Tritium concentrations in precipitation in Shanghai

Tritium concentrations in precipitation can be used as a criterion to evaluate the tritium baseline of the environment. The tritium concentration in precipitation in Shanghai during 2014-2015 was determined. Values ranged from 0.68 ± 0.04 to 4.11 ± 0.39 Bq/L, and it showed a decreasing trend compared with historical data; however,the values were slightly higher than the natural background tritium level. Additionally, the tritium concentration shows a seasonal variation: It was higher in autumn and winter and lower in summer and spring. A comparison of concentrations in precipitation in Shanghai and around the Qinshan Nuclear Power Plant reveals no correlation,implying that the nuclear power plant operations may not affect the environment of Shanghai. Thus, the raised tritium concentrations in Shanghai might be due to the effects of monsoons, spring leak, raindrop, or other activities that generate tritium there. Those activities may include chemistry research that uses tritium as a tracer.     

基于节点1-邻居图相似性的社会网络匿名技术

利用传统的k匿名技术在社会网络中进行隐私保护时会存在聚类准则单一、图中数据信息利用不足等问题.针对该问题,提出了一种利用Kullback-Leibler (KL)散度衡量节点1-邻居图相似性的匿名技术(anonymization techniques for measuring the similarity of node 1-neighbor graph based on Kullback-Leibler divergence, SNKL).根据节点1-邻居图分布的相似性对原始图节点集进行划分,按照划分好的类进行图修改,使修改后的图满足k匿名,完成图的匿名发布.实验结果表明, SNKL方法与HIGA方法相比在聚类系数上的改变量平均降低了17.3%,同时生成的匿名图与原始图重要性节点重合度保持在95%以上.所提方法在有效保证隐私的基础上,可以显著的降低对原始图结构信息的改变.     

一种基于密度的分布式聚类方法

聚类是数据挖掘领域中的一种重要的数据分析方法.它根据数据间的相似度,将无标注数据划分为若干聚簇.CSDP是一种基于密度的聚类算法,当数据量较大或数据维数较高时,聚类的效率相对较低.为了提高聚类算法的效率,提出了一种基于密度的分布式聚类方法MRCSDP,利用MapReduce框架对实验数据进行聚类.该方法定义了独立计算单元和独立计算块的概念.首先,将数据拆分为若干数据块,构建独立计算单元和独立计算块,在集群中分配独立计算块的任务;然后进行分布式计算,得到数据块的局部密度,将局部密度合并得到全局密度,根据全局密度计算中心值,由全局密度和中心值得到每个数据块中候选聚簇中心;最后,从候选聚簇中心选举出最终的聚簇中心.MRCSDP在充分降低时间复杂度的基础上得到较好的聚类效果.实验结果表明,分布式环境下的聚类方法MRCSDP相对于CSDP更能快速、有效地处理大规模数据,并使各节点负载均衡.     

Keyword Query over Error-Tolerant Knowledge Bases

With more and more knowledge provided by WWW, querying and mining the knowledge bases have attracted much research attention. Among all the queries over knowledge bases, which are usually modelled as graphs, a keyword query is the most widely used one. Although the problem of keyword query over graphs has been deeply studied for years, knowledge bases, as special error-tolerant graphs, lead to the results of the traditional defined keyword queries out of users’ satisfaction. Thus, in this paper, we define a new keyword query, called confident r-clique, specific for knowledge bases based on the r-clique definition for keyword query on general graphs, which has been proved to be the best one. However, as we prove in the paper, finding the confident r-cliques is #P-hard. We propose a filtering-and-verification framework to improve the search efficiency. In the filtering phase, we develop the tightest upper bound of the confident r-clique, and design an index together with its search algorithm, which suits the large scale of knowledge bases well. In the verification phase, we develop an efficient sampling method to verify the final answers from the candidates remaining in the filtering phase. Extensive experiments demonstrate that the results derived from our new definition satisfy the users’ requirement better compared with the traditional r-clique definition, and our algorithms are efficient.     

经管类青年教师实践教学能力不足的原因及培养途径

经管类专业较之工科专业,投资小、回收期短、收益大,因而倍受高校管理者青睐,各校开设专业多、招生多,毕业生就业竞争剧烈。如何使我校学生在竞争中胜出,培养他们的实践能力显得尤为重要。而教书育人的教师自身的实践教学能力起到了至关重要的作用。如何提高教师的相关能力,本文对此提出了一些建设性的意见和建议。     

Performance analysis of adaptive receivers for DS/CDMA communication systems

Both intersymbol interference (ISI) and multiple-access interference (MAI) are the important issues in code division multiple access (CDMA) multiuser communication systems. The step size of the traditional least-mean-square (LMS) adaptive receivers must be substantially adjusted to overcome the effect due to different channel responses or different numbers of active users. The normalized-LMS (NLMS) algorithm can automatically manipulate the adjustment to avoid the problem just discussed. This paper proposes the symbol-based interference rejection filter with NLMS algorithm and derives both finite impulse response (FIR)- and infinite impulse response (IIR)-type algorithms. We also derive the optimal step sizes and minimum mean-square errors (MSEs) for both the FIR and IIR symbol-based receivers. The complexity of our proposed FIR receiver is lower than that of the conventional chip-based receivers. In addition, it is shown that the bit error rate performance of our proposed symbol-based receivers is superior to conventional one in the simulations. Simulations also show the correctness of our theoretical analysis of minimum MSE. Copyright © 2008 John Wiley & Sons, Ltd.     

Correlated imaging with partially coherent light for remote sensing

Based on the extended Huygens–Fresnel integral and the theory of coherence of light field, we have investigated the correlated imaging by using the transverse normalized second-order intensity fluctuation correlation function with partially coherent light radiation. The imaging for a reflected object with relative long distance is determined by the feature of speckle-to-speckle correlation. By using the correlation function, we study the effects of imaging distance, the sizes of object lens and reference lens, the source’s transverse coherent width and its transverse size on the quality of correlated imaging. Numerical results show that the parameters of imaging system and the properties of partially coherent light source have significant influences on the imaging resolution and visibility. For an object lens with large enough diameter, the resolution is determined by the transverse coherent width of light source. On the contrary, it depends on the aperture of object lens. The magnification of the system depends only on the propagation distance. This speckle-to-speckle correlated imaging with unbalanced arms have potential applications in remote sensing due to its unique features.     

A note on resource allocation scheduling with position-dependent workloads

In this note, single machine scheduling with concurrent resource allocation and position-dependent workloads is studied. The aim is to find jointly the optimal sequence and the optimal resource allocation. A bicriteria analysis of the problem is provided where the first criterion is to minimize the scheduling cost (i.e. makespan, total completion time, total absolute differences in completion times, total absolute differences in waiting times) and the second criterion is to minimize the total resource consumption cost. It is proved that four bicriteria problems can be solved efficiently.     

基于机器视觉的微型摆轮质量检测系统

摆轮在精密仪器设备中经常使用,其平整度与整个仪器的精密准确性密切相关.传统摆轮检测以人工为主,本文提出一种基于机器视觉的摆轮平整度检测系统,先校正摆轮图像,然后提取其亚像素边缘信息,并通过投影映射精确计算边界信息.系统支持连续采样计算,并以摆轮边缘的动态极差作为零件的合格标准.实验结果表明,该方法实时性好,准确率高,可以满足工业检测需求.     

超高效液相色谱串联质谱法快速测定生活饮用水中草铵膦、草甘膦及其代谢物氨甲基膦酸残留

目的建立了一种非衍生-超高效液相色谱-串联质谱快速检测生活饮用水中的草铵膦、草甘膦及其代谢物氨甲基膦酸残留的方法。方法以5 mmol/L的乙酸铵-氨水溶液(pH 12.0)和乙腈为流动相,梯度洗脱,Dikma Polyamino氨基柱(2.0 mm×150 mm,5μm)色谱分离,采用电喷雾离子源负离子模式多反应监测(MRM)进行质谱测定,采用外标法定量。结果草铵膦、草甘膦、氨甲基膦酸分别在2.5～100,5～200,5～200μg/L的浓度范围内线性关系良好,相关系数(r~2)均大于0.999。方法的检出限分别为1.0、2.0、2.0μg/L,定量限为2.5、5.0、5.0μg/L。草铵膦、草甘膦、氨甲基膦酸在3档加标水平下的回收率为93.6%～102%,相对标准偏差(relative standard deviation,RSD)为4.47%～7.15%。结论本方法的样品无需衍生,简便、准确可靠,可用于生活饮用水中草铵膦、草甘膦及其代谢物氨甲基膦酸残留的快速检测。