Improved Distributed Algorithms for SCC Decomposition

We study and improve the OBF technique [Barnat, J. and P.Moravec, Parallel algorithms for finding SCCs in implicitly given graphs, in: Proceedings of the 5th International Workshop on Parallel and Distributed Methods in Verification (PDMC 2006), LNCS (2007)], which was used in distributed algorithms for the decomposition of a partitioned graph into its strongly connected components. In particular, we introduce a recursive variant of OBF and experimentally evaluate several different implementations of it that vary in the degree of parallelism. For the evaluation we used synthetic graphs with a few large components and graphs with many small components. We also experimented with graphs that arise as state spaces in real model checking applications. The experimental results are compared with that of other successful SCC decomposition techniques [Orzan, S., “On Distributed Verification and Verified Distribution,” Ph.D. thesis, Free University of Amsterdam (2004); Fleischer, L.K., B. Hendrickson and A. Pinar, On identifying strongly connected components in parallel, in: Parallel and Distributed Processing, IPDPS Workshops, Lecture Notes in Computer Science 1800, 2000, pp. 505–511].     

Symbolic PathFinder: integrating symbolic execution with model checking for Java bytecode analysis

Symbolic PathFinder (SPF) is a software analysis tool that combines symbolic execution with model checking for automated test case generation and error detection in Java bytecode programs. In SPF, programs are executed on symbolic inputs representing multiple concrete inputs and the values of program variables are represented by expressions over those symbolic inputs. Constraints over these expressions are generated from the analysis of different paths through the program. The constraints are solved with off-the-shelf solvers to determine path feasibility and to generate test inputs. Model checking is used to explore different symbolic program executions, to systematically handle aliasing in the input data structures, and to analyze the multithreading present in the code. SPF incorporates techniques for handling input data structures, strings, and native calls to external libraries, as well as for solving complex mathematical constraints. We describe the tool and its application at NASA, in academia, and in industry.     

Trains of thought on the tabletop: visualizing association of ideas improves creativity

According to the Search for Ideas in Associative Memory theory, ideas in a brainstorming session do not come one by one but rather in “trains of thought,” which are rapid accumulations of semantically related ideas. In order to visualize these trains of thought, we developed a brainwriting tabletop interface enabling users to link successive ideas together by means of graphical ropes. To test the effectiveness of this device, 48 participants (in groups of four) brainstormed for 20 min on the tabletop in one of two conditions: either with the train-of-thought interface (with graphical ropes), or without the ropes (control condition). The results show that visualizing the associations between ideas enabled the participants to produce longer trains of thought. We also assessed originality by collecting the unique ideas in the whole corpus of ideas produced by the different groups and observed that the train-of-thought condition produced more original ideas than the control one. One interpretation of this finding is that visualizing trains of thought increases cognitive stimulation, i.e., improves creativity by making others’ ideas more intelligible to the brainstorming partners, in comparison with the classical visualization of ideas as independent items.     

Metal-induced oxidative stress and plant mitochondria

A general status of oxidative stress in plants caused by exposure to elevated metal concentrations in the environment coincides with a constraint on mitochondrial electron transport, which enhances ROS accumulation at the mitochondrial level. As mitochondria are suggested to be involved in redox signaling under environmental stress conditions, mitochondrial ROS can initiate a signaling cascade mediating the overall stress response, i.e., damage versus adaptation. This review highlights our current understanding of metal-induced responses in plants, with focus on the production and detoxification of mitochondrial ROS. In addition, the potential involvement of retrograde signaling in these processes will be discussed.     

消费电子产品寿命终期的生态效益研究(三)

5.3.2中型塑料外壳产品 图14右边的三个点反映了普通传真机在采取不同回收方式情形下，环境性能和经济效益之间的变化情况。第一个箭头描述了未进行能量回收的焚烧过程与在焚烧过程中对残渣组分(包括产品中所有的塑料)进行能量回收的情况下，环境性能和经济效益之间的变化。第二个箭头描述了塑料再生利用与能量回收之间的变化。右边的两个箭头表明：与音响系统相比，中型塑料外壳的环境改善需要相对较高的单位重量成本。     

Heat Removal from Power Electronics in Two Direction Sets Using Embedded Solid State Cooling Layers a Proposed Non-Numerical Calculation Method

The use of embedded cooling layers consisting of materials with high thermal conductivities can significantly reduce peak temperatures within solid-state heat-generating media. Inversely, such layers can also allow for increases in heat-generating densities for a given maximum peak temperature. This is applicable in, for instance, integrated passive power electronics, where power densities are limited by the low thermal conductivities of materials being used. In this paper, the thermal performance of embedded cooling layers in three-dimensional rectangular heat-generating components is investigated numerically for a boundary condition where heat escapes to the ambient in two orthogonal direction sets (sets of orthogonal positive and/or negative directions). The allowable increase in heat generation density for fixed maximum peak temperatures is described for a wide range of geometric shape conditions and thermal conductivities of materials present in such composite structures. Correlations were developed for conditions with and without significant thermal resistance at the internal interfaces of the material layers and externally between the composite component structure and the environment. Conventional one-dimensional and first-order approximations traditionally used in composite solid conduction problems can accurately account for neither the relative thickness of material layers, nor the impact that internal interfacial resistance has. This paper presents a method with which the peak temperature within a stacked sandwich structure containing embedded cooling layered and where heat is removed in two orthogonal direction sets can be determined without the use of a numerical package. The method was developed for a wide range of material properties, geometric sizes and interfacial resistance values.     

Distribution of a simple shared dataspace architecture

We study a simple software architecture, in which components are coordinated by writing into and reading from a global set. This simple architecture is inspired by the industrial software architecture Splice. We present two results. First, a distributed implementation of the architecture is given and proved correct formally. In the implementation, local sets are maintained and data items are exchanged between these local sets. Next we show that the architecture is sufficiently expressive in principle. In particular, every global specification of a system's behaviour can be divided into components, which coordinate by read and write primitives on a global set only. We heavily rely on recent concepts and proof methods from process algebra.     

A rewriting approach to binary decision diagrams

Binary decision diagrams (BDDs) provide an established technique for propositional formula manipulation. In this paper, we present the basic BDD theory by means of standard rewriting techniques. Since a BDD is a DAG instead of a tree we need a notion of shared rewriting and develop appropriate theory. A rewriting system is presented by which canonical reduced ordered BDDs (ROBDDs) can be obtained and for which uniqueness of ROBDD representation is proved. Next, an alternative rewriting system is presented, suitable for actually computing ROBDDs from formulas. For this rewriting system a layerwise strategy is defined, and it is proved that when replacing the classical apply-algorithm by layerwise rewriting, roughly the same complexity bound is reached as in the classical algorithm. Moreover, a layerwise innermost strategy is defined and it is proved that the full classical algorithm for computing ROBDDs can be replaced by layerwise innermost rewriting without essentially affecting the complexity. Finally a lazy strategy is proposed sometimes performing much better than the traditional algorithm.     

The effect of pretreatment on the fermentation of honeybush tea (Cyclopia maculata)

Different pretreatments (bruising, hot and cold water) were used to study their effect on fermentation as measured by the quality parameters of honeybush tea (Cyclopia maculata). Bruising and pretreatment with water (hot and cold) were investigated as means to increase the fermentation rate and to improve product quality. The development of the desired dark-brown colour and honey-like flavour during fermentation was faster in hot and cold water treated material and gave a more uniform coloured product than with the bruising pretreatment. Liquor characteristics also improved with water pretreatment. A red–brown extract, compared with the light yellow–brown of untreated samples, was obtained with the water pretreatment. Hot water pretreatment inactivated the enzymes polyphenol oxidase (PPO) and peroxidase (POD), but did not terminate or impair fermentation. The inactivation of the enzymes, together with high temperature (>60°C) fermentation, indicated a chemical oxidation process rather than an enzymatic reaction in honeybush tea fermentation. © 1998 SCI.