Direct observation of the crystal-growth transition in undercooled silicon

Using an electromagnetic levitation facility with a laser heating unit, silicon droplets were highly undercooled in the containerless state. The crystal morphologies on the surface of the undercooled droplets during the solidification process and after solidification were recorded live by using a high-speed camera and were observed by scanning electron microscopy. The growth behavior of silicon was found to vary not only with the nucleation undercooling, but also with the time after nucleation. In the earlier stage of solidification, the silicon grew in lateral, intermediary, and continuous modes at low, medium, and high undercoolings, respectively. In the later stage of solidification, the growth of highly undercooled silicon can transform to the lateral mode from the nonlateral one. The transition time of the sample with 320 K of undercooling was about 535 ms after recalescence, which was much later than the time where recalescence was completed.     

固体氧化物燃料电池氧化还原反应热流场模拟

为了研究固体氧化物燃料电池的氧化还原反应的热流场分布情况,建立了氧化还原反应的热流场环境.设计了连接管式高温炉的气体通路,研究了固体氧化物燃料电池在氧化还原反应中热流场的控制方式,分析了氧化还原反应热流场计算条件,并使用数值模拟工具进行计算与模拟.实验结果表明:氧化还原反应热流场的温度分布可以分为293 K、324.111 K、355.222K、386.333K、417.444K、448.556K、479.667K、510.778K、541.889K和573K等9个温度场分布等值区域,X坐标方向速度场分布范围为-0.200 261~0.177 592,Y坐标方向速度场分布范围为-0.275 204~0.260 32,及速度矢量范围为0~0.284 156,有助于显现氧化还原气体分布状况和氧化还原反应渐变过程.     

响应面优化—超声辅助提取丹参多糖工艺

响应面优化超声波法提取丹参多糖工艺;方法:在单因素试验的基础上,采用三因素三水平响应面分析法,利用软件Design Expert试验设计原理得到二次线性回归方程,以多糖产率为响应面值作响应面图;结果:确定超声提取丹参多糖最佳工艺条件为:超声功率90 W、超声温度50℃、提取时间30 min、液固比为55:1,提取次数为2次,丹参多糖产率为8.23%。统计结果表明,模型相关系数R~2=0.8398。变异系数C.V值较低,说明实验有较好的稳定性;超声功率的二次项和液料比的二次项均达到极显著水平(P0.01)。验证实验表明,所得模型方程能较好地预测实验结果,拟合度较好。结论:超声提取法与传统水煮法相比,不仅能耗低、产率高,且提取时间缩短16倍。     

H ∞ Control for uncertain system with time-delay and nonlinear external disturbance via adaptive control method

This paper considers the H _∞ control problem for the uncertain time delay system with nonlinear external disturbance. Given a system containing nonlinear external disturbance, our purpose is to design a robust controller such that the uncertain system is asymptotically stable with a generalized H _∞ disturbance attenuation level ρ. In this paper we propose a new approach to design the controller for the uncertain system which is composed of a linear controller and an adaptive controller. The problem is solved by introducing a switching function and using the idea of formulation. Based on Lyapunov stability theory, new sufficient conditions are obtained in terms of linear matrix inequalities. The effectiveness and advantages of the proposed controller design are shown via a numerical example.     

Solid-Liquid Interface Energy between Silicon Crystal and Silicon-Aluminum Melt

By examining the surface morphologies of undercooled Si-20 at. pct Al alloy during and after the solidification process, it is determined that the critical undercooling for silicon to grow from lateral mode to intermediary mode ΔT* and that from intermediary mode to continuous mode ΔT** are 131 and 239 K, respectively. A method that predicts the solid-liquid interface energy of binary lateral growth materials on the basis of ΔT* and ΔT** has been developed. Formulas between the physical parameters and the solid-liquid interface energy have been obtained. The interface energy between silicon crystal and Si-Al melt predicted from ΔT* is almost equal to that from ΔT**. The present results of the solid-liquid interface energy predicted according to ΔT* and ΔT** obtained in Si-20 at. pct Al alloy are in very good agreement with the reported results of the grain-boundary method and the critical undercooling method from ΔT* and ΔT** obtained in pure silicon.     

Global Exponential Synchronization of Delayed Complex-Valued Recurrent Neural Networks with Discontinuous Activations

In this paper, we are concerned with the exponential synchronization for a class of two delayed complex-valued recurrent neural networks (CVRNNs) with disc     

高密度电阻率法在水电工程勘察中的应用

在水电工程地质勘察中,仅靠钻探手段难以达到高效、经济的要求,如果钻探结合高密度电阻率法,可大大提高工作效率及勘察成果质量。高密度电阻率法在水电工程地质勘察中合理科学的应用可以收到快速、高效、经济的效果。     

国内齿辊式破碎机常用齿板材料的组织和性能

通过组织观察、力学性能检测和磨损实验,对比研究了洗煤生产过程中齿辊式破碎机的国内4种常用齿板材料的组织和性能。结果表明,进口齿板材料的组织由板条马氏体和6.13%的残余奥氏体组成;高锰钢齿板的组织为单相奥氏体组织;ZG32CrMnSiNi2Mo齿板的组织由贝氏体铁素体板条和13.18%残余奥氏体组成;ZG22CrMnSiNiMo齿板为粒状贝氏体组织,组织中条型M-A岛比例较多,残余奥氏体量为14.9%。940℃淬火+200℃回火后,进口齿板材料具有最优的综合性能,硬度和冲击韧性分别为44.1 HRC和34.5 J;高锰钢齿板水韧处理后平均硬度为216.5 HB,冲击韧度为113.8 J;ZG32CrMnSiNi2Mo齿板900~940℃正火处理后,冲击韧度值略低于进口齿板的供货状态,但硬度高于进口齿板;960~1000℃正火处理后,ZG22CrMnSiNiMo齿板硬度略低于进口齿板材料,冲击韧度略高于进口齿板材料。选取进口齿板材料供货状态为标准,高锰钢齿板材料的相对耐磨性较低,仅为0.76;ZG32CrMnSiNi2Mo齿板材料经900~980℃正火处理后,耐磨性能较好,相对耐磨性为1.19~1.23;ZG22CrMnSiNiMo齿板材料经920~1000℃正火处理,耐磨性能介于进口齿板材料和ZG32CrMnSiNi2Mo齿板材料之间,相对耐磨性为1.10~1.13。     

深过冷Ni-21.4%Si共晶合金的凝固特性研究

对熔融玻璃净化后深过冷Ni-21.4%Si（原子分数,下同）共晶合金的凝固特性进行了实验研究,并对其均质形核过冷度进行了理论预测.结果发现,采用熔融玻璃净化可使Ni-21.4%Si共晶合金获得318 K的过冷度.理论计算表明,此过冷度达到了Ni-21.4%Si共晶合金的均质形核过冷度.Ni-21.4%Si共晶合金凝固特性与过冷度△T有关:当过冷度小于250 K时,冷却曲线有2个再辉峰,其中当过冷度小于206 K时,凝固组织由Ni3Si相和规则共晶组成,当过冷度在206 K到250 K之间时,凝固组织由α-Ni相和规则共晶组成;过冷度大于250 K后,冷却曲线只有1个再辉峰,凝固组织为反常共晶.过冷度会影响初生相Ni3Si的生长方式.随着过冷度的增大,初生相Ni₃Si的生长会由小平面生长方式转为非小平面生长方式.     

金属熔体结构及其控制技术的研究进展

综述了国内外在熔体结构研究方面的现状与进展,介绍了通过控制合金熔体的预结晶状态来改善合金组织和性能的相关技术及成果。可以得出：温度和压力可使金属熔体发生液／液结构转变,金属熔体结构随温度的变化存在滞后性,利用熔体结构随温度变化的滞后性可控制合金的凝固过程、明显细化合金的凝固组织、大大提高合金的力学性能。