One-dimensional tight-binding models with correlated diagonal and off-diagonal disorder

We study localization properties of electronic states in one-dimensional lattices with nearest-neighbour interaction. Both the site energies and the hopping amplitudes are supposed to be of arbitrary form. A few cases are considered in details. We discuss first the case in which both the diagonal potential and the fluctuating part of the hopping amplitudes are small. In this case we derive a general analytical expression for the localization length, which depends on the pair correlators of the diagonal and off-diagonal matrix elements. The second case we investigate is that of strong uncorrelated disorder, for which approximate analytical estimates are given and compared with numerical data. Finally, we study the model with short-range correlations which constitutes an extension with off-diagonal disorder of the random dimer model.Comment: 11 pages, 7 EPS figures; submitted to "Physica E

Ab-initio electron transport calculations of carbon based string structures

First-principles calculations show that monatomic strings of carbon have high cohesive energy and axial strength, and exhibit stability even at high temperatures. Due to their flexibility and reactivity, carbon chains are suitable for structural and chemical functionalizations; they form also stable ring, helix, grid and network structures. Analysis of electronic conductance of various infinite, finite and doped string structures reveal fundamental and technologically interesting features. Changes in doping and geometry give rise to dramatic variations in conductance. In even-numbered linear chains strain induces substantial decrease of conductance. The double covalent bonding of carbon atoms underlies their unusual chemical, mechanical and transport properties.Comment: 4 pages, 4 figure

The Effects of Supplemental Oxygen Respiration on Hemiplegic Aphasic Adults

TB

Pure apraxia of speech due to infarct in premotor cortex

Apraxia of speech (AOS) is now recognized as an articulation disorder distinct from dysarthria and aphasia. Various lesions have been associated with AOS in studies that are limited in precise localization due to variability in size and type of pathology. We present a case of pure AOS in setting of an acute stroke to localize more precisely than ever before the brain area responsible for AOS, dorsal premotor cortex (dPMC). The dPMC is in unique position to plan and coordinate speech production by virtue of its connection with nearby motor cortex harboring corticobulbar tract, supplementary motor area, inferior frontal operculum, and temporo-parietal area via the dorsal stream of dual-stream model of speech processing. The role of dPMC is further supported as part of dorsal stream in the dual-stream model of speech processing as well as controller in the hierarchical state feedback control model

Defect free global minima in Thomson's problem of charges on a sphere

Given $N$ unit points charges on the surface of a unit conducting sphere, what configuration of charges minimizes the Coulombic energy $\sum_{i>j=1}^N 1/r_{ij}$? Due to an exponential rise in good local minima, finding global minima for this problem, or even approaches to do so has proven extremely difficult. For \hbox{$N = 10(h^2+hk+k^2)+ 2$} recent theoretical work based on elasticity theory, and subsequent numerical work has shown, that for $N \sim >500$--1000 adding dislocation defects to a symmetric icosadeltahedral lattice lowers the energy. Here we show that in fact this approach holds for all $N$, and we give a complete or near complete catalogue of defect free global minima.Comment: Revisions in Tables and Reference

Depth spreading through empty space induced by sparse disparity cues

A key goal of visual processing is to develop an understanding of the three-dimensional layout of the objects in our immediate vicinity from the variety of incomplete and noisy depth cues available to the eyes. Binocular disparity is one of the dominant depth cues, but it is often sparse, being definable only at the edges of uniform surface regions, and visually resolvable only where the edges have a horizontal disparity component. To understand the full 3D structure of visual objects, our visual system has to perform substantial surface interpolation across unstructured visual space. This interpolation process was studied in an eight-spoke depth spreading configuration corresponding to that used in the neon color spreading effect, which generates a strong percept of a sharp contour extending through empty space from the disparity edges within the spokes. Four hypotheses were developed for the form of the depth surface induced by disparity in the spokes defining an incomplete disk in depth: low-level local (isotropic) depth propagation, mid-level linear (anisotropic) depth-contour interpolation or extrapolation, and high-level (anisotropic) figural depth propagation of a disk figure in depth. Data for both perceived depth and position of the perceived contour clearly rejected the first three hypotheses and were consistent with the high-level figural hypothesis in both uniform disparity and slanted disk configurations. We conclude that depth spreading through empty visual space is an accurately quantifiable perceptual process that propagates depth contours anisotropically along their length and is governed by high-level figural properties of 3D object structure

Dual-Frequency VSOP Observations of AO 0235+164

AO 0235+164 is a very compact, flat spectrum radio source identified as a BL Lac object at a redshift of z=0.94. It is one of the most violently variable extragalactic objects at both optical and radio wavelengths. The radio structure of the source revealed by various ground-based VLBI observations is dominated by a nearly unresolved compact component at almost all available frequencies. Dual-frequency space VLBI observations of AO 0235+164 were made with the VSOP mission in January-February 1999. The array of the Japanese HALCA satellite and co-observing ground radio telescopes in Australia, Japan, China and South Africa allowed us to study AO 0235+164 with an unprecedented angular resolution at frequencies of 1.6 and 5 GHz. We report on the sub-milliarcsecond structural properties of the source. The 5-GHz observations led to an estimate of T_B > 5.8 x 10^{13} K for the rest-frame brightness temperature of the core, which is the highest value measured with VSOP to date.Comment: 8 pages, 8 figures, to appear in Publ. Astron. Soc. Japa

The relative resistance of children to sepsis mortality: from pathways to drug candidates

Attempts to develop drugs that address sepsis based on leads developed in animal models have failed. We sought to identify leads based on human data by exploiting a natural experiment: the relative resistance of children to mortality from severe infections and sepsis. Using public datasets, we identified key differences in pathway activity (Pathprint) in blood transcriptome profiles of septic adults and children. To find drugs that could promote beneficial (child) pathways or inhibit harmful (adult) ones, we built an in silico pathway drug network (PDN) using expression correlation between drug, disease, and pathway gene signatures across 58,475 microarrays. Specific pathway clusters from children or adults were assessed for correlation with drug-based signatures. Validation by literature curation and by direct testing in an endotoxemia model of murine sepsis of the most correlated drug candidates demonstrated that the Pathprint-PDN methodology is more effective at generating positive drug leads than gene-level methods (e.g., CMap). Pathway-centric Pathprint-PDN is a powerful new way to identify drug candidates for intervention against sepsis and provides direct insight into pathways that may determine survival

Breakdown of the Korringa Law of Nuclear Spin Relaxation in Metallic GaAs

We present nuclear spin relaxation measurements in GaAs epilayers using a new pump-probe technique in all-electrical, lateral spin-valve devices. The measured T1 times agree very well with NMR data available for T > 1 K. However, the nuclear spin relaxation rate clearly deviates from the well-established Korringa law expected in metallic samples and follows a sub-linear temperature dependence 1/T1 ~ T^0.6 for 0.1 K < T < 10 K. Further, we investigate nuclear spin inhomogeneities.Comment: 5 pages, 4 (color) figures. arXiv admin note: text overlap with arXiv:1109.633