Robust H∞ control of networked control systems with access constraints and packet dropouts

We consider a class of networked control systems (NCSs) where the plant has time-varying norm-bounded parameter uncertainties, the network only provides a limited number of simultaneous accesses for the sensors and actuators, and the packet dropouts occur randomly in the network. For this class of NCSs with uncertainties and access constraints as well as packet dropouts, we derive sufficient conditions in the form of linear matrix inequalities that guarantee robust stochastic stabilisation and synthesis of H∞ controller. An example is provided to illustrate our proposed method

Optimal Controller and Filter Realisations using Finite-precision, Floating- point Arithmetic.

The problem of reducing the fragility of digital controllers and filters implemented using finite-precision, floating-point arithmetic is considered. Floating-point arithmetic parameter uncertainty is multiplicative, unlike parameter uncertainty resulting from fixed-point arithmetic. Based on first- order eigenvalue sensitivity analysis, an upper bound on the eigenvalue perturbations is derived. Consequently, open-loop and closed-loop eigenvalue sensitivity measures are proposed. These measures are dependent upon the filter/ controller realization. Problems of obtaining the optimal realization with respect to both the open-loop and the closed-loop eigenvalue sensitivity measures are posed. The problem for the open-loop case is completely solved. Solutions for the closed-loop case are obtained using non-linear programming. The problems are illustrated with a numerical example

Stability of Networked Control Systems with Random Buffer Capacity

Stability of the discrete-time networked control systems is analysed, where the controller is updated with the buffered sensor information at stochastic intervals and the amount of the buffered data for transmission under the buffer capacity constraint is time-varying. The adopted controller switches between open-loop and closed-loop modes to estimate the plant behaviour. The sufficient condition for the Lyapunov stability with the generic arbitrary transmission is derived, and the sufficient conditions for the mean square stability with the Markovian transmission are also established. An example is given to demonstrate the effectiveness of our method

Mesenchymal stem cells overexpressing MiR-126 enhance ischemic angiogenesis via the AKT/ERK-related pathway

Background: This study was designed to examine whether transplantation of mesenchymal stem cells (MSCs) overexpressing miR-126 enhances angiogenesis in the infarcted myocardium of mice. Methods: MSCs were harvested from mice using density gradient centrifugation and adherent culture. MSCs were transfected with lentiviral vectors carrying mature miR-126. Mice models of myocardial infarction were established by ligation of coronary artery. The ligated animals were randomly divided into three groups (15 in each) and after two weeks, were intramyocardially injected at the heart infarct zone with miR-126-transfected MSCs (the miR-126-MSCs group), MSCs (the MSCs group), or medium (the PBS group). Six weeks later, histological study and echocardiographic assessment were performed. Results: Capillary density of the infarcted region was significantly improved in the miR-126- MSCs group compared to the MSC group and the PBS group (both p < 0.01). Western blot showed that ERK1, pERK1, AKT and pAKT gene were dramatically enhanced in the miR-126-MSC group compared to the MSC group and the PBS group (both p < 0.05). Echocardiography showed MiR-126 led to a sustained improvement in cardiac function for at least six weeks at the injected area, as assessed by left ventricular ejection fraction and fraction of shortening. Conclusions: Transplantation of MSCs transfected with miR-126 can improve angiogenesis and cardiac function in the infarcted area of the hearts of mice, which may be due to stimulation of the AKT/ERK-related pathway. (Cardiol J 2011; 18, 6: 675&#8211;681