A fast computation method for time scale signal denoising

This paper presents a novel and fast scheme for signal denoising in the wavelet domain. It exploits the time scale structure of the wavelet coefficients by modeling them as superposition of simple atoms, whose spreading in the time scale plane formally is the solution of a couple of differential equations. In this paper, we will show how the numerical solution of such equations can be avoided leading to a speed up of the scale linking computation. This result is achieved through a suitable projection space of the wavelet local extrema, requiring just least squares and filtering operations. Intensive experimental results show the competitive performances of the proposed approach in terms of signal to noise ratio (SNR), visual quality and computing time.     

Visual analysis of particle bouncing and its effect on pressure drop in dilute phase pneumatic conveying

During the pneumatic conveying of plastic pellets, it has been observed that materials with similar physical characteristics may develop substantial difference in pressure drop, whose cause is not fully understood. This experimental study focused on the dynamic behavior of the particles during conveying and its influence on pressure drop.The bouncing of the particles during pneumatic conveying in dilute phase was visually analyzed by means of a high speed video camera. The experiments included two different plastic pellets of similar size and density but different modulus of elasticity. The conveying trials were carried out in a 0.052 m I.D. aluminum pipe conveying system approximately 35 m long. The loading was controlled by an airflow control valve and a variable speed drive rotary valve. For each material, a series of tests were performed creating a matrix of six solids rates for five different air velocities. During the conveying trials a high speed video camera was used to record the actual particle motion in a horizontal section with fully accelerated flow. The videos showed significant difference in bouncing between the soft and the hard pellets. The soft pellets showed very random and intense bouncing with strong rotation, which affected the rebound considerably. In fact, some particles bounced even backwards. On the other side, the hard pellets showed significantly less bouncing and rotation.In addition to the high speed videos, in each test the pressure drop was measured in the horizontal and vertical directions. As expected, a significant difference in pressure drop was recorded for the same conveying settings when using the different materials. The pressure drop showed a close relation to the bouncing of the particles, being much higher for the soft pellets.It can be concluded that the increased pressure drop, developed by the soft polyethylene pellets, is in part due to the multiple times the particles must be reaccelerated during their transit through the conveying system. Additionally, the reduction in the average particle velocity increases the drag force. All of this resulted in up to 3-fold increase in pressure drop across the conveying line compared to the hard polyethylene pellets that showed significantly less bouncing.     

Calculation of bulk modulus of titanium alloys by first principles electronic structure theory

A theoretical study of the electronic structure and binding energy of some hypothetical Ti-X alloys was carried out using a first-principles discrete variational cluster method. The formation energy of an alloying atom in solution of titanium was estimated based on such calculations, and the case of multi-constituent practical Ti alloys was considered in the dilute limit by a linear superimposition approach. The influences of alloying additions on the bulk modulus of the alloys were evaluated from the variation of the formation energy. The calculated moduli of the Ti alloys were found to vary linearly with the experimental values. This indicates that the present approach is appropriate for the simulation of modulus of titanium alloys. This revised version was published online in July 2006 with corrections to the Cover Date.     

关于Vallee-Poussin算子L_M~*逼近的阶

设LM*[0,2π]是周期为2π的函数所构成的Orlicz空间,Vn（f;x）为Vallee—Poussin算子。本文主要结果是: 若f∈LM*[0,2π],且M满足△2条件,则‖Vn（f;x）-f（x）‖M≤cMω(f;1/n1/2)M,其中CM是仅与M有关而与f和n无关的正常数,ω（f;δ）M是LM*空间的连续模。     

烧成制度和结合剂对刚玉-莫来石窑具性能的影响

以板状刚玉(粒度为3～1mm和≤1mm)、莫来石(粒度≤1mm)和αAl2O3微粉为原料,分别加入一定量的高岭土和硅胶-铝胶(其中Al、Si的物质的量比为3)作为结合剂,在燃油倒焰窑中经不同的烧成制度(分别加热至1000℃、1150℃、1200℃、1300℃和1500℃保温1h后,继续升温至1700℃烧成)烧制成刚玉-莫来石窑具材料,并对比研究了这两种结合剂在上述保温温度下处理1h后的相变化及其对刚玉-莫来石材料强度和抗热震性的影响。结果表明:硅胶-铝胶结合剂中莫来石的显著形成温度约为1150℃,远低于高岭土的1500℃;在相同的烧成制度下,以硅胶-铝胶为结合剂的刚玉-莫来石试样的常温抗折强度比以高岭土为结合剂的低,而其抗热震性优于以高岭土为结合剂的。     

高铝砖高温弯曲应力-应变关系

采用研制的高温弯曲应力-应变测试仪研究了Ⅰ等高铝砖DL-80、Ⅱ等高铝砖GL-75和Ⅲ等高铝砖GL-55在不同温度下的力学性能,包括应力-应变曲线、弹性模量、抗折强度和断裂时的最大变形量。结果表明:高铝砖在不同温度下的应力-应变关系可以分为弹性阶段、塑性阶段和粘滞流动阶段;在低、中温范围内,高铝砖的弹性模量和抗折强度随温度的上升而增加,到达某一转折温度后,随温度的上升而明显下降;3种高铝砖高温力学性能从高到低的排列顺序为:Ⅱ等>Ⅰ等>Ⅲ等。     

一种联合盲均衡算法

为克服数字基带信号在通过非屏蔽五类双绞线时产生的严重码间干扰(ISI),常采用自适应均衡技术来减小码间干扰,大大降低接收端信号的误码率.最小均方误差(LMS)算法能有效降低码间干扰,但需要训练序列,因此影响传输效率.基于判决引导的最小均方误差(DDLMS)算法不需要训练序列,但在眼图未睁开的情况下,可能出现误判,甚至引...     

基于回声状态网络的卫星信道在线盲均衡算法

针对非线性卫星信道,该文提出了两种基于回声状态网络(ESN)的在线盲均衡算法。利用ESN良好的非线性逼近能力,将发送信号的高阶统计量(HOS)代入ESN,结合常模算法(CMA)和多模算法(MMA)构造盲均衡的代价函数,并采用递归最小二乘(RLS)算法对ESN输出权值进行迭代寻优,实现了Volterra卫星信道下常模和多模信号的在线盲均衡。实验表明,该文算法可以有效降低非线性信道对发送信号产生的畸变,相较于传统的Volterra滤波方法,有更快的收敛速度和更低的均方误差值。     

汽车差壳铸件的铸造工艺探讨

汽车重要的零部件之一差速器壳铸件的壁厚差异大,导致差壳铸件局部极容易出现缩松、缩孔类铸造缺陷。本文通过对模数、补缩通道的运用,在实际生产过程中有效、快速地解决了铸件的缩松、缩孔问题。     

自编EXCEL程序调整混凝土用砂细度模数及颗粒级配

砂细度模数以及颗粒级配对混凝土和易性影响较大,砂级配不良易导致混凝土拌合物离析泌水。本文采用EX-CEL软件编制程序,以快速确定砂混合比例,使其混合后能符合Ⅱ区中砂的要求。