Discovery of a petrified noeggerathialean strobilus,Discinites sinensis sp. nov. from the Permian of Shizuishan, Ningxia, China

A petrified strobilusDiscinites sinensis sp. nov. is discovered from the Lower Permian of Shizuishan in Ningxia, North China. The epidermal cells of sporophyll are long and narrow, with both ends pointed. Each sporangium is ellipsoid, with the basal part contracted and short, thick sporangiophore-like. The cells of tapetum and sporangial walls are arranged longitudinally. The annulus is not developed. Mega- and microsporangia are similar in shape. They can hardly be distinguished unless they are broken, and the spores are exposed.In situ mega- and microspores are also similar in shape and both of theDeltoidospora type. The new species supports the systematic placement ofDiscinites within Noeggerathiales, and the progymnosperm affinity of the Noeggerathiales.     

Tingia unita sp. nov. （Noeggerathiales） with strobilus from the Lower Permian of Wuda, Inner Mongolia, China

A number of specimens recently collected from the Early Permian Shanxi Formation of Wuda, Inner Mongolia demonstrate that the leafy shoot and strobilus of Tingia unita sp. nov. are both sprouting from a common stem, and consequently improve our understanding of the whole plant mor- phology of this enigmatic taxon of the Cathaysian flora. The strobili are cylinder-like, 1.7-2.5 cm in diameter and over 20 cm in length, with a basal stalk 7―8 mm in width and about 7 cm long. Sporophylls are verticillate, with approximately 8-10 in a whorl. On the adaxial side of each sporophyll a sporangium is attached. The strobilus is heterosporous and the microspores are of the Punctatisporites type. Large leaves vary from linear to oblong with entire lateral margins but are slightly lobed at the apex. Small leaves are generally the same as the large leaves but much narrower. The whole plant is probably a small arborescent tree with leafy shoots and strobili forming a crown, rather than a water plant with larger leaves floating on the surface of the water as previously understood. Features of the new species are in favor of the close affinity between Tingia Halle and Noeg- gerathiales, and accordingly the affinity of Noeg- gerathiales to Progymnospermophyta.     

Noeggerathiales as coal-forming plants in Cathaysia: conclusions from an Early Permian vegetational Pompeii in Inner Mongolia

Noeggerathiales are an extinct group of sporebearing plants of uncertain systematic position that are known from Carboniferous and Permian age Euramerican and Cathaysian floras that occurred in presentday Europe, North America, and East Asia. The order Noeggerathiales includes over 50 species of more than 20 fossil genera, but their paleoecology is not well understood yet. Previously this group had been found only in extrabasinal floras or those inhabiting clastic wetlands. Noeggerathiales have never been recorded in coal ball floras. Thus, it is up to now uncertain whether this group has contributed to the formation of coal. Recent investigations of an Early Permian peatforming flora of the Taiyuan Formation near Wuda, Inner Mongolia, which was preserved in a volcanic ash fall has provided evidence that noeggerathialean plants not only existed in the peatforming vegetation but could even be the dominant group in some areas of the coal swamp. The Noeggerathiales in this particular peatforming forest include Tingia unita, Paratingia wudensis, and a new species of Paratingia. Exceptionally well-preserved specimens indicate that these noeggerathialean plants are small trees with a canopy of compound leaves and strobili near the top of an unbranched （monocaulous） stem.     

河北曲阳晚古生代植物群及古地理研究

在河北省曲阳石炭一二叠纪地层中发现古植物化石29属62种,包括真蕨纲和种子蕨纲、楔叶纲、石松纲、瓢叶纲、苏铁纲、种子化石、科达纲、银杏纲.此古植物群华夏植物群的特点明显,纵向上可划分成5个古植物组合;演化具有阶段性,组合的变化与古地理6个演化阶段相适应.     

南京地区褐家鼠和黄胸鼠的染色体分带研究...

用骨髓染色体制片方法,对南京地区褐家鼠和黄胸鼠的核型、C带和G带进行了现察分析,并与前人报道作了比较,发现它们的核型和带型均显示出一定的差异.本研究为分析我国的家鼠属动物的染色体进化提供了基本资料。     

新型高聚合度聚氯乙烯树脂的颗粒形态研究

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Columns for visual features of objects in monkey inferotemporal cortex.

At early stages of the mammalian visual cortex, neurons with similar stimulus selectivities are vertically arrayed through the thickness of the cortical sheet and clustered in patches or bands across the surface. This organization, referred to as a 'column', has been found with respect to one-dimensional stimulus parameters such as orientation of stimulus contours, eye dominance of visual inputs, and direction of stimulus motion. It is unclear, however, whether information with extremely high dimensions, such as visual shape, is organized in a similar columnar fashion or in a different manner in the brain. Here we report that the anterior inferotemporal area of the monkey cortex, the final station of the visual cortical stream crucial for object recognition, consists of columns, each containing cells responsive to similar visual features of objects.     

绵羊毛囊细胞分离培养的观察

应用0．25％与0．125％的胰酶分离绵羊毛囊细胞，获得2种不同形态的毛囊细胞；其次，对比分析了热消化法与冷消化法对分离毛囊细胞的影响，结果表明：热消化法优于冷消化法；同时，观察到新疆细毛羊与阿勒泰羊的毛囊细胞形态基本一致。     

带形状参数的五次 Bezier 曲线的扩展

给出了带2个形状参数α,γ五次多项式基函数和带3个形状参数α,β,γ的六次多项式基函数,都是五次Bernstein基函数的扩展。依据这两组基函数,并分别定义了两种带形状参数的多项式曲线。所得到的曲线具有五次Bezier曲线类似的几何性质,并且灵活性比较强。     

内压作用下弯管应力的实验研究

采用电阴应变测量技术研究了带有初始随圆度的弯管在纯内压作用下的应力分布。实验结果表明,弯头横载面上的环向应力和轴向应力分布均呈相似的“Ｗ”型,但各点环向应力的绝对值均大于轴向应力。最大应力在外弧线的环向,比直管高出６２．７％,最小应力在中线弧处,为负值。这种应力分布情况也与弯管受平面弯矩时完全不同。     

基于有效极矩法的非球形细胞高阶介电泳力研究

细胞承受介电泳力的运动模拟在微控研究占据着举足轻重的地位.传统细胞介电泳力的求解理想化地将细胞看作球体进行计算.近似求解忽略了细胞的高阶介电泳力作用,导致分子动力学仿真结果与实验观测存在较大误差.基于有效极矩方法研究了椭球和红细胞的高阶介电泳力.研究发现Pohl介电泳力表达式在球体计算中依旧有效.从1阶至9阶的高阶极子曲线来看,椭球和红细胞奇数项系数非零,且与它们的形状密切相关.中间凹陷两端凸起的红细胞介电泳力大小近似于偏心率1∶5型椭球.研究结果与Ogbi等学者的仿真完全相符.     

中国海洋鱼类单殖吸虫研究XXI.拟八铗虫科一新记录

记述采自广东汕尾长体圆鲹Decapterus macrosoma Bleeker,1851鳃上的1种单殖吸虫--拟八铗虫属Pseudodiclidophora Yamaguti,与1 965之圆鲹拟八铗虫Pseudodiclidophora decapterus Yamaguti,1965.所获标本与Yamaguti的...     

逆向工程中一种鲁棒的平移对称提取算法

为了解决逆向工程中平移对称提取的问题,提出了一种鲁棒的提取算法.首先利用特征线将模型分割成体素的集合,然后计算各个体素的形状分布曲线,通过形状分布曲线匹配的方式获取了几何形状相似的体素,并利用最小包围盒从中提取大小相似的体素,以构成对称体素的集合.利用鲁棒的PCA方法估算对称体素的初步对称信息,在此基础上利用迭代最近点算法对提取的平移对称进行优化.采用一个机械零件的三角网格模型进行实验的结果表明,体素分割结果对应构成模型的各个特征,具有明显的工程语义,对称提取结果的误差较小并具有较强的鲁棒性.     

蕨游动精细胞的研究

电镜研究表明蕨精细胞在发育早期为多角形细胞，具有细胞壁，多层结构和微管，但不具鞭毛，核圆形或椭圆形，随着精细胞的发育，质膜退缩远离细胞壁，在细胞壁和质膜之间质下一个空间，细胞核螺旋化并有大量鞭毛形成，最后精细胞发育形成具有鞭毛的游动精子。     

Solenites murrayana L.et H.在甘肃窑街煤田的发现及其地质意义

在甘肃窑街中侏罗统窑街组发现了银杏类植物化石的重要代表穆雷似管状叶Solenites murrayana L．et H．，其外形显示出不分叉的细线形叶片，宽度小于1mm．根据室内实验对其表皮构造进行了研究，主要特征是：上表皮稍厚，细胞较大，多呈矩形，纵向延伸，具毛基；下表皮较薄，细胞相对小于上表皮细胞，不规则多边形；气孔器双生型，气孔定向排列，但不相连成带状；副卫细胞角质化程度较强，毛基较发育．Solenites murrayana的气孔参数可与现存最近对应种Ginkgo biloba的气孔参数进行对比，并可用来推论中侏罗世的古大气CO2浓度．     

Ichthyosaur from Guizhou, China

A new ichthyosaur is named and described on the basis of two well-preserved skeletons from the Late Triassic Wayao Member of Falang Formation, Guizhou Province, southwestern China. The specimens represent a longipinnate ichthyosaur with a set of characters transitional from the Triassic forms to the Jurassic forms. It is similar to shastasaurids of the Triassic in the relative size and shape of the limbs but resemblesOphthalmosaurus andBaptanodon of the Jurassic in the shape of the skull. The new taxon differs from all other ichthyosaurs found in China in its unusual large orbit, distinct rostrum, and the hind limbs, that are slightly stronger than the fore ones.     

内蒙古柴胡属植物花粉形态及其分类

本文首次用扫描电镜观察了内蒙古柴胡属７种１１株植物的花粉形态。该属植物花粉形态相对一致，但在花粉粒形状、纹饰细微结构和孔膜等方面有差异。根据形状和孔膜特点本属花粉可分为近菱形，卵形和近长方形等三类；以外壁纹饰特征又可分为皱波状纹饰较明显和不明显两类，后两类与以小总苞片特征所得的类群基本吻合。柴胡属某些种花粉形态在种内有变异现象。     

Prokaryotic origin of the actin cytoskeleton.

It was thought until recently that bacteria lack the actin or tubulin filament networks that organize eukaryotic cytoplasm. However, we show here that the bacterial MreB protein assembles into filaments with a subunit repeat similar to that of F-actin-the physiological polymer of eukaryotic actin. By elucidating the MreB crystal structure we demonstrate that MreB and actin are very similar in three dimensions. Moreover, the crystals contain protofilaments, allowing visualization of actin-like strands at atomic resolution. The structure of the MreB protofilament is in remarkably good agreement with the model for F-actin, showing that the proteins assemble in identical orientations. The actin-like properties of MreB explain the finding that MreB forms large fibrous spirals under the cell membrane of rod-shaped cells, where they are involved in cell-shape determination. Thus, prokaryotes are now known to possess homologues both of tubulin, namely FtsZ, and of actin.     

Stem cells, cancer, and cancer stem cells.

Stem cell biology has come of age. Unequivocal proof that stem cells exist in the haematopoietic system has given way to the prospective isolation of several tissue-specific stem and progenitor cells, the initial delineation of their properties and expressed genetic programmes, and the beginnings of their utility in regenerative medicine. Perhaps the most important and useful property of stem cells is that of self-renewal. Through this property, striking parallels can be found between stem cells and cancer cells: tumours may often originate from the transformation of normal stem cells, similar signalling pathways may regulate self-renewal in stem cells and cancer cells, and cancer cells may include 'cancer stem cells' - rare cells with indefinite potential for self-renewal that drive tumorigenesis.     

Drosophila small cytoplasmic 19S ribonucleoprotein is homologous to the rat multicatalytic proteinase

All eukaryotic cells so far analysed contain 19S particles which share a cylinder-like shape and are composed of a set of proteins of relative molecular mass ranging typically from 19,000 to 36,000 (refs 1-10). Proposed functions have included synthetase activity, transfer RNA processing or messenger RNA repression, but their biological importance remains obscure. A multicatalytic proteinase (MCP) of similar size and shape has been isolated from mammalian tissues. The apparent similarities of these high molecular weight complexes suggest a biochemical and functional homology between the small cytoplasmic 19S particle from Drosophila melanogaster (19S-scRNP) (ref. 7) and rat MCP (ref. 14). By means of electron microscopy, immunological techniques, RNA identification and proteinase activity assays, we were able to show that the two structurally similar complexes are immunologically related ribonucleoproteins (RNPs) with similar proteolytic activity.