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Articles 1 - 30 of 32
Full-Text Articles in Physical Sciences and Mathematics
The Second Hull Of A Knotted Curve, Jason Cantarella, Greg Kuperberg, Robert B. Kusner, John M. Sullivan
The Second Hull Of A Knotted Curve, Jason Cantarella, Greg Kuperberg, Robert B. Kusner, John M. Sullivan
Robert Kusner
The convex hull of a set K in space consists of points which are, in a certain sense, "surrounded" by K. When K is a closed curve, we define its higher hulls, consisting of points which are "multiply surrounded" by the curve. Our main theorem shows that if a curve is knotted then it has a nonempty second hull. This provides a new proof of the Fary/Milnor theorem that every knotted curve has total curvature at least 4pi.
Quantum Corrections To The Schwarzschild And Kerr Metrics, N. E. J. Bjerrum-Bohr, John Donoghue, Barry R. Holstein
Quantum Corrections To The Schwarzschild And Kerr Metrics, N. E. J. Bjerrum-Bohr, John Donoghue, Barry R. Holstein
John Donoghue
We examine the corrections to the lowest order gravitational interactions of massive particles arising from gravitational radiative corrections. We show how the masslessness of the graviton and the gravitational selfinteractions imply the presence of nonanalytic pieces ;A2q2,;q2ln2q2, etc., in the form factors of the energy-momentum tensor and that these correspond to long range modifications of the metric tensor gmn of the form G2m2/r2,G2m\/r3, etc. The former coincide with well known solutions from classical general relativity, while the latter represent new quantum mechanical effects, whose strength and form is necessitated by the low energy quantum nature of the general relativity. We …
Deciding The Nature Of The Coarse Equation Through Microscopic Simulations: The Baby-Bathwater Scheme, J Li, Pg Kevrekidis, Cw Gear, Pg Kevrekidis
Deciding The Nature Of The Coarse Equation Through Microscopic Simulations: The Baby-Bathwater Scheme, J Li, Pg Kevrekidis, Cw Gear, Pg Kevrekidis
Panos Kevrekidis
Recent developments in multiscale computation allow the solution of coarse equations for the expected macroscopic behavior of microscopically evolving particles without ever obtaining these coarse equations in closed form. The closure is obtained on demand through appropriately initialized bursts ofmicroscopic simulation. The effective coupling of microscopic simulators with macrosocopic behavior requires certain decisions about the nature of the unavailable coarse equation. Such decisions include (a) the highest spatial derivative active in the coarse equation, (b) whether the equation satisfies certain conservation laws, and (c) whether the coarse dynamics is Hamiltonian. These decisions affect the number and type of boundary conditions …
Threshold Electrodisintegration Of 3he, R S. Hicks, A Hotta, S Churchwell, X Jiang, Gerald Alvin Peterson, J Shaw, B Asavapibhop, M C. Berisso, P E. Bosted, K Burchesky, R A. Miskimen, S E. Rock
Threshold Electrodisintegration Of 3he, R S. Hicks, A Hotta, S Churchwell, X Jiang, Gerald Alvin Peterson, J Shaw, B Asavapibhop, M C. Berisso, P E. Bosted, K Burchesky, R A. Miskimen, S E. Rock
Gerald Alvin Peterson
Cross sections were measured for the near-threshold electrodisintegration of 3He at momentum transfer values of q=2.4, 4.4, and 4.7fm-1. From these and prior measurements the transverse and longitudinal response functions RT and RL were deduced. Comparisons are made against previously published and new nonrelativistic A=3 calculations using the best available nucleon-nucleon NN potentials. In general, for q<2fm-1 these calculations accurately predict the threshold electrodisintegration of 3He. Agreement at increasing q demands consideration of two-body terms, but discrepancies still appear at the highest momentum transfers probed, perhaps due to the neglect of relativistic dynamics, or to the underestimation of high-momentum wave-function components.
Review Of Irwin M. Brodo, Sylvia Duran Sharnoff, Stephen Sharnoff: Lichens Of North America, Lynn Margulis
Review Of Irwin M. Brodo, Sylvia Duran Sharnoff, Stephen Sharnoff: Lichens Of North America, Lynn Margulis
Lynn Margulis (1938 - 2011)
No abstract provided.
Mobility Of Taxol In Microtubule Bundles, Jennifer Ross, D. Kuchnir Fygenson
Mobility Of Taxol In Microtubule Bundles, Jennifer Ross, D. Kuchnir Fygenson
Jennifer Ross
Mobility of taxol inside microtubules was investigated using fluorescence recovery after photobleaching on flowaligned bundles. Bundles were made of microtubules with either GMPCPP or GTP at the exchangeable site on the tubulin dimer. Recovery times were sensitive to bundle thickness and packing, indicating that taxol molecules are able to move laterally through the bundle. The density of open binding sites along a microtubule was varied by controlling the concentration of taxol in solution for GMPCPP samples. With [63% sites occupied, recovery times were independent of taxol concentration and, therefore, inversely proportional to the microscopic dissociation rate, koff. It was found …
Quantum Gravitational Corrections To The Nonrelativistic Scattering Potential Of Two Masses, N. E. J. Bjerrum-Bohr, John Donoghue, Barry R. Holstein
Quantum Gravitational Corrections To The Nonrelativistic Scattering Potential Of Two Masses, N. E. J. Bjerrum-Bohr, John Donoghue, Barry R. Holstein
John Donoghue
We treat general relativity as an effective field theory, obtaining the full nonanalytic component of the scattering matrix potential to one-loop order. The lowest order vertex rules for the resulting effective field theory are presented and the one-loop diagrams which yield the leading nonrelativistic post-Newtonian and quantum corrections to the gravitational scattering amplitude to second order in G are calculated in detail. The Fourier transformed amplitudes yield a nonrelativistic potential and our result is discussed in relation to previous calculations. The definition of a potential is discussed as well and we show how the ambiguity of the potential under coordinate …
Optimal Surface Temperature Reconstructions Using Terrestrial Borehole Data, M. E. Mann, S. Rutherford, Raymond S. Bradley, M. K. Hughes, F. T. Keimig
Optimal Surface Temperature Reconstructions Using Terrestrial Borehole Data, M. E. Mann, S. Rutherford, Raymond S. Bradley, M. K. Hughes, F. T. Keimig
Raymond S Bradley
We derive an optimal Northern Hemisphere mean surface temperature reconstruction from terrestrial borehole temperature profiles spanning the past five centuries. The pattern of borehole ground surface temperature (GST) reconstructions displays prominent discrepancies with instrumental surface air temperature (SAT) estimates during the 20th century, suggesting the presence of a considerable amount of noise and/or bias in any underlying spatial SAT signal. The vast majority of variance in the borehole dataset is efficiently retained by its two leading eigenvectors. A sizable share of the variance in the first eigenvector appears to be associated with non-SAT related bias in the borehole data. A …
Dynamics Of Conformal Maps For A Class Of Non-Laplacian Growth Phenomena, Martin Z. Bazant, Jaehyuk Choi, Benny Davidovitch
Dynamics Of Conformal Maps For A Class Of Non-Laplacian Growth Phenomena, Martin Z. Bazant, Jaehyuk Choi, Benny Davidovitch
Benny Davidovitch
Time-dependent conformal maps are used to model a class of growth phenomena limited by coupled non-Laplacian transport processes, such as nonlinear diffusion, advection, and electro- migration. Both continuous and stochastic dynamics are described by generalizing conformal- mapping techniques for viscous fingering and diffusion-limited aggregation, respectively. A gen- eral notion of time in stochastic growth is also introduced. The theory is applied to simulations of advection-diffusion-limited aggregation in a background potential flow. A universal crossover in mor- phology is observed from diffusion-limited to advection-limited fractal patterns with an associated crossover in the growth rate, controlled by a time-dependent effective Peclet number. …
Balanced Configurations Of Lattice Vectors And Gkz-Rational Toric Fourfolds In P^6, Eduardo Cattani, Alicia Dickenstein
Balanced Configurations Of Lattice Vectors And Gkz-Rational Toric Fourfolds In P^6, Eduardo Cattani, Alicia Dickenstein
Eduardo Cattani
We introduce a notion of balanced configurations of vectors. This is motivated by the study of rational A-hypergeometric functions in the sense of Gelfand, Kapranov and Zelevinsky. We classify balanced configurations of seven plane vectors up to GL(2,R)-equivalence and deduce that the only gkz-rational toric four-folds in P6 are those varieties associated with an essential Cayley configuration. We show that in this case, all rational A-hypergeometric functions may be described in terms of toric residues. This follows from studying a suitable hyperplane arrangement.
Complex C: A Low-Metallicity High-Velocity Cloud Plunging Into The Milky Way, Todd M. Tripp, Bart P. Wakker, Edward B. Jenkins, C. W. Bowers, A. C. Danks, R. F. Green, S. R. Heap, C. L. Joseph, M. E. Kaiser, J. L. Linsky, B. E. Woodgate
Complex C: A Low-Metallicity High-Velocity Cloud Plunging Into The Milky Way, Todd M. Tripp, Bart P. Wakker, Edward B. Jenkins, C. W. Bowers, A. C. Danks, R. F. Green, S. R. Heap, C. L. Joseph, M. E. Kaiser, J. L. Linsky, B. E. Woodgate
Todd M. Tripp
We present evidence that high-velocity cloud (HVC) complex C is a low-metallicity gas cloud that is plunging toward the disk and beginning to interact with the ambient gas that surrounds the Milky Way. This evidence begins with a new high-resolution (7 km s-1 FWHM) echelle spectrum of 3C 351 obtained with the Space Telescope Imaging Spectrograph (STIS). 3C 351 lies behind the low-latitude edge of complex C, and the new spectrum provides accurate measurements of O I, Si II, Al II, Fe II, and Si III absorption lines at the velocity of complex C; N I, S II, Si IV, …
Search For Neutral Baryon Resonances Below Pion Threshold, X Jiang, R Gilman, R Ransome, P Markowitz, T H. Chang, C C. Chang, Gerald Alvin Peterson
Search For Neutral Baryon Resonances Below Pion Threshold, X Jiang, R Gilman, R Ransome, P Markowitz, T H. Chang, C C. Chang, Gerald Alvin Peterson
Gerald Alvin Peterson
The reaction p(e,e′π+)X0 was studied with two high-resolution magnetic spectrometers to search for narrow baryon resonances. A missing mass resolution of 2.0 MeV was achieved. A search for structures in the mass region of 0.97
Photoproduction Of The Ω Meson On The Proton At Large Momentum Transfer, M Battaglieri, M Brunoldi, R De Vita, B Asavapibhop, R S. Hicks, D Lawrence, R Miskimen, Gerald Alvin Peterson
Photoproduction Of The Ω Meson On The Proton At Large Momentum Transfer, M Battaglieri, M Brunoldi, R De Vita, B Asavapibhop, R S. Hicks, D Lawrence, R Miskimen, Gerald Alvin Peterson
Gerald Alvin Peterson
The differential cross section, dσ/dt, for ω meson exclusive photoproduction on the proton above the resonance region (2.6
Watershed-Scale Effects Of Urbanization On Sediment Export: Assessment And Policy, Timothy O. Randhir
Watershed-Scale Effects Of Urbanization On Sediment Export: Assessment And Policy, Timothy O. Randhir
Timothy O. Randhir
Built components of watersheds are associated with impervious surfaces that alter hydrology, disrupt ecosystems, and affect water quality. This study focuses on the impervious factor as a tool for assessment and policy design to address water quality impacts. The empirical model uses a combination of watershed simulation and statistical regression modeling to study sediment loading at various stages of urbanization. The policy design is based on private behavior in a watershed setting to develop appropriate economic approaches. The incentives through taxes, subsidies, and cost sharing are based on water quality impacts. It was observed that nonlinearity in response functions resulted …
Ecological Considerations In The Design Of River And Stream Crossings, Scott D. Jackson
Ecological Considerations In The Design Of River And Stream Crossings, Scott D. Jackson
Scott D. Jackson
As long linear ecosystems, rivers and streams are particularly vulnerable to fragmentation. There is growing concern about the role of road crossings – and especially culverts – in altering habitats and disrupting river and stream continuity. Most of the culverts currently in place were designed with the principal objective of moving water across a road alignment. Little consideration was given to ecosystem processes such as the natural hydrology, sediment transport, fish and wildlife passage, or the movement of woody debris. It is not surprising then that many culverts significantly disrupt the movement of aquatic organisms. Survival of individual animals, facilitation …
Smooth(Er) Stellar Mass Maps In Candels: Constraints On The Longevity Of Clumps In High-Redshift Star-Forming Galaxies, Stijn Wuyts, Natascha M. Förster Schreiber, Reinhard Genzel, Yicheng Guo, Guillermo Barro, Eric F. Bell, Avishai Dekel, Sandra M. Faber, Henry C. Ferguson, Mauro Giavalisco, Norman A. Grogin, Nimish P. Hathi, Kuang-Han Huang, Dale D. Kocevski, Anton M. Koekemoer, David C. Koo, Jennifer Lotz, Dieter Lutz, Elizabeth Mcgrath, Jeffrey A, Newman, David Rosario, Amelie Saintonge, Linda J. Tacconi, Benjamin J. Weiner, Arjen Van Der Wel
Smooth(Er) Stellar Mass Maps In Candels: Constraints On The Longevity Of Clumps In High-Redshift Star-Forming Galaxies, Stijn Wuyts, Natascha M. Förster Schreiber, Reinhard Genzel, Yicheng Guo, Guillermo Barro, Eric F. Bell, Avishai Dekel, Sandra M. Faber, Henry C. Ferguson, Mauro Giavalisco, Norman A. Grogin, Nimish P. Hathi, Kuang-Han Huang, Dale D. Kocevski, Anton M. Koekemoer, David C. Koo, Jennifer Lotz, Dieter Lutz, Elizabeth Mcgrath, Jeffrey A, Newman, David Rosario, Amelie Saintonge, Linda J. Tacconi, Benjamin J. Weiner, Arjen Van Der Wel
Mauro Giavalisco
We perform a detailed analysis of the resolved colors and stellar populations of a complete sample of 323 star-forming galaxies at 0.5 < z < 1.5, and 326 star-forming galaxies at 1.5 < z < 2.5 in the ERS and CANDELS-Deep region of GOODS-South. Galaxies were selected to be more massive than 10^10 Msun and have specific star formation rates above 1/t_H. We model the 7-band optical ACS + near-IR WFC3 spectral energy distributions of individual bins of pixels, accounting simultaneously for the galaxy-integrated photometric constraints available over a longer wavelength range. We analyze variations in rest-frame color, stellar surface mass density, age, and extinction as a function of galactocentric radius and local surface brightness/density, and measure structural parameters on luminosity and stellar mass maps. We find evidence for redder colors, older stellar ages, and increased dust extinction in the nuclei of galaxies. Big star-forming clumps seen in star formation tracers are less prominent or even invisible on the inferred stellar mass distributions. Off-center clumps contribute up to ~20% to the integrated SFR, but only 7% or less to the integrated mass of all massive star-forming galaxies at z ~ 1 and z ~ 2, with the fractional contributions being a decreasing function of wavelength used to select the clumps. The stellar mass profiles tend to have smaller sizes and M20 coefficients, and higher concentration and Gini coefficients than the light distribution. Our results are consistent with an inside-out disk growth scenario with brief (100 - 200 Myr) episodic local enhancements in star formation superposed on the underlying disk. Alternatively, the young ages of off-center clumps may signal inward clump migration, provided this happens efficiently on the order of an orbital timescale.
Macromolecules In The 21st Century: An International Symposium On Polymer Science And Technology On The Occasion Otto Vogl's 75th Birthday, Gerald S. Kirshenbaum, Helga Roder
Macromolecules In The 21st Century: An International Symposium On Polymer Science And Technology On The Occasion Otto Vogl's 75th Birthday, Gerald S. Kirshenbaum, Helga Roder
Otto Vogl
No abstract provided.
Variability Of Snow Accumulation And Isotopic Composition On Nevado Sajama, Bolivia, D. R. Hardy, M. Vuille, Raymond S. Bradley
Variability Of Snow Accumulation And Isotopic Composition On Nevado Sajama, Bolivia, D. R. Hardy, M. Vuille, Raymond S. Bradley
Raymond S Bradley
High-elevation ice caps develop an archive of atmospheric constituents and properties through the accumulation of snowfall. The timing of precipitation events, therefore, fundamentally governs the environmental information that ice core records can provide. These events are often highly seasonal, as are various postdepositional processes influencing the snow's physical and chemical properties. Knowledge of climatic conditions at an ice core site is essential to a full understanding of the ice core record. This work reports on 4 years of meteorological measurements near the summit of Nevado Sajama, an ice-capped peak rising ∼2500 m above the South American Altiplano (elevation 6542 m), …
Rapid Lacustrine Response To Recent High Arctic Warming: A Diatom Record From Sawtooth Lake, Ellesmere Island, Nunavut, Bianca B. Perren, Raymond S. Bradley, Pierre Francus
Rapid Lacustrine Response To Recent High Arctic Warming: A Diatom Record From Sawtooth Lake, Ellesmere Island, Nunavut, Bianca B. Perren, Raymond S. Bradley, Pierre Francus
Raymond S Bradley
Diatoms from Sawtooth Lake (79 20'N, 81 51'W) on the Fosheim Peninsula in Central Ellesmere Island, Canada were analyzed to assess the temporal extent and magnitude of climatic change in the High Arctic during the late Holocene. Diatom results from the sediment cores show an absence of diatoms throughout the last ;2.5 ka (4.6 m) until the 1920s. However, ca. 1926 (5.3-cm depth), a rapid colonization of diatoms in the lake occurred. Within the uppermost section of the core (;1920 to ;1997), the diatom flora shift from a small Fragilaria-dominated assemblage to a more diverse assemblage that is dominated by …
Reply To Comment By N. D. Marsh And H. Svensmark On “Solar Influences On Cosmic Rays And Cloud Formation: A Reassessment”, B. Sun, Raymond S. Bradley
Reply To Comment By N. D. Marsh And H. Svensmark On “Solar Influences On Cosmic Rays And Cloud Formation: A Reassessment”, B. Sun, Raymond S. Bradley
Raymond S Bradley
No abstract provided.
Modeling Δ18o In Precipitation Over The Tropical Americas: 1. Interannual Variability And Climatic Controls, M. Vuille, Raymond S. Bradley, M. Werner, R. Healy, F. Keimig
Modeling Δ18o In Precipitation Over The Tropical Americas: 1. Interannual Variability And Climatic Controls, M. Vuille, Raymond S. Bradley, M. Werner, R. Healy, F. Keimig
Raymond S Bradley
We use two atmospheric general circulation models (AGCMs), the ECHAM-4 and the GISS II models, to analyze the interannual variability of δ18O in precipitation over the tropical Americas. Several different simulations with isotopic tracers forced with observed global sea surface temperatures (SST) between 1950 and 1998 reveal the influence of varying temperature, precipitation amount, and moisture source contributions on the predicted δ18O distribution. Observational evidence from climatic (NCEP-NCAR) and sparse stable isotope (IAEA-GNIP) data is used to evaluate model performance. The models capture the essential features of surface climate over the tropical Americas in terms of both their spatial and …
Modeling Δ18o In Precipitation Over The Tropical Americas: 2. Simulation Of The Stable Isotope Signal In Andean Ice Cores, M. Vuille, Raymond S. Bradley, R. Healy, M. Werner, D. R. Hardy, L. G. Thompson, F. Keimig
Modeling Δ18o In Precipitation Over The Tropical Americas: 2. Simulation Of The Stable Isotope Signal In Andean Ice Cores, M. Vuille, Raymond S. Bradley, R. Healy, M. Werner, D. R. Hardy, L. G. Thompson, F. Keimig
Raymond S Bradley
We use the ECHAM-4 and the GISS II atmospheric general circulation models (AGCM) with incorporated stable isotopic tracers and forced with observed global sea surface temperatures (SST) between 1979 and 1998, to simulate the δ18O signal in three tropical Andean ice cores, from Huascarán (Peru), Quelccaya (Peru), and Sajama (Bolivia). In both models, the simulated stable isotopic records compare favorably with the observational data, when the seasonality of precipitation and dry season loss due to sublimation and wind scour are taken into account. Our simulations indicate a significant influence of the local climatic conditions (temperature and precipitation amount) on the …
Spatial Gradients In The Cosmological Constant, John Donoghue
Spatial Gradients In The Cosmological Constant, John Donoghue
John Donoghue
It is possible that there may be differences in the fundamental physical parameters from one side of the observed universe to the other. I show that the cosmological constant is likely to be the most sensitive of the physical parameters to possible spatial variation, because a small variation in any of the other parameters produces a huge variation of the cosmological constant. It therefore provides a very powerful {\em indirect} evidence against spatial gradients or temporal variation in the other fundamental physical parameters, at least 40 orders of magnitude more powerful than direct experimental constraints. Moreover, a gradient may potentially …
Evaluation Of Dedekind Sums, Eisenstein Cocycles, And Special Values Of L-Functions, Pe Gunnells, R Sczech
Evaluation Of Dedekind Sums, Eisenstein Cocycles, And Special Values Of L-Functions, Pe Gunnells, R Sczech
Paul Gunnells
We define higher-dimensional Dedekind sums that generalize the classical Dedekind-Rademacher sums as well as Zagier's sums, and we show how to compute them effectively using a generalization of the continued-fraction algorithm. We present two applications. First, we show how to express special values of partial zeta functions associated to totally real number fields in terms of these sums via the Eisenstein cocycle introduced by R. Sczech. Hence we obtain a polynomial time algorithm for computing these special values. Second, we show how to use our techniques to compute certain special values of the Witten zeta function, and we compute some …
Bogomol'nyi, Prasad And Sommerfield Configurations In Smectics, Christian Santangelo, Randall D. Kamien
Bogomol'nyi, Prasad And Sommerfield Configurations In Smectics, Christian Santangelo, Randall D. Kamien
Christian Santangelo
It is typical in smectic liquid crystals to describe elastic deformations with a linear theory when the elastic strain is small. In smectics, certain essential nonlinearities arise from the requirement of rotational invariance. By employing the Bogomol’nyi, Prasad, and Sommerfield decomposition and relying on boundary conditions and geometric invariants, we have found a large class of exact solutions. We introduce an approximation for the deformation profile far from a spherical inclusion and find an enhanced attractive interaction at long distances due to the nonlinear elasticity, confirmed by numerical minimization.
Improved Determination Of The Electroweak Penguin Contribution To E’/E In The Chiral Limit, Vincenzo Cirigliano, John Donoghue, Eugene Golowich, Kim Maltman
Improved Determination Of The Electroweak Penguin Contribution To E’/E In The Chiral Limit, Vincenzo Cirigliano, John Donoghue, Eugene Golowich, Kim Maltman
John Donoghue
We perform a finite energy sum rule analysis of the flavor ud two-point V-A current correlator, Delta Pi (Q^2). The analysis, which is performed using both the ALEPH and OPAL databases for the V-A spectral function, Delta rho, allows us to extract the dimension six V-A OPE coefficient, a_6, which is related to the matrix element of the electroweak penguin operator, Q_8, by chiral symmetry. The result for a_6 leads directly to the improved (chiral limit) determination epsilon'/epsilon = (- 15.0 +- 2.7) 10^{-4}. Determination of higher dimension OPE contributions also allows us to perform an independent test using a …
Ground State Numerical Study Of The Three-Dimensional Random Field Ising Model, I. Dukovski, Jonathan Machta
Ground State Numerical Study Of The Three-Dimensional Random Field Ising Model, I. Dukovski, Jonathan Machta
Jonathan Machta
The random field Ising model in three dimensions with Gaussian random fields is studied at zero temperature for system sizes up to 603. For each realization of the normalized random fields, the strength of the random field, Δ and a uniform external, H is adjusted to find the finite-size critical point. The finite-size critical point is identified as the point in the H−Δ plane where three degenerate ground states have the largest discontinuities in the magnetization. The discontinuities in the magnetization and bond energy between these ground states are used to calculate the magnetization and specific heat critical exponents and …
Hecke Operators And Q-Groups Associated To Self-Adjoint Homogeneous Cones, Pe Gunnells, M Mcconnell
Hecke Operators And Q-Groups Associated To Self-Adjoint Homogeneous Cones, Pe Gunnells, M Mcconnell
Paul Gunnells
Let G be a reductive algebraic group associated to a self-adjoint homogeneous cone defined over , and let ΓG be an appropriate neat arithmetic subgroup. We present two algorithms to compute the action of the Hecke operators on for all i. This simultaneously generalizes the modular symbol algorithm of Ash-Rudolph (Invent. Math. 55 (1979) 241) to a larger class of groups, and proposes techniques to compute the Hecke-module structure of previously inaccessible cohomology groups.
Rapid Development Of Hindi Named Entity Recognition Using Conditional Random Fields And Feature Induction, Wei Li, Andrew Mccallum
Rapid Development Of Hindi Named Entity Recognition Using Conditional Random Fields And Feature Induction, Wei Li, Andrew Mccallum
Andrew McCallum
This paper describes our application of Conditional Random Fields (CRFs) with feature induction to a Hindi named entity recognition task. With only five days development time and little knowledge of this language, we automatically discover relevant features by providing a large array of lexical tests and using feature induction to automatically construct the features that most increase conditional likelihood. In an effort to reduce overfitting, we use a combination of a Gaussian prior and early-stopping based on the results of 10-fold cross validation.
Efficiently Inducing Features Of Conditional Random Fields, Andrew Mccallum
Efficiently Inducing Features Of Conditional Random Fields, Andrew Mccallum
Andrew McCallum
Conditional Random Fields (CRFs) are undirected graphical models, a special case of which correspond to conditionally-trained finite state machines. A key advantage of CRFs is their great flexibility to include a wide variety of arbitrary, non-independent features of the input. Faced with this freedom, however, an important question remains: what features should be used? This paper presents an efficient feature induction method for CRFs. The method is founded on the principle of iteratively constructing feature conjunctions that would significantly increase conditional log-likelihood if added to the model. Automated feature induction enables not only improved accuracy and dramatic reduction in parameter …