检索结果-南通市图书馆

The reconstruction of fossil planation surface in Chin

在线全文

学校读者我要写书评

暂无评论

Chinese Science Bulletin 2002年第5期47卷 434-440页

作者： FENG Jinliang & GUI ZhijiuDepartment of Urban and Environmental sciences, peking university, beijing 100871, china Institute of Geography, Hebei Academy of sciences, Shijiazhuang 050011, china Department of Urban and Environmental sciences Peking University Beijing China Institute of Geography Hebei Academy of Sciences Shijiazhuang China

On the basis of results of relative subjects, the fossil planation surface has been discussed by the authors from the point of geomorphologic view. The discussion contents included the characteristic information, research methods, paleotopography (gradient and altitude) and other problems about fossil planation surface. The recognition and reconstruction of fossil planation surface mainly rely on the following characteristic information: (i) the character of erosion unconformity surface; (ii) the paleo-weathering crust and residual deposits; (iii) the paleo-karst and filled deposit in the paleo-karst under the unconformity surface, and (iv) the character and environment of sediment above the unconformity surface. According to the above-mentioned characteristic information, the authors recognized and reconstructed two stages of fossil planation surface on Pa-leo-land of North china and Yangtze Paleo-land. These two fossil planation surfaces formed from Middle Ordovician to Lower Carboniferous and from

关键词： fossil planation surface characteristic information pa-leotopography reconstruction.

Pollution characteristics of atmospheric fine particles and their secondary components in the atmosphere of Shenzhen in summer and in winter

在线全文

学校读者我要写书评

暂无评论

Science china Chemistry 2006年第5期49卷 466-474页

作者： NIU Yuwen1,2,HE Lingyan1,2,HU Min2,ZHANG Jing2 & ZHAO Yunliang2 1. Shenzhen Graduate School of peking university,Shenzhen 518055,china 2. State Joint Key Laboratory of Environmental Simulation and Pollution Control,college of Environmental sciences,peking university,beijing 100871,china Shenzhen Graduate School of peking university Shenzhen China State Joint Key Laboratory of Environmental Simulation and Pollution Control College of Environmental Sciences Peking University Beijing China

Two field measurements for atmospheric fine particles were conducted in Baoan district of Shenzhen during the summer and winter in 2004. Totally 30 sets of 24 h samples were collected, and then the mass concentrations and chemical compositions were determined. The seasonal varia- tions and secondary pollution characteristics of fine particles during the sampling periods were dis-cussed with meteorological factors. The results show that seasonal variations of atmospheric particles are significant in Shenzhen. The average mass concentrations of PM2.5 and PM10 in summer were 35 μg·m-3 and 57 μg·m-3, respectively, and those in winter were 99 μg·m-3 and 135 μg·m-3, respec-tively. The concentrations of both PM2.5 and PM10 in winter increased 184% and 137%, respectively, compared to those in summer. PM2.5 accounted for 61% and 75% of PM10 in summer and in winter, respectively, indicating severe fine particle pollution in Shenzhen. During the summer and winter sampling periods, the mean OC/EC ratios were 3.4 and 1.6, respectively. The estimated secondary organic carbon (SOC) averagely accounted for 56% and 6% of the total OC in summer and in winter, respectively, which implies a major contribution of SOC to OC in summer. During the continuous high temperature period in summer, both the concentrations and fractions of secondary aerosol compo-nents in PM2.5 were highly elevated, suggesting severe secondary pollution again. The prevailing wind was from South china Sea in summer, and the air quality was good. The prevailing wind in winter was from china's Mainland to the north, and the polluted air mass led to poor air quality.

关键词： PM2.5, mass concentration, secondary pollution, seasonal variation, Shenzhen.

The refined theory of deep rectangular beams based on general solutions of elasticity

在线全文

学校读者我要写书评

暂无评论

Science china(Physics,Mechanics & Astronomy) 2006年第3期49卷 291-303页

The problem of deducing one-dimensional theory from two-dimensional the- ory for a homogeneous isotropic beam is investigated. Based on elasticity theory, the re- fined theory of rectangular beams is derived by using Papkovich-Neuber solution and Lur’e method without ad hoc assumptions. It is shown that the displacements and stresses of the beam can be represented by the angle of rotation and the deflection of the neutral surface. Based on the refined beam theory, the exact equations for the beam without transverse surface loadings are derived and consist of two governing differential equations: the fourth-order equation and the transcendental equation. The approximate equations for the beam under transverse loadings are derived directly from the refined beam theory and are almost the same as the governing equations of Timoshenko beam theory. In two ex- amples, it is shown that the new theory provides better results than Levinson’s beam the- ory when compared with those obtained from the linear theory of elasticity.

关键词： deep rectangular beams,the refined theory,Papkovich-Neuber solution,Lur'e method,governing equation

Systematic study of the transfer of amino acids across the water/1,2-dichloroethane interface facilitated by dibenzo-18-crown-6

在线全文

学校读者我要写书评

暂无评论

Science china Chemistry 2004年第1期47卷 24-33页

作者： CHEN Yong, YUAN Yi, ZHANG Meiqin, LI Fei, SUN Peng, GAO Zhao & SHAO YuanhuaState Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of sciences, Changchun 130022, china college of Chemistry and Molecular Engineering, peking university, beijing 100871, china Lab. of Electroanalytical Chem. Changchun Inst. of Appl. Chem. Chinese Acad. of Sci. Changchun 130022 China Coll. of Chem. and Molecular Eng. Peking Univ. Beijing 100871 China

Facilitated ion transfer reactions of 20 amino acids with dibenzo-18-crown-6 (DB18C6) at the water/1,2-dichloroethane (W/DCE) interfaces supported at the tips of micro- and nano-pipets were investigated systematically using cyclic voltammetry. It was found that there were only 10 amino acids, that is, Leu, Val, lie, Phe, Trp, Met, Ala, Gly, Cys, Gin (in brief), whose protonated forms as cations can give well-defined facilitated ion transfer voltammograms within the potential window, and the reaction pathway was proven to be consistent with the transfer by interfacial complexation/dissociation (TIC/TID) mechanisms. The association constants of DB 18C6 with different amino acids in the DCE (β0), and the kinetic parameters of reaction were evaluated based on the steady-state voltammetry of micro- or nano-pipets, respectively. The experimental results demonstrated that the selectivity of complexation of protonated amino acid by DB18C6 compared with that of alkali metal cations was low, which can be attributed to the vicinal effect arising from steric hindrance introduced by their side group and the steric bulk effect by lipophilic stabilization. Moreover, the association constants and the standard rate constants for different amino acids showed good correlations with their hydrophobicity (π), except Gly and Met, which inferred that the selectivity of such heterogeneous complex reaction for different amino acids with DB18C6, was not only affected by discrimination in binding these ions to the crown ether macro-cycle, but also significantly modified by the ion transfer Gibbs energy which was closely related to the structure of the transferred ions, protonated amino acids.

关键词： micro-/nano-pipet, water/1,2-dichloroethane interface, facilitated ion transfer, cyclic voltammetry, amino acid.

Expression of rice dwarf phytoreovirus Pns6 and the specificity analysis of its monoclonal antibodies

在线全文

学校读者我要写书评

暂无评论

Science china(life sciences) 2009年第10期52卷 958-964页

作者： JI Xu, WEI ChunHong & LI Yi peking–Yale Joint Center for Plant Molecular Genetics and Agrobiotechnology, the National Laboratory of Protein Engineering and Plant Genetic Engineering, college of life sciences, peking university, beijing 100871, china peking-Yale Joint Center for Plant Molecular Genetics and Agrobiotechnology the National Laboratory of Protein Engineering and Plant Genetic Engineering College of Life Sciences Peking University Beijing China

The genome of rice dwarf phytoreovirus (RDV) is composed of 12 double-stranded RNA segments, of which segment S6 encodes a non-structural protein Pns6 identified as the movement protein. In this report, Pns6 with a 6-histidine tag at the N-terminal was expressed in E. coli after induction under low temperature (18℃) and low concentration (0.4 mmol/L and 0.2 mmol/L) of IPTG, and then purified by Ni-chelated affinity chromatography. Stability analysis indicated that the expressed HisPns6 protein was stable at 37℃ after 24 h treatment. This recombinant protein was then used to make monoclonal antibody. Total 18 hybridoma clones were obtained. The specificity of antibodies was tested by Western blot using native Pns6 extracted from RDV-infected rice leaves, and 15 positive clones were confirmed. Mapping of the antigenic sites of Pns6 using antibodies showed that the most sensitive antigen determinant is located in the C-terminal region (the 296th-509th amino acids) of Pns6, which is confirms bioinformatics analysis.

关键词： rice dwarf virus Pns6 expression monoclonal antibody antigen determinant

Generation of pancreatic islet cells from human embryonic stem cells

在线全文

学校读者我要写书评

暂无评论

Science china(life sciences) 2009年第7期52卷 615-621页

作者： ZHANG DongHui1,2,JIANG Wei1,SHI Yan2 & DENG HongKui1,2 1 Key Laboratory of Cell Proliferation and Differentiation of the Ministry of Education,college of life sciences,peking university,beijing 100871,china 2 Laboratory of Chemical Genomics,Shenzhen Graduate School of peking university,Shenzhen 518055,china Key Laboratory of Cell Proliferation and Differentiation of the Ministry of Education College of Life Sciences Peking University Beijing China Laboratory of Chemical Genomics Shenzhen Graduate School of Peking University Shenzhen China

Efficiently obtaining functional pancreatic islet cells derived from human embryonic stem(hES) cells not only provides great potential to solve the shortage of islets sources for type I diabetes cell therapy,but also benefits the study of the development of the human pancreas and diabetes *** 2001,hES cells were reported to have the capacity to generate insulin-producing cells by spontaneous differentiation in *** then,many strategies(such as overexpression of key transcription factors,delivery of key proteins for pancreatic development,co-transplantation of differentiated hES cells along with fetal pancreas,stepwise differentiation by mimicking in vivo pancreatic development) have been employed in order to induce the differentiation of pancreatic islet cells from hES ***,patient-specific induced pluripotent stem(iPS) cells can be generated by reprogramming somatic *** cells have characteristics similar to those of ES cells and offer a new cell source for type I diabetes cell therapy that reduces the risk of immunologic *** this review,we summarize the recent progress made in the differentiation of hES and iPS cells into functional pancreatic islet cells and discuss the challenges for their future study.

关键词： human embryonic stem(hES) pancreatic islet cells differentiation induced pluripotent stem(iPS) cells

Survival of Human Metallothionein-2 Transplastomic Chlamydomonas reinhardtii to Ultraviolet B Exposure

在线全文

学校读者我要写书评

暂无评论

Acta Biochimica et Biophysica Sinica 2006年第3期38卷 187-193页

作者： Yu-Kun ZHANG~1 Gui-Fang SHEN~2 Bing-Gen RU~1*1 National Laboratory of Protein Engineering and Plant Genetic Engineering,peking university,beijing 100871,china 2 Biotechnology Research Institute,the Chinese Academy of Agricultural sciences,beijing 100081,china National Laboratory of Protein Engineering and Plant Genetic Engineering Peking UniversityBeijing 100871 China Biotechnology Research Institute the Chinese Academy of Agricultural SciencesBeijing 100081 China

Solar ultraviolet (UV) radiation has a great influence on green organisms,especially planktonlike Chlamydomonas.A human metallothionein-2 gene,which is generally considered to have an anti-radiationfunction by its coding product,was transferred into the chloroplast genome of Chlamydomonas *** dynamically measure the UV effects on Chlamydomonas cells grown in liquid tris-acetate-phosphatemedium,a new method was developed based on the relationship between the chlorophyll content of an algalculture and its absorbance at 570 nm after the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium *** this experiment,both the wild-type and the transplastomic *** ceils were cultivated in 96-well microplates containing liquid tris-acetate-phosphate medium in the absence or presence of zinc,copper,cadmium and *** transgenic *** showed a higher resistance than wild-type to UV-Bexposure under all the examined *** in the medium had positive impacts on both types of cells,but had significant influence only on the transplastomic ***,the high cell viability of the trans-genie alga at the end of the 8 h UV-B treatment disappeared after a 20-h recovery *** did notprotect cells from UV-B damage,but clearly enhanced the growth of both wild-type and transgenic ***.

关键词： ultraviolet B MTT transplastomic Chlamydomonas metallothionein

Kinematics and dynamics of the Mesozoic orogeny and late-orogenic extensional collapse in the Sino-Mongolian border areas

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

Science china Earth sciences 2005年第7期48卷 849-862页

作者： ZHENG Yadong 1 & WANG Tao2 1. Key Laboratory of Orogenic Belts and Crustal Evolution (peking university), Ministry of Education, beijing 100871, china 2. Institute of Geology, Chinese Academy of Geological sciences, beijing 100037, china Key Laboratory of Orogenic Belts and Crustal Evolution (peking university) Ministry of Education Beijing 100871 China Institute of Geology Chinese Academy of Geological Sciences Beijinq 100037 China

The Sino-Mongolian border areas underwent two important tectonic events during Mesozoic time after late Paleozoic orogeny: a late Triassic to earlier Jurassic contractional event that resulted in a large-scale south-vergent thrust during the orogeny and a late Jurassic-earlier Cretaceous extensional event in a north-south direction that formed a metamorphic core complex. The kinematic and dynamic analyses show that the thrust sheet moved southwards with a kinematic vorticity number of ca. -0.10 and sub-horizontal maximum compressive stress axis that belongs to a contraction-thickening shear. The upper plate of the late-orogenic detachment relatively moved in a 165°direction. The average kinematic vorticity in its earlier stage was 0.74 that belongs to simple shear dominated shearing and related to the maximum compressive stress axes dipping at ～66°, while the later average kinematic vorticity was ～0.55°that belongs to pure shear dominated shearing with sub-vertical maximum compressive stress axes. This suggests that the thrusting led to the crust thickened and the lower plate rocks that were originally located in the upper crust depressed through a brittle-ductile transition zone into the lower crust and became warmer. The heated rocks trended to uplift since their increasing volume and decreasing density while the loading of the upper-plate rocks increased due to the structural thickening. Under the combined effect of the loading and the thermal-uplifting, the ductile shear zone in between increased in its component of vertical pure shear. Once its pure-shear component exceeded its simple-shear one the ductile shear zone became an extension-thinned shear zone. This progressive transitional process reflects internal and essential temporal and spatial relationships: the extensional factor nucleated during the crust thickening by thrusting and increase of the extensional factor finally led to late-orogenic collapse.

关键词： Mesozoic thrusting,late-orogenic collapse,kinematic vorticity number,stress state.

Some basic concepts and problems on the petrogenesis of intra-plate ocean island basalts

在线全文

学校读者我要写书评

暂无评论

Chinese Science Bulletin 2009年第22期54卷 4148-4160页

作者： NIU Yaoling1,2,3 1 Department of Earth sciences, Durham university, Durham DH1 3LE, UK 2 School of Earth sciences and Resources, china university of Geosciences, beijing 100083, china 3 School of Earth and Space sciences, peking university, beijing 100871, china Department of Earth sciences Durham University Durham UK School of Earth sciences and Resources China University of Geosciences Beijing China School of Earth and Space sciences Peking University Beijing China

Basaltic magmatism that builds intra-plate ocean islands is often considered to be genetically associated with "hotspots" or "mantle plumes". While there have been many discussions on why ocean island basalts (OIB) are geochemically highly enriched as an integral part of the mantle plume hypothesis, our current understanding on the origin of OIB source material remains unsatisfactory, and some prevailing ideas need revision. One of the most popular views states that OIB source material is recycled oceanic crust (ROC). Among many problems with the ROC model, the ocean crust is simply too depleted (e.g., [La/Sm]PM > 1) OIB. Another popular view states that the enriched component of OIB comes from recycled continental crust (RCC, i.e.; terrigenous sediments). While both CC and OIB are enriched in many incompatible elements (e.g., both have [La/Sm]PM >>1), the CC has characteristic enrichment in Pb and deletion in Nb, Ta, P and Ti. Such signature is too strong to be eliminated such that CC is unsuitable as source material for OIB. Plate tectonics and mantle circulation permit the presence of ROC and RCC materials in mantle source regions of basalts, but they must be volumetrically insignificant in contributing to basalt magmatism. The observation that OIB are not only enriched in incompatible elements, but also enriched in the progressively more incompatible elements indicates that the enriched component of OIB is of magmatic origin and most likely associated with low-degree melt metasomatism. H2O and CO2 rich incipient melt may form in the seismic low velocity zone (LVZ). This melt will rise because of buoyancy and concentrate into a melt rich layer atop the LVZ to metasomatize the growing lithosphere, forming the metasomatic vein lithologies. Erupted OIB melts may have three components: (1) fertile OIB source material from depth that is dominant, (2) the melt layer, and (3) assimilation of the metasomatic

关键词：岩石成因论海洋 OIB 矿物学