Total joint replacement has become a widely accepted treatment for many destructive joint diseases including osteoarthritis and severe pathologic fractures. Of total joint replacements, the hip is one of the most commonly replaced joints. Hip stem design varies from long to short, thick to thin and matt to smooth. In this study the effect of hip stem length on bone remodeling after surgery which knows as stress-shielding effect was analyzed using a finite element technique. Results show that stress-shielding introduced when using long-stem hip is extended that that of using short-stem hip in a total hip replacement.

Methods to predict contact stresses in femoral prostheses can provide an improved understanding of load distribution. The objectives of this study is to apply advanced computer aided engineering techniques (CAE) for predicting stress transfer to femur after implantation of standard and short femoral stems (Proxima stem). A perspective threedimensional geometry model for the femoral bone using subject-specific geometry from Xray computed tomography image data (CTI) is used to create 3D CAD model. Forces acting on the femur in different gait regimes were reviewed and compared while loaded with standard and then with Proxima stem. And finally a developed finite element analysis model based on the created CAD model with forces acting on both femurs loaded with standard and Proxima stem is analyzed.

Total joint replacement has become a widely accepted treatment for many destructive joint diseases including osteoarthritis and severe pathologic fractures. Of total joint replacements, the hip is one of the most commonly replaced joints. Hip stem design varies from long to short, thick to thin and matt to smooth. In this study the effect of hip stem length on bone remodeling after surgery which is known as stress-shielding effect was analyzed using a finite element technique. Results show that stress-shielding introduced when using long-stem hip is much more than that of using short-stem hip in a total hip replacement for cementless implant.

On handling the problem of automation in automatic weapons (AW), it is important to analyze the motion of these weapon mechanisms during their function cycle [1,2]. Many activities are performed during the backward motion of weapon mechanisms using the power of branching gases from what known as Gas Unit (GU). These activities starts with under-slide motion, unlocking, extraction of empty Cartridge Case (c.c.), backward motion against springs, ejection of empty c.c., and ending by loading of trigger at the extreme rear position. All these activities are performed in a reversed manner during the counter recoil track.In this paper; the parameters affecting the momentum of branching gases have been extensively studied, the performance of the gas unit is converted to touchable figures in order to facilitate the evaluation. These evaluations are presented in forms of change in pressure of gases inside the GU, maximum velocity of recoil, and the displacement of recoiling parts until the pressure inside the gas unit reaches the atmospheric value [7,8]. The predicted results determine the weight of each parameter that affects the momentum of gases. Moreover, the affecting parameters of GU on the weapon performance during the function cycle may be considered on modifying the power of in-service weapons, or the newly designed generations * Egyptian armed forces.

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