Computer modeling of a two-junction, monolithic cascade solar cell

The theory and design criteria for monolithic, two-junction cascade solar cells are described. The departure from the conventional solar cell analytical method and the reasons for using the integral form of the continuity equations are briefly discussed. The results of design optimization are presented. The energy conversion efficiency that is predicted for the optimized structure is greater than 30% at 300 K, AMO and one sun. The analytical method predicts device performance characteristics as a function of temperature. The range is restricted to 300 to 600 K. While the analysis is capable of determining most of the physical processes occurring in each of the individual layers, only the more significant device performance characteristics are presented

The Background Field Method as a Canonical Transformation

We construct explicitly the canonical transformation that controls the full dependence (local and non-local) of the vertex functional of a Yang-Mills theory on a background field. After showing that the canonical transformation found is nothing but a direct field-theoretic generalization of the Lie transform of classical analytical mechanics, we comment on a number of possible applications, and in particular the non perturbative implementation of the background field method on the lattice, the background field formulation of the two particle irreducible formalism, and, finally, the formulation of the Schwinger-Dyson series in the presence of topologically non-trivial configurations.Comment: 11 pages, REVTeX. References added, some explanations extended. Final version to appear in the journa

AlGaAs-GaAs cascade solar cell

Computer modeling studies are reported for a monolithic, two junction, cascade solar cell using the AlGaAs GaAs materials combination. An optimum design was obtained through a serial optimization procedure by which conversion efficiency is maximized for operation at 300 K, AM 0, and unity solar concentration. Under these conditions the upper limit on efficiency was shown to be in excess of 29 percent, provided surface recombination velocity did not exceed 10,000 cm/sec

The application of nonlinear bistable detectors to DCT-domain watermarking schemes

Copyright 2008 Society of Photo-Optical Instrumentation Engineers. This paper was published in Complex Systems II, edited by Derek Abbott, Tomaso Aste, Murray Batchelor, Robert Dewar, Tiziana Di Matteo, Tony Guttmann, Proc. of SPIE Vol. 6802, 680215 and is made available as an electronic reprint with permission of SPIE. One print or electronic copy may be made for personal use only. Systematic or multiple reproduction, distribution to multiple locations via electronic or other means, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited.A DCT-domain watermarking scheme, based on nonlinear bistable detectors, is presented. A binary copyright character, i.e. watermark, is firstly reordered into a binary zig-zag sequence, and then mapped into pulse amplitude modulated waveforms. A certain desynchronization time delay can be arbitrarily placed into one code of the modulated signal, and is tolerated due to the superior robustness of nonlinear detectors over matched filters. The watermark signal is then embedded in a selected set of DCT coefficients of an image in a medium frequency range. The selected set of DCT coefficients is shuffled via the Arnold transform and looks more like background noise with respect to the watermark signal. The copyright character can be extracted by the nonlinear bistable detector without prior knowledge of the original image, i.e. blind watermark detection. Interestingly, a higher match between the original watermark character and the extracted one can be further achieved using a parallel array of bistable detectors via the mechanism of array stochastic resonance. Robustness of the proposed watermarking scheme is shown in the presence of noise, filtering, cropping and compression.Fabing Duan and Derek Abbot

Acoustic Signatures of a Model Fan in the NASA-Lewis Anechoic Wind Tunnel

One-third octave band and narrowband spectra and continuous directivity patterns radiated from an inlet are presented over ranges of fan operating conditions, tunnel velocity, and angle of attack. Tunnel flow markedly reduced the unsteadiness and level of the blade passage tone, revealed the cutoff design feature of the blade passage tone, and exposed a lobular directivity pattern for the second harmonic tone. The full effects of tunnel flow are shown to be complete above a tunnel velocity of 20 meters/second. The acoustic signatures are also shown to be strongly affected by fan rotational speed, fan blade loading, and inlet angle of attack

Seismic isolation of Advanced LIGO: Review of strategy, instrumentation and performance

The new generation of gravitational waves detectors require unprecedented levels of isolation from seismic noise. This article reviews the seismic isolation strategy and instrumentation developed for the Advanced LIGO observatories. It summarizes over a decade of research on active inertial isolation and shows the performance recently achieved at the Advanced LIGO observatories. The paper emphasizes the scientific and technical challenges of this endeavor and how they have been addressed. An overview of the isolation strategy is given. It combines multiple layers of passive and active inertial isolation to provide suitable rejection of seismic noise at all frequencies. A detailed presentation of the three active platforms that have been developed is given. They are the hydraulic pre-isolator, the single-stage internal isolator and the two-stage internal isolator. The architecture, instrumentation, control scheme and isolation results are presented for each of the three systems. Results show that the seismic isolation sub-system meets Advanced LIGO's stringent requirements and robustly supports the operation of the two detectors

Mutual information for examining correlations in DNA

This paper examines two methods for finding whether long-range correlations exist in DNA: a fractal measure and a mutual information technique. We evaluate the performance and implications of these methods in detail. In particular we explore their use comparing DNA sequences from a variety of sources. Using software for performing in silico mutations, we also consider evolutionary events leading to long range correlations and analyse these correlations using the techniques presented. Comparisons are made between these virtual sequences, randomly generated sequences, and real sequences. We also explore correlations in chromosomes from different species.Comment: 8 pages, 3 figure

Non-Gaussian noise benefits for coherent detection of narrowband weak signal

Non-Gaussian noise benefits for coherent detection of narrowband weak signal

Double-maximum enhancement of signal-to-noise ratio gain via stochastic resonance and vibrational resonance

Double-maximum enhancement of signal-to-noise ratio gain via stochastic resonance and vibrational resonance