Efficiency improvement of near-ultraviolet InGaN LEDs using patterned sapphire substrates

The use of conventional and patterned sapphire substrates (PSSs) to fabricate InGaN-based near-ultraviolet (410 nm) light-emitting diodes (LEDs) was demonstrated. The PSS was prepared using a periodic hole pattern (diameter: 3 /spl mu/m; spacing: 3 /spl mu/m) on the (0001) sapphire with different etching depths. From transmission-electron-microscopy and etch-pit-density studies, the PSS with an optimum pattern depth (D/sub h/=1.5 /spl mu/m) was confirmed to be an efficient way to reduce the thread dislocations in the GaN microstructure. It was found that the output power increased from 8.6 to 10.4 mW, corresponding to about 29% increases in the external quantum efficiency. However, the internal quantum efficiency (@ 20 mA) was about 36% and 38% for the conventional and PSS LEDs, respectively. The achieved improvement of the output power is not only due to the improvement of the internal quantum efficiency upon decreasing the dislocation density, but also due to the enhancement of the extraction efficiency using the PSS. Finally, better long-time reliability of the PSS LED performance was observed.     

Bending-beam measurement of solvent diffusions in polyimides: Theoretical and experimental

A general formula correlating the bending curvature variation ratio of a layered structure caused by solvent-induced swelling in its polymer overcoat with diffusion time under case II diffusion has been presented. In the event of case II diffusion, the diffusion front velocity, v, can be calculated by using this formula and measured by a bending-beam apparatus. At room temperature, the diffusion of n-methyl-pyrrolidone (NMP) solvent in the film of pyromellitic phenylene diamine (PMDA-PDA) is case II. While in PMDA-B (-benzidine) and benzophenone tetracarboxylic dianhydride (BPDA-PDA), no diffusion progress can be observed. But, the diffusion in 6F-dianhydride- (6FDA-PDA) is case I with D = 0.85 × 10^?9 cm²/s. It becomes anomalous when mixing with 25% PMDA-B, but becomes case II diffusion with more PMDA-B. The preabsorbed moisture in the films does not affect the v value. In PMDA-PDA, v = 7.3 × 10^?8 cm/s. In the 25/75 and 50/50 6FDA-PDA/PMDA-B blends, v = 6.3 and 11.3 × 10^?8 cm/s.     

Evaluation of two cooling systems under a firefighter coverall

Firemen often suffer from heat strain. This study investigated two chest cooling systems for use under a firefighting suit. In nine male subjects, a vest with water soaked cooling pads and a vest with water perfused tubes were compared to a control condition. Subjects performed 30 min walking and 10 min recovery in hot conditions, while physiological and perceptual parameters were measured. No differences were observed in heart rate and rectal temperature, but scapular skin temperature and fluid loss were lower using the perfused vest. Thermal sensation was cooler for the perfused vest than for the other conditions, while the cool pad vest felt initially cooler than control. However, comfort and RPE scores were similar. We conclude that the cooling effect of both tested systems, mainly providing a (temporally) cooler thermal sensation, was limited and did not meet the expectations.     

Solubility of Propane in Sulpholane at Elevated Pressures

The solubility of propane in sulpholane has been determined at temperatures in the range 298‐403 K at pressures up to 17.6 MPa. The experimental results were correlated by the Peng‐Robinson equation of state, and binary interaction parameters have been obtained for this system. The parameters in the Krichevsky‐Ilinskaya equation were calculated from these interaction parameters.     

Kinetics of Thermal Dehydroxylation and Carbonation of Magnesium Hydroxide

The kinetics of simultaneous dehydroxylation and carbonation of precipitated Mg(OH)₂ were studied using isothermal and nonisothermal thermogravimetric analyses. Specimens were analyzed using X-ray diffraction, transmission electron microscopy, and through measurements of the volume of carbon dioxide evolved in a subsequent reaction with hydrochloric acid. From 275° to 475°C, the kinetics of isothermal dehydroxylation in helium were best fit to a contracting-sphere model, yielding an activation energy of 146 kJ/mol, which was greater than values reported in the literature for isothermal dehydroxylation under vacuum (53–126 kJ/mol). The carbonation kinetics were complicated by the fact that dehydroxylation occurred simultaneously. The overall kinetics also could be fit to a contracting-sphere model, yielding a net activation energy of 304 kJ/mol. The most rapid carbonation kinetics occurred near 375°C. At this temperature, Mg(OH)₂ underwent rapid dehydroxylation and subsequent phase transformation, whereas thermodynamics favored the formation of carbonate. During carbonation, MgCO₃ precipitated on the surface of disrupted Mg(OH)₂ crystals acting as a kinetic barrier to both the outward diffusion of H₂O and the inward diffusion of CO₂.     

Coordinated ordering decisions for products with short lifecycle and variable selling price

The supplier–buyer coordination is an important policy in the supply chain management. The buyer in the two-echelon inventory system with regular selling season has to face the uncertainty of customer demand, supplier’s delivery time and variable price change. At the same time, the supplier has to consider the inventory holding and delay cost. The objective of this study is to develop an integrated supply chain strategy for products with short lifecycle and variable selling price to entice cooperation. The strategy must provide a win–win situation for both the supplier and the buyer. A numerical case example, sensitivity analysis and compensation mechanism are given to illustrate the model.     

An efficient blocking-matching algorithm based on fuzzy reasoning

Due to the temporal and spatial correlation of image sequence, the motion vector of a reference block is highly related to the motion vectors of its adjacent blocks in the same image frame. By using that idea, we propose a novel efficient fuzzy search (EFS) algorithm for block motion estimation. The experimental results show that the EFS performs better than other fast search algorithms, such as TSS, CS, NTSS, FSS, BBGDS, SES, and PSA in terms of picture quality, accuracy, computational complexity, and coding efficiency.