Study on the Transfer and Distribution Mechanism of Typical Impurities During Directional Solidification ofMulti-crystalline Silicon

定向凝固方法是去除多晶硅中典型金属杂质的有效途径。本研究通过实验探索，并结合热力学和动力学，研究多晶硅中的金属杂质、夹杂相杂质和气泡在定向凝固过程的迁移机理与分布规律；探究典型杂质的传输与分布规律、夹杂相杂质的形成机理以及气泡的形核和生长机理。主要研究结果如下： (1)研究冶金级硅定向凝固过程铁杂质的传输与分布规律。实验发现铁杂质含量沿晶体生长方向并未完全符合Scheil定理，而是保持恒定，达到某一凝固分数后快速递增；晶格与晶界的杂质比较，晶界处铁杂质含量比晶内的高出一个数量级；硅熔体对流对杂质传输与分布起到重要作用，使得杂质含量呈现出中间多、边缘少的规律。根据质量守恒定理，计算得到铁杂质有...Directional solidification is an effective method to remove typical impurities in multi-crystalline silicon. In the present paper, multi-crystalline silicon growth was carried out by directional solidification method. Transfer and distribution mechanism of metallic-impurities, insoluble inclusions and bubbles were investigated by experiments during the directional solidification of multi-crystalli...学位：工程硕士院系专业：材料学院_工程硕士(材料工程)学号：2072013115008

Redistribution of iron during directional solidification of metallurgical-grade silicon at low growth rate

研究冶金级硅低速定向凝固过程中杂质铁的再分布。采用ICP-MS检测铁的浓度,绘制铁在固相、液相、晶界和晶体生长方向上的浓度示意图。铁浓度在固、液相中具有明显差异。依据质量守恒定理,计算得出溶质边界层约为4 mm,铁的有效分凝系数约为2.98×10~(-4)。在低速凝固条件下,铁容易偏析聚集在晶界。在生长方向上,由于低速凝固,铁浓度在硅锭86%高度以下几乎恒定,不完全符合Scheil方程规律。讨论了对流对铁再分布的影响,对流"死区"对铁再分布具有重要影响。Redistribution of iron during directional solidification of metallurgical-grade silicon(MG-Si) was conducted at low growth rate. Concentrations of iron were examined by ICP-MS and figured in solid and liquid phases, at grain boundary and in growth direction. Concentrations are significantly different between solid and liquid phases. The thickness of the solute boundary layer is about 4 mm verified by mass balance law, and the effective distribution coefficient is 2.98×10~(-4). Iron element easily segregates at grain boundary at low growth rate. In growth direction, concentrations are almost constant until 86% ingot height, and they do not meet the Scheil equation completely, which is caused by the low growth rate. The effect of convection on the redistribution of iron was discussed in detail. Especially, the "dead zone" of convection plays an important role in the iron redistribution.Projects(51334004,51204143)supported by the National Natural Science Foundation of China;; Project(2006L2003)supported by the Scientific Technological Innovation Platform of Fujian Province,Chin

西北干旱区水资源问题研究思考/Ponder on the issues of water resources in the arid region of northwest China[J]

气候变化与水资源问题是各国政府部门、学术界和社会公众普遍关注的焦点,也是西北干旱区实现跨越式发展的重要瓶颈之一.在分析前人研究成果基础之上,指出制约西北干旱区社会经济发展和生态安全的关键因素和气候变化对西北干旱区水资源的影响；进而分析西北干旱区气候变化与水资源研究中的热点和难点问题；最后基于西北干旱区水资源研究的重要性和迫切性提出目前亟待解决的研究任务与核心内容,主要包括3个方面:(1)气候变化对西北干旱区水资源形成、转化及未来趋势的影响；(2)气候变化对西北干旱区水循环过程的影响；(3)气候变化对西北干旱区水资源安全的影响

JUNO Sensitivity on Proton Decay p→νˉK+p\to \bar\nu K^+ Searches

The Jiangmen Underground Neutrino Observatory (JUNO) is a large liquid scintillator detector designed to explore many topics in fundamental physics. In this paper, the potential on searching for proton decay in $p\to \bar\nu K^+$ mode with JUNO is investigated.The kaon and its decay particles feature a clear three-fold coincidence signature that results in a high efficiency for identification. Moreover, the excellent energy resolution of JUNO permits to suppress the sizable background caused by other delayed signals. Based on these advantages, the detection efficiency for the proton decay via $p\to \bar\nu K^+$ is 36.9% with a background level of 0.2 events after 10 years of data taking. The estimated sensitivity based on 200 kton-years exposure is $9.6 \times 10^{33}$ years, competitive with the current best limits on the proton lifetime in this channel

JUNO sensitivity on proton decay p → ν K + searches*

The Jiangmen Underground Neutrino Observatory (JUNO) is a large liquid scintillator detector designed to explore many topics in fundamental physics. In this study, the potential of searching for proton decay in the $p\to \bar{\nu} K^+$ mode with JUNO is investigated. The kaon and its decay particles feature a clear three-fold coincidence signature that results in a high efficiency for identification. Moreover, the excellent energy resolution of JUNO permits suppression of the sizable background caused by other delayed signals. Based on these advantages, the detection efficiency for the proton decay via $p\to \bar{\nu} K^+$ is 36.9% ± 4.9% with a background level of $0.2\pm 0.05({\rm syst})\pm$$0.2({\rm stat})$ events after 10 years of data collection. The estimated sensitivity based on 200 kton-years of exposure is $9.6 \times 10^{33}$ years, which is competitive with the current best limits on the proton lifetime in this channel and complements the use of different detection technologies