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Full-Text Articles in Physics

Lattice Dynamics Of Mixed Crystals Of Tise2, Roger D. Kirby, G.A. Freund, Jr. Dec 1984

Lattice Dynamics Of Mixed Crystals Of Tise2, Roger D. Kirby, G.A. Freund, Jr.

Roger Kirby Publications

We present the results of Raman scattering measurements on the mixed-crystal systems TiSe2-xSx, TiSe2-xTex, ZrxTi1-x Se2. At room temperature with the pure compounds all have crystal structures represented by the D3d(P3̃m1) space group with three atoms per unit cell. There are two Raman-active k=0 phonons, one of A1gˉ symmetry and one of Eg symmetry. In the TiSe2-xTex system, the A1gˉ and E phonon frequencies shift smoothly with concentration, and the shifts are well described by a simple virtual-crystal model ...


Segregation Of Copper To The Surface Of Copper-Nickel Alloys, Peter A. Dowben Dec 1984

Segregation Of Copper To The Surface Of Copper-Nickel Alloys, Peter A. Dowben

Peter Dowben Publications

Copper segregation profiles at the surfaces of Cu17Ni83(111) and Cu17Ni83(100) have been calculated by a semiempirical procedure based upon previously published data. These profiles indicate that surface enrichment of copper is not limited only to the topmost layer but occurs for several layers away from the surface as well. A comparison of the calculated segregation profiles based upon the experimental results for the (100) and (111) surfaces of Cu17Ni83 do not agree with predictions based upon thermodynamic models of segregation.


Yellow Giants In Young Clusters. Ii. A Comparison Of Observation With Theory, Edward G. Schmidt Dec 1984

Yellow Giants In Young Clusters. Ii. A Comparison Of Observation With Theory, Edward G. Schmidt

Edward Schmidt Publications

Luminosities and effective temperatures are calculated for 17 nonvariable yellow giants and supergiants and nine Cepheids which were previously identified as members of open clusters. These stars are identified as being in the helium core burning stage of evolution. A comparison with the predictions of pulsation theory does not show any disagreement. On the other hand, several comparisons with the theory of stellar evolution produce discrepancies which suggest that effects neglected in the calculations may play an important role in the evolution of these stars.


Model Calculations Of The Micrometer To Millimeter Intrinsic Absorption For Simple Ceramics, John R. Hardy, P. J. Edwardson, J. A. O'Gara Nov 1984

Model Calculations Of The Micrometer To Millimeter Intrinsic Absorption For Simple Ceramics, John R. Hardy, P. J. Edwardson, J. A. O'Gara

John R. Hardy Papers

A systematic study has been made of the strength of the intrinsic absorption, or loss, for millimeter to micrometer electromagnetic radiation propagating in simple ceramic materials. This study employed a number of model diatomic systems whose simplicity enabled the basic two-phonon decay process, responsible for this intrinsic loss, to be computed with precision, even at the lowest frequencies, on a dedicated microcomputer. It was found that, at least at low frequencies, the loss was a relatively structureless universal function of the atomic mass ratio, in general agreement with earlier results for real alkali halides. In particular, it was found that ...


Central-Peak-Soft-Mode, Coupling In Ferroelectric Gd2(Moo4)3, J. Petzelt, F. Smutny, V. Katkanant, F. G. Ullman, John R. Hardy, A. A. Volkov, G. V. Kozlov, S. P. Lebedev Nov 1984

Central-Peak-Soft-Mode, Coupling In Ferroelectric Gd2(Moo4)3, J. Petzelt, F. Smutny, V. Katkanant, F. G. Ullman, John R. Hardy, A. A. Volkov, G. V. Kozlov, S. P. Lebedev

John R. Hardy Papers

Transmission measurements on Gd2(MoO4)3 in the ( 5-50)-cm-1 region were performed with use of tunable backward-wave oscillator sources (5-30 cm>-1) and a Fourier spectrometer (30-50 cm>-1). The resulting dielectric spectra show an additional low-frequency dispersion which was fitted with a standard central-peak model. Its characteristic relaxation frequency is ~20 cm>-1 and the coupling between the soft mode and central mode increases near the transition temperature. This model also accounts very well for the weak anomaly in the clamped permittivity Ec measured at 63 MHz. The same central mode was used to ...


The Luminosity Scale Of Cepheid Variable Stars: A Revision, Edward G. Schmidt Oct 1984

The Luminosity Scale Of Cepheid Variable Stars: A Revision, Edward G. Schmidt

Edward Schmidt Publications

The period-luminosity-color relation for classical Cepheids is discussed in terms of a recent re-determinations of the distance moduli of open clusters with Cepheid members. The distance moduli of eight clusters with well established Cepheid members were determined from Stromgren four-color and Hβ photometry of the B stars. Possible sources of systematic errors in these distance moduli are discussed. Zero points are derived from these data for the period-luminosity-color (PLC) relation on the UBV system and the period-luminosity relations for near-infrared magnitudes. The present relations yield absolute magnitudes which are fainter by 0.4-0.6 mag than those now commonly used ...


Surface-Wave-Induced Interference Effects In Angle-Resolved Photoemission, Peter A. Dowben, D. Heskett, E.W. Plummer, Y. Sakisaka, T.N. Rhodin, Cyrus Umrigar Oct 1984

Surface-Wave-Induced Interference Effects In Angle-Resolved Photoemission, Peter A. Dowben, D. Heskett, E.W. Plummer, Y. Sakisaka, T.N. Rhodin, Cyrus Umrigar

Peter Dowben Publications

New features are observed in normal-emission photoelectron spectra from Ni(100) in a narrow range of photon energies around 25 eV. These features are inconsistent with either direct transitions from the bulk or emission from occupied surface states or resonances. We suggest that they are a consequence of interference between the ordinary direct transition emitting an electron in the normal direction and the excitation from the same initial state into a final state that would normally be emitted from the surface at Γ― in the second surface Brillouin zone, but at this energy is trapped in a surface wave.


Some Comments On The Concepts Of Dose And Dose Equivalent, Robert Katz, Werner Hofmann Oct 1984

Some Comments On The Concepts Of Dose And Dose Equivalent, Robert Katz, Werner Hofmann

Robert Katz Publications

Although dose is the simplest and most widely used measurement of a radiation field, it does not always lead to an unambiguous estimate of response. This is reflected in the very wide range of relative biologic effectiveness (RBE) values for biological systems. The ambiguity arises from the focus on energy deposition as the source of biological effect, whether in macroscopic or microscopic volumes. The properties of the biological detector play a role equally important to the properties of the radiation field in their interaction. To predict even the most experimentally accessible biological response, cell killing, we must know the probability ...


Photoionization Of Atomic Chlorine Above The 1S Threshold, Siamak Shahabi , Anthony F. Starace, T.N. Chang Oct 1984

Photoionization Of Atomic Chlorine Above The 1S Threshold, Siamak Shahabi , Anthony F. Starace, T.N. Chang

Anthony F. Starace Publications

The total photoionization cross section of the 3p subshell of atomic chlorine is presented with use of the recently developed open-shell transition-matrix method of Starace and Shahabi. The role of electron correlations is studied by comparison with Hartree-Fock and close-coupling calculations. In contrast to 3p-subshell photoionization of argon, it is shown that, in chlorine, final-state interchannel interactions are very strong while virtual pair excitations have a weak effect on the shape of the cross section, serving mainly to reduce the discrepancy between length and velocity results. Our results are compared in detail with other theoretical results above ...


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 ...


Magnetic Properties And Chemical Short-Range Order In Fe-Pd-Based Metallic Glasses , J.G. Zhao, David J. Sellmyer Sep 1984

Magnetic Properties And Chemical Short-Range Order In Fe-Pd-Based Metallic Glasses , J.G. Zhao, David J. Sellmyer

David Sellmyer Publications

High-field magnetization and ac susceptibility measurements are reported on a series of FexPd80-xSi10B10 rapidly quenched alloys for 0<~x<~80. X-ray diffraction data show that these alloys are amorphous up to at least x=40 and that the x=60 and 80 samples are partially crystalline. The ac susceptibility data can be interpreted in terms of ferromagnetic, spin-glass, and double transitions, and a qualitative magnetic phase diagram of the system is obtained. The concentration dependence of the saturation magnetization, as well as the magnetic phase diagram, exhibits sharp anomalies at about x=13. These data suggest the presence of chemical short-range order for x≳13. X-ray photoelectron and Mössbauer results are consistent with this model.


Rare-Earth—Gallium—Iron Glasses. Ii. Anomalous Magnetic Hysteresis In Alloys Based On Pr, Nd, And Sm , S.G. Cornelison, J.G. Zhao, David J. Sellmyer Sep 1984

Rare-Earth—Gallium—Iron Glasses. Ii. Anomalous Magnetic Hysteresis In Alloys Based On Pr, Nd, And Sm , S.G. Cornelison, J.G. Zhao, David J. Sellmyer

David Sellmyer Publications

Giant magnetic coercivity is reported in several metallic glasses of the form (R80G20)100-xFex where R represents Pr, Nd, or Sm, G represents Ga or Au, and 15≤x≤30. An unusual temperature variation of the coercive field is observed showing peaks at intermediate temperatures (≃90 K). In contrast to similar glasses based on heavy rare-earth metals, these glasses exhibit significant chemical short-range order and even phase separation as is shown by the Mössbauer effect and other measurements. The results are consistent with a recent theory which predicts that large coercivity can result from the ...


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 ...


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 ...


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 ...


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.


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(T22)], where Δ depends on the heat treatment of the sample.


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 the ...


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.


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 ...


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

Si-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.


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.


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 ...


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 ...


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.