The objective of this study was to develop a three-dimensional (3D) quasi-static rigid body canine pelvic limb computer model simulating a cranial cruciate ligament (CrCL) intact and CrCL-deficient stifle during walking stance to describe stifle biomechanics. The model was based on a five-year-old neutered male Golden Retriever (33 kg) with no orthopedic or neurologic disease. Skeletal geometry and ligament anatomy determined from computed tomography (CT), optimized muscle forces, motion capture kinematics, and force platform ground reaction forces were used to develop the model. Ligament loads, tibial translation, tibial rotation, and femoromeniscal contact forces were compared across the intact and CrCL-deficient stifle. The CrCL was found to be the primary intact stifle load-bearing ligament, and the caudal cruciate ligament was the primary CrCL-deficient stifle load-bearing ligament. Normalized tibial translation and rotation were 0.61 mm/kg and 0.14 degrees/kg, respectively. Our model confirmed that the CrCL stabilizes the intact stifle and limits tibial translation and rotation. Model verification was confirmed through agreement with experimentally measured kinematics and previous in vivo, in vitro, and mathematical model studies. Parametric analysis indicated outcome measure sensitivity to ligament pre-strain. Computer modeling could be useful to further investigate stifle biomechanics associated with surgical stabilization techniques.

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The Hall thruster is a high-efficiency spacecraft propulsion device that utilizes plasma to generate thrust. The most common variant of the Hall thruster is the stationary plasma thruster (SPT). Erosion of the SPT discharge chamber wall by plasma sputtering degrades thruster performance and ultimately ends thruster life. Many efforts over the past few decades have endeavored to understand wall erosion so that novel thrusters can be designed to operate for the thousands of hours required by many missions. However, due to the challenges presented by the plasma and material physics associated with erosion, a complete understanding has thus far eluded researchers. Sputtering rates are not well quantified, erosion features remain unexplained, and computational models are not yet predictive. This article reviews the physics of plasma-induced SPT erosion, highlights important experimental findings, provides an overview of modeling efforts, and discusses erosion mitigation strategies.

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