Electric current control of creation and annihilation of sub-100 nm magnetic bubbles examined by full-field transmission soft X-ray microscopy

The effect of electric current pulses on a sub-100 nm magnetic bubble state in a symmetric Pt/Co multilayer was directly observed using a full-field transmission soft X-ray microscope (MTXM). Field-induced evolution of the magnetic stripe domains into isolated bubbles with their sizes down to 100 nm was imaged under varying external magnetic fields. Electric current pulses were then applied to the created magnetic bubbles, and it was observed that the bubbles could be either created or annihilated by the current pulse depending on the strength of applied magnetic field. The results suggest that the Joule heating plays a critical role in the formation and/or elimination of the bubbles and skyrmions. Finally, the schematic phase diagram for the creation and annihilation of bubbles is presented, suggesting an optimized scheme with the combination of magnetic field and electric current necessary to utilize skyrmions in the practical devices.     

基于ANSYS Workbench热板电加热与油加热模拟及对比分析

为改善平板硫化机热板表面温度场分布的均匀性, 对规格为75mm×2400mm×2400mm的平板硫化机热板进行了有限元模拟. 利用ANSYS Workbench软件分别模拟热板电加热与导热油加热情况, 并进行对比分析. 结果表明, 针对同一块热板在加热到190℃工作温度左右时, 电加热热板表面温差为12.012℃, 导热油加热热板表面温差为9.2℃. 模拟分析结果表明, 采用导热油加热热板表面温度均匀性更高、升温速率更快; 且入口流速在4m?s-1时, 温度场均匀性得到明显改善.     

基于三维Fokker-Planck方程的电子回旋波加热与电流驱动模拟

利用反弹平均的三维Fokker-Planck方程,对电子回旋波加热和电流驱动进行数值模拟.考虑超热电子径向扩散对电流驱动的影响,在方程中加入径向扩散输运项,采用九点格式的中心差分对方程进行数值离散得到系数矩阵,采用不完全LU分解对系数矩阵进行预处理,利用双共轭梯度稳定法求解得到分布函数.在不考虑电子径向扩散输运条件下,得到电子回旋波驱动电流密度与功率沉积密度的分布;考虑径向扩散输运的计算结果与BANDIT3D进行比较,驱动电流分布的趋势基本一致.     

不同升温速率下AP/HTPB底排装置慢速烤燃的数值模拟

为研究在不同升温速率下高氯酸铵(ammonium perchlorate, AP)/端羟基聚丁二烯(tydroxyl-terminated polybutadiene, HTPB)底排装置的慢速烤燃特性,建立AP/HTPB底排推进剂二维轴对称非稳态传热模型和两步化学动力学反应模型。在不同升温速率下,分析底排装置的慢速烤燃响应特性。计算结果表明:在慢速烤燃的条件下,烤燃响应点发生在底排药柱与空气腔的接触面左侧,升温速率对底排药柱的着火延迟时间和烤燃响应点位置有较大影响。随着升温速率的提高,着火延迟时间变短,烤燃响应点向中心侧移动。升温速率对烤燃响应点的着火温度影响较小。     

Room temperature facile synthesis of CuO nanostructures by resistive heating

CuO porous layer and nanowires were in situ grown on Cu wires by a very simple catalyst-free thermal oxidation process based on resistive heating of pure metal wires at ambient conditions. The morphological, compositional and structural characterization of the obtained samples revealed that the nanowires are monoclinic single and bi-crystalline structures with mean diameters of 90–300 nm and typical length in the range 1–5 μm. The effects of the applied voltage values and treatment time on the morphology of the metal substrate and on the size of the nanowires were investigated. Different from the vapor–solid (V–S) mechanism, the growth of nanowires is found to be based on the Cu ion diffusion.     

Asymmetric shock heating and the terrestrial magma ocean origin of the Moon

One of the difficulties of the current giant impact model for the origin of the Moon is to explain the marked similarity in the isotopic compositions and the substantial differences in the major element chemistry. Physics of shock heating is analyzed to show that the degree of heating is asymmetric between the impactor and the target, if the target (the proto-Earth) had a magma-ocean but the impactor did not. The magma ocean is heated much more than the solid impactor and the vapor-rich jets come mainly from the magma-ocean from which the Moon might have been formed. In this scenario, the similarity and differences in the composition between the Moon and Earth would be explained as a natural consequence of a collision in the later stage of planetary formation. Including the asymmetry in shock heating is the first step toward explaining the chemical composition of the Moon.     

Voltage-induced pseudo-dielectric heating and its application for color tuning in a thermally sensitive cholesteric liquid crystal

ABSTRACT

We previously proposed an electrical approach enabling the tuning of the center wavelength λ_c of the cholesteric liquid crystal (CLC) bandgap in the full-color visible spectrum based on the electro-thermal effect. The idea involved the design of a negative CLC with a thermally sensitive bandgap feature and the use of a sandwich-type cell with finite electrode conductivity, allowing the control of cell temperature by applied voltage via pseudo-dielectric heating. It has been demonstrated experimentally that the induced pseudo-dielectric heating is predominated by the pseudo-dielectric relaxation originating from the designated cell geometry. On the basis of this technique, key factors determining the tuning efficacy of the temperature and thus λ_c are primarily investigated in this study. Our results suggest that lowering the electrode resistivity and the specific heat conductivity of the cell can promote the maximum tunable temperature range. Expectedly, optimizing the electrode area, cell gap and dielectric permittivity of the CLC favors a decreased relaxation frequency and, in turn, reducing the voltage as well as the frequency required for λ_c tuning.     

翼前缘层板对流冷却结构的防热效果分析

针对飞行器高超声速飞行时严重的气动加热环境, 设计一种层板对流冷却结构对翼前缘进行热防护. 提出一种壁面冷却效率参数η, 并运用流固耦合的分析方法, 研究了对流冷却结构在特定条件下的冷却效果, 其中采用水冷时头部冷却效率η 值最低为0.25. 研究表明, 对流结构冷却效果与内部冷却槽道深宽比γ 有重要关系, η值随γ 的增大而增大至一个稳定值, 此时冷却效果达到饱和, 若此时γ 继续增加则可能出现不利于冷却的现象. 冷却效果η随着前缘头部半径的减小而减弱. 研究还表明, 当层板对流冷却结构和材料固定时, η 值随冷却剂流量增加而增大, 并逐渐趋近至一个稳定值, 而冷却槽道进出口压差急剧增大. 因此需要综合考虑提高流量给供给系统带来的压力, 选取最佳流量值以达到相对较好的冷却效果. 对于材料而言, 内部冷却通道和外部耐热层都应选择导热系数较高的材料, 能够强化结构传热增强冷却效果.     

Hf-基非晶合金的力学性能研究

 利用MTS810实验机和分离式霍普金森压杆（SHPB）,对Hf_44.5Cu₂₇Ni_13.5Ti₅Al₁₀块体非晶合金进行了准静态和动态压缩实验,应变速率范围为10^-4~10³ s^-1,给出了不同应变速率下非晶合金的应力-应变曲线,并对其压缩断口形貌进行了扫描电镜观察。结果表明：在准静态压缩条件下,Hf_44.5Cu₂₇Ni_13.5Ti₅Al₁₀非晶合金不具有应变速率敏感性,在由放射区和扇形区组成的断口形貌上观察到纳米级韧窝和60 nm左右的周期性条纹结构;在动态压缩条件下,随着应变速率的增加,动态屈服强度明显减小,合金具有应变速率敏感性,同时断裂表面为夹杂着脉络条纹的絮状结构。进一步观察发现,动态压缩断口上存在3种特征断裂形貌：树枝状条纹、典型脉络花纹和合金熔体。     

一种新型的多孔太阳墙采暖房

长江中下游地区很多建筑没有安装专门的供暖设备,传统的空调采暖增加了建筑能耗。利用太阳能和建筑物自身进行采暖,具有重要的意义和价值。本文提出了一种新型的多孔太阳墙采暖房,其核心部分多孔太阳墙是由多孔陶瓷构成。在晴朗的冬季,对多孔太阳墙采暖房的采暖性能进行了实验研究;研究重点检测了不同外界环境(主要是指太阳辐射照度和环境温度)下,多孔太阳墙采暖房的采暖及储热性能。研究表明:多孔太阳墙采暖房在白天大部分时间都具有较好的采暖效果,且采暖房内的温差较小;同时具有较好的储热性能。以实验测得的武汉地区1月某天的实验数据为例,相比环境温度,当天采暖房内最高温升为19.9℃。在07:00～16:00之间,采暖房的平均温升为11.5℃;在辐射强度较弱的16:00～18:00,采暖房的平均温升为6.6℃。在07:00～18:00之间,采暖房内最大温差为1.37℃,出现在12:40。