检索结果-南通市图书馆

Non-tensorial gravitational wave background in NANOGrav 12.5-year data set

在线全文

学校读者我要写书评

暂无评论

Science China(Physics,Mechanics & Astronomy) 2021年第12期64卷 84-89页

作者： Zu-cheng chen chen Yuan Qing-Guo Huang CAS Key Laboratory of Theoretical Physics Institute of Theoretical PhysicsChinese Academy of SciencesBeijing 100190China School of Physical Sciences University of Chinese Academy of SciencesBeijing 100049China School of Fundamental Physics and Mathematical Sciences Hangzhou Institute for Advanced StudyUCASHangzhou 310024China Center for Gravitation and Cosmology College of Physical Science and TechnologyYangzhou UniversityYangzhou 225009China

We perform the first search for an isotropic non-tensorial gravitational-wave background(GWB) allowed in general metric theories of gravity in the North American Nanohertz Observatory for Gravitational Waves(NANOGrav) 12.5-year data set. By modeling the GWB as a power-law spectrum, we find strong Bayesian indication for a spatially correlated process with scalar transverse(ST) correlations whose Bayes factor versus the spatially uncorrelated common-spectrum process is 107 ± 7, but no statistically significant evidence for the tensor transverse, vector longitudinal, and scalar longitudinal polarization modes. The median and the 90% equal-tail amplitudes of ST mode are ■ , or equivalently the energy density parameter per logarithm frequency is ■, at frequency of 1/year.

关键词： gravitational wave scalar transverse polarization pulsar timing array

The evolutionary trajectory of the rural settlements in Southern Jiangsu in the past 20 years:From the perspective of urbanization and land use

在线全文

学校读者我要写书评

暂无评论

Journal of Geographical Sciences 2024年第8期34卷 1615-1635页

作者： chen Feiyu chen cheng Key Laboratory of Watershed Geographic Sciences Nanjing Institute of Geography and LimnologyCASNanjing 210008China Nanjing College University of Chinese Academy of SciencesNanjing 211135China

For a long time,due to lack of accurate data covering large areas,it is difficult to capture the continuous spatial evolutionary trajectory of rural settlements shaped by rapid urbanization and rural land use *** fill this gap,based on theoretical analysis this paper systemically detected the changing characteristics of scale,spatial morphology,distribution,and land use pattern of rural settlements in Southern Jiangsu in the past 20 years depending on the data of land resource survey in 2009 and *** study suggests that the total area and per capita size of rural settlements declined by 30%and 2%respectively as a result of rural land consolidation and the influx of enormous immigrants from underdeveloped *** spatial density and average shape index dropped by 14%and 44%respectively in the recent decade,indicating an evident trend of decentralization in spatial distribution,and regularization in the spatial ***,residential land within rural settlements decreased by 33%over the past decade while the land for industry and commercial service steadily increased,demonstrating that the function for manufacturing and diversified services had been *** the emerging issue of the aging population and new business opportunities in rural Southern Jiangsu,rural settlements regeneration might be the focus offutureresearch.

关键词： rural settlements spatial morphology land use Southern Jiangsu

L^(2) Boundedness of the Fourier Integral Operator with Inhomogeneous Phase Functions

在线全文

学校读者我要写书评

暂无评论

Acta Mathematica Sinica,English Series 2023年第8期39卷 1525-1546页

作者： Jia Wei DAI Jie cheng chen School of Electronic and Information Engineering(School of Big Data Science) Taizhou UniversityTaizhou 318000P.R.China Department of Mathematics Zhejiang Normal UniversityJinhua 321004P.R.China

In this paper,we investigate the L^(2) boundedness of the Fourier integral operator Tφ,a with smooth and rough symbols and phase functions which satisfy certain non-degeneracy *** particular,if the symbol a∈L∞Smρ,the phase functionφsatisfies some measure conditions and ∇kξφ(·,ξ)L∞≤C|ξ|−k for all k≥2,ξ≠0,and some∈>0,we obtain that Tφ,a is bounded on L^(2) if m

关键词： Fourier integral operator,L^(2)boundedness inhomogeneous phase

同方期刊数据库

Multiscale frictional behaviors of sp^(2) nanocrystallited carbon films with different ion irradiation densities

在线全文

学校读者我要写书评

暂无评论

Friction 2021年第5期9卷 1025-1037页

作者： Zelong HU Xue FAN cheng chen Institute of Nanosurface Science and Engineering Guangdong Provincial Key Laboratory of Micro/Nano Optomechatronics EngineeringCollege of Mechatronics and Control EngineeringShenzhen UniversityShenzhen 518060China

sp^(2) nanocrystallited carbon films with large nanocrystallite sizes,smooth surfaces,and relative high hardness were prepared with different ion irradiation densities regulated with the substrate magnetic coil current in an electron cyclotron resonance plasma sputtering *** multiscale frictional behaviors were investigated with macro pin‐on‐disk tribo‐tests and micro nanoscratch *** results revealed that,at an ion irradiation density of 16 mA/cm^(2),sp^(2) nanocrystallited carbon film exhibits the lowest friction coefficient and good wear resistant properties at both the macroscale and *** film sliding against a Si_(3)N_(4) ball under a contact pressure of 0.57 GPa exhibited a low friction coefficient of 0.09 and a long wear life at the ***,the film sliding against a diamond tip under a contact pressure of 4.9 GPa exhibited a stable low friction coefficient of 0.08 with a shallow scratch depth at the *** is suggested that sp^(2) nanocrystallites affect the frictional behaviors in the cases described *** the macroscale,the contact interface via the small real contact area and the sp^(2) nanocrystallited transfer layer dominated the frictional behavior,while the sp^(2) nanocrystallited structure in the film with low shear strength and high plastic resistivity,as well as the smooth surface morphology,decided the steady low nanoscratch properties at the *** findings expand multiscale tribological applications of sp^(2) nanocrystallited carbon films.

关键词： macro‐tribology micro‐tribology sp^(2)nanocrystallite carbon film ion irradiation density

Efficient policy evaluation by matrix sketching

在线全文

学校读者我要写书评

暂无评论

Frontiers of Computer Science 2022年第5期16卷 97-105页

作者： cheng chen Weinan ZHANG Yong YU Department of Computer Science Shanghai Jiao Tong UniversityShanghai 200240China

In the reinforcement learning,policy evaluation aims to predict long-term values of a state under a certain *** high-dimensional representations become more and more common in the reinforcement learning,how to reduce the computational cost becomes a significant problem to the policy *** recent works focus on adopting matrix sketching methods to accelerate least-square temporal difference(TD)algorithms and quasi-Newton temporal difference *** these sketching methods,the truncated incremental SVD shows better performance because it is stable and ***,the convergence properties of the incremental SVD is still *** this paper,we first show that the conventional incremental SVD algorithms could have enormous approximation errors in the worst *** we propose a variant of incremental SVD with better theoretical guarantees by shrinking the singular values ***,we employ our improved incremental SVD to accelerate least-square TD and quasi-Newton TD *** experimental results verify the correctness and effectiveness of our methods.

关键词： temporal difference learning policy evaluation matrix sketching

Analysis of actuator delay and its effect on uncertainty quantification for real-time hybrid simulation

在线全文

学校读者我要写书评

暂无评论

Earthquake Engineering and Engineering Vibration 2017年第4期16卷 713-725页

作者： cheng chen Weijie Xu Tong Guo Kai chen School of Engineering San Francisco State University Key Laboratory of Concrete and Prestressed Concrete Structures of the Ministry of Education Southeast University

Uncertainties in structure properties can result in different responses in hybrid simulations. Quantification of the effect of these tmcertainties would enable researchers to estimate the variances of structural responses observed from experiments. This poses challenges for real-time hybrid simulation （RTHS） due to the existence of actuator delay. Polynomial chaos expansion （PCE） projects the model outputs on a basis of orthogonal stochastic polynomials to account for influences of model uncertainties. In this paper, PCE is utilized to evaluate effect of actuator delay on the maximum displacement from real-time hybrid simulation of a single degree of freedom （SDOF） structure when accounting for uncertainties in structural properties. The PCE is first applied for RTHS without delay to determine the order of PCE, the number of sample points as well as the method for coefficients calculation. The PCE is then applied to RTHS with actuator delay. The mean, variance and Sobol indices are compared and discussed to evaluate the effects of actuator delay on uncertainty quantification for RTHS. Results show that the mean and the variance of the maximum displacement increase linearly and exponentially with respect to actuator delay, respectively. Sensitivity analysis through Sobol indices also indicates the influence of the single random variable decreases while the coupling effect increases with the increase of actuator delay.

关键词： real-time hybrid simulation actuator delay polynomial chaos expansion delay differential equation uncertainty quantification

L^p estimates for Riesz transform and their commutators associated with Schr?dinger type operator

在线全文

学校读者我要写书评

暂无评论

Applied Mathematics(A Journal of Chinese Universities) 2016年第1期31卷 112-126页

作者： chen Xiao-li chen Jie-cheng Department of Mathematics Jiangxi Normal University Nanchang 330022 China Department of Mathematics Zhejiang Normal University Jinhua 321004 China

. Let H2 = （-△）2 ＋ V2 be the Schr6dinger type operator, where V satisfies reverse HSlder inequality. In this paper, we establish the Lp boundedness for V2 H2- 1, H21 V2, VH2- 1/2 and Hfl/2V, and that of their comm... 详细信息

关键词： Schrodinger type operator Bq class BMOL commutator.

Restoring force correction based on online discrete tangent stiffness estimation method for real-time hybrid simulation

在线全文

学校读者我要写书评

暂无评论

Earthquake Engineering and Engineering Vibration 2018年第4期17卷 805-820页

作者： Huang Liang Guo Tong chen cheng chen Menghui School of Civil Engineering Southeast University Key Laboratory of Concrete and Prestressed Concrete Structures of the Ministry of Education Southeast University School of Engineering San Francisco State University

In real-time hybrid simulation（RTHS）, it is difficult if not impossible to completely erase the error in restoring force due to actuator response delay using existing displacement-based compensation methods. This paper proposes a new force correction method based on online discrete tangent stiffness estimation（online DTSE） to provide accurate online estimation of the instantaneous stiffness of the physical substructure. Following the discrete curve parameter recognition theory, the online DTSE method estimates the instantaneous stiffness mainly through adaptively building a fuzzy segment with the latest measurements, constructing several strict bounding lines of the segment and calculating the slope of the strict bounding lines, which significantly improves the calculation efficiency and accuracy for the instantaneous stiffness estimation. The results of both computational simulation and real-time hybrid simulation show that：（1） the online DTSE method has high calculation efficiency, of which the relatively short computation time will not interrupt RTHS; and（2） the online DTSE method provides better estimation for the instantaneous stiffness, compared with other existing estimation methods. Due to the quick and accurate estimation of instantaneous stiffness, the online DTSE method therefore provides a promising technique to correct restoring forces in RTHS.

关键词： online discrete tangent stiffness estimation restoring force correction fuzzy segment parameter updating real-time hybrid simulation

Fatigue Assessment Method for Composite Wind Turbine Blade

在线全文

学校读者我要写书评

暂无评论

Transactions of Nanjing University of Aeronautics and Astronautics 2016年第1期33卷 102-111页

作者： chen cheng Wang Tongguang Jiangsu Key Laboratory of Hi-Tech Research for Wind Turbine Design Nanjing University of Aeronautics and Astronautics

Fatigue strength assessment of a horizontal axis wind turbine(HAWT)composite blade is *** load cases are identified,and loads are calculated by the GH Bladed software which is specified at the IEC61400 international specification and GL(Germanisher Lloyd)regulations for the wind energy conversion *** analysis is performed with a 3-D finite element method(FEM).Considering Saint-Venant′s principle,a uniform cross section FEM model is built at each critical *** transformation matrixes(STM)are set up by applied six unit load components on the FEM model *** can be used to convert the external load into stresses in the linear elastic *** main material of composite wind turbine blade is fiber reinforced plastics(FRP).In order to evaluate the degree of fatigue damage of FRP,the stresses of fiber direction are extracted and the well-known strength criterion-Puck theory is *** total fatigue damage of each laminate on the critical point is counted by the rain-flow counting method and Miner′s damage law based on general S-N *** sections of a 45.3mblade of a 2 MW wind turbine are studied using the fatigue evaluation *** performance of this method is compared with far more costly business software *** results show that the fatigue damage of multi-axis FRP can be assessed conveniently by the FEM-STM *** the proposed method gives a reliable and efficient method to analyze the fatigue damage of slender composite structure with variable cross-sections.

关键词： fatigue assessment wind turbine blade finite element method(FEM) stress transformation matrix