Optimal Sequencing of Items In a Consecutive-2-out-of-n System

A consecutive-2-out-of-n system is an array of n items in a line such that the system fails if and only if two consecutive items both fail. Suppose that the items have different probabilities of failing and that the system can be arranged into any sequence of the n items. Which sequence minimizes the probability of a system failure? It has been conjectured that the best sequence is one which essentially interlaces the more reliable items with the less reliable items. This paper partially supports the conjecture by proving it for the case that: a) the n probabilities take on only two distinct values, and b) the n probabilities take on only three distinct values, including either a zero or a one.     

Determining Component Reliability and Redundancy for Optimum System Reliability

The usual constrained reliability optimization problem is extended to include determining the optimal level of component reliability and the number of redundancies in each stage. With cost, weight, and volume constraints, the problem is one in which the component reliability is a variable, and the optimal trade-off between adding components and improving individual component reliability is determined. This is a mixed integer nonlinear programming problem in which the system reliability is to be maximized as a function of component reliability level and the number of components used at each stage. The model is illustrated with three general non linear constraints imposed on the system. The Hooke and Jeeves pattern search technique in combination with the heuristic approach by Aggarwal et al, is used to solve the problem. The Hooke and Jeeves pattern search technique is a sequential search routine for maximizing the system reliability, RS (R, X). The argument in the Hooke and Jeeves pattern search is the component reliability, R, which is varied according to exploratory moves and pattern moves until the maximum of RS (R, X) is obtained. The heuristic approach is applied to each value of the component reliability, R, to obtain the optimal number of redundancies, X, which maximizes RS (R, X) for the stated R.     

State assignment in finite state machines for minimal switchingpower consumption

A state assignment algorithm for minimal switching power consumption is proposed. It minimises the switching activity caused by state transitions by assigning codes closer in Hamming distance to the states with higher state transition probabilities. Experimental results show that the switching activity obtained by the proposed algorithm is, on the average, ~45% less than that of NOVA with only a ~3% increase in the number of product terms     

An experimental study of convective instability in the thermal entrance region of a horizontal parallel-plate channel heated from below

This paper presents results of an experimental investigation on the onset of longitudinal columnar vortices due to buoyant forces in the thermal entrance region of a horizontal parallel-plate channel heated from below. Channels with width 30 cm and heights h = 2, 3 and 4.5 cm were employed in the experiment. The instability of the convective motion is caused by the effects of temperature gradients in both longitudinal and vertical directions and was observed by a direct flow-visualization technique using smoke. Photographs of the front and top views of the vortex rolls are presented. Experimental results indicate that the wave number of vortex rolls remains constant along the flow direction and tends to approach the theoretical value as the channel width-height ratio increases. It was also observed that the critical Rayleigh number from flow visualization is 1.4 to 10 times higher than the critical value from linear theory.     

Consecutive-2-of-n:F systems with node and link failures

It has always been assumed that nodes can fail but not links, although most examples given for the consecutive-k-out-of-n :F system show no reason for such an assumption. The system described not only allows links to fail, but allows both nodes and links to fail, with distinct probabilities. For the k=2 case, the authors set up recursive equations for system reliability, and give a closed-form solution. It is proved that for n large, the reliability is decreasing in n (with one exceptional case) and higher reliability should be provided to the nodes, and then to the longer links rather than to shorter links     

Effect of B on the microstructure and mechanical properties of mechanically milled TiAl alloys

The present study is concerned with γ-(Ti₅₂Al₄₈)_100−x B _x (x=0, 0.5, 2, 5) alloys produced by mechanical milling/vacuum hot pressing (VHPing) using melt-extracted powders. Microstructure of the as-vacuum hot pressed (VHPed) alloys exhibits a duplex equiaxed microstructure of α₂ and γ with a mean grain size of 200 nm. Besides α₂ and γ phases, binary and 0.5 pct B alloys contain Ti₂AlN and Al₂O₃ phases located along the grain boundaries and show appreciable coarsening in grain and dispersoid sizes during annealing treatment at 1300 °C for 5 hours. On the other hand, 2 pct B and 5 pct B alloys contain fine boride particles within the γ grains and show minimal coarsening during annealing. Room-temperature compressing tests of the as-VHPed alloys show low ductility, but very high yield strength >2100 MPa. After annealing treatment, mechanically milled alloys show much higher yield strength than conventional powder metallurgy and ingot metallurgy processed alloys, with equivalent ductility to ingot metallurgy processed alloys. The 5 pct B alloy with the smallest grain size shows higher yield strength than binary alloy up to the test temperature of 700 °C. At 850 °C, 5 pct B alloy shows much lower strength than the binary alloy, indicating that the deformation of fine 5 pct B alloy is dominated by the grain boundary sliding mechanism. This article is based on a presentation made in the symposium “Mechanical Behavior of Bulk Nanocrystalline Solids,” presented at the 1997 Fall TMS Meeting and Materials Week, September 14–18, 1997, in Indianapolis, Indiana, under the auspices of the Mechanical Metallurgy (SMD), Powder Materials (MDMD), and Chemistry and Physics of Materials (EMPMD/SMD) Committees.     

Bioinformatics and its role in the study of the evolution and probiotic potential of lactic acid bacteria

Food Science and Biotechnology - Due to their numerous well-established applications in the food industry, there have been many studies regarding the adaptation and evolution of lactic acid...     

Electromechanical characteristics of unidirectional glass fiber epoxy composites

Because crack detection for laminated composites in‐service is an effective method for improving structural reliability, various nondestructive methods have been studied to detect cracks in laminated composites. A recent study on the damage monitoring of composite materials using the piezoelectric method, which uses the piezoelectric characteristics of polymeric materials for the matrix of composite materials, concluded that the piezoelectric method can be a useful, nondestructive method for the damage monitoring of glass fiber epoxy composites. The dielectric and piezoelectric properties of composites are the basic properties used for the analysis of electromechanical coupling systems, along with the mechanical properties. In this research, therefore, the electromechanical characteristics of unidirectional glass fiber epoxy composites as well as their electric and mechanical characteristics were investigated. The dielectric, piezoelectric, and mechanical properties of unidirectional glass fiber epoxy composites were measured experimentally with respect to the fiber orientation, and the relationship between the piezoelectric and mechanical characteristics of unidirectional glass fiber epoxy composites was analyzed. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers