Monte Carlo Simulation of Markov, Semi-Markov, and Generalized Semi- Markov Processes in Probabilistic Risk Assessment

A standard tool of reliability analysis used at NASA-JSC is the event tree. An event tree is simply a probability tree, with the probabilities determining the next step through the tree specified at each node. The nodal probabilities are determined by a reliability study of the physical system at work for a particular node. The reliability study performed at a node is typically referred to as a fault tree analysis, with the potential of a fault tree existing.for each node on the event tree. When examining an event tree it is obvious why the event tree/fault tree approach has been adopted. Typical event trees are quite complex in nature, and the event tree/fault tree approach provides a systematic and organized approach to reliability analysis. The purpose of this study was two fold. Firstly, we wanted to explore the possibility that a semi-Markov process can create dependencies between sojourn times (the times it takes to transition from one state to the next) that can decrease the uncertainty when estimating time to failures. Using a generalized semi-Markov model, we studied a four element reliability model and were able to demonstrate such sojourn time dependencies. Secondly, we wanted to study the use of semi-Markov processes to introduce a time variable into the event tree diagrams that are commonly developed in PRA (Probabilistic Risk Assessment) analyses. Event tree end states which change with time are more representative of failure scenarios than are the usual static probability-derived end states

The use of activated alumina for reclaiming and reconditioning turbine, transformer and circuit breaker oils

Advancements during the past few years have provided oil manufacturers with ample reason to claim that good oils no longer wear out because of use, but that deterioration by various destructive agencies such as moisture, air, heat, oxidation, emulsification and electro-chemical action may have the effect of rendering the oil totally unfit for use --page 1

The relation of eternity and time to reality

In the following pages we shall undertake, first, to trace the history of our problem, sketching in order the presentation of each of the above theories and, second, to summarize what seem to be the major contributions and defects of each

Recent changes to the Federal Reserve's survey of terms of business lending

The Federal Reserve's quarterly Survey of Terms of Business Lending, which has been conducted for more than twenty years, collects information on interest rates and other characteristics of commercial bank business loans. The survey has been changed from time to time to recognize innovations in bank lending practices and to improve the measurement of the desired information. The most recent changes took effect with the May 1997 survey. The major improvement was the addition of an item measuring loan risk. In addition, the reporting panel, which had been limited to domestically chartered commercial banks was expanded to include a sample of U.S. branches and agencies of foreign banks, which now account for a significant proportion of business lending to U.S. firms. This article discusses the most recent changes made to the survey and presents some information now available from the new items being reported. It also summarizes information about the use of loan risk ratings from consultations conducted with a sample of the survey respondents during the process of planning the revisions to the survey.Commercial loans

Clinical Research Informatics

This seminar describes programs and resources available through the Biomedical Informatics component of the UMCCTS

Supraclavicularis proprius muscle associated with supraclavicular nerve entrapment

Entrapment neuropathy of the supraclavicular nerve is rare and, when it occurs, is usually attributable to branching of the nerve into narrow bony clavicular canals. We describe another mechanism for entrapment of this nerve with the aberrant muscle; supraclavicularis being found during the routine dissection of an embalmed 82-year-old cadaver. Our report details a unique location for this rare muscular variation whereby the muscle fibres originated posteriorly on the medial aspect of the clavicle before forming a muscular arch over the supraclavicular nerve and passing laterally towards the trapezius and acromion. We recommend that in clinical instances of otherwise unexplained unilateral clavicular pain or tenderness, nerve compression from the supraclavicularis muscle must be borne in mind.

Brownian Adhesive Dynamics (BRAD) for Simulating the Receptor-Mediated Binding of Viruses

Current viral docking models have relied upon the assumption that bond formation and breakage are independent of viral and docking surface geometry, as well as the forces exerted on the bonds. This assumption, known as the equivalent site hypothesis (ESH), is examined in detail using a newly developed simulation technique—Brownian adhesive dynamics (BRAD). The simulation couples the thermal motion of viral particles with adhesive dynamics models to characterize the effect of bonding on viral motion. We use the binding of HIV-like particles to CD4 expressing cells as a model system to illustrate the utility of BRAD. Comparison of the transition rates between bound states predicted by ESH and the rates resulting from BRAD simulations show dramatic differences; at values of the equilibrium crosslinking constant, KxRT, where ESH suggests all virus adhesion proteins will be bound (KxRT = 106), BRAD predicts not all virus adhesion proteins will be bound. At values of the equilibrium crosslinking constant used in typical ESH calculations of virus docking (KxRT = 1) we find BRAD simulations predict no binding. The mean bond density from BRAD models is often much lower than that predicted by ESH for equivalent parameter values. BRAD suggests that the viruses are much less well bound than ESH predicts. The differences suggest that binding models for viruses need to be reexamined closely. BRAD is a simulation technique that will be useful for quantifying the receptor-mediated binding of a wide variety of viruses to cells