Efficient graphene-based photodetector with two cavities

We present an efficient graphene-based photodetector with two Fabri-P\'erot cavities. It is shown that the absorption can reach almost 100% around a given frequency, which is determined by the two-cavity lengths. It is also shown that hysteresis in the absorbance is possible, with the transmittance amplitude of the mirrors working as an external driving field. The role of non-linear contributions to the optical susceptibility of graphene is discussed.Comment: 10 pages, 8 figures. published version: minor revisio

Disordered Carbon nanotube alloys in the Effect Medium Super Cell Approximation

We investigate a disordered single-walled carbon nanotube (SWCNT) in an effective medium super cell approximation (EMSCA). First type of disorder that we consider is the presence of vacancies. Our results show that the vacancies induce some bound states on their neighbor host sites, leading to the creation of a band around the Fermi energy in the SWCNT average density of states.Second type of disorder considered is a substitutional $B_{cb}N_{cn}C_{1-cb-cn}$ alloy due to it's applications in hetrojunctions. We found that for a fixed boron (nitrogen) concentration, by increasing the nitrogen (boron) concentration the averaged semiconducting gap, $E_{g}$, decreases and at a critical concentration it disappears. A consequence of our results for nano electronic devices is that by changing the boron(nitrogen) concentration, one can make a semiconductor SWCNT with a pre-determined energy gap.Comment: 4 page

Critical temperature of a fully anisotropic three-dimensional Ising model

The critical temperature of a three-dimensional Ising model on a simple cubic lattice with different coupling strengths along all three spatial directions is calculated via the transfer matrix method and a finite size scaling for L x L oo clusters (L=2 and 3). The results obtained are compared with available calculations. An exact analytical solution is found for the 2 x 2 oo Ising chain with fully anisotropic interactions (arbitrary J_x, J_y and J_z).Comment: 17 pages in tex using preprint.sty for IOP journals, no figure

The Rashba Hamiltonian and electron transport

The Rashba Hamiltonian describes the splitting of the conduction band as a result of spin-orbit coupling in the presence of an external field and is commonly used to model the electronic structure of confined narrow-gap semiconductors. Due to the mixing of spin states some care has to be exercised in the calculation of transport properties. We derive the velocity operator for the Rashba-split conduction band and demonstrate that the transmission of an interface between a ferromagnet and a Rashba-split semiconductor does not depend on the magnetization direction, in contrast with previous assertions in the literature.Comment: one tex file, two figures; paper to appear in this form in PRB (RC

Fundamental Oscillation Periods of the Interlayer Exchange Coupling beyond the RKKY Approximation

A general method for obtaining the oscillation periods of the interlayer exchange coupling is presented. It is shown that it is possible for the coupling to oscillate with additional periods beyond the ones predicted by the RKKY theory. The relation between the oscillation periods and the spacer Fermi surface is clarified, showing that non-RKKY periods do not bear a direct correspondence with the Fermi surface. The interesting case of a FCC(110) structure is investigated, unmistakably proving the existence and relevance of non-RKKY oscillations. The general conditions for the occurrence of non-RKKY oscillations are also presented.Comment: 34 pages, 10 figures ; to appear in J. Phys.: Condens. Mat

Antimicrobial resistance and antimicrobial use animal monitoring policies in Europe: Where are we?

The World Health Organization has recognized antimicrobial resistance as one of the top three threats to human health. Any use of antibiotics in animals will ultimately affect humans and vice versa. Appropriate monitoring of antimicrobial use and resistance has been repeatedly emphasized along with the need for global policies. Under the auspices of the European Union research project, EFFORT, we mapped antimicrobial use and resistance monitoring programs in ten European countries. We then compared international and European guidelines and policies. In resistance monitoring, we did not find important differences between countries. Current resistance monitoring systems are focused on food animal species (using fecal samples). They ignore companion animals. The scenario is different for monitoring antibiotics use. Recently, countries have tried to harmonize methodologies, but reporting of antimicrobial use remains voluntary. We therefore identified a need for stronger policies

Lipid-free Antigen B subunits from echinococcus granulosus: oligomerization, ligand binding, and membrane interaction properties

Background: The hydatid disease parasite Echinococcus granulosus has a restricted lipid metabolism, and needs to harvest essential lipids from the host. Antigen B (EgAgB), an abundant lipoprotein of the larval stage (hydatid cyst), is thought to be important in lipid storage and transport. It contains a wide variety of lipid classes, from highly hydrophobic compounds to phospholipids. Its protein component belongs to the cestode-specific Hydrophobic Ligand Binding Protein family, which includes five 8-kDa isoforms encoded by a multigene family (EgAgB1-EgAgB5). How lipid and protein components are assembled into EgAgB particles remains unknown. EgAgB apolipoproteins self-associate into large oligomers, but the functional contribution of lipids to oligomerization is uncertain. Furthermore, binding of fatty acids to some EgAgB subunits has been reported, but their ability to bind other lipids and transfer them to acceptor membranes has not been studied.<p></p> Methodology/Principal Findings: Lipid-free EgAgB subunits obtained by reverse-phase HPLC were used to analyse their oligomerization, ligand binding and membrane interaction properties. Size exclusion chromatography and cross-linking experiments showed that EgAgB8/2 and EgAgB8/3 can self-associate, suggesting that lipids are not required for oligomerization. Furthermore, using fluorescent probes, both subunits were found to bind fatty acids, but not cholesterol analogues. Analysis of fatty acid transfer to phospholipid vesicles demonstrated that EgAgB8/2 and EgAgB8/3 are potentially capable of transferring fatty acids to membranes, and that the efficiency of transfer is dependent on the surface charge of the vesicles.<p></p> Conclusions/Significance: We show that EgAgB apolipoproteins can oligomerize in the absence of lipids, and can bind and transfer fatty acids to phospholipid membranes. Since imported fatty acids are essential for Echinococcus granulosus, these findings provide a mechanism whereby EgAgB could engage in lipid acquisition and/or transport between parasite tissues. These results may therefore indicate vulnerabilities open to targeting by new types of drugs for hydatidosis therapy.<p></p&gt

Generating derivative structures: Algorithm and applications

We present an algorithm for generating all derivative superstructures--for arbitrary parent structures and for any number of atom types. This algorithm enumerates superlattices and atomic configurations in a geometry-independent way. The key concept is to use the quotient group associated with each superlattice to determine all unique atomic configurations. The run time of the algorithm scales linearly with the number of unique structures found. We show several applications demonstrating how the algorithm can be used in materials design problems. We predict an altogether new crystal structure in Cd-Pt and Pd-Pt, and several new ground states in Pd-rich and Pt-rich binary systems