- 殷雅俊;吴继业;尹杰;
To make the geometrical basis for soft matters with curved surfaces such as biomembranes as simple as possible, a symmetrical analytical system was developed in conventional differential geometry. The conventional second fundamental tensor is replaced by the so-called conjugate fundamental tensor. Because the differential properties of the conjugate fundamental tensor and the first fundamental tensor are symmetrical, the symmetrical analytical system including the symmetrical differential operators, symmetrical differential characteristics, and symmetrical integral theorems for tensor fields defined on curved surfaces can be constructed. From the symmetrical analytical system, the symmetrical integral theorems for mean curvature and Gauss curvature, with which the symmetrical Minkowski integral formulas are easily deduced just as special cases, can be derived. The applications of this symmetrical analytical system to biology not only display its simplicity and beauty, but also show its powers in depicting the symmetrical patterns of net- works of biomembrane nanotubes. All these symmetrical patterns in soft matters should be just the reason- able and natural results of the symmetrical analytical system.
2008年02期 121-126页 [查看摘要][在线阅读][下载 199K] [下载次数：119 ] |[网刊下载次数：0 ] |[引用频次：7 ] |[阅读次数：0 ] - 曾大新;张元好;刘建勇;何汉军;洪晓先;
Titanium produces different compounds in gray iron. In order to determine their characteristics, a scanning electron microscope, an energy dispersive X-ray spectroscopy, and an optical microscopy were used to analyze the morphology, distribution, and composition of titanium-containing compounds in metal- lographic specimens and machined surfaces in four gray irons. The results show that the titanium-containing compounds in the gray irons are complex compounds containing V, Nb, Mn, S, and other metals, depending on the concentration of these elements in the iron. The number of titanium-containing compounds increases with increasing Ti content in the gray iron. Most of the titanium-containing compounds are located in the pearlite matrix, with some in the steadite and carbides. The results suggest that titanium-containing com- pounds reduce tool lifetime.
2008年02期 127-131页 [查看摘要][在线阅读][下载 891K] [下载次数：57 ] |[网刊下载次数：0 ] |[引用频次：1 ] |[阅读次数：0 ] - 徐艳;康进武;黄天佑;胡永沂;
Thermal stress in castings results from nonuniform cooling. The thermal stress and the deforma- tion can change the casting and mold contact conditions which then alter the heat transfer between the cast- ing and the mold. The contact element method was used to study the interaction between a sand mold and a casting. The contact status was then fed back to the heat transfer analysis between the sand mold and the casting to re-evaluate the heat transfer coefficient based on the gap size or pressure between surfaces. The thermal and mechanical phenomena are then coupled in two directions. The method was applied to analyze stress in a stress frame specimen casting and a cylinder block. The results are more accurate than without consideration of the contact effects on the heat transfer.
2008年02期 132-136页 [查看摘要][在线阅读][下载 441K] [下载次数：98 ] |[网刊下载次数：0 ] |[引用频次：17 ] |[阅读次数：0 ] - 李大勇;石德全;王利华;
Vermicular cast iron is used in certain fields because of its special physical properties. However, it is difficult to control the quality from the front of the furnace owing to the narrow range of vermiculizer and other elements that can be added to the iron. A real time method was developed to monitor the vermicular- graphite ratio of the cast iron based on fast measurements of the melt surface tension. The system includes a detector and a control unit that measure the amplitude and frequency of bubbles rising in the melt. This paper describes the methodology for measuring the surface tension of the melt and test results monitoring the vermicular-graphite ratio of the vermicular cast iron from the front of the furnace. The relationship be- tween surface tension and graphite shape has been established. The results show that this system can quickly evaluate the vermicular-graphite ratio of the cast iron.
2008年02期 137-141页 [查看摘要][在线阅读][下载 330K] [下载次数：78 ] |[网刊下载次数：0 ] |[引用频次：2 ] |[阅读次数：0 ] - 黎振华;李言祥;周荣;
The melt quality of ductile iron can be related to the melt’s thermal analysis cooling curve. The freezing zone of the thermal analysis cooling curve was found to indicate the melt quality of the ductile iron. A comprehensive difference parameter, ?, of the thermal analysis cooling curves was found to be related to the properties of ductile iron melts such as composition, temperature, and graphite morphology. As ? ap- proached 0, the thermal analysis cooling curves were found to come together with all the properties indicat- ing melt quality about the same. A database of thermal analysis cooling curves related to the properties of the ductile iron melts was set up as a basis for a method to accurately evaluate the melt quality of ductile iron by pattern recognition of thermal analysis cooling curves. The quality of a ductile iron melt can then be immediately determined by comparing its thermal analysis cooling curve freezing zone shape to those in the database.
2008年02期 142-146页 [查看摘要][在线阅读][下载 211K] [下载次数：176 ] |[网刊下载次数：0 ] |[引用频次：16 ] |[阅读次数：0 ] - M. Nili-Ahmadabadi;F. Pahlevani;P. Babaghorbani;
Semi-solid metal casting and forming is a promising production method for a wide range of metal alloys. In spite of many applications for semi-solid processed light alloys, few works have reported on the semi-solid processing of iron and steel. In this research, an inclined plate was used to change the dendritic structure of iron to globular. The effects of the length and slope of the plate on the casting structure were examined. The results show that the process effectively changes the dendritic structure to globular. A sloped plate angle of 7.5° and length of 560 mm with a cooling rate of 67 K·s-1 gave the optimum graphite nodu- larity and solid particle globularity. The results also show that the sloped plate more easily prevents inocu- lant fading since the total time processing is rather short. In addition the semi-solid ductile cast iron prepared using the inclined plate method was reheated to examine the effect of reheating conditions on the micro- structure and coarsening kinetics of the alloy. The solid fractions at different reheating temperatures and holding times were used to find the optimum reheating temperature range.
2008年02期 147-151页 [查看摘要][在线阅读][下载 649K] [下载次数：48 ] |[网刊下载次数：0 ] |[引用频次：3 ] |[阅读次数：0 ] - S. M. Yoo ;Y. S. Cho;C. C. Lee ;J. H. Kim;C. H. Kim;J. K. Choi;
Numerical simulations were used to optimize the casting design and conditions for large cast iron castings for marine engines. Simulations of the mold filling and solidification sequences were used to ana- lyze the problems of previous casting conditions with marked improvements for large cylinder liner parts. The amount and positions of chills were optimized to improve the mechanical properties and to minimize the shrinkage and micro porosity in the castings. Ultra sonic testing, penetration testing, and mechanical prop- erty testing show no defects in the castings with the productivity significantly increased.
2008年02期 152-156页 [查看摘要][在线阅读][下载 674K] [下载次数：69 ] |[网刊下载次数：0 ] |[引用频次：2 ] |[阅读次数：0 ] - Iulian Riposan;Mihai Chisamera;Stelian Stan;Torbjorn Skaland;
The objective of this paper is to review the factors influencing the formation of degenerated graph- ite layers on the surfaces of ductile iron castings for chemical resins-acid molding and core-making systems and how to reduce this defect. In the resin mold technique the sulphur in the P-toluol sulphonic acid (PTSA), usually used as the hardener, has been identified as one factor causing graphite degeneration at the metal- mold interface. Less than 0.15% S in the mold (or even less than 0.07% S) can reduce the surface layer depth. Oxygen may also have an effect, especially for sulphur containing systems with turbulent flows in the mold, water-bearing no-bake binder systems, Mg-Silica reactions, or dross formation conditions. Despite the lower level of nitrogen in the iron melt after magnesium treatment (less than 90 ppm), nitrogen bearing res- ins have a profound effect on the frequency and severity of surface pinholes, but a limited influence on sur- face graphite degeneration.
2008年02期 157-163页 [查看摘要][在线阅读][下载 321K] [下载次数：116 ] |[网刊下载次数：0 ] |[引用频次：11 ] |[阅读次数：0 ] - Aurel Crisan;Sorin Ion Munteanu;Ioan Ciobanu;Iulian Riposan;
The chemical composition of cast iron used for casting ball bearing machining disks was varied to optimize the properties such as castability, hardenability, and durability in ball machining. The cast iron characteristics were most strongly dependent on the Ni content and the carbon saturation degree, Sc. This paper describes the types of test specimens, the working conditions, and the experimental results. The in- crease of the degree of carbon saturation reduces the tendency to form shrinkholes in the castings. The de- crease in the Ni content negatively affects the final hardening treatment. A way to control solidification de- fects in cast iron, by reducing the Ni content, has been verified on cast disks.
2008年02期 164-169页 [查看摘要][在线阅读][下载 108K] [下载次数：30 ] |[网刊下载次数：0 ] |[引用频次：0 ] |[阅读次数：0 ] - Daniel Holmgren;Attila Diószegi;Ingvar L. Svensson;
The thermal conductivity/diffusivity of pearlitic grey irons with various carbon contents was investi- gated by the laser flash method. The materials were cast in controlled thermal environments producing three dissimilar cooling rates. The cooling rates together with the carbon content largely influence the thermal conductivity of grey iron. Linear relationships exist between the thermal conductivity and the carbon content, the carbon equivalent, and the fraction of the former primary solidified austenite transformed into pearlite. The results show that the optimal thermal transport properties are obtained at medium cooling rates. Equa- tions are given for the thermal conductivity of pearlite, solidified as pre-eutectic austenite, and the eutectic of grey iron. The thermal conductivity of pearlitic grey iron is modelled at both room temperature and elevated temperatures with good accuracy.
2008年02期 170-176页 [查看摘要][在线阅读][下载 398K] [下载次数：66 ] |[网刊下载次数：0 ] |[引用频次：7 ] |[阅读次数：0 ] - E. Fraé;M. Górny;W. Kapturkiewicz;H. López;
An analytical expression is presented for the susceptibility of liquid cast iron to solidify according to the Fe-C-X metastable system (also known as the chilling tendency of cast iron, CT). The analysis incorpo- rates the nucleation and growth processes associated with the eutectic transformation. The CT is related to the physicochemical state of the liquid, the eutectic cells in the flake graphite, and the number of nodules in nodular cast iron. In particular, the CT can be related to the critical wall thickness, scr, or the chill width, Wcr, in wedge shaped castings. Finally, this work serves as a guide for understanding the effect of technical fac- tors such as the melt chemistry, the spheroidizing and inoculation practice, and the holding time and tem- perature on the resultant CT and chill of the cast iron. Theoretical calculations of scr and Wcr compare well with experimental data for flake graphite and nodular cast iron.
2008年02期 177-183页 [查看摘要][在线阅读][下载 313K] [下载次数：29 ] |[网刊下载次数：0 ] |[引用频次：2 ] |[阅读次数：0 ] - 裴永忠;白音;石永久;朱丹;王元清;
Long-span aircraft hangars have features which differ from other large structural systems. The temperature stresses due to temperature variations often greatly impact the mechanical performance of the structure. The paper presents an analysis of the heat transfer processes and factors which influence the temperature distribution. The AMECO-A380 aircraft hangar at the Beijing Capital International Airport was selected as a practical example to illustrate the use of finite volume analysis to calculate the temperature field taking into account meteorological conditions, solar radiation, heat convection, etc. The temperature distribution and the variation of the length of the upper and lower chords of the grid structure roof were ana- lyzed to develop guidelines for the temperature distributions in very large aircraft hangars. The results show that the temperature effect will be large for long-span hangars, and the temperature stresses due to non- uniform temperatures should be analyzed to guarantee the structural safety of large aircraft hangars.
2008年02期 184-190页 [查看摘要][在线阅读][下载 223K] [下载次数：130 ] |[网刊下载次数：0 ] |[引用频次：32 ] |[阅读次数：0 ] - 沈岐平;郭建锋;张建平;刘贵文;
Problem-solving processes in value management (VM) workshops in the construction industry are experience-based, and the quality of these workshops depends very much on the experience of the team members. The efficiency and effectiveness of VM workshops can be improved by better reusing the experi- ence of previous VM cases and field knowledge. This paper describes a new approach to facilitate VM workshops in the construction industry using data mining (DM) techniques. The feasibility of integrating DM techniques with VM workshops in the construction industry is demonstrated in case studies. Examples are presented to illustrate different methods of applying DM tools in VM workshops. The results show that DM techniques can help team members in VM workshops to understand their problems more clearly and to generate more ideas for current problems.
2008年02期 191-201页 [查看摘要][在线阅读][下载 244K] [下载次数：213 ] |[网刊下载次数：0 ] |[引用频次：5 ] |[阅读次数：0 ] - 张崇厚;刘彦生;Yoshiaki Goto;
Thick cylindrical shells under transverse loading exhibit an elephant foot buckling mode, whereas moderately thick cylindrical shells show a diamond buckling mode. There exists some intermediate geome- try at which the transition between buckling modes can take place. This behavior is significantly influenced by the radius-to-thickness ratio and the material yield strength, rather than the length-to-radius ratio and the axial force. This paper presents a critical value at which the transition of buckling modes occurs as a func- tion of the radius-to-thickness ratio and the material yield strength. The result shows that the circumferential wave number of the diamond buckling mode increases with decreasing wall thickness. The strain concentra- tion is also intensified for the diamond buckling modes compared with the elephant foot buckling modes.
2008年02期 202-210页 [查看摘要][在线阅读][下载 357K] [下载次数：59 ] |[网刊下载次数：0 ] |[引用频次：0 ] |[阅读次数：0 ] - 石京;应习文;
The accessibility of a destination-based transportation system is defined to quantify the perform- ance of transportation systems which access a distinct destination. The access cost is used to reflect the utility of the transportation system including the fatigue and inconvenience in the total cost. The cost is quan- tified by two coefficients which represent the different characteristics of various people. The average cost and the income-relative accessibility are used to describe various aspects of the accessibility and to evaluate the accessibility of a destination-based system. A case study uses data from the Kunming transpor- tation system to evaluate the accessibility of the present city airport. The calibrated coefficients are then used to evaluate the transportation system to the new Kunming international airport. The results show that this transportation accessibility evaluation can be combined with transportation planning to study transporta- tion sub-systems.
2008年02期 211-219页 [查看摘要][在线阅读][下载 346K] [下载次数：130 ] |[网刊下载次数：0 ] |[引用频次：8 ] |[阅读次数：0 ] - 陈煜东;张毅;胡坚明;
The two important features of self-organizing maps (SOM), topological preservation and easy visualization, give it great potential for analyzing multi-dimensional time series, specifically traffic flow time series in an urban traffic network. This paper investigates the application of SOM in the representation and prediction of multi-dimensional traffic time series. First, SOMs are applied to cluster the time series and to project each multi-dimensional vector onto a two-dimensional SOM plane while preserving the topological relationships of the original data. Then, the easy visualization of the SOMs is utilized and several explora- tory methods are used to investigate the physical meaning of the clusters as well as how the traffic flow vec- tors evolve with time. Finally, the k-nearest neighbor (kNN) algorithm is applied to the clustering result to perform short-term predictions of the traffic flow vectors. Analysis of real world traffic data shows the effec- tiveness of these methods for traffic flow predictions, for they can capture the nonlinear information of traffic flows data and predict traffic flows on multiple links simultaneously.
2008年02期 220-228页 [查看摘要][在线阅读][下载 256K] [下载次数：278 ] |[网刊下载次数：0 ] |[引用频次：27 ] |[阅读次数：0 ] - 胡坚明;宋靖雁;张鸣晨;康晓京;
This paper presents an optimized topology for urban traffic sensor networks. Small world theory is used to improve the performance of the wireless communication system with a heterogeneous transmission model and an optimal transmission radius. Furthermore, a series of simulations based on the actual road network around the 2nd Ring Road in Beijing demonstrate the practicability of constructing artificial "small worlds". Moreover, the particle swarm optimization method is used to calculate the globally best distribution of the nodes with the large radius. The methods proposed in this paper will be helpful to the sensor nodes deployment of the new urban traffic sensor networks.
2008年02期 229-236页 [查看摘要][在线阅读][下载 318K] [下载次数：106 ] |[网刊下载次数：0 ] |[引用频次：11 ] |[阅读次数：0 ] - 程杰;杨新苗;邓卫;黄欣;
Roundabouts have been used successfully in cities throughout the world and are wildly used in China. The critical gap is a required parameter for calculating the capacity of roundabouts and deciding the needs for stop signs. While many studies on gap acceptance characteristics at roundabouts have been car- ried out in America and Europe, few have been done in China. This study was conducted to calibrate the critical gap in a roundabout in China. The differences between critical gaps on different days (workdays and weekends) and during different times (rush hour and non rush hour) were checked. The study was per- formed at a three-lane roundabout formed by a two-way and four-lane local road and a six-lane divided ar- tery. The data was collected at this site by a video camera. The evaluations included the cumulative prob- ability distributions of the acceptable and rejected gaps which resulted in critical gaps for all cases. The re- sults show that the critical gap during the rush hour is shorter than after the rush hour, but the difference is not large and the cumulative probability distributions can be fit by the logit functional form with parameters estimated using linear regression.
2008年02期 237-242页 [查看摘要][在线阅读][下载 98K] [下载次数：87 ] |[网刊下载次数：0 ] |[引用频次：5 ] |[阅读次数：0 ] - 董欣;杜鹏飞;佟庆远;陈吉宁;
Aquatic ecosystems require ecological water allocation to prevent from being damaged by natural disasters and undue exploitation. This paper discusses and estimates the ecological water requirements (EWRs) of typical areas in the Huaihe Basin to determine rational allocations of water resources and pro- mote regional improvements of the ecological environment. The main river course, including Hongze Lake and Nansi Lake, was selected as the study subject. Calculational methods for the river and lake EWRs were based on the reasonableness of the results and data availability. The monthly guarantee rate method was used to calculate monthly, flood period, non-flood period, and annual EWRs for the main river course and the main tributaries at two different guarantee rates. The minimum water level method was used to calculate annual EWRs for Hongze Lake and the upper and lower Nansi Lake of 1.521×109 m3, 0.637×109 m3, and 0.306×109 m3. The results were used to evaluate the rationality of the quantity of water resources allocated to ecological uses in the Huaihe Basin during 1998-2003. The result shows that the present water resource allocations in the Huaihe Basin cannot satisfy the basic ecological requirements for some years, especially years with less precipitation.
2008年02期 243-248页 [查看摘要][在线阅读][下载 370K] [下载次数：159 ] |[网刊下载次数：0 ] |[引用频次：17 ] |[阅读次数：0 ] - 宋来洲;王继斌;郑秋艳;张尊举;
A blended polymer adsorbent prepared using acrylic acid and polyvinylidene fluoride was used to remove copper from aqueous solutions. The polymer was prepared using thermally induced polymerization and phase inversion. The blended polymer was characterized by X-ray diffraction analysis (XRD), environ- mental scanning electron microscopy (ESEM), X-ray photoelectron spectroscopy (XPS), and N2 adsorp- tion/desorption experiments. The sorption data was fit to linearized adsorption isotherms of the Langmuir, Freundlich, and Dubinin-Radushkevich (D-R) isotherms models. The batch sorption kinetics was evaluated using pseudo-first-order, pseudo-second-order, and intraparticle diffusion kinetic reaction models. △H 0 is greater than 0,△G0 is lower than 0, and △S0 is greater than 0, which shows that the adsorption of Cu (Ⅱ) by the blended polymer is a spontaneous, endothermic process. The adsorption isotherm fits better to the Freundlich isotherm model and the pseudo-second-order kinetics model gives a better fit to the batch sorp- tion kinetics. The adsorption mechanism is assumed to be ion exchange between the cupric ion and the carboxylic acid functional group of the blended polymer.
2008年02期 249-256页 [查看摘要][在线阅读][下载 327K] [下载次数：57 ] |[网刊下载次数：0 ] |[引用频次：3 ] |[阅读次数：0 ] 下载本期数据