Combustion Characteristics of a Supersonic Combustor with a Large Cavity Length-to-Depth Ratio

The combustion characteristics of a hydrogen-fueled supersonic combustor featuring a large cavity length-to-depth ratio (i.e., 11) were examined by performing experimental trials while varying the fuel injector positions and equivalence ratios. During these trials, flame chemiluminescence images were acquired simultaneously from the side and bottom of the combustor under Mach 2.0 inflow conditions. The flame was observed to stabilize inside the cavity under all conditions. Proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD) analyses of sequential flame chemiluminescence images demonstrated the important effects of oblique shocks induced by fuel injection and heat release on flame stabilization. Because fluctuations in the locations of the flame and of the intense heat release zone were not observed and no dominant frequency was identified in POD and DMD analyses, the present configuration was evidently able to suppress combustion instability. The present research provides preliminary guidance for exploring the feasibility of using cavity combustors with large length-to-depth ratios in scramjet engines

Indomethacin Enhances Brown Fat Activity.

Indomethacin, a nonsteroidal anti-inflammatory drug, has been shown to induce white adipocyte differentiation; however, its roles in brown adipocyte differentiation and activation in brown adipose tissue (BAT) and obesity are unknown. To address this issue, we treated mouse brown preadipocytes with different doses of indomethacin, and delivered indomethacin to interscapular BAT (iBAT) of obese mice using implanted osmotic pumps. Indomethacin dose dependently increased brown preadipocyte differentiation and upregulated both mRNA and protein expression of uncoupling protein 1 (UCP1) and peroxisome proliferator-activated receptor (PPAR) γ coactivator 1-alpha. The mechanistic study showed that indomethacin significantly activated the reporter driven by the PPAR response element, indicating that indomethacin may work as a PPARγ agonist in this cell line. Consistently, indomethacin significantly decreased iBAT mass and fasting blood glucose levels in high-fat diet-induced obesity (DIO) mice. Histologic analysis showed that brown adipocytes of indomethacin-treated mice contained smaller lipid droplets compared with control mice, suggesting that indomethacin alleviated the whitening of BAT induced by the high-fat diet. Moreover, indomethacin significantly increased UCP1 mRNA expression in iBAT. Taken together, this study indicates that indomethacin can promote mouse brown adipocyte differentiation, and might increase brown fat and glucose oxidation capacity in DIO mice

Microstructure and Mechanical Properties in a Gd-Modified Extruded Mg-4Al-3.5Ca Alloy

In the present study, the microstructure and mechanical properties of a new Mg-4Al-3.5Ca-2Gd (AXE432) alloy are investigated. The microstructure of the as-cast AXE432 alloy consists of α-Mg, C14 (Mg2Ca), and C36((Mg, Al)2Ca) phases. After the heat treatment at 480 °C for 8 h, the C14 with fine lamellar structure changes from narrow stripes to micro-scale particles, and part of the C36 and the C14 dissolve into the α-Mg matrix, with many short needle-shaped C15 (Al2Ca) phase precipitating in the primary a-Mg grains. The AXE432 alloy extruded at a temperature as high as 420 °C exhibits a refined dynamically recrystallized (DRXed) microstructure with grain sizes less than 1.5 ± 0.5 μm and a strong {0001}1¯0> basal texture with a maximum intensity of 5.62. A complex combination of the effects from grain size, texture, second-phase particles, and strain hardening results in balanced mechanical properties, with the tensile yield strength (TYS), ultimate tensile strength (UTS), elongation (El), compressive yield strength (CYS), and ultimate compressive strength (UCS) of 331.4 ± 2.1 MPa, 336.9 ± 3.8 MPa, 16.1 ± 2.3%, 270.4 ± 1.6 MPa and 574.5 ± 12.4 MPa, respectively