Dinosaurian growth rates and bird origins

Dinosaurs, like other tetrapods, grew more quickly just after hatching than later in life. However, they did not grow like most other non-avian reptiles, which grow slowly and gradually through life. Rather, microscopic analyses of the long-bone tissues show that dinosaurs grew to their adult size relatively quickly, much as large birds and mammals do today. The first birds reduced their adult body size by shortening the phase of rapid growth common to their larger theropod dinosaur relatives. These changes in timing were primarily related not to physiological differences but to differences in growth strategy.     

Role of Cys221 and Asn116 in the zinc-binding sites of the Aeromonas hydrophila metallo-β-lactamase

The CphA metallo--lactamase produced by Aeromonas hydrophila exhibits two zinc-binding sites. Maximum activity is obtained upon binding of one zinc ion, whereas binding of the second zinc ion results in a drastic decrease in the hydrolytic activity. In this study, we analyzed the role of Asn116 and Cys221, two residues of the active site. These residues were replaced by site-directed mutagenesis and the different mutants were characterized. The C221S and C221A mutants were seriously impaired in their ability to bind the first, catalytic zinc ion and were nearly completely inactive, indicating a major role for Cys221 in the binding of the catalytic metal ion. By contrast, the binding of the second zinc ion was only slightly affected, at least for the C221S mutant. Mutation of Asn116 did not lead to a drastic decrease in the hydrolytic activity, indicating that this residue does not play a key role in the catalytic mechanism. However, the substitution of Asn116 by a Cys or His residue resulted in an approximately fivefold increase in the affinity for the second, inhibitory zinc ion. Together, these data suggested that the first zinc ion is located in the binding site involving the Cys221 and that the second zinc ion binds in the binding site involving Asn116 and, presumably, His118 and His196.Received 3 March 2003; received after revision 4 August 2003; accepted 25 August 2003     

Control of neurulation by the nucleosome assembly protein-1-like 2

Neurulation is a complex process of histogenesis involving the precise temporal and spatial organization of gene expression. Genes influencing neurulation include proneural genes determining primary cell fate, neurogenic genes involved in lateral inhibition pathways and genes controlling the frequency of mitotic events. This is reflected in the aetiology and genetics of human and mouse neural tube defects, which are of both multifactorial and multigenic origin. The X-linked gene Nap1l2, specifically expressed in neurons, encodes a protein that is highly similar to the nucleosome assembly (NAP) and SET proteins. We inactivated Nap1l2 in mice by gene targeting, leading to embryonic lethality from mid-gestation onwards. Surviving mutant chimaeric embryos showed extensive surface ectoderm defects as well as the presence of open neural tubes and exposed brains similar to those observed in human spina bifida and anencephaly. These defects correlated with an overproduction of neuronal precursor cells. Protein expression studies showed that the Nap1l2 protein binds to condensing chromatin during S phase and in apoptotic cells, but remained cytoplasmic during G1 phase. Nap1l2 therefore likely represents a class of tissue-specific factors interacting with chromatin to regulate neuronal cell proliferation.     

Evidence from Sardinian basalt geochemistry for recycling of plume heads into the Earth's mantle

Up to 10 per cent of the ocean floor consists of plateaux--regions of unusually thick oceanic crust thought to be formed by the heads of mantle plumes. Given the ubiquitous presence of recycled oceanic crust in the mantle source of hotspot basalts, it follows that plateau material should also be an important mantle constituent. Here we show that the geochemistry of the Pleistocene basalts from Logudoro, Sardinia, is compatible with the remelting of ancient ocean plateau material that has been recycled into the mantle. The Sr, Nd and Hf isotope compositions of these basalts do not show the signature of pelagic sediments. The basalts' low CaO/Al2O3 and Ce/Pb ratios, their unradiogenic 206Pb and 208Pb, and their Sr, Ba, Eu and Pb excesses indicate that their mantle source contains ancient gabbros formed initially by plagioclase accumulation, typical of plateau material. Also, the high Th/U ratios of the mantle source resemble those of plume magmas. Geochemically, the Logudoro basalts resemble those from Pitcairn Island, which contain the controversial EM-1 component that has been interpreted as arising from a mantle source sprinkled with remains of pelagic sediments. We argue, instead, that the EM-1 source from these two localities is essentially free of sedimentary material, the geochemical characteristics of these lavas being better explained by the presence of recycled oceanic plateaux. The storage of plume heads in the deep mantle through time offers a convenient explanation for the persistence of chemical and mineralogical layering in the mantle.     

声学多孔材料的孔结构优化

介绍了一种基于微结构的声学模型,可用来对多孔材料的微组织结构进行优化,从而使多孔材料具备最佳的声学性能.该模型是一种适用于低雷诺数的非稳态线性声学模型,主要微结构考虑平行排列的柱形杆件或圆球列阵,包括3个子模型:①声波传播方向平行于圆柱形杆件的子模型;②声波传播方向垂直于圆柱形杆件的子模型;③声波在圆球列阵中传播和吸收的子模型.前2个子模型通过考虑多边形周期边界条件的影响,计及了相邻圆柱形杆件间的交互作用.由于模型是线性的,因此可以结合起来描述任意角度入射声波的传播特性.第3个子模型可用于描述胞状多孔材料中节点处的情形.文中利用这3个子模型来扩大吸声材料的设计空间,根据不同用途所要求的声学特性计算最优的胞元结构,并对这种模型的应用领域进行了分析讨论.     

用光散射法测表面活性剂胶束的表观摩尔质量

介绍了光散射法测量胶束表观摩尔质量的方法，以Ｒａｙｌｅｉｇｈ散射公式为理论基础，设计并调度了实验装置，用ＣＣＤ摄像机系统对激光通过试液所产生的散射光进行采样，并由计算机进行运算处理，由此测定了表面活性剂溶液中胶束的表观摩尔质量。结果表明，随体系中添加物质的不同，因胶束界面吸附及增溶作用，表观摩尔质量随之发生变化。