Direct Dark Matter Detection with Velocity Distribution in the Eddington approach

Exotic dark matter together with the vacuum energy (associated with the cosmological constant) seem to dominate the Universe. Thus its direct detection is central to particle physics and cosmology. Supersymmetry provides a natural dark matter candidate, the lightest supersymmetric particle (LSP). One essential ingredient in obtaining the direct detection rates is the density and the velocity distribution of the LSP in our vicinity. In the present paper we study simultaneously density profiles and velocity distributions in the context of the Eddington approach. In such an approach, unlike the commonly assumed Maxwell-Boltzmann (M-B) distribution, the upper bound of the velocity arises naturally from the potential.Comment: 21 LaTex pages, 27 figure

A Field Effect Transitor based on the Mott Transition in a Molecular Layer

Here we propose and analyze the behavior of a FET--like switching device, the Mott transition field effect transistor, operating on a novel principle, the Mott metal--insulator transition. The device has FET-like characteristics with a low ``ON'' impedance and high ``OFF'' impedance. Function of the device is feasible down to nanoscale dimensions. Implementation with a class of organic charge transfer complexes is proposed.Comment: Revtex 11pages, Figures available upon reques

Long-Term Evolution of Massive Black Hole Binaries. II. Binary Evolution in Low-Density Galaxies

We use direct-summation N-body integrations to follow the evolution of binary black holes at the centers of galaxy models with large, constant-density cores. Particle numbers as large as 400K are considered. The results are compared with the predictions of loss-cone theory, under the assumption that the supply of stars to the binary is limited by the rate at which they can be scattered into the binary's influence sphere by gravitational encounters. The agreement between theory and simulation is quite good; in particular, we are able to quantitatively explain the observed dependence of binary hardening rate on N. We do not verify the recent claim of Chatterjee, Hernquist & Loeb (2003) that the hardening rate of the binary stabilizes when N exceeds a particular value, or that Brownian wandering of the binary has a significant effect on its evolution. When scaled to real galaxies, our results suggest that massive black hole binaries in gas-poor nuclei would be unlikely to reach gravitational-wave coalescence in a Hubble time.Comment: 13 pages, 8 figure

Stark shift and field ionization of arsenic donors in 28^{28}Si-SOI structures

We develop an efficient back gate for silicon-on-insulator (SOI) devices operating at cryogenic temperatures, and measure the quadratic hyperfine Stark shift parameter of arsenic donors in isotopically purified $^{28}$Si-SOI layers using such structures. The back gate is implemented using MeV ion implantation through the SOI layer forming a metallic electrode in the handle wafer, enabling large and uniform electric fields up to $\sim$ 2 V/$\mu$m to be applied across the SOI layer. Utilizing this structure we measure the Stark shift parameters of arsenic donors embedded in the $^{28}$Si SOI layer and find a contact hyperfine Stark parameter of $\eta_a=-1.9\pm0.2\times10^{-3} \mu$m$^2$/V$^2$. We also demonstrate electric-field driven dopant ionization in the SOI device layer, measured by electron spin resonance.Comment: 5 pages, 3 figure

Morphology and mechanical properties of isotactic polypropylene glass mat thermoplastic composites modified with organophilic montmorillonite

Satisfactory impregnation of glass fiber mats may be obtained with isotactic polypropylene/montmorillonite (MMT) nanocomposites under conditions comparable with industrial conditions. However, it is demonstrated here that the high melt viscosity of the nanocomposite matrix at low shear rates may significantly influence the release of the compressive load in the glass mat and hence the glass fiber distribution in consolidated specimens. Thus, depending on the initial lay-up and overall glass fiber content, the bending modulus may either increase or decrease with increasing MMT content, whereas the tensile modulus is more consistent with micromechanical models assuming a uniform glass fiber distribution. Results from fractographic analyses show that the presence of matrix rich layers at the specimen surfaces may also lead to premature crack initiation and failure in flexio

Applications of the Gauss-Bonnet theorem to gravitational lensing

In this geometrical approach to gravitational lensing theory, we apply the Gauss-Bonnet theorem to the optical metric of a lens, modelled as a static, spherically symmetric, perfect non-relativistic fluid, in the weak deflection limit. We find that the focusing of the light rays emerges here as a topological effect, and we introduce a new method to calculate the deflection angle from the Gaussian curvature of the optical metric. As examples, the Schwarzschild lens, the Plummer sphere and the singular isothermal sphere are discussed within this framework.Comment: 10 pages, 1 figure, IoP styl

Quantum Statistics and Slow Neutron Scattering by Gases

A surprisingly simple expression in ``closed form'' for the cross section d2σ/dΩdϵ for the scattering of thermal neutrons (including polarized neutrons) from an ideal quantum gas is derived. This result extends the work of Van Hove on the quantum gas. An expansion is obtained for dσ/dϵ. The case of elastic scattering is treated separately. From these expressions is obtained a criterion for ignoring the statistics of the scatterer in favor of classical (Boltzmann) statistics. This criterion should have some validity for weakly interacting systems. It is shown that the effects of statistics on the neutron cross section for a helium‐4 gas range from 5% or less for the noninteracting gas up to as much as 40% for the interacting system.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70882/2/JCPSA6-47-12-4923-1.pd

Controls on the recent speed-up of Jakobshavn Isbrae, West Greenland

This is the published version, also available here: http://dx.doi.org/10.3189/002214311797409776.Jakobshavn Isbrae, West Greenland, underwent a large, rapid and not well understood change in flow dynamics in 1998, leading to a doubling of its ice discharge rates. We calculate the width-averaged forces controlling flow of Jakobshavn Isbrae in 1995, 2000 and 2005 to elucidate processes responsible for this change in flow speed. In contrast to earlier suggestions, we conclude that the observed acceleration was not caused by the loss of back-stress due to weakening and subsequent break-up of the floating ice tongue alone. Gradients in longitudinal stress are small at all times considered (∼3% of the driving stress) and basal and lateral drag provide resistance to flow. Over the 10 year period considered, the average driving stress increased by 20 kPa, which was balanced by a comparable increase in lateral drag. We surmise that the velocity changes resulted from weakening of the ice in the lateral shear margins and perhaps a change in properties at the bed. Possible mechanisms for weakening of ice in the lateral shear margins include cryo-hydrologic warming of subsurface ice in the ablation zone and hydraulic weakening due to higher water content of ice in the shear margins

Controls on the recent speed-up of Jakobshavn Isbræ, West Greenland

This is the publisher's version, also available electronically from "http://www.ingentaconnect.com/".Jakobshavn Isbrae, West Greenland, underwent a large, rapid and not well understood change in flow dynamics in 1998, leading to a doubling of its ice discharge rates. We calculate the width-averaged forces controlling flow of Jakobshavn Isbrae in 1995, 2000 and 2005 to elucidate processes responsible for this change in flow speed. In contrast to earlier suggestions, we conclude that the observed acceleration was not caused by the loss of back-stress due to weakening and subsequent break-up of the floating ice tongue alone. Gradients in longitudinal stress are small at all times considered (∼3% of the driving stress) and basal and lateral drag provide resistance to flow. Over the 10 year period considered, the average driving stress increased by 20 kPa, which was balanced by a comparable increase in lateral drag. We surmise that the velocity changes resulted from weakening of the ice in the lateral shear margins and perhaps a change in properties at the bed. Possible mechanisms for weakening of ice in the lateral shear margins include cryo-hydrologic warming of subsurface ice in the ablation zone and hydraulic weakening due to higher water content of ice in the shear margins