Characterisation of High Current Density Resonant Tunneling Diodes for THz Emission Using Photoluminescence Spectroscopy

We discuss the numerical simulation of high current density InGaAs/AlAs/InP resonant tunneling diodes with a view to their optimization for application as THz emitters. We introduce a figure of merit based upon the ratio of maximum extractable THz power and the electrical power developed in the chip. The aim being to develop high efficiency emitters as output power is presently limited by catastrophic failure. A description of the interplay of key parameters follows, with constraints on strained layer epitaxy introduced. We propose an optimized structure utilizing thin barriers paired with a comparatively wide quantum well that satisfies strained layer epitaxy constraints

One-line γ ray spectroscopic investigation of the 180Hg(T 1/2 = 3 s) decay chain

With the rebuilt ISOLDE 2 facility we have investigated on-line the 18080Hg decay products. The decay half-lives, the energies and intensities of the main γ lines of both 180Hg(T 1/2 = 3.0 ± 0.3 s) and 18079Au(T1/2 = 8.1 ± 0.3 s) , and a tentative decay scheme of 18078Pt are given

Deductive Biocomputing

BACKGROUND: As biologists increasingly rely upon computational tools, it is imperative that they be able to appropriately apply these tools and clearly understand the methods the tools employ. Such tools must have access to all the relevant data and knowledge and, in some sense, “understand” biology so that they can serve biologists' goals appropriately and “explain” in biological terms how results are computed. METHODOLOGY/PRINCIPAL FINDINGS: We describe a deduction-based approach to biocomputation that semiautomatically combines knowledge, software, and data to satisfy goals expressed in a high-level biological language. The approach is implemented in an open source web-based biocomputing platform called BioDeducta, which combines SRI's SNARK theorem prover with the BioBike interactive integrated knowledge base. The biologist/user expresses a high-level conjecture, representing a biocomputational goal query, without indicating how this goal is to be achieved. A subject domain theory, represented in SNARK's logical language, transforms the terms in the conjecture into capabilities of the available resources and the background knowledge necessary to link them together. If the subject domain theory enables SNARK to prove the conjecture—that is, to find paths between the goal and BioBike resources—then the resulting proofs represent solutions to the conjecture/query. Such proofs provide provenance for each result, indicating in detail how they were computed. We demonstrate BioDeducta by showing how it can approximately replicate a previously published analysis of genes involved in the adaptation of cyanobacteria to different light niches. CONCLUSIONS/SIGNIFICANCE: Through the use of automated deduction guided by a biological subject domain theory, this work is a step towards enabling biologists to conveniently and efficiently marshal integrated knowledge, data, and computational tools toward resolving complex biological queries

Two-dimensional limit of exchange-correlation energy functional approximations in density functional theory

We investigate the behavior of three-dimensional (3D) exchange-correlation energy functional approximations of density functional theory in anisotropic systems with two-dimensional (2D) character. Using two simple models, quasi-2D electron gas and two-electron quantum dot, we show a {\it fundamental limitation} of the local density approximation (LDA), and its semi-local extensions, generalized gradient approximation (GGA) and meta-GGA (MGGA), the most widely used forms of which are worse than the LDA in the strong 2D limit. The origin of these shortcomings is in the inability of the local (LDA) and semi-local (GGA/MGGA) approximations to describe systems with 2D character in which the nature of the exchange-correlation hole is very nonlocal. Nonlocal functionals provide an alternative approach, and explicitly the average density approximation (ADA) is shown to be remarkably accurate for the quasi-2D electron gas system. Our study is not only relevant for understanding of the functionals but also practical applications to semiconductor quantum structures and materials such as graphite and metal surfaces. We also comment on the implication of our findings to the practical device simulations based on the (semi-)local density functional method.Comment: 21 pages including 9 figures, to be published in Phys. Rev.

Bring Your Own Device (BYOD): Current Status, Issues, and Future Directions

The smart mobile device has emerged as an extension of the self, closely tied to the personal behaviors and preferences. This panel discussion covers the current status, real world cases, adoption, pros/cons, issues (security, privacy), and future direction of the use and adoption of Bring-Your-Own-Device (BYOD). The panel also covers BYOS (Bring-Your-Own-Service) and BYOA (Bring-Your-Own-Apps)

Le niveau de compréhension de l’anglais des étudiants en médecine peut être amélioré. Résultats d’une stratégie d’évaluation systématique

Objectives To describe the level of English of a population of medical students and the improvement after the implementation of systematic assessment that all students achieve a minimal level. Population and methods For the past 5 years, all medical students in our medical school have been taking the Test of English for International Communication (TOEIC). The baseline population (students entering second year in 2004) had no specific obligation. After 2004, a score above 600 was mandatory for graduation. Teaching was oriented towards training for the TOEIC and the number of hours was more important for low-level students. Results The mean score has increased from 618 ± 146 in 2004, to 687 ± 94, 717 ± 97, 733 ± 96 and 731 ± 104 for the next four years. The proportion of students who do not achieve a score of 550 (B1 level of the European framework) has decreased from 30 to 0%. Discussion Improving the level of English of French medical students is possible, if this is made a priority. The objective, as set in engineering studies, that all medical students reach a B2 level would require national guidelines

Preheating After Modular Inflation

We study (p)reheating in modular (closed string) inflationary scenarios, with a special emphasis on Kahler moduli/Roulette models. It is usually assumed that reheating in such models occurs through perturbative decays. However, we find that there are very strong non-perturbative preheating decay channels related to the particular shape of the inflaton potential (which is highly nonlinear and has a very steep minimum). Preheating after modular inflation, proceeding through a combination of tachyonic instability and broad-band parametric resonance, is perhaps the most violent example of preheating after inflation known in the literature. Further, we consider the subsequent transfer of energy to the standard model sector in scenarios where the standard model particles are confined to a D7-brane wrapping the inflationary blow-up cycle of the compactification manifold or, more interestingly, a non-inflationary blow up cycle. We explicitly identify the decay channels of the inflaton in these two scenarios. We also consider the case where the inflationary cycle shrinks to the string scale at the end of inflation; here a field theoretical treatment of reheating is insufficient and one must turn instead to a stringy description. We estimate the decay rate of the inflaton and the reheat temperature for various scenarios.Comment: 34 pages, 10 figures. Accepted for publication in JCA

Immunization with a synthetic consensus hepatitis C virus E2 glycoprotein ectodomain elicits virus-neutralizing antibodies

Global eradication of hepatitis C virus (HCV) infection will require an efficacious vaccine capable of eliciting protective immunity against genetically diverse HCV strains. Natural spontaneous resolution of HCV infection is associated with production of broadly neutralizing antibodies targeting the HCV glycoproteins E1 and E2. As such, production of cross-neutralizing antibodies is an important endpoint for experimental vaccine trials. Varying success generating cross-neutralizing antibodies has been achieved with immunogens derived from naturally-occurring HCV strains. In this study the challenge of minimising the genetic diversity between the vaccine strain and circulating HCV isolates was addressed. Two novel synthetic E2 glycoprotein immunogens (NotC1 and NotC2) were derived from consensus nucleotide sequences deduced from samples of circulating genotype 1 HCV strains. These two synthetic sequences differed in their relative positions in the overall genotype 1a/1b phylogeny. Expression of these constructs in Drosophila melanogaster S2 cells resulted in high yields of correctly-folded, monomeric E2 protein, which were recognised by broadly neutralizing monoclonal antibodies. Immunization of guinea pigs with either of these consensus immunogens, or a comparable protein representing a circulating genotype 1a strain resulted in high titres of cross-reactive anti-E2 antibodies. All immunogens generated antibodies capable of neutralizing the H77 strain, but NotC1 elicited antibodies that more potently neutralized virus entry. These vaccine-induced antibodies neutralized some viruses representing genotype 1, but not strains representing genotype 2 or genotype 3. Thus, while this approach to vaccine design resulted in correctly folded, immunogenic protein, cross-neutralizing epitopes were not preferentially targeted by the host immune response generated by this immunogen. Greater immunofocussing by vaccines to common epitopes is necessary to successfully elicit broadly neutralizing antibodies

An integrated approach to modelling the fluid-structure interaction of a collapsible tube

The well known collapsible tube experiment was conducted to obtain flow, pressure and materials property data for steady state conditions. These were then used as the boundary conditions for a fully coupled fluid-structure interaction (FSI) model using a propriety computer code, LS-DYNA. The shape profiles for the tube were also recorded. In order to obtain similar collapse modes to the experiment, it was necessary to model the tube flat, and then inflate it into a circular profile, leaving residual stresses in the walls. The profile shape then agreed well with the experimental ones. Two departures from the physical properties were required to reduce computer time to an acceptable level. One of these was the lowering of the speed of sound by two orders of magnitude which, due to the low velocities involved, still left the mach number below 0.2. The other was to increase the thickness of the tube to prevent the numerical collapse of elements. A compensation for this was made by lowering the Young's modulus for the tube material. Overall the results are qualitatively good. They give an indication of the power of the current FSI algorithms and the need to combine experiment and computer models in order to maximise the information that can be extracted both in terms of quantity and quality