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71.
72.
超分子构筑调控合成结构规整的梯形聚合物及其应用研究 总被引:1,自引:1,他引:0
综述了"超分子构筑调控的逐步偶联/聚合法",该方法将高分子化学与超分子化学相结合,利用多种类型的超分子弱键协同作用首先构筑预期的梯形超分子结构,再经聚合得到共价键梯形高分子.利用该方法合成了一系列结构规整的氧桥基和有机桥基梯形聚硅氧烷以及碳基梯形聚酯,并利用侧基间π-π叠加作用实现了对聚合物立体构型控制.扼要介绍了梯形聚合物在先进材料方面的应用,例如梯形聚硅氧烷液晶光致取向膜;由梯形聚硅氧烷合成的管状聚硅氧烷在高室温储存期微电子环氧塑封料方面的应用;以及基于梯形聚硅氧烷的拟筛板聚合物在二阶非线性光学材料方面的应用等. 相似文献
73.
There is an increasing demand to produce injection molded thermoplastic parts with high performance and more uniform microstructure. In this study, an injection mold with dynamic mold temperature control was developed to create a thermo-mechanical environment in which a high mold temperature and slow cooling rate were retained. Two-dimensional wide angle X-ray diffraction (2D-WAXD) and polarized optical microscopy (POM) studies were carried out to investigate the morphological distribution of isotactic polypropylene (iPP) through the depth. Due to the fast relaxation of polymer chains at a high temperature, the macroscopic orientated structure of iPP in conventional injection molding was eliminated, that is transited from the hierarchical morphology distribution to a more homogeneous formation. A homogeneous appearance without layer boundary was shown and many radial spherulites with loosely packed lamellae distributed uniformly throughout the sample. 相似文献
74.
This paper presents a novel non-contact method for evaluating the resonant frequency of a microstructure, Firstly, the microstructure under test is excited by ultrasonic waves. This excitation method does not impose any undefined load on the specimen like the electrostatic excitation and also this is the first actual use of ultrasonic wave for exciting a microstructure in the literature. Secondly, the amplitudes of the microstructure are determined by image edge detection using a Mexican hat wavelet transform on the vibrating images of the microstructure. The vibrating images are captured by a CCD camera when the microstructure is vibrated by ultrasonic waves at a series of discrete high frequencies (〉30 kHz). Upon processing the vibrating images, the amplitudes at various excitation frequencies are obtained and an amplitude-frequency spectrum is obtained from which the resonant frequency is subsequently evaluated. A micro silicon structure consisting of a perforated plate (192 × 192 μm) and two cantilever beams (76 × 43 μm) which is about 4 μm thickness is tested. Since laser interferometry is not required, thermal effects on a test object can be avoided. Hence, the setup is relatively simple. Results show that the proposed method is a simple and effective approach for evaluating the dynamic characteristics of microstructures. 相似文献
75.
76.
Sebastian Schlund Eline M. Basílio Janke Klaus Weisz Bernd Engels 《Journal of computational chemistry》2010,31(4):665-670
This study investigates how the various components (method, basis set, and treatment of solvent effects) of a theoretical approach influence the relative energies between keto and enol forms of acetylacetone, which is an important model system to study the solvent effects on chemical equilibria from experiment and theory. The computations show that the most popular density functional theory (DFT) approaches, such as B3LYP overestimate the stability of the enol form with respect to the keto form by ~10 kJ mol?1, whereas the very promising SCS‐MP2 approach is underestimating it. MP2 calculations indicate that in particular the basis set size is crucial. The Dunning Huzinaga double ζ basis (D95z(d,p)) used in previous studies overestimates the stability of the keto form considerably as does the popular split‐valence plus polarization (SVP) basis. Bulk properties of the solvent included by continuum approaches strongly stabilize the keto form, but they are not sufficient to reproduce the reversal in stabilities measured by low‐temperature nuclear magnetic resonance experiments in freonic solvents. Enthalpic and entropic effects further stabilize the keto form, however, the reversal is only obtained if also molecular effects are taken into account. Such molecular effects seem to influence only the energy difference between the keto and the enol forms. Trends arising due to variation in the dielectric constant of the solvent result from bulk properties of the solvent, i.e., are already nicely described by continuum approaches. As such this study delivers a deep insight into the abilities of various approaches to describe solvent effects on chemical equilibria. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010 相似文献
77.
The microstructure, hardness and corrosion resistance of commercially pure Ti treated by low energy high current pulsed electron beam (LEHCPEB) have been investigated. The thin near-surface melted layer rapidly solidified into β and subsequently transformed into ultrafine α′ martensite. This has led to a drastic improvement of the corrosion properties and a significant increase (more than 60%) in hardness of the top surface. 相似文献
78.
Longlong YangPing Shen Qiaoli LinFeng Qiu Qichuan Jiang 《Applied Surface Science》2011,257(14):6276-6281
The isotherm wetting and spreading behaviors of the molten Cu-Cr alloys with 0.5, 1.0 and 2.0 at.% Cr on porous graphite substrates were investigated at 1373 K in a flowing Ar atmosphere using a modified sessile drop method. The wettability improves with increasing Cr content in the alloy as a result of phase transition from Cr3C2 to more wettable and metallic-like Cr7C3 developed at the interface. The spreading kinetics are controlled by the interfacial reaction in the early stage and the diffusion of Cr from the drop bulk to the triple junction in the later stage together with a transition in the intermediate stage. 相似文献
79.
Ferritic/martensitic (F/M) steels are good candidate structural materials for the future fusion reactors and spallation sources. However, irradiation of steels is known to produce hardening, loss of ductility, shift in ductile to brittle transition temperature (DBTT) and reduction of fracture toughness and creep resistance starting at low doses. Helium (He), produced by transmutation during the irradiation, also impacts mechanical properties. Numerous experimental and theoretical studies on the evolution of the microstructure of steels under irradiation have been conducted until now. We review the effect of irradiation-induced point defects and in particular of He on the mechanical properties of F/M steels. To cite this article: R. Schäublin et al., C. R. Physique 9 (2008). 相似文献
80.
Multistage stochastic programs with interstage independent random parameters have recourse functions that do not depend on
the state of the system. Decomposition-based algorithms can exploit this structure by sharing cuts (outer-linearizations of
the recourse function) among different scenario subproblems at the same stage. The ability to share cuts is necessary in practical
implementations of algorithms that incorporate Monte Carlo sampling within the decomposition scheme. In this paper, we provide
methodology for sharing cuts in decomposition algorithms for stochastic programs that satisfy certain interstage dependency
models. These techniques enable sampling-based algorithms to handle a richer class of multistage problems, and may also be
used to accelerate the convergence of exact decomposition algorithms.
Research leading to this work was partially supported by the Department of Energy Contract DE-FG03-92ER25116-A002; the Office
of Naval Research Contract N00014-89-J-1659; the National Science Foundation Grants ECS-8906260, DMS-8913089; and the Electric
Power Research Institute Contract RP 8010-09, CSA-4O05335.
This author's work was supported in part by the National Research Council under a Research Associateship at the Naval Postgraduate
School, Monterey, California. 相似文献