检索结果-南通市图书馆

Halo Mass of Three-Dimension Milky Way

在线全文

学校读者我要写书评

暂无评论

Chinese Physics Letters 2000年第5期17卷 385-387页

作者： peng Fang peng Qiu he Department of Astronomy Nanjing UniversityNanjing 210093 Chinese Academy of Sciences-Peking University Joint Beijing Astrophysical Center Beijing UniversityBeijing 100871

We emphasize the effects of several factors on halo mass for our Galaxy,such as the disk thickness,the local surface density,and the shape of the rotation *** fitting the observed rotation curve of our Galaxy with the five-component model,we deduce a halo with a mass of 6.62×10^(11)M■within 50kpc and a local density of 0.009M■pc^(-3).It is found that the realistic Galaxy needs only about half of the halo mass that the Galaxy with an inGnitesmally thin disk requires.

关键词： Galaxy curve. rotation

Numerical Research on the Cold Start-up Strategy of a PEMFC Stack from-30℃

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

Journal of Thermal Science 2023年第3期32卷 898-910页

作者： LEI Le he Pu he peng TAO Wen-quan Shaanxi Collaborative Innovation Center for PEMFC Performance Improvement Key Laboratory of Thermal Fluid Science and Engineering of MOESchool of Energy and Power EngineeringXi’an Jiaotong UniversityXi'an 710049China

The cold start-up of the PEMFC(proton exchange membrane fuel cell)stack from sub-zero temperature is considered one of the significant obstacles to its expansive commercial *** the cold start-up process,with the progress of hydrogen/oxygen chemical reaction,the produced water will freeze into ice,occupying the pores of the porous electrode,thus leading to a rapid deterioration of output performance and even making the cold start-up *** this work,a one-dimensional numerical model is adopted to study a cold start-up process of the PMEFC stack starting from-30℃.The stepwise-changed current loading mode is employed in the *** assisted preheating method is used to explore an optimal operating condition for a successful cold *** numerical results are validated by comparing the numerical result with the experimental data in reference,and they agree with the experimental data very *** results show that the optimal heating power in the studied range is 100 *** the initial current slope increased,the current peak value increased,but the cold start-up process ***,the start-up time and ice volume fraction are highly dependent on the initial current *** optimal initial current slope is 0.7 A/***,a higher initial current slope will cause a significant inner ohmic *** resistance of CLa(catalyst layer of the anode)is the key and primary part of the total ohmic *** details of the research and the analyzed results will help design the cold start-up strategy for the PEMFC stack start-up from-30℃.

关键词： cold start-up IPEMFCstack stepwise-changed current loading mode preheating

The Best Extending Cover-preserving Geometric Lattices of Semimodular Lattices

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7期39卷 1369-1388页

作者： peng he Xue Ping WANG College of Applied Mathematics Chengdu University of Information TechnologyChengdu 610225China School of Mathematical Sciences Sichuan Normal UniversityChengdu 610066China

In 2010,Gábor Czédli and ***ás Schmidt mentioned that the best cover-preserving embedding of a given semimodular lattice is not known yet[A cover-preserving embedding of semimodular lattices into geometric *** in Mathematics,225,2455-2463(2010)].That is to say:What are the geometric lattices G such that a given finite semimodular lattice L has a cover-preserving embedding into G with the smallest|G|?In this paper,we propose an algorithm to calculate all the best extending cover-preserving geometric lattices G of a given semimodular lattice L and prove that the length and the number of atoms of every best extending cover-preserving geometric lattice G equal the length of L and the number of non-zero join-irreducible elements of L,***,we solve the problem on the best cover-preserving embedding of a given semimodular lattice raised by Gábor Czédli and ***ás Schmidt.

关键词： Finite atomistic lattice semimodular lattice geometric lattice cover-preserving embedding

Microstructure and Strength of Brazed Joints of Ti_(3)Al Base Alloy with Cu-P Filler Metal

在线全文

学校读者我要写书评

暂无评论

Journal of Materials Science & Technology 2005年第4期21卷 493-498页

作者： peng he Jicai FENG heng ZHOU National Key Laboratory of Advanced Welding Production Technology Harbin Institute of Technology Harbin 15{}001 China

Brazing of Ti3Al alloys with the filler metal Cu-P was carried out at 1173-1273 K for 60-1800 s. When products are brazed, the optimum brazing parameters are as follows： brazing temperature is 1215-1225 K; brazing time is 250-300 s. Four kinds of reaction products were observed during the brazing of Ti3Al alloys with the filler metal Cu-P, i.e., Ti3Al phase with a small quantity of Cu （Ti3Al（Cu）） formed close to the Ti3Al alloy; the TiCu intermetallic compounds layer and the Cu3P intermetallic compounds layer formed between Ti3Al（Cu） and the filler metal, and a Cu-base solid solution formed with the dispersed Cu3P in the middle of the joint. The interracial structure of brazed Ti3Al alloys joints with the filler metal Cu-P is Ti3Al/Ti3Al（Cu）/TiCu/Cu3P/Cu solid solution （Cu3P）/Cu3P/TiCu/Ti3Al（Cu）/Ti3Al, and this structure will not change with brazing time once it forms. The thickness of TiCu＋Cu3P intermetallic compounds increases with brazing time according to a parabolic law. The activation energy Q and the growth velocity/to of reaction layer TiCu＋Cu3P in the brazed joints of Ti3Al alloys with the filler metal Cu-P are 286 kJ/mol and 0.0821 m2/s, respectively, and growth formula was y2=O.O821exp（-34421.59/T）*** control of the growth for the reaction layer TiCu＋Cu3P can influence the final joint strength. The formation of the intermetallic compounds TiCu＋Cu3P results in embrittlement of the joint and poor joint properties. The Cu-P filler metal is not fit for obtaining a high-quality joint of Ti3Al brazed.

关键词： Brazed joints Microstructure Ti3Al base alloy

Effect of Brazing Conditions on Microstructure and Mechanical Properties of Al_2O_3/Ti—6Al—4V Alloy Joints Reinforced by TiB Whiskers

在线全文

学校读者我要写书评

暂无评论

Journal of Materials Science & Technology 2013年第10期29卷 961-970页

作者： Minxuan Yang peng he Tiesong Lin State Key Laboratory of Advanced Welding and Joining Harbin Institute of Technology Beijing Power Machinery Research Institute

Al2O3 and Ti-6Al-4V alloy were brazed with Ag-Cu-Ti ＋B fillers in different brazing conditions. Effects of brazing temperature, holding time and additive Ti content on joints microstructure and shear strength were investigated by scanning electron microscopy, energy dispersive spectrometry, X-ray diffraction, transmission electron microscopy and shear testing. Results indicate that TiCu and Ti（Cu,Al） decrease, but Ti2Cu and -Ti2（Cu,Al） increase in brazing seam with increasing brazing temperature, holding time and additive Ti content. Area consisting of Ti3（Cu,Al）30 and TiO near Al2O3 becomes gradually discontinuous from continuity when brazing temperature rises or holding time extends. As Ti additive content increases, TiO is absent near Al2O3, area consisting of only Ti3（Cu,Al）30 thickens. TiB whiskers are in situ synthesized by Ti and B atoms during brazing process. The brazing temperature, holding time and additive Ti content on joints microstructure influence the joints shear strength directly. The shear strength of joints, obtained at 850 ℃ holding for 10 min, reaches the maximum of 78 MPa. According to the experimental results, phase diagram and thermodynamics calculation, the interface evolution mechanism of the Al2O3/Ti-6Al-4V alloy joint was analyzed.

关键词： Active brazing Addition of B and Ti Al2O3 Ti--6Al--4V alloy

New estimates of scale heights and spiral structures for non-edge-on spiral galaxies

在线全文

学校读者我要写书评

暂无评论

Research in Astronomy and Astrophysics 2014年第7期14卷 869-874页

作者： Tao Hu Qiu-he peng Department of Automation Shanghai University Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of SciencesYunnan Observatories Department of Astronomy Nanjing University

On the basis of Poisson＇s equation for the logarithmic perturbation of matter density, we provide improved estimates of scale heights and spiral structures for non-edge-on spiral galaxies by subtracting the surface brightness distributions from observed images. As examples, the non-edge-on spiral galaxies PGC 24996, which is face-on, and M31, which is inclined, are studied. The scale height, pitch angle and inclination angle of M31, our nearest neighbor, that are presented in this work, agree well with previous research.

关键词： galaxy: disk -- galaxies: fundamental parameters -- galaxies: spiral --galaxies: structure

A PREDICTION TECHNIQUE FOR DYNAMIC ANALYSIS OF FLAT PLATES IN MID-FREQUENCY RANGE

在线全文

学校读者我要写书评

暂无评论

Acta Mechanica Solida Sinica 2007年第4期20卷 333-341页

作者： Weicai peng Zeng he peng Li Jiaqiang Wang School of Civil Engineering and Mechanics Huazhong University of Science and Technology Wuhan 430074 China

The wave-based method （WBM） has been applied for the prediction of mid-frequency vibrations of fiat plates. The scaling factors, Gauss point selection rule and truncation rule are introduced to insure the wave model to converge. Numerical results show that the prediction tech- nique based on WBM is with higher accuracy and smaller computational effort than the one on FEM, which implies that this new technique on WBM can be applied to higher-frequency range.

关键词： mid-frequency range Trefftz method computational efficiency numerical prediction technique

Scale heights of Non-Edge-on Spiral Galaxies

在线全文

学校读者我要写书评

暂无评论

Chinese Journal of Astronomy and Astrophysics 2006年第1期6卷 43-51页

作者： Tao Hu Qiu-he peng Ying-he Zhao Department of Astronomy Nanjing University Nanjing 210093 Joint Astrophysics Center of Chinese Academy of Science-Peking University Beijing 100871 The Open Laboratory of Cosmic Ray and High Energy Astrophysics Chinese Academy of Sciences Beijing 100039

We present a method of calculating the scale height of non-edge-on spiral galaxies, together with a formula for errors. The method is based on solving Poisson＇s equation for a logarithmic disturbance of matter density in spiral galaxies. We show that the spiral arms can not extend to inside the ＂forbidden radius＂ r0, due to the effect of the finite thickness of the disk. The method is tested by re-calculating the scale heights of 71 northern spiral galaxies previously calculated by Ma, peng ＆ Gu. Our results differ from theirs by less than 9%. We also present the scale heights of a further 23 non-edge-on spiral galaxies.

关键词： galaxy: disk -- galaxies: fundamental parameters -- galaxies: spiral --galaxies: structure

An algorithm for Monte Carlo simulation of bremsstrahlung emission by electrons

在线全文

学校读者我要写书评

暂无评论

Nuclear Science and Techniques 2017年第5期28卷 86-94页

作者： Muhammad Abdul Wasaye Hui Wang peng he Key Laboratory of Neutronics and Radiation Safety Institute of Nuclear Energy Safety Technology Chinese Academy of Sciences Hefei 230031 China Collaborative Innovation Center of Radiation Medicine of Jiangsu Higher Education Institutions Suzhou 215006 China School of Nuclear Science and Technology University of Science and Technology of China Hefei 230027 China

An algorithm for Monte Carlo simulation of bremsstrahlung emission by electrons based on the framework of Super MC is presented in this paper with efficient and accurate methods to sample the angular distribution and energy of bremsstrahlung photons. The photon energy is sampled according to scaled energy-loss differential cross sections tabulated by Seltzer and Berger. A novel hybrid model for photon angular distribution by low-and high-energy incident electrons is developed. The model uses Tsai's full form of angular distribution function with atomic form factors for high-energy incident electrons. For electrons o\500 ke V, a simple efficient and accurate analytical distribution function is developed, using adjustable parameters determined from the fitting of numerical values of the shape functions tabulated by Kissel et al. The efficiency of sampling photon energy is 80%. Our angular sampling algorithm for high-energy electron bremsstrahlung based on Tsai distribution function is very efficient(sampling efficiency*70%) in the useful photon energy range.

关键词： Bremsstrahlung Monte Carlo SuperMC Differential cross section Angular distribution