Open Access. Powered by Scholars. Published by Universities.®

Physics Commons™

Open Access. Powered by Scholars. Published by Universities.®

University of Nebraska - Lincoln

Discipline
Keyword
Publication Year
Publication

Articles 3061 - 3090 of 3506

Full-Text Articles in Physics

Rare-Earth—Gallium—Iron Glasses. I. Magnetic Ordering And Hysteresis In Alloys Based On Gd, Tb, And Er , S.G. Cornelison, David J. Sellmyer Sep 1984

Rare-Earth—Gallium—Iron Glasses. I. Magnetic Ordering And Hysteresis In Alloys Based On Gd, Tb, And Er , S.G. Cornelison, David J. Sellmyer

David Sellmyer Publications

Results of magnetic measurements are presented on the new metallic glass systems (R80Ga20)100-xFex and (R80Ga20)90B10, where R denotes the heavy rare earths Gd, Tb, and Er, for x=10, 20, and 30, respectively. High-field magnetization (to 80 kOe) and ac and dc susceptibility measurements were made from 1.4 to 300 K. The Gd-Fe glasses are simple ferrimagnets with opposing Gd and Fe moments. The Gd-B glass exhibits two apparent transitions (paramagnetic—ferromagnetic—like, and ferromagnetic spin-glass) as the temperature is lowered. As Fe is added, the low-temperature transition …

Go to article

Effects Of Magnetic And Electric Fields On Highly Excited Atoms, Charles W. Clark, K. T. Lu, Anthony F. Starace Aug 1984

Effects Of Magnetic And Electric Fields On Highly Excited Atoms, Charles W. Clark, K. T. Lu, Anthony F. Starace

Anthony F. Starace Publications

This review describes primarily recent theoretical developments on highly excited atoms in uniform external fields, and complements the experimental review of Gay in the present volume. The Zeeman and Stark effects on low-lying atomic states, on the other hand, constitute a mature field of study which has been reviewed previously by Garstang, Kollath and Standage, Bayfield, and Kleppner. Most theoretical work on highly excited states in laboratory strength fields has heretofore focused on the prototype system of atomic hydrogen, and accordingly hydrogen receives special emphasis in this article. For nonhydrogenic atoms we review theoretical work using the framework of quantum …

Go to article

Speed Of The Photorefractive Effect In A Batio3 Single Crystal, Stephen Ducharme, Jack Feinberg Aug 1984

Speed Of The Photorefractive Effect In A Batio3 Single Crystal, Stephen Ducharme, Jack Feinberg

Stephen Ducharme Publications

We present data on the speed of light-induced refractive index changes in a BaTiO3 single crystal. The light-induced erasure rate of a refractive index grating is shown to depend on optical intensity as I x where x<1. The exponent x depends weakly on temperature and increases from 0.62±0.02 to 0.71±0.02 when the temperature is varied between 12 and 40 °C. The sublinear dependence of rate on intensity implies that higher optical intensity is required to achieve high-speed operation of BaTiO3 devices than previously thought. The dark erasure rate has an anomolously strong temperature dependence; it increases by a factor of …

Go to article

Yellow Giants In Young Clusters. I. Photometric Observations, Edward G. Schmidt Jul 1984

Yellow Giants In Young Clusters. I. Photometric Observations, Edward G. Schmidt

Edward Schmidt Publications

To enable a study of the properties of luminous yellow stars, a list has been compiled of 84 stars which appear to be in the appropriate region in the color-magnitude diagrams of 41 young clusters. Proper motions, radial velocities, UBV photometry, and spectral types from the literature have been used in those cases where such data are available to assign membership probabilities. DDO and uvby photometry have also been obtained of most of the stars in the list, and these data are analyzed to remove stars from the sample which have the wrong luminosity or the wrong color excess for …

Go to article

Effect Of Nickel Impurities On Charge-Density-Wave Formation In Tas3, M.H. Rashid, David J. Sellmyer, Roger D. Kirby May 1984

Effect Of Nickel Impurities On Charge-Density-Wave Formation In Tas3, M.H. Rashid, David J. Sellmyer, Roger D. Kirby

Roger Kirby Publications

Introduction of nickel impurities into TaS3 has the effect of smearing the charge-density-wave transitions in TaS3 of both orthorhombic and monoclinic phases. The orthorhombic doped crystals show non-Ohmic conductivity beyond threshold fields that are much larger than the threshold field of the pure phase, possibly due to additional pinning of the charge-density wave by nickel impurities. The charge-density-wave state is completely destroyed as 10 at % or more Ta atoms are replaced by Ni atoms and metallic behavior between 4.2 and 30 K is observed in these cases.

Go to article

Temperature-Dependent Resistivity Of Highly Disordered Ni-Cr-Al Alloys , R. Hight, C. Plough, David J. Sellmyer May 1984

Temperature-Dependent Resistivity Of Highly Disordered Ni-Cr-Al Alloys , R. Hight, C. Plough, David J. Sellmyer

David Sellmyer Publications

Measurements are reported on the electrical resistivity of highly disordered Ni-Cr-Al films between 4.2 and 300 K. X-ray diffraction measurements show the films to be crystalline with a bcc structure. Negative temperature coefficients are observed and the resistivity data above about 50 K can be fitted by the expression ρ(T)=ρ0 [1-cln(T2+Δ2)], where Δ depends on the heat treatment of the sample.

Go to article

The Chromospheres Of Classical Cepheids. 11. High-Resolution Profiles Of The Mg Ii H And K Lines, Edward G. Schmidt, Sidney B. Parsons Apr 1984

The Chromospheres Of Classical Cepheids. 11. High-Resolution Profiles Of The Mg Ii H And K Lines, Edward G. Schmidt, Sidney B. Parsons

Edward Schmidt Publications

High-resolution spectra have been obtained with the long-wavelength camera of the International Ultraviolet Explorer for five Cepheids at a number of phases each. These data were used to study the profiles of the Mg II h and k lines near 2900 Å. An emission feature often appears at the centers of the two lines. There are also central absorption features due to circumstellar or interstellar gas. They are often multiple and may or may not divide the emission into two peaks. The velocities of the circumstellar absorption components imply that they originate in a region which is at least several …

Go to article

The Chromospheres Of Classical Cepheids. 111. A Search For Transition Region Emission Lines, Edward G. Schmidt, Sidney B. Parsons Apr 1984

The Chromospheres Of Classical Cepheids. 111. A Search For Transition Region Emission Lines, Edward G. Schmidt, Sidney B. Parsons

Edward Schmidt Publications

In previous studies of Cepheid chromospheres with the IUE, we found that the chromospheric emission is strongly dependent on the period of the star and varies substantially through the cycle. For the shortest period star in our sample, δ Cep, we were able to detect little significant chromospheric emission in the short wavelength region, and we were only able to detect transition region emission in the longest period star, 1 Car. However, the upper limits on these emissions were slightly above expected flux levels for nonvariable stars. To detect them or place lower and physically more interesting limits on …

Go to article

A Search For Chromospheric Emission In Tu Cassiopeiae Spectra, Arne A. Henden, Robert H. Cornett, Edward G. Schmidt Apr 1984

A Search For Chromospheric Emission In Tu Cassiopeiae Spectra, Arne A. Henden, Robert H. Cornett, Edward G. Schmidt

Edward Schmidt Publications

We have searched high-resolution spectra of the multimode cepheid TU Cas for evidence of chromospheric emission. Spectral regions covered include the Ca II near-IR triplet near 8600 Å, Hα, CanII H and K, Mg II h and k; phase coverage in both primary and secondary modes was reasonably complete. There was no evidence for changes other than those caused by temperature variation. The observed lack of emission makes unlikely current mass loss (and resulting helium enrichment) by means of stellar winds.

Go to article

Spin-Glass-Like Freezing In Disordered Mnpd3 And Crpd3 Alloys, M.H. Rashid, David J. Sellmyer Mar 1984

Spin-Glass-Like Freezing In Disordered Mnpd3 And Crpd3 Alloys, M.H. Rashid, David J. Sellmyer

David Sellmyer Publications

We report studies of dc and ac susceptibility and high-field magnetization on disordered samples of MnPd3 and CrPd3. Both samples undergo spin-glass-like transitions, as is evident from susceptibility peaks at 45 and 37 K, respectively. The effective paramagnetic moments deduced from Curie–Weiss fits of the susceptibility in the paramagnetic region are 0.38µB/Mn and 0.4µB/Cr. Both materials show saturation effects at high applied fields and a flat χ(T) below the spin-freezing temperature in the field-cooled state. The data are discussed in terms of a cluster-glass model with local antiferromagnetic interactions. Journal of …

Go to article

Magnetic Hardening In Rapidly Quenched Fe-Pr And Fe-Nd Alloys, David J. Sellmyer, A. Ahmed, G. Muench, George C. Hadjipanayis Mar 1984

Magnetic Hardening In Rapidly Quenched Fe-Pr And Fe-Nd Alloys, David J. Sellmyer, A. Ahmed, G. Muench, George C. Hadjipanayis

David Sellmyer Publications

We report studies of high-field magnetization and thermomagnetic effects in rapidly quenched and heat treated alloys based on Fe-Pr and Fe-Nd. Coercivities up to ~40 kOe and large energy products result from the precipitation of a finely dispersed crystalline phase. Studies of varying the alloy composition and heat treatment are reported. Journal of Applied Physics is copyrighted by The American Institute of Physics.

Go to article

Mössbauer Study Of Sputtered Fe-Ti Alloys With Wide Composition Range, Sy_Hwang Liou, C.L. Chien Mar 1984

Mössbauer Study Of Sputtered Fe-Ti Alloys With Wide Composition Range, Sy_Hwang Liou, C.L. Chien

Sy-Hwang Liou Publications

FexTi100-x alloys over a wide composition range has been made by high-rate sputtering and studied by 57Fe Mössbauer spectroscopy. Samples with 30 ≤ x ≤ 80 are amorphous whereas samples with x ≥ 85 are metastable crystalline bcc alloys. Large differences in magnetic properties (e.g., Tc) and hyperfine interactions (Heff, isomer shift) are found between the amorphous and bcc alloys. Comparison of FeTi and Fe2Ti in amorphous and crystalline states show that the short-range order in the amorphous state has no resemblence to that of the crystalline compounds.

Go to article

H- And He In A Uniform Magnetic Field: Ground-State Wave Functions, Energies, And Binding Energies For Fields Below 109 G, Chang-Hwan Park, Anthony F. Starace Feb 1984

H- And He In A Uniform Magnetic Field: Ground-State Wave Functions, Energies, And Binding Energies For Fields Below 109 G, Chang-Hwan Park, Anthony F. Starace

Anthony F. Starace Publications

Wave functions, energies, and binding energies for the lowest singlet states of H- and He in uniform magnetic fields B<109 G are calculated using an adiabatic approximation in hyperspherical coordinates. In computing the angular part of the wave functions, a coupled expansion in one-electron oblate spheroidal angle functions is used. In addition to contracting the two-electron wave function radially, the magnetic field is found to distort the angular part of the wave function mainly by reducing the ss1S character of the state and replacing it with an sd 1D character. Results for energies and binding energies …

Go to article

Multiple Ionization Of Rare Gases By H+ And He+ Impact, R. D. Dubois, L. H. Toburen, M. Eugene Rudd Jan 1984

Multiple Ionization Of Rare Gases By H+ And He+ Impact, R. D. Dubois, L. H. Toburen, M. Eugene Rudd

M. Eugene Rudd Publications

Absolute cross sections for multiple ionization (σq)of He, Ne, Ar, and Kr are presented for proton-impact energies between 10 and 4000 keV. Charge states up to 6 + are observed for Kr. The results are obtained by measuring relative yields of multiply charged ions with a time-of-flight spectrometer and normalizing to total ion-production cross sections σT= ∑qσq. The results are compared with existing proton- and electron-impact data. Relative multiple- to single-ionization cross-section ratios are also presented for He+ impact.

Go to article

Cross Sections For Ionizaton Of Gases By 5-4000-Kev Protons And For Electron Capture By 5-150-Kev Protons, M. Eugene Rudd, R. D. Dubois, L. H. Toburen, C. A. Ratcliffe, T. V. Goffe Dec 1983

Cross Sections For Ionizaton Of Gases By 5-4000-Kev Protons And For Electron Capture By 5-150-Kev Protons, M. Eugene Rudd, R. D. Dubois, L. H. Toburen, C. A. Ratcliffe, T. V. Goffe

M. Eugene Rudd Publications

Using the parallel-plate-capacitor method and a capacitance manometer to determine pressures, total cross sections for the production of positive and negative charges were measured for 5-4000- keV-proton impact on He, Ne, Ar, Kr, Hz, N2, CO, 02, CH4, and C02. From these, ionization and electron-capture cross sections were obtained and fitted to semi-empirical equations describing the energy dependence in terms of a few parameters. At high energies very good agreement is obtained in the comparison of the ionization cross sections to earlier proton- and electron-impact measurements and with theoretical treatments where they …

Go to article

Ionic-Configuration-Interaction Effects On Xe 5S-Subshell Photoionization Processes, Göran Wendin, Anthony F. Starace Nov 1983

Ionic-Configuration-Interaction Effects On Xe 5S-Subshell Photoionization Processes, Göran Wendin, Anthony F. Starace

Anthony F. Starace Publications

Recent measurements of the 5s-subshell photoelectron angular distribution of xenon have found larger values for the asymmetry parameter β in the region of the 5s-subshell cross-section minimum than predicted by relativistic random-phase-approximation calculations. Final-state ionic configuration interaction is adduced as a possible explanation for this and other discrepancies.

Go to article

Atomic Photoionization, Anthony F. Starace Aug 1983

Atomic Photoionization, Anthony F. Starace

Anthony F. Starace Publications

We present here a brief overview of the theory of atomic photoionization. The main aim is to describe current theoretical understanding of the dynamics of the photon-atom collision process. In particular the discussion focuses on those kinds of electron correlation that have been found to be most important for photoionization processes. The general theoretical formulation of the interaction between an incident photon and an N-electron atom is presented first. This is followed by a description of those quantitative and qualitative features of the photoionization cross section that can be understood within a central potential model. The particle-hole type of electron …

Go to article

Using Nuclear Resonance Excitation To Observe United Atoms In Symmetric Ion-Atom Collisions, James M. Feagin, Ladislov Kocbach Apr 1983

Using Nuclear Resonance Excitation To Observe United Atoms In Symmetric Ion-Atom Collisions, James M. Feagin, Ladislov Kocbach

Department of Physics and Astronomy: Faculty Publications

We consider nuclear resonance excitation as a means to observe the distribution of united-atom orbitals in symmetric ion-atom collisions. We develop this possibility with the application of a two-state adiabatic model to an analysis of a 8Be nuclear resonance experiment. To test our model, and to provide a more direct determination of the nuclear resonance width, we propose that the 8Be experiment be repeated with metastable helium targets.

Go to article

Interpretation Of Anomalies In The Raman Spectrum Of K2Seo4 In Terms Of Oxygen Sublattice Disorder, Nestor Massa, Frank Ullman, John R. Hardy Feb 1983

Interpretation Of Anomalies In The Raman Spectrum Of K2Seo4 In Terms Of Oxygen Sublattice Disorder, Nestor Massa, Frank Ullman, John R. Hardy

John R. Hardy Papers

Raman scattering from K2SeO4 crystals has been studied in the (20-800)-K temperature range. Three portions of the spectrum are discussed: defect-induced scattering, primarily below 100 cm-1, the external mode spectrum below 200 cm-1, and the internal mode spectra in two regions, 300-500 and 800-950 cm-1. The temperature dependence of the low-frequency, defect-induced scattering has been correlated (in previous studies) with the temperature dependence of certain nonzero-wave-vector phonons that have been observed by others using inelastic neutron scattering. Close to the incommensurate transition temperature, Ti= 129 K, a large enhancement …

Go to article

Quality Factor For Low Doses Of High-Let Radiations, Werner Hofmann, Robert Katz Feb 1983

Quality Factor For Low Doses Of High-Let Radiations, Werner Hofmann, Robert Katz

Robert Katz Publications

The International Commission on Radiological Protection (ICRP77) and the International Commision on Radiation Units and Measurements (ICRU70) have recommended that the evaluation of radiation hazards be based on the “dose equivalent” defined as the product of the absorbed dose and some modifying factors, the most important of which is the quality factor (Q). The quality factor is intended to allow for the effect on the resulting detriment of the microscopic distribution of the absorbed energy. It is therefore defined as a function of the collision stopping power (L∞) in water at the point of interest. Thus Q rises …

Go to article

Track Formation In Plastics, Robert Katz Jan 1983

Track Formation In Plastics, Robert Katz

Robert Katz Publications

It is proposed that the “threshold for etchable track formation” in plastics is associated with the linear density of activated polymeric clusters along the path of an ion, in the “grain-count regime.” Existing data for CR-39 reveal a change in etching rate in the neighborhood of z/β having the value of about 15-20. We infer that this defines the transition from the grain count regime to the track width regime, as the activation cross-section exceeds the cross-sectional area of the cluster. This interpretation is consistent with available data for the G value for polymer scission and the dose of gamma-rays …

Go to article

Thermal Propagation And Stability In Superconducting Films, Kenneth E. Gray, Robert T. Kampwirth, John F. Zasadzinski, Stephen P. Ducharme Jan 1983

Thermal Propagation And Stability In Superconducting Films, Kenneth E. Gray, Robert T. Kampwirth, John F. Zasadzinski, Stephen P. Ducharme

Stephen Ducharme Publications

Thermal propagation and stable hot spots (normal domains) are studied in various high Tc superconducting films (Nb3Sn, Nb, NbN and Nb3Ge). The prediction of the thermal propagation velocity of the long-standing model of Broom and Rhoderick (1960) is verified quantitatively in the regime of its validity. A new energy balance model is shown to give reasonable quantitative agreement of the dependence of the propagation velocity on the length of short normal domains. The steady state (zero velocity) measurements indicate the existence of two distinct situations for films on high thermal conductivity (sapphire) substrates. For low power per unit area the …

Go to article

Intermediate-Band Photometry Of Stars In Three Clusters Containing Classical Cepheids, Edward G. Schmidt Jan 1983

Intermediate-Band Photometry Of Stars In Three Clusters Containing Classical Cepheids, Edward G. Schmidt

Edward Schmidt Publications

Four-color and Hβ photometry has been carried out of stars in three sparse and distant clusters which are thought to contain Cepheids. From these data the distance moduli and color excesses of the clusters have been derived. In general the new values agree with those in the literature but are somewhat more precise.

Go to article

Comment On Coefficients Of Fractional Parentage Of The Form (L2L+1|}L2L+2), Anthony F. Starace Jan 1983

Comment On Coefficients Of Fractional Parentage Of The Form (L2L+1|}L2L+2), Anthony F. Starace

Anthony F. Starace Publications

For the special case of half-filled subshells, Racah showed in 1943 that his formula relating the coefficients of fractional parentage for a given particle configuration to those for the corresponding hole configuration requires an additional phase factor (-1) (v-1)/2, where v is the seniority of the half-filled configuration. This phase factor is incorrectly printed in Racah's 1943 paper as (-1) v-1/2. Furthermore, this phase factor is omitted in the 1952 paper by Rosenzweig, resulting in sign errors in the table of (d5|}d6) coefficients. These rather old errors have often …

Go to article

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 Dec 1982

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.

Go to article

Effect Of Anisotropy Strength On Phase Transitions In Random Anisotropy Magnets, Michael J. O'Shea, David J. Sellmyer Nov 1982

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 …

Go to article

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 Nov 1982

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 …

Go to article

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 Nov 1982

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 …

Go to article

Resistivity And Galvanomagnetic Coefficients Of Iron Group Metallic Glasses With Chromium Substitutions, J.R. Long, George C. Hadjipanayis, David J. Sellmyer Nov 1982

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 …

Go to article

Electron Transport In Tb- And Pr-Based Metallic Glasses, S.G. Cornelison, David J. Sellmyer Nov 1982

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.

Go to article

First Prev Next Last