Ramarao Inguva

Optical bistability in small metallic particle composites

We predict that a composite dielectric material composed of silver particles can have an optical bistable transmission without cavity feedback. Our model includes propagation and exhibits an inhomogeneous absorption characteristic that can be useful for device applications. Results are presented for quantum‐size silver particles embedded in silica glass.

Photonic Bands: Ellipsoidal Dielectric Atoms in an F.C.C. Lattice

Photonic band structure has been computed using ellipsoidal grains in f.c.c. lattice. Bandgaps have been found and the conditions for the appearance of such gaps are discussed. The effective long-wavelength dielectric constants for the ordinary and the extraordinary rays are calculated and compared with the predictions of effective medium and Maxwell-Garnett theories.

Comparison of two microwave radiobrightness models and validation with field measurements

This paper compares microwave brightness temperature (T/sub B/) estimated by two radiobrightness models: a multilayer coherent radiative transfer (CRT) model and a single-layer Fresnel reflectance model. Two dielectric mixing schemes were used along with the models to calculate permittivity (real part of the dielectric constant). Model T/sub B/ and permittivity estimates were compared and validated against Huntsville, AL 1998 field experiment measurements. Model differences can be attributed to the mixing scheme, the radiobrightness model, or the vertical profile representation. Two sets of simulations were performed to quantify the sources of variation, one using observed son temperature and moisture profiles as input, and another using uniform profiles. Using uniform profiles, systematic differences in permittivity estimated by the mixing schemes resulted in T/sub B/ differences as large as 15 K. However, for uniform profiles, differences in T/sub B/ estimated by the radiobrightness models for a given permittivity value were less than 2 K. For cases using observed profiles, near-surface drying of the profiles resulted in T/sub B/ values from the CRT model 6-10 K higher than estimates from the Fresnel model, which determines T/sub B/ based on 0-5 cm mean moisture and temperature. Therefore, the major sources of T/sub B/ variations were the dielectric mixing scheme and the shape of the near-surface moisture profile. No radiobrightness/mixing scheme combination exhibited superiority across all plots and times.

Heat conduction in layered, composite materials

A solution to the heat conduction equation for multidimensional composite media, with discontinuities of thermal properties, and having contact resistance at inclusion interfaces is presented. The temperature is expressed as an integral over sources and boundary surfaces in terms of a Green function. The solution is thereby reduced to solving the related eigenfunction problem for the Green function. This solution is also expressed in an alternative form utilizing a technique developed by Olcer which promotes faster convergence of the eigenfunction expansion in regions of discontinuities. The solution technique is summarized, and numerical results are presented for one‐dimensional layered slabs, with and without contact resistance specified at layer interfaces.

Mathematical model for in situ oil shale retorting by electromagnetic radiation

Abstract A mathematical model for electromagnetic heating of oil shales is developed. The model simulates the process of oil and gas evolution and transfer through consolidated blocks of oil shale. The model includes equations for temperature, pressure, saturations, chemical reactions, mass conservation and source terms. The inert gases are all assumed to form one bulk species and the oil is assumed to be either in the gaseous or liquid phase. The chemical reactions include pyrolysis of kerogen and char, release of bound water, coking and decomposition of carbonates. Porosity and permeability are dynamic functions of the shale constituents. Non-linear relationships for viscosity, thermal properties and source terms are used as inputs to the model. A detailed solution to the monopole applicator fields is presented. A finite difference approximation to the differential equations is derived and solved using Newtons iteration technique. For the cases studied the solutions are quite stable. Numerical results are included and a preliminary study of the optimization of the heating process is presented. Reasonable agreement is obtained between the model and experimental results when a monopole antenna is used as a heat source.

Electrodynamics in a dispersive medium: E, B, D, and H

Various constitutive relations between the sources and electromagnetic fields in a dispersive medium at rest are reviewed. The constitutive relations which are considered lead to the traditional, the Lindhard, and the external‐dielectric tensor formulations of electrodynamics; also a formulation which is a generalization of all of these is developed. Finally, the fluid equations are employed in a calculation of the Lindhard dielectric tensor of a magnetized plasma.

Multifeature fusion using Pulse Coupled Neural networks

We propose an unbiased multifeature fusion Pulse Coupled Neural Network (PCNN) algorithm. The method shares linking between several PCNNs running in parallel. We illustrate the PCNN fusion technique with a clean and noisy three-band color image example.

Nonlinear optical properties of composite materials

The optical properties of a new class of composite nonlinear materials composed of coated grains, such as cadmium sulfide with a silver coating, are examined. These materials exhibit intrinsic optical bistability and resonantly enhanced conjugate reflectivity. The threshold for intrinsic optical bistability is low enough for practical applications in optical communications and optical computing. Some problems associated with the fabrication of these materials are addressed. Based on preliminary results, switching times are expected to be in the subpicosecond range.

Coordinate-free operators based on one vector. I. Formal considerations

In many systems, the tensors used to describe physical properties must acquire their structure from one vector. Knowledge of that fact alone leads to an interesting line of analysis for such systems. The analysis begins with a discussion of the types of dyadics that can be constructed from one vector. Attention is focused on certain exemplary dyadic operators, which, because of their geometrical properties, would appear particularly basic; the algebra of these dyadics is developed in detail. The algebra is then used in a derivation of the expansion of general functions of these dyadics. Several applications of the general expansion are presented: the inverse of a general dyadic operator (when it exists), a general rotation operator that includes strains and reflections, the determinant of a general dyadic operator, and operators, including some new ones, used in constructing Lorentz boosts. Finally, a coordinate-free representation of the Levi-Civita tensor is provided.

Heat transfer in layered media with application to oil shale materials

The problem of heat conduction in layered materials has been investigated. Equations for heat conduction developed earlier by Murakami et al. have been used to perform numerical studies for oil shale materials. The resulting solutions are compared to the solutions of the heat equation with effective thermal properties. The comparison yields limits on the validity of using effective medium values of thermal properties for time-dependent problems. The anisotropic nature of heat conduction in layered materials is also studied.