We study the statistics and characteristics of rare intense events in two types of two-dimensional complex Ginzburg-Landau (CGL) equation based models. Our numerical simulations show finite amplitude collapselike solu...
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We study the statistics and characteristics of rare intense events in two types of two-dimensional complex Ginzburg-Landau (CGL) equation based models. Our numerical simulations show finite amplitude collapselike solutions which approach the infinite amplitude solutions of the nonlinear Schrödinger equation in an appropriate parameter regime. We also determine the probability distribution function of the amplitude of the CGL solutions, which is found to have enhanced (as compared to Gaussian) probability for the amplitude to be large. Our results suggest a general picture in which an incoherent background of weakly interacting waves, occasionally, “by chance,” initiates intense, coherent, self-reinforcing, highly nonlinear events.
Polarization effects in surface plasmon polaritonic crystals (two-dimensional photonic crystals on a metal surface) are observed in the optical transmission of metallic nanostructures and the directional switching bet...
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We consider the long time dependence for the moments of displacement 〈|r|q〉 of infinite horizon billiards, given a bounded initial distribution of particles. For a variety of billiard models we find 〈|r|q〉∼tγq (...
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We consider the long time dependence for the moments of displacement 〈|r|q〉 of infinite horizon billiards, given a bounded initial distribution of particles. For a variety of billiard models we find 〈|r|q〉∼tγq (up to factors of lnt). The time exponent, γq, is piecewise linear and equal to q/2 for q<2 and q−1 for q>2. We discuss the lack of dependence of this result on the initial distribution of particles and resolve apparent discrepancies between this time dependence and a prior result. The lack of dependence on initial distribution follows from a remarkable scaling result that we obtain for the time evolution of the distribution function of the angle of a particle’s velocity vector.
Photon tunneling gated by light at a different wavelength in an artificially created array of nanometer scale cylindrical channels in a thick gold film is described. This observation suggests the possibility of buildi...
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Photon tunneling gated by light at a different wavelength in an artificially created array of nanometer scale cylindrical channels in a thick gold film is described. This observation suggests the possibility of building a new class of "gated" photon tunneling devices for massive parallel all-optical signal and image processing.
In this paper, we present the experimental cold-test results of the new input cavity and the hot tests of this new 4 cavity, frequency-doubling coaxial gyroklystron. The input cavity was redesigned to have a lower qua...
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In this paper, we present the experimental cold-test results of the new input cavity and the hot tests of this new 4 cavity, frequency-doubling coaxial gyroklystron. The input cavity was redesigned to have a lower quality factor and located the lossy absorbers inside the cavity structure, rather than in the adjacent drift tube sections. The average radius of the cavity was increased to make that cavity less susceptible to spurious oscillations. The designed 4 cavity frequency doubling system have a high large signal gain above 50 dB.
Simultaneous perturbation stochastic approximation (SPSA) algorithms have been found to be very effective for high-dimensional simulation optimization problems. The main idea is to estimate the gradient using simulati...
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Simultaneous perturbation stochastic approximation (SPSA) algorithms have been found to be very effective for high-dimensional simulation optimization problems. The main idea is to estimate the gradient using simulation output performance measures at only two settings of the N -dimensional parameter vector being optimized rather than at the N + 1 or 2N settings required by the usual one-sided or symmetric difference estimates, respectively. The two settings of the parameter vector are obtained by simultaneously changing the parameter vector in each component direction using random perturbations. In this article, in order to enhance the convergence of these algorithms, we consider deterministic sequences of perturbations for two-timescale SPSA algorithms. Two constructions for the perturbation sequences are considered: complete lexicographical cycles and much shorter sequences based on normalized Hadamard matrices. Recently, one-simulation versions of SPSA have been proposed, and we also investigate these algorithms using deterministic sequences. Rigorous convergence analyses for all proposed algorithms are presented in detail. Extensive numerical experiments on a network of M/G/1 queues with feedback indicate that the deterministic sequence SPSA algorithms perform significantly better than the corresponding randomized algorithms.
The magnetization behavior of arrays of cobalt and permaloy rings has been studied using high-resolution magnetic imaging techniques. Isolated rings form two stable magnetic states: a totally flux closed vortex state ...
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ISBN:
(纸本)8882020096
The magnetization behavior of arrays of cobalt and permaloy rings has been studied using high-resolution magnetic imaging techniques. Isolated rings form two stable magnetic states: a totally flux closed vortex state and a polarized 'onion' state with two head-to-head domain boundaries. The transition from the polarized into the vortex state is shown to occur through the motion and annihilation of the domain boundaries. The effect of interactions between the rings has been investigated in arrays of chains of touching rings. For fields applied parallel to the chains, rings in extended sections of the chains are found to switch simultaneously. Neighboring rings in these sections display alternating chirality (rotation of magnetization) in direct analogy with behavior of gears in mechanical gear trains.
We report on intersubband transitions in InxGa1-xAs/AlGaAs multiple quantum wells (MQWs) grown by molecular beam epitaxy. The conduction band offset for this material system is larger than that of the well known GaAs/...
We report on intersubband transitions in InxGa1-xAs/AlGaAs multiple quantum wells (MQWs) grown by molecular beam epitaxy. The conduction band offset for this material system is larger than that of the well known GaAs/AlGaAs system, thus making it possible to design, grow, and fabricate quantum well infrared photodetectors operational beyond the 14 μm spectral region with minimized dark current. We have grown InxGa1-xAs/AlGaAs MQWs with indium compositions ranging from x = 0.08 to 0.20 verified by in situ RHEED oscillations, band offset measurements, and high-resolution X-ray diffraction. Band-to-band transitions were verified by photoluminescence measurements, and intersubband transitions were measured using Fourier transform infrared (FTIR) spectroscopy. Due to the high strain and introduction of dislocations associated with the high indium content, wells with indium compositions above ∼ 0.12 did not result in intersubband transitions at silicon doping levels of 2×1018 cm-3. A thick linear graded InxGa1-xAs buffer was grown below the MQW structures to reduce the strain and resulting dislocations. Intersubband transitions were measured in InxGa1-xAs wells with indium compositions of x = 0.20 and greater when grown on top of the linear graded buffer. In addition to these results, FTIR measurements on InGaAs/AlGaAs MQW multi-color, long-wavelength infrared detector structures are reported.
Radio Frequency (RF) effects are a major factor in limiting integrated circuit (IC) performance. The complex IC interconnect structure forms a network of coupled transmission lines. Parasitic coupling between these ne...
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ISBN:
(纸本)0780381394
Radio Frequency (RF) effects are a major factor in limiting integrated circuit (IC) performance. The complex IC interconnect structure forms a network of coupled transmission lines. Parasitic coupling between these network elements form significant barriers in the development of high-speed digital and analog IC's. Accurate modeling of modem on-chip interconnects (including coupling and losses) usually requires a full-wave solution to Maxwell's equations. However, such a solution is difficult because the wavelengths of interest are much larger than the fine topological structure of IC's. (Wavelengths are typically on the mm to cm scale, while chip structures are on the micron scale.) In addition, digital and mixed (broad band) signal applications require analysis in the time domain. Conventional Maxwell solvers typically use the explicit Finite-Difference-Time-Domain (FDTD) method. However, the conventional method is limited by the Courant's condition, which requires prohibitively small time steps to resolve fine structure on the submicron scale. To overcome this problem, we have applied the Altemating-Direction-Implicit (ADI) method [1, 2] to solve the Maxwell's Equation in ICs, and have overcome the Courant's limit. We have used the method to model the Metal-Insulator-Semiconductor-Substrate (MISS) structure. The simulations allow us to calculate in detail parasitic current flow inside the substrate;propagation losses, skindepth and dispersion of digital signals on non-ideal interconnects. We have found considerable substrate currents and losses that depend on the substrate doping.
Polarization effects in surface plasmon polaritonic crystals (two-dimensional photonic crystals on a metal surface) are observed in the optical transmission of metallic nanostructures and the directional switching bet...
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Polarization effects in surface plasmon polaritonic crystals (two-dimensional photonic crystals on a metal surface) are observed in the optical transmission of metallic nanostructures and the directional switching between line-defect waveguides. This new effect can be regarded as a polarization-domain analog of the spectral superprism effect in photonic crystals.
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