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Photorefractive Effect in Poly(N-vinylcarbazole)-Based Composite Sensitised by C_(60)

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Chinese Chemical Letters 1997年第9期8卷 807-810页

作者： Zhi Jie ZHANG Yi Wang CHEN Yuan Kang HE and Hui Ying CHEN(Institute of polymer science, college of chemistry, peking university, beijing, 100871)Zhi Jian CHEN Shu feng WANG and qi Huang GONG(department of Physics, Mesoscopic Physics Laboratory, peking U Institute of polymer science College of Chemistry Peking University Beijing 100871 China department of Physics Mesoscopic Physics Laboratory Peking University Beijing 100871 China

A new PVK-based photorefractive polymer composite sensitized by C60 and doped with a higher content of EO chromophore was prepared. The high optical quality thin-film was formed between two ITOcovered glass electrodes. Two-beam-coupling (2BC) experiment was performed by using a He-Ne laser (at wavelength 632.8nm), and an obvious photorefractive performance was observed. The dependence of two-beamcoupling gain coefficient on the applied poling dc electric field was measured.

关键词： Photorefractive Effect in Poly Based Composite Sensitised by C N-vinylcarbazole Rev

A stochastic method for convective storm identification,tracking and nowcasting

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Progress in Natural science:Materials International 2008年第12期18卷 1557-1563页

作者： Lei Han~(a,b) Shengxue Fu~a Guang Yang~c Hongqing Wang~b Yongguang Zheng~d Yingjing Lin~b a college of Information science and engineering.Ocean university of china,qingdao 266101,china b department of Atmospheric science,peking university,beijing 100871,china c department of Probability and Statistics,peking university,beijing 100871,china d National Meteorological Center,beijing 100081,china college of Information science and engineering Ocean University of China Qingdao 266101 China department of Atmospheric science Peking University Beijing 100871 China department of Probability and Statistics Peking University Beijing 100871 China National Meteorological Center Beijing 100081 China

The convective storm identification,tracking and nowcasting method is one of the important nowcasting methodologies against severe convective *** severe convective cases,such as storm shape or rapid velocity changes,existing methods are apt to provide unsatisfied storm identification,tracking and nowcasting *** overcome these difficulties,this paper proposes a novel approach to identify,track and short-term forecast (nowcast) of convective storms.A mathematical morphology-based storm identification method is adopted which can identify storm cells accurately in a cluster of *** for the difficult tracking problem,sequential Monte Carlo (SMC) method is utilized to simplify the tracking *** is not only inherently suitable for handling complicated splits and mergers, but also capable of handling the case of storm-missing *** order to provide more accurate forecast of a storm position,this method takes the advantages of the cross-correlation *** qualitative and quantitative evaluations show the efficiency and robustness of the proposed approach.

关键词： Convective storm Doppler radar Nowcasting

Luminescence and energy transfer of Ce^(3+) and Dy^(3+) in BaLaB_9O_(16)

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Chinese Journal of chemistry 1994年第4期12卷 328-333页

作者： HUANG, Xiao-Huadepartment of chemistry, Suzhou Railway Teacher’s college, Suzhou, Jiangsu 215009, chinaGUO, feng-Yudepartment of chemistry, peking university, beijing 100871, china department of chemistry Suzhou Railway Teacher's College Suzhou Jiangsu 215009 China department of chemistry Peking University Beijing 100871 China

Under the excitation of UV light, the composition dependence of luminescence properties of Ce3+ and Dy3+ in BaLaB9O16 has been studied. The mechanisms of energy transfer from Ce3+ to Dy3+ and of concentration quenchin... 详细信息

关键词： Lanthanum cerium dysprosium luminescence energy transfer.

Asymptotic theory for the MLE from randomly censored exponential samples

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Chinese science Bulletin 1998年第13期43卷 1071-1076页

作者： WANG qihua department of Probability and Statistics, peking university, beijing 100871, china department of Probability and Statistics Peking University Beijing China

The MLE of the parameter of the exponential population from the censored observations is considered. The Edgeworth expansions for the Studentized MLE are established by representing the relevant statistic as a U\|statistic plus a remainder. A semiparametric bootstrap method is introduced to the random censored model and the accuracy of bootstrap approximation of the MLE is investigated. Furthermore, it is shown that the MLE is asymptotically minimax efficient.

关键词： maximum likelihood estimate Edgeworth expansion bootstrap approximation asymptotic minimax efficiency law of iterated logarithm.

Oxidative Methylation of Toluene with Methane over Basic Zeolite Catalysts Promoted with Alkali Metal Bromides and Alkali Metal Oxides

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Chinese Chemical Letters 2000年第9期11卷 827-830页

作者： Ling Ping zhou Wei LI Ke Yi TAO Xuan Wen LI He Xuan LI college of chemistry and Molecular engineering, peking university, beijing 100871 department of chemistry, Nankai university, Tianjin 300071 Coll. of Chem. and Molec. Eng. Peking University Beijing 100871 China department of chemistry Nankai University Tianjin 300071 China

The catalytic effects for the oxidative methylation of toluene with methane over the basic zeolite catalysts prepared by promoting KY, KX, KM, KZSM-5 or KP with alkali-metal bromides and alkali-metal oxides have been investigated comparatively. The alkali-metal bromides promoted substrates are more effective than the alkali-metal oxides promoted systems. Moreover, the NaBr promoted systems are more active than KBr promoted systems. The most effective catalytic system (8wt%NaBr)/KZSM-5 gave a toluene conversion as high as 76.3% and a total C-8 selectivity of 76.4% (styrene/ethylbenzene=9.76) resulting in a total C-8 yield of 58.3%.

关键词： styrene methane oxidative methylation alkali-metal oxides alkali-metal bromides

Experimental measurement of growth patterns on fossil corals:Secular variation in ancient Earth-Sun distances

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Chinese science Bulletin 2010年第35期55卷 4010-4017页

作者： ZHANG WeiJia1,3,4,LI ZhengBin2,3 & LEI Yang1 1 department of Physics,peking university,beijing 100871,china 2 department of Electrical engineering and Computer science,peking university,beijing 100871,china 3 State Key Laboratory of Advanced Optical Communication Systems & Networks,peking university,beijing 100871,china 4 Committee of Yuanpei Honors Program,peking university,beijing 100871,china department of Physics Peking University Beijing China State Key Laboratory of Advanced Optical Communication Systems & Networks Peking University Beijing China Committee of Yuanpei Honors Program Peking University Beijing China department of Electrical engineering and Computer science Peking University Beijing China

In recent years,much attention has been given to the increase in the Earth-Sun distance,with the modern rate reported as 5-15 m/cy on the basis of astronomical ***,traditional methods cannot measure the ancient leaving rates,so a myriad of research attempting to provide explanations were met with unmatched *** this paper we consider that the growth patterns on fossils could reflect the ancient Earth-Sun *** mechanical analysis of both the Earth-Sun and Earth-Moon systems,these patterns confirmed an increase in the Earth-Sun *** a large number of well-preserved specimens and new technology available,both the modern and ancient leaving rates could be measured with high precision,and it was found that the Earth has been leaving the Sun over the past 0.53 billion *** Earth's semi-major axis was 146 million kilometers at the beginning of the Phanerozoic Eon,equating to 97.6% of its current *** modern leaving rates are 5-14 m/cy,whereas the ancient rates were much *** results indicate a special expansion with an average expansion coefficient of 0.57H0 and deceleration in the form of Hubble *** the basis of experimental results,the Earth's semi-major axis could be represented by a simple formula that matches fossil measurements.

关键词：地球太阳古代距离生长模式实验石珊瑚量化

polymerIZATION OF p-DIETHYNYLBENZENE INITIATED BY Ni(C≡CC_6H_4C≡CH)_2(PPH_3)_2

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Chinese Journal of polymer science 2001年第3期19卷 303-309页

作者： Mu-jie Yang Xiao-wei Zhan department of polymer science and engineering Zhejiang university Hangzhou 310027, china Present address: Institute of chemistry, Chinese Academy of sciences, beijing 100080, china 浙江大学浙江杭州

Homogeneous polymerization of p-diethynylbenzene initiated by nickel acetylide Ni(C ≡ C C_6H_4 C ≡ CH)_2(PPh_3)_2has been investigated in terms of different solvents, addition agents, atmosphere gases, catalyst concentrations, monomerconcentrations and polymerization temperatures. The yield and catalytic efficiency approach 88% and 11. 1 kg polymer/molNi, respectively, under the optimum conditions: [cat] = 0.01 mol/L, [M] = 1.0 mol/L, NEt_3/cat (mol ratio) = 3～5, 1,4-dioxane/toluene (volume ratio) = 1 and T = 25℃ for 5 h. The polymerization rate equation can be expressed as R_p =k_p[M][cat]~2, where k_p= 0.47 L^2. mol^(-2)·S^(-1) (25℃). The overall polymerization activation energy was found to be203 kJ·mol^(-1). Poly(p-diethynylbenzene) so obtained is soluble in THF, CHCl_3 and toluene with weight-average molecularweights as high as 27, 100 and a rich-trans extended π-conjugated polyene chain structure with pendent groups ofp-C_6H_4C≡CH.

关键词： polymerization p-Diethynylbenzene Nickel acetylide Catalyst

Synthesis and intrinsic blue fluorescence study of hyperbranched poly(ester-amide-ether)

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science china chemistry 2010年第12期53卷 2452-2460页

作者： ZHANG Yong,FU qi & SHI WenFang CAS Key Laboratory of Soft Matter chemistry department of polymer science and engineering,university of science and Technology of china,Hefei 230026,china CAS Key Laboratory of Soft Matter chemistry department of polymer science and engineering University of Science and Technology of China Hefei China

A series of hyperbranched poly(ester-amide-ether)s (H-PEAEs) were synthesized via the A2+CB3 approach by the self-transesterification of ethyl ester-amide-ethers end-capped with three hydroxyl groups and ethyl ester group at two *** molecular structures were characterized with 1H NMR and FT-IR *** number average molecular weights were estimated by GPC analysis to possess bimodal wide distribution from 1.57 to *** strong inherent blue fluorescence was observed at 330 nm for excitation and 390 nm for ***,the emission intensity and fluorescence quantum yield increased along with the incorporated ether chain length,as well as almost linearly with the H-PEAE concentration in an aqueous *** comparing the fluorescence performance,the linear poly(ester-amide-ether) (L-PEAE) and hyperbranched poly(ester-amide) (H-PEA) were *** results showed that the coexistence of ether bond and carboxyl group in the molecular chain was essential for generating the strong ***,the compact backbone of H-PEAE would be propitious to the enhancement of fluorescence properties.

关键词： synthesis self-transesterification hyperbranched poly(ester-amide-ether) fluorescence property

Calculation of traversal time in tunneling by double-wave theory

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Chinese science Bulletin 1998年第9期43卷 723-727页

作者： HUANG Xiangyou department of Physics, peking university, beijing 100871, china department of Physis Peking University Beijing China

Becausethe information contained in a wave function is not enough to describe an individual particle, the suggestion to define the state of a particle by two-wave functions is used. In the double-wave description, a general formula telling the traversal time of a particle in tunneling is obtained. When the double-wave description over an initial parameter is averaged , it reduces to the usual description. Two new relations between the transmission and the reflected coefficients are founded in the new cescription.

关键词： tunneling double-wave theory ensemble.