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.

Potential Effects of Chlorpyrifos on Fetal Growth Outcomes: Implications for Risk Assessment

Abstract: Chlorpyrifos (CPF) is one of the most widely used organophosphate insecticides in the United States. By December 2000, nearly all residential uses were voluntarily canceled, so that today, CPF is only used to control insect pests on a variety of crops. Periodic review of the potential effects of CPF on all developmental outcomes is necessary in the United States because the Food Quality Protection Act mandates special consideration of risk assessments for infants and children. This article reviews epidemiologic studies examining the association of potential CPF exposure with growth indices, including birth weight, birth length, and head circumference, and animal studies focusing on related somatic developmental endpoints. It differs from earlier reviews by including an additional cohort study and providing in-depth systematic evaluation of the patterns of association across different studies with respect to specificity of biomarkers for CPF, consistency, dose response, strength of association, temporality, and biological plausibility (Hill 1965), as well as consideration of the potential role of effect modification and bias. The review did not identify any strong associations exhibiting consistent exposure-response patterns that were observed in more than one of the four cohort studies evaluated. In addition, the animal data indicate that developmental effects occur at doses that produce substantial maternal toxicity and red blood cell (RBC) acetylcholinesterase (AChE) inhibition. Based on consideration of both the epidemiologic and animal data, maternal RBC AChE inhibition is a more sensitive endpoint for risk assessment than somatic developmental effects reviewed in this article.

Reliability and Fatigue Testing of MEMS

Abstract: Microelectromechanical structures (MEMS) utilize brittle materials such as polycrystalline silicon (polysilicon) under potentially severe mechanical and environmental loading conditions. These structures may be subjected to high frequency, cyclic loading conditions, accumulating large numbers of cycles in relatively short periods of time. Failure Analysis Associates has developed a technique for characterization of fatigue crack initiation and growth in MEMS materials. Preliminary results show that fatigue cracks can initiate and grow in polysilicon MEMS devices, and that water vapor is important in sub-critical crack advance. This research provides a basis for characterizing long-term durability and stability of micron-scale structures.

Postoperative Pain After Primary Total Knee Arthroplasty: Comparison of Local Injection Analgesic Cocktails and the Role of Demographic and Surgical Factors

Abstract: Background It has been reported that pain-related outcomes after total knee arthroplasty (TKA) may vary with different analgesic techniques and with patient demographics. The purposes of this study were to compare local infiltration of regular bupivacaine (periarticular infiltration [PAI] group) vs liposomal bupivacaine (LBUP group) and to examine the effect of patient characteristics on postoperative pain after TKA. Methods The study sample included 665 consecutive TKA cases performed between December 2011 and August 2013. The primary outcome measures were the average visual analog scale (VAS) pain score and the percent of VAS pain scores that indicated no pain. Multivariable regression analyses investigated the effect of age, race, ethnicity, body mass index, gender, surgeon, and analgesic protocol on outcomes. For the analgesic groups, the "PAI" group received injections of a cocktail including bupivacaine, ketorolac, and morphine, whereas the "LBUP" group received injections of LBUP. Results The regression analysis demonstrated that postoperative pain was higher in females ( P P P P = .250), race ( P = .205), or ethnicity ( P = .961) in this sample. Conclusion This multivariate regression analysis study showed that in patients undergoing primary TKA, postoperative pain was lower in males, older patients, and those treated with LBUP. Awareness of these factors may assist in developing patient-specific multimodal postoperative pain and education protocols that reduce opioid reliance and related adverse events.

Total Knee Replacement Polyethylene Stresses During Loading in a Knee Simulator

Abstract: We investigated the stresses and kinematics of a total knee replacement during the duty cycle of a knee simulator. Finite element models were constructed of the tibial and the femoral component of a commercially available cruciate retaining total knee replacement. Time dependent flexion/extension, axial loading, and anterior/posterior loading were applied to the components of the arthroplasty to match those generated by the knee simulator. We evaluated the effect of varying the stiffness of a spring-loaded bumper system for anterior-posterior constraint on the joint kinematics as well as on the stresses within the polyethylene tibial component. Both the joint kinematics and the stresses and strains subjected to the polyethylene tibial component, were found to be comparatively insensitive to the stiffness of the spring bumper system for this design. When the stiffness of the bumper system was increased by two orders of magnitude, the maximum contact stresses, von Mises stresses, and von Mises strains in the polyethylene tibial component varied by only 15 to 59 percent. In general, increasing the stiffness of the bumper system decreased the displacements of the base plate, but the relationships were nonlinear, possibly due to the added constraints imposed by the tibiofemoral contact interaction. The long-term goal of this research is to develop a validated structural model to predict the stresses, kinematics, and ultimately, the wear, of total joint replacement components in a contemporary knee joint simulator.