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Full-Text Articles in Physical Sciences and Mathematics
Measurement Of Spin-Exchange Effects In Electronhydrogen Collisions: Further Studies Of Impact Ionization, Timothy J. Gay, G. D. Fletcher, M. J. Alguard, V. W. Hughes, P. F. Wainwright, M. S. Lubell
Measurement Of Spin-Exchange Effects In Electronhydrogen Collisions: Further Studies Of Impact Ionization, Timothy J. Gay, G. D. Fletcher, M. J. Alguard, V. W. Hughes, P. F. Wainwright, M. S. Lubell
Timothy J. Gay Publications
Using a Fano-effect polarized electron source and a state-selected thermally dissociated hydrogen beam, we measured the interference between the direct and exchange scattering amplitudes for electron-impact ionization of atomic hydrogen between 14.1 and 30.3 eV. We report the data from these measurements and the results of corrections applied to previously published data.
Effect Of Anisotropy Strength On Phase Transitions In Random Anisotropy Magnets, Michael J. O'Shea, David J. Sellmyer
Effect Of Anisotropy Strength On Phase Transitions In Random Anisotropy Magnets, Michael J. O'Shea, David J. Sellmyer
David Sellmyer Publications
ac susceptibility and magnetization measurements are reported for a number of Gd and Tb based glasses. Raman magnetic anisotropy effects are observed in both the Gd and Tb glasses. The Gd glasses show a transition to an infinite susceptibility state and in some cases a further transition to an hysteretic state at low temperatures in which field-cooling and magnetic viscosity effects are observed. The Tb glass shows only a small speromagnetic peak at low temperatures. The ratio of anisotropy strength to exchange was varied in the Gd glasses by alloying, and the effect of this on the resulting magnetic states …
Magnetic And Crystallization Studies Of Splat-Cooled Praseodymium–Gallium–Iron Alloys, George C. Hadjipanayis, S.H. Woollins, R.C. Hazelton, K.R. Lawless, R. Prestipino, David J. Sellmyer
Magnetic And Crystallization Studies Of Splat-Cooled Praseodymium–Gallium–Iron Alloys, George C. Hadjipanayis, S.H. Woollins, R.C. Hazelton, K.R. Lawless, R. Prestipino, David J. Sellmyer
David Sellmyer Publications
Magnetic hysteresis and crytallization studies are reported for several (Pr80Ga20)100-xFex metallic glasses, where 30≤x≤80. Thermomagnetic data show the presence of two magnetic phases which are probably responsible for the relatively high coercive fields observed at cryogenic temperatures. As the iron content of the sample is increased, the magnetic moment increases substantially but the coercivity is drastically reduced. In (Pr80Ga20)70Fe30 the observed coercive fields are strongly temperature dependent indicating strong thermal activation effects which are consistent with the magnetic viscosity measurements. The hard magnetic properties disappear after …
Magnetic Properties Of Hydrides Of Rare Earth–Transition Metal Glasses, C.G. Robbins, Z.D. Chen, J.G. Zhao, Michael J. O'Shea, David J. Sellmyer
Magnetic Properties Of Hydrides Of Rare Earth–Transition Metal Glasses, C.G. Robbins, Z.D. Chen, J.G. Zhao, Michael J. O'Shea, David J. Sellmyer
David Sellmyer Publications
The effect of hydrogen on magnetic properties of metallic glasses of the form (R80Ga20)1-xTxHy where R=Pr, Nd, Gd, Tb, Er; T=Cr, Fe, Co, B; 0≤x≤0.3 and 0≤y≤1.7 is reported. The anisotropic rare earth glasses without H all exhibit speromagnetic (spin-glass-like) transitions and the effect of hydrogen, in most cases, is to lower the peak in χac significantly but leave TC relatively unchanged. For the Gd glass with T=Fe and x=0.1 the introduction of H at the level y=0.55 causes a large decrease in TC and a significant increase …
Resistivity And Galvanomagnetic Coefficients Of Iron Group Metallic Glasses With Chromium Substitutions, J.R. Long, George C. Hadjipanayis, David J. Sellmyer
Resistivity And Galvanomagnetic Coefficients Of Iron Group Metallic Glasses With Chromium Substitutions, J.R. Long, George C. Hadjipanayis, David J. Sellmyer
David Sellmyer Publications
Magnetic field and temperature dependences of the electrical resistivities and Hall resistivities were measured for the metallic glass ferromagnets Fe13Ni60Cr5Si10B12, Fe37Ni36Cr5Si10B12, Fe81B13.5Si3.5C2, and Fe5Co75Si15B5. Resistance minima and magnetoresistivity of the FeNiCr glasses have been found to be consistent with a modified Kondo model of low temperature scattering. The Hall resistivities are positive and large. The spontaneous Hall coefficients of the FeNiCr glasses are in …
Electron Transport In Tb- And Pr-Based Metallic Glasses, S.G. Cornelison, David J. Sellmyer
Electron Transport In Tb- And Pr-Based Metallic Glasses, S.G. Cornelison, David J. Sellmyer
David Sellmyer Publications
Electrical resistivity measurements are reported on several metallic glasses based on Pr and Tb, and Ga and various transition metals as the glass formers. In general negative temperature coefficients were observed and these are discussed in terms of the extended Ziman theory and the tunneling or localization theory. Low temperature structure in the resistivity can be understood with the coherent exchange scattering model of Asomoza et al. Journal of Applied Physics is copyrighted by The American Institute of Physics.
Amorphous FeXNb100-X With Wide Composition Range, C.L. Chien, K.M. Unruh, Sy_Hwang Liou
Amorphous FeXNb100-X With Wide Composition Range, C.L. Chien, K.M. Unruh, Sy_Hwang Liou
Sy-Hwang Liou Publications
Sputtered amorphous FexNb100-x (30 ≤ x ≤ 85) has been studied by Mössbauer spectroscopy and resistivity measurements. The samples with x< 60 are nonmagnetic. The magnetic ordering temperatures of the samples with x ≥ 60 increase with Fe content. Small magnetic hyperfine fields are observed in the magnetic samples, consistent with the small Fe moments measured. The resistivity of the magnetic and nonmagnetic samples show different temperature dependences. Only the magnetic samples exhibit a resistivity minimum, indicating a Kondo-like mechanism.
Theoretical Study Of The Long-Wavelength Optical Properties Of Nacl, Kcl, Kbr, And Ki, John R. Hardy, A. M. Karo
Theoretical Study Of The Long-Wavelength Optical Properties Of Nacl, Kcl, Kbr, And Ki, John R. Hardy, A. M. Karo
John R. Hardy Papers
We have made a detailed theoretical study of the long-wavelength absorption of NaCl, KCl, KBr, and KI, associated with two-phonon difference processes caused by third-order anharmonic terms in the lattice potential energy. It was found that a simple nearest neighbor approximation to the anharmonicity, combined with lattice-dynamical eigenfrequencies and eigenvectors generated with the use of a deformation dipole model, can generally account for most of the observed absorption. This agreement was obtained without the use of any disposable parameters, as the form of the first-neighbor potential was predetermined. It was also found that discrepancies between theory and experiment can generally …
Thresholds In Radiobiology, Robert Katz, Werner Hofmann
Thresholds In Radiobiology, Robert Katz, Werner Hofmann
Robert Katz Publications
Interpretations of radiation effects frequently call upon the word “threshold.” In this letter we wish to explore the meaning of this word, its relationship to the fundamental character of radiation effects, and to the question of perception. We make no distinction between “stochastic effects” and “non-stochastic effects” (ICRU 1971, ICRP 1977). As conceived here, all interactions of radiation with matter are probabilistic. At the cellular or molecular level, where most radiation effects originate, the statistical nature of ionization and excitation events gives rise to considerable fluctuation in the number of these primary events in sensitive sites. Whatever the array of …
1981 Oersted Medal: I. I . Rabi And Melba Newell Phillips Award 1982, Robert Fuller
1981 Oersted Medal: I. I . Rabi And Melba Newell Phillips Award 1982, Robert Fuller
Robert G. Fuller Publications
This award is given for exceptional contributions to physics education through leadership in the American Association of Physics Teachers. The award will not be given annually, but occasionally to an outstanding physics educator.
Temporary Negative Ions In The Chloromethanes Chcl2F And Ccl2F2: Characterization Of The Σ* Orbitals, Paul Burrow, A. Modelli, N.S. Chiu, K.D. Jordan
Temporary Negative Ions In The Chloromethanes Chcl2F And Ccl2F2: Characterization Of The Σ* Orbitals, Paul Burrow, A. Modelli, N.S. Chiu, K.D. Jordan
Paul Burrow Publications
The electron transmission spectra of chlorometers CHCl2F and CCl2F2 are presented. The electron affinities are evaluted compared with thoses calculated using self-consistent field methods.
Intermediate-Band Photometry In The Open Cluster Ngc 6664, Edward G. Schmidt
Intermediate-Band Photometry In The Open Cluster Ngc 6664, Edward G. Schmidt
Edward Schmidt Publications
Four-color and Hβ photometry is given for early-type stars in the open cluster NGC 6664. From these data the true distance modulus is found to be 10.7 and the reddening is found to range from E (b – y) = 0.48 to 0.63 across the cluster. The distance modulus agrees well with some values from the literature, but the present color excesses are about 0.1 mag larger than published values. There are two or perhaps three blue stragglers in the cluster and its age is estimated to be 46 × 106 yr.
New Perspectives On Electron Correlations, Anthony F. Starace
New Perspectives On Electron Correlations, Anthony F. Starace
Anthony F. Starace Publications
Two formulations for describing electronic excitations developed by Fano and his school are reviewed. The transition matrix formulation of atomic photoionization has provided new perspectives on the well-known random phase approximation and on its relation to configuration interaction. The hyperspherical coordinate approach to two electron states and collision processes has provided new perspectives on the classification of two-electron excitation channels and on the evolution of highly excited electronic states.
Measurement Of Spin-Exchange Effects In Electron-Hydrogen Collisions: 90° Elastic Scattering From 4 To 30 Ev, G. D. Fletcher, M. J. Alguard, Timothy J. Gay, V. W. Hughes, C. W. Tu, P. F. Wainwright, M. S. Lubell, W. Raith, F. C. Tang
Measurement Of Spin-Exchange Effects In Electron-Hydrogen Collisions: 90° Elastic Scattering From 4 To 30 Ev, G. D. Fletcher, M. J. Alguard, Timothy J. Gay, V. W. Hughes, C. W. Tu, P. F. Wainwright, M. S. Lubell, W. Raith, F. C. Tang
Timothy J. Gay Publications
With use of a Fano-effect polarized electron source and a state-selected thermally dissociated hydrogen beam, the interference between the direct and the exchange scattering amplitudes was measured for 90° elastic scattering of electrons from atomic hydrogen for energies between 4 and 30 eV.
Biological Effects Of Low Doses Of Ionizing Radiations: Particle Tracks In Radiobiology, Robert Katz, Werner Hofmann
Biological Effects Of Low Doses Of Ionizing Radiations: Particle Tracks In Radiobiology, Robert Katz, Werner Hofmann
Robert Katz Publications
A radiation field is made up of a tangle of particle tracks, from the primary particle and secondary and higher generation electron interactions, well isolated at low doses and with multiple intersections in cell nuclei at high doses. Low dose effects in multicellular systems are therefore the sum of individual track structures. Until we can state with confidence the structure of a particle track in biological matter for all end-points of interest, at least as well as we can for nuclear emulsions, our knowledge of low dose effects should be regarded as uncertain and inadequate. In this context “track structure” …
Simple Vibrating Sample Magnetometer, J.A. Gerber, W.L. Burmester, David J. Sellmyer
Simple Vibrating Sample Magnetometer, J.A. Gerber, W.L. Burmester, David J. Sellmyer
David Sellmyer Publications
Design features of a simple and relatively inexpensive homemade vibrating sample magnetometer are described. These include signal electronics which employs an analog divider rather than the usual electromechanical feedback circuit, and a method for gas cleaning during sample changes allowing long experiments at liquid helium temperatures in a superconducting solenoid. Review of Scientific Instruments is copyrighted by The American Institute of Physics.
Book Review: The Theory Of Atomic Structure And Spectra By Robert D. Cowan, Anthony F. Starace
Book Review: The Theory Of Atomic Structure And Spectra By Robert D. Cowan, Anthony F. Starace
Anthony F. Starace Publications
The field of atomic spectroscopy is currently experiencing a resurgence of interest owing on the one hand to its applications in astrophysics, plasma physics, and other fields and on the other hand to the development of new experimental tools to probe atomic structures. One example of the latter is the use of tunable lasers to study highly excited atoms in the presence of strong external electric and magnetic fields. Another is the use of synchrotron radiation to probe with increasing detail the inner shell structure of rare earth, actinide, and other heavy atoms.
Photoelectron Angular Distributions: Energy Dependence For S Subshells, Steven T. Manson, Anthony F. Starace
Photoelectron Angular Distributions: Energy Dependence For S Subshells, Steven T. Manson, Anthony F. Starace
Anthony F. Starace Publications
An overview of the theory of photoelectron angular distributions for atoms is presented. Its features, which are embodied in a single asymmetry parameter β in the electric dipole approximation, are examined within the framework of the angular momentum transfer formulation. The β parameter is in principle always energy dependent. Within the LS coupling approximation, however, there are instances, each representing a multitude of particular photoionization processes, in which β is an analytically determined constant. The energy dependence of the β parameters in such instances is due entirely to spin-orbit and other relativistic interactions. The study of the energy dependence of …
Four-Color And Hβ Photometry Of The Galactic Cluster M25, Edward G. Schmidt
Four-Color And Hβ Photometry Of The Galactic Cluster M25, Edward G. Schmidt
Edward Schmidt Publications
Four-color and Hβ photometry has been obtained for 39 stars in the field of the galactic cluster M25. The membership of the individual stars is discussed. From 27 stars which are considered likely members we obtain a mean distance modulus of 8.76 and a mean color excess of E(b – y) = 0.341.
Random-Phase Approximation To One-Body Transition Matrix Elements For Open-Shell Atoms, Anthony F. Starace, Siamak Shahabi
Random-Phase Approximation To One-Body Transition Matrix Elements For Open-Shell Atoms, Anthony F. Starace, Siamak Shahabi
Anthony F. Starace Publications
A graphical procedure is presented for evaluating each term in the equation satisfied by the first-order transition matrix for an arbitrary (open-shell) atom. For those terms involving the interaction of excited virtual pairs of electrons with the ionic core, we introduce the approximation that there is no exchange of orbital or spin angular momentum with the ionic core. This approximation is shown to lead to the random-phase approximation (RPA) equations in the closed-shell-atom case; we use it to define the RPA for open-shell atoms. The single equation satisfied by the first-order transition matrix is used to obtain a set of …
Intermediate-Band Photometry Of The Open Cluster Ngc 3114, Edward G. Schmidt
Intermediate-Band Photometry Of The Open Cluster Ngc 3114, Edward G. Schmidt
Edward Schmidt Publications
Four-color and Hβ photometry has been obtained of 33 stars in the southern galactic cluster NGC 3114. This cluster contains many interesting stars including blue stragglers, red giants, and stars with spectral peculiarities. The distance modulus was found to be V0 – Mv = 10.26 which corresponds to 1130 pc. The color excess is E(b – y) = 0m.060. The cluster appears to be slightly older than the Pleiades. There are two extreme blue stragglers and six additional stars which might be considered milder cases of the same phenomenon. The distance moduli of …
Giant Coercivities And Chemical Short-Range Order In Pr-Ga-Fe Metallic Glasses, S.G. Cornelison, David J. Sellmyer, J.G. Zhao, Z.D. Chen
Giant Coercivities And Chemical Short-Range Order In Pr-Ga-Fe Metallic Glasses, S.G. Cornelison, David J. Sellmyer, J.G. Zhao, Z.D. Chen
David Sellmyer Publications
Results of magnetic, Mössbauer, and structural studies are presented for (Pr80Ga20)100-xFex metallic glasses, where 0≤x≤30. For x≥20 two magnetic transitions are observed and the structural studies indicate the presence of a phase separation into at least two glassy phases, one being Fe-rich and the other Fe-deficient. Coercivities above 60 kOe are observed and the results are discussed in terms of a model involving the magnetic properties of the two phases. Journal of Applied Physics is copyrighted by The American Institute of Physics.
Are Vpd3 And Nbpd3 Itinerant Ferromagnets?, W.L. Burmester, David J. Sellmyer
Are Vpd3 And Nbpd3 Itinerant Ferromagnets?, W.L. Burmester, David J. Sellmyer
David Sellmyer Publications
Low-field magnetic susceptibility and high-field magnetization results are reported for polycrystalline samples of NbPd3, VPd3, and iron doped VPd3. Recent self-consistent, spin-polarized band calculations have predicted that the pure compounds are itinerant ferromagnets. Down to 1.6 K there is no evidence for either magnetic ordering or exchange enhancement in VPd3 and NbPd3. The Fe-doped alloys exhibit transitions at low temperatures to a magnetic cluster-glass state. Journal of Applied Physics is copyrighted by The American Institute of Physics.
Magnetic, Mössbauer, And Resistivity Studies Of Amorphous Fe74Zr26 And Fe81Hf19 Alloys, C. L. Chien, K. M. Unruh, A. Levy, Sy_Hwang Liou, J. P. Stokes, R.J. Gambino, K. Fukamichi
Magnetic, Mössbauer, And Resistivity Studies Of Amorphous Fe74Zr26 And Fe81Hf19 Alloys, C. L. Chien, K. M. Unruh, A. Levy, Sy_Hwang Liou, J. P. Stokes, R.J. Gambino, K. Fukamichi
Sy-Hwang Liou Publications
Amorphous metal-metal samples of Fe74Zr26 and Fe81Hf19 have been studied by bulk magnetic, Mössbauer spectroscopy and resistivity measurements. The values of Tc have been determined to be 285 K and 295 K for Fe74Zr26 and Fe81Hf19, respectively. Both the magnetic isotherms and Mössbauer measurements indicate that these samples are ferromagnetics. The isomer shifts and the quadrupole interactions are much smaller than those of amorphous Fe-metalloid systems. The P(H) are broad and extend to small H values. Negative temperature coefficients of the resistivity are observed at low …
Review Of Atoms And Molecules By M. Weissbluth, Anthony F. Starace
Review Of Atoms And Molecules By M. Weissbluth, Anthony F. Starace
Anthony F. Starace Publications
The advent of high-powered lasers and of dedicated synchrotron light sources and the needs of research in such areas as astrophysics and fusion have led to a resurgence of interest in atomic and molecular physics. Concurrently, there have been significant advances in atomic and molecular theory, not only in the ability to make more reliable numerical predictions but also in the detailed understanding of the dynamics of atomic and molecular collisions. The nonspecialist or beginning graduate student who must read the scientific journals to learn of these advances often finds that the requisite basic knowledge is extensive. Mitchel Weissbluth, whose …
Polarization Of Fluorescence Radiation Subsequent To Inner-Shell Photoionization: Ls-Coupling Formulas, Anthony F. Starace
Polarization Of Fluorescence Radiation Subsequent To Inner-Shell Photoionization: Ls-Coupling Formulas, Anthony F. Starace
Anthony F. Starace Publications
The polarization and angular distribution of fluorescence radiation subsequent to inner-shell photoionization in atoms are presented here in the important special case that dynamic amplitudes are calculated in LS coupling taking full account of anisotropic electron-ion interactions. The resulting formulas require for their evaluation no more dynamical information than is usually obtained in an LS-coupling calculation of the photoionization cross section. Exact geometrical relationships which are obscured in more general treatments become apparent in an LS-coupling formulation. Thus it is shown that in LS coupling the fluorescence resulting from photoionization of an s subshell in an atom having …
The Chromospheres Of Classical Cepheids. I. Low Resolution Iue Spectra, Edward G. Schmidt, Sidney B. Parsons
The Chromospheres Of Classical Cepheids. I. Low Resolution Iue Spectra, Edward G. Schmidt, Sidney B. Parsons
Edward Schmidt Publications
We have undertaken a program to study the behavior of chromospheres in classical Cepheids using both ground-based and satellite-based observations. Five stars, δ Cep, η Aql, β Dor, ζ Gem, and l Car, have been included, and where possible the various types of data have been obtained simultaneously. The first part of this investigation concerns low dispersion spectra from the IUE satellite. Fine error sensor (FES) magnitudes are presented for the five Cepheids and, in the case of one, η Aql, are used to re-discuss the period. The "artificial viscosity dip" predicted by some theoretical calculations may be present in …
The Light Curves Of Rr Lyrae Field Stars, Norman R. Simon, Terry J. Teays
The Light Curves Of Rr Lyrae Field Stars, Norman R. Simon, Terry J. Teays
Department of Physics and Astronomy: Faculty Publications
Fourier decompositions have been made of the light curves of a large sample of RR Lyrae field stars. The coefficients have been tabulated. Following the scheme of an earlier investigation of classical Cepheids, certain combinations of the low-order coefficients - φ21, R21, and φ31 - are plotted against period. The Bailey-type c pulsators stand out from the type ab stars, particularly on the R21 plot which is found to be a more sensitive discriminator of Bailey type than is the traditionally employed amplitude-period diagram. We compare the RR Lyrae plots of φ21, …