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2001

University of Massachusetts Amherst

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Articles 1 - 30 of 99

Full-Text Articles in Physical Sciences and Mathematics

Institutsdagen At The Royal Institute Of Technology, Stockholm, Sweden, May 3, 2000, Otto Vogl, Ann Christine Albertsson Dec 2001

Institutsdagen At The Royal Institute Of Technology, Stockholm, Sweden, May 3, 2000, Otto Vogl, Ann Christine Albertsson

Emeritus Faculty Author Gallery

No abstract provided.


Institutsdagen At The Royal Institute Of Technology, Stockholm, Sweden, May 3, 2000, Otto Vogl, Ann Christine Albertsson Dec 2001

Institutsdagen At The Royal Institute Of Technology, Stockholm, Sweden, May 3, 2000, Otto Vogl, Ann Christine Albertsson

Otto Vogl

No abstract provided.


Poly Millennial 2000 Hilton Waikoloa Villages, Hawaii, December 9-13, 2000, Otto Vogl, William Daly Nov 2001

Poly Millennial 2000 Hilton Waikoloa Villages, Hawaii, December 9-13, 2000, Otto Vogl, William Daly

Emeritus Faculty Author Gallery

No abstract provided.


Poly Millennial 2000 Hilton Waikoloa Villages, Hawaii, December 9-13, 2000, Otto Vogl, William Daly Nov 2001

Poly Millennial 2000 Hilton Waikoloa Villages, Hawaii, December 9-13, 2000, Otto Vogl, William Daly

Otto Vogl

No abstract provided.


Investigating The Long-Term Evolution Of Galaxies: Noise, Cuspy Halos And Bars, Martin D. Weinberg Oct 2001

Investigating The Long-Term Evolution Of Galaxies: Noise, Cuspy Halos And Bars, Martin D. Weinberg

Astronomy Department Faculty Publication Series

I review the arguments for the importance of halo structure in driving galaxy evolution and coupling a galaxy to its environment. We begin with a general discussion of the key dynamics and examples of structure dominated by modes. We find that simulations with large numbers of particles (N ≥ 106) are required to resolve the dynamics. Finally, I will describe some new results which demonstrates that a disk bar can produce cores in a cuspy CDM dark-matter profile within a gigayear. An inner Lindblad-like resonance couples the rotating bar to halo orbits at all radii through the cusp, rapidly flattening …


A Polytope Combinatorics For Semisimple Groups, Jared E. Anderson Oct 2001

A Polytope Combinatorics For Semisimple Groups, Jared E. Anderson

Mathematics and Statistics Department Faculty Publication Series

Mirkovi and Vilonen discovered a canonical basis of algebraic cycles for the intersection homology of (the closures of the strata of) the loop Grassmannian. The moment map images of these varieties are a collection of polytopes, and they may be used to compute weight multiplicities and tensor product multiplicities for representations of a semisimple group. The polytopes are explicitly described for a few low rank groups.


Relativistic Effects And Two-Body Currents In 2h(E⃗,E′P)N Using Out-Of-Plane Detection, Z L. Zhou, X Jiang, R Hicks, A Hotta, R Miskimen, Gerald Alvin Peterson, J Shaw Oct 2001

Relativistic Effects And Two-Body Currents In 2h(E⃗,E′P)N Using Out-Of-Plane Detection, Z L. Zhou, X Jiang, R Hicks, A Hotta, R Miskimen, Gerald Alvin Peterson, J Shaw

Gerald Alvin Peterson

Measurements of the 2H(e⃗,e′p)n reaction were performed with the out-of-plane magnetic spectrometers (OOPS) at the MIT-Bates Linear Accelerator. The longitudinal-transverse, fLT and fLT′, and the transverse-transverse, fTT, interference responses at a missing momentum of 210MeV/c were simultaneously extracted in the dip region at Q2 = 0.15 (GeV/c)2. In comparison to models of deuteron electrodisintegration, the data clearly reveal strong effects of relativity and final-state interactions and the importance of two-body meson-exchange currents and isobar configurations. We demonstrate that such effects can be disentangled by extracting these responses using the novel out-of-plane technique.


Electroproduction Of The Λ(1520) Hyperon, S P. Barrow, L Dennis, S B. Mcaleer, B Asavapibhop, R S. Hicks, D Lawrence, R Miskimen, Gerald Alvin Peterson, J Shaw Aug 2001

Electroproduction Of The Λ(1520) Hyperon, S P. Barrow, L Dennis, S B. Mcaleer, B Asavapibhop, R S. Hicks, D Lawrence, R Miskimen, Gerald Alvin Peterson, J Shaw

Gerald Alvin Peterson

The reaction ep⃗e′K+Λ(1520) with Λ(1520)→p′K- was studied at electron beam energies of 4.05, 4.25, and 4.46 GeV, using the CLAS detector at the Thomas Jefferson National Accelerator Facility. The cosθK+, φK+, Q2, and W dependencies of Λ(1520) electroproduction are presented for the kinematic region 0.9


Elliptic Functions And Equations Of Modular Curves, Lev A. Borisov, Paul E. Gunnells, Sorin Popescu Aug 2001

Elliptic Functions And Equations Of Modular Curves, Lev A. Borisov, Paul E. Gunnells, Sorin Popescu

Paul Gunnells

Let P≥5 be a prime. We show that the space of weight one Eisenstein series defines an embedding into P(p−3)/2 of the modular curve X1(p) for the congruence group Γ1(p) that is scheme-theoretically cut out by explicit quadratic equations.


Measurement Of The Elastic Magnetic Form Factor Of 3he At High Momentum Transfer, I Nakagawa, J Shaw, S Churchwell, X Jiang, B Asavapibhop, M C. Berisso, P E. Bosted, K Burchesky, R S. Hicks, A Hotta, R A. Miskimen, Gerald Alvin Peterson, S E. Rock Jun 2001

Measurement Of The Elastic Magnetic Form Factor Of 3he At High Momentum Transfer, I Nakagawa, J Shaw, S Churchwell, X Jiang, B Asavapibhop, M C. Berisso, P E. Bosted, K Burchesky, R S. Hicks, A Hotta, R A. Miskimen, Gerald Alvin Peterson, S E. Rock

Gerald Alvin Peterson

New electron scattering measurements have been made that extend data on the 3He elastic magnetic form factor up to Q2 = 42.6fm-2. These new data test theoretical conjectures regarding non-nucleonic effects in the three-body system. The very small cross sections, as low as 10-40cm2/sr, required the use of a high-pressure cryogenic gas target and a detector system with excellent background rejection capability. No existing theoretical calculation satisfactorily accounts for all the available data.


A Solid State 13c Nmr Study Of Kerogen Degradation During Black Shale Weathering, Steven T. Petsch, R. J. Smernik, T. I. Eglinton, J. M. Oades Jun 2001

A Solid State 13c Nmr Study Of Kerogen Degradation During Black Shale Weathering, Steven T. Petsch, R. J. Smernik, T. I. Eglinton, J. M. Oades

Steven T. Petsch

Solid state 13C nuclear magnetic resonance (NMR) spectroscopy is used to examine kerogen composition in weathering profiles of the Monterey, Green River, Woodford, and New Albany formations. Techniques include cross polarization (CP) and Bloch decay (BD) spectral acquisition, dipolar dephasing (DD), spin counting, experiments to provide estimates of relaxation times (T1ρH and T1H), and proton spin relaxation editing (PSRE). It is demonstrated that CP/MAS (cross polarization/magic angle spinning) spectra obtained on isolated kerogens provide reliable characterization of kerogen composition (compared with BD spectra and whole-rock samples). Highly aliphatic (polymethylenic) kerogens are not appreciably altered during weathering. Aromatic and/or branched aliphatic …


Exclusive Electroproduction Of Φ Mesons At 4.2 Gev, K Lukashin, E S. Smith, B Asavapibhop, R A. Hicks, D Lawrence, R Miskimen, Gerald Alvin Peterson, J Shaw May 2001

Exclusive Electroproduction Of Φ Mesons At 4.2 Gev, K Lukashin, E S. Smith, B Asavapibhop, R A. Hicks, D Lawrence, R Miskimen, Gerald Alvin Peterson, J Shaw

Gerald Alvin Peterson

We studied the exclusive reaction ep⃗e′p′φ using the φ⃗K+K- decay mode. The data were collected using a 4.2 GeV incident electron beam and the CEBAF Large Acceptance Spectrometer (CLAS) at the Thomas Jefferson National Accelerator Facility. Our experiment covers the range in Q2 from 0.7 to 2.2 GeV2, and W from 2.0 to 2.6 GeV. Taken together with all previous data, we find a consistent picture of φ production on the proton. Our measurement shows the expected decrease of the t slope with the vector-meson formation time cΔτ below 2 fm. At 〈cΔτ〉=0.6 fm, we measure bφ=2.27±0.42 GeV-2. The cross …


A Homotopy Theory Of Orbispaces, Weimin Chen Chen May 2001

A Homotopy Theory Of Orbispaces, Weimin Chen Chen

Weimin Chen

An orbifold is a singular space which is locally modeled on the quotient of a smooth manifold by a smooth action of a finite group. It appears naturally in geometry and topology when group actions on manifolds are involved and the stabilizer of each fixed point is finite. The concept of an orbifold was first introduced by Satake under the name “V -manifold” in a paper where he also extended the basic differential geometry to his newly defined singular spaces (cf. [32]). The local structure of an orbifold – being the quotient of a smooth manifold by a finite group …


Language Models For Hierarchical Summarization (Proposal For Dissertation), Dawn Lawrie May 2001

Language Models For Hierarchical Summarization (Proposal For Dissertation), Dawn Lawrie

Computer Science Department Faculty Publication Series

Hierarchies have long been used for organization, summarization, and access to information. In this proposal we define summarization in terms of a probabilistic language model and use the definition to explore new techniques for automatically generating topic hierarchies. One technique applies a graph-theoretic algorithm, which is an approximation of the Dominating Set Problem. Another technique uses an entropy-based approach to choose topic terms. Both techniques efficiently select terms according to a language model. We compare the new techniques to previous methods proposed for constructing topic hierarchies including subsumption and lexical hierarchies, as well as words found using TF.IDF. Our preliminary …


A New Cohomology Theory Of Orbifold, Weimin Chen Chen Mar 2001

A New Cohomology Theory Of Orbifold, Weimin Chen Chen

Weimin Chen

No abstract provided.


Quaternionic Holomorphic Geometry: Plucker Formula, Dirac Eigenvalue Estimates And Energy Estimates Of Harmonic 2-Tori, D Ferus, K Leschke, F Pedit, U Pinkall Jan 2001

Quaternionic Holomorphic Geometry: Plucker Formula, Dirac Eigenvalue Estimates And Energy Estimates Of Harmonic 2-Tori, D Ferus, K Leschke, F Pedit, U Pinkall

Mathematics and Statistics Department Faculty Publication Series

No abstract provided.


Geometric Representation Theory Of Restricted Lie Algebras, I Mirkovic, D Rumynin Jan 2001

Geometric Representation Theory Of Restricted Lie Algebras, I Mirkovic, D Rumynin

Mathematics and Statistics Department Faculty Publication Series

We modify the Hochschild -map to construct central extensions of a restricted Lie algebra. Such central extension gives rise to a goup scheme that leads to a geometric construction of unrestricted representations. For a classical semisimple Lie algebra, we construct equivariant line bundles whose global sections afford representations with a nilpotentp-character.


4. Bengt Rånby (1920-2000), Otto Vogl, Gerald S. Kirshenbaum Jan 2001

4. Bengt Rånby (1920-2000), Otto Vogl, Gerald S. Kirshenbaum

Emeritus Faculty Author Gallery

No abstract provided.


Department Of Physics Newsletter: Spring 2001, Gerry Peterson, Bob Krotkov, Mary Ann Ryan, Kristine Reopell Jan 2001

Department Of Physics Newsletter: Spring 2001, Gerry Peterson, Bob Krotkov, Mary Ann Ryan, Kristine Reopell

Physics Newsletters

No abstract provided.


On-Line Matrix Removal Of Lead For The Determination Of Trace Elements In Forensic Bullet Samples By Flow Injection Inductively Coupled Plasma-Mass Spectrometry, Er Yourd, Jf Tyson, Rd Koons Jan 2001

On-Line Matrix Removal Of Lead For The Determination Of Trace Elements In Forensic Bullet Samples By Flow Injection Inductively Coupled Plasma-Mass Spectrometry, Er Yourd, Jf Tyson, Rd Koons

Chemistry Department Faculty Publication Series

No abstract provided.


Microwave-Assisted Extraction Of Monomethyl Arsonic Acid From Soil And Sediment Standard Reference Materials, Pm Yehl, H Gurleyuk, Jf Tyson, Pc Uden Jan 2001

Microwave-Assisted Extraction Of Monomethyl Arsonic Acid From Soil And Sediment Standard Reference Materials, Pm Yehl, H Gurleyuk, Jf Tyson, Pc Uden

Chemistry Department Faculty Publication Series

No abstract provided.


Statistical Equilibrium Measures In Micromagnetics, Ma Katsoulakis, P Plechac Jan 2001

Statistical Equilibrium Measures In Micromagnetics, Ma Katsoulakis, P Plechac

Mathematics and Statistics Department Faculty Publication Series

We derive an equilibrium statistical theory for the macroscopic description of a ferromagnetic material at positive finite temperatures. Our formulation describes the most-probable equilibrium macrostates that yield a coherent deterministic large-scale picture varying at the size of the domain, as well as it captures the effect of random spin fluctuations caused by the thermal noise. We discuss connections of the proposed formulation to the Landau-Lifschitz theory and to the studies of domain formation based on Monte Carlo lattice simulations.


Phenomenological Issues In The Determination Of Delta Gamma(D), E Golowich, S Pakvasa Jan 2001

Phenomenological Issues In The Determination Of Delta Gamma(D), E Golowich, S Pakvasa

Physics Department Faculty Publication Series

We consider the issue of determining the D0– width difference ΔΓD experimentally. The current situation is reviewed and suggestions for further study are given. We propose a number of D0 decay modes in addition to those studied in the recent E791, FOCUS and BELLE lifetime determination experiments. Then we address prospects for determining CF-CDS strong phase differences, like δKπ which appears in the CLEO study of D0→K+π− transitions. We show how to extract δK*π with CDS data and furthermore show when D→KLπ data becomes available that δKπ can also be obtained.


Worm Algorithms For Classical Statistical Models, Nikolai Prokof'ev, Boris Svistunov Jan 2001

Worm Algorithms For Classical Statistical Models, Nikolai Prokof'ev, Boris Svistunov

Physics Department Faculty Publication Series

We show that high-temperature expansions provide a basis for the novel approach to efficient Monte Carlo simulations. “Worm” algorithms utilize the idea of updating closed-path configurations (produced by high-temperature expansions) through the motion of end points of a disconnected path. An amazing result is that local, Metropolis-type schemes using this approach appear to have dynamical critical exponents close to zero (i.e., their efficiency is comparable to the best cluster methods) as proved by finite-size scaling of the autocorrelation time for various universality classes.


Single-Hole Spectral Function And Spin-Charge Separation In The T-J Model, A Mishchenko, Nikolai Prokof'ev, Boris Svistunov Jan 2001

Single-Hole Spectral Function And Spin-Charge Separation In The T-J Model, A Mishchenko, Nikolai Prokof'ev, Boris Svistunov

Physics Department Faculty Publication Series

Worm algorithm Monte Carlo simulations of the hole Green function with subsequent spectral analysis were performed for 0.1<~J/t<~0.4 on lattices with up to L×L=32×32 sites at a temperature as low as T=J/40, and present, apparently, the hole spectral function in the thermodynamic limit. Spectral analysis reveals a δ-function-sharp quasiparticle peak at the lower edge of the spectrum that is incompatible with the power-law singularity and thus rules out the possibility of spin-charge separation in this parameter range. Spectral continuum features two peaks separated by a gap ∼4÷5 t.


Diagrammatic Quantum Monte Carlo For Two-Body Problems: Applied To Excitons, E Burovski, A Mishchenko, Nikolai Prokof'ev, B Svistunov Jan 2001

Diagrammatic Quantum Monte Carlo For Two-Body Problems: Applied To Excitons, E Burovski, A Mishchenko, Nikolai Prokof'ev, B Svistunov

Physics Department Faculty Publication Series

We present a novel method for the precise numeric solution of the irreducible two-body problem and apply it to excitons in solids. The approach is based on the Monte Carlo simulation of the two-body Green function specified by Feynman’s diagrammatic expansion. Our method does not rely on the specific form of the electron and hole dispersion laws and is valid for any attractive electron-hole potential. We establish limits of validity of the Wannier (large radius) and Frenkel (small radius) approximations, present accurate data for the intermediate radius excitons, and give evidence for the charge transfer nature of the monopolar exciton …


Calibrations And Fayyazuddin-Smith Spacetimes, Hyunji Cho, Moataz Emam, David Kastor, Jennie Traschen Jan 2001

Calibrations And Fayyazuddin-Smith Spacetimes, Hyunji Cho, Moataz Emam, David Kastor, Jennie Traschen

Physics Department Faculty Publication Series

We show that a class of spacetimes introduced by Fayyazuddin and Smith to describe intersecting M5-branes admits a generalized Kähler calibration. Equipped with this understanding, we are able to construct spacetimes corresponding to further classes of calibrated p-brane world-volume solitons. We note that these classes of spacetimes also describe the fields of p-branes wrapping certain supersymmetric cycles of Calabi-Yau manifolds.


Subleading Corrections To Parity-Violating Pion Photoproduction, Sl Zhu, S Puglia, Br Holstein, Mj Ramsey-Musolf Jan 2001

Subleading Corrections To Parity-Violating Pion Photoproduction, Sl Zhu, S Puglia, Br Holstein, Mj Ramsey-Musolf

Physics Department Faculty Publication Series

We compute the photon asymmetry Bγ for near threshold parity-violating (PV) pion photoproduction through subleading order. We show that subleading contributions involve a new combination of PV couplings not included in previous analyses of hadronic PV. We argue that existing constraints on the leading order contribution to Bγ—obtained from the PV γ-decay of 18F—suggest that the impact of the subleading contributions may be more significant than expected from naturalness arguments.


Introduction To Effective Field Theory, Br Holstein Jan 2001

Introduction To Effective Field Theory, Br Holstein

Physics Department Faculty Publication Series

This review summarizes effective field theory techniques, which are the modern theoretical tools for exploiting the existence of hierarchies of scale in a physical problem. The general theoretical framework is described and evaluated explicitly for a simple model. Power-counting results are illustrated for a few cases of practical interest, and several applications to quantum electrodynamics are described.


Chiral Symmetry And The Parity-Violating Nn Pi Yukawa Coupling, Sl Zhu, Sj Puglia, Br Holstein, Mj Ramsey-Musolf Jan 2001

Chiral Symmetry And The Parity-Violating Nn Pi Yukawa Coupling, Sl Zhu, Sj Puglia, Br Holstein, Mj Ramsey-Musolf

Physics Department Faculty Publication Series

We construct the complete SU(2) parity-violating (PV) π,N,Δ interaction Lagrangian with one derivative, and calculate the chiral corrections to the PV Yukawa NNπ coupling constant hπ through O(1/Λχ3) in the leading order of heavy baryon expansion. We discuss the relationship between the renormalized hπ, the measured value of hπ, and the corresponding quantity calculated microscopically from the standard model four-quark PV interaction. We observe that the renormalized hπ depends strongly on a number of a priori unknown parameters in the PV effective Lagrangian.