A Model for Partial Viscous Sintering

A mathematical model describing the sintering rate of a viscous material powder bed is presented. This model assumes that the powder bed is composed of cubic packed, equal-size spherical particles. The sintering rate equation is derived in terms of a unit cell dimension or the relative density of a powder bed. A mathematical factor, fraction of sintering, is introduced to explain the phenomena of partial sintering. Key words: model, viscous sintering.Mechanical Engineerin

Parametric Analysis of the Selective Laser Sintering Process

Qualitative and quantitative analyses are required to develop Selective Laser Sintering into a viable Manufacturing process. A simplified mathematical model for sintering incorporating the heat tJ;ansfer equation. and the sintering rate equation, but using temperature independent thermal properties, is presented in this paper. A practical result is the calculation of sintering depthdeftned as the depth of powder where the void fraction is less than 0.1 as a function of control parameters, such as the laser power intensity, the laser scanning velocity, and the initial bedtemperature. We derive the general behavior of laser sintering. A comparison of model predictions with laser sinterlng tests is provided.Mechanical Engineerin

Multiple material systems for selective beam sintering

A method and apparatus for selectively sintering a layer of powder to produce a part comprising a plurality of sintered layers. The apparatus includes a computer controlling a laser to direct the laser energy onto the powder to produce a sintered mass. The computer either determines or is programmed with the boundaries of the desired cross-sectional regions of the part. For each cross-section, the aim of the laser beam is scanned over a layer of powder and the beam is switched on to sinter only the powder within the boundaries of the cross-section. Powder is applied and successive layers sintered until a completed part is formed. Preferably, the powder comprises a plurality of materials having different dissociation or bonding temperatures. The powder preferably comprises blended or coated materials.Board of Regents, University of Texas Syste

A Spitzer IRS Spectral Atlas of Luminous 8 micron Sources in the Large Magellanic Cloud

We present an atlas of Spitzer Space Telescope Infrared Spectrograph (IRS) spectra of highly luminous, compact mid-infrared sources in the Large Magellanic Cloud. Sources were selected on the basis of infrared colors and 8 micron (MSX) fluxes indicative of highly evolved, intermediate- to high-mass stars with current or recent mass loss at large rates. We determine the chemistry of the circumstellar envelope from the mid-IR continuum and spectral features and classify the spectral types of the stars. In the sample of 60 sources, we find 21 Red Supergiants (RSGs), 16 C-rich Asymptotic Giant Branch (AGB) stars, 11 HII regions, 4 likely O-rich AGB stars, 4 Galactic O-rich AGB stars, 2 OH/IR stars, and 2 B[e] supergiants with peculiar IR spectra. We find that the overwhelming majority of the sample AGB stars (with typical IR luminosities ~1.0E4 L_sun) have C-rich envelopes, while the O-rich objects are predominantly luminous RSGs with L_IR ~ 1.0E5 L_sun. We determine mean bolometric corrections to the stellar K-band flux densities and find that for carbon stars, the bolometric corrections depend on the infrared color, whereas for RSGs, the bolometric correction is independent of IR color. Our results reveal that objects previously classified as PNe on the basis of IR colors are in fact compact HII regions with very red IRS spectra that include strong atomic recombination lines and PAH emission features. We demonstrate that the IRS spectral classes in our sample separate clearly in infrared color-color diagrams that use combinations of 2MASS data and synthetic IRAC/MIPS fluxes derived from the IRS spectra. On this basis, we suggest diagnostics to identify and classify, with high confidence levels, IR-luminous evolved stars and HII regions in nearby galaxies using Spitzer and near-infrared photometry.Comment: 46 pages, 9 figures; accepted for publication in AJ; abstract abridge

Ethylenediamine Addition Improves Performance and Suppresses Phase Instabilities in Mixed-Halide Perovskites

We show that adding ethylenediamine (EDA) to perovskite precursor solution improves the photovoltaic device performance and material stability of high-bromide-content, methylammonium-free, formamidinium cesium lead halide perovskites FA1-xCsxPb(I1-yBry)3 which are currently of interest for perovskite-on-Si tandem solar cells. Using spectroscopy and hyperspectral microscopy, we show that the additive improves film homogeneity and suppresses the phase instability that is ubiquitous in high-Br perovskite formulations, producing films that remain stable for over 100 days in ambient conditions. With the addition of 1 mol% EDA we demonstrate 1.69 eV-gap perovskite single-junction p-i-n devices with a VOC of 1.22 V, and a champion maximum power point tracked power conversion efficiency of 18.8%, comparable to the best reported methylammonium-free perovskites. Using nuclear magnetic resonance (NMR) spectroscopy and X-ray diffraction techniques, we show that EDA reacts with FA+ in solution, rapidly and quantitatively forming imidazolinium cations. It is the presence of imidazolinium during crystallization which drives the improved perovskite thin-film properties

HtrA, fatty acids, and membrane protein interplay in Chlamydia trachomatis to impact stress response and trigger early cellular exit

UNLABELLED: Chlamydia trachomatis is an intracellular bacterial pathogen that undergoes a biphasic developmental cycle, consisting of intracellular reticulate bodies and extracellular infectious elementary bodies. A conserved bacterial protease, HtrA, was shown previously to be essential for Chlamydia during the reticulate body phase, using a novel inhibitor (JO146). In this study, isolates selected for the survival of JO146 treatment were found to have polymorphisms in the acyl-acyl carrier protein synthetase gene (aasC). AasC encodes the enzyme responsible for activating fatty acids from the host cell or synthesis to be incorporated into lipid bilayers. The isolates had distinct lipidomes with varied fatty acid compositions. A reduction in the lipid compositions that HtrA prefers to bind to was detected, yet HtrA and MOMP (a key outer membrane protein) were present at higher levels in the variants. Reduced progeny production and an earlier cellular exit were observed. Transcriptome analysis identified that multiple genes were downregulated in the variants especially stress and DNA processing factors. Here, we have shown that the fatty acid composition of chlamydial lipids, HtrA, and membrane proteins interplay and, when disrupted, impact chlamydial stress response that could trigger early cellular exit.IMPORTANCE: Chlamydia trachomatis is an important obligate intracellular pathogen that has a unique biphasic developmental cycle. HtrA is an essential stress or virulence protease in many bacteria, with many different functions. Previously, we demonstrated that HtrA is critical for Chlamydia using a novel inhibitor. In the present study, we characterized genetic variants of Chlamydia trachomatis with reduced susceptibility to the HtrA inhibitor. The variants were changed in membrane fatty acid composition, outer membrane proteins, and transcription of stress genes. Earlier and more synchronous cellular exit was observed. Combined, this links stress response to fatty acids, membrane proteins, and HtrA interplay with the outcome of disrupted timing of chlamydial cellular exit.</p

Architecture Optimization Dramatically Improves Reverse Bias Stability in Perovskite Solar Cells: A Role of Polymer Hole Transport Layers

We report that device architecture engineering has a substantial impact on the reverse bias instability that has been reported as a critical issue in commercializing perovskite solar cells. We demonstrate breakdown voltages exceeding -15 V in typical pin structured perovskite solar cells via two steps: i) using polymer hole transporting materials; ii) using a more electrochemically stable gold electrode. While device degradation can be exacerbated by higher reverse bias and prolonged exposure, our as-fabricated perovskite solar cells completely recover their performance even after stressing at -7 V for 9 hours both in the dark and under partial illumination. Following these observations, we systematically discuss and compare the reverse bias driven degradation pathways in perovskite solar cells with different device architectures. Our model highlights the role of electrochemical reaction rates and species in dictating the reverse bias stability of perovskite solar cells

Probing the Type I Seesaw Mechanism with Displaced Vertices at the LHC

The observation of Higgs decays into heavy neutrinos would be strong evidence for new physics associated to neutrino masses. In this work we propose a search for such decays within the Type I seesaw model in the few-GeV mass range via displaced vertices. Using 300 fb−1 of integrated luminosity, at 13 TeV, we explore the region of parameter space where such decays are measurable. We show that, after imposing pseudorapidity cuts, there still exists a region where the number of events is larger than O(10). We also find that conventional triggers can greatly limit the sensitivity of our signal, so we display several relevant kinematical distributions which might aid in the optimization of a dedicated trigger selection

Characterisation of a dipolar chromophore with third-harmonic generation applications in the near-IR

E-2-Tricyanovinyl-3-n-hexyl-5-[4-{bis(4-n-butylphenyl)amino}-2-methoxystyryl]-thiophene, 1, has previously been used to demonstrate applications relying on frequency tripling of 1.55 μm light. Here we report the synthesis and chemical characterisation of 1, along with quantum-chemical calculations and additional experimental investigations of its third-order nonlinear properties that give more insight into its frequency tripling properties. Although 1 can be processed into amorphous films, crystals can also be grown by slow evaporation of solutions; the crystal structure determined by X-ray diffraction shows evidence of significant contributions from zwitterionic resonance forms to the ground-state structure, and reveals centrosymmetric packing exhibiting π–π and C–H···N≡C interactions. Both solutions and films of 1 exhibit near-infrared two-photon absorption into the low-lying one-photon-allowed state with a peak two-photon cross-section of cɑ. 290 GM (measured using the white-light continuum method with a pump wavelength of 1800 nm) at a transition energy equivalent to degenerate two-photon absorption at cɑ. 1360 nm; two related chromophores are also found to show comparable near-IR two-photon cross-sections. Closed-aperture Z-scan measurements and quantum-chemical calculations indicate that the nonlinear refractive index and third-harmonic generation properties of 1 are strongly dependent on frequency in the telecommunications range, due the aforementioned two-photon resonance

Rotavirus NSP1 Inhibits NFκB Activation by Inducing Proteasome-Dependent Degradation of β-TrCP: A Novel Mechanism of IFN Antagonism

Mechanisms by which viruses counter innate host defense responses generally involve inhibition of one or more components of the interferon (IFN) system. Multiple steps in the induction and amplification of IFN signaling are targeted for inhibition by viral proteins, and many of the IFN antagonists have direct or indirect effects on activation of latent cytoplasmic transcription factors. Rotavirus nonstructural protein NSP1 blocks transcription of type I IFNα/β by inducing proteasome-dependent degradation of IFN-regulatory factors 3 (IRF3), IRF5, and IRF7. In this study, we show that rotavirus NSP1 also inhibits activation of NFκB and does so by a novel mechanism. Proteasome-mediated degradation of inhibitor of κB (IκBα) is required for NFκB activation. Phosphorylated IκBα is a substrate for polyubiquitination by a multisubunit E3 ubiquitin ligase complex, Skp1/Cul1/F-box, in which the F-box substrate recognition protein is β-transducin repeat containing protein (β-TrCP). The data presented show that phosphorylated IκBα is stable in rotavirus-infected cells because infection induces proteasome-dependent degradation of β-TrCP. NSP1 expressed in isolation in transiently transfected cells is sufficient to induce this effect. Targeted degradation of an F-box protein of an E3 ligase complex with a prominent role in modulation of innate immune signaling and cell proliferation pathways is a unique mechanism of IFN antagonism and defines a second strategy of immune evasion used by rotaviruses