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Physics Faculty Research & Creative Works

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Articles 1261 - 1290 of 1959

Full-Text Articles in Physical Sciences and Mathematics

Neutron Diffraction Analysis Of Melt Spun 2:14:1 Type (Ndpr)-Fe-B Compounds With Ti And Zr Additions, Z. Chu, William B. Yelon, B. M. Ma, Z. Chen, D. N. Brown May 2002

Neutron Diffraction Analysis Of Melt Spun 2:14:1 Type (Ndpr)-Fe-B Compounds With Ti And Zr Additions, Z. Chu, William B. Yelon, B. M. Ma, Z. Chen, D. N. Brown

Physics Faculty Research & Creative Works

There has been continued technological and research interest in Nd 2Fe 14B-based compounds due to their excellent intrinsic magnetic properties [(BH) max*∼64MGOe,Ha∼73kOe]. It is found that Ti and Zr substitution in Nd 2Fe 14B leaves its magnetic properties largely unaffected. We have carried out neutron diffraction studies on Zr and Ti substituted 2:14:1 compounds. Three specimens of melt spun alloys of compositions (Nd 0.75Pr 0.25) 12Fe 80B 8, (Nd 0.75Pr 0.25) 8.4Fe 79.7Ti 4.7B 7.2 and (Nd 0.75Pr 0.25) 9.2Fe 79.2Ti 2 …

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Saturation Of Charge Carrier Velocity With Increasing Electric Fields: Theoretical Investigations For Pure Organic Crystals, Vasudev M. Kenkre, Paul Ernest Parris May 2002

Saturation Of Charge Carrier Velocity With Increasing Electric Fields: Theoretical Investigations For Pure Organic Crystals, Vasudev M. Kenkre, Paul Ernest Parris

Physics Faculty Research & Creative Works

Should one expect injected charge carrier velocities to saturate as the applied electric field is increased simply because of the nonparabolicity of bands? Does the apparent saturation observed in recent experiments in hydrocarbon crystals signify, as supposed in some current interpretations of the data, that the carrier motion is coherent or bandlike and that the disappearance of the saturation at higher temperatures is indicative of a crossover from coherent to incoherent motion? These questions are addressed with the help of general theoretical investigations involving Drude-like considerations, quantum kinetic equations, and a Fokker-Planck analysis.

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Orbital Ordering In Paramagnetic Lamno₃ And Kcuf₃, Julia E. Medvedeva, Michael A. Korotin, Vladimir I. Anisimov, Arthur J. Freeman May 2002

Orbital Ordering In Paramagnetic Lamno₃ And Kcuf₃, Julia E. Medvedeva, Michael A. Korotin, Vladimir I. Anisimov, Arthur J. Freeman

Physics Faculty Research & Creative Works

Ab initio studies of the stability of orbital ordering, its coupling to magnetic structure and its possible origins (electron-phonon and/or electron-electron interactions) are reported for two perovskite systems, LaMnO3 and KCuF3. We present an average spin state calculational scheme that allowed us to treat a paramagnetic state and to succesfully describe the experimental magnetic or orbital phase diagram of both LaMnO3 and KCuF3 in crystal structures when the Jahn-Teller distortions are neglected. Hence, we conclude that the orbital ordering in both compounds is purely electronic in origin.

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Projectile And Target Ionization In Mev U⁻¹ Collisions Of Xe Ions With N2, Ronald E. Olson, R. L. Watson, V. Horvat, K. E. Zaharakis Apr 2002

Projectile And Target Ionization In Mev U⁻¹ Collisions Of Xe Ions With N2, Ronald E. Olson, R. L. Watson, V. Horvat, K. E. Zaharakis

Physics Faculty Research & Creative Works

Experimental cross sections are presented for single and multiple electron stripping from Xe18+ projectiles in collisions with N2 at energies 2.0-9.3 MeV u-1. The data are compared to 2-30 MeV u-1 n-body classical trajectory Monte Carlo calculations that explicitly include electrons on both centres. Two-centre electron-electron (e-e) and electron-screened nuclear interactions contribute to the ionization reactions. The computations are in reasonable accord for the total stripping cross section but underestimate the higher stages of multiple electron loss. An energy deposition model gives improved agreement with experiment. The energy dependence of the total stripping cross section …

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Three-Body Dynamics In Hydrogen Ionization By Fast Highly Charged Particles, J. Fiol, Ronald E. Olson Apr 2002

Three-Body Dynamics In Hydrogen Ionization By Fast Highly Charged Particles, J. Fiol, Ronald E. Olson

Physics Faculty Research & Creative Works

Electron double and triple differential cross sections are calculated as a function of projectile momentum transfer for ionization of ground and excited state hydrogen by 3.6 MeV u-1 C6+ and Au53+ ions. These three-body Coulomb systems are investigated using the classical-trajectory Monte Carlo and continuum distorted wave methods that incorporate all interactions including the nuclear-nuclear potential. The calculations allow one to distinguish cross section features associated with three collision mechanisms. The first is due to distance collisions that lead primarily to a binary interaction between the projectile and electron. The second is a strong three-body interaction by …

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Local Versus Nonlocal Order-Parameter Field Theories For Quantum Phase Transitions, Dietrich Belitz, Theodore R. Kirkpatrick, Thomas Vojta Apr 2002

Local Versus Nonlocal Order-Parameter Field Theories For Quantum Phase Transitions, Dietrich Belitz, Theodore R. Kirkpatrick, Thomas Vojta

Physics Faculty Research & Creative Works

General conditions are formulated that allow us to determine which quantum phase transitions in itinerant electron systems can be described by a local Landau-Ginzburg-Wilson (LGW) theory solely in terms of the order parameter. A crucial question is the degree to which the order parameter fluctuations couple to other soft modes. Three general classes of zero-wave-number order parameters, in the particle-hole spin-singlet and spin-triplet channels and in the particle-particle channel, respectively, are considered. It is shown that the particle-hole spin-singlet class does allow for a local LGW theory, while the other two classes do not. The implications of this result for …

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Electron-Impact Excitation From The (4p⁵5s) Metastable States Of Krypton, Arati K. Dasgupta, Klaus Bartschat, D. Vaid, Alexei N. Grum-Grzhimailo, Don H. Madison, Milan Blaha, John L. Giuliani Apr 2002

Electron-Impact Excitation From The (4p⁵5s) Metastable States Of Krypton, Arati K. Dasgupta, Klaus Bartschat, D. Vaid, Alexei N. Grum-Grzhimailo, Don H. Madison, Milan Blaha, John L. Giuliani

Physics Faculty Research & Creative Works

Theoretical results from multistate semirelativistic Breit-Pauli R-matrix calculations and two first-order distorted-wave calculations are presented for electron-impact excitation of krypton from the (4p55s) J = 0,2 metastable states to the (4p55s) and (4p55p) manifolds. Except for a few cases, in which the method to account for relativistic effects becomes surprisingly critical, fair overall agreement between the predictions from the various theoretical models is achieved for intermediate and high energies. However, significant discrepancies remain with the few available experimental data.

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Doubly Differential Electron-Emission Spectra In Single And Multiple Ionization Of Noble-Gas Atoms By Fast Highly-Charged-Ion Impact, Tom Kirchner, Laszlo Gulyas, Robert Moshammer, Michael Schulz, Joachim Hermann Ullrich Apr 2002

Doubly Differential Electron-Emission Spectra In Single And Multiple Ionization Of Noble-Gas Atoms By Fast Highly-Charged-Ion Impact, Tom Kirchner, Laszlo Gulyas, Robert Moshammer, Michael Schulz, Joachim Hermann Ullrich

Physics Faculty Research & Creative Works

Low-energy electron emission spectra are studied in collisions of 3.6 MeV/amu Au53+ ions with neon and argon atoms for well-defined degrees of target ionization. We calculate doubly differential cross sections as functions of the recoil-ion charge state in the continuum-distorted-wave with eikonal initial-state approximation using a binomial analysis of the total and differential ionization probabilities, and compare them with the present and with previously published experimental data. Very good agreement is found for the single-ionization spectra and for double ionization of neon, while some discrepancies are observed in the spectra for double and triple ionization of argon.

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Structural Investigation Of Ag-Pd Clusters Synthesized With The Radiolysis Method, Carmen M. Doudna, Massimo F. Bertino, Akira T. Tokuhiro Mar 2002

Structural Investigation Of Ag-Pd Clusters Synthesized With The Radiolysis Method, Carmen M. Doudna, Massimo F. Bertino, Akira T. Tokuhiro

Physics Faculty Research & Creative Works

The structure of Ag-Pd clusters synthesized with the radiolysis method was investigated. The clusters were characterized with transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS). These techniques showed that the synthesized clusters had face-centered cubic (fcc) crystalline structure and were free of contamination.

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Three-Body Dynamics In The Ionization Of Hydrogen By Positron Impact, J. Fiol, Ronald E. Olson Mar 2002

Three-Body Dynamics In The Ionization Of Hydrogen By Positron Impact, J. Fiol, Ronald E. Olson

Physics Faculty Research & Creative Works

Three-body dynamics are investigated for single ionization of hydrogen by 50 and 100 eV positron impact. The momentum distributions of the electron, the projectile and the recoiling target nucleus are investigated. The present results show that, despite the large mass of the target nucleus, it actively participates in the dynamics of the ionizing collisions. In particular, a strong correlation between the positron and the recoil-ion momenta is found, which is especially important at the lower collision energy of this study.

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Superconducting Studies On The Ho (Ba2-Y Lay) Cu3 Oz (0 ≤ Y ≤0.5) System, Amish G. Joshi, S. K. Malik, William B. Yelon Mar 2002

Superconducting Studies On The Ho (Ba2-Y Lay) Cu3 Oz (0 ≤ Y ≤0.5) System, Amish G. Joshi, S. K. Malik, William B. Yelon

Physics Faculty Research & Creative Works

Structural and superconducting properties of the Ho(Ba2-yLay)Cu3Oz system, with 0.0≤y≤0.5, have been investigated through neutron diffraction, resistivity and magnetization studies. It is observed that on increasing La in Ho(Ba2-yLay)Cu3Oz, the oxygen occupancy at the O(1) site (at 0, 1/2, 0 in space group Pmmm) decreases and that at the O(5) (1/2, 0, 0) site increases, resulting in a decrease in orthorhombicity. As Ba2+ is replaced by La3+, the oxygen content per formula unit increases beyond 7. The variation in the superconducting transition …

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Depression Of Superconducting Transition Temperature Due To Pr In The (La2.5-X Prxnd0.5) Caba3cu7oz System, Darshan C. Kundaliya, Reeta Vij, R. G. Kulkarni, William B. Yelon, S. K. Malik Mar 2002

Depression Of Superconducting Transition Temperature Due To Pr In The (La2.5-X Prxnd0.5) Caba3cu7oz System, Darshan C. Kundaliya, Reeta Vij, R. G. Kulkarni, William B. Yelon, S. K. Malik

Physics Faculty Research & Creative Works

Structural and superconducting properties of (La2.5-xPrxNd0.5)CaBa3Cu7Oz (0≤x≤0.7) compounds have been investigated. Neutron diffraction studies reveal that these crystallize in the triple-perovskite structure (space group P4/mmm) with an oxygen content of 16.6 per formula unit nearly independent of the Pr content. The superconducting transition temperature, Tc, of x = 0 compound is ∼ 79K and decreases almost linearly with increasing x to ∼ 42K for x = 0.7. In order to see if the depression of Tc due to Pr can be compensated by Ca, we examined the compounds (La …

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Intermixing Of Fe At Cu(1)-Chain And Cu(2)-Plane Sites In Fesr2ycu2o7.30 System: A Neutron Diffraction And Mössbauer Spectroscopic Study, V. P.S. Awana, S. K. Malik, William B. Yelon, J. Lindén, M. Karppinen, H. Yamauchi Mar 2002

Intermixing Of Fe At Cu(1)-Chain And Cu(2)-Plane Sites In Fesr2ycu2o7.30 System: A Neutron Diffraction And Mössbauer Spectroscopic Study, V. P.S. Awana, S. K. Malik, William B. Yelon, J. Lindén, M. Karppinen, H. Yamauchi

Physics Faculty Research & Creative Works

The presently prepared FeSr2YCu2Oz (Fe-1212) sample crystallizes in a tetragonal structure (space group P4/mmm). Rietveld structural refinement of the room temperature neutron diffraction data reveal that nearly half of the Fe remains at the Cu(1)-chain site while the other half goes to the Cu(2)-plane site in the nominal Cu(1)Sr2YCu(2)2O7 or Cu-1212 structure. In this compound, Cu is distributed over the chain and plane sites appropriately. Oxygen content of the present Fe-1212 sample, as determined from the oxygen occupancies, is 7.30(2) per formula unit. Existence of Fe at the two different …

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Neutron Diffraction, Nmr And Magneto-Transport Properties In The Pr0.6sr0.4mno3 Perovskite Manganite, W. Boujelben, M. Ellouze, A. Cheikh-Rouhou, J. Pierre, Q. Cai, William B. Yelon, K. Shimizu, C. Dubourdieu Feb 2002

Neutron Diffraction, Nmr And Magneto-Transport Properties In The Pr0.6sr0.4mno3 Perovskite Manganite, W. Boujelben, M. Ellouze, A. Cheikh-Rouhou, J. Pierre, Q. Cai, William B. Yelon, K. Shimizu, C. Dubourdieu

Physics Faculty Research & Creative Works

A Pr0.6Sr0.4MnO3 powder was synthesized by the solid-state reaction method at 1400°C. Magnetic measurements show that our sample exhibits a paramagnetic-ferromagnetic transition with decreasing temperature. The paramagnetic to ferromagnetic transition is followed by a decrease of the magnetization below 100 K. The Curie temperature TC is found to be 310 K. Electrical studies show a semiconductor-metallic transition at Tρ=260 K. Our sample displays a magnetoresistance effect in 8 T of about 45% below 250 K. Neutron diffraction studies show that our sample crystallizes in the orthorhrombic system with Pnma space group at room temperature and …

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Comment On "A Convergent Series For The Qed Effective Action", Darrell R. Lamm, Sree Ram Valluri, Ulrich D. Jentschura, Ernst Joachim Weniger Feb 2002

Comment On "A Convergent Series For The Qed Effective Action", Darrell R. Lamm, Sree Ram Valluri, Ulrich D. Jentschura, Ernst Joachim Weniger

Physics Faculty Research & Creative Works

No abstract provided.

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Electric Field Gradients In S-, P-, And D-Metal Diborides And The Effect Of Pressure On The Band Structure And TC In Mgb₂, Nadezhda I. Medvedeva, Alexander L. Ivanovskii, Julia E. Medvedeva, Arthur J. Freeman, Dmitrii L. Novikov Feb 2002

Electric Field Gradients In S-, P-, And D-Metal Diborides And The Effect Of Pressure On The Band Structure And TC In Mgb₂, Nadezhda I. Medvedeva, Alexander L. Ivanovskii, Julia E. Medvedeva, Arthur J. Freeman, Dmitrii L. Novikov

Physics Faculty Research & Creative Works

Results of full-potential linear muffin-tin orbital generalized gradient approximation calculations of the band structure and boron electric field gradients (EFG's) for the new medium-Tc superconductor MgB2 and related diborides MB2, M = Be, Al, Sc, Ti, V, Cr, Mo, and Ta are reported. The boron EFG variations are found to be related to specific features of their band structure and particularly to the M-B hybridization. The strong charge anisotropy at the B site in MgB2 is completely defined by the valence electrons - a property which sets MgB2 apart from other diborides. The boron …

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Simultaneous Projectile-Target Ionization: A Novel Approach To (E, 2e) Experiments On Ions, Holger Kollmus, Robert Moshammer, Ronald E. Olson, Siegbert Hagmann, Michael Schulz, Joachim Hermann Ullrich Feb 2002

Simultaneous Projectile-Target Ionization: A Novel Approach To (E, 2e) Experiments On Ions, Holger Kollmus, Robert Moshammer, Ronald E. Olson, Siegbert Hagmann, Michael Schulz, Joachim Hermann Ullrich

Physics Faculty Research & Creative Works

A kinematically complete experiment for simultaneous ionization of a projectile and target has been performed for 3.6 MeV/u C2+ on He collisions measuring the final vector momenta of the He1+ recoil ion and of two electrons (projectile, target) in coincidence with the emerging C3+ projectile. The feasibility of an event-by-event separation of the various reaction channels, among them the ionization of C2+ by the interaction with a quasifree target electron, is demonstrated in agreement with six-body classical trajectory Monte Carlo calculations, paving the way to kinematically complete electron-ion scattering experiments.

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Effect Of Deuterium Absorption On The Heavy-Fermion Compound Updin, P. Raj, A. Sathyamoorthy, S. K. Dhar, Z. Chu, William B. Yelon, S. K. Malik Jan 2002

Effect Of Deuterium Absorption On The Heavy-Fermion Compound Updin, P. Raj, A. Sathyamoorthy, S. K. Dhar, Z. Chu, William B. Yelon, S. K. Malik

Physics Faculty Research & Creative Works

The heavy fermion compound UPdIn is found to absorb deuterium without disproportionation to yield (formula presented) Magnetization, heat capacity, x-ray, and neutron-diffraction measurements have been carried out to probe the structural and magnetic properties of this deuteride. It is found that deuterium absorption results in a highly anisotropic lattice expansion, without changing the (formula presented)-type hexagonal structure of the parent compound. The magnetic ordering temperature is enhanced to 80 K and the low-temperature uranium moment to (formula presented) from their corresponding values of 21 K and (formula presented) respectively, in the parent compound. Neutron-diffraction studies on the deuteride reveal antiferromagnetic …

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Quantum Gravitational Corrections To Black Hole Geometries, Marco Cavaglia, A. Fabbri Jan 2002

Quantum Gravitational Corrections To Black Hole Geometries, Marco Cavaglia, A. Fabbri

Physics Faculty Research & Creative Works

We calculate perturbative quantum gravity corrections to eternal two-dimensional black holes. We estimate the leading corrections to the AdS2 black hole entropy and determine the quantum modification of N-dimensional Schwarzschild spacetime.

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Effect Of Oxygen Vacancies On The Magnetic Structure Of The La₀.₆Sr₀.₄Feo3-Δ Perovskite: A Neutron Diffraction Study, Zili Chu, William B. Yelon, Jinbo Yang, William Joseph James, Harlan U. Anderson, Yixiang Xie, Satish K. Malik Jan 2002

Effect Of Oxygen Vacancies On The Magnetic Structure Of The La₀.₆Sr₀.₄Feo3-Δ Perovskite: A Neutron Diffraction Study, Zili Chu, William B. Yelon, Jinbo Yang, William Joseph James, Harlan U. Anderson, Yixiang Xie, Satish K. Malik

Physics Faculty Research & Creative Works

Magnetic interactions in perovskite compounds of the type La1-xSrxMO3-δ (M=3d transition such as Mn and Fe) are presumed to arise through a super exchange between 3d electrons of the magnetic ions via oxygen orbitals. The magnetic structure of La0.6Sr0.4FeO3-δ has been studied with neutron diffraction. Oxygen vacancies were created by annealing samples under various gases including N2, air and mixtures of CO/CO2. All La0.6Sr0.4FeO3-δ compounds maintain the rhombohedral structure (space group R3̄c). The air- or oxygen-annealed samples have almost no oxygen …

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Electrical And Magnetotransport Properties Of Canted Antiferromagnet Dy₅Si₂Ge₂, R. Nirmala, V. Sankaranarayanan, K. Sethupathi, Zili Chu, William B. Yelon, V. Prasad, A. V. Morozkin, Satish K. Malik, S. V. Subramanyam Jan 2002

Electrical And Magnetotransport Properties Of Canted Antiferromagnet Dy₅Si₂Ge₂, R. Nirmala, V. Sankaranarayanan, K. Sethupathi, Zili Chu, William B. Yelon, V. Prasad, A. V. Morozkin, Satish K. Malik, S. V. Subramanyam

Physics Faculty Research & Creative Works

Summary form only given. Since the giant magnetocaloric effect is encountered in a ferromagnetic Gd5Si2Ge2 alloy near room temperature it is considered as a suitable material for magnetic refrigerator applications. Also a commensurate structural transition occurs at the magnetic transition temperature and there is a good correlation between the crystal structure and magnetic properties. Such observations have triggered numerous experimental studies on similar rare earth alloys and compounds. We have synthesized its Dy- analogue, namely, Dy5Si2Ge2 and have characterized it by means of room temperature X-ray diffraction, ac magnetic susceptibility (15 K - 300 K), electrical resistivity (at zero field …

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Large Enhancement Of Spontaneous Emission Rates Of Inas Quantum Dots In Gaas Microdisks, W. Fang, Alexey Yamilov, Yinfa Ma, J. Y. Xu, S. T. Ho, G. S. Solomon, Hui Cao Jan 2002

Large Enhancement Of Spontaneous Emission Rates Of Inas Quantum Dots In Gaas Microdisks, W. Fang, Alexey Yamilov, Yinfa Ma, J. Y. Xu, S. T. Ho, G. S. Solomon, Hui Cao

Physics Faculty Research & Creative Works

Control of spontaneous emission in a microcavity has many important applications, e.g. improvement of the efficiency of light emitting devices. InAs quantum dots (QDs) embedded in microdisks are ideal systems for spontaneous emission control. The whispering gallery (WG) modes of microdisks have low volume and high quality factor. The homogeneous linewidth of InAs quantum dots is smaller than the spectral width of WG modes. Thus, a large enhancement of the spontaneous emission rates should be expected for QDs coupled to WG modes. However, large inhomogeneous broadening of the QD energy levels and random spatial distribution of the QDs in a …

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Time-Dependent Current-Density-Functional Theory For The Linear Response Of Weakly Disordered Systems, Carsten A. Ullrich, G. Vignale Jan 2002

Time-Dependent Current-Density-Functional Theory For The Linear Response Of Weakly Disordered Systems, Carsten A. Ullrich, G. Vignale

Physics Faculty Research & Creative Works

Time-dependent density-functional theory (TDFT) provides a way of calculating, in principle exactly, the linear response of interacting many-electron systems, and thus allows one to obtain their excitation energies. For extended systems, there exist excitations of a collective nature, such as bulk and surface plasmons in metals or intersubband plasmons in doped semiconductor quantum wells. This paper develops a quantitatively accurate first-principles description for the frequency and the linewidth of such excitations in inhomogeneous weakly disordered systems. A finite linewidth in general has intrinsic and extrinsic sources. At low temperatures and outside the region where electron-phonon interaction occurs, the only intrinsic …

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Intercomparison Of Number Concentration Measurements By Various Aerosol Particle Counters, A. Ankilov, A. Baklanov, M. Colhoun, K. H. Enderle, J. Gras, Yu Julanov, D. Kaller, A. Lindner, A. A. Lushnikov, R. Mavliev, F. Mcgovern, T. C. O'Connor, Josef Podzimek, O. Preining Jan 2002

Intercomparison Of Number Concentration Measurements By Various Aerosol Particle Counters, A. Ankilov, A. Baklanov, M. Colhoun, K. H. Enderle, J. Gras, Yu Julanov, D. Kaller, A. Lindner, A. A. Lushnikov, R. Mavliev, F. Mcgovern, T. C. O'Connor, Josef Podzimek, O. Preining

Physics Faculty Research & Creative Works

Total aerosol particle number concentrations, as measured by means of 16 different measurement systems, have been quantitatively compared during an international workshop at the Institute for Experimental Physics of the University of Vienna, Austria, which was coordinated within the Committee on Nucleation and Atmospheric Aerosols (ICCP-IUGG). The range of measuring instruments includes Pollak counters (PCO) in use already for several decades, presently available commercial particle counters, as well as laboratory prototypes. The operation of the instruments considered was based on different measurement principles: (1) adiabatic expansion condensation particle counter, (2) flow diffusion condensation particle counter, (3) turbulent mixing condensation particle …

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Particle Size Dependent Response Of Aerosol Counters, A. Ankilov, A. Baklanov, M. Colhoun, K. H. Enderle, J. Gras, Yu Julanov, D. Kaller, A. Lindner, A. A. Lushnikov, R. Mavliev, F. Mcgovern, T. C. O'Connor, Josef Podzimek, O. Preining Jan 2002

Particle Size Dependent Response Of Aerosol Counters, A. Ankilov, A. Baklanov, M. Colhoun, K. H. Enderle, J. Gras, Yu Julanov, D. Kaller, A. Lindner, A. A. Lushnikov, R. Mavliev, F. Mcgovern, T. C. O'Connor, Josef Podzimek, O. Preining

Physics Faculty Research & Creative Works

During an international workshop at the Institute for Experimental Physics of the University of Vienna, Austria, which was coordinated within the Committee on Nucleation and Atmospheric Aerosols (IAMAS-IUGG), 10 instruments for aerosol number concentration measurement were studied, covering a wide range of methods based on various different measuring principles. In order to investigate the detection limits of the instruments considered with respect to particle size, simultaneous number concentration measurements were performed for monodispersed aerosols with particle sizes ranging from 1.5 to 50 nm diameter and various compositions. The instruments considered show quite different response characteristics, apparently related to the different …

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Effect Of Rare Locally Ordered Regions On A Disordered Itinerant Quantum Antiferromagnet With Cubic Anisotropy, Rajesh S. Narayanan, Thomas Vojta Dec 2001

Effect Of Rare Locally Ordered Regions On A Disordered Itinerant Quantum Antiferromagnet With Cubic Anisotropy, Rajesh S. Narayanan, Thomas Vojta

Physics Faculty Research & Creative Works

We study the quantum phase transition of an itinerant antiferromagnet with cubic anisotropy in the presence of quenched disorder, paying particular attention to the locally ordered spatial regions that form in the Griffiths region. We derive an effective action where these rare regions are described in terms of static annealed disorder. A one-loop renormalization-group analysis of the effective action shows that for order-parameter dimensions p<4, the rare regions destroy the conventional critical behavior, and the renormalized disorder flows to infinity. For order-parameter dimensions p>4, the critical behavior is not influenced by the rare regions; it is described by the conventional dirty cubic fixed point. We also discuss the influence of the rare regions on the fluctuation-driven first-order transition …

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Electron-Impact Excitation To The 4p⁵5s And 4p⁵5p Levels Of Kr | Using Different Distorted-Wave And Close-Coupling Methods, Arati K. Dasgupta, Klaus Bartschat, D. Vaid, Alexei N. Grum-Grzhimailo, Don H. Madison, Milan Blaha, John L. Giuliani Nov 2001

Electron-Impact Excitation To The 4p⁵5s And 4p⁵5p Levels Of Kr | Using Different Distorted-Wave And Close-Coupling Methods, Arati K. Dasgupta, Klaus Bartschat, D. Vaid, Alexei N. Grum-Grzhimailo, Don H. Madison, Milan Blaha, John L. Giuliani

Physics Faculty Research & Creative Works

Electron-impact excitation of the 4p55s and 4p55p levels of Kr I has been investigated in detail by calculating cross sections using distorted-wave and close-coupling approaches. The results are presented from the excitation thresholds up to 50 eV incident energy. They are contrasted among the different calculations and compared with other theoretical predictions and experimental data. Significant disagreement is found with many of the recent experimental data of Chilton et al. [Phys. Rev. A 62, 032714 (2000)].

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Three-Body Coulomb Problem Probed By Mapping The Bethe Surface In Ionizing Ion-Atom Collisions, Robert Moshammer, Appathurai N. Perumal, Michael Schulz, V. D. Rodriguez, Holger Kollmus, Rido Mann, Siegbert Hagmann, Joachim Hermann Ullrich Nov 2001

Three-Body Coulomb Problem Probed By Mapping The Bethe Surface In Ionizing Ion-Atom Collisions, Robert Moshammer, Appathurai N. Perumal, Michael Schulz, V. D. Rodriguez, Holger Kollmus, Rido Mann, Siegbert Hagmann, Joachim Hermann Ullrich

Physics Faculty Research & Creative Works

The three-body Coulomb problem has been explored in kinematically complete experiments on single ionization of helium by 100 MeV / u C 6 + and 3.6 MeV / u u 5 3 + impact. Low-energy electron emission (E e < 150 eV ) as a function of the projectile deflection ϑ p (momentum transfer), i.e., the Bethe surface [[15]], has been mapped with Δ ϑ p ± 25 nanoradian resolution at extremely large perturbations (3.6 MeV / uAu53+ ) where single ionization occurs at impact parameters of typically 10 times the He K -shell radius. The experimental data are not in agreement with state-of-the-art continuum distorted wave-eikonal initial state theory.

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Mapping Of The Bethe Surface In Single-Ionization Ion-Atom Collisions, Ronald E. Olson, J. Fiol Oct 2001

Mapping Of The Bethe Surface In Single-Ionization Ion-Atom Collisions, Ronald E. Olson, J. Fiol

Physics Faculty Research & Creative Works

The three-body Coulomb problem is explored using classical-trajectory Monte Carlo and continuum distorted-wave methods that include all interactions, including the nuclear-nuclear term. Calculations for low-energy electron emission as a function of projectile deflection, the Bethe surface, are compared with experiment for single ionization of He by 100 MeVu-1 C6+ and 3.6 MeV u-1 Au53+. Good agreement is realized for the C6+ system. For Au53+ poor agreement with experiment is obtained, indicating that the proposed lack of the nuclear-nuclear interaction is not the source of the discrepancy. The calculations further show that significant cross sections …

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Measurements Of C V Flows From Thermal Charge-Exchange Excitation In Divertor Plasmas, B. Zaniol, R. C. Isler, N. H. Brooks, W. P. West, Ronald E. Olson Oct 2001

Measurements Of C V Flows From Thermal Charge-Exchange Excitation In Divertor Plasmas, B. Zaniol, R. C. Isler, N. H. Brooks, W. P. West, Ronald E. Olson

Physics Faculty Research & Creative Works

Certain transitions of C IV (C3+) from n=7 to n=6 (≈7226 Å) and from n=6 to n=5 (≈=4660 Å) sometimes appear much brighter in tokamak divertors than expected for electron-impact excitation from the ground state. This situation occurs because of charge exchange between C V (C4+) and recycling thermal deuterium atoms in the n=2 level. As a result, it is possible to extend parallel flow measurements of carbon, which have previously been performed on C II-C IV ions using Doppler shift spectroscopy, to include flows of the He-like C V ions. The work described here includes …

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