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Uncertainty in crossing time of 2 °C warming threshold over China

Science Bulletin 2016年第18期61卷 1451-1459页

作者： Xiaolong chen Tianjun Zhou State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics Institute of Atmospheric Physics Chinese Academy of SciencesBeijing 100029 China

The 2 ℃ warming target has been used widely in global and regional climate change research. Previous studies have shown large uncertainties in the time when surface air temperature （SAT） change over China will reach 2℃ rela- tive to the pre-industrial era. To understand the uncertainties, we analyzed the projected SAT in the twenty-first century using 40 state-of-the-art climate models under two Repre- sentative Concentration Pathways （RCP4.5 and RCPS.5） from the Coupled Model Intercomparison Project Phase 5. The 2℃ threshold-crossing time （TCT） of SAT averaged across China was around 2033 and 2029 for RCP4.5 and RCP8.5, respectively. Considering a 4-1o- range of inter- model SAT change, the upper and lower bounds of the 2 ℃ TCT could differ by about 25 years or even more. Uncer- tainty in the projected SAT and the warming rate around the TCT are the two main factors responsible for the TCT uncertainty. The former is determined by the climate sensi- tivity represented by the global mean surface temperature response. About 45 % of the intermodel variance of the projected 2 ~C TCT for averaged SAT over China can be explained by climate sensitivity across the models, which is contributed mainly by central and southern China. In a cli- mate more sensitive to CO2 forcing, stronger greenhouse effect, less stratus cloud over the East Asian monsoon region, and less snow cover on the Tibetan Plateau result in increased downward longwave radiation, increased shortwave radia- tion, and decreased shortwave radiation reflected by the surface, respectively, all of which may advance the TCT.

关键词： 2 °C threshold Projection uncertainty China region CMIP5 Climate sensitivity

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FlexCore: Dynamic Virtual Machine Scheduling Using VCPU Ballooning

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Tsinghua Science and Technology 2015年第1期20卷 7-16页

作者： Tianxiang Miao Haibo chen Institute of Parallel And Distributed System (IPADS) the School of SoftwareShanghai Jiao Tong University

As multi-core processors become the de-facto configuration in modern computers, the adoption of SMP Virtual Machines（VMs） has been increasing, allowing for more efficient use of computing resources. However,because of existence of schedulers in both the hypervisor and the guest VMs, this creates a new research problem,viz., double scheduling. Although double scheduling may cause many issues including lock-holder preemption,v CPU stacking, CPU fragmentation, and priority inversion, prior approaches have either introduced new problems and/or addressed the problem incompletely. In this paper, we describe the design and implementation of Flex Core,a new scheduling scheme using v CPU ballooning, which dynamically adjusts the number of v CPUs of a VM at runtime. This essentially eliminates unnecessary scheduling in the hypervisor layer, and thus, boosts performance significantly. An evaluation using a complete KVM-based implementation shows that the average performance improvement for PARSEC applications on a 12-core Intel machine is approximately 52.9%, ranging from 35.4% to79.6%.

关键词： virtualization SMP virtual machine multicore processor vCPU ballooning

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ENSEMBLE OF MULTIPLE kNN CLASSIFIERS FOR SOCIETAL RISK CLASSIFICATION

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Journal of Systems Science and Systems Engineering 2017年第4期26卷 433-447页

作者： Jindong chen Xijin Tang Academy of Mathematics and Systems Science Chinese Academy of SciencesBeijing 100190 P.R. China China Aerospace Academy of Systems Science and Engineering Beijing 100048 P.R. China

Societal risk classification is a fundamental and complex issue for societal risk perception. To conduct societal risk classification, Tianya Forum posts are selected as the data source, and four kinds of representations： string representation, term-frequency representation, TF-IDF representation and the distributed representation of BBS posts are applied. Using edit distance or cosine similarity as distance metric, four k-Nearest Neighbor （kNN） classifiers based on different representations are developed and compared. Owing to the priority of word order and semantic extraction of the neural network model Paragraph Vector, kNN based on the distributed representation generated by Paragraph Vector （kNN-PV） shows effectiveness for societal risk classification. Furthermore, to improve the performance of societal risk classification, through different weights, kNN-PV is combined with other three kNN classifiers as an ensemble model. Through brute force grid search method, the optimal weights are assigned to different kNN classifiers. Compared with kNN-PV, the experimental results reveal that Macro-F of the ensemble method is significantly improved for societal risk classification.

关键词： Societal risk classification Tianya Forum k-Nearest Neighbor ensemble Paragraph Vector

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Influence of thermal-decomposition temperatures on structures and properties of V2O5 as cathode materials for lithium ion battery

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Progress in natural Science:Materials International 2015年第1期25卷 42-46页

作者： Yu chen cheng chen Wei chen Heng Liu Jianguo Zhu School of Aeronautics and Astronautics Sichuan University chengdu University of Information and Technology Beijing Beiji Mechanical & Electric Industry Co. Ltd College of Materials Science and Engineering Sichuan University

Submicron spherical V2O5 particles with a uniform size and a lower crystallinity were successfully synthesized by a chemical precipitationthermal decomposition technique using the commercial V2O5 powders as starting material. The crystal structure and grain morphology of samples were characterized by X-ray diffraction(XRD) and scanning electron microscopy(SEM), respectively. Electrochemical testing such as discharge–charge cycling(CD) and cyclic voltammetry(CV) were employed in evaluating their electrochemical properties as cathode materials for lithium ion battery. Results reveal that the crystallinity and crystalline size of V2O5 particles increased when the thermal-decomposition temperature increased from 400 ℃ to 500 ℃, and their adhesiveness was also synchronously increased. This indicate that the thermaldecomposition temperature palyed a significant influence on electrochemical properties of V2O5 cathodes. The V2O5 sample obtained at 400 ℃ delivered not only a high initial discharge capacity of 330 m A h g-1and also the good cycle stability during 50 cycles due to its higher values ofα in crystal structure and better dispersity in grain morphology.

关键词： V2O5 Thermal decomposition Crystal structure Grain morphology Electrochemical properties

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Analysis on decision-making model of plan evaluation based on grey relation projection and combination weight algorithm

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Journal of Systems Engineering and Electronics 2018年第4期29卷 789-796页

作者： ZHANG Zhicai chen Li Army Logistical University of PLA Chongqing 401311China Logistics University of PAP Tianjin 300309 China

In military service joint operations, when there are more operational forces, more multifarious materials are consumed, the support is more complex and fuzzy, the deployment of personnel is more rapid, and the support provided by wartime military material support powers can be more effective. When the principles,requirements, influencing factors and goals of military material support forces are deployed in wartime, an evaluation indicator system is established. Thus, a new combined empowerment method based on an analytic hierarchy process（AHP） is developed to calculate the subjective weights, and the rough entropy method is used to calculate the objective weights. Combination weights can be obtained by calculating the weight preference coefficient error, which is determined by combining the cooperative game method and the minimum deviation into objectives. This approach can determine the grey relation projection coefficient and synthesize the measure scheme superiority to finally optimize the deployment plan using the grey relation projection decision-making method. The results show that the method is feasible and effective;it can provide a more scientific and practical decision-making basis for the military material support power deployment in wartime.

关键词： method for grey relation projection decision-making military supply power in war deployment plan optimization ana-lytic hierarchy process (AHP) rough entropy method

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Numerical Investigation on the Self-Induced Unsteadiness in Tip Leakage Flow of a Micro-Axial Fan Rotor

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Journal of Thermal Science 2015年第4期24卷 334-343页

作者： chen Jinxin LAI Huanxin School of Mechanical and Power Engineering East China University of Science and Technology

The self-induced unsteadiness in tip leakage flow(TLF)of a micro-axial fan rotor is numerically studied by solving Reynolds-averaged navier-Stokes *** micro-axial fan,which is widely used in cooling systems of electronic devices,has a tip clearance of 6%of the axial chord length of the *** the design rotation speed,four cases near the peak efficiency point(PEP)with self-induced unsteadiness and four steady cases which have much weaker pressure fluctuations are *** the"interface"separating the incoming main flow and the TLF defined by Duet al.[1],an explanation based on the propagation of the low energy spot and its multi-passing through the high gradient zone of the relative total pressure,is proposed to clarify the originating mechanism of the *** the operating points near the PEP,the main flow is weaker than the TLF and the interface moves *** low energy spot which propagates along in the close behind of the interface has opportunity to circulate in the circumferential direction and passes through the sensitive interfaces several times,a slight perturbation therefore may be magnified significantly and develops into the self-induced *** explanation is demonstrated by numerical results.

关键词： micro-axial fan tip leakage flow (TLF) self-induced unsteadiness secondary flow mechanism.

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A piezoelectric energy harvester based on internal resonance

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Acta Mechanica Sinica 2015年第2期31卷 223-228页

作者： Liqun chen Wenan Jiang Department of Mechanics Shanghai University Shanghai Institute of Applied Mathematics and Mechanics Shanghai University Shanghai Key Laboratory of Mechanics in Energy Engineering Shanghai University

A vibration-based energy harvester is essentially a resonator working in a limited frequency *** increase the working frequency range is a challenging *** paper reveals a novel possibility for enhancing energy harvesting via internal *** internal resonance energy harvester is *** excitation is successively assumed as the Gaussian white noise,the colored noise defined by a second-order filter,the narrow-band noise,and exponentially correlated *** corresponding averaged root-meansquare output voltages are *** results demonstrate that the internal resonance increases the operating bandwidth and the output voltage.

关键词： Vibration energy harvesting Internal resonance Stochastic excitations

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Wide-beam SAR autofocus based on blind resampling

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Science China(Information Sciences) 2023年第4期66卷 79-92页

作者： Jianlai chen Hanwen YU School of Automation Central South University School of Resources and Environment University of Electronic Science and Technology of China

Long synthetic aperture time and large instantaneous beam can turn airborne synthetic aperture radar(SAR) autofocus into a wide-beam autofocus problem; i.e., the motion error is both range-and azimuth-spatial variant. A typical two-step Mo Co method cannot process wide-beam airborne SAR ***, traditional wide-beam SAR Mo Co algorithms, such as sub-aperture topography and aperturedependent(SATA), precise topography-and aperture-dependent(PTA), and frequency division(FD), are highly dependent on high-precision inertial navigation system/global positioning system(INS/GPS) data and belong to the sub-aperture method, which may result in serious grant-lobe or stitching problems in the image. Alternatively, this article proposes a full-aperture autofocus method for wide-beam SAR based on blind RS. The proposed method does not require INS/GPS data and avoids the problems of traditional subaperture methods, which can significantly improve the overall image quality. The measured data processing results of the wide-beam SAR verify the effectiveness of the proposed algorithm.

关键词： synthetic aperture radar SAR wide-beam autofocus nonlinear chirp scaling NCS resampling (RS)

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Investigation on mechanism of polymer filling in high-aspect-ratio trenches for through-silicon-via(TSV) application

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Science China(Technological Sciences) 2014年第8期57卷 1616-1625页

作者： DING YingTao YAN YangYang chen QianWen WANG ShiWei chen Xiu chen YueYang School of Information and Electronics Beijing Institute of Technology

Vacuum-assisted spin-coating is an effective polymer filling technology for sidewall insulating of through-silicon-via(TSV).This paper investigated the flow mechanism of the vacuum-assisted polymer filling process based on experiments and numerical simulation,and studied the effect of vacuum pressure,viscosity of polymer and aspect-ratio of trench on the filling performance.A 2D axisymmetric model,consisting of polymer partially filled into the trench and void at the bottom of trench,was developed for the computational fluid dynamics(CFD)*** simulation results indicate that the vacuum-assisted polymer filling process goes through four stages,including bubble formation,bubble burst,air elimination and polymer ***,the simulation results suggest that the pressure significantly affects the bubble formation and the polymer re-filling procedure,and the polymer viscosity and the trench aspect-ratio influence the duration of air elimination.

关键词： through-silicon-via (TSV) vacuum process polymer filling computational fluid dynamics (CFD)

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A study of the upper limit of solid scatters density for gray Lattice Boltzmann Method

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Acta Mechanica Sinica 2008年第5期24卷 515-522页

作者： Yongli chen Keqin Zhu Department of Engineering Mechanics Tsinghua University Beijing 100084 China

The upper limit of the solid scatters density ns （x）, a key parameter for the simulation of flows in porous media with a gray Lattice Boltzmann Method, is studied by an analytical way for the infiltration Poiseuille flow between two infinite parallel plates. Analyses of three different gray Lattice Boltzmann schemes, separately proposed by Gao and Sharma et al., Dardis and McCloskey, and Thorne and Sukop, indicate that the effective domain of Gao and Sharma＇s scheme is restricted to ns 〈 1/2√3≈0.289, Dardis and McCloskey＇s scheme is restricted to ns 〈（√57-1）/28≈0.234, and that there is no extra restriction on ns（x） with Thorne and Sukop＇s scheme. These results are obtained for the dimensionless relaxation time τ= 1. The above analytical results are verified by our numerical simulations. The use of a gray LBM is further illustrated by simulating the flow at the interface of a porous medium. Simulation results yield velocity profiles which agree very well with Brinkman＇s prediction.

关键词： Gray Lattice Boltzmann Method Infiltration flow Scattering density Porous media

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