Excess coffee consumption in simulated complex work settings: detriment or facilitation of performance?

Twenty-four managers who normally consume between 400 and 1,000 mg of caffeine per day participated in all-day quasi-experimental simulations. In a crossover, doubleblind design, they made complex managerial decisions either on treatment with their typical daily dose of caffeine or on treatment with 400 mg of caffeine in excess of daily consumption. The effect of caffeine treatment on various validated performance indicators was investigated. The impact of excess caffeine consumption was mild. Increased caffeine facilitated speed of response to incoming information but decreased utilization of opportunity. No significance was obtained for other measures of managerial effectiveness (such as activity, breadth, strategy, and emergency response).     

The bid method for the steady-state Navier-Stokes equations

The Biharmonic Driver (BID) method uses direct (non-iterative) linear biharmonic solvers to obtain solutions to the nonlinear two-dimensional steady-state incompressible Navier-Stokes equations. Low Reynolds number recirculating flows are solved in 6–8 non-time-like iterations. Modifications are suggested for flow-through problems, and comparisons are made with other semidirect methods.     

Factors affecting performance using touch-entry systems: Tactual recognition fields and system accuracy.

Two laboratory experiments were conducted that investigated the effects of a number of factors on performance using an on-display touch-entry system. Experiment 1 (n?=?60) was carried out using a video display in a seated work station; horizontal angle of regard between the user and the display, size of the targets used, and gender were manipulated as factors. Experiment 2 (n?=?72) was carried out in a standing work station; both horizontal and vertical angle of regard between the user and the display, presence or absence of optical parallax, and gender were manipulated as factors. Results showed that all of the factors affected how accurately the touch-entry system accepted the touches. Statistical simulation models were then constructed by computing system accuracy as a function of the size of tactual recognition field used to capture the touch. It was possible both to accommodate the variability in performance among users and to minimize the effects of the manipulated factors on performance. This was the outcome for both seated and standing work stations. Implications of these results for the design of touch-entry systems are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Analysis of SiC/SiC composites for energy applications at ambient conditions

Plain weave planar and biaxially braided tubular SiC/SiC CMCs are evaluated in tension and four-point bending, respectively, at ambient conditions. Custom-designed fixtures for CMC testing are developed for each loading mode and are coupled with three-dimensional digital image correlation. Stereoscopic image correlation analysis reveals crack initiation and failure sites to provide insight into stress redistribution mechanisms. Scanning electron microscopy is performed postmortem to determine the influence of microstructural features on crack initiation and failure. Crack spacing is measured in situ by stereoscopic image correlation and confirmed by SEM measurements to relate to underlying tow-tow crossing points. Triangulated surface heights of plain weave tow architecture are used to determine that subtle differences in neighboring transverse tow angle, which vary within a range of ±4° from horizontal, have no significant effect on final fracture location. The results presented reaffirm the state of current SiC/SiC CMCs developed for energy applications and will help to further improve SiC/SiC and other CMCs.     

Unveiling hermetic failure of ceramic tubes by digital image correlation and acoustic emission

A new, in situ hermeticity testing apparatus has been developed to allow helium leak evaluation of ceramic tubes, including nuclear-grade SiC/SiC fuel cladding ceramic matrix composites (CMC), during four-point bending with simultaneous monitoring of local deformation and damage, using stereoscopic digital image correlation (DIC) and acoustic emissions. The capabilities of the experimental apparatus are demonstrated using alumina, borosilicate glass, and 4130 steel tubes with representative cladding dimensions and then applied to study the deformation-hermeticity relationship of SiC/SiC CMCs. Results of three CMCs appear to indicate that matrix cracking occurs near the deviation from linearity strain at strains ranging from 0.04% to 0.06% and is shortly followed by an initial loss of gas tightness by 0.09% bending strain. Leaking increased in distinct steps over 0.1%-0.2% bending strain, and within this range, results indicate that prior to fiber fracture, it is likely possible to regain gas tightness upon unloading. This technique and uncovered hermetic failure behavior are intended to progress the standardization of a test methodology for nuclear reactor components and to begin to resolve the mechanisms controlling distinct steps of ceramic matrix composite failure.     

Characterization of emissions of volatile organic compounds from interior alkyd paint

Alkyd paint continues to be used indoors for application to wood trim, cabinet surfaces, and some kitchen and bathroom walls. Alkyd paint may represent a significant source of volatile organic compounds (VOCs) indoors because of the frequency of use and amount of surface painted. The U.S. Environmental Protection Agency (EPA) is conducting research to characterize VOC emissions from paint and to develop source emission models that can be used for exposure assessment and risk management. The technical approach for this research involves both analysis of the liquid paint to identify and quantify the VOC contents and dynamic small chamber emissions tests to characterize the VOC emissions after application. The predominant constituents of the primer and two alkyd paints selected for testing were straight-chain alkanes (C9-C12); C8-C9 aromatics were minor constituents. Branched chain alkanes were the predominant VOCs in a third paint. A series of tests were performed to evaluate factors that may affect emissions following application of the coatings. The type of substrate (glass, wallboard, or pine board) did not have a substantial impact on the emissions with respect to peak concentrations, the emissions profile, or the amount of VOC mass emitted from the paint. Peak concentrations of total volatile organic compounds (TVOCs) as high as 10,000 mg/m3 were measured during small chamber emissions tests at 0.5 air exchanges per hour (ACH). Over 90% of the VOCs were emitted from the primer and paints during the first 10 hr following application. Emissions were similar from paint applied to bare pine board, a primed board, or a board previously painted with the same paint. The impact of other variable, including film thickness, air velocity at the surface, and air-exchange rate (AER) were consistent with theoretical predictions for gas-phase, mass transfer-controlled emissions. In addition to the alkanes and aromatics, aldehydes were detected in the emissions during paint drying. Hexanal, the predominant aldehyde in the emissions, was not detected in the liquid paint and was apparently an oxidation product formed during drying. This paper summarizes the results of the product analyses and a series of small chamber emissions tests. It also describes the use of a mass balance approach to evaluate the impact of test variables and to assess the quality of the emissions data.     

Modeling small-scale spills of aqueous solutions in the indoor environment

A mass transfer model is proposed to estimate the rates of chemical emissions from aqueous solutions spilled on hard surfaces inside buildings. The model is presented in two forms: a set of four ordinary differential equations and a simplified exact solution. The latter can be implemented in a spreadsheet. User input includes ten parameters, which represent either the properties of the source or those of the building. All of them can be readily obtained. The proposed model is tested against and in good agreement with the measurements of simulated spill events in a room-sized environmental chamber. This model can be used by emergency response planners to estimate the time history of contaminant concentrations in indoor air.     

Evaluation of low-VOC latex paints

Four commercially available low-volatile organic compound (VOC) latex paints were evaluated as substitutes for conventional latex paints by assessing both their emission characteristics and their performance as coatings. Bulk analysis indicated that the VOC contents of all four paints tested were considerably lower than those of conventional latex paints. Low VOC emissions were confirmed by small chamber emission tests. However, significant emissions of several aldehydes, especially formaldehyde which is a hazardous air pollutant, were detected in emissions from two of the four paints. American Society for Testing and Materials (ASTM) methods were used to evaluate the hiding power, scrub resistance, washability, dry to touch and yellowness index. The results indicated that one of the four low-VOC paints tested showed performance equivalent or superior to that of a conventional latex paint used as control. It was concluded that low-VOC latex paint can be a viable option to replace conventional latex paints for prevention of indoor air pollution. However, paints marketed as "low-VOC" may still have significant emissions of some individual VOCs, and some may not have performance characteristics matching those of conventional latex paints.     

Uncertainty and sensitivity analysis results obtained in the 1992 performance assessment for the waste isolation pilot plant

Uncertainty and sensitivity analysis results obtained in the 1992 performance assessment (PA) for the Waste Isolation Pilot Plant (WIPP) are presented. The primary performance measure under study is the complementary cumulative distribution function (CCDF) used in assessing compliance with the U.S. Environmental Protection Agency's (EPA's) standard for the geologic disposal of radioactive waste (40 CFR 191, Subpart B). The analysis considers releases to the accessible environment initiated by exploratory drilling for natural resources and models cuttings removal to the surface due to drilling intrusions, brine and gas flow in the vicinity of the repository and through drilling intrusions away from the repository, radionuclide transport by the flow of brine through intruding boreholes, and brine flow and radionuclide transport in permeable formations overlying the repository (i.e., the Culebra Dolomite). The effects of 49 imprecisely known variables are assessed with techniques based on Latin hypercube sampling and regression analysis. In addition, the effects of several alternative conceptual models for radionuclide transport in the Culebra Dolomite are investigated. Important issues identified in the analysis include (1) the importance of characterizing retardations and solubilities for individual elements, (2) the impact of assumptions involving human activities, including the rate and properties of drilling intrusions, and (3) the need to resolve the question of whether a single-porosity or dual-porosity transport model is appropriate for use in the Culebra Dolomite.