分布式大规模监控视频存储系统THNVR

通过分析网络视频监控应用中的存储需求特点,提出了一种采用低成本SATA硬盘的高性能存储解决方案。该方案使用定长文件,并将结构化与非结构化数据分别存储和检索,彻底克服了传统解决方案中磁盘碎片导致存储性能下降的问题。该方案还采用了自适应的缓冲技术,对磁盘访问进行了有效的规整和调度,充分利用了磁盘的写入带宽。此外,该方案还实现了容错、扩展等重要功能。性能分析显示,该方案在普通计算机和SATA磁盘上能够同时记录256路D1或512路CIF视频数据流。     

面向安卓自动化测试工具综合评估

自动化测试工具是安卓应用质量保障的主要手段.随着安卓版本多样性、底层硬件差异性(碎片化)以及逻辑复杂性增加,自动化测试迎来新的挑战.为解决这些问题,近年来,业界开发出大量自动化测试工具.但是现有工具数量多,并且测试重点多样,测试人员选择工具时存在一定的困扰.为帮助测试人员选择最佳测试工具,实现对自动化测试工具的统一评估,提出了面向安卓自动化测试工具多特征综合评估方法(comprehensiveevaluation of Android automated testing, CEAT),并将其实现为便于测试人员使用的平台. CEAT在引入测试领域广泛接受的3个评估指标,即代码覆盖率、异常检出率、融合多版本兼容度得分的基础上,进一步基于变异测试的思想引入变异杀死率,并从用户体验出发引入UI控件覆盖率.以上5个指标构成CEAT整个体系,从而实现安卓自动化测试工具的综合多维评估.为验证CEAT的效果,生成了1 089个变异应用的待测应用集,在包含6个移动设备的真机集群中部署实验,对5个自动化测试工具适配并执行5 040次测试任务.最终结果表明:i) 5个指标从不同角度对自动化测试工具进行评估,...     

流媒体视频存储服务器设计与研究

详细分析了在视频监控系统中流媒体视频存储服务器的作用和功能,针对传统的流媒体定时长存储方式的不足提出了"固定空间存储"的新策略.该存储策略将总空间初始化为多个固定大小的数据文件,每个数据文件中存储的流媒体时长可能是不相同的.针对新存储策略下出现的"1秒尾巴","事件尾巴"等新问题,提出了解决方案."固定空间存储"策略虽然增加了索引的复杂度,但是有效避免了磁盘碎片的产生,对于改善流媒体视频存储服务器性能具有重要作用.     

基于关系分解的外包数据库机密性保护方案研究

针对外包数据库服务中数据库服务提供商本身并不完全可信等潜在威胁引起的隐私数据机密性威胁,提出了一种基于关系分解的外包关系数据库机密性保护方案。设计了考虑查询类型和属性所处查询位置的属性分解代价计算策略,并以此计算策略为评价标准,给出了求解最小属性分解代价方案的算法。然后,对各数据切片进行了准标识符的抗共谋攻击处理,并进行了性能测试。实验对比结果表明该方案对不同的应用查询类型有较好的适应性,有效降低了关系分解代价,提高了查询执行效率。     

Influence of Matrix Properties on Fragmentation Test

Physical aging was used to vary the mechanical properties of model single fiber composites without changing the chemistry at the interface in order to study how property changes affect the measurement of interfacial adhesion by the fragmentation test. The properties of epoxy matrix/AS4 single fiber composites driven to full cure (T_g = 166°C) are altered by annealing below T_g. Neat resin samples with identical thermal histories are tested. All aged panels show roughly the same embrittlement with aging characterized by an average 30% decrease in tensile failure strain and 7.3% increase in compressive yield relative to quenched samples. Fragmentation results indicated no change between aged and quenched samples. Results are discussed in terms of micromechanics models for the fragmentation test. Strain at fragmentation increased with aging. This was related to the residual stress state in the model composite and the possibility of the zero stress state of the single fiber composites increasing with thermal annealing.     

On the probabilistic-deterministic transition involved in a fragmentation process of brittle materials

Dynamic loadings produce high stress waves leading to the fragmentation of brittle materials such as ceramics, concrete, glass and rocks. The main mechanism used to explain the change of the number of fragments with stress rate is a shielding phenomenon. However, under quasi-static loading conditions, a weakest link hypothesis may be applicable. Therefore, depending on the local strain or stress rate, different fragmentation regimes are observed. One regime corresponds to single fragmentation for which a probabilistic approach is needed. Conversely, the multiple fragmentation regime may be described by a deterministic approach. The transition between the two fragmentation regimes is discussed for high performance concrete, glass and SiC ceramics.     

Scaling of energy dissipation in crushing and fragmentation: a fractal and statistical analysis based on particle size distribution

An extensive experimental investigation on concrete specimens under crushing and fragmentation over a large scale range (1:10) – exploring even very small specimen dimensions (1 cm) – was carried out to evaluate the influence of fragment size distribution on energy density dissipation and related size effect. To obtain a statistically significant fragment production as well as the total energy dissipated in a given specimen, the experimental procedure was unusually carried out up to a strain of approximately –95%, practically corresponding to the initial fragment compaction between the loading platens. The experimental fragment analysis suggests a fractal law for the distribution in particle size; this simply means that fragments derived from a given specimen appear geometrically self-similar at each observation scale. In addition, clear size effects on dissipated energy density are experimentally observed. Fractal concepts permit to quantify the correlation between fragment size distribution and size effect on dissipated energy density, the latter being governed by the total surface area of produced fragments. The experimental results agree with the proposed multi-scale interpretation satisfactorily.     

沱茶中茶多酚的分析与鉴定

用索氏提取器以三氯甲烷为萃取剂,在95 ℃下从沱茶中提取茶多酚。用旋转蒸发器将滤液浓缩,有机相中加入三氯甲烷(V(三氯甲烷):V(浓缩液)=3:1)将咖啡因萃取分离、去除。水相中加入乙酸乙脂(V(乙酸乙酯):V(水)=3:1)将沱茶提取物萃取分离。以硅胶G作填充剂,以乙酸乙酯(V(乙酸乙酯):V(乙醚)=4:1)为洗脱剂进行柱层析。用傅里立变换-红外光谱法(FT/IR)测定沱茶提取物待测组分的红外光谱图,提供官能团的有关信息。确定待测组分的可能结构;应用气相色谱-质谱法(GC/MS)对其进行分析与鉴定,由电子电离源质谱(EI/MS)获得待测组分的质谱图和相关数据,进而对子离子裂解途径和特征离子进行辅助解析,确证待测组分为茶多酚。为开发利用沱茶提供了科学依据。     

Tandem mass spectrometry in the study of fatty acids,bile acids,and steroids

Over the last 50 years, the mass spectrometry of lipids has evolved to become one of the most mature techniques in biomolecule analysis. Many volatile and non-polar lipids are directly amenable to analysis by gas-chromatography-mass spectrometry (GC-MS), a technique that combines the unsurpassed separation properties of gas-chromatography with the sensitivity and selectivity of electron ionization mass spectrometry. Less volatile and/or thermally labile lipids can be analyzed by GC-MS, following appropriate sample derivatization. However, many complex lipids are not readily analyzed by GC-MS, and it is these molecules that are the subject of the current review. Since the early 1970s, there have been three outstanding developments in mass spectrometry that are particularly appropriate in lipid analysis; i.e., the introduction of (i) fast atom bombardment (FAB); (ii) electrospray (ES); and (iii) tandem mass spectrometry (MS/MS). The FAB and ES ionization techniques will be discussed in relation to MS/MS, and examples of their application in biochemical studies will be presented. The review will concentrate on the analysis of fatty acids, bile acids, steroid conjugates, and neutral steroids.     

甾醇及其衍生物的质谱学规律（Ⅲ）5α－饱和甾核－甾醇乙酸酯、4－甲基－5α－饱和甾核－甾醇乙酸酯和△~4－3－甾酮的质谱特征

在研究海洋甾类化合物的过程中，本文总结了５α－饱和甾核－甾醇乙酸酯、４－甲基－５α－饱和甾核－甾醇乙酸酯和△４－３－甾酮的质谱中最重要碎片峰的裂解机理和这些甾美化合物的质谱学规律。