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.     

The effects of closer monitoring on driver compliance with interlock restrictions

This randomized controlled trial of 2168 DWI multiple offenders assigned to a state-wide ignition interlock program in Maryland compared non-compliance with interlock requirements among drivers who were closely monitored (by Westat staff) and drivers who received standard monitoring (by the Motor Vehicle Administration). Compliance comparisons relied on datalogger data from MVA's interlock providers plus driver records that contained demographic information, prior alcohol-related traffic violations, their dispositions, and interlock duration. Measures for quantifying non-compliance included rates per 1000 engine starts for initial breath test failures at varying BAC levels and time periods, retest failures, retest refusals, interlock disconnects, startup violations, and summation measures. Regression analysis estimated the effects of closer monitoring on non-compliance, using linear mixed models that included random driver effects and fixed effects for study-group assignment, prior alcohol-related traffic violations, and months of continuous datalogger data with a quadratic function that assessed changes and rates of change in interlock non-compliance over time.All the separate non-compliance rates and summary measures derived from them were lower for closer monitored than control drivers for continuous data series of at least 6, 12, or 24 months. The differences for initial test failures and the two summary measures were statistically significant. Most measures of non-compliance decreased significantly as continuous time on the interlock increased. Parallel trends in each study group indicated that drivers learned to improve their compliance over time. Thus, this study convincingly demonstrates that closer monitoring substantially enhanced compliance with requirements of the ignition interlock and that regardless of group assignment, compliance increased over time.     

Hierarchical modeling using generalized linear models

In a complex manufacturing environment, there are hundreds of interrelated processes that form a complex hierarchy. This is especially true of semiconductor manufacturing. In such an environment, modeling and understanding the impact of critical process parameters on final performance measures such as defectivity is a challenging task. In addition, a number of modeling issues such as a small number of observations compared to process variables, difficulty in formulating a high‐dimensional design matrix, and missing data due to failures pose challenges in using empirical modeling techniques such as classical linear modeling as well as generalized linear modeling (GLM) approaches. Our approach is to utilize GLM in a hierarchical structure to understand the impact of key process and subprocess variables on the system output. A two‐level approach, comprising subprocess modeling and meta‐modeling, is presented and modeling related issues such as bias and variance estimation are considered. The hierarchical GLM approach helps not only in improving output measures, but also in identifying and improving subprocess variables attributed to poor output quality. Copyright © 2011 John Wiley & Sons, Ltd.     

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.