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181.
Bai-suo JIN~ 《中国科学A辑(英文版)》2007,50(9):1303-1315
In the factor analysis model with large cross-section and time-series dimensions,we pro- pose a new method to estimate the number of factors.Specially if the idiosyncratic terms satisfy a linear time series model,the estimators of the parameters can be obtained in the time series model. The theoretical properties of the estimators are also explored.A simulation study and an empirical analysis are conducted. 相似文献
182.
本文采用解析的方法计算了应变Si1-xGex层中p型杂质电离度与Ge组分x、温度T以及掺杂浓度N的关系.发现常温时,在同一Ge组分下,随着掺杂浓度的升高,杂质的电离度的先变小,而后又迅速上升到1.在同一掺杂浓度下,轻掺杂时,杂质的电离度随Ge组分的增加先变大,而后几乎不变;重掺杂时,杂质电离能变为0后,杂质电离度为1.低温下,轻掺杂时,载流子低温冻析效应较为明显,杂质的电离度普遍较小,当掺杂浓度大于Mott转换点时,载流子冻析效应不再明显,电离率迅速上升到1.在同一Ge组分下,随着掺杂浓度的升高,杂质的电离度先变小,后变大,而后又迅速上升到1.在同一掺杂浓度下,轻掺杂时,杂质的电离度随Ge组分的增加变大;重掺杂时,杂质电离能变为0后,杂质电离度为1. 相似文献
183.
Wei Mingjun Zhu Wanzhen 《Annals of Differential Equations》2007,23(4):511-518
In this paper we consider the system of classical particles coupled with a Klein-Gordon field in two dimensions.We establish a-priori-bounds on the solutions of this system with initial data satisfying a size restriction derived from conservation of energy.This result,together with the smoothing of"velocity averaging",yields the existence of global weak solutions to the corresponding restricted initial value problem.The size restriction is necessary since energy of the system is indefinite.Finally,we show that the weak solutions preserve the total mass. 相似文献
184.
185.
Xiao‐Hui Liu Yan‐Guo Li Ying Lin Yue‐Sheng Li 《Journal of polymer science. Part A, Polymer chemistry》2007,45(7):1272-1281
The reversible addition–fragmentation chain transfer (RAFT) polymerization of acrylonitrile (AN) mediated by 2‐cyanoprop‐2‐yl dithiobenzoate was first applied to synthesize polyacrylonitrile (PAN) with a high molecular weight up to 32,800 and a polydispersity index as low as 1.29. The key to success was ascribed to the optimization of the experimental conditions to increase the fragmentation reaction efficiency of the intermediate radical. In accordance with the atom transfer radical polymerization of AN, ethylene carbonate was also a better solvent candidate for providing higher controlled/living RAFT polymerization behaviors than dimethylformamide and dimethyl sulfoxide. The various experimental parameters, including the temperature, the molar ratio of dithiobenzoate to the initiator, the molar ratio of the monomer to dithiobenzoate, the monomer concentration, and the addition of the comonomer, were varied to improve the control of the molecular weight and polydispersity index. The molecular weights of PANs were validated by gel permeation chromatography along with a universal calibration procedure and intrinsic viscosity measurements. 1H NMR analysis confirmed the high chain‐end functionality of the resultant polymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1272–1281, 2007 相似文献
186.
Crosslinking behaviors of acrylonitrile butadiene rubber (NBR)/poly (vinyl chloride) (PVC) alloy, filled with anhydrous copper sulfate (CuSO4) particles, were investigated for the first time by dynamic mechanical analysis (DMA) under hetero and isothermal modes, respectively. In the heterothermal testing, (NBR/PVC)/CuSO4 compound showed two marked increases in the storage modulus (E′), corresponding to coordination crosslinking of NBR-CuSO4 and self-crosslinking of NBR and PVC respectively. During the isothermal testing, a dramatic increase in E′ was found at the initial stage while that of original NBR/PVC alloy was not detected. The marked increase in E′ of (NBR/PVC)/CuSO4 compound was mainly due to the crosslinking induced by coordination between CN and Cu2+. The increasing extent of E′ increased with the rise of CuSO4 content, suggesting the formation of a greater number of crosslinks. Moreover, the activation energy (Ea) of crosslinking process was about 139 kJ/mol. In this work, fourier transform infrared spectrum (FT-IR) and equilibrium swelling method were also performed for the characterization of the compound. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 41–51, 2007 相似文献
187.
In this paper a class of impulsive differential inclusions is investigated. The existence of solution bundle is proved. And we also construct a nonlinear semigroup of operators on cb(E) (closed-bounded subset of E) to describe the set of attainable states. 相似文献
188.
Tracy Huziak‐Clark Stephen J. Van Hook Julie Nurnberger‐Haag Lena Ballone‐Duran 《School science and mathematics》2007,107(8):311-324
This article focuses on the impact a collaborative project between university graduate fellows and K‐12 classroom teachers had on improved pedagogy in the classroom and in the future at the university. Nine teams participated in a yearlong professional development project to improve pedagogy and communication skills of the participants. This study shows that the participants, the fellows and the K‐12 teacher partners, made changes in planning, implementation, and even motivation for using inquiry‐based methods in their classroom. External observations of the teams further support the individuals' claims of improved pedagogy using inquiry and impact on student conceptual understanding. The Horizon Classroom Observation instrument was used for these observations. The teams showed an overall increase in scores, as well as overall effective and exemplarily implementation of their planning. The program design, the implementation, and the results of this three‐year study will be elaborated in this article. 相似文献
189.
190.
In this paper, we discuss the local and global existence ofweak solutions for some hyperbolicparabolic systems modellingchemotaxis. 相似文献