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Full-Text Articles in Physics

Quantum Chaos In A Double Square-Well: An Approach Based On Bohm's View Of Quantum Mechanics, O. F. De Alcantara Bonfim, J. Florencio, F. C. Sá Barreto Nov 1998

Quantum Chaos In A Double Square-Well: An Approach Based On Bohm's View Of Quantum Mechanics, O. F. De Alcantara Bonfim, J. Florencio, F. C. Sá Barreto

Physics Faculty Publications and Presentations

We study the dynamics of a quantum particle in a double square-well potential within a deterministic framework using Bohm’s quantum mechanics. Phase portraits, Fourier spectral analysis, Poincaré sections, and Lyapunov exponents clearly indicate that the particle undergoes periodic, quasiperiodic, and chaotic motions depending on the initial form of the wave packet. We also make a detailed comparison between the predictions of the present approach and those of conventional quantum mechanics for the same problem.


Simple Model For Linear And Nonlinear Mixing At Unstable Fluid Interfaces With Variable Acceleration, John D. Ramshaw Nov 1998

Simple Model For Linear And Nonlinear Mixing At Unstable Fluid Interfaces With Variable Acceleration, John D. Ramshaw

Physics Faculty Publications and Presentations

A simple model is described for predicting the time evolution of the half-width h of a mixing layer between two initially separated immiscible fluids of different density subjected to an arbitrary time-dependent variable acceleration history a(t). The model is based on a heuristic expression for the kinetic energy per unit area of the mixing layer. This expression is based on that for the kinetic energy of a linearly perturbed interface, but with a dynamically renormalized wavelength which becomes proportional to h in the nonlinear regime. An equation of motion for h is then derived from Lagrange's equations. This ...


Flux Measurements And Sampling Strategies: Applications To Methane Emissions From Rice Fields, M. A. K. Khalil, R. A. Rasmussen, Martha J. Shearer Oct 1998

Flux Measurements And Sampling Strategies: Applications To Methane Emissions From Rice Fields, M. A. K. Khalil, R. A. Rasmussen, Martha J. Shearer

Physics Faculty Publications and Presentations

The emissions of methane from rice fields and other sources are often measured by placing chambers on the surface and taking sequential samples. Although static chambers pose several problems that affect the accuracy of the data, there are a few parameters that, if carefully chosen, can improve the reliability of the data and reduce the uncertainties. These parameters are the length of time the chamber is kept on the rice plants, the number of samples that are drawn to estimate the flux, the basal area and height of the chamber, the frequency of measurements during the growing season, and the ...


Effects Of Production And Oxidation Processes On Methane Emissions From Rice Fields, M. Khalil, R. A. Rasmussen, Martha J. Shearer Oct 1998

Effects Of Production And Oxidation Processes On Methane Emissions From Rice Fields, M. Khalil, R. A. Rasmussen, Martha J. Shearer

Physics Faculty Publications and Presentations

The emission of methane from rice fields is the difference between the amount produced in the anaerobic zone below the soil and the amount oxidized in the root zone. Plants can also contribute to methane production by exuding organic compounds that may be utilized by methanogenic bacteria. We measured methane emissions from rice fields at Tu Zu in China between 1988 and 1994, which gave average emissions of about 30 mg m⁻² h⁻¹. We estimate that 45-60% of the methane produced was oxidized before reaching the atmosphere; and root exudates may have contributed of the order of 10 ...


Measurements Of Methane Emissions From Rice Fields In China, M. A. K. Khalil, R. A. Rasmussen, Martha J. Shearer, R. W. Dalluge, Lixin Ren, Chang-Lin Duan Oct 1998

Measurements Of Methane Emissions From Rice Fields In China, M. A. K. Khalil, R. A. Rasmussen, Martha J. Shearer, R. W. Dalluge, Lixin Ren, Chang-Lin Duan

Physics Faculty Publications and Presentations

Rice fields have always been regarded as one of the largest anthropogenic sources of atmospheric methane. Here we report the results of a 7-year study of methane emissions from rice fields in the Sichuan Province of China. In this region, there is one crop of rice per year, the fields are continuously flooded from transplanting to harvest, and there is heavy use of organic fertilizers. Emissions over the entire growing season were measured from each of up to 24 plots. Environmental variables were measured and relevant supporting data on the agricultural practices were recorded. The fields were studied under prevailing ...


Factors Affecting Methane Emissions From Rice Fields, M. A. K. Khalil, R. A. Rasmussen, Martha J. Shearer, R. W. Dalluge, Lixin Ren, Chang-Lin Duan Oct 1998

Factors Affecting Methane Emissions From Rice Fields, M. A. K. Khalil, R. A. Rasmussen, Martha J. Shearer, R. W. Dalluge, Lixin Ren, Chang-Lin Duan

Physics Faculty Publications and Presentations

Methane emissions from rice fields are affected by a number of environmental and agricultural factors. We have analyzed our 7-year data set on methane emissions from rice fields in Tu Zu, China, to delineate the relationships between emissions and a number of variables that were measured at the same time. Our work was done in fields that were managed under prevailing agricultural practices of the region. Consequently, only the effect of factors that vary from year to year or during the growing season can be calculated. In our study we measured the effects of environmental variables (soil temperature, wind speed ...


A Note On The Green Dyadic Calculation Of The Decay Rates For Admolecules At Multiple Planar Interfaces, P.T. Leung, R. L. Hartman, Scott M. Cohen Oct 1998

A Note On The Green Dyadic Calculation Of The Decay Rates For Admolecules At Multiple Planar Interfaces, P.T. Leung, R. L. Hartman, Scott M. Cohen

Physics Faculty Publications and Presentations

The Green dyadic formulation for calculating classical decay rates of admolecules at multiple planar interfaces first published by Chance, Prock and Silbey is reexamined. It is pointed out that, for the case of fluorescing molecules sandwiched between a system of super- and substrate interfaces, the original formalism requires significant modifications in order to lead to results consistent with those obtained from the Sommerfeld radiation theory.


Chaotic Dynamics In Billiards Using Bohm’S Quantum Mechanics, O. F. De Alcantara Bonfim, J. Florencio, F. C. Sá Barreto Sep 1998

Chaotic Dynamics In Billiards Using Bohm’S Quantum Mechanics, O. F. De Alcantara Bonfim, J. Florencio, F. C. Sá Barreto

Physics Faculty Publications and Presentations

The dynamics of a particle in square and circular billiards is studied within the framework of Bohm’s quantum mechanics. While conventional quantum mechanics predicts that the system shows no indication of chaotic behavior for these geometries from either the eigenvalue spectra distribution or the structure of the eigenfunctions, we find that in Bohm’s quantum mechanics these systems exhibit both regular and chaotic behavior, depending on the form of the initial wave packet and on the particle’s initial position.


Path Integral For The Quantum Harmonic Oscillator Using Elementary Methods, Scott M. Cohen Jun 1998

Path Integral For The Quantum Harmonic Oscillator Using Elementary Methods, Scott M. Cohen

Physics Faculty Publications and Presentations

We present a purely analytical method to calculate the propagator for the quantum harmonic oscillator using Feynman’s path integral. Though the details of the calculation are involved, the general approach uses only matrix diagonalization and well-known integrals, techniques which an advanced undergraduate should understand. The full propagator, including both the prefactor and the classical action, is obtained from a single calculation which involves the exact diagonalization of the discretized action for the system.


General Formulation Of The Semirelativistic Approach To Atomic Sum Rules, P.T. Leung, Scott M. Cohen Jun 1998

General Formulation Of The Semirelativistic Approach To Atomic Sum Rules, P.T. Leung, Scott M. Cohen

Physics Faculty Publications and Presentations

A general scheme is presented for obtaining systematic relativistic corrections to quantum-mechanical sum rules for various calculations in atomic physics. The single-particle picture and the Foldy-Wouthuysen transformation [Phys. Rev. 78, 29 (1950)] are adopted to derive such corrections. Results are obtained for the ldquogeneralized Bethe sums,rdquo which include all higher moments of the energy transfer, and explicit results are given to the lowest order of relativistic corrections.


The Surface Plasmon Enhancement Effect On Adsorbed Molecules At Elevated Temperatures, P.T. Leung, Hai-Pang Chiang, W. S. Tse Feb 1998

The Surface Plasmon Enhancement Effect On Adsorbed Molecules At Elevated Temperatures, P.T. Leung, Hai-Pang Chiang, W. S. Tse

Physics Faculty Publications and Presentations

The surface plasmon enhancement effect on adsorbed molecules at elevated substrate temperatures is studied theoretically using surface enhanced Raman scattering (SERS) as an example. The surface structure is idealized to be a monodisperse spherical particle with its nonlocal dielectric response accounted for. The temperature effects are modeled using a temperature-dependent collision frequency in the Drude model. Numerical results show that only a small decrease in the SERS enhancement ratio occurs for temperatures up to the melting point of the substrate, even for scattering close to the surface plasmon resonance frequency of the metal. More definitive results are subjected to more ...


Self-Consistent Effective Binary Interaction Approximation For Strongly Coupled Multifluid Dynamics, John D. Ramshaw Jan 1998

Self-Consistent Effective Binary Interaction Approximation For Strongly Coupled Multifluid Dynamics, John D. Ramshaw

Physics Faculty Publications and Presentations

An improved self-consistent effective binary diffusion approximation for multicomponent diffusion was recently described [1]. Here we develop an analogous self-consistent effective binary interaction (SCEBI) approximation for simplifying multifluid dynamical descriptions in which each fluid is strongly coupled to the other fluids by pairwise frictional forces. The net drag force on each fluid is the summation of the drag forces due to each of the other fluids. This summation is approximated by a single term proportional to the velocity of the fluid in question relative to an appropriately weighted average velocity. This approximation permits an explicit numerical solution for the fluid ...