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Articles 1  18 of 18
FullText Articles in Physical Sciences and Mathematics
Neutron Diffraction And Mössbauer Effect Study Of Several Nd₂Fe₁₇₋ₓAlₓ Solid Solutions, William B. Yelon, H. Xie, Gary J. Long, Oran Allan Pringle, Fernande Grandjean, K. H. J. Buschow
Neutron Diffraction And Mössbauer Effect Study Of Several Nd₂Fe₁₇₋ₓAlₓ Solid Solutions, William B. Yelon, H. Xie, Gary J. Long, Oran Allan Pringle, Fernande Grandjean, K. H. J. Buschow
Physics Faculty Research & Creative Works
Aluminumsubstituted Nd_{2}Fe_{17x}Al_{x} solid solutions with x=2.30, 4.44, 6.13, 8.00, and 9.40 have been studied by neutron diffraction and Mössbauer spectroscopy. A Rietveld analysis of the neutron scattering indicates that the aluminum atoms have a high initial affinity for the 18h site, show a high affinity for the 6c site at high aluminum concentrations, and are absent from the 9d site at all aluminum concentrations. The Mössbauer spectra show a maximum in both the maximum and weighted average hyperfine field for x≅2. This indicates that the lattice expansion which ...
Comment On "Critical Behavior Of The Coulomb Glass", Thomas Vojta, Michael Schreiber
Comment On "Critical Behavior Of The Coulomb Glass", Thomas Vojta, Michael Schreiber
Physics Faculty Research & Creative Works
No abstract provided.
Cosmological And Wormhole Solutions In LowEnergy Effective String Theory, Mariano Cadoni, Marco Cavaglia
Cosmological And Wormhole Solutions In LowEnergy Effective String Theory, Mariano Cadoni, Marco Cavaglia
Physics Faculty Research & Creative Works
We derive and study a class of cosmological and wormhole solutions of lowenergy effective string field theory. We consider a general fourdimensional string effective action where moduli of the compactified manifold and the electromagnetic field are present. The cosmological solutions of the twodimensional effective theory obtained by dimensional reduction of the former are discussed. In particular we demonstrate that the twodimensional theory possesses a scalefactor duality invariance. Eucidean fourdimensional instantons describing the nucleation of the baby universes are found and the probability amplitude for the nucleation process given.
Quantum Electromagnetic Wormholes And Geometrical Description Of The Electric Charge, Marco Cavaglia
Quantum Electromagnetic Wormholes And Geometrical Description Of The Electric Charge, Marco Cavaglia
Physics Faculty Research & Creative Works
I present and discuss a class of solutions of the WheelerDeWitt equation describing wormholes generated by coupling of gravity to the electromagnetic field for KantowskiSachs and Bianchi typeI spacetimes. Since the electronic charge can be viewed as electric lines of force trapped in a finite region of spacetime, these solutions can be interpreted as the quantum corresponding to the EinsteinRosenMisnerWheeler electromagnetic geon.
NeutronDiffraction And Mössbauer Effect Study Of The Tb₂Fe₁₇₋ₓAlₓ Solid Solutions, Gaya Kanishka Marasinghe, Sanjay R. Mishra, Oran Allan Pringle, Gary J. Long, Zhong Bo Hu, William B. Yelon, Fernande Grandjean, D. P. Middleton, K. H. J. Buschow
NeutronDiffraction And Mössbauer Effect Study Of The Tb₂Fe₁₇₋ₓAlₓ Solid Solutions, Gaya Kanishka Marasinghe, Sanjay R. Mishra, Oran Allan Pringle, Gary J. Long, Zhong Bo Hu, William B. Yelon, Fernande Grandjean, D. P. Middleton, K. H. J. Buschow
Physics Faculty Research & Creative Works
The magnetic properties of a series of Tb_{2}Fe_{17x}Al_{x} solid solutions, with nominal x compositions of 0, 2, 3, 4, 5, 6, 7, and 8, have been studied by neutron diffraction and Mössbauer spectroscopy. Neutrondiffraction data indicate that the compounds all crystallize with the Th_{2}Zn_{17} structure and that the aluminum atoms are excluded from the 9d site and show a distinct preference for the 6c site only for an aluminum content greater than 6. The unitcell volume increases by approximately 1% per aluminum atom substituted in the formula unit. The magnetic moment per ...
Differential Double Excitation Cross Sections In ProtonHelium Collisions Studied By EnergyLoss Spectroscopy, W. T. Htwe, Tibor Vajnai, M. Barnhart, A. D. Gaus, Michael Schulz
Differential Double Excitation Cross Sections In ProtonHelium Collisions Studied By EnergyLoss Spectroscopy, W. T. Htwe, Tibor Vajnai, M. Barnhart, A. D. Gaus, Michael Schulz
Physics Faculty Research & Creative Works
We have measured ion energyloss spectra for 150 keV protonhelium collisions as a function of the projectile scattering angle. From the data we obtained double excitation cross sections differential in the proton scattering angle as well as the ratios of both double excitation and single ionization to single excitation. In these ratios pronounced peak structures are observed at about 0.7 mrad. Two alternative interpretations of these peak structures are offered: They may be due to binary collisions between the projectile and the target electrons, or they could be a manifestation of an interference between different transition amplitudes leading to ...
LandauZener Treatment Of IntensityTuned Multiphoton Resonances Of Potassium, J. Greg Story, D. I. Duncan, Thomas F. Gallagher
LandauZener Treatment Of IntensityTuned Multiphoton Resonances Of Potassium, J. Greg Story, D. I. Duncan, Thomas F. Gallagher
Physics Faculty Research & Creative Works
When exposed to intense light of ~580 nm, the ground state of K shifts up in energy, passing through two photon resonances with Rydberg states, and finally crossing the twophoton ionization limit. We have used laser pulses of varying duration to study the nature of the population transfer from the ground state to the excited state due to the intensitytuned resonances encountered during the rising edge of the pulse. A dynamic Floquet approach in which the resonances are treated as avoided crossings of the Floquet energy levels is used to model the population transfer and gives excellent agreement with the ...
Effect Of Carrier Gas Pressure On Condensation In A Supersonic Nozzle, Barbara Ellen Wyslouzil, Gerald Wilemski, M. G. Beals, Michael B. Frish
Effect Of Carrier Gas Pressure On Condensation In A Supersonic Nozzle, Barbara Ellen Wyslouzil, Gerald Wilemski, M. G. Beals, Michael B. Frish
Physics Faculty Research & Creative Works
Supersonic nozzle experiments were performed with a fixed water or ethanol vapor pressure and varying amounts of nitrogen to test the hypothesis that carrier gas pressure affects the onset of condensation. Such an effect might occur if nonisothermal nucleation were important under conditions of excess carrier gas in the atmospheric pressure range, as has been suggested by Ford and Clement [J. Phys. A 22, 4007 (1989)]. Although a small increase was observed in the condensation onset temperature as the stagnation pressure was reduced from 3 to 0.5 atm, these changes cannot be attributed to any nonisothermal effects. The pulsed ...
NeutronDiffraction Study Of ΓFe At High Pressure, Oran Allan Pringle, Rafael Calvo, R. E. Parra
NeutronDiffraction Study Of ΓFe At High Pressure, Oran Allan Pringle, Rafael Calvo, R. E. Parra
Physics Faculty Research & Creative Works
Facecenteredcubic iron (γFe) coherently precipitated in a single crystal of Cu has been studied by neutron diffraction at high pressures up to 0.9 GPa and in the temperature range from about 5 to 110 K. It undergoes antiferromagnetic ordering at 67±2 K at ambient pressure. The ordering temperature T_{N} monotonically decreases with increasing pressure following a relation T_{N}(K)=6712.8p  11.1p^{2}  6.17p^{3}, where p is in units of GPa. The change of T_{N} in γFe is discussed in terms of the volume change caused by pressurization or by alloying.
Critical Correlations And Susceptibilities In The RandomField Spherical Model, Thomas Vojta, Michael Schreiber
Critical Correlations And Susceptibilities In The RandomField Spherical Model, Thomas Vojta, Michael Schreiber
Physics Faculty Research & Creative Works
We investigate the behavior of the correlation function and the susceptibility of the randomfield spherical model at the critical point. In particular we calculate the critical exponents η and η describing the divergences of the susceptibility and its disconnected part, respectively. In the case of shortrange interactions we obtain η=η=0. For powerlaw interactions Uij~rijσ we find η=1/2η=D+2σ (for D<σ
A Magnetic, Neutron Diffraction, And Mössbauer Spectral Study Of Nd₂Fe₁₅Ga₂ And The Tb₂Fe₁₇₋ₓGaₓ Solid Solutions, Zhong Bo Hu, William B. Yelon, Sanjay R. Mishra, Gary J. Long, Oran Allan Pringle, D. P. Middleton, K. H. J. Buschow, Fernande Grandjean
A Magnetic, Neutron Diffraction, And Mössbauer Spectral Study Of Nd₂Fe₁₅Ga₂ And The Tb₂Fe₁₇₋ₓGaₓ Solid Solutions, Zhong Bo Hu, William B. Yelon, Sanjay R. Mishra, Gary J. Long, Oran Allan Pringle, D. P. Middleton, K. H. J. Buschow, Fernande Grandjean
Physics Faculty Research & Creative Works
An xray diffraction study of the substitution of gallium in Tb _{2}Fe_{17} to form the Tb_{2}Fe_{17x}Ga_{x} solid solutions indicates that the compounds adopt the rhombohedral Th_{2}Zn_{17} structure. The unit cell volume and the aaxis lattice parameter increase linearly with increasing gallium content. The caxis lattice parameter increases linearly from x=0 to 6 and then decreases between x=7 and 8. Magnetic studies show the Curie temperature increases by ~150° above that of Tb_{2}Fe_{17} to reach a maximum between x=3 and 4, and then decreases with ...
Differential Transfer Ionization Cross Sections For 50175Kev ProtonHelium Collisions, S. W. Bross, S. M. Bonham, A. D. Gaus, Jerry Peacher, Tibor Vajnai, Michael Schulz, Horst SchmidtBocking
Differential Transfer Ionization Cross Sections For 50175Kev ProtonHelium Collisions, S. W. Bross, S. M. Bonham, A. D. Gaus, Jerry Peacher, Tibor Vajnai, Michael Schulz, Horst SchmidtBocking
Physics Faculty Research & Creative Works
We have measured coincidences between neutralized projectiles and He recoil ions for 50175keV protonhelium collisions. From the data we obtained transfer ionization (TI) cross sections differential in the projectile scattering angle. Laboratory scattering angles range from 0 to 2.0 mrad. The experimental method allowed separation of the postcollision charge states of the target atoms. The ratio of the cross sections for TI to the sum of TI and single capture, F, is presented as a function of projectile scattering angle. Comparison is made to previous measurements of this ratio where data is available. The differential cross sections are compared ...
Anisotropic Wormhole: Tunneling In Time And Space, Marco Cavaglia, Vittorio De Alfaro, Fernado De Felice
Anisotropic Wormhole: Tunneling In Time And Space, Marco Cavaglia, Vittorio De Alfaro, Fernado De Felice
Physics Faculty Research & Creative Works
We discuss the structure of a gravitational Euclidean instanton obtained through coupling of gravity to electromagnetism. This Euclidean solution can be interpreted as a tunneling to a hyperbolic space (baby universe) or alternatively as a static wormhole that joins two asymptotically flat spaces of a ReissnerNordström type solution.
Channel Closing In Multiphoton Ionization Of Mg, J. Greg Story, D. I. Duncan, Thomas F. Gallagher
Channel Closing In Multiphoton Ionization Of Mg, J. Greg Story, D. I. Duncan, Thomas F. Gallagher
Physics Faculty Research & Creative Works
Experimental data are presented showing the channel closing of fourphoton ionization of Mg. It is shown that, for circularly polarized light, the ionization versus intensity spectra exhibit sharp breaks from the normal I^{4} intensity dependence at the critical intensity where the channel closing occurs. Above the critical intensity, the population of Rydberg states which survives the laser pulse is observed. The residual Rydberg population is found to be greatly reduced for linearly polarized light due to the relatively large probability of ionization of the lowangularmomentum Rydberg states. The data are in good agreement with a model which includes averaging ...
SpinResolved (E,2e) Coincidences For Heavy RareGas Targets, Stephenie J. Jones, Don H. Madison, G. Friedrich Hanne
SpinResolved (E,2e) Coincidences For Heavy RareGas Targets, Stephenie J. Jones, Don H. Madison, G. Friedrich Hanne
Physics Faculty Research & Creative Works
It has been well established that the Coulomb force alone can produce spindependent effects for electronimpact excitation of heavy raregas atoms if the incident electrons are spin polarized and the final J state of the atom is resolved. This effect has become known as the finestructure effect. Here we demonstrate that the same type of effect may be expected for electronimpact ionization.
Generalized Coulomb Gap In The Spherical Version Of A Lattice Model Of Disordered And Correlated Localized Particles, Thomas Vojta, Michael Schreiber
Generalized Coulomb Gap In The Spherical Version Of A Lattice Model Of Disordered And Correlated Localized Particles, Thomas Vojta, Michael Schreiber
Physics Faculty Research & Creative Works
We study the spherical version of a model of localized particles in a random potential which are subject to a powerlaw interaction U_{ij} ~ r_{ij}^{σ}. In the case of a repulsive interaction with σ = 1 the model is identical to the spherical version of the Coulombglass model of disordered localized electrons. The use of continuous variables instead of discrete occupation numbers of the sites renders the model exactly solvable. Analytic results are obtained for the free energy and for the singleparticle density of states (DOS) as an example for singleparticle properties. The zerotemperature DOS shows a hard gap ...
Correlated TwoElectron Wave Functions Of Any Symmetry, Christopher Bottcher, David R. Schultz, Don H. Madison
Correlated TwoElectron Wave Functions Of Any Symmetry, Christopher Bottcher, David R. Schultz, Don H. Madison
Physics Faculty Research & Creative Works
Using a procedure originally due to Hylleraas, a convenient expansion in coupled spherical harmonics which terminates in a very small number of terms is applied to the treatment of fully correlated twoelectron wave functions of any symmetry (total angular momentum, parity, and spin). Coupled equations satisfied by these wave functions are derived which are well adapted to computation and which we discretize on a numerical lattice utilizing the basisspline collocation method. Use of this method which relies on very flexible basis functions is intended to facilitate subsequently the consideration of timedependent rearrangments such as autoionization, photoionization, and electronimpact excitation and ...
The Spatial Evolution Of Particles Diffusing In The Presence Of Randomly Placed Traps, David H. Dunlap, Randall A. Laviolette, Paul Ernest Parris
The Spatial Evolution Of Particles Diffusing In The Presence Of Randomly Placed Traps, David H. Dunlap, Randall A. Laviolette, Paul Ernest Parris
Physics Faculty Research & Creative Works
The evolution of a particle undergoing a continuoustime random walk in the presence of randomly placed imperfectly absorbing traps is studied. At long times, the spatial probability distribution becomes strongly localized in a sequence of trapfree regions. The subsequent intermittent transfer of the survival probability from small trapfree regions to larger trapfree regions is described as a timedirected variable range hopping among localized eigenstates in the Lifshitz tail. An asymptotic expression for the configurational average of the spatial distribution of surviving particles is obtained based on this description. The distribution is an exponential function of distance which expands superdiffusively, with ...