Stable two--brane models with bulk tachyon matter

We explore the possibility of constructing stable, warped two--brane models which solve the hierarchy problem, with a bulk non--canonical scalar field (tachyon matter) as the source term in the action. Among our examples are two models--one with a warp factor (denoted as $e^{-2f(\sigma)}$) which differs from that of the standard Randall--Sundrum by the addition of a quadratic piece in the $f(\sigma)$ and another, where the warping is super-exponential. We investigate the issue of resolution of hierarchy and perform a stability analysis by obtaining the effective inter-brane potentials, in each case. Our analysis reveals that there does exist stable values of the modulus consistent with hierarchy resolution in both the models. Thus, these models, in which the bulk scalar field generates the geometry and also ensures stability, provide viable alternatives to the standard Randall--Sundrum two-brane scenario.Comment: Final version published in Int. Jr. Mod. Phys

Parametric Pension Reform with Higher Retirement Ages: A Computational Investigation of Alternatives for A Pay-As-You-Go Pension System

Cataloged from PDF version of article.This. paper discusses parametric reform options to control losses generated by a publicly managed pay-as-you-go (PAYG) pension system under alternative deficit reduction (reform) strategies involving changes in contribution and replacement rates and statutory retirement ages. Two different problems corresponding to different pension reform strategies are considered using computational techniques. The techniques are illustrated through exercises employing data for the financially troubled pension system in Turkey. (C) 2001 Elsevier Science B.V. All rights reserved

Cosmology with decaying tachyon matter

We investigate the case of a homogeneous tachyon field coupled to gravity in a spatially flat Friedman-Robertson-Walker spacetime. Assuming the field evolution to be exponentially decaying with time we solve the field equations and show that, under certain conditions, the scale factor represents an accelerating universe, following a phase of decelerated expansion. We make use of a model of dark energy (with p=-\rho) and dark matter (p=0) where a single scalar field (tachyon) governs the dynamics of both the dark components. We show that this model fits the current supernova data as well as the canonical \LambdaCDM model. We give the bounds on the parameters allowed by the current data.Comment: 14 pages, 6 figures, v2, Discussions and references addede

Frequency-tunable metamaterials using broadside-coupled split ring resonators

We present frequency tunable metamaterial designs at terahertz (THz) frequencies using broadside-coupled split ring resonator (BC-SRR) arrays. Frequency tuning, arising from changes in near field coupling, is obtained by in-plane horizontal or vertical displacements of the two SRR layers. For electrical excitation, the resonance frequency continuously redshifts as a function of displacement. The maximum frequency shift occurs for displacement of half a unit cell, with vertical displacement resulting in a shift of 663 GHz (51% of f0) and horizontal displacement yielding a shift of 270 GHz (20% of f0). We also discuss the significant differences in tuning that arise for electrical excitation in comparison to magnetic excitation of BC-SRRs

XPS investigation of thin SiOx and SiOxNy overlayers

Cataloged from PDF version of article.Angle-resolved XPS is used to determine the thickness and the uniformity of the chemical composition with respect to oxygen and nitrogen of the very thin silicon oxide and oxynitride overlayers grown on silicon. (C) 1999 Elsevier Science B.V. All rights reserved

Exchange Bias Effect in Au-Fe3O4 Nanocomposites

We report exchange bias (EB) effect in the Au-Fe3O4 composite nanoparticle system, where one or more Fe3O4 nanoparticles are attached to an Au seed particle forming dimer and cluster morphologies, with the clusters showing much stronger EB in comparison with the dimers. The EB effect develops due to the presence of stress in the Au-Fe3O4 interface which leads to the generation of highly disordered, anisotropic surface spins in the Fe3O4 particle. The EB effect is lost with the removal of the interfacial stress. Our atomistic Monte-Carlo studies are in excellent agreement with the experimental results. These results show a new path towards tuning EB in nanostructures, namely controllably creating interfacial stress, and open up the possibility of tuning the anisotropic properties of biocompatible nanoparticles via a controllable exchange coupling mechanism.Comment: 28 pages, 6 figures, submitted to Nanotechnolog