Water alteration of rocks and soils on Mars at the Spirit rover site in Gusev crater

Gusev crater was selected as the landing site for the Spirit rover because of the possibility that it once held a lake. Thus one of the rover's tasks was to search for evidence of lake sediments. However, the plains at the landing site were found to be covered by a regolith composed of olivine-rich basaltic rock and windblown 'global' dust. The analyses of three rock interiors exposed by the rock abrasion tool showed that they are similar to one another, consistent with having originated from a common lava flow. Here we report the investigation of soils, rock coatings and rock interiors by the Spirit rover from sol (martian day) 1 to sol 156, from its landing site to the base of the Columbia hills. The physical and chemical characteristics of the materials analysed provide evidence for limited but unequivocal interaction between water and the volcanic rocks of the Gusev plains. This evidence includes the softness of rock interiors that contain anomalously high concentrations of sulphur, chlorine and bromine relative to terrestrial basalts and martian meteorites; sulphur, chlorine and ferric iron enrichments in multilayer coatings on the light-toned rock Mazatzal; high bromine concentration in filled vugs and veins within the plains basalts; positive correlations between magnesium, sulphur and other salt components in trench soils; and decoupling of sulphur, chlorine and bromine concentrations in trench soils compared to Gusev surface soils, indicating chemical mobility and separation.     

Membranes are more mosaic than fluid

The wealth of new data on membrane protein structures and functions is changing our general view of membrane architecture. Some of the key themes that are emerging are that membranes are patchy, with segregated regions of structure and function, that lipid regions vary in thickness and composition, and that crowding and ectodomains limit exposure of lipid to the adjacent aqueous regions.     

Disturbance and diversity in experimental microcosms

External agents of mortality (disturbances) occur over a wide range of scales of space and time, and are believed to have large effects on species diversity. The "intermediate disturbance hypothesis", which proposes maximum diversity at intermediate frequencies of disturbance, has received support from both field and laboratory studies. Coexistence of species at intermediate frequencies of disturbance is thought to require trade-offs between competitive ability and disturbance tolerance, and a metapopulation structure, with disturbance affecting only a few patches at any given time. However, a unimodal relationship can also be generated by global disturbances that affect all patches simultaneously, provided that the environment contains spatial niches to which different species are adapted. Here we report the results of tests of this model using both isogenic and diverse populations of the bacterium Pseudomonas fluorescens. In both cases, a unimodal relationship between diversity and disturbance frequency was generated in heterogeneous, but not in homogeneous, environments. The cause of this relationship is competition among niche-specialist genotypes, which maintains diversity at intermediate disturbance, but not at high or low disturbance. Our results show that disturbance can modulate the effect of spatial heterogeneity on biological diversity in natural environments.     

纳米技术与发展中国家

作者将“nano*”与世界银行确定的每个经济类主题词组合检索，结果发现发展中国家普遍在从事
纳米技术研发。进一步研究表明，尽管发展中国家纳米技术的研发能力随着合作和信息利用的加强而提高，
但是这些国家已经偏离了纳米技术的“社会开发”这一通常被认为是最适于发展中国家的研究宗旨。另外，
对卫生保健相关专利的分析证实，各国实力严重不平衡，存在所谓的“纳米鸿沟”现象。在发展中国家中，
中国拥有的专利权所占份额很高，因此“纳米鸿沟”不仅存在于发展中国家和发达国家之间，在发展中国
家也同样存在。发展中国家的研发水平较低，纳米技术有可能走向以往导致全球技术大分裂的技术老路。     

Mammalian chiasma frequencies as a test of two theories of recombination

A broad survey of asexuality in the animal kingdom is sufficient to reject all theories of sex and recombination except two: the Red Queen and the Tangled Bank. The Red Queen theory states that an organism's biotic environment tends to be 'contrary', consistently evolving to the detriment of the organism; sex and recombination result in progeny genetically distinct from their parents and grandparents and thus less susceptible to the antagonistic advances made during the previous generations, particularly by their parasites. The alternative theory, the Tangled Bank, states that sex and recombination function to diversify the progeny from each other, thus reducing competition between them. An extensive survey of mammalian recombination shows that the total number of chiasmata in excess of one per bivalent is strongly correlated with generation time but uncorrelated with fecundity. We conclude that crossing-over may function to combat antagonists with short generation times but does not function to reduce sib competition. Chromosome number is selectively neutral with respect to these factors.