Computational chemistry study of the environmentally important acid-catalyzed hydrolysis of atrazine and related 2-chloro-s-triazines

Many chlorine-containing pesticides, for example 2-chloro-s-triazines, are of great concern both environmentally and toxicologically. As a result, ascertaining or predicting the fate and transport of these compounds in soils and water is of current interest. Transformation pathways for 2-chloro-s-triazines in the environment include dealkylation, dechlorination (hydrolysis), and ring cleavage. This study explored the feasibility of using computational chemistry, specifically the hybrid density functional theory method, B3LYP, to predict hydrolysis trends of atrazine (2-chloro-N4-ethyl-N6-isopropyl-1,3,5-triazine-2,4-diamine) and related 2-chloro-s-triazines to the corresponding 2-hydroxy-s-triazines. Gas-phase energetics are described on the basis of calculations performed at the B3LYP/6-311++G(d,p)//B3LYP/6-31G* level of theory. Calculated free energies of hydrolysis (delta h G298) are nearly the same for simazine (2-chloro-N4,N6-diethyl-1,3,5-triazine-2,4-diamine), atrazine, and propazine (2-chloro-N4,N6-di-isopropyl-1,3,5-triazine-2,4-diamine), suggesting that hydrolysis is not significantly affected by the side-chain amine-nitrogen alkyl substituents. High-energy barriers also suggest that the reactions are not likely to be observed in the gas phase. Aqueous solvation effects were examined by means of self-consistent reaction field methods (SCRF). Molecular structures were optimized at the B3LYP/6-31G* level using the Onsager model, and solvation energies were calculated at the B3LYP/6-311++G(d,p) level using the isodensity surface polarizable continuum model (IPCM). Although the extent of solvent stabilization was greater for cationic species than neutral ones, the full extent of solvation is underestimated, especially for the transition state structures. As a consequence, the calculated hydrolysis barrier for protonated atrazine is exaggerated compared with the experimentally determined one. Overall, the hydrolysis reactions follow a concerted nucleophilic aromatic substitution (SNAr) pathway.     

Relationships between landcover proportion and indices of landscape spatial pattern

Recent studies have related percolation theory and critical phenomena to the spatial pattern of landscapes. We generated simulated landscapes of forest and non-forest landcover to investigate the relationship between the proportion of forest (P_i) and indices of patch spatial pattern. One set of landscapes was generated by randomly assigning each pixel independently of other pixels, and a second set was generated by randomly assigning rectilinear clumps of pixels. Indices of spatial pattern were calculated and plotted against P_i. The random-clump landscapes were also compared with real agricultural landscapes. The results support the use of percolation models as neutral models in landscape ecology, and the performance of the indices studied with these neutral models can be used to help interpret those indices calculated for real landscapes.     

披碱草属野生种质材料在干旱与半干旱区适应性评价

应用灰色理论系统,以搜集自我国8省区的38份披碱草属植物野生种质材料为研究对象,对其株高、叶面积生长动态、草产量、茎叶比、鲜干比及种子产量进行灰色关联度分析.结果表明,株高从拔节期到抽穗期增幅较大,而叶面积从分蘖期到拔节期增幅较大;38份材料鲜草及干草产量差异较大,变异系数分别为39.275％和43.087％;大部分种质材料茎叶比在1.0～2.0之间;不同材料种子产量的变异系数较大;产量与各主要农艺性状的关联度大小顺序为:鲜干比＞种子产量＞茎叶比＞叶面积＞株高.综合分析发现,适应性较好的种质材料有NMC32、BJT37、QHD19、SXD36、XJD11、XJD15、XJS8、XJT2、XJE13和XJD5.     

湖州市杉木林立地质量的数量化评价

本文运用数量化理论Ⅰ模型对湖州市杉木实生林地位指数与多元立地因子之间的关系进行了回归。分析结果表明,在所选择的项目中发现对地位指数起主导影响作用的是母岩、土壤类型、土层厚度和坡度,起次主导作用的是坡位、土壤容重、土壤有机质和硝态氮含量。对剩余标准差S_y,复相关系数R_(ym),偏相关系数r_(ym),以及残差绝对值和相对值分布的检验结果证明,本得分表的精度较高,可应用于生产实际,并且以运用模型7和模型8为好,既可保证一定精度,又简便易行。     

法国畜产品贸易分析

主要利用FAO最新统计数据对1961年以来法国的畜产品贸易情况进行了分析。通过分析贸易量、贸易额和进出口国别结构变化等,明确提出了目前法国畜产品的贸易结构及其在世界贸易中的地位,并分析了中法贸易情况,为进一步加强双方的贸易合作提供一定的参考。     

Fish movement and habitat use depends on water body size and shape

Abstract –  Home ranges are central to understanding habitat diversity, effects of fragmentation and conservation. The distance that an organism moves yields information on life history, genetics and interactions with other organisms. Present theory suggests that home range is set by body size of individuals. Here, we analyse estimates of home ranges in lakes and rivers to show that body size of fish and water body size and shape influence home range size. Using 71 studies including 66 fish species on five continents, we show that home range estimates increased with increasing water body size across water body shapes. This contrasts with past studies concluding that body size sets home range. We show that water body size was a consistently significant predictor of home range. In conjunction, body size and water body size can provide improved estimates of home range than just body size alone. As habitat patches are decreasing in size worldwide, our findings have implications for ecology, conservation and genetics of populations in fragmented ecosystems.     

辽宁省刺槐人工林立地质量评价的研究

选择Ｒｉｃｈａｒｄｓ生长函数Ｈ＝ａ（１－ｅ－ｂＡ）ｃ作为辽宁省刺槐优势高生长模型．用差分法展开导向曲线编制了单形立地指数表；应用分组整理后解析木资料，拟合出最优多形立地指数模型，编制了多形立地指数表．在综合分析影响刺槐生长发育的环境因子基础上，选择了７个立地因子，运用数量化理论Ⅰ方法，建立与立地指数的回归模型，经减少项目法筛选出包含５个因子的立地指数最佳预估方程，编制了数量立地指数得分表．     

实现农村信息化的理论与实证分析

笔者在对我国实现农村信息化的理论及必要性阐述的基础上，以四川省为背景，对农村广泛应用信息技术进行了实证分析。     

湿垫内“水─气”间热质交换过程的理论分析

为完善湿垫风机系统在农业建筑夏季蒸发冷却中的应用，研究了湿垫冷却装置在喷淋水完全蒸发条件下的热质交换特征，经理论推导给出了确定喷淋水量及湿垫合理参数的计算式。