Impact of ethanol on the natural attenuation of MTBE in a normally sulfate-reducing aquifer

Side-by-side experiments were conducted in an aquifer contaminated with methyl-tert-butyl ether (MTBE) at a former fuel station to evaluate the effect of ethanol release on the fate of pre-existing MTBE contamination. On one side, for approximately 9 months we injected groundwater amended with 1-3 mg/L benzene, toluene, and o-xylene (BToX). On the other side, we injected the same, adding approximately 500 mg/L ethanol. The fates of BToX in both sides ("lanes") were addressed in a prior publication. No MTBE transformation was observed in the "No Ethanol Lane." In the "With Ethanol Lane", MTBE was transformed to tert-butyl alcohol (TBA) underthe methanogenic and/or acetogenic conditions induced by the in situ biodegradation of the ethanol downgradient of the injection wells. The lag time before onset of this transformation was less than 2 months and the pseudo-first-order reaction rate estimated after 7-8 months was 0.046 d(-1). Our results imply that rapid subsurface transformation of MTBE to TBA may be expected in situations where strongly anaerobic conditions are sustained and fluxes of requisite nutrients and electron donors allow development of an active acetogenic/methanogenic zone beyond the reach of inhibitory effects such as those caused by high concentrations of ethanol.     

Application‐driven analysis of two generations of capability computing: the transition to multicore processors

Multicore processors form the basis of most traditional high performance parallel processing architectures. Early experiences with these computers showed significant performance problems, both with regard to computation and inter‐process communication. The transition from Purple, an IBM POWER5‐based machine, to Cielo, a Cray XE6, as the main capability computing platform for the United States Department of Energy's Advanced Simulation and Computing campaign provides an opportunity to reexamine these issues after experiences with a few generations of multicore‐based machines. Experiences with Purple identified some important characteristics that led to strong performance of complex scientific application programs at very large scales. Herein, we compare the performance of some Advanced Simulation and Computing mission critical applications at capability scale across this transition to multicore processors. Copyright © 2012 John Wiley & Sons, Ltd.     

Efficacy and food safety considerations of poultry competitive exclusion products

Competitive exclusion (CE) products are anaerobic cultures of bacteria that are applied to poultry hatchlings to establish a protective enteric microbiota that excludes intestinal colonization by human food-borne pathogens. For safety of the poultry flock and human consumers, the identities of bacteria in CE products need to be known. A CE product is a culture of intestinal contents from adult chickens. It may be microbiologically defined by analysis of bacteria isolated from the culture, but many bacteria are hard to reliably isolate, identify, and characterize with conventional techniques. Sequence analysis of 16S ribosomal RNA (rRNA) genes may be more reliable than conventional techniques to identify CE bacteria. Bacteria in CE products may contain antimicrobial drug resistance and virulence mechanisms that could be transferred to the enteric bacteria of the food animal and to the human consumer. Detection methods for specific antimicrobial drug resistance and virulence genes and the integrase genes of conjugative transposons, mostly utilizing PCR technology, are being developed that can be applied to assess these risks in CE bacteria. With improvements in efficacy, bacterial identification, and detection and control of the possible risks of gene transfer, CE product technology can be made a more effective food safety tool.     

Development of Grain Boundary Precipitate-Free Zones in a Ni-Mo-Cr-W Alloy

In this study, the morphology and development of precipitate-free zones (PFZs) near grain boundaries (GBs) in low coefficient of thermal expansion (CTE) Ni-Mo-Cr-W alloys (based on Haynes 244) have been investigated as a function of thermal history and composition using electron microscopy techniques. It is shown that the formation of wide, continuous PFZs adjacent to GBs can be largely attributed to a vacancy depletion mechanism. It is proposed that variations in the vacancy distributions that develop after solution heat treatment (SHT) and subsequent quenching and aging greatly influence the development of the γ′-Ni₂(Mo,Cr) precipitates during the aging process and result in the development of PFZs of varying sizes. The relatively large (5 to 10 μm) PFZs are distinct from the smaller, more common PFZs that result from solute depletion due to GB precipitation that are typically observed after prolonged aging. During the course of this investigation, heat treatment parameters, such as aging time, SHT temperature, cooling rate after SHT, and heating rate to the aging temperature—all of which change vacancy concentration and distribution adjacent to GBs—were investigated and observed to have significant influence on both the size and morphology of the observed PFZs. In contrast to results from other Ni-based alloys studied previously, PFZ development in the current alloys was observed across a broad range of aging temperatures. This appears to be due to the high misfit strain energy of the γ′ precipitates, resulting in a nucleation process that is sensitive to vacancy concentration. It is also shown that a slightly modified alloy with higher Mo concentrations develops smaller, more typical PFZs; this is presumably due to an increased driving force for γ′ precipitation which overshadows the influence of misfit strain energy, thereby decreasing the sensitivity of precipitation on vacancy concentration.

     

Fabrication procedures and process sensitivities for CdS/CdTe solar cells

This paper details the laboratory processes used to fabricate CdS/CdTe solar cells at the National Renewable Energy Laboratory. The basic fabrication technique includes low‐pressure chemical vapor deposited SnO₂ , chemical‐bath deposited CdS, close‐spaced sublimated CdTe, solution‐CdCl₂ treatment, and an acid‐contact etch, followed by application of a doped‐graphite paste. This paper also describes the results of a reproducibility study in which cells were produced by multiple operators with an average AM1·5 efficiency of 12·6%. And finally, this paper discusses process sensitivities and alternative cell fabrication procedures and reports the fabrication of a cell with an AM1·5 efficiency of 15·4%. Copyright © 1999 John Wiley & Sons, Ltd.     

Specifying and animating facial signals for discourse in embodied conversational agents

People highlight the intended interpretation of their utterances within a larger discourse by a diverse set of non‐verbal signals. These signals represent a key challenge for animated conversational agents because they are pervasive, variable, and need to be coordinated judiciously in an effective contribution to conversation. In this paper, we describe a freely available cross‐platform real‐time facial animation system, RUTH , that animates such high‐level signals in synchrony with speech and lip movements. RUTH adopts an open, layered architecture in which fine‐grained features of the animation can be derived by rule from inferred linguistic structure, allowing us to use RUTH , in conjunction with annotation of observed discourse, to investigate the meaningful high‐level elements of conversational facial movement for American English speakers. Copyright © 2004 John Wiley & Sons, Ltd.