科研成果 by Year: 2013

Measurements of ambient OH and HO2 radicals were performed by laser induced fluorescence (LIF) during CAREBeijing2006 (Campaigns of Air Quality Research in Beijing and Surrounding Region 2006) at the suburban site Yufa in the south of Beijing in summer 2006. On most days, local air chemistry was influenced by aged air pollution that was advected by a slow, almost stagnant wind from southern regions. Observed daily concentration maxima were in the range of (4-17) x 10(6) cm(-3) for OH and (2-24) x 10(8) cm(-3) for HO2 (including an estimated interference of 25% from RO2). During daytime, OH reactivities were generally high (10-30 s(-1)) and mainly contributed by observed VOCs and their calculated oxidation products. The comparison of modelled and measured HOx concentrations reveals a systematic underprediction of OH as a function of NO. A large discrepancy of a factor 2.6 is found at the lowest NO concentration encountered (0.1 ppb), whereas the discrepancy becomes insignificant above 1 ppb NO. This study extends similar observations from the Pearl-River Delta (PRD) in South China to a more urban environment. The OH discrepancy at Yufa can be resolved, if NO-independent additional OH recycling is assumed in the model. The postulated Leuven Isoprene Mechanism (LIM) has the potential to explain the gap between modelled and measured OH at Beijing taking into account conservative error estimates, but lacks experimental confirmation. This and the hereby unresolved discrepancy at PRD suggest that other VOCs besides isoprene might be involved in the required, additional OH recycling. Fast primary production of ROx radicals up to 7 ppb h(-1) was determined at Beijing which was dominated by the photolysis of O-3, HONO, HCHO, and dicarbonyls. For a special case, 20 August, when the plume of Beijing city was encountered, a missing primary HOx source (about 3 ppb h(-1)) was determined under high NOx conditions similar to other urban areas like Mexico City. CAREBeijing2006 emphasizes the important role of OVOCs as a radical source and sink, and the need for further investigation of the chemical degradation of VOCs in order to better understand radical chemistry in VOC-rich air.

Lake Dianchi, one of the main water sources for Kunming, China, experiences severe cyanobacterial blooms due to rapid urbanization and local industrial development. Scientific interest in the mechanisms that cause blooms has been increasing. An integrated model combining rough set theory with binary logistic regression was used to examine the correlation between weather conditions and cyanobacterial blooms in Lake Dianchi based on daily monitoring data. The binary logistic regression yielded quantitative correlations between cyanobacterial blooms and the assessed meteorological variables, including temperature, wind velocity, and wind direction. The rough decision process connected the weather conditions and cyanobacterial blooms, which were used to verify the binary regression model results. It was shown that by comparing the methods, the rough decision-adjusted binary logistic regression model significantly improved model accuracy. The integrated model of cyanobacterial blooms in Lake Dianchi may inform decision-makers at local water purification plants of the water quality in the lake and assist them in making more cost-effective decisions.

2012年,全球高等教育领域最热的词就是"MOOC",虽然这股热潮在2011年秋季就已涌起,当时斯坦福大学三门计算机课程宣布对全球免费开放,注册人数均超过或接近十万人,2011年12月底MIT宣布成立MITx,主打MOOC形式的开放教育。深受经济不景气影响的美国高等教育界视MOOC为降低大学学费、为弱势群体提供高等教育的良机,基金会和风险投资公司在2012年纷纷注资,带来了一片繁荣景象。这里依据《美国高等教育纪事》全年对MOOC活动的有关报道,梳理了2012年有关MOOC发展的重大事件。

本文探讨了MOOCs课程与现行高等教育体系的融合模式,提出如果将MOOCs与传统高等教育体系类比为平面上的两条直线的话,两者之间不外乎平行、重合和相交三种关系。

<正>什么是MOOC1.概念MOOC是今年教育领域最热的话题,MOOC,Massive Open Online Courses,大规模、开放、在线、课程四个要素缺一不可,构成了MOOC之所以在短时间内能够被采纳被推广的重要因素。Massive,大规模。在上课过程中,人数最多的课有190多个国家的十几万人同时在学,一个学生提出问题,15分钟内肯定有回答,这种没有时差的回应对学生是动机上的激励,这是教学中很重要的一个因素。另外,我们在校内向学生推广网络学习平台时最大的问题是学生缺乏积极性,不爱上论坛发帖子或回复帖子,在MOOC这种大规模的平台上,即使发帖的人比例不大,也足以覆盖观点的维度,这有助于教学目标的完成。