TEM Observation of Crack- and Pit-Shaped Defects in Electrically Degraded GaN HEMTs

AlGaN/GaN high-electron mobility transistors stressed under dc bias at various channel temperatures were studied using transmission electron microscopy for evidence of physical damage. Stressed devices consistently developed crack- and pit-shaped defects in the AlGaN/GaN crystal material under the drain-side edge of the gate, whereas side-by-side as-processed unstressed devices did not show these features. Furthermore, the amount of physical damage was found to correlate to the amount of electrical degradation as measured by the change in IDmax from before and after stress. The formation of these defects is consistent with the theory of damage from the inverse piezoelectric effect.     

Arsenic removal from aqueous solutions by adsorption on magnetite nanoparticles

Magnetite nanoparticles were used to treat arsenic‐contaminated water. Because of their large surface area, these particles have an affinity for heavy metals by adsorbing them from a liquid phase. The results of the study showed that the maximum arsenic adsorption occurred at pH 2, with a value of approximately 3.70 mg/g for both As(III) and As(V) when the initial concentration of both arsenic species was maintained at 2 mg/L. The study showed that, apart from pH, the removal of arsenic from contaminated water also depends on the contact time, the initial concentration of arsenic, the phosphate concentration in the water and the adsorbent concentration. The results suggest that arsenic adsorption involved the formation of weak arsenic–iron oxide complexes at the magnetite surface. At a fixed adsorbent (magnetite nanoparticles) concentration of 0.4 g/L, percent arsenic removal decreased with increasing phosphate concentration. Magnetite nanoparticles removed <50% of arsenic from water containing >6 mg/L phosphate. In this case, an optimum design for achieving high arsenic removal by magnetite nanoparticles may be required.     

Shelf life of several marine fish species of Bangladesh during ice storage

Organoleptic, biochemical and bacteriological aspects of five tropical marine fish such as silver jewfish, Bombay duck, big-eye tuna, Chinese pomfret and ribbon fish stored in ice were studied. Organoleptically all fish were found acceptable for 10–13 days before becoming inedible. Proximate analysis showed that moisture content increased slightly; protein and lipid content decreased gradually and ash had little or no significant change. pH, TVB-N, peroxide and aerobic plate count values increased with increasing storage period but the values were within acceptable range up to 10 days of storage. Changes in myofibrillar ATPase activity and solubility of these fishes showed that Ca²⁺ ATPase in the presence of both 0.1  m and 0.5  m KCl decreased gradually whereas no marked changes were observed in the Mg⁺² ATPase activities in the presence/absence of Ca⁺². Myofibrillar protein solubility of all fish samples also decreased considerably during ice storage. The decrement in Ca²⁺ ATPase activity and solubility indicates denaturation of myofibrillar protein of fish samples during ice storage.     

Growth and differentiation potentials in confluent state of culture of human skeletal muscle myoblasts

The transitional behaviors of myoblasts toward differentiation were investigated in the cultures at the low and high seeding densities (respectively, X₀ = 1.0 × 10³ and 2.0 × 10⁵ cells/cm²). In the culture at the low seeding density, an increase in confluence degree accompanied a decrease in growth potential (R_p), being R_p = 0.85 and 0.11 at t = 48 and 672 h, respectively. Myoblasts seeded at the high density resulted in the immediate cessation of growth with keeping the low range of R_p = 0.02–0.09 throughout the culture. The reduction of R_p led to the generation of three subpopulations of cells in proliferative, quiescent and differentiated states. Close cell contacts in the confluent state of high seeding culture induced cell quiescence to a higher extent with suppressing differentiation.     

Mixed convective heat transfer enhancement in a ventilated cavity by flow modulation via rotating plate

The present study numerically explores the mixed convection phenomena in a differentially heated ventilated square cavity with active flow modulation via a rotating plate. Forced convection flow in the cavity is attained by maintaining external fluid flow through an opening at the bottom of the left cavity wall while leaving it through another opening at the right cavity wall. A counter-clockwise rotating plate at the center of the cavity acts as an active flow modulator. Moving mesh approach is used for the rotation of the plate and the numerical solution is achieved using arbitrary Lagrangian-Eulerian finite element formulation with a quadrilateral discretization scheme. Transient parametric simulations have been performed for various frequency of the rotating plate for a fixed Reynolds number (Re) of 100 based on maximum inlet flow velocity while the Richardson number (Ri) is maintained at unity. Heat transfer performance has been evaluated in terms of spatially averaged Nusselt number and time-averaged Nusselt number along the heated wall. Power spectrum analysis in the frequency domain obtained from the fast Fourier transform analysis indicates that thermal frequency and plate frequency start to deviate from each other at higher values of velocity ratio (>4).     

Numerical investigation on the electronic components' cooling for different coolants by finite element method

In this study, we conducted a numerical simulation to examine the cooling performance of an aluminum finned heat sink attached to a silicon chip, placed in a chamber of a rectangular cross-section. The heat sink is cooled by convective heat transfer utilizing nine commercially available gaseous coolants, namely air, hydrogen, helium, nitrogen, oxygen, carbon dioxide, freon12 vapor, propane, and ammonia. To select an appropriate coolant for electronic devices in terms of thermal–hydraulic performance, the maximum temperature on the chip domain and the associated pressure drop in the cooling channel as a function of coolant velocity are analyzed for the aforementioned fluids. It has been found that the minimum temperature is recorded for propane and freon12 vapor, which is approximately 31.1°C, for a coolant velocity of 0.5 m/s, but freon12 vapor shows the highest pressure drop, approximately 900 mPa, among all coolants. In the overall velocity regime, hydrogen shows the best cooling performance in terms of both cooling capacity and hydrodynamic characteristics. But considering safety issues, helium can be a better alternative. This comprehensive study provides a better understanding of different coolant performances, which will aid engineers to develop an effective cooling technique to accommodate the inexorably rising power demand.