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  • 1
    Publication Date: 2018
    Description: Copper–graphite composites reinforced with SiO2 particles were fabricated by powder metallurgy technique. Electroless copper plating was introduced to improve the interfacial bonding between SiO2 particles and copper matrix. The microstructure, density, and hardness of the composites were characterized. The tribological properties, such as friction coefficient and wear rate of the composites, were studied using a pin-on-ring tribometer. The results show that the hard SiO2 can restrict the severe plastic deformation and adhesion contact in the process of wear. At the same time, parts of SiO2 particles can be broken into fine particles during wear process, which is helpful for decreasing adhesion wear and abrasive wear. Therefore, the addition of SiO2 leads to increasing friction stability and friction coefficient, and decreasing wear rate. In addition, the electroless copper plating improves the interfacial bonding between SiO2 and copper matrix, which prevents separation of SiO2 from copper matrix and further increase tribological properties of the composites.
    Electronic ISSN: 1996-1944
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Published by MDPI
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  • 2
    Publication Date: 2018
    Description: Numerous global-scale land-cover datasets have greatly contributed to the study of global environmental change and the sustainable management of natural resources. However, land-cover datasets inevitably experience information loss because of the nature of the uncertainty in the interpretation of remote-sensing images. Therefore, analyzing the spatial consistency of multi-source land-cover datasets on the global scale is important to maintain the consistency of time and consider the effects of land-cover changes on spatial consistency. In this study, we assess the spatial consistency of five land-cover datasets, namely, GLC2000, CCI LC, MCD12, GLOBCOVER and GLCNMO, at the global and continental scales through climate and elevation partitions. The influencing factors of surface conditions and data producers on the spatial inconsistency are discussed. The results show that the global overall consistency of the five datasets ranges from 49.2% to 67.63%. The spatial consistency of Europe is high, and the multi-year value is 66.57%. In addition, the overall consistency in the EF climatic zone is very high, around 95%. The surface conditions and data producers affect the spatial consistency of land-cover datasets to different degrees. CCI LC and GLCNMO (2013) have the highest overall consistencies on the global scale, reaching 67.63%. Generally, the consistency of these five global land-cover datasets is relatively low, increasing the difficulty of satisfying the needs of high-precision land-surface-process simulations.
    Electronic ISSN: 2072-4292
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Published by MDPI
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  • 3
    Publication Date: 2017-07-26
    Description: With the increasing of well depth, the hardness of rock increases which will lead to rock is difficult to be broken. Therefore, Resonance Enhanced Drilling as one of new efficient drilling technologies is presented to improve the efficiency of drilling. The paper is focused on the feasibility study on Resonance Enhanced Drilling, showing the results of the numerical analysis and presenting the implementation methods of the technology. Two kinds of numerical simulations are performed, including modal analysis and harmony analysis of rock and indenter. Also, the excitation frequency is optimized under the actual operation conditions to analyze whether Resonance Enhanced Drilling can be achieved. Our investigations confirm that both rock and drill bit can be resonant, and there are different resonant frequencies and vibration modes in different orders which are only related to their inherent characteristics. In addition, when the rock drilled is resonant and easily broken, the drill bit will not be destroyed. As a result, the Resonance Enhanced Drilling can be achieved and the optimization of excitation frequency is the resonant frequency of rock drilled. We suggest that although there are some methods and apparatus have been proposed to achieve resonance drilling technology, more researches are still needed to be conducted to further understand the rock breaking mechanism and promote the realization of the Resonance Enhanced Drilling.
    Print ISSN: 1925-542X
    Electronic ISSN: 1925-5438
    Topics: Geosciences
    Published by CSCanada
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