Dynamic Evasion-Interrogation Games with Uncertainty in the Context of Electromagetics

We consider two player electromagnetic evasion-pursuit games where each player must incorporate significant uncertainty into their design strategies to disguise their intension and confuse their opponent.In this paper,the evader is allowed to make dynamic changes to his strategies in response to the dynamic input with uncertainty from the interrogator.The problem is formulated in two different ways;one is based on the evolution of the probability density function of the intensity of reflected signal and leads to a controlled forward Kolmogorov or Fokker-Planck equation.The other formulation is based on the evolution of expected value of the intensity of reflected signal and leads to controlled backward Kolmogorov equations.In addition,a number of numerical results are presented to illustrate the usefulness of the proposed approach in exploring problems of control in a general dynamic game setting.

Detection of Arterial Occlusions Using Viscoelastic Wave Propagation

We consider the problem of detecting cardiac artery occlusions using stenosis driven viscoelastic(VE)waves propagated through biotissue to body surface sensors.We investigate possible statistical model formulations(ordinary least squares(OLS),generalized least squares(GLS))and post analysis techniques(residual plots)to ascertain uncertainty in estimates as well as validity of the statistical models as part of a methodology for stenosis detection using viscoelastic waves.

Viscoelastic Models for Passive Arterial Wall Dynamics

This paper compares two models predicting elastic and viscoelastic properties of large arteries.Models compared include a Kelvin(standard linear)model and an extended 2-term exponential linear viscoelastic model.Models were validated against in-vitro data from the ovine thoracic descending aorta and the carotid artery.Measurements of blood pressure data were used as an input to predict vessel cross-sectional area.Material properties were predicted by estimating a set of model parameters that minimize the difference between computed and measured values of the cross-sectional area.The model comparison was carried out using generalized analysis of variance type statistical tests.For the thoracic descending aorta,results suggest that the extended 2-term exponential model does not improve the ability to predict the observed cross-sectional area data,while for the carotid artery the extended model does statistically provide an improved fit to the data.This is in agreement with the fact that the aorta displays more complex nonlinear viscoelastic dynamics,while the stiffer carotid artery mainly displays simpler linear viscoelastic dynamics.

Modelling of Propagating Shear Waves in Biotissue Employing an Internal Variable Approach to Dissipation

The ability to reliably detect coronary artery disease based on the acousticnoises produced by a stenosis can provide a simple, non-invasive technique for diagnosis.Current research exploits the shear wave fields in body tissue to detect andanalyze coronary stenoses. The methods and ideas outlined in earlier efforts [6] includinga mathematical model utilizing an internal strain variable approximation tothe quasi-linear viscoelastic constitutive equation proposed by Fung in [19] is extendedhere. As an initial investigation, a homogeneous two-dimensional viscoelastic geometryis considered. Being uniform in θ, this geometry behaves as a one dimensionalmodel, and the results generated from it are compared to the one dimensional resultsfrom [6]. To allow for different assumptions on the elastic response, several variationsof the model are considered. A statistical significance test is employed to determine ifthe more complex models are significant improvements. After calibrating the modelwith a comparison to previous findings, more complicated geometries are considered.Simulations involving a heterogeneous geometrywith a uniformring running throughthe original medium, a θ-dependent model which considers a rigid partial occlusionformed along the inner radius of the geometry, and a model which combines the ringand occlusion are presented.

Determination of Interrogating Frequencies to Maximize Electromagnetic Backscatter from Objects with Material Coatings

The electromagnetic backscattering of a crosscut of a cruise missile coated by a thin homogeneous layer made of radar absorbent material is modeled using a finite element method.Based on the radar cross section and a reflection coefficient,optimization problems are formulated for evaders and interrogators leading to optimal material parameters for the coating and optimal monostatic radar operating frequencies,respectively.Optimal coating materials are constructed for several radar frequencies.Tuning only dielectric permittivity gives a narrow frequency range of high absorption while also tuning magnetic permeability widens it significantly.However the coating layers considered do not provide substantial reduction of backscattering in the entire frequency range from 0.2 to 1.6 GHz.Computational experiments also demonstrate that the reflection coefficient based on a simple planar geometry can predict well the strength of radar cross section in the sector of interest with a substantially reduced computational burden.