Reverse Unfolding of Petri Nets and its Application in Program Data Race Detection

The unfolding technique can partially alleviate the state explosion in Petri nets through branching processes. However, all states of a system are still contained in its unfolding net. To deal with some practical problems, only the coverability determination of a specific state is needed. In view of this, reducing the scale of the unfolding net is feasible. This study proposes a target-oriented reverse unfolding algorithm for the coverability determination of 1-safe Petri nets, which combines a heuristic technique to reduce the scale of unfolding nets, thereby improving the efficiency of coverability determination. Furthermore, the reverse unfolding is applied to the formal verification of concurrent programs, and their data race detection is converted into the coverability determination of a specific state in 1-safe Petri nets. The experiment compares the efficiency between forward nfolding and reverse unfolding in the coverability determination of a Petri net. The results show that when the Petri net has more forward branches than backward branches, reverse unfolding is more efficient than forward unfolding. Finally, the key factors influencing the efficiency of reverse unfolding are analyzed.     

轴承内环感应加热拆卸器的研制及其有限元仿真

在理论分析的基础上,研制了基于工频感应加热技术的轴承内环感应拆卸器。通过ANSYS有限元软件,构建了感应拆卸器的基本模型。对感应加热过程中拆卸器内的电磁场和工件内的温度场进行了计算机仿真,得出了磁场强度和温度的分布规律及温度对时间历程的变化规律。仿真结果不仅证明了涡流集肤效应的存在,而且通过对拆卸器磁场和温度场的有限元耦合分析,获得了轴承内环拆卸器的设计参数。通过对轴承内环感应加热温度的测试实验,证明了计算机仿真的正确性。     

新型稀土混凝剂在处理黄河水中的应用

介绍了一种新型稀土絮凝剂.通过该絮凝剂在黄河水处理中的应用研究,并且与聚合氯化铝絮凝剂（PAC）、聚合硫酸铁（PFC）进行了比较,结果表明：PRC混凝剂具有絮体生成速率快、絮体大而密实、污泥体积小、沉降速度大、浊度去除率高等显著优点,是一种高效水处理剂.     

Bandwidth improvement of rat‐race couplers having left‐handed transmission‐line sections

A novel broadband rat‐race coupler has been investigated. The coupler utilizes an artificial left‐handed transmission line section for broadband phase response realization. Moreover, a narrowband model of left‐handed section has been shown to prove the couplers equivalent circuit at the center frequency. To broaden the operational bandwidth multisection quarter‐wave transformers have been proposed. The exemplary rat‐race coupler with two‐section impedance transformers has been designed and manufactured. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:341–347, 2014.     

Data race avoidance and replay scheme for developing and debugging parallel programs on distributed shared memory systems

Distributed shared memory (DSM) allows parallel programs to run on distributed computers by simulating a global virtual shared memory, but data racing bugs may easily occur when the threads of a multi-threaded process concurrently access the physically distributed memory. Earlier tools to help programmers locate data racing bugs in non-DSM parallel programs are not easily applied to DSM systems. This study presents the data race avoidance and replay scheme (DRARS) to assist debugging parallel programs on DSM or multi-core systems. DRARS is a novel tool which controls the consistency protocol of the target program, automatically preventing a large class of data racing bugs when the parallel program is subsequently run, obviating much of the need for manual debugging. For data racing bugs that cannot be avoided automatically, DRARS performs a deterministic replay-type function on DSM systems, faithfully reproducing the behavior of the parallel program during run time. Because one class of data racing bugs has already been eliminated, the remaining manual debugging task is greatly simplified. Unlike previous debugging methods, DRARS does not require that the parallel program be written in a specific style or programming language. Moreover, DRARS can be implemented in most consistency protocols. In this paper, DRARS is realized and verified in real experiments using the eager release consistency protocol on a DSM system with various applications.     

类Unix文件系统中TOCTTOU缺陷的静态分析方法

文件系统中的TOCTTOU缺陷是类Unix操作系统面临的一个严重安全问题,现有的静态检测方法具有很高的误报率.原因有2点:一是对导致TOCTTOU缺陷的函数对缺乏精确定义和分析;二是分析过程过度抽象,忽略了很多重要的程序信息.因此,首先对TOCTTOU缺陷进行了分类,并系统分析了C标准库中可以导致TOCTTOU缺陷的函...     

星形套闭塞模锻光塑性模拟研究

利用光塑性方法以聚碳酸脂为模拟材料研究轿车等速万向节星形套闭塞模锻成形过程，获得星形套闭塞模锻成形过程的三维光塑性应变分布，提出其应变分布特征，并对典型截面应变进行计算分析，研究结果可实际钢质星形套闭塞模锻工艺和模具设计起一定的指导作用。     

The welfare effects of occupational segregation by gender and race: Differences across US Regions

Using tools rooted in welfare economics, this paper explores the social welfare loss that arises from occupational segregation by gender and race in the US at the regional level. After controlling for characteristics, the losses are lower in the Northeast than in the South and West according to a wide range of indicators, including those that take into account the relative size of disadvantaged groups (incidence), the magnitude of their losses (intensity), and the inequality among those groups. The West has the highest (conditional) losses, although the intensity of the phenomenon barely differs from that in the South or Midwest.     

Analyzing CRA Lending During the Tsunami in Subprime Lending and Foreclosure in the Philadelphia MSA

Until the onset of the financial meltdown, independent mortgage companies (IMCs) had begun to originate an increasing share of subprime loans, a high proportion of which went into foreclosure. In this study, we compare and contrast the characteristics of neighborhoods that have high proportions of loans made by Community Reinvestment Act (CRA)-regulated institutions with those that have high proportions made by IMCs. We find that IMC-dominated neighborhoods are characterized by high proportions of Blacks/African-Americans, low average family incomes and low nominal average family income increases, an old housing stock with inexpensive homes, a low homeownership rate, high vacancy rates, and a high proportion of high-cost loans. Based on t-tests and regression analyses, we find that areas dominated by IMCs are different from neighborhoods dominated by CRA Lenders and that the proportion of people of color helps explain foreclosure rates.     

Thrust bearing groove race defect measurement by wavelet decomposition of pre-processed vibration signal

Nature of vibration signal from a ball bearing system reveals location of fault and its severity. A proper signal processing technique is required to extract relevant information from a vibration signal. In this work measurement of groove race defect width in thrust bearing is presented by processing vibration signal using wavelet based technique. In the first step, pre-processing of vibration signal is done by multiplying the signal amplitude with its own absolute values. It helps to overcome the problem of detection of weak burst in normal vibration signal retaining sign of the original signal. In the second step, Symlet5 wavelet based decomposition is applied to the pre-processed signal to measure the size of seeded defect in outer groove race of thrust bearing. The decomposition based on Symlet wavelet is preferred because it reduces the ambiguity in detecting the entry point and exit point of the defect as it is having linear phase in nature. Measurement has been done for the groove defect width over the range of 0.4399–1.4854 mm. Measurement of defect has been also verified using image examination. Maximum deviation in result has been found in the cases which have minimum axial load (48 N) for every size of defect. With increase in axial load to 73 N and further to 98 N the bearing system gets properly stressed, which increases the accuracy of measurement. With further increase in axial load to 126 N and above, it has been observed that the burst disappears due to prevailing over-stressed condition of the loading disk and additional stiffness and damping of the flexible shaft at increased load.