Principal Components Analysis of Driving Simulator Variables in Novice Drivers.

Objective: Although driving simulators are powerful tools capable of measuring a wide-ranging set of tactical and operational level driving behaviors, comparing these behaviors across studies is problematic because there is no core set of driving variables to report when assessing driving behavior in simulated driving scenarios. To facilitate comparisons across studies, researchers need consistency in how driving simulator variables combine to assess driving behavior. With inter-study consistency, driving simulator research could support stronger conclusions about safe driving behaviors and more reliably identify future driver training goals. The purpose of the current study was to derive empirically and theoretically meaningful composite scores from driving behaviors of young people in a driving simulator, utilizing driving data from across a variety of driving environments and from within the individual driving environments. Method: One hundred ninety adolescent participants aged 16 years or 18 years at enrollment provided demographic data and drove in a high-fidelity driving simulator. The simulated scenario included 4 distinct environments: Urban, Freeway, Residential, and a Car Following Task (CFT). A Principal Components Analysis (PCA) was conducted on the variable output from the driving simulator to select optimal factor solutions and loadings both across the multi-environmental drive and within the four individual driving environments. Results: The PCA suggested two components from the multi-environmental simulated drive: vehicle control and speed. The individual driving environments also indicated two components: vehicle control and tactical judgment. Conclusion: These findings are among the first steps for identifying composite driving simulator variables to quantify theoretical conceptualizations of driving behavior. Currently, driving behavior and performance measured by driving simulators lack "gold standards" via driving scores or benchmarks. The composites derived in this analysis may be studied for further use where driving behavior standards are increasingly sought by clinicians and practitioners for a variety of populations, as well as by parents concerned about the readiness of their novice driving teen.

Social support buffers the negative influence of perceived injustice on pain interference in people living with HIV and chronic pain.

INTRODUCTION: A growing literature attests to the overwhelming prevalence of disabling chronic pain among people living with HIV (PLWH), yet very little is known about psychosocial contributors to poor chronic pain outcomes in this population. Pain-related perception of injustice may promote pain interference by hindering engagement in daily activities among individuals with chronic pain. Social support has been shown to buffer the negative impact of harmful beliefs on well-being and facilitate adjustment to chronic pain. OBJECTIVE: This cross-sectional study tested the buffering hypothesis of social support to determine whether increasing levels of social support mitigate the negative influence of perceived injustice on pain interference. METHODS: A total of 60 PLWH with chronic pain completed measures of perceived injustice, social support, pain severity, and interference, as well as depressive symptoms. RESULTS: In a regression-based model adjusted for age, sex, depressive symptoms, and pain severity, results indicated that social support significantly moderated (ie, buffered) the association between perceived injustice and pain interference (P = 0.028). Specifically, it was found that perceived injustice was significantly associated with greater pain interference among PLWH with low levels of social support (P = 0.047), but not those with intermediate (P = 0.422) or high levels of social support (P = 0.381). CONCLUSION: Pain-related injustice perception reflects harmful beliefs regarding severity of loss consequent to chronic pain development, a sense of unfairness, and irreparability of loss. Access to a social support network may provide an adaptive means of mitigating the negative effects of perceived injustice.

Isoprene formation in Bacillus subtilis: a barometer of central carbon assimilation in a bioreactor?

Isoprene (2-methyl-1,3-butadiene) is a volatile hydrocarbon of uncertain function in Bacillus subtilis, and we hypothesized that it is an overflow metabolite produced during excess carbon utilization. Here we tested this idea for phase 2 of isoprene release, a phase that occurs during extracellular acetoin accumulation and its reassimilation. Phase 2 isoprene formation could be disrupted in three different ways, all related to acetoin metabolism. Disruption of a gene essential for acetoin biosynthesis (acetolactic acid synthase, alsS) blocked acetoin formation and led to cessation of phase 2 isoprene formation as well as a variety of pleiotropic effects related to loss of pH control. Growth of the alsS mutant with external pH control reversed most of these effects. Disruption of acetoin catabolism (acetoin dehydrogenase, acoA), also eliminated phase 2 isoprene formation and caused cells to transition directly from phase 1 to phase 3; the latter is attributed to amino acid catabolism. A third alteration of acetoin metabolism was detected in the widely used strain 168 (trpC2) but not in strain MS175, a trpC mutant constructed in the Marburg strain genetic background. Strain 168 exhibited slow acetoin assimilation compared to that of MS175 or the parental strain, with little or no isoprene formation during this growth phase. These findings support the idea that isoprene release occurs primarily when the rate of carbon catabolism exceeds anabolism and that this volatile hydrocarbon is a product of overflow metabolism when precursors are not required for higher isoprenoid biosynthesis. It is suggested that isoprene release might serve as a useful barometer of the rise and fall of central carbon fluxes during the growth of Bacillus strains in industrial bioreactors.

Potential of on-line CIMS for bioprocess monitoring.

Chemical-ionization mass spectrometry (CIMS) using flow reactors is an emerging method for on-line monitoring of trace concentrations of organic compounds in the gas phase. In this study, a flow-reactor CIMS instrument, employing the H(3)O(+) cation as the ionizing reagent, was used to simultaneously monitor several volatile metabolic products as they are released into the headspace during bacterial growth in a bioreactor. Production of acetaldehyde, ethanol, acetone, butanol, acetoin, diacetyl, and isoprene by Bacillus subtilis is reported. Ion signal intensities were related to solution-phase concentrations using empirical calibrations and, in the case of isoprene, were compared with simultaneous gas chromatography measurements. Identification of volatile and semivolatile metabolites is discussed. Flow-reactor CIMS techniques should be useful for bioprocess monitoring applications because of their ability to sensitively and simultaneously monitor many volatile metabolites on-line.