Performance Monitoring of Control Systems using Likelihood Methods

Evaluating deterioration in performance of control systems using closed loop operating data is addressed. A framework is proposed in which acceptable performance is expressed as constraints on the closed loop transfer function impulse response coefficients. Using likelihood methods, a hypothesis test is outlined to determine if control deterioration has occurred. The method is applied to a simulation example as well as data from an operational distillation column, and the results are compared to those obtained using minimum variance estimation approaches

Optimal and Robust Design of Integrated Control and Diagnostic Modules

The problem of designing an integrated control and diagnostic module is considered. The four degree of freedom controller is recast into a general framework wherein results from optimal and robust control theory can be easily implemented. For the case of an H2 objective, it is shown that the optimal control-diagnostic module involves constructing an optimal controller, closing the loop with this controller, and then designing an optimal diagnostic module for the closed loop. When uncertain plants are involved, this two-step method does not lead to reasonable diagnostics, and the control and diagnostic modules must be synthesized simultaneously. An example shows how this design can be accomplished with available methods

The triangle of microfinance

The initial success of microfinance programs in the 1970s led pioneers to think that many essential problems of the poor might be resolved by access to credit alone the ability to acquire assets, to start businesses, to finance emergency needs and to insure against illness and disaster. Part of that vision has certainly been realized. But much remains to be done. Most microfinance institutions (MFIs) are still small and vulnerable to constraints on their resources and to the risks inherent in single-issue portfolios. Most depend upon donors and governments to remain in operation. There is much waste and duplication, and some mature programs have declining loan recovery rates, even as competition for borrowers rises from conventional banks and finance companies. Analyzing the failures of credit programs aimed at small farmers and the successes of other programs showed the need for new understanding of the ways that poor households make spending, borrowing, and saving decisions. This area was previously neglected in policymaking on food security issues. The International Food Policy Research Institute (IFPRI) supported household surveys in nine Asian and African countries during the 1990s that analyzed formal and informal financial transactions, and it also evaluated the success of innovative approaches at some MFIs. The overall goal was to clarify the conditions under which state investment in microfinance programs might improve life for poor people more than state investment of the same funds in education, health, nutrition, or infrastructure development. The research led to the concept of the "critical triangle of microfinance" the need for any MFI to manage simultaneously the problems of outreach (reaching the poor both in terms of numbers and depth of poverty), financial sustainability (meeting operating and financial costs over the long term), and impact (having discernible effect upon clients' quality of life). This book elaborates on these objectives and shows that the most successful MFIs expand all sides of that triangle. Tradeoffs are sometimes inevitable, but even so, synergies among the three make the concept valuable from Author's Abstract.Microfinance ,

Avery Final Report: Identification and Cross-Directional Control of Coating Processes

Coating refers to the covering of a solid with a uniform layer of liquid. Of special industrial interest is the cross-directional control of coating processes, where the cross-direction refers to the direction perpendicular to the substrate movement. The objective of the controller is to maintain a uniform coating under unmeasured process disturbances. Assumptions that are relevant to coating processes found in industry are used to develop a model for control design. We show how to identify the model from input-output data. This model is used to derive a model predictive controller to maintain flat profiles of coating across the substrate by varying the liquid flows along the cross direction. The model predictive controller computes the control action which minimizes the predicted deviation in cross-directional uniformity. The predictor combines the estimate obtained from the model with the measurement of the cross-directional uniformity to obtain a prediction for the next time step. A filter is used to obtain robustness to model error and insensitivity to measurement noise. The tuning of the noise filter and different methods for handling actuator constraints are studied in detail. The three different constraint-handling methods studied are: the weighting of actuator movements in the objective function, explicitly adding constraints to the control algorithm, i.e. constrained model predictive control, and scaling infeasible control actions calculated from an unconstrained control law to be feasible. Actuator constraints, measurement noise, model uncertainty, and the plant condition number are investigated to determine which of these limit the achievable closed loop performance. From knowledge of how these limitations affect the performance we find how the plant could be modified to improve the process uniformity. Also, because identification of model parameters is time-consuming and costly, we study how accurate the identification must be to achieve a given level of performance. The theory developed throughout the paper is rigorously verified though simulations and experiments on a pilot plant. The effect of interactions on the closed loop performance is shown to be negligible for this pilot plant. The measurement noise and the actuator constraints are shown to have the largest effect on closed loop performance

Stability of three neutrino flavor conversion in supernovae

Neutrino-neutrino interactions can lead to collective flavor conversion in the dense parts of a core collapse supernova. Growing instabilities that lead to collective conversions have been studied intensely in the limit of two-neutrino species and occur for inverted mass ordering in the case of a perfectly spherical supernova. We examine two simple models of colliding and intersecting neutrino beams and show, that for three neutrino species instabilities exist also for normal mass ordering even in the case of a fully symmetric system. Whereas the instability for inverted mass ordering is associated with $\Delta m_{31}^2$, the new instability we find for normal mass ordering is associated with $\Delta m_{21}^2$. As a consequence, the growth rate of these new instabilities for normal ordering is smaller by about an order of magnitude compared to the rates of the well studied case of inverted ordering.Comment: 18 pages, 5 figures Minor update on the consistency of the formulae and prefactors, actualized plot

Quantum-Matter-Spacetime : Peter Mittelstaedt's Contributions to Physics and Its Foundations

In a period of over 50 years, Peter Mittelstaedt has made substantial and lasting contributions to several fields in theoretical physics as well as the foundations and philosophy of physics. Here we present an overview of his achievements in physics and its foundations which may serve as a guide to the bibliography (printed in this Festschrift) of his publications. An appraisal of Peter Mittelstaedt's work in the philosophy of physics is given in a separate contribution by B. Falkenburg