32,989 research outputs found

    Theory of disorder-induced multiple coherent scattering in photonic crystal waveguides

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    We introduce a theoretical formalism to describe disorder-induced extrinsic scattering in slow-light photonic crystal waveguides. This work details and extends the optical scattering theory used in a recent \emph{Physical Review Letter} [M. Patterson \emph{et al.}, \emph{Phys. Rev. Lett.} \textbf{102}, 103901 (2009)] to describe coherent scattering phenomena and successfully explain complex experimental measurements. Our presented theory, that combines Green function and coupled mode methods, allows one to self-consistently account for arbitrary multiple scattering for the propagating electric field and recover experimental features such as resonances near the band edge. The technique is fully three-dimensional and can calculate the effects of disorder on the propagating field over thousands of unit cells. As an application of this theory, we explore various sample lengths and disordered instances, and demonstrate the profound effect of multiple scattering in the waveguide transmission. The spectra yield rich features associated with disorder-induced localization and multiple scattering, which are shown to be exasperated in the slow light propagation regime

    Improving the method of calculating electronic properties of narrow bandgap semiconductors

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    A previously developed code for calculating the mobility of charge carriers in narrow bandgap semiconductors does not predict the correct temperature dependence in all cases. It is thought that this is due to the way the electronic screening of the carriers is treated in the model. The objective of this research is to improve the handling of the screening by going beyond the current first Born approximation. Much of this work is directly related to the alloy semiconductor Hg sub 1-xCd sub xTe which is important for infrared detectors and is a good candidate for microgravity crystal growth. The principal conclusion, so far, is that the major difficulty is probably the treatment of short range screening at higher temperatures

    On the admissibility of unboundedness properties of forced deterministic and stochastic sublinear Volterra summation equations

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    In this paper we consider unbounded solutions of perturbed convolution Volterra summation equations. The equations studied are asymptotically sublinear, in the sense that the state--dependence in the summation is of smaller than linear order for large absolute values of the state. When the perturbation term is unbounded, it is elementary to show that solutions are also. The main results of the paper are mostly of the following form: the solution has an additional unboundedness property UU if and only if the perturbation has property UU. Examples of property UU include monotone growth, monotone growth with fluctuation, fluctuation on R\mathbb{R} without growth, existence of time averages. We also study the connection between the times at which the perturbation and solution reach their running maximum, and the connection between the size of signed and unsigned running maxima of the solution and forcing term.Comment: 45 page

    Blow-up and superexponential growth in superlinear Volterra equations

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    This paper concerns the finite-time blow-up and asymptotic behaviour of solutions to nonlinear Volterra integrodifferential equations. Our main contribution is to determine sharp estimates on the growth rates of both explosive and nonexplosive solutions for a class of equations with nonsingular kernels under weak hypotheses on the nonlinearity. In this superlinear setting we must be content with estimates of the form limtτA(x(t),t)=1\lim_{t\to\tau}A(x(t),t) = 1, where τ\tau is the blow-up time if solutions are explosive or τ=\tau = \infty if solutions are global. Our estimates improve on the sharpness of results in the literature and we also recover well-known blow-up criteria via new methods.Comment: 24 page

    Subexponential Growth Rates in Functional Differential Equations

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    This paper determines the rate of growth to infinity of a scalar autonomous nonlinear functional differential equation with finite delay, where the right hand side is a positive continuous linear functional of f(x)f(x). We assume ff grows sublinearly, and is such that solutions should exhibit growth faster than polynomial, but slower than exponential. Under some technical conditions on ff, it is shown that the solution of the functional differential equation is asymptotic to that of an auxiliary autonomous ordinary differential equation with righthand side proportional to ff (with the constant of proportionality equal to the mass of the finite measure associated with the linear functional), provided ff grows more slowly than l(x)=x/logxl(x)=x/\log x. This linear--logarithmic growth rate is also shown to be critical: if ff grows more rapidly than ll, the ODE dominates the FDE; if ff is asymptotic to a constant multiple of ll, the FDE and ODE grow at the same rate, modulo a constant non--unit factor.Comment: 10 page

    On the beneficial role of noise in resistive switching

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    We study the effect of external noise on resistive switching. Experimental results on a manganite sample are presented showing that there is an optimal noise amplitude that maximizes the contrast between high and low resistive states. By means of numerical simulations, we study the causes underlying the observed behavior. We find that experimental results can be related to general characteristics of the equations governing the system dynamics.Comment: 4 pages, 5 figure

    Rendering PostScript<sup>TM</sup> fonts on FPGAs

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    This paper describes how custom computing machines can be used to implement a simple outline font processor. An FPGA based co-processor is used to accelerate the compute intensive portions of font rendering. The font processor builds on several PostScript components previously presented by the authors to produce a system that can rapidly render fonts. A prototype implementation is described followed by an explanation of how this could be extended to build a complete system

    Polymerizable disilanols having in-chain perfluoroalkyl groups

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    Disilanols containing in-chain perfluoroalkyl and aromatic groups and the process by which they were prepared are discussed. The disilanols, when reacted with a diaminosilane and cured, produce polymeric material resistant to hydrocarbon fuels and stable at elevated temperatures
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