基于移位算子时域有限差分的色散薄层节点修正算法

提出了一种时域有限差分（FDTD）计算中色散介质薄层问题处理的新算法.对于厚度小于一个元胞尺度的电小尺寸色散介质薄层问题,采用将元胞内电位移矢量和磁感应强度加权平均的方法,求得薄层所在元胞内修正点处的等效介质参数.然后根据常见色散介质模型,包括Debye模型、Lorenz模型、Drude模型等,介电常数和磁导率可以表示为jω分式多项式的特点,结合频域到时域的转换关系（即用/t代替jω）和移位算子方法得到了修正点处的时域本构关系,进而获得时域递推计算式.数值结果表明,该方法具有通用、节省计算时间、节省内存和计算精度良好等优点.     

Analytical electron microscopy of a reaction-bonded Si3N4-based ceramic containing oxide additions

The microstructure of a silicon nitride (Si₃N₄)-based ceramic, prepared by a process combining direct nitridation and reactive liquid phase sintering of silicon/ceramic oxide powder compacts, has been characterised using analytical transmission electron microscopy. The presence of the reactive liquid phase, promoted by the addition of oxides from the CaO-Al₂O₃-SiO₂ ternary system, resulted in an as-fired microstructure containing a mixture of crystalline phases based on -Si₃N₄, β-Si₃N₄ and Si₂ N₂O, and distinct amorphous regions rich in Si, Al and Ca. X-ray microanalysis revealed the calcium to be wholly partitioned to the glassy phase, while significant concentrations of aluminium were detected in both β-Si₃N₄ and Si₂N₂O. The observed compositions of these phases, together with measured lattice parameters systematically in excess of those of the pure compounds, imply that they are in fact β- and O-sialons respectively. Semi-quantitative energy dispersive X-ray spectroscopy, using an ultra-thin window detector, is demonstrated to be capable of distinguishing clearly between these phases according to their oxygen content and of determining the aluminium content of both phases to within ± 1 equ.%, even at concentration levels of <5 equ.%.     

分散固相萃取-分散液液微萃取/气相色谱-串联质谱法测定蔬菜中19种有机磷农药残留

采用分散固相萃取和分散液液微萃取联用方法,建立了气相色谱-串联质谱法(GC-MS/MS)同时测定蔬菜中19种有机磷农药残留量的分析方法。分散固相萃取方法以乙腈为萃取液,以N-丙基-乙二胺(PSA)和C18为吸附剂。对影响分散液液微萃取效率的因素(萃取溶剂种类及体积、分散剂体积等)进行优化,同时分析了实验过程中添加掩蔽试剂L-古洛糖酸γ-内酯(AP)对基质效应补偿作用的影响。在最佳实验条件下,19种有机磷在辣椒和大葱中3个添加水平(0.05,0.1,0.5 mg/kg)的回收率为76.9%~126.8%,相对标准偏差为0.6%~7.3%,检出限(S/N=3)为0.10~0.50μg/kg。该方法简单、高效、重现性好、富集倍数高,可用于蔬菜中有机磷农药的快速检测。     

分散式固相萃取净化-气相色谱-质谱联用测定土壤中的邻苯二甲酸酯

建立了土壤中18种邻苯二甲酸酯类内分泌干扰物的微波提取-分散式固相萃取净化-GC/MS分析方法.10 g土壤样品经20 mL二氯甲烷和丙酮混合溶剂微波提取后,以丙酮为置换溶剂并浓缩至1.5 mL.浓缩液中加入0.2 g C18吸附剂,振摇3 min后离心10 min(8000 r/min),取1.0 mL上层清液经正己烷置换后用气相色谱-质谱联用分析,并通过基质标准加入校准曲线补偿邻苯二甲酸酯的基体效应.净化所需时间少于20 min.净化后土壤萃取液的基质去除率达到72.7%.方法线性范围7.5～750 μg/kg,相关系数大于0.998; 6次土壤样品测定值的RSD在5.5%～12.1%之间; 加标土壤样品测定值RSD在7.3%～19.4%之间; 平均回收率在94.4%～114.6%之间; 检出限为1.2～4.3 μg/kg.     

Trace-level determination of eight cholesterol oxidation products in human plasma by dispersive liquid–liquid microextraction and ultra-performance liquid chromatography–tandem mass spectrometry

7α-Hydroxy cholesterol (7α-OHC), 25-hydroxy cholesterol (25-OHC), 27-hydroxy cholesterol (27-OHC), 4β-hydroxy cholesterol (4β-OHC), 7α-hydroxy-4-cholesten-3-one (7α-C4), 5β-cholestane-3α, 7α, 12α-triol (5β-Triol), cholic acid (CA), and chenodeoxycholic acid (CDCA) are known biomarkers of neurodegenerative diseases. A method for their simultaneous determination in human plasma has been optimized using dispersive liquid–liquid microextraction and ultra-performance liquid chromatography–tandem mass spectrometry. The limits of quantification of the target compounds were in the range of 0.3–3.3?µg/L. The precision achieved by this method was less than 13.4% for intraday and interday analyses. The proposed method was used to analyze eight cholesterol oxidation products in 30 human plasma samples. The analytical results were in a concentration range of 1.6–87.4?µg/L for 7α-OHC, 6.3–58.2?µg/L for 25-OHC, 12.1–98.5?µg/L for 27-OHC, 5.7–64.8?µg/L for 4β-OHC, 1.5–124.1?µg/L for 7α-C4, 0.5–16.5?µg/L for 5β-Triol, 13.1–245?µg/L for CA, and 19.6–487?µg/L for CDCA in the samples. The method may be used for the analysis of biomarkers of neurodegenerative diseases.     

Recent trends in replacement of disperser solvent in dispersive liquid-liquid microextraction methods

Since its innovation in 2006, the dispersive liquid-liquid microextraction (DLLME) method has attracted the attention of analytical chemists in the field of sample preparation. This method has been successfully applied to determine trace amounts of pollutants in various matrices, but the restriction in the choice of suitable disperser and extraction solvents, and high disperser solvent consumption leading to decreased partition coefficients of the analytes between aqueous phase and extractant are its problems. To solve these drawbacks and develop environmentally friendly techniques, various alternatives for the conventional DLLME have been presented. The current review will begin with an introduction to the sample preparation, implementation of DLLME, and its advantages. Then, we focus on its drawbacks, which result mainly from the use of disperser solvent. Afterward, some of the most interesting approaches that have been employed and published until now are reviewed. Finally, an outlook on the future of these techniques will be given.     

Operation of Kerr-lens mode-locked Ti:sapphire laser in thenon-soliton regime

A Kerr-lens mode-locked Ti:sapphire laser operating in a non-soliton regime is demonstrated. Dispersive wave generation is observed as a result of third order dispersion in the vicinity of zero dispersion. The characteristics of the Ti:sapphire laser operating in a positive dispersion regime are presented, where the oscillator directly generates pulses with duration continuously tunable from 0.37~ps to 2.11~ps, and 36~fs pulses are achieved after extracavity compression. The oscillation is numerically simulated with an extended nonlinear Schr?dinger equation, and the simulation results are in good agreement with the experimental results.     

超声辅助分散液液微萃取/超高效液相色谱-串联质谱法检测水中多种磺胺类抗生素残留

建立了水中13种磺胺类抗生素的超声辅助分散液液微萃取/超高效液相色谱-串联质谱(UADLLME/UPLC-MS/MS)测定方法。以乙腈为分散剂,四氯乙烷为萃取剂,通过超声分散方式协同萃取水样中的目标化合物,采用C_(18)(色谱柱(100 mm×2.1 mm,1.7μm)分离,以乙腈-0.1%甲酸溶液为流动相,采用UPLC-MS/MS多反应监测模式(MRM)测定。优化了萃取剂和分散剂的类型和用量、萃取时间、氯化钠浓度和p H值等条件。在优化条件下,13种磺胺类抗生素在一定质量浓度范围内线性关系良好,相关系数均大于0.998,方法检出限(S/N=3)为0.6~2.4 ng/L;3个加标水平的平均回收率为80.3%~101.8%,相对标准偏差(RSD,n=5)为0.7%~4.5%。该方法前处理简单、环保、灵敏,适用于水样中多种磺胺类抗生素的测定。     

Global existence and uniform decay of solutions for a system of wave equations with dispersive and dissipative terms

In this paper, we consider a system of two coupled wave equations with dispersive and viscosity dissipative terms under Dirichlet boundary conditions. The global existence of weak solutions as well as uniform decay rates (exponential one) of the solution energy are established.     

超短脉冲高斯光束通过透镜的聚焦特性

利用傅里叶积分变换法研究了超短脉冲高斯光束通过透镜的聚焦特性,给出了透镜焦平面上光强的空间、时间分布,以及能量密度分布。在所用数学处理中未使用缓变包络近似,结果对于包括单周期超短脉冲情况都是成立的。数值计算结果和物理分析表明,不考虑色散时,焦点附近的脉冲宽度相对于初始脉冲几乎不变。对于色散透镜,研究了透镜色差和群速度色散影响。透镜色差使焦点附近的脉冲(特别是脉冲前沿)显著展宽,能量密度分布展宽,峰值功率降低。群速度色散会进一步使脉冲展宽,脉冲前沿出现振荡,峰值功率降低,但它对脉冲光束的能量密度分布影响很小。更高阶的色散效应影响较小。