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Articles 29011 - 29040 of 36693

Full-Text Articles in Physical Sciences and Mathematics

Cyclotron Frequency Coupled Enhancement Of Kerr Rotation In Low Refractive Index-Dielectric/Magneto-Optic Bilayer Thin-Film Structures, A. De, A. Puri Jan 2002

Cyclotron Frequency Coupled Enhancement Of Kerr Rotation In Low Refractive Index-Dielectric/Magneto-Optic Bilayer Thin-Film Structures, A. De, A. Puri

Physics Faculty Publications

We investigate the enhancement of magneto-optic polar Kerr rotation over a broad range of optical frequencies. The Drude model for the dielectric tensor is considered. Resonance-like peaks in the Kerr rotation and ellipticity caused in the vicinity of a plasma edge is extended throughout the visible spectrum by deriving an expression for the cyclotron frequency such that Re(ϵxx)∼1 at any given incident photon energy and plasma frequency of the material. The Kerr rotation obtained by use of this expression was studied for the case of InSb and further enhancement of Kerr rotation was achieved in the …

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Energy Flow And Fluorescence Near A Small Metal Particle, Purna C. Das, Ashok Puri Jan 2002

Energy Flow And Fluorescence Near A Small Metal Particle, Purna C. Das, Ashok Puri

Physics Faculty Publications

We examine the classical energy-balance equation for a fluorescing system consisting of a molecule near a small, spherical metal particle capable of sustaining electromagnetic resonances and irradiated with laser light. From the energy-flow distribution in the entire system, we obtain the enhancement factor for the fluorescence emission of the adsorbed molecule. Numerical results demonstrate that the electromagnetic interactions of the molecule and the surface can be understood in terms of energy flow through the entire system and applied to investigate spectroscopic properties of adsorbates in similar systems. Absorption and emission rates of the adsorbed molecule are determined considering the energy-flow …

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Effect Of Ga Content On Defect States In Cuin1-XGaXSe2 Photovoltaic Devices, Jennifer T. Heath, J. David Cohen, William N. Shafarman, Dongxiang Liao, Angus Rockett Jan 2002

Effect Of Ga Content On Defect States In Cuin1-XGaXSe2 Photovoltaic Devices, Jennifer T. Heath, J. David Cohen, William N. Shafarman, Dongxiang Liao, Angus Rockett

Faculty Publications

Defects in the band gap of CuIn1-xGaxSe2 have been characterized using transient photocapacitance spectroscopy. The measured spectra clearly show response from a band of defects centered around 0.8 eV from the valence band edge as well as an exponential distribution of band tail states. Despite Ga contents ranging from Ga/(In+Ga)=0.0 to 0.8, the defect bandwidth and its position relative to the valence band remain constant. This defect band may act as an important recombination center, contributing to the decrease in device efficiency with increasing Ga content.

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Electronic-Structure-Based Investigation Of Magnetism In The Fe8 Molecular Magnet, Mark R. Pederson, Jens Kortus, S. N. Khanna Jan 2002

Electronic-Structure-Based Investigation Of Magnetism In The Fe8 Molecular Magnet, Mark R. Pederson, Jens Kortus, S. N. Khanna

Physics Publications

We have performed density-functional-based electronic structure calculations on a single Fe8 molecular nanomagnet. Our calculated total moments and local moments are in excellent agreement with experiment. By including spin–orbit coupling we determine the easy, medium, and hard axes and find the ordering of the principle axes also agrees with experiment. From our calculated anisotropy Hamiltonian, we calculate the oscillations in the tunnel splittings and compare to the experimental results.

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Caging Of Ni Clusters By Benzene Molecules And Its Effect On The Magnetism Of Ni Clusters, B. K. Rao, P. Jena Jan 2002

Caging Of Ni Clusters By Benzene Molecules And Its Effect On The Magnetism Of Ni Clusters, B. K. Rao, P. Jena

Physics Publications

Global optimization of the geometry of small Ni clusters interacting with benzene molecules yields equilibrium structures where the Ni atoms find themselves caged between the benzene molecules. This leads to quenching of the Ni magnetic moment in most of the complexes even though the structure of the caged Ni clusters remain relatively unchanged from their otherwise free gas phase geometry. The accuracy of these predictions, based on density functional theory with generalized gradient approximation for exchange and correlation, is established by the good agreement achieved between the calculated and available experimental dissociation energies and ionization potentials.

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Spectroscopy Of Ni-N(Benzene)(M) Anion Complexes, B. K. Rao, P. Jena Jan 2002

Spectroscopy Of Ni-N(Benzene)(M) Anion Complexes, B. K. Rao, P. Jena

Physics Publications

Total energy calculations based on the generalized gradient approximation to the density functional theory reveal that the Ni(benzene) and Ni(benzene)2 anions are unstable against autodetachment of the additional electron while other anion complexes containing more than one Ni atom are stable. Although the adiabatic electron affinities increase with Ni content, they are significantly smaller than those in pure Ni clusters containing the same number of Ni atoms. The difference between adiabatic electron affinities and vertical detachment energies are around 0.2 eV in most cases, indicating that the equilibrium geometries of Nin(benzene)−m are not significantly altered from their corresponding neutral geometries. …

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Magnetic Moment And Anisotropy In Fencom Clusters, J. Kortus, T. Baruah, M. R. Pederson, C. Ashman, Shiv N. Khanna Jan 2002

Magnetic Moment And Anisotropy In Fencom Clusters, J. Kortus, T. Baruah, M. R. Pederson, C. Ashman, Shiv N. Khanna

Physics Publications

Electronic structure calculations of FenCom (n+m=5 and 13) are used to examine the effects of alloying on the magnetic moment and magnetic anisotropies. Our density-functional studies show that many mixed clusters have moments comparable to or higher than the pure clusters. The mixed clusters, however, have very low anisotropies and could be ideal as soft magnetic materials. It is shown that shape, composition, and compositional ordering must be considered for optimization of anisotropy energies.

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Selected Reflection Imaging: A Useful Tool For Imaging Nanocomposite Magnetic Materials, Yi Liu, Y. Qiang, M. Yu, J. Ping Liu, David J. Sellmyer Jan 2002

Selected Reflection Imaging: A Useful Tool For Imaging Nanocomposite Magnetic Materials, Yi Liu, Y. Qiang, M. Yu, J. Ping Liu, David J. Sellmyer

David Sellmyer Publications

The great strength of transmission electron microscope (TEM) is its capability to access to both real space (imaging) and reciprocal space (diffraction). Selected reflection imaging (SRI) can relate the diffraction of nanostructured materials with the image, providing information otherwise not possible. The experimental set up of SRI is given by Liu and Sellmyer [I]. In this paper we present some new measurements on nanocomposite magnetic materials.

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Implications Of Single-Particle Experiments For Track Theory, Therapy And Radiation Protection, Robert Katz, Francis Cucinotta Jan 2002

Implications Of Single-Particle Experiments For Track Theory, Therapy And Radiation Protection, Robert Katz, Francis Cucinotta

Robert Katz Publications

‘‘Because the predominant exposure of cells in humans is to single isolated tracks, a critical question is what effects a single track is capable of producing and with what probabilities.’’ ‘‘Most of the current biophysical models. . . make the clear prediction that a single track can produce virtually all of the detrimental stochastic effects of interest.’’ ‘‘But one model, in particular (the amorphous track model of Katz and coworkers), disagrees fundamentally that a single low LET track has the ability to cause the cellular changes.’’ ‘‘This model leads to very dramatic differences in the predicted risk at low doses. …

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Holographic Recording Of Fast Events On A Ccd Camera, Zhiwen Liu, Martin Centurion, George Panotopoulos, John Hong, Demetri Psaltis Jan 2002

Holographic Recording Of Fast Events On A Ccd Camera, Zhiwen Liu, Martin Centurion, George Panotopoulos, John Hong, Demetri Psaltis

Martin Centurion Publications

We report on holographic recording of nanosecond events on a conventional CCD camera. Three frames of an air-discharge event, with resolution of 5.9 ns and frame interval of 12 ns, are recorded in a single CCD frame. Each individual frame is reconstructed by digital filtering of the CCD frame, since successively recorded holograms are centered at different carrier frequencies in the spatial frequency domain.

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Multispectrum, Spatially Addressable Polarization Interference Filter, Salman Saeed, Philip Bos Jan 2002

Multispectrum, Spatially Addressable Polarization Interference Filter, Salman Saeed, Philip Bos

Philip J. Bos

We review current synthesis techniques for generating and improving birefringent filters. The relationship between wave-plate orientation and the resulting spectral output is shown to be that of a simple Fourier transform. By using this relationship and starting from the fan Sole configuration, we easily generated plate orientations providing lower sidelobe levels and improved finesse. We outline a method by which filters can be constructed to provide from 0 to 100% of the desired passband in a continuous fashion. Such a filter can be stacked to allow rapid control of any number of passbands and is shown, as an example in …

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Laplace Transform Of Spherical Bessel Functions, Andrei Ludu Jan 2002

Laplace Transform Of Spherical Bessel Functions, Andrei Ludu

Andrei Ludu

No abstract provided.

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A Comparison Of Haloe V19 With Sage Ii V6.00 Ozone Observations Using Trajectory Mapping, Gary A. Morris, James F. Gleason, James M. Russell Iii, Mark R. Schoeberl, M. Patrick Mccormick Jan 2002

A Comparison Of Haloe V19 With Sage Ii V6.00 Ozone Observations Using Trajectory Mapping, Gary A. Morris, James F. Gleason, James M. Russell Iii, Mark R. Schoeberl, M. Patrick Mccormick

Gary A. Morris

We apply trajectory mapping to an 8-year intercomparison of ozone observations from the Halogen Occultation Experiment (HALOE) (V19) and Stratospheric Aerosol and Gas Experiment (SAGE) II (V6.00) for the months March, May, June, September, October, and December from the period December 1991 to October 1999. Our results, which represent the most extensive such intercomparison of these two data sets to date, suggest a root-mean-square difference between the two data sets of >15% below 22 km in the tropics and of 4–12% throughout most of the rest of the stratosphere. In addition, we find a bias with HALOE ozone low relative …

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Growing Correlation Length On Cooling Below The Onset Of Caging In A Simulated Glass-Forming Liquid, N. Lacevic, Francis W. Starr, T. B. Schrøder, V. N. Novikov, S. C. Glotzer Jan 2002

Growing Correlation Length On Cooling Below The Onset Of Caging In A Simulated Glass-Forming Liquid, N. Lacevic, Francis W. Starr, T. B. Schrøder, V. N. Novikov, S. C. Glotzer

Francis Starr

No abstract provided.

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Molecular Dynamics Simulation Of A Polymer Melt With A Nanoscopic Particle, Francis W. Starr, T. B. Schroder, S. C. Glotzer Jan 2002

Molecular Dynamics Simulation Of A Polymer Melt With A Nanoscopic Particle, Francis W. Starr, T. B. Schroder, S. C. Glotzer

Francis Starr

No abstract provided.

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Transitions Between Inherent Structures In Water, Nicolas Giovambattista, Francis W. Starr, Francesco Sciortino, Sergey V. Buldyrev, H. Eugene Stanley Jan 2002

Transitions Between Inherent Structures In Water, Nicolas Giovambattista, Francis W. Starr, Francesco Sciortino, Sergey V. Buldyrev, H. Eugene Stanley

Francis Starr

No abstract provided.

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Inclusive Gluon Production In Deep Inelastic Scattering At High Parton Density, Yuri V. Kovchegov, Kirill Tuchin Jan 2002

Inclusive Gluon Production In Deep Inelastic Scattering At High Parton Density, Yuri V. Kovchegov, Kirill Tuchin

Kirill Tuchin

We calculate the cross section of single inclusive gluon production in deep inelastic scattering at very high energies in the saturation regime, where the parton densities inside hadrons and nuclei are large and the evolution of structure functions with energy is nonlinear. The expression we obtain for the inclusive gluon production cross section is generated by this nonlinear evolution. We analyze the rapidity distribution of the produced gluons as well as their transverse momentum spectrum given by the derived expression for the inclusive cross section. We propose an ansatz for the multiplicity distribution of gluons produced in nuclear collisions which …

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Three-Dimensional Landau Theory For Multivariant Stress-Induced Martensitic Phase Transformations. Ii. Multivariant Phase Transformations And Stress Space Analysis, Valery I. Levitas, Dean L. Preston Jan 2002

Three-Dimensional Landau Theory For Multivariant Stress-Induced Martensitic Phase Transformations. Ii. Multivariant Phase Transformations And Stress Space Analysis, Valery I. Levitas, Dean L. Preston

Valery I. Levitas

In this paper, the three-dimensional Landau model of austenite-martensite transformations constructed in Part I is generalized to include transformations between an arbitrary number of martensitic variants. The model can incorporate all temperature-dependent thermomechanical properties of both phases for arbitrary crystal symmetries, including higher-order elastic constants, and it correctly describes the characteristic features of stress-strain curves for shape-memory alloys and steels, namely, constant transformation strain tensors, constant or weakly temperature dependent stress hysteresis, and transformation at nonzero tangent moduli. Geometric representations of the conditions for phase equilibrium and phase transformations in six-dimensional stress space are developed. For the cubic-tetragonal phase transformation, …

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Three-Dimensional Landau Theory For Multivariant Stress-Induced Martensitic Phase Transformations. I. Austenite↔Martensite, Valery I. Levitas, Dean L. Preston Jan 2002

Three-Dimensional Landau Theory For Multivariant Stress-Induced Martensitic Phase Transformations. I. Austenite↔Martensite, Valery I. Levitas, Dean L. Preston

Valery I. Levitas

A three-dimensional Landau theory of stress-induced martensitic phase transformations is presented. It describes transformations between austenite and martensitic variants and transformations between martensitic variants. The Landau free energy incorporates all temperature-dependent thermomechanical properties of both phases. The theory accounts for the principal features of martensitic transformations in shape memory alloys and steels, namely, stress-strain curves with constant transformation strain and constant, or weakly temperature dependent, stress hysteresis, as well as nonzero tangent elastic moduli at the phase transformation point. In part I, the austenite↔martensite phase transformation is treated, while transformations between martensitic variants are considered in part II.

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Low-Cost Manufacturing Process For Nanostructured Metals And Alloys, Travis L. Brown, Srinivasan Swaminathan, Srinivasan Chandrasekar, W. Dale Compton, Alexander H. King, Kevin P. Trumble Jan 2002

Low-Cost Manufacturing Process For Nanostructured Metals And Alloys, Travis L. Brown, Srinivasan Swaminathan, Srinivasan Chandrasekar, W. Dale Compton, Alexander H. King, Kevin P. Trumble

Alexander H. King

In spite of their interesting properties, nanostructured materials have found limited uses because of the cost of preparation and the limited range of materials that can be synthesized. It has been shown that most of these limitations can be overcome by subjecting a material to large-scale deformation, as occurs during common machining operations. The chips produced during lathe machining of a variety of pure metals, steels, and other alloys are shown to be nanostructured with grain (crystal) sizes between 100 and 800 nm. The hardness of the chips is found to be significantly greater than that of the bulk material.

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Altitude Dependence Of Middleand Low-Latitude Thermospheric Disturbance Winds Measured By Windii, J. T. Emmert, Bela G. Fejer, G. G. Shepard, B. H. Solheim Jan 2002

Altitude Dependence Of Middleand Low-Latitude Thermospheric Disturbance Winds Measured By Windii, J. T. Emmert, Bela G. Fejer, G. G. Shepard, B. H. Solheim

Bela G. Fejer

[1] Thermospheric neutral winds exhibit strong altitudinal and latitudinal variation during geomagnetically quiet and active times. We use daytime middle and low-latitude neutral winds measured by the Wind Imaging Interferometer (WINDII) instrument on board the Upper Atmosphere Research Satellite (UARS) over the 90–275 km height range to study the altitude and season dependent climatology of disturbance winds (i.e., with quiet time patterns removed) in magnetic coordinates. The daytime perturbations winds are generally equatorward and westward and decrease toward the magnetic equator. Both the zonal and meridional components decrease sharply below 120 km and are essentially insignificant below 100 km. The …

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Ultra-Dense Phosphorous Delta-Layer Grown Into Silicon From Ph3 Molecular Precursors, T. -C. Shen, J. -Y. Ji, M. A. Zudov, R. -R. Du, J. S. Kline, J. R. Tucker Jan 2002

Ultra-Dense Phosphorous Delta-Layer Grown Into Silicon From Ph3 Molecular Precursors, T. -C. Shen, J. -Y. Ji, M. A. Zudov, R. -R. Du, J. S. Kline, J. R. Tucker

T. -C. Shen

Phosphorous δ-doping layers were fabricated in silicon by PH3 deposition at room temperature, followed by low-temperature Si epitaxy.Scanning tunneling microscope images indicate large H coverage, and regions of c(2×2) structure. Hall data imply full carrier activation with mobility<40 cm2/V s when the surface coverage is ≲0.2 ML. Conductivity measurements show a ln(T) behavior at low temperatures, characteristic of a high-density two-dimensional conductor. Possible future applications to atom-scale electronics and quantum computation are briefly discussed.

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Ripening Of Porous Media, Benny Davidovitch, Deniz Ertas, Thomas C. Halsey Jan 2002

Ripening Of Porous Media, Benny Davidovitch, Deniz Ertas, Thomas C. Halsey

Benny Davidovitch

We address the surface tension-driven dynamics of porous media in nearly saturated pore-space solutions. We linearize this dynamics in the reaction-limited regime near its fixed points – surfaces of constant mean curvature (CMC surfaces). We prove that the only stable interface for this dynamics is the plane, and estimate the time scale for a CMC surface to become unstable. We also discuss the differences between open and closed system dynamics, pointing out the unlikelihood that CMC surfaces are ever realized in these systems on any time scale.

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Invaded Cluster Simulations Of The Xy Model In Two And Three, I. Dukovski, Jonathan Machta, L. V. Chayes Jan 2002

Invaded Cluster Simulations Of The Xy Model In Two And Three, I. Dukovski, Jonathan Machta, L. V. Chayes

Jonathan Machta

The invaded cluster algorithm is used to study the XY model in two and three dimensions up to sizes 20002 and 1203, respectively. A soft spin O(2) model, in the same universality class as the three-dimensional XY model, is also studied. The static critical properties of the model and the dynamical properties of the algorithm are reported. The results are Kc=0.45412(2) for the three-dimensional XY model and η=0.037(2) for the three-dimensional XY universality class. For the two-dimensional XY model the results are Kc=1.120(1) and η=0.251(5). The invaded cluster algorithm does not show any critical slowing for the magnetization or critical …

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Iterated Conformal Dynamics And Laplacian Growth, Felipe Barra, Benny Davidovitch, Itamar Procaccia Jan 2002

Iterated Conformal Dynamics And Laplacian Growth, Felipe Barra, Benny Davidovitch, Itamar Procaccia

Benny Davidovitch

The method of iterated conformal maps for the study of diffusion limited aggregates (DLA) is generalized to the study of Laplacian growth patterns and related processes. We emphasize the fundamental difference between these processes: DLA is grown serially with constant size particles, while Laplacian patterns are grown by advancing each boundary point in parallel, proportional to the gradient of the Laplacian field. We introduce a two-parameter family of growth patterns that interpolates between DLA and a discrete version of Laplacian growth. The ultraviolet putative finite-time singularities are regularized here by a minimal tip size, equivalently for all the models in …

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Quantum Corrections To The Reissner–Nordström And Kerr-Newman Metrics, John Donoghue, Barry R. Holstein, Björn Garbrecht, Thomas Konstandin Jan 2002

Quantum Corrections To The Reissner–Nordström And Kerr-Newman Metrics, John Donoghue, Barry R. Holstein, Björn Garbrecht, Thomas Konstandin

John Donoghue

We use effective field theory techniques to examine the quantum corrections to the gravitational metrics of charged particles, with and without spin. In momentum space the masslessness of the photon implies the presence of non-analytic pieces , q2log(−q2), etc. in the form factors of the energy–momentum tensor. We show how the former reproduces the classical non-linear terms of the Reissner–Nordström and Kerr–Newman metrics while the latter can be interpreted as quantum corrections to these metrics, of order Gαℏ/mr3

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Coiling Instabilities Of Multilamellar Tubes, Christian Santangelo, P. Pincus Jan 2002

Coiling Instabilities Of Multilamellar Tubes, Christian Santangelo, P. Pincus

Christian Santangelo

Myelin figures are densely packed stacks of coaxial cylindrical bilayers that are unstable to the formation of coils or double helices. These myelin figures appear to have no intrinsic chirality. We show that such cylindrical membrane stacks can develop an instability when they acquire a spontaneous curvature or when the equilibrium distance between membranes is decreased. This instability breaks the chiral symmetry of the stack and may result in coiling. A unilamellar cylindrical vesicle, on the other hand, will develop an axisymmetric instability, possibly related to the pearling instability.

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Classical Gluodynamics In Curved Space-Time And The Soft Pomeron, Dmitri Kharzeev, Eugene Levin, Kirill Tuchin Jan 2002

Classical Gluodynamics In Curved Space-Time And The Soft Pomeron, Dmitri Kharzeev, Eugene Levin, Kirill Tuchin

Kirill Tuchin

QCD at the classical level possesses scale invariance which is broken by quantum effects. This "dimensional transmutation" phenomenon can be mathematically described by formulating classical gluodynamics in a curved, conformally flat, space-time with non-vanishing cosmological constant. We study QCD high-energy scattering in this theory. We find that the properties of the scattering amplitude at small momentum transfer are determined by the energy density of vacuum fluctuations. The approach gives rise to the power growth of the total hadron-hadron cross section with energy, i.e., the pomeron. The intercept of the pomeron and the multiplicity of produced particles are evaluated. We also …

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A Simple Demonstration Of Mie Scattering Using An Overhead Projector, Charles L. Adler, James A. Lock Jan 2002

A Simple Demonstration Of Mie Scattering Using An Overhead Projector, Charles L. Adler, James A. Lock

James A. Lock

No abstract provided.

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The Effect Of Phase Separation On Charge Ordering State In La12xcaxmno3 (X ¼ 1/2, 2/3, And 3/4), H. D. Zhou, G. Li, S. J. Feng, Y. Liu, T. Qian, Xiaojuan Fan, X. G. Li Jan 2002

The Effect Of Phase Separation On Charge Ordering State In La12xcaxmno3 (X ¼ 1/2, 2/3, And 3/4), H. D. Zhou, G. Li, S. J. Feng, Y. Liu, T. Qian, Xiaojuan Fan, X. G. Li

Physics Faculty Research

The magnetic phase separation characteristics are found in manganese perovskite La1/3Ca2/3MnO3 by electron spin resonance (ESR) and magnetization measurements. An extra resonance signal observed in ESR spectra just above the charge ordering (CO) temperature TCO provides strong evidence for the existence of ferromagnetic (FM) clusters near the CO state. The investigation of the resistivity of La1-xCaxMnO3 (x=1/2, 2/3, and 3/4) in different magnetic fields up to 14 T shows that the effect of magnetic fields on CO state decreases with increasing x. Our results indicate that the percolative characteristics …

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