Conserving quasiparticle calculations for small metal clusters

A novel approach for GW-based calculations of quasiparticle properties for finite systems is presented, in which the screened interaction is obtained directly from a linear response calculation of the density-density correlation function. The conserving nature of our results is shown by explicit evaluation of the $f$-sum rule. As an application, energy renormalizations and level broadenings are calculated for the closed-shell Na$_9^+$ and Na$_{21}^+$ clusters, as well as for Na$_4$. Pronounced improvements of conserving approximations to RPA-level results are obtained

Large magneto-Seebeck effect in magnetic tunnel junctions with half-metallic Heusler electrodes

Spin caloritronics studies the interplay between charge-, heat- and spin-currents, which are initiated by temperature gradients in magnetic nanostructures. A plethora of new phenomena has been discovered that promises, e.g., to make wasted heat in electronic devices useable or to provide new read-out mechanisms for information. However, only few materials have been studied so far with Seebeck voltages of only some {\mu}V, which hampers applications. Here, we demonstrate that half-metallic Heusler compounds are hot candidates for enhancing spin-dependent thermoelectric effects. This becomes evident when considering the asymmetry of the spin-split density of electronic states around the Fermi level that determines the spin-dependent thermoelectric transport in magnetic tunnel junctions. We identify Co$_2$FeAl and Co$_2$FeSi Heusler compounds as ideal due to their energy gaps in the minority density of states, and demonstrate devices with substantially larger Seebeck voltages and tunnel magneto-Seebeck effect ratios than the commonly used Co-Fe-B based junctions.Comment: 9 pages, 4 figure

Enhancement of thermovoltage and tunnel magneto-Seebeck effect in CoFeB based magnetic tunnel junctions by variation of the MgAl2_2O4_4 and MgO barrier thickness

We investigate the influence of the barrier thickness of Co$_{40}$Fe$_{40}$B$_{20}$ based magnetic tunnel junctions on the laser-induced tunnel magneto-Seebeck effect. Varying the barrier thickness from 1nm to 3nm, we find a distinct maximum in the tunnel magneto-Seebeck effect for 2.6nm barrier thickness. This maximum is independently measured for two barrier materials, namely MgAl$_2$O$_4$ and MgO. Additionally, samples with an MgAl$_2$O$_4$ barrier exhibit a high thermovoltage of more than 350$\mu$V in comparison to 90$\mu$V for the MTJs with MgO barrier when heated with the maximum laser power of 150mW. Our results allow for the fabrication of improved stacks when dealing with temperature differences across magnetic tunnel junctions for future applications in spin caloritronics, the emerging research field that combines spintronics and themoelectrics

Lack of the Sodium-Driven Chloride Bicarbonate Exchanger NCBE Impairs Visual Function in the Mouse Retina

Regulation of ion and pH homeostasis is essential for normal neuronal function. The sodium-driven chloride bicarbonate exchanger NCBE (Slc4a10), a member of the SLC4 family of bicarbonate transporters, uses the transmembrane gradient of sodium to drive cellular net uptake of bicarbonate and to extrude chloride, thereby modulating both intracellular pH (pHi) and chloride concentration ([Cl-]i) in neurons. Here we show that NCBE is strongly expressed in the retina. As GABAA receptors conduct both chloride and bicarbonate, we hypothesized that NCBE may be relevant for GABAergic transmission in the retina. Importantly, we found a differential expression of NCBE in bipolar cells: whereas NCBE was expressed on ON and OFF bipolar cell axon terminals, it only localized to dendrites of OFF bipolar cells. On these compartments, NCBE colocalized with the main neuronal chloride extruder KCC2, which renders GABA hyperpolarizing. NCBE was also expressed in starburst amacrine cells, but was absent from neurons known to depolarize in response to GABA, like horizontal cells. Mice lacking NCBE showed decreased visual acuity and contrast sensitivity in behavioral experiments and smaller b-wave amplitudes and longer latencies in electroretinograms. Ganglion cells from NCBE-deficient mice also showed altered temporal response properties. In summary, our data suggest that NCBE may serve to maintain intracellular chloride and bicarbonate concentration in retinal neurons. Consequently, lack of NCBE in the retina may result in changes in pHi regulation and chloride-dependent inhibition, leading to altered signal transmission and impaired visual function

The Cl--channel TMEM16A is involved in the generation of cochlear Ca2+ waves and promotes the refinement of auditory brainstem networks in mice

Before hearing onset (postnatal day 12 in mice), inner hair cells (IHCs) spontaneously fire action potentials, thereby driving pre-sensory activity in the ascending auditory pathway. The rate of IHC action potential bursts is modulated by inner supporting cells (ISCs) of Kölliker’s organ through the activity of the Ca2+-activated Cl--channel TMEM16A (ANO1). Here, we show that conditional deletion of Ano1 (Tmem16a) in mice disrupts Ca2+ waves within Kölliker’s organ, reduces the burst-firing activity and the frequency selectivity of auditory brainstem neurons in the medial nucleus of the trapezoid body (MNTB), and also impairs the functional refinement of MNTB projections to the lateral superior olive. These results reveal the importance of the activity of Kölliker’s organ for the refinement of central auditory connectivity. In addition, our study suggests the involvement of TMEM16A in the propagation of Ca2+ waves, which may also apply to other tissues expressing TMEM16A

Nanodrawing of aligned single carbon nanotubes with a nanopen

Single-walled carbon nanotubes (SWCNTs) are considered pivotal components for molecular electronics. Techniques for SWCNT lithography today lack simplicity, flexibility, and speed of direct, oriented deposition at specific target locations. In this paper SWCNTs are directly drawn and placed with chemical identification and demonstrated orientation using fountain pen nanolithography (FPN) under ambient conditions. Placement across specific electrical contacts with such alignment is demonstrated and characterized. The fundamental basis of the drawing process with alignment has potential applications for other related systems such as inorganic nanotubes, polymers, and biological molecules

Deletion of the glycosyltransferase bgsB of Enterococcus faecalis leads to a complete loss of glycolipids from the cell membrane and to impaired biofilm formation

<p>Abstract</p> <p>Background</p> <p>Deletion of the glycosyltransferase <it>bgsA </it>in <it>Enterococcus faecalis </it>leads to loss of diglucosyldiacylglycerol from the cell membrane and accumulation of its precursor monoglucosyldiacylglycerol, associated with impaired biofilm formation and reduced virulence in vivo. Here we analyzed the function of a putative glucosyltransferase EF2890 designated <it>biofilm-associated glycolipid synthesis B (bgsB) </it>immediately downstream of <it>bgsA</it>.</p> <p>Results</p> <p>A deletion mutant was constructed by targeted mutagenesis in <it>E. faecalis </it>strain 12030. Analysis of cell membrane extracts revealed a complete loss of glycolipids from the cell membrane. Cell walls of 12030Δ<it>bgsB </it>contained approximately fourfold more LTA, and ¹H-nuclear magnetic resonance (NMR) spectroscopy suggested that the higher content of cellular LTA was due to increased length of the glycerol-phosphate polymer of LTA. 12030Δ<it>bgsB </it>was not altered in growth, cell morphology, or autolysis. However, attachment to Caco-2 cells was reduced to 50% of wild-type levels, and biofilm formation on polystyrene was highly impaired. Despite normal resistance to cationic antimicrobial peptides, complement and antibody-mediated opsonophagocytic killing in vitro, 12030Δ<it>bgsB </it>was cleared more rapidly from the bloodstream of mice than wild-type bacteria. Overall, the phenotype resembles the respective deletion mutant in the <it>bgsA </it>gene. Our findings suggest that loss of diglucosyldiacylglycerol or the altered structure of LTA in both mutants account for phenotypic changes observed.</p> <p>Conclusions</p> <p>In summary, BgsB is a glucosyltransferase that synthesizes monoglucosyldiacylglycerol. Its inactivation profoundly affects cell membrane composition and has secondary effects on LTA biosynthesis. Both cell-membrane amphiphiles are critical for biofilm formation and virulence of <it>E. faecalis</it>.</p

International health IT benchmarking:learning from cross-country comparisons

Objective, to pilot benchmark measures of health information and communication technology (ICT) availability and use to facilitate cross-country learning. Materials and Methods, a prior Organization for Economic Cooperation and Development-led effort involving 30 countries selected and defined functionality-based measures for availability and use of electronic health records, health information exchange, personal health records, and telehealth. In this pilot, an Organization for Economic Cooperation and Development Working Group compiled results for 38 countries for a subset of measures with broad coverage using new and/or adapted country-specific or multinational surveys and other sources from 2012 to 2015. We also synthesized country learnings to inform future benchmarking. Results, while electronic records are widely used to store and manage patient information at the point of care- all but 2 pilot countries reported use by at least half of primary care physicians; many had rates above 75%- patient information exchange across organizations/settings is less common. Large variations in the availability and use of telehealth and personal health records also exist. Discussion, pilot participation demonstrated interest in cross-national benchmarking. Using the most comparable measures available to date, it showed substantial diversity in health ICT availability and use in all domains. The project also identified methodological considerations (e.g., structural and health systems issues that can affect measurement) important for future comparisons. Conclusion, while health policies and priorities differ, many nations aim to increase access, quality, and/or efficiency of care through effective ICT use. By identifying variations and describing key contextual factors, benchmarking offers the potential to facilitate cross-national learning and accelerate the progress of individual countries

Enterococcus faecalis Glycolipids Modulate Lipoprotein-Content of the Bacterial Cell Membrane and Host Immune Response

In this study, we investigated the impact of the cell membrane composition of E. faecalis on its recognition by the host immune system. To this end, we employed an E. faecalis deletion mutant (Delta bgsA) that does not synthesize the major cell membrane glycolipid diglycosyl-diacylglycerol (DGlcDAG). Proteomic analysis revealed that 13 of a total of 21 upregulated surface-associated proteins of E. faecalis Delta bgsA were lipoproteins. This led to a total lipoprotein content in the cell membrane of 35.8% in Delta bgsA compared to only 9.4% in wildtype bacteria. Increased lipoprotein content strongly affected the recognition of Delta bgsA by mouse macrophages in vitro with an increased stimulation of TNF-alpha production by heat-fixed bacteria and secreted antigens. Inactivation of the prolipoprotein diacylglycerol transferase (lgt) in Delta bgsA abrogated TNF-alpha induction by a Delta bgsA_lgt double mutant indicating that lipoproteins mediate increased activation of mouse macrophages by Delta bgsA. Heatfixed Delta bgsA bacteria, culture supernatant, or cell membrane lipid extract activated transfected HEK cells in a TLR2-dependent fashion;the same was not true of wild-type bacteria. In mice infected intraperitoneally with a sublethal dose of E. faecalis we observed a 70% greater mortality in mice infected with Delta bgsA compared with wild-type-infected mice. Increased mortality due to Delta bgsA infection was associated with elevated plasma levels of the inflammatory cytokines TNF-alpha, IL-6 and MIP-2. In summary, our results provide evidence that an E. faecalis mutant lacking its major bilayer forming glycolipid DGlcDAG upregulates lipoprotein expression leading to increased activation of the host innate immune system and virulence in vivo

Simultaneous Swift X-ray and UV views of comet C/2007 N3 (Lulin)

We present an analysis of simultaneous X-Ray and UV observations ofcomet C/2007 N3 (Lulin) taken on three days between January 2009 and March 2009 using the Swift observatory. For our X-ray observations, we used basic transforms to account for the movement of the comet to allow the combination of all available data to produce an exposure-corrected image. We fit a simple model to the extracted spectrum and measured an X-ray flux of 4.3+/-1.3 * 10^-13 ergs cm-2 s-1 in the 0.3 to 1.0 keV band. In the UV, we acquired large-aperture photometry and used a coma model to derive water production rates given assumptions regarding the distribution of water and its dissociation into OH molecules about the comet's nucleus. We compare and discuss the X-ray and UV morphology of the comet. We show that the peak of the cometary X-ray emission is offset sunward of the UV peak emission, assumed to be the nucleus, by approximately 35,000 km. The offset observed, the shape of X-ray emission and the decrease of the X-ray emission comet-side of the peak, suggested that the comet was indeed collisionally thick to charge exchange, as expected from our measurements of the comet's water production rate (6--8 10^28 mol. s-1). The X-ray spectrum is consistent with solar wind charge exchange emission, and the comet most likely interacted with a solar wind depleted of very highly ionised oxygen. We show that the measured X-ray lightcurve can be very well explained by variations in the comet's gas production rates, the observing geometry and variations in the solar wind flux.Comment: Paper accepted for publication in Astronomy and Astrophysics, 6 March 2012, 12 pages, 8 colour figures, one tabl