Energy coupling in catastrophic collisions

The prediction of events leading to the catastrophic collisions and disruption of solar system bodies is fraught with the same difficulties as are other theories of impact events; since one simply cannot perform experiments in the regime of interest. In the catastrophic collisions of asteroids that regime involves bodies of a few tons to hundred of kilometers in diameter, and velocities of several kilometers pre second. For hundred kilometer bodies, gravitational stresses dominate material fracture strengths, but those gravitational stresses are essentially absent for laboratory experiments. Only numerical simulations using hydrocodes can in principle analyze the true problems, but they have their own major uncertainties about the correctness of the physical models and properties. The question of the measure of the impactor and its energy coupling is investigated using numerical code calculations. The material model was that of a generic silicate rock, including high pressure melt and vapor phases, and includes material nonlinearity and dissipation via a Mie-Gruniesen model. A series of calculations with various size ratios and impact velocities are reported

Displacement Damage Effects in GeSn Light Emitting Diodes

Potential future use on Earth-orbiting satellites calls for investigation into the suitability of GeSn based photonic devices in high energy proton environments. The electroluminescence (EL) intensity of Ge1-xSnx (x = 0, 0.02, 0.069, and 0.094) light emitting diodes was measured before and after irradiation by 2 MeV protons at relatively high fluence levels. The results showed that GeSn devices with higher Sn content were up to 10 times more resistant against proton displacement damage than the pure Ge (x = 0) devices. As Sn concentration increased, the band gap decreased, and V-P hole trap energy level moved further from the mid-gap level, resulting in less EL degradation via Shockley Read Hall (SRH) process

Excited nucleon spectrum from lattice QCD with maximum entropy method

We study excited states of the nucleon in quenched lattice QCD with the spectral analysis using the maximum entropy method. Our simulations are performed on three lattice sizes $16^3\times 32$, $24^3\times 32$ and $32^3\times 32$, at $\beta=6.0$ to address the finite volume issue. We find a significant finite volume effect on the mass of the Roper resonance for light quark masses. After removing this systematic error, its mass becomes considerably reduced toward the direction to solve the level order puzzle between the Roper resonance $N'(1440)$ and the negative-parity nucleon $N^*(1535)$.Comment: Lattice2003(spectrum), 3 pages, 4 figure

Sustainability of multi-field inflation and bound on string scale

We study the effects of the interaction terms between the inflaton fields on the inflationary dynamics in multi-field models. With power law type potential and interactions, the total number of e-folds may get considerably reduced and can lead to unacceptably short period of inflation. Also we point out that this can place a bound on the characteristic scale of the underlying theory such as string theory. Using a simple multi-field chaotic inflation model from string theory, the string scale is constrained to be larger than the scale of grand unified theory.Comment: (v1) 9 pages, 1 figure;(v2) 10 pages, references added; (v3) 15 pages, 4 figures, more discussions about parameters and observable quantities, references added, to appear in Modern Physics Letters