4,499 research outputs found

    WKB Approximation to the Power Wall

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    We present a semiclassical analysis of the quantum propagator of a particle confined on one side by a steeply, monotonically rising potential. The models studied in detail have potentials proportional to xαx^{\alpha} for x>0x>0; the limit α\alpha\to\infty would reproduce a perfectly reflecting boundary, but at present we concentrate on the cases α=1\alpha =1 and 2, for which exact solutions in terms of well known functions are available for comparison. We classify the classical paths in this system by their qualitative nature and calculate the contributions of the various classes to the leading-order semiclassical approximation: For each classical path we find the action SS, the amplitude function AA and the Laplacian of AA. (The Laplacian is of interest because it gives an estimate of the error in the approximation and is needed for computing higher-order approximations.) The resulting semiclassical propagator can be used to rewrite the exact problem as a Volterra integral equation, whose formal solution by iteration (Neumann series) is a semiclassical, not perturbative, expansion. We thereby test, in the context of a concrete problem, the validity of the two technical hypotheses in a previous proof of the convergence of such a Neumann series in the more abstract setting of an arbitrary smooth potential. Not surprisingly, we find that the hypotheses are violated when caustics develop in the classical dynamics; this opens up the interesting future project of extending the methods to momentum space.Comment: 30 pages, 8 figures. Minor corrections in v.

    First principles design of divacancy defected graphene nanoribbon based rectifying and negative differential resistance device

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    We have elaborately studied the electronic structure of 555-777 divacancy (DV) defected armchair edged graphene nanoribbon (AGNR) and transport properties of AGNR based two-terminal device constructed with one defected electrode and one N doped electrode, by using density functional theory and non-equilibrium Green's function based approach. The introduction of 555-777 DV defect into AGNRs, results in a shifting of the {\pi} and {\pi}* bands towards the higher energy value which indicates a shifting of the Fermi level towards the lower energy. Formation of a potential barrier, very similar to that of conventional p-n junction, has been observed across the junction of defected and N doped AGNR. The prominent asymmetric feature of the current in the positive and negative bias indicates the diode like property of the device with high rectifying efficiency within wide range of bias voltages. The device also shows robust negative differential resistance (NDR) with very high peak-to-valley ratio. The analysis of the shifting of the energy states of the electrodes and the modification of the transmission function with applied bias provides an insight into the nonlinearity and asymmetry observed in the I-V characteristics. Variation of the transport properties on the width of the ribbon has also been discussed.Comment: 28 Pages, 12 Figures and 1 tabl

    Enhanced bone marrow derived mesenchymal stem cell differentiation when isolated and expanded with human platelet rich plasma and differentiation media is supplemented with vitamin D

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    Vitamin D3 is well known to be involved in bone formation during foetal development and has been shown to be actively involved from gestational day 13 during foetal rat development [1]. Vitamin D3 and its associated enzyme 1-alpha-hydroxylase a member of the cytochrome P450 super family and encoded for by the gene CYP27B1. In this study we supplemented osteogenic media with vitamin D at a concentration of 10-4M and differentiated for 21 days with samples analysed by means of quantitative alizarin red assay and qPCR for the bone markers RUNX2, ALPL and HPRT

    Vaginal cuff recurrence after radical cystectomy: an under - studied site of bladder cancer relapse

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    Vaginal cuff recurrence of tumor following radical cystectomy is a rare site of disease recurrence, however it has never been specifically studied. The aim of the study is to evaluate incidence, risk factors, and long-term oncologic outcomes of vaginal cuff recurrence in a cohort of female patients treated with radical cystectomy for invasive urothelial carcinoma of the bladder

    A First Principles Calculation of Ferromagnetic EuFe4Sb12

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    AbstractThe filled skutterudite compounds have attracted much attention of their wide variety of strongly correlated electron behaviour. Density functional theory (DFT) based calculations of electronic and magnetic properties of the filled skutterudites EuFe4Sb12 have been performed using full-potential linearized augmented plane wave (FP-LAPW) method within the framework of the local spin density approximation (LSDA) approach. FeSb-based filled skutterudite compound exhibits variety of interesting features, since there coexist localized 4f-electrons and 3d-electrons with high density of states near Fermi level originating from Eu and Fe. The calculation performed near the Fermi level for density of states shows the compound to be suitable for effective thermoelectric application. The exchange-splitting of Eu-4f states were analysed to explain the ferromagnetic behaviour of EuFe4Sb12 with magnetic moment of 5.35μB
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