Observation of defects in GaN epilayers

GaN epilayers grown on sapphire substrates nitridated for various lengthy periods were investigated by light scattering tomography (LST) and Raman scattering. In the LST images of the plane-view epilayers, the light scattering defects distribute in [<11(2)over bar 0>] directions. The defect density is lower in epilayer grown on substrate nitridated for a longer period. The defects are believed to be straight threading edge dislocations on {<1(1)over bar 00>} planes. The Raman shift of E-2 mode is larger in the sample grown on substrate nitridated for a longer period. Our results show that the stress is higher in the sample with fewer dislocations.

Oscillation flow induced by underwater supersonic gas jets

This paper describes an experimental study on the oscillation flow characteristics of submerged supersonic gas jets issued from Laval nozzles. The flow pattern during the jet development and the jet expansion feedback phenomenon are studied using a high-speed camera and a pressure measurement system. The experimental results indicate that along the downstream distance, the jet has three flow regimes: (1) momentum jet; (2) buoyant jet; (3) plume. In the region near the nozzle exit a so-called bulge phenomenon is found. Bulging of the jet occurs many times before the more violent jet expansion feedback occurs. During the feedback process, the jet diameter can become several times that of the original one depending on the jet Mach number. The frequencies of the jet bulging and the jet expansion feedback are measured.

Experimental Investigation of Performance of a Miniature Direct Methanol Fuel Cell in Short-Term Microgravity

Experimental study of a liquid fed direct methanol fuel cell has been conducted in different gravity environments. A small single cell with 5 cm x 5 cm active area has single serpentine channel on the graphite cathode polar plate and 11 parallel straight channels on the graphite anode flow bed. Cell voltage and current have been measured and two-phase flow in anode channels has been in situ visually observed. The experimental results indicate that the effect of gravity on power performance of the direct methanol fuel cell is large when the concentration polarization governs fuel cells operation. Gravitational effect becomes larger at higher current density. Increasing methanol feeding molarity is conducive to weaken the influence of gravity on performance of liquid fed direct methanol fuel cells. Increasing feeding flow rate of methanol solution from 6 to 15 ml/min could reduce the size of carbon dioxide bubbles, while the influence of gravity still exist. Transport phenomena inside direct methanol fuel cells in microgravity is also analyzed and discussed.

中国科学院力学研究所环境力学重点实验室研究工作进展

中国科学院力学研究所环境力学重点实验室(Key Laboratory of Environmental Mechanics, LEM)是力学研究所重点培育发展的实验室之一.中国科学院力学研究所最早在国内倡导环境力学研究,积极推动力学与环境科学的交叉与融合.早在1960年代就开始环境问题研究,1986年正式组建了环境流体力学研究组,1989年和1992年成立了环境流体力学和环境工程研究室. 1995年合并成立了环境科学与技术研究中心,2007年成立了环境力学中心.经过20余年的发展,人才队伍建设和科研能力建设都达到了较高水平,尤其在流域及海洋水环境、重大工程中的环境与灾害、大气与城市环境、工业节能减排和废弃物处理等方面,逐步形成学科优势,取得了丰硕科研成果,于2008年12月正式成立了环境力学重点实验室