铀系法年代学研究进展及在高原盐湖中的应用

 高原盐湖在形成的各个阶段,都详尽记录和保存着其咸化阶段的环境变化信息,是研究极端干旱气候的重要载体。年代学是盐湖古气候研究最重要的一项内容,也是后续研究工作的基础。目前除了最常用的¹⁴C定年、光释光（OSL）定年、电子磁悬共振（ESR）和古地磁定年等方法外,铀系法定年在盐湖沉积的年代学研究中也得到了广泛的应用。随着技术发展,铀系测年技术方法经历了α谱法、热电离质谱法（TIMS）再到多接受器电感耦合等离子体质谱技术（MC-ICP-MS）的不同发展阶段。而这些技术方法在不同时期和阶段对第四纪及高原盐湖的定年研究做出了一定的贡献。盐湖沉积中的碳酸盐黏土、石盐和石膏等盐类矿物都可以作为铀系定年的研究材料。随着质谱技术的发展,盐类矿物的微区定年也逐渐成为可能。同时,盐湖沉积中盐类矿物的铀系定年研究仍然有限,未来多开展这些方面的研究将对铀系测年技术在盐湖沉积中的应用产生积极作用。     

Bottom-up effects of plant diversity on multitrophic interactions in a biodiversity experiment

Biodiversity is rapidly declining, and this may negatively affect ecosystem processes, including economically important ecosystem services. Previous studies have shown that biodiversity has positive effects on organisms and processes across trophic levels. However, only a few studies have so far incorporated an explicit food-web perspective. In an eight-year biodiversity experiment, we studied an unprecedented range of above- and below-ground organisms and multitrophic interactions. A multitrophic data set originating from a single long-term experiment allows mechanistic insights that would not be gained from meta-analysis of different experiments. Here we show that plant diversity effects dampen with increasing trophic level and degree of omnivory. This was true both for abundance and species richness of organisms. Furthermore, we present comprehensive above-ground/below-ground biodiversity food webs. Both above ground and below ground, herbivores responded more strongly to changes in plant diversity than did carnivores or omnivores. Density and richness of carnivorous taxa was independent of vegetation structure. Below-ground responses to plant diversity were consistently weaker than above-ground responses. Responses to increasing plant diversity were generally positive, but were negative for biological invasion, pathogen infestation and hyperparasitism. Our results suggest that plant diversity has strong bottom-up effects on multitrophic interaction networks, with particularly strong effects on lower trophic levels. Effects on higher trophic levels are indirectly mediated through bottom-up trophic cascades.     

Multiple roles of class I HDACs in proliferation, differentiation, and development

Class I Histone deacetylases (HDACs) play a central role in controlling cell cycle regulation, cell differentiation, and tissue development. These enzymes exert their function by deacetylating histones and a growing number of non-histone proteins, thereby regulating gene expression and several other cellular processes. Class I HDACs comprise four members: HDAC1, 2, 3, and 8. Deletion and/or overexpression of these enzymes in mammalian systems has provided important insights about their functions and mechanisms of action which are reviewed here. In particular, unique as well as redundant functions have been identified in several paradigms. Studies with small molecule inhibitors of HDACs have demonstrated the medical relevance of these enzymes and their potential as therapeutic targets in cancer and other pathological conditions. Going forward, better understanding the specific role of individual HDACs in normal physiology as well as in pathological settings will be crucial to exploit this protein family as a useful therapeutic target in a range of diseases. Further dissection of the pathways they impinge on and of their targets, in chromatin or otherwise, will form important avenues of research for the future.     

First fossil chimpanzee

There are thousands of fossils of hominins, but no fossil chimpanzee has yet been reported. The chimpanzee (Pan) is the closest living relative to humans. Chimpanzee populations today are confined to wooded West and central Africa, whereas most hominin fossil sites occur in the semi-arid East African Rift Valley. This situation has fuelled speculation regarding causes for the divergence of the human and chimpanzee lineages five to eight million years ago. Some investigators have invoked a shift from wooded to savannah vegetation in East Africa, driven by climate change, to explain the apparent separation between chimpanzee and human ancestral populations and the origin of the unique hominin locomotor adaptation, bipedalism. The Rift Valley itself functions as an obstacle to chimpanzee occupation in some scenarios. Here we report the first fossil chimpanzee. These fossils, from the Kapthurin Formation, Kenya, show that representatives of Pan were present in the East African Rift Valley during the Middle Pleistocene, where they were contemporary with an extinct species of Homo. Habitats suitable for both hominins and chimpanzees were clearly present there during this period, and the Rift Valley did not present an impenetrable barrier to chimpanzee occupation.     

阶形杆纵向振动的最优控制

讨论了阶形杆纵向振动的一类最优控制问题，并给出一种算法，通过计算机仿真表明这一算清和最优控制效果的有效性。     

Observation of a pairing pseudogap in a two-dimensional Fermi gas

Pairing of fermions is ubiquitous in nature, underlying many phenomena. Examples include superconductivity, superfluidity of (3)He, the anomalous rotation of neutron stars, and the crossover between Bose-Einstein condensation of dimers and the BCS (Bardeen, Cooper and Schrieffer) regime in strongly interacting Fermi gases. When confined to two dimensions, interacting many-body systems show even more subtle effects, many of which are not understood at a fundamental level. Most striking is the (as yet unexplained) phenomenon of high-temperature superconductivity in copper oxides, which is intimately related to the two-dimensional geometry of the crystal structure. In particular, it is not understood how the many-body pairing is established at high temperature, and whether it precedes superconductivity. Here we report the observation of a many-body pairing gap above the superfluid transition temperature in a harmonically trapped, two-dimensional atomic Fermi gas in the regime of strong coupling. Our measurements of the spectral function of the gas are performed using momentum-resolved photoemission spectroscopy, analogous to angle-resolved photoemission spectroscopy in the solid state. Our observations mark a significant step in the emulation of layered two-dimensional strongly correlated superconductors using ultracold atomic gases.     

Anthrax toxins cooperatively inhibit endocytic recycling by the Rab11/Sec15 exocyst

Bacillus anthracis is the causative agent of anthrax in humans and other mammals. In lethal systemic anthrax, proliferating bacilli secrete large quantities of the toxins lethal factor (LF) and oedema factor (EF), leading to widespread vascular leakage and shock. Whereas host targets of LF (mitogen-activated protein-kinase kinases) and EF (cAMP-dependent processes) have been implicated in the initial phase of anthrax, less is understood about toxin action during the final stage of infection. Here we use Drosophila melanogaster to identify the Rab11/Sec15 exocyst, which acts at the last step of endocytic recycling, as a novel target of both EF and LF. EF reduces levels of apically localized Rab11 and indirectly blocks vesicle formation by its binding partner and effector Sec15 (Sec15-GFP), whereas LF acts more directly to reduce Sec15-GFP vesicles. Convergent effects of EF and LF on Rab11/Sec15 inhibit expression of and signalling by the Notch ligand Delta and reduce DE-cadherin levels at adherens junctions. In human endothelial cells, the two toxins act in a conserved fashion to block formation of Sec15 vesicles, inhibit Notch signalling, and reduce cadherin expression at adherens junctions. This coordinated disruption of the Rab11/Sec15 exocyst by anthrax toxins may contribute to toxin-dependent barrier disruption and vascular dysfunction during B. anthracis infection.