关键词： Mechanical milling   Microstructure   TGA-DSC   Electrical characterisation   Dielectric loss factor  

摘要： In this work, milling effect on chemically synthesized nanocrystalline Zinc Cobaltite (ZnCo2O4) has been investigated and we report how the structural and electrical properties vary with the milling span. Phase pure ZnCo2O4 has been successfully synthesized via simple and cost-effective co-precipitation method and then it has been milled for one, four and 8 h respectively. XRD confirms formation of single phase cubic structure for both milled and unmilled nano-powders. Different microstructural parameters has been estimated from Rietveld analysis, which shows particle size reduction from similar to 29.64 nm for unmilled sample to similar to 18.13 nm for 8 h milled sample. TGA-DSC curve of as prepared sample shows good temperature stability that helps to estimate the appropriate sintering temperature for the samples. TEM analysis also gives values of grain size in agreement with Reitveld analysis. Frequency dependent ac conductivity curve obeys universal Jonscher power law and temperature dependence of frequency exponent is explained by small polaron transaction. Comparable activation energies from hopping mechanism and relaxation process indicates similar transport mechanism. Superimposed scaling spectra obeys TTSP principle. AC conductivity increases with frequency as a result of hopping of the charge carriers. Smaller particles with reduced strain gives enhanced conductivity as well as enhanced value of hopping frequency. This further suggests creation of excess charge carriers in milled samples. Cole-Cole plot shows non-Debye type behaviour of the samples. The dielectric loss factor increases with lowering of particle size since smaller grains contributes to faster charge conduction. (C) 2019 Elsevier B.V. All rights reserved.

关键词： neural network   plateau   singular region   statistical mechanics  

摘要： The plateau phenomenon, wherein the loss value stops decreasing during the process of learning, is troubling. Various studies suggest that the plateau phenomenon is frequently caused by the network being trapped in the singular region on the loss surface, a region that stems from the symmetrical structure of neural networks. However, these studies all deal with networks that have a one-dimensional output, and networks with a multidimensional output are overlooked. This paper uses a statistical mechanical formalization to analyze the dynamics of learning in a two-layer perceptron with multidimensional output. We derive order parameters that capture macroscopic characteristics of connection weights and the differential equations that they follow. We show that singular-region-driven plateaus diminish or vanish with multidimensional output, in a simple setting. We found that the more non-degenerative (i.e. far from one-dimensional output) the model is, the more plateaus are alleviated. Furthermore, we showed theoretically that singular-region-driven plateaus seldom occur in the learning process in the case of orthogonalized initializations.

关键词： 工程机械   底盘测功机   动力性能   挂车  

摘要： 为减小测功机自身损耗功率对底盘动力性能测量精度的影响,提出一种反拖模拟挂车测量测功机自身损耗功率的方法,测量结果用于对底盘损耗功率进行修正。对某型工程机械进行底盘动力性能测试和实验数据分析,评价机械底盘的传动效率与发动机的输出功率,结果表明,该方法有效地降低工程机械自重导致测功机自身损耗功率变化对底盘动力性能测试的影响,提高测量结果的精度,为工程机械底盘维修提供有力的数据支持。

关键词： 机械设计制造   学院   三峡大学   能源与动力工程   机械电子工程   材料成型   控制工程   工业工程  

摘要： 2014年1月原机械与材料学院更名为机械与动力学院,学院现设有机械设计制造及其自动化、机械电子工程、材料成型及控制工程、工业工程、能源与动力工程、核工程与核技术六个本科专业,其中机械设计制造及其自动化为国家特色专业、第二批卓越工程师教育培养计划专业和省本科品牌专业,材料成型及控制工程为第三批卓越工程师教育培养计划专业。

关键词： 机械动力   下水道防堵   地漏   模型设计  

摘要： 下水道堵塞问题在建筑设计中一直是重点问题,目前存在的解决办法中,固态无动力拦截设计占据了大量的比例,机械式排堵装置又因动力问题难以设计使用;针对问题主体,堵塞物,设计一种采取水动力﹑机械式的地漏装置予以解决,解决堵塞问题的同时保证排水量的正常。

关键词： 机械动力设备   检修   管理   策略  

摘要： 企业的安全生产和长远发展都离不开机械动力设备的检修管理,检修管理主要包括检修频度、检修水准、检修成本等。由于机械动力设备的检修管理对于一个企业来说意义重大,而机械动力设备一旦出现故障,不仅会影响企业的正常运作,还会阻碍企业的正常盈利。所以有必要了解目前机械制造行业动力设备的检修管理现状,并且依据现状中暴露出的问题提出相应优化对策,为机械动力设备检修管理提供可参考的依据。

关键词： 混合动力   工程机械   动力系统   构成理论  

摘要： 在建设工程项目施工时,我们以工程机械为主要单位。随着气候、污染环境以及污染变化的加剧,如今,节能减排已经成为发展的主要内容。在消耗能源时工程机械可谓其中的主力,为了更好的了解这方面内容,文章以混合工程机械动力系统构成原理为切入点展开了分析。

关键词： Epoxy resin   Carbon nanobuds   Molecular dynamics   Mechanical properties   Thermal conductivity  

摘要： Epoxy resin systems based on Diglycidyl ethers bisphenol A (DGEBA) and methyl tetrahydrophthalic anhydride (MTHPA) often experience problems related to brittleness, large internal stress, undesirable shock resistance, low fatigue durability and heat resistance. It is thus of vital importance to improve the thermal and mechanical properties of the DGEBA/MTHPA epoxy resins. In this study, the effects of the addition of carbon nanobud (CNB) to the mechanical properties and thermal conductivities of cross-linked epoxy resins based on the DGEBA and MTHPA are investigated using molecular dynamics (MD) simulations. Different molecular models are constructed, and comparisons are made for the pure DGEBA/MTHPA and their nanocomposites containing carbon nanotube (CNT), single CNB, functionalized nanobuds with one and four fullerenes attached to the CNT, respectively. It has been shown that all these reinforced epoxy systems have an increased glass transition temperature (Tg), Young's modulus and shear modulus, whereas the DGEBA/MTHPA/FCNBs performs the best. Compared with pure DGEBA/MTHPA, the Tg value of the DGEBA/MTHPA/FCNBs increases by 34.3% (140 K). The improvement of the Young's modulus and shear modulus is also significant, with an increase of 44.5% and 51.8%, respectively. The enhancement in the thermal conductivity, however, is limited due to the small length of SWCNTs/CNBs introduced.

关键词： 新能源汽车   智能网   上海交通大学   产业化   博士生导师   工程学院   科技创新   机械  

摘要： 张希认为,现阶段全世界主要汽车强国的智能网联新能源汽车的研发与产业化几乎处于同一发展水平线,正是我国突破汽车技术垄断的绝佳时期。目前智能网联新能源汽车是全球汽车业的热点,大力推进智能网联新能源汽车在我国的发展是促进中国汽车产业转型升级、抢占国际竞争制高点的紧迫任务,也是推动绿色发展、智能出行、培育新的经济增长点的重要举措。