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Full-Text Articles in Physics

U-Duality, D-Branes And Black Hole Emission Rates: Agreements And Disagreements, Fay Dowker, David Kastor, Jennie Traschen Nov 1998

U-Duality, D-Branes And Black Hole Emission Rates: Agreements And Disagreements, Fay Dowker, David Kastor, Jennie Traschen

David Kastor

An expression for the spacetime absorption coefficient of a scalar field in a five dimensional, near extremal black hole background is derived, which has the same form as that presented by Maldacena and Strominger, but is valid over a larger, U-duality invariant region of parameter space and in general disagrees with the corresponding D-brane result. We develop an argument, based on D-brane thermodynamics, which specifies the range of parameters over which agreement should be expected. For neutral emission, the spacetime and D-brane results agree over this range. However, for charged emission, we find disagreement in the `Fat Black Hole' regime ...


Spectral Features Of The Stimulated Raman Backscattering Of Modulated Laser Pulses In A Plasma, Nikolai E. Andreev, Serguei Y. Kalmykov Sep 1998

Spectral Features Of The Stimulated Raman Backscattering Of Modulated Laser Pulses In A Plasma, Nikolai E. Andreev, Serguei Y. Kalmykov

Serge Youri Kalmykov

The characteristic features of the stimulated Raman backscattering of short modulated (multi-frequency) laser pulses in an underdense plasma are investigated. A laser pulse consisting of a given pair of spectral components with the frequency difference close to the double plasma frequency is studied in the weak mode coupling approximation. The scattering of the component with the higher frequency is shown to be a five-wave resonant process, and the conditions under which this process is totally suppressed are found. The scattering of the component with the lower frequency is an ordinary three-wave decay process without any suppression. When the difference between ...


Investigation Of The 10b(Γ,P) Reaction Using Tagged Photons, L J. De Bever, R S. Hicks, R A. Miskimen, Gerald Alvin Peterson Jul 1998

Investigation Of The 10b(Γ,P) Reaction Using Tagged Photons, L J. De Bever, R S. Hicks, R A. Miskimen, Gerald Alvin Peterson

Gerald Alvin Peterson

The reaction 10B(γ,p) has been studied using tagged photons of mean energies Eγ=57.6 and 72.9 MeV. Angular distributions and derived single-particle momentum distributions for protons leading to the ground state of 9Be and higher excited states are compared to various calculations made using model parameters constrained by 10B(e,e′p)9Be and 9Be(p,p′)9Be measurements. The effects of varying final-state interactions (including channel couplings) and meson exchange currents are considered. A sizable discrepancy between direct-knockout calculations and the experimental results is observed. If meson exchange currents are included in an approximate fashion ...


Measurements Of The Δ(1232) Transition Form Factor And The Ratio Σn/Σp From Inelastic Electron-Proton And Electron-Deuteron Scattering, L M. Stuart, R S. Hicks, R A. Miskimen, Gerald Alvin Peterson, S H. Rokni Jun 1998

Measurements Of The Δ(1232) Transition Form Factor And The Ratio Σn/Σp From Inelastic Electron-Proton And Electron-Deuteron Scattering, L M. Stuart, R S. Hicks, R A. Miskimen, Gerald Alvin Peterson, S H. Rokni

Gerald Alvin Peterson

Measurements of inclusive electron-scattering cross sections using hydrogen and deuterium targets in the region of the Δ(1232) resonance are reported. A global fit to these new data and previous data in the resonance region is also reported for the proton. Transition form factors have been extracted from the proton cross sections for this experiment over the four-momentum transfer squared range 1.64


Resistivity Of Boron-Doped Diamond Microcrystals, M. D. Jaeger, S. Hyun, Anthony Roy Day, M. F. Thorpe, B. Golding May 1998

Resistivity Of Boron-Doped Diamond Microcrystals, M. D. Jaeger, S. Hyun, Anthony Roy Day, M. F. Thorpe, B. Golding

Anthony Roy Day

We describe measurements of the electrical resistivity of micron-size crystallites of boron-doped diamond. Electron-beam lithography was employed for writing sample-specific contacts on small, well-faceted diamond crystals grown by chemical-vapor deposition on silicon substrates. After generating a three-dimensional computer model of the crystallite, a finite-element analysis was used to calculate the internal electrostatic potential distribution. Multiterminal resistance measurements, in conjunction with a computed geometrical factor, enabled the absolute resistivity to be determined. We find that the resistivities obtained from two different crystallites agree to better than 10%. The results are compared with transport measurements on a large-area homoepitaxial diamond film grown ...


Radial Dependence Of The Nucleon Effective Mass In 10b, L J. De Bever, R S. Hicks, R A. Miskimen, Gerald Alvin Peterson May 1998

Radial Dependence Of The Nucleon Effective Mass In 10b, L J. De Bever, R S. Hicks, R A. Miskimen, Gerald Alvin Peterson

Gerald Alvin Peterson

The dynamic properties of the atomic nucleus depend strongly on correlations between the nucleons. We present a combined analysis of inelastic electron-scattering data and electron-induced proton knockout measurements in an effort to obtain phenomenological information on nucleon-nucleon correlations. Our results indicate that the ratio of radial wave functions extracted from precise 10B(e,e′) and 10B(e,e′p) measurements evolve from an interior depression for small Em, characteristic of short-range correlations, to a surface-peaked enhancement for larger Em, characteristic of long-range correlations. This observation can be interpreted in terms of the nucleon effective mass.


Quantum-Statistical Properties Of Two Coupled Modes Of Electromagnetic Field, Serguei Y. Kalmykov, Mikhail E. Veisman Apr 1998

Quantum-Statistical Properties Of Two Coupled Modes Of Electromagnetic Field, Serguei Y. Kalmykov, Mikhail E. Veisman

Serge Youri Kalmykov

Squeezing the quantum fluctuations of the two-mode light due to the nonstationary coupling between the quadrature components q_1 and q_2 is examined. The delta-function and step-function mode couplings are considered. The conditions of weak and strong step-function coupling are distinguished, the latter being the condition of the instability for the classical counterpart of the quantum system under study. Under the conditions of weak coupling the quadrature squeezing is established in both a two-mode electromagnetic noise in thermal equilibrium (the thermal state) and a two- mode correlated coherent state (CCS). Squeezing in the thermal state is suppressed at a high temperature ...


Anthropic Considerations In Multiple Domain Theories And The Scale Of Electroweak Symmetry Breaking, V. Agrawal, S. M. Barr, John Donoghue, D. Seckel Mar 1998

Anthropic Considerations In Multiple Domain Theories And The Scale Of Electroweak Symmetry Breaking, V. Agrawal, S. M. Barr, John Donoghue, D. Seckel

John Donoghue

One of the puzzles of the standard model is why the mass parameter m2, which determines the weak interaction scale, is closer to the quantum chromodynamics scale than to the grand unification or Planck scales. We consider a novel approach to this problem, based upon the idea that m2 takes different values in different domains of the Universe. The whole range of values for m2, from 1M2 P to 2M2 P, is explored, and it is found that only for values in a narrow window is life likely to be possible. The observed value of m2 is fairly typical of ...


Density Fluctuations In Vibrated Granular Materials , E.R. Nowak, J.B. Knight, E. Ben-Naim, H.M Jaeger, S.R. Nagel Jan 1998

Density Fluctuations In Vibrated Granular Materials , E.R. Nowak, J.B. Knight, E. Ben-Naim, H.M Jaeger, S.R. Nagel

Eli Ben-Naim

We report systematic measurements of the density of a vibrated granular material as a function of time. Monodisperse spherical beads were confined to a cylindrical container and shaken vertically. Under vibrations, the density of the pile slowly reaches a final steady-state value about which the density fluctuates. We have investigated the frequency dependence and amplitude of these fluctuations as a function of vibration intensity Γ. The spectrum of density fluctuations around the steady state value provides a probe of the internal relaxation dynamics of the system and a link to recent thermodynamic theories for the settling of granular material. In ...


Crossing Of Disclinations In Nematic Slabs, T. Ishikawa, Oleg Lavrentovich Jan 1998

Crossing Of Disclinations In Nematic Slabs, T. Ishikawa, Oleg Lavrentovich

Oleg Lavrentovich

It is shown experimentally that crossing and intercommutation of disclinations in a bounded nematic cell depend on surface orientation of the director and the relative strength of disclinations. Lines of opposite strength switch the pinned ends between the bounding plates and vanish independently of each other if the surface orientation is tangential. In contrast, tilted surface orientation preserves the stability of lines.


Resistivity Determination From Small Crystallites, S. Hyun, M. Thorpe, B. Golding, M. Jaeger, Anthony Day Dec 1997

Resistivity Determination From Small Crystallites, S. Hyun, M. Thorpe, B. Golding, M. Jaeger, Anthony Day

Anthony Roy Day

We determine the resistivity of small micrometer-sized conductors with arbitrary shapes. It is shown that with n terminals attached to the sample, there are n(n􏰝1)/2 independent measurements of the resistance that can be made; from which the sample resistivity and the contact resistances can be extracted. An image of the sample is digitized and a finite element analysis is used to determine the geometrical factors that arise from the nonuniform current flow and hence control the resistance measurements. It is shown that all the elements of the resistance matrix for the sample are generated from the diagonal ...


Measurements Of Kleinman-Disallowed Hyperpolarizability In Conjugated Chiral Molecules, S. Hubbard, R. Petschek, K. Singer, N. D'Sidocky, C. Hudson, Liang-Chy Chien, C. Henderson, P. Cahill Dec 1997

Measurements Of Kleinman-Disallowed Hyperpolarizability In Conjugated Chiral Molecules, S. Hubbard, R. Petschek, K. Singer, N. D'Sidocky, C. Hudson, Liang-Chy Chien, C. Henderson, P. Cahill

Liang-Chy Chien

We have designed a hyper-Rayleigh scattering scheme to measure six scalar invariants of the squared hyperpolarizability tensor beta(2). OUT theoretical approach expresses the rotational invariants of the irreducible beta components as scalars, which eliminates the need for difficult frame transformations. We applied our scheme to several conjugated chiral molecules and found that there are significant Kleinman-disallowed pseudotensor contributions to their hyperpolarizability. These components, along with a large optical rotation and the results of quantum-chemical calculations, indicate a handed nonplanar delocalization of the charge-transfer system in such molecules as predicted by quantum-chemical calculations and are expected to lead to macroscopic ...