Optimal On-Line Scheduling of Multiple Control Tasks: A Case Study

We study the problem of dynamically scheduling a set of state-feedback control tasks controlling a set of linear plants. We consider an on-line non-preemptive scheduling policy that is optimal in the sense that it minimizes a quadratic performance criterion for the overall system. The optimal scheduling decision at each point in time is a function of the states of the controlled plants. To be able to solve the scheduling problem for realistic examples, we use the technique of relaxed dynamic programming to compute suboptimal solutions with error bounds. The approach is compared to earlier approaches in a case study involving simultaneous control of one ball-and-beam process and two DC-servo processes. We also show how the scheduling policy can be modified to allow for background tasks to execute when the need for control is small. 1

Stability-Aware Analysis and Design of Embedded Control Systems

Abstract—Many embedded systems comprise several controllerssharingavailableresources.Itiswellknownthat such resource sharing leads to complex timing behavior that can jeopardize stability of control applications, if it is not properly taken into account in the design process, e.g., mapping and scheduling. As opposed to hard real-time systems where meeting the deadline is a critical requirement, control applications do not enforce hard deadlines. Therefore,thetraditionalreal-timeanalysisapproachesare not readily applicable to control applications. Rather, in the context of control applications, stability is often the main requirement to be guaranteed, and can be expressed as the amount of delay and jitter a control application can tolerate. The nominal delay and response-time jitter can be regarded as the two main factors which relate the real-time aspects of a system to control performance and stability. Therefore, it is important to analyze the impact of variations in scheduling parameters, i.e., period and priority, on the nominal delay and response-time jitter and, ultimately, on stability. Based on such an analysis, we address, in this paper, priority assignment and sensitivity analysis problems for control applications considering stability as the main requirement. I

The bromotyrosine derivative Ianthelline isolated from the Arctic marine sponge Stryphnus fortis inhibits marine micro- and macrobiofouling

International audienceThe inhibition of marine biofouling by the bromotyrosine derivative ianthelline, isolated from the Arctic marine sponge Stryphnus fortis, is described. All major stages of the fouling process are investigated. The effect of ianthelline on adhesion and growth of marine bacteria and microalgae is tested to investigate its influence on the initial microfouling process comparing with the known marine antifoulant barettin as a reference. Macrofouling is studied via barnacle (Balanus improvisus) settlement assays and blue mussel (Mytilus edulis) phenoloxidase inhibition. Ianthelline is shown to inhibit both marine micro-and macrofoulers with a pronounced effect on marine bacteria (minimum inhibitory concentration (MIC) values 0.1-10 mu g/mL) and barnacle larval settlement (IC50= 3.0 mu g/mL). Moderate effects are recorded on M. edulis (IC50= 45.2 mu g/mL) and microalgae, where growth is more affected than surface adhesion. The effect of ianthelline is also investigated against human pathogenic bacteria. Ianthelline displayed low micromolar MIC values against several bacterial strains, both Gram positive and Gram negative, down to 2.5 mu g/mL. In summary, the effect of ianthelline on 20 different representative marine antifouling organisms and seven human pathogenic bacterial strains is presented

Dimer-induced signal propagation in Spo0A

Spo0A, the response regulator protein controlling the initiation of sporulation in Bacillus, has two distinct domains, an N-terminal phosphoacceptor (or receiver) domain and a C-terminal DNA-binding (or effector) domain. The phosphoacceptor domain mediates dimerization of Spo0A on phosphorylation. A comparison of the crystal structures of phosphorylated and unphosphorylated response regulators suggests a mechanism of activation in which structural changes originating at the phosphorylatable aspartate extend to the alpha(4)beta(5)alpha(5) surface of the protein. In particular, the data show an important role in downstream signalling for a conserved aromatic residue (Phe-105 in Spo0A), the conformation of which alters upon phosphorylation. In this study, we have prepared a Phe-105 to Ala mutant to probe the contribution of this residue to Spo0A function. We have also made an alanine substitution of the neighbouring residue Tyr-104 that is absolutely conserved in the Spo0As of spore-forming Bacilli. The spo0A(Y104A) and spo0A(F105A) alleles severely impair sporulation in vivo. In vitro phosphorylation of the purified proteins by phosphoramidate is unaffected, but dimerization and DNA binding are abolished by the mutations. We have identified intragenic suppressor mutations of spo0A(F105A) and shown that these second-site mutations in the purified proteins restore phosphorylation-dependent dimer formation. Our data support a model in which dimerization and signal transduction between the two domains of Spo0A are mediated principally by the alpha(4)beta(5)alpha(5) signalling surface in the receiver domain

PHYSICIAN HOSPITAL ARRANGEMENT INFLUENCE ON NONPROFIT HOSPITAL QUALITY,FINANCIAL PERFORMANCE AND COMMUNITY BENEFIT EXPENDITURES

Federal policy has encouraged hospitals to provide certain quality outcomes and cost containment. Hospitals have responded by forming physician hospital organizations in attempts to achieve quality outcomes and capture reimbursements. At the same time, federal policy has awarded hospitals with nonprofit status with the requirement to provide community benefits in exchange for the tax exemption they receive. With the formation of physician hospital organizations, there remains the question of whether hospitals are achieving desired quality metrics and whether hospitals are financially viable. There is also public and media interest recently regarding whether nonprofit hospitals fulfill their obligations for community benefit in line with the large tax exemption they receive. This study attempted to understand whether the hospital physician arrangements within nonprofit hospitals influence the hospitals’ quality, financial health, and any unintended effects there may be on community benefit expenditures. Data from the American Hospital Association and the tax return 990 schedule H was used to understand the types of hospital physician arrangements and to assess whether there was an association with nonprofit spending on quality, financial health and community benefit expenditures. This study showed that there is an association with higher Acute Myocardial Infarction 30 day mortality rates and Central Line-Associated Blood Stream Infection scores with physician hospital organizations with high integration; an undesirable outcome. High integration involves more physician and hospital economic, administrative, and group involvement and more shared accountability. This study also showed that there is an association with these physician hospital organizations and lower Acute Myocardial Infarction 30 day readmission rates, higher operating margin, and higher community benefits. No clear direction is apparent for the federal government regarding payer policies causing unintended consequences regarding hospital community benefits spending; however, the formation of physician hospital organizations with high integration may not have the quality metrics desired. The federal government will have to consider its policy effects and downstream consequences and whether they may be counter-productive to community benefit expenditures or whether they even achieve their intended purposes

The Real-Time Control Systems Simulator -Reference manual

A Matlab / Simulink-based simulator for real-time control systems is described. The simulator facilitates co-simulation of plant dynamics, controller code execution, and real-time scheduling. Three examples are given. The kernel primitives are described in detail

Merging Real-Time and Control Theory for Improving the Performance of Embedded Control Systems

This report describes the work carried out within the research project ``Merging Real-Time and Control Theory for Improving the Performance of Embedded Control Systems''. The overall objective of the work has been to develop integrated control and scheduling methods for improving the performance of real-time control systems with limited resources. The work has fallen into three categories. First, overrun methods for control tasks has been investigated. Specifically, a reservation-based scheduling concept called the Control Server has been further developed, and control experiments on a ball-and-place process have been performed. Second, the issue of jitter in real-time control systems has been explored. The concept of Jitter Margin has been introduced as a link between control stability theory and scheduling theory. In this context, best-case response-time analysis under earliest-deadline-first scheduling has been researched. Third, some development work on the S.Ha.R.K. real-time kernel has been performed. The rate-monotonic and earliest-deadline-first scheduling modules have been extended, and new modules for the elastic task model and the control server model have been implemented

Improved Scheduling of Control Tasks

The paper considers the implementation of digital controllers as real-time tasks in priority-preemptive systems. The performance of a digital feedback control system depends critically on the timing of its sampling and control actions. It is desirable to minimize the computational delay in the controller, as well as the sampling jitter and the control jitter. It is shown that by scheduling the two main parts of a control algorithm as separate tasks, the computational delay can often be reduced significantly. A heuristic method for assigning deadlines to the parts is presented. Further modifications are given to reduce the jitter and to facilitate delay compensation. The result is improved control performance under maintained schedulability

Stability and Worst-Case Performance Analysis of Sampled-Data Control Systems with Input and Output Jitter

When a feedback controller is implemented in a networked embedded system, the computations and communications induce delays and jitter, which may destabilize the control loop. The majority of previous work on analysis of control loops with time-varying delays has focused on output (actuation) jitter. In many embedded systems, input (sampling) jitter is also an issue. In this paper, we analyze the combined effect of input and output jitter on the stability and performance of linear sampled-data control systems. The analysis is performed via a loop transformation involving two time-varying uncertainties. We show how the input-output gains of the linear part of the transformed system can be computed using a fast-sampling/fast-hold approximation. At the same time, we reduce the conservativeness of a previous stability theorem for pure output jitter