Improving performance of high-power indium gallium nitride/gallium nitride-based vertical light-emitting diodes by employing simple n-type electrode pattern

In this work, simple n-type electrode structures were used to enhance the electrical and optical performances of fully packaged commercially mass-produced vertical-geometry light-emitting diodes (VLEDs). The forward bias voltage of the VLED with a Y-pattern electrode increased less rapidly than that of VLEDs with a reference electrode. The VLEDs with the reference and Y-pattern electrodes exhibited forward voltages of 2.93±0.015 and 2.89±0.015 V at 350 mA and 3.77±0.015 and 3.53±0.015 V at 2000 mA, respectively. The VLEDs with the Y-pattern electrode resulted in a higher light output than the VLEDs with the reference electrode with increase in the drive current to 2000 mA. The emission images showed that the VLEDs with the Y-pattern electrode exhibited better current spreading behavior and lower junction temperatures than the VLEDs with the reference electrode. With increase in the current from 350 to 2000 mA, the VLEDs with the Y-pattern electrode experienced a 39.4% reduction in the wall plug efficiency, whereas the VLEDs with the reference electrode suffered from a 43.3% reduction.     

Fracture analysis of plane piezoelectric/piezomagnetic multiphase composites under transient loading

The transient response of cracked composite materials made of piezoelectric and piezomagnetic phases, when subjected to in-plane magneto-electro-mechanical dynamic loads, is addressed in this paper by means of a mixed boundary element method (BEM) approach. Both the displacement and traction boundary integral equations (BIEs) are used to develop a single-domain formulation. The convolution integrals arising in the time-domain BEM are numerically computed by Lubich’s quadrature, which determines the integration weights from the Laplace transformed fundamental solution and a linear multistep method. The required Laplace-domain fundamental solution is derived by means of the Radon transform in the form of line integrals over a unit circumference. The singular and hypersingular BIEs are numerically evaluated in a precise and efficient manner by a regularization procedure based on a simple change of variable, as previously proposed by the authors for statics. Discontinuous quarter-point elements are used to properly capture the behavior of the extended crack opening displacements (ECOD) around the crack-tip and directly evaluate the field intensity factors (stress, electric displacement and magnetic induction intensity factors) from the computed nodal data. Numerical results are obtained to validate the formulation and illustrate its capabilities. The effect of the combined application of electric, magnetic and mechanical loads on the dynamic field intensity factors is analyzed in detail for several crack configurations under impact loading.     

The influence of the nitriding process on the dry wear resistance of 15-5 PH stainless steel

The dry wear resistance of 15-5 PH stainless steel nitrided using various methods was investigated. The methods included gas nitriding in cracked ammonia, plasma or ion nitriding and ion implantation of nitrogen. The dry wear resistance and the topography of the wear surface were studied as a function of load and sliding distance. It was found that the wear resistance of the plasma-nitrided specimens is higher than that of the gas-nitrided specimens. The wear resistance of the ion-implanted specimens was even better. However, because of the very small thickness of the implanted layer, only partial results were obtained.     

Seasonal fluctuations of organochlorine and triazines pesticides in the aquatic system of Ioannina basin (Greece)

For the period September 1984 to November 1985 water samples from the aquatic system of Ioannina basin were analyzed every second month for organochlorine and triazines pesticides. The detected compounds were found to follow a seasonal pattern, with an increment during summer followed by a decrease during winter and an increase again during late spring. This pattern was apparent for Ioannina lake as well as for the Kalamas river connected to it through the Lapsista's canal and tunnel. The results are discussed in terms of the amounts of the detected pesticides used for farming in the vicinity of the Ioannina basin and the seasonal rainfall.     

An improved method for the stabilization of NaI-photomultiplier gamma detectors against thermal and other drift

Alpha peaks have been used as part of servo systems to stabilize NaI-photomultiplier gamma detectors against drift. However, alpha peaks shift with temperature change differently than do gamma peaks, thus spoiling what would otherwise be a workable scheme for stabilizing against probably the most serious source of NaI-p.m. detector drift, namely thermal effects. It has been found possible to accurately compensate for the difference in the shift with temperature versus gamma peaks using the signal derived from a thermistor in thermal contact with the NaI crystal to control the bias of a discriminator in the servo circuit. The servo circuit utilizing this principle has been used in commercial multichannel analyzers of the type intended for field use under adverse ambient conditions.     

Hedging downside risk of oil refineries: A vine copula approach

The financial health of an oil refinery greatly depends on its refining margin or the difference between the prices of its refined products (typically, gasoline and heating oil) and the cost of crude oil. The refinery may hedge against the downside risk of unfavorable price movements using crude oil, gasoline, and heating oil futures. This paper examines the use of a vine copula approach to estimate multiproduct hedge ratios that minimize the downside risk of the refinery. The advantage of the vine copula approach is that it allows us to capture important characteristics of petroleum price changes, including skewness and fat-tailedness in the marginal distributions of individual price change series as well as heterogeneous (tail) dependence patterns between different pairs of price changes. The out-of-sample hedging effectiveness of two popular classes of vine copula models – canonical (C-) and drawable (D-) vine copula models – are evaluated and compared with that of the widely used nonparametric method and three standard multivariate copula models. The empirical results reveal that the D-vine copula model is a good and safe choice in managing the downside risk of the refinery.     

2005年我国LED显示屏产业发展综述

文章总结了2005年国内LED显示屏产业发展总体情况,对LED显示屏产业和市场发展进行了分析,介绍了LED显示屏产业技术和标准化进展,展望了LED显示屏产业的未来发展趋势。     

Description of adsorption equilibrium on type A zeolites with use of the Polanyi-Dubinin potential theory

A correlation between the adsorption of both water and methanol and the sodium exchange for various cations was studied on type A zeolites, and the adsorption isotherms were plotted. The isotherms were described with both the Dubinin-Astakhov (DA) and the modified Dubinin-Radushkevich-Stoeckli (DRS) equations. The type of adsorbate as well as cation influence the shape of the function of adsorption potential distribution obtained for the zeolites examined.     

Photoelectrochemical behaviour of n-silicon photoanodes coated with chromium(III) oxide films and Cr2O3 containing composite layers

n-Type silicon single crystals coated with Cr₂O₃-containing composite and/or p-Cr₂O₃ thin films were studied as photoanodes for electrocatalytic photo-oxidation of isopropanol in aqueous media. Film deposition was by pyrolysis of organometallic compounds (i.e. chemical vapour deposition) for Cr₂O₃ and by a ceramic technique for the Cr₂O₃-containing composite. The photocurrent at the heterojunction electrodes illuminated with visible light is produced by holes which are photoexcited in n-silicon only. There is no energy barrier for minority carriers to be transferred across the n-p heterojunction, so considerable quantum efficiencies of photocurrent are observed. Heterogeneous redox catalysis is responsible for the oxidation of isopropanol with Cr₂O₃ as electrocatalyst. The use of a composite coating makes the photoanode highly stable, kinetics at the electrode/electrolyte interface being a key factor for the stability against photocorrosion.     

Photoluminescence properties of Eu-activated BaCa2Al8O15 nanophosphors

A new blue-emitting nanophosphor of Eu²⁺-activated BaCa₂Al₈O₁₅ was synthesized by the Pechini method. The phosphors were investigated by X-ray powder diffraction (XRD) measurement and confirmed to be a pure crystalline phase of BaCa₂Al₈O₁₅. The photoluminescence excitation and emission spectra, the luminescence decay and the color coordinates were taken to investigate the luminescence characteristics. The dependence of luminescence intensities BaCa₂Al₈O₁₅:Eu²⁺ on the doping concentrations was investigated. This nanophosphor can be efficiently excited by UV light and presents bright blue luminescence. Under the same conditions, the light yield of BaCa₂Al₈O₁₅:Eu²⁺ is about 1.2 times higher than that of blue-emitting phosphor BaMgAl₁₀O₁₇:Eu²⁺. Eu²⁺-activated BaCa₂Al₈O₁₅ nanophosphor exhibits the long-lasting phosphorescence, which was analyzed by measuring the afterglow decay curves. The co-doped Eu³⁺ ions and some defects were suggested to be the possible trap-centers.