检索结果-南通市图书馆

A TVD-WAF-based hybrid finite volume and finite difference scheme for nonlinearly dispersive wave equations

Water Science and Engineering 2015年第3期8卷 239-247页

作者： Jing yin Jia-wen Sun zi-feng Jiao National Marine Environment Monitoring Center State Oceanic Administration State Key Laboratory of Coastal and Offshore Engineering Dalian University of Technology

A total variation diminishing-weighted average flux （TVD-WAF）-based hybrid numerical scheme for the enhanced version of nonlinearly dispersive Boussinesq-type equations was developed. The one-dimensional governing equations were rewritten in the conservative form and then discretized on a uniform grid. The finite volume method was used to discretize the flux term while the remaining terms were approximated with the finite difference method. The second-order TVD-WAF method was employed in conjunction with the Harten-Lax-van Leer （HLL） Riemann solver to calculate the numerical flux, and the variables at the cell interface for the local Riemann problem were reconstructed via the fourth- order monotone upstream-centered scheme for conservation laws （MUSCL）. The time marching scheme based on the third-order TVD Runge- Kutta method was used to obtain numerical solutions. The model was validated through a series of numerical tests, in which wave breaking and a moving shoreline were treated. The good agreement between the computed results, documented analytical solutions, and experimental data demonstrates the correct discretization of the governing equations and high accuracy of the proposed scheme, and also conforms the advantages of the proposed shock-capturing scheme for the enhanced version of the Boussinesq model, including the convenience in the treatment of wave breaking and moving shorelines and without the need for a numerical filter.

关键词： Hybrid scheme Finite volume method (FVM) Finite difference method (FDM) Total variation diminishing-weighted average flux (TVD-WAF) Boussinesq-type equations Nonlinear shallow water equations (NSWEs)

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

Constraints on generalized Chaplygin gas model including gamma-ray bursts

引用

Chinese Journal of Astronomy and Astrophysics 2009年第5期9卷 547-557页

作者： Fa-yin Wang zi-Gao Dai Shi Qi Department of Astronomy Nanjing University Nanjing 210093 China Purple Mountain Observatory Chinese Academy of Sciences Nanjing 210008 China Joint Center for Particle Nuclear Physics and Cosmology Nanjing University- Purple Mountain Observatory Nanjing 210093 China

Generalized Chaplygin gas （whose equation of state is PGCG = -A/ρGCG^α） was proposed as a candidate for unification of dark energy and dark matter. We investigate constraints on this model with the latest observed data. We test the model with type-Ia supernovae （SNe Ia）, cosmic microwave background （CMB） anisotropy, X-ray gas mass fractions in clusters, and gamma-ray bursts （GRBs）. We calibrate the GRB luminosity relations without assuming any cosmological models using SNe Ia. We show that GRBs can extend the Hubble diagram to higher redshifts （z 〉 6）. The GRB Hubble diagram is well behaved and delineates the shape of the Hubble diagram well. We measure As≡A/ρGCG,0^α＋1 =0.68-0.08^＋0.04（where PGCG,0 is the energy density today） and α=-0.22 -0.13^＋0.15 at the 1σ confidence level using all the datasets. Our results rule out the standard Chaplygin gas model （α = 1） at the 3σ confidence level. The ACDM is allowed at the 2σ confidence level. We find that acceleration could have started at a redshift of z - 0.70. The concordance of the generalized Chaplygin gas model with the age estimate of an old high redshift quasar is found. In addition, we show that GRBs can break the degeneracy between the generalized Chaplygin gas model and the XCDM model.

关键词： gamma-rays bursts -- cosmology theory

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

Preparation and Acid Catalytic Activity of TiO2 Grafted Silica MCM-41 with Sulfate Treatment

引用

Chinese Journal of Chemical Physics 2008年第1期21卷 21-26页

作者： Dai-shi Guo zi-feng Ma Chun-sheng yin Qi-zhong Jiang Department of Chemical Engineering Shanghai Jiao Tong University Shanghai 200240 China School of Environmental Science and Engineering Shanghai Jiao Tong University Shanghai 200240China

TiO2 grafted silica MCM-41 catalyst with and without sulfate treatment were prepared. The structural and acid properties of these materials were investigated by XRD, N2 adsorption-desorption, element analysis, thermal analysis, Raman and FTIR measurements. Their acid-catalytic activities were evaluated using the cyclization reaction of pseudoionone. It was found that the obtained materials possess well-ordered mesostructure, and the grafted TiO2 components were in highly dispersed amorphous form. T/MCM41 without sulfation contained only Lewis acid sites, while Brφnsted and Lewis acidities were remarkably improved for the sulfated materials ST/MCM41 and d-ST/MCM41. T/MCM-41 was not active for the cyclization reaction of pseudoionone, but ST/MCM-41 and d-ST/MCM-41 possessed favorable catalytic activities. The catalytic performance of ST/MCM-41 was comparable with that of the commercial solid acid catalyst of Amberlyst-15, and better than that of d-ST/MCM-41, although the latter underwent a second TiO2 grafting process and accordingly had higher Ti and S content. The specific surface structure of Si-O-Ti-O-S=O in ST/MCM-41 and the bilateral induction effect of Si and S=O on Si-O-Ti bonds were speculated to account for its higher acid catalytic activity.

关键词： TiO2 grafting Sulfate treatment Silica MCM-41 Acid catalytic activity Cyclization of pseudoionone

来源：

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

Determination of Surface Roughness in Wire and Arc Additive Manufacturing Based on Laser Vision Sensing

引用

Chinese Journal of Mechanical Engineering 2018年第4期31卷 133-139页

作者： Jun Xiong Yan-Jiang Li zi-Qiu yin Hui Chen School of Materials Science and Engineering Southwest Jiaotong University

Wire and arc additive manufacturing(WAAM) shows a great promise for fabricating fully dense metal parts by means of melting materials in layers using a welding heat source. However, due to a large layer height produced in WAAM, an unsatisfactory surface roughness of parts processed by this technology has been a key issue. A methodology based on laser vision sensing is proposed to quantitatively calculate the surface roughness of parts deposited by *** for a camera and a laser plane of the optical system are presented. The reconstruction precision of the laser vision system is verified by a standard workpiece. Additionally, this determination approach is utilized to calculate the surface roughness of a multi-layer single-pass thin-walled part. The results indicate that the optical measurement approach based on the laser vision sensing is a simple and effective way to characterize the surface roughness of parts deposited by WAAM. The maximum absolute error is less than 0.15 mm. The proposed research provides the foundation for surface roughness optimization with different process parameters.

关键词： Wire and arc additive manufacturing Surface roughness measurement Laser vision sensing Three-dimensional reconstruction

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

Ring-opening Polymerization of 2-Oxabicyclo[2.2.2]octan-3-one and the Influence of Stereochemistry on the Thermal Properties of the Polyesters

引用

Chinese Journal of Polymer Science 2022年第10期40卷 1173-1182,I0008页

作者： Tong Zhou Yu-Ting Guo Fu-Sheng du zi-Chen Li Beijing National Laboratory for Molecular Sciences(BNLMS) Key Laboratory of Polym.Chem.&Physics of Ministry of EducationDepartment of Polymer Science&EngineeringCollege of Chemistry and Molecular EngineeringCenter for Soft Matter Science and EngineeringPeking UniversityBeijing 100871China

Polyesters with cyclic structures in the main chain typically possess superior mechanical and thermal properties together with chemical ***-opening polymerization(ROP)of bridged or fused bicyclic lactones is a simple,and in most cases controlled method to synthesize polyesters with alicyclic moieties in the polymer *** stereochemistry of the alicyclic structures has a great effect on the polymer properties,which can be regulated by varying the polymerization ***,we report a systematic investigation on the ROP of 2-oxabicyclo[2.2.2]octan-3-one([2.2.2]VL)under different *** initiated byn-butyl lithium(n-BuLi)or catalyzed by trifluoromethanesulfonic acid(TfOH)in the presence of benzyl alcohol,P[2.2.2]VLs containing all cis^(-1),4 disubstituted cyclohexane ring were ***,P[2.2.2]VLs initiated by sodium methoxide(MeONa)or catalyzed by organic superbase contained both cis and trans isomeric structural *** cis to trans transformation mechanism under these conditions was manifested,and the effect of stereochemical variations on the properties ofP[2.2.2]VLwas *** stereoregularP[2.2.2]VLs,bothcisandtrans,exhibited higher crystallinity and melting temperatures(Tm)than those of the stereoirregular ***,the degradation of P[2.2.2]VL with acid at high temperature could recover 3-cyclohexenecarboxylic acid.

关键词： 2-Oxabicyclo[2.2.2]octan-3-one Ring-opening polymerization Stereochemistry Polyester Thermal properties

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

Novel Nano-composites SDC–LiNaSO_4 as Functional Layer for ITSOFC

引用

Nano-Micro Letters 2015年第3期7卷 268-275页

作者： Weiming Lv Ze Tong Yi-Mei yin Jiewei yin zi-Feng Ma Shanghai Electrochemical Energy Devices Research Center School of Chemistry and Chemical Engineering Shanghai Jiao Tong University Shanghai Research and Development Center for Polymer Materials

As an ionic conductive functional layer of intermediate temperature solid oxide fuel cells(ITSOFC), samarium-doped ceria(SDC)–Li Na SO4nano-composites were synthesized by a sol–gel method and their properties were investigated. It was found that the content of Li Na SO4 strongly affected the crystal phase, defect concentration, and conductivity of the composites. When the content of Li Na SO4 was 20 wt%, the highest conductivity of the composite was found to be, respectively, 0.22, 0.26, and 0.35 S cm-1at temperatures of 550, 600, and 700 °C, which are much higher than those of SDC. The peak power density of the single cell using this composite as an interlayer was improved to, respectively, 0.23, 0.39, and 0.88 W cm-2at 500, 600, and 700 °C comparing with that of the SDC-based cell. Further, the SDC–Li Na SO4(20 wt%)-based cell also displayed better thermal stability according to the performance measurements at 560 °C for 50 h. These results reveal that SDC–Li Na SO4 composite may be a potential good candidate as interlayer for ITSOFC due to its high ionic conductivity and thermal stability.

关键词： Nano-composite SDC–Li Na SO4 Ionic conductor Solid oxide fuel cell

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

The Global Convergence of Self-Scaling BFGS Algorithm with Nonmonotone Line Search for Unconstrained Nonconvex Optimization Problems

引用

Acta Mathematica Sinica,English Series 2007年第7期23卷 1233-1240页

作者： Hong Xia yin Dong Lei du Chinese Academy of Sciences Research Center on Data Technology and Knowledge Economy Department of Mathematics Graduate University of the Chinese Academy of Sciences Faculty of Administration University of New Brunswick

The self-scaling quasi-Newton method solves an unconstrained optimization problem by scaling the Hessian approximation matrix before it is updated at each iteration to avoid the possible large eigenvalues in the Hessian approximation matrices of the objective function. It has been proved in the literature that this method has the global and superlinear convergence when the objective function is convex （or even uniformly convex）. We propose to solve unconstrained nonconvex optimization problems by a self-scaling BFGS algorithm with nonmonotone linear search. Nonmonotone line search has been recognized in numerical practices as a competitive approach for solving large-scale nonlinear problems. We consider two different nonmonotone line search forms and study the global convergence of these nonmonotone self-scale BFGS algorithms. We prove that, under some weaker condition than that in the literature, both forms of the self-scaling BFGS algorithm are globally convergent for unconstrained nonconvex optimization problems.

关键词： nonmonotone line search self-scaling BFGS method global convergence

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

Improved Lossless Data Hiding for JPEG Images Based on Histogram Modification

引用

Computers, Materials & Continua 2018年第6期55卷 495-507页

作者： Yang du Zhaoxia yin Xinpeng Zhang Key Laboratory of Intelligent Computing&Signal Processing Ministry of EducationAnhui UniversityHefei230601P.R.China Department of Computer Science Purdue UniversityWest lafayette47906USA School of Communication and Information Engineering Shanghai UniversityShanghai 200072P.R.China

This paper proposes a lossless and high payload data hiding scheme for JPEG images by histogram *** most in JPEG bitstream consists of a sequence of VLCs(variable length codes)and the appended *** VLC has a corresponding RLV(run/length value)to record the AC/DC *** achieve lossless data hiding with high payload,we shift the histogram of VLCs and modify the DHT segment to embed *** we sort the histogram of VLCs in descending order,the filesize expansion is *** paper’s key contribution includes:Lossless data hiding,less filesize expansion in identical pay-load and higher embedding efficiency.

关键词： Lossless data hiding histogram VLC JPEG.

来源：

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

Optic tecta I superficial inter neurons detect motion in larval zebrafish

引用

Protein & Cell 2019年第4期10卷 238-248页

作者： Chen yin Xiaoquan Li Jiulin du Institute of Neuroscience State Key Laboratory of NeuroscieneeCenter for Excellenee in Brain Science and Intelligenee TechnologyChinese Academy of SciencesShanghai 200031China School of Future Technology University of Chinese Academy of SciencesBeijing 100049China School of Life Science and Technology ShanghaiTech UniversityShanghai 200031China

Detection of moving objects is an essential skill for animals to hunt prey,recognize conspecifics and avoid *** zebrafish,as a vertebrate model,primarily uses its elaborate visual system to distinguish moving objects against background *** optic tectum(OT)receives and integrates inputs from various types of retinal ganglion cells(RGCs),including direction-selective(DS)RGCs and size-selective RGCs,and is required for both prey capture and predator ***,it remains largely unknown how motion information is processed within the *** we performed in vivo whole-cell recording and calcium imaging to investigate the role of superficial interneurons(SINs),a specific type of optic tecta I neurons,in motion detection of larval *** mainly receive excitatory synaptic inputs,exhibit transient ON-or OFF-type of responses evoked by light flashes,and possess a large receptive field(RF).One fifth of SINs are DS and classified into two subsets with separate preferred ***,SINs show size-dependent responses to moving *** are efficiently activated by moving objects but not static ones,capable of showing sustained responses to moving objects and having less visual adaptation than periventricular neurons(PVNs),the principal tecta I ***,ablation of SINs impairs prey capture,which requires local motion detection,but not global looming-evoked ***,starvation enhances the gain of SINs'motion responses while maintaining their size tuning and *** results indicate that SINs serve as a motion detector for sensing and localizing sized moving objects in the visual field.

关键词： optic tectum motion detection direction selectivity visual adaptation zebrafish

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

Efficient molten salt CO_(2)capture and selective electrochemical transformation processes toward carbon neutrality:advances,challenges,and prospects

引用

Science China Chemistry 2023年第11期66卷 3116-3135页

作者： Bowen Deng Huayi yin Kaifa du Dihua Wang School of Resource and Environmental Sciences Hubei International Scientific and Technological Cooperation Base of Sustainable Resource and EnergyWuhan UniversityWuhan 430072China

Atmospheric carbon dioxide(CO_(2))concentration has reached record levels due to excessive anthropogenic CO_(2)emissions from massive industrial ***-energy-driven CO_(2)electroreduction is an effective method of directly converting CO_(2)into various value-added chemicals or materials without subsequent geological disposal *** to their promising thermal stability,wide electrochemical window,tunable oxo-basicity,and nontoxic nature,molten salt electrolytes endow intrinsic advantages,such as fast CO_(2)absorption and selective electrochemical transformation,among different electrolyte species,wherein advanced carbon materials,CO,and hydrocarbons can be generated at relatively high current ***,we review the recent advances in molten salt CO_(2)capture and electrochemical transformation(MSCC-ET)technologies,including reaction mechanisms,CO_(2)absorption kinetics,electrode reaction kinetics,and product *** review highlights feasible strategies for regulating nanostructures,carbon product crystallinity,energy efficiency,overall CO_(2)conversion efficiency,and MSCC-ET adaptability toward practical flue ***,suitable cost-effective inert anode candidates for the oxygen evolution reaction are discussed.

关键词： carbon dioxide electroreduction CO_(2)capture molten salt electrode reaction energy efficiency

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

欢迎您,

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

请选择保存的检索档案：

请选择收藏分类：

通借通还

欢迎您,

建议与咨询 留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

请选择保存的检索档案： 新增检索档案 确定 取消

请选择收藏分类： 新增自定义分类 确定 取消

通借通还

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

请选择保存的检索档案：

请选择收藏分类：