Flexible tree-structured signal expansions using time-varyingwavelet packets

Addresses the problem of finding the best time-varying filter bank tree-structured representation for a signal. The tree is allowed to vary at regular intervals, and the spacing of these changes can be arbitrarily short. The question of how to choose tree-structured representations of signals based on filter banks is considered. Wavelets and their adaptive version, known as wavelet packets, represent one approach that is popular. Wavelet packets are subband trees where the tree is chosen to match the characteristics of the signal. Variations where the tree varies over time have been proposed as the double tree and the time-frequency tree algorithms. Time-variation adds a further level of adaptivity. In all of the approaches proposed so far, the tree must be either fixed for the whole duration of the signal or fixed for its dyadic subintervals. The solution that we propose, as it allows more flexible variation, is an advance on the wavelet packet algorithm, the double tree algorithm, and the recently proposed time-frequency tree algorithm. Our solution is based on casting it in a dynamic programming (DP) setting. Focusing on compression applications, we use a Lagrangian cost of distortion +λ×rate as the objective function and explain our algorithm in detail, pointing out its relation to existing approaches to the problem. We demonstrate that the new algorithm indeed searches a larger library of representations than previously possible and that overcoming the constraint of dyadic time segmentations gives a significant improvement in practice     

双极性步进电机细分驱动器的设计与实现

论述了一种双极性步进电动机驱动器的工作原理，该驱动器能较好地改善步进电动机的运行性能，具有实用性强，结构简单，成本低的优点。针对实际调试中出现的问题进行分析后，提出了对策；最后给出了试验结果。     

激光焊接超细基胎体金刚石薄壁钻

采用激光焊接超细预合金粉胎体，开发了新的薄壁钻产品，通过对与现有的产品工艺、性能测试以及实际使用分析对比，结果表明：激光焊接与普通钎焊相比结合强度提高2－3倍，克服了胎体脱落问题，胎体耐磨性提高了50％－120％，其中轴向磨损速率提高1．2倍；钻削速度提高30．4％，工矿适应性增加，使用寿命提高25％－108％。     

品种和加工方式对双低菜粕有效能和氨基酸有效性的影响_注

用精确饲喂技术评价了 3个品种的中国双低油菜和 1个加拿大卡诺拉的脱脂种籽和商品饼粕的能量和氨基酸的有效性。结果表明 ,4个脱脂种籽的氮校正真代谢能和氨基酸真消化率没有差异 (P >0 .0 5 ) ;而 4个商品饼粕的脱脂样品的氮校正真代谢能和氨基酸真消化率有极显著或显著差异。研究结果证实 ,不适当的加工方式不仅降低了氨基酸的有效性 ,而且影响家禽对能量的利用效率。     

Dislocation configurations in highT c oxide BiSrCaCuO

A study of dislocation configurations in superconducting oxide BiSrCaCuO has been made by transmission electron microscopy. Evidence was found for the presence of dislocation pairs composed of two parallel single dislocations holding together with the same Burgers vectors. The pair can further dissociate into partials, giving rise to a four-fold ribbon. Networks consisting of dislocation pairs were also observed. These phenomena are attributed to the possible ordering of strontium and calcium ions and the existence of some oxygen sheet of the Aurivillius type in the oxide crystal. Schemes to illustrate the configurations are suggested and discussed.     

T型薄壁管节点应力集中系数有限元分析

通过有限元的方法,分析了T型薄壁管节点受平面内弯矩作用下的疲劳行为,得到了应力最大值的位置和拟合出用于预测T型薄壁管节点受平面内弯矩作用下的应力集中系数的参数公式。     

Sensory Evaluation of Regina Freestone Peaches Treated with Low Doses of Gamma Radiation

regina freestone peaches from california were given low postharvest doses of gamma radiation (65-75 krads) and were compared with non-irradiated controls approximately one month after harvest. Practiced judges were used, with a technique of minimal cross-sensory interference, as an analytical tool to guide subsequent instrumental analysis. Strong differences were found in odor and components of taste not associated with sweetness. Lesser trends were noted for firmness and appearance. Untrained subjects also detected gross sensory differences.     

基于自组织神经网络的实时统计特征抽取方法

应用人工神经网络讨论统计了特征抽取的原理，提出了相应的抽取方法。该方法具有实时性，容错性，高数据压缩率和良好的特征分辨率。通过计算机仿真和桥梁索力状态的实例计算分析证实了该技术具有广泛的应用价值。     

Synthesis and characterization of block copolymers from D,L-lactide and poly(tetramethylene ether glycol)

The copolymer from D ,L -lactide and poly(tetramethyene ether glycol) (PTMG) was prepared in bulk with an isotributyl aluminum–water–phosphoric acid complex catalyst as the initiator and characterized by H-NMR, GPC, and DSC. The effects of the temperature and the amount of PTMG on the polymerization rate and the molecular weight of copolymers were studied. The behavior of the degradation and delivery rate of Levonorgestrel microspheres in vitro was observed. The results show that the degradation and the delivery rate can be controlled by adjusting the molar rate of hydrophilic and hydrophobic segments of the copolymer © 1995 John Wiley & Sons, Inc.