Exponent

About: Exponent is a company organization based out in Menlo Park, California, United States. It is known for research contribution in the topics: Population & Risk assessment. The organization has 1589 authors who have published 2680 publications receiving 88140 citations.

An Enhanced Dynamic Battery Model of Lead-Acid Batteries Using Manufacturers' Data

Abstract: Modeling and simulation of lead acid batteries is of utmost importance for transportation systems such as hybrid and electric vehicles, golf carts, electric scooters, and wheelchairs; and for battery backup systems such as UPS for computers and telecommunication systems. Considerable effort is put into the selection of the appropriate battery with specific regard to the battery's State of Charge (SOC) and battery reserve time during the discharge profile for the various loading conditions expected. A previous technical paper presented a dynamic battery model by the same authors [1]. The new enhanced model has increased accuracy; it includes voltage, current, and power monitoring functions and further permits modeling of the cycle-by-cycle charge/discharge characteristics which is imperative for regenerative applications. Furthermore, the operating features of this enhanced battery model are demonstrated for two regenerative simulations. The new battery model is interfaced to a full-bridge, bi-directional, PWM controller with bi-polar voltage switching. The load is a dc motor model with motor parameters such as load torque, viscous torque and inertia. The power converter/dc motor system presents bi-directional power flow to the battery model. The purpose of the first simulation is to demonstrate real-world operation of the battery model including regeneration. A second simulation has an ultra-capacitor bank connected across the battery terminals to compare the battery model charge/discharge parameters such as voltage, current and power when the ultra-capacitor bank is absent and when present in the system.

The drive to ban the NOEC/LOEC in favor of ECx is misguided and misinformed

Abstract: Challenges to the use of the no observed effect concentration (NOEC) in ecotoxicology have appeared over the years, with a recent call for banning its use in favor of the x% effects concentration (ECx). This article presents an opposing view, providing reasons for the continued use of the NOEC, and for hypothesis testing in general. Although the use of ECx values is appropriate in many situations, there are numerous real-world examples where it is not suitable and offers no advantage over the use of hypothesis testing. These examples are presented with recommended data analysis techniques, illustrating the variety of statistical approaches that are meaningful in analyzing ecotoxicity data. Thoughtful consideration of study design and proper analysis and interpretation of the results will go further to advance the science of ecotoxicology than attempting to implement a blanket prohibition or endorsement of any single statistical approach.

Digitally Controlled Simple Shear Apparatus for Dynamic Soil Testing

Abstract: We describe the characteristics of a simple shear apparatus capable of applying realistic multidirectional earthquake loading to soil specimens. This device, herein termed the Digitally Controlled Simple Shear (DC-SS) apparatus, incorporates features such as servohydraulic actuation and true digital control to overcome control limitations of some previous dynamic soil testing machines. The device is shown to be capable of reproducing sinusoidal and broadband command signals across a wide range of frequencies and amplitudes, although the device has limited control capabilities for very small command displacements (less than approximately 0.005 mm). The small deformation limitation results from noise introduced to the control system from analog-to-digital conversion of feedback signals. We demonstrate that bidirectional command signals can be accurately imparted with minimal cross coupling, which results from an innovative multiple-input, multiple-output digital control system. The capabilities of the device are demonstrated with a series of broadband tests on unsaturated soil specimens subjected to uni- and bidirectional excitation.

Exposure reconstruction for the TCDD-exposed NIOSH cohort using a concentration- and age-dependent model of elimination.

Abstract: 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. In-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.

Deformation of metal-backed acetabular components and the impact of liner thickness in a cadaveric model

Abstract: Shell deformation of resurfacing and all-metal modular cups following press-fit implantation has been reported, but not for conventional metal-backed cups with polyethylene liners. The deformation of acetabular components with historical and thin polyethylene inserts after press-fit insertion was evaluated using a cadaveric model. All shells and liners deformed upon implantation. Following joint loading, shell pinch decreased from 0.32 to 0.22 mm (p = 0.019) and from 0.29 to 0.13 mm (p = 0.003) for the thin and thick liner groups, respectively. Liner pinch also decreased from 0.17 to 0.04 mm (p = 0.031) and from 0.06 to 0 mm (p = 0.103) for the thin and thick liner groups, respectively. There were no significant differences between the thin and thick liners. Liner deformation was influenced by the initial shell deformation and donor bone quality. Shell and liner pinch decreased following joint loading, suggesting a settling in effect.