Jeong-Hyung Park

The characteristics of the underwater acoustic channel present special problems in the design of covert communication systems. In this paper we consider communications at relatively short distances, less than 20,000 yds., and well below the water surface. Covertness is measured in terms of the parameter d associated with the interceptor receiver operating characteristic and curves are given that relate d to the distance ratio between intercepter and receiver. The results clearly show the dominan

Let (M,g) be a compact m dimensional Einstein manifold with smooth boundary. Let <TEX>$\Delta$</TEX><TEX>$_{p}$</TEX>,B be the realization of the p form valued Laplacian with a suitable boundary condition B. Let Spec(<TEX>$\Delta$</TEX><TEX>$_{p}$</TEX>,B) be the spectrum where each eigenvalue is repeated according to multiplicity. We show that certain geometric properties of the boundary may be spectrally characterized in terms of this data where we fix the Einstein constant.ant.

Abstract We study the geometric properties of a base manifold whose unit tangent sphere bundle, equipped with the standard contact metric structure, is H -contact. We prove that a necessary and sufficient condition for the unit tangent sphere bundle of a four-dimensional Riemannian manifold to be H -contact is that the base manifold is 2-stein.

We study the spectral geometry of a Riemannian submersion : Z Y where Z and Y are compact Riemannian manifolds with smooth boundaries and where : Z Y is also a Riemannian submersion. We impose suitable boundary conditions and give necessary and sufficient conditions that * preserve all the eigenforms of the Laplacian. We also study when a single eigenvalue can change.

As a natural generalization of the contact metric manifolds, Kim, Park and Sekigawa discussed quasi contact metric manifolds based on the geometry of the corresponding quasi K¨ahler cones. In this paper, we show that a quasi contact metric manifold is a contact manifold.