Physical properties of thermoelectric zinc antimonide using first-principles calculations

We report first principles calculations of the structural, electronic, elastic and vibrational properties of the semiconducting orthorhombic ZnSb compound. We study also the intrinsic point defects in order to eventually improve the thermoelectric properties of this already very promising thermoelectric material. Concerning the electronic properties, in addition to the band structure, we show that the Zn (Sb) crystallographically equivalent atoms are not exactly equivalent from the electronic point of view. Lattice dynamics, elastic and thermodynamic properties are found to be in good agreement with experiments and they confirm the non equivalency of the zinc and antimony atoms from the vibrational point of view. The calculated elastic properties show a relatively weak anisotropy and the hardest direction is the y direction. We observe the presence of low energy modes involving both Zn and Sb atoms at about 5-6 meV, similarly to what has been found in Zn4Sb3 and we suggest that the interactions of these modes with acoustic phonons could explain the relatively low thermal conductivity of ZnSb. Zinc vacancies are the most stable defects and this explains the intrinsic p-type conductivity of ZnSb.Comment: 33 pages, 8 figure

Experimental constraints on the ordinary chondrite shock darkening caused by asteroid collisions

Context. Shock-induced changes in ordinary chondrite meteorites related to impacts or planetary collisions are known to be capable of altering their optical properties. Thus, one can hypothesize that a significant portion of the ordinary chondrite material may be hidden within the observed dark C/X asteroid population. Aims. The exact pressure-temperature conditions of the shock-induced darkening are not well constrained. Thus, we experimentally investigate the gradual changes in the chondrite material optical properties as a function of the shock pressure. Methods. A spherical shock experiment with Chelyabinsk LL5 was performed in order to study the changes in its optical properties. The spherical shock experiment geometry allows for a gradual increase of shock pressure from similar to 15 GPa at a rim toward hundreds of gigapascals in the center. Results. Four distinct zones were observed with an increasing shock load. The optical changes are minimal up to similar to 50 GPa. In the region of similar to 50-60 GPa, shock darkening occurs due to the troilite melt infusion into silicates. This process abruptly ceases at pressures of similar to 60 GPa due to an onset of silicate melting. At pressures higher than similar to 150 GPa, recrystallization occurs and is associated with a second-stage shock darkening due to fine troilite-metal eutectic grains. The shock darkening affects the ultraviolet, visible, and near-infrared region while changes to the MIR spectrum are minimal. Conclusions. Shock darkening is caused by two distinct mechanisms with characteristic pressure regions, which are separated by an interval where the darkening ceases. This implies a reduced amount of shock-darkened material produced during the asteroid collisions.Peer reviewe

Orbital-selective band hybridisation at the charge density wave transition in monolayer TiTe2

Funding: We gratefully acknowledge support from the Leverhulme Trust and the Royal Society. W.R. is grateful to University College London for awarding a Graduate Research Scholarship and an Overseas Research Scholarship. O.J.C. and K.U. acknowledge PhD studentship support from the UK Engineering and Physical Sciences Research Council (EPSRC, Grant Nos. EP/K503162/1 and EP/L015110/1). I.M. and E.A.-M. acknowledge studentship support from the International Max-Planck Research School for Chemistry and Physics of Quantum Materials. S.R.K. acknowledges the EPSRC Centre for Doctoral Training in the Advanced Characterisation of Materials (CDT-ACM, EP/S023259/1) for funding a PhD studentship.Reducing the thickness of a material to its two dimensional (2D) limit can have dramatic consequences for its collective electronic states, including magnetism, superconductivity, and charge and spin ordering. An extreme case is TiTe2, where a charge density wave (CDW) emerges in the single-layer which is absent for the bulk compound, and whose origin is still poorly understood. Here, we investigate the electronic band structure evolution across this CDW transition using temperature-dependent angle-resolved photoemission spectroscopy. Our study reveals an orbital-selective band hybridisation between the backfolded conduction and valence bands occurring at the CDW phase transition, which in turn leads to a significant electronic energy gain, underpinning the CDW transition. For the bulk compound, we show how this energy gain is almost completely suppressed due to the three-dimensionality of the electronic band structure, including via a kz-dependent band inversion which switches the orbital character of the valence states. Our study thus sheds new light on how control of the electronic dimensionality can be used to trigger the emergence of new collective states in 2D materials.Publisher PDFPeer reviewe

INFLUENCE OF PROBIOTICS ON CYTOKINE PRODUCTION IN THE IN VITRO AND IN VIVO SYSTEMS

Modulatory effects of three probiotic bacterial strains (Lactobacillus rhamnosus K32 (L), Bifidobacterium longum GT15 (B, Enterococcus faecium L-3 (E) on expression level and contents of key cytokines were studied using PCR techniques with reverse transcription, and enzyme-linked immunosorbent assay. Both cell cultures and an experimental model of intestinal dysbiosis were used in this study.The genes encoding bacteriocins, surface membrane component, pili and exopolysaccharides involved in host immune system modulation were previously identified in the B and Ebacterial strains.Investigation of probiotic strains and effects of their supernatants expression of cytokines in cell cultures of promonocyte origin (HTP-1) showed increased expression of TNFα, due to E and L supernatants. Moreover, the Bl culture induced IL-8 and IL-10 expression.In a model of Wistar rats with ampicillinand metronidazole-induced intestinal dysbiosis corrected with probiotics we have shown that the dysbiosis was accompanied by sufficient alterations in microbiota composition (Klebsiella spp. overgrowth and low contents of Faecalobacterium prausnitzii) that were observed only in the animals untreated with probiotics (control), or after administration of L.In contrast to these results, the animals treated with E and B, the following changes were revealed: 1) low expression of proinflammatory cytokines IL-8, TNFα, MCP-1 inmesenteric lymph nodes and appropriate changes of their serum contents, 2) increased serum content of the anti-inflammatory TGFβ cytokine. Hence, the present study, having used two complementary models, has detected some individual features of immune modulation produced by the probiotictic strains of L. rhamnosus K32, B. longum GT15 и E. faecium L-3 which exert differential effects upon the intestinal microbiota

MEDICINAL FORM OF TNF-α FOR LOCAL ADMINISTRATION

Composite preparation of tumor necrosis factor alpha and rheopolyglukin and polyethylene glycol (TNF-α+PG+PEG) was obtained. The specific activity of the samples was 4,13 х 107 IU/mg. The cytolytic activity of drugs TNF-α+PG+PEG and rhTNF-α did not change after 4 months when stored at 6 °С. Preparation TNF-α+PG+PEG provided a moderately prolonged elevation of TNF-alpha in blood of laboratory mice in contrast to TNF-α when they applied to the skin. The composite preparation did not have toxic, allergic and locally irritating action in experiments on laboratory animals

Prediction and measurement of the size-dependent stability of fluorescence in diamond over the entire nanoscale

Fluorescent defects in non-cytotoxic diamond nanoparticles are candidates for qubits in quantum computing, optical labels in biomedical imaging and sensors in magnetometry. For each application these defects need to be optically and thermodynamically stable, and included in individual particles at suitable concentrations (singly or in large numbers). In this letter, we combine simulations, theory and experiment to provide the first comprehensive and generic prediction of the size, temperature and nitrogen-concentration dependent stability of optically active NV defects in nanodiamonds.Comment: Published in Nano Letters August 2009 24 pages, 6 figure