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Open Access Publications from the University of California

Scholarly Works (39 results)

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UC Santa Cruz Previously Published Works (2019)
© 2018 IEEE. Cost evaluation problems for hybrid inclusions are studied. Sufficient conditions, in the form of Lyapunov-like inequalities, are provided to derive an upper bound on the cost associated with the solution to a hybrid inclusion with respect to a hybrid cost functional. Under additional sufficient conditions, we determine the cost exactly without computing solutions. Constructive results are proposed to solve cost evaluation problems in some relevant applications. Numerical examples are presented.
    Cover page: Cost Evaluation for Hybrid Inclusions: A Lyapunov Approach
    • Article
    • Peer Reviewed
    UC Santa Cruz Previously Published Works (2019)
    © 2019, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved. We formulate an optimal control problem for hybrid systems with inputs and propose conditions for the design of state-feedback laws solving the optimal control problem. The optimal control problem has the flavor of an infinite horizon problem, but it also allows solutions to have a bounded domain of definition, which is possible in hybrid systems with deadlocks. Design conditions for optimal feedback laws are obtained by relating a quite general hybrid cost functional to a Lyapunov like function. These conditions guarantee closed-loop optimality and are given by constrained steady-state-like Hamilton-Jacobi-Bellman-type equations. Applications and examples of the proposed results are presented.
      Cover page: Certifying optimality in hybrid control systems via Lyapunov-like conditions
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      • Peer Reviewed
      UC Santa Cruz Previously Published Works (2018)
      © 2018 AACC. State-feedback optimal control and cost evaluation problems for constrained difference inclusions are considered. Sufficient conditions, in the form of Lyapunov-like inequalities, are provided to derive an upper bound on the cost associated with the solution to a constrained difference inclusion with respect to a given cost functional. Under additional sufficient conditions, we determine the cost exactly without computing solutions. The proposed approach is extended to study an optimal control problem for discrete-time systems with constraints. In this setting, sufficient conditions for closed-loop optimality are given in terms of a constrained steady-state-like Hamilton-Jacobi-Bellman equation. Applications and examples of the proposed results are presented.
        Cover page: On the Optimality of Lyapunov-based Feedback Laws for Constrained Difference Inclusions
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        • Peer Reviewed
        UC Santa Cruz Previously Published Works (2018)
        © 2017 IEEE. This paper deals with robust minimum-time control of a class of asymptotically null-controllable with bounded input planar systems. A hybrid controller is proposed to robustly achieve global finite time stability of a set of points wherein the plant state is zero. The resulting controller provides time optimal response from initial conditions in a certain subset of the state space, and finite time convergence elsewhere. Finally, the effectiveness of the proposed methods is demonstrated in a numerical example.
          Cover page: Hybrid robust minimum-time control for a class of non-exponentially unstable planar systems
          • Article
          • Peer Reviewed
          UC Santa Cruz Previously Published Works (2018)
            Cover page: Hybrid Regional Stabilization of Linear Systems with Actuator Saturation and Multi-Rate Samplers.
            • Article
            • Peer Reviewed
            UCLA Previously Published Works (2006)

            Background and objectives: This study attempts to assess the intensity and quality of pain and health-related quality of life in patients with sacroiliac syndrome and to compare those constructs to patients with lumbar radiculopathy. Methods: A retrospective review of patient records with the diagnosis of sacroiliac syndrome or lumbar radiculopathy was performed. Patients with sacroiliac syndrome were age and gender matched to patients with lumbar radiculopathy. Data from the McGill Pain Questionnaire, visual numerical pain scores, and SF-36 health-related quality of life measure (version 2) were compared between groups. Results: The age of patients with a traumatic etiology for sacroiliac syndrome was lower than those with previous back surgery and "idiopathic" etiologies (P < .02). Duration of pain in patients with "idiopathic" etiology was longer in comparison to those with previous back surgery (P < .005). No statistical difference occurred between patients with sacroiliac syndrome and lumbar radiculopathy with respect to McGill pain scores, visual numerical pain scores, and SF-36 health-related quality of life measure. Conclusions: The results of this study suggest the following: (1) no true difference exists in the health-related quality of life or pain scores/descriptors between patients with SI syndrome or lumbar radiculopathy, or (2) the presence of comorbid spinal conditions confounds the ability of the SF-36 to detect disparities in health-related quality of life among differing etiologies of low-back pain, despite the use of rigorous diagnostic criteria, and/or (3) other factors besides the diagnostic categories of low-back pain (e.g., functional capability, psychological stress) may be primary determinants of health-related quality of life. To our knowledge, no other study has attempted to use the SF-36 to detect differences in health-related quality of life among patients with different spinal diagnoses.

              Cover page: Health-related quality of life in sacroiliac syndrome: A comparison to lumbosacral radiculopathy
              • Article
              • Peer Reviewed
              UC Santa Cruz Previously Published Works (2018)
              © 2018 European Control Association (EUCA). Regional stability analysis of linear systems with multi-rate samplers and actuator saturation is studied. A hybrid controller is used to perform a fusion of measurements sampled at different times. In between sampling events, the controller behaves as a copy of the plant. When a new measurement is available, the controller state undergoes a jump. The resulting system is analyzed in a hybrid system framework. Sufficient conditions in the form of matrix inequalities are given to determine estimates of the basin of attraction of the closed-loop system. Finally, the effectiveness of the proposed methodology is shown in an example.
                Cover page: Hybrid Regional Stabilization of Linear Systems with Actuator Saturation and Multi-Rate Samplers
                • Article
                • Peer Reviewed
                UC Santa Cruz Previously Published Works (2015)
                © 2015 American Automatic Control Council. We consider the problem of stabilizing a linear time-invariant system in the presence of sporadic output measurements and intermittent access to the plant input. The plant is equipped with a zero-order hold device which stores the value of the input between transmissions. We propose an observer-based controller composed consisting of a measurement-triggered observer which experiences jumps in its state whenever a new measure is available, a state-feedback control law computed from the estimated state, and a copy of the zero-order hold device feeding the plant, which jumps whenever the control input is transmitted to the plant. The closed-loop system is modeled as a hybrid system that includes two timers triggering the two different events. The resulting hybrid system is analyzed as the cascade of hybrid systems and its asymptotic stability properties are established through a separation principle. In addition, an efficient design procedure is presented and illustrated in an example.
                  Cover page: Observer-based control design for linear systems in the presence of limited measurement streams and intermittent input access
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                  • Peer Reviewed
                  UC Santa Cruz Previously Published Works (2014)
                  © IFAC. This paper deals with the estimation of the state of linear time invariant systems for which measurements of the output are available sporadically. An observer with jumps triggered by the arrival of such measurements is proposed and studied in a hybrid systems framework. The resulting system is written in estimation error coordinates and augmented with a timer variable that triggers the event of new measurements arriving. The design of the observer is performed to achieve uniform global asymptotic stability (UGAS) of a closed set including the points for which the state of the plant and its estimate coincide. Furthermore, a computationally tractable design procedure for the proposed observer is presented and illustrated in an example.
                    Cover page: An observer with measurement-triggered jumps for linear systems with known input
                    • Article
                    • Peer Reviewed
                    UC Santa Cruz Previously Published Works (2019)
                      Cover page: L-2 State Estimation With Guaranteed Convergence Speed in the Presence of Sporadic Measurements
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