PETRI NET BASED MODELING OF PARALLEL PROGRAMS EXECUTING ON DISTRIBUTED MEMORY MULTIPROCESSOR SYSTEMS

The development of parallel programs following the paradigm of communicating sequen- tial processes to be executed on distributed memory multiprocessor systems is addressed. The key issue in programming parallel machines today is to provide computerized tools supporting the development of efficient parallel software, i.e. software effectively har- nessing the power of parallel processing systems. The critical situations where a parallel programmer needs help is in expressing a parallel algorithm in a programming language, in getting a parallel program to work and in tuning it to get optimum performance (for example speedup). . We show that the Petri net formalism is higly suitable as a performance modeling technique for asynchronous parallel systems, by introducing a model taking care of the parallel program, parallel architecture and mapping influences on overall system perfor- mance. PRM -net (Program-Resource- Mapping) models comprise a Petri net model of the multiple flows of control in a parallel program, a Petri net model of the parallel hardware and the process-to-processor mapping information into a single integrated performance model. Automated analysis of PRM-net models addresses correctness and performance of parallel programs mapped to parallel hardware. Questions upon the correctness of parallel programs can be answered by investigating behavioural properties of Petri net programs like liveness, reachability, boundedness, mutualy exclusiveness etc. Peformance of parallel programs is usefully considered only in concern with a dedicated target hard- ware. For this reason it is essential to integrate multiprocessor hardware characteristics into the specification of a parallel program. The integration is done by assigning the concurrent processes to physical processing devices and communication patterns among parallel processes to communication media connecting processing elements yielding an in- tegrated, Petri net based performance model. Evaluation of the integrated model applies simulation and markovian analysis to derive expressions characterising the peformance of the program being developed. Synthesis and decomposition rules for hierarchical models naturally give raise to use PRM-net models for graphical, performance oriented parallel programming, support- ing top-down (stepwise refinement) as well as bottom-up development approaches. The graphical representation of Petri net programs visualizes phenomena like parallelism, syn- chronisation, communication, sequential and alternative execution. Modularity of pro- gram blocks aids reusability, prototyping is promoted by automated code generation on the basis of high level program specifications

SPECI, a simulation tool exploring cloud-scale data centres

There is a rapid increase in the size of data centres (DCs) used to provide cloud computing services. It is commonly agreed that not all properties in the middleware that manages DCs will scale linearly with the number of components. Further, "normal failure" complicates the assessment of the per-formance of a DC. However, unlike in other engineering domains, there are no well established tools that allow the prediction of the performance and behav-iour of future generations of DCs. SPECI, Simulation Program for Elastic Cloud Infrastructures, is a simulation tool which allows exploration of aspects of scaling as well as performance properties of future DCs

04122 Abstracts Collection -- Wireless Sensor Networks and Applications

From 14.03.04 to 19.03.04, the Dagstuhl Seminar 04122 ``Wireless Sensor Networks and Applications\u27\u27 was held in the International Conference and Research Center (IBFI), Schloss Dagstuhl. During the seminar, several participants presented their current research, and ongoing work and open problems were discussed. Abstracts of the presentations given during the seminar as well as abstracts of seminar results and ideas are put together in this paper. The first section describes the seminar topics and goals in general. Links to extended abstracts or full papers are provided, if available

17 Human-Car confluence: “Socially-Inspired driving mechanisms”

With self-driving vehicles announced for the 2020s, today’s challenges in Intelligent Transportation Systems (ITS) lie in problems related to negotiation and decision making in (spontaneously formed) car collectives. Due to the close coupling and interconnectedness of the involved driver-vehicle entities, effects on the local level induced by cognitive capacities, behavioral patterns, and the social context of drivers, would directly cause changes on the macro scale. To illustrate, a driver’s fatigue or emotion can influence a local driver-vehicle feedback loop, which is directly translated into his or her driving style, and, in turn, can affect driving styles of all nearby drivers. These transitional, yet collective driver state and driving style changes raise global traffic phenomena like jams, collective aggressiveness, etc. To allow harmonic coexistence of autonomous and self-driven vehicles, we investigate in this chapter the effects of socially-inspired driving and discuss the potential and beneficial effects its application should have on collective traffic

Human Computer Confluence. Transforming Human Experience Through Symbiotic Technologies

Human-computer confluence refers to an invisible, implicit, embodied or even implanted interaction between humans and system components. New classes of user interfaces are emerging that make use of several sensors and are able to adapt their physical properties to the current situational context of users. A key aspect of human-computer confluence is its potential for transforming human experience in the sense of bending, breaking and blending the barriers between the real, the virtual and the augmented, to allow users to experience their body and their world in new ways. Research on Presence, Embodiment and Brain-Computer Interface is already exploring these boundaries and asking questions such as: Can we seamlessly move between the virtual and the real? Can we assimilate fundamentally new senses through confluence? The aim of this book is to explore the boundaries and intersections of the multidisciplinary field of HCC and discuss its potential applications in different domains, including healthcare, education, training and even arts

Parallel and Distributed Simulation of Discrete Event Systems

The achievements attained in accelerating the simulation of the dynamics of complex discrete event systems using parallel or distributed multiprocessing environments are comprehensively presented. While parallel discrete event simulation (DES) governs the evolution of the system over simulated time in an iterative SIMD way, distributed DES tries to spatially decompose the event structure underlying the system, and executes event occurrences in spatial subregions by logical processes (LPs) usually assigned to different (physical) processing elements. Synchronization protocols are necessary in this approach to avoid timing inconsistencies and to guarantee the preservation of event causalities across LPs. Included in the survey are discussions on the sources and levels of parallelism, synchronous vs. asynchronous simulation and principles of LP simulation. In the context of conservative LP simulation (Chandy/Misra/Bryant) deadlock avoidance and deadlock detection/recovery strategies, Conservative Time Windows and the Carrier Nullmessage protocol are presented. Related to optimistic LP simulation (Time Warp), Optimistic Time Windows, memory management, GVT computation, probabilistic optimism control and adaptive schemes are investigated. (Also cross-referenced as UMIACS-TR-94-100

Mechanosensation of tight junctions depends on ZO-1 phase separation and flow

Cell-cell junctions respond to mechanical forces by changing their organization and function. To gain insight into the mechanochemical basis underlying junction mechanosensitivity, we analyzed tight junction (TJ) formation between the enveloping cell layer (EVL) and the yolk syncytial layer (YSL) in the gastrulating zebrafish embryo. We found that the accumulation of Zonula Occludens-1 (ZO-1) at TJs closely scales with tension of the adjacent actomyosin network, revealing that these junctions are mechanosensitive. Actomyosin tension triggers ZO-1 junctional accumulation by driving retrograde actomyosin flow within the YSL, which transports non-junctional ZO-1 clusters toward the TJ. Non-junctional ZO-1 clusters form by phase separation, and direct actin binding of ZO-1 is required for stable incorporation of retrogradely flowing ZO-1 clusters into TJs. If the formation and/or junctional incorporation of ZO-1 clusters is impaired, then TJs lose their mechanosensitivity, and consequently, EVL-YSL movement is delayed. Thus, phase separation and flow of non-junctional ZO-1 confer mechanosensitivity to TJs