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.

Aortic Regurgitation Generates a Kinematic Obstruction Which Hinders Left Ventricular Filling.

Abstract: An incompetent aortic valve (AV) results in aortic regurgitation (AR), where retrograde flow of blood into the left ventricle (LV) is observed. In this work, we parametrically characterized the detailed changes in intra-ventricular flow during diastole as a result of AR in a physiological in vitro left-heart simulator (LHS). The loss of energy within the LV as the level of AR increased was also assessed. The validated LHS consisted of an optically-clear, flexible wall LV and a modular AV holder. Two-component, planar, digital particle image velocimetry was used to visualize and quantify intra-ventricular flow. A large coherent vortical structure which engulfed the whole LV was observed under control conditions. In the cases with AR, the regurgitant jet was observed to generate a “kinematic obstruction” between the mitral valve and the LV apex, preventing the trans-mitral jet from generating a coherent vortical structure. The regurgitant jet was also observed to impinge on the inferolateral wall of the LV. Energy dissipation rate (EDR) for no, trace, mild, and moderate AR were found to be 1.15, 2.26, 3.56, and 5.99 W/m3, respectively. This study has, for the first time, performed an in vitro characterization of intra-ventricular flow in the presence of AR. Mechanistically, the formation of a “kinematic obstruction” appears to be the cause of the increased EDR (a metric quantifiable in vivo) during AR. EDR increases non-linearly with AR fraction and could potentially be used as a metric to grade severity of AR and develop clinical interventional timing strategies for patients.

Electromyographic activity and posturing of the human neck during rollover tests

Abstract: Lateral head motions, torso motions, lateral neck bending angles, and electromyographic (EMG) activity patterns of five human volunteer passengers are compared to lateral motions of a Hybrid III ATD during right-left and left-right fishhook steering maneuvers leading to vehicular tip-up. While the ATD maintained relatively fixed lateral neck angles, live subjects leaned their heads slightly inward and actively utilized their neck musculature to stiffen their necks against the lateral inertial loads. Except for differences in neck lateral bending, the Hybrid III ATD reasonably reflects occupant kinematics during the pre-trip phase of on-road rollovers.

Enhancement of a Class of Adjoint Design Methods via Optimization of Parameters

Abstract: CD = drag coefficient CL = lift coefficient Cp = pressure coefficient CW = structural weight coefficient F = design variable G = gradient G = modified gradient using Sobolev inner product i, j, k = cell indices in the three computational coordinate directions I = cost function M1 = freestream Mach number R = residual R = implicitly smoothed residual r = scaled spectral radii of the flux Jacobian matrices = angle of attack l = weighing coefficients in cost function = smoothing coefficient factor = variation = gradient smoothing coefficient " = residual smoothing coefficient = step size = computational coordinate