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Physics Faculty Research & Creative Works

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Articles 1051 - 1080 of 1762

Full-Text Articles in Physical Sciences and Mathematics

A Problematic Set Of Two-Loop Self-Energy Corrections, Ulrich D. Jentschura, Jorg Evers, Christoph H. Keitel, Krzysztof Pachucki Jul 2002

A Problematic Set Of Two-Loop Self-Energy Corrections, Ulrich D. Jentschura, Jorg Evers, Christoph H. Keitel, Krzysztof Pachucki

Physics Faculty Research & Creative Works

We investigate a specific set of two-loop self-energy corrections involving squared decay rates and point out that their interpretation is highly problematic. The corrections cannot be interpreted as radiative energy shifts in the usual sense. Some of the problematic corrections find a natural interpretation as radiative nonresonant corrections to the natural line shape. They cannot uniquely be associated with one and only one atomic level. While the problematic corrections are rather tiny when expressed in units of frequency (a few hertz for hydrogenic P levels) and do not affect the reliability of quantum electrodynamics at the current level of experimental …

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Electron Correlation In Double Ionization Of Excited Helium By Fast Ion Impact, L. G. Gerchikov, S. A. Sheinerman, Michael Schulz, R. Moshammer, J. Ullrich Jun 2002

Electron Correlation In Double Ionization Of Excited Helium By Fast Ion Impact, L. G. Gerchikov, S. A. Sheinerman, Michael Schulz, R. Moshammer, J. Ullrich

Physics Faculty Research & Creative Works

The correlation function between two emitted electrons has been calculated as a function of their momentum difference for double ionization of 1s2s excited He atoms by fast ion impact. A simple quantum mechanical approach is developed to take into account the dynamics of two-electron ejection as well as the effects of electron exchange and correlated electron motion in the final state. A clear difference between the correlation functions of the excited and ground state targets is reported.

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Mechanism For Carrier Velocity Saturation In Pure Organic Crystals, Vasudev M. Kenkre, Paul Ernest Parris Jun 2002

Mechanism For Carrier Velocity Saturation In Pure Organic Crystals, Vasudev M. Kenkre, Paul Ernest Parris

Physics Faculty Research & Creative Works

We present a possible mechanism for the saturation of the velocity of photoinjected charge carriers in pure organic crystals, the analysis having been motivated by observations in pentacene. The mechanism is based on the strong wave vector dependence of the damping coefficient appearing in the appropriate effective mass equation. Our primary goal is to explore this mechanism in general terms rather than to apply it to a specific system such as pentacene. Our analysis is based on a Fokker-Planck equation treatment. We indicate how the damping coeffcient is related to relaxation times in usual Boltzmann equations and how it can …

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Differential Cross Sections And Cross-Section Ratios For The Electron-Impact Excitation Of The Neon 2p⁵3s Configuration, Murtadha A. Khakoo, James M. Wrkich, Mary Lu Larsen, G. Kleiban, Isik Kanik, Sandor Trajmar, Michael J. Brunger, P. J O Teubner, Albert Crowe, Christopher J. Fontes, Robert E H Clark, Vlado Zeman, Klaus Bartschat, Don H. Madison, Rajesh C. Srivastava, Allan Daniel Stauffer Jun 2002

Differential Cross Sections And Cross-Section Ratios For The Electron-Impact Excitation Of The Neon 2p⁵3s Configuration, Murtadha A. Khakoo, James M. Wrkich, Mary Lu Larsen, G. Kleiban, Isik Kanik, Sandor Trajmar, Michael J. Brunger, P. J O Teubner, Albert Crowe, Christopher J. Fontes, Robert E H Clark, Vlado Zeman, Klaus Bartschat, Don H. Madison, Rajesh C. Srivastava, Allan Daniel Stauffer

Physics Faculty Research & Creative Works

Electron-impact differential cross-section measurements for the excitation of the 2p53s configuration of Ne are reported. The Ne cross sections are obtained using experimental differential cross sections for the electron-impact excitation of the n = 2 levels of atomic hydrogen [Khakoo et al., Phys. Rev. A 61, 012701-1 (1999)], and existing experimental helium differential cross-section measurements, as calibration standards. These calibration measurements were made using the method of gas mixtures (Ne and H followed by Ne and He), in which the gas beam profiles of the mixed gases are found to be the same within our experimental errors. We …

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Possible Ordering Of Ru And Cu In The Charge-Reservoir Of Magneto-Superconductor Rusr₂Gdcu₂O₈ (Ru-1212): Magnetic, Transport, And Tem Microstructural Studies, V. P. S. Awana, S. Ichihara, J. Nakamura, M. Karppinen, H. Yamauchi, Jinbo Yang, William B. Yelon, William Joseph James, Satish K. Malik May 2002

Possible Ordering Of Ru And Cu In The Charge-Reservoir Of Magneto-Superconductor Rusr₂Gdcu₂O₈ (Ru-1212): Magnetic, Transport, And Tem Microstructural Studies, V. P. S. Awana, S. Ichihara, J. Nakamura, M. Karppinen, H. Yamauchi, Jinbo Yang, William B. Yelon, William Joseph James, Satish K. Malik

Physics Faculty Research & Creative Works

Magnetization vs temperature behavior of RuSr2GdCu2O8-δ (Ru-1212) measured in an field of 5 Oe, shows a clear branching of zero-field-cooled (ZFC) and field-cooled (FC) curves around 140 K, a cusp at 135 K, and a diamagnetic transition around 20 K (in the ZFC branch). The cusp at 135 K is due to the antiferromagnetic ordering of the Ru moments. The magnetization-field isotherms, below 50 K, show a nonlinear contribution from a ferromagnetic component. The resistance vs temperature behavior of the compound, in applied fields of 0, 3, and 7 T, confirms that the sample is …

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Magnetic And Neutron Diffraction Studies On Prmnsb₂, Satish K. Malik, Zili Chu, Amish G. Joshi, Jinbo Yang, William B. Yelon, Qingsheng Cai, William Joseph James, Kishore Kamaraju May 2002

Magnetic And Neutron Diffraction Studies On Prmnsb₂, Satish K. Malik, Zili Chu, Amish G. Joshi, Jinbo Yang, William B. Yelon, Qingsheng Cai, William Joseph James, Kishore Kamaraju

Physics Faculty Research & Creative Works

Magnetic and neutron diffraction studies have been carried out on PrMnSb2. Magnetization data in the temperature range of 5-400 K show two magnetic transitions: one at ∼175 K attributed to the antiferromagnetic ordering of the Mn moments, and the other at ∼35 K possibly due to the antiferromagnetic ordering of the Pr moments. The magnetization-field isotherms at various temperatures are consistent with the above. Neutron diffraction data obtained at various temperatures can be fitted with a nearly antiferromagnetically coupled Mn moment of ∼3μB at 70 K. At 10 K, moments both on Mn (∼3.5μB) and …

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Observation Of Novel Disordered Rhombohedral R₂Fe₁₇ (R=Rare Earth) Based Compounds, William B. Yelon, William Joseph James, Jinbo Yang, Kishore Kamaraju, Qingsheng Cai, Zili Chu, Satish K. Malik May 2002

Observation Of Novel Disordered Rhombohedral R₂Fe₁₇ (R=Rare Earth) Based Compounds, William B. Yelon, William Joseph James, Jinbo Yang, Kishore Kamaraju, Qingsheng Cai, Zili Chu, Satish K. Malik

Physics Faculty Research & Creative Works

A recent study of (SmGd)Fe 14Si3 showed an anomalous x-ray diffraction pattern [P. C. Ezekwenna, G. K. Marasinghe, J.-H. Nam, W. J. James, W. B. Yelon, M. Ellouze, and Ph. I'Héritier, J. Appl. Phys. 87, 6716 (2000)]. Although all observed peaks could be indexed to the rhombohedral 2:17 phase (R-3m) many lines were strongly reduced in intensity. Subsequently, the same phenomenon was seen in neutron diffraction patterns from Nd2-xDysFe17-ySiy alloys and conventional refinement using the rhombohedral phase left significant residuals. Fourier mapping revealed additional density along the c-axis chains of Fe dumbbells …

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Structure And Superconductivity Of Dy (Ba2-Y Lay) Cu3 Oz (0 ≤ Y ≤ 0.5) System, Amish G. Joshi, S. K. Malik, William B. Yelon May 2002

Structure And Superconductivity Of Dy (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 single-phase La-substituted compounds of the formula Dy(Ba 2-yLay)Cu3Oz (0.0≤y≤0.5) have been investigated by neutron diffraction, electrical resistivity, and magnetization measurements. The compound DyBa 2Cu3O7-δ (orthorhombic, space group Pmmm) exhibits superconductivity with transition temperature, T c, of about 90 K. Rietveld analysis of the neutron diffraction data on La containing compounds reveals that the orthorhombicity decreases with increasing La concentration and the compounds become tetragonal for higher La content. The overall oxygen content increases as divalent Ba is replaced by trivalent La and approximately compensates for …

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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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Magnetic And Mössbauer Studies On Oxygen Deficient Perovskite, La₀.₆Sr₀.₄Feo3-Δ, Jinbo Yang, William B. Yelon, William Joseph James, X.-D. Zhou, Yixiang Xie, Harlan U. Anderson, Zili Chu May 2002

Magnetic And Mössbauer Studies On Oxygen Deficient Perovskite, La₀.₆Sr₀.₄Feo3-Δ, Jinbo Yang, William B. Yelon, William Joseph James, X.-D. Zhou, Yixiang Xie, Harlan U. Anderson, Zili Chu

Physics Faculty Research & Creative Works

Samples of La0.6Sr0.4Fe3-δ with varying oxygen vacancy contents were prepared by heating them in different gas flows. Magnetization measurement showed that samples with low oxygen vacancies have a magnetic ordering temperature in the range of 300-325 K while those with 9%-12% oxygen vacancies have a magnetic ordering temperature of 800 K and higher. Mössbauer spectra at 300 K exhibit paramagnetic or weak magnetic characteristics for the N2, O2, and air-quenched samples, whereas an average hyperfine field of 52 T is found for the CO/CO2 reduced samples. The heat treatment in …

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Structure And Magnetic Properties Of The Mnbi Low Temperature Phase, Jinbo Yang, William B. Yelon, William Joseph James, Qingsheng Cai, Samit Roy, Naushad Ali May 2002

Structure And Magnetic Properties Of The Mnbi Low Temperature Phase, Jinbo Yang, William B. Yelon, William Joseph James, Qingsheng Cai, Samit Roy, Naushad Ali

Physics Faculty Research & Creative Works

High purity MnBi low temperature phase has been prepared and analyzed using magnetic measurements and neutron diffraction. The low-temperature phase of the MnBi alloy has a coercivity μ0iHc of 2.0 T at 400 K, and exhibits a positive temperature coefficient from 0 to at least 400 K. The neutron data refinement indicated that the Mn atom changes its spin direction from c axis above room temperature to nearly perpendicular to the c axis at 50 K. A canted magnetic structure has been observed below 200 K. The anisotropy field increases with increasing temperature which gives rise to …

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Magnetic Properties Of Iron-Rich Mixed Rare-Earth Sm₂-ₓtbₓfe17-YSiY Compounds, Kishore Kamaraju, Jinbo Yang, William B. Yelon, Oran Allan Pringle, William Joseph James, Ph. I'Héritier May 2002

Magnetic Properties Of Iron-Rich Mixed Rare-Earth Sm₂-ₓtbₓfe17-YSiY Compounds, Kishore Kamaraju, Jinbo Yang, William B. Yelon, Oran Allan Pringle, William Joseph James, Ph. I'Héritier

Physics Faculty Research & Creative Works

A series of Sm2-xTbxFe17-ySiy solid solutions with x = 0, 1, and 1.5 and y = 1, 2, and 3 were prepared by induction melting stoichiometric amounts of high purity elements. The x-ray diffraction data confirm that the postannealed samples are 2:17 intermetallics of the R3 space group. The lattice parameters and the unit cell volumes were calculated using a modified Rietveld program. The fitted intensities showed behavior related to a disordered rhombohedral structure as inferred from neutron data. It was observed that for a particular y, the unit cell volume decreased almost …

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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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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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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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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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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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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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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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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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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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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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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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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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