两波长定域同步荧光光谱法快速测定苯并(a)芘的研究

本文提出了快速测定环境样品中强致癌物BaP的两波长定域同步荧光光谱法(SFDW),样品经有机溶剂超声提取后,可以不经过预分离而直接用于测定,该方法操作简单、快速、灵敏,分析一个样品的时间由原来的1小时缩短为几分钟。其检测限为10~(-10)g,定量的线性范围至少可达三个数量级,该方法直接检测BaP的结果和样品经过分离后,采用高效液相色谱法(HPLC)测定的结果相近,其相对误差小于±20％,易于实现仪器化。     

铬渣中六价铬水浸动力学研究

采用连续反应器,考察了铬渣水浸工艺参数,研究了铬渣中Cr(VI)的水浸动力学。结果表明,铬渣水浸过程速率为通过固膜的扩散所控制,通过对整个过程分阶段分别进行拟合,建立了Cr(VI)水浸过程的动力学模型,后阶段反应模型在α=0.05上显著,两个反应阶段表观活化能分别为18 kJ/mol和10.25 kJ/mol。     

施工误差对RC框架结构层间位移角限值可靠度的影响研究

施工质量的变异性是造成钢筋混凝土框架结构体系可靠度不确定的重要原因之一。结合增量变异性分析方法,考虑施工质量的随机性,利用ANSYS有限元软件,考虑各楼层的失效相关性,对钢筋混凝土框架结构的体系可靠度进行计算,分析层间位移角对施工质量的灵敏性,定量地说明施工质量的变异性对框架结构的体系可靠度的影响,并基于可靠度理论对施工误差限值进行了研究,得到了钢筋混凝土框架结构施工误差限值建议值。研究结果表明:材料强度和结构几何尺寸的随机性对框架结构楼层层间位移角均具有较大影响,尤其是混凝土抗压强度。体系可靠度随混凝土抗压强度的均值增大逐渐增大,随标准差的增大而减小。截面尺寸、箍筋间距的均值变异性对整体可靠度的影响也较明显,其次就是钢筋保护层标准差的变异。施工误差限值的建议值为:梁柱截面高度偏差限值为(-6,12)mm,箍筋间距偏差限值为(-26,26)mm,保护层厚度偏差限值为(-5.5,5.5)mm。     

中国半个世纪以来夏季降水量变化总趋势

全球气候变化已经影响到人类生存环境的方方面面.全球升温及其幅度的区域差异,必然引起降水在区域分布的变化.文章利用160站点的夏季降水资料,分别计算出各个站点1951-2002年的变化斜率,以展示我国各地在这半个世纪中的降水总趋势变化的区域差异.通过分析发现,降水量总的变化趋势存在着随纬度而变化的规律:31°N以北区域近半个世纪降水量总的变化趋势是减少,31°N以南地区降水量以增加为主.40°N以北地区的降水变化幅度相对要小得多.区域上,中国西北和东南存在一个降水增多的趋势.中国降水的区域变化,在季风区受季风强弱变化影响;在非季风区,受西风强弱变化影响.     

生物流化床去除水中腐殖酸的动力学模式

对腐殖酸的吸附机理作了论述。在Monod方程基础上,结合生物量、世代时间及停留时间之间的关系,推导出稳态条件下腐殖酸（HA）的降解动力学模式ss₀＝11＋a₁s₀＋a₂θ。利用非线性最小二乘法,对动力学模式中的待定参数a₁、a₂进行了优化估计,得出a₁＝0.0171,a₂＝0.079。以实验数据对该动力学模式加以验证,结果令人满意     

油污土壤中微生物数量变化与原油降解速率关系的实验研究

微生物法治理油污土壤具有成本低、效果好的特点 ,其原理是微生物利用油烃作为碳源合成自身物质 ,进行生长繁殖 ,从而使油烃的含量得到减少。而与此同时 ,微生物的数量也会发生相应的变化。目前油污土壤微生物的研究主要局限于对污染土壤中分离提纯的单一菌种的降解效能的研究。本文对土著油污土壤微生物在适宜条件下的数量和种类变化进行了实验分析 ,并对油烃的化学组成作了初步探讨。分离出 4株对石油具有耐受性和降解能力的微生物。结果表明 ,在 4株微生物数量都增加的时候 ,石油烃的降解速度最快。     

基于BP网络理论的岩爆预测方法

选取影响岩爆的一些主要因素,如地应力大小、岩石抗压和抗拉强度、岩石弹性能量指数,采用人工神经网络理论,根据国内外一些岩石地下工程实例构造样本集,建立了一种新的岩爆预测模型.此模型可以直接应用于岩石地下工程,对岩爆的发生与否及烈度大小进行预测.实例表明,预测结果与实际情况符合得很好,说明了此模型的有效性.     

Challenges to saving China’s freshwater biodiversity: Fishery exploitation and landscape pressures

China has over 1320 freshwater fish species, 877 of which are endemic. In recent decades, over-exploitation and landscape pressures have threatened them and led to a severe aquatic biodiversity crisis. In response, large-scale fishing bans have been promulgated to protect freshwater biodiversity in major Chinese rivers since the early 1980s. Here, we present the historical background and current challenges to the fishing bans. Implementing large-scale fishing bans may help improve China’s current freshwater biological resources and biodiversity to some extent. But implementing fishing bans alone is not sufficient to solve the crisis because of shortcomings of the current bans and expanding human pressures in most river basins. Thus, we recommend regulating other anthropogenic pressures, expanding duration and extent of current fishing regulations, establishing a comprehensive monitoring program, and initiating basin-scale ecological rehabilitation. These programs are also needed in other developing countries facing similar biodiversity crises and human pressures.     

Comparative effects on arsenic uptake between iron (hydro)oxides on root surface and rhizosphere of rice in an alkaline paddy soil

The iron (Fe) (hydro)oxides deposited around rice roots play an important role in arsenic (As) sequestration in paddy soils, but there is no systematic study on the relative importance of Fe (hydro)oxides on root surface and in rhizosphere soil in limiting As bioavailability. Twenty-seven rice genotypes were selected to investigate effects of Fe (hydro)oxides on As uptake by rice in an alkaline paddy soil. Results indicated that the As content was positively correlated with the Fe content on root surface, and most of As (88–97%) was sequestered by poorly crystalline and crystalline Fe (hydro)oxides in the alkaline paddy soil. The As sequestration by Fe (hydro)oxides on root surface (IAS_root 16.8–25.0 mg As/(g Fe)) was much higher than that in rhizosphere (IAS_rhizo 1.4–2.0 mg As/(g Fe)); therefore, in terms of As immobilization, the Fe (hydro)oxides on root surface were more important than that in rhizosphere. However, the As content in brown rice did not have significant correlation with the As content on root surface but was significantly correlated (R²?=?0.43, P?<?0.05) with the partition ratio (PR_As?=?IAS_root/IAS_rhizo) of As sequestration on root surface and in rhizosphere, which suggested that Fe (hydro)oxides on root surface did not play the controlling role in lowering As uptake, and the partition ratio PR_As would be a better indicator to evaluate effects of Fe (hydro)oxides around roots on As uptake by rice.