ALBERT

Notes: Measurements of equation of state (EOS) points on the principal Hugoniots of Cu, Au, Pb and the plastics Parylene-C and brominated CH at multimegabar pressures have been made using the 1 TW HELEN laser at AWE. The aim was 1% accuracy in shock velocity measurement (3%–4% in pressure) in order to compare with data from gas-gun and nuclear underground test experiments and the theoretical EOS's based on, or supported by, these data. Experiments comprised a hohlraum heated by two 500 J, 0.53 μm wavelength, 1 ns Gaussian laser pulses generating an x-ray flux which drove a shock into a target consisting of a base, with steps of a known EOS material and of the material of unknown EOS. Shock breakout from base and steps was detected by monitoring light emission from the target with optical streak cameras and shock velocities were derived from the transit times across the known-height steps. © 2002 American Institute of Physics.

Notes: A model of carrier phase measurement (as carried out by a satellite navigation receiver) is formulated based on electromagnetic theory. The model shows that the phase of the open-circuit voltage induced in the receiver antenna with respect to a local oscillator (in the receiver) depends on the relative orientation of the receiving and transmitting antennas. The model shows that using a single receiving antenna, and making carrier phase measurements to seven satellites, the three-axis attitude of a user platform (in addition to its position and time) can be computed relative to an initial point. This measurement model can also be used to create high-fidelity satellite signal simulators that take into account the effect of platform rotation as well as translation. © 2002 American Institute of Physics.

Notes: We present a simple model of the signals transmitted by global positioning system (GPS) satellites and of the reception of these signals by a GPS receiver, neglecting atmospheric effects. The model idealizes the receiver and transmitter as electric dipole antennas. We derive the open-circuit voltage induced in the antenna of the receiver as a function of time, position, velocity, and orientation of the respective antenna. As an application of this model, we show that by using a single dipole antenna, a user of the GPS can compute his position, time, and two angles of attitude, by tracking the phases of the open-circuit antenna voltages for six GPS satellites.

Notes: Recent studies demonstrating a concentration dependence of elimination of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) suggest that previous estimates of exposure for occupationally exposed cohorts may have underestimated actual exposure, resulting in a potential overestimate of the carcinogenic potency of TCDD in humans based on the mortality data for these cohorts. Using a database on U.S. chemical manufacturing workers potentially exposed to TCDD compiled by the National Institute for Occupational Safety and Health (NIOSH), we evaluated the impact of using a concentration- and age-dependent elimination model (CADM) (Aylward et al., 2005) on estimates of serum lipid area under the curve (AUC) for the NIOSH cohort. These data were used previously by Steenland et al. (2001) in combination with a first-order elimination model with an 8.7-year half-life to estimate cumulative serum lipid concentration (equivalent to AUC) for these workers for use in cancer dose-response assessment. Serum lipid TCDD measurements taken in 1988 for a subset of the cohort were combined with the NIOSH job exposure matrix and work histories to estimate dose rates per unit of exposure score. We evaluated the effect of choices in regression model (regression on untransformed vs. ln-transformed data and inclusion of a nonzero regression intercept) as well as the impact of choices of elimination models and parameters on estimated AUCs for the cohort. Central estimates for dose rate parameters derived from the serum-sampled subcohort were applied with the elimination models to time-specific exposure scores for the entire cohort to generate AUC estimates for all cohort members. Use of the CADM resulted in improved model fits to the serum sampling data compared to the first-order models. Dose rates varied by a factor of 50 among different combinations of elimination model, parameter sets, and regression models. Use of a CADM results in increases of up to five-fold in AUC estimates for the more highly exposed members of the cohort compared to estimates obtained using the first-order model with 8.7-year half-life. This degree of variation in the AUC estimates for this cohort would affect substantially the cancer potency estimates derived from the mortality data from this cohort. Such variability and uncertainty in the reconstructed serum lipid AUC estimates for this cohort, depending on elimination model, parameter set, and regression model, have not been described previously and are critical components in evaluating the dose-response data from the occupationally exposed populations.

Notes: The extensive data from the Blair et al.(1) epidemiology study of occupational acrylonitrile exposure among 25,460 workers in eight plants in the United States provide an excellent opportunity to update quantitative risk assessments for this widely used commodity chemical. We employ the semiparametric Cox relative risk (RR) regression model with a cumulative exposure metric to model cause-specific mortality from lung cancer and all other causes. The separately estimated cause-specific cumulative hazards are then combined to provide an overall estimate of age-specific mortality risk. Age-specific estimates of the additional risk of lung cancer mortality associated with several plausible occupational exposure scenarios are obtained. For age 70, these estimates are all markedly lower than those generated with the cancer potency estimate provided in the USEPA acrylonitrile risk assessment.(2) This result is consistent with the failure of recent occupational studies to confirm elevated lung cancer mortality among acrylonitrile-exposed workers as was originally reported by O'Berg,(3) and it calls attention to the importance of using high-quality epidemiology data in the risk assessment process.

Notes: Consumption of ground beef has been implicated in the majority of outbreaks of disease from Escherichia coli O157:H7. There is a great need for rapid, sensitive, and specific microbial detection and isolation methods for the detection and recovery of pathogens such as E. coli O157:H7. Evanescent wave, fiber optic biosensors are an innovative, cutting-edge technology with the potential to meet such a need. Food pathogens such as E. coli O157:H7 can be detected in minutes using the biosensor assay rather than days using conventional methods. The biosensor assay is sensitive and presently has the ability to directly detect 102 CFU of E. coli O157:H7 in E. coli O157:H7-seeded PBS or ground beef. In this study, it was determined that once the pathogen had been positively identified, it could then be recovered by culturing the cells captured on the waveguide used in the biosensor assay. E. coli O157:H7-seeded PBS or ground beef samples were assayed using an evanescent wave, fiber optic biosensor. After a positive identification on the biosensor, the waveguide was added to modified LB medium supplemented with 10 μg/mL acriflavin (mLB) and incubated at 42C for a minimum of 4 h followed by selection on Rainbow O157 agar incubated 16 to 18 h at 37C. E. coli O157:H7 was confirmed using agglutination with E. coli O157:H7 antiserum. It was possible to recover E. coli O157:H7 colonies in E. coli O157:H7-seeded PBS or ground beef when 1 mL samples containing at least 2.0 × 103 CFU of E. coli O157:H7 had been injected into the biosensor. It took only 24 h to detect the target pathogen, recover the pathogen from the sample, and grow isolated colonies. This total time included sample preparation, detection, enrichment culture, and growth of cells to produce isolated colonies on a selective and differential medium. The identification of isolated colonies was then quickly confirmed using slide agglutination with the appropriate antiserum. This method significantly improved the speed of the confirmation of the presence of the pathogen and of the isolation of the pathogen, from 4 days using conventional methods to one day using the biosensor assay.