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Articles 211 - 240 of 255

Full-Text Articles in Physics

Quantum-Mechanical Harmonic Chain Attached To Heat Baths I: Equilibrium Properties, Ulrich Zürcher, Peter Talkner Sep 1990

Quantum-Mechanical Harmonic Chain Attached To Heat Baths I: Equilibrium Properties, Ulrich Zürcher, Peter Talkner

Physics Faculty Publications

Starting from quantum Langevin equations for operators we study thermal properties of a one-dimensional harmonic chain to whose ends independent heat baths are attached. In this paper, we mainly discuss the thermal equilibrium state that the chain eventually approaches if the heat baths are at equal temperatures. In the classical limit, this state is determined by the Gibbs ensemble of the free chain, whereas in the quantal case, this is only true if the strength of coupling between chain and heat baths is made infinitely small. We find that corrections for finite coupling strength are appreciable only in boundary layers …

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Random-Field Blume-Capel Model: Mean-Field Theory, Miron Kaufman, M. Kanner Aug 1990

Random-Field Blume-Capel Model: Mean-Field Theory, Miron Kaufman, M. Kanner

Physics Faculty Publications

The global phase diagram of the Blume-Capel model in a random field obeying the bimodal symmetric distribution is determined by using the mean-field method. The phase diagram includes an isolated ordered critical end point and two lines of tricritical points. A new phase emerges for strong enough random fields: the ferromagnetic-nonmagnetic phase. It is argued that such a phase occurs in three dimensions.

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Interference Enhancement Of The Internal Fields At Structural Scattering Resonances Of A Coated Sphere, James A. Lock Jul 1990

Interference Enhancement Of The Internal Fields At Structural Scattering Resonances Of A Coated Sphere, James A. Lock

Physics Faculty Publications

We examine the interior electromagnetic energy density of a coated nonabsorbing sphere at a number of scattering resonances. As is the case for an uncoated sphere, the interior energy density becomes large at the apl and bpl resonances. It becomes especially large for p - 1 values of the coating thickness at resonance. These p - 1 enhancements are analogous to the interference maxima that occur in the intensity reflectance of two thin films in contact.

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Polymerization On The Diamond Hierarchical Lattice: The Migdal-Kadanoff Renormalization-Group Scheme, Miron Kaufman, J. E. Touma Apr 1990

Polymerization On The Diamond Hierarchical Lattice: The Migdal-Kadanoff Renormalization-Group Scheme, Miron Kaufman, J. E. Touma

Physics Faculty Publications

The thermodynamics of the equilibrium polymerization model (grand-canonical ensemble of self-avoiding walks) in two dimensions is worked out by means of the Migdal-Kadanoff renormalization-group technique. This method involves renormalization-group flows in an eight-dimensional parameter space. At the critical point the number of relevant fields (positive exponents) is four. The leading exponent value differs by less than 1% from the (presumed) exact value. The results are exact for the polymerization problem defined on the diamond hierarchical lattice. Some results are peculiar to this lattice and are not expected to hold for Bravais lattices. For instance, the polymerized phase (infinite polymerization index) …

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Observability Of Atmospheric Glories And Supernumerary Rainbows, James A. Lock Dec 1989

Observability Of Atmospheric Glories And Supernumerary Rainbows, James A. Lock

Physics Faculty Publications

The finite spatial coherence width of sunlight at the Earth imposes restrictions on the production of scattering phenomena based on the interference of light waves. With the spatial coherence properties of sunlight taken into account, the visibility of the supernumerary rainbow sequence adjacent to the primary rainbow and the radii of the water droplets that produce the optimum glory intensity were calculated. A substantial reduction was found in the contrast of all the supernumeraries beyond the first few, and the peak observability of the glory occurred for water droplets with radii between 10 and 20 µm.

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An Improved Correction Algorithm For Number Density Measurements Made With The Forward-Scattering Spectrometer Probe, James A. Lock, Edward A. Hovenac Jun 1989

An Improved Correction Algorithm For Number Density Measurements Made With The Forward-Scattering Spectrometer Probe, James A. Lock, Edward A. Hovenac

Physics Faculty Publications

A correction factor to the number density measured by the Forward Scattering Spectrometer Probe (FSSP) which compensates for dead time and coincidence errors was determined by calculating the probabilities of and the average number of particles in the six possible types of dead time and coincidence events. These probabilities and averages were calculated by means of a probabilistic model based on Poisson statistics. A Monte Carlo computer simulation of the FSSP operation was also carried out and the number density correction factor was compared with the Monte Carlo data. For an actual number density of 2000/cm3, it was …

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A Correction Algorithm For Particle-Size Distribution Measurements Made With The Forward-Scattering Spectrometer Probe, James A. Lock, Edward A. Hovenac Jun 1989

A Correction Algorithm For Particle-Size Distribution Measurements Made With The Forward-Scattering Spectrometer Probe, James A. Lock, Edward A. Hovenac

Physics Faculty Publications

Multiparticle coincidence events in the scattering volume of the forward-scattering spectrometer probe (FSSP) cause the instrument to bias the measurement of the particle size distribution of atmospheric aerosols toward large diameters. We employ a probabilistic model based on Poisson statistics to determine the average diameter and rms width of the actual size distribution as functions of the average diameter and rms width of the measured distribution. We compare our predictions to a Monte Carlo simulation of the FSSP operation

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An Alternative Approach To The Teaching Of Rotational Dynamics, James A. Lock May 1989

An Alternative Approach To The Teaching Of Rotational Dynamics, James A. Lock

Physics Faculty Publications

An alternative approach to the stability of torque-free rotations and to top nutation that emphasizes conservation laws and physical reasoning is examined. It is felt that such an approach, which is largely free of sophisticated mathematics, would be useful in teaching these topics in rotational motion at the introductory physics level.

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Equilibrium Polymerization On The Equivalent-Neighbor Lattice, Miron Kaufman Apr 1989

Equilibrium Polymerization On The Equivalent-Neighbor Lattice, Miron Kaufman

Physics Faculty Publications

The equilibrium polymerization problem is solved exactly on the equivalent-neighbor lattice. The Flory-Huggins entropy of mixing is exact for this lattice. We verify the discrete version of the n-vector model when n→0 is equivalent to the equal reactivity polymerization process in the whole parameter space, including the polymerized phase. The polymerization processes for polymers satisfying the Schulz distribution exhibit nonuniversal critical behavior. A close analogy is found between the polymerization problem of index r and the Bose-Einstein ideal gas in d=-2r dimensions, with the critical polymerization corresponding to the Bose-Einstein condensation.

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An Analysis Of Two Unusual Reflection Caustics, James A. Lock, Judith R. Woodruff Mar 1989

An Analysis Of Two Unusual Reflection Caustics, James A. Lock, Judith R. Woodruff

Physics Faculty Publications

A reflection caustic consisting of an x or a cross surrounded by a circle was observed using two different reflector geometries. Double-glazed insulating windows that have become bowed, and circularly symmetric cookie trays and cake covers possessing two different curvatures at different distances from the symmetry axis, produce similar caustics when plane waves are incident far off-axis. For the case of the insulating windows, it was found that the concavely bowed outer pane produced the x portion of the caustic and the convexly bowed inner pane produced the circle portion. For the case of the circularly symmetric reflectors, the x …

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Non-Debye Enhancements In The Mie Scattering Of Light From A Single Water Droplet, James A. Lock, Judith R. Woodruff Feb 1989

Non-Debye Enhancements In The Mie Scattering Of Light From A Single Water Droplet, James A. Lock, Judith R. Woodruff

Physics Faculty Publications

The glare spots usually seen on a single water droplet which has been illuminated by a plane wave are produced by geometrical rays which correspond to the different terms of the Debye series expansion of the Mie scattered field. Recently other glare spot enhancements have been predicted which correspond to scattering resonances coupling to the orbiting rays associated with high-order geometrical rainbows. We observed the non-Debye enhancement of the eleventh-order rainbow glare spot at an observation angle of 90° on a 3.5-mm water droplet illuminated by polarized He-Ne laser light.

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Cooperative Effects Among Partial Waves In Mie Scattering, James A. Lock Dec 1988

Cooperative Effects Among Partial Waves In Mie Scattering, James A. Lock

Physics Faculty Publications

Observations of an illuminated water droplet at a close distance are described mathematically by the Fourier transform of the Mie-scattering amplitude convolved with the aperture function of the observer’s eye. Most of the sharp enhancements found in the Fourier transform correspond to geometrical rays associated with the various terms in the Debye-series expansion of the Mie amplitude. However, there are some enhancements that cannot be ascribed to any individual Debye-series term. Instead, they arise from a constructive interference cooperation of the phase of a scattering resonance in a single partial wave with the region of the stationary phase corresponding to …

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Transport Critical Current And Magnetization Measurements Of Melt-Processed Yba2cu3o7-X, A. H. Hermann, Z. Z. Sheng, W. Kiehl, D. Marsh, A. Elali, Paul D. Hambourger, C. Almasan, J. Estrada, T. Datta Nov 1988

Transport Critical Current And Magnetization Measurements Of Melt-Processed Yba2cu3o7-X, A. H. Hermann, Z. Z. Sheng, W. Kiehl, D. Marsh, A. Elali, Paul D. Hambourger, C. Almasan, J. Estrada, T. Datta

Physics Faculty Publications

We report magnetic field dependence of the transport critical current and dc magnetic susceptibility measurements on YBa2Cu3O7−x superconductors formed by melt-solid reactions at 950 °C between Ba-Cu-O (or Tb-Ba-Cu-O) and solid nonstoichiometric Y-Ba-Cu-oxide. Four-probe dc critical current measurements at 77, 64, and 4.2 K show strong depression of the critical current density with increasing magnetic field in agreement with a model of weakly linked superconducting regions. Diamagnetic shielding and Meissner flux expulsion measurements in the temperature range 10–300 K show about one third volume fraction of perfect superconductivity. Both shielding and flux expulsion were observed to be approximately temperature independent …

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Cayley-Tree Ising Model With Antiferromagnetic Nearest-Neighbor And Ferromagnetic Equivalent-Neighbor Interactions, Miron Kaufman, M. Kahana May 1988

Cayley-Tree Ising Model With Antiferromagnetic Nearest-Neighbor And Ferromagnetic Equivalent-Neighbor Interactions, Miron Kaufman, M. Kahana

Physics Faculty Publications

The phase diagram of the Ising model with antiferromagnetic nearest-neighbor interactions and ferromagnetic equivalent-neighbor interactions on the Cayley tree is determined exactly. A nonuniversal critical line separates the disordered and the ordered phases. A line of first-order transitions separating ferromagnetic order from antiferromagnetic order ends in the midst of the ordered phase at a classical ordered critical point. For a small range of values of the ratio of the two couplings, two transitions occur as the temperature is varied. In this case the uniform magnetization is not a monotonic function of the temperature.

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Theory Of The Observations Made Of High-Order Rainbows From A Single Water Droplet, James A. Lock Dec 1987

Theory Of The Observations Made Of High-Order Rainbows From A Single Water Droplet, James A. Lock

Physics Faculty Publications

Over a dozen rainbows have been observed in a single water droplet. They appear as glare spots on the water droplet which take on coloration at the appropriate rainbow angles. The appearance of rainbows as colored glare spots in this situation is understood in terms of the caustics created in the vicinity of the droplet by the refracting light rays. The angular positions of the glare spots are understood in terms of the Fourier transform of the geometric scattering amplitude. The rainbow glare spots are also found to appear numerically in the Fourier transform of the Mie scattered fields. An …

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Moment Analysis Of The Cluster-Size-Distribution Approach To Scaling During Coagulation, Thomas W. Taylor, C. M. Sorensen Dec 1987

Moment Analysis Of The Cluster-Size-Distribution Approach To Scaling During Coagulation, Thomas W. Taylor, C. M. Sorensen

Physics Faculty Publications

We study the temporal approach of a cluster size distribution to its asymptotic scaling form. By enforcing consistency between the distribution’s zeroth moment derived from both the Smoluchowski equation and the scaling distribution ansatz, we find values for the scaling exponents w and z in terms of the scaling exponent τ and the kernel homogeneity λ which are not equivalent to their asymptotic, scaling forms. The predicted values do agree well, however, with intermediate time values found in simulations by Kang, Redner, Meakin, and Leyvraz [Phys Rev. A 33, 1171 (1986)]. By enforcing consistency between all moment orders, the asymptotic …

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Generating Problem Sets With Word Processing Software, Jearl D. Walker Dec 1987

Generating Problem Sets With Word Processing Software, Jearl D. Walker

Physics Faculty Publications

No abstract provided.

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Numerical Methods In Optics: A Course About Learning Physics Through Computing, James A. Lock Dec 1987

Numerical Methods In Optics: A Course About Learning Physics Through Computing, James A. Lock

Physics Faculty Publications

Many advanced undergraduates find it difficult to connect abstract mathematical formalisms with the concrete physical phenomena that they describe. A course in optics from a numerical methods point of view is described. Its purpose is to exploit the students’ familiarity with computng in order to more effectively learn the physics involved in a number of realistic phenomena. The combination of demonstrations, computer calculations, and computer graphics display of the results can prove to be a useful tool in developing physical intuition in students.

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Square-Lattice Ising Model In A Weak Uniform Magnetic Field: Renormalization Group Analysis, Miron Kaufman Sep 1987

Square-Lattice Ising Model In A Weak Uniform Magnetic Field: Renormalization Group Analysis, Miron Kaufman

Physics Faculty Publications

For the two-dimensional ferromagnetic Ising critical point, I show that the known values of the critical exponents imply the absence of logarithms of the reduced temperature in the leading contributions to any field derivative of the free energy at zero magnetic field. For the square-lattice Ising antiferromagnet in a weak magnetic field, I compute the critical line Tc(H)=Tc0(1-0.038 023 259H2) and the leading contribution to the susceptibility χ=0.014 718 006 6H2ln(1/ǁtǁ), where t is the reduced temperature.

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Multicritical Susceptibility Sum Rules, Miron Kaufman, Michael Ma Mar 1987

Multicritical Susceptibility Sum Rules, Miron Kaufman, Michael Ma

Physics Faculty Publications

Asymptotically close to the Nth-order multicritical point of an N-phase system, there are N-1 sum rules involving the mean-field susceptibilities measured in each of the coexisting phases. These sum rules provide the experimentalist a convenient and stringent test of the theory. In particular, they facilitate the detection of nonclassical effects, especially valuable for N>3 where the fluctuation effect is dominated by the classical contribution for three-dimensional systems.

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Fresnel Diffraction Effects In Misfocused Vision, James A. Lock Mar 1987

Fresnel Diffraction Effects In Misfocused Vision, James A. Lock

Physics Faculty Publications

If a narrow line stimulus on an opposite contrast background is observed with appropriately misfocused vision, the stimulus appears as a number of alternating bright and dark fringes. A numerical calculation of this effect was performed. As a result it was found that the banding phenomenon is a Fresnel diffraction effect depending on the details of both the narrow line stimulus and the eye pupil.

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Multicritical Points In An Ising Random-Field Model, Miron Kaufman, Philip E. Klunzinger, A. Khurana Oct 1986

Multicritical Points In An Ising Random-Field Model, Miron Kaufman, Philip E. Klunzinger, A. Khurana

Physics Faculty Publications

The phase diagram of the mean-field Ising model in a random field obeying a symmetric three-peak distribution is determined. This distribution is relevant to diluted antiferromagnets in a uniform magnetic field. The phase diagram includes a fourth-order point, tricritical points, ordered critical points, critical end points, and a double critical end point. An ordered phase persists for arbitrarily large random fields at low temperatures.

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Origin Of Nonuniversality In Micellar Solutions: Comment, R. G. Caflisch, Miron Kaufman, J. R. Banavar Jun 1986

Origin Of Nonuniversality In Micellar Solutions: Comment, R. G. Caflisch, Miron Kaufman, J. R. Banavar

Physics Faculty Publications

No abstract provided.

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The Temporary Capture Of Light By A Dielectric Film, James A. Lock Oct 1985

The Temporary Capture Of Light By A Dielectric Film, James A. Lock

Physics Faculty Publications

When a wave packet of light passes through a dielectric film it is found that at a transmission maximum, the group velocity of the light wave packet within the film attains its minimum value. Similarly, at a transmission minimum, it is found that the group velocity of the light wave packet within the film attains its maximum value. The measurability of this effect is also discussed.

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Incident Beam Polarization For Laser Doppler Velocimetry Employing A Sapphire Cylindrical Window, James A. Lock, Harold J. Schock Jul 1985

Incident Beam Polarization For Laser Doppler Velocimetry Employing A Sapphire Cylindrical Window, James A. Lock, Harold J. Schock

Physics Faculty Publications

For laser Doppler velocimetry studies employing sapphire windows as optical access ports, the birefringency of sapphire produces an extra beam intersection volume which serves to effectively smear the acquired velocity flow field data. It is shown that for a cylindrical window geometry, the extra beam intersection volume may be eliminated with minimal decrease in the fringe visibility of the remaining intersection volume by suitably orienting the polarizations of the initial laser beams. For horizontally incident beams, these polarizations were measured at three intersection locations within the cylinder. It was found that the measured polarization angles agreed with the theoretical predictions.

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The Rotated Diffraction Grating: A Laboratory Experiment, James A. Lock Jan 1985

The Rotated Diffraction Grating: A Laboratory Experiment, James A. Lock

Physics Faculty Publications

No abstract provided.

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Relativistic Invariance And Zitterbewegung, James A. Lock Mar 1984

Relativistic Invariance And Zitterbewegung, James A. Lock

Physics Faculty Publications

We examine the question of what it is about the structure of relativistic quantum mechanics that causes the nonintuitive phenomenon of the Zitterbewegung of particle position to exist. Further, we examine various assumptions concerning the measurement process which are implicit in the observation of Zitterbewegung.

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Center-Of-Mass Properties Of Composite Systems Subject To Non-Linear External Interactions, James A. Lock Aug 1983

Center-Of-Mass Properties Of Composite Systems Subject To Non-Linear External Interactions, James A. Lock

Physics Faculty Publications

If two bound nonrelativistic quantum particles are each subject to a nonlinear external potential, their Schrödinger equation does not separate in relative and center-of-mass coordinates. For this case, the details of internal state of the composite affect its center-of-mass properties. The extent of this internal state influence is examined for an exactly soluble one-dimensional model system.

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Study Of Lattice Instabilities In Snx Euy-X Mo6s8 (Y=1.0 And 1.2), Paul D. Hambourger, J. C. Ho, C. Y. Huang, H. L. Luo Aug 1982

Study Of Lattice Instabilities In Snx Euy-X Mo6s8 (Y=1.0 And 1.2), Paul D. Hambourger, J. C. Ho, C. Y. Huang, H. L. Luo

Physics Faculty Publications

An anomaly in the heat capacity of Eu1.2Mo6S8 at ∼120 K (T0) has been observed and identified as a structural transformation. The heat capacity, electrical resistance, and Hall coefficient for the Eu-rich pseudoternaries have been measured under pressure to obtain the pressure dependence of T0. The depression of T0 by pressure is used to explain the pressure dependence of the superconducting transition temperature and the anomalous temperature dependence of the critical field.

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Negative Acceleration Components For A Relativistic Particle, James A. Lock Jul 1981

Negative Acceleration Components For A Relativistic Particle, James A. Lock

Physics Faculty Publications

Newtonian acceleration is considered in the light of special relativity theory with the result that the component of acceleration in the direction of an arbitrary applied force is always positive.(AIP)

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