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##3. doi : 10. 1016 / s0306 - 4573 ( 99 ) 00056 - 4. issn 0306 - 4573. jansen, bernard j. ; spink, amanda ( 2006 ). " how are we searching the world wide web? a comparison of nine search engine transaction logs " ( pdf ). information processing and management. 42 ( 1 ) : 248 β 263. doi : 10. 1016 / j. ipm. 2004. 10. 007. issn 0306 - 4573. jones, rosie ; klinkner, kristina lisa ( 2008 ). " beyond the session timeout : automatic hierarchical segmentation of search topics in query logs ". proceedings of the 17th acm conference on information and knowledge management ( pdf ). acm. pp. 699 β 708. doi : 10. 1145 / 1458082. 1458176. isbn 9781595939913. s2cid 6548724. khoo, michael ; pagano, joe ; washington, anne l. ; recker, mimi ; palmer, bart ; donahue, robert a. ( 2008 ). " using web metrics to analyze digital libraries " ( pdf ). proceedings of the 8th acm / ieee - cs joint conference on digital libraries. acm. lam, heidi ; russell, daniel ; tang, diane ( 2007 ). " session viewer : visual exploratory analysis of web session logs ". ieee symposium on visual analytics science and technology. ieee. mehrzadi, david ; feitelson, dror g. ( 2012 ). " on extracting session data from activity logs " ( pdf ). proceedings of the 5th annual international systems and storage conference. systor'12. acm. citeseerx 10. 1. 1. 381. 1956. doi : 10. 1145 / 2367589. 2367592. isbn 978 - 1 - 4503 - 1448 - 0. s2cid 8820623. meiss, mark ; duncan, john ; goncalves, bruno ; ramasco, jose j. ; menczer, filippo ( 2009 ). " what's in a session : tracking individual behavior on the web " ( pdf ). proceedings of the 20th acm conference on hypertext and hypermedia. acm. pp. 173 β 182. arxiv : 1003. 5325. doi : 10. 1145 /
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individual behavior on the web " ( pdf ). proceedings of the 20th acm conference on hypertext and hypermedia. acm. pp. 173 β 182. arxiv : 1003. 5325. doi : 10. 1145 / 1557914. 1557946. isbn 9781605584867. s2cid 6564335. menasce, daniel a. ; almeida, v. ; fonseca, r. ; mendes, m. ( 1999 ). " a methodology for workload characterization of e - commerce sites " ( pdf ). proceedings of the 1st acm conference on electronic commerce. acm. pp. 119 β 128. doi : 10. 1145 / 336992. 337024. isbn 1581131763. s2cid 7239612. murray, g. craig ; lin, jimmy ; chowdhury, abdur ( 2006 ). " identification of user sessions with hierarchical agglomerative clustering " ( pdf ). proceedings of the american society for information science and technology. 43 ( 1 ) : 1 β 9. doi : 10. 1002 / meet. 14504301312. ortega, j. l. ; aguillo, i. ( 2010 ). " differences between web sessions according to the origin of their visits " ( pdf ). journal of informetrics. 4 ( 3 ) : 331 β 337. doi : 10. 1016 / j. joi. 2010. 02. 001. issn 1751 - 1577. spiliopoulou, myra ; mobasher, bamshad ; berendt, bettina ; nakagawa, miki ( 2003 ). " a framework for the evaluation of session reconstruction heuristics in web - usage analysis " ( pdf ). informs journal on computing. 15 ( 2 ) : 171 β 190. citeseerx 10. 1. 1. 621. 3037. doi : 10. 1287 / ijoc. 15. 2. 171. 14445. issn 1526 - 5528. weischdel, birgit ; huizingh, eelko k. r. e. ( 2006 ). " website optimization with web metrics ". proceedings of the 8th international conference on electronic commerce the new e - commerce : innovations for conquering current barriers, obstacles and limitations to conducting successful business on the internet - icec'06 ( pdf ). p. 46
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with web metrics ". proceedings of the 8th international conference on electronic commerce the new e - commerce : innovations for conquering current barriers, obstacles and limitations to conducting successful business on the internet - icec'06 ( pdf ). p. 463. doi : 10. 1145 / 1151454. 1151525. isbn 978 - 1595933928. s2cid 2965255.
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a bajada consists of a series of coalescing alluvial fans along a mountain front. these fan - shaped deposits form by the deposition of sediment within a stream onto flat land at the base of a mountain. the usage of the term in landscape description or geomorphology derives from the spanish word bajada, generally having the sense of " descent " or " inclination ". = = formation and occurrence = = when a stream flows downhill, it picks up sediment along with other materials. as this stream emerges from a mountain front, the sediment carried begins to be deposited, such that coarser sediment is deposited closest to the base and the finer sediment grades outwards and deposits in a fan - shape away from the mountain face. the sediment is transported across a pediment into a closed basin where the bajadas grade back into a pediment, making the boundary difficult to distinguish. bajadas frequently contain playa lakes. bajadas are common in dry climates ( e. g., the southwestern us ) where flash floods deposit sediment over time, although they are also common in wetter climates where streams are nearly continuously depositing sediment. = = references = =
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in computer science, thrashing occurs in a system with virtual memory when a computer's real storage resources are overcommitted, leading to a constant state of paging and page faults, slowing most application - level processing. this causes the performance of the computer to degrade or even collapse. the situation can continue indefinitely until the user closes some running applications or the active processes free up additional virtual memory resources. after initialization, most programs operate on a small number of code and data pages compared to the total memory the program requires. the pages most frequently accessed at any point are called the working set, which may change over time. when the working set is not significantly greater than the system's total number of real storage page frames, virtual memory systems work most efficiently, and an insignificant amount of computing is spent resolving page faults. as the total of the working sets grows, resolving page faults remains manageable until the growth reaches a critical point at which the number of faults increases dramatically and the time spent resolving them overwhelms the time spent on the computing the program was written to do. this condition is referred to as thrashing. thrashing may occur on a program that randomly accesses huge data structures, as its large working set causes continual page faults that drastically slow down the system. satisfying page faults may require freeing pages that will soon have to be re - read from disk. the term is also used for various similar phenomena, particularly movement between other levels of the memory hierarchy, wherein a process progresses slowly because significant time is being spent acquiring resources. " thrashing " is also used in contexts other than virtual memory systems β for example, to describe cache issues in computing, or silly window syndrome in networking. = = overview = = virtual memory works by treating a portion of secondary storage such as a computer hard disk as an additional layer of the cache hierarchy. virtual memory allows processes to use more memory than is physically present in main memory. operating systems supporting virtual memory assign processes a virtual address space and each process refers to addresses in its execution context by a so - called virtual address. to access data such as code or variables at that address, the process must translate the address to a physical address in a process known as virtual address translation. in effect, physical main memory becomes a cache for virtual memory, which is in general stored on disk in memory pages. programs are allocated a certain number of pages as needed by the operating system. active memory pages exist in both ram and on disk. inactive pages are removed from the cache and written
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for virtual memory, which is in general stored on disk in memory pages. programs are allocated a certain number of pages as needed by the operating system. active memory pages exist in both ram and on disk. inactive pages are removed from the cache and written to disk when the main memory becomes full. if processes are utilizing all main memory and need additional memory pages, a cascade of severe cache misses known as page faults will occur, often leading to a noticeable lag in the operating system responsiveness. this process together with the futile, repetitive page swapping that occurs is known as " thrashing ". this frequently leads to high, runaway cpu utilization that can grind the system to a halt. in modern computers, thrashing may occur in the paging system ( if there is not sufficient physical memory or the disk access time is overly long ), or in the i / o communications subsystem ( especially in conflicts over internal bus access ), etc. depending on the configuration and algorithms involved, the throughput and latency of a system may degrade by multiple orders of magnitude. thrashing is when the cpu performs'productive'work less and'swapping'work more. the overall memory access time may increase since the higher level memory is only as fast as the next lower level in the memory hierarchy. the cpu is busy swapping pages so much that it cannot respond to users'programs and interrupts as much as required. thrashing occurs when there are too many pages in memory, and each page refers to another page. real memory reduces its capacity to contain all the pages, so it uses'virtual memory '. when each page in execution demands that page that is not currently in real memory ( ram ) it places some pages on virtual memory and adjusts the required page on ram. if the cpu is too busy doing this task, thrashing occurs. = = = causes = = = in virtual memory systems, thrashing may be caused by programs or workloads that present insufficient locality of reference : if the working set of a program or a workload cannot be effectively held within physical memory, then constant data swapping, i. e., thrashing, may occur. the term was first used during the tape operating system days to describe the sound the tapes made when data was being rapidly written to and read. a worst case might occur on vax processors. a single movl crossing a page boundary could have a source operand using a displacement deferred addressing mode, where the longword containing the operand
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was being rapidly written to and read. a worst case might occur on vax processors. a single movl crossing a page boundary could have a source operand using a displacement deferred addressing mode, where the longword containing the operand address crosses a page boundary, and a destination operand using a displacement deferred addressing mode, where the longword containing the operand address crosses a page boundary, and the source and destination could both cross page boundaries. this single instruction references ten pages ; if not all are in ram, each will cause a page fault. the total number of pages thus involved in this particular instruction is ten, and all ten pages must be simultaneously present in memory. if any one of the ten pages cannot be swapped in ( for example to make room for any of the other pages ), the instruction will fault, and every attempt to restart it will fail until all ten pages can be swapped in. a system thrashing is often a result of a sudden spike in page demand from a small number of running programs. swap - token is a lightweight and dynamic thrashing protection mechanism. the basic idea is to set a token in the system, which is randomly given to a process that has page faults when thrashing happens. the process that has the token is given a privilege to allocate more physical memory pages to build its working set, which is expected to quickly finish its execution and release the memory pages to other processes. a timestamp is used to hand over the tokens one by one. the first version of swap - token is implemented in linux. the second version is called preempt swap - token. in this updated swap - token implementation, a priority counter is set for each process to track the number of swap - out pages. the token is always given to the process with a high priority, which has a high number of swap - out pages. the length of the time stamp is not a constant but is determined by the priority : the higher the number of swap - out pages of a process, the longer the time stamp for it will be. = = other uses = = thrashing is best known in the context of memory and storage, but analogous phenomena occur for other resources, including : cache thrashing where main memory is accessed in a pattern that leads to multiple main memory locations competing for the same cache lines, resulting in excessive cache misses. this is most likely to be problematic for caches with associativity. tlb thrashing where the translation lookaside buffer (
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pattern that leads to multiple main memory locations competing for the same cache lines, resulting in excessive cache misses. this is most likely to be problematic for caches with associativity. tlb thrashing where the translation lookaside buffer ( tlb ) acting as a cache for the memory management unit ( mmu ) which translates virtual addresses to physical addresses is too small for the working set of pages. tlb thrashing can occur even if instruction cache or data cache thrashing is not occurring because these are cached in different sizes. instructions and data are cached in small blocks ( cache lines ), not entire pages, but address lookup is done at the page level. thus even if the code and data working sets fit into the cache, if the working sets are fragmented across many pages, the virtual address working set may not fit into tlb, causing tlb thrashing. heap thrashing frequent garbage collection, due to failure to allocate memory for an object, due to insufficient free memory or insufficient contiguous free memory due to memory fragmentation is referred to as heap thrashing. process thrashing a similar phenomenon occurs for processes : when the process working set cannot be coscheduled, i. e. such that not all interacting processes are scheduled to run at the same time, they experience " process thrashing " due to being repeatedly scheduled and unscheduled, progressing only slowly. = = see also = = page replacement algorithm β algorithm for virtual memory implementation congestion collapse β reduced quality of service due to high network trafficpages displaying short descriptions of redirect targets resource contention β in computing, a conflict over access to a shared resource out of memory β state of computer operation where no additional memory can be allocated software aging β tendency of software to fail due to external changes or prolonged operation = = references = =
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neoepitopes are a class of major histocompatibility complex ( mhc ) bounded peptides. they represent the antigenic determinants of neoantigens. neoepitopes are recognized by the immune system as targets for t cells and can elicit immune response to cancer. = = description = = epitopes, also referred to as antigenic determinants, are parts of an antigen that are recognized by the immune system. a neoepitope is an epitope the immune system has not encountered before. therefore it is not subject to tolerance mechanisms of the immune system. as the mutant gene product is only expressed in tumors and is not found in non - cancerous cells, neoepitopes may evoke a vigorous t cell response. tumor mutational burden ( tmb, the number of mutations within a targeted genetic region in the cancerous cell's dna ) correlates with the number of neoepitopes, and have been suggested to correlate with patient survival post immunotherapy, although the findings about the neoantigen / immunogenicity association are disputed. neoepitopes arise from post - translational modifications. the mrna translates information from the dna into polypeptide composed of 20 standard amino acids and then proteins. several of the standard amino acids can be posttranslationally modified by enzymatic processes, or can be altered through spontaneous ( nonenzymatic ) biochemical reactions. there is increasing evidence that immune recognition of neoepitopes produced by cancer - specific mutations is a key mechanism for the induction of immune - mediated tumor rejection. opportunities for therapeutic targeting of cancer specific neoepitopes are under investigation. = = as target for immunotherapy = = cancer is a patient - specific disease, and no two tumors are alike. thus, the immunogenicity of each tumor is unique. a novel strategy against cancer is epitope selection for mutanome - directed individualized cancer immunotherapy. individualized cancer immunotherapy leverages the adaptive immune system by targeting t cells to tumor cells that have a tumor specific mutant antigen ( neoantigen ) with neoepitopes recognized by a receptor on t cells. one challenge is to identify the neoepitopes that trigger a suitable immune response, that is, to find out which neoepitopes in the individual tumor are highly immunogenic. = = cancer vaccines = = individualized cancer immunotherapy
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is to identify the neoepitopes that trigger a suitable immune response, that is, to find out which neoepitopes in the individual tumor are highly immunogenic. = = cancer vaccines = = individualized cancer immunotherapy includes vaccination with tumor mutation - derived neoepitopes. the concept is based on a mapping of the tumor - specific individual mutanome with identification of a range of suitable neoepitopes for a patient - specific vaccine. it is expected that the neoepitopes in the vaccine will trigger t cell responses to the specific cancer. for the concept of individualized cancer vaccination first data are available. = = references = =
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in inorganic chemistry, a homoleptic chemical compound is a metal compound with all ligands identical. the term uses the " homo - " prefix to indicate that something is the same for all. any metal species which has more than one type of ligand is heteroleptic. some compounds with names that suggest that they are homoleptic are in fact heteroleptic, because they have ligands in them which are not featured in the name. for instance dialkyl magnesium complexes, which are found in the equilibrium which exists in a solution of a grignard reagent in an ether, have two ether ligands attached to each magnesium centre. another example is a solution of trimethyl aluminium in an ether solvent ( such as thf ) ; similar chemistry should be expected for a triaryl or trialkyl borane. it is possible for some ligands such as dmso to bind with two or more different coordination modes. it would still be reasonable to consider a complex which has only one type of ligand but with different coordination modes to be homoleptic. for example, the complex dichlorotetrakis ( dimethyl sulfoxide ) ruthenium ( ii ) features dmso coordinating via both sulfur and oxygen atoms ( though this is not homoleptic since there are also chloride ligands ). = = homoleptic examples = = chromium carbonyl ferrocyanide iron pentacarbonyl nickel carbonyl tetrakis ( triphenylphosphine ) palladium ( 0 ) ferrocene uranium hexafluoride tetraethyl lead tetramethyl lead tetrabutyl tin trimethylaluminium dimethylmercury diethylzinc triethylborane chromate permanganate ferroin bis ( terpyridine ) iron ( ii ) = = references = =
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in mathematics, the extended natural numbers is a set which contains the values 0, 1, 2, β¦ { \ displaystyle 0, 1, 2, \ dots } and β { \ displaystyle \ infty } ( infinity ). that is, it is the result of adding a maximum element β { \ displaystyle \ infty } to the natural numbers. addition and multiplication work as normal for finite values, and are extended by the rules n + β = β + n = β { \ displaystyle n + \ infty = \ infty + n = \ infty } ( n β n βͺ { β } { \ displaystyle n \ in \ mathbb { n } \ cup \ { \ infty \ } } ), 0 Γ β = β Γ 0 = 0 { \ displaystyle 0 \ times \ infty = \ infty \ times 0 = 0 } and m Γ β = β Γ m = β { \ displaystyle m \ times \ infty = \ infty \ times m = \ infty } for m = 0 { \ displaystyle m \ neq 0 }. with addition and multiplication, n βͺ { β } { \ displaystyle \ mathbb { n } \ cup \ { \ infty \ } } is a semiring but not a ring, as β { \ displaystyle \ infty } lacks an additive inverse. the set can be denoted by n { \ displaystyle { \ overline { \ mathbb { n } } } }, n β { \ displaystyle \ mathbb { n } _ { \ infty } } or n β { \ displaystyle \ mathbb { n } ^ { \ infty } }. it is a subset of the extended real number line, which extends the real numbers by adding β β { \ displaystyle - \ infty } and + β { \ displaystyle + \ infty }. = = applications = = in graph theory, the extended natural numbers are used to define distances in graphs, with β { \ displaystyle \ infty } being the distance between two unconnected vertices. they can be used to show the extension of some results, such as the max - flow min - cut theorem, to infinite graphs. in topology, the topos of right actions on the extended natural numbers is a category pro of projection algebras. in constructive mathematics, the extended natural numbers n β { \
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such as the max - flow min - cut theorem, to infinite graphs. in topology, the topos of right actions on the extended natural numbers is a category pro of projection algebras. in constructive mathematics, the extended natural numbers n β { \ displaystyle \ mathbb { n } _ { \ infty } } are a one - point compactification of the natural numbers, yielding the set of non - increasing binary sequences i. e. ( x 0, x 1, β¦ ) β 2 n { \ displaystyle ( x _ { 0 }, x _ { 1 }, \ dots ) \ in 2 ^ { \ mathbb { n } } } such that i β n : x i β₯ x i + 1 { \ displaystyle \ forall i \ in \ mathbb { n } : x _ { i } \ geq x _ { i + 1 } }. the sequence 1 n 0 Ο { \ displaystyle 1 ^ { n } 0 ^ { \ omega } } represents n { \ displaystyle n }, while the sequence 1 Ο { \ displaystyle 1 ^ { \ omega } } represents β { \ displaystyle \ infty }. it is a retract of 2 n { \ displaystyle 2 ^ { \ mathbb { n } } } and the claim that n βͺ { β } β n β { \ displaystyle \ mathbb { n } \ cup \ { \ infty \ } \ subseteq \ mathbb { n } _ { \ infty } } implies the limited principle of omniscience. = = notes = = = = references = = folkman, jon ; fulkerson, d. r. ( 1970 ). " flows in infinite graphs ". journal of combinatorial theory. 8 ( 1 ). doi : 10. 1016 / s0021 - 9800 ( 70 ) 80006 - 0. escardo, martin h ( 2013 ). " infinite sets that satisfy the principle of omniscience in any variety of constructive mathematics ". journal of symbolic logic. 78 ( 3 ). koch, sebastian ( 2020 ). " extended natural numbers and counters " ( pdf ). formalized mathematics. 28 ( 3 ). khanjanzadeh, zeinab ; madanshekaf, ali ( 2018 ). " weak ideal topology in the topos of right acts over a monoid ". communications in algebra. 46 ( 5 ). sakarovitch,
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##janzadeh, zeinab ; madanshekaf, ali ( 2018 ). " weak ideal topology in the topos of right acts over a monoid ". communications in algebra. 46 ( 5 ). sakarovitch, jacques ( 2009 ). elements of automata theory. translated from the french by reuben thomas. cambridge : cambridge university press. isbn 978 - 0 - 521 - 84425 - 3. zbl 1188. 68177. = = further reading = = robert, leonel ( 3 september 2013 ). " the cuntz semigroup of some spaces of dimension at most two ". arxiv : 0711. 4396. lightstone, a. h. ( 1972 ). " infinitesimals ". the american mathematical monthly. 79 ( 3 ). khanjanzadeh, zeinab ; madanshekaf, ali ( 2019 ). " on projection algebras ". southeast asian bulletin of mathematics. 43 ( 2 ). = = external links = = extended natural number at the nlab
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a dihedral angle is the angle between two intersecting planes or half - planes. it is a plane angle formed on a third plane, perpendicular to the line of intersection between the two planes or the common edge between the two half - planes. in higher dimensions, a dihedral angle represents the angle between two hyperplanes. in chemistry, it is the clockwise angle between half - planes through two sets of three atoms, having two atoms in common. = = mathematical background = = when the two intersecting planes are described in terms of cartesian coordinates by the two equations a 1 x + b 1 y + c 1 z + d 1 = 0 { \ displaystyle a _ { 1 } x + b _ { 1 } y + c _ { 1 } z + d _ { 1 } = 0 } a 2 x + b 2 y + c 2 z + d 2 = 0 { \ displaystyle a _ { 2 } x + b _ { 2 } y + c _ { 2 } z + d _ { 2 } = 0 } the dihedral angle, Ο { \ displaystyle \ varphi } between them is given by : cos Ο = | a 1 a 2 + b 1 b 2 + c 1 c 2 | a 1 2 + b 1 2 + c 1 2 a 2 2 + b 2 2 + c 2 2 { \ displaystyle \ cos \ varphi = { \ frac { \ left \ vert a _ { 1 } a _ { 2 } + b _ { 1 } b _ { 2 } + c _ { 1 } c _ { 2 } \ right \ vert } { { \ sqrt { a _ { 1 } ^ { 2 } + b _ { 1 } ^ { 2 } + c _ { 1 } ^ { 2 } } } { \ sqrt { a _ { 2 } ^ { 2 } + b _ { 2 } ^ { 2 } + c _ { 2 } ^ { 2 } } } } } } and satisfies 0 β€ Ο β€ Ο / 2. { \ displaystyle 0 \ leq \ varphi \ leq \ pi / 2. } it can easily be observed that the angle is independent of d 1 { \ displaystyle d _ { 1 } } and d 2 { \ displaystyle d _ { 2 } }. alternatively, if na and nb are normal vector to the planes, one has cos Ο = | n a β
n b | | n a | | n b |
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} and d 2 { \ displaystyle d _ { 2 } }. alternatively, if na and nb are normal vector to the planes, one has cos Ο = | n a β
n b | | n a | | n b | { \ displaystyle \ cos \ varphi = { \ frac { \ left \ vert \ mathbf { n } _ { \ mathrm { a } } \ cdot \ mathbf { n } _ { \ mathrm { b } } \ right \ vert } { | \ mathbf { n } _ { \ mathrm { a } } | | \ mathbf { n } _ { \ mathrm { b } } | } } } where na Β· nb is the dot product of the vectors and | na | | nb | is the product of their lengths. the absolute value is required in above formulas, as the planes are not changed when changing all coefficient signs in one equation, or replacing one normal vector by its opposite. however the absolute values can be and should be avoided when considering the dihedral angle of two half planes whose boundaries are the same line. in this case, the half planes can be described by a point p of their intersection, and three vectors b0, b1 and b2 such that p + b0, p + b1 and p + b2 belong respectively to the intersection line, the first half plane, and the second half plane. the dihedral angle of these two half planes is defined by cos Ο = ( b 0 Γ b 1 ) β
( b 0 Γ b 2 ) | b 0 Γ b 1 | | b 0 Γ b 2 | { \ displaystyle \ cos \ varphi = { \ frac { ( \ mathbf { b } _ { 0 } \ times \ mathbf { b } _ { 1 } ) \ cdot ( \ mathbf { b } _ { 0 } \ times \ mathbf { b } _ { 2 } ) } { | \ mathbf { b } _ { 0 } \ times \ mathbf { b } _ { 1 } | | \ mathbf { b } _ { 0 } \ times \ mathbf { b } _ { 2 } | } } }, and satisfies 0 β€ Ο < Ο. { \ displaystyle 0 \ leq \ varphi < \ pi. } in this case, switching the two half - planes gives the same result, and so does replacing b 0 { \ displays
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and satisfies 0 β€ Ο < Ο. { \ displaystyle 0 \ leq \ varphi < \ pi. } in this case, switching the two half - planes gives the same result, and so does replacing b 0 { \ displaystyle \ mathbf { b } _ { 0 } } with β b 0. { \ displaystyle - \ mathbf { b } _ { 0 }. } in chemistry ( see below ), we define a dihedral angle such that replacing b 0 { \ displaystyle \ mathbf { b } _ { 0 } } with β b 0 { \ displaystyle - \ mathbf { b } _ { 0 } } changes the sign of the angle, which can be between βΟ and Ο. = = in polymer physics = = in some scientific areas such as polymer physics, one may consider a chain of points and links between consecutive points. if the points are sequentially numbered and located at positions r1, r2, r3, etc. then bond vectors are defined by u1 = r2βr1, u2 = r3βr2, and ui = ri + 1βri, more generally. this is the case for kinematic chains or amino acids in a protein structure. in these cases, one is often interested in the half - planes defined by three consecutive points, and the dihedral angle between two consecutive such half - planes. if u1, u2 and u3 are three consecutive bond vectors, the intersection of the half - planes is oriented, which allows defining a dihedral angle that belongs to the interval ( βΟ, Ο ]. this dihedral angle is defined by cos Ο = ( u 1 Γ u 2 ) β
( u 2 Γ u 3 ) | u 1 Γ u 2 | | u 2 Γ u 3 | sin Ο = u 2 β
( ( u 1 Γ u 2 ) Γ ( u 2 Γ u 3 ) ) | u 2 | | u 1 Γ u 2 | | u 2 Γ u 3 |, { \ displaystyle { \ begin { aligned } \ cos \ varphi & = { \ frac { ( \ mathbf { u } _ { 1 } \ times \ mathbf { u } _ { 2 } ) \ cdot ( \ mathbf { u } _ { 2 } \ times \ mathbf { u } _ { 3 } ) } { | \ mathbf { u } _ { 1 } \ times \ mathbf { u } _ { 2 }
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##ot ( \ mathbf { u } _ { 2 } \ times \ mathbf { u } _ { 3 } ) } { | \ mathbf { u } _ { 1 } \ times \ mathbf { u } _ { 2 } | \, | \ mathbf { u } _ { 2 } \ times \ mathbf { u } _ { 3 } | } } \ \ \ sin \ varphi & = { \ frac { \ mathbf { u } _ { 2 } \ cdot ( ( \ mathbf { u } _ { 1 } \ times \ mathbf { u } _ { 2 } ) \ times ( \ mathbf { u } _ { 2 } \ times \ mathbf { u } _ { 3 } ) ) } { | \ mathbf { u } _ { 2 } | \, | \ mathbf { u } _ { 1 } \ times \ mathbf { u } _ { 2 } | \, | \ mathbf { u } _ { 2 } \ times \ mathbf { u } _ { 3 } | } }, \ end { aligned } } } or, using the function atan2, Ο = atan2 ( u 2 β
( ( u 1 Γ u 2 ) Γ ( u 2 Γ u 3 ) ), | u 2 | ( u 1 Γ u 2 ) β
( u 2 Γ u 3 ) ). { \ displaystyle \ varphi = \ operatorname { atan2 } ( \ mathbf { u } _ { 2 } \ cdot ( ( \ mathbf { u } _ { 1 } \ times \ mathbf { u } _ { 2 } ) \ times ( \ mathbf { u } _ { 2 } \ times \ mathbf { u } _ { 3 } ) ), | \ mathbf { u } _ { 2 } | \, ( \ mathbf { u } _ { 1 } \ times \ mathbf { u } _ { 2 } ) \ cdot ( \ mathbf { u } _ { 2 } \ times \ mathbf { u } _ { 3 } ) ). } this dihedral angle does not depend on the orientation of the chain ( order in which the point are considered ) β reversing this ordering consists of replacing each vector by its opposite vector, and exchanging the indices 1 and 3. both operations do not change the cosine, but change the sign of the sine. thus, together, they
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considered ) β reversing this ordering consists of replacing each vector by its opposite vector, and exchanging the indices 1 and 3. both operations do not change the cosine, but change the sign of the sine. thus, together, they do not change the angle. a simpler formula for the same dihedral angle is the following ( the proof is given below ) cos Ο = ( u 1 Γ u 2 ) β
( u 2 Γ u 3 ) | u 1 Γ u 2 | | u 2 Γ u 3 | sin Ο = | u 2 | u 1 β
( u 2 Γ u 3 ) | u 1 Γ u 2 | | u 2 Γ u 3 |, { \ displaystyle { \ begin { aligned } \ cos \ varphi & = { \ frac { ( \ mathbf { u } _ { 1 } \ times \ mathbf { u } _ { 2 } ) \ cdot ( \ mathbf { u } _ { 2 } \ times \ mathbf { u } _ { 3 } ) } { | \ mathbf { u } _ { 1 } \ times \ mathbf { u } _ { 2 } | \, | \ mathbf { u } _ { 2 } \ times \ mathbf { u } _ { 3 } | } } \ \ \ sin \ varphi & = { \ frac { | \ mathbf { u } _ { 2 } | \, \ mathbf { u } _ { 1 } \ cdot ( \ mathbf { u } _ { 2 } \ times \ mathbf { u } _ { 3 } ) } { | \ mathbf { u } _ { 1 } \ times \ mathbf { u } _ { 2 } | \, | \ mathbf { u } _ { 2 } \ times \ mathbf { u } _ { 3 } | } }, \ end { aligned } } } or equivalently, Ο = atan2 ( | u 2 | u 1 β
( u 2 Γ u 3 ), ( u 1 Γ u 2 ) β
( u 2 Γ u 3 ) ). { \ displaystyle \ varphi = \ operatorname { atan2 } ( | \ mathbf { u } _ { 2 } | \, \ mathbf { u } _ { 1 } \ cdot ( \ mathbf { u } _ { 2 } \ times \ mathbf { u } _ { 3 } ), ( \ mathbf { u
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{ 2 } | \, \ mathbf { u } _ { 1 } \ cdot ( \ mathbf { u } _ { 2 } \ times \ mathbf { u } _ { 3 } ), ( \ mathbf { u } _ { 1 } \ times \ mathbf { u } _ { 2 } ) \ cdot ( \ mathbf { u } _ { 2 } \ times \ mathbf { u } _ { 3 } ) ). } this can be deduced from previous formulas by using the vector quadruple product formula, and the fact that a scalar triple product is zero if it contains twice the same vector : ( u 1 Γ u 2 ) Γ ( u 2 Γ u 3 ) = [ ( u 2 Γ u 3 ) β
u 1 ] u 2 β [ ( u 2 Γ u 3 ) β
u 2 ] u 1 = [ ( u 2 Γ u 3 ) β
u 1 ] u 2 { \ displaystyle ( \ mathbf { u } _ { 1 } \ times \ mathbf { u } _ { 2 } ) \ times ( \ mathbf { u } _ { 2 } \ times \ mathbf { u } _ { 3 } ) = [ ( \ mathbf { u } _ { 2 } \ times \ mathbf { u } _ { 3 } ) \ cdot \ mathbf { u } _ { 1 } ] \ mathbf { u } _ { 2 } - [ ( \ mathbf { u } _ { 2 } \ times \ mathbf { u } _ { 3 } ) \ cdot \ mathbf { u } _ { 2 } ] \ mathbf { u } _ { 1 } = [ ( \ mathbf { u } _ { 2 } \ times \ mathbf { u } _ { 3 } ) \ cdot \ mathbf { u } _ { 1 } ] \ mathbf { u } _ { 2 } } given the definition of the cross product, this means that Ο { \ displaystyle \ varphi } is the angle in the clockwise direction of the fourth atom compared to the first atom, while looking down the axis from the second atom to the third. special cases ( one may say the usual cases ) are Ο = Ο { \ displaystyle \ varphi = \ pi }, Ο = + Ο / 3 { \ displaystyle \ varphi = + \ pi / 3 } and Ο = β Ο / 3 { \ displaystyle \ varphi = -
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= Ο { \ displaystyle \ varphi = \ pi }, Ο = + Ο / 3 { \ displaystyle \ varphi = + \ pi / 3 } and Ο = β Ο / 3 { \ displaystyle \ varphi = - \ pi / 3 }, which are called the trans, gauche +, and gaucheβ conformations. = = in stereochemistry = = in stereochemistry, a torsion angle is defined as a particular example of a dihedral angle, describing the geometric relation of two parts of a molecule joined by a chemical bond. every set of three non - colinear atoms of a molecule defines a half - plane. as explained above, when two such half - planes intersect ( i. e., a set of four consecutively - bonded atoms ), the angle between them is a dihedral angle. dihedral angles are used to specify the molecular conformation. stereochemical arrangements corresponding to angles between 0Β° and Β±90Β° are called syn ( s ), those corresponding to angles between Β±90Β° and 180Β° anti ( a ). similarly, arrangements corresponding to angles between 30Β° and 150Β° or between β30Β° and β150Β° are called clinal ( c ) and those between 0Β° and Β±30Β° or Β±150Β° and 180Β° are called periplanar ( p ). the two types of terms can be combined so as to define four ranges of angle ; 0Β° to Β±30Β° synperiplanar ( sp ) ; 30Β° to 90Β° and β30Β° to β90Β° synclinal ( sc ) ; 90Β° to 150Β° and β90Β° to β150Β° anticlinal ( ac ) ; Β±150Β° to 180Β° antiperiplanar ( ap ). the synperiplanar conformation is also known as the syn - or cis - conformation ; antiperiplanar as anti or trans ; and synclinal as gauche or skew. for example, with n - butane two planes can be specified in terms of the two central carbon atoms and either of the methyl carbon atoms. the syn - conformation shown above, with a dihedral angle of 60Β° is less stable than the anti - conformation with a dihedral angle of 180Β°. for macromolecular usage the symbols t, c, g +, gβ, a + and aβ are recommended ( ap, sp, + sc, βsc, + ac and β
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##ation with a dihedral angle of 180Β°. for macromolecular usage the symbols t, c, g +, gβ, a + and aβ are recommended ( ap, sp, + sc, βsc, + ac and βac respectively ). = = = proteins = = = a ramachandran plot ( also known as a ramachandran diagram or a [ Ο, Ο ] plot ), originally developed in 1963 by g. n. ramachandran, c. ramakrishnan, and v. sasisekharan, is a way to visualize energetically allowed regions for backbone dihedral angles Ο against Ο of amino acid residues in protein structure. in a protein chain three dihedral angles are defined : Ο ( omega ) is the angle in the chain cΞ± β c'β n β cΞ±, Ο ( phi ) is the angle in the chain c'β n β cΞ± β c'Ο ( psi ) is the angle in the chain n β cΞ± β c'β n ( called Ο β² by ramachandran ) the figure at right illustrates the location of each of these angles ( but it does not show correctly the way they are defined ). the planarity of the peptide bond usually restricts Ο to be 180Β° ( the typical trans case ) or 0Β° ( the rare cis case ). the distance between the cΞ± atoms in the trans and cis isomers is approximately 3. 8 and 2. 9 a, respectively. the vast majority of the peptide bonds in proteins are trans, though the peptide bond to the nitrogen of proline has an increased prevalence of cis compared to other amino - acid pairs. the side chain dihedral angles are designated with Οn ( chi - n ). they tend to cluster near 180Β°, 60Β°, and β60Β°, which are called the trans, gaucheβ, and gauche + conformations. the stability of certain sidechain dihedral angles is affected by the values Ο and Ο. for instance, there are direct steric interactions between the cΞ³ of the side chain in the gauche + rotamer and the backbone nitrogen of the next residue when Ο is near β60Β°. this is evident from statistical distributions in backbone - dependent rotamer libraries. = = geometry = = every polyhedron has a dihedral angle at every edge describing the relationship of the two faces that share that edge. this dihedral angle, also called the face angle, is measured as the internal angle with respect to
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libraries. = = geometry = = every polyhedron has a dihedral angle at every edge describing the relationship of the two faces that share that edge. this dihedral angle, also called the face angle, is measured as the internal angle with respect to the polyhedron. an angle of 0Β° means the face normal vectors are antiparallel and the faces overlap each other, which implies that it is part of a degenerate polyhedron. an angle of 180Β° means the faces are parallel, as in a tiling. an angle greater than 180Β° exists on concave portions of a polyhedron. every dihedral angle in a polyhedron that is isotoxal and / or isohedral has the same value. this includes the 5 platonic solids, the 13 catalan solids, the 4 kepler β poinsot polyhedra, the 2 convex quasiregular polyhedra, and the 2 infinite families of bipyramids and trapezohedra. = = law of cosines for dihedral angle = = given 3 faces of a polyhedron which meet at a common vertex p and have edges ap, bp and cp, the cosine of the dihedral angle between the faces containing apc and bpc is : cos Ο = cos ( a p b ) β cos ( a p c ) cos ( b p c ) sin ( a p c ) sin ( b p c ) { \ displaystyle \ cos \ varphi = { \ frac { \ cos ( \ angle \ mathrm { apb } ) - \ cos ( \ angle \ mathrm { apc } ) \ cos ( \ angle \ mathrm { bpc } ) } { \ sin ( \ angle \ mathrm { apc } ) \ sin ( \ angle \ mathrm { bpc } ) } } } this can be deduced from the spherical law of cosines, but can also be found by other means. = = see also = = atropisomer = = references = = = = external links = = the dihedral angle in woodworking at tips. fm analysis of the 5 regular polyhedra gives a step - by - step derivation of these exact values.
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abhyankar's inequality is an inequality involving extensions of valued fields in algebra, introduced by abhyankar ( 1956 ). abhyankar's inequality states that for an extension k / k of valued fields, the transcendence degree of k / k is at least the transcendence degree of the residue field extension plus the rank of the quotient of the valuation groups ; here the rank of an abelian group a { \ displaystyle a } is defined as dim q ( a β q ) { \ displaystyle \ dim _ { \ mathbb { q } } ( a \ otimes \ mathbb { q } ) }. = = references = = abhyankar, shreeram ( 1956 ), " on the valuations centered in a local domain ", american journal of mathematics, 78 ( 2 ) : 321 β 348, doi : 10. 2307 / 2372519, issn 0002 - 9327, jstor 2372519, mr 0082477
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architecture description languages ( adls ) are used in several disciplines : system engineering, software engineering, and enterprise modelling and engineering. the system engineering community uses an architecture description language as a language and / or a conceptual model to describe and represent system architectures. the software engineering community uses an architecture description language as a computer language to create a description of a software architecture. in the case of a so - called technical architecture, the architecture must be communicated to software developers ; a functional architecture is communicated to various stakeholders and users. some adls that have been developed are : acme ( developed by cmu ), aadl ( standardized by the sae ), c2 ( developed by uci ), sbc - adl ( developed by national sun yat - sen university ), darwin ( developed by imperial college london ), and wright ( developed by cmu ). = = overview = = the iso / iec / ieee 42010 document, systems and software engineering β architecture description, defines an architecture description language as " any form of expression for use in architecture descriptions " and specifies minimum requirements on adls. the enterprise modelling and engineering community have also developed architecture description languages catered for at the enterprise level. examples include archimate ( now a standard of the open group ), demo, abacus ( developed by the university of technology, sydney ). these languages do not necessarily refer to software components, etc. most of them, however, refer to an application architecture as the architecture that is communicated to the software engineers. most of the writing below refers primarily to the perspective of the software engineering community. a standard notation ( adl ) for representing architectures helps promote mutual communication, the embodiment of early design decisions, and the creation of a transferable abstraction of a system. architectures in the past were largely represented by box - and - line drawing annotated with such things as the nature of the component, properties, semantics of connections, and overall system behavior. adls result from a linguistic approach to the formal representation of architectures, and as such they address its shortcomings. also important, sophisticated adls allow for early analysis and feasibility testing of architectural design decisions. = = history = = adls have been classified into three broad categories : box - and - line informal drawings, formal architecture description language, and uml ( unified modeling language ) - based notations. box - and - line have been for a long time the most predominant means for describing software architectures. while providing useful documentation, the level of informal
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drawings, formal architecture description language, and uml ( unified modeling language ) - based notations. box - and - line have been for a long time the most predominant means for describing software architectures. while providing useful documentation, the level of informality limited the usefulness of the architecture description. a more rigorous way for describing software architectures was required. quoting allen and garlan ( 1997 ), " while these [ box - and - line ] descriptions may provide useful documentation, the current level of informality limits their usefulness. since it is generally imprecise what is meant by such architectural descriptions, it may be impossible to analyze an architecture for consistency or determine non - trivial properties of it. moreover, there is no way to check that a system implementation is faithful to its architectural design. " a similar conclusion is drawn in perry and wolf ( 1992 ), which reports that : " aside from providing clear and precise documentation, the primary purpose of specifications is to provide automated analysis of the documents and to expose various kinds of problems that would otherwise go undetected. " since then, a thread of research on formal languages for software architecture description has been carried out. tens of formal adls have been proposed, each characterized by different conceptual architectural elements, different syntax or semantics, focusing on a specific operational domain, or only suitable for different analysis techniques. for example, domain - specific adls have been presented to deal with embedded and real - time systems ( such as aadl, east - adl, and eadl ), control - loop applications ( diaspec ), product line architectures ( koala ), and dynamic systems ( Ο - adl ) ). analysis - specific adls have been proposed to deal with availability, reliability, security, resource consumption, data quality and real - time performance analysis ( aadl, behavioral analysis ( fractal ) ), and trustworthiness analysis ( tadl ). however, these efforts have not seen the desired adoption by industrial practice. some reasons for this lack of industry adoption have been analyzed by woods and hilliard, pandey, clements, and others : formal adls have been rarely integrated in the software life - cycle, they are seldom supported by mature tools, scarcely documented, focusing on very specific needs, and leaving no space for extensions enabling the addition of new features. as a way to overcome some of those limitations, uml has been indicated as a possible successor of existing adls. many proposals have been presented to use or extend the uml to
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and leaving no space for extensions enabling the addition of new features. as a way to overcome some of those limitations, uml has been indicated as a possible successor of existing adls. many proposals have been presented to use or extend the uml to more properly model software architectures. a 2013 study found that practitioners were generally satisfied with the design capabilities of the adls they used, but had several major concerns with them : they lacked analysis features and the ability to define extra - functional properties ; those used in practice mostly originated from industrial development rather than academic research ; they needed more formality and better usability. = = characteristics = = there is a large variety in adls developed by either academic or industrial groups. many languages were not intended to be an adl, but they turn out to be suitable for representing and analyzing an architecture. in principle, adls differ from requirements languages, because adls are rooted in the solution space, whereas requirements describe problem spaces. they differ from programming languages, because adls don't bind architectural abstractions to specific point solutions. modeling languages represent behaviors, where adls focus on representation of components. however, there are domain - specific modeling languages ( dsmls ) that focus on representation of components. minimal requirements the language must : be suitable for communicating an architecture to all interested parties support the tasks of architecture creation, refinement and validation provide a basis for further implementation, so it must be able to add information to the adl specification to enable the final system specification to be derived from the adl provide the ability to represent most of the common architectural styles support analytical capabilities or provide quick generating prototype implementations adls have in common : graphical syntax with often a textual form and a formally defined syntax and semantics features for modeling distributed systems little support for capturing design information, except through general purpose annotation mechanisms ability to represent hierarchical levels of detail including the creation of substructures by instantiating templates adls differ in their ability to : handle real - time constructs, such as deadlines and task priorities, at the architectural level support the specification of different architectural styles. few handle object oriented class inheritance or dynamic architectures support the analysis of the architecture handle different instantiations of the same architecture, in relation to product line architectures = = = positive elements of adl = = = adls are a formal way of representing architecture adls are intended to be both human and machine - readable adls support describing a system at a higher level than previously possible adls permit analysis and
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= = positive elements of adl = = = adls are a formal way of representing architecture adls are intended to be both human and machine - readable adls support describing a system at a higher level than previously possible adls permit analysis and assessment of architectures, for completeness, consistency, ambiguity, and performance adls can support automatic generation of software systems = = = negative elements of adl = = = there is no universal agreement on what adls should represent, particularly as regards the behavior of the architecture representations currently in use are relatively difficult to parse and are not supported by commercial tools most adls tend to be very vertically optimized toward a particular kind of analysis = = common concepts of architecture = = the adl community generally agrees that software architecture is a set of components and the connections among them. but there are different kind of architectures like : = = = object connection architecture = = = configuration consists of the interfaces and connections of an object - oriented system interfaces specify the features that must be provided by modules conforming to an interface connections represented by interfaces together with call graph conformance usually enforced by the programming language decomposition β associating interfaces with unique modules interface conformance β static checking of syntactic rules communication integrity β visibility between modules = = = interface connection architecture = = = expands the role of interfaces and connections interfaces specify both " required " and " provided " features connections are defined between " required " features and " provided " features consists of interfaces, connections and constraints constraints restrict behavior of interfaces and connections in an architecture constraints in an architecture map to requirements for a system most adls implement an interface connection architecture. = = architecture vs. design = = architecture, in the context of software systems, is roughly divided into categories, primarily software architecture, network architecture, and systems architecture. within each of these categories, there is a tangible but fuzzy distinction between architecture and design. to draw this distinction as universally and clearly as possible, it is best to consider design as a noun rather than as a verb, so that the comparison is between two nouns. design is the abstraction and specification of patterns and organs of functionality that have been or will be implemented. architecture is both a degree higher in abstraction and coarser in granularity. consequentially, architecture is also more topological ( i. e. overall structure and relationship between components ) in nature than design ( i. e. specific details and implementation ), in that it specifies where major components meet and how they relate to one another. architecture focuses on
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is also more topological ( i. e. overall structure and relationship between components ) in nature than design ( i. e. specific details and implementation ), in that it specifies where major components meet and how they relate to one another. architecture focuses on the partitioning of major regions of functionality into high level components, where they will physically or virtually reside, what off - the - shelf components may be employed effectively, in general what interfaces each component will expose, what protocols will be employed between them, and what practices and high level patterns may best meet extensibility, maintainability, reliability, durability, scalability, and other non - functional objectives. design is a detailing of these choices and a more concrete clarification of how functional requirements will be met through the delegation of pieces of that functionality to more granular components and how these smaller components will be organized within the larger ones. oftentimes, a portion of architecture is done during the conceptualization of an application, system, or network, and may appear in the non - functional sections of requirement documentation. canonically, design is not specified in requirements, but is rather driven by them. the process of defining an architecture may involve heuristics, acquired by the architect or architectural team through experience within the domain. as with design, architecture often evolves through a series of iterations, and just as the wisdom of a high level design is often tested when low level design and implementation occurs, the wisdom of an architecture is tested during the specification of a high level design. in both cases, if the wisdom of the specification is called into question during detailing, another iteration of either architecture or design, as the case may be, may become necessary. in summary, the primary differences between architecture and design are ones of granularity and abstraction, and ( consequentially ) chronology. ( architecture generally precedes design, although overlap and circular iteration is a common reality. ) = = examples = = archimate architecture analysis & design language c4 model ( software ) darwin ( adl ) east - adl wright ( adl ) = = approaches to system architecture = = academic approach focus on analytic evaluation of architectural models individual models rigorous modeling notations powerful analysis techniques depth over breadth special - purpose solutions industrial approach focus on wide range of development issues families of models practicality over rigor architecture as the big picture in development breadth over depth general - purpose solutions = = see also = = aadl darwin scripting language hardware description language = = references = = = =
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on wide range of development issues families of models practicality over rigor architecture as the big picture in development breadth over depth general - purpose solutions = = see also = = aadl darwin scripting language hardware description language = = references = = = = external links = = medvidovic, n. ; taylor, r. n. ( january 2000 ). " a classification and comparison framework for software architecture description languages ". ieee transactions on software engineering. 26 ( 1 ) : 70 β 93. doi : 10. 1109 / 32. 825767. malavolta, ivano ; lago, patricia ; muccini, henry ; pelliccione, patrizio ; tang, antony ( 2013 ). " what industry needs from architectural languages : a survey ". ieee transactions on software engineering. 39 ( 6 ) : 869 β 891. doi : 10. 1109 / tse. 2012. 74. s2cid 6383726. architecture description languages / / malardalen university clements, p. c. ( 1996 ). " a survey of architecture description languages " ( pdf ). proceedings of the 8th international workshop on software specification and design. pp. 16 β 25. doi : 10. 1109 / iwssd. 1996. 501143. isbn 0 - 8186 - 7361 - 3. s2cid 7307554. archived from the original ( pdf ) on 2013 - 12 - 24. abacus acme adml aesop ao - adl archimate an example of an adl for enterprise architecture byadl ( build your adl ) - university of l'aquila c2 sadl daop - adl demo another example of an enterprise architecture adl diaspec an approach and tool to generate a distributed framework from a software architecture malavolta, i. ; muccini, h. ; pelliccione, p. ; tamburri, d. ( january β february 2010 ). " providing architectural languages and tools interoperability through model transformation technologies ". ieee transactions on software engineering. 36 ( 1 ) : 119 β 140. doi : 10. 1109 / tse. 2009. 51. s2cid 6825192. dually rapide ssep unicon wright
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a flood bypass is a region of land or a large man - made structure that is designed to convey excess flood waters from a river or stream in order to reduce the risk of flooding on the natural river or stream near a key point of interest, such as a city. flood bypasses, sometimes called floodways, often have man - made diversion works, such as diversion weirs and spillways, at their head or point of origin. the main body of a flood bypass is often a natural flood plain. many flood bypasses are designed to carry enough water such that combined flows down the original river or stream and flood bypass will not exceed the expected maximum flood flow of the river or stream. flood bypasses are typically used only during major floods and act in a similar nature to a detention basin. since the area of a flood bypass is significantly larger than the cross - sectional area of the original river or stream channel from which water is diverted, the velocity of water in a flood bypass will be significantly lower than the velocity of the flood water in the original system. these low velocities often cause increased sediment deposition in the flood bypass, thus it is important to incorporate a maintenance program for the entire flood bypass system when it is not being actively used during a flood operation. when not being used to convey water, flood bypasses are sometimes used for agricultural or environmental purposes. the land is often owned by a public authority and then rented to farmers or ranchers, who in turn plant crops or herd livestock that feed off the flood plain. since the flood bypass is subjected to sedimentation during flood events, the land is often very productive and even a loss of crops due to flooding can sometimes be recovered due to the high yield of the land during the non - flood periods. = = examples = = bonnet carre spillway eastside bypass fargo - moorhead area diversion project yolo bypass = = references = =
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a vowel diagram or vowel chart is a schematic arrangement of the vowels. depending on the particular language being discussed, it can take the form of a triangle or a quadrilateral. vertical position on the diagram denotes the vowel closeness, with close vowels at the top of the diagram, and horizontal position denotes the vowel backness, with front vowels at the left of the diagram. vowels are unique in that their main features do not contain differences in voicing, manner, or place ( articulators ). vowels differ only in the position of the tongue when voiced. the tongue moves vertically and horizontally within the oral cavity. vowels are produced with at least a part of their vocal tract obstructed. in the vowel diagram, convenient reference points are provided for specifying tongue position. the position of the highest point of the arch of the tongue is considered to be the point of articulation of the vowel. the vertical dimension of the vowel diagram is known as vowel height, which includes high, central ( mid ), or low vowels. the horizontal dimension of the vowel diagram includes tongue advancement and identifies how far forward the tongue is located in the oral cavity during production. vowels are also categorized by the tenseness or laxness of the tongue. the schwa [ Ι ] is in the center of the chart and is frequently referred to as the neutral vowel. here, the vocal tract is in its neutral state and creates a near perfect tube. for other vowels, there is a necessary movement of the vocal tract and tongue away from the neutral position, either up / down or backward / forward. the next dimension for vowels are tense / lax ; here we can distinguish high / mid / low dimensions and the front / central / back dimensions. in other words, all vowels but schwas. examples of tense and lax vowels are [ i ], [ o ] and [ Ιͺ ], [ Ι ], respectively. another characteristic of vowels is rounding. for example, for [ u ], the lips are rounded, but for [ i ], the lips are spread. vowels can be categorized as rounded or unrounded. rounded vowels are [ u ], [ Κ ], [ o ], [ Ι ] and the unrounded vowels are [ i ], [ Ιͺ ], [ e ], [ Ι ], [ Γ¦ ], [ Ι ], [ Κ ], [ Ι ]. the vowel systems of most languages can be represented by vowel diagrams. usually, there is a pattern of even distribution of
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Ιͺ ], [ e ], [ Ι ], [ Γ¦ ], [ Ι ], [ Κ ], [ Ι ]. the vowel systems of most languages can be represented by vowel diagrams. usually, there is a pattern of even distribution of marks on the chart, a phenomenon that is known as vowel dispersion. for most languages, the vowel system is triangular. only 10 % of languages, including english, have a vowel diagram that is quadrilateral. such a diagram is called a vowel quadrilateral or a vowel trapezium. different vowels vary in pitch. for example, high vowels, such as [ i ] and [ u ], tend to have a higher fundamental frequency than low vowels, such as [ a ]. vowels are distinct from one another by their acoustic form or spectral properties. spectral properties are the speech sound's fundamental frequency and its formants. each vowel in the vowel diagram has a unique first and second formant, or f1 and f2. the frequency of the first formant refers to the width of the pharyngeal cavity and the position of the tongue on a vertical axis and ranges from open to close. the frequency of the second formant refers to the length of the oral cavity and the position of the tongue on a horizontal axis. [ i ], [ u ], [ a ] are often referred to as point vowels because they represent the most extreme f1 and f2 frequencies. [ a ] has a high f1 frequency because of the narrow size of the pharynx and the low position of the tongue. the f2 frequency is higher for [ i ] because the oral cavity is short and the tongue is at the front of the mouth. the f2 frequency is low in the production of [ u ] because the mouth is elongated and the lips are rounded while the pharynx is lowered. the ipa vowel chart has the cardinal vowels and is displayed in the form of a trapezium. by definition, no vowel sound can be plotted outside of the ipa trapezium because its four corners represent the extreme points of articulation. the vowel diagrams of most real languages are not so extreme. in english, for example, high vowels are not as high as the corners of the ipa trapezium, and front vowels are not as front. = = ipa vowel diagram with added material = = the official vowel chart of the international phonetic alphabet does not include vowel symbols with added diacritics as shown here, and only gives labels for the heights " close
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front vowels are not as front. = = ipa vowel diagram with added material = = the official vowel chart of the international phonetic alphabet does not include vowel symbols with added diacritics as shown here, and only gives labels for the heights " close ", " close - mid ", " open - mid ", and " open " ( shown here in bold ). = = see also = = ipa vowel chart with audio ipa consonant chart with audio = = references = =
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the midlands microcraton is a triangular block of late neoproterozoic crust of igneous and volcaniclastic origin which underlies the english midlands. its northern tip is at the southern edge of the english peak district and its other two corners are in the vicinity of london and swansea. though its northeastern edge is obscured by palaeozoic and mesozoic strata, the northwestern edge of the microcraton is clearly defined by the welsh borderland fault system. to the south it is bounded by the variscan orogen. = = references = =
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the immunisation advisory centre ( imac ) is a new zealand - wide organisation which provides information and training about immunization and vaccine - preventable diseases to health care professionals, government bodies, and individuals. it co - ordinates the nation's immunisation programmes, policy advice and research. it was launched in 1997, and is based at the university of auckland. = = recurrring situations = = every year, imac is involved in planning, promoting, and monitoring the delivery of the seasonal influenza vaccine. they are also called on to comment on social factors, such as the role that social media might have in spreading anti - vaccine conspiracy theories. = = response to outbreaks = = = = = measles ( 2019 ) = = = in 2011, there were nearly 600 cases of measles in nz. by 2017, the world health organization declared that measles was eradicated from new zealand. so the only cases originate in people arriving from overseas who carry the disease. but there was an outbreak in 2019 and by november 2019 over 2, 000 cases had been reported that year, a third of which required hospitalisation. most cases were people who were not vaccinated, or it was not known whether they had been vaccinated. the outbreak reached its peak in september 2019, and it took until 11 - 17 january 2020 before there was the first week without any new cases. imac director nikki turner released a paper analysing the factors that drove this event. it is suspected to have originated from disneyland. and a generation born between 1982 and 2007 had low immunization rates, allowing the disease to spread once it gets in. vaccination records are incomplete for that period, as the national immunisation register was only introduced in 2005. the imac instigated a program to identify the gaps in immunization, and offer the affected people information so they can fill in the gaps. turner said : " new zealand, i believe, needs to offer at least a single measles - containing vaccine to everybody under 50, who does not have a clear record. " in february 2020, the ministry of health announced funding of nz $ 23 million to build on this initiative with a combined mmr vaccine catch - up programme. = = = covid - 19 ( 2020 - 2021 ) = = = the covid - 19 pandemic arrived in new zealand early in 2020, with the first case reported on 28 february and the first fatality reported on 29 march,
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. = = = covid - 19 ( 2020 - 2021 ) = = = the covid - 19 pandemic arrived in new zealand early in 2020, with the first case reported on 28 february and the first fatality reported on 29 march, the same week that new zealand declared a state of national emergency and went into a complete lock - down. in addition to providing independent information, in february 2021 the ministry of health contracted imac to provide training to staff who will administer the vaccines. the covid - 19 vaccination rollout which started in march 2021 is the biggest such program ever undertaken in nz, so the imac briefed members of parliament on how the available vaccines work and the international data about effectiveness and side effects, advised the government on development of the four - stage vaccination framework, and worked closely with the medical profession to educate and co - ordinate the doctors. spokespeople from imac frequently provide commentary to the media on the status of the vaccination programme. = = references = = = = external links = = official website
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a convenience yield is an implied return on holding inventories. it is an adjustment to the cost of carry in the non - arbitrage pricing formula for forward prices in markets with trading constraints. let f t, t { \ displaystyle f _ { t, t } } be the forward price of an asset with initial price s t { \ displaystyle s _ { t } } and maturity t { \ displaystyle t }. suppose that r { \ displaystyle r } is the continuously compounded interest rate for one year. then, the non - arbitrage pricing formula should be f t, t = s t β
e r ( t β t ) { \ displaystyle f _ { t, t } = s _ { t } \ cdot e ^ { r ( t - t ) } } however, this relationship does not hold in most commodity markets, partly because of the inability of investors and speculators to short the underlying asset, s t { \ displaystyle s _ { t } }. instead, there is a correction to the forward pricing formula given by the convenience yield c { \ displaystyle c }. hence f t, t = s t β
e ( r β c ) ( t β t ) { \ displaystyle f _ { t, t } = s _ { t } \ cdot e ^ { ( r - c ) ( t - t ) } } this makes it possible for backwardation to be observable. = = example = = a trader has observed that the price of six - month ( t { \ displaystyle t } ) gold futures price ( f ) is $ 1, 300 per troy ounce, whereas the spot price ( s ) is $ 1, 371 per troy ounce. the ( not compounded ) borrowing rate for a six - month loan ( r { \ displaystyle r } ) is 3. 5 % per annum, and storage cost for gold is negligible ( 0 % ). since we know we have the relation : f = s [ 1 + ( r β c ) t ] { \ displaystyle f = s \ left [ 1 + ( r - c ) t \ right ] } what is the convenience yield implied by the futures price? from the formula above, we isolate the convenience yield ( c { \ displaystyle c } ), and we obtain : c = r + 1 t ( 1 β f s ) { \ displaystyle c = r + { \ frac { 1 } { t } }
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we isolate the convenience yield ( c { \ displaystyle c } ), and we obtain : c = r + 1 t ( 1 β f s ) { \ displaystyle c = r + { \ frac { 1 } { t } } \ left ( 1 - { \ frac { f } { s } } \ right ) } c = 0. 035 + 1 0. 5 ( 1 β 1300 1371 ) = 0. 13857 = 13. 9 % { \ displaystyle c = 0. 035 + { \ frac { 1 } { 0. 5 } } \ left ( 1 - { \ frac { 1300 } { 1371 } } \ right ) = 0. 13857 = 13. 9 \ % } ( per annum, not compounded ) for information, if we had a continuously compounded 6 - month borrowing rate and if we were looking for the continuously compounded convenience yield, we would have the formula : f = s β
e ( r β c ) t { \ displaystyle f = s \ cdot e ^ { ( r - c ) t } } and the convenience yield would therefore be : c = r β 1 t ln ( f s ) { \ displaystyle c = r - { \ frac { 1 } { t } } \ ln \ left ( { \ frac { f } { s } } \ right ) } c = 0. 035 β 1 0. 5 Γ ln ( 1300 1371 ) = 0. 14135 = 14. 1 % { \ displaystyle c = 0. 035 - { \ frac { 1 } { 0. 5 } } \ times \ ln \ left ( { \ frac { 1300 } { 1371 } } \ right ) = 0. 14135 = 14. 1 \ % } ( per annum, continuously compounded ) = = why should a convenience yield exist? = = users of a consumption asset may obtain a benefit from physically holding the asset ( as inventory ) prior to t ( maturity ) which is not obtained from holding the futures contract. these benefits include the ability to profit from temporary shortages, and the ability to keep a production process running. one of the main reasons that it appears is due to availability of stocks and inventories of the commodity in question. everyone who owns inventory has the choice between consumption today and investment for the future. a rational investor will choose the outcome that is best for himself. when inventories are high, this suggests an expected
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of stocks and inventories of the commodity in question. everyone who owns inventory has the choice between consumption today and investment for the future. a rational investor will choose the outcome that is best for himself. when inventories are high, this suggests an expected relatively low scarcity of the commodity today versus some time in the future. otherwise, the investor would not perceive that there is any benefit of holding onto inventory and therefore sell his stocks. hence, expected future prices should be higher than they currently are. futures or forward prices f t, t { \ displaystyle f _ { t, t } } of the asset should then be higher than the current spot price, s t { \ displaystyle s _ { t } }. from the above formula, this only tells us that r β c > 0 { \ displaystyle r - c > 0 }. the interesting line of reasoning comes when inventories are low. when inventories are low, we expect that scarcity now is greater than in the future. unlike the previous case, the investor can not buy inventory to make up for demand today. in a sense, the investor wants to borrow inventory from the future but is unable. therefore, we expect future prices to be lower than today and hence that f t, t < s t { \ displaystyle f _ { t, t } < s _ { t } }. this implies that r β c < 0 { \ displaystyle r - c < 0 }. consequently, the convenience yield is inversely related to inventory levels. = = references = =
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the frbroo ( " frbr - object oriented " ) initiative is a joint effort of the cidoc conceptual reference model and functional requirements for bibliographic records international working groups to establish " a formal ontology intended to capture and represent the underlying semantics of bibliographic information and to facilitate the integration, mediation, and interchange of bibliographic and museum information. " = = history = = the idea behind this initiative is that both the library and museum communities would benefit from harmonizing the frbr and cidoc reference models to better share library and museum information, particularly in light of the semantic web and the overall need to improve the interoperability of digital libraries and museum information management systems. this led to the formation of the international working group on frbr / cidoc crm harmonisation in 2003 with the common goals of " expressing the ifla frbr reference model with the concepts, tools, mechanisms, and notation conventions provided by the cidoc crm β¦ and aligning ( possibly even merging ) the two object - oriented models with the aim to contribute to the solution of the problem of semantic interoperability between the documentation structures used for library and museum information. " the first draft of frbroo was completed in 2006. the model expresses the attributes and relationships in the entity β relationship model of frbr, formulated as an extensions of the cidoc - crm. version 2. 4 of the frbroo model was released in november 2015. = = pressoo = = the issn international centre, the issn review group, and the bibliotheque nationale de france developed an extension of the frbroo model called pressoo in 2013. pressoo extends frbroo to describe serials and continuing resources. version 0. 1 was released in march 2013 and version 0. 2 was released in december 2013. pressoo's model includes properties and classes that recognize the dynamic nature of serials. the model includes all of the serial relationships in the issn manual. one interesting aspect of pressoo is its premise that " there is no single expression or manifestation representing a complete serial work unless the serial work is ended. " = = see also = = bibframe functional requirements for bibliographic records ( frbr ) = = references = = riva, doerr, and zumer, frbroo : enabling a common view of information from memory institutions, world library and information congress : 74th ifla general conference and council, 10 β 14 august 2008, quebec, canada = = external links
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, doerr, and zumer, frbroo : enabling a common view of information from memory institutions, world library and information congress : 74th ifla general conference and council, 10 β 14 august 2008, quebec, canada = = external links = = ifla. org / frbroo / frbroo _ v _ 2. 4. pdf frbr - crm working drafts and releases, via international council of museums working group on frbr / crm dialogue, via international federation of library associations
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in cryptography, tiger is a cryptographic hash function designed by ross anderson and eli biham in 1995 for efficiency on 64 - bit platforms. the size of a tiger hash value is 192 bits. truncated versions ( known as tiger / 128 and tiger / 160 ) can be used for compatibility with protocols assuming a particular hash size. unlike the sha - 2 family, no distinguishing initialization values are defined ; they are simply prefixes of the full tiger / 192 hash value. tiger2 is a variant where the message is padded by first appending a byte with the hexadecimal value of 0x80 as in md4, md5 and sha, rather than with the hexadecimal value of 0x01 as in the case of tiger. the two variants are otherwise identical. = = algorithm = = tiger is based on merkle β damgard construction. the one - way compression function operates on 64 - bit words, maintaining 3 words of state and processing 8 words of data. there are 24 rounds, using a combination of operation mixing with xor and addition / subtraction, rotates, and s - box lookups, and a fairly intricate key scheduling algorithm for deriving 24 round keys from the 8 input words. although fast in software, tiger's large s - boxes ( four s - boxes, each with 256 64 - bit entries totaling 8 kib ) make implementations in hardware or microcontrollers difficult. = = usage = = tiger is frequently used in merkle hash tree form, where it is referred to as tth ( tiger tree hash ). tth is used by many clients on the direct connect and gnutella file sharing networks, and can optionally be included in the bittorrent metafile for better content availability. tiger was considered for inclusion in the openpgp standard, but was abandoned in favor of ripemd - 160. = = oid = = rfc 2440 refers to tiger as having no oid, whereas the gnu coding standards list tiger as having oid 1. 3. 6. 1. 4. 1. 11591. 12. 2. in the ipsec subtree, hmac - tiger is assigned oid 1. 3. 6. 1. 5. 5. 8. 1. 3. no oid for tth has been announced yet. = = byte order = = the specification of tiger does not define the way its output should be printed but only defines the result to be three ordered 64 - bit
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. 8. 1. 3. no oid for tth has been announced yet. = = byte order = = the specification of tiger does not define the way its output should be printed but only defines the result to be three ordered 64 - bit integers. the " testtiger " program at the author's homepage was intended to allow easy testing of the test source code, rather than to define any particular print order. the protocols direct connect and adc as well as the program tthsum use little - endian byte order, which is also preferred by one of the authors. = = examples = = in the example below, the 192 - bit ( 24 - byte ) tiger hashes are represented as 48 hexadecimal digits in little - endian byte order. the following demonstrates a 43 - byte ascii input and the corresponding tiger hashes : tiger ( " the quick brown fox jumps over the lazy dog " ) = 6d12a41e72e644f017b6f0e2f7b44c6285f06dd5d2c5b075 tiger2 ( " the quick brown fox jumps over the lazy dog " ) = 976abff8062a2e9dcea3a1ace966ed9c19cb85558b4976d8 even a small change in the message will ( with very high probability ) result in a completely different hash, e. g. changing d to c : tiger ( " the quick brown fox jumps over the lazy cog " ) = a8f04b0f7201a0d728101c9d26525b31764a3493fcd8458f tiger2 ( " the quick brown fox jumps over the lazy cog " ) = 09c11330283a27efb51930aa7dc1ec624ff738a8d9bdd3df the hash of the zero - length string is : tiger ( " " ) = 3293ac630c13f0245f92bbb1766e16167a4e58492dde73f3 tiger2 ( " " ) = 4441be75f6018773c206c22745374b924aa8313fef919f41 = = cryptanalysis = = unlike md5
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##f3 tiger2 ( " " ) = 4441be75f6018773c206c22745374b924aa8313fef919f41 = = cryptanalysis = = unlike md5 or sha - 0 / 1, there are no known effective attacks on the full 24 - round tiger except for pseudo - near collision. while md5 processes its state with 64 simple 32 - bit operations per 512 - bit block and sha - 1 with 80, tiger updates its state with a total of 144 such operations per 512 - bit block, additionally strengthened by large s - box look - ups. john kelsey and stefan lucks have found a collision - finding attack on 16 - round tiger with a time complexity equivalent to about 244 compression function invocations and another attack that finds pseudo - near collisions in 20 - round tiger with work less than that of 248 compression function invocations. florian mendel et al. have improved upon these attacks by describing a collision attack spanning 19 rounds of tiger, and a 22 - round pseudo - near - collision attack. these attacks require a work effort equivalent to about 262 and 244 evaluations of the tiger compression function, respectively. = = see also = = hash function security summary comparison of cryptographic hash functions list of hash functions serpent β a block cipher by the same authors = = references = = = = external links = = the tiger home page
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modal adjectives are adjectives, such as likely, probable and necessary, that express modality, i. e., possibility, necessity, or contingency. = = in english = = modal adjectives can express modality regarding a situation or a participant in that situation. with situations, some usual syntactic patterns include an extraposed subject, such as the underlined elements in the following examples with the modal adjective in bold. here the modal adjective is analyzed semantically as a sentential modal operator. it's possible that some of them are broken. it's likely that they will come. it is necessary ( for us ) to make a choice. for participants, however, the usual syntactic construction has the adjective phrase in attributive modifier function, as in the following examples, where the modal adjective is again in bold and this time the participant in underlined. we've found a potential replacement. they need to file the necessary papers. we took the obligatory photo. other constructions are also possible. for example, contingency may be expressed as we've made an offer contingent on the sale of our house, which can be paraphrased as our offer stands if and only if we sell our house. = = in japanese = = in japanese, possibility is often expressed with the adjectives ( kanou'possible') and δΈ ( fukanou'impossible'), as in : impossibility can also be expressed with the modal adjective ( muri'impossible') as in : the modern japanese particle γΈγ ( beki'should') derives from the traditional modal adjective γΈγ ( beshi ) but no longer inflects. = = see also = = modal word = = references = =
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a criminaloid ( from the word " criminal " and suffix - oid, meaning criminal - like ) is a person who projects a respectable, upright facade in an attempt to conceal a criminal personality. this type, first defined by cesare lombroso in the later editions of his 1876 work the criminal man, unlike ordinary criminals, criminaloids enjoy the respect of society and, because they often establish connections with the government and the law, they are less likely to meet with opposition. due to their respectable standing, they generally enjoy greater prosperity than the average criminal, and have an automatic advantage over their more conscientious colleagues. from the encyclopedia of white collar and corporate crime : " the key to the criminaloid is not evil impulse, but moral insensibility. the criminaloid prefers to prey on the anonymous public. he goes beyond this by convincing others to act instead of acting himself, which protects him from liability and being labeled a criminal, and is instead immune to such scrutiny. the criminaloid practices a protective impersonation of the good. the criminaloid counterfeits the good citizen. " = = references = = = = further reading = = notes on criminal behavior encyclopedia of white - collar & corporate crime
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a direct electron ionization liquid chromatography β mass spectrometry interface ( direct - ei lc - ms interface ) is a technique for coupling liquid chromatography and mass spectrometry ( lc - ms ) based on the direct introduction of the liquid effluent into an electron ionization ( ei ) source. library searchable mass spectra are generated. gas - phase ei has many applications for the detection of hplc amenable compounds showing minimal adverse matrix effects. the direct - ei lc - ms interface provides access to well - characterized electron ionization data for a variety of lc applications and readily interpretable spectra from electronic libraries for environmental, food safety, pharmaceutical, biomedical, and other applications. = = background = = high performance liquid chromatography ( hplc ) and electron ionization mass spectrometry ( eims ) are two analytical techniques that, in principle, seem to be incompatible. however, because these two approaches share a great deal of applications in the analysis of suitable molecules, typically less than 1000 u, a large effort has been devoted by the scientific community to develop a reliable, easy - to - use, and flawless interface. the first successful and commercially available device to combine ei and hplc was designed by willoughby and browner in 1984. it was based on the conversion of the solute into a beam of particles, after the formation of spray droplets and the elimination of the solvent vapors through a multi - stage momentum separator. although its efficient interfacing mechanism and a unique trait, particle beam performance was sometimes inadequate to an increasing number of new, demanding applications and was quickly replaced by a family of atmospheric pressure ionization - based interfaces ( api ) when they became commercially available. however, the possibility to record an ei spectrum from an hplc application remained a challenge for a long time. the first direct - ei prototype was first presented in 2002 and proposed an innovative approach that improved interfacing performance compared to that of particle beam and opened new opportunities for lc - ms applications. = = mechanism = = the interfacing mechanism is contained inside a common ei source, like that found in any gc - ms system. the liquid phase from a nano hplc column is admitted from the capillary column port, where the connection tubing and the nebulizer are first introduced and sealed to prevent vacuum loss. the mechanism is based on the formation of an aerosol in high - vacuum conditions, followed by a quick
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admitted from the capillary column port, where the connection tubing and the nebulizer are first introduced and sealed to prevent vacuum loss. the mechanism is based on the formation of an aerosol in high - vacuum conditions, followed by a quick droplet desolvation and final vaporization of the solute prior to the ionization. the completion of the process is quick and complete and reduces chances of thermal decomposition as reported in the figure, where a scheme of the interface is shown. the core of the interface is represented by the micro - nebulizer. the nebulizer tip protrudes into the ion source so that the spray expansion is completely contained inside the ion volume. the eluate emerges as liquid phase at a flow rate of 300 - 500 nl / min, and any premature in - tube solvent evaporation is prevented by a convenient thermal insulation of the nebulizer and the connecting tubing from the surrounding source heat. the high temperature of the ion source, between 300 and 400Β°c, has a double function : to compensate for the latent heat of vaporization during the droplet desolvation, and to convert the solute into the gas phase. if all components of this simple interface are correctly placed and sized, then each substance separated by the nano - column is smoothly converted into the gas phase, the peak profile is nicely reproduced, and high quality mass spectra are generated. major advantages of this technical solution are the following : 1 ) it delivers high - quality, fully library matchable mass spectra of most sub - 1 kda molecules amenable by hplc, 2 ) it is a chemical ionization free interface ( unless operated intentionally ) with accurate reproduction of the expected isotope ion abundances, 3 ) response is never influenced by matrix components in the sample or in the mobile phase, 4 ) it can be considered a universal detector for small molecules because response is not related to compound polarity. = = performance and applications = = = = = mass spectral quality = = = a key feature of this interface is to produce top quality ei spectra from compounds dissolved in a liquid phase. in this case, quality is intended as a measure of the degree of success in a virtual comparison with thousands of spectra stored in the electronic libraries. identification capability in real - world applications, when peaks are small and noise is high, can be greatly influenced by the quality of ionization. a nist library version 2. 0d was used for comparison. in this case, identification capability is not compromised by the presence of
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world applications, when peaks are small and noise is high, can be greatly influenced by the quality of ionization. a nist library version 2. 0d was used for comparison. in this case, identification capability is not compromised by the presence of solvent vapor residues and matching quality tops that of a typical gc - ms system. = = = response versus matrix composition = = = in electrospray ionization ( esi ), coeluted matrix components can influence signal intensity through a competition for available charges and for the access to the droplet surface for gas - phase emission, thus creating the so - called matrix effects. matrix effects can occur at different stages of the interfacing process leading to unpredictably enhanced or suppressed signal response. direct - ei interface, using a gas phase ionization technique, can eliminate most matrix effects observed with esi. in fact, it is influenced neither by the mobile phase nor by other matrix components so that the signal response is always proportional only to analyte concentration. this simplifies sample preparation procedures that can be very complex and time - consuming prior to esi. = = = other performance aspects = = = the evaluation of the performance cannot be considered complete without considering the limit of detection, the range of linear response and the signal reproducibility. ei is known as a low - efficiency ionization technique. because less than 1 / 10 000 of the gas - phase sample molecules are ionized, impressive detection limits cannot be expected. however, the efficient interfacing mechanism of this interface allows picogram - level detection limit in selected ion monitoring ( sim ) for most substances. on the other hand, soft ionization techniques such as esi are, in some cases, far more efficient but generate fewer fragment ions. the cost of this attitude is paid in terms of structural information so that a second analyzer to generate ms / ms spectra is an obligation. a typical ei spectrum, in general, has extensive structural information, and a cheaper, single - stage mass spectrometer might be sufficient for analyte characterization or identification. as a rule of the thumb, nanogram - level sensitivity is obtained in full - scan mode for most substances. linearity and reproducibility are two point of strength of the interface. up to four orders of magnitude linearity with rsd lower than 10 % are common values in many applications. = = = applications = = = direct - ei may offer a clear advantage over esi in several applications, but it may excel
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. up to four orders of magnitude linearity with rsd lower than 10 % are common values in many applications. = = = applications = = = direct - ei may offer a clear advantage over esi in several applications, but it may excel in the following cases : large number of compounds of different polarities and chemical properties : ei can offer a shortcut, do - it - all solution when hard - to - detect substances are included or and when a combination of positive and negative ion detection runs are required for complete coverage of analyte detection. characterization of unknowns : library matching offer an invaluable tool for compound identification. detection of non chromophoric compounds that also give poor or no signal with api : for these compounds additional hplc detectors such as evaporative light scattering detector ( elsd ), refractive index ( ri ) or corona discharge aerosol detector ( cad ) are also available but each of them has limitations which restrain obtaining a universal detection with reasonable sensitivity. ei - ms would offer a suitable solution for this type of compounds, in terms of sensitivity and universal response. gc is anyway feasible only for compounds with high to medium volatility and therefore cannot be adopted for a full characterization of mixtures of complex nature. the possibility of hyphenating ei to hplc separation represents an ideal solution. quantitative analyses in presence of matrix effects : ei - ms offers a superior performance compared to esi or apci when intruding interferences from complex matrices pass cleanup procedure and cause signal suppression or enhancement. = = references = =
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planet patrol is a nasa citizen science project available in zooniverse and aimed at discovering new exoplanets with data from the tess telescope. the project is built on results produced by a computer algorithm. the algorithm measures the center - of - light of the images and automatically compares it to the catalog position of the corresponding star. the main difference with planet hunters is that planet patrol looks at objects that represent a detected planet candidate in tess data, whereas planet hunters searches through all the stars in the tess databases and asks humans to find such candidates. as of september 2020, there are 1370 volunteers and 72, 938 classifications have been done. the images representing a possible exoplanet transit show a single bright source near the middle of the image with a dot at the center. = = results = = two papers were published by planet patrol, vetting 1998 tess objects of interest ( tois ). of these tois 1461 passed as planet candidates, 286 were ruled out as false - positive and 251 were labelled as potential false - positive. the resulting catalog is named tess triple 9 ( tt9 ), named after the number of vetted tois in each paper being 999. the second tt9 paper describes interesting planet candidates, such as tic 396720998. 01 ( toi 709. 01 ), a sub - jovian around a hot subdwarf, named lb 1721. the planet candidate produces a v - shaped transit, which is different from the u - shaped transits that most planets produce. toi 709. 01 was previously classified as a false - positive by triceratops, another vetting tool. because this tool uses pre - existing knowledge of its host star and transit shape, this tool might have been confused by the small size of the host star and the resulting v - shape of a transit. toi 709. 01 would be the second transiting planet around a degenerate star if confirmed. the first transiting planet around a white dwarf was wd 1856 + 534 b. the paper also describes two planet candidates in the habitable zone : toi 715. 01 and the already confirmed toi 1227 b. = = see also = = planet hunters exoplanet explorers = = references = =
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site - specific recombination, also known as conservative site - specific recombination, is a type of genetic recombination in which dna strand exchange takes place between segments possessing at least a certain degree of sequence homology. enzymes known as site - specific recombinases ( ssrs ) perform rearrangements of dna segments by recognizing and binding to short, specific dna sequences ( sites ), at which they cleave the dna backbone, exchange the two dna helices involved, and rejoin the dna strands. in some cases the presence of a recombinase enzyme and the recombination sites is sufficient for the reaction to proceed ; in other systems a number of accessory proteins and / or accessory sites are required. many different genome modification strategies, among these recombinase - mediated cassette exchange ( rmce ), an advanced approach for the targeted introduction of transcription units into predetermined genomic loci, rely on ssrs. site - specific recombination systems are highly specific, fast, and efficient, even when faced with complex eukaryotic genomes. they are employed naturally in a variety of cellular processes, including bacterial genome replication, differentiation and pathogenesis, and movement of mobile genetic elements. for the same reasons, they present a potential basis for the development of genetic engineering tools. recombination sites are typically between 30 and 200 nucleotides in length and consist of two motifs with a partial inverted - repeat symmetry, to which the recombinase binds, and which flank a central crossover sequence at which the recombination takes place. the pairs of sites between which the recombination occurs are usually identical, but there are exceptions ( e. g. attp and attb of Ξ» integrase ). = = classification : tyrosine - vs. serine - recombinases = = based on amino acid sequence homologies and mechanistic relatedness, most site - specific recombinases are grouped into one of two families : the tyrosine ( tyr ) recombinase family or serine ( ser ) recombinase family. the names stem from the conserved nucleophilic amino acid residue present in each class of recombinase which is used to attack the dna and which becomes covalently linked to it during strand exchange. the earliest identified members of the serine recombinase family were known as resolvases or dna invertases,
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##ombinase which is used to attack the dna and which becomes covalently linked to it during strand exchange. the earliest identified members of the serine recombinase family were known as resolvases or dna invertases, while the founding member of the tyrosine recombinases, lambda phage integrase ( using attp / b recognition sites ), differs from the now well - known enzymes such as cre ( from the p1 phage ) and flp ( from the yeast saccharomyces cerevisiae ). famous serine recombinases include enzymes such as gamma - delta resolvase ( from the tn1000 transposon ), tn3 resolvase ( from the tn3 transposon ), and Οc31 integrase ( from the Οc31 phage ). there are several classes of serine recombinases, consisting of the small serine recombinase, the isxc5 resolvase, the serine transposase, and the large serine recombinase. although the individual members of the two recombinase families can perform reactions with the same practical outcomes, the families are unrelated to each other, having different protein structures and reaction mechanisms. unlike tyrosine recombinases, serine recombinases are highly modular, as was first hinted by biochemical studies and later shown by crystallographic structures. knowledge of these protein structures could prove useful when attempting to re - engineer recombinase proteins as tools for genetic manipulation. = = mechanism = = recombination between two dna sites begins by the recognition and binding of these sites β one site on each of two separate double - stranded dna molecules, or at least two distant segments of the same molecule β by the recombinase enzyme. this is followed by synapsis, i. e. bringing the sites together to form the synaptic complex. it is within this synaptic complex that the strand exchange takes place, as the dna is cleaved and rejoined by controlled transesterification reactions. during strand exchange, each double - stranded dna molecule is cut at a fixed point within the crossover region of the recognition site, releasing a deoxyribose hydroxyl group, while the recombinase enzyme forms a transient covalent bond to a dna backbone phosphate. this phosphodiester bond between the hydroxyl group of the nucle
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site, releasing a deoxyribose hydroxyl group, while the recombinase enzyme forms a transient covalent bond to a dna backbone phosphate. this phosphodiester bond between the hydroxyl group of the nucleophilic serine or tyrosine residue conserves the energy that was expended in cleaving the dna. energy stored in this bond is subsequently used for the rejoining of the dna to the corresponding deoxyribose hydroxyl group on the other dna molecule. the entire reaction therefore proceeds without the need for external energy - rich cofactors such as atp. although the basic chemical reaction is the same for both tyrosine and serine recombinases, there are some differences between them. tyrosine recombinases, such as cre or flp, cleave one dna strand at a time at points that are staggered by 6 β 8bp, linking the 3'end of the strand to the hydroxyl group of the tyrosine nucleophile ( fig. 1 ). strand exchange then proceeds via a crossed strand intermediate analogous to the holliday junction in which only one pair of strands has been exchanged. the mechanism and control of serine recombinases is much less well understood. this group of enzymes was only discovered in the mid - 1990s and is still relatively small. the now classical members gamma - delta and tn3 resolvase, but also new additions like Οc31 -, bxb1 -, and r4 integrases, cut all four dna strands simultaneously at points that are staggered by 2 bp ( fig. 2 ). during cleavage, a protein β dna bond is formed via a transesterification reaction, in which a phosphodiester bond is replaced by a phosphoserine bond between a 5'phosphate at the cleavage site and the hydroxyl group of the conserved serine residue ( s10 in resolvase ). it is still not entirely clear how the strand exchange occurs after the dna has been cleaved. however, it has been shown that the strands are exchanged while covalently linked to the protein, with a resulting net rotation of 180Β°. the most quoted ( but not the only ) model accounting for these facts is the " subunit rotation model " ( fig. 2 ). independent of the model, dna duplexes are situated outside of the protein complex, and large movement of the protein is
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most quoted ( but not the only ) model accounting for these facts is the " subunit rotation model " ( fig. 2 ). independent of the model, dna duplexes are situated outside of the protein complex, and large movement of the protein is needed to achieve the strand exchange. in this case the recombination sites are slightly asymmetric, which allows the enzyme to tell apart the left and right ends of the site. when generating products, left ends are always joined to the right ends of their partner sites, and vice versa. this causes different recombination hybrid sites to be reconstituted in the recombination products. joining of left ends to left or right to right is avoided due to the asymmetric " overlap " sequence between the staggered points of top and bottom strand exchange, which is in stark contrast to the mechanism employed by tyrosine recombinases. the reaction catalysed by cre - recombinase, for instance, may lead to excision of the dna segment flanked by the two sites ( fig. 3a ), but may also lead to integration or inversion of the orientation of the flanked dna segment ( fig. 3b ). what the outcome of the reaction will be is dictated mainly by the relative locations and orientations of the sites that are to be recombined, but also by the innate specificity of the site - specific system in question. excisions and inversions occur if the recombination takes place between two sites that are found on the same molecule ( intramolecular recombination ), and if the sites are in the same ( direct repeat ) or in an opposite orientation ( inverted repeat ), respectively. insertions, on the other hand, take place if the recombination occurs on sites that are situated on two different dna molecules ( intermolecular recombination ), provided that at least one of these molecules is circular. most site - specific systems are highly specialised, catalysing only one of these different types of reaction, and have evolved to ignore the sites that are in the " wrong " orientation. = = see also = = cre recombinase cre - lox recombination flp - frt recombination genetic recombination homologous recombination recombinase - mediated cassette exchange site - specific recombinase technology = = references = =
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the exner equation describes conservation of mass between sediment in the bed of a channel and sediment that is being transported. it states that bed elevation increases ( the bed aggrades ) proportionally to the amount of sediment that drops out of transport, and conversely decreases ( the bed degrades ) proportionally to the amount of sediment that becomes entrained by the flow. it was developed by the austrian meteorologist and sedimentologist felix maria exner, from whom it derives its name. it is typically applied to sediment in a fluvial system such as a river. the exner equation states that the change in bed elevation, Ξ· { \ displaystyle \ eta }, over time, t { \ displaystyle t }, is equal to one over the grain packing density, Ξ΅ o { \ displaystyle \ varepsilon _ { o } }, times the negative divergence of sediment flux, q s { \ displaystyle \ mathbf { q _ { s } } }, β Ξ· β t = β 1 Ξ΅ o β β
q s { \ displaystyle { \ frac { \ partial \ eta } { \ partial t } } = - { \ frac { 1 } { \ varepsilon _ { o } } } \ nabla \ cdot \ mathbf { q _ { s } } } note that Ξ΅ o { \ displaystyle \ varepsilon _ { o } } can also be expressed as ( 1 β Ξ» p ) { \ displaystyle ( 1 - \ lambda _ { p } ) }, where Ξ» p { \ displaystyle \ lambda _ { p } } equals the bed porosity. good values of Ξ΅ o { \ displaystyle \ varepsilon _ { o } } for natural systems range from 0. 45 to 0. 75. a typical value for spherical grains is 0. 64, as given by random close packing. an upper bound for close - packed spherical grains is 0. 74048 ( see sphere packing for more details ) ; this degree of packing is extremely improbable in natural systems, making random close packing the more realistic upper bound on grain packing density. often, for reasons of computational convenience and / or lack of data, the exner equation is used in its one - dimensional form. this is generally done with respect to the downstream direction x { \ displaystyle x }, as one is typically interested in the downstream distribution of erosion and deposition though a river reach β Ξ· β t = β 1 Ξ΅ o β q s
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dimensional form. this is generally done with respect to the downstream direction x { \ displaystyle x }, as one is typically interested in the downstream distribution of erosion and deposition though a river reach β Ξ· β t = β 1 Ξ΅ o β q s β x { \ displaystyle { \ frac { \ partial \ eta } { \ partial t } } = - { \ frac { 1 } { \ varepsilon _ { o } } } { \ frac { \ partial { q _ { s } } } { \ partial x } } } where q s { \ displaystyle q _ { s } } is scalar sediment flux in the downstream direction. = = references = =
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biodiversity is the variability of life on earth. it can be measured on various levels. there is for example genetic variability, species diversity, ecosystem diversity and phylogenetic diversity. diversity is not distributed evenly on earth. it is greater in the tropics as a result of the warm climate and high primary productivity in the region near the equator. tropical forest ecosystems cover less than one - fifth of earth's terrestrial area and contain about 50 % of the world's species. there are latitudinal gradients in species diversity for both marine and terrestrial taxa. since life began on earth, six major mass extinctions and several minor events have led to large and sudden drops in biodiversity. the phanerozoic aeon ( the last 540 million years ) marked a rapid growth in biodiversity via the cambrian explosion. in this period, the majority of multicellular phyla first appeared. the next 400 million years included repeated, massive biodiversity losses. those events have been classified as mass extinction events. in the carboniferous, rainforest collapse may have led to a great loss of plant and animal life. the permian β triassic extinction event, 251 million years ago, was the worst ; vertebrate recovery took 30 million years. human activities have led to an ongoing biodiversity loss and an accompanying loss of genetic diversity. this process is often referred to as holocene extinction, or sixth mass extinction. for example, it was estimated in 2007 that up to 30 % of all species will be extinct by 2050. destroying habitats for farming is a key reason why biodiversity is decreasing today. climate change also plays a role. this can be seen for example in the effects of climate change on biomes. this anthropogenic extinction may have started toward the end of the pleistocene, as some studies suggest that the megafaunal extinction event that took place around the end of the last ice age partly resulted from overhunting. = = definitions = = biologists most often define biodiversity as the " totality of genes, species and ecosystems of a region ". an advantage of this definition is that it presents a unified view of the traditional types of biological variety previously identified : taxonomic diversity ( usually measured at the species diversity level ) ecological diversity ( often viewed from the perspective of ecosystem diversity ) morphological diversity ( which stems from genetic diversity and molecular diversity ) functional diversity ( which is a measure of the number of functionally disparate species within a population ( e. g. different feeding mechanism, different motility, predator vs prey, etc. ) )
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which stems from genetic diversity and molecular diversity ) functional diversity ( which is a measure of the number of functionally disparate species within a population ( e. g. different feeding mechanism, different motility, predator vs prey, etc. ) ) biodiversity is most commonly used to replace the more clearly - defined and long - established terms, species diversity and species richness. however, there is no concrete definition for biodiversity, as its definition continues to be reimagined and redefined. to give a couple examples, the food and agriculture organization of the united nations ( fao ) defined biodiversity in 2019 as " the variability that exists among living organisms ( both within and between species ) and the ecosystems of which they are part. " the world health organization updated their website β s definition of biodiversity to be the " variability among living organisms from all sources. " both these definitions, although broad, give a current understanding of what is meant by the term biodiversity. = = number of species = = according to estimates by mora et al. ( 2011 ), there are approximately 8. 7 million terrestrial species and 2. 2 million oceanic species. the authors note that these estimates are strongest for eukaryotic organisms and likely represent the lower bound of prokaryote diversity. other estimates include : 220, 000 vascular plants, estimated using the species - area relation method 0. 7 β 1 million marine species 10 β 30 million insects ; ( of some 0. 9 million we know today ) 5 β 10 million bacteria ; 1. 5 - 3 million fungi, estimates based on data from the tropics, long - term non - tropical sites and molecular studies that have revealed cryptic speciation. some 0. 075 million species of fungi had been documented by 2001 ; 1 million mites the number of microbial species is not reliably known, but the global ocean sampling expedition dramatically increased the estimates of genetic diversity by identifying an enormous number of new genes from near - surface plankton samples at various marine locations, initially over the 2004 β 2006 period. the findings may eventually cause a significant change in the way science defines species and other taxonomic categories. since the rate of extinction has increased, many extant species may become extinct before they are described. not surprisingly, in the animalia the most studied groups are birds and mammals, whereas fishes and arthropods are the least studied animal groups. = = current biodiversity loss = = during the last century, decreases in biodiversity have been increasingly observed. it was estimated in 2007 that up to 30 % of
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are birds and mammals, whereas fishes and arthropods are the least studied animal groups. = = current biodiversity loss = = during the last century, decreases in biodiversity have been increasingly observed. it was estimated in 2007 that up to 30 % of all species will be extinct by 2050. of these, about one eighth of known plant species are threatened with extinction. estimates reach as high as 140, 000 species per year ( based on species - area theory ). this figure indicates unsustainable ecological practices, because few species emerge each year. the rate of species loss is greater now than at any time in human history, with extinctions occurring at rates hundreds of times higher than background extinction rates. and expected to still grow in the upcoming years. as of 2012, some studies suggest that 25 % of all mammal species could be extinct in 20 years. in absolute terms, the planet has lost 58 % of its biodiversity since 1970 according to a 2016 study by the world wildlife fund. the living planet report 2014 claims that " the number of mammals, birds, reptiles, amphibians, and fish across the globe is, on average, about half the size it was 40 years ago ". of that number, 39 % accounts for the terrestrial wildlife gone, 39 % for the marine wildlife gone and 76 % for the freshwater wildlife gone. biodiversity took the biggest hit in latin america, plummeting 83 percent. high - income countries showed a 10 % increase in biodiversity, which was canceled out by a loss in low - income countries. this is despite the fact that high - income countries use five times the ecological resources of low - income countries, which was explained as a result of a process whereby wealthy nations are outsourcing resource depletion to poorer nations, which are suffering the greatest ecosystem losses. a 2017 study published in plos one found that the biomass of insect life in germany had declined by three - quarters in the last 25 years. dave goulson of sussex university stated that their study suggested that humans " appear to be making vast tracts of land inhospitable to most forms of life, and are currently on course for ecological armageddon. if we lose the insects then everything is going to collapse. " in 2020 the world wildlife foundation published a report saying that " biodiversity is being destroyed at a rate unprecedented in human history ". the report claims that 68 % of the population of the examined species were destroyed in the years 1970 β 2016. of 70, 000 monitored species, around 48 % are experiencing population declines from
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biodiversity is being destroyed at a rate unprecedented in human history ". the report claims that 68 % of the population of the examined species were destroyed in the years 1970 β 2016. of 70, 000 monitored species, around 48 % are experiencing population declines from human activity ( in 2023 ), whereas only 3 % have increasing populations. rates of decline in biodiversity in the current sixth mass extinction match or exceed rates of loss in the five previous mass extinction events in the fossil record. biodiversity loss is in fact " one of the most critical manifestations of the anthropocene " ( since around the 1950s ) ; the continued decline of biodiversity constitutes " an unprecedented threat " to the continued existence of human civilization. the reduction is caused primarily by human impacts, particularly habitat destruction. since the stone age, species loss has accelerated above the average basal rate, driven by human activity. estimates of species losses are at a rate 100 β 10, 000 times as fast as is typical in the fossil record. loss of biodiversity results in the loss of natural capital that supplies ecosystem goods and services. species today are being wiped out at a rate 100 to 1, 000 times higher than baseline, and the rate of extinctions is increasing. this process destroys the resilience and adaptability of life on earth. in 2006, many species were formally classified as rare or endangered or threatened ; moreover, scientists have estimated that millions more species are at risk which have not been formally recognized. about 40 percent of the 40, 177 species assessed using the iucn red list criteria are now listed as threatened with extinction β a total of 16, 119. as of late 2022 9251 species were considered part of the iucn's critically endangered. numerous scientists and the ipbes global assessment report on biodiversity and ecosystem services assert that human population growth and overconsumption are the primary factors in this decline. however, other scientists have criticized this finding and say that loss of habitat caused by " the growth of commodities for export " is the main driver. a 2025 study found that human activities are responsible for biodiversity loss across all species and ecosystems. some studies have however pointed out that habitat destruction for the expansion of agriculture and the overexploitation of wildlife are the more significant drivers of contemporary biodiversity loss, not climate change. = = distribution = = biodiversity is not evenly distributed, rather it varies greatly across the globe as well as within regions and seasons. among other factors, the diversity of all living things ( biota ) depends on temperature, precipitation, altitude, soils, geography and the
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= = biodiversity is not evenly distributed, rather it varies greatly across the globe as well as within regions and seasons. among other factors, the diversity of all living things ( biota ) depends on temperature, precipitation, altitude, soils, geography and the interactions between other species. the study of the spatial distribution of organisms, species and ecosystems, is the science of biogeography. diversity consistently measures higher in the tropics and in other localized regions such as the cape floristic region and lower in polar regions generally. rain forests that have had wet climates for a long time, such as yasuni national park in ecuador, have particularly high biodiversity. there is local biodiversity, which directly impacts daily life, affecting the availability of fresh water, food choices, and fuel sources for humans. regional biodiversity includes habitats and ecosystems that synergizes and either overlaps or differs on a regional scale. national biodiversity within a country determines the ability for a country to thrive according to its habitats and ecosystems on a national scale. also, within a country, endangered species are initially supported on a national level then internationally. ecotourism may be utilized to support the economy and encourages tourists to continue to visit and support species and ecosystems they visit, while they enjoy the available amenities provided. international biodiversity impacts global livelihood, food systems, and health. problematic pollution, over consumption, and climate change can devastate international biodiversity. nature - based solutions are a critical tool for a global resolution. many species are in danger of becoming extinct and need world leaders to be proactive with the kunming - montreal global biodiversity framework. terrestrial biodiversity is thought to be up to 25 times greater than ocean biodiversity. forests harbour most of earth's terrestrial biodiversity. the conservation of the world's biodiversity is thus utterly dependent on the way in which we interact with and use the world's forests. a new method used in 2011, put the total number of species on earth at 8. 7 million, of which 2. 1 million were estimated to live in the ocean. however, this estimate seems to under - represent the diversity of microorganisms. forests provide habitats for 80 percent of amphibian species, 75 percent of bird species and 68 percent of mammal species. about 60 percent of all vascular plants are found in tropical forests. mangroves provide breeding grounds and nurseries for numerous species of fish and shellfish and help trap sediments that might otherwise adversely affect seagrass beds and coral reefs, which are habitats for many more marine species. forests span around 4 billion
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tropical forests. mangroves provide breeding grounds and nurseries for numerous species of fish and shellfish and help trap sediments that might otherwise adversely affect seagrass beds and coral reefs, which are habitats for many more marine species. forests span around 4 billion acres ( nearly a third of the earth's land mass ) and are home to approximately 80 % of the world's biodiversity. about 1 billion hectares are covered by primary forests. over 700 million hectares of the world's woods are officially protected. the biodiversity of forests varies considerably according to factors such as forest type, geography, climate and soils β in addition to human use. most forest habitats in temperate regions support relatively few animal and plant species and species that tend to have large geographical distributions, while the montane forests of africa, south america and southeast asia and lowland forests of australia, coastal brazil, the caribbean islands, central america and insular southeast asia have many species with small geographical distributions. areas with dense human populations and intense agricultural land use, such as europe, parts of bangladesh, china, india and north america, are less intact in terms of their biodiversity. northern africa, southern australia, coastal brazil, madagascar and south africa, are also identified as areas with striking losses in biodiversity intactness. european forests in eu and non - eu nations comprise more than 30 % of europe's land mass ( around 227 million hectares ), representing an almost 10 % growth since 1990. = = = latitudinal gradients = = = generally, there is an increase in biodiversity from the poles to the tropics. thus localities at lower latitudes have more species than localities at higher latitudes. this is often referred to as the latitudinal gradient in species diversity. several ecological factors may contribute to the gradient, but the ultimate factor behind many of them is the greater mean temperature at the equator compared to that at the poles. even though terrestrial biodiversity declines from the equator to the poles, some studies claim that this characteristic is unverified in aquatic ecosystems, especially in marine ecosystems. the latitudinal distribution of parasites does not appear to follow this rule. also, in terrestrial ecosystems the soil bacterial diversity has been shown to be highest in temperate climatic zones, and has been attributed to carbon inputs and habitat connectivity. in 2016, an alternative hypothesis ( " the fractal biodiversity " ) was proposed to explain the biodiversity latitudinal gradient. in this study, the species pool size and the fractal nature of ecosystems were combined to clarify some general
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in 2016, an alternative hypothesis ( " the fractal biodiversity " ) was proposed to explain the biodiversity latitudinal gradient. in this study, the species pool size and the fractal nature of ecosystems were combined to clarify some general patterns of this gradient. this hypothesis considers temperature, moisture, and net primary production ( npp ) as the main variables of an ecosystem niche and as the axis of the ecological hypervolume. in this way, it is possible to build fractal hyper volumes, whose fractal dimension rises to three moving towards the equator. = = = biodiversity hotspots = = = a biodiversity hotspot is a region with a high level of endemic species that have experienced great habitat loss. the term hotspot was introduced in 1988 by norman myers. while hotspots are spread all over the world, the majority are forest areas and most are located in the tropics. brazil's atlantic forest is considered one such hotspot, containing roughly 20, 000 plant species, 1, 350 vertebrates and millions of insects, about half of which occur nowhere else. the island of madagascar and india are also particularly notable. colombia is characterized by high biodiversity, with the highest rate of species by area unit worldwide and it has the largest number of endemics ( species that are not found naturally anywhere else ) of any country. about 10 % of the species of the earth can be found in colombia, including over 1, 900 species of bird, more than in europe and north america combined, colombia has 10 % of the world's mammals species, 14 % of the amphibian species and 18 % of the bird species of the world. madagascar dry deciduous forests and lowland rainforests possess a high ratio of endemism. since the island separated from mainland africa 66 million years ago, many species and ecosystems have evolved independently. indonesia's 17, 000 islands cover 735, 355 square miles ( 1, 904, 560 km2 ) and contain 10 % of the world's flowering plants, 12 % of mammals and 17 % of reptiles, amphibians and birds β along with nearly 240 million people. many regions of high biodiversity and / or endemism arise from specialized habitats which require unusual adaptations, for example, alpine environments in high mountains, or northern european peat bogs. accurately measuring differences in biodiversity can be difficult. selection bias amongst researchers may contribute to biased empirical research for modern estimates of biodiversity. in 1768, rev. gilbert white succinctly
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, alpine environments in high mountains, or northern european peat bogs. accurately measuring differences in biodiversity can be difficult. selection bias amongst researchers may contribute to biased empirical research for modern estimates of biodiversity. in 1768, rev. gilbert white succinctly observed of his selborne, hampshire " all nature is so full, that that district produces the most variety which is the most examined. " = = evolution over geologic timeframes = = biodiversity is the result of 3. 5 billion years of evolution. the origin of life has not been established by science, however, some evidence suggests that life may already have been well - established only a few hundred million years after the formation of the earth. until approximately 2. 5 billion years ago, all life consisted of microorganisms β archaea, bacteria, and single - celled protozoans and protists. biodiversity grew fast during the phanerozoic ( the last 540 million years ), especially during the so - called cambrian explosion β a period during which nearly every phylum of multicellular organisms first appeared. however, recent studies suggest that this diversification had started earlier, at least in the ediacaran, and that it continued in the ordovician. over the next 400 million years or so, invertebrate diversity showed little overall trend and vertebrate diversity shows an overall exponential trend. this dramatic rise in diversity was marked by periodic, massive losses of diversity classified as mass extinction events. a significant loss occurred in anamniotic limbed vertebrates when rainforests collapsed in the carboniferous, but amniotes seem to have been little affected by this event ; their diversification slowed down later, around the asselian / sakmarian boundary, in the early cisuralian ( early permian ), about 293 ma ago. the worst was the permian - triassic extinction event, 251 million years ago. vertebrates took 30 million years to recover from this event. the most recent major mass extinction event, the cretaceous β paleogene extinction event, occurred 66 million years ago. this period has attracted more attention than others because it resulted in the extinction of the non - avian dinosaurs, which were represented by many lineages at the end of the maastrichtian, just before that extinction event. however, many other taxa were affected by this crisis, which affected even marine taxa, such as ammonites, which also became extinct around that time. the biodiversity of the past is called paleobiodivers
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, just before that extinction event. however, many other taxa were affected by this crisis, which affected even marine taxa, such as ammonites, which also became extinct around that time. the biodiversity of the past is called paleobiodiversity. the fossil record suggests that the last few million years featured the greatest biodiversity in history. however, not all scientists support this view, since there is uncertainty as to how strongly the fossil record is biased by the greater availability and preservation of recent geologic sections. some scientists believe that corrected for sampling artifacts, modern biodiversity may not be much different from biodiversity 300 million years ago, whereas others consider the fossil record reasonably reflective of the diversification of life. estimates of the present global macroscopic species diversity vary from 2 million to 100 million, with a best estimate of somewhere near 9 million, the vast majority arthropods. diversity appears to increase continually in the absence of natural selection. = = = diversification = = = the existence of a global carrying capacity, limiting the amount of life that can live at once, is debated, as is the question of whether such a limit would also cap the number of species. while records of life in the sea show a logistic pattern of growth, life on land ( insects, plants and tetrapods ) shows an exponential rise in diversity. as one author states, " tetrapods have not yet invaded 64 percent of potentially habitable modes and it could be that without human influence the ecological and taxonomic diversity of tetrapods would continue to increase exponentially until most or all of the available eco - space is filled. " it also appears that the diversity continues to increase over time, especially after mass extinctions. on the other hand, changes through the phanerozoic correlate much better with the hyperbolic model ( widely used in population biology, demography and macrosociology, as well as fossil biodiversity ) than with exponential and logistic models. the latter models imply that changes in diversity are guided by a first - order positive feedback ( more ancestors, more descendants ) and / or a negative feedback arising from resource limitation. hyperbolic model implies a second - order positive feedback. differences in the strength of the second - order feedback due to different intensities of interspecific competition might explain the faster rediversification of ammonoids in comparison to bivalves after the end - permian extinction. the hyperbolic pattern of the world population growth arises from a second - order positive feedback between the population size and the
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competition might explain the faster rediversification of ammonoids in comparison to bivalves after the end - permian extinction. the hyperbolic pattern of the world population growth arises from a second - order positive feedback between the population size and the rate of technological growth. the hyperbolic character of biodiversity growth can be similarly accounted for by a feedback between diversity and community structure complexity. the similarity between the curves of biodiversity and human population probably comes from the fact that both are derived from the interference of the hyperbolic trend with cyclical and stochastic dynamics. most biologists agree however that the period since human emergence is part of a new mass extinction, named the holocene extinction event, caused primarily by the impact humans are having on the environment. it has been argued that the present rate of extinction is sufficient to eliminate most species on the planet earth within 100 years. new species are regularly discovered ( on average between 5 β 10, 000 new species each year, most of them insects ) and many, though discovered, are not yet classified ( estimates are that nearly 90 % of all arthropods are not yet classified ). most of the terrestrial diversity is found in tropical forests and in general, the land has more species than the ocean ; some 8. 7 million species may exist on earth, of which some 2. 1 million live in the ocean. = = = species diversity in geologic time frames = = = it is estimated that 5 to 50 billion species have existed on the planet. assuming that there may be a maximum of about 50 million species currently alive, it stands to reason that greater than 99 % of the planet's species went extinct prior to the evolution of humans. estimates on the number of earth's current species range from 10 million to 14 million, of which about 1. 2 million have been documented and over 86 % have not yet been described. however, a may 2016 scientific report estimates that 1 trillion species are currently on earth, with only one - thousandth of one percent described. the total amount of related dna base pairs on earth is estimated at 5. 0 x 1037 and weighs 50 billion tonnes. in comparison, the total mass of the biosphere has been estimated to be as much as four trillion tons of carbon. in july 2016, scientists reported identifying a set of 355 genes from the last universal common ancestor ( luca ) of all organisms living on earth. the age of earth is about 4. 54 billion years. the earliest undisputed evidence of life dates at least from 3. 7 billion
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identifying a set of 355 genes from the last universal common ancestor ( luca ) of all organisms living on earth. the age of earth is about 4. 54 billion years. the earliest undisputed evidence of life dates at least from 3. 7 billion years ago, during the eoarchean era after a geological crust started to solidify following the earlier molten hadean eon. there are microbial mat fossils found in 3. 48 billion - year - old sandstone discovered in western australia. other early physical evidence of a biogenic substance is graphite in 3. 7 billion - year - old meta - sedimentary rocks discovered in western greenland.. more recently, in 2015, " remains of biotic life " were found in 4. 1 billion - year - old rocks in western australia. according to one of the researchers, " if life arose relatively quickly on earth... then it could be common in the universe. " = = role and benefits of biodiversity = = = = = ecosystem services = = = there have been many claims about biodiversity's effect on the ecosystem services, especially provisioning and regulating services. some of those claims have been validated, some are incorrect and some lack enough evidence to draw definitive conclusions. ecosystem services have been grouped in three types : provisioning services which involve the production of renewable resources ( e. g. : food, wood, fresh water ) regulating services which are those that lessen environmental change ( e. g. : climate regulation, pest / disease control ) cultural services represent human value and enjoyment ( e. g. : landscape aesthetics, cultural heritage, outdoor recreation and spiritual significance ) experiments with controlled environments have shown that humans cannot easily build ecosystems to support human needs ; for example insect pollination cannot be mimicked, though there have been attempts to create artificial pollinators using unmanned aerial vehicles. the economic activity of pollination alone represented between $ 2. 1 β 14. 6 billion in 2003. other sources have reported somewhat conflicting results and in 1997 robert costanza and his colleagues reported the estimated global value of ecosystem services ( not captured in traditional markets ) at an average of $ 33 trillion annually. = = = = provisioning services = = = = with regards to provisioning services, greater species diversity has the following benefits : greater species diversity of plants increases fodder yield ( synthesis of 271 experimental studies ). greater species diversity of plants ( i. e. diversity within a single species ) increases overall crop yield ( synthesis of 575 experimental studies ). although another review of 100 experimental
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of plants increases fodder yield ( synthesis of 271 experimental studies ). greater species diversity of plants ( i. e. diversity within a single species ) increases overall crop yield ( synthesis of 575 experimental studies ). although another review of 100 experimental studies reported mixed evidence. greater species diversity of trees increases overall wood production ( synthesis of 53 experimental studies ). however, there is not enough data to draw a conclusion about the effect of tree trait diversity on wood production. = = = = regulating services = = = = with regards to regulating services, greater species diversity has the following benefits : greater species diversity of fish increases the stability of fisheries yield ( synthesis of 8 observational studies ) of plants increases carbon sequestration, but note that this finding only relates to actual uptake of carbon dioxide and not long - term storage ; synthesis of 479 experimental studies ) of plants increases soil nutrient remineralization ( synthesis of 103 experimental studies ), increases soil organic matter ( synthesis of 85 experimental studies ) and decreases disease prevalence on plants ( synthesis of 107 experimental studies ) of natural pest enemies decreases herbivorous pest populations ( data from two separate reviews ; synthesis of 266 experimental and observational studies ; synthesis of 18 observational studies. although another review of 38 experimental studies found mixed support for this claim, suggesting that in cases where mutual intraguild predation occurs, a single predatory species is often more effective = = = agriculture = = = agricultural diversity can be divided into two categories : intraspecific diversity, which includes the genetic variation within a single species, like the potato ( solanum tuberosum ) that is composed of many different forms and types ( e. g. in the u. s. they might compare russet potatoes with new potatoes or purple potatoes, all different, but all part of the same species, s. tuberosum ). the other category of agricultural diversity is called interspecific diversity and refers to the number and types of different species. agricultural diversity can also be divided by whether it is'planned'diversity or'associated'diversity. this is a functional classification that we impose and not an intrinsic feature of life or diversity. planned diversity includes the crops which a farmer has encouraged, planted or raised ( e. g. crops, covers, symbionts, and livestock, among others ), which can be contrasted with the associated diversity that arrives among the crops, uninvited ( e. g. herbivores, weed species and pathogens, among others ). associated biodiversity can
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##ionts, and livestock, among others ), which can be contrasted with the associated diversity that arrives among the crops, uninvited ( e. g. herbivores, weed species and pathogens, among others ). associated biodiversity can be damaging or beneficial. the beneficial associated biodiversity include for instance wild pollinators such as wild bees and syrphid flies that pollinate crops and natural enemies and antagonists to pests and pathogens. beneficial associated biodiversity occurs abundantly in crop fields and provide multiple ecosystem services such as pest control, nutrient cycling and pollination that support crop production. although about 80 percent of humans'food supply comes from just 20 kinds of plants, humans use at least 40, 000 species. earth's surviving biodiversity provides resources for increasing the range of food and other products suitable for human use, although the present extinction rate shrinks that potential. = = = human health = = = biodiversity's relevance to human health is becoming an international political issue, as scientific evidence builds on the global health implications of biodiversity loss. this issue is closely linked with the issue of climate change, as many of the anticipated health risks of climate change are associated with changes in biodiversity ( e. g. changes in populations and distribution of disease vectors, scarcity of fresh water, impacts on agricultural biodiversity and food resources etc. ). this is because the species most likely to disappear are those that buffer against infectious disease transmission, while surviving species tend to be the ones that increase disease transmission, such as that of west nile virus, lyme disease and hantavirus, according to a study done co - authored by felicia keesing, an ecologist at bard college and drew harvell, associate director for environment of the atkinson center for a sustainable future ( acsf ) at cornell university. some of the health issues influenced by biodiversity include dietary health and nutrition security, infectious disease, medical science and medicinal resources, social and psychological health. biodiversity is also known to have an important role in reducing disaster risk, including rising sea levels. for example, wetland ecosystems along coastal communities serve as excellent water filtration systems, storage, and ultimately create a buffer region between the ocean and mainland neighborhoods in order to prevent water reaching these communities under climate change pressures or storm storages. other examples of diverse species or organisms are present around the world, offering their resourceful utilities to provide protection of human survival. biodiversity provides critical support for drug discovery and the availability of medicinal resources. a significant proportion of drugs are derived, directly or indirectly
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other examples of diverse species or organisms are present around the world, offering their resourceful utilities to provide protection of human survival. biodiversity provides critical support for drug discovery and the availability of medicinal resources. a significant proportion of drugs are derived, directly or indirectly, from biological sources : at least 50 % of the pharmaceutical compounds on the us market are derived from plants, animals and microorganisms, while about 80 % of the world population depends on medicines from nature ( used in either modern or traditional medical practice ) for primary healthcare. only a tiny fraction of wild species has been investigated for medical potential. marine ecosystems are particularly important, especially their chemical and physical properties that have paved the way for numerous pharmaceutical achievements ; the immense diversity of marine organisms have led to scientific discoveries including medical treatments to cancer, viral bacteria, aids, etc. this process of bioprospecting can increase biodiversity loss, as well as violating the laws of the communities and states from which the resources are taken. = = = business and industry = = = according to the boston consulting group, in 2021, the economic value that biodiversity has on society comes down to four definable terms : regulation, culture, habitat, and provisioning. to sum these up in a relatively short manner, biodiversity helps maintain habitat and animal functions that provide considerable amounts of resources that benefit the economy. biodiversity β s economic resources are worth at around $ 150 trillion annually which is roughly twice the world β s gdp. the loss of biodiversity is actually harming the gdp of the world by costing an estimated $ 5 trillion annually. business supply chains rely heavily on ecosystems remaining relatively maintained and nurtured. a disruption to these supply chains would negatively impact many businesses that would end up costing them more than what they are gaining. = = = cultural and aesthetic value = = = philosophically it could be argued that biodiversity has intrinsic aesthetic and spiritual value to mankind in and of itself. this idea can be used as a counterweight to the notion that tropical forests and other ecological realms are only worthy of conservation because of the services they provide. biodiversity also affords many non - material benefits including spiritual and aesthetic values, knowledge systems and education. = = measuring biodiversity = = = = = analytical limits = = = less than 1 % of all species that have been described have been studied beyond noting their existence. the vast majority of earth's species are microbial. contemporary biodiversity physics is " firmly fixated on the visible [ macroscopic ] world ". for example, microbial life is metabolically and environmentally more
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have been studied beyond noting their existence. the vast majority of earth's species are microbial. contemporary biodiversity physics is " firmly fixated on the visible [ macroscopic ] world ". for example, microbial life is metabolically and environmentally more diverse than multicellular life ( see e. g., extremophile ). " on the tree of life, based on analyses of small - subunit ribosomal rna, visible life consists of barely noticeable twigs. the inverse relationship of size and population recurs higher on the evolutionary ladder β to a first approximation, all multicellular species on earth are insects ". insect extinction rates are high β supporting the holocene extinction hypothesis. = = biodiversity changes ( other than losses ) = = = = = natural seasonal variations = = = biodiversity naturally varies due to seasonal shifts. spring's arrival enhances biodiversity as numerous species breed and feed, while winter's onset temporarily reduces it as some insects perish and migrating animals leave. additionally, the seasonal fluctuation in plant and invertebrate populations influences biodiversity. = = = introduced and invasive species = = = barriers such as large rivers, seas, oceans, mountains and deserts encourage diversity by enabling independent evolution on either side of the barrier, via the process of allopatric speciation. the term invasive species is applied to species that breach the natural barriers that would normally keep them constrained. without barriers, such species occupy new territory, often supplanting native species by occupying their niches, or by using resources that would normally sustain native species. species are increasingly being moved by humans ( on purpose and accidentally ). some studies say that diverse ecosystems are more resilient and resist invasive plants and animals. many studies cite effects of invasive species on natives, but not extinctions. invasive species seem to increase local ( alpha diversity ) diversity, which decreases turnover of diversity ( beta diversity ). overall gamma diversity may be lowered because species are going extinct because of other causes, but even some of the most insidious invaders ( e. g. : dutch elm disease, emerald ash borer, chestnut blight in north america ) have not caused their host species to become extinct. extirpation, population decline and homogenization of regional biodiversity are much more common. human activities have frequently been the cause of invasive species circumventing their barriers, by introducing them for food and other purposes. human activities therefore allow species to migrate to new areas ( and thus become invasive ) occurred on time scales much shorter than historically have
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activities have frequently been the cause of invasive species circumventing their barriers, by introducing them for food and other purposes. human activities therefore allow species to migrate to new areas ( and thus become invasive ) occurred on time scales much shorter than historically have been required for a species to extend its range. at present, several countries have already imported so many exotic species, particularly agricultural and ornamental plants, that their indigenous fauna / flora may be outnumbered. for example, the introduction of kudzu from southeast asia to canada and the united states has threatened biodiversity in certain areas. another example are pines, which have invaded forests, shrublands and grasslands in the southern hemisphere. = = = hybridization and genetic pollution = = = endemic species can be threatened with extinction through the process of genetic pollution, i. e. uncontrolled hybridization, introgression and genetic swamping. genetic pollution leads to homogenization or replacement of local genomes as a result of either a numerical and / or fitness advantage of an introduced species. hybridization and introgression are side - effects of introduction and invasion. these phenomena can be especially detrimental to rare species that come into contact with more abundant ones. the abundant species can interbreed with the rare species, swamping its gene pool. this problem is not always apparent from morphological ( outward appearance ) observations alone. some degree of gene flow is normal adaptation and not all gene and genotype constellations can be preserved. however, hybridization with or without introgression may, nevertheless, threaten a rare species'existence. = = conservation = = conservation biology matured in the mid - 20th century as ecologists, naturalists and other scientists began to research and address issues pertaining to global biodiversity declines. the conservation ethic advocates management of natural resources for the purpose of sustaining biodiversity in species, ecosystems, the evolutionary process and human culture and society. conservation biology is reforming around strategic plans to protect biodiversity. preserving global biodiversity is a priority in strategic conservation plans that are designed to engage public policy and concerns affecting local, regional and global scales of communities, ecosystems and cultures. action plans identify ways of sustaining human well - being, employing natural capital, macroeconomic policies including economic incentives, and ecosystem services. in the eu directive 1999 / 22 / ec zoos are described as having a role in the preservation of the biodiversity of wildlife animals by conducting research or participation in breeding programs. = = = protection and restoration techniques = = = removal of exotic species will allow the species that they have negatively impacted to recover their ecological
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described as having a role in the preservation of the biodiversity of wildlife animals by conducting research or participation in breeding programs. = = = protection and restoration techniques = = = removal of exotic species will allow the species that they have negatively impacted to recover their ecological niches. exotic species that have become pests can be identified taxonomically ( e. g., with digital automated identification system ( daisy ), using the barcode of life ). removal is practical only given large groups of individuals due to the economic cost. as sustainable populations of the remaining native species in an area become assured, " missing " species that are candidates for reintroduction can be identified using databases such as the encyclopedia of life and the global biodiversity information facility. biodiversity banking places a monetary value on biodiversity. one example is the australian native vegetation management framework. gene banks are collections of specimens and genetic material. some banks intend to reintroduce banked species to the ecosystem ( e. g., via tree nurseries ). reduction and better targeting of pesticides allows more species to survive in agricultural and urbanized areas. location - specific approaches may be less useful for protecting migratory species. one approach is to create wildlife corridors that correspond to the animals'movements. national and other boundaries can complicate corridor creation. = = protected areas = = protected areas, including forest reserves and biosphere reserves, serve many functions including for affording protection to wild animals and their habitat. protected areas have been set up all over the world with the specific aim of protecting and conserving plants and animals. some scientists have called on the global community to designate as protected areas of 30 percent of the planet by 2030, and 50 percent by 2050, in order to mitigate biodiversity loss from anthropogenic causes. the target of protecting 30 % of the area of the planet by the year 2030 ( 30 by 30 ) was adopted by almost 200 countries in the 2022 united nations biodiversity conference. at the moment of adoption ( december 2022 ) 17 % of land territory and 10 % of ocean territory were protected. in a study published 4 september 2020 in science advances researchers mapped out regions that can help meet critical conservation and climate goals. protected areas safeguard nature and cultural resources and contribute to livelihoods, particularly at local level. there are over 238 563 designated protected areas worldwide, equivalent to 14. 9 percent of the earth's land surface, varying in their extension, level of protection, and type of management ( iucn, 2018 ). the benefits of protected areas extend
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there are over 238 563 designated protected areas worldwide, equivalent to 14. 9 percent of the earth's land surface, varying in their extension, level of protection, and type of management ( iucn, 2018 ). the benefits of protected areas extend beyond their immediate environment and time. in addition to conserving nature, protected areas are crucial for securing the long - term delivery of ecosystem services. they provide numerous benefits including the conservation of genetic resources for food and agriculture, the provision of medicine and health benefits, the provision of water, recreation and tourism, and for acting as a buffer against disaster. increasingly, there is acknowledgement of the wider socioeconomic values of these natural ecosystems and of the ecosystem services they can provide. = = = national parks and wildlife sanctuaries = = = a national park is a large natural or near natural area set aside to protect large - scale ecological processes, which also provide a foundation for environmentally and culturally compatible, spiritual, scientific, educational, recreational and visitor opportunities. these areas are selected by governments or private organizations to protect natural biodiversity along with its underlying ecological structure and supporting environmental processes, and to promote education and recreation. the international union for conservation of nature ( iucn ), and its world commission on protected areas ( wcpa ), has defined " national park " as its category ii type of protected areas. wildlife sanctuaries are areas of either shelter for animals who are unable to live in the wild on their own, or they are temporary rehabilitation centers for wildlife to improve in their overall health and wellbeing. both of these serve as places in which biodiversity can be preserved rather than harmed. according to an article published in the national park service website, national parks aim their resources at maintaining animal and habitat integrity through conservation and preservation of their ecosystems. this along with educating the general public on wildlife functions, the aim for an increase in biodiversity is one of many goals trying to be focused on through national parks. = = = forest protected areas = = = forest protected areas are a subset of all protected areas in which a significant portion of the area is forest. this may be the whole or only a part of the protected area. globally, 18 percent of the world's forest area, or more than 700 million hectares, fall within legally established protected areas such as national parks, conservation areas and game reserves. there is an estimated 726 million ha of forest in protected areas worldwide. of the six major world regions, south america has the highest share of forests in protected areas, 31 percent. the forests play
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as national parks, conservation areas and game reserves. there is an estimated 726 million ha of forest in protected areas worldwide. of the six major world regions, south america has the highest share of forests in protected areas, 31 percent. the forests play a vital role in harboring more than 45, 000 floral and 81, 000 faunal species of which 5150 floral and 1837 faunal species are endemic. in addition, there are 60, 065 different tree species in the world. plant and animal species confined to a specific geographical area are called endemic species. in forest reserves, rights to activities like hunting and grazing are sometimes given to communities living on the fringes of the forest, who sustain their livelihood partially or wholly from forest resources or products. approximately 50 million hectares ( or 24 % ) of european forest land is protected for biodiversity and landscape protection. forests allocated for soil, water, and other ecosystem services encompass around 72 million hectares ( 32 % of european forest area ). = = role of society = = = = = transformative change = = = in 2019, a summary for policymakers of the largest, most comprehensive study to date of biodiversity and ecosystem services, the global assessment report on biodiversity and ecosystem services, was published by the intergovernmental science - policy platform on biodiversity and ecosystem services ( ipbes ). it stated that " the state of nature has deteriorated at an unprecedented and accelerating rate ". to fix the problem, humanity will need a transformative change, including sustainable agriculture, reductions in consumption and waste, fishing quotas and collaborative water management. the concept of nature - positive is playing a role in mainstreaming the goals of the global biodiversity framework ( gbf ) for biodiversity. the aim of mainstreaming is to embed biodiversity considerations into public and private practice to conserve and sustainably use biodiversity on global and local levels. the concept of nature - positive refers to the societal goal to halt and reverse biodiversity loss, measured from a baseline of 2020 levels, and to achieve full so - called " nature recovery " by 2050. = = = citizen science = = = citizen science, also known as public participation in scientific research, has been widely used in environmental sciences and is particularly popular in a biodiversity - related context. it has been used to enable scientists to involve the general public in biodiversity research, thereby enabling the scientists to collect data that they would otherwise not have been able to obtain. volunteer observers have made significant contributions to on - the - ground knowledge about biodiversity, and recent improvements in technology have helped increase the flow
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general public in biodiversity research, thereby enabling the scientists to collect data that they would otherwise not have been able to obtain. volunteer observers have made significant contributions to on - the - ground knowledge about biodiversity, and recent improvements in technology have helped increase the flow and quality of occurrences from citizen sources. a 2016 study published in biological conservation registers the massive contributions that citizen scientists already make to data mediated by the global biodiversity information facility ( gbif ). despite some limitations of the dataset - level analysis, it is clear that nearly half of all occurrence records shared through the gbif network come from datasets with significant volunteer contributions. recording and sharing observations are enabled by several global - scale platforms, including inaturalist and ebird. = = legal status = = = = = international = = = united nations convention on biological diversity ( 1992 ) and cartagena protocol on biosafety ; un bbnj ( high seas treaty ) 2023 intergovernmental conference on an international legally binding instrument under the unclos on the conservation and sustainable use of marine biological diversity of areas beyond national jurisdiction ( ga resolution 72 / 249 ) convention on international trade in endangered species ( cites ) ; ramsar convention ( wetlands ) ; bonn convention on migratory species ; unesco convention concerning the protection of the world's cultural and natural heritage ( indirectly by protecting biodiversity habitats ) unesco global geoparks regional conventions such as the apia convention bilateral agreements such as the japan - australia migratory bird agreement. global agreements such as the convention on biological diversity, give " sovereign national rights over biological resources " ( not property ). the agreements commit countries to " conserve biodiversity ", " develop resources for sustainability " and " share the benefits " resulting from their use. biodiverse countries that allow bioprospecting or collection of natural products, expect a share of the benefits rather than allowing the individual or institution that discovers / exploits the resource to capture them privately. bioprospecting can become a type of biopiracy when such principles are not respected. sovereignty principles can rely upon what is better known as access and benefit sharing agreements ( abas ). the convention on biodiversity implies informed consent between the source country and the collector, to establish which resource will be used and for what and to settle on a fair agreement on benefit sharing. on the 19 of december 2022, during the 2022 united nations biodiversity conference every country on earth, with the exception of the united states and the holy see, signed onto the agreement which includes protecting 30 % of land and
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agreement on benefit sharing. on the 19 of december 2022, during the 2022 united nations biodiversity conference every country on earth, with the exception of the united states and the holy see, signed onto the agreement which includes protecting 30 % of land and oceans by 2030 ( 30 by 30 ) and 22 other targets intended to reduce biodiversity loss. the agreement includes also recovering 30 % of earth degraded ecosystems and increasing funding for biodiversity issues. = = = = european union = = = = in may 2020, the european union published its biodiversity strategy for 2030. the biodiversity strategy is an essential part of the climate change mitigation strategy of the european union. from the 25 % of the european budget that will go to fight climate change, large part will go to restore biodiversity and nature based solutions. the eu biodiversity strategy for 2030 include the next targets : protect 30 % of the sea territory and 30 % of the land territory especially old - growth forests. plant 3 billion trees by 2030. restore at least 25, 000 kilometers of rivers, so they will become free flowing. reduce the use of pesticides by 50 % by 2030. increase organic farming. in linked eu program from farm to fork it is said, that the target is making 25 % of eu agriculture organic, by 2030. increase biodiversity in agriculture. give β¬20 billion per year to the issue and make it part of the business practice. approximately half of the global gdp depend on nature. in europe many parts of the economy that generate trillions of euros per year depend on nature. the benefits of natura 2000 alone in europe are β¬200 β β¬300 billion per year. = = = national level laws = = = biodiversity is taken into account in some political and judicial decisions : the relationship between law and ecosystems is very ancient and has consequences for biodiversity. it is related to private and public property rights. it can define protection for threatened ecosystems, but also some rights and duties ( for example, fishing and hunting rights ). law regarding species is more recent. it defines species that must be protected because they may be threatened by extinction. the u. s. endangered species act is an example of an attempt to address the " law and species " issue. laws regarding gene pools are only about a century old. domestication and plant breeding methods are not new, but advances in genetic engineering have led to tighter laws covering distribution of genetically modified organisms, gene patents and process patents. governments struggle to decide whether to focus on for example, genes, genomes, or organisms
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##ation and plant breeding methods are not new, but advances in genetic engineering have led to tighter laws covering distribution of genetically modified organisms, gene patents and process patents. governments struggle to decide whether to focus on for example, genes, genomes, or organisms and species. uniform approval for use of biodiversity as a legal standard has not been achieved, however. bosselman argues that biodiversity should not be used as a legal standard, claiming that the remaining areas of scientific uncertainty cause unacceptable administrative waste and increase litigation without promoting preservation goals. india passed the biological diversity act in 2002 for the conservation of biological diversity in india. the act also provides mechanisms for equitable sharing of benefits from the use of traditional biological resources and knowledge. = = history of the term = = 1916 β the term biological diversity was used first by j. arthur harris in " the variable desert ", scientific american : " the bare statement that the region contains a flora rich in genera and species and of diverse geographic origin or affinity is entirely inadequate as a description of its real biological diversity. " 1967 β raymond f. dasmann used the term biological diversity in reference to the richness of living nature that conservationists should protect in his book a different kind of country. 1974 β the term natural diversity was introduced by john terborgh. 1980 β thomas lovejoy introduced the term biological diversity to the scientific community in a book. it rapidly became commonly used. 1985 β according to edward o. wilson, the contracted form biodiversity was coined by w. g. rosen : " the national forum on biodiversity... was conceived by walter g. rosen... dr. rosen represented the nrc / nas throughout the planning stages of the project. furthermore, he introduced the term biodiversity ". 1985 β the term " biodiversity " appears in the article, " a new plan to conserve the earth's biota " by laura tangley. 1988 β the term biodiversity first appeared in publication. 1988 to present β the united nations environment programme ( unep ) ad hoc working group of experts on biological diversity in began working in november 1988, leading to the publication of the draft convention on biological diversity in may 1992. since this time, there have been 16 conferences of the parties ( cops ) to discuss potential global political responses to biodiversity loss. most recently cop 16 in cali, colombia in 2024. = = see also = = = = references = = = = external links = = assessment report on diverse values and valuation of nature by the intergovernmental science - policy platform on biodiversity and ecosystem services
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in cali, colombia in 2024. = = see also = = = = references = = = = external links = = assessment report on diverse values and valuation of nature by the intergovernmental science - policy platform on biodiversity and ecosystem services ( ipbes ), 2022. natureserve : this site serves as a portal for accessing several types of publicly available biodiversity data biodiversity synthesis report ( pdf ) by the millennium ecosystem assessment ( ma, 2005 ) world map of biodiversity an interactive map from the united nations environment programme world conservation monitoring centre biodiversity heritage library β open access digital library of historical taxonomic literature biodiversity pmc β open access digital library of biodiversity and ecological literature mapping of biodiversity encyclopedia of life β documenting all species of life on earth.
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epidemiological studies of the health effects of low levels of ionizing radiation, in particular the incidence and mortality from various forms of cancer, have been carried out in different population groups exposed to such radiation. these have included survivors of the atomic bombings of hiroshima and nagasaki in 1945, workers at nuclear reactors, and medical patients treated with x - rays. = = life span studies of atomic bomb survivors = = survivors of the atomic bomb explosions at hiroshima and nagasaki, japan have been the subjects of a life span study ( lss ), which has provided valuable epidemiological data. the lss population went through several changes : 1945 β there were some 93, 000 individuals, either living in hiroshima or nagasaki, japan. 1950 β an additional 37, 000 were registered by this time, for a total of 130, 000 lss members. however, some 44, 000 individuals were censured or excluded from the lss project, so there remained about 86, 000 people who were followed through the study. there is a gap in knowledge of the earliest cancer that developed in the first few years after the war, which impacts the assessment of leukemia to an important extent and for solid cancers to a minor extent. table 1 shows summary statistics of the number of persons and deaths for different dose groups. these comparisons show that the doses that were received by the lss population overlap strongly with the doses that are of concern to nasa exploration mission ( i. e., 50 to 2, 000 millisieverts ( msv ) ). figure 1 shows the dose response for the excess relative risk ( err ) for all solid cancers from preston et al. tables 2 and 3 show several summary parameters for tissue - specific cancer mortality risks for females and males, respectively, including estimates of err, excess absolute risk ( ear ), and percentage attributable risks. cancer incidence risks from low - let radiation are about 60 % higher than cancer mortality risks. = = other human studies = = the beir vii report contains an extensive review of data sets from human populations, including nuclear reactor workers and patients who were treated with radiation. the recent report from cardis et al. describes a meta - analysis for reactor workers from several countries. a meta - analysis at specific cancer sites, including breast, lung, and leukemia, has also been performed. these studies require adjustments for photon energy, dose - rate, and country of origin as well as adjustments made in single population studies. table 4 shows the results that are derived from preston et al.
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, lung, and leukemia, has also been performed. these studies require adjustments for photon energy, dose - rate, and country of origin as well as adjustments made in single population studies. table 4 shows the results that are derived from preston et al. for a meta - analysis of breast cancer risks in eight populations, including the atomic - bomb survivors. the median err varies by slightly more than a factor of two, but confidence levels significantly overlap. adjustments for photon energy or dose - rate and fractionation have not been made. these types of analysis lend confidence to risk assessments as well as showing the limitations of such data sets. of special interest to nasa is the dependence on age at exposure of low - let cancer risk projections. the beir vii report prefers models that show less than a 25 % reduction in risk over the range from 35 to 55 years, while ncrp report no. 132 shows about a two - fold reduction over this range. = = see also = = radiobiology = = references = = this article incorporates public domain material from human health and performance risks of space exploration missions ( pdf ). national aeronautics and space administration. ( nasa sp - 2009 - 3405, pp. 132 - 134 ).
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in lower power systems, hierarchical value cache refers to the hierarchical arrangement of value caches ( vcs ) in such a fashion that lower level vcs observe higher hit - rates, but undergo more switching activity on vc hits. the organization is similar to memory hierarchy, where lower - level caches enjoy higher hit rates, but longer hit latencies. the architecture for hierarchical value cache is mainly organized along two approaches : hierarchical unified value cache ( huvc ) and hierarchical combinational value cache ( hcvc ). = = hierarchical unified value cache = = this architecture of value cache employs all value caches storing full data values, with larger value caches in the lower levels of the hierarchy. this architecture suffers from high area overhead, but reduces the bus switching activity. the cache in huvc in managed by lru policy, with each vc storing 32 - bit values. for incoming data, it is simultaneously checked with the vc on each level, with the uppermost vc hit getting encoded. each hit at the ith level of the huvc incurs i bits switching activity. by switching any bit of 32 - bit data bus, we can get ( 32! ) / ( ( 32 - i )! i! ) numbers. that is, we could have ( 32! ) / ( ( 32 - i )! i! ) entries. however, it would require complicated logic to map vc indexes to bus values. for easy vc index encoding, we partition the data bus into i segments and switch one bit in each segment. thus, the huvc scheme requires n control signals, where n is the depth of the vc hierarchy. the i - th control signal switched to indicate that the vc of level i hits. for 4 - level huvc, and 32 - bit data bus, the total vc size is 22. 4kb. the size of the vc is too large to be feasible in practice. = = hierarchical combinational value cache = = in hcvc, level i contains 2 ^ ( i - 1 ) vcs that store only partial values, instead of full values as in huvc. except the case of first level, all vcs in hcvc store partial data values only. 2 ^ ( i - 1 ) segments are generated by partitioning the data values, and each vc stores one data segment. similar to the huvc, the incoming data is simultaneously checked with the vc on each level, with the uppermost vc hit getting encoded. the hcvc scheme requires n control signals, where i is the number
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and each vc stores one data segment. similar to the huvc, the incoming data is simultaneously checked with the vc on each level, with the uppermost vc hit getting encoded. the hcvc scheme requires n control signals, where i is the number of vcs. the i - th control signal is switched to indicate the formula vc hit. the total vc size of the i - th level is 32 / ( 2 ^ ( i - 1 ) ) words. for 4 - level hcvc with 32 - bit data bus, the total vc size is only 240 bytes. = = references = =
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in medicine, a port or chemoport is a small appliance that is installed beneath the skin. a catheter ( plastic tube ) connects the port to a vein. under the skin, the port has a septum ( a silicone membrane ) through which drugs can be injected and blood samples can be drawn many times, usually with less discomfort for the patient ( and clinician ) than a more typical " needle stick ". = = terminology = = a port is more correctly known as a " totally implantable venous access device ". they are also commonly referred to as a portacath or chemo port. brand names include eco port, clip - a - port, smartport, microport, bardport, powerport, passport, port - a - cath, infuse - a - port, medi - port, and bioflo. = = structure = = ports are used mostly to treat hematology and oncology patients. ports were previously adapted for use in hemodialysis patients, but were found to be associated with increased rate of infections and are no longer available in the us. the port is usually inserted in the upper chest ( known as a " chest port " ), just below the clavicle or collar bone, with the catheter inserted into the jugular vein. a port consists of a reservoir compartment ( the portal ) that has a silicone bubble for needle insertion ( the septum ), with an attached plastic tube ( the catheter ). the device is surgically inserted under the skin in the upper chest or in the arm and appears as a bump under the skin. it requires no special maintenance other than occasional flushing to keep clear. it is completely internal so swimming and bathing are not a problem. the catheter runs from the portal and is surgically inserted into a vein ( usually the jugular vein or less optimally the subclavian vein ). ideally, the catheter terminates in the superior vena cava or the right atrium. this position allows infused agents to be spread throughout the body quickly and efficiently. the septum is made of a special self - sealing silicone ; it can be punctured hundreds of times before it weakens significantly. to administer treatment or to withdraw blood, a health care professional will first locate the port and disinfect the area, then access the port by puncturing the overlying skin with a huber point ( non - coring ) needle. due to its design,
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or to withdraw blood, a health care professional will first locate the port and disinfect the area, then access the port by puncturing the overlying skin with a huber point ( non - coring ) needle. due to its design, there is a very low infection risk, as the breach of skin integrity is never larger than the caliber of the needle. this gives it an advantage over indwelling lines such as the hickman line. negative pressure is created to withdraw blood into the vacuumized needle, to check for blood return and see if the port is functioning normally. next, the port is flushed with a saline solution. then, treatment will begin. = = uses = = ports have many uses : to deliver chemotherapy to cancer patients who must undergo treatment frequently. chemotherapy is often toxic, and can damage skin and muscle tissue, and therefore should not be delivered through these tissues. ports provide a solution, delivering drugs quickly and efficiently through the entire body via the circulatory system. to deliver coagulation factors in patients with severe hemophilia. to withdraw ( and / or return ) blood to the body in patients who require frequent blood tests, and in hemodialysis patients. to deliver antibiotics to patients requiring them for a long time or frequently, such as those with cystic fibrosis and bronchiectasis. delivering medications to patients with immune disorders. for treating alpha 1 - antitrypsin deficiency with replacement therapy for delivering radiopaque contrast agents, which enhance contrast in ct imaging. to fill or withdraw fluid from the lap - band or realize gastric bands used in bariatric surgeries. to administer analgesics to patients with chronic pain, such as cancer patients and those with sickle - cell disease = = contraindications = = installation of a port is absolutely contraindicated when a patient has bacteremia or sepsis. in those with contrast allergy, or allergy to food or medications, the procedure can still be carried out with prednisolone coverage. other relative contraindications include coagulopathy ( abnormal coagulation ) or platelet count less than 50x109 / l. however, if the port is needed urgently, platelet transfusion may be given while the procedure is ongoing on table. = = insertion = = a port is most commonly inserted as an outpatient surgery procedure in a hospital or clinic by an interventional radiologist or surgeon, under moderate sedation. implantation is increasingly performed by intervention
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the procedure is ongoing on table. = = insertion = = a port is most commonly inserted as an outpatient surgery procedure in a hospital or clinic by an interventional radiologist or surgeon, under moderate sedation. implantation is increasingly performed by interventional radiologists due to advancements in techniques and their facile use of imaging technologies. when no longer needed, the port can be removed in the interventional radiology suite or an operating room. fluoroscopy is useful in guiding the insertion of ports. = = = interventional radiology = = = right internal jugular vein ( ijv ) is frequently chosen as the site of access. a 19g puncture needle is used to obtain access to the vein under ultrasound guidance. the needle should be pointed away from the common carotid artery ( cca ) as the cca just lie medially to the ijv. if there is difficult puncture, micropuncture set can be used to puncuture the vein and later switch to a bigger access system. if bilateral ijvs are thrombosed, then right external jugular vein is chosen as the puncture site. the puncture site should not be the same side as the pathological site such as breast cancer site or an area that is chosen as the potential site for radiation therapy. after the entry site is punctured with ultrasound, a guidewire is inserted with the tip of the guidewire reaching the inferior vena cava. the proximal end of the guidewire is secured to prevent dislodgement. then a chemoport pocket is created on the deltopectoral region at 2. 5 cm below the level of clavicle by using a scalpel. bupivacaine with adrenaline ( 0. 25 % ) is used as local anesthetic to reduce the formation of haematoma and prolong the anesthetic effect. after the pocket is created, a trocar is used insert a silicone catheter from the pocket towards the internal jugular vein puncture site. a peel - away sheath is then inserted to facilitate the insertion of the silicone catheter into the cavoatrial junction. silicone catether insertion should be done during breath hold at inspiration. the peel - away sheath should be pinched to prevent air embolism. the proximal end of the catheter is connected to the port within the skin pocket later after irrigation of the pocket with normal saline. the port is
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at inspiration. the peel - away sheath should be pinched to prevent air embolism. the proximal end of the catheter is connected to the port within the skin pocket later after irrigation of the pocket with normal saline. the port is then sutured on two sites to the underlying muscles. the tip of the catheter is checked for kinks and position using a fluoroscope. besides that, aspiration of blood and contrast injection through the chemoport can also be used to confirm the position. the port is the closed in two layers ( subcutaneous tissue is sutured first, followed by the skin ). sterile dressing is then placed on the port. the optimum site to park the tip of the catheter is at the cavo - atrial junction or with margin of error of not more than 4 cm above the junction. = = = surgery = = = the insertion site of the ijv is fixed between the two heads ( sternal and clavicular heads ) of the sternocleidomastoid. 2 % lignocaine is to infiltrate the puncture site. using a 24g needle attached to 5 cc syringe, the needle is advanced through the puncture site with its tip pointing towards the nipple of the same side. once the backflow of venous blood is seen in the syringe, the puncture of the ijv is considered successful. then a port needle is advanced through the pre - existing 24g needle and backflow of blood is confirmed by aspirating another syringe attached to the port needle. then a guidewire is inserted through the port needle. the guidewire should not extend past the sa node of the right atrium as it can stimulate the heart arrhythmia. the port needle is then removed and the guidewire is fixed in place. the puncture is then widened by using 11 - number knife and mosquito haemostat. the port access site is fixed at 5 cm below the midline of the clavicle and 9 to 10 cm lateral to the midline of the chest. then, a 5 to 6 cm incision is made to create a subcutaneous tissue pouch for the placement of port access site. a tunnel is made from the port access site until adjacent to the internal jugular neck wound. a port catheter is passed through the tunnel where one end is attached to the chemport and another end is left hanging out near the ijv insertion site. the
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the port access site until adjacent to the internal jugular neck wound. a port catheter is passed through the tunnel where one end is attached to the chemport and another end is left hanging out near the ijv insertion site. the length of the hanging port catheter should be about 16 to 17 cm ( or can be measured from the ijv insertion site until 2 cm below the sternal angle where the right atrium should begin ). this portion of the port catheter should later be inserted through the ijv insertion site until it reaches the aortocaval junction. the ijv insertion is dilated using a plastic dilator. peel - off sheath was then inserted over the guidewire. blood is aspirated from the catheter to confirm the position. then, the free - end of the port catheter is inserted through the peel - off sheath. after the tip of the port catheter is confirmed at the aortocaval junction, the peel - off sheath is taken - off by peeling away with two hands. while peeling off, the port catheter should remain in - situ. stitches are only removed after 14 days post operation. a follow - up on a chest radiograph can immediately detect complications associated with the procedure such as pneumothorax, hemothorax and malpositions of the catheter. however, routine chest radiography is not needed due to the low complication rates associated with the procedure. the chest radiograph is only done if there is clinical suspicion of a complication. the side of the patients'chest the port is implanted in will usually be chosen to avoid damage to the port and the veins by the seat belt in case of accident when seated as the driver. thus, there is a potential conflict by left - and right - hand traffic as the rule of the road. ports can be put in the upper chest or arm. the exact positioning itself is variable as it can be inserted to avoid visibility when wearing low cut shirts, and to avoid excess contact due to a backpack or bra strap. the most common placement is on the upper right portion of the chest, with the catheter itself looping through the right jugular vein, and down towards the patient's heart. = = models = = there are many different models of ports. the particular model selected is based on the patient's specific medical conditions. portals : can be made of plastic, stainless steel, or titanium can be single chamber or
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' s heart. = = models = = there are many different models of ports. the particular model selected is based on the patient's specific medical conditions. portals : can be made of plastic, stainless steel, or titanium can be single chamber or dual chamber vary in height, width and shape. catheters : can be made of biocompatible, medical - grade polyurethane or silicone can vary in length and diameter for applications such as ct scan, high pressure infusion allowing ports are needed. = = = manufacturers = = = the major manufacturers of ports are angiodynamics, b. braun medical, bard access systems, cook medical, medcomp, navilyst medical, norfolk medical products, and smiths medical. = = risks and complications = = the most common complications are : catheter blockage ( 7. 4 % ), and catheter - related infection ( 5. 6 % ). other complications are : malpositioning of the catheter, venous thrombosis, catheter leak or dislodgement. the common carotid artery may be injured during the puncture of the internal jugular vein as the artery lies close to the vein. this mostly due to the needle overshooting into the artery rather than the inability to recognise vein and artery under ultrasound guidance. the risk of puncture increases when the artery lies superficial to the vein and for those with short neck and obese people. however, these cases can be easily controlled using compression and it does not leave a hematoma at the site of puncture. the overall risk of arterial puncture is 0. 5 %. the subclavian artery can be inadvertently punctured while attempting a subclavian vein access, leading to a subcutaneous hematoma and occasionally a pseudoaneurysm. an alternative site may need to be used for port placement. puncture of the carotid artery is significantly more rare, since attempts to access the nearby jugular vein are increasingly done with ultrasound guidance. the incidence of catheter fracture is 2. 3 %. the fracture can be due to " pinch - off syndrome " when the vein and the catheter is compressed when passes between the clavicle and first rib before turning 90 degrees into the superior vena cava. fractured catheter component can dislodge most commonly into pulmonary arteries ( 35 % ), right atrium ( 27 % ), right ventricle ( 22 % ), and
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rib before turning 90 degrees into the superior vena cava. fractured catheter component can dislodge most commonly into pulmonary arteries ( 35 % ), right atrium ( 27 % ), right ventricle ( 22 % ), and superior vena cava and peripheral veins ( 15. 4 % ). malpositioning of the catheter happens in 0. 1 to 5. 6 % of the time. this can be due to malposition within or outside the superior vena cava. causes includes : unexpected branches of the veins, vessel angulations, vein stenosis or venous tortousity. thrombosis or the formation of a blood clot in the catheter may block the device irrevocably. it happens in 0. 3 to 28. 3 % of the cases. administering cancer drugs through the port, frequent injury to the vessel during usage, or simply prolonged usage of the port can contribute to clot formation within the catheter. to prevent risk of thrombosis, right internal jugular vein is usually selected, as it has the lowest risk of thrombus formation than subclavian vein. once thrombosis happens, either anticoagulant therapy is given or the port is totally removed. attempts to gain access to the subclavian vein can injure the lung coverings, potentially causing a pneumothorax. the risk of pneumothorax is 1. 5 to 6 % depending upon the surgeon's experience. age : if the device is put into a child, the child's growth means that the catheter becomes relatively shorter and will move towards the head. it may become necessary to remove or replace it. vascular occlusion : formation of a blood clot between the catheter and the vascular wall leading to partial or complete occlusion of the vein. the occlusion is cleared by removal of the port if possible. if not, then heparin therapy may clear the occlusion. intravenous drug use : if an intravenous drug user is discharged to be treated with a port in place to be treated on an outpatient basis, they may be likely to use the port improperly to inject illicit drugs. this use poses a serious risk of injury or severe infection, including of the heart lining. = = maintenance = = to reduce damage or coring of the septum ( cutting out small pieces of membrane with the needle, plugging it
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illicit drugs. this use poses a serious risk of injury or severe infection, including of the heart lining. = = maintenance = = to reduce damage or coring of the septum ( cutting out small pieces of membrane with the needle, plugging it up ), low or non coring needles are to be used. after every cycle of chemotherapy, the port should be flushed with 1 : 10 diluted heparin ( 5000 iu / ml ) to prevent clot formation within the port. if the port is not used for a long time, it should be flushed with diluted heparin every two months. = = alternatives = = sometimes, the physical condition of the patient, especially the structure of their veins, does not allow for the insertion of a port. an alternative is the picc line, despite drawbacks such as external entry point and limited lifespan of the device. = = in popular culture = = in the 1984 cyberpunk novel neuromancer, a minor character, peter riviera, has a kind of medical port placed in his arm to facilitate his recreational drug use. = = history = = niederhuber et al. first reported the use of totally implantable central venous port system ( ticvps ) in 1982. = = see also = = hickman line peripherally inserted central catheter or " picc " groshong line central venous catheter = = notes = = = = references = = = = further reading = = mallon wk ( march 2001 ). " is it acceptable to discharge a heroin user with an intravenous line to complete his antibiotic therapy for cellulitis at home under a nurse's supervision? no : a home central line is too hazardous ". point - counterpoint ( column ). the western journal of medicine. 174 ( 3 ) : 157. doi : 10. 1136 / ewjm. 174. 3. 157. pmc 1071292. pmid 11238332. = = external links = = www. breastcancer. org : ports for chemo a photo - essay on what it's like to have a port an overview of chemo ports / portacaths
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lower risk was a classification formerly used by the iucn red list, superseded by the least concern classification. species are classified into one of nine red list categories : extinct, extinct in the wild, critically endangered, endangered, vulnerable, near threatened, least concern, data deficient, and not evaluated. the iucn defined an animal with the conservation status of lower risk is one with populations levels high enough to ensure its survival. animals with this status did not qualify as being threatened or extinct. however, natural disasters or certain human activities would cause them to change to either of these classifications. when it was in use, this classification was sub - divided into three types : conservation dependent - where cessation of current conservation measures may result in it being classified at a higher risk level. near threatened - may become vulnerable to endangerment in the near future but not meeting the criteria. least concern - where neither of the two above apply. = = see also = = biodiversity action plan endangered species = = references = =
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conditional random fields ( crfs ) are a class of statistical modeling methods often applied in pattern recognition and machine learning and used for structured prediction. whereas a classifier predicts a label for a single sample without considering " neighbouring " samples, a crf can take context into account. to do so, the predictions are modelled as a graphical model, which represents the presence of dependencies between the predictions. the kind of graph used depends on the application. for example, in natural language processing, " linear chain " crfs are popular, for which each prediction is dependent only on its immediate neighbours. in image processing, the graph typically connects locations to nearby and / or similar locations to enforce that they receive similar predictions. other examples where crfs are used are : labeling or parsing of sequential data for natural language processing or biological sequences, part - of - speech tagging, shallow parsing, named entity recognition, gene finding, peptide critical functional region finding, and object recognition and image segmentation in computer vision. = = description = = crfs are a type of discriminative undirected probabilistic graphical model. lafferty, mccallum and pereira define a crf on observations x { \ displaystyle { \ boldsymbol { x } } } and random variables y { \ displaystyle { \ boldsymbol { y } } } as follows : let g = ( v, e ) { \ displaystyle g = ( v, e ) } be a graph such that y = ( y v ) v β v { \ displaystyle { \ boldsymbol { y } } = ( { \ boldsymbol { y } } _ { v } ) _ { v \ in v } }, so that y { \ displaystyle { \ boldsymbol { y } } } is indexed by the vertices of g { \ displaystyle g }. then ( x, y ) { \ displaystyle ( { \ boldsymbol { x } }, { \ boldsymbol { y } } ) } is a conditional random field when each random variable y v { \ displaystyle { \ boldsymbol { y } } _ { v } }, conditioned on x { \ displaystyle { \ boldsymbol { x } } }, obeys the markov property with respect to the graph ; that is, its probability is dependent only on its neighbours in g : p ( y v | x, { y w : w = v }
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##symbol { x } } }, obeys the markov property with respect to the graph ; that is, its probability is dependent only on its neighbours in g : p ( y v | x, { y w : w = v } ) = p ( y v | x, { y w : w v } ) { \ displaystyle p ( { \ boldsymbol { y } } _ { v } | { \ boldsymbol { x } }, \ { { \ boldsymbol { y } } _ { w } : w \ neq v \ } ) = p ( { \ boldsymbol { y } } _ { v } | { \ boldsymbol { x } }, \ { { \ boldsymbol { y } } _ { w } : w \ sim v \ } ) }, where w v { \ displaystyle { \ mathit { w } } \ sim v } means that w { \ displaystyle w } and v { \ displaystyle v } are neighbors in g { \ displaystyle g }. what this means is that a crf is an undirected graphical model whose nodes can be divided into exactly two disjoint sets x { \ displaystyle { \ boldsymbol { x } } } and y { \ displaystyle { \ boldsymbol { y } } }, the observed and output variables, respectively ; the conditional distribution p ( y | x ) { \ displaystyle p ( { \ boldsymbol { y } } | { \ boldsymbol { x } } ) } is then modeled. = = = inference = = = for general graphs, the problem of exact inference in crfs is intractable. the inference problem for a crf is basically the same as for an mrf and the same arguments hold. however, there exist special cases for which exact inference is feasible : if the graph is a chain or a tree, message passing algorithms yield exact solutions. the algorithms used in these cases are analogous to the forward - backward and viterbi algorithm for the case of hmms. if the crf only contains pair - wise potentials and the energy is submodular, combinatorial min cut / max flow algorithms yield exact solutions. if exact inference is impossible, several algorithms can be used to obtain approximate solutions. these include : loopy belief propagation alpha expansion mean field inference linear programming relaxations = = = parameter learning = =
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##ial min cut / max flow algorithms yield exact solutions. if exact inference is impossible, several algorithms can be used to obtain approximate solutions. these include : loopy belief propagation alpha expansion mean field inference linear programming relaxations = = = parameter learning = = = learning the parameters ΞΈ { \ displaystyle \ theta } is usually done by maximum likelihood learning for p ( y i | x i ; ΞΈ ) { \ displaystyle p ( y _ { i } | x _ { i } ; \ theta ) }. if all nodes have exponential family distributions and all nodes are observed during training, this optimization is convex. it can be solved for example using gradient descent algorithms, or quasi - newton methods such as the l - bfgs algorithm. on the other hand, if some variables are unobserved, the inference problem has to be solved for these variables. exact inference is intractable in general graphs, so approximations have to be used. = = = examples = = = in sequence modeling, the graph of interest is usually a chain graph. an input sequence of observed variables x { \ displaystyle x } represents a sequence of observations and y { \ displaystyle y } represents a hidden ( or unknown ) state variable that needs to be inferred given the observations. the y i { \ displaystyle y _ { i } } are structured to form a chain, with an edge between each y i β 1 { \ displaystyle y _ { i - 1 } } and y i { \ displaystyle y _ { i } }. as well as having a simple interpretation of the y i { \ displaystyle y _ { i } } as " labels " for each element in the input sequence, this layout admits efficient algorithms for : model training, learning the conditional distributions between the y i { \ displaystyle y _ { i } } and feature functions from some corpus of training data. decoding, determining the probability of a given label sequence y { \ displaystyle y } given x { \ displaystyle x }. inference, determining the most likely label sequence y { \ displaystyle y } given x { \ displaystyle x }. the conditional dependency of each y i { \ displaystyle y _ { i } } on x { \ displaystyle x } is defined through a fixed set of feature functions of the form f ( i, y i β 1, y i, x ) { \ displaystyle f ( i, y _ { i - 1 }, y _ { i }, x ) }, which can
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fixed set of feature functions of the form f ( i, y i β 1, y i, x ) { \ displaystyle f ( i, y _ { i - 1 }, y _ { i }, x ) }, which can be thought of as measurements on the input sequence that partially determine the likelihood of each possible value for y i { \ displaystyle y _ { i } }. the model assigns each feature a numerical weight and combines them to determine the probability of a certain value for y i { \ displaystyle y _ { i } }. linear - chain crfs have many of the same applications as conceptually simpler hidden markov models ( hmms ), but relax certain assumptions about the input and output sequence distributions. an hmm can loosely be understood as a crf with very specific feature functions that use constant probabilities to model state transitions and emissions. conversely, a crf can loosely be understood as a generalization of an hmm that makes the constant transition probabilities into arbitrary functions that vary across the positions in the sequence of hidden states, depending on the input sequence. notably, in contrast to hmms, crfs can contain any number of feature functions, the feature functions can inspect the entire input sequence x { \ displaystyle x } at any point during inference, and the range of the feature functions need not have a probabilistic interpretation. = = variants = = = = = higher - order crfs and semi - markov crfs = = = crfs can be extended into higher order models by making each y i { \ displaystyle y _ { i } } dependent on a fixed number k { \ displaystyle k } of previous variables y i β k,..., y i β 1 { \ displaystyle y _ { i - k },..., y _ { i - 1 } }. in conventional formulations of higher order crfs, training and inference are only practical for small values of k { \ displaystyle k } ( such as k β€ 5 ), since their computational cost increases exponentially with k { \ displaystyle k }. however, another recent advance has managed to ameliorate these issues by leveraging concepts and tools from the field of bayesian nonparametrics. specifically, the crf - infinity approach constitutes a crf - type model that is capable of learning infinitely - long temporal dynamics in a scalable fashion. this is effected by introducing a novel potential function for crfs that is based on the
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. specifically, the crf - infinity approach constitutes a crf - type model that is capable of learning infinitely - long temporal dynamics in a scalable fashion. this is effected by introducing a novel potential function for crfs that is based on the sequence memoizer ( sm ), a nonparametric bayesian model for learning infinitely - long dynamics in sequential observations. to render such a model computationally tractable, crf - infinity employs a mean - field approximation of the postulated novel potential functions ( which are driven by an sm ). this allows for devising efficient approximate training and inference algorithms for the model, without undermining its capability to capture and model temporal dependencies of arbitrary length. there exists another generalization of crfs, the semi - markov conditional random field ( semi - crf ), which models variable - length segmentations of the label sequence y { \ displaystyle y }. this provides much of the power of higher - order crfs to model long - range dependencies of the y i { \ displaystyle y _ { i } }, at a reasonable computational cost. finally, large - margin models for structured prediction, such as the structured support vector machine can be seen as an alternative training procedure to crfs. = = = latent - dynamic conditional random field = = = latent - dynamic conditional random fields ( ldcrf ) or discriminative probabilistic latent variable models ( dplvm ) are a type of crfs for sequence tagging tasks. they are latent variable models that are trained discriminatively. in an ldcrf, like in any sequence tagging task, given a sequence of observations x = x 1, β¦, x n { \ displaystyle x _ { 1 }, \ dots, x _ { n } }, the main problem the model must solve is how to assign a sequence of labels y = y 1, β¦, y n { \ displaystyle y _ { 1 }, \ dots, y _ { n } } from one finite set of labels y. instead of directly modeling p ( y | x ) as an ordinary linear - chain crf would do, a set of latent variables h is " inserted " between x and y using the chain rule of probability : p ( y | x ) = h p ( y | h, x ) p ( h | x ) { \ displaystyle p ( \ mathbf { y } | \ mathbf { x } ) = \ sum
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rule of probability : p ( y | x ) = h p ( y | h, x ) p ( h | x ) { \ displaystyle p ( \ mathbf { y } | \ mathbf { x } ) = \ sum _ { \ mathbf { h } } p ( \ mathbf { y } | \ mathbf { h }, \ mathbf { x } ) p ( \ mathbf { h } | \ mathbf { x } ) } this allows capturing latent structure between the observations and labels. while ldcrfs can be trained using quasi - newton methods, a specialized version of the perceptron algorithm called the latent - variable perceptron has been developed for them as well, based on collins'structured perceptron algorithm. these models find applications in computer vision, specifically gesture recognition from video streams and shallow parsing. = = see also = = hammersley β clifford theorem maximum entropy markov model ( memm ) = = references = = = = further reading = = mccallum, a. : efficiently inducing features of conditional random fields. in : proc. 19th conference on uncertainty in artificial intelligence. ( 2003 ) wallach, h. m. : conditional random fields : an introduction. technical report ms - cis - 04 - 21, university of pennsylvania ( 2004 ) sutton, c., mccallum, a. : an introduction to conditional random fields for relational learning. in " introduction to statistical relational learning ". edited by lise getoor and ben taskar. mit press. ( 2006 ) online pdf klinger, r., tomanek, k. : classical probabilistic models and conditional random fields. algorithm engineering report tr07 - 2 - 013, department of computer science, dortmund university of technology, december 2007. issn 1864 - 4503. online pdf
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