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991.
用2种硬质合金涂层刀具进行铁基高温合金GH2132的高速干铣削试验,采用电子扫描显微镜(scanning electron microscopy,SEM)观察刀具的磨损形貌,对刀具的主要磨损机理进行了分析.结果表明:刀具的磨损形态主要是后刀面磨损;KC725M涂层由TiN、TiAlN组成,涂层易剥落;KC525M涂层只有1层TiAlN,涂层不易脱落,但由于机械冲击产生沟槽磨损,形成应力集中,导致在切削刃处产生较大的磨损;不论KC525M还是KC725M,涂层剥落后,切削区产生的瞬时高温均使基体中粘结相发生软化,造成硬质相颗粒脱落和基体的剧烈磨损.研究结果可用于指导高速切削刀具材料的设计、合理选用及刀具磨损控制. 相似文献
992.
993.
994.
995.
摘 要 研究目的:从西方经济学的原理出发,通过对我国土地资源配置中市场失灵和政府失灵问题的分 析,寻求在市场和政府的双重作用机制下土地资源高效配置的实现途径。研究方法:文献资料分析法、比 较分析法。研究结果:在市场经济条件下,单纯地依靠市场或政府,不可能实现我国土地资源的优化配置, 必须将二者结合起来,以规划的宏观调控来弥补和矫正市场失灵的缺陷,但是当前的土地利用规划存在失 效的负面影响。研究结论:应该从加强土地利用规划的政府宏观调控与完善土地市场机制两个途径入手, 实现土地资源的高效配置。 相似文献
996.
On the numerical simulation of active scalar, a new explicit algebraic expression on active scalar flux was derived based
on Wikstr?m, Wallin and Johansson model (a
WWJ
model). Reynolds stress algebraic expressions were added by a term to account for the buoyancy effect. The new explicit Reynolds
stress and active scalar flux model was then established. Governing equations of this model were solved by finite volume method
with unstructured grids. The thermal shear stratified cylinder wake flow was computed by this new model. The computational
results are in good agreement with laboratorial measurements. This work is the development on modeling of explicit algebraic
Reynolds stress and scalar flux, and is also a further modification of the a
WWJ
model for complex situations such as a shear stratified flow.
Supported by the National Nature Science Foundation of China (Grant Nos. 50679019, 50009001), the National Basic Research
Program of China (“973” Project) (Grant No. 2008CB418202), the Project of “Six Talent Peak” of Jiangsu Province (08-C), Social
Technology Development Foundation of Jiangsu Province (Grant No. BS2006095) and the “908” Special Foundation of Jiangsu Province
(Grant No. JS-908-02-06) 相似文献
997.
Tao Zhang JunHong Jin DaYong Hu ShengLin Yang Guang Li JianMing Jiang 《中国科学E辑(英文版)》2009,52(4):906-909
The effect of coagulation temperature on the morphology, microstructures and mechanical properties of dihydroxy poly(p-phenylene benzobisoxazole) (DHPBO) fibers was investigated during dry-jet wet-spinning process, in which the coagulation
bath concentration and drawn ratio were kept as 10 wt% of PPA in water and 1.7, respectively. The structures and mechanical
properties of the as-spun DHPBO fibers were characterized by FTIR, XRD, SEM, and single fiber tensile testing. The results
indicated that in PPA/H2O coagulation system, when the coagulation temperature was 25°C, highly crystallized DHPBO as-spun fibers possessing fine
crystallites, circular and smooth morphology, and excellent mechanical properties could be achieved.
Supported by the National Natural Science Foundation of China (Grant No. 50673017), Shanghai Leading Academic Discipline Project
(Grant No. B603) and the Program of Introducing Taleuts of Discipline to University of People’s Republic of China (“111” Program)
(Grant No. 111-2-04) 相似文献
998.
The dynamics of a mechanical system in the Lagrange space yields a set of differential equations of the second order and involves
much less variables and constraints than that described in the state space. This paper presents a so-called Legendre pseudo-spectral
(PS) approach for directly estimating the costates of the Bolza problem of optimal control of a set of dynamic equations of
the second order. Under a set of closure conditions, it is proved that the Karush-Kuhn-Tucker (KKT) multipliers satisfy the
same conditions as those determined by collocating the costate equations of the second order. Hence, the KKT multipliers can
be used to estimate the costates of the Bolza problem via a simple linear mapping. The proposed approach can be used to check
the optimality of the direct solution for a trajectory optimization problem involving the dynamic equations of the second
order and to remove any conversion of the dynamic system from the second order to the first order. The new approach is demonstrated
via two classical benchmark problems.
Supported by the National Natural Science Foundation of China (Grant Nos. 10372039, 10672073), and the Innovation Fund for
Graduate Students of NUAA (Grant No. 4003-019016) 相似文献
999.
Introduction of fluorin into PBO polymer chains: Toward higher thermal stability and lower dielectric constant 总被引:1,自引:0,他引:1
Tao Zhang DaYong Hu JunHong Jin ShengLin Yang Guang Li JianMing Jiang 《中国科学E辑(英文版)》2009,52(1):232-237
A series of novel fluorinated benzoxazole polymers (6FPBO's) with high thermal stability and low dielectric constant were synthesized by copolymerization of 1,3-diamino-4, 6-dihydroxybenzene dihy-drochloride (DAR), 1,4-benzenedicarboxylic acid (PTA) and various amount of 4'4- (hexafluoroisopro-pylidene) bis (benzoic acid) (BIS-B-AF) in the medium of polyphosphoric acid (PPA). 6FPBO fibers were then obtained via dry-jet wet-spinning technique and characterized by means of Fourier transform infrared (FTIR) spectra, thermogravimetric analysis (TGA), single fiber tensile testing machine and scanning electron microscopy (SEM). FTIR spectrum of 6FPBO fibers indicated that the fluorine groups had been incorporated into PBO molecular chains successfully. TGA curves revealed that 6FPBO fibers possessed high thermal stability just as pure PBO fibers. Moreover, dielectric constant spectrum of 6FPBO exhibited that the polymers had low dielectric constant, especially in the range of high- frequency. 相似文献
1000.
Research on indoor experimentation of range SAL imaging system 总被引:1,自引:0,他引:1
GUO Liang XING MengDao ZHANG Long TANG Yu & BAO Zheng State Key Laboratory of Radar Signal Processing Xidian University Xi’an China Xi’an Polytechnic University Xi’an 《中国科学E辑(英文版)》2009,52(10):3098-3104
By means of advantages of both SAR and lidar, the combination of the techniques of (inverse) synthetic aperture and lidar makes it possible to obtain high resolution 2-D image. In this paper, an indoor experimental system of inverse synthetic aperture lidar imaging is given and a processing approach is presented. The given system is in the mode of lidar system with separated receiver and transmitter, which can effectively eliminate the jamming from the lens or/and the intersection between two optic fibers. ... 相似文献