- 陈俊达;金观昌;孟利波;
In structure inspections, applications of optical techniques are rare, but the advantages of a non-contact, full field technique using a simple apparatus are attractive. The main requirements for structure in- spection are the full-field strain measurement with the required precision and on-site measurement ability. The digital correlation method (DCM), a new optical deformation measurement tool, can satisfy all of the re-quirements for structure inspection. A smoothing algorithm which can greatly improve the strain measure-ment precision, and a 3-D DCM have been developed in this paper. For verifying this improvement, a com-parison of strain measurements by computer-simulated speckle images has been carried out. Additionally, three structure inspection examples that cover typical materials and structure styles are presented: the inter-face shear stress distribution for reinforced concrete piles bedded on rock, the 3-D strain distribution of a composite vessel structure, and stresses in a hookup that connects two steel bridge structures. All the ex- amples show that the new structural inspection tool is exemplary and illustrates the obvious advantages of this optical non-destructive technique.
2007年03期 237-243页 [查看摘要][在线阅读][下载 559K] [下载次数：115 ] |[网刊下载次数：0 ] |[引用频次：18 ] |[阅读次数：0 ] - 张彤;庄茁;
Iterated function system (IFS) models have been used to represent discrete sequences where the attractor of the IFS is piece-wise self-affine in R 2 or R 3 (R is the set of real numbers). In this paper, the piece-wise self-affine IFS model is extended from R 3 to Rn (n is an integer greater than 3), which is called the multi-dimensional piece-wise self-affine fractal interpolation model. This model uses a "mapping partial derivative" , and a constrained inverse algorithm to identify the model parameters. The model values depend continuously on all the model parameters, and represent most data which are not multi-dimensional self-affine in Rn . Therefore, the result is very general. The class of functions obtained is much more diverse because their values depend continuously on all of the variables, with all the coefficients of the possible multi-dimensional affine maps determining the functions.
2007年03期 244-251页 [查看摘要][在线阅读][下载 164K] [下载次数：48 ] |[网刊下载次数：0 ] |[引用频次：2 ] |[阅读次数：0 ] - 周晓舟;朱克勤;
This paper discusses the relationship between natural coordinates in fluid mechanics and or-thogonal curvilinear coordinates. Since orthogonal curvilinear coordinates have some excellent mathemati-cal properties, natural coordinates can be applied more widely if they can be transformed to orthogonal cur-vilinear coordinates. Frenet formulas which describe the differential properties of natural coordinates were compared with the derivative formulas of orthogonal curvilinear coordinates to show that natural coordinates are not generally orthogonal curvilinear coordinates. A method was introduced to transform natural coordi-nates into orthogonal curvilinear coordinates by rotating the normal planes of the natural coordinates about the streamlines. The transformation is true as long as the natural coordinates satisfy several equations. Vor-ticity decomposition in the natural coordinates is used to show that these conditional equations are satisfied only if the streamlines are perpendicular to the vortexlines on every given point in the flow field. These equa-tions apply in both planar flows and axisymmetric flows without a circumferential velocity component, but do not apply in some 3-D flows such as Beltrami flow.
2007年03期 252-255页 [查看摘要][在线阅读][下载 98K] [下载次数：67 ] |[网刊下载次数：0 ] |[引用频次：1 ] |[阅读次数：0 ] - Vadim Zakirov;Vladimir Pavshook;
This paper is to promote investigation into the nuclear rocket engine (NRE) propulsion option that is considered as a key technology for manned Mars exploration. Russian NRE developed since the 1950s in the former Soviet Union to a full-cale prototype by the 1990s is viewed as advantageous and the most suit-able starting point concept for manned Mars mission application study. The main features of Russian het-erogeneous core NRE design are described and the most valuable experimental performance results are summarized. These results have demonstrated the significant specific impulse performance advantage of the NRE over conventional liquid rocket engine (LRE) propulsion technologies. Based on past experience, the recent developments in the field of high-temperature nuclear fuels, and the latest conceptual studies, the developed NRE concept is suggested to be upgraded to the nuclear power and propulsion system (NPPS), more suitable for future manned Mars missions. Although the NRE still needs development for space appli-cation, the problems are solvable with additional effort and funding.
2007年03期 256-260页 [查看摘要][在线阅读][下载 256K] [下载次数：117 ] |[网刊下载次数：0 ] |[引用频次：19 ] |[阅读次数：0 ] - 卿涛;邵天敏;温诗铸;
An apparatus was specifically developed for micro-friction and adhesion measurements. The force measurement range is 10-2000 μN with a horizontal speed of 10-400 μm/s . The apparatus was tested us-ing a 0.7-mm diameter steel ball as the upper specimen to measure the micro friction and adhesion behav-iour of a Si (100) wafer and a TiB2 film. The effects of rest time, speed, and load were studied. The results show that the maximum static and sliding friction forces of both the Si (100) wafer and the TiB2 film increase with the load. At low speeds, the influence of speed on the friction force is significant. The adhesion forces of the Si (100) wafer and the TiB2 film increase with rest time, reaching stable values after about 3000 s. The TiB2 film has significantly less adhesion and micro friction forces than the Si (100) wafer.
2007年03期 261-268页 [查看摘要][在线阅读][下载 189K] [下载次数：125 ] |[网刊下载次数：0 ] |[引用频次：4 ] |[阅读次数：0 ] - 吴军;李铁民;刘辛军;王立平;
Closed-form solutions were developed to optimize kinematics design of a 2-degree-of-freedom (2-DOF) planar parallel manipulator. The optimum design based on the workspace was presented. Meanwhile, a global, comprehensive conditioning index was introduced to evaluate the kinematic designs. The optimal parallel manipulator is incorporated into a 5-DOF hybrid machine tool which includes a 2-DOF rotational mill-ing head and a long movement worktable. The results show that the planar parallel manipulator-based ma-chine tool can be successfully used to machine blades and guide vanes for a hydraulic turbine.
2007年03期 269-275页 [查看摘要][在线阅读][下载 270K] [下载次数：378 ] |[网刊下载次数：0 ] |[引用频次：16 ] |[阅读次数：0 ] - 牟鹏;向东;段广洪;
Printed circuit boards (PCBs) are in all electronic equipment, so with the sharp increase of elec-tronic waste, the recovery of PCB components has become a critical research field. This paper presents a study of the reclaimation and reuse of nonmetallic materials recovered from waste PCBs. Mechanical proc-esses, such as crushing, milling, and separation, were used to process waste PCBs. Nonmetallic materials in the PCBs were separated using density-based separation with separation rates in excess of 95/. The re-covered nonmetals were used to make models, construction materials, composite boards, sewer grates, and amusement park boats. The PCB nonmetal products have better mechanical characteristics and dura-bility than traditional materials and fillers. The flexural strength of the PCB nonmetallic material composite boards is 30/ greater than that of standard products. Products derived from PCB waste processing have been brought into industrial production. The study shows that PCB nonmetals can be reused in profitable and environmentally friendly ways.
2007年03期 276-283页 [查看摘要][在线阅读][下载 429K] [下载次数：159 ] |[网刊下载次数：0 ] |[引用频次：45 ] |[阅读次数：0 ] - 王晓亮;何榕;Toshiyuki Suda;Junichi Sato;
Partial agglomeration is a major problem in fluidized beds. A chaotic analytical method based on the phase-plane invariant of the pressure fluctuations in the fluidized beds has been used to warn of ag-glomeration at an early stage. Cold tests (no combustion) and hot tests (combustion) in fluidized beds show that the phase-plane invariant of the pressure fluctuations can distinguish the dynamic behavior of fluidized beds with different flow rates in cold tests. With combustion, when the flow rate was kept constant, agglom-eration was detected very early by looking at the phase-plane invariant. The phase-plane invariant can be used to distinguish changes in fluidized beds due to changes in the flow rate, agglomeration, or various other factors. Therefore, this reliable agglomeration early warning system can be used for better control of circulating fluidized beds.
2007年03期 284-289页 [查看摘要][在线阅读][下载 189K] [下载次数：52 ] |[网刊下载次数：0 ] |[引用频次：0 ] |[阅读次数：0 ] - 董光;王大志;张金换;黄世霖;
Side impact accidents of passenger cars with fixed poles may result in severe injuries to the vehi-cle occupants. In this paper, side structure intrusion was considered as the criterion for passenger cars crashworthiness during side impact with a pole. The relationship between side intrusions and the side struc-ture stiffness was analyzed. The acceleration of the unstruck side vehicle body was selected as the criterion for studying the influence of different side structure components on the side structure stiffness during pas-senger car pole side impacts. The behavior was analyzed using finite element simulations. The results show that the rocker and the lower part of the B-pillar are the key parts of the side structures in determining the passenger car side stiffness. Passenger car pole side impact crashworthiness is, therefore, most sensitive to these two components.
2007年03期 290-295页 [查看摘要][在线阅读][下载 193K] [下载次数：160 ] |[网刊下载次数：0 ] |[引用频次：32 ] |[阅读次数：0 ] - 闫焉服;冯丽芳;张柯柯;文九巴;
The creep properties of solder alloys are an important factor affecting the reliability of soldered joints in surface mount technologies. Particle-enhancement is one way to improve the properties of solder alloys. The temperature of the solder joint is one of the primary factors affecting the solder joint creep prop-erties. Single shear lap creep specimens with a 1 mm2 cross-sectional area were fabricated using Ag parti-cle enhancement 99.3Sn0.7Cu based composite solder and 99.3Sn0.7Cu eutectic solder to examine the in-fluence of temperature on the creep behavior of solder joints. The results show that the solder joint creep resistance of the composite solder joint was generally superior to that of the 99.3Sn0.7Cu solder joint. The creep rupture life of the composite solder joint was reduced by increasing temperatures at a faster rate than that of the 99.3Sn0.7Cu eutectic solder joint.
2007年03期 296-301页 [查看摘要][在线阅读][下载 620K] [下载次数：83 ] |[网刊下载次数：0 ] |[引用频次：9 ] |[阅读次数：0 ]
- 张红;翁少群;周旋;
The mechanisms affecting housing prices were studied using the equilibrium housing prices based on classic supply/demand theory. The fluctuations of the actual housing prices were then analyzed relative to the equilibrium prices. The equilibrium prices for each area were calculated from economic statistics and housing prices in 35 China metropolitan areas. The fluctuations of the actual prices are then manifested as functions of the equilibrium price, the mean reversion, and the autocorrelation coefficient. The results show that the equilibrium prices are determined by the basic economic conditions in China and that the equilib-rium prices greatly affect the fluctuation of the actual prices, which return to the equilibrium price through self-adjustments. The data also shows that the actual prices in China have the trend of continuing to rise in the future.
2007年03期 302-308页 [查看摘要][在线阅读][下载 80K] [下载次数：313 ] |[网刊下载次数：0 ] |[引用频次：10 ] |[阅读次数：0 ] - Intikhab Ahmed Qureshi;陆化普;
The uncontrolled growth in urbanization and motorization generally contributes to an urban land use and transportation system that is socially, economically, and environmentally unsustainable. This paper uses Karachi as a case study, which is the largest urban and economic centre of Pakistan, passing through an uncontrolled phase of rapid urbanization and motorization. The paper first reviews research related to sustainable transportation systems to comprehend the concept of sustainable development and transporta-tion. The paper then evaluates the existing transportation and infrastructure system, national transportation policies, and urban transportation projects to determine if the current paradigm is moving toward or away from sustainable transportation. Furthermore, the principles for sustainable urban transportation are devel-oped to see what significance national transportation policies have given to urban transportation from a sus-tainable transportation point of view. Finally some strategies are suggested, adoption of which may lead to a sustainable urban development and transportation system in Karachi.
2007年03期 309-317页 [查看摘要][在线阅读][下载 211K] [下载次数：236 ] |[网刊下载次数：0 ] |[引用频次：11 ] |[阅读次数：0 ] - 王殿海;梁春岩;景春光;王国华;
Chinese traffic is typically composed of bicycles and motor vehicles on the same road. The effi-ciency of bicycle traffic in time and space at intersections was investigated for eight typical intersections in the cities of Tianjin, Shenyang, and Changchun, all in China, by means of video recording. Models were de-veloped to calculate the through bicycle traffic and the left-turn bicycle traffic conversion factors in intersec-tions where bicycles and motor vehicles share the same road. The results indicate that the through bicycle conversion factor is 0.28 and the left-turn bicycle conversion factor is 0.33. This conclusion differs from the current value used in China. More research on the conversion factor is necessary to evaluate the impact of intersections.
2007年03期 318-323页 [查看摘要][在线阅读][下载 291K] [下载次数：134 ] |[网刊下载次数：0 ] |[引用频次：7 ] |[阅读次数：0 ] - 李玲;Shigeo Kimura;
The transport of yellow sand over mountain regions in the presence of internal gravity waves has been investigated numerically. The motion of yellow sand particles has been simulated in a Lagrangian frame of reference by solving the time-dependent Reynolds averaged Navier-Stokes equations. An implicit time integration in a fitted body grid arrangement was used to simulate the stratified flow over an isolated ideally bell-shaped mountain. The transport and deposition of particles of various sizes, and of the altitudes where particles were released have been analyzed. Particular attention was given to transport patterns of different sized particles in various atmospheric conditions. The results show that the particle size and the re-lease altitude are both important factors in determining the trajectories of the particles. Small particles tend to be transported a long distance over the mountains, whereas heavier particles settle down around the re-lease source. Due to the existence of an internal gravity wave, the particle release altitude affects the trajec-tory of the particles. The analysis and results provide a very useful tool for the study of atmospheric flow and transport of pollutants over real topographies.
2007年03期 324-331页 [查看摘要][在线阅读][下载 215K] [下载次数：19 ] |[网刊下载次数：0 ] |[引用频次：0 ] |[阅读次数：0 ] - 李玲;Shigeo Kimura;
The characteristics of stratified flow over an isolated mountain ridge have been investigated nu-merically. The two-dimensional model equations, based on the time-dependent Reynolds averaged Navier-Stokes equations, are solved numerically using an implicit time integration in a fitted body grid arrangement to simulate stratified flow over an isolated ideally bell-shaped mountain. The simulation results are in good agreement with the existing corresponding analytical and approximate solutions. It is shown that for atmos-pheric conditions where non-hydrostatic effects become dominant, the model is able to reproduce typical flow features. The dispersion characteristics of gaseous pollutants in the stratified flow have also been stud-ied. The dispersion patterns for two typical atmospheric conditions are compared. The results show that the presence of a gravity wave causes vertical stratification of the pollutant concentration and affects the diffu-sive characteristics of the pollutants.
2007年03期 332-336页 [查看摘要][在线阅读][下载 116K] [下载次数：21 ] |[网刊下载次数：0 ] |[引用频次：0 ] |[阅读次数：0 ]
-
<正>The Tsinghua team won a gold medal in the 31st Annual ACM (Association for Computing Machinery) Interna-tional Collegiate Programming Contest World Finals on March 15 in Tokyo.
2007年03期 251页 [查看摘要][在线阅读][下载 19K] [下载次数：21 ] |[网刊下载次数：0 ] |[引用频次：0 ] |[阅读次数：0 ] <正>The Tsinghua team of the STEP( the Stanford-Tsinghua Exchange Program), consisting of 20 2nd year MBA stu-dents, visited Stanford Graduate School of Business
2007年03期 255页 [查看摘要][在线阅读][下载 41K] [下载次数：19 ] |[网刊下载次数：0 ] |[引用频次：0 ] |[阅读次数：0 ] -
<正>The 2nd National Master of Public Administration (MPA) outstanding theses selection was announced recently. Al-together ten papers were selected from 70 papers.
2007年03期 268页 [查看摘要][在线阅读][下载 16K] [下载次数：19 ] |[网刊下载次数：0 ] |[引用频次：0 ] |[阅读次数：0 ] <正>Prime Minister Jens Stoltenberg of Norway visited Tsinghua on March 27. Tsinghua President Gu Binglin wel-comed Mr. Stoltenberg. The two exchanged ideas on climate change,
2007年03期 283页 [查看摘要][在线阅读][下载 18K] [下载次数：11 ] |[网刊下载次数：0 ] |[引用频次：0 ] |[阅读次数：0 ] -
<正>Dr. Craig Mello, the Nobel Prize Winner of 2006 in Physiology or Medicine, delivered a speech entitled "Return to The RNA World:Rethinking Gene Expression, Evolution
2007年03期 301页 [查看摘要][在线阅读][下载 17K] [下载次数：37 ] |[网刊下载次数：0 ] |[引用频次：0 ] |[阅读次数：0 ] <正>A Memorandum of Understanding was recently signed between Tsinghua and Imperial College London, during the visit of Imperial College London Deputy Rector Sir Leszek Borysiewicz.
2007年03期 331页 [查看摘要][在线阅读][下载 60K] [下载次数：13 ] |[网刊下载次数：0 ] |[引用频次：0 ] |[阅读次数：0 ] -
<正>Tsinghua Science and Technology (Tsinghua Sci Technol), a comprehensive academic journal sponsored by Tsinghua University,
2007年03期 361页 [查看摘要][在线阅读][下载 563K] [下载次数：10 ] |[网刊下载次数：0 ] |[引用频次：0 ] |[阅读次数：0 ] 下载本期数据