Switched linear systems have long been subject to high interest and intense research efforts, not only because many real world systems happen to exhibit switching behaviors, but also because the control of many complex systems is only possible via the combination of classical continuous control laws with supervisory switching logic. A particularly important problem is that of estimator and observer design, since the state of a system is usually only available through partial, often noise-corrupted, measurements. Even though hybrid estimation has been around for at least thirty years, a veil of mystery has surrounded the concept of ``observability' in switched linear systems. It is not until recently, with the recent renewal of interest toward deterministic hybrid systems, that observer design and observability analysis have fuelled sustained research efforts. It is in this context that this work is grounded. More precisely, the objective of this research is twofold: - To define proper concepts of observability in discrete-time switched linear systems, to characterize them, and to analyze their main properties, among which decidability is of special importance. - To propose and analyze observers - deadbeat and asymptotic - for such systems. The main contributions of this dissertation are as follows. It is shown that pathwise observability, i.e. state observability under arbitrary mode sequences, is decidable. Furthermore, the Kalman-Bertram sampling criterion is carried over to switched linear systems. Under unknown modes, mode and state observability are both characterized through simple linear algebraic tests, and are shown to be decidable in the autonomous case. As for asymptotic observers, a direct algebraic approach is proposed for the class of linear systems subjected to switching in the measurement equation.

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Thesis (Ph.D.)--Boston University / PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you. / This dissertation is dedicated to optimization of Stochastic Hybrid Systems (SHS). The concentration is on both online optimization of these systems and extending the known optimal policies in Discrete-Event Systems (DES) to a broader context of SHS. A SHS involves both continuous and discrete dynamics and is suitable for modeling almost any physical system of interest. The first part of this dissertation focuses on applications of SHS and, particularly, a subclass known as Stochastic Flow Models (SFM) used in fluid scheduling. To this end, a classic problem for optimally allocating a resource to multiple competing user queues is considered in the DES context and placed in the framework of SFMs. Infinitesimal Perturbation Analysis (IPA) is used to calculate the gradient estimates for the average holding cost of this system with respect to resource allocation parameters. The monotonicity property of these estimates allows us to prove the optimality of a well-known rule called the "c - mu-rule" under non-idling policies. Furthermore, nonlinear cost functions are considered, yielding simple distribution-free cost sensitivity estimates. Next, we take the first step in using IPA for optimally calculating timeout thresholds in SHS. A Transmission Control Protocol (TCP) communication link is used to examine the effectiveness of SHS and IPA in calculating derivative estimates of a goodput objective with respect to a timeout parameter. The analysis is also extended to the case of multinode communications. Our results reveal a great potential in using IPA to control delay thresholds and motivate more investigations in future. Finally, we propose a general framework for analysis and on-line optimization of SHS which facilitates the use of IPA. In doing so, we modify the previous structure of a Stochastic Hybrid Automaton (SHA) and show that every transition is associated with an explicit event which is defined through a "guard function." This enables us to uniformly treat all events observed on the sample path of the SHS. As a result, a unifying matrix notation for IPA equations is developed which eliminates the need for the case-by-case analysis of event classes as usually done in prior works involving IPA for SHS. / 2999-01-01

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This thesis discusses the security of sensor networks. First, an overview of the security architectures of two dominant implementations of sensor networks in the market today is presented: the TinyOS stack and the IEEE 802.15.4 stack. Their similarities and differences are explored and their strength and limitations are discussed. Where applicable, comparisons are made with IEEE 802.11 Wireless LAN to highlight improvements and lessons learned. It is pointed out that in general, IEEE 802.15.4 offers better security, but replay protection is effectively missing in today's implementations and access control is poorly implemented. Consequently, TinyOS is still the better option for devices with severe resource constraints. Finally, as a tool to aid in the security analysis of sensor network, the design and implementation of a TinyOS sniffer is presented and captured frames for a simple sensor network application are analyzed for the purpose of validation.

<p>Various engineering systems have become rapidly automated and intelligent as sensing, communication, and computing technologies have been increasingly advanced. The dynamical behaviors of such systems have also become complicated as they need to meet requirements on performance and safety in various operating conditions. Due to the heterogeneity in its behaviors for different operating modes, it is not appropriate to use a single dynamical model to describe its dynamics, which motivates the development of the stochastic hybrid system (SHS). The SHS is defined as a dynamical system which contains interacting time-evolving continuous state and event-driven discrete state (also called a mode) with uncertainties. Due to its flexibility and effectiveness, the SHS has been widely used for modeling complex engineering systems in many applications such as air traffic control, sensor networks, biological systems, and etc.</p><p>One of the key research areas related to the SHS is the inference or estimation of the states of the SHS, which is also known as the hybrid state estimation. This task is very challenging because both the continuous and discrete states need to be inferred from noisy measurements generated from mixed time-evolving and event-driven behavior of the SHS. This becomes even more difficult when the dynamical behavior or measurement contains nonlinearity, which is the case in many engineering systems that can be modeled as the SHS.</p><p>This research aims to 1) propose a stochastic nonlinear hybrid system model and develop novel nonlinear hybrid state estimation algorithms that can deal with the aforementioned challenges, and 2) apply them to safety-critical applications in air traffic control systems such as aircraft tracking and estimated time of arrival prediction, and unmanned aircraft system traffic management.</p>

During the decade of 1950s, the intensive rural to urban migration, in search for new job opportunities, created a high housing demand that was partially solved by the dictatorial government of Marcos Perez Jimenez. However, in the absence of effective public policy and failed housing projects, the population started to create solutions of their own to satisfy their housing needs, settling themselves in an improvised way around the urbanized areas and constituting what we know today as informal settlements or barrios. By 1957, around 35% of the population of Caracas lived in barrios. During the past decade, Venezuela has experienced a series of changes that have modified the economic, political and social model that governed the country. During Chavez's government, there have been many policy changes regarding property, land, economic and social organization, in search for solutions to the housing problem that integrate the marginalized sector of the population. However, a different pattern of informal settlements has emerged. Some organized communities have started to invade not only vacant land in the city peripheries; they are now invading buildings that are inserted in the center of the city, contrasting to the formal systems already existing in the city. There is now a new interpretation of what is legal and what is not. We are experiencing the changes and understanding the consequences of their implementation. The purpose of this research is to understand the current processes of housing production and acquisition in formal and informal communities in Caracas through a review of existing literature and qualitative studies of the relationships between stakeholders. I analyze the new policies and the current housing production organization system and contrast it to what is actually happening in practice. I also investigated how incremental changes in existing practices can contribute to the development of safe and legible housing production processes. My recommendations are the result of hybrid systems that consider different actors and perspectives of the same reality in order to find a healthier and more sustainable building culture in Caracas. / text

This thesis describes the application of the stochastic-flow-modeling (SFM) approach to represent the quality behavior of a manufacturing system. Initially, a simple, one-product type SFM is discussed and then a more complex multiple-product manufacturing system is developed. This quality SFM-based model has aggregation by station, product, and operational shift. Subsequently, potential supervisory control architectures that could be used in conjunction with this quality-based SFM are discussed and developed. Distribution parameter fitting is explored using static and adaptive approaches and a comparison between these two approaches is given. Then, the accuracy of the SFM modeling technique is demonstrated using two simulation examples. Effective equipment maintenance is essential for a manufacturing plant seeking to produce high quality products. The impact of equipment reliability and quality on throughput have been well established, but the relationship between maintenance and quality is not always clear nor direct. Therefore, after developing a SFM to represent the quality of a manufacturing system, the focus of this work shifts towards identifying correlations between maintenance and quality. This thesis describes a statistical modeling method that makes use of a Kalman filter to identify correlations between independent sets of maintenance and quality data. With such a method, maintenance efforts can be better prioritized to satisfy both production and quality requirements. In addition, this method is used to compare results from the theoretical maintenance-quality model to data from an actual manufacturing system. Results of the analysis indicate the potential for this method to be applied to preventive, as well as reactive maintenance decisions, since ageing aspects of equipment are also considered in the model. / Thesis (Master, Chemical Engineering) -- Queen's University, 2008-06-25 11:18:16.925

Thesis (Ph.D)--Electrical and Computer Engineering, Georgia Institute of Technology, 2010. / Committee Chair: Egerstedt, Magnus; Committee Co-Chair: Wardi, Yorai; Committee Member: Riley, George; Committee Member: Taylor, David; Committee Member: Tovey, Craig; Committee Member: Yezzi, Anthony. Part of the SMARTech Electronic Thesis and Dissertation Collection.

This thesis is concerned with the problem of formal verification of correctness specifications for continuous and hybrid dynamical systems. Our main focus will be on developing and automating general proof principles for temporal properties of systems described by non-linear ordinary differential equations (ODEs) under evolution constraints. The proof methods we consider will work directly with the differential equations and will not rely on the explicit knowledge of solutions, which are in practice rarely available. Our ultimate goal is to increase the scope of formal deductive verification tools for hybrid system designs. We give a comprehensive survey and comparison of available methods for checking set invariance in continuous systems, which provides a foundation for safety verification using inductive invariants. Building on this, we present a technique for constructing discrete abstractions of continuous systems in which spurious transitions between discrete states are entirely eliminated, thereby extending previous work. We develop a method for automatically generating inductive invariants for continuous systems by efficiently extracting reachable sets from their discrete abstractions. To reason about liveness properties in ODEs, we introduce a new proof principle that extends and generalizes methods that have been reported previously and is highly amenable to use as a rule of inference in a deductive verification calculus for hybrid systems. We will conclude with a summary of our contributions and directions for future work.