二维随机变量概率分布的求解方法

每一个随机试验的整体概率可以用一个相应的随机变量及其概率分布来描述.基于对一维随机变量的理解,采用分布函数法和函数分步法,给出了求二维随机变量概率分布的基本规律.     

射电源的流量密度与核主导系数的关系及相对论束流模型

计算了2个河外射电源样本的核主导系数,并研究了核主导系数与核及延展元的流量密度的关系。结果显示：当核主导系数较小时,核主导系数与核流量密度线性相关;当核主导系数较大时,核流量密度与核主导系数没有相关,而与延展元流量有线性相关。因此,2个样本的这些关系依赖于流量密度与核主导系数,利用相对论喷流模型能解释用2个样本所得到的相关结果。     

2000-2010年长春市中心城区人口空间演变与扩张机制研究

分别以街道、社区为单位将长春市中心城区第五次、第六次普查数据通过ArcGIS软件导入城镇数据,对长春市中心城区人口分布现状进行分析,并通过MATLAB软件对十年以来长春市中心城区人口密度模型进行拟合分析.结果表明:2000年-2010年间长春市一直处于向南方发展的"圈层式扩张"的城市化,加幂指数模型能较完美拟合长春市人口空间变化.长春人口扩张既有历史、规划的原因,也有产业布局和轨道交通的原因.     

离散加权信源与熵密度偏差的极限性质

利用熵密度偏差，研究了服从几分分布的离散加权信源的极限性质，其主要结果推广了离散信源Shannon－Mcmillan定理。     

金红石TiO2(011)表面的理论研究进展

基于密度泛函理论 (DFT) 的第一性原理 (First-principles) 计算方法，就金红石TiO₂(011)表面在理论方面的研究进展做了介绍.首先，通过阐述研究金红石TiO₂(011)表面的必要性和实验在其结构方面的研究进展，介绍了金红石TiO₂(011)表面的电子结构和光学性质，指出并验证了该表面对可见光有较强的响应能力.随后，介绍了金红石TiO₂(011)表面的缺陷和杂质，指出吸附H原子和形成O缺陷后还能显著增强其在红外区的红外吸收.在此基础上，不仅从理论上提供了一些传统实验所无法提及的数据资料，还弥补了相关实验在微观领域研究中的不足.最后，就目前金红石TiO₂(011)表面研究中存在的问题做了展望，指出金红石TiO₂(011)表面各种表面现象的微观本质是未来研究的重点内容.     

The impact of parameter and model uncertainty on market risk predictions from GARCH‐type models

We study the effect of parameter and model uncertainty on the left‐tail of predictive densities and in particular on VaR forecasts. To this end, we evaluate the predictive performance of several GARCH‐type models estimated via Bayesian and maximum likelihood techniques. In addition to individual models, several combination methods are considered, such as Bayesian model averaging and (censored) optimal pooling for linear, log or beta linear pools. Daily returns for a set of stock market indexes are predicted over about 13 years from the early 2000s. We find that Bayesian predictive densities improve the VaR backtest at the 1% risk level for single models and for linear and log pools. We also find that the robust VaR backtest exhibited by linear and log pools is better than the backtest of single models at the 5% risk level. Finally, the equally weighted linear pool of Bayesian predictives tends to be the best VaR forecaster in a set of 42 forecasting techniques.     

Studies on induction hardening of powder-metallurgy-processed Fe-Cr/Mo alloys

Induction hardening of dense Fe-Cr/Mo alloys processed via the powder-metallurgy route was studied. The Fe-3Cr-0.5Mo, Fe-1.5Cr-0.2Mo, and Fe-0.85Mo pre-alloyed powders were mixed with 0.4wt%, 0.6wt%, and 0.8wt% C and compacted at 500, 600, and 700 MPa, respectively. The compacts were sintered at 1473 K for 1 h and then cooled at 6 K/min. Ferrite with pearlite was mostly observed in the sintered alloys with 0.4wt% C, whereas a carbide network was also present in the alloys with 0.8wt% C. Graphite at prior particle boundaries led to deterioration of the mechanical properties of alloys with 0.8wt% C, whereas no significant induction hardening was achieved in alloys with 0.4wt% C. Among the investigated samples, alloys with 0.6wt% C exhibited the highest strength and ductility and were found to be suitable for induction hardening. The hardening was carried out at a frequency of 2.0 kHz for 2-3 s. A case depth of 2.5 mm was achieved while maintaining the bulk (interior) hardness of approximately HV 230. A martensitic structure was observed on the outer periphery of the samples. The hardness varied from HV 600 to HV 375 from the sample surface to the interior of the case hardened region. The best combination of properties and hardening depth was achieved in case of the Fe-1.5Cr-0.2Mo alloy with 0.6wt% C.     

含时线性谐振子系统密度算符的研究

主要是研究含时线性谐振子系统的量子解问题.首先运用李代数方法得到含时线性谐振子系统的密度算符随时间演化的量子精确解,然后对得到的解析式进行了验证和分析.结果显示,我们得到的含时谐振子系统密度算符的解析解能准确的描述含时谐振子系统密度算符随时间的演化.     

丁酸甲酯高温分解的过渡态理论研究(英文)

选取了丁酸甲酯高温分解的十三个反应路径中较为重要的两个反应:CH3OCO=CH3+CO2(R1)和CH3OCO=CH3O+CO(R2).使用密度泛函理论方法在B3LYP/TZVP基组水平上寻找了反应的过渡态,并且得到了两个反应的势能曲线.R1的势垒高度远远低于R2,同时R1的产物CH3和CO2拥有较低的能量,处于相对稳定的状态.因此,反应CH3OCO=CH3+CO2更容易发生.结论为丁酸甲酯的动力学模型研究提供了一定的理论依据.     

菊糖同分异构体活性的密度泛函研究

采用密度泛函(DFT)中B3LYP方法,在6-311+G(d,p)基组水平上对葡萄糖、吡喃型果糖、呋喃型果糖、D-万寿菊糖进行了几何构型优化、频率分析、红外光谱、自然电荷布居、NBO分析、分子能量及前线轨道能级计算,推导出分子的稳定性顺序为:呋喃型果糖吡喃型果糖葡萄糖菊糖.引入概念DFT活性指数分析表明菊糖分子的化学势μ数值大、化学硬度η小、亲电指数ω大,表明了它具有特殊的活性.Fukui指数扫描表明菊糖分子中C2原子具有较大的给电子能力,是整个分子的活性中心.抗氧化能力的EBDE数值计算表明2-H最容易断裂,其数值是为94.65 kcal·mol-1,远小于它的绝热电离势,这可为解释菊糖分子的抗氧化活性做合理的理论指导.