High-frequency dynamical response of Abrikosov vortex lattice in flux-flow region

The dynamical response of the Abrikosov vortex lattice in the presence of an oscillating driving field is calculated by constructing an analytical solution of the time-dependent Ginzburg-Landau equation. The solution is steady-state, and work done by the input signal is dissipated through vortex cores, mainly by scattering with phonons. The response is nonlinear in the input signal, and is verified for consistency within the theory. The existence of well-defined parameters to control nonlinear effects is important for any practical application in electronics, and a normalised distance from the normal-superconducting phase-transition boundary is found to be such a parameter to which the response is sensitive. Favourable comparison with NbN experimental data in the optical region is made, where the effect is in the linear regime. Predictions are put forward regarding the suppression of heating and also the lattice configuration at high frequency.Comment: 13 pages, 7 figures, revtex; V2: clarifications, reference added, mended typo

On the study of four-parallelogram filter banks

The most commonly used 2-D filter banks are separable filter banks, which can be obtained by cascading two 1-D filter banks in the form of a tree. The supports of the analysis and synthesis filters in the separable systems are unions of four rectangles. The natural nonseparable generalization of such supports are those that are unions of four parallelograms. We study four parallelogram filter banks, which is the class of 2-D filter banks in which the supports of the analysis and synthesis filters consist of four parallelograms. For a given a decimation matrix, there could be more than one possible configuration (the collection of passbands of the analysis filters). Various types of configuration are constructed for four-parallelogram filter banks. Conditions on the configurations are derived such that good design of analysis and synthesis filters are possible. We see that there is only one category of these filter banks. The configurations of four-parallelogram filter banks in this category can always be achieved by designing filter banks of low design cost

Effect of Impurities on the Superheating field of Type II superconductors

We consider the effect of nonmagnetic and magnetic impurities on the superheating field $H_s$ in a type-II superconductor. We solved the Eilenberger equations, which take into account the nonlinear pairbreaking of Meissner screening currents, and calculated $H_s(T)$ for arbitrary temperatures and impurity concentrations in a single-band s-wave superconductor with a large Ginzburg-Landau parameter. At low temperatures nonmagnetic impurities suppress a weak maximum in $H_s(T)$ which has been predicted for the clean limit, resulting instead in a maximum of $H_s$ as a function of impurity concentration in a moderately clean limit. It is shown that nonmagnetic impurities weakly affect $H_s$ even in the dirty limit, while magnetic impurities suppress both $H_s$ and the critical temperature $T_c$. The density of quasiparticles states $N(\epsilon)$ is strongly affected by an interplay of impurity scattering and current pairbreaking. We show that a clean superconductor at $H=H_s$ is in a gapless state, but a quasiparticle gap $\epsilon_g$ in $N(\epsilon)$ at $H=H_s$ appears as the concentration of nonmagnetic impurities increases. As the nonmagnetic scattering rate $\alpha$ increases above $\alpha_c=0.36$, the quasiparticle gap $\epsilon_g(\alpha)$ at $H=H_s$ increases, approaching $\epsilon_g\approx 0.32\Delta_0$ in the dirty limit $\alpha\gg 1$, where $\Delta_0$ is the superconducting gap parameter at zero field. The effects of impurities on $H_s$ can be essential for the nonlinear surface resistance and superconductivity breakdown by strong RF fields.Comment: 12 pages, 13 figure

GROWTH THEORY AND ACCOUNTING FOR GROWTH OF THE TAIWANESE ECONOMY

A growth accounting and an econometric exercise are used to provide insights into the evolution of the Taiwanese economy over the period 1966-96. The approach links the GDP function of a multiple sector neoclassical growth model to growth accounting and, subsequently to the estimation of the parameters of this function. The growth accounting results show that the contribution of total factor productivity (TFP) to growth in GDP averaged about 32 percent over the period, and this contribution increased as the economy approached its long-run equilibrium during the decade of the 1980s, with evidence of some departure during 1991-96. Growth in TFP increased output growth in industry and services while growth in skilled labor benefited all sectors. Growth in capital stock increased the growth of the industrial sector the most, followed by services, but the effect on agricultural output growth was negative. Growth in TFP and capital stock appear to have increased the capacity of the industrial and service sectors to pull resources from agriculture.economic growth, productivity, technological change, International Development, Productivity Analysis, O3, O4, O5,