西安城市热岛的时空分布特征

选取1959-2008年西安市常规气象站和城区加密自动站逐小时气温资料,采用城、郊气温对比法研究西安城市热岛效应的时间变化和空间分布。结果表明：西安城市热岛效应逐年增加,具有明显的季节变化特征;热岛强度日变化呈现双峰分布,两个峰值分别出现在05时和21时左右,最低值出现在11时左右。在西安市城区一直存在一个强城市强热岛...     

Study on Water-Soluble Organic Reducing Substances: II. Organic Reducing Substances Produced from Anaerobic Decomposition of Milk Vetch (Astragalus sinicus L.)

The characteristics of electric charge and molecular weight distribution,oxidation-reduction regimes,e.g.Eh and amounts of organic reducing substances produced by milk vetch during anaerobic decomposition process,were studied by using electrochemical methods.Interaction between soils and organic reducing substances was also observed.The results indicate that the organic reducing substances were mainly the organic compounds with negative and amphoteric charges,which were distributed in two groups at anodic peak potentials of 0.25 and 0.69 volt in differential pulse voltammograms,respectively.Their apparent molecular weights are all less than 700 daltons,in which those active in oxidation-reducion reaction were distributed in the fraction with apparent molecular weight less than 200 daltons.The organic reduction substances can be oxidized by manganese oxides in their interaction with soils.     

一个可以在常规实验室条件下操作的测定根系高铁还原酶活性的方法

Based on the strong chelating property of bathophenanthroline disulfonic acid (BPDS) with Fe(Ⅱ), root Fe(Ⅲ) chelate reductase activity is usually measured with a spectrophotometer using MES (2-morpholinoethanesulfonic acid) or HEPES(2-(4-(2-Hydroxyethyl)-l-piperazinyl) ethanesulfonic acid) buffer in the dark because of high autoreduction rate of Fe(Ⅲ)in the presence of light. However, the exclusion of light is inconvenient, especially when analyzing a large number of samples. The objective of this study was to develop a new method for determination of root reductase activity under normal laboratory conditions using a suitable buffer composition and Fe(Ⅲ) concentration to eliminate the autoreduction of Fe(Ⅲ). A modified method using a Tris (2-amino-2-hydroxymethyl-l,3-propanediol) buffer at pH 7.5 instead of MES or HEPES buffer and a decreased FeEDTA (Fe ethylene diamine tetraacetic acid) concentration of 50 μmol L^-1 was developed. The autoreduction of Fe(Ⅲ) using the Tris buffer was undetectable for temperatures at 4 and 28 ℃ and was also much lower than that using the other buffers even with sunlight during measurement of Fe(Ⅲ) reduction.Furthermore, the differences in Fe(Ⅲ) reductase activity among 5 plant species and 14 red clover cultivars (Trifolium pratense L.) could be easily detected with the modified method. The method developed in this study to measure root Fe chelate reductase activity was not only effective and reliable but also easily managed under normal laboratory light conditions.     

强度耕作对^137Cs、^210Pbex和有机质剖面分布的影响

很少有关于直接测定强度耕作侵蚀引起土壤退化过程的报道。我们的目的是确定应用137Cs和210Pbex直接定量评价耕作侵蚀对土壤有机质(SOM)坡面运移影响的可能性。我们在黄土高原陡坡耕地上进行了50次犁耕活动,并将与其相临的另一块陡坡耕地作为对照。在对照坡地不同坡位,137Cs浓度均匀分布于上部0～30cm土层,而210Pbex浓度在坡上部和坡中部随土层深度增加呈现线性递减,在坡下部呈指数函数递减。0～30cm土层中土壤有机质含量显著大于30cm深度以下土层,并在坡中部和坡下部呈现与210Pbex类似的土壤剖面分布特征。与对照坡地比较,50次犁耕活动导致坡上部、坡中部0～45cm土层的SOM含量分别降低了38%和47%,坡下部0～100cm土层中的SOM含量却提高了18%。坡上部土壤剖面中137Cs浓度的加权平均值从1.48Bq/kg降低到0.29Bq/kg,坡中部从2.53Bq/kg减少到0.33Bq/kg,坡下部从1.48Bq/kg提高到2.81Bq/kg。210Pbex浓度的剖面加权平均值在坡上部从27.71Bq/kg下降到6.15Bq/kg,在坡中部和坡下部分别从35.46Bq/kg和25.53Bq/kg降低到1.57Bq/kg和19.40Bq/kg。137Cs和210Pbex的剖面分布与SOM在p<0.001水平呈显著相关,相关系数R2值在对照坡地为0.81～0.86,在犁耕实验坡地为0.86～0.91。实验结果表明,环境放射性核素137Cs和210Pbex在黄     

硫酸盐还原菌的分离与生态特点研究

采用S培养基进行富集培养的方法对硫酸盐还原菌(SRB)进行了分离与鉴定。实验通过对SRB的生理和生化特性的了解,结合其生存条件和存在状态进行研究,得出主要的环境因素中pH值和温度对SRB的腐蚀作用的影响关系,并提出采用合适的环境因素来更好的控制SRB的生长代谢活动,得出有效的防治措施来控制硫酸盐还原菌引起的腐蚀,延长有关设备的正常使用寿命。     

粘性土壤剪切强度与容重和含水量之间关系的研究

本文在Mitchell等人关于土壤剪切强度唯一性研究的基础上,利用热力学第二定律作指导,由试验和分析建立了剪切强度与热扩散系数之间关系。据此关系,综合De Vries和佐滕用三相比表达热扩散系数的方程式,得到一个四参数剪切强度-干容重-含水量模型。对于一种粘土在各种容重和含水量下进行了三轴剪切试验,本模型拟合实测数据的精度(用相关系数表示)皆在0.9以上。     

湿软土壤剪切应力—剪切速度—时间关系及其应用(第2报)——湿软土壤的剪切应力—剪切速度—时间关系

从位错理论出发导出了湿软土壤的剪切应力—剪切应变—时间关系。理论分析和试验结果表明土壤剪切应力与剪切速度成幂函数关系;与其本身可能抵抗的最大剪应力相比的相对剪应力水平只与剪切位移有关而与剪切速度无关。     

北京地区不同设计暴雨强度下凹式绿地的减流效果

[目的]研究不同汇水面积的周边外来雨水径流,计算绿地产流过程的动态径流系数以及对径流的削减率。[方法]采用人工模拟的下凹式绿地,模拟绿地的不同暴雨强度。[结果](1)30%下凹式绿地面积比基本可以拦蓄3年,5年一遇暴雨,稳定后径流系数在0.30以下;(2)下凹式绿地面积比为20%时,雨水口高8cm和5cm时对3年,5年一遇暴雨产生的径流削减率均在40%以上,稳定后的径流系数均在0.90以上,且两种雨水口高度下的削减率差异不明显,相比之下5cm雨水口高度设计较8cm更为合理;(3)绿地的产流速率变化过程曲线呈"几"字形,汇水面积越大、暴雨强度越大,产流速率稳定时的峰值就越大,产流历时也越长。[结论]下凹式绿地对暴雨条件下产生的径流有很好的削减作用,其所占面积比越大,削减效果越好。     

边界积分方程法在工程机械结构件强度计算中的应用

采用弹性问题的Ｋｅｌｖｅｎ基本解，建立了边界积分方程的两种离散求解方法。编制了相应的计算程序。对两种对称工况下ＺＬ８０装载机动臂板强度、ＺＬ６０Ｅ装载机铰接系统铰接点区域应力场进行了计算。同时，进行了实车应力测试，对计算结果进行了验证