Validation of Advanced EM Models for UXO Discrimination

The work reported here details basic validation of our advanced physics-based EMI forward and inverse models against data collected by the NRL TEMTADS system. The data was collected under laboratory-type conditions using both artificial spheroidal targets and real UXO. The artificial target models are essentially exact, and enable detailed comparison of theory and data in support of measurement platform characterization and target identification. Real UXO targets cannot be treated exactly, but it is demonstrated that quantitative comparisons of the data with the spheroid models nevertheless aids in extracting key target discrimination information, such as target geometry and hollow target shell thickness.Comment: 15 pages, 16 figure

Second sound spectroscopy of a nonequilibrium superfluid-normal interface

An experiment is proposed to test a previously developed theory of the hydrodynamics of a nonequilibrium heat current-induced superfluid-normal interface. It is shown that the interfacial ``trapped'' second sound mode predicted by the theory leads to a sharp resonant dip in the reflected signal from an external second sound pulse propagated towards the interface when its horizontal phase speed matches that of the interface mode. The influence of the interface on thermal fluctuations in the bulk superfluid is shown to lead to slow power dependence of the order parameter, and other quantities, on distance from it.Comment: 4 pages, 3 figure

Layering transitions, disordered flat phases, reconstruction, and roughening

We study in light of recent ellipsometry, vapor pressure isotherm and specific-heat measurements on the thermodynamics of adsorbed thin films on graphite, the connection between the layering phase diagrams of thin films on periodic substrates and the thermodynamics of the solid-vapor interface of a semi-infinite crystal. The latter is the limit of the former when the film becomes infinitely thick, and we are interested in connecting this limiting behavior to the thermodynamics of films of finite thickness. We argue that the concepts of surface roughening, preroughening, and reconstruction provide a quantitatively useful framework within which to discuss this connection. Through general renormalization-group arguments and, in more detail, through a self-consistent mean-field treatment that explicitly accounts for all relevant phases, we show that the same types of interactions that lead to these different surface phases lead also to the reentrant layering transitions seen in the recent experiments. By appropriate tuning of the mean-field parameters we can semiquantitatively reconstruct all the observed experimental phase diagrams. It turns out that certain experimental phase diagrams with “zippers” require that the preroughening transition become first order. Our renormalization-group arguments predict such behavior in certain parameter ranges. In addition, for different parameters we predict the existence of an, as yet unobserved, θ disordered flat phase with spontaneously broken particle-hole symmetry and continuously varying surface height with an accompanying intermeshing layering phase diagram. The underlying lattice in the experiments is triangular, and this actually enhances the stability of the disordered flat phase and the corresponding reentrant layering transitions in the films

Particle-Hole Symmetry and the Bose Glass to Superfluid Transition

The generic Hamiltonian describing the zero temperature transition between the insulating Bose glass phase and the superfluid phase lacks particle-hole symmetry, but a statistical version of this symmetry is believed to be restored at the critical point. We show that the renormalization group relevance of particle-hole asymmetry may be explored in a controlled fashion only for small time dimensions, ετ≪1, where we find a stable particle-hole asymmetric and an unstable particle-hole symmetric fixed point, but we provide evidence that the two merge for some finite ετ≈2/3, which tends to confirm symmetry restoration at the physical ετ = 1

Zippering and Intermeshing: Novel Phase Diagrams for Interfaces and Films

New surface and layering phase diagrams are proposed based on generalized sine-Gordon models with and without a substrate potential. In particular, we find that the preroughening transition can be driven first order, explaining “zipper” features in heat capacity data for argon and krypton on graphite substrates. For different parameters, we predict the existence of a novel variant of den Nijs' disordered flat phase with spontaneously broken particle-hole symmetry and continuously varying surface height with an accompanying intermeshing layering phase diagram. The restricted solid-on-solid model displays zippering for sufficiently large second neighbor coupling