检索结果-南通市图书馆

TSC STUDIES ON SUB-Tg STORAGE OF POLYETHYLENE TEREPHTHALATE

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Chinese Journal of Polymer Science 1987年第4期5卷 285-291页

作者：李炜童刚周漪琴漆宗能 Academia Sinica Academla sinica Beijing Beliing Department of Applied Chemistry hefei hefei Institute of Chermstry Institute of Chemistry university of Science and technology of China

The Thermally Stimulated Current （TSC） spectra of a series of Sub-T;annealed polyethylene terephthalate （PET） specimens have been measured. It is found that there is only one peak at 80℃above room temperature, which related to the thermo-relaxation of frozen-in dipoles. The activation energy of such dipole motion has been calculated. The relation between the maximum current and the storage time can be explained by the free volume theory and agrees with the results from the excess thermodynamic properties. Compared with Differential Scanning Calorimeter （DSC） and tensile stress-strain method, TSC is a simpler and more sensitive method in studying Sub-T;annealed polymers.

关键词： Polyethylene terephthalate Sub-T_θ Storage TSC Studies.

A DEEP LEARNING BASED DISCONTINUOUS GALERKIN METHOD FOR HYPERBOLIC EQUATIONS WITH DISCONTINUOUS SOLUTIONS AND RANDOM UNCERTAINTIES

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

Journal of Computational Mathematics 2023年第6期41卷 1281-1304页

作者： Jingrun Chen Shi Jin Liyao Lyu School of Mathematical Sciences University of Science and Technology of ChinaHefei 230026China Suzhou Institute for Advanced Research University of Science and Technology of ChinaSuzhou 215123China School of Mathematical Sciences Institute of Natural Sciencesand MOE-LSCShanghai Jiao Tong UniversityShanghai200240China Department of Computational Mathematics Scienceand EngineeringMichigan State UniversityEast LansingMI48824USA

We propose a deep learning based discontinuous Galerkin method(D2GM)to solve hyperbolic equations with discontinuous solutions and random *** main computational challenges for such problems include discontinuities of the solutions and the curse of dimensionality due to *** learning techniques have been favored for high-dimensional problems but face difficulties when the solution is not smooth,thus have so far been mainly used for viscous hyperbolic system that admits only smooth *** alleviate this difficulty by setting up the loss function using discrete shock capturing schemes–the discontinous Galerkin method as an example–since the solutions are smooth in the discrete *** convergence of D2GM is established via the Lax equivalence theorem kind of *** high-dimensional random space is handled by the Monte-Carlo *** a setup makes the D2GM approximate high-dimensional functions over the random space with satisfactory accuracy at reasonable *** D2GM is found numerically to be first-order and second-order accurate for(stochastic)linear conservation law with smooth solutions using piecewise constant and piecewise linear basis functions,*** examples are given to verify the efficiency and the robustness of D2GM with the dimensionality of random variables up to 200 for(stochastic)linear conservation law and(stochastic)Burgers’equation.

关键词： Discontinuous Galerkin method Loss function Convergence analysis Deep learning Hyperbolic equation

1,4-Migration of Transition Metals in Organic Synthesis

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Chinese Journal of Chemistry 2019年第9期37卷 929-945页

作者： Abdur Rahim Jia Feng Zhenhua Gu Department of Chemistry Center for Excellence in Molecular Synthesisand Hefei National Laboratory for Physical Sciences at the MicroscaleUniversity of Science and Technology of China96 Jinzhai RoadHefeiAnhui 230026China

Generation of carbon-metal species is extremely important in transition metal-catalyzed organic *** the various methods,1,4-metal migration is a very useful way to create new carbon-metal species,which are not readily accessible via classic *** review summarized recent advances in transition metal-catalyzed reactions,which involved one or more steps of 1,4-metal *** focused mostly on the achievements in Pd and Rh-catalyzed reactions,along with some of the remarkable results in Pt,Ir,Co,Fe-involved transformations.

关键词： 1,4-Migration Transition Metals Organic Synthesis

Competition between Buneman and Langmuir Instabilities

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Chinese Physics Letters 2012年第3期29卷 146-149页

作者：郭俊于彬 College of Mathematics and Physics Qingdao University of Science and TechnologyQingdao 266061 Key Laboratory of Geospace Environment University of Science and Technology of ChinaHefei 230026

The electron-ion beam instabilities are studied by one-dimensional electrostatic particle-in-cell *** simulation results show that both the low-frequency Buneman mode and high-frequency Langmuir wave(LW)are excited in the nonlinear *** power of Buneman instability is stronger than that of the *** Buneman instability is firstly *** the backward LW appears,which is probably excited by the particles trapped in the wave potential and moving opposite to the original beam *** some time,the forward LW can be found,which has a larger maximum frequency than that of the backward *** the decrease of the electron drift velocity,the instabilities become weaker;the LW appears to have almost equal intensities and becomes symmetric for forward and backward propagation *** LW can also heat the electron,so the relative drift speed cannot far exceed the electron thermal speed,which is not helpful to the development of Buneman instability.

关键词： backward excited beam

REACTION MECHANISM OF BENZOPHENONE-PHOTOINITIATED CROSSLINKING OF POLYETHYLENE

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Chinese Journal of Polymer Science 2002年第4期20卷 291-307页

作者： Bao-jun Qu State Key Laboratory of Fire Science and Department of Polymer Science and Engineering university of Science and technology of China hefei 230026 China university of Science and technology of China State Key Laboratory of Fire Science and Department of Polymer Science and Engineering Hefei 230026

The radical intermediates, the crosslink microstructures, and the reaction mechanism of benzophenone (BP)-photoinitiated crosslinking of low-density polyethylene (LDPE) and model compounds (MD) have been reviewed in detail. The spin-trapping electron spin resonance (ESR) spectra obtained from the LDPE/BP systems with spin-trap agents show that two kinds of polymer radical intermediates are mainly formed: tertiary carbon and secondary carbon radicals. The spin-trapping ESR studies of MD/BP systems give further evidence that photocrosslinking reactions of PE predominantly take place a sites of tertiary carbon, secondary carbon, and especially allylic carbon when available. The high resolution C-13-NMR spectra obtained from LDPE and MD systems show that the crosslink microstructures have H- and Y-type links and that their concentrations are of the same order. The fluorescence, ESR, C-13 and H-1-NMR spectra from the PE and MD systems demonstrate that the main photoreduction product of BP (PPB) is benzpinacol formed by the recombination of two diphenylhydroxymethyl (K-.) radical intermediates. Two new PPB products: an isomer of benzpinacol with quinoid structure, 1-phenylhydroxymethylene-4-diphenylhydroxymethyl-2,5-cyclobexadiene and three kinds of alpha-alkyl-benzhydrols have been detected and identified. These results provide new experimental evidence for elucidating the reaction mechanism in the BP-photoinitiated crosslinking of polyethylene.

关键词： photocrosslinking mechanism polymer radical intermediates crosslink microstructures photolytic products of benzophenone polyethylene model compound

REDSHIFT DISTRIBUTION AND EVOLUTION FUNCTION OF QUASI-STELLAR OBJECTS

在线全文

学校读者我要写书评

暂无评论

Science China Mathematics 1991年第5期34卷 598-612页

作者：周又元胡岳东 China Center of Advanced Science and technology (World Laboratory) Beijing 100080 PRC Center for Astrophysics University of Science and Technology of China. Hefei 230026. PRC Center for Astrophysics University of Science and Technology of China Hefei 230026 PRC

Taking account of the selection effect in the line identification, under the cosmologicalredshift hypothesis we calculate the redshift-distribution functions of quasi-stellar objects(QSOs) selected with the slitless technique, using three kinds of evolution functions forQSOs, i. e. the Schmidt-Green function, the Mathez function and the Heisler-Ostriker func-tion, and compare them with the observed distribution. The comparison shows that withregards to both the global behavior and the detailed properties, the predictions agree wellwith observations. We also tried to throw light on the redshift distribution of radio-selectedand color-selected QSOs. Therefore, the obtained results draw to the conclusion that thecosmological-redshift hypothesis is compatible with the redshift distibution of QSOs. Using the redshift distribution of QSOs, we also compare various evolution functionswith observations, and indicate which functions in what range can well explain the observeddistributions.

关键词： cosmology redshif evolution function selection effect quasars.

Extracting viewer interests for automated bookmarking in video-on-demand services

在线全文

学校读者我要写书评

暂无评论

Frontiers of Computer Science 2015年第3期9卷 415-430页

作者： Yang ZHAO Ye TIAN Yong LIU university of Science and technology of China Hefei 230027 China Polytechnic Institute of New York university Brooklyn 11201 USA

Video-on-demand （VoD） services have become popular on the Internet in recent years. In VoD, it is challeng- ing to support the VCR functionality, especially the jumps, while maintaining a smooth streaming quality. Previous stud- ies propose to solve this problem by predicting the jump tar- get locations and prefetching the contents. However, through our analysis on traces from a real-world VoD service, we find that it would be fundamentally difficult to improve a viewer＇s VCR experience by simply predicting his future jumps, while ignoring the intentions behind these jumps. Instead of the prediction-based approach, in this paper, we seek to support the VCR functionality by bookmark- ing the videos. There are two key techniques in our pro- posed methodology. First, we infer and differentiate view- ers＇ intentions in VCR jumps by decomposing the inter- seek times, using an expectation-maximization （EM） algo- rithm, and combine the decomposed inter-seek times with the VCR jumps to compute a numerical interest score for each video segment. Second, based on the interest scores, we pro- pose an automated video bookrnarking algorithm. The algo- rithm employs the time-series change detection techniques of CUSUM and MB-GT, and bookmarks videos by detecting the abrupt changes on their interest score sequences. We evaluate our proposed techniques using real-world VoD traces from dozens of videos. Experimental results suggest that with our methods, viewers＇ interests within a video can be precisely extracted, and we can position bookmarks on the video＇shighlight events accurately. Our proposed video bookmark- ing methodology does not require any knowledge on video type, contents, and semantics, and can be applied on various types of videos.

关键词： video-on-demand (VoD) highlight bookmark-ing time-series change detection

Photoluminescence study of SiO_2 coated Eu^(3+):Y_2O_3 core-shells under high pressure

在线全文

学校读者我要写书评

暂无评论

Journal of Rare Earths 2010年第S1期28卷 241-245页

作者：代如成王中平张增明丁泽军 hefei National Laboratory for Physical Sciences at the Microscale and Department of Physics University of Science and Technology of China The Centre of Physical Experiments University of Science and Technology of China

Uniform core-shell Eu3+:Y2O3/SiO2 spheres were synthesized via precipitation and the Stber *** structural transition of core-shell Eu3+:Y2O3/SiO2 was studied by using high pressure photoluminescence *** pressure increasing,the emission intensities of 5D0→7F0,1,2 transitions of Eu3+ ions decreased and the transition lines showed a red *** relative luminescence intensity ratio of 5D0→7F2 to 5D0→7F1 transitions decreased with increasing pressure,indicating lowering asymmetry around Eu3+ *** compression,structural transformation for cores in the present core-shell Eu3+:Y2O3/SiO2 sample from cubic to monoclinic took place at 7.5 GPa,and then the monoclinic structure turned into hexagonal above 15.2 *** the pressure was released,the hexagonal structure transformed back to monoclinic and the monoclinic structure was kept stable to ambient pressure.

关键词： Eu3+:Y2O3/SiO2 core-shell photoluminescence high pressure phase transition rare earths

Fault Diagnosis for Nonlinear Mechatronic System Using Particle Swarm Optimization

在线全文

学校读者我要写书评

暂无评论

Fault Diagnosis for Nonlinear Mechatronic System Using Parti...