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91.
通过采集2004-2005年北京市海淀区采样点大气PM10样品,经过索氏抽提和层析柱分析,对其可溶有机物的浓度水平、季节性变化和分布特征进行探讨。结果表明,2004-2005年北京市海淀区大气PM10中可溶有机物的质量浓度为17．6μg／m^3,对比2000年的28．38μg／m^3和2001．10-2002．08的23．41μg／m^3,大气有机污染的状况有一定的好转。其中,秋冬季的有机污染最为严重。各组分质量浓度的排列顺序为饱和烃〈芳烃〈非烃〈沥青质,沥青质舍量最高,说明主要污染来自烟尘和汽车尾气。 相似文献
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93.
Thirty-six daily time interval PM2.5 samples were collected in different seasonal dates in urban Shanghai, and the concentrations of four anions （Cl- , NO3-, SO4^2-, C2O4^2-） and five cations （NH＋, Na＋, K＋, Ca2＋, Mg2＋） were analyzed with ion chromatography. Sulfate, nitrate and ammonium were found to be the dominant species, accounting for about 80% of the total ions. The daily nitrate to sulfate mass ratio ranged from 0.31 to 0.82, indicating that coal combustion was still the main pollution source in Shanghai. The equivalent ratio of ammonium to stun of nitrate and sulfate showed fixed diurnal variation pattern in all the sampling days with higher values in the nighttime, suggesting that fine particles in the night were more neutralized. The oxalate to sulfate ratio was lower in the winter sampling days than that in hotter summer and autumn sampling days. Oxalate was significantly correlated with sulfate in winter sampling days, but not in the summer and autumn, suggesting that the formation mechanism of oxalate and sulfate was similar in winter, however different in hot days. 相似文献
94.
ABSTRACTThis paper proposes a new way of interpreting particulate matter deposition indoors. The rate of deposition of dust in surfaces is presented as the result of the combination of two main factors: the concentration of suspended particles close to surfaces, and their capacity to deposit, expressed as the deposition velocity. We suggest that either of these two factors can be altered in order to mitigate deposition. The implications of this perspective are explored using in-situ measurements in a historic property (Apsley House, London) and a computational fluid dynamics model of aerosol deposition. The cases studied involve the effect of outdoor wind on the ingress of particles, the consequences of leaving the main door open, and the effects of the ventilation system on deposition. The results demonstrate that simulations can be used reliably to explore hypothetical scenarios or situations that would be experimentally challenging. The inputs and outputs of the computational model are discussed in view of its usability in preventive conservation. 相似文献
95.
针对中职学校采用"2+1"学制模式下人才培养方案存在的不足,围绕《现代职业教育体系建设规划(2014—2020年)》,从中职电气运行与控制专业培养目标定位、现代职业教育立交桥体系建设的需求出发,探索了基于工学结合的中职"2.5+0.5"学制人才培养新方案制定,并对新方案中的课程体系建设、教学模式、实训条件和师资队伍建设展开探讨,旨在使新方案能在培养中职生的职业素质和职业能力方面发挥重要指导作用。 相似文献
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97.
D-异维生素C钠(D-V_cNa)是维生素C钠(L-V_cNa)的一种旋光异构体。它的氧化速度很慢,变化极小,热稳定性比L-V_c高,不影响人体对V_c的吸收,是一种安全无毒的食品抗氧剂和防腐剂,主要应用于鱼类,蔬莱、水果等的保鲜,并能抑制致癌物亚硝胺的形成,亦可代替亚硝酸钠作为肉类的发色剂。关于V_c的极谱学研究已有许多报导,但对D-V_c的极谱学研究却未见到,文献中亦没有V_c(L-V_c)的2.5次微分极谱分析(2.5DPA)的报 相似文献
98.
为全面掌握中国细颗粒物（PM2.5）的污染现状水平及空间分布格局,本文运用统计学、空气质量评价规范、聚类分析方法对全国74个城市2013年的监测数据进行分析,结果表明：①目前中国PM2.5污染程度整体较重,74个城市中仅有拉萨、海口和舟山3个城市达到年均值二级标准,邢台、邯郸和石家庄3个城市PM2.5的超标天数比例超过70%;②PM2.5浓度季节变化特征大体表现为冬季>秋季>春季>夏季,重度及以上污染主要集中在12月和1月;③从浓度水平来看,沿海城市总体优于中部内陆地区,污染最重的区域主要分布在河北南部地区;④受城市经济发展水平、产业结构、气候、地形等多因素影响,全国PM2.5污染状况区域特征明显。 相似文献
99.
使用2014年我国31省(市、区)数据,采用空间计量经济学方法,对我国PM_(2.5)的影响因素进行分析,并试图考查EKC假说。全局Moran's I指数表明我国PM_(2.5)存在空间正自相关性,局部Moran's I指数显示我国雾霾污染存在较强的空间溢出效应。空间滞后模型显示,我国雾霾污染与经济增长之间不存在EKC假说,雾霾污染与城镇化之间存在倒U型曲线,支持EKC假说。第二产业比重与雾霾污染呈同方向变动。降雨量的提高会降低PM_(2.5),从而减缓雾霾污染问题。最后,提出地方政府间要加强环境领域的合作,区域联动,加强环境规制,推进新型城镇化进程,优化产业结构等建议。 相似文献
100.
《Africa Education Review》2013,10(4):664-679
ABSTRACTThe considerable transformation of higher education (HE), driven by the South African government's demand for accountability of resources for the attainment of its mandate has altered the ‘business’ of academia. In response to the financial austerity measures, performance management (PM) systems have been implemented in South African HE to monitor and enhance staff performance. This article conceptualizes PM in higher education using agency and stewardship theories. Data emanates from a phenomenological study of academic heads of department's (HOD) experiences of PM. There is evidence that agency theory may be an appropriate mechanism to achieve explicit accountability, and to monitor and enhance performance. However, it is fraught with problems within academic contexts. The findings demonstrate limitations of agency theory with regard to the stewardship of academics. Thus foregrounding the need for the retention of approaches underpinned by stewardship theory. This article thus makes a contribution in terms of providing a proposition for an analytical framework that integrates agency and stewardship theories in researching PM in HE. Central to this proposition is working within a continuum of these theories to mediate the apparent tension between control and collaboration/collegiality. 相似文献