Entropy-based optimization of wavelet spatial filters

A new class of spatial filters for surface electromyographic (EMG) signal detection is proposed. These filters are based on the 2-D spatial wavelet decomposition of the surface EMG recorded with a grid of electrodes and inverse transformation after zeroing a subset of the transformation coefficients. The filter transfer function depends on the selected mother wavelet in the two spatial directions. Wavelet parameterization is proposed with the aim of signal-based optimization of the transfer function of the spatial filter. The optimization criterion was the minimization of the entropy of the time samples of the output signal. The optimized spatial filter is linear and space invariant. In simulated and experimental recordings, the optimized wavelet filter showed increased selectivity with respect to previously proposed filters. For example, in simulation, the ratio between the peak-to-peak amplitude of action potentials generated by motor units 20 degrees apart in the transversal direction was 8.58% (with monopolar recording), 2.47% (double differential), 2.59% (normal double differential), and 0.47% (optimized wavelet filter). In experimental recordings, the duration of the detected action potentials decreased from (mean +/- SD) 6.9 +/- 0.3 ms (monopolar recording), to 4.5 +/- 0.2 ms (normal double differential), 3.7 +/- 0.2 (double differential), and 3.0 +/- 0.1 ms (optimized wavelet filter). In conclusion, the new class of spatial filters with the proposed signal-based optimization of the transfer function allows better discrimination of individual motor unit activities in surface EMG recordings than it was previously possible.     

Linear optimization in synthesis of nonlinear spatial filters

Generally, the synthesis of coherent spatial filters is restricted to the linear region of the transfer characteristic of a photographic film. However, a technique of synthesizing a nonlinear spatial filter such that the signal detection may be optimum will be described. In this paper, a generalized linear optimization technique is formulated. The application of this optimization technique toward a simple nonlinear spatial filter is demonstrated, and the extension of this optimization technique for a more complicated nonlinear spatial filter is also given. The signal detection by nonlinear optimum spatial filtering is analyzed. Finally, it is concluded that, instead of restricting the spatial-filter recording to the linear region of the transfer characteristic of the photographic film, an optimum nonlinear spatial filter may be achieved.     

Combined and iterative form of spatial and temporal error concealment for video signals

Video transmission over unreliable channels may suffer from the data loss or corruption. To facilitate the transmission, video content is compressed to save the bandwidth. The compression algorithms remove the redundancies in the video signal, meanwhile increasing the dependencies among symbols in the compressed bit-stream. Thus, when errors occur, they may propagate in both space and time. Among various error control techniques, error concealment (EC) is an effective method that is performed at the decoder to mitigate the influence of errors on the quality of reconstructed images. In this paper, a joint spatial and temporal EC algorithm (JSTEC) is presented. First, several existing temporal EC algorithms are combined in an appropriate order. Then, the spatial correlation in the video is exploited in an iterative form to improve the performance of the temporal EC. Experimental results show that JSTEC performs better both in peak signal-to-noise ratio and subjective quality of images than the existing algorithms.     

Complex spatial filters for image deconvolution

The history and principles of image distortion correction by means of holographic spatial filtering are reviewed. Both predetection and postdetection filtering are considered. These and other principle applications of complex spatial filtering are assessed. The major problem areas are discussed, along with possible solutions.     

Method for improving ladder bulk acoustic wave filters rejection

This paper address design guidelines for improving the rejection of ladder bulk acoustic wave filters. An overview of the bulk acoustic wave filters technology enables to outcome the principal features of ladder filters. The lack of out-of-band rejection is currently an important weakness of this topology. The design technique presented enables to improve bulk acoustic wave ladder filters rejection by using their input/output bonding wires. Finally, the technique is used for design and fabrication of a bulk acoustic wave ladder filter for application in W-CDMA reception (2.11–2.17 GHz) front-ends. The filter measurement results show a significant improvement on the filter rejection at the transmission band (from ?19 to 34 dB) and on the return loss (from ?10 to ?16 dB) without considerable modification of filter insertion loss and selectivity.     

Evolutionary-programming-based optimization of reduced-rank adaptive filters for reference generation in active power filters

We introduce an evolutionary-programming-based method for designing robust and computationally efficient adaptive bandpass filters. These predictive filters are optimized for generating current references in active power filters (APFs). The accuracy (phase/amplitude) of the reference current is crucial in current-injection-type systems, because it directly affects the harmonics reduction ability of the APF. Our digital filtering approach has the following advantages: selective bandpass response, efficient attenuation of specific harmonic components, capability to handle typical frequency alteration, small number of multiplications, and structural simplicity. In addition, practically no prior knowledge of the electricity distribution network and its loading characteristics is needed for designing the current reference generator. In an illustrative example, the total harmonic distortion of an artificial current waveform was reduced from 36.7% to less than 3.7% within the line frequency range 49-51 Hz. The proposed scheme is a combination of the hard-computing (HC)-type multiplicative general parameter method and evolutionary programming that, on the other hand, is a constituent of soft computing (SC). Such open-minded fusion thinking is emerging among researchers and engineers, and it can potentially lead to efficient combinations of HC and SC methodologies*both on the algorithm level and on the system level.     

Spatio-spectral filters for improving the classification of single trial EEG

Data recorded in electroencephalogram (EEG)-based brain-computer interface experiments is generally very noisy, non-stationary, and contaminated with artifacts that can deteriorate discrimination/classification methods. In this paper, we extend the common spatial pattern (CSP) algorithm with the aim to alleviate these adverse effects. In particular, we suggest an extension of CSP to the state space, which utilizes the method of time delay embedding. As we will show, this allows for individually tuned frequency filters at each electrode position and, thus, yields an improved and more robust machine learning procedure. The advantages of the proposed method over the original CSP method are verified in terms of an improved information transfer rate (bits per trial) on a set of EEG-recordings from experiments of imagined limb movements.     

融合MODIS与Landsat数据生成高时间分辨率Landsat数据

遥感数据时空融合技术是一种低空间分辨率影像与中空间分辨率影像在时间域和空间域的融合技术,利用遥感数据时空融合技术获得的融合影像既具备低空间分辨率影像的高时间分辨率特征,又具备中空间分辨率影像的高空间分辨率特征.提出了一种新的遥感数据时空融合方法(STDFA).该方法从时序MODIS数据中提取地物的时间变化信息,结合早期Landsat-TM影像的纹理信息,融合出具有MODIS时间分辨率和TM空间分辨率的影像.以江苏省南京市江宁区为研究区,以Landsat红波段和近红外波段为融合波段,对该方法进行了测试.结果显示,该方法能够产生高精度的中空间分辨率影像,融合影像与真实影像间的相关系数达到0.939.融合影像计算的NDVI与真实中空间分辨率影像计算的NDVI间的相关性达到0.938.     

Synergizing spatial and temporal texture

Temporal texture accounts for a large proportion of motion commonly experienced in the visual world. Current temporal texture techniques extract primarily motion-based features for recognition. We propose a representation where both the spatial and the temporal aspects of texture are coupled together. Such a representation has the advantages of improving efficiency as well as retaining both spatial and temporal semantics. Flow measurements form the basis of our representation. The magnitudes and directions of the normal flow are mapped as spatiotemporal textures. These textures are then aggregated over time and are subsequently analyzed by classical texture analysis tools. Such aggregation traces the history of a motion which can be useful in the understanding of motion types. By providing a spatiotemporal analysis, our approach gains several advantages over previous implementations. The strength of our approach was demonstrated in a series of experiments, including classification and comparisons with other algorithms.     

激光与物质相互作用的时空分辩研究

本文报道在激光与靶互作用过程中所测量的发光光谱、发光温度和生成物对激光的反作用(吸收和散射等)参数,同时,还报道激光与某些物质互作用过程的时空分辨和钻孔效应的测量结果。     

Curved waveguides for spatial mode filters in semiconductor lasers

Curved waveguides are used as a lateral spatial mode filter to increase the threshold for the first-order mode in high-power narrow stripe semiconductor lasers. Beam propagation analysis is used to determine optimal waveguide geometries and radii of curvature to establish appropriate amounts of bend loss. Curved waveguide devices are fabricated and compared against conventional devices. Use of a curved waveguide increases the current level at which lateral beam instabilities occur from /spl sim/400 to /spl sim/700 mA with no decline in slope efficiency.     

Motion-compensated DCT temporal filters for efficient spatio-temporal scalable video coding

Although most of the proposals for implementing motion-compensated temporal filtering (MCTF) schemes are based on the wavelet transform, in this paper, we propose an MCTF framework based on the discrete cosine transform (DCT). Using DCT decimation and interpolation, several temporal decomposition structures named motion-compensated DCT temporal filters (MCDCT-TF) are introduced. These structures are able to employ filters of any length with particular emphasis on 5/3 DCT and 7/4 DCT. The proposed MCDCT-TF and the two-dimensional (2D) DCT decimation technique are incorporated into H.264/AVC to provide spatio-temporal scalability. Compared with the current MCTF-based lifting schemes such as Haar, and 5/3 wavelet filters, simulation results show that the proposed MCDCT-TF utilizing longer tap DCT filters achieves a significant improvement in coding gain. The impact of odd/even group of frames, the decimation/interpolation ratios, and motion-compensated connectivity on the MCDCT-TF performance are also analyzed. Moreover, simulation results show that the performance of the presented scalable video coding is close to the single layer H.264/AVC and is slightly inferior to the temporal scalability supported in JSVM, the state-of-the-art scalable video coding standard, that gets its gain from Hierarchical B-pictures. However, our spatio-temporal coding scheme outperforms the spatio-temporal supported in JSVM even if it uses hierarchical B-pictures to improve its gain.     

The performance of minimax spatial resampling filters for focussingwide-band arrays

The design and performance of linear shift-variant filters for coherent wideband processing are examined via spatial resampling. In particular, a minimax error criterion is used to obtain realizable resampling filters, and an approximate statistical analysis of wideband spatially resampled minimum variance spatial spectral estimation is presented. Simulation results indicate that spatial resampling provides a computationally efficient means of reducing the threshold observation time required to obtain high-resolution estimates of source location     

Parametric optimization of multichannel rejection filters

The number of channels of a multichannel rejection filter (MRF) has been optimized by the energy and probabilistic criteria. The matrix of MRF coefficients is defined. The paper includes analysis of the gain in signal detection effectiveness, in the presence of interference, as compared to the single-channel rejection filter.     

Reference frame modification techniques for temporal and spatial scalability

Compressed video is usually transmitted over channels which are not necessarily error free. Channel errors can result in a mismatch between the encoder and the decoder, and because of the predictive structures used in video coding, the errors will propagate both temporally and spatially. Consequently, the quality of the received video at the decoder may degrade significantly. In order to improve the quality of the received video, several error resilient methods have been proposed. In this paper, the introduced mismatch is reduced by modifying the prediction structure and forming a more robust reference frame. The proposed technique combines error robustness of previous Intra coded blocks, better prediction achieved using the previous reference frame, and exponential decay of error propagation caused by the leaky prediction. This technique was examined with the scalable extension of H.264/AVC. Furthermore, the technique was also used in combination with random Intra refresh and error resilience mode decision techniques to achieve better robustness. Simulation results show the effectiveness of our scheme, especially for medium and high motion sequences.     

真空空间滤波器的窗口畸变

利用横向剪切干涉法和轴向全息干涉法分别测量了处于大气压下和真空状态中的空间滤波器的窗口畸变;滤波器处于真空状态下,中心区域畸变量小于0.1λ,边缘最大的畸变量为0.41λ;分别利用全息复元法和数值计算法给出了这种畸变光束的焦体分布;计算了该窗口在不同功率密度的激光作用下的非线性畸变,它是高功率激光系统中的主要象差来源.     

Synthesis of spatial filters with Chebyshev characteristics

A spatial filtering technique using layered dielectrics for the reduction of antenna grating lobes or sidelobes is introduced and developed. The filters are used as a radome at the array face, and can be synthesized to have Chebyshev behavior in the spatial domain. Data are given for the design of two, three, and four layer filters with various spatial passband ranges and ripple levels.     

Low-voltage low-power Gm-C filters: a modified configuration for improving performance

In this paper, after addressing the effect of finite output impedance of Gm cells on the performance of Gm-C filters, a modified configuration suitable for low-voltage operation is presented. In the proposed architecture, to efficiently increase the output impedance, body-driven impedance boosting is employed. The circuit-level topology of Gm cells is modified in order to increase the output impedance with minimized power consumption. To show the effectiveness of the proposed scheme, a 0.9-V 5-th order Butterworth low-pass filter with 8 MHz cutoff frequency is designed and simulated in 90-nm CMOS technology. Employing the proposed technique, power consumption is reduced from 0.7 mW to 0.5 mW.     

Preprocessing and meta-classification for brain-computer interfaces

A brain-computer interface (BCI) is a system which allows direct translation of brain states into actions, bypassing the usual muscular pathways. A BCI system works by extracting user brain signals, applying machine learning algorithms to classify the user's brain state, and performing a computer-controlled action. Our goal is to improve brain state classification. Perhaps the most obvious way to improve classification performance is the selection of an advanced learning algorithm. However, it is now well known in the BCI community that careful selection of preprocessing steps is crucial to the success of any classification scheme. Furthermore, recent work indicates that combining the output of multiple classifiers (meta-classification) leads to improved classification rates relative to single classifiers (Dornhege et al., 2004). In this paper, we develop an automated approach which systematically analyzes the relative contributions of different preprocessing and meta-classification approaches. We apply this procedure to three data sets drawn from BCI Competition 2003 (Blankertz et al., 2004) and BCI Competition III (Blankertz et al., 2006), each of which exhibit very different characteristics. Our final classification results compare favorably with those from past BCI competitions. Additionally, we analyze the relative contributions of individual preprocessing and meta-classification choices and discuss which types of BCI data benefit most from specific algorithms.