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161.
162.
Stefansson H Helgason A Thorleifsson G Steinthorsdottir V Masson G Barnard J Baker A Jonasdottir A Ingason A Gudnadottir VG Desnica N Hicks A Gylfason A Gudbjartsson DF Jonsdottir GM Sainz J Agnarsson K Birgisdottir B Ghosh S Olafsdottir A Cazier JB Kristjansson K Frigge ML Thorgeirsson TE Gulcher JR Kong A Stefansson K 《Nature genetics》2005,37(2):129-137
A refined physical map of chromosome 17q21.31 uncovered a 900-kb inversion polymorphism. Chromosomes with the inverted segment in different orientations represent two distinct lineages, H1 and H2, that have diverged for as much as 3 million years and show no evidence of having recombined. The H2 lineage is rare in Africans, almost absent in East Asians but found at a frequency of 20% in Europeans, in whom the haplotype structure is indicative of a history of positive selection. Here we show that the H2 lineage is undergoing positive selection in the Icelandic population, such that carrier females have more children and have higher recombination rates than noncarriers. 相似文献
163.
Jarillo-Herrero P Kong J van der Zant HS Dekker C Kouwenhoven LP De Franceschi S 《Nature》2005,434(7032):484-488
Progress in the fabrication of nanometre-scale electronic devices is opening new opportunities to uncover deeper aspects of the Kondo effect--a characteristic phenomenon in the physics of strongly correlated electrons. Artificial single-impurity Kondo systems have been realized in various nanostructures, including semiconductor quantum dots, carbon nanotubes and individual molecules. The Kondo effect is usually regarded as a spin-related phenomenon, namely the coherent exchange of the spin between a localized state and a Fermi sea of delocalized electrons. In principle, however, the role of the spin could be replaced by other degrees of freedom, such as an orbital quantum number. Here we show that the unique electronic structure of carbon nanotubes enables the observation of a purely orbital Kondo effect. We use a magnetic field to tune spin-polarized states into orbital degeneracy and conclude that the orbital quantum number is conserved during tunnelling. When orbital and spin degeneracies are present simultaneously, we observe a strongly enhanced Kondo effect, with a multiple splitting of the Kondo resonance at finite field and predicted to obey a so-called SU4 symmetry. 相似文献
164.
笔者研究了一类三阶三点边值问题解的存在性,在非线性项半正且奇异的情况下,利用Guo—Kmsnoselskii不动点定理证明了解的存在性. 相似文献
165.
Effects of five heavy metals at sub-lethal concentrations on the growth and photosynthesis of Chlorella vulgaris 总被引:1,自引:0,他引:1
HuiLing Ouyang XiangZhen Kong Wei He Ning Qin QiShuang He Yan Wang Rong Wang FuLiu Xu 《科学通报(英文版)》2012,57(25):3363-3370
The impact of sub-lethal concentrations(0.05,0.5,5 μmol L 1) of the heavy metals copper(Cu),chromium(Cr),zinc(Zn),cadmium(Cd) and lead(Pb) on the growth and photosynthesis of Chlorella vulgaris was studied during 96 h exposure experiments.The results showed that the effects of these five metals on the growth of Chlorella vulgaris were dependent on both concentration and exposure time.It was found that 5 μmol L 1 treatments of Cu,Cr,Zn,Cd and Pb significantly inhibited the growth of Chlorella vulgaris,and the effect became weaker with an increase in exposure duration.Different effects on chlorophyll fluorescence were found for different metals,with Cu and Cr having an inhibiting effect and Zn and Cd having a promoting effect.The effects of heavy metals upon the growth and photosynthesis of Chlorella vulgaris were independent of each other and not causally related. 相似文献
166.
Rui-ting Liu Jie Liu Jie-qiong Tong Tao Tang Wei-Chao Kong Xiao-wen Wang Ying Li Jin-tian Tang 《自然科学进展(英文版)》2012,22(1):31-39
Magnetic fluid hyperthermia (MFH) promises to be a viable alternative in the treatment of localized cancerous tumors.The treatment consists of introducing nanoparticles as energy absorbent agents in tu... 相似文献
167.
168.
为了揭示复杂泵体水力的不稳定性,以减压塔底泵为例,利用计算流体动力学(CFD)对泵内部非定常流场进行数值模拟计算.根据得到的蜗壳内压力脉动情况,对其时域和频域进行分析.结果表明:各工况下压力脉动频率均以叶片通过频率为主,且次级蜗壳内的压力脉动比首级要明显;蜗壳内压力脉动最大值出现在隔舌附近,且沿蜗壳流道螺旋线方向压力脉动幅值依次减小;设计工况下蜗壳内压力脉动强度小于非设计工况下的,次级蜗壳隔舌处小流量工况下压力脉动幅值约为设计流量时的2.63倍. 相似文献
169.
通过野外调查采样和室内测定分析,研究了三江平原碟形洼地-岛状林土壤阳离子交换量(cation exchange capacity,CEC)分布特征及其与水文地貌、土壤养分和群落特征的关系.结果 表明,三江平原碟形洼地-岛状林土壤CEC为9.83~37.97 cmol/kg;碟形洼地-岛状林方向上,0~40 cm深度土壤CEC平均值先增大后减小而后稍有增大,呈"N"字形,毛薹草群落区土壤阳离子交换量最大(26.82 cmol/kg),乌拉薹草群落区最小(23.26 cmol/kg);垂直方向上,随着土层深度增加,土壤CEC逐渐减少,基本处于低度和中度变异.土壤CEC分布主要受土壤有机质的积累状况影响,土壤全磷全氮含量与土壤CEC含量呈极显著的正相关,土壤钾含量与土壤CEC呈极显著的负相关. 相似文献
170.
路易斯·I·康作为一位将结构,材料,空间秩序及哲学理念完美融合在一起的建筑大师,他的设计作品传达着对结构设计独特的诠释。本文通过解析其作品中结构设计与建筑设计的关系,挖掘出内在所遵循的结构理性和设计启示。 相似文献