Stability analysis of impulsive control systems

This paper studies impulsive control systems. Several stability criteria are established by employing the method of Lyapunov functions. These criteria may be used for impulsive feedback control design. As an application, impulsive control of the Lorenz chaotic system is discussed. Numerical experiments are carried out for the control of the Lorenz system. It is shown that small and frequent impulses need to be used in order to stabilize the Lorenz system.     

A class of optimal state-delay control problems

We consider a general nonlinear time-delay system with state-delays as control variables. The problem of determining optimal values for the state-delays to minimize overall system cost is a non-standard optimal control problem–called an optimal state-delay control problem–that cannot be solved using existing optimal control techniques. We show that this optimal control problem can be formulated as a nonlinear programming problem in which the cost function is an implicit function of the decision variables. We then develop an efficient numerical method for determining the cost function’s gradient. This method, which involves integrating an auxiliary impulsive system backwards in time, can be combined with any standard gradient-based optimization method to solve the optimal state-delay control problem effectively. We conclude the paper by discussing applications of our approach to parameter identification and delayed feedback control.     

Characteristics and origin of clusters in submicron WC-Co cermets

The microstructure of the WC phase in submicron WC-Co alloys has been investigated by transmission electron microscopy. The existence of clusters formed by several grains mainly related by Σ =1 and Σ=2 high-coincidence orientation relationships is shown. The features of these grain boundaries are studied using high-resolution electron microscopy. Two cases of Σ =1 orientation are investigated. In one case, the boundary contrast arises from the presence at the interface of a nanometric intermediate layer. In the other case, a grain boundary separating domains with different carbon positions is evidenced. Investigations of the starting WC powder indicate the existence of clusters already in particles and reveal the polygonal shape of WC grains before sintering. Some microstructure characteristics of the clusters suggest that the majority of clusters observed in the sintered material arise from the powder.     

Optimal Control of Nonlinear Fractional-Order Systems with Multiple Time-Varying Delays

Journal of Optimization Theory and Applications - This paper considers an optimal control problem governed by nonlinear fractional-order systems with multiple time-varying delays and subject to...     

Solid-phase assembly and in situ screening of protein tyrosine phosphatase inhibitors

A highly efficient solid-phase strategy for assembly of small molecule inhibitors against protein tyrosine phosphatase 1B (PTP1B) is described. The method is highlighted by its simplicity and product purity. A 70-member combinatorial library of analogues of a known PTP1B inhibitor has been synthesized, which upon direct in situ screening revealed a potent inhibitor ( Ki = 7.0 microM) against PTP1B.     

Carcinogenic Chromium(VI) Compounds Formed by Intracellular Oxidation of Chromium(III) Dietary Supplements by Adipocytes

Chromium(III) nutritional supplements are widely consumed for their purported antidiabetic activities. X‐ray fluorescence microscopy (XFM) and X‐ray absorption near‐edge structure (XANES) studies have now shown that non‐toxic doses of [Cr₃O(OCOEt)₆(OH₂)₃]⁺ ( A ), a prospective antidiabetic drug that undergoes similar H₂O₂ induced oxidation reactions in the blood as other Cr supplements, was also oxidized to carcinogenic Cr^VI and Cr^V in living cells. Single adipocytes treated with A had approximately 1 μm large Cr hotspots containing Cr^III, Cr^V, and Cr^VI (primarily Cr^VI thiolates) species. These results strongly support the hypothesis that the antidiabetic activity of Cr^III and the carcinogenicity of Cr^VI compounds arise from similar mechanisms involving highly reactive Cr^VI and Cr^V intermediates, and highlight concerns over the safety of Cr^III nutritional supplements.