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941.
在普通物理实验教学中实施创新教育的思考与实践 总被引:3,自引:0,他引:3
文章从转变教学观念,革新教学内容,改革教学方法和成绩考核方法等方面,阐述了笔者对于在高等师范院校普通物理实验教学中实施创新教育的认识和实践情况。 相似文献
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CFD analysis of the HyShot II scramjet combustor 总被引:1,自引:0,他引:1
C. Fureby M. Chapuis E. Fedina S. Karl 《Proceedings of the Combustion Institute》2011,33(2):2399-2405
The development of novel air-breathing engines such as supersonic combustion ramjets (scramjets) depends on the understanding of supersonic mixing, self-ignition and combustion. These aerothermochemical processes occur together in a scramjet engine and are notoriously difficult to understand. In the present study, we aim at analyzing the HyShot II scramjet combustor mounted in the High Enthalpy Shock Tunnel Göttingen (HEG) by using Reynolds Averaged Navier Stokes (RANS) and Large Eddy Simulation (LES) models with detailed and reduced chemistry. To account for the complicated flow in the HEG facility a zonal approach is adopted in which RANS is used to simulate the flow in the HEG nozzle and test-section, providing the necessary inflow boundary conditions for more detailed RANS and LES of the reacting flow in the HyShot combustor. Comparison of predicted wall pressures and heat fluxes with experimental data show good agreement, and in particular does the LES agree well with the experimental data. The LES results are used to elucidate the flow, mixing, self-ignition and subsequent combustion processes in the combustor. The combustor flow can be separated into the mixing zone, in which turbulent mixing from the jet-in-cross flow injectors dominates, the self-ignition zone, in which self-ignition rapidly takes place, and the turbulent combustion zone, located towards the end of the combustor, in which most of the heat release and volumetric expansion takes place. Self-ignition occurs at some distance downstream of the injectors, resulting in a distinct pressure rise further downstream due to the volumetric expansion as observed in the experiments. The jet penetration is about 30% of the combustor height and the combustion efficiency is found to be around 83%. 相似文献
946.
Dynamics of polymers in mixed solvents are investigated on the basis of linear response theory and mean field arguments. Particular attention is given to the coupling between polymer and fluid fluctuations. This coupling is enhanced by polymer–solvent interaction asymmetry and mixed solvent incompatibility. Cooperative and fluid diffusion constants are analyzed in terms of the interactions in the medium and some predictions for light scattering experiments are made. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3976–3980, 2004 相似文献
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Shu-xin Huang Chuan-jing Lu Department of Engineering Mechanics Shanghai Jiao Tong University Shanghai China 《高分子科学》2006,(6):609-617
The theoretical characterizations on the triangular-form thixotropy-loop tests of an LDPE melt (PE-FSB-23D022/Q200) were conducted in the present paper by using a new thixotropy model, which is constituted by the upper convected Maxwell model and a rate-type kinetic equation. The new thixotropic Maxwell model can partially describe well three reported thixotropy-loop experiments by comparison with the previous calculations of the variant form of the thixotropy-type Huang model. It is noted that the stress deviations between the experiments and the predictions of the new thixotropic Maxwell model are much slighter than those deviations obtained by using the variant Huang model at the same condition, although both models include five parameters. The constitution of the new thixotropic Maxwell model is more reasonable than that of the variant Huang model. 相似文献
949.
K. Moshirvaziri 《Journal of Optimization Theory and Applications》1998,98(1):83-108
This paper presents a method for constructing test problems with known global solutions for concave minimization under linear constraints with an additional convex constraint and for reverse convex programs with an additional convex constraint. The importance of such a construction can be realized from the fact that the well known d.c. programming problem can be formulated in this form. Then, the method is further extended to generate test problems with more than one convex constraint, tight or untight at the global solution. 相似文献
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R. C. M. Brekelmans L. T. Driessen H. J. M. Hamers D. den. Hertog 《Journal of Optimization Theory and Applications》2005,126(3):529-551
In this paper, we analyze different schemes for obtaining gradient estimates when the underlying functions are noisy. Good gradient estimation is important e.g. for nonlinear programming solvers. As error criterion, we take the norm of the difference between the real and estimated gradients. The total error can be split into a deterministic error and a stochastic error. For three finite-difference schemes and two design of experiments (DoE) schemes, we analyze both the deterministic errors and stochastic errors. We derive also optimal stepsizes for each scheme, such that the total error is minimized. Some of the schemes have the nice property that this stepsize minimizes also the variance of the error. Based on these results, we show that, to obtain good gradient estimates for noisy functions, it is worthwhile to use DoE schemes. We recommend to implement such schemes in NLP solvers.We thank our colleague Jack Kleijnen for useful remarks on an earlier version of this paper and Gül Gürkan for providing us with relevant literature. Moreover, we thank the anonymous referee for valuable remarks. 相似文献