Investigation of Magnitude and Position of Maximum von Mises Stress in The Cylindrical Contact Problems

In the analysis of contact mechanics problems, determination of stress field in mechanical elements is essential. Between the stress components the von Mises stress is more important, because it is used in the investigation of yield criteria and fatigue fracture of elements. The aim of this study is to present formulas for determining the magnitude and position of maximum von Mises stress. For this purpose, the effect of various material properties, element geometries and loading conditions on these two parameters are investigated. By applying Hertzian contact stress and von Mises relations, the magnitude and position of maximum von Mises stress are determined. The von Mises stress is assumed to be a function of material properties, geometry of the element and loading conditions and finally two formulas are presented for the calculation of the magnitude and position of maximum von Mises stress. The results of these presented formulas are in close agreement with the literature. The error is less than 1% for depth prediction and less than 6% for stress value prediction, which confirms the accuracy of the presented formulas

Induced Pluripotent Stem Cells: Challenges and Opportunities

Regenerative capacity of mammals is limited and can rarely regenerate a specific organ or tissue fully. Due to these limitations, regenerative medicine seeks efficient and safe cell sources for regeneration of damaged tissues and organs or treatment for incurable diseases. Human embryonic stem cells (HESCs) hold two important properties called self renewal and pluripotency. However, the use of embryonic pluripotent stem cells in cell therapy faces two major obstacles. First, immunological incompatibility of ES cells with the recipient, and the second, ethical concerns about the destruction of human embryos during the ES cells. Thus, induction of somatic cells of individuals can be a proper way to overcome these problems. So far, several methods have been utilized to induce Pluripotency in Somatic cells. One of these methods is the technology of induced pluripotent stem cells (iPS) in contribution with Pluripotency factors. Yet, the use of these cells in the clinic, owing to application of viral vectors to transfer Pluripotency inducing factors, is quite limited. Therefore, recognition of a combination of small molecules to be replaced with exogenous factors is the ultimate goal of the study for the purpose of generating iPS cells. Recent progresses in development of iPS cells will be discussed here.   Keywords: IPS, Plupotency, Repair, Regeneration, Stem Cell