Emergency Locator Transmitter Survivability and Reliability Study

A comprehensive study of Emergency Locator Transmitter (ELT) performance was conducted over a three year period concluding in 2016 in support of the Search and Rescue (SAR) Mission Office at National Aeronautics and Space Administration (NASA) Goddard Space Flight Center (GSFC). The study began with a review of reported performance cited in a collection of works published as early as 1980 as well as analysis of a focused set of contemporary aviation crash reports. Based on initial research findings, a series of subscale and fullscale system tests were performed at NASA Langley Research Center (LaRC) with the goals of investigating ELT system failure modes and developing recommended improvements to the Radio Technical Commission for Aeronautics (RTCA) Minimum Operational Performance Specification (MOPS) that will result in improved system performance. Enhanced performance of ELT systems in aviation accidents will reduce unnecessary loss of human life and make SAR operations safer and less costly by reducing the amount of time required to locate accident sites

Methodology to identify subject-specific dynamic laxity tests to stretch individual parts of knee ligaments

The mechanical properties of ligaments are important for multiple applications and are often estimated from laxity tests. However, the typical laxity tests are not optimized for this application and, a potential exists to develop better laxity tests in this respect. Therefore, the purpose of this study was to develop a methodology to identify optimal, dynamic laxity tests that isolate the stretch of the individual ligaments from each other. To this end, we applied an existing rigid body-based knee model and a dataset of ∼100.000 random samples of applied forces (0–150 N), moments (0–10 Nm) and knee flexion angles (0–90°) through Monte Carlo Simulations. For each modelled ligament bundle, we identified ten load cases; one producing the highest force and nine equally spaced between the maximal and zero force, where the maximal force in all other ligament bundles were minimized. We compared these novel laxity tests to standard internal/external and varus/valgus laxity tests using an isolation metric.We found that no laxity test could stretch the anterior part of the posterior cruciate and medial cruciate ligaments (PCL and MCL), whereas for all other ligaments, except the posterior PCL, the new laxity tests isolated the ligament stretch 28 % to 450 % better than standard tests.From our study, we conclude that it is possible to define better laxity tests than currently exist and these may be highly relevant for determination of mechanical properties of ligaments in vivo. Future studies should generalize our results and translate them to modern laxity measurements technologies

The effect of thickness variation on the rigidity of ankle foot orthoses provided to the NHS:A case for the need for quality control

BackgroundDrape-forming is a cost-effective method used worldwide to manufacture bespoke ankle foot orthoses (AFOs). It involves draping a heated polymer material sheet over a positive cast of the user’s limb. The manual nature of drape-forming can influence the thickness of the final AFO and even lead to structures that are inadequately rigid to be clinically effective. This study assesses the difference between the prescribed and the final thickness of AFOs meant for use by UK’s National Health Service (NHS) and estimates its potential impact on AFO rigidity.MethodsA clinically relevant method to measure AFO thickness as part of the manufacturing process was developed and validated. This method was used by three major UK manufacturers for all bespoke rigid AFOs they provided to the NHS within a predefined period. A validated finite element model was used to estimate the impact of the observed difference between prescribed and final thickness on AFO stiffness.Results86 AFOs were assessed in total. Final thickness was between 4.0% and 35.5% lower than the prescribed one (median thickness reduction= 17.4%). This discrepancy in thickness led to a relative reduction in AFO stiffness ranging between 7.0% and 80.0% (median stiffness reduction= 30.7%).DiscussionThe adequacy of AFO thickness cannot be judged based on prescription thickness. Measurements of final thickness as part of standard practice should be considered to enhance the provision of bespoke AFOs. Further research is needed to establish thresholds of acceptable manufacturing-induced deviation from the prescribed AFO thickness

A parametric investigation on seat/occupant contact forces and their relationship with initially perceived discomfort using a configurable seat

The present work investigates the contact forces between sitters and seat as well as their correlations with perceived discomfort. Twelve different economy class airplane seat configurations were simulated using a multi-adjustable experimental seat by varying seat pan and backrest angles as well as seat pan compressed surface. 18 males and 18 females, selected by their body mass index and stature, tested these configurations for two sitting postures. Perceived discomfort was significantly affected by seat parameters and posture, and correlated both with normal force distribution on the seat-pan surface and with normal forces at the lumbar and head supports. Lower discomfort ratings were obtained for more evenly distributed normal forces on the seat pan. Shear force at the seat pan surface was at its lowest when sitters were allowed to self-select their seat-pan angle, supporting that a shear force should be reduced but not zeroed to improve seating comfort. Practitioner Summary: The effects of seat-pan and backrest angle, anthropometric dimensions and sitting posture on contact forces and perceived discomfort were investigated using a multi-adjustable experimental seat. In addition to preferred seat profile parameters, the present work provides quantitative guidelines on contact force requirement for improving seating comfort

Assessment of the effect of a total contact cast on lower limb kinematics and joint loading

Background Total contact casts (TCCs) are used to immobilize and unload the foot and ankle for the rehabilitation of ankle fractures and for the management of diabetic foot complications. The kinematic restrictions imposed by TCCs to the foot and ankle also change knee and hip kinematics, however, these changes have not been quantified before. High joint loading is associated with discomfort and increased risk for injuries. To assess joint loading, the effect of the muscle forces acting on each joint must also be considered. This challenge can be overcome with the help of musculoskeletal modelling. Research question How does a TCC affect lower extremity joint loading? Methods Twelve healthy participants performed gait trials with and without a TCC. Kinematic and kinetic recordings served as input to subject-specific musculoskeletal models that enabled the computation of joint angles and loading. Cast-leg interaction was modelled by means of reaction forces between a rigid, zero-mass cast segment and the segments of the lower extremity. Results and Significance: Reduced ankle, knee and hip range of motion was observed for the TCC condition. Statistical parametric mapping indicated decreased hip abduction and flexion moments during initial contact with the TCC. The anterior knee force was significantly decreased during the mid and terminal stance and the second peak of the compressive knee force was significantly reduced for the TCC. As expected, the TCC resulted in significantly reduced ankle loading. Significance This study is the first to quantify the effect of a TCC on lower limb joint loading. Its results demonstrate the efficiency of a TCC in unloading the ankle joint complex without increasing the peak loads on knee and hip. Future studies should investigate whether the observed knee and hip kinematic and kinetic differences could lead to discomfort

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