comparative genomic hybridization can be described as a method that uses fish in a parallel manner with the comparison of the hybridization strength
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can be useful in determining the fine architecture of the biofilm. = = = comparative genomic hybridization = = = comparative genomic hybridization can be described as a method that uses fish in a parallel manner with the comparison of the hybridization strength to recall any major disruptions in the duplication process of the dna sequences in the genome of the nucleus. = = = virtual karyotype = = = virtual karyotyping is another cost - effective, clinically available alternative to fish panels using thousands to millions of probes on a single array to detect copy number changes, genome - wide, at unprecedented resolution. currently, this type of analysis will only detect gains and losses of chromosomal material and will not detect balanced rearrangements, such as translocations and inversions which are hallmark aberrations seen in many types of leukemia and lymphoma. = = = spectral karyotype = = = spectral karyotyping is an image of colored chromosomes. spectral karyotyping involves fish using multiple forms of many types of probes with the result to see each chromosome labeled through its metaphase stage. this type of karyotyping is used specifically when seeking out chromosome arrangements. = = chromosome evolution = = fish can be used to study the evolution of chromosomes. species that are related have similar chromosomes. this homology can be detected by gene or genome sequencing but also by fish. for instance, human and chimpanzee chromosomes are very similar, and fish can demonstrate that the common ancestor of chimpanzees and humans had two smaller chromosomes, and in the human lineage these fused to result in one human chromosome. similarly, species that are more distantly related, have similar chromosomes but with increasing genetic distance, chromosomes tend to break and fuse and thus result in mosaic chromosomes. this can be impressively demonstrated by fish ( see figure ). = = see also = = chromogenic in situ hybridization ( cish ) eukaryotic chromosome fine structure g banding gene mapping genome evolution happy mapping in situ hybridization, the technique used for labelling molecular cytogenetics virtual karyotype = = gallery = = = = references = = = = further reading = = = = external links = = fluorescent + in + situ + hybridization at the u. s. national library of medicine medical subject headings ( mesh ) information on fiber fish from the olympus corporation a guide to fiber fish from octavian henegariu fibre fish protocol archived
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= fluorescent + in + situ + hybridization at the u. s. national library of medicine medical subject headings ( mesh ) information on fiber fish from the olympus corporation a guide to fiber fish from octavian henegariu fibre fish protocol archived 2006 - 10 - 23 at the wayback machine from the human genome project at the sanger centre card - fish, biominewiki archived 2020 - 07 - 28 at the wayback machine preparation of complex dna probe sets for 3d fish with up to six different fluorochromes fish technical notes and protocols from genedetect. com fluorescence in situ hybridization photos of bacteria archived 2015 - 02 - 05 at the wayback machine rational design of polynucleotide probe mixes to identify particular genes in defined taxa : www. dnabaser. com / polypro
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circular dichroism ( cd ) is dichroism involving circularly polarized light, i. e., the differential absorption of left - and right - handed light. left - hand circular ( lhc ) and right - hand circular ( rhc ) polarized light represent two possible spin angular momentum states for a photon, and so circular dichroism is also referred to as dichroism for spin angular momentum. this phenomenon was discovered by jean - baptiste biot, augustin fresnel, and aime cotton in the first half of the 19th century. circular dichroism and circular birefringence are manifestations of optical activity. it is exhibited in the absorption bands of optically active chiral molecules. cd spectroscopy has a wide range of applications in many different fields. most notably, far - uv cd is used to investigate the secondary structure of proteins. uv / vis cd is used to investigate charge - transfer transitions. near - infrared cd is used to investigate geometric and electronic structure by probing metal d→d transitions. vibrational circular dichroism, which uses light from the infrared energy region, is used for structural studies of small organic molecules, and most recently proteins and dna. = = physical principles = = = = = circular polarization of light = = = electromagnetic radiation consists of an electric e { \ displaystyle { \ boldsymbol { e } } } and magnetic b { \ displaystyle { \ boldsymbol { b } } } field that oscillate perpendicular to one another and to the propagating direction, a transverse wave. while linearly polarized light occurs when the electric field vector oscillates only in one plane, circularly polarized light occurs when the direction of the electric field vector rotates about its propagation direction while the vector retains constant magnitude. at a single point in space, the circularly polarized - vector will trace out a circle over one period of the wave frequency, hence the name. the two diagrams below show the electric field vectors of linearly and circularly polarized light, at one moment of time, for a range of positions ; the plot of the circularly polarized electric vector forms a helix along the direction of propagation k { \ displaystyle { \ boldsymbol { k } } }. for left circularly polarized light ( lcp ) with propagation towards the observer, the electric vector rotates counterclockwise. for right circularly polarized light ( rcp
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##tyle { \ boldsymbol { k } } }. for left circularly polarized light ( lcp ) with propagation towards the observer, the electric vector rotates counterclockwise. for right circularly polarized light ( rcp ), the electric vector rotates clockwise. = = = interaction of circularly polarized light with matter = = = when circularly polarized light passes through an absorbing optically active medium, the speeds between right and left polarizations differ ( c l = c r { \ displaystyle c _ { \ mathrm { l } } \ neq c _ { \ mathrm { r } } } ) as well as their wavelength ( λ l = λ r { \ displaystyle \ lambda _ { \ mathrm { l } } \ neq \ lambda _ { \ mathrm { r } } } ) and the extent to which they are absorbed ( ε l = ε r { \ displaystyle \ varepsilon _ { \ mathrm { l } } \ neq \ varepsilon _ { \ mathrm { r } } } ). circular dichroism is the difference δ ε ≡ ε l − ε r { \ displaystyle \ delta \ varepsilon \ equiv \ varepsilon _ { \ mathrm { l } } - \ varepsilon _ { \ mathrm { r } } }. the electric field of a light beam causes a linear displacement of charge when interacting with a molecule ( electric dipole ), whereas its magnetic field causes a circulation of charge ( magnetic dipole ). these two motions combined cause an excitation of an electron in a helical motion, which includes translation and rotation and their associated operators. the experimentally determined relationship between the rotational strength r { \ displaystyle r } of a sample and the δ ε { \ displaystyle \ delta \ varepsilon } is given by r e x p = 3 h c 10 3 ln ( 10 ) 32 π 3 n a δ ε ν d ν { \ displaystyle r _ { \ mathrm { exp } } = { \ frac { 3hc10 ^ { 3 } \ ln ( 10 ) } { 32 \ pi ^ { 3 } n _ { \ mathrm { a } } } } \ int { \ frac { \ delta \ varepsilon } { \ nu } } \ mathrm { d } { \ nu } } the rotational strength has also
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3 } n _ { \ mathrm { a } } } } \ int { \ frac { \ delta \ varepsilon } { \ nu } } \ mathrm { d } { \ nu } } the rotational strength has also been determined theoretically, r t h e o = 1 2 m c i m ψ g m ^ ( e l e c. d i p o l e ) ψ e d τ ψ g m ^ ( m a g. d i p o l e ) ψ e d τ { \ displaystyle r _ { \ mathrm { theo } } = { \ frac { 1 } { 2mc } } \ mathrm { im } \ int \ psi _ { g } { \ widehat { m } } _ { \ mathrm { ( elec. dipole ) } } \ psi _ { e } \ mathrm { d } \ tau \ bullet \ int \ psi _ { g } { \ widehat { m } } _ { \ mathrm { ( mag. dipole ) } } \ psi _ { e } \ mathrm { d } \ tau } we see from these two equations that in order to have non - zero δ ε { \ displaystyle \ delta \ varepsilon }, the electric and magnetic dipole moment operators ( m ^ ( e l e c. d i p o l e ) { \ displaystyle { \ widehat { m } } _ { \ mathrm { ( elec. dipole ) } } } and m ^ ( m a g. d i p o l e ) { \ displaystyle { \ widehat { m } } _ { \ mathrm { ( mag. dipole ) } } } ) must transform as the same irreducible representation. c n { \ displaystyle \ mathrm { c } _ { n } } and d n { \ displaystyle \ mathrm { d } _ { n } } are the only point groups where this can occur, making only chiral molecules cd active. simply put, since circularly polarized light itself is " chiral ", it interacts differently with chiral molecules. that is, the two types of circularly polarized light are absorbed to different extents. in a cd experiment, equal amounts of left and right circularly polarized light of a selected wavelength are alternately radiated into a ( chiral ) sample. one of the two polarizations is absorbed more than the other one, and
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different extents. in a cd experiment, equal amounts of left and right circularly polarized light of a selected wavelength are alternately radiated into a ( chiral ) sample. one of the two polarizations is absorbed more than the other one, and this wavelength - dependent difference of absorption is measured, yielding the cd spectrum of the sample. due to the interaction with the molecule, the electric field vector of the light traces out an elliptical path after passing through the sample. it is important that the chirality of the molecule can be conformational rather than structural. that is, for instance, a protein molecule with a helical secondary structure can have a cd that changes with changes in the conformation. = = = = delta absorbance = = = = by definition, δ a = a l − a r { \ displaystyle \ delta a = a _ { \ mathrm { l } } - a _ { \ mathrm { r } } \, } where δ a { \ displaystyle \ delta a } ( delta absorbance ) is the difference between absorbance of left circularly polarized ( lcp ) and right circularly polarized ( rcp ) light ( this is what is usually measured ). δ a { \ displaystyle \ delta a } is a function of wavelength, so for a measurement to be meaningful the wavelength at which it was performed must be known. = = = = molar circular dichroism = = = = it can also be expressed, by applying beer's law, as : δ a = ( ε l − ε r ) c l { \ displaystyle \ delta a = ( \ varepsilon _ { \ mathrm { l } } - \ varepsilon _ { \ mathrm { r } } ) cl \, } where ε l { \ displaystyle \ varepsilon _ { \ mathrm { l } } } and ε r { \ displaystyle \ varepsilon _ { \ mathrm { r } } } are the molar extinction coefficients for lcp and rcp light, c { \ displaystyle c } is the molar concentration, l { \ displaystyle l } is the path length in centimeters ( cm ). then δ ε = ε l − ε r { \ displaystyle \ delta \ varepsilon = \ varepsilon _ { \ mathrm { l } } - \ varepsilon _ { \ mathrm { r } } \, } is the mo
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− ε r { \ displaystyle \ delta \ varepsilon = \ varepsilon _ { \ mathrm { l } } - \ varepsilon _ { \ mathrm { r } } \, } is the molar circular dichroism. this intrinsic property is what is usually meant by the circular dichroism of the substance. since δ ε { \ displaystyle \ delta \ varepsilon } is a function of wavelength, a molar circular dichroism value ( δ ε { \ displaystyle \ delta \ varepsilon } ) must specify the wavelength at which it is valid. = = = = extrinsic effects on circular dichroism = = = = in many practical applications of circular dichroism ( cd ), as discussed below, the measured cd is not simply an intrinsic property of the molecule, but rather depends on the molecular conformation. in such a case the cd may also be a function of temperature, concentration, and the chemical environment, including solvents. in this case the reported cd value must also specify these other relevant factors in order to be meaningful. in ordered structures lacking two - fold rotational symmetry, optical activity, including differential transmission ( and reflection ) of circularly polarized waves also depends on the propagation direction through the material. in this case, so - called extrinsic 3d chirality is associated with the mutual orientation of light beam and structure. = = = = molar ellipticity = = = = although δ a { \ displaystyle \ delta a } is usually measured, for historical reasons most measurements are reported in degrees of ellipticity. molar ellipticity is circular dichroism corrected for concentration. molar circular dichroism and molar ellipticity, [ θ ] { \ displaystyle [ \ theta ] }, are readily interconverted by the equation : [ θ ] = 3298. 2 δ ε. { \ displaystyle [ \ theta ] = 3298. 2 \, \ delta \ varepsilon. \, } this relationship is derived by defining the ellipticity of the polarization as : tan θ = e r − e l e r + e l { \ displaystyle \ tan \ theta = { \ frac { e _ { \ mathrm { r } } - e _ { \ mathrm { l } } } { e _ { \ mathrm { r } } + e _ { \ mathrm { l } } }
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{ \ frac { e _ { \ mathrm { r } } - e _ { \ mathrm { l } } } { e _ { \ mathrm { r } } + e _ { \ mathrm { l } } } } \, } where e r { \ displaystyle e _ { \ mathrm { r } } } and e l { \ displaystyle e _ { \ mathrm { l } } } are the magnitudes of the electric field vectors of the right - circularly and left - circularly polarized light, respectively. when e r { \ displaystyle e _ { \ mathrm { r } } } equals e l { \ displaystyle e _ { \ mathrm { l } } } ( when there is no difference in the absorbance of right - and left - circular polarized light ), θ { \ displaystyle \ theta } is 0° and the light is linearly polarized. when either e r { \ displaystyle e _ { \ mathrm { r } } } or e l { \ displaystyle e _ { \ mathrm { l } } } is equal to zero ( when there is complete absorbance of the circular polarized light in one direction ), θ { \ displaystyle \ theta } is 45° and the light is circularly polarized. generally, the circular dichroism effect is small, so tan θ { \ displaystyle \ tan \ theta } is small and can be approximated as θ { \ displaystyle \ theta } in radians. since the intensity or irradiance, i { \ displaystyle i }, of light is proportional to the square of the electric - field vector, the ellipticity becomes : θ ( radians ) = ( i r 1 / 2 − i l 1 / 2 ) ( i r 1 / 2 + i l 1 / 2 ) { \ displaystyle \ theta ( { \ text { radians } } ) = { \ frac { ( i _ { \ mathrm { r } } ^ { 1 / 2 } - i _ { \ mathrm { l } } ^ { 1 / 2 } ) } { ( i _ { \ mathrm { r } } ^ { 1 / 2 } + i _ { \ mathrm { l } } ^ { 1 / 2 } ) } } \, } then by substituting for i using beer's law in natural logarithm form : i = i 0 e − a
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} + i _ { \ mathrm { l } } ^ { 1 / 2 } ) } } \, } then by substituting for i using beer's law in natural logarithm form : i = i 0 e − a ln 10 { \ displaystyle i = i _ { 0 } \ mathrm { e } ^ { - a \ ln 10 } \, } the ellipticity can now be written as : θ ( radians ) = ( e − a r 2 ln 10 − e − a l 2 ln 10 ) ( e − a r 2 ln 10 + e − a l 2 ln 10 ) = e δ a ln 10 2 − 1 e δ a ln 10 2 + 1 { \ displaystyle \ theta ( { \ text { radians } } ) = { \ frac { ( \ mathrm { e } ^ { { \ frac { - a _ { \ mathrm { r } } } { 2 } } \ ln 10 } - \ mathrm { e } ^ { { \ frac { - a _ { \ mathrm { l } } } { 2 } } \ ln 10 } ) } { ( \ mathrm { e } ^ { { \ frac { - a _ { \ mathrm { r } } } { 2 } } \ ln 10 } + \ mathrm { e } ^ { { \ frac { - a _ { \ mathrm { l } } } { 2 } } \ ln 10 } ) } } = { \ frac { \ mathrm { e } ^ { \ delta a { \ frac { \ ln 10 } { 2 } } } - 1 } { \ mathrm { e } ^ { \ delta a { \ frac { \ ln 10 } { 2 } } } + 1 } } \, } since δ a 1 { \ displaystyle \ delta a \ ll 1 }, this expression can be approximated by expanding the exponentials in a taylor series to first - order and then discarding terms of δ a { \ displaystyle \ delta a } in comparison with unity and converting from radians to degrees : θ ( degrees ) = δ a ( ln 10 4 ) ( 180 π ) { \ displaystyle \ theta ( { \ text { degrees } } ) = \ delta a \ left ( { \ frac { \ ln 10 } { 4 } } \
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= δ a ( ln 10 4 ) ( 180 π ) { \ displaystyle \ theta ( { \ text { degrees } } ) = \ delta a \ left ( { \ frac { \ ln 10 } { 4 } } \ right ) \ left ( { \ frac { 180 } { \ pi } } \ right ) \, } the linear dependence of solute concentration and pathlength is removed by defining molar ellipticity as, [ θ ] = 100 θ c l { \ displaystyle [ \ theta ] = { \ frac { 100 \ theta } { cl } } \, } then combining the last two expression with beer's law, molar ellipticity becomes : [ θ ] = 100 δ ε ( ln 10 4 ) ( 180 π ) = 3298. 2 δ ε { \ displaystyle [ \ theta ] = 100 \, \ delta \ varepsilon \ left ( { \ frac { \ ln 10 } { 4 } } \ right ) \ left ( { \ frac { 180 } { \ pi } } \ right ) = 3298. 2 \, \ delta \ varepsilon \, } the units of molar ellipticity are historically ( deg · cm2 / dmol ). to calculate molar ellipticity, the sample concentration ( g / l ), cell pathlength ( cm ), and the molecular weight ( g / mol ) must be known. if the sample is a protein, the mean residue weight ( average molecular weight of the amino acid residues it contains ) is often used in place of the molecular weight, essentially treating the protein as a solution of amino acids. using mean residue ellipticity facilitates comparing the cd of proteins of different molecular weight ; use of this normalized cd is important in studies of protein structure. = = = = mean residue ellipticity = = = = methods for estimating secondary structure in polymers, proteins and polypeptides in particular, often require that the measured molar ellipticity spectrum be converted to a normalized value, specifically a value independent of the polymer length. mean residue ellipticity is used for this purpose ; it is simply the measured molar ellipticity of the molecule divided by the number of monomer units ( residues ) in the molecule. = = application to biological molecules = = circular dichroism ( cd ) spectroscopy is a powerful tool in biophysical and biochemical research, providing unique insights into the structural and stability characteristics of bio
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monomer units ( residues ) in the molecule. = = application to biological molecules = = circular dichroism ( cd ) spectroscopy is a powerful tool in biophysical and biochemical research, providing unique insights into the structural and stability characteristics of biomolecules. because cd arises from the differential absorption of left - and right - circularly polarized light by optically active molecules, it is inherently sensitive to the chiral nature of biological macromolecules. this makes it particularly valuable for analyzing secondary structures, as seen in the characteristic cd spectral signatures of the α - helices and β - sheets of proteins and the double helices of nucleic acids. while high - resolution techniques such as x - ray crystallography, nmr, and cryo - em reveal atomic - level structural details, and interaction - based methods like itc and spr probe molecular interactions, cd spectroscopy offers a rapid, label - free means of detecting structural changes and stability shifts. its ability to provide complementary data makes it an essential component of the modern biophysical toolbox, with applications spanning virtually every field of biomolecular research. cd spectroscopy is widely used in academia and the biopharmaceutical industry to study biomolecules, particularly proteins and peptides. cd spectra provide valuable insights into both secondary and tertiary structure. secondary structure information is derived from signals arising from peptide bonds that absorb in the far - uv range ( spanning approximately 180 nm to 260 nm ), enabling the identification and fractional assignments of structural elements such as the alpha - helix, beta - sheet, beta - turn, and random coil. these structural assignments place important constraints on the possible secondary conformations that the protein can be in. cd cannot, in general, say where the alpha helices that are detected are located within the molecule or even completely predict how many there are. despite this, cd is a valuable tool, especially for showing changes in conformation. it can, for instance, be used to study how the secondary structure of a molecule changes as a function of temperature ( in a thermal denaturation temperature ramp experiment ) or of the concentration of denaturing agents ( in a chemical denaturation experiment ), e. g. guanidinium chloride or urea. in this way it can reveal important thermodynamic information about the molecule ( such as the enthalpy and gibbs free energy of denaturation ) that cannot otherwise be easily obtained. anyone attempting to study a protein will find cd a valuable tool
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this way it can reveal important thermodynamic information about the molecule ( such as the enthalpy and gibbs free energy of denaturation ) that cannot otherwise be easily obtained. anyone attempting to study a protein will find cd a valuable tool for verifying that the protein is in its native conformation ( i. e., as a quality control technique ) before undertaking extensive and / or expensive experiments with it. moreover, cd spectroscopy has been used in bioinorganic interface studies ; specifically, it has been used to analyze the differences in secondary structure of an engineered protein before and after titration with a reagent. insight into tertiary structure is obtained from spectral contributions of aromatic amino acids, which absorb in the near - uv range ( spanning approximately 250 nm to 350 nm ). the signals obtained in this region are due to the absorption, dipole orientation, and nature of the surrounding environment of the phenylalanine, tyrosine, cysteine ( or s - s disulfide bridges ) and tryptophan amino acids. unlike in far - uv cd, the near - uv cd spectrum cannot be assigned to any particular 3d structure. rather, the near - uv range can be considered a fingerprint region because its spectral profile is exquisitely dependent on the composition of aromatic residues and the conformation and environment of their side chains. visible cd spectra ( spanning approximately 350 nm to 700 nm ) provide structural information on the nature of the prosthetic groups in proteins, e. g., the heme groups in hemoglobin and cytochrome c. visible cd spectroscopy is a very powerful technique to study metal – protein interactions and can resolve individual d – d electronic transitions as separate bands. cd spectra in the visible light region are generally only produced when a metal ion is in a chiral environment, thus, free metal ions in solution are not detected. this has the advantage of only observing the protein - bound metal, so ph dependence and stoichiometries are readily obtained. optical activity in transition metal ion complexes have been attributed to configurational, conformational, and vicinal effects. klewpatinond and viles ( 2007 ) have produced a set of empirical rules for predicting the appearance of visible cd spectra for cu ( ii ) and ni ( ii ) square - planar complexes involving histidine and main - chain coordination. beyond proteins and peptides, uv - cd spectroscopy is a powerful tool for characterizing the secondary structure of nucleic acids, providing insight
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( ii ) and ni ( ii ) square - planar complexes involving histidine and main - chain coordination. beyond proteins and peptides, uv - cd spectroscopy is a powerful tool for characterizing the secondary structure of nucleic acids, providing insight into dna helices and rna structural motifs such as g - quadruplexes. different dna conformations — a - dna, b - dna, and z - dna — exhibit distinct cd spectral signatures due to variations in base stacking and helical geometry. similarly, rna structures, including stem - loops, pseudoknots, and g - quadruplexes, produce unique cd spectra that reflect their specific folding patterns and base interactions. g - quadruplexes, in particular, show characteristic positive and negative bands in the cd spectrum depending on their topology ( parallel, antiparallel, or hybrid ). these spectral features make uv - cd an essential technique for studying nucleic acid folding, stability, and interactions with ligands. cd gives less specific structural information than x - ray crystallography and protein nmr spectroscopy, for example, which both give atomic resolution data. however, cd spectroscopy is a quick method that does not require large amounts of proteins or extensive data processing. thus cd can be used to survey many solvent conditions, varying temperature, ph, salinity, and the presence of various cofactors. cd spectroscopy is usually used to study proteins in solution, and thus it complements methods that study the solid state. this is also a limitation, in that many proteins are embedded in membranes in their native state, and solutions containing membrane structures are often strongly scattering. cd can also be measured in thin films and powders. for instance, cd spectroscopy has been conducted on solid state semiconducting materials such as tio2 to obtain large signals in the uv wavelength range, where the electronic transitions for biomolecules often occur. = = higher order structure comparisons = = modern protein cd spectroscopy is most powerful for comparative analysis of secondary and tertiary structure, commonly referred to as higher order structure ( hos ) comparisons. examples include assessing batch - to - batch consistency in biotherapeutics, evaluating the effects of mutations, and studying the properties of charge variants or glycovariants to a parent protein. hos analysis is also highly effective for studying the impact of formulation excipients, ph, and ionic strength on protein conformation. hos comparisons have a wide range of applications and play a critical role at every stage of
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a parent protein. hos analysis is also highly effective for studying the impact of formulation excipients, ph, and ionic strength on protein conformation. hos comparisons have a wide range of applications and play a critical role at every stage of biotherapeutic development — from early - stage analytical assessments to late - stage quality control ; from formulation development to forced degradation shelf stability assessments. higher order structure comparisons leverage both far - and near - uv wavelength ranges to enable statistically robust, reproducible, and quantifiable data analysis. an hos comparison quantitatively evaluates whether any two spectra differ and, by extension, whether their underlying structural information is different. this is often difficult, if not impossible, to do by visual inspection. detecting these subtle differences requires multiple independent spectra and robust statistical analysis, as many variations are too small to be discernible by eye. there are various approaches to hos comparisons and numerous spectral comparison methods are described in the literature, however, regardless of the hos comparison method or application, all methods are mathematical approaches that have the same goal of yielding a single value as a measure of similarity for pair - wise spectral comparisons. one such method is the weighted spectral difference ( wsd ) method, an hos comparison method favored by many biopharmaceutical companies and regulatory authorities. over the last decade, hos comparisons have been established as an essential tool to consolidate cd data in submissions for new biologics drug applications. particularly in biosimilars development, hos comparisons are indispensable to meet requirements by the fda, ema, and other regulatory bodies. the rationale for this guidance is to regulate and control the safety, quality, and efficacy of therapeutic agents available to the public. = = additional applications and related techniques = = = = = fluorescence = = = fluorescence measurements in cd spectroscopy, recorded at a 90 degree angle to the incident light, often serve as a complementary data channel, providing additional insights into protein stability and conformational changes. by detecting intrinsic fluorescence from aromatic residues such as tryptophan and tyrosine, researchers can assess environmental shifts that accompany structural transitions. fluorescence data can be acquired alongside cd signals, particularly in temperature ramp experiments, where it helps monitor unfolding events by tracking changes in emission intensity or wavelength shifts. this process could be followed by recording cd spectra at intervals of 1 °c, for example, while increasing the temperature continuously at 1 °c per minute. the excitation bandwidth required for the flu
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##folding events by tracking changes in emission intensity or wavelength shifts. this process could be followed by recording cd spectra at intervals of 1 °c, for example, while increasing the temperature continuously at 1 °c per minute. the excitation bandwidth required for the fluorescence spectra is usually larger than what would be used as spectral bandwidth for cd measurements, so sometimes the use of different spectral bandwidths for cd and fluorescence measurements is necessary. this dual approach enhances the interpretation of protein behavior under varying conditions, improving confidence in structural and stability assessments. there are multiple approaches to collecting fluorescence data, including the use of a photomultiplier tube ( pmt ) to record total fluorescence, the use of a ccd fluorometer to record full - spectrum fluorescence, or the use of a scanning emission monochromator ( sem ) to allow for scanning the fluorescence spectrum at a fixed excitation wavelength. = = = optical rotatory dispersion ( ord ) = = = cd is closely related to the technique of optical rotatory dispersion ( ord ). optical rotation is the rotation of linearly polarized light as a result of it passing through an optically active material, and is a consequence of a difference in refractive index between the left and right circularly polarized components of the light ( linearly polarized light can be considered to be an equal combination of right and left circularly polarized light ). optical rotatory dispersion is the variation in optical rotation with wavelength. ord and cd spectra both derive from the interaction of polarized ( circularly or linearly ) light with chiral molecules and are directly related : each can be derived from the other using the kramers - kronig transform. measurements of ord and cd give essentially the same information, but experimentally each technique has been favored for particular applications. cd is the higher resolution technique since it is only observed at wavelengths where the chiral molecule absorbs light. this makes complicated spectra involving multiple absorbance bands easier to interpret. alternatively, ord measurements can be obtained at wavelengths where the chiral molecule being measured does not necessarily absorb light. this means that ord measurements can be made on materials with high concentrations or where absorbance bands are obscured by solvent or buffer salt absorbance. ord is particularly useful for unsubstituted sugars as this class of biomolecule does not possess chromophores that absorb in the uv - vis regions accessible via commercial cd instruments. = = =
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buffer salt absorbance. ord is particularly useful for unsubstituted sugars as this class of biomolecule does not possess chromophores that absorb in the uv - vis regions accessible via commercial cd instruments. = = = linear dichroism ( ld ) = = = with the appropriate accessory, it is possible to perform linear dichroism ( ld ) measurements on cd spectrophotometers. linear dichroism is the difference in the absorbance of light polarized parallel and perpendicular to an orientation axis : δa = apara - aperp where a is the absorbance of the linearly polarized light, and the subscripts indicate parallel and perpendicular, respectively. for a sample to have non - zero ld it must be anisotropic ; the anisotropy may be intrinsic, as in liquid crystals for example, or it may be induced, for example, by stretching a polymer film, by the application of an electrical field, or by alignment or deformation in a shear field ( e. g., nucleic acids such as dna ). an ld device uses a couette cell to generate a shear field. the sample is contained in the annular gap between two concentric quartz cylinders, the outer of which, the rotor, is rotated about its cylindrical axis, while the inner, the stator, is stationary. this arrangement is named after its originator, maurice couette. shearing can cause large particles in the liquid to align or deform. for example, rigid, rod - like particles, such as carbon nanotubes and glass fibers, will align, whereas vesicles, micelles, and flexible polymers will deform from their equilibrium conformations, extending in the direction of shear. linear dichroism is then used to determine the direction of net electron transfer in an absorbed chromophore relative to the shear direction, and thereby to the alignment direction of the absorbing species or the deformation direction of its environment. for more information on ld and its measurement, consult this book. = = = magnetic circular dichroism ( mcd ) = = = magnetic circular dichroism ( mcd ) is the differential absorption of left and right circularly polarized light in the presence of a magnetic field oriented parallel to the direction of light propagation. mcd differs from natural cd in that it does not require a chiral sample ; the origins of cd and mcd are quite different. there are three contributions to
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light in the presence of a magnetic field oriented parallel to the direction of light propagation. mcd differs from natural cd in that it does not require a chiral sample ; the origins of cd and mcd are quite different. there are three contributions to an mcd spectrum, known as the a -, b -, and c - terms. at room temperature, the a - and b - terms dominate, especially for non - magnetic chromophores, and form the majority of what can be observed in a standard mcd experiment. the a - term is due to zeeman splitting of degenerate excited states by a difference in spin. the result is a small shift apart in the wavelengths of the uv - visible spectrum for each spin state, with each state preferentially absorbing left or right circularly polarized light. the a - term mcd spectrum is observed as a derivative of an absorbance transition with a sharp transition around the absorbance peak. because of the a - term bands, the mcd spectrum is more structured than the absorbance or natural cd spectrum, multiple overlapping chromophores can be quantified much more easily, and changes in individual chromophores can be tracked. the b - term is due to mixing of non - degenerate ground states. it is normally observed as a single absorption band type peak, which may be either positive or negative. the c - term is due to changes in populations of molecules over the zeeman sublevels due to the response to the field of a paramagnetic ground state. they become significant in the mcd spectrum only at very low temperatures, and the instrumentation requirements of high field strengths and cryogenic temperatures are very similar to those of the related technique of electron paramagnetic resonance ( epr ). this is an expensive and dedicated system, and access to the c - terms is therefore beyond the scope of an easily interchangeable mcd accessory on a benchtop cd instrument. collection of mcd data is similar to that of natural cd, except that there are two possible orientations of the magnet, with either the north or south pole closer to the detector. normally a spectrum is acquired with the magnet in each orientation ; since the mcd contribution to the spectrum changes sign when the magnetic field is reversed, whereas the natural cd contribution does not, both contributions can be obtained by averaging the two spectra. for further information on mcd see this book. = = = circularly polarized luminescence ( cpl )
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the magnetic field is reversed, whereas the natural cd contribution does not, both contributions can be obtained by averaging the two spectra. for further information on mcd see this book. = = = circularly polarized luminescence ( cpl ) = = = circularly polarized luminescence ( cpl ) is the emission analog of cd. while cd examines the geometry of molecules in their ground state, cpl, typically observed perpendicular to the incident light beam, provides insight into the geometry of molecules in their excited or luminescent state. in a cpl experiment, the emitted light is analyzed for its contents of left and right circularly polarized light. the difference in intensity between left and right circularly polarized emitted light, δi, is given by : δi = il – ir where il and ir are the intensity of left and right circularly polarized emitted light, respectively. the average luminescence intensity is given by : i = ( il + ir ) / 2 both δi and i are in relative units because in luminescence experiments not all the luminescent light is detected, only that in a restricted solid angle. moreover, an absolute value for the concentration of luminescent molecules may be hard to obtain. for these reasons, a dissymmetry factor in the luminescence is defined as : glum = δi / i with glum being an absolute number that is unique to each cpl - active molecule under specific conditions. many commercially available cd spectrophotometers can be adapted with an accessory to measure the circularly polarized luminescence of a sample. = = = analysis of solid samples = = = it is possible to analyze solid - state samples by cd spectroscopy. there are a few options to accomplish this. samples are often prepared in the form of discs, either by compression with an inert dispersant such as potassium bromide or potassium chloride or by deposition of the sample as a thin film on top of the disc. this technique is well established in ir absorbance spectroscopy, and it has also been used in uv / visible spectroscopy. the sample is measured in transmission mode, with the light passing through the sample to a detector mounted in the spectrometer transmission port. to eliminate the effect of anisotropy, the sample is usually mounted in a wheel and can be manually rotated to allow measurements to be made at several angular positions. the spectra of all positions can then be averaged. if the solid samples exist in
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to eliminate the effect of anisotropy, the sample is usually mounted in a wheel and can be manually rotated to allow measurements to be made at several angular positions. the spectra of all positions can then be averaged. if the solid samples exist in the form of a powder, they can be measured via diffuse reflectance by using a device known as an integrating sphere. integrating spheres were developed early in the twentieth century and were originally used to measure the total output of a light source without reference to the original direction of the light. they are now commonly used when measuring the uv / visible or ir absorption spectra of solid samples, and their use can be extended to the uv / visible cd spectroscopy of solids. light enters the sphere through an inlet port, and the internal surfaces of the sphere are usually white, reflective, and diffuse, so that the light becomes equally distributed within the sphere through multiple scattering reflections. a detector is placed at an outlet port and the intensity of the light is measured. for cd spectroscopy, the sample can be placed either at the inlet port, so that the light passes through it before entering the sphere, or at a point on the sphere opposite the inlet port, so that light is diffusely reflected from the sample after entering the sphere. these two operating modes are called transmission and diffuse reflectance, respectively. in both cases the sample is prepared in powder form. for transmission mode, it must then be dispersed in either potassium bromide or potassium chloride and compressed into a disc. for diffuse reflectance mode, it remains as a free powder, if necessary dispersed in a diluent such as barium sulphate or polytetrafluoroethylene ( ptfe ). = = = studying fast reactions = = = many commercially available cd spectrophotometers are designed to be outfitted with a stopped - flow device for studying the kinetics of fast reactions in solution. in the simplest form of the technique, the solutions of two reactants are rapidly mixed by being forced through a mixing chamber, on emerging from which the mixed fluid passes through an optical observation cell. at some point in time, the flow is suddenly stopped, and the reaction is monitored using a suitable spectroscopic probe, such as absorbance, fluorescence, fluorescence polarization, or circular dichroism. the change in spectroscopic signal as a function of time is recorded, and the rate constants that define the reaction kinetics can then be obtained by fitting the data using a suitable model. = = experimental limitations = =
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dichroism. the change in spectroscopic signal as a function of time is recorded, and the rate constants that define the reaction kinetics can then be obtained by fitting the data using a suitable model. = = experimental limitations = = cd has also been studied in carbohydrates, but with limited success due to the experimental difficulties associated with measurement of cd spectra in the vacuum ultraviolet ( vuv ) region of the spectrum ( 100 to 200 nm ), where the corresponding cd bands of unsubstituted carbohydrates lie. substituted carbohydrates with bands above the vuv region have been successfully measured. measurement of far - uv cd is also complicated by the fact that typical aqueous buffer systems at physiological buffer and salt concentrations often significantly absorb in the far - uv range. phosphate, tris, and hepes are tolerated, but the concentration should be minimized ( e. g., ideally 10 - 20 mm ). buffer salts also exhibit surprisingly high absorbance at the lower end of the far - uv range and it should be endeavored to stay below approximately 50 mm ( pathlength dependent ). some experimenters have substituted fluoride for chloride ion because fluoride absorbs less in the far uv, and some have worked in pure water. even water itself will absorb below approximately 180 nm. one notable workaround includes switching from h2o to d2o, thus potentially enabling measurements to as low as 171 nm. because cd is fundamentally an absorption technique and obeys beer ’ s law, another trick is to minimize buffer absorption by using shorter path length cells / cuvettes when working in the far - uv ; 0. 1 - 0. 5 mm path lengths are not uncommon in this work. on the other hand, near - uv experiments do not suffer from most of these considerations and are typically conducted at higher concentrations in standard 10 mm pathlength cuvettes. concentration and pathlength form a mathematical product to make absorbance and are therefore linearly interchangeable to achieve the same absorbance value. in addition to measuring in aqueous systems, cd, particularly far - uv cd, can be measured in organic solvents e. g. ethanol, methanol, acetonitrile, trifluoroethanol ( tfe ) up to varying percentages of organic solvent. tfe has the advantage of being well - tolerated and inducing structure formation of proteins, inducing beta - sheets in some and alpha helices
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##rile, trifluoroethanol ( tfe ) up to varying percentages of organic solvent. tfe has the advantage of being well - tolerated and inducing structure formation of proteins, inducing beta - sheets in some and alpha helices in others, which would not be observed under normal aqueous conditions. many common organic solvents such as acetone, thf, dioxane, chloroform, and dichloromethane are generally incompatible with far - uv cd. it may be of interest to note that the protein cd spectra used in secondary structure estimation are related to the π to π * and n to π * orbital transitions of the amide bonds in the amino acid backbone. these absorption bands lie partly in the so - called vacuum ultraviolet ( wavelengths less than about 200 nm ). the wavelength region of interest is actually inaccessible in air because of the strong absorption of light by oxygen at these wavelengths, which also results in the production of ozone. ozone is a highly reactive gas that is damaging to health and to the optical components of the spectrometer. moreover, even trace amounts of oxygen or ozone present in the lamp or monochromator will hinder acquisition of cd data. ozone has a strong and broad absorbance peak at approximately 250 nm, and a further broad peak around 600 nm, thereby attenuating the light from the spectrometer lamp across a large portion of its wavelength range, particularly in the uv region. in practice these spectra are measured not in vacuum but in an oxygen - free instrument ( purged with high - pure nitrogen gas from a tank or dewar ). once oxygen has been eliminated, perhaps the second most important technical factor in working below 200 nm is to design the rest of the optical system to have low losses in this region. critical in this regard is the use of aluminized mirrors whose coatings have been optimized for low loss in the far - uv region of the spectrum. the usual light source in these instruments is a high pressure, xenon arc lamp. xenon light sources are very stable and produce a broad and even emission spectrum from the far - uv through the near - ir. ordinary xenon arc lamps are unsuitable for use in the low uv. instead, specially constructed xenon arc lamps with envelopes made from high - purity synthetic fused silica must be used. light from synchrotron sources has a much higher flux at short wavelengths, and has been used to record cd down to 160 nm
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specially constructed xenon arc lamps with envelopes made from high - purity synthetic fused silica must be used. light from synchrotron sources has a much higher flux at short wavelengths, and has been used to record cd down to 160 nm. in 2010 the cd spectrophotometer at the electron storage ring facility isa at the university of aarhus in denmark was used to record solid state cd spectra down to 120 nm. at the quantum mechanical level, the feature density of circular dichroism and optical rotation are identical. optical rotary dispersion and circular dichroism share the same quantum information content. = = see also = = = = references = = = = external links = = circular dichroism spectroscopy by alliance protein laboratories, a commercial service provider an introduction to circular dichroism spectroscopy by applied photophysics, an equipment supplier an animated, step - by - step tutorial on circular dichroism and optical rotation by prof valev.
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prosocial behavior is a social behavior that " benefit [ s ] other people or society as a whole ", " such as helping, sharing, donating, co - operating, and volunteering ". the person may or may not intend to benefit others ; the behavior's prosocial benefits are often only calculable after the fact. ( consider : someone may intend to'do good'but the effects may be catastrophic. ) obeying the rules and conforming to socially accepted behaviors ( such as stopping at a " stop " sign or paying for groceries ) are also regarded as prosocial behaviors. these actions may be motivated by culturally influenced value systems ; empathy and concern about the welfare and rights of others ; egoistic or practical concerns, such as one's social status or reputation, hope for direct or indirect reciprocity, or adherence to one's perceived system of fairness ; or altruism, though the existence of pure altruism is somewhat disputed, and some have argued that this falls into the philosophical rather than psychological realm of debate. evidence suggests that prosociality is central to the well - being of social groups across a range of scales, including schools. prosocial behavior in the classroom can have a significant impact on a student's motivation for learning and contributions to the classroom and larger community. in the workplace, prosocial behavior can have a significant impact on team psychological safety, as well as positive indirect effects on employee's helping behaviors and task performance. empathy is a strong motive in eliciting prosocial behavior, and has deep evolutionary roots. prosocial behavior fosters positive traits that are beneficial for children and society. it helps many beneficial functions by bettering production of any league and its organizational scale. evolutionary psychologists use theories such as kin - selection theory and inclusive fitness as an explanation for why prosocial behavioral tendencies are passed down generationally, according to the evolutionary fitness displayed by those who engaged in prosocial acts. encouraging prosocial behavior may also require decreasing or eliminating undesirable social behaviors. although the term " prosocial behavior " is often associated with developing desirable traits in children, the literature on the topic has grown since the late 1980s to include adult behaviors as well. the term " prosocial " has grown into a world - wide movement, using evolutionary science to create real - world pro - social changes from working groups to whole cultures. = = origin of the term = = according to the psychology researcher daniel batson,
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" prosocial " has grown into a world - wide movement, using evolutionary science to create real - world pro - social changes from working groups to whole cultures. = = origin of the term = = according to the psychology researcher daniel batson, the term " was created by social scientists as an antonym for antisocial. " = = reciprocity vs. altruism in motivation = = the purest forms of prosocial behavior are motivated by altruism, an unselfish interest in helping another person. according to psychology professor john w. santrock, the circumstances most likely to evoke altruism are empathy for an individual in need, or a close relationship between the benefactor and the recipient. however, many prosocial behaviors that appear altruistic are in fact motivated by the norm of reciprocity, which is the obligation to return a favor with a favor. people feel guilty when they do not reciprocate and they may feel angry when someone else does not reciprocate. reciprocal altruism suggests that " such helping is driven by a genetic tendency ". thus some professionals argue that altruism may not exist, and is completely motivated by reciprocity. either reciprocity or altruism may motivate many important prosocial behaviors, including sharing. = = situational and individual factors = = prosocial behavior is mediated by both situational and individual factors. = = = situational factors = = = one of the most common situation factors is the occurrence of the bystander effect. the bystander effect is the phenomenon that an individual's likelihood of helping decreases when passive bystanders are present in a critical situation. for example, when someone drops a stack of papers on a crowded sidewalk, most people are likely to continue passing him / her by. this example can be extended to even more urgent situations, such as a car crash or natural disaster. the decision model of bystander intervention noted that whether or not an individual gives aid in a situation depends upon their analysis of the situation. an individual will consider whether or not the situation requires their assistance, if the assistance is the responsibility of the individual, and how to help. this model, proposed by professors bibb latane and john m. darley, describes five things that must occur in order for a person to intervene : notice the situation construe it as an emergency. develop feelings of responsibility. believe they have skills to succeed. reach a conscious decision to help
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john m. darley, describes five things that must occur in order for a person to intervene : notice the situation construe it as an emergency. develop feelings of responsibility. believe they have skills to succeed. reach a conscious decision to help. the number of individuals present in the situation requiring help is also a mediating factor in one's decision to give aid, where the more individuals are present, the less likely it is for one particular individual to give aid due to a reduction in perceived personal responsibility. this is known as diffusion of responsibility, where the responsibility one feels for the person ( s ) in need is divided by the number of bystanders. another factor that comes into play is evaluation apprehension, which simply refers to the fear of being judged by other bystanders. finally, pluralistic ignorance may also lead to someone not intervening. this refers to relying on the reaction of others, before reacting yourself. additionally, psychology professors john f. dovidio, jane allyn piliavin, and colleagues ( 1981 ) noted that individuals are likely to maximize their rewards and minimize their costs when determining whether or not to give aid in a situation – that is, that people are rationally self - motivated. prosocial behavior is more likely to occur if the cost of helping is low ( i. e. minimal time, or minimal effort ), if helping would actually benefit the individual providing the help in some way, and if the rewards of providing the help are large. if it is in an individual's interest to help, they will most likely do so, especially if the cost of not providing the help is great. people are also more likely to help those in their social group, or their " in group ". with a sense of shared identity with the individual requiring assistance, the altruist is more likely to provide help, on the basis that one allocates more time and energy towards helping behavior within individuals of their own group. the labeling of another individual as a member of one's " in - group " leads to greater feelings of closeness, emotional arousal, and a heightened sense of personal responsibility for the other's welfare, all of which increase the motivation to act prosocially. researchers have also found that social exclusion decreases the likelihood of prosocial behavior occurring. in a series of seven experiments conducted in 2007 by professor jean m. twenge and colleagues, researchers manipulated social inclusion or exclusion by telling research participants that other participants had purposefully excluded them, or that they would probably
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prosocial behavior occurring. in a series of seven experiments conducted in 2007 by professor jean m. twenge and colleagues, researchers manipulated social inclusion or exclusion by telling research participants that other participants had purposefully excluded them, or that they would probably end up alone later in life. they found that this preliminary social exclusion caused prosocial behavior to drop significantly, noting that " socially excluded people donated less money to a student fund, were unwilling to volunteer for further lab experiments, were less helpful after a mishap, and cooperated less in a mixed - motive game with another student. " this effect is thought to be due to the fact that prosocial behavior, again, is motivated by a sense of responsibility in caring for and sharing resources with members of one's own group. = = = individual factors = = = individuals can be compelled to act prosocially based on learning and socialization during childhood. operant conditioning and social learning positively reinforces discrete instances of prosocial behaviors. cognitive capacities like intelligence for example, are almost always related to prosocial likings. helping skills and a habitual motivation to help others is therefore socialized, and reinforced as children understand why helping skills should be used to help others around them. social and individual standards and ideals also motivate individuals to engage in prosocial behavior. social responsibility norms, and social reciprocity norms reinforce those who act prosocially. as an example, consider the child who is positively reinforced for " sharing " during their early childhood years. when acting prosocially, individuals reinforce and maintain their positive self - images or personal ideals, as well as help to fulfill their own personal needs. the correlation between a helper's state and helping tendencies are greatly restricted to the relationship between whoever takes part in the situation. emotional arousal is an additional important motivator for prosocial behavior in general. batson's ( 1987 ) empathy - altruism model examines the emotional and motivational component of prosocial behavior. feeling empathy towards the individual needing aid increases the likelihood that the aid will be given. this empathy is called " empathetic concern " for the other individual, and is characterized by feelings of tenderness, compassion, and sympathy. agreeableness is thought to be the personality trait most associated with inherent prosocial motivation. prosocial thoughts and feelings may be defined as a sense of responsibility for other individuals, and a higher likelihood of experiencing empathy ( " other - oriented empathy " ) both affect
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thought to be the personality trait most associated with inherent prosocial motivation. prosocial thoughts and feelings may be defined as a sense of responsibility for other individuals, and a higher likelihood of experiencing empathy ( " other - oriented empathy " ) both affectively ( emotionally ) and cognitively. these prosocial thoughts and feelings correlate with dispositional empathy and dispositional agreeableness. = = = = wealth = = = = subjective wealth correlated positively with all aspects of prosociality in a preregistered study of 80, 337 people from 76 countries, representing 90 % of global population. objective wealth correlated positively with positive reciprocity, donating, volunteering, and helping strangers but negatively with trust. the results were highly consistent across the world, without any systematic variation. = = = other factors = = = in addition to situational and individualistic factors, there are some categorical characteristics that can impact prosocial behavior. several studies have indicated a positive relationship between prosocial behavior and religion as well as social status. in addition, there may be sex differences in prosocial behavior, particularly as youths move into adolescence. research suggests that while women and men both engage in prosocial behaviors, women tend to engage in more communal and relational prosocial behaviors whereas men tend to engage in more agentic prosocial behaviors. a recent study examining workplace charitable giving looked at the role of both sex and ethnicity. results showed that women gave significantly more than men, and caucasians gave significantly more than minority groups. however, the percent of minority individuals in the workplace was positively associated with workplace charitable giving by minorities. culture, sex, and religion are important factors to consider in understanding prosocial behavior on an individual and group level. = = in childhood through early adolescence = = prosocial behavior in childhood often begins with questions of sharing and fairness. from age 12 – 18 months, children begin to display prosocial behavior in presenting and giving their toys to their parents, without promoting or being reinforced by praise. the development of prosocial behavior continues throughout the second year of life, as children begin to gain a moral understanding of the world. as obedience to societal standards becomes important, children's ability to exhibit prosocial behavior strengthens, with occurrence and diversity of these behaviors increasing with age and cognitive maturity. what is important developmentally is that the child has developed a belief that sharing is an obligatory part of a social relationship and involves a question of right and wrong. so, as children
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with occurrence and diversity of these behaviors increasing with age and cognitive maturity. what is important developmentally is that the child has developed a belief that sharing is an obligatory part of a social relationship and involves a question of right and wrong. so, as children move through childhood, their reasoning changes from being hedonistic and needs - oriented to becoming more concerned with approval and more involved in complex cognitive forms of perspective taking and reciprocity reasoning. additionally, children's prosocial behavior is typically more centered around interest in friends and concern for approval, whereas adolescents begin to develop reasoning that is more concerned with abstract principles such as guilt and positive affect. parents can set examples that children carry into their interactions and communication with peers, but parents are not present during all of their children's peer exchanges. the day - to - day constructions of fairness standards is done by children in collaboration and negotiation with each other. recent research demonstrates that invoking the self using subtle linguistic cues ( e. g. identifying someone as a " helper " versus labeling the action, " helping " ) fosters the perception that a behavior reflects identity, and increases helping, or prosocial, behaviors in children significantly across tasks. another study by psychology professor amelie nantel - vivier and colleagues ( 2009 ) used a multi - informant model to investigate the development of prosocial behaviour in both canadian and italian adolescents aged 10 – 15. their findings have indicated that, in early adolescence, although empathy and moral reasoning continue to advance, the development of prosocial behaviors reaches a plateau. theories for this change in development suggest that it is the result of more individualized and selective prosocial behaviors. during adolescence, youth begin to focus these behaviors toward their peer groups and / or affiliations. consistent with previous analyses, this study also found a tendency toward higher prosocial behaviors in young adolescent girls compared to their male classmates. the earlier maturation in females may be a possible explanation for this disparity. a more recent study that focused on the effects of pubertal timing found that early maturation in adolescents has a positive impact on prosocial behaviors. while their findings apply to both genders, this study found a much more pronounced effect in males. this suggests that earlier onset of puberty has a positive correlation with the development of prosocial behaviors. in many indigenous american communities, prosocial behavior is a valued means of learning and child rearing. such behaviors are seen as contributing in an eagerly collaborative and flexible environment, aimed at teaching consideration,
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correlation with the development of prosocial behaviors. in many indigenous american communities, prosocial behavior is a valued means of learning and child rearing. such behaviors are seen as contributing in an eagerly collaborative and flexible environment, aimed at teaching consideration, responsibility, and skills with the guidance and support of adults. culturally valued developmental goals are integrally tied to children's participation in these contexts. it is also helpful for children to learn cultural mores in addition to individual personality development. children learn functional life skills through real - time observation of adults and interactive participation of these learned skills within their community. = = in education = = prosocial behavior can act as a strong motivator in education, for it provides students with a purpose beyond themselves and the classroom. this purpose beyond the self, or self - transcendence, is an innate human need to be a part of something bigger than themselves. when learning in isolation, the way western academics are traditionally designed, students struggle to make connections to the material and its greater overarching purpose. this disconnection harms student learning, motivation, and attitudes about education. if teachers make space for prosocial behavior in education and social learning, then they can illustrate that what students are learning will have a direct impact on the world that they live in. this would be considered a mutually constituting relationship, or a relationship in which both individuals and culture develop interdependently. in other words, what students are learning in a classroom could be intimately connected with a purpose towards a greater cause, deepening the learning itself. studies by yeager et al. test the effects of having a self - transcendent purpose for learning, with the results showing that such a purpose for learning led to fewer future college dropouts, increased high school math and science gpas, and persistence on boring tasks. this self transcendent purpose may not only encourage persistence on boring tasks, but may help to make boring tasks more meaningful and engaging. a person's ideas and opinions are largely shaped by the world that they grow up in, which in turn determines what sort of change they want to instill in the world. for example : a girl who grew up in poverty becoming a social worker. the environment she grew up in gave her an awareness of the workings of poverty, motivating her to instill change in either the institutions that cause it, or help those affected by poverty. there aren't many opportunities to make prosocial contributions in school ; which makes school feel isolated and
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of the workings of poverty, motivating her to instill change in either the institutions that cause it, or help those affected by poverty. there aren't many opportunities to make prosocial contributions in school ; which makes school feel isolated and irrelevant. by encouraging students to find a self - transcendent purpose in their learning, others enable them to enjoy their learning and make connections to community contributions. = = in the workplace = = studies and meta - studies have shown an association between pro - social behaviour and successful outcomes for an organisation, such as increased profitability and shareholder value. the association holds true for pro - social behaviour on the part of both workers and bosses. = = influences = = = = = media programming and video games on children = = = studies have shown that different types of media programming may evoke prosocial behaviors in children. the channels aimed at younger viewers like nickelodeon and disney channel had significantly more acts of altruism than the general - audience demographic channels like a & e and or tnt, according to one large - scale study. this study examined the programming of 18 different channels, including more than 2, 000 entertainment shows, during a randomly selected week on television. the study revealed that nearly three quarters ( 73 percent ) of programs contained at least one act of altruism and on average viewers saw around three acts of altruism an hour. around one - third of those behaviors were explicitly rewarded in the plot, potentially sending the message that these acts of prosocial behavior can come with positive consequences. another study on the topic was conducted by university at buffalo, iowa state university and university of minnesota professors. they studied children for two years for the purpose of investigating the role of media exposure on prosocial behavior for young boys and girls. the study concluded that media exposure could possibly predict outcomes related to prosocial behavior. other experimental research has suggested that prosocial video games may increase prosocial behavior in players although some of this work has proven difficult to replicate. however other scholars have been critical of this work for tending to falsely dichotomize video games into prosocial / violent categories despite significant overlap as well as methodological flaws in the experimental studies. for instance a study by ferguson and garza found that exposure to violent video games was associated with increased prosocial behavior, both on - line as well as volunteering in the real world. the authors speculated this may be due to the prosocial themes common in many violent games, as well as team oriented play in
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games was associated with increased prosocial behavior, both on - line as well as volunteering in the real world. the authors speculated this may be due to the prosocial themes common in many violent games, as well as team oriented play in many games. = = = = legislation = = = = in the united states, in an effort to get stations to air education and prosocial programming for children, the children's television act was adopted in 1990. it states that channels must produce and air programming developed specifically for children as a condition to renew broadcast licenses. after discussions as to what the definition of " specifically designed for children " really means, in 1996 guidelines were passed to correct this ambiguity. = = = arts = = = the arts are increasingly recognized as influential for health behaviors in strengthening social bonds and cohesion and promoting prosocial behavior. evidence of the impact of different arts is emerging and research is growing on literature, movies and theatre. a review of current literature argues that performative arts are more prone to elicit empathic concern which is linked with more durable prosocial behavior during stressful situations such as the covid - 19 pandemic outbreak : in particular theatre and virtual reality are seen as promising. an active role of the arts in sustaining prosocial behavior should however integrate an ethical approach to avoid the risk of mass manipulation and intergroup bias. = = = observation = = = people are generally much more likely to act pro - socially in a public setting rather than in a private setting. one explanation for this finding has to do with perceived status, being publicly recognized as a pro - social individual often enhance one's self - image and desirability to be considered for inclusion in social groups. other research has shown that merely given people the " illusion " that they are being observed ( e. g., by hanging up posters of " staring " human eyes ) can generate significant changes in pro - social acts such as charitable giving and less littering. pictures of human eyes trigger an involuntary neural gaze detection mechanism, which primes people to act pro - socially. there are two different forms of prosocial behaviors. ordinary prosocial behavior requires " situational and sociocultural demands ". extraordinary prosocial behavior doesn't include as much. this indicates that one form is used for a more selfish result while the other is not. = = perception of responsibility and guilt = = guilt has long been regarded as a motivator for prosocial behavior. extensive data from a 2012 study
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. this indicates that one form is used for a more selfish result while the other is not. = = perception of responsibility and guilt = = guilt has long been regarded as a motivator for prosocial behavior. extensive data from a 2012 study conducted by de hooge, demonstrates that when a secondary individual repairs a transgressors'damage caused to victims, the transgressors'guilt feelings, reparative intentions, and prosocial behavior drastically diminish. thus, reduction of guilt may have more to do with reparative actions broadly, rather than necessarily prosocial behaviors taken on by oneself. = = social media effects = = global use of social media is growing, especially among adolescent social media users. the negative effects of social media has been a large focus of scientific research ; however, social media can also be a catalyst for prosocial behavior both online and offline. social media is one of the most newly profound ways to spread awareness. erreygers and colleagues define online prosocial behavior as " voluntary behavior carried out in an electronic context with the intention of benefitting particular others or promoting harmonious relations with others ". examples of online prosocial behavior include electronic donation of money to specific causes or the sharing of information and resources, such as in times of natural disaster. one example of online prosocial behavior during natural disasters is the relief efforts in the wake of the 2011 tohoku earthquake and tsunami off the coast of japan, when users turned to facebook and twitter to provide financial and emotional support via their social networks. direct donations to japanese relief were possible on the red cross fan page on facebook, and via online discount sites like groupon and livingsocial. = = relation to mood and emotion = = mood and prosocial behavior are closely linked. people often experience the " feel good - do good " phenomena, where being in a good mood increases helping behaviors. being in a good mood helps us to see the " good " in other people, and prolongs our own good mood. for example, mood and work behaviors have frequently been examined in research ; studies show that positive mood at work is associated with more positive work - related behaviors ( e. g., helping co - workers ). similarly, prosocial behaviors increase positive mood. several studies have shown the benefits of volunteering and other prosocial behaviors on self - esteem, life satisfaction, and overall mental health. additionally, negative mood can also impact prosocial behavior. research has shown that guilt
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behaviors increase positive mood. several studies have shown the benefits of volunteering and other prosocial behaviors on self - esteem, life satisfaction, and overall mental health. additionally, negative mood can also impact prosocial behavior. research has shown that guilt often leads to prosocial behaviors, whereas other negative mood states, such as fear, do not lead to the same prosocial behaviors. a recent pilot study examined whether an intervention increasing prosocial behavior ( kind acts ) in young adults with social anxiety would both increase positive affect and decrease social anxiety in participants. participants randomly assigned to a four - week kind acts intervention, where individuals were instructed to engage in three kind acts each day twice a week over the four - week period, showed both higher self - reported positive mood and increased satisfaction with relationships at the end of the intervention. this intervention demonstrates ways in which prosocial behavior may be beneficial in improving mood and mental health. a meta - analysis from 2020 by hui et al., which looked at 126 prior studies involving almost 200, 000 participants, found that spontaneous instances of prosocial behavior, such as helping an older neighbor carry groceries, had a stronger positive effect on well - being than did more formal instances of prosocial behavior, such as volunteering for a charity at a pre - scheduled time. other research suggests that cultivating positive emotions, such as gratitude, may also facilitate prosocial behavior. a study by bartlett & desteno examined the ability of gratitude to shape costly prosocial behavior, demonstrating that gratitude increases efforts to assist a benefactor even when such efforts are costly ( i. e., hedonically negative ), and that this increase is qualitatively different from efforts given from just general positive affective state. they also show that gratitude can increase assistance provided to strangers, not just close social ties. awe is another positive emotional state that has been closely linked to inspiring generosity and prosocial behavior. piff et al. studied this phenomenon through experiments using economic and ethical - decision making games and explain, " when people experience awe they really want to share that experience with other people, suggesting that it has this particularly viral component to it... awe binds people together — by causing people to want to share their positive experiences collectively with one another. " = = psychopathy and lack of prosocial behavior = = in 1941, hervey cleckley described psychopathy as a disorder in which individuals often initially appear intelligent, charming, and even kind but are in fact egocentric,
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another. " = = psychopathy and lack of prosocial behavior = = in 1941, hervey cleckley described psychopathy as a disorder in which individuals often initially appear intelligent, charming, and even kind but are in fact egocentric, grandiose and impulsive. he described individuals who would, on a whim, leave their families to cross the country gambling, drinking and fighting, only to return and act as if nothing was out of the ordinary. today, psychopathy is described as a personality disorder that is characterized by decreased anxiety, fear, and social closeness as well as increased impulsivity, manipulativeness, interpersonal dominance and aggression. these traits lead to numerous types of antisocial behavior including high rates of substance abuse, serial short term relationships, and various forms of criminal behavior. one common misconception about psychopathy though is that all psychopaths are serial killers or other vicious criminals. in reality, many researchers do not consider criminal behavior to be a criterion for the disorder although the role of criminality in the disorder is strongly debated. additionally, psychopathy is being researched as a dimensional construct that is one extreme of normal range personality traits instead of a categorical disorder. in regards to the lack of prosocial behavior in psychopathy, there are several theories that have been proposed in the literature. one theory suggests that psychopaths engage in less prosocial behavior ( and conversely more antisocial behavior ) because of a deficit in their ability to recognize fear in others, particularly fearful facial expressions. because they are unable to recognize that their actions are causing another distress, they continue that behavior in order to obtain some goal that benefits them. a second theory proposes that psychopaths have a sense of " altruistic punishment " where they are willing to punish other individuals even if it means they will be harmed in some way. there has also been an evolutionary theory proposed stating that psychopaths lack of prosocial behavior is an adaptive mating strategy in that it allows them to spread more of their genes while taking less responsibility for their offspring. finally, there is some evidence that in some situations psychopaths behavior may not be antisocial but instead it may be more utilitarian than other individuals. in a recent study, bartels & pizarro ( 2011 ) found that when making decisions about traditional moral dilemmas such as the trolley problem, individuals high in psychopathic traits actually make more utilitarian ( and therefore more moral in some views ) choices. this finding is particularly
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& pizarro ( 2011 ) found that when making decisions about traditional moral dilemmas such as the trolley problem, individuals high in psychopathic traits actually make more utilitarian ( and therefore more moral in some views ) choices. this finding is particularly interesting because it suggests that psychopaths, who are often considered immoral or even evil, may actually make better moral decisions than non - psychopaths. the authors of this study conclude that individuals high in psychopathic traits are less influenced by their emotions and therefore make more " mathematical " decisions and choose the option that leads to the lowest number of deaths. the theories discussed above are not intended to be a comprehensive list but instead to provide a sense of how psychopaths differ in their approach to social interactions. as with most psychological / social phenomena, it is likely a combination of these factors that leads to psychopaths'lack of prosocial behavior. further research is needed to determine the causal nature of any one of these individual deficits as well as if there is any way to help these individuals develop more prosocial patterns of behavior. = = helper's high = = psychologists have shown that helping others can produce " feel - good " neurotransmitters such as oxytocin and that, similar to any other pleasurable activity, the act of volunteering, giving and behaving pro - socially can become addictive ( warm - glow giving ). some work has been done on utilizing this principle through the concept of helper therapy, in which therapeutic benefits are gleaned from assisting others. community health workers have been found to gain helper benefits that include positive feelings about self, a sense of belonging, valuable work experience, and access to health information and skills through their prosocial vocation, which may buffer against the various stressors inherent in this line of work. in addition, helper therapy may also be highly beneficial for distressed adolescents experiencing suicidal thoughts. studies indicate that when help - seeking youth use online community forums, the help - seekers often begin to provide support for other help seekers, and develop a reciprocal prosocial community battling depression together. = = prosocial dissidence = = stefano passini and davide morselli argue that groups will obey authority so long as its system, basis, and demands are viewed as legitimate. passini and morselli distinguish between anti - social disobedience, which they see as destructive, and prosocial disobedience, which they see as constructive. " di
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its system, basis, and demands are viewed as legitimate. passini and morselli distinguish between anti - social disobedience, which they see as destructive, and prosocial disobedience, which they see as constructive. " disobedience becomes prosocial when it is enacted for the sake of the whole society, including all its different levels and groups. in contrast, anti - social disobedience is enacted mainly in favour of one's own group, in order to attain individual rights. " a main difference between anti - social and pro - social dissidence is the way that they relate to authority ; anti - social dissidents reject authority and disobey its norms and laws, while pro - social dissidents understand the important roles that societal laws play in maintaining order, but also recognize and address the flaws in authoritative reasoning. pro - social protests, if viewed in a positive manner, can increase freedoms and equality for the general public, and improve democratic institutions. = = labor market outcomes = = recent scientific research shows that individuals who volunteer have better labor market outcomes in terms of hiring opportunities and wages. = = see also = = altruism – concern for the well - being of others cooperation – groups working or acting together eusociality – highest level of animal sociality a species can attain friendship – mutual affection between people helping behavior – voluntarily prosocial behaviour humanitarian aid – material or logistical assistance for people in need reciprocal altruism – form of behaviour between organisms rescue – operations for life saving, removal from danger and liberation from restrain sharing – joint use of a resource or space social animal – form of collective animal behaviourpages displaying short descriptions of redirect targets socialization – the lifelong process of inheriting and disseminating norms, customs and ideologies social psychology – study of social effects on people's thoughts, feelings, and behaviors social support – support systems for individuals social value orientations – gamespages displaying wikidata descriptions as a fallbackpages displaying short descriptions with no spaces volunteering – act of freely giving time and labor tootling – reporting of only positive, rather than inappropriate, social behaviors = = references = = = = further reading = = eisenberg, nancy ; paul henry mussen ( 1989 ). the roots of prosocial behavior in children. cambridge university press. isbn 978 - 0 - 521 - 33771 - 7. zimmerman, barbara j. ; gary d. levy ( 2000 ). " social cognitive
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mussen ( 1989 ). the roots of prosocial behavior in children. cambridge university press. isbn 978 - 0 - 521 - 33771 - 7. zimmerman, barbara j. ; gary d. levy ( 2000 ). " social cognitive predictors of prosocial behavior toward same and alternate race children among white pre - schoolers. ( statistical data included ) ". current psychology. 19 ( 3 ) : 175. doi : 10. 1007 / s12144 - 000 - 1014 - 8. s2cid 144309649. muus, harriet ( 12 august 2024 ). " evolutionary ethics and mate selection ". psyarxiv. center for open science. doi : 10. 31234 / osf. io / c659q. prosocial behavior. excerpt from " more about generosity : an addendum to the generosity, social psychology and philanthropy literature reviews ", university of notre dame, july 7, 2009 penner, louis a ; dovidio, john f ; piliavin, jane a ; schroeder, david a ( 2005 ). " prosocial behavior : multilevel perspectives ". annual review of psychology. 56 : 365 – 92. doi : 10. 1146 / annurev. psych. 56. 091103. 070141. pmid 15709940. patrick, christopher j. ( 2006 ). handbook of the psychopathy. new york : guilford press. paciello, m ; fida r ; cerniglia l ; tramontano c ; cole e ( 2013 ). " high cost helping scenario : the role of empathy, prosocial reasoning and moral disengagement on helping behavior ". personality and individual differences. 55 : 3 – 7. doi : 10. 1016 / j. paid. 2012. 11. 004. biglan, anthony ( 2015 ) the nurture effect : how the science of human behavior can improve our lives and our world. new harbinger, oakland, california = = external links = = prosocial behavior page, us dept. of health and human services, administration for children and families prosocial behavior, psychwiki. com informational report describing prosocial behaviour npr interview with commentary on prosocial behavior from david sloan wilson, aug. 28, 2011, 7 min. the greater good institute : research on altruism, empathy and prosocial behavior changing minds the evolution institute
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david ricardo serrano goncalves sobral ( born 11 february 1986 ) is a portuguese astrophysicist, best known for the discovery of galaxy cr - 7. he was an astrophysics lecturer and reader at lancaster university from january 2016 to august 2022. = = publications = = a large h alpha survey at z = 2. 23, 1. 47, 0. 84 and 0. 40 : the 11 gyr evolution of star - forming galaxies from hizels, monthly notices of the royal astronomical society in 2013 evidence for popiii - like stellar populations in the most luminous lyα emitters at the epoch of reionization : spectroscopic confirmation, the astrophysical journal 808 ( 2 ) chasing a starlight : investigating one of the oldest known galaxies with muse = = references = =
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a carboxypeptidase ( ec number 3. 4. 16 - 3. 4. 18 ) is a protease enzyme that hydrolyzes ( cleaves ) a peptide bond at the carboxy - terminal ( c - terminal ) end of a protein or peptide. this is in contrast to an aminopeptidases, which cleave peptide bonds at the n - terminus of proteins. humans, animals, bacteria and plants contain several types of carboxypeptidases that have diverse functions ranging from catabolism to protein maturation. at least two mechanisms have been discussed. = = functions = = initial studies on carboxypeptidases focused on pancreatic carboxypeptidases a1, a2, and b in the digestion of food. most carboxypeptidases are not, however, involved in catabolism. instead they help to mature proteins, for example post - translational modification. they also regulate biological processes, such as the biosynthesis of neuroendocrine peptides such as insulin requires a carboxypeptidase. carboxypeptidases also function in blood clotting, growth factor production, wound healing, reproduction, and many other processes. = = mechanism = = carboxypeptidases hydrolyze peptides at the first amide or polypeptide bond on the c - terminal end of the chain. carboxypeptidases act by replacing the substrate water with a carbonyl ( c = o ) group. the carboxypeptidase a hydrolysis reaction has two mechanistic hypotheses, via a nucleophilic water and via an anhydride. in the first proposed mechanism, a promoted - water pathway is favoured as glu270 deprotonates the nucleophilic water. the zn2 + ion, along with positively charged residues, decreases the pka of the bound water to approximately 7. glu 270 has a dual role in this mechanism as it acts as a base to allow for the attack at the amide carbonyl group during nucleophilic addition. it acts as an acid during elimination when the water proton is transferred to the leaving nitrogen group. the oxygen on the amide carbonyl group does not coordinate to the zn2 + until the addition of the water. the deprotonation of the zn2 + coordinated water by glu 270 provides an activated hydro
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leaving nitrogen group. the oxygen on the amide carbonyl group does not coordinate to the zn2 + until the addition of the water. the deprotonation of the zn2 + coordinated water by glu 270 provides an activated hydroxide nucleophile which attacks the amide carbonyl group in the peptide bond in a nucleophilic addition. the negatively charged intermediates that are formed during hydrolysis are stabilized by the zn2 + ion. the interaction between the carbonyl group and the neighbouring arginine, arg 217, also stabilizes the negatively charged intermediates. the zinc - bound hydroxide interacts with the amide with the electrostatic stabilization of the transition state provided by the zn2 + ion and the neighbouring arginine. the second proposed mechanism via an anhydride has similar steps but there is a direct attack of glu270 on the carbonyl group, and then the interaction of glu270 on the zn2 + - bound amide forms an anhydride instead which can subsequently be hydrolyzed by water. = = classifications = = = = = by active site mechanism = = = carboxypeptidases are usually classified into one of several families based on their active site mechanism. enzymes that use a metal in the active site are called " metallo - carboxypeptidases " ( ec number 3. 4. 17 ). other carboxypeptidases that use active site serine residues are called " serine carboxypeptidases " ( ec number 3. 4. 16 ). those that use an active site cysteine are called " cysteine carboxypeptidase " ( or " thiol carboxypeptidases " ) ( ec number 3. 4. 18 ). these names do not refer to the selectivity of the amino acid that is cleaved. = = = by substrate preference = = = another classification system for carboxypeptidases refers to their substrate preference. in this classification system, carboxypeptidases that have a stronger preference for those amino acids containing aromatic or branched hydrocarbon chains are called carboxypeptidase a ( a for aromatic / aliphatic ). carboxypeptidases that cleave positively charged amino acids ( arginine, lysine ) are called carboxypeptidase b ( b for basic ). a metallo - carboxypept
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##phatic ). carboxypeptidases that cleave positively charged amino acids ( arginine, lysine ) are called carboxypeptidase b ( b for basic ). a metallo - carboxypeptidase that cleaves a c - terminal glutamate from the peptide n - acetyl - l - aspartyl - l - glutamate is called " glutamate carboxypeptidase ". a serine carboxypeptidase that cleaves the c - terminal residue from peptides containing the sequence - pro - xaa ( pro is proline, xaa is any amino acid on the c - terminus of a peptide ) is called " prolyl carboxypeptidase ". = = activation = = some, but not all, carboxypeptidases are initially produced in an inactive form ; this precursor form is referred to as a procarboxypeptidase. in the case of pancreatic carboxypeptidase a, the inactive zymogen form - pro - carboxypeptidase a - is converted to its active form - carboxypeptidase a - by the enzyme trypsin. this mechanism ensures that the cells wherein pro - carboxypeptidase a is produced are not themselves digested. = = see also = = carboxypeptidase e carboxypeptidase a enzyme category ec number 3. 4 thrombin - activatable fibrinolysis inhibitor aka plasma carboxypeptidase b2 bacterial transpeptidase, an alanine carboxypeptidase bradykinin is broken down among other enzymes by carboxypeptidase n dd - ala carboxypeptidase is a penicillin - binding protein phenylalanine might inhibit carboxypeptidase a martha l. ludwig = = references = = = = further reading = = = = external links = = carboxypeptidases at the u. s. national library of medicine medical subject headings ( mesh )
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process - centered design ( pcd ) is a design methodology, which proposes a business centric approach for designing user interfaces. because of the multi - stage business analysis steps involved right from the beginning of the pcd life cycle, it is believed to achieve the highest levels of business - it alignment that is possible through ui. = = purpose = = this method is aimed at enterprise applications where there is a business process involved. unlike content oriented systems such as websites or portals, enterprise applications are built to enable a company's business processes. enterprise applications often have a clear business goal and a set of specific objectives like - improve employee productivity, increase business performance by a certain percent, etc. = = comparison between other popular ui design methods = = although there are proven ui design methodologies ( like the most popular " user - centered design ", which helps design highly usable interfaces ), pcd differentiates itself by precisely catering to business process intensive software which has not been the case with other ui design methodologies. = = process - ui alignment = = process - ui alignment is a component of pcd, which ensures tight alignment between the business process and the enterprise application being developed. ui design activities are affected by pcd. for example : a call center software used by a customer support agent, if designed for high process - ui alignment will achieve tremendous agent productivity improvement and call center performance ; which is not likely to be seen if it were designed only for user satisfaction, ease of use, etc. = = see also = = business process overall labor effectiveness user - centered design usability = = references = = = = external links = = align journal, october 3, 2007, retrieved on aug 01, 2008. process - user interface alignment : new value from a new level of alignment more research exploring the relation between business process and user interfaces : acm sac 2008 : sousa, mendonca, vanderdonckt
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flatness in systems theory is a system property that extends the notion of controllability from linear systems to nonlinear dynamical systems. a system that has the flatness property is called a flat system. flat systems have a ( fictitious ) flat output, which can be used to explicitly express all states and inputs in terms of the flat output and a finite number of its derivatives. = = definition = = a nonlinear system x ( t ) = f ( x ( t ), u ( t ) ), x ( 0 ) = x 0, u ( t ) ∈ r m, x ( t ) ∈ r n, rank ∂ f ( x, u ) ∂ u = m { \ displaystyle { \ dot { \ mathbf { x } } } ( t ) = \ mathbf { f } ( \ mathbf { x } ( t ), \ mathbf { u } ( t ) ), \ quad \ mathbf { x } ( 0 ) = \ mathbf { x } _ { 0 }, \ quad \ mathbf { u } ( t ) \ in r ^ { m }, \ quad \ mathbf { x } ( t ) \ in r ^ { n }, { \ text { rank } } { \ frac { \ partial \ mathbf { f } ( \ mathbf { x }, \ mathbf { u } ) } { \ partial \ mathbf { u } } } = m } is flat, if there exists an output y ( t ) = ( y 1 ( t ),..., y m ( t ) ) { \ displaystyle \ mathbf { y } ( t ) = ( y _ { 1 } ( t ),..., y _ { m } ( t ) ) } that satisfies the following conditions : the signals y i, i = 1,..., m { \ displaystyle y _ { i }, i = 1,..., m } are representable as functions of the states x i, i = 1,..., n { \ displaystyle x _ { i }, i = 1,..., n } and inputs u i, i = 1,..., m { \ displaystyle u _ { i }, i = 1,..., m } and a finite number of derivatives with respect to time u i ( k ), k = 1,..., α i { \ displaystyle
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{ \ displaystyle u _ { i }, i = 1,..., m } and a finite number of derivatives with respect to time u i ( k ), k = 1,..., α i { \ displaystyle u _ { i } ^ { ( k ) }, k = 1,..., \ alpha _ { i } } : y = φ ( x, u, u,..., u ( α ) ) { \ displaystyle \ mathbf { y } = \ phi ( \ mathbf { x }, \ mathbf { u }, { \ dot { \ mathbf { u } } },..., \ mathbf { u } ^ { ( \ alpha ) } ) }. the states x i, i = 1,..., n { \ displaystyle x _ { i }, i = 1,..., n } and inputs u i, i = 1,..., m { \ displaystyle u _ { i }, i = 1,..., m } are representable as functions of the outputs y i, i = 1,..., m { \ displaystyle y _ { i }, i = 1,..., m } and of its derivatives with respect to time y i ( k ), i = 1,..., m { \ displaystyle y _ { i } ^ { ( k ) }, i = 1,..., m }. the components of y { \ displaystyle \ mathbf { y } } are differentially independent, that is, they satisfy no differential equation of the form ( y, y, y ( γ ) ) = 0 { \ displaystyle \ phi ( \ mathbf { y }, { \ dot { \ mathbf { y } } }, \ mathbf { y } ^ { ( \ gamma ) } ) = \ mathbf { 0 } }. if these conditions are satisfied at least locally, then the ( possibly fictitious ) output is called flat output, and the system is flat. = = relation to controllability of linear systems = = a linear system x ( t ) = a x ( t ) + b u ( t ), x ( 0 ) = x 0 { \ displaystyle { \ dot { \ mathbf { x } } } ( t ) = \ mathbf { a } \ mathbf { x } (
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( t ) + b u ( t ), x ( 0 ) = x 0 { \ displaystyle { \ dot { \ mathbf { x } } } ( t ) = \ mathbf { a } \ mathbf { x } ( t ) + \ mathbf { b } \ mathbf { u } ( t ), \ quad \ mathbf { x } ( 0 ) = \ mathbf { x } _ { 0 } } with the same signal dimensions for x, u { \ displaystyle \ mathbf { x }, \ mathbf { u } } as the nonlinear system is flat, if and only if it is controllable. for linear systems both properties are equivalent, hence exchangeable. = = significance = = the flatness property is useful for both the analysis of and controller synthesis for nonlinear dynamical systems. it is particularly advantageous for solving trajectory planning problems and asymptotical setpoint following control. = = literature = = m. fliess, j. l. levine, p. martin and p. rouchon : flatness and defect of non - linear systems : introductory theory and examples. international journal of control 61 ( 6 ), pp. 1327 - 1361, 1995 [ 1 ] a. isidori, c. h. moog et a. de luca. a sufficient condition for full linearization via dynamic state feedback. 25th cdc ieee, athens, greece, pp. 203 - 208, 1986 [ 2 ] = = see also = = control theory control engineering controller ( control theory ) flat pseudospectral method
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parasitic chromosomes are " selfish " chromosomes that propagate throughout cell divisions, even if they confer no benefit to the overall organism's survival. parasitic chromosomes can persist even if slightly detrimental to survival, as is characteristic of some selfish genetic elements. parasitic chromosomes are often b chromosomes, such that they are not necessarily present in the majority of the species population and are not needed for basic life functions, in contrast to a chromosomes. parasitic chromosomes are classified as selfish genetic elements. parasitic chromosomes, if detrimental to an organism's survival, often are selected against by natural selection over time, but if the chromosome is able to act like a selfish dna element, it can spread throughout a population. an example of a parasitic chromosome is the b24 chromosome in grasshoppers. = = references = =
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in computer engineering, a load – store architecture ( or a register – register architecture ) is an instruction set architecture that divides instructions into two categories : memory access ( load and store between memory and registers ) and alu operations ( which only occur between registers ). : 9 – 12 some risc architectures such as powerpc, sparc, risc - v, arm, and mips are load – store architectures. : 9 – 12 for instance, in a load – store approach both operands and destination for an add operation must be in registers. this differs from a register – memory architecture ( for example, a cisc instruction set architecture such as x86 ) in which one of the operands for the add operation may be in memory, while the other is in a register. : 9 – 12 the earliest example of a load – store architecture was the cdc 6600. : 54 – 56 almost all vector processors ( including many gpus ) use the load – store approach. = = see also = = load – store unit register – memory architecture = = references = =
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interfacial polymerization is a type of step - growth polymerization in which polymerization occurs at the interface between two immiscible phases ( generally two liquids ), resulting in a polymer that is constrained to the interface. there are several variations of interfacial polymerization, which result in several types of polymer topologies, such as ultra - thin films, nanocapsules, and nanofibers, to name just a few. = = history = = interfacial polymerization ( then termed " interfacial polycondensation " ) was first discovered by emerson l. wittbecker and paul w. morgan in 1959 as an alternative to the typically high - temperature and low - pressure melt polymerization technique. as opposed to melt polymerization, interfacial polymerization reactions can be accomplished using standard laboratory equipment and under atmospheric conditions. this first interfacial polymerization was accomplished using the schotten – baumann reaction, a method to synthesize amides from amines and acid chlorides. in this case, a polyamide, usually synthesized via melt polymerization, was synthesized from diamine and diacid chloride monomers. the diacid chloride monomers were placed in an organic solvent ( benzene ) and the diamene monomers in a water phase, such that when the monomers reached the interface they would polymerize. since 1959, interfacial polymerization has been extensively researched and used to prepare not only polyamides but also polyanilines, polyimides, polyurethanes, polyureas, polypyrroles, polyesters, polysulfonamides, polyphenyl esters and polycarbonates. in recent years, polymers synthesized by interfacial polymerization have been used in applications where a particular topological or physical property is desired, such as conducting polymers for electronics, water purification membranes, and cargo - loading microcapsules. = = mechanism = = the most commonly used interfacial polymerization methods fall into 3 broad types of interfaces : liquid - solid interfaces, liquid - liquid interfaces, and liquid - in - liquid emulsion interfaces. in the liquid - liquid and liquid - in - liquid emulsion interfaces, either one or both liquid phases may contain monomers. there are also other interface categories, rarely used, including liquid - gas, solid - gas, and solid - solid. in a liquid - solid interface, polymerization begins at the interface, and results in a polymer attached to the surface
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monomers. there are also other interface categories, rarely used, including liquid - gas, solid - gas, and solid - solid. in a liquid - solid interface, polymerization begins at the interface, and results in a polymer attached to the surface of the solid phase. in a liquid - liquid interface with monomer dissolved in one phase, polymerization occurs on only one side of the interface, whereas in liquid - liquid interfaces with monomer dissolved in both phases, polymerization occurs on both sides. an interfacial polymerization reaction may proceed either stirred or unstirred. in a stirred reaction, the two phases are combined using vigorous agitation, resulting in a higher interfacial surface area and a higher polymer yield. in the case of capsule synthesis, the size of the capsule is directly determined by the stirring rate of the emulsion. although interfacial polymerization appears to be a relatively straightforward process, there are several experimental variables that can be modified in order to design specific polymers or modify polymer characteristics. some of the more notable variables include the identity of the organic solvent, monomer concentration, reactivity, solubility, the stability of the interface, and the number of functional groups present on the monomers. the identity of the organic solvent is of utmost importance, as it affects several other factors such as monomer diffusion, reaction rate, and polymer solubility and permeability. the number of functional groups present on the monomer is also important, as it affects the polymer topology : a di - substituted monomer will form linear chains whereas a tri - or tetra - substituted monomer forms branched polymers. most interfacial polymerizations are synthesized on a porous support in order to provide additional mechanical strength, allowing delicate nano films to be used in industrial applications. in this case, a good support would consist of pores ranging from 1 to 100 nm. free - standing films, by contrast, do not use a support, and are often used to synthesize unique topologies such as micro - or nanocapsules. in the case of polyurethanes and polyamides especially, the film can be pulled continuously from the interface in an unstirred reaction, forming " ropes " of polymeric film. as the polymer precipitates, it can be withdrawn continuously. it is interesting to note that the molecular weight distribution of polymers synthesized by interfacial polymerization is broader than the flory – schulz distribution due to the high concentration of monomers near the interfacial site
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it can be withdrawn continuously. it is interesting to note that the molecular weight distribution of polymers synthesized by interfacial polymerization is broader than the flory – schulz distribution due to the high concentration of monomers near the interfacial site. because the two solutions used in this reaction are immiscible and the rate of reaction is high, this reaction mechanism tends to produce a small number of long polymer chains of high molecular weight. = = mathematical models = = interfacial polymerization has proven difficult to model accurately due to its nature as a nonequilibrium process. these models provide either analytical or numerical solutions. the wide range of variables involved in interfacial polymerization has led to several different approaches and several different models. one of the more general models of interfacial polymerization, summarized by berezkin and co - workers, involves treating interfacial polymerization as a heterogenous mass transfer combined with a second - order chemical reaction. in order to take into account different variables, this interfacial polymerization model is divided into three scales, yielding three different models : the kinetic model, the local model, and the macrokinetic model. the kinetic model is based on the principles of kinetics, assumes uniform chemical distribution, and describes the system at a molecular level. this model takes into account thermodynamic qualities such as mechanisms, activation energies, rate constants, and equilibrium constants. the kinetic model is typically incorporated into either the local or the macrokinetic model in order to provide greater accuracy. the local model is used to determine the characteristics of polymerization at a section around the interface, termed the diffusion boundary layer. this model can be used to describe a system in which the monomer distribution and concentration are inhomogeneous, and is restricted to a small volume. parameters determined using the local model include the mass transfer weight, the degree of polymerization, topology near the interface, and the molecular weight distribution of the polymer. using local modeling, the dependence of monomer mass transfer characteristics and polymer characteristics as a function of kinetic, diffusion, and concentration factors can be analyzed. one approach to calculating a local model can be represented by the following differential equation : ∂ c i ∂ t = ∂ ∂ y ( d i ∂ c i ∂ y ) + j i { \ displaystyle { \ partial c _ { i } \ over \ partial t } = { \ partial \ over \ partial y } ( d _ { i } { \ partial c _ {
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i ∂ c i ∂ y ) + j i { \ displaystyle { \ partial c _ { i } \ over \ partial t } = { \ partial \ over \ partial y } ( d _ { i } { \ partial c _ { i } \ over \ partial y } ) + j _ { i } } in which ci is the molar concentration of functional groups in the ith component of a monomer or polymer, t is the elapsed time, y is a coordinate normal to the surface / interface, di is the molecular diffusion coefficient of the functional groups of interest, and ji is the thermodynamic rate of reaction. although precise, no analytical solution exists for this differential equation, and as such solutions must be found using approximate or numerical techniques. in the macrokinetic model, the progression of an entire system is predicted. one important assumption of the macrokinetic model is that each mass transfer process is independent, and can therefore be described by a local model. the macrokinetic model may be the most important, as it can provide feedback on the efficiency of the reaction process, important in both laboratory and industrial applications. more specific approaches to modeling interfacial polymerization are described by ji and co - workers, and include modeling of thin - film composite ( tfc ) membranes, tubular fibers, hollow membranes, and capsules. these models take into account both reaction - and diffusion - controlled interfacial polymerization under non - steady - state conditions. one model is for thin film composite ( tfc ) membranes, and describes the thickness of the composite film as a function of time : t = − ( e 0 b 0 + a 0 d 0 b 0 2 + c 0 a 0 2 b 0 2 ) ln ( 1 − x x m a x ) − c 0 2 b 0 x 2 − ( d 0 b 0 + c 0 a 0 b 0 2 ) x { \ displaystyle t = - ( { e _ { 0 } \ over b _ { 0 } } + { a _ { 0 } d _ { 0 } \ over b _ { 0 } ^ { 2 } } + { c _ { 0 } a _ { 0 } ^ { 2 } \ over b _ { 0 } ^ { 2 } } ) \ ln ( 1 - { x \ over x _ { max } } ) - { c _ { 0 } \ over 2b _ { 0 } } x ^ { 2 } - ( { d _ { 0 }
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