Tribological behavior of a silicon carbide/carbone dry contact

The development of new high-performance mechanical seals working in severe conditions requires higher material performances. Sintered silicon carbide (SSC), widely used as a hard mating material, is a potential candidate but its friction and wear properties need to be investigated in the scope of these new applications. Silicon carbide offers good mechanical properties (high hardness, high Young modulus), good corrosion resistance and good thermal conductivity, that make it suitable for tribological applications in different atmosphere (in air, argon or vacuum) and in dry or lubricated sliding. Combined with a counter-face ring made of a softer carbon-graphite, the dry sliding of SSC can be sustained even under severe conditions of pressure and speed. Graphite has been intensively studied in tribology since Bragg first described its lamellar structure. It has been thought during many years that graphite could act as a solid lubricant thanks to this structure. In fact, the environmental conditions strongly influence its tribological behavior. The hardness of the ceramic facing the carbon seal has also an impact on its friction properties. A transfer layer of carbon is generally found on the ceramic surface. In this study, a first experiment assesses the tribological behavior of SSC sliding against itself and three different carbon-graphite materials. Dry friction and ring-on-ring configuration are considered. A second test uses an infrared camera to estimate the temperature variations of a SiC/C couple during sliding, which determines relationship between displacement resistance and the heat generation

Design and proof of concept of an innovative very high temperature ceramic solar absorber

International audienc

Subthalamic nucleus stimulation in severe obsessive-compulsive disorder.

International audienceBACKGROUND: Severe, refractory obsessive-compulsive disorder (OCD) is a disabling condition. Stimulation of the subthalamic nucleus, a procedure that is already validated for the treatment of movement disorders, has been proposed as a therapeutic option. METHODS: In this 10-month, crossover, double-blind, multicenter study assessing the efficacy and safety of stimulation of the subthalamic nucleus, we randomly assigned eight patients with highly refractory OCD to undergo active stimulation of the subthalamic nucleus followed by sham stimulation and eight to undergo sham stimulation followed by active stimulation. The primary outcome measure was the severity of OCD, as assessed by the Yale-Brown Obsessive Compulsive Scale (Y-BOCS), at the end of two 3-month periods. General psychopathologic findings, functioning, and tolerance were assessed with the use of standardized psychiatric scales, the Global Assessment of Functioning (GAF) scale, and neuropsychological tests. RESULTS: After active stimulation of the subthalamic nucleus, the Y-BOCS score (on a scale from 0 to 40, with lower scores indicating less severe symptoms) was significantly lower than the score after sham stimulation (mean [+/-SD], 19+/-8 vs. 28+/-7; P=0.01), and the GAF score (on a scale from 1 to 90, with higher scores indicating higher levels of functioning) was significantly higher (56+/-14 vs. 43+/-8, P=0.005). The ratings of neuropsychological measures, depression, and anxiety were not modified by stimulation. There were 15 serious adverse events overall, including 1 intracerebral hemorrhage and 2 infections; there were also 23 nonserious adverse events. CONCLUSIONS: These preliminary findings suggest that stimulation of the subthalamic nucleus may reduce the symptoms of severe forms of OCD but is associated with a substantial risk of serious adverse events. (ClinicalTrials.gov number, NCT00169377.