Fabrication and Hypersonic Wind Tunnel Validation of a MEMS Skin Friction Sensor Based on Visual Alignment Technology.

MEMS-based skin friction sensors are used to measure and validate skin friction and its distribution, and their advantages of small volume, high reliability, and low cost make them very important for vehicle design. Aiming at addressing the accuracy problem of skin friction measurements induced by existing errors of sensor fabrication and assembly, a novel fabrication technology based on visual alignment is presented. Sensor optimization, precise fabrication of key parts, micro-assembly based on visual alignment, prototype fabrication, static calibration and validation in a hypersonic wind tunnel are implemented. The fabrication and assembly precision of the sensor prototypes achieve the desired effect. The results indicate that the sensor prototypes have the characteristics of fast response, good stability and zero-return; the measurement ranges are 0-100 Pa, the resolution is 0.1 Pa, the repeatability accuracy and linearity are better than 1%, the repeatability accuracy in laminar flow conditions is better than 2% and it is almost 3% in turbulent flow conditions. The deviations between the measured skin friction coefficients and numerical solutions are almost 10% under turbulent flow conditions; whereas the deviations between the measured skin friction coefficients and the analytical values are large (even more than 100%) under laminar flow conditions. The error resources of direct skin friction measurement and their influence rules are systematically analyzed.

Decreased Serum Lipid Levels and Ratios Correlate with Low Prevalence of Coronary Heart Disease in Patients with Parkinson's Disease.

BACKGROUND: Patients with Parkinson's disease (PD) are at a lower risk of suffering cardiovascular events, but the underlying factors for this decreased risk remain unclear. Serum triglycerides (TG) and total cholesterol (TC), and their expression relative to high-density lipoprotein cholesterol (TG/HDL-C and TC/HDL-C), are independent predictors of cardiovascular events. This study aimed to determine if PD patients have decreased lipid levels and lipid ratios, which may underlie the decreased risk of coronary heart disease (CHD). METHODS: This retrospective study included 92 PD patients (PD group), 450 control subjects with no CHD (OD group), and 450 CHD patients (CHD group). We analyzed serum lipid levels and lipid ratios in each group. RESULTS: There were significant differences in TC (F = 10.459, p < 0.0001), TG (F = 46.856, p < 0.0001), low density lipoprotein cholesterol (LDL-C) (F = 6.910, p = 0.001), high density lipoprotein cholesterol HDL-C (F = 30.694, p < 0.0001), TC/HDL-C (F = 32.675, p < 0.0001), and TG/HDL-C (F = 45.554, p < 0.0001) between all three groups; TC/LDL-C (F = 2.518, p = 0.081) was not significantly different between groups. Compared to the CHD group, PD patients had lower TC (p < 0.0001), TG (p < 0.0001), LDL-C (p = 0.001), TG/HDL-C (p < 0.0001), and TC/HDL-C (p < 0.0001); TC/LDL-C (p = 0.563) and HDL-C (p = 0.196) were not significantly different. TC and LDL-C levels were positively correlated within individual groups (all p < 0.0001). In addition, TG and HDL-C were negatively correlated in the OD and CHD groups (p < 0.0001); no significant negative association was observed in the PD group (p = 0.077). TG/HDL and LDL-C levels were inversely correlated in the CHD group (p < 0.0001) and weakly positively correlated in the PD (p = 0.159) and OD (p = 0.199) groups. CONCLUSIONS: TC/HDL and TG/HDL ratios were significantly lower in PD patients compared to CHD patients, suggesting there is a strong correlation between lipid ratios and incidence of CHD in PD patients.