System integration report

Several areas that arise from the system integration issue were examined. Intersystem analysis is discussed as it relates to software development, shared data bases and interfaces between TEMPUS and PLAID, shaded graphics rendering systems, object design (BUILD), the TEMPUS animation system, anthropometric lab integration, ongoing TEMPUS support and maintenance, and the impact of UNIX and local workstations on the OSDS environment

Specification of tools for message sequence charts

. The recent formalization of the semantics of Message Sequence Charts enables the derivation of tools for MSCs directly from this formal definition. We use the Asf+Sdf Meta-environment to make a straightforward implementation of tools for transformation, simulation and requirements testing. In this paper we present the complete specification of the tools. 1 Introduction Message Sequence Charts (MSCs) are a graphical method for the description of the interaction between system components [IT94]. Due to the recent formalization [MR94a, MR94b, IT95] of the semantics of Message Sequence Charts, we can consider MSC as a formal description technique. Currently, this formalization has already influenced the development of the language (in particular with respect to composition of MSCs, for which algebraic operators are considered) and it is expected to also influence the use of MSCs. Formalization will also have impact on the work of tool builders. The behavior of tools can be validated aga..

The neural circuitry of fear conditioning : a theoretical account

In the last decades, fear conditioning has been established as one of the most successful paradigms for studying the neural substrates of emotional learning. Experimental research has revealed a complex circuitry of brain regions—most prominently the amygdala—underlying the acquisition, extinction and generalization of conditioned fear. As the wealth of experimental data grows, theoretical models that help interpret results and generate new hypotheses play an increasingly important role. In this thesis, two computational models of the neural substrates of fear conditioning are presented. The first model is a biologically realistic spiking neural network model of the central amygdala, the main output structure of the amygdala. Based on a recent experimental study that demonstrated the importance of tonic extrasynaptic inhibition for fear generalization, the effects of changes in neuronal membrane conductance on input processing are analyzed in the model. Consistent with experimental results, it is shown that subpopulation-specific changes in tonic inhibitory conductance increase the responsiveness of the network to phasic inputs, presumably causing the increase in fear generalization. On the basis of this result, the model is analyzed from a functional perspective. It is argued that tonic inhibition in the central amygdala acts as a controller by which network sensitivity is flexibly adjusted to relevant features of the environment, such as predictability of threat, and concrete predictions that follow from this proposition as well as possible adjustment mechanisms are discussed. In addition, a systems level model is presented that is based on a recent high-level approach to conditioning and proposes a specific physiological implementation in the basolateral amygdala, prefrontal cortex and the intercalated cell clusters of the amygdala. It is a central hypothesis of the model that the interaction between fear and extinction neurons in the basal amygdala, which has been described experimentally, is a neural substrate of the switching between socalled latent states, which allow the animal to organize its experience and infer structure in the environment. Important behavioral phenomena are reproduced in the model and the effect of de-activation of model structures is shown to be in good agreement with results from lesion studies. Finally, predictions and questions that follow from the main hypothesis are considered. Taken together, the two models provide a coherent theoretical account of the neural basis of acquisition and extinction of conditioned fear, as well as the control of fear generalization. Importantly, this account combines different levels of analysis. By virtue of this combination, the scope of predictions that can be derived is expanded and the models become more amenable to experimental testing

Operating strategies to preserve the adequacy of power systems circuit breakers

The objective of the proposed research is to quantify the limits of overstressed and aging circuit breakers in terms of probability of failure and to provide guidelines to determine network reconfigurations, generator commitment, and economic dispatch strategies that account for these limits. The proposed temporary power system operating strategies address circuit breaker adequacy issues and allow overstressed breakers to be operated longer and more reliably until they are replaced with adequate equipment. The expansion of electric networks with new power sources (nuclear plants, distributed generation) results in increased short-circuit or fault currents levels. As fault currents increase, they will eventually exceed circuit breaker ratings. Circuit breakers exposed to fault currents in excess of their ratings are said to be overstressed, underrated, or inadequate. Insufficient ratings expose overstressed breakers to increased failure probabilities. Extensive common-mode outages caused by circuit breaker failures reduce the reliability of power systems. To durably avoid outages and system unreliability, overstressed breakers must eventually be replaced. Large-scale replacements of overstressed breakers cannot be completed in a short time because of budgetary limits, capital improvement schedules, and manufacturer-imposed constraints. Meanwhile, to preserve the ability of old and overstressed breakers to safely interrupt faults, short-circuit currents must be kept within the limits imposed by the ratings and the age of these breakers by using the substation reconfiguration and generator commitment strategies described in this study. The immediate benefit of the above-mentioned operating strategies is a reduction of the failure probability of overstressed breakers obtained by avoiding the interruption of currents in excess of breaker ratings. Other benefits include (i) increased network reliability, (ii) restored operating margins with respect to existing equipment, and (iii) prioritized equipment upgrades that enhance the long-term planning of power systems.Ph.D.Committee Chair: Meliopoulos, A. P. Sakis; Committee Member: Divan, Deepakraj M.; Committee Member: Harley, Ronald G.; Committee Member: Johnson, Ellis L.; Committee Member: Taylor, David G

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