An Al0.25Ga0.75N/GaN Lateral Field Emission Device with a Nano Void Channel

We report an Al0.25Ga0.75N/GaN based lateral field emission device with a nanometer scale void channel. A -45 nm void channel is obtained by etching out the SiO2 sacrificial dielectric layer between the semiconductor emitter and the metal collector. Under an atmospheric environment instead of vacuum conditions, the OaN- based field emission device shows a low turn-on voltage of 2.3 V, a high emission current of -40 μA （line current density 2.3mA/cm） at a collector bias Vc = 3 V, and a low reverse leakage of 3nA at Vc = -3 V. These characteristics are attributed to the nanometer scale void channel as well as the high density of two-dimensional electron gas in the AlGaN/GaN heterojunction. This type of device may have potential applications in high frequency mieroelectronics or nanoelectronics.

PM10 emissions from industrial coal-fired chain-grate boilers

Industrial coal-fired boiler is an important air pollutant emission source in China. The chain-grate boiler is the most extensively used type of industrial coal-fired boiler. An electrical low-pressure impactor, and a Dekati？ Low Pressure Impactor were applied to determine mass and number size distributions of PM10 at the inlet and the outlet of the particulate emission control devices at six coalfired chain-grate boilers. The mass size distribution of PM10 generated from coal-fired chain-grate boilers generally displays a bimodal distribution that contains a submicron mode and a coarse mode. The PM in the submicron mode for burning with raw coal contributes to 33% ± 10 % of PM10 emissions, much higher than those for pulverized boilers. And the PM in the submicron mode for burning with briquette contributes up to 86 % of PM10 emissions. Multiclones and scrubbers are not efficient for controlling PM10 emission. Their average collection efficiencies for sub-micron particle and super-micron particle are 34% and 78%, respectively. Operating conditions of industrial steam boilers have influence on PM generation. Peak of the submicron mode during normal operation period is larger than the start-up period.

PM_(2.5) in China:Measurements,sources,visibility and health effects,and mitigation

Concern over the health effects of fine particles in the ambient environment led the U.S. Environmental Protection Agency to develop the first standard for PM2.5 （particulate matter less than 2.5 μm） in 1997. The Particle Technology Laboratory at the University of Minnesota has helped to establish the PM2.5 standard by developing many instruments and samplers to perform atmospheric measurements. In this paper, we review various aspects of PM2.5, including its measurement, source apportionment, visibility and health effects, and mitigation. We focus on PM2.s studies in China and where appropriate, compare them with those obtained in the U.S. Based on accurate PM2.5 sampling, chemical analysis, and source apportionment models, the major PM2.5 sources in China have been identified to be coal combustion, motor vehicle emissions, and industrial sources. Atmospheric visibility has been found to correlate well with PM2.s concentration. Sulfate, ammonium, and nitrate carried by PM2.s, commonly found in coal burning and vehicle emissions, are the dominant contributors to regional haze in China. Short-term exposure to PM2.s is strongly associated with the increased risk of morbidity and mortality from cardiovascular and respiratory diseases in China. The strategy for PMzs mitigation must be based on reducing the pollutants from the two primary sources of coal-fired power plants and vehicle emissions. Although conventional Particulate Emission Control Devices （PECD） such as electrostatic precipitators in Chinese coal-fired power plants are generally effective for large particles, most of them may not have high collection efficiency of PM2.5. Baghouse filtration is gradually incorporated into the PECD to increase the PM2.5 collection efficiency. By adopting stringent vehicle emissions standard such as Euro 5 and 6, the emissions from vehicles can be gradually reduced over the years. An integrative approach, from collaboration among academia, government, and industries, can effectively manage and mitigate the PM2.s pollution in China.