The morphogenesis of feathers

Feathers are highly ordered, hierarchical branched structures that confer birds with the ability of flight. Discoveries of fossilized dinosaurs in China bearing 'feather-like' structures have prompted interest in the origin and evolution of feathers. However, there is uncertainty about whether the irregularly branched integumentary fibres on dinosaurs such as Sinornithosaurus are truly feathers, and whether an integumentary appendage with a major central shaft and notched edges is a non-avian feather or a proto-feather. Here, we use a developmental approach to analyse molecular mechanisms in feather-branching morphogenesis. We have used the replication-competent avian sarcoma retrovirus to deliver exogenous genes to regenerating flight feather follicles of chickens. We show that the antagonistic balance between noggin and bone morphogenetic protein 4 (BMP4) has a critical role in feather branching, with BMP4 promoting rachis formation and barb fusion, and noggin enhancing rachis and barb branching. Furthermore, we show that sonic hedgehog (Shh) is essential for inducing apoptosis of the marginal plate epithelia, which results in spaces between barbs. Our analyses identify the molecular pathways underlying the topological transformation of feathers from cylindrical epithelia to the hierarchical branched structures, and provide insights on the possible developmental mechanisms in the evolution of feather forms.     

黄壤供氮能力预测的研究

利用^15N稳定性同位素进行水稻、烤烟的盆栽与田间试验,结果表明,贵州黄壤的供氮能力可以用“A”值表示,不同海拔高度的土壤养分校正系数在0．2－0．3之间。     

用PLD实现桶形移位器的功能

PLD器件具有灵活方便、设计周期短、保密性强等特点、可反映编程。     

Diverse supernova sources of pre-solar material inferred from molybdenum isotopes in meteorites

Variations in the isotopic composition of some components in primitive meteorites demonstrate that the pre-solar material was not completely homogenized, nor was it processed at sufficiently high temperatures to erase the signatures of the diverse stellar sources. This is in accord with the observation that accretion disks of young stellar objects are at relatively low temperatures. Carbonaceous chondrites are considered to represent the 'average' Solar System composition; the rare pre-solar grains in the matrixes of carbonaceous chondrites have been used to identify some sources of the pre-solar material. Here we report that the molybdenum isotopic composition of bulk carbonaceous chondrites is distinctly different from the accepted average solar value. We show that the Mo data require the presence of material produced in at least two different r-processes, and that the contribution from the p-process material is decoupled from the r-process, all occurring in supernova explosions. This is consistent with the emerging picture of diverse sources inferred from short-lived isotopes in the early Solar System and elemental analyses of metal-poor stars.     

Preservation of ancient and fertile lithospheric mantle beneath the southwestern United States

Stable continental regions, free from tectonic activity, are generally found only within ancient cratons-the centres of continents which formed in the Archaean era, 4.0-2.5 Gyr ago. But in the Cordilleran mountain belt of western North America some younger (middle Proterozoic) regions have remained stable, whereas some older (late Archaean) regions have been tectonically disturbed, suggesting that age alone does not determine lithospheric strength and crustal stability. Here we report rhenium-osmium isotope and mineral compositions of peridotite xenoliths from two regions of the Cordilleran mountain belt. We found that the younger, undeformed Colorado plateau is underlain by lithospheric mantle that is 'depleted' (deficient in minerals extracted by partial melting of the rock), whereas the older (Archaean), yet deformed, southern Basin and Range province is underlain by 'fertile' lithospheric mantle (not depleted by melt extraction). We suggest that the apparent relationship between composition and lithospheric strength, inferred from different degrees of crustal deformation, occurs because depleted mantle is intrinsically less dense than fertile mantle (due to iron having been lost when melt was extracted from the rock). This allows the depleted mantle to form a thicker thermal boundary layer between the deep convecting mantle and the crust, thus reducing tectonic activity at the surface. The inference that not all Archaean crust developed a strong and thick thermal boundary layer leads to the possibility that such ancient crust may have been overlooked because of its intensive reworking or lost from the geological record owing to preferential recycling.     

基于上行信道盲估计的宽带码分多址用户检测器

针对宽带码分多址（CDMA）系统中同时存在多址干扰与码间串扰的情况进行研究,给出了适用于宽带CDMA系统的卷积模型,利用子空间技术及已知的扩频码信息,将适用于单用户的单输入多输出系统信道盲估计方法扩展到码发侈址系统中,实现了多用户上行信道的盲估计,利用有限码集特性,解决了上行信道盲估计中存在不确定复系数的问题,在此基础上,给出了最小均方误差多用户检测器的实现方案,计算机仿真实验证明,提出的方法可以同时克服多址干扰及码间串扰,是实现宽码分多址系统多用户检测的一个有效途径,同时该方法还可以推广到基站采用智能天线的系统中,实现对矢量信道冲激响应有的盲估计。     

SHRIMP dating of zircons from the Caledonian Xiongdian eclogite, western Dabie Mountains, China

This note reports the SHRIMP U-Pb data of zircons from the Caledonian Xiongdian eclogite, western Dabie Mountains. Zircons from the rock occur mainly in garnet and other metamorphic minerals with sharp boundaries and exhibit textures growing under metamorphic conditions. Analyses of 7 grains give ²⁰⁶Pb/²³⁸U ages ranging from 335 to 424 Ma, showing a certain degree of radiogenic lead loss. This suggests a minimum age of (424±5) Ma for the metamorphic zircons, as well as the high-pressure metamorphic event. The outer peripheral zone of a zircon gives ²⁰⁶Pb/²³⁸U age of about 300 Ma. Combined with Sm-Nd, ⁴⁰Ar-³⁹Ar, U-Pb and ²⁰⁷Pb/²⁰⁶Pb ages, the peak metamorphism of the Xiongdian eclogite is documented between 424—480 Ma.     

Role of the prolyl isomerase Pin1 in protecting against age-dependent neurodegeneration

The neuropathological hallmarks of Alzheimer's disease and other tauopathies include senile plaques and/or neurofibrillary tangles. Although mouse models have been created by overexpressing specific proteins including beta-amyloid precursor protein, presenilin and tau, no model has been generated by gene knockout. Phosphorylation of tau and other proteins on serine or threonine residues preceding proline seems to precede tangle formation and neurodegeneration in Alzheimer's disease. Notably, these phospho(Ser/Thr)-Pro motifs exist in two distinct conformations, whose conversion in some proteins is catalysed by the Pin1 prolyl isomerase. Pin1 activity can directly restore the conformation and function of phosphorylated tau or it can do so indirectly by promoting its dephosphorylation, which suggests that Pin1 is involved in neurodegeneration; however, genetic evidence is lacking. Here we show that Pin1 expression is inversely correlated with predicted neuronal vulnerability and actual neurofibrillary degeneration in Alzheimer's disease. Pin1 knockout in mice causes progressive age-dependent neuropathy characterized by motor and behavioural deficits, tau hyperphosphorylation, tau filament formation and neuronal degeneration. Thus, Pin1 is pivotal in protecting against age-dependent neurodegeneration, providing insight into the pathogenesis and treatment of Alzheimer's disease and other tauopathies.     

无钴高强高韧钢中奥氏体相价的电子结构

利用固体与分子经验电子理论(EET)对无钴高强高韧钢奥氏体中含碳与不含碳晶胞的价电子结构进行了计算和分析·得到含碳晶胞的nA值大于不含碳晶胞的nA值,故在相的转变中主要考虑含碳晶胞的影响·在含碳晶胞中合金元素Ni,Si,Cr,Mo与碳原子形成偏聚区,且Ni,Si与C的结合力比Cr,Mo的大,偏聚区能降低C的扩散能力,阻碍位错运动,推迟马氏体相变;使基体中保持高度的位错,也会导致材料中有一定数量的残余奥氏体,并细化奥氏体晶粒,使转变的马氏体尺寸减小,这对材料的韧性有利·