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Comparison of dark energy models:A perspective from the latest observational data

中国科学：物理学、力学、天文学英文版 2010年第9期53卷 1631-1645页

作者： LI Miao1,2,LI XiaoDong2,3 & ZHANG Xin1,4 1Kavli Institute for theoretical Physics china,Chinese Academy of sciences,Beijing 100190,china 2Key Laboratory of Frontiers in theoretical Physics,Institute of theoretical Physics,Chinese Academy of sciences,Beijing 100190,china 3.nterdisciplinary center for theoretical study,university of science and technology of china,hefei 2.0026,china 4Department of Physics,College of sciences,Northeastern university,Shenyang 110004,china Kavli Institute for theoretical Physics china Chinese Academy of Sciences Beijing China Key Laboratory of Frontiers in theoretical Physics Institute of Theoretical Physics Chinese Academy of Sciences Beijing China Interdisciplinary center for theoretical study University of Science and Technology of China Hefei China Department of Physics College of Sciences Northeastern University Shenyang China

We compare some popular dark energy models under the assumption of a flat universe by using the latest observational data including the type Ia supernovae Constitution compilation,the baryon acoustic oscillation measurement from the Sloan Digital Sky Survey,the cosmic microwave background measurement given by the seven-year Wilkinson Microwave Anisotropy Probe observations and the determination of H0 from the Hubble Space *** comparison statistics such as the Bayesian and Akaike information criteria are applied to assess the worth of the *** statistics favor models that give a good fit with fewer *** on this analysis,we find that the simplest cosmological constant model that has only one free parameter is still preferred by the current *** other dynamical dark energy models,we find that some of them,such as the αdark energy,constant w,generalized Chaplygin gas,Chevalliear-Polarski-Linder parametrization,and holographic dark energy models,can provide good fits to the current data,and three of them,namely,the Ricci dark energy,agegraphic dark energy,and Dvali-Gabadadze-Porrati models,are clearly disfavored by the data.

关键词： dark energy models observational constraints model comparison information criteria

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BRST quantization and canonical Ward identity of the supersymmetric electromagnetic interaction system

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science china(Physics,Mechanics & Astronomy) 2007年第3期50卷 339-347页

作者： HUANG YongChang1,3,4, JIANG YunGuo1 & LI XinGuo2,3 1 Institute of theoretical Physics, College of Applied sciences, Beijing university of technology, Beijing 100022, china 2 Institute of Modern Physics, Chinese Academy of sciences, Lanzhou 730000, china 3 center of theoretical Nuclear Physics, National Laboratory of Heavy Ion Collisions, Chinese Academy of sciences, Lanzhou 730000, china 4 china center of Advanced science and technology (World Laboratory), Beijing 100080, china Institute of theoretical Physics College of Applied Sciences Beijing University of Technology Beijing China center of theoretical Nuclear Physics National Laboratory of Heavy Ion Collisions Chinese Academy of Sciences Lanzhou China china center of Advanced science and technology (World Laboratory) Beijing China Institute of Modern Physics Chinese Academy of Sciences Lanzhou China

According to the method of path integral quantization for the canonical constrained system in Becchi-Rouet-Stora-Tyutin scheme, the supersymmetric electromagnetic interaction system was quantized. Both the Hamiltonian of the supersymmetric electromagnetic interaction system in phase space and the quantization procedure were simplified. The BRST generator was constructed, and the BRST transforma- tions of supersymmetric fields were gotten; the effective action was calculated, and the generating functional for the Green function was achieved; also, the gauge generator was constructed, and the gauge transformation of the system was ob- tained. Finally, the Ward-Takahashi identities based on the canonical Noether theorem were calculated, and two relations between proper vertices and propaga- tors were obtained.

关键词： supersymmetric electromagnetic interaction BRST quantization Ward identity

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theoretical research progress in new-generation Internet architecture

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science in china(Series F) 2008年第11期51卷 1634-1660页

作者： WU JianPing1,2,3,LIU Ying2,3 & WU Qian2,3 1 Department of Computer science,Tsinghua university,Beijing 100084,china 2 Network Research center,Tsinghua university,Beijing 100084,china 3 Tsinghua National Laboratory for Information science and technology(TNList) ,Beijing 100084,china Department of Computer science Tsinghua University Beijing China Network Research center Tsinghua University Beijing China Tsinghua National Laboratory for Information science and technology (TNList) Beijing China

Internet has become the most important information infrastructure supporting modern socio-economic development, social progress and technological Innovation. Invented 30 years ago, today Internet is facing increasingly severe technical challenges. This paper introduces the progress of the major international newgeneration Internet research plans; analyzes its basic characteristics and the principal contradictions during the development; detsiledly introduces the research carried out by 973 Project ＂Research of Future Internet Architecture＂ on the key scientific issues of new-generation Internet architecture and its latest research results; and looks to the future of the research-focus faced with the new situations of the basic research of new-generation Internet architecture as well as the new demands of innovative applications on Internet architecture.

关键词： new-generation Internet network architecture multi-dimension scalability

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Shell effect and capture cross sections in the synthesis of superheavy nuclei

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science china(Physics,Mechanics & Astronomy) 2009年第10期52卷 1489-1493页

作者： DU SaiSai1,2,BIAN BaoAn1,2,3,LIU Min1,2,4,FENG ZhaoQing5,6 & ZHANG FengShou1,2,6 1 Key Laboratory of Beam technology and Material Modification of Ministry of Education,College of Nuclear science and technology,Beijing Normal university,Beijing 100875,china 2 Beijing Radiation center,Beijing 100875,china 3 School of science,Jiangnan university,Wuxi 214122,china 4 College of Physics and technology,Guangxi Normal university,Guilin 541004,china 5 Institute of Modern Physics,Chinese Academy of sciences,Lanzhou 730000,china 6 center of theoretical Nuclear Physics,National Laboratory of Heavy Ion Accelerator of Lanzhou,Lanzhou 730000,china Key Laboratory of Beam technology and Material Modification of Ministry of Education College of Nuclear Science and Technology Beijing Normal University Beijing China Beijing Radiation center Beijing China School of science Jiangnan University Wuxi China College of Physics and technology Guangxi Normal University Guilin China Institute of Modern Physics Chinese Academy of Sciences Lanzhou China center of theoretical Nuclear Physics National Laboratory of Heavy Ion Accelerator of Lanzhou Lanzhou China

The shell effect is included in the improved isospin dependent quantum molecular dynamics model in which the shell correction energy of the system is calculated by using the deformed two-center shell model. A switch function is introduced to connect the shell correction energy of the projectile and the target with that of the compound nucleus during the dynamical fusion process. It is found that the calculated capture cross sections reproduce the experimental data quantitatively at the energy near the Coulomb barrier. The capture cross sections for reaction 35 80 Br + 82 208 Pb → 117 288 X are also calculated and discussed.

关键词： superheavy nuclei transport theory shell effect cross sections

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A theoretical analysis of optical-to-THz conversion efficiency via optical rectification

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science china(Technological sciences) 2008年第12期51卷 2080-2088页

作者： LI DeHua1,QI XiaoDong2 & LIU ShengGang3 1 Terahertz Institute of Shandong university of science & technology,Qingdao 266510,china 2 Changchun Institute of Optics,Fine Mechanics and Physics,Chinese Academy of sciences,Changchun 130033,china 3 Terahertz research center,Physical Electronics College,university of Electronics science,Chengdu 610054,china Terahertz Institute of Shandong university of science & technology Qingdao China Changchun Institute of Optics Fine Mechanics and Physics Chinese Academy of Sciences Changchun China Terahertz research center Physical Electronics College University of Electronics Science Chengdu China

A theoretical analysis of an ultra-short pulse converted to Terahertz radiation via optical rectification in nonlinear optical crystal is presented here;several factors that affect optical-to-THz conversion efficiencies are discussed;pulse durations affect the conversion efficiency effectively:when crystal length is equal to the optimal crystal length lc,optical-to-THz conversion efficiency is the highest,but for the periodically-inverted electro-optic crystals,conversion efficiency is almost proportional to the crystal length when absorption can be *** account of the absorption of crystals,effective length of crystal is Leff=0.63/α,there is no apparent increase of conversion efficiency and the conversion efficiency approaches to a constant eventually when the crystal length is increased.

关键词： optical rectification periodically inverted effective length conversion efficiency

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Systematic study of survival probability of excited superheavy nuclei

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science china(Physics,Mechanics & Astronomy) 2011年第S1期54卷 109-113页

作者： XIA ChengJun1, SUN BaoXi1, ZHAO EnGuang2,3 & ZHOU ShanGui2,3 1College of Applied sciences, Beijing university of technology, Beijing 100124, china 2Institute of theoretical Physics, Chinese Academy of sciences, Beijing 100190, china 3center of theoretical Nuclear Physics, National Laboratory of Heavy Ion Accelerator, Lanzhou 730000, china College of Applied sciences Beijing University of Technology Beijing China Institute of theoretical Physics Chinese Academy of Sciences Beijing China center of theoretical Nuclear Physics National Laboratory of Heavy Ion Accelerator Lanzhou China

The stability of excited superheavy nuclei (SHN) with 100 Z 134 against neutron emission and fission is investigated by using a statistical model. In particular, a systematic study of the survival probability against fission in the 1n-channel of these SHN is made. The present calculations consistently take the neutron separation energies and shell correction energies from the calculated results of the finite range droplet model which predicts an island of stability of SHN around Z = 115 and N = 179. It turns out that this island of stability persists for excited SHN in the sense that the calculated survival probabilities in the 1n-channel of excited SHN at the optimal excitation energy are maximized around Z = 115 and N = 179. This indicates that the survival probability in the 1n-channel is mainly determined by the nuclear shell effects.

关键词： survival probability superheavy elements island of stability neutron emission fission

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Collision dynamics of He@C_(60)+He@C_(60) at low energies

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science china(Physics,Mechanics & Astronomy) 2008年第7期51卷 765-772页

作者： ZHAO Qiang1,2, ZHANG FengShou1,2,3 & ZHOU HongYu1,2 1 Key Laboratory of Beam technology and Material Modification of Ministry of Education, Institute of Low Energy Nuclear Physics, Beijing Normal university, Beijing 100875, china 2 Beijing Radiation center, Beijing 100875, china 3 center of theoretical Nuclear Physics, National Laboratory of Heavy Ion Accelerator of Lanzhou, Lanzhou 730000, china Key Laboratory of Beam technology and Material Modification of Ministry of Education Institute of Low Energy Nuclear Physics Beijing Normal University Beijing China Beijing Radiation center Beijing China center of theoretical Nuclear Physics National Laboratory of Heavy Ion Accelerator of Lanzhou Lanzhou China

A semi-empirical molecular dynamics model is developed. The central collisions of C60+C60 and He@C60+He@C60 at different incident energies are investigated based on this model. It is found that the dimer structures have been produced at proper incident energies and these fullerene dimers could be formed by a self-assembly of C60 fullerene and He@C60. The He atom has a significant effect at higher incident energy and this embedded He atom can enhance the stability of the dimer structure.

关键词： C60 He@C60 collision molecular dynamics

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Synthesis of superheavy nuclei with ^(238)U target

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science china(Physics,Mechanics & Astronomy) 2009年第10期52卷 1482-1488页

作者： LIU ZuHua1,3 & BAO JingDong2,4 1 Key Laboratory of Beam technology and Material Modification of Ministry of Education,Beijing Normal university,Beijing 100875,china 2 Department of Physics,Beijing Normal university,Beijing 100875,china 3 china Institute of Atomic Energy,Beijing 102413,china 4 center of theoretical Nuclear Physics,National Laboratory of Heavy Ion Accelerator of Lanzhou,Lanzhou 730000,china Key Laboratory of Beam technology and Material Modification of Ministry of Education Beijing Normal University Beijing China china Institute of Atomic Energy Beijing China Department of Physics Beijing Normal University Beijing China center of theoretical Nuclear Physics National Laboratory of Heavy Ion Accelerator of Lanzhou Lanzhou China

The production of superheavy nuclei with Z=108-116 via hot fusion reactions of the neutron-rich projectiles with 238U target is systematically *** results show that the production cross sections of superheavy nuclei do not decrease monotonously as the atomic number Z *** cross sections of the superheavy nuclei at Z = 112 and 115 are enhanced as compared with the whole Z-trend in synthesis of the superheavy nuclei,which clearly illustrates that the reactions with large negative Q-value and shell correction are more favorable to synthesize superheavy nuclei.

关键词： superheavy nuclei fusion reaction cross section 238U target

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Thermal-stress Simulation of Direct-chill Casting of AZ31 Magnesium Alloy Billets

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Journal of Wuhan university of technology(Materials science) 2009年第3期24卷 376-382页

作者：胡红军 College of Materials science and Engineering Chongqing University National Engineering Research center for Magnesium Alloys Chongqing University College of Material science and Engineering Chongqing University of Technology

Two-dimensional （2D） transient coupled finite element model was developed to compute the temperature and stress field in cast billets, so as to predict the defects of the I-type billets made from AZ31 magnesium alloy and find the causes and solutions for surface cracks and shrinkages during direct-chill （DC） casting process. Method of equivalent specific heat was used in the heat conduction equation. The boundary and initial conditions used for primary and secondary cooling were elucidated on the basis of the heat transfer during the solidification of the billet. The temperature and the thermal-stress fields were simulated with the thermal-structural coupled module of ANSYS software. The influences of casting parameters on the distributions of temperature and stress were studied, which helped optimize the parameters （at pouring temperature of 680 ℃, casting speed of 2 min/s, heat-transfer coefficient of the second cooling equals to 5 000 W/m^2.℃^-1）. The simulation results of thermal stress and strain fields reveal the formation mechanism of some casting defects, which is favourable for optimizing the casting parameters and obtain high quality billets. Some measures of controlling processes were taken to prevent the defects for direct-chill casting billets.

关键词： magnesium alloy direct-chill casting temperature and stress fields numerical simulation solidification model

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Shape phase transitions in nuclei:Effective order parameters and trajectories

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science china(Physics,Mechanics & Astronomy) 2011年第S1期54卷 88-97页

作者： ZHANG Yu1,2, HOU ZhanFeng2 & LIU YuXin2,3 1Department of Physics, Liaoning Normal university, Dalian 116029, china 2Department of Physics and the State Key Laboratory of Nuclear Physics and technology, Peking university, Beijing 100871, china 3center of theoretical Nuclear Physics, National Laboratory of Heavy Ion Accelerator, Lanzhou 72.000, china Department of Physics Liaoning Normal University Dalian China Department of Physics and the State Key Laboratory of Nuclear Physics and technology Peking University Beijing China center of theoretical Nuclear Physics National Laboratory of Heavy Ion Accelerator Lanzhou China

We analyze systematically the effective order parameters in nuclear shape phase transition both in experiments and in the interacting boson model. We find that energy ratios and B(E2) ratios can distinguish the first from the second-order phase transition in theory above a certain boson number N (about 50), but in experiments, only those quantities, such as E(L1+)/E(02+) and B(E2; (L+2)1 → L1)/B(E2; 21 → 01), etc., of which the monotonous transitional behavior in the second-order phase transition is broken in the first order phase transition independent of N, are qualified as the effective order parameters. By implementing the originally proposed effective order parameters and the new ones, we find that the isotones with neutron number Nn = 62 are a trajectory of the second order phase transition. In addition, we predict that the transitional behavior of isomer shifts of Xe, Ba isotopes and Nn = 62 isotones is approximately monotonous due to the finiteness of nuclear system.

关键词： nuclear shape phase transition interacting boson model effective order parameter finite particle number effect transition trajectory

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