干式变压器有限元仿真模型的电磁和振动分析

随着电力需求的逐年增长,干式变压器的数量也在不断增加。干式变压器在运行时存在着振动和噪声的问题,为了对干式变压器振动的规律与特点进行研究,本文建立了干式变压器本体振动的有限元仿真模型,通过电磁分析获得相应的磁场分布,然后利用结构动力学分析得到其本体振动的相关规律。通过对处于运行状态的变压器振动数据进行实测分析,得到变压器振动的特征频率,然后对仿真结果进行对比分析,可以发现振动幅度与频率之间存在的关系。本文的研究结果可对干式变压器的减振降噪研究提供参考。     

Influence of external load on friction coefficient of Fe-polytetrafluoroethylene

A coarse-grained molecular dynamics simulation model was developed in this study to investigate the friction process occurring between Fe and polytetrafluoroethylene(PTFE).We investigated the effect of an external load on the friction coefficient of Fe–PTFE using the molecular dynamics simulations and experimental methods.The simulation results show that the friction coefficient decreases with the external load increasing,which is in a good agreement with the experimental results.The high external load could result in a larger contact area between the Fe and PTFE layers,severer springback as a consequence of the deformed PTFE molecules,and faster motion of the PTFE molecules,thereby affecting the friction force and normal force during friction and consequently varying the friction coefficient.     

Use of generalized refined composite multiscale fractional dispersion entropy to diagnose the faults of rolling bearing

Nonlinear Dynamics - A typical symptom of vibration signals collected from rolling bearings with local faults is the existence of periodic transients, which makes the intrinsic structure of...     

Luminescent Thin Films Enabled by CsPbX3 (X=Cl,Br, I) Precursor Solution

Inorganic cesium lead halide perovskite nanocrystals are candidates for lighting and display materials due to their outstanding optoelectronic properties. However, the dissolution issue of perovskite nanocrystals in polar solvents remains a challenge for practical applications. Herein, we present a newly designed one-step spin-coating strategy to prepare a novel multicolor-tunable CsPbX₃ (X=Cl, Br, I) nanocrystal film, where the CsPbX₃ precursor solution was formed by dissolving PbO, Cs₂CO₃, and CH₃NH₃X into the ionic liquid n-butylammonium butyrate. The as-designed CsPbX₃ nanocrystal films show high color purity with a narrow emission width. Also, the blue CsPb(Cl/Br)₃ film demonstrates an absolute photoluminescence quantum yields (PLQY) of 15.6 %, which is higher than 11.7 % of green CsPbBr₃ and 8.3 % of red CsPb(Br/I)₃ film. This study develops an effective approach to preparing CsPbX₃ nanocrystal thin films, opening a new avenue to design perovskite nanocrystals-based devices for lighting and display applications.     

枝晶生长理论中的热-动力学协同

随加工工艺趋于复杂化和极端化,基于热力学驱动力和动力学能垒相对独立的枝晶生长理论已无法精确描述多种机制共同作用的非平衡凝固过程,大大限制了该理论与工业应用的结合。首先,本文综述基于热-动力学相对独立的枝晶生长理论的发展,分析其内涵的本征热-动力学相关性,并集成于以双辊薄带连铸技术为背景的基于热-动力学相关性的枝晶生长模型。其次,定量证明了热力学驱动力和动力学能垒的相关性,通过选择不同的驱动力-能垒组合,试图在双辊薄带连铸技术中实现合金设计和工艺优化。最后,通过分析现有模型的不足,对进一步枝晶生长模型的发展以及与工艺的结合进行展望。     

周期激励下的前包钦格呼吸神经元的簇振荡现象研究

研究周期激励作用下的非自治前包钦格呼吸神经元模型,结果表明当外界激励频率与系统固有频率存在着量级差距时,系统可以产生典型的簇放电模式.由于激励频率远小于系统的固有频率,因此将整个周期激励项视为慢变参数,从而可以利用稳定性分析理论研究慢变参数变化下的平衡点的分岔类型,进一步应用快慢动力学分析方法给出簇模式产生的动力学机理.本文的结果说明外界激励对神经元的动力学行为有着重要影响,为进一步揭示呼吸节律的产生机制提供了重要帮助.     

Facile Synthesis of Enantiopure Sugar Alcohols: Asymmetric Hydrogenation and Dynamic Kinetic Resolution Combined

An unprecedented Ir/f‐amphox‐catalyzed asymmetric hydrogenation of racemic 2,3‐syn‐dihydroxy‐1,4‐diones is presented involving dynamic kinetic resolution, which produces (1R,2R,3R,4R)‐tetraols. This protocol constitutes an efficient and straightforward approach to accessing sugar alcohols bearing four contiguous stereocenters. The strategy exhibits various advantages over existing methods, including excellent yields (up to 98 %), exceptional stereoselectivities (up to 99:1 dr, 99.9 % ee), operational simplicity and substrate generality. Moreover, the nature of the reaction was revealed as a stepwise transformation by in situ Fourier‐transform infrared spectroscopy and isolation of intermediates.     

Fast Liquid Phase Epitaxial Growth for Perovskite Single Crystals

Semiconductors grown by the solution-processed method have shown low-cost,facile fabrication process and comparable performance.However,there are many reasons why it is difficult to achieve high quality films.For example,lattice constant mismatch is one of the problems when photovoltaic devices made of organ metallic perovskites.In this work,MAPbBr^{MA=CH3NH3^+}perovskites single crystals grown on the surface of MAPbBr2.5 CI0.5 perovskites single crystals via liquid epitaxial growth method is demonstrated.It is found that when the lattice constants of the two perovskite single crystals are matched,another crystal can be grown on the surface of one crystal by epitaxial growth.The whole epitaxy growth process does not require high heating temperature and long heating time.X-ray diffraction method is used to prove the lattice plane of the substrate and the epitaxial grown layer.A scanning electron microscope is used to measure the thickness of the epitaxial layer.Compared with perovskite-based photodetectors without epitaxial growth layer,perovskite-based photodetectors with epitaxial growth layer have lower dark current density and higher optical responsibility.