R.D. Maurer [and] Melvin A. Herlin. / "June 13, 1949." / Bibliography: p. 5. / Army Signal Corps Contract No. W36-039-sc-32037 Project No. 102B. Dept. of the Army Project No. 3-99-10-022.

J.R. Pellam. / "November 25, 1948." / Bibliography: p. 22. / Army Signal Corps Contract No. W36-039-sc-32037 Project No. 102B. Dept. of the Army Project No. 3-99-10-022.

A.D. MacDonald and Sanborn C. Brown. / "October 23, 1948." / Bibliography: p. 16. / Army Signal Corps Contract No. W36-039-sc-32037 Project No. 102B. Dept. of the Army Project No. 3-99-10-022.

by John R. Pellam. / "November 7, 1947." / Bibliography: p. 17. / Army Signal Corps Contract No. W-36-039 sc-32037.

by John R. Pellam and Charles F. Squire. / "August 1, 1947." / Bibliography: p. 16. / Army Signal Corps Contract No. W-36-039 sc-32037

The main theme of this thesis is the interplay between superuidity and localization, in a system of strongly correlated Bose particles. Driving this investigation is the search for yet unobserved phases of matter, such as the so-called supersolid. Using state-of-the- art, numerically exact computer simulations, we have carried out an extensive theoretical investigation of the effects of long-range interactions, inhomogeneity, disorder and frustration in a simple model of lattice Bosons. In particular, we explore the scenario of vacancy- and interstitial-based supersolid phases of hard core bosons on a square lattice, interacting repulsively via a nearest-neighbour and next-nearest neighbour potential. Secondly, in an attempt to model the physics of a layer of helium adsorbed on a corrugated substrate, an additional superlattice of the absorption sites is imposed to the system of hard core bosons, and the resulting low temperature phase diagram is studied. Finally, the possibility of actually inducing by disorder superuidity (superglass) in a system that does not display it in the absence of disorder is demonstrated. The quantitative and qual- itative predictions at which we have arrived appear to be at least in principle testable experimentally, for example by performing measurements on ultracold atoms in optical lattices.

Abstract Detailed in this manuscript is a methodology to model ground state properties of 4He droplets at zero pressure and zero Kelvin using a density functional theory of liquid helium. The density functional approach examined here consists of two noted functionals from the literature and corresponding mean field definitions. A mean field and trial density are defined for each system and optimized to self-consistency using a matrix diagonalization technique. Initial calculations of planar slabs are performed and demonstrate reasonable agreement with experiment and with prior studies using density functional theory. Quantum properties of droplets and droplets containing atomic dopants are calculated. Three different He-dopant potentials are examined to test the limits of the functional methods. For each impurity interaction, an average of 12 atoms were found to reside in the first solvation shell with an atomic dopant placed at the droplet center. Maximum densities in the first solvation shell reached those of solid helium as predicted by DF methods.

The trapping behavior of deuterium and helium in polycrystalline tungsten (PCW) under D+-only, He+-only, sequential and simultaneous irradiation was studied as a function of incident ion fluences and irradiation temperature. Deuterium implanted at 300 and 500 K gets trapped at surface adsorption sites, vacancy-related traps, or extended defects. No deuterium was trapped for 700 K implantations. Results were affected by tungsten-carbide impurities in PCW specimens. It is suggested that He trapping occurs via the formation of He clusters, at impurity sites, or as part of He-vacancy complexes. For sequential implantations, D and He were found to de-trap each other, with He impeding the trapping of D when implanted first at 300 K. Under simultaneous irradiation a decrease in D inventories was observed for all cases, and a re-distribution of He to higher energy traps (associated with He-vacancy complex formation) was observed for higher fluences and temperatures.

The trapping behavior of deuterium and helium in polycrystalline tungsten (PCW) under D+-only, He+-only, sequential and simultaneous irradiation was studied as a function of incident ion fluences and irradiation temperature. Deuterium implanted at 300 and 500 K gets trapped at surface adsorption sites, vacancy-related traps, or extended defects. No deuterium was trapped for 700 K implantations. Results were affected by tungsten-carbide impurities in PCW specimens. It is suggested that He trapping occurs via the formation of He clusters, at impurity sites, or as part of He-vacancy complexes. For sequential implantations, D and He were found to de-trap each other, with He impeding the trapping of D when implanted first at 300 K. Under simultaneous irradiation a decrease in D inventories was observed for all cases, and a re-distribution of He to higher energy traps (associated with He-vacancy complex formation) was observed for higher fluences and temperatures.

We introduce the de Broglie-Bohm causal interpreation of quantum mechanics and compare it to the standard interpretation of quantum mechanics, the Copenhagen interpretation. We examine the possibility of experimentally distinguishing between the two theories, as well as the potential for the causal interpretation to more easily bridge the gap between the physics of the quantum and classical worlds. We then use the causal interpretation to construct a deterministic model of the helium atom in which the two electrons move along trajectories through space and time about a stationary nucleus. The dynamics are governed by the non-relativistic Schrödinger equation and the spin vectors of both electrons are assumed to be constant along their respective trajectories. We examine the Bohmian trajectories associated with (approximations to) eigenstates of the helium Hamiltonian as well as the trajectories associated with some non-eigenstates. We also compute an approximation to the ground state energy of the helium atom using a representation of the helium wavefunction in terms of hydrogenic eigenfunctions which is motivated by a perturbation approach.