193 research outputs found

    Diffusion and viscosity in a supercooled polydisperse system

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    We have carried out extensive molecular dynamics simulations of a supercooled polydisperse Lennard-Jones liquid with large variations in temperature at a fixed pressure. The particles in the system are considered to be polydisperse both in size and mass. The temperature dependence of the dynamical properties such as the viscosity (η\eta) and the self-diffusion coefficients (DiD_i) of different size particles is studied. Both viscosity and diffusion coefficients show super-Arrhenius temperature dependence and fit well to the well-known Vogel-Fulcher-Tammann (VFT) equation. Within the temperature range investigated, the value of the Angell's fragility parameter (D 1.4\approx 1.4) classifies the present system into a strongly fragile liquid. The critical temperature for diffusion (ToDiT_o^{D_i}) increases with the size of the particles. The critical temperature for viscosity (ToηT_o^{\eta}) is larger than that for the diffusion and a sizeable deviations appear for the smaller size particles implying a decoupling of translational diffusion from viscosity in deeply supercooled liquid. Indeed, the diffusion shows markedly non-Stokesian behavior at low temperatures where a highly nonlinear dependence on size is observed. An inspection of the trajectories of the particles shows that at low temperatures the motions of both the smallest and largest size particles are discontinuous (jump-type). However, the crossover from continuous Brownian to large length hopping motion takes place at shorter time scales for the smaller size particles.Comment: Revtex4, 7 pages, 8 figure

    Multifunctional Devices and Logic Gates With Undoped Silicon Nanowires

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    We report on the electronic transport properties of multiple-gate devices fabricated from undoped silicon nanowires. Understanding and control of the relevant transport mechanisms was achieved by means of local electrostatic gating and temperature dependent measurements. The roles of the source/drain contacts and of the silicon channel could be independently evaluated and tuned. Wrap gates surrounding the silicide-silicon contact interfaces were proved to be effective in inducing a full suppression of the contact Schottky barriers, thereby enabling carrier injection down to liquid-helium temperature. By independently tuning the effective Schottky barrier heights, a variety of reconfigurable device functionalities could be obtained. In particular, the same nanowire device could be configured to work as a Schottky barrier transistor, a Schottky diode or a p-n diode with tunable polarities. This versatility was eventually exploited to realize a NAND logic gate with gain well above one.Comment: 6 pages, 5 figure

    Epstein Barr Virus-positive large T-cell lymphoma presenting as acute appendicitis 17 years after cadaveric renal transplant: a case report

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    <p>Abstract</p> <p>Introduction</p> <p>The majority of post-transplant lymphoproliferative disorders in renal transplant patients are of the B-cell phenotype, while the T-cell phenotype is rare. We report a case of Epstein Barr Virus-positive, T-cell lymphoma in a renal transplant patient, presenting unusually as acute appendicitis.</p> <p>Case presentation</p> <p>A 45-year-old Hispanic male renal transplant patient presented with right-side abdominal pain 17 years after transplant. The laboratory studies were unremarkable. Laparoscopic exploration showed an inflamed appendix so a laparoscopic appendectomy was performed. Pathology of the appendix showed large cells positive for CD3, CD56 and Epstein Barr Virus-encoded RNA staining, and negative for CD20 and CD30. The tissue tested positive for T-cell receptor gene rearrangement by polymerase chain reaction analysis. Treatment management involved reduction of immunosuppression and initiation of chemotherapy with cisplatin, etoposide, gemcitabine, and solumedrol followed by cyclophosphamide, hydroxydaunorubicin, vincristine and prednisone). He recovered and the allo-grafted kidney is fully functional.</p> <p>Conclusion</p> <p>We report a rare case of post-renal transplant large T-cell lymphoma, with an unusual presentation of acute appendicitis and Epstein Barr Virus-positivity, which responded well to chemotherapy.</p

    Mechanisms underlying electro-mechanical dysfunction in the Zucker diabetic fatty rat heart: a model of obesity and type 2 diabetes

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    Diabetes mellitus (DM) is a major and worsening global health problem, currently affecting over 450 million people and reducing their quality of life. Type 2 diabetes mellitus (T2DM) accounts for more than 90% of DM and the global epidemic of obesity, which largely explains the dramatic increase in the incidence and prevalence of T2DM in the past 20 years. Obesity is a major risk factor for DM which is a major cause of morbidity and mortality in diabetic patients. The electro-mechanical function of the heart is frequently compromised in diabetic patients. The aim of this review is to discuss the pathophysiology of electro-mechanical dysfunction in the diabetic heart and in particular, the Zucker diabetic fatty (ZDF) rat heart, a well-studied model of T2DM and obesity

    Stratified graphene/noble metal systems for low-loss plasmonics applications

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    We propose a composite layered structure for tunable, low-loss plasmon resonances, which consists of a noble metal thin film coated in graphene and supported on a hexagonal boron nitride (hBN) substrate. We calculate electron energy loss spectra (EELS) for these structures, and numerically demonstrate that bulk plasmon losses in noble metal films can be significantly reduced, and surface coupling enhanced, through the addition of a graphene coating and the wide-band-gap hBN substrate. Silver films with a trilayer graphene coating and hBN substrate demonstrated surface plasmon-dominant spectral profiles for metallic layers as thick as 34 nm. A continued-fraction expression for the effective dielectric function, based on a specular reflection model which includes boundary interactions, is used to systematically demonstrate plasmon peak tunability for a variety of configurations. Variations include substrate, plasmonic metal, and individual layer thickness for each material. Mesoscale calculation of EELS is performed with individual layer dielectric functions as input to the effective dielectric function calculation, from which the loss spectra are directly determined
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