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Uncertainty in magnetic activity indices

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Science china(Technological Sciences) 2008年第10期51卷 1659-1664页

作者： XU WenYao institute of Geology and geophysics, Chinese Academy of Sciences, beijing 100029, china institute of Geology and geophysics Chinese Academy of Sciences

Magnetic activity indices are widely used in theoretical studies of solar-terrestrial coupling and space weather prediction. However, the indices suffer from various uncertainties, which limit their application and even mislead to incorrect conclu-sion. In this paper we analyze three most popular indices, Kp, AE and Dst. Three categories of uncertainties in magnetic indices are discussed: "data uncertainty" originating from inadequate data processing, "station uncertainty" caused by in-complete station covering, and "physical uncertainty" stemming from unclear physical mechanism. A comparison between magnetic disturbances and related indices indicate that the residual Sq will cause an uncertainty of 1―2 in K meas-urement, the uncertainty in saturated AE is as much as 50%, and the uncertainty in Dst index caused by the partial ring currents is about a half of the partial ring cur-rent.

关键词： magnetic activity indices Kp AE Dst solar-terrestrial coupling space weather

Density functional theory study of the reaction paths of reactions of CH3C（O）O2 radicals with HO2 in the gas phase

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Progress in Natural Science:Materials International 2006年第12期16卷 1269-1274页

作者： ZHOU Yuzhi~ 1,2 , ZHANG Shaowen~1 and LI Qianshu~1**(1. State Key Laboratory of Explosion Science and Technology, beijing institute of Technology, beijing 100081, china 2. beijing institute of Education, beijing 100044, china) State Key Laboratory of Explosion Science and Technology Beijing Institute of Technology Beijing 100081 China beijing institute of Education Beijing 100044 China

A DFT study on the reactions between CH_3C（O）O_2and HO_2radicals has been carried out. It is suggested that both the triplet and singlet potential surfaces involve a complex mechanism with the formation of loosely bound intermediate complexes of reactants and products. The reaction prefers to occur on the triplet surface to produce peracetic acid (CH_3C（O）O_2H) and triplet O_2molecule. The CH_3C（O）O_2H can further convert into CH_3C（O）O and HO radicals.

关键词： acetyl peroxy radicals HO2 radicals reaction mechanism DFT.

Synthesis of SiC/Al Co-Continuous Composite by Spontaneous Melt Infiltration

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Journal of Materials Science & Technology 2000年第5期16卷 466-470页

作者： Guangwei HAN and Di FENG (Central Iron & Steel Research institute, beijing 100081, china) Central Iron and Steel Research institute Beijing 100081 China

Investigation has been made on the process of synthesizing SiC/Al co-continuous composite by spontaneous melt infiltration. It is found that nitrogen atmosphere is an indispensable factor for spontaneous infiltration of melt Al into SiC preform with continuous porosity. The critical temperature for spontaneous infiltration occurrence can be lowered and spontaneous infiltration rate increased by doping a small amount of Mg into the Al alloy. Adding fine SiO2 powders into the ceramic preform can play the similar role as Mg-doping by increasing wetting through the chemical reaction of 3SiO2+4AI=2Al2O3+3Si at the infiltration front. Infiltration rate can also be increased by Si-doping to lower the viscosity of the molten Al alloy. In addition, sufficient Si content in the molten Al is also indispensable to avoid the formation of Al4C in the synthesized composite.

关键词： Co SiC Synthesis of SiC/Al Co-Continuous Composite by Spontaneous Melt Infiltration Al

On the fluorescence of C_60 at room temperature

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Science china(Physics,Mechanics & Astronomy) 2010年第1期53卷 95-99页

作者： ZHANG Fang & ZHANG XiaoLing Department of Chemistry, beijing institute of Technology, beijing 100081, china beijing institute of Technology Department of Chemistry Beijing China (GRID:grid.43555.32) (ISNI:***)

The fluorescence properties of C 60 in different organic solvents have been investigated at room temperature. Three fluorescence emission centers are discovered and ascribed to different aggregations of C 60 in solvent. A series of blue fluorescence peaks centered at 440 nm derive from C 60 nanoparticles; a distinctive yellow-green fluorescence band in 575 nm region arises from the aggregates of C 60 nanoparticles; a more informative salmon fluorescence band around 700 nm originates from C 60 microcrystals. And the distinct configurations of C 60 aggregations are closely associated with the characteristic interaction between C 60 and solvent molecules.

关键词： C 60 fluorescence TEM confocal fluorescence spectroscopy

Oscillatory periodic solutions of differential-delay equations with multiple lags

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Chinese Science Bulletin 1997年第6期42卷 444-447页

作者： GE WeigaoDepartment of Applied Mathematics, beijing institute of Technology, beijing 100081, china Department of Applied Mathematics Beijing Institute of Technology Beijing China

BASED on the Nussbaum’s results, we studied in ref. [2] the conditions for the existence of oscillatory periodic solutions to the differential-delay equations (DDEs)

关键词： differential-delay equation periodic solution multiple lags.

Arabian Peninsula-North Pacific Oscillation and its association with the Asian summer monsoon

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Science china Earth Sciences 2008年第7期51卷 1001-1012页

作者： SUN JianQi1, YUAN Wei2 & GAO YuZhong3 1 Nansen-Zhu International Research Centre, institute of Atmospheric Physics, Chinese Academy of Sciences, beijing 100029, china 2 china Meteorological administration Training Centre, beijing 100081, china 3 Heilongjiang Meteorological Observatory, Harbin 150030, china Nansen-Zhu International Research Centre Institute of Atmospheric Physics Chinese Academy of Sciences Beijing China china Meteorological administration Training Centre Beijing China Heilongjiang Meteorological Observatory Harbin China

Using correlation and EOF analyses on sea level pressure from 57-year NCEP-NCAR reanalysis data, the Arabian Peninsula-North Pacific Oscillation (APNPO) is identified. The APNPO reflects the co-variability between the North Pacific high and South Asian summer monsoon low. This teleconnec- tion pattern is closely related to the Asian summer monsoon. On interannual timescale, it co-varies with both the East Asian summer monsoon (EASM) and South Asian summer monsoon (SASM); on decadal timescale, it co-varies with the EASM: both exhibit two abrupt climate changes in the middle 1960s and the late 1970s respectively. The possible physical process for the connections between the APNPO and Asian summer monsoon is then explored by analyzing the APNPO-related atmospheric circulations. The results show that with a strong APNPO, the Somali Jet, SASM flow, EASM flow, and South Asian high are all enhanced, and an anomalous anticyclone is produced at the upper level over northeast china via a zonal wave train. Meanwhile, the moisture transportation to the Asian monsoon regions is also strengthened in a strong APNPO year, leading to a strong moisture convergence over India and northern china. All these changes of circulations and moisture conditions finally result in an anoma- lous Asian summer monsoon and monsoon rainfall over India and northern china. In addition, the APNPO has a good persistence from spring to summer. The spring APNPO is also significantly corre- lated with Asian summer monsoon variability. The spring APNPO might therefore provide valuable in- formation for the prediction of Asian summer monsoon.

关键词： Arabian Peninsula-North Pacific Oscillation East Asian summer monsoon South Asian summer monsoon wave train abrupt climate change

Void damage model and service life prediction for solid high polymer

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Chinese Science Bulletin 2001年第21期46卷 1842-1845页

作者： SHEN TingfangDepartment of Applied Physics, beijing institute of Technology, beijing 100081, china Department of Applied Physics Beijing Institute of Technology Beijing China

Based on the analysis of three void damage variety models, this note presents (i) a method that regards the void content as a damage variation of the grain and (ii) a geometric model for micro-unit of void damage. Equations of the void damage variety containing void content are analyzed. This work is focused on the measurement of internal damage level and the damage variety estimation is directly related to the life predication in the practical engineering applications. Nowadays, the critical service life of the solid grain/polymers is usually presumed at domestic and international level. The strength or strain reduction of 20% or the stabilizer consumption of 50% is generally regarded as a critical storage life of the solid grain/polymers, and the service life is predicted by the extrapolation method on An-henius formula. The applications, however, show that the above method is unreliable and has significant errors. With the aid of the discontiguous automatic measuring device of real time volume

关键词： void content void damage thermal aging service life damage mechanics.

Lie symmetry and conservation law of Birkhoffian system

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Chinese Science Bulletin 1999年第4期44卷 318-320页

作者： MEI FengxiangDepartment of Applied Mechanics , beijing institute of Technology, beijing 100081, china Department of Applied Mechanics Beijing Institute of Technology Beijing China

The Lie symmetry of Birkhoffian system was studied, the condition under which the system admits the one-parameter Lie group of transformation with infinitesimal generator was given, and the structural equation and the... 详细信息

关键词： symmetry conservation law Birknoffian system.

Structures and aromaticity of the planar Al_2P_2^(n-) (n=1―4) clusters

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Science china Chemistry 2009年第12期52卷 2237-2242页

作者： XU WenGuo,ZHANG YuanChun & ZHAI Lei institute of Chemical Physics,beijing institute of Technology,beijing 100081,china institute of Chemical Physics Beijing Institute of Technology Beijing China

Clusters Al2P2n-(n = 1―4) were theoretically investigated using density functional theory (DFT) methods at the B3LYP/6-311+G* and B3PW91/6-311+G* levels of theory. The calculated results showed that the planar structure (D2h symmetry) of Al2P2n-(n = 1―4) species was the global minimum. And the negative nucleus-independent chemical shift (NICS) value of Al2P2n-(n = 1―4) species indicated the existence of a ring current in the planar structure (D2h symmetry). A detailed molecular orbital (MO) analysis revealed that the planar structures (D2h symmetry) had π aromaticity,which further exhibited the strongly aromatic character for Al2P2n-(n = 1―4) species.

关键词： DFT calculation geometric structure nucleus-independent chemical shift molecular orbital