Does increasing applied load lead to contact changes indicative of knee osteoarthritis? A subject-specific FEA study.

This study investigated whether increased loading (representing obesity) in the extended knee and flexed knee led to increased stresses in areas of typical medial and lateral osteoarthritis cartilage lesions, respectively. We created two paired sets of subject-specific finite element models; both sets included models of extended knees and of flexed knees. The first set represented normal loading; the second set represented increased loading. All other variables were held constant. The von Mises stresses and contact areas calculated on the tibial cartilage surfaces of the paired models were then compared. In the extended knee models, applying a larger load led to increased stress in the anterior and central regions of the medial tibial cartilage. These are the typical locations of medial osteoarthritis cartilage lesions. Therefore, the results support that increased loading in the extended knee may result in medial osteoarthritis. In the flexed knee models, applying a larger load increased stress in the anterior and central regions of the lateral tibial cartilage. Lateral osteoarthritis cartilage lesions typically occur centrally and posteriorly. Therefore, these results do not support our hypothesis. Shear stress was increased in areas of typical lateral lesions, however, and should be investigated in future studies.

Interpersonal interactions on online forums addressing eating concerns.

OBJECTIVE: Although some research suggests that online eating disorder forums promote "pro-eating-disorder" lifestyles and discourage recovery, other research suggests that such forums are an important source of interpersonal support. The current study extends this research by exploring the positive and negative behaviors encouraged on these forums and by comparing forum members' perceptions of support received from online and offline relationships to support received in relationships of age-matched controls. METHOD: In a survey of 60 forum members, we assessed information exchanged and support provided on eating disorder forums. Further, we assessed perceptions of social support for general and specific life concerns in this group of forum members as well as 64 age-matched university controls. RESULTS: Results show that both adaptive and maladaptive behaviors are encouraged on the forums, and that this encouragement has some influence on forum members trying out these behaviors. Overall, forum members reported receiving less support for their eating concerns as compared to their general life stressors, and they perceived less support for both their general concerns and eating concerns in their offline relationships as compared to their online forum relationships. Moreover, forum members reported receiving less support from their offline relationships as compared to support received in relationships by age-matched controls. DISCUSSION: Forum members perceive less support in their important relationships than other peers do, and they seek out and participate in forums as a means of attaining greater social support. However, our research suggests that these forums also encourage dysregulated eating behaviors. Implications of online forum support and its impact on recovery are discussed further.

Adsorption energies for a nanoporous carbon from gas-solid chromatography and molecular mechanics.

Gas-solid chromatography was used to obtain second gas-solid virial coefficients, B2s, in the temperature range 342-613 K for methane, ethane, propane, butane, 2-methylpropane, chloromethane, chlorodifluoromethane, dichloromethane, and dichlorodifluoromethane. The adsorbent used was Carbosieve S-III (Supelco), a carbon powder with fairly uniform, predominately 0.55 nm slit width pores and a N2 BET surface area of 995 m2/g. The temperature dependence of B2s was used to determine experimental values of the gas-solid interaction energy, E*, for each of these molecular adsorbates. MM2 and MM3 molecular mechanics calculations were used to determine the gas-solid interaction energy, E*(cal), for each of the molecules on various flat and nanoporous model surfaces. The flat model consisted of three parallel graphene layers with each graphene layer containing 127 interconnected benzene rings. The nanoporous model consisted of two sets of three parallel graphene layers adjacent to one another but separated to represent the pore diameter. A variety of calculated adsorption energies, E*(cal), were compared and correlated to the experimental E* values. It was determined that simple molecular mechanics could be used to calculate an attraction energy parameter between an adsorbed molecule and the carbon surface. The best correlation between the E*(cal) and E* values was provided by a 0.50 nm nanoporous model using MM2 parameters.