Nematoda from the terrestrial deep subsurface of South Africa

Since its discovery over two decades ago, the deep subsurface biosphere has been considered to be the realm of single-cell organisms, extending over three kilometres into the Earth's crust and comprising a significant fraction of the global biosphere. The constraints of temperature, energy, dioxygen and space seemed to preclude the possibility of more-complex, multicellular organisms from surviving at these depths. Here we report species of the phylum Nematoda that have been detected in or recovered from 0.9-3.6-kilometre-deep fracture water in the deep mines of South Africa but have not been detected in the mining water. These subsurface nematodes, including a new species, Halicephalobus mephisto, tolerate high temperature, reproduce asexually and preferentially feed upon subsurface bacteria. Carbon-14 data indicate that the fracture water in which the nematodes reside is 3,000-12,000-year-old palaeometeoric water. Our data suggest that nematodes should be found in other deep hypoxic settings where temperature permits, and that they may control the microbial population density by grazing on fracture surface biofilm patches. Our results expand the known metazoan biosphere and demonstrate that deep ecosystems are more complex than previously accepted. The discovery of multicellular life in the deep subsurface of the Earth also has important implications for the search for subsurface life on other planets in our Solar System.     

A lamprey from the Devonian period of South Africa

Lampreys are the most scientifically accessible of the remaining jawless vertebrates, but their evolutionary history is obscure. In contrast to the rich fossil record of armoured jawless fishes, all of which date from the Devonian period and earlier, only two Palaeozoic lampreys have been recorded, both from the Carboniferous period. In addition to these, the recent report of an exquisitely preserved Lower Cretaceous example demonstrates that anatomically modern lampreys were present by the late Mesozoic era. Here we report a marine/estuarine fossil lamprey from the Famennian (Late Devonian) of South Africa, the identity of which is established easily because many of the key specializations of modern forms are already in place. These specializations include the first evidence of a large oral disc, the first direct evidence of circumoral teeth and a well preserved branchial basket. This small agnathan, Priscomyzon riniensis gen. et sp. nov., is not only more conventionally lamprey-like than other Palaeozoic examples, but is also some 35 million years older. This finding is evidence that agnathans close to modern lampreys had evolved before the end of the Devonian period. In this light, lampreys as a whole appear all the more remarkable: ancient specialists that have persisted as such and survived a subsequent 360 million years.     

基于延迟调度截止时间约束提前预留接纳控制

针对截止时间约束的预留任务,提出了一种在预留任务接纳之后并不立即确定所用资源,而是根据可用资源和其他任务的情况,来动态决定何时为其分配资源和如何分配资源的延迟调度机制.分别对支持延迟调度的接纳判断方法、接纳时为任务进行预调度的算法以及对任务进行调度的条件和实际调度方案的选择方法进行了研究.仿真实验证实了该方案的可行性,实验结果表明该机制能提高预留任务的接纳率和资源利用率5%以上.     

Deputy President of the Republic of South Africa Delivers Speech

Ms. Phumzile Mlambo-Ngcuka, Deputy President of the Republic of South Africa, visited Tsinghua and delivered a speech entitled ＂The Nature of the Desired Relation between China and South Africa＂ on September 26, 2007.