A complex three-unit system

A three-unit standby redundant system has been studied. All the random variables involved are discrete. The life time of a unit while online is an arbitrarily distributed random variable. Also it is assumed that the probability of the repair completion is a constant. Using the regeneration point technique, the availability of the system is derived.     

Integrated design approach for advanced aerospace vehicles

Advanced aerospace vehicle design requires special design features that should meet the mission requirements of high payload to weight ratio in the case of space launchers and low radar cross-section for specific missiles/aircraft. The conventional design packages used are discussed in relation to their constraints. An interactive integrated design approach to eliminate the constraints imposed by individual design modules through interface design modules is discussed. Typical examples of such interface design modules are given. Also, a computer network necessary for an interactive integrated design approach interfacing the mainframe with a computer-aided design and drafting system and parallel processing is presented. This note has been prepared based on detailed discussions with designers in various areas of technology.     

A redundant system with non-instantaneous switchover and “preparation time” for the repair facility

This paper discusses two models of two-unit standby redundant systems in which the switchover time is a random variable and the repair facility is not available for a random time immediately after each repair completion. In model I the probability distributions of the life time of the online unit and switchover time are general while all the other distributions are exponential. Model II is a cold standby system in which the probability distributions of the “preparation time” of the repair facility is exponential and all the other distributions are general. Using the regeneration point technique the availability functions of the two systems are determined. Several special cases are also discussed.     

A game theoretic approach to optimal control in the presence of uncertainty

The optimal control problem, in the presence of uncertainty in the plant, is formulated as a game between the uncertainty and the control variables. This approach gives an optimal control strategy which is effective even under the "worst" conditions of uncertainty. The optimal control of a second-order plant with uncertainty in frequency brings out several interesting features. In particular, the existence of a barrier demarcating the controllable and uncontrollable regions in the phase plane is revealed, which is absent in the corresponding one-sided optimization.     

End effects in a MHD channel with diverging electrode walls

End effects phenomena in a Faraday type generator with diverging electrode walls for two types of velocity profiles—one with a source velocity and the other with a fully developed velocity—are discussed. The electric potential is determined numerically using the successive overrelaxation method in polar coordinates. It is found that the viscous forces increase the end losses and create current concentrations on the electrodes even at far distances from the entrance.     

Queuing Models for Estimating Aircraft Fleet Availability

The availability of a small fleet of aircraft in a flying-base, repair-depot combination is modeled and studied. First, a deterministic flow model relates parameters of interest and represents the state-of-the art in the planning of such systems. Second, a cyclic queue model shows the effect of the principal uncertainties in operation and repair and shows the consequent decrease in the availability of aircraft at the flying-base. Several options such as increasing fleet size, investments in additional repair facilities, or building reliability and maintainability into the individual aircraft during its life-cycle are open for increasing the availability. A life-cycle cost criterion brings out some of these features. Numerical results confirm Rose's prediction that there exists a minimal cost combination of end products and repair-depot capability to achieve a prescribed operational availability.     

Variation of structural and superconducting properties with initial stoichiometry variation in (Bi,Pb)-Sr-Ca-Cu-O bulk superconductor

The effect of the initial stoichiometry variation (variation in Bi, Pb, Sr, Ca and Cu) on various structural and superconducting properties of Pb-doped Bi-based superconductor has been studied. The sample having the initial stoichiometry of (Bi_1.8Pb_0.4)Sr₂Ca_2.2Cu₃O₁₀ was found to give best structural and superconducting properties. The most important factors affectingJ _c in the samples were the type of impurity phases present in the sample, their amount and distribution in the superconducting matrix. Cu-rich stoichiometry enhanced the formation of 110 K phase, but large amounts of undesirable impurities present in the samples decreasedJ _c. The formation of 110 K phase and texturing of (001) planes in a sample depended on the period of heat treatment and stoichiometry.     

Self-assembly through hydrogen-bonding and C–Hπ interactions in metal complexes of N-functionalised glycine

The complex [Ni(L1)₂(py)₂]. toluene (L1 is N-phthaloylglycinato and py is pyridine) was prepared from solid state reaction whereas co-crystals having composition 2[Ni(L1)₂(py)₃(H₂O)] · [Ni(L1)₂(py)₂(H₂O)₂] · 2py · 2H₂O was obtained from solution state reaction.     

Catalytic alcoholysis of quinolin-8-yl esters by manganese complexes

The role of different oxidation states of manganese in manganese(II) acetate promoted methanolysis reaction of p-nitrobenzoic acid quinolin-8-yl ester is presented.