Use of Demorgan's theorem in system reliability studies

A method of obtaining a minimized system reliability or unreliability expression using Demorgan's theorem is presented. Some formulae based on this theorem are provided, from which the minimized expression of system unreliability can be obtained by knowledge of pathsets. At the same time, this expression can also provide minimum cutsets of the system easily. On the other hand, one can obtain the minimum pathsets of a system without much difficulty, if the minimum cutsets are known.     

An efficient approach for multiple criteria redundancy optimization problems

The present paper provides an efficient approach to multiple criteria redundancy optimization problems, often encountered in reliability design of engineering systems. A search technique introduced earlier [10,11] in combination with the multicriteria optimization methods, based on min-max concept for finding Pareto optimal solution of multicriteria optimization problems, provides an efficient and excellent approach for solving redundancy optimization problems. The approach is illustrated through several numerical examples. Further, based on this approach, a very general computer code called ESMOP (Efficient Search Multi-Objective Programming) has also been developed. It is capable of considering any type of redundancy, constraint or individual cost function and thus offers to solve many reliability design problems.     

Critical appraisal of piping phenomena in earth dams

This paper presents a comprehensive review of published literature on soil piping phenomena. The first tools to design earth dams to resist piping were developed during 1910–1935. Filter criteria for dispersive soils was refined in the 1970’s. Piping phenomena are generally defined as: (1) heave, (2) internal erosion, (3) backwards erosion, although other modes are possible. Recent work on piping highlights the limitations of the occurrence of piping and the role that design and construction may play in a large percentage of piping failures. Standardized laboratory procedures are available to assess piping potential in cohesive materials, but no such methods exist for non-cohesive soils. However, methods are available for evaluation of self-filtration potential. Recent advances in computer technology have facilitated the evaluation of seepage and deformation in embankments but computational methods for evaluation of piping potential are currently limited.      

Perinephric abscess (presenting as abdominal pain) due to Listeria monocytogenes

The development of a haematoma after wide excision of breast tumours is not uncommon. Suction drainage is commonly used to prevent this but often increases the hospital stay and can create unsightly wounds. Argon beam coagulation is a new technique which permits large 'raw' areas to be coagulated with minimal tissue damage. We believe that this technique may reduce the development of haematomas and seromas after breast surgery. We present our initial results using argon beam coagulation after wide excision of breast tumours in 80 patients without suction drainage. One patient required a single aspiration of a seroma at the site of breast lump excision and none required surgical drainage. Argon beam coagulation appears a useful adjunct in breast surgery and may help reduce hospital stay.     

Component Overpressure Growth and Characterization of High-Resistivity CdTe Crystals for Radiation Detectors

Spectrometer-grade CdTe single crystals with resistivities higher than 10⁹ Ω cm have been grown by the modified Bridgman method using zone-refined precursor materials (Cd and Te) under a Cd overpressure. The grown CdTe crystals had good charge-transport properties (μτ _e = 2 × 10⁻³ cm² V⁻¹, μτ _h = 8 × 10⁻⁵ cm² V⁻¹) and significantly reduced Te precipitates compared with crystals grown without Cd overpressure. The crystal growth conditions for the Bridgman system were optimized by computer modeling and simulation, using modified MASTRAPP program, and applied to crystal diameters of 14 mm (0.55′′), 38 mm (1.5′′), and 76 mm (3′′). Details of the CdTe crystal growth operation, structural, electrical, and optical characterization measurements, detector fabrication, and testing using ²⁴¹Am (60 keV) and ¹³⁷Cs (662 keV) sources are presented.     

Temperature rise in a viscoplastic material during dynamic crack growth

Dynamic steady-state crack growth has been analyzed under mode I plane stress, small-scale yielding conditions using a finite element procedure. A Perzyna type viscoplastic constitutive equation has been employed in this analysis. The viscoplastic work rate is converted into heat input and the temperature distribution is determined by solving the governing conduction/convection equation also by a finite element method. The Stream-line Upwinding Petrov-Galerkin formulation has been employed for this purpose because of the high Péclet number that results in such a type of analysis. The effect of strain rate sensitivity and crack speed on the temperature distribution near the crack tip is examined.     

An Improved Algorithm for Reliability Optimization

This paper proposes a modification of the Aggarwal et al. algorithm for reliability optimization by introducing a new heuristic criterion for selecting the subsystem where redundancy is to be added. This criterion accounts for the relative decrement in unreliability versus the largest of the relative increments in resources. The method applies to multiple separable constraint problems (which need not be linear) and to systems which may be complex or series. The method is simple, fast, and easily programmed. The results are compared with those of the Aggarwal et al. algorithm and are better in many problems.     

Analytical and experimental investigation on cool-down of short cryogenic transfer lines

Cool-down of cryogenic transfer lines is studied analytically and experimentally. Analytical expressions are derived for estimating cool-down time of uninsulated and vacuum insulated lines. The experimental results prove that for short sections the mass flow-rate does not affect the cool-down very significantly. It is also found that the analytical zero mass flow-rate cool-down curve predicts a reasonably accurate cool-down time for all mass flow-rates. The reverse annular flow theory explains many phenomena during cool-down. The cool-down curves are given for uninsulated glass, copper, aluminium and stainless steel pipelines.