Superconvergence of a two‐grid method for fourth‐order dispersive‐dissipative wave equations

In this paper, the superconvergence analysis of a two‐grid method (TGM) with low‐order finite elements is presented for the fourth‐order dispersive‐dissipative wave equations for a second order fully discrete scheme. The superclose estimates in the H¹‐norm on the two grids are obtained by the combination technique of the interpolation and Ritz projection. Then, with the help of the interpolated postprocessing technique, the global superconvergence properties are deduced. Finally, numerical results are provided to show the performance of the proposed TGM for conforming bilinear element and nonconforming element, respectively. It shows that the TGM is an effective method to the problem considered of our paper compared with the traditional Galerkin finite element method (FEM).     

优质立方六面体金刚石大单晶的生长研究

高温高压静压触媒法合成的金刚石单晶,往往呈现六八面体形貌,因为立方六面体单晶{100}面的生长区间相对较小.本研究利用高温高压温度梯度法,自制Fe-Ni合金触媒,通过对合成组装和工艺进行合理调整后,控制晶体在相对低温适合{100}面生长区域内生长,得到的晶体均呈现完整立方六面体形貌;同时为抑制包裹体和其他杂质的进入,人为的提高晶体的径向平铺生长速度,抑制其轴向生长速度.以在33 h内合成的优质立方六面体晶体为例,晶体最大方向尺寸达到7.3 mm,重1.2克拉,其径向生长速度达到0.22 mm/h,轴向生长速度仅为0.08 mm/h,增重速度为7.3 mg/h.     

在FeNi-C-FeS-B体系内宝石级金刚石单晶的高温高压合成研究

本研究利用高温高压温度梯度法,在5.4 GPa、1550 K生长条件下,考察了FeNi-C体系中单掺FeS以及FeS-B共掺杂对单晶生长宝石级金刚石品质的影响.结果表明:在单掺FeS体系中,随着FeS的增加,晶体的质量以及透明度逐渐下降,(100)晶面存在的倒方形蚀坑面积逐渐增大,同时晶体的颜色也由黄色转变成灰黑色;在共掺杂体系中,当添加剂FeS含量一定时,随着协同添加剂B的增加,晶体品质呈现出先优化后劣化的变化趋势,晶面上蚀坑的分布逐渐由(100)晶面向(111)转移,晶体颜色也由灰黑色逐渐变浅到黄色、再到B单独发生作用时导致的蓝黑色.XRD光谱分析发现,在FeNi-C-FeS-B体系中出现了某种或者某些不明物质.     

Supercritical fluid extraction and gas chromatography analysis of arsenic species from solid matrices

A method in combination with derivatization-supercritical fluid extraction(SFE) and gas chromatography(GC) for the speciation and quantitative determination of dimethylarsinate(DMA), monomethylarsonate(MMA) and inorganic arsenic in solid matrices was investigated. Thioglycolic acid methyl ester(TGM) and thioglycolic acid ethyl ester(TGE) were evaluated as derivatization reagents. The effects of pressure, temperature, flow rate of supercritical CO_2, extraction time, modifier and microemulsion on the efficiency of extraction were systematically investigated. The procedure was applied to the analysis of real soil and sediment samples. Results showed that TGE was more effective for arsenic speciation as a derivatization reagent. Modifying supercritical CO_2 with methanol can greatly improve the extraction efficiency. Further, the addition of microemulsion containing surfactant Triton X-100 can further enhance recoveries of arsenic species. The optimum extraction conditions were 100 ℃, 30 MPa, 10 min static and 25 min dynamic extraction with 5%(v/v) methanol, and surfactant modified supercritical CO_2. Detection limits in solid matrices were 0.15, 0.3 and 1.2 mg/kg for DMA, MMA and inorganic arsenic,respectively. The method was validated by the recovery data. The resulting method was fast, easy to perform and selective in the extraction and detection of various arsenic species in solid matrices.     

温度梯度法宝石级金刚石的合成及表征

利用温度梯度法,在5．0—5．7GPa,1250---1600℃条件下,研究了FeNiMnCo触媒合成宝石级金刚石的温度和压力区间,给出了P-T相图．基于有限元法的温度场模拟及碳素浓度梯度拟合结果表明,I型温度场只适合生长大尺寸优质板状及小尺寸塔状金刚石单晶;II型温度场可以合成出大尺寸优质板状或塔状金刚石单晶．该结论被Ib型及掺硼宝石级金刚石晶体生长实验所证实．提出碳素浓度梯度是决定晶体生长速度及合成晶体品质的关键因素．研究得到了只有触媒中温度场分布与晶体尺寸、形貌相匹配时,才能合成出优质宝石级金刚石单晶的晶体生长规律．揭示了{110},和{113}高指数晶面在Ib型金刚石“V”形区内的分布规律．通过傅里叶红外光谱检测发现,FeNiMnCo触媒合成金刚石的氮含量较低,较低的氮含量是由铁会降低金刚石氮含量所致．氮含量低有利于金刚石的光谱透过性．