Theoritical investigations of phase stability, elastic and thermodynamic properties of γ’ phase in Co-Ta based superalloys

Ni基高温合金因具备优异的高温力学性能、抗氧化性和抗燃气腐蚀性被广泛应用于航天领域中，这与其特殊的γ+γ’两相结构有着密不可分的关系。研究者们通过在Co-Al二元合金添加W元素提高了亚稳相Co3Al的结构稳定性。这种新型Co-Al-W三元系合金中的有序沉淀相γ’-Co3(Al，W)类似于Ni基高温合金中的γ’-Ni3Al，其结构稳定性和弹性性质是Co基高温合金具有良好的高温力学性能的关键。这一发现为开发多组分Co基高温合金提供了思路。在这种情况下，研究合金元素对Co基高温合金中亚稳相的结构稳定性的影响是非常必要的。 为了指导多组分Co基高温合金的设计和开发，基于密度泛函理论基础，本研究采用第...Ni-base superalloys are widely used in Aerospace field because of their excellent high temperature mechanical property, oxidation resistance and gas corrosion resistance. The high temperature comprehensive properties of Ni-base superalloys has inseparable relation with their special γ+γ’ two-phase structures. Researchers have improved the structural stability of metastable phase Co3Al by adding W ...学位：工学硕士院系专业：材料学院_工程硕士(材料工程)学号：2072014115013

Electrochemical Nucleation of Au on n-Type Semiconductor Silicon Electrode Surface

在成功实现半导体硅表面电沉积致密金膜的柠檬酸盐镀金实际应用体系中,运用循环伏安和电位阶跃法研究了Au在n型SI(111)电极表面的电沉积过程和成核机理.结果表明,在该体系中,Au在SI表面呈现不可逆电极过程,成核过电位达到250 M V;根据COTTrEll方程求得扩散系数d=(1.81±0.14)x10–4 CM2 S–1;运用SCHArIfkEr-HIllS(SH)理论模型对比分析拟合实验结果,表明Au在n型SI表面遵循扩散控制下的三维连续成核机理;通过扫描电子显微镜观察Au初期成核、生长形貌,进一步证实了Au的三维连续成核机制,并讨论了阶跃电位和阶跃时间对Au核形貌和密度的影响.Cyclic voltammetry and chronoamperometry have been used to investigate the mechanism of gold electrodeposition on the n-Si(111) electrode surface from a citrate bath, which had successfully applied to directly electroplate a dense gold film on the silicon surface.The results show that Au electrodeposition on the n-type silicon surface is an irreversible process, and the nucleation overpotential reaches 250 m V.According to Cottrell equation, the diffusion coefficient(D) is calculated to be(1.81 ± 0.14) × 10-4 cm2 s-1.The Scharifker-Hills(SH) model was used to analyze the experimental data.Agreement between the fitting curves and the theoretical curves confirms that the nucleation process of Au electrodeposition on the n-type silicon surface follows the progressive nucleation mechanism with three-dimensional growth under diffusion control.To further confirm the progressive nucleation mechanism, scanning electron microscopy(SEM) was used to observe the nucleation and growth of Au deposits at the initial stage of electrodeposition.The SEM results show that the morphology and density of the Au deposits are affected by the electrochemical deposition potential and time.国家重大科学仪器设备开发专项(2011YQ03012406); 国家自然科学基金界面电化学创新群体(21321062)及国家自然科学基金(21373172)资助项目~

巴西热带雨林森林景观转化时空特征及破碎化分析

巴西热带雨林地区森林景观转化及破碎化导致森林生态系统的功能和区域环境发生变化,并引起全球范围内的关注。以欧洲太空局全球土地利用/土地覆被数据和Landsat解译数据为基础,利用热点提取、信息熵、地统计分析模型及轨迹分析的方法探讨不同砍伐阶段森林破碎性的变化特点以及森林破碎化与整个区域景观格局变化的相关性。结果表明:1热带雨林地区的森林面积迅速减少,其中,Rondonia州、Maton Grosso州和Para州最为典型。2森林破碎性的变化趋势并非整体性的增加或减少,而是出现明显的局地性特点;3森林砍伐的数量与土地系统的信息熵呈正相关,即森林的数量及质量直接决定巴西热带雨林地区的土地系统稳定性

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