Analytical expressions for the distortion of asynchronous sigma-delta modulators

This brief investigates the commonly used asynchronous sigma-delta modulator, which consists of a Schmitt trigger and a continuous-time loop filter. A detailed analysis is presented to accurately predict the distortion of such modulators. The extracted expressions are compared with simulation results, and they illustrate an excellent match. The results are also compared with a previous work by Roza, and they show a drastic improvement in accuracy

Disordered cellular automaton traffic flow model: Phase separated state, density waves and self organized criticality

We suggest a disordered traffic flow model that captures many features of traffic flow. It is an extension of the Nagel-Schreckenberg (NaSch) stochastic cellular automata for single line vehicular traffic model. It incorporates random acceleration and deceleration terms that may be greater than one unit. Our model leads under its intrinsic dynamics, for high values of braking probability $p$, to a constant flow at intermediate densities without introducing any spatial inhomogeneities. For a system of fast drivers $p\to 0$, the model exhibits a density wave behavior that was observed in car following models with optimal velocity. The gap of the disordered model we present exhibits, for high values of $p$ and random deceleration, at a critical density, a power law distribution which is a hall mark of a self organized criticality phenomena.Comment: 23 pages, 14 figure

Analyzing distortion in ASDMs with loop delay

Recently nearly exact expressions for the distortion in a commonly used family of Pulse Width Modulators (PWMs) known as Asynchronous Sigma Delta Modulators (ASDMs) were presented. Such an ASDM consists of a feedback loop with a schmitt-trigger (or a comparator), and a continuous time loop filter. However these previous results are not yet practically applicable because the effect of unavoidable loop delay (e.g. in the schmitt trigger) was not taken into account. Therefore we now present a more general theory that is also valid when there is a nonzero loop delay. A comparison of the resulting equations with computer simulations demonstrated a very good matching, confirming the validness of the theory. This way, a designer can now easily understand the relationship between the loop filter dynamics and the linearity of an ASDM

Theoretical vs. Empirical Classification and Prediction of Congested Traffic States

Starting from the instability diagram of a traffic flow model, we derive conditions for the occurrence of congested traffic states, their appearance, their spreading in space and time, and the related increase in travel times. We discuss the terminology of traffic phases and give empirical evidence for the existence of a phase diagram of traffic states. In contrast to previously presented phase diagrams, it is shown that "widening synchronized patterns" are possible, if the maximum flow is located inside of a metastable density regime. Moreover, for various kinds of traffic models with different instability diagrams it is discussed, how the related phase diagrams are expected to approximately look like. Apart from this, it is pointed out that combinations of on- and off-ramps create different patterns than a single, isolated on-ramp.Comment: See http://www.helbing.org for related wor

Design of a Continuous-Time (CT) Sigma-Delta modulator for class D audio power amplifiers

Dissertação apresentada na Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa para obtenção do Grau de Mestre em Engenharia Electrotécnica e de Computadore

Organizational Institutionalism and Sociology: A Reflection

[Excerpt] In 1991, DiMaggio and Powell observed: Institutional theory presents a paradox. Institutional analysis is as old as Emile Durkheim\u27s exhortation to study \u27social facts as things\u27, yet sufficiently novel to be preceded by new in much of the contemporary literature. (1991: 1) We argue that this paradox is, at least in part, the result of a long-standing tension in sociology between more materialist, interest-driven explanations of behavior and ideational, normative explanations, a tension that has often driven oscillating waves of sociological theorizing. It underlies many classical debates (e.g., between Spencer and Durkheim, Weber and Marx, and even Parsons and Mills), and the waves of theory associated with it have produced a variety of \u27neo-isms\u27, including neo-Marxist as well as neo-institutionalist theories. This distinction in explanatory approaches is linked to a more general theoretical problematic for sociologists: how to provide a single, coherent account of both stable, persisting patterns of social behavior, and the breakdown and elimination of what were once deeply-entrenched patterns. In this chapter, we examine the history of these distinctive explanatory approaches in sociology, and locate the origins of contemporary institutional work on organizations within this context. We also consider how more recent organizational analyses in the tradition of institutional theory have been driven by and reflect this basic tension

Protecting the Force: Reducing Combat Vehicle Accidents via Improved Organizational Processes

Despite extraordinary efforts by leaders at all levels throughout the U.S. Army, dozens of soldiers are killed each year as a result of both combat and motor vehicle accidents. The objective of this study is to look beyond the events and symptoms of accidents which normally indicate human error, and instead study the upper-level organizational processes and problems that may constitute the actual root causes of accidents. Critical to this process is identifying critical variables, establishing causality between variables, and quantifying variables that lead to both resilience against accidents and propensities for accidents. After reviewing the available literature we report on our development of a System Dynamics model, which is an analytical model of the system that allows for extensive simulation. The results of these simulations suggest that high-level decisions that balance mission rate and operations tempo with troop availability, careful management of the work-rest cycle for deployed troops, and improvement of the processes for evaluating the lessons learned from accidents, will lead to a reduction in Army combat and motor vehicle accidents