564 research outputs found

    Ab initio Pseudopotential Plane-wave Calculations of the Electronic Structure of YBa_2Cu_3O_7

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    We present an ab initio pseudopotential local density functional calculation for stoichiometric high-Tc cuprate YBa_2Cu_3O_7 using the plane-wave basis set. We have overcome well-known difficulties in applying pseudopotential methods to first-row elements, transition metals, and rare-earth materials by carefully generating norm-conserving pseudopotentials with excellent transferability and employing an extremely efficient iterative diagonalization scheme optimized for our purpose. The self-consistent band structures, the total and site-projected densities of states, the partial charges and their symmetry-decompositions, and some characteristic charge densities near E_f are presented. We compare our results with various existing (F)LAPW and (F)LMTO calculations and establish that the ab initio pseudopotential method is competitive with other methods in studying the electronic structure of such complicated materials as high-Tc cuprates. [8 postscript files in uuencoded compressed form]Comment: 14 pages, RevTeX v3.0, 8 figures (appended in postscript file), SNUTP 94-8

    Direct observation of localized defect states in semiconductor nanotube junctions

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    Scanning tunneling microscopy of semiconductor-semiconductor carbon nanotube junctions with different band gaps was studied. Characteristic features of the wave functions at different energy levels were exhibited in the atomically resolved scanning tunneling microscopy. The experimental observations in terms of the pentagon-heptagon defects in the junction were interpreted.open888

    Thermal and Tunneling Pair Creation of Quasiparticles in Quantum Hall Systems

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    We make a semiclassical analysis of thermal pair creations of quasiparticles at various filling factors in quantum Hall systems. It is argued that the gap energy is reduced considerably by the Coulomb potential made by impurities. It is also shown that a tunneling process becomes important at low temperature and at strong magnetic field. We fit typical experimental data excellently based on our semiclassical results of the gap energy.Comment: 6 pages, 6 PS figures, to be published in Phys.Rev.

    Zoonotic Diseases Report 2013

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    De Staat van zoönosen 2013 geeft een overzicht van de mate waarin zoönosen in Nederland voorkomen en ontwikkelingen daarin op de lange termijn. Zoönosen zijn infectieziekten die van dier op mens overgaan. Net als in voorgaande jaren waren er in 2013 geen uitgesproken veranderingen te zien in de mate waarin zoönosen in Nederland voorkomen. Zoals ieder jaar deden zich ook in 2013 enkele opmerkelijke voorvallen voor, zoals een geval van hazenpest. In deze jaarlijkse uitgave van het RIVM en de NVWA is het thema 'huis-, tuin- en keukenzoönosen': zoönosen die mensen kunnen oplopen in en om het huis. Opmerkelijke voorvallen Bij een haas afkomstig uit Noord-Limburg werd in mei 2013 hazenpest (tularemie) vastgesteld. Vervolgens werd ook bij een jongeman tularemie vastgesteld, die de infectie waarschijnlijk via een dazenbeet in een natuurgebied in Limburg had opgelopen. In 2011 is er mogelijk ook een in Nederland opgelopen geval van tularemie geweest, terwijl in de jaren daarvoor alleen sporadisch gevallen gemeld werden die in het buitenland waren opgelopen. Een andere opmerkelijke gebeurtenis betrof een uitbraak van Campylobacter onder bezoekers van een pluimveeslachthuis die waarschijnlijk via de lucht aan de ziekteverwekker waren blootgesteld. Negen mensen werden ziek. Ook blijkt uit een onderzoek naar de vossenlintworm (Echinococcus multilocularis) onder vossen en honden, dat deze lintworm bij vossen in Zuid-Limburg veel vaker voorkomt dan in voorgaande jaren. Thema: huis-, tuin- en keukenzoönosen Juist in en om het huis kunnen mensen worden blootgesteld aan allerlei zoönoseverwekkers. Duizenden mensen krijgen jaarlijks via hun huisdieren ringworm, een schimmelinfectie. Ook kunnen zoönosen afkomstig zijn van huisdieren of dieren die hun behoefte doen in de tuin. Verder komen voedselgerelateerde zoönosen aan de orde, waarbij aandacht is voor het feit dat zoönosen ook via groenten kunnen worden opgelopen.The Zoonotic Diseases Report is an annual publication of the Dutch National Institute for Public Health and the Environment (RIVM) and the Netherlands Food and Consumer Product Safety Authority (NVWA). The report provides an overview of the incidence of zoonotic diseases in the Netherlands, as well as the associated long-term trends. Zoonotic diseases or zoonoses are infectious diseases that can be transmitted from animals to humans. As in previous years, no marked changes were observed in 2013 in the incidence of zoonotic diseases in the Netherlands. Every year a number of notable incidents occurres. In 2013 this included a case of rabbit fever (tularemia). This year's edition of the Zoonotic Diseases Report focuses in particular on 'zoonoses close to home', i.e. the risk of contracting a zoonotic disease in or around the house. Notable incidents In May 2013, rabbit fever (tularemia) was discovered in a hare originating from the north of the province of Limburg. Tularemia was later also diagnosed in a young man, who had probably contracted the infection after having been bitten by a horse fly in a nature reserve in Limburg. Another person possibly contracted tularemia in the Netherlands in 2011. In previous years only incidental cases were reported, with the disease being contracted abroad. Another notable incident concerned an outbreak of Campylobacter infection among visitors to a poultry slaughterhouse who had probably been exposed to airborne pathogens. Nine people fell ill as a result of this outbreak. An investigation into the incidence of Echinococcus multilocularis in foxes and dogs showed that this tapeworm was much more common in foxes in the south of Limburg province than in previous years. 'Zoonoses close to home' Humans can be exposed to various zoonotic disease pathogens in or around the house. Every year, thousands of people contract dermatophytosis (a fungal infection commonly known in the Netherlands as 'ringworm') from their pets. Zoonotic diseases can also be contracted from pets or from animals defecating in the garden. The report also devotes attention to food-related zoonotic diseases, with a particular focus on the risk of contracting zoonoses through the consumption or handling of vegetables.NVW

    Magnetic Quantum Dot: A Magnetic Transmission Barrier and Resonator

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    We study the ballistic edge-channel transport in quantum wires with a magnetic quantum dot, which is formed by two different magnetic fields B^* and B_0 inside and outside the dot, respectively. We find that the electron states located near the dot and the scattering of edge channels by the dot strongly depend on whether B^* is parallel or antiparallel to B_0. For parallel fields, two-terminal conductance as a function of channel energy is quantized except for resonances, while, for antiparallel fields, it is not quantized and all channels can be completely reflected in some energy ranges. All these features are attributed to the characteristic magnetic confinements caused by nonuniform fields.Comment: 4 pages, 4 figures, to be published in Physical Review Letter

    Association of MCP-1 and CCR2 polymorphisms with the risk of late acute rejection after renal transplantation in Korean patients

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    Among the factors modulating transplant rejection, chemokines and their respective receptors deserve special attention. Increased expression of monocyte chemoattractant protein-1 (MCP-1) and its corresponding receptor (chemokine receptor-2, CCR2) has been implicated in renal transplant rejection. To determine the impact of the MCP-1-2518G and CCR2-64I genotypes on renal allograft function, 167 Korean patients who underwent transplantation over a 25-year period were evaluated. Genomic DNA was genotyped using polymerase chain reaction followed by restriction fragment length polymorphism analysis. Fifty-five (32.9%) patients were homozygous for the MCP-1-2518G polymorphism. Nine (5.4%) patients were homozygous for the CCR2-64I polymorphism. None of the investigated polymorphism showed a significant shift in long-term allograft survival. However, a significant increase was noted for the risk of late acute rejection in recipients who were homozygous for the MCP-1-2518G polymorphism (OR, 2.600; 95% CI, 1.125–6.012; P = 0.022). There was also an association between the MCP-1-2518G/G genotype and the number of late acute rejection episodes (P = 0.024). Although there was no difference in the incidence of rejection among recipients stratified by the CCR2-V64I genotype, recipients with the CCR2-V64I GG genotype in combination with the MCP-1-2518G/G genotype had a significantly higher risk of acute or late acute rejection among the receptor-ligand combinations (P = 0.006, P = 0.008, respectively). The MCP-1 variant may be a marker for risk of late acute rejection in Korean patients

    Effects of charge doping and constrained magnetization on the electronic structure of an FeSe monolayer

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    The electronic structural properties in the presence of constrained magnetization and a charged background are studied for a monolayer of FeSe in non-magnetic, checkerboard-, and striped-antiferromagnetic (AFM) spin configurations. First principles techniques based on the pseudopotential density functional approach and the local spin density approximation are utilized. Our findings show that the experimentally observed shape of the Fermi surface is best described by the checkerboard AFM spin pattern. To explore the underlying pairing mechanism, we study the evolution of the non-magnetic to the AFM-ordered structures under constrained magnetization. We estimate the strength of electronic coupling to magnetic excitations involving an increase in local moment and, separately, a partial moment transfer from one Fe atom to another. We also show that the charge doping in the FeSe can lead to an increase in the density of states at the Fermi level and possibly produce higher superconducting transition temperatures

    Calculations of the A_1 phonon frequency in photoexcited Tellurium

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    Calculations of the A_1 phonon frequency in photoexcited tellurium are presented. The phonon frequency as a function of photoexcited carrier density and phonon amplitude is determined. Recent pump probe experiments are interpreted in the light of these calculatons. It is proposed that, in conjunction with measurements of the phonon period in ultra-fast pump-probe reflectivity experiments, the calculated frequency shifts can be used to infer the evolution of the density of photoexcited carriers on a sub-picosecond time-scale.Comment: 15 pages Latex, 3 postscript figure

    Effects of oxygen adsorption on carbon nanotube field emitters

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    Effects of oxygen adsorption on the field emission of carbon nanotubes are studied through first-principles calculations. Calculated emission currents are significantly enhanced when oxygen is adsorbed at the tip and the underlying physics is explained in terms of the change in the electronic structure by oxidation and the local field increase at the adsorption site. The issue of the current degradation accompanied by the oxidative etching is also addressed. The field-emission-microscopy images on the phosphor screen are simulated, displaying various patterns characteristic of each adsorption configuration.open546
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