Genetic variation in the 5q31 cytokine gene cluster confers susceptibility to Crohn disease

Linkage disequilibrium (LD) mapping provides a powerful method for fine-structure localization of rare disease genes, but has not yet been widely applied to common disease. We sought to design a systematic approach for LD mapping and apply it to the localization of a gene (IBD5) conferring susceptibility to Crohn disease. The key issues are: (i) to detect a significant LD signal (ii) to rigorously bound the critical region and (iii) to identify the causal genetic variant within this region. We previously mapped the IBD5 locus to a large region spanning 18 cM of chromosome 5q31 (P<10(-4)). Using dense genetic maps of microsatellite markers and single-nucleotide polymorphisms (SNPs) across the entire region, we found strong evidence of LD. We bound the region to a common haplotype spanning 250 kb that shows strong association with the disease (P< 2 x 10(-7)) and contains the cytokine gene cluster. This finding provides overwhelming evidence that a specific common haplotype of the cytokine region in 5q31 confers susceptibility to Crohn disease. However, genetic evidence alone is not sufficient to identify the causal mutation within this region, as strong LD across the region results in multiple SNPs having equivalent genetic evidence-each consistent with the expected properties of the IBD5 locus. These results have important implications for Crohn disease in particular and LD mapping in general.     

Chaos in a long-term experiment with a plankton community

Mathematical models predict that species interactions such as competition and predation can generate chaos. However, experimental demonstrations of chaos in ecology are scarce, and have been limited to simple laboratory systems with a short duration and artificial species combinations. Here, we present the first experimental demonstration of chaos in a long-term experiment with a complex food web. Our food web was isolated from the Baltic Sea, and consisted of bacteria, several phytoplankton species, herbivorous and predatory zooplankton species, and detritivores. The food web was cultured in a laboratory mesocosm, and sampled twice a week for more than 2,300 days. Despite constant external conditions, the species abundances showed striking fluctuations over several orders of magnitude. These fluctuations displayed a variety of different periodicities, which could be attributed to different species interactions in the food web. The population dynamics were characterized by positive Lyapunov exponents of similar magnitude for each species. Predictability was limited to a time horizon of 15-30 days, only slightly longer than the local weather forecast. Hence, our results demonstrate that species interactions in food webs can generate chaos. This implies that stability is not required for the persistence of complex food webs, and that the long-term prediction of species abundances can be fundamentally impossible.     

低碳锰钢中周期性带状组织

用扫描电镜和电子探针研究了低碳锰钢中的周期性带状组织，结果表明，在全部研究用钢中，钢锭经热轧后均出现这种组织，其严重程度随钢的成分而异，并随坯带加工顺序而增加，带状组织与锰的显微偏析等因素有关，适当的调整碳锰以及形成模跨铁素体带的转变产物可降低带状组织的严重程度。     

面向公共机构与私营企业之间知识转移的组织行为与人力资源管理：文献分析综述（1）

基于人力资源视角对目前有关高校与私营企业之间知识转移渠道的学术研究成果予以述评，给出了文献分析的一般框架，明确了在面向高校一企业知识转移的组织行为和人力资源管理方面的认识缺陷。分析表明：具有最高“关系强度”的知识转移渠道最受企业重视，而大多数知识转移渠道目前并未制度化和正规化。结论认为，在高校．企业的知识转移方面存在显著的管理挑战，这要求对个体参与知识转移的性质和程度有深入的了解。但是，现有研究关注的重点在于知识转移的结果而非过程，因此，未来研究需要重视对个人和组织层面知识转移过程的分析，从而为更优决策的制定提供有价值的信息。