22 resultados para 1781

em Chinese Academy of Sciences Institutional Repositories Grid Portal


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结合近年来发表的对金属材料采用球形压头的微压痕实验结果及Johnson对应原理,讨论了在传统弹塑性理论下锥形压头在计及压头顶端曲率半径影响时硬度的解答形式。进而得出结论:压头尖端曲率半径不是引起尺度效应的根源,相反,它全使尺度效应减弱。

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It has been predicted that the floating potential of particles in plasma may become positive when the particle surface temperature is high enough, but, to our knowledge, no positive floating potential has been obtained yet. In the present paper the floating potential theory of high-temperature particles in plasma is developed to cover the positive potential range for the first time, and a general approximate analytical formula for the positive floating potential with a thin plasma sheath and subsonic plasma flow is derived from the new model recently proposed by the authors. The results show that when the floating potential is positive, the net flux of charge incident on the particle approaches a constant similar to the 'electron saturation' phenomena in the case of the electric probes.

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绣球科绣球族包含9属:草绣球属、叉叶蓝属、Broussaisia、常山属、绣球属、蛛网萼属、赤壁木属、冠盖藤属和钻地风属。到目前为止,绣球族内的属间关系还不清楚,族内的系统发育关系还有争论。本研究的目的是在前人研究的基础上,进一步发现新的系统学性状,为绣球族乃至绣球科补充新的证据;并综合多学科的研究结果进行分析,探讨绣球族的系统学关系。 本文研究了绣球族的外部形态学、花发育形态学、解剖学、分子系统学和分支系统学。 主要内容包括: 1. 形态学 通过标本室研究和野外观察,对绣球族植物的形态分化进行了分析。发现习性、地上茎的生存期限、花冠卷叠式、花瓣联合与否、花柱的联合程度、雄蕊的数目及排列具有系统学价值;放射花和果实是很好的分类性状,但并非可靠的系统学性状。 2. 花发育形态学 在扫描电子显微镜下,研究了绣球族常山属、绣球属、冠盖藤属、蛛网萼属共4种植物花器官发生和发育的全过程。发现它们的花萼均为螺旋式相继发生,花瓣的发生近乎同时。冠盖藤、马桑绣球及常山具两轮雄蕊,第一轮雄蕊发生于花瓣内轮正对萼片中部的位置,随后第二轮雄蕊发生于正对花瓣中部的位置。在第一轮雄蕊略靠内的位置形成第二轮雄蕊的时候,多数情况下,相邻的对萼雄蕊之间只形成1个对瓣雄蕊,但有时却形成2个对瓣雄蕊,使雄蕊群的数目略多于花被的数目。对萼雄蕊与对瓣雄蕊的分化方式基本一致,但它们在花芽中空间取向不同。 蛛网萼雄蕊数目极多,雄蕊群的发生式样较为独特,并不始于对萼三联体。最早的雄蕊于杯状体近基部发生,之后雄蕊的发生大致沿杯状体壁向上,具离心趋势。在雄蕊发生过程中杯状体继续伸长,为众多雄蕊的发生提供了空间。蛛网萼雌蕊的发生明显早于雄蕊,其它3种植物雌蕊的发生晚于雄蕊。4种植物的雌蕊在发生上较为相似,发育却不同。在常山、马桑绣球和蛛网萼中,花柱从开始到发育成熟始终分离,柱头在每个花柱的顶端形成;而冠盖藤属的花柱裂片从开始就是联合的,最终形成单一的花柱,柱头从合生花柱顶端远轴面分化形成。 3. 解剖学 在光学显微镜和扫描电子显微镜下,观察了绣球族9属42种1变种及近缘8属11种共53种1变种的叶表皮特征。发现气孔的分布、气孔器的类型、表皮细胞的形状及其垂周壁式样、毛被等具有一定的系统学意义和分类价值。绣球族各属的气孔仅散生于下表皮;而在绣球族的几个近缘属中,上下表皮均有气孔分布。气孔器在多数类群中为无规则型,仅常山属和绣球属离瓣组的成员为平列型。气孔多为椭圆形,稀近圆形;外拱盖表面通常光滑,仅在钻地风属中具条状纹饰;外拱盖内缘具环状加厚,近全缘、不规则波状或浅波状。表皮细胞在多数种中为不规则形,垂周壁波状、浅波状或深波状;在有些种中为(近)多边形,垂周壁平直或弓形。叶表皮细胞形状、垂周壁式样在绣球族寡种属属级水平比较稳定,但在绣球属中变化较大。表皮角质膜纹饰形态多样,有网纹、粗网纹、浅波状条纹、波状条纹、条纹、粗条纹及丝状条纹;在钻地风属及绣球属的少数种中,角质膜条纹有时汇集呈球形或玫瑰型。表皮毛状附属物有单细胞2分枝毛(黄山梅属)、多细胞星状毛(星毛冠盖藤)、单细胞星状毛(溲疏属)和单细胞不分枝毛四种。对钻地风属所有种的观察结果表明,仅在椭圆钻地风的下表皮细胞中央观察到乳突状结构,而在白背钻地风和圆叶钻地风中并未观察到前人描述的附属物。 4. 叶绿体DNA trnL-F序列的分析 首次对绣球族9属23种及近缘类群3属3种的trnL-F序列进行了测定。序列长度在860 bp~970 bp范围内变化。在以山梅花属、溲疏属和黄山梅属为外类群,基于trnL-F序列构建的系统树上,绣球族作为一个单系群得到很高的支持率。绣球属的种出现在不同的分支上,表明该属不是一个单系群。绣球族被分为两大支:第一支由绣球属离瓣组的中国绣球、绣球、以及常山和Broussaisia arguta组成;第二支由绣球属另外的9个种与草绣球属、叉叶蓝属、蛛网萼属、赤壁木属、冠盖藤属以及钻地风属组成。在第二支中,下列类群的近缘关系得到支持:① 草绣球与叉叶蓝属;② 绣球属挂苦子组的东陵绣球、圆锥绣球和挂苦绣球。③ 钻地风属、赤壁木属和冠盖藤属;④ 蜡莲绣球、莼兰绣球、马桑绣球、粗枝绣球。 5. 分支分析 以山梅花属为外类群,基于形态、解剖、花发育、孢粉等32个性状(或性状状态)对绣球族9属的系统发育关系进行了分支分析。结果表明:草绣球属和叉叶蓝属为基出类群,这两个属有多个共同特征;绣球族其余的成员聚成一支,该支又有5个分支。其中蛛网萼属和绣球属冠盖组各为单独的分支,它们有多个自衍征,可能有各自独立的演化线;绣球属离瓣组与常山属聚成一分支,二者的密切关系得到解剖学证据的支持;绣球属绣球组和星毛组聚成一分支,这两个组包含了绣球属的多数种类;钻地风属、赤壁木属、冠盖藤属、Broussaisia和绣球属挂苦子组聚成一分支。其中钻地风属、赤壁木属与冠盖藤属具多个近裔衍征,表明它们是绣球族的晚出类群。 通过对绣球族植物外部形态、花器官发生、叶表皮微形态特征、叶绿体DNA trnL-F区的研究以及基于形态性状的分支分析,并综合已有的研究结果,我们认为: 1. 绣球族是一个单系群;绣球属不是一个单系群。 2. 在绣球族中,草绣球属和叉叶蓝属关系密切,它们可能是绣球族其余成员的姐妹群。 3. 绣球组和星毛组可能是绣球属的核心成员;离瓣组和常山属关系密切;冠盖组有单独的演化线。 4. 赤壁木属、冠盖藤属和钻地风属为单系群,它们在绣球族处于较高的演化位置。 5. 绣球属需重新界定。

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本发明涉及眼镜王蛇毒蛋白酶抑制剂及其衍生物,与其它天然来源小分子量蛋白酶抑制剂相比,具有结构简单、基因表达产量高、活性特殊的有益特点。本发明眼镜王蛇毒蛋白酶抑制剂的制备方法可以是从蛇毒粗毒进行分离纯化获得,也可以通过基因工程表达获得。本发明还提供眼镜王蛇毒蛋白酶抑制剂及其衍生物的应用,其具有同时抑制胰蛋白酶以及胰凝乳蛋白酶的双重抑制活性,且对二种蛋白酶的抑制常数基本在同一个数量级,还具有钠通道的抑制活性。

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The in-plane optical anisotropy of three groups of GaAs/AlGaAs quantum well structures has been studied by reflectance-difference spectroscopy (RDS). For GaAs/Al0.36Ga0.64As single QW structures, it is found that the optical anisotropy increases quickly as the well width is decreased. For an Al0.02Ga0.98As/AlAs multiple QW with a well width of 20nm, the optical anisotropy is observed not only for the transitions between ground states but also for those between the excited states with transition index n up to 5. An increase of the anisotropy with the transition energy, or equivalently the transition index n, is clearly observed. The detailed analysis shows that the observed anisotropy arises from the interface asymmetry of QWs, which is introduced by atomic segregation or anisotropic interface roughness formed during the growth of the structures. More, when the 1 ML InAs is inserted at one interface of GaAs/AlGaAs QW, the optical anisotropy of the QW can be increased by a factor of 8 due to the enhanced asymmetry of the QW. These results demonstrate clearly that the RDS is a sensitive and powerful tool for the characterization of semiconductor interfaces.

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We consider the effect of image forces, arising due to a difference in dielectric permeabilities of the well layer and barrier layers, on the energy spectrum of an electron confined in a rectangular potential well under a magnetic field. Depending on the value and the sign of the dielectric mismatch, image forces can localize electrons near the interfaces of the well or in well centre and change the direct intersubband gaps into indirect ones. These effects can be controlled by variation of the magnetic field, offering possibilities for exact tuning of electronic devices.

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<正>在相对论连续无规位相近似(RCRPA)框架下研究了矢量介子流和库仑相互作用对核多极激发的影响。在这个方法中,用单粒子格林函数方法严格处理连续态对粒子-空穴(ph)激发的贡献。在无海近似下,单粒子格林函数中同时包含了狄拉克海负能态。数值计算中,单粒子格林函数由狄拉克方程的正规解和非正规解的适当乘积得到。我们采用完全自洽的RCRPA计算,即在同一个拉氏量下描述核基态性质和ph相互作用,这里,我们选用参数NL3。矢量介子空间分量即流虽然对

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A 3 T superconducting magnet with a 70 mm diameter warm bore and energy storage of 47 kJ has been successfully fabricated and tested, which can be used to calibrate Hall sensors in high magnetic field as well as conduct superconducting experiments. The magnet consists of three solenoid coils and an iron yoke. The homogeneity of the magnetic field in the region of interest (ROI) is +/- 6.0 x 10(-5). The coils of the magnet were fabricated with NbTi-Cu superconducting wire and the stray magnetic field is shielded by an iron yoke. The coils and yoke are fully immersed in a helium vessel. The optimized structural design, stress and quench simulation, fabrication and test results are presented in this paper.

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利用Li-6400便携式CO2分析系统测定长白山原始阔叶红松林生态系统土壤呼吸、乔灌木的枝干呼吸和叶呼吸;同步监测森林小气候气象因子;建立土壤、树干、叶与环境因子间的模型.根据阔叶红松林植被群落的特性,估算阔叶红松林生态系统不同组分呼吸速率.结果表明,阔叶红松林生态系统呼吸具有明显的成熟林特征,生态系统总呼吸量为1602.8gC.m-2.整个生态系统年平均呼吸速率为(4.37±2.98)μmol.m-2.s-1(24h平均数).其中,土壤呼吸、枝干和叶呼吸分别占整个森林生态系统呼吸的63%、16%和21%.乔木、灌木和草本叶呼吸速率分别占阔叶红松林生态系统植物呼吸的89.82%、5.57%和4.61%.阔叶红松林生态系统呼吸速率与大气和土壤温度之间呈显著的指数关系.大气和土壤温度能分别反映阔叶红松林生态系统呼吸的87%和95%.