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Articles 1 - 25 of 25
Full-Text Articles in Physics
Differences Between Regular And Random Order Of Updates In Damage-Spreading Simulations, Thomas Vojta, Michael Schreiber
Differences Between Regular And Random Order Of Updates In Damage-Spreading Simulations, Thomas Vojta, Michael Schreiber
Physics Faculty Research & Creative Works
We investigate the spreading of damage in the three-dimensional Ising model by means of large-scale Monte Carlo simulations. Within the Glauber dynamics we use different rules for the order in which the sites are updated. We find that the stationary damage values and the spreading temperature are different for different update order. In particular, random update order leads to larger damage and a lower spreading temperature than regular order. Consequently, damage spreading in the Ising model is nonuniversal not only with respect to different update algorithms (e.g., Glauber vs heat-bath dynamics) as already known, but even with respect to the …
Production Of Bound Μ⁺Μˉ Systems In Relativistic Heavy Ion Collisions, Ilya F. Ginzburg, Ulrich D. Jentschura, Savely Karshenboim, Frank Krauss, Valery G. Serbo, Gerhard Soff
Production Of Bound Μ⁺Μˉ Systems In Relativistic Heavy Ion Collisions, Ilya F. Ginzburg, Ulrich D. Jentschura, Savely Karshenboim, Frank Krauss, Valery G. Serbo, Gerhard Soff
Physics Faculty Research & Creative Works
Dimuonium (the bound system of two muons, the μ+ μ--atom system) has not been observed yet. In this paper we discuss the electromagnetic production of dimuonium at RHIC and LHC in relativistic heavy ion collisions. The production of parastates is analyzed in the equivalent photon approximation. For the treatment of orthostates, we develop a three-photon formalism. We determine the production rates at RHIC and LHC with an accuracy of a few percent and discuss problems related to the observation of dimuonium.
Charge Exchange From D(N = 2) Atoms To Low-Z Receiver Ions, R. Hoekstra, H. Anderson, F. W. Bliek, M. Von Hellermann, C. F. Maggi, Ronald E. Olson, H. P. Summers
Charge Exchange From D(N = 2) Atoms To Low-Z Receiver Ions, R. Hoekstra, H. Anderson, F. W. Bliek, M. Von Hellermann, C. F. Maggi, Ronald E. Olson, H. P. Summers
Physics Faculty Research & Creative Works
To elucidate the influence on charge-exchange spectroscopy of metastable deuterium donors, the corresponding cross sections for state-selective charge transfer have been calculated using the classical trajectory Monte Carlo method. The cross sections for electron capture from D(n = 2) by fully stripped low-Z ions are contrasted with those for capture from ground state D to indicate the importance of metastable donors. Using the new data, effective emission coefficients for the spectral lines of H-like light impurities used in charge-exchange spectroscopy have been calculated. These results incorporate the presence of excited n = 2 donors in the beam and apply to …
Nonanalytic Magnetization Dependence Of The Magnon Effective Mass In Itinerant Quantum Ferromagnets, Dietrich Belitz, Theodore R. Kirkpatrick, Andrew J. Millis, Thomas Vojta
Nonanalytic Magnetization Dependence Of The Magnon Effective Mass In Itinerant Quantum Ferromagnets, Dietrich Belitz, Theodore R. Kirkpatrick, Andrew J. Millis, Thomas Vojta
Physics Faculty Research & Creative Works
The spin-wave dispersion relation in both clean and disordered itinerant quantum ferromagnets is calculated. It is found that effects akin to weak-localization physics cause the frequency of the spin waves to be a nonanalytic function of the magnetization m. For low frequencies Ω, small wave vectors k, and m→0, the dispersion relation is found to be of the form Ω=const x m1-αk2, with α = (4-d)/2 (2 < d < 4) for disordered systems, and α = (3-d) (1 < d < 3) for clean ones. In d = 4 (disordered) and d = 3 (clean), Ωαm ln (1/m) k2. Experiments to test these predictions are proposed.
Double Differential Cross Section Of Helium Ionization By Proton Impact, A. L. Godunov, V. A. Schipakov, Michael Schulz
Double Differential Cross Section Of Helium Ionization By Proton Impact, A. L. Godunov, V. A. Schipakov, Michael Schulz
Physics Faculty Research & Creative Works
A theoretical analysis for doubly differential cross sections of the single ionization of helium by proton impact as a function of the scattering angle and projectile energy loss is presented. We have used two different theoretical methods. The first approach involved an approximate solution of Faddeev-Merkuriev equations for the three-body Coulomb problem. The second approach employed the expansion of the transition amplitude in the Born series over the projectile-target interaction up to second order. A relation between these two methods was established for the case of fast collisions. It has been demonstrated that, for small scattering angles, the post-collision interaction …
Ultralow-Energy Electrons From Fast Heavy-Ion Helium Collisions: The “Target Cusp“, W. Schmitt, R. Moshammer, F. S.C. O'Rourke, H. Kollmus, L. Sarkadi, R. Mann, S. Hagmann, Ronald E. Olson, J. Ullrich
Ultralow-Energy Electrons From Fast Heavy-Ion Helium Collisions: The “Target Cusp“, W. Schmitt, R. Moshammer, F. S.C. O'Rourke, H. Kollmus, L. Sarkadi, R. Mann, S. Hagmann, Ronald E. Olson, J. Ullrich
Physics Faculty Research & Creative Works
Doubly differential cross sections d2σ / dν ‖ dν⊥ have been obtained by mapping the 3-dimensional velocity space of ultralow- and low-energy electrons \ (1.5 meV < = Ee < = 100 eV \) emitted in singly ionizing 3.6 MeV / u Au53+ on helium collisions. A sharp \ ( ΔEFWHMe⊥< = 22 meV \) asymmetric peak centered at = 0 is observed to emerge at ultralow energies from the strongly forward shifted low-energy electron velocity distribution. The shape of this "target cusp," which is very sensitive on the details of the two-center potential, is in excellent accord with theoretical predictions. © 1998 The American Physical Society.
Essential Role Of Correlations In Governing Charge Transport In Disordered Organic Materials, Sergei V. Novikov, David H. Dunlap, Vasudev M. Kenkre, Paul Ernest Parris, Anatoly V. Vannikov
Essential Role Of Correlations In Governing Charge Transport In Disordered Organic Materials, Sergei V. Novikov, David H. Dunlap, Vasudev M. Kenkre, Paul Ernest Parris, Anatoly V. Vannikov
Physics Faculty Research & Creative Works
The transport of photoinjected charges in disordered organic films is often interpreted using a formula based on a Gaussian disorder model (GDM) that neglects spatial correlations due to charge-dipole interactions, even though such correlations have recently been shown to explain the universal electric field dependence observed in these systems. Based on extensive computer simulations of a 3D disorder model that includes such correlations, we present a new formula for analyzing experiments that accurately describes transport in these materials.
Do Interactions Increase Or Reduce The Conductance Of Disordered Electrons? It Depends!, Thomas Vojta, Frank Epperlein, Michael Schreiber
Do Interactions Increase Or Reduce The Conductance Of Disordered Electrons? It Depends!, Thomas Vojta, Frank Epperlein, Michael Schreiber
Physics Faculty Research & Creative Works
We investigate the influence of electron-electron interactions on the conductance of two-dimensional disordered spinless electrons. We present an efficient numerical method based on diagonalization in a truncated basis of Hartree-Fock states to determine with high accuracy the low-energy properties in the entire parameter space. We find that weak interactions increase the dc conductance in the strongly localized regime while they decrease the dc conductance for weak disorder. Strong interactions always decrease the conductance. We also study the localization of single-particle excitations at the Fermi energy which turns out to be only weakly influenced by the interactions.
Comparison Of Electron-Atom Collision Parameters For S To P Transitions Under Reversal Of Energy Transfer, Max Shurgalin, Andrew James Murray, William R. Macgillivray, M. C. Standage, Don H. Madison, Kathrin D. Winkler, Igor Bray
Comparison Of Electron-Atom Collision Parameters For S To P Transitions Under Reversal Of Energy Transfer, Max Shurgalin, Andrew James Murray, William R. Macgillivray, M. C. Standage, Don H. Madison, Kathrin D. Winkler, Igor Bray
Physics Faculty Research & Creative Works
Inelastic and superelastic electron scattering from the optically prepared 32P3/2 state of sodium has enabled atomic collision parameters to be deduced for the 4S-3P deexcitation and the 3S-3P excitation processes. These data are compared with convergent close coupling and second order distorted wave Born calculations. For excitation, both theories agree with experiment, whereas for deexcitation the close coupling theory is in better agreement. A long-standing proposal relating to the sign of the transferred angular momentum is not supported.
Ionization Of Aligned Rydberg Atoms By Ion Impact, K. R. Cornelius, J. Wang, Ronald E. Olson
Ionization Of Aligned Rydberg Atoms By Ion Impact, K. R. Cornelius, J. Wang, Ronald E. Olson
Physics Faculty Research & Creative Works
The classical trajectory Monte Carlo method has been used to calculate capture and ionization cross sections and final-state electron momentum distributions in H+ + H(n = 25) collisions to show how the collision mechanisms evolve over the range of intermediate projectile speeds v* = vp/ve = 1.0-5.0. A circular Rydberg target was aligned in two orientations defined by the orbital angular momentum vector of the electron being either antiparallel or perpendicular to the incident momentum vector of the projectile. Aligning the target atom in this manner helps us to single out specific collision processes otherwise obscured in a randomly oriented …
Evidence Of Initial-State Two-Center Effects For (E, 2e) Reactions, Sindu P. Jones, Don H. Madison
Evidence Of Initial-State Two-Center Effects For (E, 2e) Reactions, Sindu P. Jones, Don H. Madison
Physics Faculty Research & Creative Works
Coincidence, or (e, 2e), measurements of electron-impact ionization of atoms have established that the largest values of triply differential cross sections are obtained in collisions involving small momentum transfer to the target. Absolute measurements for these reactions are now available for hydrogen at 54.4-eV impact energy, and relative data have recently been reported at 27.2 eV. Previous theoretical works have concentrated on employing asymptotically correct two-center wave functions for the final state, leaving the initial state described by the Born approximation. Here we report results for which asymptotically correct two-center wave functions are used for both the initial and final …
Shakeoff Measurement Of The L = 3 States Of Barium, Heider N. Ereifej, J. Greg Story
Shakeoff Measurement Of The L = 3 States Of Barium, Heider N. Ereifej, J. Greg Story
Physics Faculty Research & Creative Works
Isolated core excitation was used to produce low-energy continuum electrons in the l = 3 angular momentum state of barium. Data were taken over a region of energy that coincided with the energy of the 6p3/2nf doubly excited states. Analysis of the data using multichannel quantum defect theory allowed the measurement of the widths of the 6p3/2nf states and the energy-dependent phase of the continuum electronic wave functions due to interaction with the doubly excited states. The phase of the continuum electrons is shown to vary continuously with energy, due to the anomalously broad widths of …
Protein Fragmentation Due To Slow Highly Charged Ion Impact, Christiane Ruehlicke, Dieter Schneider, Markus Schneider, Robert D. Dubois, Rod Balhorn
Protein Fragmentation Due To Slow Highly Charged Ion Impact, Christiane Ruehlicke, Dieter Schneider, Markus Schneider, Robert D. Dubois, Rod Balhorn
Physics Faculty Research & Creative Works
We present first results of experiments on the fragmentation of biomolecules using highly charged heavy ions. Fragmentation and modification of oligopeptides, such as dimerization and attachment of ionic salt components, have been observed by means of mass spectrometry. Plasmid DNA molecules were imaged with an atomic force microscope after ion irradiation and profound molecular damage was found.
Low-Field Hopping Among Randomly-Distributed Sites With Uncorrelated Energetic Disorder, Paul Ernest Parris
Low-Field Hopping Among Randomly-Distributed Sites With Uncorrelated Energetic Disorder, Paul Ernest Parris
Physics Faculty Research & Creative Works
The low-field mobility μ of a small concentration of charge carriers hopping among a random distribution of transport sites is studied, as a function of the mean interparticle spacing ρ and the temperature T, for model systems having different site-energy distribution functions. For a uniform density of states our calculations show that the mobility obeys empirical scaling laws similar to those found in the theory of variable-range hopping. For a binary distribution of site energies we observe a crossover as a function of site density between trap-limited conduction and trap-mediated conduction. For a Gaussian density of states our results confirm …
Nature Of Resonant Photoemission In Gd, Shubhra R. Mishra, Thomas K. Cummins, George Daniel Waddill, W. J. Gammon, Gerrit V. Van Der Laan, Kyle W. Goodman, James G. Tobin
Nature Of Resonant Photoemission In Gd, Shubhra R. Mishra, Thomas K. Cummins, George Daniel Waddill, W. J. Gammon, Gerrit V. Van Der Laan, Kyle W. Goodman, James G. Tobin
Physics Faculty Research & Creative Works
The phenomenon of resonant photoemission happens when, in addition to a direct photoemission channel, a second indirect channel opens up as the absorption threshold of a core level is crossed. A massive increase in emission cross section can occur, but the nature of the process remains clouded. Using novel magnetic linear dichroism in photoelectron spectroscopy experiments and theoretical calculations, we can now clearly demonstrate that temporal matching of the processes as well as energy matching is a requirement for true "resonant photoemission.".
Next-To-Leading Order Qcd Corrections For The B⁰B⁰ Mixing With An Extended Higgs Sector, Jorg Org Urban, Frank Krauss, Ulrich D. Jentschura, Gerhard Soff
Next-To-Leading Order Qcd Corrections For The B⁰B⁰ Mixing With An Extended Higgs Sector, Jorg Org Urban, Frank Krauss, Ulrich D. Jentschura, Gerhard Soff
Physics Faculty Research & Creative Works
We present a calculation of the B0B0 mixing including next-to-leading order (NLO) QCD corrections within the Two-Higgs Doublet Model (2HDM). The QCD corrections at NLO are contained in the factor denoted by η2 which modifies the result obtained at the lowest order of perturbation theory. In the Standard Model case, we confirm the results for η2 obtained by Buras, Jamin and Weisz [Nucl. Phys, B 347 (1990) 491]. The factor η2 is gauge and renormalization prescription invariant and it does not depend on the infrared behaviour of the theory, which constitutes an important test …
Nonlinear Field Dependence Of The Mobility Of A Charge Subjected To A Superposition Of Dichotomous Stochastic Potentials, A. M. Kenkre, Marek Kus, David H. Dunlap, Paul Ernest Parris
Nonlinear Field Dependence Of The Mobility Of A Charge Subjected To A Superposition Of Dichotomous Stochastic Potentials, A. M. Kenkre, Marek Kus, David H. Dunlap, Paul Ernest Parris
Physics Faculty Research & Creative Works
A general prescription is presented to address a large variety of forms of the nonlinear dependence of the static charge mobility on the applied electric field. The system consists of a classical charge subjected to an arbitrarily strong steady state electric field and to a stochastic potential consisting of a linear superposition of an unlimited number of dichotomous potentials in one-dimensional space. It is shown that the nonlinear mobility can be calculated for arbitrary forms of the density function of the individual dichotomous components of the stochastic potential. Specific cases of physical interest are analyzed. One of them provides a …
Particulate Sizing And Emission Indices For A Jet Engine Exhaust Sampled At Cruise, Donald E. Hagen, Philip D. Whitefield, J. Paladino, Max B. Trueblood, H. Lilenfeld
Particulate Sizing And Emission Indices For A Jet Engine Exhaust Sampled At Cruise, Donald E. Hagen, Philip D. Whitefield, J. Paladino, Max B. Trueblood, H. Lilenfeld
Physics Faculty Research & Creative Works
Particle size and emission indices measurements for jet engines, primarily the Rolls Royce RB211 engines on a NASA 757 aircraft are reported. These data were used to estimate the fraction of fuel sulfur that was converted to particulates. These measurements were made in-situ with the sampling aircraft several kilometers behind the source. Some complimentary ground measurements on the same source aircraft and engines are also reported. Significant differences are seen between the ground observations and the in-situ observations, indicating that plume processes are changing the aerosol' s characteristics.
Sources And Chemistry Of Noₓ In The Upper Troposphere Over The United States, Lyatt Jaegle, Daniel J. Jacob, Yuhua Wang, Andrew J. Weinheimer, Brian A. Ridley, Teresa L. Campos, Glen W. Sachse, Donald E. Hagen
Sources And Chemistry Of Noₓ In The Upper Troposphere Over The United States, Lyatt Jaegle, Daniel J. Jacob, Yuhua Wang, Andrew J. Weinheimer, Brian A. Ridley, Teresa L. Campos, Glen W. Sachse, Donald E. Hagen
Physics Faculty Research & Creative Works
The origin of NOx in the upper troposphere over the central United States is examined using aircraft observations obtained during the SUCCESS campaign in April–May of 1996. Correlations between NOy (sum of NOx and its oxidation products) and CO at 8–12 km altitude indicate that NOx originates primarily from convective transport of polluted boundary layer air. Lightning and aircraft emissions appear to be only minor sources of NOx. Chemical steady state model calculations constrained by local observations of NO underestimate the measured NOx/NOy concentration ratio at 8–12 km altitude by a …
Particulate Sizing And Emission Indices For A Jet Engine Exhaust Sampled At Cruise, Donald E. Hagen, Philip D. Whitefield, Jonathan D. Paladino, Max B. Trueblood
Particulate Sizing And Emission Indices For A Jet Engine Exhaust Sampled At Cruise, Donald E. Hagen, Philip D. Whitefield, Jonathan D. Paladino, Max B. Trueblood
Physics Faculty Research & Creative Works
Particle size and emission indices measurements for jet engines, primarily the Rolls Royce RB211 engines on a NASA 757 aircraft are reported. These data were used to estimate the fraction of fuel sulfur that was converted to particulates. These measurements were made in-situ with the sampling aircraft several kilometers behind the source. Some complimentary ground measurements on the same source aircraft and engines are also reported. Significant differences are seen between the ground observations and the in-situ observations, indicating that plume processes are changing the aerosol's characteristics.
Solvable Model Of Two-Dimensional Dilaton Gravity Coupled To A Massless Scalar Field, Marco Cavaglia
Solvable Model Of Two-Dimensional Dilaton Gravity Coupled To A Massless Scalar Field, Marco Cavaglia
Physics Faculty Research & Creative Works
We present a solvable model of two-dimensional dilaton-gravity coupled to a massless scalar field. We locally integrate the field equations and briefly discuss the properties of the solutions. For a particular choice of the coupling between the dilaton and the scalar field the model can be interpreted as the two-dimensional effective theory of 2+1 cylindrical gravity minimally coupled to a massless scalar field.
Ionization Dynamics In Fast Ion-Atom Collisions. Ii. Final-State Momentum Distributions Of The Ionization Products In Collisions Of He With Bare Carbon Ions, Lokesh C. Tribedi, P. Richard, Y. D. Wang, C. D. Lin, Ronald E. Olson, L. Gulyas
Ionization Dynamics In Fast Ion-Atom Collisions. Ii. Final-State Momentum Distributions Of The Ionization Products In Collisions Of He With Bare Carbon Ions, Lokesh C. Tribedi, P. Richard, Y. D. Wang, C. D. Lin, Ronald E. Olson, L. Gulyas
Physics Faculty Research & Creative Works
We have used the energy and angular distributions of the low-energy electron emission cross sections from the preceding paper [Lokesh C. Tribedi et al., Phys. Rev. A 58, 3619 (1998)] to derive the doubly differential final-state longitudinal momentum distributions of the electrons, recoil ions, and projectiles in ion-atom ionization for [Formula Presented] The complementary nature of the electron spectroscopy and the recoil-ion momentum spectroscopy have been investigated using a formulation based on three-body kinematics to explore the ionization dynamics in detail. The influence of the three-body ionization as well as the binary-encounter processes on the recoil-ion (and projectile) longitudinal momentum …
Effect Of Exchange Interactions At Antiferromagnetic/Ferromagnetic Interfaces On Exchange Bias And Coercivity, D. Dimitrov, Shufeng Zhang
Effect Of Exchange Interactions At Antiferromagnetic/Ferromagnetic Interfaces On Exchange Bias And Coercivity, D. Dimitrov, Shufeng Zhang
Physics Faculty Research & Creative Works
We report on the correlation between unidirectional and uniaxial anisotropy in exchange-biased ferromagnetic Permalloy layers. The dependence of exchange bias and coercivity on temperature and the antiferromagnetic and ferromagnetic layer thickness was studied and compared with the predictions of different theoretical models. A thorough explanation of the experimental data is provided by theoretical extension of Malozemoff's model. © 1998 The American Physical Society.
Complete Single-Ionization Momentum Spectra For Strong Perturbation Collisions, Ronald E. Olson, C. J. Wood, H. Schmidt-Böcking, R. Moshammer, J. Ullrich
Complete Single-Ionization Momentum Spectra For Strong Perturbation Collisions, Ronald E. Olson, C. J. Wood, H. Schmidt-Böcking, R. Moshammer, J. Ullrich
Physics Faculty Research & Creative Works
The combination of recoil ion and ionized electron momentum spectroscopy provides an unparalleled method to investigate the details of ion-atom collision dynamics in kinematically complete experiments. To predict single ionization scattering behavior at the level now realized by experiment, the classical trajectory three-body Monte Carlo method has been used to obtain complete momenta information for the ionized electron, recoil ion, and projectile in the collision plane defined by the incident projectile and outgoing recoil ion. Strongly coupled systems were considered where the charge state of the projectile divided by the speed of the collision [Formula Presented] is greater than unity. …
Aerosol Particle Scavenging By Fog And Haze Droplets, Josef Podzimek
Aerosol Particle Scavenging By Fog And Haze Droplets, Josef Podzimek
Physics Faculty Research & Creative Works
Droplet imprints in thin gelatin layers have been used for the investigation of coarse particles embedded in fog (haze) droplets in comparison to interstitial particles. Droplet samples were taken in less polluted regions of Missouri and Illinois and also in more polluted marine-urban environment in Italy. Considerable differences in particle size distribution and particle location inside the droplets have been found in samples collected on four sampling sites. The deduced relationships can be applied for the description of the aerosol scavenging process in fogs. The pollution of fog (haze) droplets may be related to the droplet mean volume radius and …