Evidence for cultivar adoption and emerging complexity during the mid-Holocene in the La Plata basin

Multidisciplinary investigations at the Los Ajos archaeological mound complex in the wetlands of southeastern Uruguay challenge the traditional view that the La Plata basin was inhabited by simple groups of hunters and gatherers for much of the pre-Hispanic era. Here we report new archaeological, palaeoecological and botanical data indicating that during an increasingly drier mid-Holocene, at around 4,190 radiocarbon (14C) years before present (bp), Los Ajos became a permanent circular plaza village, and its inhabitants adopted the earliest cultivars known in southern South America. The architectural plan of Los Ajos during the following Ceramic Mound Period (around 3,000-500 14C yr bp) is similar to, but earlier than, settlement patterns demonstrated in Amazonia, revealing a new and independent architectural tradition for South America.     

基于人工神经网络的高考扩招趋势预测研究

高考扩招系统足一个“黑箱”,各因素问是否存在因果关系还很模糊,基于人工神经网络自身的特点,采用BP模型,借助MATLAB语言对高考扩招系统进行预测研究．通过对历史数据的处理、程序的设计、网络的训练等进行分析,最终预测出中国未来20年高等教育发展的趋势,为国家相关政策的制定提供参考依据．     

Identification of swelling-activated Cl<Superscript>-</Superscript> current in rabbit cardiac Purkinje cells

The presence and functional role of the swelling-activated Cl^- current (I_Cl(swell)) in rabbit cardiac Purkinje cells was examined using patch-clamp methodology. Extracellular hypotonicity (210 or 135 mOsm) activated an outwardly rectifying, time-independent current with a reversal potential close to the calculated Cl^- equilibrium potential (E_Cl). The magnitude of this current was related to tonicity of the superfusate. The current was blocked by 0.5 mM 4,4-diisothiocyanostilbene-2,2-disulfonic acid (DIDS). These features are comparable to those of I_Cl(swell) found in sinoatrial nodal, atrial, and ventricular myocytes. I_Cl(swell) activation at 210 and 135 mOsm depolarized the resting membrane potential with 6 and 10 mV and shortened the action potential by 18 and 33%, respectively. DIDS partially reversed I_Cl(swell)-induced action potential changes. We conclude that I_Cl(swell) is present in Purkinje cells and its activation leads to action potential shortening and resting membrane potential depolarization, both of which can promote the development of reentrant arrhythmias.Received 20 January 2004; received after revision 17 February 2004; accepted 25 February 2004     

FK506 sensitizes mammalian cells to high osmolarity by modulating p38 MAP kinase activation

The immunosuppressants tacrolimus (FK506) and cyclosporin A (CsA) have increased the survival rates in organ transplantation. Both drugs inhibit the protein phosphatase calcineurin (CaN) in activated T cells, exhibiting similar side-effects. Diabetes is observed more often in FK506 than CsA therapy, probably due to inhibition of new molecular targets other than CaN. We studied FK506 toxicity in mammalian cells. FK506, but not CsA, regulated p38 activation by osmotic stress, and decreased viability in osmostressed cells. In addition, FK506 treatment strongly increased the phosphorylation of the eukaryotic initiation factor-2a (eIF-2a) subunit. eIF-2a phosphorylation, p38 inhibition and cell lethality were relieved by addition of excess amino acids to the medium, suggesting that amino acid availability mediated FK506 toxicity. Therefore, these FK506-dependent responses could be relevant to the non-therapeutic effects of FK506 therapy.Received 16 October 2003; received after revision 8 January 2004; accepted 14 January 2004     

Coulomb blockade and the Kondo effect in single-atom transistors

Using molecules as electronic components is a powerful new direction in the science and technology of nanometre-scale systems. Experiments to date have examined a multitude of molecules conducting in parallel, or, in some cases, transport through single molecules. The latter includes molecules probed in a two-terminal geometry using mechanically controlled break junctions or scanning probes as well as three-terminal single-molecule transistors made from carbon nanotubes, C(60) molecules, and conjugated molecules diluted in a less-conducting molecular layer. The ultimate limit would be a device where electrons hop on to, and off from, a single atom between two contacts. Here we describe transistors incorporating a transition-metal complex designed so that electron transport occurs through well-defined charge states of a single atom. We examine two related molecules containing a Co ion bonded to polypyridyl ligands, attached to insulating tethers of different lengths. Changing the length of the insulating tether alters the coupling of the ion to the electrodes, enabling the fabrication of devices that exhibit either single-electron phenomena, such as Coulomb blockade, or the Kondo effect.     

Large Cretaceous sphenodontian from Patagonia provides insight into lepidosaur evolution in Gondwana

Sphenodontian reptiles successfully radiated during Triassic and Jurassic times, but were driven almost to extinction during the Cretaceous period. The sparse Early Cretaceous record of sphenodontians has been interpreted as reflecting the decline of the group in favour of lizards, their suspected ecological successors. However, recent discoveries in Late Cretaceous beds in Patagonia partially modify this interpretation. Numerous skeletons of a new sphenodontian, Priosphenodon avelasi gen. et sp. nov., were collected from a single locality in the Cenomanian-Turonian Candeleros Formation, where it is more abundant than any other tetrapod group recorded in the quarry (for example, Crocodyliformes, Serpentes, Dinosauria and Mammalia). Adult specimens of Priosphenodon reached one metre in length, larger than any previously known terrestrial sphenodontian. Here we propose, using available evidence, that sphenodontians were not a minor component of the Cretaceous terrestrial ecosystems of South America, and that their ecological replacement by squamates was delayed until the early Tertiary. The new discovery helps to bridge the considerable gap in the fossil record (around 120 million years) that separates the Early Cretaceous sphenodontians from their living relatives (Sphenodon).     

Juxtaposed regions of extensive and minimal linkage disequilibrium in human Xq25 and Xq28

Linkage disequilibrium (LD), or the non-random association of alleles, is poorly understood in the human genome. Population genetic theory suggests that LD is determined by the age of the markers, population history, recombination rate, selection and genetic drift. Despite the uncertainties in determining the relative contributions of these factors, some groups have argued that LD is a simple function of distance between markers. Disease-gene mapping studies and a simulation study gave differing predictions on the degree of LD in isolated and general populations. In view of the discrepancies between theory and experimental observations, we constructed a high-density SNP map of the Xq25-Xq28 region and analysed the male genotypes and haplotypes across this region for LD in three populations. The populations included an outbred European sample (CEPH males) and isolated population samples from Finland and Sardinia. We found two extended regions of strong LD bracketed by regions with no evidence for LD in all three samples. Haplotype analysis showed a paucity of haplotypes in regions of strong LD. Our results suggest that, in this region of the X chromosome, LD is not a monotonic function of the distance between markers, but is more a property of the particular location in the human genome.     

求解延迟微分方程块θ-方法的GPLm-稳定性

讨论了带有多个滞时量的延时微分方程的数值稳定性,分析了用块θ–方法求解多延迟微分方程GPm–稳定和GPLm–稳定的条件,基于Lagrange插值,证明了块θ–方法GPm–稳定的充分必要条件是方法是A-稳定的,块θ–方法GPLm–稳定的充分必要条件是θ=1。     

6种凤仙花属(Impatiens L.)植物叶表皮特征的微形态学研究

应用扫描电子显微镜技术首次研究了6种凤仙花属(Impatiens L.)植物的叶表皮微形态学特征,结果表明:6种凤仙花属植物叶片上表皮纹饰为网状、不规则细波状或曲叉状,其中曲叉状纹饰为一种较特殊的纹饰特征;气孔仅分布在叶片的下表面,呈不规则排列,形状为椭圆形或宽椭圆形,长度在10.5-25.6μm之间,气孔外拱盖内缘平滑或近平滑,多数种类气孔的保卫细胞两极具“T”型加厚.叶表面纹饰,气孔的形状、大小及气孔保卫细胞两极“T”型加厚等特征在种间具有一定的差异,可作为该属植物分类的重要特征之一.文中还探讨了叶表皮微形态学特征在凤仙花属分类中的意义及有关紫花黄金凤的分类学地位问题.