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International Conference on Actual Problems of Electron Devices Engineering

作者： Ryskin, N. M. Khavroshin, O. S. Saratov NG Chernyshevskii State Univ Saratov Russia

ISBN: (纸本)9781424421213

Self-modulation instability is typical for special distributed oscillators especially with time delayed feedback. This instability results in generation of multiple frequencies or even spread spectrum chaotic signal. In this paper, we propose a method for suppressing the self-modulation that is a modification of the well-known time-delayed controlling chaos technique. Numerical results for delayed feedback klystron and traveling-wave tube oscillators are presented showing that application of the method allows stabilization of unstable single frequency regimes and improves performance of the oscillators.

关键词： Oscillators differential pulse code modulation feedback oscillators Delayed Feedback application methods IN-VACUO

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Probing of nonlinear evolution of laser wakefield by Raman scattering of laser light

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PHYSICS OF PLASMAS 2008年第9期15卷 093107-093107页

作者： Zhou, Weimin Mima, Kunioki Nakamura, Tatsufumi Nagatomo, Hideo Osaka Univ Grad Sch Engn Suita Osaka 5650871 Japan Osaka Univ Inst Laser Engn Suita Osaka 5650871 Japan

When a weak probe laser pulse is injected into a wakefield excited by a short high-intensity pump laser pulse, the probe pulse will be Raman scattered by the wakefield. It is possible to determine the density profile from the spectrum of this forward Raman scattered probe laser [R. E. Slusher and C. M. Surko, Phys. Fluids 23, 472 (1980)]. In this paper, an analytical solution for the multiple sidebands of the forward Raman scattering of the probe laser pulse is presented. These multiple sidebands are connected with the steepening of density perturbation of the wakefield. More detailed information of the laser wakefield can be obtained from these multiple sidebands. The propagation of the probe pulse in wakefields is studied with one-dimensional particle-in-cell (PIC) simulations. The analytical solution and the results of PIC simulations are consistent with each other and other experiments. (c) 2008 American Institute of Physics.

关键词： WAKE-FIELD ACCELERATOR HIGH-INTENSITY LASERS ELECTRON ACCELERATION PLASMA-WAVES SELF-modulation COLD PLASMA pulse OSCILLATIONS PROPAGATION BACKSCATTER differential pulse code modulation High intensity lasers Plasma oscillations Raman spectrometry backscattering Exploration with a probe DENSITY PERTURBATION laser beams Raman Scattering electron acceleration Cold plasma Sidebands

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differential pulse code modulation predictor design procedure using a genetic algorithm

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OPTICAL ENGINEERING 2003年第6期42卷 1649-1655页

作者： Wu, YG Leader Univ Dept Comp Sci & Informat Engn Inst Appl Informat Tainan Taiwan

Digitized images are used widely in current industrial applications;however, digital images cost a huge storage capacity, leading to transmission bandwidth constraints. Therefore, an image compression technique was developed to solve this drawback. differential pulse code modulation (DPCM) is the most widely used method among predictive image coding schemes. It is based on the notation of quantizing a prediction error signal after the prediction operation to reduce the original data complexity. The design of the predictor influences the performance of the whole DPCM. Therefore, the predictor constitutes a central topic in the DPCM system. We make efforts toward the design of a predictor by using a genetic algorithm (GA). By the operations of crossover and mutation, several predictor coefficients are yielded after hundreds of generations. The predictor generated by the GA outperforms the current eight different predictive schemes in Joint Photographic Experts Group lossless (JPEG-LS) still image compression standard. Because the JPEG-LS compression scheme is currently the most widely used lossless compression method, our results contribute to the applications of compression. (C) 2003 Society of Photo-Optical Instrumentation Engineers.

关键词： genetic algorithm differential pulse code modulation image compression signal processing

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Robust Predictive Quantization: Analysis and Design Via Convex Optimization

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IEEE JOURNAL OF SELECTED TOPICS IN SIGNAL PROCESSING 2007年第4期1卷 618-632页

作者： Fletcher, Alyson K. Rangan, Sundeep Goyal, Vivek K. Ramchandran, Kannan Univ Calif Berkeley Berkeley CA 94720 USA Qualcomm Flar Technol Bedminster NJ 07921 USA MIT Cambridge MA 02139 USA

Predictive quantization is a simple and effective method for encoding slowly-varying signals that is widely used in speech and audio coding. It has been known qualitatively that leaving correlation in the encoded samples can lead to improved estimation at the decoder when encoded samples are subject to erasure. However, performance estimation in this case has required Monte Carlo simulation. Provided here is a novel method for efficiently computing the mean-squared error performance of a predictive quantization system with erasures via a convex optimization with linear matrix inequality constraints. The method is based on jump linear system modeling and applies to any autoregressive moving average (ARMA) signal source and any erasure channel described by an aperiodic and irreducible Markov chain. In addition to this quantification for a given encoder filter, a method is presented to design the encoder filter to minimize the reconstruction error. Optimization of the encoder filter is a nonconvex problem, but we are able to parameterize with a single scalar a set of encoder filters that yield low MSE. The design method reduces the prediction gain in the filter, leaving the redundancy in the signal for robustness. This illuminates the basic tradeoff between compression and robustness.

关键词： differential pulse code modulation erasure channels joint source-channel coding linear matrix inequalities

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Self-modulation of infrared waves in rutile

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PHYSICS LETTERS A 2007年第6期360卷 742-745页

作者： Tan, C. Z. Yan, C. Nanjing Univ Solid State Microstruct Lab Nanjing 210093 Peoples R China Nanjing Univ Dept Mat Sci & Engn Nanjing 210093 Peoples R China

Electromagnetic waves carry angular and linear momentums and exert torques on anisotropic dielectrics, arising from the fact of the tensor property of the dielectric constant, that is, the direction of electric displacement is not parallel to the electric field vector of the incident light. The torque per unit volume exerted on a wave plate is given by P x E, where P is the polarization and E is the electric field, which induces the rotations of eigenvibration direction in the crystals. The rotation angles increase with the intensity of the incident light and the dielectric constant of the crystals. Because of the large dielectric constants, self-modulation of the incident light in the infrared frequency region was clearly demonstrated in the infrared transmission spectra of ferroelectric and piezoelectric crystals. Rutile (TiO2) is a non-ferroelectric and non-piezoelectric crystal, but it also has the large dielectric constants. Rotations of the vibration direction of the ordinary (o-ray) and the extraordinary (e-ray) waves were shown in the infrared transmission spectra recorded by incidence of the plane-polarized light and transmission through a rutile plate. Interference of the o-ray and the e-ray waves transmitted through the crystals confirms the rotations of eigenvibration direction, a self-modulation effect of light in the crystal of large dielectric constants and large birefringence in the infrared range. (c) 2006 Published by Elsevier B.V.

关键词： LIGHT CRYSTALS TIO2 rutile dielectric properties Electric fields Infrared transmission differential pulse code modulation Dielectric constant infrared spectra Torque ROTATION ANGLE crop rotation TRANSMISSION SPECTROSCOPY plane-polarized light Light incident light crystals

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Uniform scalar quantization based Wyner-Ziv coding of Laplace-Markov source

Uniform scalar quantization based Wyner-Ziv coding of Laplac...

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32nd IEEE International Conference on Acoustics, Speech and Signal Processing

作者： Sheinin, Vadim Jagniohan, Ashish He, Dake IBM T. J. Watson Research United States

ISBN: (纸本)9781424407286

Wyner-Ziv coding has recently emerged as an alternative to conventional DPCM coding for compression of sources with memory, particularly in video compression. This paper studies the operational rate-distortion performance of Wyner-Ziv coding, using uniform scalar quantization followed by perfect Slepian-Wolf coding, for compression of a Laplace-Markov source. The performance gap of this technique relative to DPCM coding is characterized through derived rate-distortion expressions and numerical simulations.

关键词： quantization source coding Wyner-Ziv coding differential pulse code modulation Laplace-Markov source

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Virtually lossless compression of astrophysical images

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EURASIP JOURNAL ON APPLIED SIGNAL PROCESSING 2005年第15期2005卷 2521-2535页

作者： Lastri, C Aiazzi, B Alparone, L Baronti, S CNR Italian Natl Res Council IFAC Inst Appl Phys Nello Carrara I-50127 Florence Italy Univ Florence DET I-50139 Florence Italy

We describe an image compression strategy potentially capable of preserving the scientific quality of astrophysical data, simultaneously allowing a consistent bandwidth reduction to be achieved. Unlike strictly lossless techniques, by which moderate compression ratios are attainable, and conventional lossy techniques, in which the mean square error of the decoded data is globally controlled by users, near-lossless methods are capable of locally constraining the maximum absolute error, based on user's requirements. An advanced lossless/near-lossless differential pulse code modulation (DPCM) scheme, recently introduced by the authors and relying on a causal spatial prediction, is adjusted to the specific characteristics of astrophysical image data (high radiometric resolution, generally low noise, etc.). The background noise is preliminarily estimated to drive the quantization stage for high quality, which is the primary concern in most of astrophysical applications. Extensive experimental results of lossless, near-lossless, and lossy compression of astrophysical images acquired by the Hubble space telescope show the advantages of the proposed method compared to standard techniques like JPEG-LS and JPEG2000. Eventually, the rationale of virtually lossless compression, that is, a noise-adjusted lossles/near-lossless compression, is highlighted and found to be in accordance with concepts well established for the astronomers' community.

关键词： astrophysical images differential pulse code modulation lossless compression near-lossless compression noise estimation statistical context modeling

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Recurrent pi-sigma networks for DPCM image coding

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NEUROCOMPUTING 2003年第1-2期55卷 363-382页

作者： Hussain, AJ Liatsis, P UMIST Dept Elec Engn & Elect Control Syst Ctr Intelligent Syst & Sensing Lab Manchester M60 1QD Lancs England Liverpool John Moores Univ Sch Comp & Math Sci Liverpool L3 3AF Merseyside England

This work proposes a new recurrent polynomial neural network that utilises both the temporal dynamics of the image formation process and the multi-linear interactions between the pixels for 1D/2D predictive image coding. The network consists of a layer of summing units followed by a product unit and incorporates a feedback link from the output to the input layer. It is trained using a small size training set through dynamic backpropagation. Its performance is evaluated on a database of 15 images and compared to the higher-order neural network, the feed-forward pi-sigma neural network, and the standard linear predictor. (C) 2002 Elsevier B.V. All rights reserved.

关键词： recurrent networks higher-order neural networks differential pulse code modulation image compression

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Unsteady beam-plasma discharge: I. Mathematical model and linear theory

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PLASMA PHYSICS REPORTS 2003年第9期29卷 740-747页

作者： Bliokh, YP Lyubarsky, MG Podobinsky, VO Fainberg, YB Technion IL-3200 Haifa Israel Karazin Natl Univ UA-61077 Kharkov Ukraine Kharkov Phys & Technol Inst Inst Plasma Elect & New Accelerat Methods Ctr Nat Sci UA-61108 Kharkov Ukraine

A mathematical model is constructed that describes the development of the beam-plasma instability in a traveling-wave tube amplifier in the presence of a neutral gas. Steady solutions are derived for conditions of microwave discharges in a magnetized plasma-tilled traveling-wave tube amplifier, and their stability is investigated. It is shown that the steady-state amplification regime may become unstable and change to the self-modulation regime. The relationships between the amplifier parameters at the instability threshold are obtained, and the frequencies of the excited ion acoustic waves are determined. The results of numerical modeling are found to agree well with the analytical results. (C) 2003 MAIK "Nauka/Interperiodica".

关键词： differential pulse code modulation Unstable plasma instabilities ION ACOUSTIC WAVES Travelling wave tube amplifiers ELECTRON TUBE AMPLIFIERS Unsteady high-frequency discharges

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Effect of the ponderomotive force on the development of beam-plasma instability

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PLASMA PHYSICS REPORTS 2003年第4期29卷 307-327页

作者： Bliokh, YP Lyubarsky, MG Zemlyansky, NM Mirny, VI Podobinsky, VO Sotnikov, GV Fainberg, YB Technion Israel Inst Technol Dept Phys IL-32000 Haifa Israel Karazin Natl Univ UA-61077 Kharkov Ukraine Kharkov Inst Phys & Technol Ctr Nat Sci Inst Plasma Elect & New Accelerat methods UA-61108 Kharkov Ukraine

The amplitude of the wave generated in a plasma during the development of beam-plasma instability is nonuniform in the longitudinal direction. The ponderomotive force associated with this nonuniformity leads to a redistribution of the plasma density;as a result, the wave amplitude and its spatial distribution change. As the beam current grows, the ponderomotive force plays an increasingly important role and radically changes the mechanism by which the beam-plasma instability saturates. Ion acoustic waves generated by the ponderomotive force propagate in the direction opposite to the propagation direction of the beam, thereby ensuring distributed feedback and giving rise to a strong low-frequency self-modulation of the wave amplitude and phase. Results are presented from experimental investigations of the self-modulation regime of the beam-plasma instability in a magnetized plasma waveguide. Theoretical estimates of the parameters of the low-frequency self-modulation agree well with the experimental data. (C) 2003 MAIK "Nauka/Interperiodica".

关键词： beam currents differential pulse code modulation plasma instabilities Force ION ACOUSTIC WAVES distributed feedback Wave amplitude plasma density Plasma filled waveguides nonuniformity propagation direction

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