Backscattering response from periodic spatial patterns in random media

Abstract

In wave-based remote sensing or radio-location of distant objects in a random medium, a high-frequency electromagnetic wave is scattered by object discontinuities, and portions of the scattered radiation can traverse the same random inhomogeneities as the initial incident field. The statistical dependence of the forward–backward travelling events results in an anomaly in the backscattered intensity pattern that carries information about the scattering object. The quality of this information depends on the ability to resolve the fine-structure elements. In this work we investigate the resolving properties of periodic spatial objects by using the random propagators of the stochastic geometrical theory of diffraction.     

Optimal algorithms for the α-neighbor p-center problem

Assigning multiple service facilities to demand points is important when demand points are required to withstand service facility failures. Such failures may result from a multitude of causes, ranging from technical difficulties to natural disasters. The α-neighbor p-center problem deals with locating p service facilities. Each demand point is assigned to its nearest α service facilities, thus it is able to withstand up to α − 1 service facility failures. The objective is to minimize the maximum distance between a demand point and its αth nearest service facility. We present two optimal algorithms for both the continuous and discrete α-neighbor p-center problem. We present experimental results comparing the performance of the two optimal algorithms for α = 2. We also present experimental results showing the performance of the relaxation algorithm for α = 1, 2, 3.     

Cytoplasmic Changes in Cardiac Cells During a Contraction Cycle Detected by Fluorescence Polarization

Intracellular structural changes, occurring in a cardiac myocyte during a contraction cycle, were investigated by means of intracellular fluorescein fluorescence polarization (IFFP), in comparison to cytoplasmic concentration of Ca²⁺ [Ca²⁺]_i measured by indo-1. A simple physical model is presented. It assumes a biphase intracellular matrix, differing in its potency to restrict hosting fluorescent probe mobility. The first is a mobile nonrestricting phase, made mostly of aqua (aqua zone), while the second is a mobile-restricting phase, allocated mainly at the proximity of the filament sites. Their physicochemical properties such as [Ca²⁺], viscosity, and pH, may differ, thereby influencing the hosting probe fluorescence characteristics differently. These possible influences were examined experimentally. Based on experimental data, the model enables the evaluation, to first order of approximation, of the relative number of fluorescent probes populating the two phases and the time variation viscosity (_r(t)) of the mobile-restricting filament zones taking place throughout the contraction cycle.     

Slow rotation in the bimetric theory of gravitation

The equations describing the moment of inertia and the dragging of inertial frames of slowly rotating neutron stars are derived according to Rosen's bimetric theory of gravitation. Numerical calculations of the properties of neutron stars according to the bimetric theory and general relativity were made using several equations of state. The general trend found is that in the bimetric theory neutron stars with a given mass induce a smaller dragging of inertial frames than in general relativity. The moment of inertia of low-mass stars also is smaller in the bimetric theory. For high-mass stars, however, the moment of inertia is found to be larger in the bimetric theory.In partial fulfillment of the requirements for the D.Sc. degree.     

On the role of transport in the combustion kinetics of a steady-state premixed laminar CO + H2 + O2 flame

The role of mechanistic steps, diffusion, and their interrelation is explored in a steady-state premixed laminar CO + H₂ + O₂ flame using a numerical model. Sensitivity coefficients and Green's functions calculated for this system offer systematic characterization of the role of diffusion and exothermicity in carbon monoxide oxidation kinetics. The results reveal that the uncertainties in transport parameters are as important to the model predictions as those in the kinetic steps. The rate controlling steps of the CO + H₂ + O₂ reaction are found to be different for adiabatic and nonadiabatic premixed flames, and also for systems with and without transport. In particular, the reactions of the hydroperoxyl radical with hydrogen, oxygen, and hydroxyl radicals are found to be important at all temperatures in the fuel lean (40 torr) adiabatic flame studied here. The diffusive mixing of chemical species from the low and the high temperature portions of the flame and the larger heats of reaction associated with the hydroperoxyl radicals are found to be responsible for the increased importance of these reactions. © 1994 John Wiley & Sons, Inc.     

Energy transfer between coronene and rhodamine 6G in PMMA matrices

The fluorescence lifetime of coronene and the rate of dipole-dipole energy transfer from coronene to rhodamine 6G in PMMA matrices were found to be temperature dependent. For both these photophysical processes an activation energy of about 500 cm^?1 is obtained. The energy transfer results can be analyzed in terms of a model involving thermally activated energy transfer from excited states of coronene.     

On finite sets of points inP 3

Given a finite set of points Γ₀ which span a projective spaceP ³, we show here that a plane spanned by points of Γ₀ can be a neighbour of at most eight points of Γ₀, these being the vertices of a projective cube; the common neighbour plane is then elementary with the three only points of Γ₀ in it being diagonal points of the cube. This extends toP ³ some results of L. M. Kelly and W. O. J. Moser in the planeP ².     

Reference-wave solutions for high-frequency fields propagating in random media

Ray theory plays an important role in determining the propagation properties of high-frequency fields and their statistical measures in complicated random environments. According to the ray approach, the field at the observer can be synthesized from a variety of field species arriving along multiple ray trajectories resulting from refraction and scattering from boundaries and from scattering centers embedded in the random medium. For computations of the statistical measures, it is desirable therefore to possess a solution for the high-frequency field propagating along an isolated ray trajectory. For this reason, a new reference-wave method was developed to provide an analytic solution of the parabolic-wave equation.