Thermostatic Valves Containing Silicone-Oil Actuators

Flow-splitting and flow-mixing thermally actuated spool valves have been developed for controlling flows of a heat-transfer fluid in a temperature-regulation system aboard the Mars Science Laboratory (MSL) rover. Valves like these could also be useful in terrestrial temperature-regulation systems, including automobile air-conditioning systems and general refrigeration systems. These valves are required to provide smoother actuation over a wider temperature range than the flow-splitting, thermally actuated spool valves used in the Mars Explorer Rover (MER). Also, whereas the MER valves are unstable (tending to oscillate) in certain transition temperature ranges, these valves are required not to oscillate. The MER valves are actuated by thermal expansion of a wax against spring-loaded piston rods (as in common automotive thermostats). The MSL valves contain similar actuators that utilize thermal expansion of a silicone oil, because silicone-oil actuators were found to afford greater and more nearly linear displacements, needed for smoother actuation, over the required wider temperature range. The MSL valves also feature improved spool designs that reflect greater understanding of fluid dynamics, consideration of pressure drops in valves, and a requirement for balancing of pressures in different flow branches

A systematic review of associations between functional MRI activity and polygenic risk for schizophrenia and bipolar disorder

Genetic factors account for up to 80% of the liability for schizophrenia (SCZ) and bipolar disorder (BD). Genome-wide association studies have successfully identified several genes associated with increased risk for both disorders. This has allowed researchers to model the aggregate effect of genes associated with disease status and create a polygenic risk score (PGRS) for each individual. The interest in imaging genetics using PGRS has grown in recent years, with several studies now published. We have conducted a systematic review to examine the effects of PGRS of SCZ, BD and cross psychiatric disorders on brain function and connectivity using fMRI data. Results indicate that the effect of genetic load for SCZ and BD on brain function affects task-related recruitment, with frontal areas having a more prominent role, independent of task. Additionally, the results suggest that the polygenic architecture of psychotic disorders is not regionally confined but impacts on the task-dependent recruitment of multiple brain regions. Future imaging genetics studies with large samples, especially population studies, would be uniquely informative in mapping the spatial distribution of the genetic risk to psychiatric disorders on brain processes during various cognitive tasks and may lead to the discovery of biological pathways that could be crucial in mediating the link between genetic factors and alterations in brain networks

Use of filler wire for laser welding of Ti-6Al-4V

Owing to the high specific strength and excellent corrosion resistance, Ti-6Al-4V has been widely applied in aerospace industries. In this study, the welding performance of 3\ub72 and 5\ub71 mm thick Ti-6Al-4V sheets was studied using a 4 kW continuous wave Nd:YAG laser. It is found that the use of filler wire, matching the parent metal composition, can bridge the joint gap and produce full penetrated welds up to a width of 0\ub76 mm without cracking. The laser welds were characterised in terms of the bead geometry, defects, microstructures and hardness. With increasing joint gap, the percent porosity area increased, reaching just over 1% of the fusion zone area at a gap width of 0\ub76 mm for the 3\ub72 and 5\ub71 mm thick sheets. The maximum underfill depth in the Ti-6Al-4V laser welds was about 5%or 7%of the sheet thickness for the 3\ub72 and5\ub72 mmthick materials, respectively, meeting the AWS D17-1 specification. The microindentation hardness was maximum in the fusion zone and sharply decreased through the heat affected zone until reaching the base metal value. \ua9 2012 Crown in Right of Canada.Peer reviewed: YesNRC publication: Ye

Effect of welding speed and defocusing distance on Ti-5Al-5V-5Mo-3Cr alloy welded using a 4 kW Nd:YAG Laser

Peer reviewed: YesNRC publication: Ye

Laser welding of Ti-5Al-5V-5Mo-3Cr

Ti-5Al-5V-5Mo-3Cr butt joints were welded using a 4 kW continuous wave Nd:YAG laser. The effect of welding speed and defocusing distance on the weld quality was investigated. Welds with full penetration were achieved at a defocusing distance ranging from-1 to 0 mm and welding speeds from 2\ub725 to 6\ub70 m min -1. Underfill and porosity were the two main defects most frequently observed; however, within the optimum process window, these defects could be maintained to meet aerospace specification tolerances. The fusion zone consisted entirely of retained \u3b2 with a refined dendritic morphology. Compared with the bimodal \u3b1+\u3b2 microstructure of the base metal, dissolution of the \u3b1 phase in the heat affected zone and the presence of entirely metastable/retained \u3b2 phase in the fusion zone were observed, which led to a significant decrease in the HAZ and FZ hardness. To determine the tensile properties of the welds, an automated three-dimensional deformation measurement system was used to measure the local strain in the weld region. The yield strength and ultimate tensile strength increased with welding speed, achieving a maximum joint efficiency of 75%, albeit with a concomitant reduction in the ductility. \ua9 2011 Canadian Institute of Mining, Metallurgy and Petroleum.Peer reviewed: YesNRC publication: Ye

Tolerances of joint gaps in Nd: YAG laser welded Ti-6AI-4V alloy with the addition of filler wire

International audienceThe effect of joint gap on the butt joint quality of Ti-6Al-4V alloy welded using a 4 k W Nd:yttrium aluminum garnet laser was evaluated in terms of the welding defects, microstructure, hardness, and tensile properties. The joint gap was proportionally filled using the filler wire with the compositions of the parent alloy. Fully penetrated welds without cracking were obtained up to a joint gap of 0.5 mm. The main defects observed in the welds were porosity and underfill. Specifically, the porosity area increased with increasing joint gap but remained less than 1% of the fusion zone area. Large underfill defects appeared in the weldments in the absence of a joint gap, but filler wire addition was observed to reduce this defect in the presence of a joint gap. The weld hardness decreased slightly with increasing joint gap, but the tensile properties were optimized at an intermediary gap size, probably due to the compromise between the low underfill after the use of a filler wire and a limited amount of porosity