AgAlSe2晶体高压相变的第一性原理研究

基于密度泛函理论,采用广义梯度近似法,研究了黄铜矿结构AgAlSe₂在高压下的晶体结构、晶格动力学稳定性与电子结构.结果显示:在0 GPa时AgAlSe₂的晶格参数与实验值吻合,在13.9 GPa附近,质量密度、Se-Ag键长、Se-Al键长、晶格常数a突然增大,相对晶胞体积V/V₀、晶格常数c突然减小,声子谱出现虚频,结构变得不稳定,带隙发生突变,数值呈减小趋势.表明AgAlSe₂晶体在13.9 GPa附近发生结构相变.该研究为AgAlSe₂晶体在理论上所能承受的高压提供信息支撑.     

Novel rubidium polyfluorides with F_3, F_4, and F_5 species

Pressure has an important effect on chemical bonds and their chemical properties. The atypical compounds NaCl_3 and CsF_3 are predicted to be stable at high pressure and show unique physical and chemical properties. By using ab initio random structure searching and density functional theory calculations, we predicted multiple thermodynamically stable atypical compounds, which are RbF_2, RbF_3, RbF_4, and RbF_5 in the pressure range of 0–300 GPa. In these stable compounds, homonuclear bondings of F_3, F_4, and F_5 species are easily formed. The electron structure calculation showed that except for Fd-3 m phase of RbF_2, these stable compounds are insulators and F 5 p orbitals play an important role in the Fermi level. It is interesting that the compounds RbF_5 could be stable at nearly ambient pressure and 0 K which will stimulate experimental studies in the future.     

雾化辅助化学气相沉积法氧化镓薄膜生长研究

采用自主设计搭建的雾化辅助化学气相沉积系统设备,开展了Ga₂O₃薄膜制备及其特性研究工作。通过X射线衍射研究了沉积温度、系统沉积压差对Ga₂O₃薄膜结晶质量的影响。结果表明,Ga₂O₃在425~650 ℃温度区间存在物相转换关系。随着沉积温度从425 ℃升高至650 ℃,薄膜结晶分别由非晶态、纯α-Ga₂O₃结晶状态向α-Ga₂O₃、β-Ga₂O₃两相混合结晶状态改变。通过原子力显微镜表征探究了生长温度对Ga₂O₃薄膜表面形貌的影响,从475 ℃升高至650 ℃时,薄膜表面粗糙度由26.8 nm下降至24.8 nm。同时,高分辨X射线衍射仪测试表明475 ℃、5 Pa压差条件下的α-Ga₂O₃薄膜样品半峰全宽仅为190.8″,为高度结晶态的单晶α-Ga₂O₃薄膜材料。     

Disjoining pressure and the film-height-dependent surface tension of thin liquid films: New insight from capillary wave fluctuations

In this paper we review simulation and experimental studies of thermal capillary wave fluctuations as an ideal means for probing the underlying disjoining pressure and surface tensions, and more generally, fine details of the Interfacial Hamiltonian Model. We discuss recent simulation results that reveal a film-height-dependent surface tension not accounted for in the classical Interfacial Hamiltonian Model. We show how this observation may be explained bottom-up from sound principles of statistical thermodynamics and discuss some of its implications.     

(C5H6N)4[Be6(HPO3)8]·H2O: A low-density open-framework beryllium phosphite with multidirectional 12-ring channels

Employing the common pyridine (=py) solvent as the source of structure-directing agents (SDAs), a novel three-dimensional open-framework beryllium phosphite (Hpy)₄[Be₆(HPO₃)₈]·H₂O (1), has been solvothermally synthesized and structurally characterized by IR, elemental analysis, thermogravimetric analysis, powder and single-crystal X-ray diffractions. It crystallizes in the orthorhombic system, space group Pbca (No. 61), a = 20.0034(4) Å, b = 20.2188(4) Å, c = 20.9731(3) Å, V = 8482.5(3) Å³, and Z = 8. The alternating connection of BeO₄ tetrahedra and HPO₃ pseudopyramids give rise to a (3, 4)-connected network with multidirectional intersecting 12-ring channels. The compound possesses a low density and a new {4.8.10}{4².6.8.10.12}{4².6}₃{4².8.10².12}{4³.6².8} topology.     

Method development for the determination of 24S‐hydroxycholesterol in human plasma without derivatization by high‐performance liquid chromatography with tandem mass spectrometry in atmospheric pressure chemical ionization mode

We developed a highly sensitive and specific high‐performance liquid chromatography with tandem mass spectrometry method with an atmospheric pressure chemical ionization interface to determine 24S‐hydroxycholesterol, a major metabolite of cholesterol formed by cytochrome P450 family 46A1, in human plasma without any derivatization step. Phosphate buffered saline including 1% Tween 80 was used as the surrogate matrix for preparation of calibration curves and quality control samples. The saponification process to convert esterified 24S‐hydroxycholesterol to free sterols was optimized, followed by liquid–liquid extraction using hexane. Chromatographic separation of 24S‐hydroxycholesterol from other isobaric endogenous oxysterols was successfully achieved with gradient mobile phase comprised of 0.1% propionic acid and acetonitrile using L‐column2 ODS (2 μm, 2.1 mm id × 150 mm). This assay was capable of determining 24S‐hydroxycholesterol in human plasma (200 μL) ranging from 1 to 100 ng/mL with acceptable intra‐ and inter‐day precision and accuracy. The potential risk of in vitro formation of 24S‐hydroxycholesterol by oxidation from endogenous cholesterol in human plasma was found to be negligible. The stability of 24S‐hydroxycholesterol in relevant solvents and human plasma was confirmed. This method was successfully applied to quantify the plasma concentrations of 24S‐hydroxycholesterol in male and female volunteers.     

Rapid preparative isolation of erythrocentaurin from Enicostemma littorale by medium‐pressure liquid chromatography,its estimation by high‐pressure thin‐layer chromatography,and its α‐amylase inhibitory activity

Erythrocentaurin is a relatively simple natural product present among the members of Gentianaceae. A preparative method for the isolation of erythrocentaurin from the ethyl acetate fraction of Enicostemma littorale using medium‐pressure liquid chromatography has been reported. The method consisted of a simple step gradient from 10 to 20% ethyl acetate in n‐hexane. Using a 70 × 460 mm Si60 column, this method is capable of processing 20 g of material in <3 h (purity ≈ 97%). The recovery of erythrocentaurin was 87.77%. Estimation of erythrocentaurin in extracts and fractions based on high‐pressure thin‐layer chromatography was carried out on silica gel 60 F₂₅₄ plates with toluene/ethyl acetate/formic acid (80:18:2 v/v/v) as the mobile phase. The densitometric analysis was performed at 230 nm. A well‐separated compact band of erythrocentaurin appeared at R_f 0.54 ± 0.04. The analytical method showed good linearity in the concentration range of 200–1500 ng/band with a correlation coefficient of 0.99417. The limits of detection and quantification were found to be ≈60 and ≈180 ng/band, respectively. Erythrocentaurin exhibited a concentration‐dependent α‐amylase inhibition (IC₅₀ 1.67 ± 0.28 mg/mL). The outcome of the study should be considered for pharmacokinetic and biotransformation studies involving E. littorale.     

Low‐temperature headspace‐trap gas chromatography with mass spectrometry for the determination of trace volatile compounds from the fruit of Lycium barbarum L.

The total saccharides content of Lycium barbarum L. is very high, and a high temperature would result in saccharide decomposition and the emergence of a large amount of water. Moreover, the volatile compounds from the fruit of L. barbarum L. are rather low in concentration. Hence, it is difficult for a conventional headspace method to study the volatile compounds from the fruit of L. barbarum L. Since headspace‐trap gas chromatography with mass spectrometry is an excellent method for trace analysis, a headspace‐trap gas chromatography with mass spectrometry method based on low‐temperature (30°C) enrichment and multiple headspace extraction was developed to explore the volatile compounds from the fruit of L. barbarum L. The headspace of the sample was extracted in 17 cycles at 30°C. Each time, the compounds extracted were concentrated in the trap (Tenax TA and Tenax GR, 1:1). Finally, all the volatile compounds were delivered into the gas chromatograph after thermal desorption. With the method described above, a total of 57 compounds were identified. The identification was completed by mass spectral search, retention index, and accurate mass measurement.     

侵入气体沿井筒的上升规律研究

地层气体侵入井筒后形成气液两相流动体系,气体沿井筒向上滑脱运移,随着所受压力的降低其发展变化过程会很快,如果不及时处理就会演变为井涌、井喷,甚至井喷失控.因此,准确的预测侵入气体沿井筒的上升规律,有助于认识气侵发展过程,同时为现场采取井控措施提供理论依据,有效避免井下复杂事故.基于侵入气体沿井筒运动的力学特性,建立了气体的上升速度模型,模型模拟分析表明:地层渗透率越高、机械钻速越快、单位时间内侵入井筒的气体量越多、气体上升速度越快,井底压力波动越大;施加一定的井口回压可以有效抑制气体的膨胀运移.     

考虑底部隆起的浅埋隧道围岩压力计算分析

针对浅埋隧道开挖后底部隆起变形现象,应用极限分析上限法构造了考虑底部隆起变形的围岩压力计算模型,结合线性Mohr-Coulomb准则等推导出极限围岩压力的理论表达式。通过约束条件将围岩压力的计算转化为数学中的最优化问题,编制程序进行了优化计算。将计算结果与工程实测数据及文献计算结果进行了对比,验证了当前方法的可靠性。同时,指出在运用极限分析法处理浅埋隧道围岩压力问题过程中应将隧道底部一同考虑,对隧道底部支护会对整个围岩压力产生影响,有助于隧道结构的整体稳定。研究可以为浅埋隧道的开挖、支护提供一定的理论指导.