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Articles 31 - 60 of 63
Full-Text Articles in Physics
Split Quaterionic Representation Of Sdym (Su(1,1) Instantons In S2- × S2+, Sungwook Lee, Khin Maung Maung
Split Quaterionic Representation Of Sdym (Su(1,1) Instantons In S2- × S2+, Sungwook Lee, Khin Maung Maung
Faculty Publications
Using split‐quaternions, we find explicit SDYM SU(1,1) instanton solutions in S2- × S2+ which is the conformal compactification of the semi‐Euclidean 4‐spacetime R2+2 of split signature (-,-,+,+). It is also shows that SDYM and ASDYM fields in S2- × S2+ can be described as simple split-quaternionic 2-forms.
Parametrizations Of Inclusive Cross Sections For Pion Production In Proton-Proton Collisions. Ii. Comparison To New Data, John W. Norbury, Lawrence W. Townsend
Parametrizations Of Inclusive Cross Sections For Pion Production In Proton-Proton Collisions. Ii. Comparison To New Data, John W. Norbury, Lawrence W. Townsend
Faculty Publications
A set of new, precise data have recently been made available by the NA49 Collaboration for charged pion production in proton-proton and proton-Carbon reactions at 158 GeV. The current paper compares this new data to five currently available arithmetic parameterizations. Although a precise fit is not expected, two of the parameterizations do not work very well but the other three are able to provide a moderately good, but not precise fit to the proton-proton data. The best two of these three parameterizations are scaled to the proton-Carbon data and again provide a moderately good, but not precise fit.
Threshold Meson Production And Cosmic Ray Transport, John W. Norbury, Lawrence W. Townsend, Ryan B. Norman
Threshold Meson Production And Cosmic Ray Transport, John W. Norbury, Lawrence W. Townsend, Ryan B. Norman
Faculty Publications
An interesting accident of nature is that the peak of the cosmic ray spectrum, for both protons and heavier nuclei, occurs near the pion production threshold. The Boltzmann transport equation contains a term which is the cosmic ray flux multiplied by the cross section. Therefore when considering pion and kaon production from proton - proton reactions, small cross sections at low energy can be as important as larger cross sections at higher energy. This is also true for subthreshold kaon production in nuclear collisions, but not for subthreshold pion production.
Differential Cross Sections For Electromagnetic Dissociation, John W. Norbury, Anne Adamczyk
Differential Cross Sections For Electromagnetic Dissociation, John W. Norbury, Anne Adamczyk
Faculty Publications
Differential cross; sections for electromagnetic dissociation in nucleus-nucleus collisions are calculated. The kinetic energy distributions is parameterized with a Boltzmann distribution and the angular distribution is assumed isotropic in the projectile frame. In order to be useful for three-dimensional transport codes, these cross sections are available in both the projectile and lab frames. Comparison between theory and experiment is good. The formalism applies to single and multiple nucleon removal, a particle removal, and fission in electromagnetic reactions of nuclei. (c) 2006 Elsevier B.V. All rights reserved.
Parameterized Total Cross Sections For Pion Production In Nuclear Collisions, John W. Norbury, Lawrence W. Townsend
Parameterized Total Cross Sections For Pion Production In Nuclear Collisions, John W. Norbury, Lawrence W. Townsend
Faculty Publications
Total inclusive cross sections for neutral and charged pion production in proton–nucleus and nucleus–nucleus reactions have been calculated and compared to experiment. Nucleon–nucleon theoretical cross sections have been scaled up to nuclear collisions using a scaling factor similar to (APAT)2/3, where AP and AT are the nucleon numbers of the projectile and target nuclei. Variations in the power of this scaling factor have been studied and a good fit to experiment is obtained with a small modification of the power. Theoretical cross sections are written in a form that is very …
Pair Production From Nuclear Collisions And Cosmic Ray Transport, John W. Norbury
Pair Production From Nuclear Collisions And Cosmic Ray Transport, John W. Norbury
Faculty Publications
Modern cosmic ray transport codes, that are capable of use for a variety of applications, need to include all significant atomic, nuclear and particle reactions at a variety of energies. Lepton pair production from nucleus-nucleus collisions has not been included in transport codes to date. Using the methods of Baur, Bertulani and Baron, the present report provides estimates of electron positron pair production cross sections for nuclei and energies relevant to cosmic ray transport. It is shown that the cross sections are large compared to other typical processes such as single neutron removal due to strong or electromagnetic interactions. Therefore, …
Induced Matter: Curved N-Manifolds Encapsulated In Riemann-Flat N+1 Dimensional Space, Harry I. Ringermacher, Lawrence R. Mead
Induced Matter: Curved N-Manifolds Encapsulated In Riemann-Flat N+1 Dimensional Space, Harry I. Ringermacher, Lawrence R. Mead
Faculty Publications
Liko and Wesson have recently introduced a new five-dimensional induced matter solution of the Einstein equations, a negative curvature Robertson-Walker space embedded in a Riemann-flat five-dimensional manifold. We show that this solution is a special case of a more general theorem prescribing the structure of certain N+1 dimensional Riemann-flat spaces which are all solutions of the Einstein equations. These solutions encapsulate N-dimensional curved manifolds. Such spaces are said to "induce matter" in the submanifolds by virtue of their geometric structure alone. We prove that the N-manifold can be any maximally symmetric space. (c) 2005 American Institute of Physics.
Relative Charge Transfer Cross Section From Rb(4d), M.H. Shah, H.A. Camp, M.L. Trachy, X. Fléchard, M.A. Gearba, H. Nguyen, R. Brédy, S.R. Lundeen, B.D. Depaola
Relative Charge Transfer Cross Section From Rb(4d), M.H. Shah, H.A. Camp, M.L. Trachy, X. Fléchard, M.A. Gearba, H. Nguyen, R. Brédy, S.R. Lundeen, B.D. Depaola
Faculty Publications
Relative charge transfer cross section measurements for the excited state Rb (4d) with 7 keV Na+ is reported. The specific channels reported as Na+ + Rb (4d5/2) → Na (nl) + Rb+, where the dominant transfer cross sections channels were nl = 3d and 4s. Using a combination of a magneto-optical trap and recoil ion momentum spectroscopy (MOTRIMS methodology), the cross sections were measured relative to the previously studied Na+ + Rb (5s, 5p) systems at the same collision energy.
Relaxation To Native Conformation Of A Bond-Fluctuating Protein Chain With Hydrophobic And Polar Nodes, Johan Bjursell, Ras B. Pandey
Relaxation To Native Conformation Of A Bond-Fluctuating Protein Chain With Hydrophobic And Polar Nodes, Johan Bjursell, Ras B. Pandey
Faculty Publications
The conformation and dynamics of a protein chain with hydrophobic and polar nodes are examined by the bond-fluctuation model using Monte Carlo simulations on a cubic lattice. The minimal (nearest neighbor) interaction leads to standard (self-avoiding walk) conformation, i.e., the scaling of the radius of gyration Rg with the molecular weight N Rg ∝ Nγ with γ ≃ 3/5/ Specific interactions with longer range and higher strength are needed to approach the native globular conformations with γ < 3/5. Relaxation into the globular ground state shows a weak power-law decay, i.e., Rg ∝ t-α, α ~ 0.06-0.12.
Diode Laser Microwave Induced Plasma Cavity Ringdown Spectrometer: Performance And Perspective, Chuji Wang, Sudip P. Koirala, Susan T. Scherrer, Yixiang Duan, Christopher B. Winstead
Diode Laser Microwave Induced Plasma Cavity Ringdown Spectrometer: Performance And Perspective, Chuji Wang, Sudip P. Koirala, Susan T. Scherrer, Yixiang Duan, Christopher B. Winstead
Faculty Publications
Recent studies combining an atmospheric-pressure plasma source (inductively coupled plasma or microwave induced plasma) with cavity ringdown spectroscopy (plasma-CRDS) have indicated significant promise for ultra-sensitive elemental measurements. Initial plasma-CRDS efforts employed an inductively coupled plasma as the atomization source and a pulsed laser system as the light source. In an effort to improve the portability and reduce the cost of the system for application purposes, we have modified our approach to include a compact microwave induced plasma and a continuous wave diode laser. A technique for controlling the coupling of the continuous wave laser to the ringdown cavity has been …
Density And Conformation With Relaxed Substrate, Bulk, And Interface In Electrophoretic Deposition Of Polymer Chains, F.W. Bentrem, J. Xie, Ras B. Pandey
Density And Conformation With Relaxed Substrate, Bulk, And Interface In Electrophoretic Deposition Of Polymer Chains, F.W. Bentrem, J. Xie, Ras B. Pandey
Faculty Publications
Characteristics of relaxed density profile and conformation of polymer chains are studied by a Monte Carlo simulation on a discrete lattice in three dimensions using different segmental (kink-jump (K), crank-shaft (C), reptation (R)) dynamics. Three distinct density regimes, substrate, bulk, and interface, are identified. With the KC segmental dynamics, we find that the substrate coverage grows with a power law, ds∝tγ with a field (E) dependent non-universal exponent γ=0.23+0.7E. The bulk volume fraction db and the substrate polymer density (ds) increases with the field with power-laws (db …
Density Profile And Flow Of Miscible Fluid With Dissimilar Constituent Masses, Ras B. Pandey, D. Stauffer, R. Seyfarth, Luis A. Cueva, J.F. Gettrust, Warren Wood
Density Profile And Flow Of Miscible Fluid With Dissimilar Constituent Masses, Ras B. Pandey, D. Stauffer, R. Seyfarth, Luis A. Cueva, J.F. Gettrust, Warren Wood
Faculty Publications
A computer simulation model is used to study the density profile and flow of a miscible gaseous fluid mixture consisting of differing constituent masses (m(A) = m(B)/3) through an open matrix. The density profile is found to decay with the height proportional to exp(-m(A(B))h), consistent with the barometric height law. The flux density shows a power-law increase proportional to (p(c) - p)(a) with mu similar or equal to 2.3 at the porosity 1 - p above the pore percolation threshold 1 - p(c). (C) 2002 Elsevier Science B.V. All rights reserved.
Interface Relaxation In Electrophoretic Deposition Of Polymer Chains: Effects Of Segmental Dynamics, Molecular Weight, And Field, Frank W. Bentrem, Jun Xie, Ras B. Pandey
Interface Relaxation In Electrophoretic Deposition Of Polymer Chains: Effects Of Segmental Dynamics, Molecular Weight, And Field, Frank W. Bentrem, Jun Xie, Ras B. Pandey
Faculty Publications
Using different segmental dynamics and relaxation, characteristics of the interface growth is examined in an electrophoretic deposition of polymer chains on a three (2+1)-dimensional discrete lattice with a Monte Carlo simulation. Incorporation of faster modes such as crankshaft and reptation movements along with the relatively slow kink-jump dynamics seems crucial in relaxing the interface width. As the continuously released polymer chains are driven (via segmental movements) and deposited, the interface width W grows with the number of time steps t, W∝tβ, (β ~0.4-0.8), which is followed by its saturation to a steady-state value Ws …
Concentration Gradient, Diffusion, And Flow Through Open Porous Medium Near Percolation Threshold Via Computer Simulations, Ras B. Pandey, J.F. Gettrust, D. Stauffer
Concentration Gradient, Diffusion, And Flow Through Open Porous Medium Near Percolation Threshold Via Computer Simulations, Ras B. Pandey, J.F. Gettrust, D. Stauffer
Faculty Publications
The interacting lattice gas model is used to simulate fluid flow through an open percolating porous medium with the fluid entering at the source-end and leaving from the opposite end. The shape of the steady-state concentration profile and therefore the gradient field depends on the porosity (p). The root mean square (rms) displacements of fluid and its constituents (tracers) show a drift power-law behavior, R∝t in the asymptotic regime (t→∞). The flux current density (j) is found to scale with the porosity according to, j∝(Δp)β with Δp …
Comment On "Observation Of Superluminal Behaviors In Wave Propagation", Harry Ringermacher, Lawrence R. Mead
Comment On "Observation Of Superluminal Behaviors In Wave Propagation", Harry Ringermacher, Lawrence R. Mead
Faculty Publications
No abstract provided.
Characteristics Of Driven Polymer Surfaces: Growth And Roughness, Grace M. Foo, Ras B. Pandey
Characteristics Of Driven Polymer Surfaces: Growth And Roughness, Grace M. Foo, Ras B. Pandey
Faculty Publications
Using a Monte Carlo simulation, the growth and roughness characteristics of polymer surfaces are studied in 2 + 1 dimensions. Kink-jump and reptation dynamics are used to move polymer chains under a driving field where they deposit onto an impenetrable attractive wall. Effects of field (E) chain length (Lc) and the substrate size (L) on the growing surfaces are studied. In low field, the interface width (W) shows a crossover from one power-law growth in time (W∼tβ1) to another (W∼tβ2 …
Polymerization-Induced Phase Separation, J.C. Lee
Polymerization-Induced Phase Separation, J.C. Lee
Faculty Publications
A molecular dynamics simulation is performed to study the kinetics of microphase separation in a polymer-dispersed-liquid-crystal forming process. An equimolar mixture of monomers and liquid crystal molecules are thermalized in a well mixed state. The monomers are then polymerized at the same temperature. The end product is a spanning gel with liquid crystal molecules aggregating in droplets here and there. The peak position of the equal-time structure function suggests that the growth of the droplets may be described with t-0.23. The small growth exponent is just one of several features which may be attributed to the growing elastic …
Discrete-To-Continuum Simulation Approach To Polymer Chain Systems: Subdiffusion, Segregation, And Chain Folding, Grace M. Foo, Ras B. Pandey
Discrete-To-Continuum Simulation Approach To Polymer Chain Systems: Subdiffusion, Segregation, And Chain Folding, Grace M. Foo, Ras B. Pandey
Faculty Publications
A discrete-to-continuum approach is introduced to study the static and dynamic properties of polymer chain systems with a bead-spring chain model in two dimensions. A finitely extensible nonlinear elastic potential is used for the bond between the consecutive beads with the Lennard-Jones (LJ) potential with smaller (Rc=21/6σ=0.95) and larger (Rc=2.5σ=2.1) values of the upper cutoff for the nonbonding interaction among the neighboring beads. We find that chains segregate at temperature T =1.0 with Rc=2.1 and remain desegregated with Rc=0.95. At low temperature (T=0.2), chains become folded, …
Electrophoretic Deposition Of Polymer Chains On An Adsorbing Surface In (2+1) Dimensions: Conformational Anisotropy And Nonuniversal Coverage, Grace M. Foo, Ras B. Pandey
Electrophoretic Deposition Of Polymer Chains On An Adsorbing Surface In (2+1) Dimensions: Conformational Anisotropy And Nonuniversal Coverage, Grace M. Foo, Ras B. Pandey
Faculty Publications
Electrophoretic deposition of polymer chains flowing in a (2 + 1)-dimensional system is studied by computer simulations. Steady-state surface coverage θj is found to decay with the chain's length, i.e., θj∼Lc-a with a nonuniversal exponent α≃0.0-0.9 depending on the magnitude of driving field and temperature. Conformational crossover occurs for chains from a surface or wall to an adjacent bulk region with different scaling exponents for their longitudinal and transverse spread.
Nonuniversal Scaling And Conformational Crossover Of Polymer Chains In An Electrophoretic Deposition, Grace M. Foo, Ras B. Pandey
Nonuniversal Scaling And Conformational Crossover Of Polymer Chains In An Electrophoretic Deposition, Grace M. Foo, Ras B. Pandey
Faculty Publications
A computer simulation model of electrodeposition of polymer chains on an impenetrable wall is used to evaluate the power-law scaling exponents (νx(y)) for the longitudinal and transverse spread, Rgx(y)∼Lcνx(y); we find that the exponents νx(y) depend on the field strength, i.e., they are nonuniversal. A conformational crossover is observed for the transverse spread from the bulk with νy≃1/3-2/3 to the wall with νy≃2/3-1. A similar crossover also occurs for the longitudinal component of Rg but with an opposite trend, i.e., magnitude of νx is larger …
Crossover Dynamics For Polymer Simulation In Porous Media, V. Yamakov, D. Stauffer, A. Milchev, G.M. Foo, R.B. Pandey
Crossover Dynamics For Polymer Simulation In Porous Media, V. Yamakov, D. Stauffer, A. Milchev, G.M. Foo, R.B. Pandey
Faculty Publications
Off-lattice Monte Carlo simulations show anomalous diffusion at intermediate times without a clear Rouse regime, for the motion of chains through a random porous medium.
Conformation Of Interacting Polymer Chains: Effects Of Temperature, Bias, Polymer Concentration, And Porosity, Grace M. Foo, Ras B. Pandey
Conformation Of Interacting Polymer Chains: Effects Of Temperature, Bias, Polymer Concentration, And Porosity, Grace M. Foo, Ras B. Pandey
Faculty Publications
The conformations of interacting polymer chains driven by a biased field in heterogeneous media are studied using Monte Carlo simulations in three dimensions. In addition to excluded volume, a nearest-neighbor interaction is considered with polymer-polymer repulsion and polymer-solvent attraction. Two types of heterogeneous media are considered: (i) a homogeneous-annealed system consisting of mobile polymer chains and solvents and (ii) quenched porous media, generated by adding a random distribution of quenched barriers. Effects of polymer concentration (p), bias (B), temperature (T), and porosity (ps) on the magnitude of the radius of gyration (Rg) of the …
Computer Simulation Study Of The Permeability Of Driven Polymers Through Porous Media, Grace M. Foo, Ras B. Pandey
Computer Simulation Study Of The Permeability Of Driven Polymers Through Porous Media, Grace M. Foo, Ras B. Pandey
Faculty Publications
A computer simulation model is used to study the permeability of polymer chains driven by a biased flow field through a porous medium in two dimensions. The chains are modeled by constrained self-avoiding walks, which reptate through the heterogeneous medium with a biased probability imposed by the driven field. A linear response description is used to evaluate an effective permeability. The permeability σ shows an unusual decay behavior on reducing the porosity ps. We find that the permeability decreases on increasing the bias above a characteristic value Bc. This characteristic bias shows a logarithmic decay on …
Computer-Simulation Study Of The Permeability Of A Porous Sediment Model, Ras B. Pandey, Jeffrey L. Becklehimer
Computer-Simulation Study Of The Permeability Of A Porous Sediment Model, Ras B. Pandey, Jeffrey L. Becklehimer
Faculty Publications
A computer simulation model is used to study the permeability of fluid flow through porous media generated by the random distribution of the sediments in a two-dimensional lattice. Fluid particles are confined to pore space with the sediments forming the rigid barriers at the pore boundaries. An interaction between the fluid particles and the pore substrate is introduced to incorporate the additional drag in the pore space. The pressure gradient causes a bias to drive the fluid and the Metropolis algorithm is used to hop the fluid particles. The permeability of this system is studied as a function of the …
Driven Front And Interface Of A Fluid-Flow Model In 2+1-Dimensions, Michael J. Leaseburg, Ras B. Pandey
Driven Front And Interface Of A Fluid-Flow Model In 2+1-Dimensions, Michael J. Leaseburg, Ras B. Pandey
Faculty Publications
Computer simulations are performed to study the motion of the front and the growth of the interface width in a model of fluid flow driven by a biased field in 2+1 dimensions. The initial motion of the front is diffusive, which is followed by a nondiffusive power-law behavior in the long-time regime; the power-law exponent is nonuniversal, varying with the strength of the driven field. The growth of the interface width saturates in the asymptotic time regime. The saturated width W scales with both the driven field B as well as the transverse length L of the sample, leading to …
Driven Diffusion Of Particles, First-Passage Front, And Interface Growth, R. Bidaux, Ras B. Pandey
Driven Diffusion Of Particles, First-Passage Front, And Interface Growth, R. Bidaux, Ras B. Pandey
Faculty Publications
We study a computer-simulation model for driven particles on a discrete lattice where a fraction p of the lattice sites is randomly occupied by frozen impurities (barriers), and an imposed bias governs the particles’ hopping through the lattice. These particles (the carriers) are initially released from a source of wetting fluid from one end of the lattice in order to wet and the dry lattice on their trails. We study the transport of particles, frontier of their trail, and the growth of the interface between the wet and dry regions as a function of the biased field and the number …
Driven Diffusion, Kawasaki Dynamics, Mixing, And Spatial Ordering In An Interacting Lattice-Gas, Yan He, Ras B. Pandey
Driven Diffusion, Kawasaki Dynamics, Mixing, And Spatial Ordering In An Interacting Lattice-Gas, Yan He, Ras B. Pandey
Faculty Publications
Kawasaki dynamics is used to study the transport properties of a nonequilibrium steady state system of interacting lattice gas of oppositely charged particles in a linear gradient field in two dimensions. The rms displacements show unusual nondiffusive transport. The effective conductivity varies with the temperature which deviates from the Arrhenius law and depends on the range of interaction. Density of a fully mixed state decays with temperature with a power law. Onset of spatial ordering occurs in a certain temperature range at a fixed range of interaction.
Ordering Processes In Porous-Media, J.C. Lee
Ordering Processes In Porous-Media, J.C. Lee
Faculty Publications
The ordering processes in a binary liquid mixture confined in a Vycor type of pore and at temperatures near the transition temperature of the pure system Tc are studied using a kinetic Ising model and the method of Monte Carlo simulations. The results for dynamics show quite clear signatures of the pore width but no notable difference between T > Tc and T < Tc. In the results for statics, the small angle part of the structure factor increases rapidly as T approaches Tc in the one-phase region. This suggests the onset of ordering but the fluctuation of …
Evidence Of A Nondiffusive Transport In A Monodisperse Screened Coulomb System By A Molecular-Dynamics Simulation, Michael Wild, Ras B. Pandey
Evidence Of A Nondiffusive Transport In A Monodisperse Screened Coulomb System By A Molecular-Dynamics Simulation, Michael Wild, Ras B. Pandey
Faculty Publications
A molecular-dynamics simulation is carried out for particles (tracers) interacting with a screened Coulomb potential in three dimensions. A phase transition is observed from a liquid to an fcc solid on reducing the temperature at a fixed density, consistent with previous studies. In the liquid phase, the variation of the rms displacement Rtr of the charged particles with time seems to depend on the density and the temperature. In the short-time regime, the effective exponent k for the subdiffusive power-law behavior, i.e., Rtr∼tk, decreases on increasing the density and lowering the temperature. A crossover from …
Transport Properties Of An Interacting Lattice Gas Model In A Charge Density Gradient By Monte Carlo Simulation, Ras B. Pandey, Songping Gao
Transport Properties Of An Interacting Lattice Gas Model In A Charge Density Gradient By Monte Carlo Simulation, Ras B. Pandey, Songping Gao
Faculty Publications
A two-dimensional lattice is considered with a linear charge-density gradient produced by a charge source at one end and a sink at the opposite end. A fraction p of the lattice sites are occupied by mobile particles that interact only with neighboring particles and empty sites (the substrate) and carry charges from source to sink; the charge neutrality of the whole lattice is maintained. The root-mean-square (rms) displacement of the particles (i.e., the tracers) and their effective conductivity for the charge transport are studied as a function of temperature and concentration p. The rms displacement shows a crossover from diffusion …