检索结果-南通市图书馆

Wave decomposition phenomenon and spectrum evolution over submerged bars

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

Acta Oceanologica Sinica 2009年第3期28卷 82-92页

作者： LI Benxia YU Xiping National Marine Environmental Forecasting center State Oceanic Administration Beijing 100081China department of Hydraulic engineering Tsinghua University Beijing 100084 China

Wave decomposition phenomenon and spectrum evolution over submerged bars are investigated by a previously developed numerical model. First, the computed free surface displacements of regular waves at various locations are compared with the available experimental data to confirm the validity of the numerical model, and satisfactory agreements are obtained. In addition, variations of decomposition characteristics with incident wave parameters and the change of energy spectrum for regular waves are also studied. Then the spectrum evolution of irregular waves over submerged bars, as well as the influence of incident peak wave period and the steepness of the front slope of the bar on spectrum evolution, is investigated. Wave decomposition and spectral shape are found to be significantly influenced by the incident wave conditions. When the upslope of the bar becomes 1：2, the length of the slope becomes shorter and will not benefit the generation of high frequency energy, so spectrum evolution is not significant.

关键词： wave decomposition spectrum evolution nonlinear waves irregular waves submerged bars

Preparation of nanoparticles with an environment-friendly approach

在线全文

学校读者我要写书评

暂无评论

Journal of Environmental Sciences 2009年第6期21卷 727-730页

作者： YAO Kefu,PENG Zhen,FAN Xiaolin Key Laboratory of Advanced Materials Processing Technology,Ministry of Education of china,department of Mechanical engineering,tsinghua university,beijing 100084,china. [a]Key Laboratory of Advanced Materials Processing Technology Ministry of Education of China Department of Mechanical Engineering Tsinghua University Beijing 100084 China

Developing various approaches for preparing high performance materials has long been topics and tasks both for scientists and for engineers. Despite that many methods have been developed for preparing nanomaterials, developing simple and environment-friendly ways for preparing nanomaterials is very attractive. Here a simple approach of synthesizing Fe3O4 nanoparticles by arc-discharge submerging in water was reported. The results showed that by this method Fe3O4 nanoparticles can be synthesized at large scale. The as-prepared Fe3O4 nanoparticles exhibited uniform spherical shape and their diameters varied with arc-discharging parameters. The experimental results showed that the size of the synthesized Fe3O4 nanoparticles can be controlled through adjusting the processing parameters. Since no vacuum system has been used, the synthesizing process is greatly simplified. In addition, only cheap deionized water and industrial iron bar are used and no pollution or harmful byproducts are found in the synthesis process. It indicated that the present approach is a simple, low-cost and environment-friendly one for preparing nanoparticles.

关键词： nanoparticles preparation approach Fe3O4

On the tribological characteristics of dynamically loaded journal bearing with micropolar fluids

在线全文

学校读者我要写书评

暂无评论

Science china(physics,Mechanics & Astronomy) 2004年第z1期47卷 45-50页

作者： WANG Xiaoli, WANG Kongying & ZHU KeqinSchool of Mechanical and Vehicular engineering, beijing Institute of Technology, beijing 100081, china department of engineering Mechanics, tsinghua university, beijing 100084, china beijing Inst Technol Sch Mech & Vehicular Engn Beijing 100081 Peoples R China Tsing Hua Univ Dept Engn Mech Beijing 100084 Peoples R China

The addition of the additives to the lubricant oil to enhance the characteristics of the lubricant will influence the performance of the bearings. Based on the theory of micropolar fluids, the tribological characteristics of a dynamically-loaded journal bearing are numerically studied. Comparisons are made between the Newtonian fluids and the micropolar fluids. It is shown that for a dynamically-loaded journal bearing, the micropolar fluids yield an increase not only in the friction force, but also in the friction coefficient. In addition, the oil film pressure and the oil film thickness are obviously higher than that of Newtonian fluids.

关键词： micropolar fluids, dynamic loads journal bearing tribological characteristics.

On the definition of fractional derivatives in rheology

在线全文

学校读者我要写书评

暂无评论

Theoretical & Applied Mechanics Letters 2011年第1期1卷 62-65页

作者： Fan Yang~(1,2,a)) and Ke-Qin Zhu~(1,b)) 1)department of engineering Mechanics,tsinghua university,beijing 100084,china 2.department of physics,the Chinese university of Hong Kong,Hong Kong,china department of physics the Chinese University of Hong Kong Hong Kong China

During the last two decades fractional calculus has been increasingly applied to physics, especially to *** is well known that there are obivious differences between Riemann-Liouville (R-L) definition and Caputo definition,which are the two most commonly used definitions of fractional *** multiple definitions of fractional derivatives have hindered the application of fractional calculus in *** this paper,we clarify that the R-L definition and Caputo definition are both Theologically unreasonable with the help of the mechanical analogues of the fractional element *** also find that to make them more reasonable Theologically,the lower terminals of both definitions should be put to—∞.We further prove that the R-L definition with lower terminal—∞and the Caputo definition with lower terminal—∞are equivalent in the differentiation of functions that are smooth enough and functions that have finite number of singular *** we can define the fractional derivatives in rheology as the R-L derivatives with lower terminal—∞(or,equivalently,the Caputo derivatives with lower terminal—∞) not only for steady-state processes,but also for transient processes.

关键词： fractional derivative Caputo definition Riemann-Liouville definition Scott-Blair model

Quality evaluation for air plasma spray thermal barrier coatings with pulsed thermography

在线全文

学校读者我要写书评

暂无评论

Progress in Natural Science:Materials International 2011年第4期21卷 301-306页

作者： Shi-bin ZHAO~1,Cun-lin ZHANG~2,Nai-ming WU~3,Hua-ming WANG~1 1.School of Materials Science and engineering,Beihang university,beijing 100191,china 2.department of physics,Capital Normal university,beijing 100048,china 3.School of Jet Propulsion,Beihang university,beijing 100191,china [a] School of Materials Science and engineering Beihang University Beijing 100191 China [b] department of physics Capital Normal University Beijing 100048 China [c] School of Jet Propulsion Beihang University Beijing 100191 China

Pulsed thermography(PT) as a non-contact non-destructive evaluation(NDE) technique was employed to examine as-sprayed air plasma spray(APS) thermal barrier coatings(TBCs) for quality *** and micro-structural characteristics play a vital role in determining the *** this paper,PT logarithmic peak second-derivative method was adopted to measure the thickness of top *** dependent thermal images were used to characterize the microstructure which was confirmed by scanning electron microscope(SEM).The results showed that there was relationship between the temperature distribution of the surface and microstructure change in *** distribution in thermal images and measurement results of thickness were in fairly good agreement with the microstructure *** can be concluded that it was possible to employ these NDE methods as quality evaluation for as-sprayed TBCs.

关键词： thermal barrier coatings(TBCs) non-destructive evaluation(NDE) pulsed thermography microstructure thickness measurement

The effect of hydrogen on the electronic structure of kink in bcc iron

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

Science china(Technological Sciences) 2009年第5期52卷 1212-1218页

作者： CHEN LiQun1,QIU ZhengChen1,YU Tao2 & WANG ChongYu2,3,4 1 College of Sciences,Central South university of Forestry and Technology,Changsha 410004,china 2 Central Iron and Steel Research Institute,beijing 100081,china 3 department of physics,tsinghua university,beijing 100084,china 4 International center for Materials physics,Chinese Academy of Sciences,Shenyang 110016,china 1. College of Sciences Central South University of Forestry and Technology Changsha 410004 China 2. Central Iron and Steel Research Institute Beijing 100081 China 3. department of physics Tsinghua University Beijing 100084 China 4. International center for Materials physics Chinese Academy of Sciences Shenyang 110016 China

The electronic structures of kinks in the [100](010) and 1/2[111](-110) edge dislocations in bcc iron containing hydrogen are investigated by means of the first-principles DMol method and the discrete variational *** effects of hydrogen on the kinks are *** results show that hydro-gen forms weak bonding states with its neighboring host atoms,and since hydrogen draws charge from its neighboring host atoms,the interactions between most of the host atoms are weakened com-pared with those of the corresponding atomic pairs in the clean *** indicates that the migration of kink,*** motion of dislocation,is easier in the doping hydrogen kink than in the clean kink,which may be the solid solution softening effect resulting from the impurity hydrogen.

关键词： electronic structure dislocation kink impurity

The Process of TiB_2-Cu Composite Phase and Structure Formation during Combustion Synthesis

在线全文

学校读者我要写书评

暂无评论

Journal of Wuhan university of Technology(Materials Science) 2006年第4期21卷 113-116页

作者：徐强 School of Materials Science and engineering Beijing Insitute of TechnologyBeijing 100081China

The reaction process of combustion synthesis for TiB2 -Cu was investigated in detail using combustion-wave arresting experiment, X-ray diffraction （ XRD ） analysis, SEM analysis and differential thermal analysis （ DTA ）. The XRD analysis results for the different parts of the quenched specimen show that TiCux intermetallic phase firstly forms with the propagation of combustion wave, and then Ti1.87 B50 and Ti3B4 metastable phases come forth due to the diffusion of B atoms and finally the stable TiB2 phase forms because of the continuous diffusion of B atoms. The formation of TiB2 phase is uot completed by one step, but undergoes several transient processes. The process of reaction synthesis for Ti-B-Cu ternary system can be divided into three main stages： melting of Cu and Ti , and the formation of Cu- Ti melt and few TiCux , TiBx intermetallic phases ; large numbers of TiCux intermetallic phases formation and some fine TiB2 particles precipitation ; and the TiB2 particles coarsening and the stable TiB2 and Cu two phases formation in the final product.

关键词： combustion synthesis reaction process TiB2 phase combustion-wave arresting experiment

Molecular dynamics simulation of kink in 〈100〉 edge dislocation in body centred cubic iron

在线全文

学校读者我要写书评

暂无评论

Chinese Science Bulletin 2007年第16期52卷 2291-2296页

作者： CHEN LiQun1,2,WANG ChongYu2,3,4 & YU Tao2 1 College of Sciences,Central South university of Forestry & Technology,Changsha 410004,china 2 Central Iron and Steel Research Institute,beijing 100081,china 3 department of physics,tsinghua university,beijing 100084,china 4 International center for Materials physics,Chinese Academy of Sciences,Shenyang 110016,china College of Sciences Central South University of Forestry and Technology Changsha 410004 China

Using the molecular dynamics method,we have constructed two kink models corresponding to the 〈100〉{010} and 〈100〉{011} edge dislocations (EDs) in body centred cubic (bcc) Fe. It is found that the geometric structure of a kink depends on the type of edge dislocation and the structural energies of the atoms sites in the dislocation core region. The formation energies,migration energies and widths of the kinks in different types of EDs are calculated. The results show that formation and migration of the kink in the 〈100〉{010} edge dislocation are difficult. The 〈100〉{011} edge dislocation moves primarily through kink nucleation,rather than kink migration.

关键词：分子动力学边缘位移铁纽结结构

Frontal genesis of moisture atmosphere during the early 2008 persistent freezing-rain event in southern china

在线全文

学校读者我要写书评

暂无评论

Science china Earth Sciences 2010年第3期53卷 454-464页

作者： QIAN WeiHong1 & FU JiaoLan1,2 1 department of Atmospheric Sciences, School of physics, Peking university, beijing 100871, china 2 National Meteorological center of CMA, beijing, 100081, china 1. department of Atmospheric Sciences School of Physics Peking University Beijing 100871 China2. National Meteorological Center of CMA Beijing 100081 China

From January 10 to February 2, 2008, a severe and persistent freezing-rain event occurred in southern and southwestern china. Here we use an observational analysis to compare the persistent freezing-rain event in the early 2008 with the winter precipita- tion in the late 2007 over south of the Yangtze River (Jiangnan). The persistent freezing-rain event was directly linked to the activity of quasi-stationary front. The gradient of equivalent temperature (ET) can well indicate the frontal genesis of moist atmosphere (moisture front) and its activity as well as its relationship with precipitation belt. The precipitation types (snow and freezing rains) are related to the vertical structure of moisture front. The inversion profile of ET vertical distribution is a typical synoptic condition that caused the freezing-rain event. The horizontal gradient of ET with a criterion of 10℃ / 100 km, which reflects the accumulation and release of atmospheric energy, can be applied to predict the precipitation 5-10 days in advance.

关键词： freezing-rain event frontal genesis extended-range weather forecast winter Jiangnan