不同地质体中氨基酸的外消旋作用

引言 十九世纪初期,人们观察到几种天然产生的无机晶体和生物化合物的溶液,能够顺时针或反时针旋转平面偏振光。就晶体而言,这种物理性质和晶体粗略的几何结构的关系是容易明白的。但是,直到1874年,范霍夫(Van't Hoff)和勒贝尔(Le Bel)     

斯莱夫-邱吉尔碰撞构造

对加拿大地盾的斯莱夫(Slave)克拉通(最后的主要变形～2500百万年)和邱吉尔(Churcill)克拉通(最后的主要变形～1740百万年)西部的碰撞,这里用大体类似的平板凹入模型作了定性的解释。该模型成功地预测了该碰撞带一些大规模的变形特征。麦肯齐(Mckenzie)用一个硬骰子撞击软金属板近似地描述了非洲板块(阿拉伯     

矿化花岗岩及其成因

<正> 对于花岗岩成因及其伴生矿化之间的关系的解释,导致建立一个使科学家能够区别矿化与“无矿”花岗岩的标准。本文回顾了本研究领域最近,尤其是在国际地质对比计划26号专题——“与酸性岩浆作用伴生的矿化作用”——开展以来在野外、分析及实验方面的进展。作者提出了几种模式来解释形成工业矿床的锡及其伴生金属的运移和沉淀的过程。     

与含矿性有关的花岗岩类建造的时代系列中地球化学演化的研究(以中哈萨克斯坦为例)

<正> 现今已积累了各地区花岗岩类中稀有元素和成矿元素分布特征的大量资料。数据的加工通常在於计算不同地区花岗岩类或某些侵入杂岩和岩体的元素平均含量,然后将计算的平均值与全球性克拉克值,或与其他地区同类侵入岩的含量进行对比,以便查明地块、个别建造、杂岩及岩体的地球化学专属性。在研究少量元素的行为时,很少考虑它们与造岩氧化物的关系,也很少注意成矿元素和稀有元素在侵入杂岩和岩     

旅游业:对气候敏感的行业

1988年,世界气象组织与联合国环境规划署共同成立一个政府间气候变化专家委员会（IPCC）来评价气候变化（全球变暖）的潜在影响。世界气象组织也协调了特别适用于旅游业社会经济规划与运行的、与气候有关的方法的大气研究与开发。在国家层次上,已经出现几项关于气候变化潜在影响的研究与评价。国家气象服务部门通过提供一般信息和专门天气预报,有助于缓解气候变化的潜在有害影响。本文第二部分评论了加拿大大气环境服务局（AES）的工作。     

声和热试验设备

提出了将高级半人马号最终飞行构型暴露在强烈的声和高热环境中的要求。为满足这一要求,建造了一台大型的声和热试验设备。该设备由一个1840.8m~3的混响室和一台安放在单净化环境设备中的1316.9m~3热箱组成。     

减少氯代溶剂的消费:每年70吨一个样板—穆里涅公司(Moulinex)

对于大批生产烘、烤、炸器具所需要的金属脱脂,穆里涅公司使用了Atochem公司开发的、商品名为Altene D6的三氯乙烯溶剂。对设备和脱脂操作方法的研究,使得溶剂的消耗减少了大约60％,也减少了溶剂向工作场所的排放。     

Extrinsic and intrinsic controls of zooplankton diversity in lakes

Pelagic crustacean zooplankton were collected from 336 Norwegian lakes covering a wide range of latitude, altitude, lake area, mean depth, production (as chlorophyll a), and fish community structure. Mean zooplankton species richness during the ice-free season was generally low at high latitudes and altitudes. Further, lower species richness was recorded in western lakes, possibly reflecting constraints on migration and dispersal. However, despite obvious spatial limitations, geographic boundaries were only weak predictors of mean zooplankton richness. Similarly, lake surface area did not contribute positively to mean richness such as seen in other ecosystem surveys. Rather, intrinsic factors such as primary production and fish community (planktivore) structure were identified by regression analysis as the major predictors of zooplankton diversity, while a positive correlation was observed between species richness and total zooplankton biomass. However, in spite of a large number of variables included in this study, the predictive power of multiple regression models was modest (<50% variance explained), pointing to a major role for within-lake properties, as yet unidentified intrinsic forces, stochasticity, or dispersal as constraints on zooplankton diversity in these lakes.     

Predicting biodiversity change: outside the climate envelope, beyond the species-area curve

Efforts to anticipate threats to biodiversity take the form of species richness predictions (SRPs) based on simple correlations with current climate and habitat area. We review the major approaches that have been used for SRP, species-area curves and climate envelopes, and suggest that alternative research efforts may provide more understanding and guidance for management. Extinction prediction suffers from a number of limitations related to data and the novelty of future environments. We suggest additional attention to (1) identification of variables related to biodiversity that are diagnostic and potentially more predictable than extinction, (2) constraints on species dispersal and reproduction that will determine population persistence and range shifts, including limited sources or potential immigrants for many regions, and (3) changes in biotic interactions and phenology. We suggest combinations of observational and experimental approaches within a framework available for ingesting heterogeneous data sources. Together, these recommendations amount to a shift in emphasis from prediction of extinction numbers to identification of vulnerabilities and leading indicators of change, as well as suggestions for surveillance tools needed to evaluate important variables and the experiments likely to provide most insight.     

Amphibian embryo and parental defenses and a larval predator reduce egg mortality from water mold

Water molds attack aquatic eggs worldwide and have been associated with major mortality events in some cases, but typically only in association with additional stressors. We combined field observations and laboratory experiments to study egg stage defenses against pathogenic water mold in three temperate amphibians. Spotted salamanders (Ambystoma maculatum) wrap their eggs in a protective jelly layer that prevents mold from reaching the embryos. Wood frog (Rana sylvatica) egg masses have less jelly but are laid while ponds are still cold and mold growth is slow. American toad (Bufo americanus) eggs experience the highest infection levels. They are surrounded by thin jelly and are laid when ponds have warmed and mold grows rapidly. Eggs of all three species hatched early when infected, yielding smaller and less developed hatchlings. This response was strongest in B. americanus. Precocious hatching increased vulnerability of wood frog hatchlings to invertebrate predators. Finally, despite being potential toad hatchling predators, R. sylvatica tadpoles can have a positive effect on B. americanus eggs. They eat water mold off infected toad clutches, increasing their hatching success.