Recursive least squares for online dynamic identification on gas turbine engines

Online identification for a gas turbine engine is vital for health monitoring and control decisions because the engine electronic control system uses the identified model to analyze the performance for optimization of fuel consumption, a response to the pilot command, as well as engine life protection. Since a gas turbine engine is a complex system and operating at variant working conditions, it behaves nonlinearly through different power transition levels and at different operating points. An adaptive approach is required to capture the dynamics of its performance

Feedback Controlled Software Systems

Software systems generally suffer from a certain fragility in the face of disturbances such as bugs, unforeseen user input, unmodeled interactions with other software components, and so on. A single such disturbance can make the machine on which the software is executing hang or crash. We postulate that what is required to address this fragility is a general means of using feedback to stabilize these systems. In this paper we develop a preliminary dynamical systems model of an arbitrary iterative software process along with the conceptual framework for stabilizing it in the presence of disturbances. To keep the computational requirements of the controllers low, randomization and approximation are used. We describe our initial attempts to apply the model to a faulty list sorter, using feedback to improve its performance. Methods by which software robustness can be enhanced by distributing a task between nodes each of which are capable of selecting the best input to process are also examined, and the particular case of a sorting system consisting of a network of partial sorters, some of which may be buggy or even malicious, is examined

A framework for proving the self-organization of dynamic systems

This paper aims at providing a rigorous definition of self- organization, one of the most desired properties for dynamic systems (e.g., peer-to-peer systems, sensor networks, cooperative robotics, or ad-hoc networks). We characterize different classes of self-organization through liveness and safety properties that both capture information re- garding the system entropy. We illustrate these classes through study cases. The first ones are two representative P2P overlays (CAN and Pas- try) and the others are specific implementations of \Omega (the leader oracle) and one-shot query abstractions for dynamic settings. Our study aims at understanding the limits and respective power of existing self-organized protocols and lays the basis of designing robust algorithm for dynamic systems

Autopoietic organization of firm: an illustration for the construction industry

Generally poor productivity, delays, low profitability and exceeded budgets are Common problems in modern construction management, however it seems that a basic obstacle lies far deeper in the understanding of a firm's fundamental mission, its existence. The main objective of this paper therefore is to examine the operational living of a construction firm and by doing that to reveal the key problem or the solution for a construction firm - its organization. A firm as a social system in which interactions between its constitutive components (employees) are surordinated to its maintenance (keeping a system alive) is an autopoietic social system. Two domains of external perturbations are uncovered to which a construction firm has to adapt (market driven and project driven perturbations). Constructed conceptual model of an autopoietic organization is based upon two necessary and sufficient operational domains that a firm has to create in order to become an autopoietic, adaptive social system. The first one is a domain of interactions between employees and other operationally external systems, which is representing an idea-generating domain of interactions. The second is employee's autonomous operational domain, which embodies employee's autonomy and individuality and represents a necessary condition for the establishment of an idea-generating domain. Finally, it is recognized that interactions within these four domains keep a construction firm alive

Stabilizing Neighborhoods Impacted by Concentrated Foreclosures: Scattered-Site Rental Housing Challenges and Opportunities

The negative impacts of concentrated foreclosures have been destabilizing communities across the country. Community development corporations (CDCs) and other nonprofits that are active in these neighborhoods face falling property values, decreased lending activity and other consequences that are complicating their efforts at community revitalization through acquisition, rehabilitation and resale of vacant and foreclosed housing stock. Given the current crisis in the housing and credit markets, community development corporations aiming for neighborhood stabilization may wish to acquire foreclosed single-family properties and operate them as scattered-site rental units instead. This study presents the challenges that nonprofits pursuing such a plan are likely to face. It discusses the main management, financing and political issues associated with developing and operating scattered-site rental housing while providing a foundation upon which CDCs considering such activities can evaluate their capacity and willingness to meet the challenges. The paper explores how local market conditions, internal organizational capacity and the current policy environment affect nonprofit efforts to acquire, rehabilitate and rent foreclosed properties. The study includes operational and advocacy recommendations for improving the context in which scattered-site rental housing can be managed. The paper also considers the unique difficulties of the current situation and concludes that comprehensive revitalization efforts that emphasize cross-sectoral partnerships and enjoy strong local government support are most likely to exert a positive impact on a community

Minimizing Message Size in Stochastic Communication Patterns: Fast Self-Stabilizing Protocols with 3 bits

This paper considers the basic $\mathcal{PULL}$ model of communication, in which in each round, each agent extracts information from few randomly chosen agents. We seek to identify the smallest amount of information revealed in each interaction (message size) that nevertheless allows for efficient and robust computations of fundamental information dissemination tasks. We focus on the Majority Bit Dissemination problem that considers a population of $n$ agents, with a designated subset of source agents. Each source agent holds an input bit and each agent holds an output bit. The goal is to let all agents converge their output bits on the most frequent input bit of the sources (the majority bit). Note that the particular case of a single source agent corresponds to the classical problem of Broadcast. We concentrate on the severe fault-tolerant context of self-stabilization, in which a correct configuration must be reached eventually, despite all agents starting the execution with arbitrary initial states. We first design a general compiler which can essentially transform any self-stabilizing algorithm with a certain property that uses $\ell$-bits messages to one that uses only $\log \ell$-bits messages, while paying only a small penalty in the running time. By applying this compiler recursively we then obtain a self-stabilizing Clock Synchronization protocol, in which agents synchronize their clocks modulo some given integer $T$, within $\tilde O(\log n\log T)$ rounds w.h.p., and using messages that contain $3$ bits only. We then employ the new Clock Synchronization tool to obtain a self-stabilizing Majority Bit Dissemination protocol which converges in $\tilde O(\log n)$ time, w.h.p., on every initial configuration, provided that the ratio of sources supporting the minority opinion is bounded away from half. Moreover, this protocol also uses only 3 bits per interaction.Comment: 28 pages, 4 figure

Edsger Wybe Dijkstra (1930 -- 2002): A Portrait of a Genius

We discuss the scientific contributions of Edsger Wybe Dijkstra, his opinions and his legacy.Comment: 10 pages. To appear in Formal Aspects of Computin

Predicting Financial Crisis in Developing Economies: Astronomy or Astrology?

In the aftermath of the European currency crisis of 1992-3, the Mexican financial crisis of 1994-5 and the Asian financial crisis of 1997-8, neoclassical economists in the academy and policy community have been engaged in a project to develop predictors or indicators of currency, banking and generalized financial crises in developing economies. This paper critically examines the efforts of the economics profession in this regard on both empirical and theoretical grounds. The paper argues that these predictors perform poorly on empirical grounds--indeed, the predictors developed after each of these crises failed to predict the next major crisis. These predictors are also rejected on theoretical grounds. From a post-Keynesian perspective, there is no reason to expect that the mere provision of information will prevent crises by changing agents' behaviors. The paper will also propose several indicators that are consonant with post-Keynesian economic theory, although it will be argued that these indicators do not represent a sufficient means to prevent financial crisis. Ironically, as agents develop confidence in the predictive capacity of crisis indicators, they may engage in actions that increase the economy's vulnerability to crisis. Far more important to the project of preventing financial crisis in developing economies is the implementation of constraints on those investor behaviors that render liberalized, internationally integrated financial systems inherently prone to instability and crisis. Hence, intellectual capital would be more productively expended on devising appropriate changes in the overall regime in which investors operate (such as measures that compel changes in financing strategies) rather than in searching for new predictors of crisis.Financial Crisis