On the controllability and observability of composite systems

Necessary and sufficient conditions for a linear multivariable feedback composite system to be completely controllable and completely observable are derived. The present derivation also provides a simple proof of the Hsu-Chen Theorem.     

On the global controllability of perturbed controllable systems

By using a recent theorem of Davison and Kunze [1], it is shown that, if certain conditions hold such that the systemdot{x} = A(x,t)x + B(x,t)uis globally controllable, then the perturbed systemdot{x} = [A(x,t) + epsilontilde{A}(x,t)]x + [B(x,t) + epsilontilde{B}(x,t)u, wheretilde{A}andtilde{B}are bounded, is also globally controllable, provided ε is small enough. In particular, ifdot{x} = A(t)x + B(t)uis controllable, then so is the perturbed systemdot{x} = [A(t) + epsilontilde{A}(x,t)]x + [B(t) + epsilontilde{B}(x,t)]u.     

Connectability and structural controllability of composite systems

The notion of connectability for multivariable composite systems consisting of a number of subsystems interconnected in an arbitrary way is introduced in this paper. It is shown that connectability plays a fundamental role in composite systems; in particular, it is shown that under certain mild conditions, almost all composite interconnected systems are controllable and observable from any nontrivial input and output if and only if the resultant composite system is connectable. A class of composite systems called general input-output hierarchical systems, which has the property of always being connectable is then defined. Since such systems are almost always controllable, this observation perhaps gives some insight in explaining why so many real world systems have as their basis a hierarchical structure. An application of the previous results is then made to show that a system (C, A, B) is structurally controllable and observable if and only if it is connectable and a certain non-pathological rank condition holds.     

Antibiotic activity of cultures of the species of the genus Actinomadura

Sixty five cultures of Actinomadura were isolated from samples of different soils. The study of their antibiotic activity on liquid nutrient media showed that 49 of them were active against gram-postive bacteria. The antibiotics isolated fromsome cultures of Am. carminata, Am. rubra, Am. coerulea and Am. luteofluorescens had antitumor effect in experiments on animals.     

Neurohypophyseal hormones in the cerebrospinal fluid with different degrees of hydration

Antidiuretic and oxytocic activities of venous blood plasma and liquor of ambient cistern of the cerebrum were studied in chronic experiments on alert dogs at different levels of hydration. Liquor was found to have oxytocic activity and practically no antidiuretic activity at ordinary hydration and after two days of thirst. After three days of thirst, dog's liquor caused antidiuretic reaction in rats anesthetized with alcohol, the reaction being lesser than those caused by simultaneously received plasma samples. Liquor displayed an obvious antidiuretic reaction similar to that of vasopressin after prolonged i.v. administration of hypotonic NaCl solution, while plasma samples only had the diuretic effect.