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1984

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Full-Text Articles in Physics

(Super)Conformal Symmetry Breaking, Andrew Strominger, V. Parameswaran Nair Dec 1984

(Super)Conformal Symmetry Breaking, Andrew Strominger, V. Parameswaran Nair

Publications and Research

We argue that the only consistent way to break conformal invariance in a quantum theory of gravity is spontaneously in a finite locally conformal supersymmetric theory. This generically occurs whenever scalar fields are present. Covariant surface-integral expressions for the super-charge and four-momentum in terms of asymptotically constant spinor fields are derived. These are used to discuss stability and other aspects of the theory.


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.


A Model For Orientation Effects In Electron‐Transfer Reactions, Paul Siders, Robert J. Cave, R.A. Marcus Dec 1984

A Model For Orientation Effects In Electron‐Transfer Reactions, Paul Siders, Robert J. Cave, R.A. Marcus

All HMC Faculty Publications and Research

A method for solving the single‐particle Schrödinger equation with an oblate spheroidal potential of finite depth is presented. The wave functions are then used to calculate the matrix element TBA which appears in theories of nonadiabatic electron transfer. The results illustrate the effects of mutual orientation and separation of the two centers on TBA. Trends in these results are discussed in terms of geometrical and nodal structure effects. Analytical expressions related to TBA for states of spherical wells are presented and used to analyze the nodal structure effects for TBA for the spheroidal wells.


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 ...


Absence Of Minimum Metallic Conductivity In Gd(3-X)Vxs4 At Very Low Temperature And Evidence For A Coulomb Gap, S. Washburn, Richard A. Webb, S. Von Molnar, F. Holtzberg Nov 1984

Absence Of Minimum Metallic Conductivity In Gd(3-X)Vxs4 At Very Low Temperature And Evidence For A Coulomb Gap, S. Washburn, Richard A. Webb, S. Von Molnar, F. Holtzberg

Faculty Publications

Gd(3-x)vxS4 provides a convenient analog of a compensated semiconductor in which, for x≃0.3, the mobility edge can be tuned smoothly through the Fermi energy by the application of a magnetic field. The results of a search for a minimum metallic conductivity demonstrate that, down to T=6 mK, the metal-insulator transition is smooth. In the insulating regime, the temperature dependence of the conductivity was more consistent with the theory of mutual interactions than with the theory of pure localization.


String Induced Space Compactification, P. G. Freund, P. Oh, James Thomas Wheeler Nov 1984

String Induced Space Compactification, P. G. Freund, P. Oh, James Thomas Wheeler

All Physics Faculty Publications

Motivated by the possibility of a finite theory of gravity provided by superstrings in ten space-time dimensions, we analyze the problem of space compactification in the context of string dynamics. Such an analysis is hampered by conceptual and technical problems, stemming from the existence of the quantum string's own graviton mode on the one hand, and from Witten's observation of anomalies in a not specially chosen curves space-time on the other hand. Still, in the context of a classical local field presentation of string theory à la Nambu and Hosotani, supplemented by gravitational and Kalb-Ramond interactions, we are ...


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 ...


Cosmic Rays And The Emission-Line Regions Of Active Galactic Nuclei, Gary J. Ferland, R. F. Mushotzky Nov 1984

Cosmic Rays And The Emission-Line Regions Of Active Galactic Nuclei, Gary J. Ferland, R. F. Mushotzky

Physics and Astronomy Faculty Publications

We discuss the effects that the synchrotron emitting relativistic electrons, which are known to exist throughout many distance scales in active nuclei, could have on the emission-line regions that characterize these objects. Detailed models of both the inner, dense, broad-line region and the outer, lower density, narrow-line region are presented, together with the first models of the optically emitting gas often found within extended radio lobes. We show that, in all cases, if the relativistic gas that produces the synchrotron radio emission is mixed with the gas in the emission-line region, then significant changes in the emission-line spectrum will result ...


Superspace Ward Identities In Supersymmetric Gauge Theories, Asim Gangopadhyaya, Darwin Chang Nov 1984

Superspace Ward Identities In Supersymmetric Gauge Theories, Asim Gangopadhyaya, Darwin Chang

Physics: Faculty Publications and Other Works

In superspace formulation of supersymmetric gauge theories, gauge invariance requires an infinite set of identities between the infinite set of renormalization constants. Using Ward identities in superspace, the same is derived. These identities at one loop level are also demonstrated.


The Spectral Momentum Density Of Amorphous Carbon From (E, 2e) Spectroscopy, A. L. Ritter, Jr Dennison, R. Jones Nov 1984

The Spectral Momentum Density Of Amorphous Carbon From (E, 2e) Spectroscopy, A. L. Ritter, Jr Dennison, R. Jones

All Physics Faculty Publications

The spectral momentum density of the valence band of an amorphous carbon film has been measured by (e, 2e) spectroscopy. Two "bands," energy as a function of momentum, are resolved. One extends from 23 eV below the Fermi energy to about 10 eV below EF. The other, ∼ 9 eV below EF, does not disperse significantly. Although the existence of diamond bonding in the film cannot be ruled out, the bands are more suggestive of the graphite band structure.


Multiple Determination Of The Optical Constants Of Thin-Film Coating Materials, D. P. Arndt, R. M.A. Azzam, J. M. Bennett, J. P. Borgogno, C. K. Carniglia, W. E. Case, J. A. Dobrowolski, U. J. Gibson, T. Tuttle Hart, F. C. Ho, V. A. Hodgkin, W. P. Klapp, H. A. Macleod, E. Pelletier, M. K. Purvis, D. M. Quinn, D. H. Strome, R. Swenson, P. A. Temple, T. F. Thonn Oct 1984

Multiple Determination Of The Optical Constants Of Thin-Film Coating Materials, D. P. Arndt, R. M.A. Azzam, J. M. Bennett, J. P. Borgogno, C. K. Carniglia, W. E. Case, J. A. Dobrowolski, U. J. Gibson, T. Tuttle Hart, F. C. Ho, V. A. Hodgkin, W. P. Klapp, H. A. Macleod, E. Pelletier, M. K. Purvis, D. M. Quinn, D. H. Strome, R. Swenson, P. A. Temple, T. F. Thonn

Electrical Engineering Faculty Publications

The seven participating laboratories received films of two different thicknesses of Sc2O3 and Rh. All samples of each material were prepared in a single deposition run. Brief descriptions are given of the various methods used for determination of the optical constants of these coating materials. The measurement data are presented, and the results are compared. The mean of the variances of the Sc2O3refractive-index determinations in the 0.40–0.75-nm spectral region was 0.03. The corresponding variances for the refractive index and absorption coefficient of Rh were 0.35 and 0.26 ...


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 ...


Statement Of Dr. David Hafemeister Regarding The Need To Convert Domestic Research Reactors From Highly Enriched To Low-Enriched Uranium Fuels, David W. Hafemeister Oct 1984

Statement Of Dr. David Hafemeister Regarding The Need To Convert Domestic Research Reactors From Highly Enriched To Low-Enriched Uranium Fuels, David W. Hafemeister

Physics

No abstract provided.


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 ...


Magnetoresistance Of Small, Quasi-One-Dimensional, Normal-Metal Rings And Lines, C. P. Umbach, S. Washburn, R. B. Laibowitz, Richard A. Webb Oct 1984

Magnetoresistance Of Small, Quasi-One-Dimensional, Normal-Metal Rings And Lines, C. P. Umbach, S. Washburn, R. B. Laibowitz, Richard A. Webb

Faculty Publications

The magnetoresistance of sub-0.4-μm-diam Au and Au60Pd40 rings was measured in a perpendicular magnetic field at temperatures as low as 5 mK in search of simple, periodic resistance oscillations that would be evidence of flux quantization in normal-metal rings. However, instead of simple oscillations, a very complex structure developed in the magnetoresistance at low temperatures. Fourier analysis of all the data did not reveal convincing evidence for flux quantization in the rings. Complex structure similar to that observed in the rings was also found in the magnetoresistance of short, narrow, Au and Au60 ...


Radiation Pressure And The Stability Of Broad-Line Region Clouds, Gary J. Ferland, Moshe Elitzur Oct 1984

Radiation Pressure And The Stability Of Broad-Line Region Clouds, Gary J. Ferland, Moshe Elitzur

Physics and Astronomy Faculty Publications

We discuss two constraints on the existence and stability of quasar emission-line gas. The case of a constant pressure photoionized cloud in pressure equilibrium with a surrounding hot gas is considered. We show that the radiation pressure of the internally generated line emission makes a significant contribution to the total pressure in standard broad-line region models, and that models with either a higher ionization parameter or lower gas density are dominated by radiation pressure and hence unstable. Further, clouds with ionization parameters lower than the standard value cannot be supported by any hot gas which is heated only by the ...


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 ...


Percolation In Dimensions D≥4, Joan Adler, Amnon Aharony, A. Brooks Harris Sep 1984

Percolation In Dimensions D≥4, Joan Adler, Amnon Aharony, A. Brooks Harris

Department of Physics Papers

In this paper we present extended mean cluster size series for the bond percolation problem for hypercubic lattices in d dimensions and analyze them for 4≤d≤9. Values of the critical exponent γ and the leading correction exponent Δ1 are deduced, and the Δ1 values for d>6 are compared with new analytic results.


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 ...


Ε Expansion For The Conductivity Of A Random Resistor Network, A. Brooks Harris, Soobang Kim, Tom C. Lubensky Aug 1984

Ε Expansion For The Conductivity Of A Random Resistor Network, A. Brooks Harris, Soobang Kim, Tom C. Lubensky

Department of Physics Papers

We present a reanalysis of the renormalization-group calculation to first order in ε=6−d, where d is the spatial dimensionality, of the exponent, t, which describes the behavior of the conductivity of a percolating network at the percolation threshold. If we set t=(d−2)νp+ζ, where νp is the correlation-length exponent, then our result is ζ=1+(ε/42). This result clarifies several previously paradoxical results concerning resistor networks and shows that the Alexander-Orbach relation breaks down at order ε.


Three-Reflection Halfwave And Quarterwave Retarders Using Dielectric-Coated Metallic Mirrors, T. F. Thonn, R. M.A. Azzam Aug 1984

Three-Reflection Halfwave And Quarterwave Retarders Using Dielectric-Coated Metallic Mirrors, T. F. Thonn, R. M.A. Azzam

Electrical Engineering Faculty Publications

A design procedure is described to determine the thicknesses of single-layer coatings of a given dielectric on a given metallic substrate so that a specified net phase retardance (and/or a net relative amplitude attenuation) between the p and s polarizations is achieved after three reflections from a symmetrical arrangement of three mirrors that maintain collinearity of the input and output beams. Examples are presented of halfwave and quarterwave retarders (HWR and QWR) that use a ZnS-Ag film-substrate system at the CO2-laser wavelength λ = 10.6 µm. The equal net reflectances for the p and s polarizations are ...


Structure, Morphology And Crystal Growth Of Bacterial Magnetite, Stephen Mann, Richard B. Frankel, Richard P. Blakemore Aug 1984

Structure, Morphology And Crystal Growth Of Bacterial Magnetite, Stephen Mann, Richard B. Frankel, Richard P. Blakemore

Physics

Recent high-resolution transmission electron microscopy (HRTEM) studies of the structure and morphology of bacterial magnetite (Fe3O4) crystals isolated from a magnetotactic coccus1 and from an unidentified bacterium extracted from sediment2 have shown the crystals to be well ordered single-domain particles with a morphology based on a hexagonal prism of {011} faces truncated by specific low index planes. We report here a HRTEM study of intact magnetite crystals (magnetosomes) in the microaerophilic bacterium Aquaspirillum magnetotacticum, grown in pure culture3,4. Our aim has been to investigate the structure, morphology and crystal growth of the magnetite ...


Critical Behavior Of The One-Dimensional S = 1 Xy Model With Single-Ion Anisotropy, O. F. De Alcantara Bonfim, T. Schneider Aug 1984

Critical Behavior Of The One-Dimensional S = 1 Xy Model With Single-Ion Anisotropy, O. F. De Alcantara Bonfim, T. Schneider

Physics Faculty Publications and Presentations

We study the quantum critical behavior of the one-dimensional, S = 1 XY model in the presence of a single-ion anisotropy. Using a path-integral approach, we obtain, at T = 0 and for a positive anisotropy constant, a classical free-energy functional that allows discussion of the critical properties. The rescaling of frequencies is governed by the critical exponent z = 1. Renormalization-group arguments reveal that at criticality the system belongs to the same universality class as the isotropic 2-d XY model.


Bags Vs. Strings: Hadrons In Type I And Type Ii Superconducting Vacua, V. Parameswaran Nair, C. Rosenzweig Aug 1984

Bags Vs. Strings: Hadrons In Type I And Type Ii Superconducting Vacua, V. Parameswaran Nair, C. Rosenzweig

Publications and Research

Two popular models for hadronic structure are bags and strings. Both involve analogies with superconductivity. We claim that the most appropriate analogies are type I superconductors for bags and type II superconductors for strings. The structures of hadrons is somewhat different for the two situations. In principle, and in practice in the real world, it is the similarities which are most important. These include linear confining potentials, linearly rising Regge trajectories and short distance Coulomb potentials. These are all generic properties of bound states in a superconductor and the main distinctions between bags and strings is under what circumstances these ...