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1.
Selective laser melting (SLM) is one type of additive manufacturing which produces metal parts by powder bed fusion. Since the materials undergo repeated and sharp heating/cooling cycles, the SLMed parts have unique microstructures. The relations among SLM processing parameters, resultant microstructures, and mechanical properties have been investigated by many researchers. However, the wear performance of SLMed materials under various contact conditions has not been carried out until recently. This paper is a presentation of previous and recent research related to wear performance. This is a crucial aspect if SLM is to be expanded to produce friction pairs. Wear rates and mechanisms of the SLMed materials under dry, boundary lubrication, cavitation erosion, and corrosion conditions are discussed and compared with conventionally processed (CP) materials. SLMed materials benefit from fine grains and high hardness, which have higher wear resistance than CP materials. Moreover, a unique tribo-layer on the surface of the SLMed part is found to protect the bulk material under boundary lubrication conditions. An optimized combination of processing parameters increases part density, which further improves the wear resistance. Future work includes studying the influence of pores on the deforming and lubricating behaviors from dry conditions to different lubrication regimes. The final target is to actively control the processing parameters to obtain desirable material properties for improving wear performance. 相似文献
2.
高等教育成本回收对公平的影响 总被引：26，自引：0，他引：26
本文简述了中国实行高等教育成本回收政策的发展历程 ,并讨论了这一政策对公平的影响。结果表明 :第一 ,招生并轨使社会经济地位低的学生获得了更公平的接受高等教育的机会 ,但成本回收在一定程度上抵消了并轨所带来的公平效应 ;第二 ,在实行成本回收的条件下 ,由于不同收入家庭学生选择高校与专业的倾向性不同 ,使低收入家庭学生在高等教育公共资助的分配中处于更为不利的地位 ;第三 ,实行高等教育成本回收能够促进整个教育系统中公共资源配置的结构公平 相似文献
3.
4.
李猛 《辽宁科技学院学报》2004,6(3):3-5
通过二维水模型模拟实验,研究了在顶吹转炉吹炼过程中,在不同渣量、不同顶吹气流量、不同枪位条件下,炉渣在钢水中的分布性质.应用分形理论对炉渣在钢液中的分布分形维数进行了计算,讨论了渣量、气体流量及枪位对分形维数的影响,得到了三者对分布分形维数影响的经验公式. 相似文献
5.
Microstructure Refinement of Sn-Sb Peritectic Alloy under High-Intensity Ultrasound Treatment 总被引：2，自引：0，他引：2
In this paper the solidification behavior of Sn-Sb peritectic alloy and the mechanism of grain refinement in solidification process under high-intensity ultrasonic field are investigated. Three different powers of high-intensity ultrasound are introduced into molten Sn-Sb peritectic alloy to study the refining effectiveness. The results show that the application of high-intensity ultrasound during solidification process of Sn-Sb peritectic alloy can refine a phase and β phase and eliminate gravity segregation of the alloy. As acoustic intensity is increased from 400 W to 800 W, not only the homogenous fine structure can be obtained, but also the cubic β phase crystals tend to be spherical. Microstructure of the sample treated by 600 W high-intensity ultrasound demonstrates the best refining effect. 相似文献
6.
In this paper the solidification behavior of Sn-Sb peritectic alloy and the mechanism of grain refinement in solidification process under high-intensity ultrasonic field are investigated. Three different powers of high-intensity ultrasound are introduced into molten Sn-Sb peritectic alloy to study the refining effectiveness. The results show that the application of high-intensity ultrasound during solidification process of Sn-Sb peritectic alloy can refine α phase and β phase and eliminate gravity segregation of the alloy. As acoustic intensity is increased from 400 W to 800 W, not only the homogenous fine structure can be obtained, but also the cubic β phase crystals tend to be spherical. Microstructure of the sample treated by 600 W high-intensity ultrasound demonstrates the best refining effect. 相似文献
7.
《British Educational Research Journal》2003,29(2):189-204
This article reports the findings of a retrospective study of ‘tracked’ grouping in a mathematics department in a co‐educational comprehensive school in Greater London. Tracking consisted here of just two tracks, a ‘fast track’ for the top 25‐30% of a cohort, and a ‘mixed track’ for the remainder. The article outlines the reasons for introducing tracking and explores its effects through interviews with teachers and data on the progress of students from age 14 to age 16. The teachers reported that tracking impacted differently on different students, and this is borne out by the quantitative data. It was not possible to provide for ‘setting’ across all the mathematics classrooms in the focal cohort, and therefore one mixed‐ability class was created. The use of analysis of covariance (ANCOVA) models shows that fast‐track students were not significantly advantaged by their placement in these tracks, but the progress of students in the mixed‐ability group showed a significant interaction between progress and prior attainment, with placement in the mixed‐ability group conferring a significant advantage on lower attaining students, while the disadvantage to higher attaining students was much smaller. 相似文献
8.
对氧化铝进行高温高压处理,所得的氧化铝样品用X射线衍射（XRD）和扫描电镜（SEM）进行了鉴定和表征。研究结果表明：高温高压处理对氧化铝的晶体形貌和晶粒大小有一定的影响。高压下,随着温度的升高,氧化铝晶粒尺寸逐渐增大,烧结体密度逐渐增加。 相似文献
9.
Ulrike Hochpöchler Wolfgang Schnotz Thorsten Rasch Mark Ullrich Holger Horz Nele McElvany Jürgen Baumert 《European Journal of Psychology of Education - EJPE》2013,28(4):1105-1126
When students read for learning, they frequently are required to integrate text and graphics information into coherent knowledge structures. The following study aimed at analyzing how students deal with texts and how they deal with graphics when they try to integrate the two sources of information. Furthermore, the study investigated differences between students from different school types and grades. Forty students from grades 5 and 8 from higher track and lower track of the German school system were asked to process and integrate texts and graphics in order to answer items from different levels of a text–picture integration taxonomy. Students’ eye movements were recorded and analyzed. Results suggest fundamentally different functions of text and graphics, which are associated with different processing strategies. Texts are more likely to be used according to a coherence-formation strategy, whereas graphics are more likely to be used on demand as visual cognitive tools according to an information-selection strategy. Students from different tracks of schooling revealed different adaptivity with regard to the requirements of combining text and graphic information. 相似文献
10.
《浙江大学学报(A卷英文版)》2021,(1)
The dynamic behaviour of slab and ballast tracks was investigated using measurements and calculations. Hammer impacts and train passages were analysed and measurements were made using geophones(velocity transducers) which had been time-integrated to displacements. The calculations were carried out in the frequency-wavenumber domain for multi-beamon-continuous soil models. The characteristics of the different tracks and track elements were established in theory and by experiment. The frequency-dependent compliances(displacement transfer functions) showed clear rail-on-railpad resonances or highly damped track-soil resonances. Compared to the rail and sleeper, the track slab had much lower amplitudes. The slab track usually had the highest rail amplitudes due to soft railpads. Train passage yielded track displacements which were a superposition of the axle loads from the two neighbouring axles of a bogie and from the two bogies of two neighbouring carriages. This global behaviour was characteristic of the track slab of the slab track, whereas the rails of the slab and the ballast tracks behaved more locally with only one bogie of influence. The measurements agreed very well with the theory of continuous soil in the case of the six measured slab tracks and acceptably well for the six measured ballast tracks. The measurements allowed us to find appropriate model parameters and to check the models. For example, the Winkler model of the soil was found to be less appropriate because it reacted more locally. 相似文献
11.
Jie Zhang Xin-biao Xiao Xiao-zhen Sheng Rong Fu Dan Yao Xue-song Jin 《浙江大学学报(A卷英文版)》2017,18(8):617-630
This paper presents an investigation into the characteristics of interior noise of a Chinese high-speed train under several typical conditions. Interior noises within Vehicle TC01, which can be used as a head car or an end car, and Vehicle TP03, the third car counting from TC01, are measured for the train running at speeds from 260 km/h to 385 km/h, along two types of track including a slab track and a ballast track and either on the ground surface or in a tunnel. Data analyses are performed for sound pressure overall levels, frequency, area contributions, and possible generation mechanisms, showing how they are affected by train speed, running direction, track type, and tunnel. The results show that, whether TC01 is used as head car or end car, the interior noise characteristics in the VIP cabin are mostly related to aerodynamic noise. Differences in interior noise between tracks become smaller as the train speed increases. The effect of a tunnel on the interior noise is more important for the middle coach than that for the head coach. This study can provide a basis for noise control of high-speed trains. 相似文献
12.
混沌系统的特性可用其混沌吸引子在相空间中的轨迹来表征。大量的研究表明、一个混沌吸引子是由无穷多个不稳定的周期轨道所组成的。通过对不稳定周期轨道的幅度或相位进行调制，则可实现对信息的保密传输。据此，在一个混沌时间序列的每一个不稳定周期轨道中、通过调制不同的信息流，就可以用单一的混沌时间序列来传输多路信息。 相似文献
13.
Christoph Michael Müller Verena Hofmann 《School Effectiveness & School Improvement》2016,27(2):95-115
Previous research suggests that the 1st year in secondary school for some students goes hand in hand with an increase in adjustment difficulties. One factor that might influence this process on an individual, compositional, and institutional level is the academic track a student attends. It was hypothesized that being assigned to a low-qualifying track predicts a stronger increase in adjustment problems than being assigned to higher tracks. A sample of 734 seventh-grade students from Switzerland attending 1 of 3 regular academic tracks or special educational classes participated. Pupils reported anonymously on their antisocial behavior, anger control problems, self-worth, and emotional distress. Multilevel analyses were performed, predicting end of seventh-grade adjustment by track controlling for initial adjustment and background variables. Students enrolled in the low-qualifying regular track increased significantly more than students from other tracks regarding their problems with global adjustment, antisocial behavior, and emotional distress. 相似文献
14.
Micro-plasma arc surface melting of 0Cr19Ni9 shielded metal arc welding joint with a micro-plasma arc welder produced a thin surface melted layer with a refined microstructure. The surface treatment changed the anodic polarization behavior in 0.5 mol/L H2SO4 solution. The polarization tests showed that for the as-welded joint both the heat-affected zone and the weld metal decreased in resistance to corrosion compared with the as-Received parent material while for the micro-plasma arc surface melted joint the corrosion resistance increased significantly. This increase in corrosion resistance is attributed to the rapid solidification of the melted layer. Rapid solidification of the melted layer refines its microstructure, decreases its microsegregation, and inhibits the precipitation of chromium carbides at the grain boundaries.received parent material while for the micro-plasma arc surface melted joint the corrosion resistance increased significantly. This increase in corrosion resistance is attributed to the rapid solidification of the melted layer. Rapid solidification of the melted layer refines its microstructure, decreases its microsegregation, and inhibits the precipitation of chromium carbides at the grain boundaries. 相似文献
15.
马昭胜 《赣南师范学院学报》2007,28(6):103-106
以柴油机性能实验台为物理模型,完成了柴油机常见参数的测量,通过LabVIEW虚拟仪器环境完成参数测量并生成数据文件;利用MATLAB软件的可视化等优点,完成了复杂的矩阵计算和图形处理,而在MATLAB环境中设计了GUI图形用户界面,实现了对在LabVIEW测试系统中生成的数据文件的访问,并进行处理,得到图形,直观的反映了测试参数在特定的时刻的轨迹. 相似文献
16.
钢液真空循环精炼过程的物理模拟 总被引：2，自引：0，他引：2
魏季和 《上海大学学报(英文版)》2003,7(1):1-17
1 Ｉｎｔｒｏｄｕｃｔｉｏｎ Ａｓａｓｅｃｏｎｄａｒｙｓｔｅｅｌｍａｋｉｎｇｔｅｃｈｎｏｌｏｇｙ ,ｔｈｅＲＨ(Ｒｕｈｒｓｔａｈｌ Ｈｅｒａｅｕｓ)ｖａｃｕｕｍｃｉｒｃｕｌａｔｉｏｎｒｅｆｉｎｉｎｇｐｒｏ ｃｅｓｓｈａｓｂｅｅｎａｐｐｌｉｅｄｗｉｄｅｌｙａｎｄｄｅｖｅｌｏｐｅｄｒａｐｉｄｌｙｉｎｐｒｅｖｉｏｕｓｆｏｕｒｄｅｃａｄｅｓ .Ｗｉｔｈａｃｏｎｔｉｎｕｏｕｓｌｙｇｒｏｗｉｎｇｄｅｍａｎｄｆｏｒｈｉｇｈｑｕａｌｉｔｙａｎｄｈｉｇｈｌｙｃｌｅａｎｓｔｅｅｌ,ｉｔｈａｓｎｏｗｂｅｃｏｍｅ ,ｔｏａｃｏｎｓ… 相似文献
17.
Antti Nurmikolu 《浙江大学学报(A卷英文版)》2012,13(11):825-835
This paper presents an overview on the wide-ranging track structure studies at the Tampere University of Technology (TUT), Finland dealing with the key aspects of track geotechnics related to high-speed passenger traffic on ballasted tracks. Special attention is paid to ballast and sub-ballast, while also considering frost action, embankment stability, track stiffness, track geometry and transition zones. As a result, this paper states that understanding the ballast degradation mechanism and its consequences and assessment of its condition occupy an important role in the construction and maintenance of a smooth high-speed rail line. The choices related to building the sub-ballast also have a dramatic impact on later track deformations and maintenance needs. In cold climate, especially where seasonal frost occurs, understanding and taking into account the frost action mechanism is crucial. Especially in the maintenance and rehabilitation planning of existing tracks, high-class analyses of ground penetrating radar data and its integrated analysis with other data can yield considerable benefits. 相似文献
18.
Peter Keith Woodward Abdellah El Kacimi Omar Laghrouche Gabriela Medero Meysam Banimahd 《浙江大学学报(A卷英文版)》2012,13(11):836-849
There are many issues surrounding the performance of critical assets on high-speed ballasted railway lines. At assets like switch & crossings and bridge transitions high track forces can be produced resulting in higher ballast settlements and hence track misalignments. The latter result in higher track forces and hence more settlement, leading to the need for increased track maintenance to ensure comfort and safety. Current technologies for solving issues like ballast movement under high-speed loading regimes are limited. However, a technique that has been well used across the UK and now increasingly overseas to stabilise and reinforce ballasted railway tracks is the application of in-situ polyurethane polymers, termed XiTRACK. This paper discusses how this technique can be used to solve these types of long-standing issues and presents actual polymer application profiles at two typical critical sites, namely a junction and a transition onto concrete slab-track. 相似文献
19.
Walter Kaminsky 《浙江大学学报(A卷英文版)》2001,2(1):1-8
Metallocenes and other transition metal compounds comprise a new generation of single site catalysts for the production of
precisely designed polyolefins and engineering plastics. The discovery of metallocene methylalumoxane (MAO) catalysts has
opened a frontier in the area of polymer synthesis and processing. A great number of symmetric and chiral zirconocenes have
been synthesized to give isotactic, syndiotatic, isoblock, or stereoblock polymers with increased impact strength and toughness,
better melt characteristics or elasticity, and improved clarity in films. Cycloolefin copolymers (COC) and syndiotactic polystyrene
can be produced by metallocene catalysts. These are new types of polymers with special properties and a high potential as
engineering plastics. Norbornene-ethene copolymers are most interesting for technical uses because of the easily available
monomers. Due to different incorporation values of the cyclic olefin in the copolymer, the glass transition temperature can
vary over a wide range and reaches 180°C. 相似文献
20.
针对多传感器目标跟踪问题,研究了一种多传感器异步航迹融合算法。由于不同传感器的采样时间各不相同,关联算法首先利用最小二乘法将局部航迹同步化,然后利用加权关联算法将局部航迹进行关联.仿真结果表明该算法能够较好地解决异步航迹的关联问题,在跟踪四个交叉目标的情况下,关联正确率接近90%. 相似文献