Testing the Inverse Born Procedure for Spheroidal Voids

Previously we have shown that the inverse Born approximation allows an accurate determination of the radius of spherical flaws in Ti. Here we report the results of extending that analysis to spheroidal voids. Both oblate and prolate spheroids are considered. Using scattering amplitude generated by the T-matrix method, we find that both the major and minor axes of 2-1 spheroids are accurately determined. Inversion results using experimental data will be presented for the 2-1 oblate spheroid: a comparison of the experimental and theoretical results will be given

Sensitivity of Failure Prediction to Flaw Geometry

The assumption of ellipsoidal flaw geometry has been widely used in calculations of the probability of structural failure conditioned on nondestructive (ND) measurements. Clearly, in most cases the flaw geometry is not ellipsoidal and in the particular case of cracks the actual geometry may deviate significantly from a degenerate ellipsoid (i.e., a planar crack with an elliptical plan-view shape). We have investigated the sensitivity of a late stage of the evolution of fatigue failure to model errors of the latter type (i.e., deviations from elliptical shape for planar cracks) by considering two different overall theoretical processes. In the first, we start with a non-elliptical crack and calculate its geometry after a given large number of cycles of uniaxial stress applied perpendicular to the crack plane. In the second process, we start with the same crack but perform a simulated set of ND measurements coupled with an inversion procedure based on the assumption of elliptical geometry and then calculate the geometry of this initially elliptical crack after subjection to the above stress history. A measure of sensitivity to model error is then provided by a comparison of the two terminal geometries. Results for several choices of non-elliptical crack shapes and sets of ND measurements will be discussed

Tunability of the dielectric response of epitaxially strained SrTiO3 from first principles

The effect of in-plane strain on the nonlinear dielectric properties of SrTiO3 epitaxial thin films is calculated using density-functional theory within the local-density approximation. Motivated by recent experiments, the structure, zone-center phonons, and dielectric properties with and without an external electric field are evaluated for several misfit strains within +-3% of the calculated cubic lattice parameter. In these calculations, the in-plane lattice parameters are fixed, and all remaining structural parameters are permitted to relax. The presence of an external bias is treated approximately by applying a force to each ion proportional to the electric field. After obtaining zero-field ground state structures for various strains, the zone-center phonon frequencies and Born effective charges are computed, yielding the zero-field dielectric response. The dielectric response at finite electric field bias is obtained by computing the field dependence of the structure and polarization using an approximate technique. The results are compared with recent experiments and a previous phenomenological theory. The tunability is found to be strongly dependent on the in-plane lattice parameter, showing markedly different behavior for tensile and compressive strains. Our results are expected to be of use for isolating the role of strain in the tunability of real ultrathin epitaxial films.Comment: 11 pages, with postscript figures embedded. Uses REVTEX and epsf macros. Also available at http://www.physics.rutgers.edu/~dhv/preprints/ant_srti/index.htm

The Off-Shell Electromagnetic T-matrix: momentum-dependent scattering from spherical inclusions with both dielectric and magnetic contrast

The momentum- and frequency-dependent T-matrix operator for the scattering of electromagnetic waves by a dielectric/conducting and para- or diamagnetic sphere is derived as a Mie-type series, and presented in a compact form emphasizing various symmetry properties, notably the unitarity identity. This result extends to magnetic properties one previously obtained for purely dielectric contrasts by other authors. Several situations useful to spatially-dispersive effective-medium approximations to one-body order are examined. Partial summation of the Mie series is achieved in the case of elastic scattering.Comment: 22 pages. Preprint of a paper to appear in `Waves in Complex And Random Media' ((c) Taylor and Francis, 2011

Ubistatins Inhibit Proteasome-Dependent Degradation by Binding the Ubiquitin Chain

To identify previously unknown small molecules that inhibit cell cycle machinery, we performed a chemical genetic screen in Xenopus extracts. One class of inhibitors, termed ubistatins, blocked cell cycle progression by inhibiting cyclin B proteolysis and inhibited degradation of ubiquitinated Sic1 by purified proteasomes. Ubistatins blocked the binding of ubiquitinated substrates to the proteasome by targeting the ubiquitin-ubiquitin interface of Lys^(48)-linked chains. The same interface is recognized by ubiquitin-chain receptors of the proteasome, indicating that ubistatins act by disrupting a critical protein-protein interaction in the ubiquitin-proteasome system

Technology, infrastructure and enterprise trade-off: Strengthening smallholder farming systems in Tamil Nadu State of India for sustainable income and food security

The complexities of smallholder farming systems pose a challenge in demonstrating the potential benefits or risks of new technologies and policies. Using Integrated Analysis Tool, a rule-based dynamic simulation model, this study tried to improve the performance of major farming systems in the Tamil Nadu State of India. Amongst the four major farming systems viz. Black gram-based (BFS), Paddy-based (PFS), and Integrated Farming Systems (IFS) in Villupuram district and Dryland Farming System (DFS) in Virudhunagar district, IFS was found to be the most profitable and resilient based on their performance simulated for a 3-year rotation. Setting IFS as a benchmark, potential interventions were evaluated under other farming systems to improve their relative performance. The analysis allowed understanding the interactions in smallholder farming systems and the potential impact of interventions in a whole farm way considering the cash flows, cost intensity, and input-output trade-offs. While multi-bloom technology in black gram increased the net profit of BFS without much stress on input and labour, area expansion under rainfed groundnut incurred high expenditure. Trading-off paddy with maize and groundnut significantly increased the net profit of PFS but replacing sugarcane with tapioca and turmeric was not remunerative. Improved livestock management practices have substantially increased the net profit of DFS wherein crop yield could not be enhanced substantially without the prospects of good irrigation infrastructure. The irrigation endowed PFS has achieved 90% performance, whereas the water-starved BFS and DFS could achieve only 65% performance of IFS. We conclude that agricultural policy must not only focus on potential interventions that are profitable but also consider what is acceptable to the farmer, considering synergies and trade-offs between competing resources at the farm level

Lattice instabilities of PbZrO3/PbTiO3 [1:1] superlattices from first principles

Ab initio phonon calculations for the nonpolar reference structures of the (001), (110), and (111) PbZrO_3/PbTiO_3 [1:1] superlattices are presented. The unstable polar modes in the tetragonal (001) and (110) structures are confined in either the Ti- or the Zr-centered layers and display two-mode behavior, while in the cubic (111) case one-mode behavior is observed. Instabilities with pure oxygen character are observed in all three structures. The implications for the ferroelectric behavior and related properties are discussed.Comment: 12 pages, 2 figures, 7 tables, submitted to PR

Structural insight into SUMO chain recognition and manipulation by the ubiquitin ligase RNF4

The small ubiquitin-like modifier (SUMO) can form polymeric chains that are important signals in cellular processes such as meiosis, genome maintenance and stress response. The SUMO-targeted ubiquitin ligase RNF4 engages with SUMO chains on linked substrates and catalyses their ubiquitination, which targets substrates for proteasomal degradation. Here we use a segmental labelling approach combined with solution nuclear magnetic resonance (NMR) spectroscopy and biochemical characterization to reveal how RNF4 manipulates the conformation of the SUMO chain, thereby facilitating optimal delivery of the distal SUMO domain for ubiquitin transfer