Efficient reliability estimate of passive thermal hydraulic safety system with automatic differentiation

An approach for efficient estimation of passive safety system functional reliability has been developed and applied to a simplified model of the passive residual heat transport system typical of sodium cooled fast reactors to demonstrate the reduction in computational time. The method is based on generating linear approximations to the best estimate computer code, using the technique of automatic reverse differentiation. This technique enables determination of linear approximation to the code in a few runs independent of the number of input variables for each response variable. The likely error due to linear approximation is reduced by augmented sampling through best estimate code in the neighborhood of the linear failure surface but in a sub domain where linear approximation error is relatively more. The efficiency of this new approach is compared with importance sampling MCS which uses the linear approximation near the failure region and with Direct Monte-Carlo Simulation. In the importance sampling MCS, variants employing random sampling with Box-Muller algorithm and Markov Chain algorithm are inter-compared. The significance of the results with respect to system reliability is also discussed.     

Use of newborn screening program blood spots for exposure assessment: declining levels of perluorinated compounds in New York State infants

Temporal biomonitoring studies can assess changes in population exposures to contaminants, but collection of biological specimens with adequate representation and sufficient temporal resolution can be resource-intensive. Newborn Screening Programs (NSPs) collect blood as dried spots on filter paper from nearly all infants born in the United States (U.S.). In this study, we investigated the use of NSP blood spots for temporal biomonitoring by analyzing perfluorooctane sulfonate (PFOS), perfluorooctane sulfonamide (PFOSA), perfluorohexane sulfonate (PFHxS), perfluorooctanoic acid (PFOA), and perfluorononanoic acid (PFNA) in 110 New York State (NYS) NSP blood spot composite specimens collected between 1997 and 2007, representing a total of 2640 infants. All analytes were detected in > or =90% of the specimens. Concentrations of PFOS, PFOSA, PFHxS, and PFOA exhibited significant exponential declines after the year 2000, coinciding with the phase-out in PFOS production in the U.S. Calculated disappearance half-lives for PFOS, PFHxS, and PFOA (4.4, 8.2, and 4.1 years, respectively) were similar to biological half-lives reported for retired fluorochemical workers. Our results suggest sharp decreases in perinatal exposure of NYS infants to PFOS, PFOSA, PFHxS, and PFOA and demonstrate, for the first time, the utility of NSP blood spots for assessment of temporal trends in exposure.     

An improved photographic process for convergent beam electron diffraction applications

The use of a surface developer, pyrocatechol, to process transmission electron microscope negatives has been shown to have significant advantages over the conventional D-19 process. The process described here is tolerant of a large margin of error in the electron exposure and produces a negative that not only retains details both in the highlight as well as the faint regions, but also preserves local contrast. These characteristics are particularly useful in convergent beam electron diffraction applications where one encounters a wide contrast range. Improved acuteness and an enhanced signal to noise ratio due to the prolonged exposures associated with this process have also been observed.     

Hydrothermal synthesis of chromium dioxide powders and their characterisation

Chromium dioxide (CrO₂) powders have been synthesised by decomposing CrO₃ and Cr₂O₅ powders under hydrothermal conditions in the temperature range of 300–500°C and pressure range of 250–1200 bars. Oxides of antimony and iron have been used as modifiers to induce acicular morphology. A novel method of using alkali metal salts such as chlorides and carbonates as mineralisers produces CrO₂ with superior magnetic characteristics. The particle size distributions have been correlated with the magnetic properties of the materials. The products obtained have properties rendering them useful for magnetic recording applications.     

Nonsteroidal anti-inflammatory drug induced duodenal web

Duodenal webs represent an unusual cause of intestinal obstruction in adults. These anomalies are generally considered to be congenital in origin and usually present in infancy. However, they occasionally become symptomatic in adulthood. In these cases, because of the delay in symptoms, the etiology of duodenal webs in adults is uncertain. Gastrointestinal webs in adults have also been reported in the small intestine and colon. It is generally accepted that these lesions are an acquired defect related to long term nonsteroidal anti-inflammatory drug (NSAID) use. We report a patient with a history of long term NSAID use who presented with symptoms of gastric outlet obstruction due to the presence of a duodenal web.     

Dioxin-like and non-dioxin like effects of polychlorinated biphenyls: Implications for risk assessment

Polychlorinated biphenyls (PCBs) are persistent, bioaccumulative and toxic contaminants in the environment. Individual PCB congeners exhibit different physicochemical properties and biological activities that result in different environmental distributions and toxicity profiles. The variable composition of PCB residues in environmental matrices and their different mechanisms of toxicity complicate the development of scientifically based regulations for risk assessment. Various approaches for the assessment of risks of PCBs have been critically examined. Recent developments in the toxic equivalency factor (TEF) approach for the assessment of toxic effects due to dioxin‐like PCBs have been examined. The PCB exposure studies that describe non‐dioxin‐like toxic effects, particularly neurobehavioural effects and their effective doses in animals, were compiled. A comparative assessment of effective doses for dioxin‐like and non‐dioxin‐like effects by PCBs has been made to evaluate the relative significance of non‐ortho and ortho‐substituted PCBs in risk assessment. Using mink as an example, relative merits and implications of using TEF and total PCB approaches for assessing the potential for toxic effects in wildlife were examined. There are several advantages and limitations associated with each method used for PCB risk assessment. Toxic effects due to coplanar PCBs occur at relatively smaller concentrations than those due to non‐dioxin‐like PCBs and, therefore, the TEF approach derives the risk assessment of PCBs in the environment. The need for the refinement of the TEF approach for more accurate assessment of risks is discussed.     

Probability of first passage analysis of a two-stage transfer-line production system with storage and rework

In this paper, we study some of the transient state characteristics of a two-stage transfer-line production system subject to an initial storage of unlimited capacity and reworking the defective products in the respective stages. This paper provides a complete analysis to consider manufacturing, inspection and reworking in two-stage transfer-line production systems. The first stage of the system is never starved and the second stage is never blocked. A stochastic model is developed to analyse the system and explicit analytical expressions for some of the system characteristics have been obtained using the state space method and regeneration point technique. All the random variables involved in the analysis are assumed to be arbitrary (general).     

Novel AB crosslinked polymer networks based on 1‐vinylimidazole‐ terminated polyurethane and poly(methyl methacrylate)

1‐Vinylimidazole‐terminated telechelic polyurethanes were prepared from 1‐vinylimidazole and bromine‐terminated polyurethane. This vinyl‐terminated telechelic polyurethane (VTPU) and methyl methacrylate were polymerized in the presence of benzoyl peroxide to prepare novel AB crosslinked polymer networks (ABCPs). These were characterized by spectral, thermal and mechanical studies. The absence of the characteristic peak of vinyl group in infrared spectra of ABCP films confirms the occurrence of crosslinking. Static mechanical testing showed that the tensile strength of ABCP increases with increasing poly(methyl methacrylate) content. Dynamic mechanical studies revealed that ABCPs, at equal compositions of VTPU and methyl methacrylate, show good damping properties. Copyright © 2006 Society of Chemical Industry     

A COAL PYROLYSIS REACTOR SYSTEM WITH FAST ON-LINE COMPOSITION ANALYSIS BY GAS CHROMATOGRAPHY

The development of a coal pyrolysis reactor and a novel gas chromatography method for fast on-line composition analysis of pyrolysis products are presented. The annular fluidized bed reactor system minimizes particle agglomeration during the pyrolysis of plastic coals and the new column switching technique significantly reduces the time required for measuring the composition of low-volatile pyrolysis gases on a conventional gas chromatograph. Data from representative pyrolysis runs are presented and discussed.