2009/4

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    Analyses of Real Email Traffic Properties
    (Společnost pro radioelektronické inženýrství, 2009-12) Malinka, Kamil; Hanacek, Petr; Cvrcek, Dan
    In this paper, we perform an empirical analysis of email traffic logs obtained from a large university to better understand its impact on the effectiveness and efficiency of anonymous mix remailers. We analyzed data containing records of almost 790,000 emails sent over a period of forty days – the largest dataset we are aware of. The initial analysis of data is followed by an exploration of how variance in message arrival time and size impact the anonymity and efficiency provided by timed and threshold mixes, respectively. The analysis results are subsequently explored for their possible impact on traffic analysis.
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    Modeling of Scientific Images Using GMM
    (Společnost pro radioelektronické inženýrství, 2009-12) Svihlik, Jan
    This paper deals with modeling of scientific and multimedia images in the wavelet domain. Images transformed into wavelet domain have a special shape of probability density function (PDF). Thus wavelet coefficients PDFs are usually modeled using generalized Laplacian PDF model (GLM), which is characterized by two parameters. The wavelet coefficients modeling can be more efficient, while the Gaussian mixture model (GMM) is utilized. GMM model is given by addition of at least two Gaussian PDFs with different standard deviations. The equation system derived by moment method for GMM model parameters estimation will be presented. The equation system was derived for an addition of two GMM models. So it is suitable for advanced denoising systems, where an addition of two GMM random variables is considered (e.g. dark current). This paper presents a continuing of previous work [11], deals with dark current elimination (novel approach) and shows a better way of to modeling light image and dark current.
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    Utilization of Birefringent Fiber as Sensor of Temperature Field Disturbance
    (Společnost pro radioelektronické inženýrství, 2009-12) Dvorak, Filip; Maschke, Jon; Vlcek, Cestmir
    The paper deals with utilization of induced birefringence sensitivity to temperature field in birefringent optical fibers. The propagating optical wave and optical fibers are described by means of coherency and Jones matrices, which are decomposed into unitary matrix and spin matrices. The development of polarization caused by temperature field is interpreted on the Poincare sphere by means of MATLAB® environment. The temperature sensitivity of Panda and bow-tie fiber has been measured for circular polarization excitation. Curves of intensity fluctuation caused by the temperature dependence are presented.
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    Analysis of Periodic Errors for Synthesized-Reference-Wave Holography
    (Společnost pro radioelektronické inženýrství, 2009-12) Pidanic, Jan; Schejbal, Vladimir; Cermak, Dusan
    Synthesized-reference-wave holographic techniques offer relatively simple and cost-effective measurement of antenna radiation characteristics and reconstruction of complex aperture fields using near-field intensity-pattern measurement. These methods allow utilization of advantages of methods for probe compensations for amplitude and phasing near-field measurements for the planar and cylindrical scanning including accuracy analyses. The paper analyzes periodic errors, which can be created during scanning, using both theoretical results and numerical simulations.
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    Traction Permanent Magnet Synchronous Motor Torque Control with Flux Weakening
    (Společnost pro radioelektronické inženýrství, 2009-12) Dolecek, Radovan; Novak, Jaroslav; Cerny, Ondrej
    The paper deals with analysis of dynamic behavior of a feedback flux weakening control of PMSM traction drive for light vehicles. The PMSM flux weakening is very important for traction drives. Two torque control structures were analyzed - pure feedback control and feedback control with prediction of the field producing current component. The principles, control structures, simulation and experimental results are given.