Abstract Models of Storage

This note is a historical survey of Christopher Strachey's influence on the development of semantic models of assignment and storage management in procedural languages.     

东非铬钒钙铝榴石（察沃石）宝石的矿物学和地球化学研究现状

东非（包括肯尼亚、坦桑尼亚和马达加斯加）铬钒钙铝榴石（察沃石）均赋存于新元古代莫桑比克变质带的钙质硅酸盐石墨片麻岩中。矿物学研究表明,东非察沃石为宝石级钒（±铬）钙铝榴石,以ω（V2O3）≈0.20%或ω（Cr2O3）≈0.30%为分界线可划分为钒钙铝榴石、铬钙铝榴石和铬钒钙铝榴石3类,其中以钒钙铝榴石为主。东非察沃石的晶体化学式为（Ca2.792～3.005Fe0～0.013 Mn0.008～0.080 Mg0.022～0.078）2.948～3.110（Al1.787～1.968Ti0.005～0.028Cr0.001～0.072Fe0～0.080V0.005～0.163）1.890～2.052[Al0～0.288Si2.712～3.017O12],可简写成Ca3（Al,Cr,Fe,V）2[SiO4]3;其端员组分为Grs87.61～96.79Gld0.16～5.66Uvr0.02～2.46Pyr0.73～2.68Sps0.28~2.75Adr0.00～2.71Alm0.00～0.43,表明它由钙铝榴石（87.61%～96.79%）、钙钒榴石（0.16%～5.66%）和钙铬榴石（0.02%～2.46%）组成。以往研究表明,东非不同国家所产的察沃石之间V/Cr质量分数比值存在明显差异,它们的化学成分是可变的,但同一矿床的V/Cr质量分数比值通常是不变的;并且它们还具有3组一致的δ＾18 O值,依次为9.5‰~11.0‰、11.6‰～14.8‰和15.5‰～21.1‰,利用O同位素与V-Cr-Mn微量元素含量相结合的方法,可鉴别其地质和地理来源。     

中国各产地软玉的化学成分分析

软玉的主要化学成分是SiO2,MgO和CaO,类质同象替代使其还含有少量的FeO,K2O,Na2O和Al2O3等杂质成分.通过对中国各产地软玉晶体化学式的计算及化学成分之间相互关系的分析,发现其平均化学成分与透闪石的理论值接近,说明了软玉的主要矿物组成是透闪石.化学成分在一定程度上可以反映软玉的产地及品种特征,尤其是Fe2 的类质同象替代使w(FeO)成为区分软玉产地和品种的重要标志.     

基于IT技术的现代机械设计方法

通过对优化设计、并行设计、网络协同设计等先进方法的介绍，结合实例说明，随着IT技术的不断发展及其各项功能的不断完善，为机械产品设计的异地合作与协同提供了广阔的平台，以快速、高效地满足消费者个性化的要求。     

Exploiting the performance gains of modern disk drives by enhancing data locality

Due to the widening performance gap between RAM and disk drives, a large number of I/O optimization methods have been proposed and designed to alleviate the impact of this gap. One of the most effective approaches of improving disk access performance is enhancing data locality. This is because the method could increase the hit ratio of disk cache and reduce the seek time and rotational latency. Disk drives have experienced dramatic development since the first disk drive was announced in 1956. This paper investigates some important characteristics of modern disk drives. Based on the characteristics and the observation that data access on disk drives is highly skewed, the frequently accessed data blocks and the correlated data blocks are clustered into objects and moved to the outer zones of a modern disk drive. The idea attempts to enhance spatial locality, improve the efficiency of aggressive sequential prefetch, and take advantage of Zoned Bit Recording (ZBR). An experimental simulation is employed to investigate the performance gains generated by the enhanced data locality. The performance gains are analyzed by breaking down the disk access time into seek time, rotational latency, data transfer time, and hit ratio of the disk cache. Experimental results provide useful insights into the performance behaviours of a modern disk drive with enhanced data locality.     

Reducing Off-Chip Memory Access via Stream-Conscious Tiling on Multimedia Applications

The iteration space of a loop nest is the set of all loop iterations bounded by the loop limits. Tiling the iteration space can effectively exploit the available parallelism, which is essential to multiprocessor compiling and pipelined architecture design. Another improvement brought by tiling is the better data locality that can dramatically reduce memory access and, consequently, the relevant memory access energy consumptions. However, previous studies on tiling were based on the data dependence, thus arrays without dependencies such as input arrays (data streams) were not considered. In this paper, we extend the tiling exploration to also accommodate those dependence-free arrays, and propose a stream-conscious tiling scheme for off-chip memory access optimization. We show that input arrays are as important, if not more, as the arrays with data dependencies when the focus is on memory access optimization instead of parallelism extraction. Our approach is verified on TI’s low power C55X DSP with popular multimedia applications, exhibiting off-chip memory access reduction by 67% on average over the traditional iteration space tiling.     

系统极零点与频率特性的关系

采用定量计算的方法,分析了单极点、单零点以及共轭极点、共轭零点对系统频率响应的影响.分析表明单极、零点时以及共轭极点、共轭零点位于特定区域时,系统频率响应的幅频峰值,谷值的频率与极、零点位置所在频率严格一致.通过对多极、零点系统幅频响应的分析得出结论,出现幅频峰值,谷值的频率相对极、零点位置所在频率可能有偏移,但是仍然可以说:极点所在频率位置附近频率响应幅度出现峰值,零点所在频率位置附近频率响应幅度出现谷点.     

基于Gabor和核监督局部保持投影的单样本人脸识别算法

针对目前主流人脸识别算法,在单样本条件下,当性能严重下降根本无法工作时,提出了一种结合Gabor和核监督局部保持投影的单样本人脸识别算法.选取数据库中中性表情的近正面人脸图像作为训练样本,通过几何变换产生15幅虚拟样本,对每幅样本图像提取Gabor特征,采用核监督局部保持投影方法进行特征提取,欧氏距离最近邻分类器进行分类.根据ORL数据库、Yale数据库和FERET数据库上的实验结果表明,核监督局部保持投影(GKSLPP)算法具有较好的识别效果.     

二进制翻译后端指令分级索引策略

随着硬件平台的多元化,软件兼容性问题日益突出,二进制翻译技术是解决软件兼容性问题的重要手段.鉴于二进制翻译系统大部分执行时间消耗在后端指令的查找和执行过程中,高效的指令索引策略可以减少系统的指令查找开销,提高系统的整体效率.在对二进制翻译系统后端指令局部性特征进行统计分析的基础上,设计了一种能充分挖掘现代计算机系统硬件性能的二进制翻译指令分级索引策略.该策略结合二进制翻译系统后端指令特殊的局部性特征,使用针对性的替换算法对后端指令进行缓存,降低了系统的指令查找开销.在引入了LIIS索引策略后,开源二进制翻译系统QEMU的后端指令查找时间减少了70％,整个系统执行效率提高了15％.