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A physically based compact analytical model is proposed for a ferromagnetic single electron transistor (FSET). This model is based on the orthodox theory and solves the master equation, spin conservation equation, and charge neutrality equation simultaneously. The model can be applied to both symmetric and asymmetric devices and does not introduce any limitation on the applied bias voltages. This feature makes the model suitable for both analog and digital applications. To verify the accuracy of the model, its results regarding a typical FSET in both low and high voltage regimes are compared with the existing numerical results. Moreover, the model's results of a parallel configuration FSET, where no spin accumulation exists in the island, are compared with the results obtained from a Monte Carlo simulation using SIMON. These two comparisons show that our model is valid and accurate. As another comparison, the model is compared analytically with an existing model for a double barrier ferromagnetic junction (having no gate). This also verifies the accuracy of the model. [ABSTRACT FROM AUTHOR]

The nonparametric estimation of the distribution of relaxation-time approach is not as frequently used in the analysis of dispersed response of dielectric or conductive materials as are other immittance data analysis methods based on parametric curve fitting techniques. Nevertheless, such distributions can yield important information about the physical processes present in measured material. In this paper, we apply two quite different numerical inversion methods to estimate the distribution of relaxation times for glassy Li0.5La0.5TiO3 dielectric frequency-response data at 225 K. Both methods yield unique distributions that agree very closely with the actual exact one accurately calculated from the corrected bulk-dispersion Kohlrausch model established independently by means of parametric data fit using the corrected modulus formalism method. The obtained distributions are also greatly superior to those estimated using approximate function equations given in the literature. [ABSTRACT FROM AUTHOR]

The current-voltage and spectral characteristics of a flux flow oscillator (FFO) based on a long Josephson junction are studied. The investigations are performed in the range of small bias currents and magnetic fields where the FFO radiates a quasi-chaotic signal with extremely large radiation linewidth, and the displaced linear slope (DLS) is observed at the current-voltage characteristic. Using direct numerical simulation of the sine-Gordon equation, it is shown that for large lengths of the Josephson junction or in the case of partial matching of the FFO with external waveguide system, the DLS with extremely large linewidth is transformed into Fiske steps with very narrow linewidth. As for Fiske steps, the appearance of regime of chaotic oscillations can be explained by multiple reflections of the traveling waves from junction ends rather than simply by excitation of the internal oscillation modes in the 'soft' fluxon chain at weak magnetic fields. [ABSTRACT FROM AUTHOR]

Numerical simulations of shock wave propagation through discretely represented powder mixtures were performed to investigate the characteristics of deformation and mixing in the Ni+Al system. The initial particle arrangements and morphologies were imported from experimentally obtained micrographs of powder mixtures pressed at densities in the range of 45%–80% of the theoretical maximum density (TMD). Simulations were performed using these imported micrographs for each density compact subjected to driver velocities (Up) of 0.5, 0.75, and 1 km/s, and the resulting shock velocity (Us) was used to construct the Us-Up equation of state. The simulated equation of state for the 60% TMD mixture was validated by matching results obtained from previous gas-gun experiments. The details of shock wave propagation through the Ni+Al powder mixtures were explored on several scales. It is shown that the shock compression of mixtures of powders of dissimilar densities and strength is associated with heterogeneous deformation processes leading to focused flow, particulation, and vortex formation, resulting in local fluctuations in pressure and temperature, which collectively are responsible for highly irregular “shock” fronts and unstable high-pressure states in granular media. [ABSTRACT FROM AUTHOR]

A closed form analytical solution for the electric field distribution inside a metallic cylindrical disk specimen has been derived for the problem of a two-probe impedance measurement. A two-probe impedance measurement can be treated as current injection and extraction by means of source and sink electrodes that are placed on opposite sides of a specimen. The analytical formulation is based on Maxwell’s equations for conductors and the derivation has been conducted on the premise of continuum considerations within the specimen. The derived field expressions for axial [Ez(r,z)] and radial [Er(r,z)] fields are expressed in terms of Bessel series. As an extension to this problem, a semi-infinite solution is also given for the case of an infinitely long cylinder. The analytical solutions thus derived have been verified by computer simulations using a commercially available finite element package. The electric field distributions inside the specimen obtained via analytical and finite element solutions are in excellent agreement with each other. The dependence of skin-effect and constriction behaviors on specimen geometry (radius r0 and thickness t0) and contact radius of the electrode (rc) has been investigated by varying them in a systematic fashion. The skin-effect behavior at high frequencies is strictly a function of the dimensions of the disk (r0,t0) and is independent of the contact radius of the electrodes (rc). The constriction behavior, however, is predominantly governed by rc, although it depends on all three geometric parameters. Lastly, the idea of a limiting thickness (t0,lim) and a limiting field profile ( Ez,lim|z=t0,lim/2) is discussed so as to determine the range of applicability of the analytical solutions. The analytical solution derived for the disk shows good agreement with the finite element solutions for all values of t0, while the semi-infinite solution is only valid for large values of t0. [ABSTRACT FROM AUTHOR]

The classical electrostatic problem of two nonintersecting conducting spheres in a uniform incident electric field is considered. Starting from the basic Kelvin’s image principle, the two spheres are replaced with equivalent series of image sources, from which the polarizability is calculated. Explicit expressions for the axial and transversal components of the polarizability dyadic are found by solving the recurrence equations. Efficient numerical evaluation of the different series is also discussed. [ABSTRACT FROM AUTHOR]