Modeling and simulation of data communication networks using SARA

The selection of an appropriate simulation language can have a profound impact on the success of a simulation study. The available options range from domain-specific simulation languages to general-purpose programming languages. These languages are often supported by a collection of tools which form a simulation system. This paper examines UCLA's SARA (Systems ARchitects' Apprentice) system and explores its' usefulness in modeling and simulating a data communications network. Based on experimental use of SARA's tools, the system is evaluated with respect to required expertise, modeling power, as well as measurement and reporting capability

The use of Petri nets for modeling pipelined processors

This paper discusses the use of Petri Nets for modeling and analyzing pipelined processors. Petri Nets are particularly well-suited to modeling the synchronization, buffering, resource contention and delicate timing so common in pipelined processors. Tools for simulating, animating and analyzing the behavior of the models are described. The usefulness of the tools and the analysis methods they support in evaluating the performance and analyzing the detailed timing of pipelined microprocessors is illustrated through an example

Tools for efficient analysis of concurrent software systems

The ever increasing use of distributed computing as a method of providing added computing power and reliability has sparked interest in methods to model and analyze concurrent hardware/ software systems. Efficient automated analysis tools are needed to aid designers of such systems. The Distributed Systems Project at UCI has been developing a suite of tools (dubbed the P-NUT system) which supports efficient analysis of models of concurrent software. This paper presents the principles which guide the development of P-NUT tools and discusses the development of one of the tools: the Reachability Graph Builder (RGB). The P-NUT approach to tool development has resulted in the production of a highly efficient tool for constructing reachability graphs. The careful design of data structures and associated algorithms has significantly enlarged the class of models which can be analyzed

Computer-aided analysis of concurrent systems

The introduction of concurrency into programs has added to the complexity of the software design process. This is most evident in the design of communications protocols where concurrency is inherent to the behavior of the system. The complexity exhibited by such software systems makes more evident the needs for computer-aided tools for automatically analyzing behavior.The Distributed Systems project at UCI has been developing a suite of tools, based on Petri nets, which support the design and evaluation of concurrent software systems. This paper focuses attention on one of the tools: the reachability graph analyzer (RGA). This tool provides mechanisms for proving general system properties (e.g., deadlock-freeness) as well as system-specific properties. The tool is sufficiently general to allow a user to apply complex user-defined analysis algorithms to reachability graphs. The alternating-bit protocol with a bounded channel is used to demonstrate the power of the tool and to point to future extensions

Performance analysis using timed Petri Nets

Petri Nets have been successfully used to model and evaluate the performance of distributed systems. Several researchers have extended the basic Petri Net model to include time, and have demonstrated that restricted classes of Petri Nets can be analyzed efficiently. Unfortunately, the restrictions prohibit the techniques from being applied to many interesting systems, e.g. communication protocols. This paper proposes a version of timed Petri Nets which accurately models communication protocols, and which can be analyzed using Timed Reachability Graphs. Procedures for constructing and analyzing these graphs are presented. The analysis is shown to be applicable to a larger class of Timed Petri Nets than previously thought. The model and the analysis technique are demonstrated using a simple communication protocol

Decay properties of spectral projectors with applications to electronic structure

Motivated by applications in quantum chemistry and solid state physics, we apply general results from approximation theory and matrix analysis to the study of the decay properties of spectral projectors associated with large and sparse Hermitian matrices. Our theory leads to a rigorous proof of the exponential off-diagonal decay ("nearsightedness") for the density matrix of gapped systems at zero electronic temperature in both orthogonal and non-orthogonal representations, thus providing a firm theoretical basis for the possibility of linear scaling methods in electronic structure calculations for non-metallic systems. We further discuss the case of density matrices for metallic systems at positive electronic temperature. A few other possible applications are also discussed.Comment: 63 pages, 13 figure

Effet de l'irrigation déficitaire contrôlée sur la croissance et le développement foliaire du palmier dattier (Phoenix dactylifera L.)

L'eau est un facteur limitant pour le développement de l'agriculture oasienne. L'amélioration de son efficience d'utilisation est donc nécessaire et peut passer par des stratégies d'irrigation déficitaire. La réponse du palmier dattier à de telles stratégies a ainsi été évaluée par l'étude expérimentale de leurs effets sur la croissance végétative des palmiers adultes de la variété Majhoul. L'expérimentation a été conduite au Tafilalet (Maroc) pendant deux années consécutives (mars 2012-février 2014). Le cycle annuel de la croissance et du développement de cette variété a été découpé en trois périodes distinctes : la première de novembre à février, la seconde de mars à juin et la dernière de juillet à octobre. Pendant ces périodes, sept régimes hydriques ont été appliqués sous irrigation localisée : régime agriculteur (T0), 100 % évapotranspiration maximale [ETM] (T1), 80 % (T2), 60 % (T3), 80–100–60 % (T4), 150 % (T5) et 60–100–80 % (T6). Les mesures ont porté sur le suivi des paramètres météorologiques, les apports d'eau et l'évolution de la biomasse végétative (émission, croissance et sénescence des palmes, et le suivi de l'indice foliaire). Les résultats obtenus montrent que : le régime hydrique et la périodisation affectent significativement la phénologie du palmier dattier en deuxième année d'expérimentation ; les apports en eau d'irrigation correspondant à l'ETM sont en moyenne de 51 m3/pied/an, variables entre 30 et 76 m3/pied/an ; le T6, l'irrigation déficitaire régulée à 60–100–80 % de l'ETM selon les saisons, a amélioré la productivité végétative du palmier et a permis la conservation de 14 % de l'eau d'irrigation comparativement au T1. La stratégie de l'irrigation déficitaire régulée pourrait donc contribuer à la rationalisation de l'eau et à la durabilité des oasis. (Résumé d'auteur

The derivation of performance expressions for communication protocols from timed Petri net models

Petri Net models have been extended in a variety of ways and have been used to prove the correctness and evaluate the performance of communication protocols. Several extensions have been proposed to model time. This work uses a form of Timed Petri Nets and presents a technique for symbolically deriving expressions which describe system performance. Unlike past work on performance evaluation of Petri Nets which assumes a priori knowledge of specific time delays, the technique presented here applies to a wide range of time delays so long as the delays satisfy a set of timing constraints. The technique is demonstrated using a simple communication protocol

Dosage calculation for intravenous thrombolysis of ischemic stroke: to weigh or to estimate?

Background: Estimation is a widely used method of assessing the weight of patients with acute stroke. Because the dosage of tissue plasminogen activator (tPA) is weight-dependent, errors in estimation lead to incorrect dosing. Methods: We installed a ground-level scale in the computed tomography (CT) suite of our hospital and also integrated a scale into the CT table of our Mobile Stroke Unit in order to prospectively assess the differences between reported, estimated, and measured weights of acute stroke patients. An independent rater asked patients to report their weight. The patients’ weights were also estimated by the treating physician and measured with a scale. Differences between reported, estimated, and measured weights were analyzed statistically. Results: For 100 consecutive patients, weighing was possible without treatment delays. Weights estimated by the physician diverged from measured weights by 10% or more for 27 patients and by 20% or more for 6 patients. Weights reported by the patient diverged from measured weights by 10% or more for 12 patients. Weights reported by the patients differed significantly less from measured weights (mean, 4.1 ± 3.1 kg) than did weights estimated by the physician (5.7 ± 4.4 kg; p = 0.003). Conclusion: This first prospective study of weight assessment in acute stroke shows that the use of an easily accessible scale makes it feasible to weigh patients with acute stroke without the treatment delay associated with additional patient transfers. Physicians’ estimates of patients’ weights demonstrated substantial aberrations from measured weights. Avoiding these deviations would improve the accuracy of tPA dosag