The derivation of the equations of motion for liquid helium II usually involves the notional separation of the liquid into two ingredients, normal fluid and superfluid. The total mass density of the liquid is taken to...
The derivation of the equations of motion for liquid helium II usually involves the notional separation of the liquid into two ingredients, normal fluid and superfluid. The total mass density of the liquid is taken to be the sum of the mass densities of these two ingredients. Using the techniques of generalised continuum mechanics, we show how a general theory for the liquid may be derived in a more direct manner without making such an assumption. We show how a special case of our theory reduces to the usual two-fluid theory and exhibit the links with other singleingredient approaches.
The analysis of HF dual-radar wave measurements taken during the NURWEC2 experiment indicates that the method used to invert radar Doppler spectra overestimates energy at very long ocean wavelengths (> 400 m). This...
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The analysis of HF dual-radar wave measurements taken during the NURWEC2 experiment indicates that the method used to invert radar Doppler spectra overestimates energy at very long ocean wavelengths (> 400 m). This overprediction of energy can be mainly attributed to the effects of shallow water. The paper develops and discusses modifications necessary to account for the effects of shallow water in the simulation and inversion of radar Doppler spectra. The results illustrate the effect of shallow water processes on the radar Doppler spectrum and the improvements obtained in inverted directional wave data when they are accounted for.
Domain decomposition methods are a major area of contemporary research in the numerical analysis of partial differential equations. They provide robust, parallel, and scalable preconditioned iterative methods for the ...
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Domain decomposition methods are a major area of contemporary research in the numerical analysis of partial differential equations. They provide robust, parallel, and scalable preconditioned iterative methods for the large linear systems arising when continuous problems are discretized by finite elements, finite differences, or spectral methods. This paper presents numerical experiments on a distributed-memory parallel computer, the 512-processor Touchstone Delta at the California Institute of Technology. An overlapping additive Schwarz method is implemented for the mixed finite-element discretization of second-order elliptic problems in three dimensions arising from flow models in reservoir simulation. These problems are characterized by large variations in the coefficients of the elliptic operator, often associated with short correlation lengths, which make the problems very ill-conditioned. The results confirm the theoretical bound on the condition number of the iteration operator and show the advantage of domain decomposition preconditioning as opposed to the simpler but less robust diagonal preconditioner.
We address the optimal design problem associated with introducing passive damping devices into a structure in such a way that all vibration frequencies are moved as far as possible into the left-half plane. As this na...
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We address the optimal design problem associated with introducing passive damping devices into a structure in such a way that all vibration frequencies are moved as far as possible into the left-half plane. As this natural objective function lacks a bounded derivative we are forced to adopt a derivative-free direct search method. We report on our application of parallel direct search to the optimal design of both shear buildings and strings.
In this paper, we present a novel enhancement to the conventional hr-adaptive finite element methods for parabolic equations, integrating traditional h-adaptive and r-adaptive methods via neural networks. A major chal...
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Disordered hyperuniform many-particle systems are recently discovered exotic states of matter, characterized by the complete suppression of normalized infinite-wavelength density fluctuations, as in perfect crystals, ...
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Disordered hyperuniform many-particle systems are recently discovered exotic states of matter, characterized by the complete suppression of normalized infinite-wavelength density fluctuations, as in perfect crystals, while lacking conventional long-range order, as in liquids and glasses. In this work, we begin a program to quantify the structural properties of nonhyperuniform and hyperuniform networks. In particular, large two-dimensional (2D) Voronoi networks (graphs) containing approximately 10,000 nodes are created from a variety of different point configurations, including the antihyperuniform hyperplane intersection process (HIP), nonhyperuniform Poisson process, nonhyperuniform random sequential addition (RSA) saturated packing, and both non-stealthy and stealthy hyperuniform point processes. We carry out an extensive study of the Voronoi-cell area distribution of each of the networks by determining multiple metrics that characterize the distribution, including their average areas and corresponding variances as well as higher-order cumulants (i.e., skewness γ1 and excess kurtosis γ2). We show that the HIP distribution is far from Gaussian, as evidenced by a high skewness (γ1=3.16) and large positive excess kurtosis (γ2=16.2). The Poisson (with γ1=1.07 and γ2=1.79) and non-stealthy hyperuniform (with γ1=0.257 and γ2=0.0217) distributions are Gaussian-like distributions, since they exhibit a small but positive skewness and excess kurtosis. The RSA (with γ1=0.450 and γ2=−0.0384) and the highest stealthy hyperuniform distributions (with γ1=0.0272 and γ2=−0.0626) are also non-Gaussian because of their low skewness and negative excess kurtosis, which is diametrically opposite of the non-Gaussian behavior of the HIP. The fact that the cell-area distributions of large, finite-sized RSA and stealthy hyperuniform networks (e.g., with N≈10,000 nodes) are narrower, have larger peaks, and smaller tails than a Gaussian distribution implies that in the thermodynamic limit th
A new Rayleigh quotient, which was introduced and briefly considered in a previous paper, is now examined in greater detail. When used in conjunction with polarised finite difference schemes established in earlier pap...
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A new Rayleigh quotient, which was introduced and briefly considered in a previous paper, is now examined in greater detail. When used in conjunction with polarised finite difference schemes established in earlier papers, it enables semivectorial E-field and H-field propagation modes of waveguide structures, which may contain any arbitrary distribution of horizontal and vertical dielectric discontinuities, to be determined without the need to solve matrix eigenvalue problems. The absence of a matrix enables the finite difference grid to incorporate substantially more points and smaller step lengths, thereby improving the accuracy of computed solutions. Results are presented for single rib waveguides and for rib waveguide directional couplers fabricated from III-V semiconductors.
This paper studies the constraint conditions for coherence destruction in tunneling by using perturbation theory and numerical simulation for an AC-field with bias and Coulomb interaction between electrons in a quantu...
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This paper studies the constraint conditions for coherence destruction in tunneling by using perturbation theory and numerical simulation for an AC-field with bias and Coulomb interaction between electrons in a quantum dot molecule. Such conditions can be described by using the roots of a Bessel function Jn（x）, where n is determined by both the bias and the Coulomb interactions, and x is the ratio of the amplitude to the frequency of the AC-field. Under such conditions, a coherent suppression of tunneling occurs between localized electronic states, which results from the dynamical localization phenomenon. All the conditions are verified with numerical simulations.
The implications of interpolation and resampling for the statistics of Synthetic Aperture Radar (SAR) images are analyzed. Interpolation of the complex data conserves the statistical distribution and all moments if a ...
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The feasibility of matching templates representing map features to features in Synthetic Aperture Radar images is investigated. The performance of template matching using cross-correlation (which has no knowledge of s...
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The feasibility of matching templates representing map features to features in Synthetic Aperture Radar images is investigated. The performance of template matching using cross-correlation (which has no knowledge of speckle) is compared with a correlation measure, based on a Kolmogorov-Smirnov test of fit, which does take speckle into consideration. This is shown to perform better than cross-correlation in simulated images. However, neither method performs well on real data. This is due to the exponential speckle model being inappropriate for linear features in real data. Alternative methods for matching map features to SAR images are suggested.
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