540 research outputs found

    Static fracture and modal analysis simulation of a gas turbine compressor blade and bladed disk system

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    This paper presents a methodology for conducting a 3-D static fracture analysis with applications to a gas turbine compressor blade. An open crack model is considered in the study and crack-tip driving parameters are estimated by using 3-D singular crack-tip elements in ANSYS. The static fracture analysis is verified with a special purpose fracture code (FRANC3D). Once the crack front is perfectly defined and validated, a free vibration study is conducted by analyzing the natural frequencies and modeshapes for both a single blade and bladed disk system. Taking advantage of high performance computing resources, a high fidelity finite element model is considered in the parametric investigation. In the fracture simulation, the influence of the size of a single edged crack as well as the rotational velocity on fracture parameters (stress intensity factors and J-Integral) are evaluated. Results demonstrate that for the applied loading condition, a mixed mode crack propagation is expected. In the modal analysis study, increasing the depth of the crack leads to a decrease in the natural frequencies of both the single blade and bladed disk system, while increasing the rotational velocity increases the natural frequencies. The presence of a crack also leads to mode localization for all mode families, a phenomenon that cannot be captured by a single blade analysis.The authors gratefully acknowledge the support of the Qatar National Research Fund through Grant number NPRP 7-1153-2-432. The authors also thank Texas A&M at Qatar?s Advanced Scientific Computing (TASC) for access to the RAAD Supercomputer.Scopu

    Composition of gut microbiota in infants in China and global comparison

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    FePt@CoS2 yolk-shell nanocrystals as a potent agent to kill HeLa cells

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    In situ gap-mode Raman spectra were acquired in an electrochemical environment on a single-crystal gold electrode employing a Au(100)|4,4'-biphenyldithiol (BPDT)|Au-NP(55 nm) sandwich assembly. This geometry enabled an investigation of the influence of an applied electrochemical gate field on the conformational changes in nanojunctions, such as the torsion angle (phi) of molecules. A linear correlation between the intensity ratio I-C=C/ICring-S and cos(2) phi in 4,4'-BPDT-type molecular junctions was established and subsequently utilized to estimate the potential dependence of the torsion angle of the "flexible" molecule M1 at different potentials. The latter decreases as the potential (charge) becomes more negative, resulting in better pi-pi coupling, which correlates with enhanced junction conductance. The demonstrated spectroelectrochemical strategy and the direct correlation of the spectroscopic results with (single) molecular conductance studies may guide the selection and elucidation of functional molecules for potential applications in novel nanodevices

    Suppression subtractive hybridization coupled with microarray analysis to examine differential expression of genes in virus infected cells

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    High throughput detection of differential expression of genes is an efficient means of identifying genes and pathways that may play a role in biological systems under certain experimental conditions. There exist a variety of approaches that could be used to identify groups of genes that change in expression in response to a particular stimulus or environment. We here describe the application of suppression subtractive hybridization (SSH) coupled with cDNA microarray analysis for isolation and identification of chicken transcripts that change in expression on infection of host cells with a paramyxovirus. SSH was used for initial isolation of differentially expressed transcripts, a large-scale validation of which was accomplished by microarray analysis. The data reveals a large group of regulated genes constituting many biochemical pathways that could serve as targets for future investigations to explore their role in paramyxovirus pathogenesis. The detailed methods described herein could be useful and adaptable to any biological system for studying changes in gene expression

    W18O49 Nanowires as Ultraviolet Photodetector

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    Photodetectors in a configuration of field effect transistor were fabricated based on individual W18O49 nanowires. Evaluation of electrical transport behavior indicates that the W18O49 nanowires are n-type semiconductors. The photodetectors show high sensitivity, stability and reversibility to ultraviolet (UV) light. A high photoconductive gain of 104 was obtained, and the photoconductivity is up to 60 nS upon exposure to 312 nm UV light with an intensity of 1.6 mW/cm2. Absorption of oxygen on the surface of W18O49 nanowires has a significant influence on the dark conductivity, and the ambient gas can remarkably change the conductivity of W18O49 nanowire. The results imply that W18O49 nanowires will be promising candidates for fabricating UV photodetectors

    Bright light-emitting diodes based on organometal halide perovskite.

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    Solid-state light-emitting devices based on direct-bandgap semiconductors have, over the past two decades, been utilized as energy-efficient sources of lighting. However, fabrication of these devices typically relies on expensive high-temperature and high-vacuum processes, rendering them uneconomical for use in large-area displays. Here, we report high-brightness light-emitting diodes based on solution-processed organometal halide perovskites. We demonstrate electroluminescence in the near-infrared, green and red by tuning the halide compositions in the perovskite. In our infrared device, a thin 15 nm layer of CH3NH3PbI(3-x)Cl(x) perovskite emitter is sandwiched between larger-bandgap titanium dioxide (TiO2) and poly(9,9'-dioctylfluorene) (F8) layers, effectively confining electrons and holes in the perovskite layer for radiative recombination. We report an infrared radiance of 13.2 W sr(-1) m(-2) at a current density of 363 mA cm(-2), with highest external and internal quantum efficiencies of 0.76% and 3.4%, respectively. In our green light-emitting device with an ITO/PEDOT:PSS/CH3NH3PbBr3/F8/Ca/Ag structure, we achieved a luminance of 364 cd m(-2) at a current density of 123 mA cm(-2), giving external and internal quantum efficiencies of 0.1% and 0.4%, respectively. We show, using photoluminescence studies, that radiative bimolecular recombination is dominant at higher excitation densities. Hence, the quantum efficiencies of the perovskite light-emitting diodes increase at higher current densities. This demonstration of effective perovskite electroluminescence offers scope for developing this unique class of materials into efficient and colour-tunable light emitters for low-cost display, lighting and optical communication applications.This is the author accepted manuscript and will be under embargo until 3/2/15. The final version is published in Nature Nanotechnology: http://www.nature.com/nnano/journal/vaop/ncurrent/full/nnano.2014.149.html

    Update on the Risk of Hepatocellular Carcinoma in Chronic Hepatitis B Virus Infection

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    Chronic hepatitis B virus infection is an important cause of liver-related morbidity and mortality, with hepatocellular carcinoma being the most life-threatening complication. Because of the highly variable clinical course of the disease, enormous research efforts have been made with the aim of revealing the factors in the natural history that are relevant to hepatocarcinogenesis. These include epidemiological studies of predisposing risk groups, viral studies of mutations within the hepatitis B viral genome, and clinical correlation of these risk factors in predicting the likelihood of development of hepatocellular cancer in susceptible hosts. This update addresses these risks, with emphasis on the latest research relevant to hepatocarcinogenesis
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