Theory of electron spin resonance in bulk topological insulators Bi2Se3, Bi2Te3 and Sb2Te3

We report a theoretical study of electron spin resonance in bulk topological insulators, such as Bi2Se3, Bi2Te3 and Sb2Te3. Using the effective four-band model, we find the electron energy spectrum in a static magnetic field and determine the response to electric and magnetic dipole perturbations, represented by oscillating electric and magnetic fields perpendicular to the static field. We determine the associated selection rules and calculate the absorption spectra. This enables us to separate the effective orbital and spin degrees of freedom and to determine the effective g-factors for electrons and holes.Comment: 10 pages, 4 figure

First principles studies of a Si tip on Si(100) 2x1 reconstructed surface

We present a systematic study of the interaction between a silicon tip and a reconstructed Si(100)2×1 surface by means of total energy calculations using Density Functional Theory. We perform geometry optimisation to obtain the reconstructed Si surface using the Local Density Approximation and the Generalized Gradient Approximation methods and compare our results with those obtained experimentally. We then study the effects of the tip of a scanning probe of an Atomic Force Microscope (AFM) on the behaviour of atoms on the reconstructed surface when the tip translates at distances close to it. Our results show that at certain positions of the tip relative to the surface and depending on the direction of the scan, the Si dimer on the surface flips, resulting to a local reconstruction of the surface into p(2×2) or c(4×2) configurations. These configurations exhibit energy lower by 0.05 eV/dimer compared to the Si(100)2×1 structure

Multiple-Input Multiple-Output Gaussian Broadcast Channels with Common and Confidential Messages

This paper considers the problem of the multiple-input multiple-output (MIMO) Gaussian broadcast channel with two receivers (receivers 1 and 2) and two messages: a common message intended for both receivers and a confidential message intended only for receiver 1 but needing to be kept asymptotically perfectly secure from receiver 2. A matrix characterization of the secrecy capacity region is established via a channel enhancement argument. The enhanced channel is constructed by first splitting receiver 1 into two virtual receivers and then enhancing only the virtual receiver that decodes the confidential message. The secrecy capacity region of the enhanced channel is characterized using an extremal entropy inequality previously established for characterizing the capacity region of a degraded compound MIMO Gaussian broadcast channel.Comment: Submitted to the IEEE Transactions on Information Theory, July 200

Using Pinch Gloves(TM) for both Natural and Abstract Interaction Techniques in Virtual Environments

Usable three-dimensional (3D) interaction techniques are difficult to design, implement, and evaluate. One reason for this is a poor understanding of the advantages and disadvantages of the wide range of 3D input devices, and of the mapping between input devices and interaction techniques. We present an analysis of Pinch Gloves™ and their use as input devices for virtual environments (VEs). We have developed a number of novel and usable interaction techniques for VEs using the gloves, including a menu system, a technique for text input, and a two-handed navigation technique. User studies have indicated the usability and utility of these techniques

Comparison of results from turbulence models for the Nomad flaperon-configured aerofoil

Incidents involving low speed flutter of the wing-flaperon configured Government Aircraft Factories Nomad N22 and N24 have been reported. Wind tunnel experiments are unable to reproduce the effect. To better understand what could have caused the reported flutter, a computational fluid dynamics based investigation was undertaken, employing a complex commercial simulation software, with the aim to study the local flowfield structures around this configuration, focusing specifically on turbulence effects. Inviscid and viscous flows incorporating the Spalart--Allmaras and RNG $k$-$\epsilon$ turbulence models were computed. Comparisons with experimental data showed excellent agreement among the results, with the predicted section lift coefficients being within 10% of the measured values

Generating elliptic grids in three dimensions by a method of false transients

A finite difference method based scheme incorporating a method of false transients and an approximate factorisation technique is presented for solution of a system of Poisson's equations used for grid generation. A time step cycling process with repeated endpoints is incorporated into the scheme to enhance the convergence rate. The scheme required much less computational effort than all other numerical schemes compared in this article, to obtain a high quality grid over a body (converged solution) in three dimensions. Although, the superiority of the scheme has been demonstrated for a grid generation problem, it may be applied for other problems requiring the numerical solution of a set of similar partial differential equations

Automatic elliptic grid generation by an approximate factorisation algorithm

A procedure for automatic numerical generation of a structured grid system with coordinate lines coinciding with all boundaries of a general two-dimensional region containing a body of arbitrary shape is presented. The solution procedure incorporated the method of false transients and the approximate factorisation algorithm, where a sequence of time steps is cycled in a geometric fashion with repeated endpoints, and has a capability for clustering grid lines close to the body. The procedure requires significantly much less computational effort to obtain a converged solution than a point or line successive over-relaxation iterative scheme. Although, the superiority of the presented algorithm has been demonstrated for the grid generation problem, it can be utilised for other problems requiring the solution of a set of elliptic partial differential equations of similar nature

Shiga toxin production and translocation during microaerobic human colonic infection with Shiga toxin-producing E. coli O157:H7 and O104:H4

Haemolytic uraemic syndrome caused by Shiga toxin-producing E. coli (STEC) is dependent on release of Shiga toxins (Stxs) during intestinal infection and subsequent absorption into the bloodstream. An understanding of Stx-related events in the human gut is limited due to lack of suitable experimental models. In this study, we have used a vertical diffusion chamber system with polarized human colon carcinoma cells to simulate the microaerobic (MA) environment in the human intestine and investigate its influence on Stx release and translocation during STEC O157:H7 and O104:H4 infection. Stx2 was the major toxin type released during infection. Whereas microaerobiosis significantly reduced bacterial growth as well as Stx production and release into the medium, Stx translocation across the epithelial monolayer was enhanced under MA versus aerobic conditions. Increased Stx transport was dependent on STEC infection and occurred via a transcellular pathway other than macropinocytosis. While MA conditions had a similar general effect on Stx release and absorption during infection with STEC O157:H7 and O104:H4, both serotypes showed considerable differences in colonization, Stx production, and Stx translocation which suggest alternative virulence strategies. Taken together, our study suggests that the MA environment in the human colon may modulate Stx-related events and enhance Stx absorption during STEC infection

High-Resolution Structure of the N-Terminal Endonuclease Domain of the Lassa Virus L Polymerase in Complex with Magnesium Ions

Lassa virus (LASV) causes deadly hemorrhagic fever disease for which there are no vaccines and limited treatments. LASV-encoded L polymerase is required for viral RNA replication and transcription. The functional domains of L–a large protein of 2218 amino acid residues–are largely undefined, except for the centrally located RNA-dependent RNA polymerase (RdRP) motif. Recent structural and functional analyses of the N-terminal region of the L protein from lymphocytic choriomeningitis virus (LCMV), which is in the same Arenaviridae family as LASV, have identified an endonuclease domain that presumably cleaves the cap structures of host mRNAs in order to initiate viral transcription. Here we present a high-resolution crystal structure of the N-terminal 173-aa region of the LASV L protein (LASV L173) in complex with magnesium ions at 1.72 Å. The structure is highly homologous to other known viral endonucleases of arena- (LCMV NL1), orthomyxo- (influenza virus PA), and bunyaviruses (La Crosse virus NL1). Although the catalytic residues (D89, E102 and K122) are highly conserved among the known viral endonucleases, LASV L endonuclease structure shows some notable differences. Our data collected from in vitro endonuclease assays and a reporter-based LASV minigenome transcriptional assay in mammalian cells confirm structural prediction of LASV L173 as an active endonuclease. The high-resolution structure of the LASV L endonuclease domain in complex with magnesium ions should aid the development of antivirals against lethal Lassa hemorrhagic fever