国产农用喷雾器喷头性能参数测定与分析     

李秉礼  吴罗罗  阴景润  E.Moser  K.Schmidt 《中国农业大学学报》1989,(1):119-125

本文介绍了国产喷雾器喷头的几个主要性能参数与国外著名喷头公司产品的对比结果、并提出了改进我国喷头产品的若干建议。如:1.影响侧向进液式喷头喷量变异的因素。2.缝隙式扇雾喷头药液沉积横向分布中的牛角、对喷杆式喷雾器药液沉积分布均匀性有着极坏的影响。  相似文献   

A maximum in the strength of nanocrystalline copper     

Schiøtz J  Jacobsen KW 《Science (New York, N.Y.)》2003,301(5638):1357-1359

We used molecular dynamics simulations with system sizes up to 100 million atoms to simulate plastic deformation of nanocrystalline copper. By varying the grain size between 5 and 50 nanometers, we show that the flow stress and thus the strength exhibit a maximum at a grain size of 10 to 15 nanometers. This maximum is because of a shift in the microscopic deformation mechanism from dislocation-mediated plasticity in the coarse-grained material to grain boundary sliding in the nanocrystalline region. The simulations allow us to observe the mechanisms behind the grain-size dependence of the strength of polycrystalline metals.  相似文献   

A CHEMICAL DIFFERENCE BETWEEN PROTEIN-LINKED AND FREE NUCLEIC ACID     

Schmidt G 《Science (New York, N.Y.)》1936,83(2140):15

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Physical mapping of a translocation breakpoint in neurofibromatosis   总被引：13，自引：0，他引：13  

J W Fountain  M R Wallace  M A Bruce  B R Seizinger  A G Menon  J F Gusella  V V Michels  M A Schmidt  G W Dewald  F S Collins 《Science (New York, N.Y.)》1989,244(4908):1085-1087

The gene for von Recklinghausen neurofibromatosis (NF1), one of the most common autosomal-dominant disorders of humans, was recently mapped to chromosome 17 by linkage analysis. The identification of two NF1 patients with balanced translocations that involved chromosome 17q11.2 suggests that the disease can arise by gross rearrangement of the NF1 locus, and that the NF1 gene might be identified by cloning the region around these translocation breakpoints. To further define the region of these translocations, a series of chromosome 17 Not I-linking clones has been mapped to proximal 17q and studied by pulsed-field gel electrophoresis. One clone, 17L1 (D17S133), clearly identifies the breakpoint in an NF1 patient with a t(1;17) translocation. A 2.3-megabase pulsed-field map of this region was constructed and indicates that the NF1 breakpoint is only 10 to 240 kilobases away from 17L1. This finding prepares the way for the cloning of NF1.  相似文献   

Spatial regulators for bacterial cell division self-organize into surface waves in vitro     

Loose M  Fischer-Friedrich E  Ries J  Kruse K  Schwille P 《Science (New York, N.Y.)》2008,320(5877):789-792

In the bacterium Escherichia coli, the Min proteins oscillate between the cell poles to select the cell center as division site. This dynamic pattern has been proposed to arise by self-organization of these proteins, and several models have suggested a reaction-diffusion type mechanism. Here, we found that the Min proteins spontaneously formed planar surface waves on a flat membrane in vitro. The formation and maintenance of these patterns, which extended for hundreds of micrometers, required adenosine 5'-triphosphate (ATP), and they persisted for hours. We present a reaction-diffusion model of the MinD and MinE dynamics that accounts for our experimental observations and also captures the in vivo oscillations.  相似文献   

Materials science. How nanowires grow     

Schmidt V  Gösele U 《Science (New York, N.Y.)》2007,316(5825):698-699

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Pyroclastic activity at Home Plate in Gusev Crater, Mars     

Squyres SW  Aharonson O  Clark BC  Cohen BA  Crumpler L  de Souza PA  Farrand WH  Gellert R  Grant J  Grotzinger JP  Haldemann AF  Johnson JR  Klingelhöfer G  Lewis KW  Li R  McCoy T  McEwen AS  McSween HY  Ming DW  Moore JM  Morris RV  Parker TJ  Rice JW  Ruff S  Schmidt M  Schröder C  Soderblom LA  Yen A 《Science (New York, N.Y.)》2007,316(5825):738-742

Home Plate is a layered plateau in Gusev crater on Mars. It is composed of clastic rocks of moderately altered alkali basalt composition, enriched in some highly volatile elements. A coarsegrained lower unit lies under a finer-grained upper unit. Textural observations indicate that the lower strata were emplaced in an explosive event, and geochemical considerations favor an explosive volcanic origin over an impact origin. The lower unit likely represents accumulation of pyroclastic materials, whereas the upper unit may represent eolian reworking of the same pyroclastic materials.  相似文献   

TAF1B is a TFIIB-like component of the basal transcription machinery for RNA polymerase I     

Naidu S  Friedrich JK  Russell J  Zomerdijk JC 《Science (New York, N.Y.)》2011,333(6049):1640-1642

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Three-dimensional orientation mapping in the transmission electron microscope     

Liu HH  Schmidt S  Poulsen HF  Godfrey A  Liu ZQ  Sharon JA  Huang X 《Science (New York, N.Y.)》2011,332(6031):833-834

Over the past decade, efforts have been made to develop nondestructive techniques for three-dimensional (3D) grain-orientation mapping in crystalline materials. 3D x-ray diffraction microscopy and differential-aperture x-ray microscopy can now be used to generate 3D orientation maps with a spatial resolution of 200 nanometers (nm). We describe here a nondestructive technique that enables 3D orientation mapping in the transmission electron microscope of mono- and multiphase nanocrystalline materials with a spatial resolution reaching 1 nm. We demonstrate the technique by an experimental study of a nanocrystalline aluminum sample and use simulations to validate the principles involved.  相似文献   

Trans-endocytosis of CD80 and CD86: a molecular basis for the cell-extrinsic function of CTLA-4   总被引：1，自引：0，他引：1  

Qureshi OS  Zheng Y  Nakamura K  Attridge K  Manzotti C  Schmidt EM  Baker J  Jeffery LE  Kaur S  Briggs Z  Hou TZ  Futter CE  Anderson G  Walker LS  Sansom DM 《Science (New York, N.Y.)》2011,332(6029):600-603

Cytotoxic T lymphocyte antigen 4 (CTLA-4) is an essential negative regulator of T cell immune responses whose mechanism of action is the subject of debate. CTLA-4 shares two ligands (CD80 and CD86) with a stimulatory receptor, CD28. Here, we show that CTLA-4 can capture its ligands from opposing cells by a process of trans-endocytosis. After removal, these costimulatory ligands are degraded inside CTLA-4-expressing cells, resulting in impaired costimulation via CD28. Acquisition of CD86 from antigen-presenting cells is stimulated by T cell receptor engagement and observed in vitro and in vivo. These data reveal a mechanism of immune regulation in which CTLA-4 acts as an effector molecule to inhibit CD28 costimulation by the cell-extrinsic depletion of ligands, accounting for many of the known features of the CD28-CTLA-4 system.  相似文献