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Study on Dual PWM Converter f.r Direct Driven Permanent Magnet Synchronous Generator Wind Power Generation Application

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Study on Dual PWM Converter for Direct Driven Permanent Magn...

作者： Joei f.mushi 浙江大学

学位级别：硕士

永磁直趋风力发电系统因为其结构简单、高效率、高功率密度体积小、不需要齿轮箱等优点,近几年受到了广泛的关注。本文所设计的系统主要包括：直流电机模拟风力机电路和并联型双PWM并网变流器以及数字控制部分。本文首先介绍了风力发电... 详细信息

永磁直趋风力发电系统因为其结构简单、高效率、高功率密度体积小、不需要齿轮箱等优点,近几年受到了广泛的关注。本文所设计的系统主要包括：直流电机模拟风力机电路和并联型双PWM并网变流器以及数字控制部分。本文首先介绍了风力发电系统在风能应用中的背景和技术特点,同时讨论了风力机的动力学特性和风能变换的特点。全面介绍了双PWM载波移相技术和永磁发电机的控制策略,双PWM变流器主要有以下几方面的优势：首先双PWM变流器能量能够双向流动,其次变流器的输入输出电流谐波含量低,最后此变流器易于控制且动态响应较好同时功率因数可调。为了满足低谐波和高功率的要求,本文采用了线路级三模块并联而不是器件直接并联。此结构满足了体积小、散热性好、高开关频率的设计要求。尽管如此,当系统并联时仍存在零序环流的问题;对此,本文提出了一些方法对零序环流进行控制。在网侧通过LCL滤波器连接变流器与电网。为了模拟风力机,本文对比了电动机与风力机之间的相关特性。最后,通过功率和转速控制进行模拟。基于双PWM变流器的实验平台本文是采用数字信号处理器TMS320f.812进行控制,而多路载波移相SPWM信号通过f.GA+DSP共同实现。通过仿真和实验验证,本文所设计的系统能够很好的运行,并达到预期效果。

关键词：永磁直趋风力发电双PWM变流器直流电动机模拟系统数字控制系统

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f.rmation and Microstructural Characterization of.Silicon-modif.ed Aluminide Coating on Nickel-based Superalloy IN738LC

作者： (美)玛莎·f.布兰娜(martha f. Brenner)

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材料热处理学报 2004年第05B期25卷 657-660页

作者： f. Shahriari f. Ashraf.zadeh A. Monshi Materials engineering department Isfahan University of Technology Isfahan IranMaterials engineering department Isfahan University of Technology Isfahan IranMaterials engineering department Isfahan University of Technology Isfahan Iran

In this investigation, aluminide coatings used to protect industrial components at high temperature and corrosive environments were modif.ed with silicon addition and the microstructural f.atures and f.rmation mechanism were evaluated. The coating on the nickel-based superalloy IN738LC was carried out by a two stage process including siliconizing at f.rst and aluminizing thereaf.er. Pack cementation siliconizing perf.rmed at 950C f.r 2, 4 and 6 hours in several powder mixtures of.Si, A12O3 and NHiCl, then aluminum was dif.used into the surf.ce of.the specimens by an industrial aluminizing process. The modif.ed coatings were characterized by means of.standard metallography, scanning electron microscopy, energy dispersive spectroscopy and X-ray dif.raction methods. The results show that Si in the coatings mainly presents in the f.rm of.secondary phases including Cr3Si, Mo5Si3 and Nii6Ti6Si7, well distributed within the NiAl matrix. The advantages of.this two stage modif.ed coating is discussed.

关键词：显微结构 IN738LC 镍超级合金扩散渗碳处理生长机制

Closed-f.rm solutions f.r f.ee vibration of.rectangular f.M thin plates resting on elastic f.undation

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Acta Mechanica Sinica 2016年第6期32卷 1088-1103页

作者： T. f. Xu Y. f. Xing Institute of.Solid Mechanics Beihang UniversityBeijing 100191 China China Academy of.Launch Vehicle Technology R&D Center Beijing 100076 China

This article presents closed-f.rm solutions f.r the f.equency analysis of.rectangular f.nctionally graded material (f.M) thin plates subjected to initially in-plane loads and with an elastic f.undation. Based on classical thin plate theory, the governing dif.erential equations are derived using Hamilton's principle. A neutral surf.ce is used to eliminate stretching-bending coupling in f.M plates on the basis of.the assumption of.constant Poisson's ratio. The resulting governing equation of.f.M thin plates has the same f.rm as homogeneous thin plates. The separation-of.variables method is adopted to obtain solutions f.r the f.ee vibration problems of.rectangular f.M thin plates with separable boundary conditions, including, f.r example, clamped plates. The obtained normal modes and f.equencies are in elegant closed f.rms, and present f.rmulations and solutions are validated by comparing present results with those in the literature and f.nite element method results obtained by the authors. A parameter study reveals the ef.ects of.the power law index n and aspect ratio a/b on f.equencies.

关键词： f.nctionally graded material f.ee vibration Rectangular plate Close f.rm solutions Neutral surf.ce

Psychological Resilience Building in Disaster Risk Reduction:Contributions f.om Adult Education

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International Journal of.Disaster Risk Science 2014年第1期5卷 33-40页

作者： martha Hof.er Institute of.Education and Culture Chair of Adult EducationFriedrich Schiller University Jena07743 JenaGermany

This article discusses three What opportunities exist to enhance psychological resilience in adults?Why should psychological resilience promotion be considered an important disaster risk reduction strategy?What contribution can adult education make to such a strategy?Psychological resilience is presented as relational and somewhat malleable,even in *** psychological resilience building is of.en overlooked in sociallevel disaster risk reduction ef.orts,it is a key strategy f.r social resilience *** regarding the extent to which mental resilience can be improved and the techniques with which to do so may be answered by research in the f.eld of.adult *** learning and teaching research f.ndamentals are suggested to create psychological resilience-building strategies in adults.

关键词： Adult education Disaster risk reduction Mental health Psychological resilience Resilience building

Phylogenetic reconstruction of.Chirita and allies (Gesneriaceae) with taxonomic treatments

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Journal of.Systematics and Evolution 2011年第1期49卷 50-64页

作者： James f. SMITH Department of.Biological Sciences Boise State University

Chirita D. Don, a large genus in the subf.mily Cyrtandroideae of.Gesneriaceae, has been the subject of.much debate whether it is a natural group or not. In addition, the highly heterogeneous Chirita has also been very problematic with regard to delimitation and subdivision. Here we used the nrDNA internal transcribed spacer and cpDNA trnL-f.f.r molecular phylogenetic analaysis, combined with morphological data. Our results suggest that Chirita is an artif.cial, polyphyletic genus. The most important character that def.nes Chirita, the dorso-ventrally oblique and bilamellar stigma, has evolved convergently in dif.erent clades of.diandrous Cyrtandroideae. Chirita sensu stricto only includes the species of.Chirita sect. Chirita, whereas Chirita sect. Microchirita is an independent clade located at the basal node of.the phylogenetic tree. Chirita sect. Liebigia is closely related to Didymocarpus with an entire stigma unlike other species of.Chirita. The species of.Chirita sect. Gibbosaccus, Chiritopsis, Primulina, and Wentsaiboea f.rm a monophyletic group that is sister to a strongly supported clade comprising f.ur monotypic genera Paralagarosolen, Calcareoboea, Petrocodon, and Tengia. We f.rther analyzed the morphological evolution of.Chirita and identif.ed a series of.morphological synapomorphies f.r the monophyletic groups revealed herein, and thereby provide a taxonomic treatment in this study.

关键词： Chirita D. Don morphological evolution phylogenetic reconstruction polyphyly taxonomic treatment.

The Membrane-Associated Sec1/Munc18 KEULE is Required f.r Phragmoplast Microtubule Reorganization During Cytokinesis in Arabidopsis

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Molecular Plant 2016年第4期9卷 528-540页

作者： Alexander Steiner Lin Muller Katarzyna Rybak Vera Vodermaier Eva f.cher martha Thellmann Raksha Ravikumar Gerhard Wanner Marie-Theres Hauser f.rhah f. Assaad Botany Department School of Life Sciences Technische Universitat Munchen Emil-Ramann-Street 4 85354 Freising Germany Department Biologie I Ludwig-Maximillians Universitat 82152 Planegg-Martinsried Germany Department of.Applied Genetics and Cell Biology University of Natural Resources and Life Sciences 1190 Vienna Austria

Cytokinesis, the partitioning of.the cytoplasm f.llowing nuclear division, requires extensive coordination between membrane traf.icking and cytoskeletal dynamics. In plants, the onset of.cytokinesis is characterized by the assembly of.a bipolar microtubule array, the phragmoplast, and of.a transient membrane compartment, the cell plate. Little is known about the coordination between membrane deposition at the cell plate and the dynamics of.phragmoplast microtubules. In this study, we monitor the localization dynamics of.microtubule and membrane markers throughout cytokinesis. Our spatiotemporal resolution is consistent with the general view that microtubule dynamics drive membrane movements. Nonetheless, we provide evidence f.r active sorting at the cell plate and show that this is, at least in part, mediated by the TRAPPII tethering complex. We also characterize phragmoplast microtubule organization and cell plate f.rmation in a suite of.cytokinesis-def.ctive mutants. Of.f.ur mutant lines with def.cts in phragmoplast microtubule organization, only morl microtubule-associated mutants exhibited aberrant cell plates. Conversely, the mutants with the strongest impairment in phragmoplast microtubule reorganization are keule alleles, which have a primary def.ct in membrane f.sion. Our f.ndings identif. the SEC1/Munc18 protein KEULE as a central regulatory node in the coordination of.membrane and microtubule dynamics during plant cytokinesis.

关键词： cytokinesis cell plate phragmoplast microtubule KEULE KNOLLE PLEIADE/MAP65-3

Nanoscale displacement of.the image of.an atomic source of.radiation

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Chinese Optics Letters 2009年第2期7卷 149-151页

作者： Henk f. Arnoldus Department of.Physics and Astronomy Mississippi State University

Light emitted by an atomic source of.radiation appears to travel along a straight line （ray） f.om the location of.the source to the observer in the f.r f.eld. However, when the energy f.ow pattern of.the radiation is resolved with an accuracy better than an optical wavelength, it turns out that the f.eld lines are usually curved. We consider electric dipole radiation, a prime example of.which is the radiation emitted by an atom during an electronic transition, and we show that the f.eld lines of.energy f.ow are in general curves. Near the location of.the dipole, the f.eld lines exhibit a vortex structure, and in the f.r f.eld they approach a straight line. The spatial extension of.the vortex in the optical near f.eld is of.nanoscale dimension. Due to the rotation of.the f.eld lines near the source, the asymptotic limit of.a f.eld line is not exactly in the radially outward direction and as a consequence, the image in the f.r f.eld is slightly shif.ed. This sub-wavelength displacement of.the image of.the source should be amenable to experimental observation with contemporary nanoscale-precision techniques.

关键词： Atoms Electric dipole moments f.ow patterns Nanotechnology Vortex f.ow

Inf.uence of.Processing Parameters on the Strength of.Air Brazed Alumina Joints Using Aluminium Interlayer

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Journal of.Materials Science & Technology 2011年第7期27卷 641-646页

作者： A. Ibrahim f. Hasan Department of.Metallurgical and Materials Engineering University of Engineering and TechnologyLahore Pakistan

Alumina specimens were joined together with thin aluminium interlayer at 750 and 900°C under dif.erent applied pressures and holding time in air. f.exural strength of.the joints was then measured using a standard f.ur-point bend test method. Characterization of.the interf.ce was carried out to correlate the increase in f.exural strength with the applied pressure, holding temperature and time. The study showed that the strength of.joint is af.ected by all three parameters, i.e., processing temperature, holding time as well as applied pressure.

关键词： Pressure-assisted air brazing Alumina Aluminum Brazing Joining and Ceramic