Development of a model-based optimal control strategy of Centrifugal Chiller System

2006-2007 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe

Two-electron-satellite transition of donor bound exciton in ZnO: Radiative Auger effect

Two-electron-satellite (TES) transition of donor bound exciton (D 0X) is an interesting many-body quantum process. In this letter, precise luminescence spectra and temperature behaviors of the TES transition of aluminum bound exciton in two kinds of zinc oxide single crystals were investigated in detail. It is found that the TES transition can be treated as a radiative Auger process in which the temperature dependence of the emission intensity of the transition can be fitted very well with a model taking into account the temperature dependent Auger term and thermal dissociation of the D0X excitons. © 2013 AIP Publishing LLC.published_or_final_versio

Optimal control of multi-zone vav air-conditioning system

2006-2007 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe

Experimental investigation of a solar collector integrated with a pulsating heat pipe and a compound parabolic concentrator

The paper reports an experimental investigation of a newly proposed solar collector that integrates a closed-end pulsating heat pipe (PHP) and a compound parabolic concentrator (CPC). The PHP is used as an absorber due to its simple structure and high heat transfer capacity. The CPC has a concentration ratio of 3.4 and can be readily manufactured by three-dimensional printing. The CPC can significantly increase the incident solar irradiation intensity to the PHP absorber and also reduce the heat loss due to the decrease in the area of the hot surface. A prototype of the solar collector has been built, consisting of a PHP absorber bent by 4 mm diameter copper tube, CPC arrayed by 10 × 2 CPC units with the collection area of 300 × 427.6 mm2, a hot water tank and a glass cover. HFE7100 was utilized as the working fluid at a filling ratio of 40%. The operating characteristics and thermal efficiency of the solar collector were experimentally studied. The steady and periodic temperature fluctuations of the evaporation and condensation sections of the PHP absorber indicate that the absorber works well with a thermal resistance of about 0.26 °C/W. It is also found that, as the main factor to the the thermal performance of the collector, thermal resistance of the PHP absorber decreases with increasing evaporation temperature. The collector apparently shows start-up, operational and shutdown stages at the starting and ending temperatures of 75 °C. When the direct normal irradiance is 800 W/m2, the instantaneous thermal efficiency of the solar collector can reach up to 50%.The work was financially supported by the National Natural Science Foundation of China (51506004), Beijing Natural Science Foundation (3162009), Scientific Research Project of Beijing Educational Committee (KM201410016001) and Research Fund of Beijing University of Civil Engineering and Architecture

Raman and photoluminescence characterization of focused ion beam patterned InGaN/GaN multi-quantum-wells nanopillar array

High crystal quality GaN nanopillar arrays containing InGaN/GaN multi-quantum wells (MQWs) have been fabricated by focused ion beam followed by wet etch treatments to remove the ion damage. The first order Raman spectra reveal a well-built additional peak when the diameter of the nanopillars is less than 220 nm. This peak is also observed in the GaN pillars without MQW and is clearly assigned to the surface optical (SO) mode originating from the A 1 phonon in wurtzite GaN. The frequency of this SO mode is found to be sensitive with the diameter and surface roughness of the nanopillars. Temperature-variable photoluminescence measurements show that a broadband emission in the as-grown sample split into the two well-resolved bands for nanopillars and the emission band at the higher energy side quickly thermally quenched. © 2011 American Institute of Physics.published_or_final_versio

Adaptive optimal control of seawater cooling system in centralized air-conditioning system

2006-2007 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe

Research and development in HVAC system diagnosis

2006-2007 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe

Evidence for a Type-II band alignment between cubic and hexagonal phases of GaN

The study of photoluminescence spectra of a series of thin, undoped, hexagonal GaN films containing cubic GaN inclusions grown by molecular-beam epitaxy on 6H-SiC was presented. It was shown that an emission peak at ∼3.17 eV in thin, hexagonal GaN films exhibits behaviors typical of a spatially indirect transition. The values of the band offsets extracted from the data were in good agreement with theoretical predictions.published_or_final_versio

激光探针等离子体质谱用于错石Pb-Pb定年的分析和校正方法的进一步探讨

激光探针等离子体质谱可对错石进行快速准确的Pb一Pb 同位素定年。本文进一步探讨了该方法应用中的几个问题。对不同样品采用不同的聚焦方式可以对U/Pb 分异有一定的控制作用。在一定的条件下, 不连续和连续采样模式都可以得到较高精度和准确度的结果。连续采样模式还可以得到同位素计数的深度剖面。不同的侧量滞留时间会影响测量结果的精度。20Ins 为适合错石ZO7Pb/206Pb 分析的最佳侧量滞留时间。在对侧定结果进行校正时, 可以采用玻璃标样NIST61O 和错石标样两种不同的校正方法。Laser probe-inductively coupled plasma mass spectrometry (LP-ICPMS) provides a rapid,precise and accurate technique for Pb-Pb zircon chronology. Different conditions affect massfractionation during laser ablation. Fixed-focus-mode and active-focus-mode, focus-mode anddefocus-mode, time-average mode (single point method) and time-resolved mode (depth pro-filing method), are compared. Both time-average mode and time-resolved mode can give rel-atively high precise, accurate results, and depth profile can only be obtained by time-resolvedmode. Comparing the results of time-resolved mode using different dwell time, it is found that20 ms is the best dwell time with highest precision and accuracy. It is shown that both NIST610and Zircon Standard give satisfactory calibration results for zircon 207Pb/206Pb isotopic age.Therefore, time resolved mode with dwell time of 20 ms is preferred for zircon analysis.published_or_final_versio

Simple and efficient methods for isolation and activity measurement of the recombinant hirudin variant 3 from Bacillus subtilis

A simple purification approach of the recombinant hirudin variant 3 from the Bacillus subtilis was established, by which the hirudin could be purified to the purity of 95% through one-step chromatography with the total recovery rate of 83.9%. A modified Markwardt thrombin titration method for measuring hirudin activity was also set up. Briefly, a series of concentrations of thrombin was prepared and titrated to hirudin sample, respectively and the anti-thrombin activity-range of hirudin was narrowed down by several thrombin solutions at high or low concentration and the optimum group of thrombin concentrations was determined for titration of the hirudin sample. In this modified method, the hirudin activity was determined more accurately, concisely and promptly than the classic Markwardt method.Key words: Hirudin, thrombin titration method, chromatography, purification