First evidence of a venom delivery apparatus in extinct mammals

Numerous non-mammalian vertebrates have evolved lethal venoms to aid either in securing prey or as protection from predators, but modern mammals that use venoms in these ways are rare, including only the duck-billed platypus (Ornithorhynchus), the Caribbean Solenodon, and a few shrews (Soricidae) (Order Insectivora). Here we report evidence of a venom delivery apparatus in extinct mammals, documented by well-preserved specimens recovered from late Palaeocene rocks in Alberta, Canada. Although classified within Eutheria, these mammals are phylogenetically remote from modern Insectivora and have evolved specialized teeth as salivary venom delivery systems (VDSs) that differ markedly from one another and from those of Solenodon and shrews. Our discoveries therefore show that mammals have been much more flexible in the evolution of VDSs than previously believed, contradicting currently held notions that modern insectivorans are representative of the supposedly limited role of salivary venoms in mammalian history. Evidently, small predatory eutherians have paralleled colubroid snakes in evolving salivary venoms and their delivery systems several times independently.     

The suppression of star formation by powerful active galactic nuclei

The old, red stars that constitute the bulges of galaxies, and the massive black holes at their centres, are the relics of a period in cosmic history when galaxies formed stars at remarkable rates and active galactic nuclei (AGN) shone brightly as a result of accretion onto black holes. It is widely suspected, but unproved, that the tight correlation between the mass of the black hole and the mass of the stellar bulge results from the AGN quenching the surrounding star formation as it approaches its peak luminosity. X-rays trace emission from AGN unambiguously, whereas powerful star-forming galaxies are usually dust-obscured and are brightest at infrared and submillimetre wavelengths. Here we report submillimetre and X-ray observations that show that rapid star formation was common in the host galaxies of AGN when the Universe was 2-6 billion years old, but that the most vigorous star formation is not observed around black holes above an X-ray luminosity of 10(44) ergs per second. This suppression of star formation in the host galaxy of a powerful AGN is a key prediction of models in which the AGN drives an outflow, expelling the interstellar medium of its host and transforming the galaxy's properties in a brief period of cosmic time.     

A photometric redshift of z = 6.39 +/- 0.12 for GRB 050904

Gamma-ray bursts (GRBs) and their afterglows are the most brilliant transient events in the Universe. Both the bursts themselves and their afterglows have been predicted to be visible out to redshifts of z approximately 20, and therefore to be powerful probes of the early Universe. The burst GRB 000131, at z = 4.50, was hitherto the most distant such event identified. Here we report the discovery of the bright near-infrared afterglow of GRB 050904 (ref. 4). From our measurements of the near-infrared afterglow, and our failure to detect the optical afterglow, we determine the photometric redshift of the burst to be z = 6.39 - 0.12 + 0.11 (refs 5-7). Subsequently, it was measured spectroscopically to be z = 6.29 +/- 0.01, in agreement with our photometric estimate. These results demonstrate that GRBs can be used to trace the star formation, metallicity, and reionization histories of the early Universe.     

Relativistic ejecta from X-ray flash XRF 060218 and the rate of cosmic explosions

Over the past decade, long-duration gamma-ray bursts (GRBs)--including the subclass of X-ray flashes (XRFs)--have been revealed to be a rare variety of type Ibc supernova. Although all these events result from the death of massive stars, the electromagnetic luminosities of GRBs and XRFs exceed those of ordinary type Ibc supernovae by many orders of magnitude. The essential physical process that causes a dying star to produce a GRB or XRF, and not just a supernova, is still unknown. Here we report radio and X-ray observations of XRF 060218 (associated with supernova SN 2006aj), the second-nearest GRB identified until now. We show that this event is a hundred times less energetic but ten times more common than cosmological GRBs. Moreover, it is distinguished from ordinary type Ibc supernovae by the presence of 10(48) erg coupled to mildly relativistic ejecta, along with a central engine (an accretion-fed, rapidly rotating compact source) that produces X-rays for weeks after the explosion. This suggests that the production of relativistic ejecta is the key physical distinction between GRBs or XRFs and ordinary supernovae, while the nature of the central engine (black hole or magnetar) may distinguish typical bursts from low-luminosity, spherical events like XRF 060218.     

易变质新产品定价与补货联合决策模型

考虑新产品情境下,产品扩散,重复购买和产品变质特征对企业定价与补货决策的影响.将重复购买率引入包含价格效应的Bass模型构建了需求演化函数,从而建立了易变质新产品定价与动态批量补货联合决策模型,设计了求解算法,并给出了算例分析.结果显示,定价与补货联合决策是必要的.最优价格与产品扩散速度及重复购买率呈先减小后增大的U型关系.最优价格随着消费者主动购买意愿的增加而增大,随着产品易变质程度的增加而减小.     

Towards uranium catalysts

The forefront of research into the complexes of uranium reveals chemical transformations that challenge and expand our view of this unique element. Certain ligands form multiple bonds to uranium, and small, inert molecules such as nitrogen and carbon dioxide become reactive when in complex with the metal. Such complexes provide clues to the catalytic future of uranium, in which the applications of the element extend far beyond the nuclear industry. Most excitingly, the ability of uranium to use its outermost f electrons for binding ligands might enable the element to catalyse reactions that are impossible with conventional, transition-metal catalysts.     

分布式物资调运指挥系统流程设计研究

以龙滩水电工程物资调运为背景,在分析其供应组织管理体系和业务流程的基础上,提出了该类分布式物资调运指挥系统的信息工作流程,对类似大型物资调运指挥系统的构造具有借鉴意义。     

企业员工-管理者互动行为的定性模拟实现

采用定性模拟方法研究了企业员工一管理者互动行为．根据定性模拟和组织行为学相关理论,将管理者任职后与下属员工相处的过程视为相互影响的动态变化过程,建立了能够表达这种动态变化的定性状态变量和作用规则;采用C＋＋语言实现了定性模拟程序QSHR;通过一个例子的有效性验证说明所设计程序能够表达互动行为的定性模型,所得结论符合管理原则．通过一个对比不同状态下管理者和员工群体行为表现实际应用,论述了QSHR的应用方法和对管理实践的重要参考意义．     

并行处理机的算法

一旦采用少许一般性技术,许多小型计算机就能有效地同时运行,由此可以解决从空气动力学到天体物理各门学科中需要大量计算的问题。由于计算机技术的发展,我们正在开始一场计算革命。超大规模集成电路的进展不仅导致更快的计算机,也导致更加便宜、更加小型化的计算机——由几片集成块组成的计算机。这些计算机的实用价值大得令人瞠目结舌,而且也使得制造“超大功能计算机”,或称之为“超计算机”成为现实可行,这即是由许许多多的小型计算机组成的并行处理机。