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Articles 1 - 27 of 27
Full-Text Articles in Physics
Simulating The Outer Layers Of Rapidly Rotating Stars, Frank J. Robinson, Joel Tanner, Sarbani Basu
Simulating The Outer Layers Of Rapidly Rotating Stars, Frank J. Robinson, Joel Tanner, Sarbani Basu
Chemistry & Physics Faculty Publications
This paper presents the results of a set of radiative hydrodynamic (RHD) simulations of convection in the near-surface regions of a rapidly rotating star. The simulations use microphysics consistent with stellar models, and include the effects of realistic convection and radiative transfer. We find that the overall effect of rotation is to reduce the strength of turbulence. The combination of rotation and radiative cooling creates a zonal velocity profile in which the motion of fluid parcels near the surface is independent of rotation. Their motion is controlled by the strong up and down flows generated by radiative cooling. The fluid …
Kinetic Effects In 2d And 3d Quantum Dots: Comparison Between High And Low Electron Correlation Regimes, Marlina Slamet, Viraht Sahni
Kinetic Effects In 2d And 3d Quantum Dots: Comparison Between High And Low Electron Correlation Regimes, Marlina Slamet, Viraht Sahni
Chemistry & Physics Faculty Publications
Kinetic related ground state properties of a two-electron 2D quantum dot in a magnetic field and a 3D quantum dot (Hooke’s atom) are compared in the Wigner high (HEC) and low (LEC) electron correlation regimes. The HEC regime corresponds to low densities sufficient for the creation of a Wigner molecule. The LEC regime densities are similar to those of natural atoms and molecules. The results are determined employing exact closed-form analytical solutions of the Schrödinger-Pauli and Schrödinger equations, respectively. The properties studied are the local and nonlocal quantal sources of the density and the single particle density matrix; the kinetic …
Measurement Of The Neutron Radius Of (208)Pb Through Parity Violation In Electron Scattering, S. Abrahamyan, Timothy Holmstrom, Prex Collaboration
Measurement Of The Neutron Radius Of (208)Pb Through Parity Violation In Electron Scattering, S. Abrahamyan, Timothy Holmstrom, Prex Collaboration
Chemistry & Physics Faculty Publications
We report the first measurement of the parity-violating asymmetry APV in the elastic scattering of polarized electrons from 208Pb. APV is sensitive to the radius of the neutron distribution (Rn). The result APV=0.656±0.060(stat)±0.014(syst) ppm corresponds to a difference between the radii of the neutron and proton distributions Rn-Rp=0.33-0.18+0.16 fm and provides the first electroweak observation of the neutron skin which is expected in a heavy, neutron-rich nucleus.
New Precision Limit On The Strange Vector Form Factors Of The Proton, Z. Ahmed, Timothy Holmstrom, Happex Collaboration
New Precision Limit On The Strange Vector Form Factors Of The Proton, Z. Ahmed, Timothy Holmstrom, Happex Collaboration
Chemistry & Physics Faculty Publications
The parity-violating cross-section asymmetry in the elastic scattering of polarized electrons from unpolarized protons has been measured at a four-momentum transfer squared Q2=0.624 GeV2 and beam energy Eb=3.48 GeV to be APV=-23.80±0.78(stat)±0.36(syst) parts per million. This result is consistent with zero contribution of strange quarks to the combination of electric and magnetic form factors GEs+0.517GMs=0.003±0.010(stat)±0.004(syst)±0.009(ff), where the third error is due to the limits of precision on the electromagnetic form factors and radiative corrections. With this measurement, the world data on strange contributions to nucleon form factors …
Beam-Target Double-Spin Asymmetry A(Lt) In Charged Pion Production From Deep Inelastic Scattering On A Transversely Polarized (3)He Target At 1.4, J. Huang, Timothy Holmstrom, Jefferson Lab Hall A Collaboration
Beam-Target Double-Spin Asymmetry A(Lt) In Charged Pion Production From Deep Inelastic Scattering On A Transversely Polarized (3)He Target At 1.4, J. Huang, Timothy Holmstrom, Jefferson Lab Hall A Collaboration
Chemistry & Physics Faculty Publications
We report the first measurement of the double-spin asymmetry ALT for charged pion electroproduction in semi-inclusive deep-inelastic electron scattering on a transversely polarized 3He target. The kinematics focused on the valence quark region, 0.1622. The corresponding neutron ALT asymmetries were extracted from the measured 3He asymmetries and proton over 3He cross section ratios using the effective polarization approximation. These new data probe the transverse momentum dependent parton distribution function g1Tq and therefore provide access to quark spin-orbit correlations. Our results indicate a positive azimuthal asymmetry for π- production on 3He and …
Search For A New Gauge Boson In Electron-Nucleus Fixed-Target Scattering By The Apex Experiment, S. Abrahamyan, Timothy Holmstrom, Jefferson Lab
Search For A New Gauge Boson In Electron-Nucleus Fixed-Target Scattering By The Apex Experiment, S. Abrahamyan, Timothy Holmstrom, Jefferson Lab
Chemistry & Physics Faculty Publications
We present a search at the Jefferson Laboratory for new forces mediated by sub-GeV vector bosons with weak coupling α′ to electrons. Such a particle A′ can be produced in electron-nucleus fixed-target scattering and then decay to an e+e- pair, producing a narrow resonance in the QED trident spectrum. Using APEX test run data, we searched in the mass range 175–250 MeV, found no evidence for an A′→e+e- reaction, and set an upper limit of α′/α≃10-6. Our findings demonstrate that fixed-target searches can explore a new, …
Single Spin Asymmetries In Charged Pion Production From Semi-Inclusive Deep Inelastic Scattering On A Transversely Polarized (3)He Target At Q(2)=1.4–2.7 Gev(2), X. Qian, Timothy Holmstrom, Jefferson Lab Hall A Collaboration
Single Spin Asymmetries In Charged Pion Production From Semi-Inclusive Deep Inelastic Scattering On A Transversely Polarized (3)He Target At Q(2)=1.4–2.7 Gev(2), X. Qian, Timothy Holmstrom, Jefferson Lab Hall A Collaboration
Chemistry & Physics Faculty Publications
We report the first measurement of target single spin asymmetries in the semi-inclusive 3He(e,e′π±)X reaction on a transversely polarized target. The experiment, conducted at Jefferson Lab using a 5.9 GeV electron beam, covers a range of 0.1622. The Collins and Sivers moments were extracted from the azimuthal angular dependence of the measured asymmetries. The π± Collins moments for 3He are consistent with zero, except for the π+ moment at x=0.35, which deviates from zero by 2.3σ. While the π- Sivers moments are consistent with zero, the π+ Sivers moments favor …
Exclusive Neutral Pion Electroproduction In The Deeply Virtual Regime, E. Fuchey, Timothy Holmstrom, Jefferson Lab Hall A Collaboration
Exclusive Neutral Pion Electroproduction In The Deeply Virtual Regime, E. Fuchey, Timothy Holmstrom, Jefferson Lab Hall A Collaboration
Chemistry & Physics Faculty Publications
We present measurements of the ep→epπ0 cross section extracted at two values of four-momentum transfer Q2=1.9 GeV2 and Q2=2.3 GeV2 at Jefferson Lab Hall A. The kinematic range allows one to study the evolution of the extracted cross section as a function of Q2 and W. Results are confronted with Regge-inspired calculations and GPD predictions. An intepretation of our data within the framework of semi-inclusive deep inelastic scattering is also discussed.
Measurements Of The Electric Form Factor Of The Neutron Up To Q(2)=3.4 Gev2 Using The Reaction (3)(He)Over-Right-Arrowe((E)Over-Right-Arrow, E ' N)Pp, S. Riordan, Timothy Holmstrom
Measurements Of The Electric Form Factor Of The Neutron Up To Q(2)=3.4 Gev2 Using The Reaction (3)(He)Over-Right-Arrowe((E)Over-Right-Arrow, E ' N)Pp, S. Riordan, Timothy Holmstrom
Chemistry & Physics Faculty Publications
The electric form factor of the neutron was determined from studies of the reaction 3He⃗(e⃗,e′n)pp in quasielastic kinematics in Hall A at Jefferson Lab. Longitudinally polarized electrons were scattered off a polarized target in which the nuclear polarization was oriented perpendicular to the momentum transfer. The scattered electrons were detected in a magnetic spectrometer in coincidence with neutrons that were registered in a large-solid-angle detector. More than doubling the Q2 range over which it is known, we find GEn=0.0236±0.0017(stat)±0.0026(syst), 0.0208±0.0024±0.0019, and 0.0147±0.0020±0.0014 for Q2=1.72, 2.48, and 3.41 GeV2, respectively.
Continued Development Of An Empirical Function For Predicting And Rationalizing Protein–Protein Binding Affinities, Joseph Audie
Continued Development Of An Empirical Function For Predicting And Rationalizing Protein–Protein Binding Affinities, Joseph Audie
Chemistry & Physics Faculty Publications
Here we summarize recent work on the continued development of our fast and simple empirical equation for predicting and structurally rationalizing protein–protein and protein–peptide binding affinities. Our empirical expression consists of six regression-weighted physical descriptors and derives from two key simplifying assumptions: (1) the assumption of rigid-body association and (2) the assumption that all contributions not explicitly considered in the equation make a net contribution to binding of ≈0 kcal. Within the strict framework of rigid-body association, we tested relative binding affinity predictions using our empirical equation against the corresponding experimental binding free energy data for 197 interface alanine mutants. …
Development And Validation Of An Empirical Free Energy Function For Calculating Protein–Protein Binding Free Energy Surfaces, Joseph Audie
Development And Validation Of An Empirical Free Energy Function For Calculating Protein–Protein Binding Free Energy Surfaces, Joseph Audie
Chemistry & Physics Faculty Publications
In a previous paper, we described a novel empirical free energy function that was used to accurately predict experimental binding free energies for a diverse test set of 31 protein–protein complexes to within ≈1.0 kcal. Here, we extend that work and show that an updated version of the function can be used to (1) accurately predict native binding free energies and (2) rank crystallographic, native-like and non-native binding modes in a physically realistic manner. The modified function includes terms designed to capture some of the unfavorable interactions that characterize non-native interfaces. The function was used to calculate one-dimensional binding free …
Deeply Virtual Compton Scattering Off The Neutron, M. Mazouz, Timothy Holmstrom, Jefferson Lab Hall A Collaboration
Deeply Virtual Compton Scattering Off The Neutron, M. Mazouz, Timothy Holmstrom, Jefferson Lab Hall A Collaboration
Chemistry & Physics Faculty Publications
The present experiment exploits the interference between the deeply virtual Compton scattering (DVCS) and the Bethe-Heitler processes to extract the imaginary part of DVCS amplitudes on the neutron and on the deuteron from the helicity-dependent D(e⃗,e′γ)X cross section measured at Q2=1.9 GeV2 and xB=0.36. We extract a linear combination of generalized parton distributions (GPDs) particularly sensitive to Eq, the least constrained GPD. A model dependent constraint on the contribution of the up and down quarks to the nucleon spin is deduced.
A Novel Empirical Free Energy Function That Explains And Predicts Protein–Protein Binding Affinities, Joseph Audie, Suzanne Scarlata
A Novel Empirical Free Energy Function That Explains And Predicts Protein–Protein Binding Affinities, Joseph Audie, Suzanne Scarlata
Chemistry & Physics Faculty Publications
A free energy function can be defined as a mathematical expression that relates macroscopic free energy changes to microscopic or molecular properties. Free energy functions can be used to explain and predict the affinity of a ligand for a protein and to score and discriminate between native and non-native binding modes. However, there is a natural tension between developing a function fast enough to solve the scoring problem but rigorous enough to explain and predict binding affinities. Here, we present a novel, physics-based free energy function that is computationally inexpensive, yet explanatory and predictive. The function results from a derivation …
Investigation Of Proton-Proton Short-Range Correlations Via The (12)C(E,E′Pp) Reaction, R. Shneor, Timothy Holmstrom, Jefferson Hall Lab A Collaboration
Investigation Of Proton-Proton Short-Range Correlations Via The (12)C(E,E′Pp) Reaction, R. Shneor, Timothy Holmstrom, Jefferson Hall Lab A Collaboration
Chemistry & Physics Faculty Publications
We investigated simultaneously the 12C(e,e′p) and 12C(e,e′pp) reactions at Q2=2 (GeV/c)2, xB=1.2, and in an (e, e′p) missing-momentum range from 300 to 600 MeV/c. At these kinematics, with a missing momentum greater than the Fermi momentum of nucleons in a nucleus and far from the delta excitation, short-range nucleon-nucleon correlations are predicted to dominate the reaction. For (9.5±2)% of the 12C(e,e′p) events, a recoiling partner proton was observed back-to-back to the 12C(e,e′p) missing-momentum vector, an experimental signature of correlations.
Search For Σ(5)(0), N(5)(0), And Θ++ Pentaquark States, Y. Qiang, Timothy Holmstrom, Jefferson Lab Hall Collaboration
Search For Σ(5)(0), N(5)(0), And Θ++ Pentaquark States, Y. Qiang, Timothy Holmstrom, Jefferson Lab Hall Collaboration
Chemistry & Physics Faculty Publications
A high-resolution (σinstr.=1.5 MeV) search for narrow states (ΓMeV) with masses of Mx≈1500–1850 MeV in ep→e′K+X,e′K-X, and e′π+X electroproduction at small angles and low Q2 was performed. These states would be candidate partner states of the reported Θ+(1540) pentaquark. No statistically significant signal was observed in any of the channels at 90% C.L. Upper limits on forward production were determined to be between 0.8% and 4.9% of the Λ(1520) production cross section, depending on the channel and the assumed mass and …
Scaling Tests Of The Cross Section For Deeply Virtual Compton Scattering, C. Muñoz Camacho, Timothy Holmstrom, Jefferson Lab Hall A Collaboration
Scaling Tests Of The Cross Section For Deeply Virtual Compton Scattering, C. Muñoz Camacho, Timothy Holmstrom, Jefferson Lab Hall A Collaboration
Chemistry & Physics Faculty Publications
We present the first measurements of the e⃗p→epγ cross section in the deeply virtual Compton scattering (DVCS) regime and the valence quark region. The Q2 dependence (from 1.5 to 2.3 GeV2) of the helicity-dependent cross section indicates the twist-2 dominance of DVCS, proving that generalized parton distributions (GPDs) are accessible to experiment at moderate Q2. The helicity-independent cross section is also measured at Q2=2.3 GeV2. We present the first model-independent measurement of linear combinations of GPDs and GPD integrals up to the twist-3 approximation.
Parity-Violating Electron Scattering From (4)He And The Strange Electric Form Factor Of The Nucleon, K. A. Aniol, Timothy Holmstrom, Happex Collaboration
Parity-Violating Electron Scattering From (4)He And The Strange Electric Form Factor Of The Nucleon, K. A. Aniol, Timothy Holmstrom, Happex Collaboration
Chemistry & Physics Faculty Publications
We have measured the parity-violating electroweak asymmetry in the elastic scattering of polarized electrons from 4He at an average scattering angle ⟨θlab⟩=5.7° and a four-momentum transfer Q2=0.091 GeV2. From these data, for the first time, the strange electric form factor of the nucleon GEs can be isolated. The measured asymmetry of APV=(6.72±0.84(stat)±0.21(syst))×10-6 yields a value ofGEs=-0.038±0.042(stat)±0.010(syst), consistent with zero.
Search For The Lepton-Number-Violating Decay Ξ-→Pμ-Μ-, D. Rajaram, Timothy Holmstrom, Hypercp Collaboration
Search For The Lepton-Number-Violating Decay Ξ-→Pμ-Μ-, D. Rajaram, Timothy Holmstrom, Hypercp Collaboration
Chemistry & Physics Faculty Publications
A sensitive search for the lepton-number-violating decay Ξ-→pμ-μ- has been performed using a sample of ∼109 Ξ- hyperons produced in 800 GeV/c p-Cu collisions. We obtain B(Ξ-→pμ-μ-)<4.0×10-8 at 90% confidence, improving on the best previous limit by 4 orders of magnitude.
Measurement Of The Α Asymmetry Parameter For The Ω-→Λk- Decay, Y. C. Chen, Timothy Holmstrom, Hypercp Collaboration
Measurement Of The Α Asymmetry Parameter For The Ω-→Λk- Decay, Y. C. Chen, Timothy Holmstrom, Hypercp Collaboration
Chemistry & Physics Faculty Publications
We have measured the α parameter of the Ω-→ΛK- decay using data collected with the HyperCP spectrometer during the 1997 fixed-target run at Fermilab. Analyzing a sample of 0.96×106 Ω-→ΛK-, Λ→pπ- decays, we obtain αΩαΛ=[1.33±0.33(stat)±0.52(syst)]×10-2. With the accepted value ofαΛ, αΩ is found to be [2.07±0.51(stat)±0.81(syst)]×10-2.
Evidence For The Decay Σ+→Pμ+Μ-, H. K. Park, Timothy Holmstrom, Hypercp Collaboration
Evidence For The Decay Σ+→Pμ+Μ-, H. K. Park, Timothy Holmstrom, Hypercp Collaboration
Chemistry & Physics Faculty Publications
We report the first evidence for the decay Σ+→pμ+μ- from data taken by the HyperCP (E871) experiment at Fermilab. Based on three observed events, the branching ratio is B(Σ+→pμ+μ-)=[8.6-5.4+6.6(stat)±5.5(syst)]×10-8. The narrow range of dimuon masses may indicate that the decay proceeds via a neutral intermediate state, Σ+→pP0,P0→μ+μ- with a P0 mass of 214.3±0.5 MeV/c2 and branching ratio B(Σ+→pP0,P0→μ+μ-)=[3.1-1.9+2.4(stat)±1.5(syst)]×10-8.
High Statistics Search For The Θ+ (1.54) Pentaquark State, M. J. Longo, Timothy Holmstrom, Hypercp Collaboration
High Statistics Search For The Θ+ (1.54) Pentaquark State, M. J. Longo, Timothy Holmstrom, Hypercp Collaboration
Chemistry & Physics Faculty Publications
We have searched for θ+(1.54)→K0p decays using data from the 1999 run of the HyperCP experiment at Fermilab. We see no evidence for a narrow peak in the KS0p mass distribution near 1.54 GeV/c among 106 000 KS0p candidates, and obtain an upper limit for the fraction of θ+(1.54) to KS0p candidates of
Probability Distribution Of Distance In A Uniform Ellipsoid: Theory And Applications To Physics, Michelle Parry, Ephraim Fischbach
Probability Distribution Of Distance In A Uniform Ellipsoid: Theory And Applications To Physics, Michelle Parry, Ephraim Fischbach
Chemistry & Physics Faculty Publications
A number of authors have previously found the probability Pn(r) that two points uniformly distributed in an n-dimensional sphere are separated by a distance r. This result greatly facilitates the calculation of self-energies of spherically symmetric matter distributions interacting by means of an arbitrary radially symmetric two-body potential. We present here the analogous results for P2(r;ϵ) and P3(r;ϵ) which respectively describe an ellipse and an ellipsoid whose major and minor axes are 2a and 2b. It is shown that …
Blending History With Physics: Acoustic Refraction, Charles D. Ross
Blending History With Physics: Acoustic Refraction, Charles D. Ross
Chemistry & Physics Faculty Publications
A brief overview of atmospheric acoustics is followed by a description of how acoustic refraction can provide an interesting way of blending history with a traditional physics topic.
Orthogonal Polynomial Projectors For The Projector Augmented Wave Method Of Electronic Structure Calculations, N. A. W. Holzwarth, G. E. Matthews, A. R. Tackett, Rodney Dunning
Orthogonal Polynomial Projectors For The Projector Augmented Wave Method Of Electronic Structure Calculations, N. A. W. Holzwarth, G. E. Matthews, A. R. Tackett, Rodney Dunning
Chemistry & Physics Faculty Publications
The projector augmented wave (PAW) method for electronic structure calculations developed by Blochl [Phys. Rev. B 50, 17 953 (1994)] has been very successfully used for density functional studies. It has the numerical advantages of pseudopotential techniques while retaining the physics of all-electron formalisms. We describe a method for generating the set of atom-centered projector and basis functions that are needed for the PAW method. This scheme chooses the shapes of the projector functions from a set of orthogonal polynomials multiplied by a localizing weight factor. Numerical benefits of the scheme result from having direct control of the …
Teaching College Physics To A Blind Student, Michelle Parry, Mark Brazier, Ephraim Fischbach
Teaching College Physics To A Blind Student, Michelle Parry, Mark Brazier, Ephraim Fischbach
Chemistry & Physics Faculty Publications
No abstract provided.
Comparison Of The Projector Augmented-Wave, Pseudopotential, And Linearized Augmented-Plane-Wave Formalisms For Density-Functional Calculations Of Solids, N. A. W. Holzwarth, G. E. Matthews, Rodney Dunning, A. R. Tackett, Y. Zeng
Comparison Of The Projector Augmented-Wave, Pseudopotential, And Linearized Augmented-Plane-Wave Formalisms For Density-Functional Calculations Of Solids, N. A. W. Holzwarth, G. E. Matthews, Rodney Dunning, A. R. Tackett, Y. Zeng
Chemistry & Physics Faculty Publications
The projector augmented-wave (PAW) method was developed by Blöchl as a method to accurately and efficiently calculate the electronic structure of materials within the framework of density-functional theory. It contains the numerical advantages of pseudopotential calculations while retaining the physics of all-electron calculations, including the correct nodal behavior of the valence-electron wave functions and the ability to include upper core states in addition to valence states in the self-consistent iterations. It uses many of the same ideas developed by Vanderbilt in his "soft pseudopotential'' formalism and in earlier work by Blöchl in his "generalized separable potentials,'' and has been successfully …
The Physics Of Motocross, Jeffrey R. Giles, Charles D. Ross
The Physics Of Motocross, Jeffrey R. Giles, Charles D. Ross
Chemistry & Physics Faculty Publications
The article describes how the laws of physics allow the motocross rider to control the flight of a motorcycle.