Reflection high-energy electron diffraction patterns of CrSi_2 films on (111) silicon

Highly oriented films of the semiconducting transition metal silicide, CrSi2, were grown on (111) silicon substrates, with the matching crystallographic faces being CrSi_2(001)/Si(111). Reflection high‐energy electron diffraction (RHEED) yielded symmetric patterns of sharp streaks. The expected streak spacings for different incident RHEED beam directions were calculated from the reciprocal net of the CrSi_2(001) face and shown to match the observed spacings. The predominant azimuthal orientation of the films was thus determined to be CrSi_2〈210〉∥Si〈110〉. This highly desirable heteroepitaxial relationship may be described with a common unit mesh of 51 Å^2 and a mismatch of −0.3%. RHEED also revealed the presence of limited film regions of a competing azimuthal orientation, CrSi_2〈110〉∥Si〈110〉. A new common unit mesh for this competing orientation is suggested; it possesses an area of 612 Å^2 and a mismatch of −1.2%

The topological classification of one-dimensional symmetric quantum walks

We give a topological classification of quantum walks on an infinite 1D lattice, which obey one of the discrete symmetry groups of the tenfold way, have a gap around some eigenvalues at symmetry protected points, and satisfy a mild locality condition. No translation invariance is assumed. The classification is parameterized by three indices, taking values in a group, which is either trivial, the group of integers, or the group of integers modulo 2, depending on the type of symmetry. The classification is complete in the sense that two walks have the same indices if and only if they can be connected by a norm continuous path along which all the mentioned properties remain valid. Of the three indices, two are related to the asymptotic behaviour far to the right and far to the left, respectively. These are also stable under compact perturbations. The third index is sensitive to those compact perturbations which cannot be contracted to a trivial one. The results apply to the Hamiltonian case as well. In this case all compact perturbations can be contracted, so the third index is not defined. Our classification extends the one known in the translation invariant case, where the asymptotic right and left indices add up to zero, and the third one vanishes, leaving effectively only one independent index. When two translationally invariant bulks with distinct indices are joined, the left and right asymptotic indices of the joined walk are thereby fixed, and there must be eigenvalues at $1$ or $-1$ (bulk-boundary correspondence). Their location is governed by the third index. We also discuss how the theory applies to finite lattices, with suitable homogeneity assumptions.Comment: 36 pages, 7 figure

Pre-Congestion Notification (PCN) Architecture

This document describes a general architecture for flow admission and termination based on pre-congestion information in order to protect the quality of service of established, inelastic flows within a single Diffserv domain.\u

Channeling of MeV ions in polyatomic epitaxial films: ReSi2 on Si(100)

Channeling of a He beam in the energy range from 1.4 to 2.7 MeV in a polyatomic epitaxial ReSi2 film (∼150 nm thick) was studied by detecting backscattered He ions. The critical angles and the minimum yields of both the heavy (Re) and the light (Si) elements are obtained directly from backscattering measurements. The critical angles of both Re and Si scale as √1/E. The critical angle of Re is always about 2.3 times that of Si. The minimum yields of both Re and Si do not change over this energy range. The minimum yield of Re (2%) is about 1/7 that of Si (14%). The results are explained qualitatively and quantitatively by the continuum model suitably extended for polyatomic crystals. An important corollary is that a high value for the minimum yield of the light element in a polyatomic single crystal does not necessarily mean that the sublattice of the light element is disordered

Genome mining in Amycolatopsis balhimycina for ferredoxins capable of supporting cytochrome P450 enzymes involved in glycopeptide antibiotic biosynthesis

Ferredoxins are required to supply electrons to the cytochrome P450 enzymes involved in cross-linking reactions during the biosynthesis of the glycopeptide antibiotics balhimycin and vancomycin. However, the biosynthetic gene clusters for these antibiotics contain no ferredoxin- or ferredoxin reductase-like genes. In a search for potential ferredoxin partners for these P450s, here, we report an in silico analysis of the draft genome sequence of the balhimycin producer Amycolatopsis balhimycina, which revealed 11 putative Fe-S-containing ferredoxin genes. We show that two members (balFd-V and balFd-VII), produced as native-like holo-[3Fe-4S] ferredoxins in Escherichia coli, could supply electrons to the P450 OxyB (CYP165B) from both A. balhimycina and the vancomycin producer Amycolatopsis orientalis, and support in vitro turnover of peptidyl carrier protein-bound peptide substrates into monocyclic cross-linked products. These results show that ferredoxins encoded in the antibiotic-producing strain can act in a degenerate manner in supporting the catalytic functions of glycopeptide biosynthetic P450 enzymes from the same as well as heterologous gene cluster

Midgut microbiota of the malaria mosquito vector Anopheles gambiae and Interactions with plasmodium falciparum Infection

The susceptibility of Anopheles mosquitoes to Plasmodium infections relies on complex interactions between the insect vector and the malaria parasite. A number of studies have shown that the mosquito innate immune responses play an important role in controlling the malaria infection and that the strength of parasite clearance is under genetic control, but little is known about the influence of environmental factors on the transmission success. We present here evidence that the composition of the vector gut microbiota is one of the major components that determine the outcome of mosquito infections. A. gambiae mosquitoes collected in natural breeding sites from Cameroon were experimentally challenged with a wild P. falciparum isolate, and their gut bacterial content was submitted for pyrosequencing analysis. The meta-taxogenomic approach revealed a broader richness of the midgut bacterial flora than previously described. Unexpectedly, the majority of bacterial species were found in only a small proportion of mosquitoes, and only 20 genera were shared by 80% of individuals. We show that observed differences in gut bacterial flora of adult mosquitoes is a result of breeding in distinct sites, suggesting that the native aquatic source where larvae were grown determines the composition of the midgut microbiota. Importantly, the abundance of Enterobacteriaceae in the mosquito midgut correlates significantly with the Plasmodium infection status. This striking relationship highlights the role of natural gut environment in parasite transmission. Deciphering microbe-pathogen interactions offers new perspectives to control disease transmission.Institut de Recherche pour le Developpement (IRD); French Agence Nationale pour la Recherche [ANR-11-BSV7-009-01]; European Community [242095, 223601]info:eu-repo/semantics/publishedVersio

Oocyte expression with injection of purified T7 RNA polymerase.

International audienceThe Xenopus oocyte is a widely used system for protein expression. Investigators have had the choice between two different techniques: injection into the cytoplasm of in vitro transcribed complementary RNA (cRNA) or injection into the nucleus of complementary DNA (cDNA). We report on a third expression technique that is based on the combined injection of cDNA and purified T7 RNA polymerase directly into the cytoplasm of oocytes

Persistence within dendritic cells marks an antifungal evasion and dissemination strategy of Aspergillus terreus

Aspergillus terreus is an airborne human fungal pathogen causing life-threatening invasive aspergillosis in immunocompromised patients. In contrast to Aspergillus fumigatus, A. terreus infections are associated with high dissemination rates and poor response to antifungal treatment. Here, we compared the interaction of conidia from both fungal species with MUTZ-3-derived dendritic cells (DCs). After phagocytosis, A. fumigatus conidia rapidly escaped from DCs, whereas A. terreus conidia remained persisting with long-term survival. Escape from DCs was independent from DHN-melanin, as A. terreus conidia expressing wA showed no increased intracellular germination. Within DCs A. terreus conidia were protected from antifungals, whereas A. fumigatus conidia were efficiently cleared. Furthermore, while A. fumigatus conidia triggered expression of DC activation markers such as CD80, CD83, CD54, MHCII and CCR7, persistent A. terreus conidia were significantly less immunogenic. Moreover, DCs confronted with A. terreus conidia neither produced pro-inflammatory nor T-cell stimulating cytokines. However, TNF-α addition resulted in activation of DCs and provoked the expression of migration markers without inactivating intracellular A. terreus conidia. Therefore, persistence within DCs and possibly within other immune cells might contribute to the low response of A. terreus infections to antifungal treatment and could be responsible for its high dissemination rates

Prediction and Topological Models in Neuroscience

In the last two decades, philosophy of neuroscience has predominantly focused on explanation. Indeed, it has been argued that mechanistic models are the standards of explanatory success in neuroscience over, among other things, topological models. However, explanatory power is only one virtue of a scientific model. Another is its predictive power. Unfortunately, the notion of prediction has received comparatively little attention in the philosophy of neuroscience, in part because predictions seem disconnected from interventions. In contrast, we argue that topological predictions can and do guide interventions in science, both inside and outside of neuroscience. Topological models allow researchers to predict many phenomena, including diseases, treatment outcomes, aging, and cognition, among others. Moreover, we argue that these predictions also offer strategies for useful interventions. Topology-based predictions play this role regardless of whether they do or can receive a mechanistic interpretation. We conclude by making a case for philosophers to focus on prediction in neuroscience in addition to explanation alone