A type-II censored, log test time based, component-testingprocedure for a parallel system

The authors consider the problem of acceptance testing for a parallel (1-out-of-n:G) system of different components with constant failure rates. The components are individually tested and the tests are terminated as soon as a preassigned number of each component fails. The authors provide a criterion for accepting or rejecting the system based on the sum of the logarithms of the total times on test for each component. The critical level for the test statistic is chosen so as to guarantee that the specified consumer and producer risks on the system reliability are not exceeded. The use of this statistic makes the computation of these critical values much simpler as compared with that of a previously used statistic based on the product of the total times on test for each component. Several approximate procedures are considered for deriving these critical values. The authors also formulate the optimization problem for deriving the minimum-cost component-testing plans when a type-II censored component-test procedure is used for a parallel system     

Detection of edges from projections

In a number of applications of computerized tomography, the ultimate goal is to detect and characterize objects within a cross section. Detection of edges of different contrast regions yields the required information. The problem of detecting edges from projection data is addressed. It is shown that the class of linear edge detection operators used on images can be used for detection of edges directly from projection data. This not only reduces the computational burden but also avoids the difficulties of postprocessing a reconstructed image. This is accomplished by a convolution backprojection operation. For example, with the Marr-Hildreth edge detection operator, the filtering function that is to be used on the projection data is the Radon transform of the Laplacian of the 2-D Gaussian function which is combined with the reconstruction filter. Simulation results showing the efficacy of the proposed method and a comparison with edges detected from the reconstructed image are presented.     

A system-based component test plan for a series system, withtype-II censoring

Acceptance testing is analyzed for a series system of n components, each having an unknown, different, constant failure rate. Components are tested individually, and tests are terminated when a preassigned number of failures is observed for each component. The total time-on-test for each component is noted, and a statistic is constructed using observed test times and the number of failures of the components; the statistic is based on the maximum likelihood estimation of system reliability. This statistic is then used in specifying a decision rule for accepting or rejecting the entire system. The design of the test plan is stated as an optimization problem which minimizes test costs while ensuring that specified consumer and producer risks on system reliability are not exceeded. Numerical examples are provided, and implications of the test plan are discussed     

Modular operational test plans for inferences on softwarereliability based on a Markov model

This paper considers the problem of assessing the reliability of a software system that can be decomposed into a finite number of modules. It uses a Markovian model for the transfer of control between modules in order to develop the system reliability expression in terms of the module reliabilities. An operational test procedure is considered in which only the individual modules are tested and the system is considered acceptable if, and only if, no failures are observed. The minimum number of tests required of each module is determined such that the probability of accepting a system whose reliability falls below a specified value R₀ is less than a specified small fraction β. This sample size determination problem is formulated as a two-stage mathematical program and an algorithm is developed for solving this problem. Two examples from the literature are considered to demonstrate the procedure     

Selective synthesis of 3-picoline via the vapor-phase methylation of pyridine with methanol over Ni1-x Co x Fe2O4 (x = 0, 0.2, 0.5, 0.8 and 1.0) type ferrites

A series of Ni–Co ferrites with the general formula Ni_1-x Co _x Fe₂O₄ (x = 0, 0.2, 0.5, 0.8 and 1.0) was prepared by a low-temperature hydroxide coprecipitation route. The catalyst systems were characterized by adopting various physico-chemical techniques. Alkylation of pyridine with methanol was carried out in a down-flow vapor-phase reactor. The influence of surface acid–base properties, cation distribution in the spinel lattice and various reaction parameters are discussed. It was observed that the systems possessing x values 0.5 are selective for 3-picoline formation, whereas the ones with x values 0 and 0.2 give a mixture of 2- and 3-picolines. Pyridine conversion increased with the progressive substitution of Ni²⁺ ions by Co²⁺ ions. Cation distribution in the spinel lattice influences their acidic and basic properties, and these factors have been adequately considered as helpful to evaluate the activity of the systems.     

Design of high-order filters with restricted component values

The feasibility of realising a high-order LC filter with a small set of different capacitor values, without sacrificing the frequency response specifications, is indicated. This idea could be conveniently adopted in other filter structures also?for example the FDNR transformed filter realisations.     

Redesign of vaccine distribution networks

In most low- and middle-income countries supported by the World Health Organization's Expanded Program on Immunization, vaccines are distributed through a legacy medical supply chain that is typically not cost-efficient. Vaccines require storage and transport in a temperature-controlled environment; this requires a “cold” distribution chain with capacity constraints on cold storage and cold transport. We propose an approach to redesigning the vaccine distribution chain that includes locating a set of intermediate distribution centers (DCs) and determining the flow paths from the central store (where vaccines are received into a country) through one or more of these to health clinics where vaccination actually occurs. In addition, the transport vehicles to allocate to each flow path, and the cold storage devices to use at each clinic or intermediate DC are determined. The redesigned network does not have to follow the current four-tiered, arborescent structure commonly found in practice, but can use alternative network structures. To redesign this network optimally, we develop a mixed-integer programming (MIP) model that can be used for small-to-medium-sized problems and also present a hybrid heuristic–MIP method to obtain good solutions for larger problems. Numerical results are shown using data reflecting distribution networks in several countries in sub-Saharan Africa.     

Optimization of indoor wireless communication network layouts

Radio Frequency Data Communications (RFDC)technology is rapidly becoming a critical component of many traditional industrial engineering functions including materials tracking, inventory control, warehousing, order processing, shipping and database management. As a means of moving information, RFDC has many attractive features, such as speed, accuracy, reliability, convenience and low operating costs. When implementing RFDC systems a major problem is to quickly and efficiently determine the locations where transceivers should be placed so that effective radio communication can take place. The research described in this paper addresses this issue by developing a computerized layout simulation system that incorporates heuristic optimization methods to solve the placement problem. The effectiveness of this unique automated layout methodology is demonstrated by comparing it with the current method of utilizing manual site surveys, as well as with other placement methods. The methodology and solutions are validated by field-testing at actual facilities.     

Copper-alginates: a biopolymer supported Cu(II) catalyst for 1,3-dipolar cycloaddition of alkynes with azides and oxidative coupling of 2-naphthols and phenols in water

Copper(II) ions immobilized onto a biopolymer (sodium alginate) is an effective heterogeneous catalyst for 1,3-dipolar cycloaddition of alkynes with azides and oxidative coupling of 2-naphthols and phenols in water to afford the 1,4-disubstituted 1,2,3-triazoles and biaryl compounds respectively in good yields. The catalyst was recovered quantitatively by simple filtration and reused for several times without significant loss of activity.     

An improved specimen loader for cryo-scanning electron microscopy

Cryo-electron microscopy of cryofixed samples is a well-established and accepted technique for imaging liquid-containing specimens without removing water and other volatile components. There are many steps between cryofixation and cryo-observation in the microscope, during which the sample and sample holder need to be handled. One such major step is the loading of the specimen onto the sample holder and the fixing of the sample holder onto the transfer mechanism. During this handling, the specimen is often exposed (mostly inadvertently) to moisture in the atmosphere, which results in frost deposition. The new specimen loader described here is designed to overcome the traditional tedious handling and to achieve ease in specimen loading. The modifications made are mainly towards allowing movement of the liquid freon cup, eliminating the need for a lock-screw and improving the shape of the stage holder, which makes the mounting of the specimen holder easy, thereby permitting smooth specimen loading without too much handling and with consequent reduced frost deposition.