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id stringlengths 40 40	title stringlengths 15 120	text stringlengths 41 3.14k	source stringclasses 2 values
5e26e0288392be731f93770b1dcd074d5ba22e85	pcfg design impacts the secondary structure prediction accuracy.	pcfg design impacts the secondary structure prediction accuracy. any useful structure prediction probabilistic model based on pcfg has to maintain simplicity without much compromise to prediction accuracy. too complex a model of excellent performance on a single sequence may not scale. a grammar based model should be a...	wikipedia
d59210f55c632d4eccd5c53f175913eb880496c5	different implementation of these approaches exist. for example,	different implementation of these approaches exist. for example, pfold is used in secondary structure prediction from a group of related rna sequences, covariance models are used in searching databases for homologous sequences and rna annotation and classification, rnapromo, cmfinder and teiser are used in finding stab...	wikipedia
a558700aba2d52d5e99b656c4340d5896e7b1d2e	every possible string x a grammar generates is	every possible string x a grammar generates is assigned a probability weight p (x \| θ) {\displaystyle p(x\|\theta)} given the pcfg model θ {\displaystyle \theta }. it follows that the sum of all probabilities to all possible grammar productions is ∑ x p (x \| θ) = 1 {\displaystyle \sum _{\text{x}}p(x\|\theta)=1}. the scor...	wikipedia
6f8b37896d7b7f28670d39a6a3529652c1f154cd	a pcfg model extendibility allows constraining structure prediction	a pcfg model extendibility allows constraining structure prediction by incorporating expectations about different features of an rna. such expectation may reflect for example the propensity for assuming a certain structure by an rna. however incorporation of too much information may increase pcfg space and memory compl...	wikipedia
36acac3595ca5692076ac89d29026c9c100aeb1a	the above grammar generates a string in an	the above grammar generates a string in an outside-in fashion, that is the basepair on the furthest extremes of the terminal is derived first. so a string such as a a b a a b a a {\displaystyle aabaabaa} is derived by first generating the distal a 's on both sides before moving inwards:	wikipedia
b7a5f1835b107dfd056c42606f840b122c1fde30	the types of various structure that can be	the types of various structure that can be modeled by a pcfg include long range interactions, pairwise structure and other nested structures. however, pseudoknots can not be modeled. pcfgs extend cfg by assigning probabilities to each production rule. a maximum probability parse tree from the grammar implies a maximum ...	wikipedia
5b8f837c9d210cd24bf8fab3e293af220ef6bf49	energy minimization and pcfg provide ways of predicting	energy minimization and pcfg provide ways of predicting rna secondary structure with comparable performance. however structure prediction by pcfgs is scored probabilistically rather than by minimum free energy calculation. pcfg model parameters are directly derived from frequencies of different features observed in dat...	wikipedia
36e89f692b1802d9af978904fa443db0f6c47875	a weighted context-free grammar (wcfg) is a more	a weighted context-free grammar (wcfg) is a more general category of context-free grammar, where each production has a numeric weight associated with it. the weight of a specific parse tree in a wcfg is the product (or sum) of all rule weights in the tree. each rule weight is included as often as the rule is used in th...	wikipedia
4455b51aa502fa9ad9c757eae66f9689ad2cfd52	assigning probability to production rules makes a pcfg.	assigning probability to production rules makes a pcfg. these probabilities are informed by observing distributions on a training set of similar composition to the language to be modeled. on most samples of broad language, probabilistic grammars where probabilities are estimated from data typically outperform hand-craf...	wikipedia
b152cc7b21095c658a249e21205f8ecc3b285b6e	probabilistic grammars circumvent these problems by ranking various	probabilistic grammars circumvent these problems by ranking various productions on frequency weights, resulting in a "most likely" (winner-take-all) interpretation. as usage patterns are altered in diachronic shifts, these probabilistic rules can be re-learned, thus updating the grammar.	wikipedia
e898f3fc2e26421f2519a7726e7b17f92879cb46	one strategy of dealing with ambiguous parses (originating	one strategy of dealing with ambiguous parses (originating with grammarians as early as pāṇini) is to add yet more rules, or prioritize them so that one rule takes precedence over others. this, however, has the drawback of proliferating the rules, often to the point where they become difficult to manage. another diffic...	wikipedia
4d794bf83727fe3f3d02634c323268bba214998a	terminals in a grammar are words and through	terminals in a grammar are words and through the grammar rules a non-terminal symbol is transformed into a string of either terminals and/or non-terminals. the above grammar is read as "beginning from a non-terminal s the emission can generate either a or b or ϵ {\displaystyle \epsilon } ".its derivation is:	wikipedia
66f1127df93f0afefb090859ad9f02fff177d05b	context-free grammars are represented as a set of	context-free grammars are represented as a set of rules inspired from attempts to model natural languages. the rules are absolute and have a typical syntax representation known as backus–naur form. the production rules consist of terminal { a, b } {\displaystyle \left\{a,b\right\}} and non-terminal s symbols and a blan...	wikipedia
7fe39a521a7e6e9ece242b613d5d2e782f8b188d	the inside-outside algorithm is an analogue of the	the inside-outside algorithm is an analogue of the forward-backward algorithm. it computes the total probability of all derivations that are consistent with a given sequence, based on some pcfg. this is equivalent to the probability of the pcfg generating the sequence, and is intuitively a measure of how consistent the...	wikipedia
9bbb0ae846d7aeeea2ae7df25494a3988be9889d	an example of a parser for pcfg grammars	an example of a parser for pcfg grammars is the pushdown automaton. the algorithm parses grammar nonterminals from left to right in a stack-like manner. this brute-force approach is not very efficient. in rna secondary structure prediction variants of the cocke–younger–kasami (cyk) algorithm provide more efficient alte...	wikipedia
725a5c3c4dfe6a9a98778e0514bcc10c3e5e1a30	pcfgs have application in areas as diverse as	pcfgs have application in areas as diverse as natural language processing to the study the structure of rna molecules and design of programming languages. designing efficient pcfgs has to weigh factors of scalability and generality. issues such as grammar ambiguity must be resolved. the grammar design affects results a...	wikipedia
87df2ba2c9ed030d43a27d6f58fca39f9036d7f9	pcfgs extend context-free grammars similar to how hidden	pcfgs extend context-free grammars similar to how hidden markov models extend regular grammars. each production is assigned a probability. the probability of a derivation (parse) is the product of the probabilities of the productions used in that derivation. these probabilities can be viewed as parameters of the model,...	wikipedia
af45881fc06388661cb8847022335087ac50f3cd	grammar theory to model symbol strings originated from	grammar theory to model symbol strings originated from work in computational linguistics aiming to understand the structure of natural languages. probabilistic context free grammars (pcfgs) have been applied in probabilistic modeling of rna structures almost 40 years after they were introduced in computational linguist...	wikipedia
c45f390e1595832328439012cc44c611f4c848d3	multiaxis machining is a manufacturing process that involves	multiaxis machining is a manufacturing process that involves tools that move in 4 or more directions and are used to manufacture parts out of metal or other materials by milling away excess material, by water jet cutting or by laser cutting. this type of machining was originally performed mechanically on large complex ...	wikipedia
794345b1c54ba7a92e8a0297889191ede6d24145	the cnc controller, this is how data is	the cnc controller, this is how data is transferred/stored within machine, and input data is processed and executed. multiaxis machines offer several improvements over other cnc tools, at the cost of increased complexity and price of the machine: the amount of human labor is reduced, if the piece would otherwise have t...	wikipedia
8a383da1e462dc97aa25f21d2a2c62dd3de01885	higher quality parts. what once required multiple setups	higher quality parts. what once required multiple setups now can be executed in only a few if not one, reducing steps and decreasing the opportunity for error. the number of axes for multiaxis machines varies from 4 to 9. each axis of movement is implemented either by moving the table, or by moving the tool. the actual...	wikipedia
e35cf4e2577d0f15bd372c11a0c955a6e0fa673d	cam software automates the process of converting 3d	cam software automates the process of converting 3d models into tool paths, the route the multiaxis machine takes to mill a part (fig. 1). this software takes into account the different parameters of the tool head (in the case of a cnc router, this would be the bit size), dimensions of the blank, and any constraints th...	wikipedia
aa8cb3f9bd92149e71fe55cbf15da9e1c7307329	the number of axes for multiaxis machines varies	the number of axes for multiaxis machines varies from 4 to 9. each axis of movement is implemented either by moving the table (into which the workpiece is attached), or by moving the tool. the actual configuration of axes varies, therefore machines with the same number of axes can differ in the movements that can be pe...	wikipedia
01a1555635957eb1364c4424585271f96493b7d3	there are now many cam (computer aided manufacturing)	there are now many cam (computer aided manufacturing) software systems available to support multiaxis machining including software that can automatically convert 3-axis toolpaths into 5-axis toolpaths. prior to the advancement of computer aided manufacturing, transferring information from design to production often req...	wikipedia
61706023eccd44a6b63d9431c9b07e390e513168	typical cnc tools support translation in 3 axis;	typical cnc tools support translation in 3 axis; multiaxis machines also support rotation around one or multiple axis. 5-axis machines are commonly used in industry in which the workpiece is translated linearly along three axes (typically x, y, and z) and the tooling spindle is capable of rotation about an addition 2 a...	wikipedia
8d250f76e1e4ef094807ef79f510bc5aa115002f	multiaxis machining is a manufacturing process that involves	multiaxis machining is a manufacturing process that involves tools that move in 4 or more directions and are used to manufacture parts out of metal or other materials by milling away excess material, by water jet cutting or by laser cutting. this type of machining was originally performed mechanically on large complex ...	wikipedia
2a243741c08fe19762b7e1a4cd45daa0ea4febe1	a scintillation counter is an instrument for detecting	a scintillation counter is an instrument for detecting and measuring ionizing radiation by using the excitation effect of incident radiation on a scintillating material, and detecting the resultant light pulses. it consists of a scintillator which generates photons in response to incident radiation, a sensitive photode...	wikipedia
0f9202c0effc5880764f846c2e9ed22bae1d3504	the spectrometer consists of a suitable scintillator crystal,	the spectrometer consists of a suitable scintillator crystal, a photomultiplier tube, and a circuit for measuring the height of the pulses produced by the photomultiplier. the pulses are counted and sorted by their height, producing a x-y plot of scintillator flash brightness vs number of the flashes, which approximate...	wikipedia
8e282c22b0a1ca0b23f0b613962934d06a0a3a4d	scintillators often convert a single photon of high	scintillators often convert a single photon of high energy radiation into high number of lower-energy photons, where the number of photons per megaelectronvolt of input energy is fairly constant. by measuring the intensity of the flash (the number of the photons produced by the x-ray or gamma photon) it is therefore po...	wikipedia
5104779e7f128768b02a3426fd20ab3a281575eb	a scintillator such as zinc sulphide is used	a scintillator such as zinc sulphide is used for alpha particle detection, whilst plastic scintillators are used for beta detection. the resultant scintillation energies can be discriminated so that alpha and beta counts can be measured separately with the same detector, this technique is used in both hand-held and fix...	wikipedia
1c4a59453a9ddd5c3b2a8ae138212675d2e53106	radioactive contamination monitors, for area or personal surveys	radioactive contamination monitors, for area or personal surveys require a large detection area to ensure efficient and rapid coverage of monitored surfaces. for this a thin scintillator with a large area window and an integrated photomultiplier tube is ideally suited. they find wide application in the field of radioac...	wikipedia
10776013df0cbdd4c651fba98f8d2e57315992a5	in the united kingdom, the health and safety	in the united kingdom, the health and safety executive, or hse, has issued a user guidance note on selecting the correct radiation measurement instrument for the application concerned. this covers all radiation instrument technologies, and is a useful comparative guide to the use of scintillation detectors.	wikipedia
7c4038e485cd64c86b1dfd77918c37e8ec98cf65	several products have been introduced in the market	several products have been introduced in the market utilising scintillation counters for detection of potentially dangerous gamma-emitting materials during transport. these include scintillation counters designed for freight terminals, border security, ports, weigh bridge applications, scrap metal yards and contaminati...	wikipedia
fb4af8ef328061dd3d61b4314ea2c1f332274b1e	the quantum efficiency of a gamma-ray detector (per	the quantum efficiency of a gamma-ray detector (per unit volume) depends upon the density of electrons in the detector, and certain scintillating materials, such as sodium iodide and bismuth germanate, achieve high electron densities as a result of the high atomic numbers of some of the elements of which they are compo...	wikipedia
9a88139964b137ec883e4ea7651cba872c1c3dcd	cesium iodide (csi) in crystalline form is used	cesium iodide (csi) in crystalline form is used as the scintillator for the detection of protons and alpha particles. sodium iodide (nai) containing a small amount of thallium is used as a scintillator for the detection of gamma waves and zinc sulfide (zns) is widely used as a detector of alpha particles. zinc sulfide ...	wikipedia
1d41b6ff6812df79908d4ad551b7bb0cef326b6a	the scintillator must be shielded from all ambient	the scintillator must be shielded from all ambient light so that external photons do not swamp the ionization events caused by incident radiation. to achieve this a thin opaque foil, such as aluminized mylar, is often used, though it must have a low enough mass to minimize undue attenuation of the incident radiation be...	wikipedia
456dc4b99381da9341dd2751f06b8bb728f82f7f	the resultant output signal at the anode is	the resultant output signal at the anode is a measurable pulse for each group of photons from an original ionizing event in the scintillator that arrived at the photocathode and carries information about the energy of the original incident radiation. when it is fed to a charge amplifier which integrates the energy info...	wikipedia
20f969fca7cedb5d9a4a39bf6a319f4b3297743f	the chemistry of atomic de-excitation in the scintillator	the chemistry of atomic de-excitation in the scintillator produces a multitude of low-energy photons, typically near the blue end of the visible spectrum. the quantity is proportional to the energy deposited by the ionizing particle. these can be directed to the photocathode of a photomultiplier tube which emits at mos...	wikipedia
3081712b52dda937f5a3f8af508d0f27a35d0594	when an ionizing particle passes into the scintillator	when an ionizing particle passes into the scintillator material, atoms are excited along a track. for charged particles the track is the path of the particle itself. for gamma rays (uncharged), their energy is converted to an energetic electron via either the photoelectric effect, compton scattering or pair production.	wikipedia
e0cc770d7127dc9ae252852488f67ef25d03bc11	this built upon the work of earlier researchers	this built upon the work of earlier researchers such as antoine henri becquerel, who discovered radioactivity whilst working on the phosphorescence of uranium salts in 1896. previously, scintillation events had to be laboriously detected by eye, using a spinthariscope (a simple microscope) to observe light flashes in t...	wikipedia