Dark Matter with Time-Dependent Mass

We propose a simple model in which the cosmological dark matter consists of particles whose mass increases with the scale factor of the universe. The particle mass is generated by the expectation value of a scalar field which does not have a stable vacuum state, but which is effectively stabilized by the rest energy of the ambient particles. As the universe expands, the density of particles decreases, leading to an increase in the vacuum expectation value of the scalar (and hence the mass of the particle). The energy density of the coupled system of variable-mass particles (``vamps'') redshifts more slowly than that of ordinary matter. Consequently, the age of the universe is larger than in conventional scenarios.Comment: 14 pages, 2 figures; based on a talk by SMC at Cosmo-97, September 1997, Ambleside, England. Important references adde

Investigation of Defect Production and Displacement Energies in Wurtzite Aluminum Nitride

Aluminum Nitride is an active element of sensors that monitor the performance and well-being of the nuclear reactors due to its piezoelectric properties. Yet, the variations of its properties under irradiation are largely unexplored. We report the results of the molecular dynamics simulations of the structural changes in AlN under irradiation via the knock-on atom technique. By creating and evolving the irradiation cascades due to energetic particle interaction with the atom of the crystalline lattice we determine the rate of the defect production as a function of the deposited energy. Further, we determine a displacement energy, a key characteristic that describes how efficient the defect production in the given material is. Comparison with the isostructural GaN is provided --Abstract, p. ii

The Effect of Irradiating AlN on its Dielectric Properties

Aluminum Nitride is an active element of sensors that monitor the performance and well-being of the nuclear reactors due to its piezoelectric properties. Yet, the variations of its properties under irradiation are largely unexplored. Here, we report the results of the molecular dynamics simulations of the structural changes in AlN under irradiation via the knock-on atom technique. By creating and evolving the irradiation cascades due to energetic particle interaction with the atom of the crystalline lattice we determine the rate of the defect production as a function of the deposited energy. Further, we determine a displacement energy, a key characteristic that describes how efficient the defect production in the given material is. Comparison with the isostructural GaN is provided

A linguistic model of minimalist syntax composes Tebe Poem

HonorsCognitive ScienceUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/167886/1/seanpaul.pd