检索结果-南通市图书馆

A general law of human mobility

在线全文

学校读者我要写书评

暂无评论

Science China(Information Sciences) 2015年第10期58卷 24-37页

作者： liang xiao ZHAO JiChang XU Ke Key Laboratory of Technology in Geo-spatial Information Processing and Application System Institute of Electronics Chinese Academy of Sciences School of Economics and Management Beihang University State Key Laboratory of Software Development Environment Beihang University

The intrinsic factors that drive human mobility have remained unclear for decades. Our observations from both intra-urban and inter-urban trips demonstrate a general law of human mobility. Specifically, the probability that a trip will occur is inversely proportional to the size of population located inside a circle with radius equal to the travel distance centered at the trip origin. A simple parameterless rank-based model is presented; this model can predict human flows with a convincing fidelity. Moreover, existing models can be implemented as special cases of our model, suggesting that our model is stable at more spatial scales. Our model also creates a fundamental bridge between individual mobility and social relationships.

关键词： human mobility social mobility general law rank-based model flux prediction

A statistical approach to determine 2D optimal equivalent linear parameters with application to earthquake engineering

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

Earthquake Engineering and Engineering Vibration 2012年第3期11卷 415-425页

作者： Su liang xiao Nan Wang Yi College of Civil Engineering and Architecture Zhejiang University Hangzhou 310058 China China Aviation Planning and Construction Development Co. Ltd Beijing 100120 China

The equivalent linearization method approximates the maximum displacement response of nonlinear structures through the corresponding equivalent linear system. By using the particle swarm optimization technique, a new statistical approach is developed to determine the key parameters of such an equivalent linear system over a 2D space of period and damping ratio. The new optimization criterion realizes the consideration of the structural safety margin in the equivalent linearization method when applied to the performance-based seismic design/evaluation of engineering structures. As an application, equations for equivalent system parameters of both bilinear hysteretic and stiffness degrading single-degree-of- freedom systems are deduced with the assumption of a constant ductility ratio. Error analyses are also performed to validate the proposed approach.

关键词： equivalent linearization particle swarm optimization structural safety nonlinear displacement response performance-based engineering

Rapid Hydrothermal Synthesis of Submillimeter Ultralong Flexible Hydroxyapatite Fiber Using Different pH Regulators

在线全文

学校读者我要写书评

暂无评论

Acta Metallurgica Sinica(English Letters) 2016年第7期29卷 609-613页

作者： Mei-li Qi gui-yong xiao Yu-peng Lu Key Laboratory for Liquid-Solid Structural Evolution and Processing of Materials Ministry of EducationShandong University School of Materials Science and Engineering Shandong University

Hydroxyapatite fiber （HAF） was fabricated via a one-step hydrothermal route by using urea （CA）, acetamide （AA） and propanamide （PA） as pH regulators, respectively, and the reaction time was only 0.5 h. The HAF synthesized by CA as the pH regulator was agglomerated with irregular morphology, while using AA or PA as the pH regulator, the HAF was composed of well-dispersed fibers with lengths larger than 200 pm. Two different morphologies form mainly due to the different hydrolysis rates of the pH regulators. Most of the fibers synthesized by the three pH regulators showed curving appearance, implying their outstanding flexibility. The technique in this paper allows the rapid formation of flexible HAF and may have wider applications in the restorations and reinforcement composites.

关键词： Hydroxyapatite Fiber Hydrothermal PH regulators

Activation of Carbon Dioxide by Gas-phase Metal Species

在线全文

学校读者我要写书评

暂无评论

Chinese Journal of Structural Chemistry 2021年第10期40卷 1385-1403页

作者： LIU Yun-Zhu LI xiao-Na HE Sheng-gui State Key Laboratory for Structural Chemistty of Unstable and Stable Species Institute of ChemistryChinese Academy of SciencesBeijing 100190China University of Chinese Academy of Sciences Beijing 100049China Beijing National Laboratory for Molecular Sciences and CAS Research/Educatiou Center of Excellence in Molecular Sciences Beijing 100190China

Catalytic conversion of carbon dioxide(CO_(2)) into value-added chemicals is an important and active field in both of the condensed-phase and gas-phase studies. This mini-review summarizes a variety of experimentally identified reactions in the activation and transformation of CO_(2) by metal species in the gas phase. The use of advanced mass spectrometric instrumentation in conjunction with quantum chemistry calculations can uncover the mechanistic details and determine the vital factors that control the activation of CO_(2). This review focuses mainly on three topics: the activation of CO_(2) by(1) bare metal ions and metal oxide species,(2) metal hydrides, and(3) other gas-phase metal species. Emphasis is placed on the latest advances in the hydrogenation of CO_(2) mediated with metal hydrides. A potential prospect toward the future effort in the activation and transformation of CO_(2) in gas phase has also been discussed.

关键词： carbon dioxide activation gas-phase metal species mass spectrometry quantum chemistry calculations

Seiberg-Witten/Whitham Equations and Instanton Corrections in N = 2 Supersymmetric Yang-Mills Theory

在线全文

学校读者我要写书评

暂无评论

Communications in Theoretical Physics 2018年第5期69卷 558-568页

作者： Jia-liang Dai En-gui Fan School of Mathematical Science Fudan University Shanghai 200433 China

We obtain the instanton correction recursion relations for the low energy effective prepotential in pure Ν = 2SU(n) supersymmetric Yang-Mills gauge theory from Whitham hierarchy and Seiberg-Witten/Whitham equations. These formulae provide us a powerful tool to calculate arbitrary order instanton corrections coefficients from the perturbative contributions of the effective prepotential in Seiberg-Witten gauge theory. We apply this idea to evaluate one-and two-order instanton corrections coefficients explicitly in SU(n) case in detail through the dynamical scale parameter expressed in terms of Riemann's theta-function.

关键词： Whitham hierarchy Seiberg-Witten/Whitham equations instanton corrections recursion relations

Numerical Study of Propulsion Mechanism for Oscillating Rigid and Flexible Tuna-Tails

在线全文

学校读者我要写书评

暂无评论

Journal of Bionic Engineering 2011年第4期8卷 406-417页

作者： liang Yang Yumin Su Qing xiao State Key Laboratory of Autonomous Underwater Vehicle Harbin Engineering University Harbin 150001 P. R. China Department of Naval Architecture and Marine Engineering University of Strathelyde Glasgow G40LZ United Kingdom

Numerical study on the unsteady hydrodynamic characteristics of oscillating rigid and flexible tuna-tails in viscous flow-field is performed. Investigations are conducted using Reynolds-Averaged Navier-Stokes （RANS） equations with a moving adaptive mesh. The effect of swimming speed, flapping amplitude, frequency and flexure amplitude on the propulsion performance of the rigid and flexible tuna-tails are investigated. Computational results reveal that a pair of leading edge vortices develop along the tail surface as it undergoes an oscillating motion. The propulsive efficiency has a strong correlation with various locomotive parameters. Peak propulsive efficiency can be obtained by adjusting these parameters. Particularly, when input power coeffcient is less than 2.8, the rigid tail generates larger thrust force and higher propulsive efficiency than flexible tail. However, when input power coefficient is larger than 2.8, flexible tail is superior to rigid tail.

关键词： tuna-tail RANS propulsion mechanism hydrodynamic characteristics viscous flow-fields

Crystalline Morphology and Crystallization Characteristics of In-situ Blends of Anionic Polyamide 6 with Noncrystallizable Semiaromatic Polyamide Copolymer

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Chemical Research in Chinese Universities 2007年第3期23卷 360-365页

作者： WANG xiao-chun ZHENG Qiang YANG gui-sheng Department of Polymer Science and Engineering Zhejiang University Hangzhou 310027 P. R. China Key Laboratory of Macromolecular Synthesis and Functionalization Ministry of Education Hangzhou 310027 P. R. China Key Laboratory＇of Engineering Plastics Institute of Chemistry Chinese Academy of Sciences Beijing 100080 P. R. China

A noncrystallizable semiaromatic polyamide copolymer（NSAP） was dissolved in molten caprolactam, and PA6/ NSAP blends were produced in-situ via the anionic ring-opening polymerization of caprolactam. The presence of a single loss tangent（tanS） peak measured by means of dynamic mechanical analysis（DMA） proves the miscibility between PA6 and NSAP in the blends. It was found that there existed drastic changes in the crystallographic form and crystallization kinetics for the in-situ blends, e.g. , when 20% NSAP was added, nearly all crystallites existed in the ,y form and the crystallization could hardly occur upon cooling even at a rate of 2.5 ℃/min. Moreover, cold crystallization appears during the subsequent heating, and its melting point is 40 ℃ lower than that of the virgin system. On the other hand, the size of the spherulites only decreases modestly. It is suggested that the introduction of irregular stiff segments originated from NSAP into PA6 macromolecule chain, which resulted from transamidation during the polymerization play a dominant role in the drastic change of crystallization kinetics and the resultant morphology of the in-situ blends.

关键词： In-situ blend Noncrystallizable polyamide copelymer Anionic polymerization Morphology Crystallization

Reduction of recruitment of Acartia pacifica nauplii from benthic resting eggs due to organochlorine pesticides

在线全文

学校读者我要写书评

暂无评论

Journal of Environmental Sciences 2006年第3期18卷 552-556页

作者： JIANG xiao-dong WANG gui-zhong LI Shao-jing SOA Key Laboratory for Polar Science Polar Research Institute of China Shanghai 200136 China Department of Oceanography State Key Laboratory of Marine Environmental Science Xiamen University Xiamen 361005 China

Many estuarine and coastal planktonic copepods depend on the hatching of benthic resting eggs for recruitment ofnauplii to the water column population. The potential effects of two organochlorine pesticides, hexchloriobinzene （HCH） and dichlorodiphenyltrichloroethane （DDT）, on the recruitment of A ccu＇tla pacifica nauplii from benthic resting eggs in the seabed of Xiamen Bay were experimentally investigated. The abundance of A. pacifica nauplii hatched from the sediment significantly decreased with the increase of pesticide concentration. Trimmed Spearman-Karber analysis gave sediment 96-h LC50 values were 84.81 ng/g for HCH, and 157.94 ng/g for DDT. The median AI （Al50） was -0.77, which suggested that the combined effect of riCH and DDT showed a weak effect than individual effects. There was a positive relationship between mortality and exposure time in DDT treatment, while the relationship was not significant in HCH treatment. The results suggest that organochlorine pesticides can reduce recruitment of A. pacifica nauplii from benthic resting eggs to planktonic population.

关键词： organochlorine pesticide resting egg recruitment A cartia pacifica

Spin Polarization Properties of Na Doped Meridianal Tris（8-Hydroxyquinoline） Aluminum Studied by First Principles Calculations

在线全文

学校读者我要写书评

暂无评论

Chinese Physics Letters 2014年第4期31卷 193-196页

作者： REN Jun-Feng YUAN xiao-Bo HU gui-Chao College of Physics and Electronics Shandong Normal University Jinan 250014

We theoretically investigate the electronic structure and spin polarization properties of Na-doped meridianal tris（S-hydroxyquinoline） aluminum （Alq3） by first principles calculations. It is found that the spin density is distributed mainly in the Alq3 part in the Alq3：Na complex. Electron charge transfer takes place from the Na atom to the Alq3 molecule, which induces asymmetric changing of the molecule bond lengths, thus the spin density distribution becomes asymmetric. Spin polarization of the complex originates from the preferable filling of the spin-split nitrogen and carbon p-orbitals because of the different bond length changes of the Aiq3 molecule upon Na doping.

关键词： SPIN polarization ELECTRONIC structure SODIUM -- Spectra SEMICONDUCTOR doping HYDROXYQUINOLINE CHARGE exchange