Current Search: Green's functions (x)
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 Title
 Fluctuation and correlation effects in a charged surface immersed in an asymmetric electrolyte solution.
 Creator
 Acharya, Pramod, Lau, Andy W. C., Graduate College
 Date Issued
 20130412
 PURL
 http://purl.flvc.org/fcla/dt/3361263
 Subject Headings
 Green's functions, Field theory (Physics), Electrostatics
 Format
 Document (PDF)
 Title
 Nonequilibrium transport phenomena in lowdimensional quantum systems.
 Creator
 Valtchinov, Vladimir Ivanov., Florida Atlantic University, Wille, Luc T.
 Abstract/Description

In this thesis we have introduced and extensively studied a model for describing some essential nonequilibrium transport properties of a quantum system with reduced dimensionality. The problem of finding some of the kinetic characteristics of such a model system is formulated as that of finding a solution of a tunneling Hamiltonian with a Hubbard term. To solve this Hamiltonian we first make use of the path integral formalism, generalized for systems far from equilibrium, to perform the...
Show moreIn this thesis we have introduced and extensively studied a model for describing some essential nonequilibrium transport properties of a quantum system with reduced dimensionality. The problem of finding some of the kinetic characteristics of such a model system is formulated as that of finding a solution of a tunneling Hamiltonian with a Hubbard term. To solve this Hamiltonian we first make use of the path integral formalism, generalized for systems far from equilibrium, to perform the quantumstatistical average. The spectral function for the electrons in the well is calculated for different relevant sets of parameters. The possible presence of a Kondo peak in the interacting density of states is discussed. We calculate the frequencydriven conductance and energy losses in the linear response approximation. Numerical simulations of the general expressions show that for a given set of parameters consistent with the particular physical situation of interest, a resonant behavior is obtained for both the conductance and energy absorption for external frequencies equal to the Coulomb repulsion energy E(C).
Show less  Date Issued
 1993
 PURL
 http://purl.flvc.org/fcla/dt/14938
 Subject Headings
 Statistical mechanics, Quantum theory, Green's functions, Equilibrium
 Format
 Document (PDF)
 Title
 Scattering and response Green's function modeling of a fluidloaded coated cylindrical shell.
 Creator
 Treffot, Carole., Florida Atlantic University, Cuschieri, Joseph M., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
 Abstract/Description

An acoustic compliant coating is applied on a fluidloaded structure to control the radiated pressure, by decoupling the fluid medium from the vibrating surface. In this thesis the problem of an infinite cylindrical shell immersed in a fluid and entirely covered with an acoustic compliant layer, excited either by a ring force or an incident acoustic plane wave is considered. To model this problem two different approaches are used. The first one, which is available in the literature, is based...
Show moreAn acoustic compliant coating is applied on a fluidloaded structure to control the radiated pressure, by decoupling the fluid medium from the vibrating surface. In this thesis the problem of an infinite cylindrical shell immersed in a fluid and entirely covered with an acoustic compliant layer, excited either by a ring force or an incident acoustic plane wave is considered. To model this problem two different approaches are used. The first one, which is available in the literature, is based on multilayer shell theory. In this approach the scalar and the vector potential formulation are used to solve for the response and the scattering from the cylinder. The second approach is based on modeling the compliant layer by a normally reacting impedance layer on the surface of the shell. The velocity response Green's function of the shell is found using the hybrid numerical/analytical method. Results for the radiated and scattered pressure from the shell are also presented. The advantage of this second approach is that it can be used to model complex coating geometries. The results obtained with both approaches are compared.
Show less  Date Issued
 2001
 PURL
 http://purl.flvc.org/fcla/dt/12775
 Subject Headings
 Green's functions, Elastic plates and shells
 Format
 Document (PDF)
 Title
 ThreeDimensional Inversion Technique in Ocean Acoustics Using the Parabolic Equation Method.
 Creator
 Roa, Camilo Carlos, Frisk, George V., Florida Atlantic University, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
 Abstract/Description

A threedimensional parabolic equation (PE) and perturbation approach is used to invert for the depth and rangedependent geoacoustic characteristics of the seabed. The model assumes that the sound speed profile is the superposition of a known rangeindependent profile and an unknown depth and rangedependent perturbation. Using a Green’s function approach, the total measured pressure field in the water column is decomposed into a background field, which is due to the rangeindependent...
Show moreA threedimensional parabolic equation (PE) and perturbation approach is used to invert for the depth and rangedependent geoacoustic characteristics of the seabed. The model assumes that the sound speed profile is the superposition of a known rangeindependent profile and an unknown depth and rangedependent perturbation. Using a Green’s function approach, the total measured pressure field in the water column is decomposed into a background field, which is due to the rangeindependent profile, and a scattered field, which is due to the rangedependent perturbation. When the Born approximation is applied to the resulting integral equation, it can be solved for the rangedependent profile using linear inverse theory. Although the method is focused on inverting for the sound speed profile in the bottom, it can also invert for the sound speed profile in the water column. For simplicity, the sound speed profile in the water column was assumed to be known with a margin of error of ± 5 m/s. The rangedependent perturbation is added to the index of refraction squared n2(r), rather than the sound speed profile c(ro). The method is implemented in both Cartesian (x,y,z) and cylindrical (r,q,z) coordinates with the forward propagation of the field in x and r, respectively. Synthetic data are used to demonstrate the validity of the method [1]. Two inversion methods were combined, a Monte Carlo like algorithm, responsible for a starting approximation of the sound speed profile, and a steepest descent method, that finetuned the results. In simulations, the inversion algorithm is capable of inverting for the sound speed profile of a flat bottom. It was tested, for three different frequencies (50 Hz, 75 Hz, and 100 Hz), in a Pekeris waveguide, a rangeindependent layered medium, and a rangedependent medium, with errors in the inverted sound speed profile of less than 3%. Keywords: Threedimensional parabolic equation method, geoacoustic inversion, rangedependent sound speed profile, linear inversion, Born approximation, Green’s functions.
Show less  Date Issued
 2017
 PURL
 http://purl.flvc.org/fau/fd/FA00004868, http://purl.flvc.org/fau/fd/FA00004868
 Subject Headings
 Ocean tomography., Ocean bottom., Born approximation., Green's functions.
 Format
 Document (PDF)
 Title
 Boundary reflection coefficient estimation from depth dependence of the acoustic Green's function.
 Creator
 Conrad, Alexander., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
 Abstract/Description

Sound propagation in a waveguide is greatly dependent on the acoustic properties of the boundaries. The effect of these properties can be described by a bottom reflection coefficient RB, and surface reflection coefficient RS. Two methods for estimating reflection coefficients are used in this research. The first, the ratio method, is based on the variations of the Green's function with depth utilizing the ratio of the wavenumber spectra at two depths. The second, the pole method, is based on...
Show moreSound propagation in a waveguide is greatly dependent on the acoustic properties of the boundaries. The effect of these properties can be described by a bottom reflection coefficient RB, and surface reflection coefficient RS. Two methods for estimating reflection coefficients are used in this research. The first, the ratio method, is based on the variations of the Green's function with depth utilizing the ratio of the wavenumber spectra at two depths. The second, the pole method, is based on the wavenumbers of the modal peaks in the spectrum at a particular depth. A method to invert for sound speed and density is also examined. Estimates of RB and RS based on synthetic data by the ratio method were very close to their predicted values, especially for higher frequencies and longer apertures. The pole method returned less precise estimates though with longer apertures, the estimates were better. Using experimental data, results of the pole method as well a geoacoustic inversion technique based on them were mixed. The ratio method was used to estimate RS based on the actual data and returned results close to the predicted phase of p.
Show less  Date Issued
 2010
 PURL
 http://purl.flvc.org/FAU/3164094
 Subject Headings
 Underwater acoustics, Acoustic surface waves, Green's functions, Electromagnetic waves, Mathematics, Wave equation, Numerical solutions
 Format
 Document (PDF)