2007/1

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    Face Recognition Methods Based on Feedforward Neural Networks, Principal Component Analysis and Self-Organizing Map
    (Společnost pro radioelektronické inženýrství, 2007-04) Oravec, Milos; Pavlovicova, Jarmila
    In this contribution, human face as biometric is considered. Original method of feature extraction from image data is introduced using MLP (multilayer perceptron) and PCA (principal component analysis). This method is used in human face recognition system and results are compared to face recognition system using PCA directly, to a system with direct classification of input images by MLP and RBF (radial basis function) networks, and to a system using MLP as a feature extractor and MLP and RBF networks in the role of classifier. Also a two-stage method for face recognition is presented, in which Kohonen self-organizing map is used as a feature extractor. MLP and RBF network are used as classifiers. In order to obtain deeper insight into presented methods, also visualizations of internal representation of input data obtained by neural networks are presented.
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    Transient Effects at Power-Supply System of the Czech Railways from EMC Viewpoint
    (Společnost pro radioelektronické inženýrství, 2007-04) Dolecek, Radovan; Hlava, Karel
    The paper deals with the behavior of the traction power-supply system 25 kV, 50 Hz at the Czech Railways. Electrical conditions on a contact line affect electrical conditions in a feeding station. This relation represents galvanic coupling from EMC viewpoint. Explanation of transient effects during short-circuits at the contact line can be considered as the main problem. These effects can arise during a failure in a traction circuit. Therefore, the attention is turned to an adjustment protection design of the traction circuit. Simulation diagrams were created. The design can be utilizable for a feeding station with Filter-Compensation Equipment, which is designed for the EMI reduction.
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    A New Defected Ground Structure for Different Microstrip Circuit Applications
    (Společnost pro radioelektronické inženýrství, 2007-04) Parui, Susanta Kumar; Das, Santanu
    In this paper, a microstrip transmission line combined with a new U-headed dumb-bell defected ground structure (DGS) is investigated. The proposed DGS of two U-shape slots connected by a thin transverse slot is placed in the ground plane of a microstrip line. A finite cutoff frequency and attenuation pole is observed and thus, the equivalent circuit of the DGS unit can be represented by a parallel LC resonant circuit in series with the transmission line. A two-cell DGS microstrip line yields a better lowpass filtering characteristics. The simulation is carried out by the MoM based IE3D software and in the experimental measurements a vector network analyzer is used. The effects of the transverse slot width and the distance between arms of the U-slot on the filter response curve are studied. This DGS is utilized for different microstrip circuit applications. The DGS is placed in the ground of a capacitive loaded microstrip line and a very low cutoff frequency is obtained. The DGS is adopted under the coupled lines of a parallel line coupler and an improvement in coupling coefficient is noticed. The proposed DGS is also incorporated in the ground plane under the feed lines and the coupled lines of a bandpass filter to improve separately the stopband and passband performances.
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    The Effects of MIMO Antenna System Parameters and Carrier Frequency on Active Control Suppression of EM Fields
    (Společnost pro radioelektronické inženýrství, 2007-04) Mohammed, Abbas; Hult, Tommy
    In this paper we propose a new approach employing adaptive active control algorithms combined with a Multiple-Input Multiple-Output (MIMO) antenna system to suppress the electromagnetic field at a certain volume in space (e.g., at the human head). We will investigate the effects of the size and number of MIMO antenna elements on the system performance and test the algorithms at different carrier frequencies (e.g., GSM bands and UMTS).
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    Implementations of HVS Models in Digital Image Watermarking
    (Společnost pro radioelektronické inženýrství, 2007-04) Foris, Peter; Levicky, Dusan
    In the paper two possible implementations of Human Visual System (HVS) models in digital watermarking of still images are presented. The first method performs watermark embedding in transform domain of Discrete Cosine Transform (DCT) and the second method is based on Discrete Wavelet Transform (DWT). Both methods use HVS models to select perceptually significant transform coefficients and at the same time to determine the bounds of modification of selected coefficients in watermark embedding process. The HVS models in DCT and DWT domains consist of three parts which exploit various properties of human eye. The first part is the HVS model in DCT (DWT) domain based on three basic properties of human vision: frequency sensitivity, luminance sensitivity and masking effects. The second part is the HVS model based on Region of Interest (ROI). It is composed of contrast thresholds as a function of spatial frequency and eye\'s eccentricity. The third part is the HVS model based on noise visibility in an image and is described by so called Noise Visibility Function (NVF). Watermark detection is performed without use of original image and watermarks have a form of real number sequences with normal distribution zero mean and unit variance. The robustness of presented perceptual watermarking methods against various types of attacks is also briefly discussed.