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Full-Text Articles in Physics

Virasoro Model Space, Hoseong La, Philip C. Nelson, A S. Schwarz Dec 1990

Virasoro Model Space, Hoseong La, Philip C. Nelson, A S. Schwarz

Department of Physics Papers

The representations of a compact Lie group G can be studied via the construction of an associated “model space”. This space has the property that when geometrically quantized its Hilbert space contains every irreducible representation of G just once. We construct an analogous space for the group Diff S1. It is naturally a complex manifold with a holomorphic, free action of Diff S1 preserving a family of pseudo-Kahler structures.All of the “good” coadjoint orbits are obtained from our space by Hamiltonian constraint reduction. We briefly discuss the connection to the work of Alekseev and Shatashvili.


Wetting Transitions In A Cylindrical Pore, Andrea J. Liu, Douglas J. Durian, Eric Herbolzheimer, S. A. Safran Oct 1990

Wetting Transitions In A Cylindrical Pore, Andrea J. Liu, Douglas J. Durian, Eric Herbolzheimer, S. A. Safran

Department of Physics Papers

The wetting behavior of two-phase systems confined inside cylindrical pores is studied theoretically. The confined geometry gives rise to wetting configurations, or microstructures, which have no analog in the well-studied planar case. Many features observed in experiments on binary liquid mixtures in porous media, previously interpreted in terms of random fields, are shown to be consistent with wetting in a confined geometry with no randomness.


Capillary Behavior Of Binary Liquid Mixtures Near Criticality: Rise And Kinetics, Douglas J. Durian, Kumudini Abeysuriya, Susan K. Watson, Carl Franck Oct 1990

Capillary Behavior Of Binary Liquid Mixtures Near Criticality: Rise And Kinetics, Douglas J. Durian, Kumudini Abeysuriya, Susan K. Watson, Carl Franck

Department of Physics Papers

In three different phase-separated binary liquid mixtures we have observed stationary capillary rises in which the meniscus curvature is inconsistent with the sign of the rise. This ‘‘inverted-meniscus’’ configuration occurs within approximately 50 mK of the mixture’s critical temperature and shows no sign of decay after much longer than the characteristic time for relaxation. We also report experiments showing that perturbation of the wetting layer inside the capillary tube can dramatically affect the capillary rise. This motivates three scenarios in which the behavior of the wetting layer foils an equilibrium capillary rise measurement of the contact angle and produces ...


Beyond Conformal Field Theory, Philip C. Nelson Jun 1990

Beyond Conformal Field Theory, Philip C. Nelson

Department of Physics Papers

This is an account of some recent work done with H. S. La [1] [2], based ultimately on the work of Fischler and Susskind [3] and Polchinski [4].


High-Temperature Series For Random-Anisotropy Magnets, Ronald Fisch, A. Brooks Harris Jun 1990

High-Temperature Series For Random-Anisotropy Magnets, Ronald Fisch, A. Brooks Harris

Department of Physics Papers

High-temperature series expansions for thermodynamic functions of random-anisotropy-axis models in the limit of infinite anisotropy are presented, for several choices of the number of spin components, m. In three spatial dimensions there is a divergence of the magnetic susceptibility χM for m=2. We find Tc/J=1.78±0.01 on the simple cubic lattice, and on the face-centered cubic lattice, we find Tc/J=4.29±0.01. There is no divergence of χM at finite temperature for m≥3 on either lattice. We also give results for simple hypercubic lattices.


Many-Body Potentials And Atomic-Scale Relaxations In Noble-Metal Alloys, Graeme J. Ackland, Vaclav Vitek May 1990

Many-Body Potentials And Atomic-Scale Relaxations In Noble-Metal Alloys, Graeme J. Ackland, Vaclav Vitek

Departmental Papers (MSE)

We derive empirical many-body potentials for noble-metal alloy systems in the framework of the Finnis-Sinclair model [Philos. Mag. A 50, 45 (1984)] which is based on a second-moment approximation to the tight-binding density of states for transition metals [F. Cyrot, J. Phys. Chem. Solids 29, 1235 (1968)]. The most important extension of the model is a simple incorporation of interspecies interactions which involves fitting the alloying energies. The importance of properly accounting for the local atomic relaxations when constructing the potentials is emphasized. The observed principal features of the phase diagrams of the alloys are all well reproduced by this ...


Phase Locking In Heisenberg Helimagnets, A. Brooks Harris, Enrico Rastelli, Armando Tassi May 1990

Phase Locking In Heisenberg Helimagnets, A. Brooks Harris, Enrico Rastelli, Armando Tassi

Department of Physics Papers

We consider a Heisenberg model with ferromagnetic nearest‐neighbor and competing further‐neighbor exchange interactions in a small applied magnetic field at low temperature T. As a function of the exchange constants, the modulation vector is shown to have devil’s staircase behavior. We consider the effects of nonzero temperature and quantum effects. We find a special modulation wave vector at which the incommensurability energy vanishes for the classical system at T=0.


Series Study Of Percolation Moments In General Dimension, Joan Adler, Yigal Meir, Amnon Aharony, A. Brooks Harris May 1990

Series Study Of Percolation Moments In General Dimension, Joan Adler, Yigal Meir, Amnon Aharony, A. Brooks Harris

Department of Physics Papers

Series expansions for general moments of the bond-percolation cluster-size distribution on hypercubic lattices to 15th order in the concentration have been obtained. This is one more than the previously published series for the mean cluster size in three dimensions and four terms more for higher moments and higher dimensions. Critical exponents, amplitude ratios, and thresholds have been calculated from these and other series by a variety of independent analysis techniques. A comprehensive summary of extant estimates for exponents, some universal amplitude ratios, and thresholds for percolation in all dimensions is given, and our results are shown to be in excellent ...


Long Range Order In Random Anisotropy Magnets, Ronald Fisch, A. Brooks Harris May 1990

Long Range Order In Random Anisotropy Magnets, Ronald Fisch, A. Brooks Harris

Department of Physics Papers

High temperature series for the magnetic susceptibility, χ, of random anisotropy axis models in the limit of infinite anisotropy are presented, for two choices of the number of spin components, m. For m=2, we find T c =1.78 J on the simple cubic lattice, and on the face‐centered cubic lattice we find T c =4.29 J. There is no divergence of χ at finite temperature for m=3 on either lattice. For the four‐dimensional hypercubic lattice, we find finite temperature divergences of χ for both m=2 and m=3.


Remarks On Virasoro Model Space, Hoseong La, Philip C. Nelson, A. S. Schwarz Mar 1990

Remarks On Virasoro Model Space, Hoseong La, Philip C. Nelson, A. S. Schwarz

Department of Physics Papers

A model space for the Virasoro group is constructed and some remarks on its properties are given. Presented by Philip C. Nelson at Texas A&M Superstring Workshop, March 12-17, 1990.


Resistance Distributions Of The Random Resistor Network Near The Percolation Threshold, A. Brooks Harris, Yigal Meir, Amnon Aharony Mar 1990

Resistance Distributions Of The Random Resistor Network Near The Percolation Threshold, A. Brooks Harris, Yigal Meir, Amnon Aharony

Department of Physics Papers

We study the generalized resistive susceptibility, χ(λ)≡Σx’[exp[-1/2λ2R(xx’)]]av where [ ]av denotes an average over all configurations of clusters with weight appropriate to bond percolation, R(x,x’) is the resistance between nodes x and x’ when occupied bonds are assigned unit resistance and vacant bonds infinite resistance. For bond concentration p near the percolation threshold at pc, we give a simple calculation in 6-ε dimensions of χ(λ) from which we obtain the distribution of resistances between two randomly chosen terminals. From χ(λ) we also obtain the qth-order ...


Effective Field Equations For Fermionic Strings, Hoseong La, Philip C. Nelson Feb 1990

Effective Field Equations For Fermionic Strings, Hoseong La, Philip C. Nelson

Department of Physics Papers

We show how to obtain loop-corrected effective field equations in tachyon-free heterotic string theories. The corrections are automatically gauge-invariant; they simultaneously secure Brst-decoupling and unambiguous loop amplitudes. We introduce a cutoff for two-dimensional field theory which is more general than the choice of a world-sheet metric, and using this we give an invariant description of factorization of fermionic amplitudes. As an example we work out the linearized corrections for the O(16) × O(16) heterotic string. They come from a finite corrected effective action.


First-Order Phase Transition Induced By Quantum Fluctuations In Heisenberg Helimagnets, Enrico Rastelli, A. Brooks Harris Feb 1990

First-Order Phase Transition Induced By Quantum Fluctuations In Heisenberg Helimagnets, Enrico Rastelli, A. Brooks Harris

Department of Physics Papers

We calculate the ground-state energy of an isotropic quantum Heisenberg ferromagnet on an hexagonal lattice with ferromagnetic exchange interactions J1 and J’ between nearest neighbors in the same basal plane and adjacent basal planes and, respectively, competing interactions J2 and J3 between second- and third-nearest neighbors in the same basal plane, respectively. When the ground-state energy of a helical state with wave vector Q is expanded for small Q as EG(Q)=E0+E2Q2+E4Q4+...., then the coefficients E2 and E4 can be evaluated exactly at zero ...


Scaling Of Negative Moments Of The Growth Probability Of Diffusion-Limited Aggregates, A. Brooks Harris, Michael Cohen Jan 1990

Scaling Of Negative Moments Of The Growth Probability Of Diffusion-Limited Aggregates, A. Brooks Harris, Michael Cohen

Department of Physics Papers

The qth moment M(q) of the growth probability of diffusion-limited aggregates is studied for q<0 in terms of the value [M(q,N)]av obtained by averaging M(q) over the ensemble of all aggregates of a given number of particles N. For a range of structures that are susceptible to precise analysis, we verify that all moments, even those for q<0, obey asymptotic power-law scaling in N. Since we cannot analyze completely arbitrary structures, our analysis is not definitive. However, it does suggest the validity of a recent proposal by one of us that there is no ...