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Downburst in thunderstorm mainly refers to the outflow on frontier and the strong wind shear caused by the downburst. In this paper, the thunderstorm evolution is divided into three stages as growing, mature and dissipating stages according to its development. Based on meteorological data, trends of relevant parameters are presented. Then with the 3D ring vortices method, the classical fluid mechanics theory is applied through adding linear source model to simulate the distribution of velocity in the wind shear field and its evolution over time. This modeling method could effectively simulate the evolution of downburst, and is suitable for engineering application.

In this research, a new developed optimization method for light guide plate design is proposed in order to achieve its exiting-light uniformity by varying the light-scattering microstructure sizes or pitches at different areas of a liquid crystal display (LCD) light guide plate. The light-scattering hemispheric microstructures on a light guide plate are studied in this paper due to less light absorption compared to the conventional V-cut pattern design. The results show success in uniformity. To validate the effectiveness of this design method on the improvement of exiting-light uniformity, the "advance system analysis program" (ASAP) simulation is performed. Based on the proposed design method, it is illustrated that the exiting-light uniformity significantly improves by more than 13% for the case study.

The optical properties of a GaN-based vertical-cavity surface-emitting laser (VCSEL) with two dielectric distributed Bragg reflectors were investigated under optically pumped operation. The laser emits blue-violet light at a wavelength of 414 nm at room temperature with a high spontaneous emission coupling factor (� -factor) of 2 � 10 � 2 and a linewidth of 0.25 nm. The optical gain was determined by the Hakki–Paoli method by measuring the photoluminescence spectra below threshold conditions. At room temperature, an optical gain of 2900 cm � 1 was obtained under threshold condition. The linewidth enhancement factor (� -factor) is estimated from the ratio of the wavelength and gain derivation with respect to the carrier density, and the � -factor at room temperature is estimated to be 2.8. Strong exciton-photon coupling in the microcavity was observed at room temperature. A 9 meV Rabi splitting with 60% peak-to-valley contrast was determined from the photoluminescence measurements. Emission spectra showing the evolution of anticrossing behavior were also observed. [DOI: 10.1143/JJAP.47.6655]

We review the fabrication technology and performance characteristics of optically pumped GaN-based vertical cavity surface emitting lasers (VCSELs). Two types of VCSELs with different microcavity structures are described. First type of VCSEL has a hybrid microcavity structure that consists of an epitaxially grown AlN/GaN distributed Bragg reflector (DBR), a GaN active layer with InGaN/GaN multiple quantum wells (MQWs), and a Ta2O5/SiO2 dielectric DBR. Second type of VCSEL has a dielectric DBR microcavity structure that has a similar InGaN/GaN MQWs active layer sandwiched in two dielectric DBRs formed by Ta2O5/SiO2 and TiO2/SiO2. Both types of VCSELs achieved laser action under optical pumping at room temperature with emission wavelength of 448 and 414 nm for hybrid DBR VCSEL and dielectric DBR VCSEL, respectively. Both lasers showed narrow emission linewidth with high degree of polarization and large spontaneous emission coupling factors of about 10-2. In addition, a high characteristic temperature of over 240 K was measured, and a distinct spatially inhomogeneous emission pattern was observed.

We propose a method of realizing strong ultraviolet emission from InGaN/AlGaN multiple quantum wells (MQWs) grown by a multi-step process. During growth of the quantum well layer, only trimethylindium (TMIn) and ammonia were introduced into the reactor, followed by a growth interruption treatment before growth of AlGaN barriers. The growth temperature of QWs dominates the photoluminescence (PL) emission peak position and surface morphologies of the films. It was found that the PL spectra of the samples with MQWs grown at 685 °C showed a strong UV emission at 380 nm. The correlation between surface structures and optical characteristics was studied by cathodoluminescence microscopy. The electroluminescence spectra under various injection currents showed a weak carrier localization effect induced by a quantum-confined Stark effect in the MQW.

This investigation describes the development of a InGaN/GaN light-emitting diode (LED) with textured sidewalls using natural lithography with polystyrene spheres (PSs) as the etching mask and dry etching the epitaxial layers of LEDs to achieve nano-scale textured sidewalls. The LED with textured sidewalls increased the output power of the InGaN?GaN multiple quantum well (MQW) LEDs by a factor of 1.3, indicating that the LED with nano-scale textured sidewalls had larger light extraction efficiency. The wall-plug efficiency of nitride-based LEDs was increased by 30% using textured sidewalls.

The InGaN/GaN light-emitting diode (LED) with a top p-GaN surface nanoroughened using Ni nanomasks and laser etching has been fabricated. The light output power of the InGaN/GaN LED with a nanoroughened top p-GaN surface is 1.55-fold that of a conventional LED. The series resistance of InGaN/GaN LED was reduced by 32% due to the increase in the contact area of the nanoroughened surface.

Room-temperature optically pumped GaN-based vertical-cavity surface-emitting lasers (VCSELs) were demonstrated by laser lift-off. A VCSEL was fabricated by combining a GaN-based cavity with two dielectric distributed Bragg reflectors: SiO2/TiO2 and SiO2/Ta2O5. The Q factor of the VCSEL is 518 indicating a good interfacial layer quality of the structure. The laser emits blue-violet wavelength light at 414 nm under optical pumping at room temperature with a threshold pumping energy of 270 nJ. The laser emission has a narrow linewidth of 0.25 nm and a degree of polarization of 70%. The laser emission patterns clearly indicate a vertical lasing action of the VCSEL.

The 1.27-/spl mu/m InGaAs:Sb-GaAs-GaAsP vertical cavity surface emitting lasers (VCSELs) were grown by metalorganic chemical vapor deposition and exhibited excellent performance and temperature stability. The threshold current varies from 1.8 to 1.1 mA and the slope efficiency falls less than /spl sim/35% from 0.17 to 0.11 mW/mA as the temperature is raised from room temperature to 75/spl deg/C. The VCSELs continuously operate up to 105/spl deg/C with a slope efficiency of 0.023 mW/mA. With a bias current of only 5 mA, the 3-dB modulation frequency response was measured to be 8.36 GHz, which is appropriate for 10-Gb/s operation. The maximal bandwidth is estimated to be 10.7 GHz with modulation current efficiency factor of /spl sim/5.25GHz/(mA)/sup 1/2/. These VCSELs also demonstrate high-speed modulation up to 10 Gb/s from 25/spl deg/C to 70/spl deg/C. We also accumulated life test data up to 1000 h at 70/spl deg/C/10 mA.

We report the electrical and optical characteristics of GaN light emitting diode (LED) with beryllium (Be) implanted Mg-doped GaN layer. The p-type layer of Be-implanted GaN LED showed a higher hole carrier concentration of 2.3 10 18 cm 3 and low specific contact resistance value of 2.0 10 4 Vcm 2 than as-grown p-GaN LED samples without Be-implantation. The Be-implanted GaN LEDs with InGaN/GaN MQW show slightly lower light output (about 10%) than the as-grown GaN LEDs, caused by the high RTA temperature annealing process. # 2004 Elsevier B.V. All rights reserved.

The fabrication process and performance characteristics of the laser lift-off (LLO) GaN light-emitting diodes (LEDs) were investigated. The LLO-GaN LEDs were fabricated by lifting off the GaN LED wafer structure grown on the original sapphire substrate by a KrF excimer laser at 248 nm wavelength with the laser fluence of 0.6 J/cm2 and transferring it onto a Cu substrate. The LLO-GaN LEDs on Cu show a nearly four-fold increase in the light output power over the regular LLO-LEDs on the sapphire substrate. High operation current up to 400 mA for the LLO-LEDs on Cu was also demonstrated. Based on the emission wavelength shift with the operating current data, the LLO-LEDs on Cu show an estimated improvement of heat dissipation capacities by nearly four times over the light-emitting devices on sapphire substrate. The LLO process should be applicable to other GaN-based LEDs in particular for those high light output power and high operation current devices.

A method for determining the cake properties in centrifugal dewatering is proposed in this study. By substituting experimental data of cake saturation versus time into the proposed procedures, the values of capillary pressure and filter cake permeability under various cake saturations can be estimated. Two kinds of particulate samples, CaCO3 and polystyrene powder, were used in the centrifugal dewatering experiments. The results show that both cakes exist in their funicular state for most times of dewatering. The value of capillary pressure increases while the permeability of cake decreases during the course of centrifugal dewatering. The regression functions relating the capillary pressure and permeability to the cake saturation are in agreement with the empirical equations used in previous work. A program was also designed to simulate the variation of cake saturation during centrifugal dewatering. A good agreement between the simulated results and the experimental data was obtained. The optimum operatin...

We report a fabrication and demonstration of a GaN-based high-Q vertical-cavity light-emitting diode (VCLED). The GaN VCLED is composed of a 25-pair high-reflectivity (98%) GaN/AlN distributed Bragg reflector (DBR), an eight-pair SiO2/Ta2O5 dielectric DBR (99%), and a three-lambda optical thickness InGaN/GaN active region. It shows a very narrow linewidth of 0.52 nm, corresponding to a cavity Q -value of 895 at a driving current of 10 mA and a dominant emission peak wavelength at 465.3 nm. In addition, this VCLED emission linewidth continues to decrease with an increasing injection current, suggesting a possible realization of GaN-based vertical-cavity surface emitting lasers.