Linearized Gravity in Brane Backgrounds

A treatment of linearized gravity is given in the Randall-Sundrum background. The graviton propagator is found in terms of the scalar propagator, for which an explicit integral expression is provided. This reduces to the four-dimensional propagator at long distances along the brane, and provides estimates of subleading corrections. Asymptotics of the propagator off the brane yields exponential falloff of gravitational fields due to matter on the brane. This implies that black holes bound to the brane have a "pancake"-like shape in the extra dimension, and indicates validity of a perturbative treatment off the brane. Some connections with the AdS/CFT correspondence are described.Comment: 31 pages, harvmac. v2: minor typo and reference corrections. v3: minor corrections to eqs and discussio

The embedding of the spacetime in five dimensions: an extension of Campbell-Magaard theorem

We extend Campbell-Magaard embedding theorem by proving that any n-dimensional semi-Riemannian manifold can be locally embedded in an (n+1)-dimensional Einstein space. We work out some examples of application of the theorem and discuss its relevance in the context of modern higher-dimensional spacetime theories.Comment: 22pages, Revte

Why supersymmetry should be restored at the TeV scale

It is explained why the curvature associated to the vacuum energy density arising from SUSY breaking cannot be completely transferred to the extra spatial dimensions of a bulk space-time manifold, and it is shown -- without using hierarchy arguments but only the results of current large-scale observations -- why the Tev scale should correspond to the maximal allowed SUSY-breaking scale.Comment: 6 pages. Essay written for the 2008 Awards for Essays on Gravitation (Gravity Research Foundation, USA), and awarded with "Honorable Mention

Fabrication and Characterization of Controllable Grain Boundary Arrays in Solution Processed Small Molecule Organic Semiconductor Films

We have produced solution-processed thin films of 6,13-bis(triisopropyl-silylethynyl) pentacene with grain sizes from a few micrometers up to millimeter scale by lateral crystallization from a rectangular stylus. Grains are oriented along the crystallization direction, and the grain size transverse to the crystallization direction depends inversely on the writing speed, hence forming a regular array of oriented grain boundaries with controllable spacing. We utilize these controllable arrays to systematically study the role of large-angle grain boundaries in carrier transport and charge trapping in thin film transistors. The effective mobility scales with the grain size, leading to an estimate of the potential drop at individual large-angle grain boundaries of more than one volt. This result indicates that the structure of grain boundaries is not molecularly abrupt, which may be a general feature of solution processed small molecule organic semiconductor thin films where relatively high energy grain boundaries are typically formed. This may be due to the crystal Transient measurements after switching from positive to negative gate bias or between large and small negative gate bias reveal reversible charge trapping with time constants on the order of 10 s, and trap densities that are correlated with grain boundary density. We suggest that charge diffusion along grain boundaries and other defects is the rate determining mechanism of the reversible trapping.Comment: 12 pages, 11 figure

Active galactic nucleus feedback in clusters of galaxies

Observations made during the last ten years with the Chandra X-ray Observatory have shed much light on the cooling gas in the centers of clusters of galaxies and the role of active galactic nucleus (AGN) heating. Cooling of the hot intracluster medium in cluster centers can feed the supermassive black holes found in the nuclei of the dominant cluster galaxies leading to AGN outbursts which can reheat the gas, suppressing cooling and large amounts of star formation. AGN heating can come in the form of shocks, buoyantly rising bubbles that have been inflated by radio lobes, and the dissipation of sound waves.Comment: Refereed review article published in Chandra's First Decade of Discovery Special Feature edition of the Proceedings of the National Academy of Science

Iodine sorption study on the proposed use of Viton A in a shuttle galley water accumulator

The installation of a Viton A accumulator in the Shuttle galley has been proposed to prevent overpressurization of the hot water supply system. A laboratory study has been conducted to determine if there would be any interaction between the Viton A material and the iodine used to disinfect the water. Coupons of Viton A were exposed for 24 hours to aqueous iodine solutions similar in quality to the Shuttle's potable water. Changes in the iodine residual were monitored to determine the rate of iodine sorption by the coupon. Total organic carbon (TOC) was monitored to determine the rate of desorption of organic materials from the Viton A. The same coupons were then soaked in reagent-grade water for 24 hours, and iodine was monitored to determine the rate of iodine desorption. The coupons were again exposed to iodine solutions for 24 hours and iodine and TOC were monitored. No significant change in the iodine sorption rate was detected between the first and second exposures. A triangle taste test indicated at a 1 percent confidence level that the water exposed to Viton A had a different taste which was less acceptable to the panelists

Enhancing Export Potential for Northern Plains Mustard

International Relations/Trade,