ZM6 铸造镁合金表面斑点缺陷形成机理分析

目的 为探究 ZM6 铸造镁合金表面斑点缺陷产生的原因及其形成机理。 方法 通过扫描电子显微镜( SEM) 对未经机加工和经机加工后的 ZM6 铸造镁合金表面不同形态的斑点缺陷进行形貌分析,并结合能量色散 X 射线 谱(EDS)对斑点缺陷的化学成分进行检测,最后耦合合金铸态组织和力学性能进行综合分析。 结果 未经机加工的 ZM6 铸造镁合金表面斑点缺陷呈深黑色,而经机加工后的 ZM6 铸造镁合金表面斑点缺陷呈白色,且部分白色斑点 中心有一小块黑色区域。 不过未经机加工和经机加工后的 ZM6 铸造镁合金表面斑点缺陷都呈现龟裂状、其与基 体的过渡界面处均未发现任何空隙存在,且其主要成分均为 Mg 的氧化物或氢氧化物、同时含有 Cl、K 等由溶剂引 入的杂质元素,但未经机加工的 ZM6 铸造镁合金表面斑点缺陷中 Cl 元素的含量相对较高,而经机加工后的 ZM6 铸造镁合金表面斑点缺陷中 K 元素的含量相对较高。 值得指出的是,经机加工后的 ZM6 铸造镁合金表面白色斑 点中黑色区域存在微小气孔。 结论 ZM6 铸造镁合金表面斑点缺陷的产生是由 Mg 的化学腐蚀及电偶腐蚀造成的, 而不是由氧化夹杂造成的。 因此,通过加强 ZM6 铸造镁合金精炼效果以获得化学成分均匀的熔体是获得高质量 构件的有效途径。     

单官能团分子在缩聚反应中对分子量及其分布的影响

本文建立了单官能团分子对A-B 型、A-A、B-B 型二类线型缩聚反应产物的分子量分布影响的偏微分方程,并用Laplace 变换法求解,得到此二类缩聚反应类型的分子量分布.文中还详细讨论了缩聚反应产物中端基结构不同的分子的分子量分布.     

长波正则方程的广义差分法

讨论长波正则（ＲＬＷ）方程的初边值问题的广义差分法，证明半离散和全离散格式的稳定性与收敛性。     

Generalized Fibonacci broadcasting: An efficient VOD scheme with user bandwidth limit

Broadcasting is attractive in delivering popular videos in video-on-demand service, because the server broadcast bandwidth is independent of the number of users. However, the required server bandwidth does depend on how much bandwidth each user can use, as well as on the user's initial waiting time. This paper addresses the issue of limiting the user bandwidth, and proposes a new broadcasting scheme, named Generalized Fibonacci Broadcasting (GFB). In terms of many performance graphs, we show that, for any given combination of the server bandwidth and user bandwidth, GFB can achieve the least waiting time among all the currently known fixed-delay broadcasting schemes. Furthermore, it is very easy to implement GFB. We also demonstrate that there is a trade-off between the user waiting time and the buffer requirement at the user.     

Simultaneous determination of 5-hydroxytryptamine and dopamine using ionic liquid functionalized graphene

Ionics - An electrochemical sensor for simultaneous determination of 5-hydroxytryptamine (5-HT) and dopamine (DA) was developed in this paper based on an ionic liquid functionalized-graphene...     

关于一个Smarandache数列的研究

对于任意的正整数n,设a(n)表示将每个自然数n重复n次得到的数列.给出该数列的一个通项公式,然后利用初等方法研究了该数列与Euler函数的均值,以及与δk(n)的复合函数的均值,并给出其渐近公式.     

First-principles study on the structure,elastic and electronic properties of hexagonal HfPtAl under pressure

We have investigated the structure, elastic and electronic properties in hexagonal HfPtAl by a first-principles ultrasoft pseudopotential of the plane wave within the density functional theory (DFT) plus the generalized gradient approximation (GGA) in the scheme of Perdew–Burke–Ernzerhof (PBE). All properties are calculated as a function of external pressure. The results of structural parameters have a good agreement with reported experiments and can predict the properties under pressure well. The hexagonal HfPtAl is mechanically stable and behaves in a ductile manner. The TDOS is occupied by Pt-d, Hf-d and Al-p.     

Pressure-dependent structure,mechanical and thermodynamic properties of tetragonal AsTiZr arsenide: A density functional theory study

Recent discoveries of the novel properties of arsenides prompt us to theoretically predict the tetragonal AsTiZr ternary compound under pressure, in order to exploit new functional materials. The structure, elastic and thermodynamic properties of AsTiZr have been investigated under various pressures, based on density functional theory (DFT). For the sake of consistency, the approach of the generalized gradient approximation (GGA) of Perdew–Burke–Ernzerhof (PBE) was used. The calculated structural data at zero pressure are in good agreement with previous report. The dependence of relative changes of lattice parameters (a₀ and c₀) and volume V₀, elastic constants, bulk, shear and Young's modulus, and Debye temperature on pressure has been investigated. The thermodynamic properties like heat capacity C, enthalpy E, free energy F and entropy S with pressure are successfully obtained and discussed.     

高斯谢尔光束通过湍流大气漫射目标的散射统计

基于广义惠更斯菲涅耳原理分析了高斯谢尔光束通过湍流大气漫射目标的散射统计特性。假定相位结构函数起主导作用,根据高斯谢尔光束的交叉密度函数,推导了散斑场的互相干函数表达式,进而得出接收面处的散斑尺寸大小和强湍流起伏的时延协方差函数表达式。数值分析了源相干长度、波长、湍流强度对互相干函数的影响。对理想漫射目标,接收面的散斑尺寸大小由束腰宽度、源相干长度和湍流强度确定,随着湍流强度的增加,散斑尺寸变小;在弱湍流区,散斑尺寸由源相干长度决定,当湍流增强时,散斑尺寸大小逐渐趋于一致。     

咪唑基介孔有机硅材料固载磷钼酸催化剂的制备及烯烃环氧化性能

以含有咪唑阳离子的周期性介孔有机硅（PMO-ILs）材料为载体,制备了一类固载化磷钼酸（PMA）多相催化材料（PMA@PMO-ILs）,并采用N₂吸附-脱附实验、X射线衍射、原子吸收光谱、差热-热重分析、红外光谱、紫外光谱及固体核磁共振技术研究了材料的结构及物理化学性质. 结果表明,磷钼酸通过静电相互作用被成功固载到PMO-ILs载体表面和孔道中,且在制备过程中磷钼酸及载体基本结构均未发生变化. 反应结果表明,PMA@PMO-ILs材料在以叔丁基过氧化氢为氧化剂的环辛烯环氧化反应中表现出一定的催化活性和很高的选择性. 中断实验结果表明,催化剂的主要活性中心在反应过程中未发生明显流失,且催化剂经多次循环使用后活性及选择性基本保持不变. PMO-ILs中大量的咪唑阳离子能有效稳定磷钼酸阴离子,使该催化材料表现出良好的稳定性.