郑西客运专线铁路张茅隧道近饱和黄土体初期支护应力变形特征研究

 黄土的特性是其工程性质受含水量的影响很大,郑西客运专线铁路张茅隧道穿越含水量20%的近饱和黄土体,施工难度大。通过系统分析张茅隧道的施工地质条件,确定具有针对性的隧道开挖步序。针对施工需要快速封闭开挖面的特点,结合隧道断面规模特征,研究三维非接触变形观测方法,对开挖后初期支护的拱顶下沉和两壁收敛等特征变形量进行现场长期测试;结合布置在初期支护上的土压力盒与表面应变计的测试,对初期支护的土压力特征和表面接触力特征进行研究,获得近饱和黄土体在三台阶七步开挖条件下的变形和应力特征,总结出该类开挖施工方法下黄土隧道初期支护的极限变形量指标特征,为类似工程提供参考。     

激光二极管抽运Nd:YAG双薄片激光器

激光介质的热效应是高平均功率固体激光器面临的最大挑战,采用薄片激光介质是解决热效应的有效手段之一。当在抽运区尺寸远大于薄片厚度并且抽运光均匀分布的条件下,热流近似为沿厚度方向的一维分布,从而大大降低介质的热透镜效应和热致应力双折射。设计了四通光学耦合系统,通过提高二极管激光器阵列输出激光强度分布的均匀性,并优化经微柱透镜准直后光束的发散角,实现了抽运光的近平顶分布。采用两片1 mm厚的Nd∶YAG薄片激光介质,在两个峰值功率2000 W,占空比为15%的二极管激光器阵列抽运下,获得了峰值功率1440 W,平均功率216 W的准连续激光输出,光光转换效率达到36%,电光转换效率超过16%,在稳腔下测得的光束质量M2 因子约为12×13。     

多光谱遥感图像CCSDS动态码率控制近无损压缩

基于空间数据系统咨询委员会(CCSDS-123.0-B-1)推荐的多光谱图像无损压缩算法,提出了一种前向自适应调整量化步长的码率控制方法以实现定码率近无损压缩。介绍了CCSDS标准的预测方法,分析了Golomb-Rice编码的上界与下界的范围。通过分析预测误差均值与压缩比的对应关系,建立了均值与压缩比之间近似线性映射曲线。根据预测误差均值,前向自适应估计量化步长,初步控制Golomb-Rice码长。考虑到星载条件下多光谱图像码率控制策略,通过压缩比反馈微调量化步长,实现压缩码率的精确控制。最后总结了CCSDS多光谱近无损压缩码率控制流程。实验结果表明,k值(Golomb编码变量)的分布区域稳定,在4∶1压缩时,本文方法的峰值信噪比(PSNR)平均为60.42dB,比单谱段JPEG2000、差分JPEG-LS压缩等方法提高了5.51dB和2.89dB。实验显示本文方法码率控制准确,易于硬件实现,适合航天工程使用。     

Design nearly equiripple FIR filter by gradient scheme with dynamic step size

This paper proposes a gradient‐based algorithm with dynamic step size to design the nearly equiripple finite impulse response (FIR) filter, which iteratively updates the filter coefficient vector along the negative gradient direction of the peak approximation error. Moreover, besides the direction, the step size for updating is also an important parameter to be determined, and this paper proposes a dynamic method to find an appropriate step size at each round of iteration. Our results show that this dynamic step‐size scheme achieves a fast convergence rate, i.e. it can, i.e. it can design the nearly equiripple filters within a number of iterations. Specifically, by using the proposed method, the updating step size is relatively large at the early stage of iterations, which reduces the peak approximation error significantly. While, at the later stage of iterations, the updating step size becomes relatively small to approach to the equiripple solution as soon as possible. The extensive computer simulation demonstrates that the proposed algorithm outperforms the conventional algorithm in terms of the iteration number, the convergency and the performance. Copyright © 2013 John Wiley & Sons, Ltd.     

Control of Crystallographic Structure of Aluminum Nitride Films Prepared by Magnetron Sputtering

Aluminum nitride (AlN) films were prepared by using reactive magnetron (RMS). The substrate temperature (T_s) was varied from room temperature to 700°C, and RF power (P _w) from 100 to 250 W, and three different substrate materials (e.g. Si(100), Pt(111)/Si(100) and Al₂O₃(00·1)) were used. The mean free path of the species in the vacuum was controlled to be much shorter than the target-to-substrate distance, so that T_s and P _w have the equivalent effect in affecting the effective thermal energy of the species after landing on the substrate. With these conditions, the film structure was found to cover a broad range, varying from nearly amorphous (na-), polycrystalline (p-), (00·1) texture (t-) and epitaxial (e-) structure. The structural change is supposed to be governed the successive increase in the thermal energy of the species on the substrate. The use of substrate material having lattice matching with the AlN structure further assists the (00·1) preferential growth when the species are mobile enough at the settings of high T_s and P _w.     

Standard of nearly zero energy buildings in Germany

The European Union intends to reduce the energy consumption in the building sector. The European Directive 2010/31/EU requires the definition of national standards for nearly zero energy buildings. This article presents a research study supported as part of the research initiative “Zukunft Bau” of the Federal Ministry for the Environment, Nature Conservation, Building and Nuclear Safety for the definition of a nearly zero energy building standard for new buildings in Germany. First, the methodology is discussed, then the first results of a variant study on a model building are presented and discussed.     

Influence of particle-specific gravity and particle shape on the averaged axial velocity of nearly neutrally buoyant particles in horizontal pipes

This paper presents an experimental study on the velocities of single, nearly neutrally buoyant particles in water in horizontal flows. Particle specific gravity was found to have a strong effect on the particle velocity. The modified particle Froude number was found to be an effective parameter to reflect the effect of density. A force-balance model has been developed that includes the effects of particle specific gravity and particle shape.     

超高水材料阻隔式充填开采技术

超高水材料是一种水体积可达95%～97%,水灰比接近11∶1的采空区充填材料。结合超高水材料的基本性能,针对近水平煤层充填开采的难点,提出了阻隔式充填方法,通过对地表移动变形的观测表明,充填对控制地表下沉产生了决定性作用。该充填方式成功实施说明:超高水材料是性能良好的采空区充填材料;超高水材料阻隔式填开采技术是一种适合于近水平煤层的充填方法。     

定向钻进套铣打捞钻杆的设计

通过对常用定向钻进配套钻具打捞工艺的对比分析,明确了采用套铣打捞工艺处理煤矿井下近水平定向钻进中出现的塌孔、卡钻、埋钻等孔内事故的可行性与实用性。根据其工艺施工要求,结合煤矿井下近水平定向钻进系统配套钻具具体参数,研制了能够满足额定扭矩6000 N·m钻机使用要求的定向钻进套铣打捞钻杆。成庄矿的应用表明,采用套铣打捞工艺处理近水平定向钻进时孔内事故(塌孔、卡钻、埋钻等)可行性较强,且套铣打捞钻杆结构设计合理,能满足套铣打捞工艺的使用要求。     

序同态的N－连续性

以近似良紧性为基础，在ＬＦ拓扑空间上提出了序同态的Ｎ－连续性、分子网的Ｎ－收敛性及Ｎ－闭包算子等概念。系统地研究了这些概念的特性及其相互关系。借助于Ｎ－连续性概念，得到了连续和几乎连续序同态的一些特征。