Ultrasound-assisted dispersive liquid–liquid microextraction for the determination of six pyrethroids in river water

A simple ultrasound-assisted dispersive liquid–liquid microextraction method combined with liquid chromatography was developed for the preconcentration and determination of six pyrethroids in river water samples. The procedure was based on a ternary solvent system to formatting tiny droplets of extractant in sample solution by dissolving appropriate amounts of water-immiscible extractant (tetrachloromethane) in watermiscible dispersive solvent (acetone). Various parameters that affected the extraction efficiency (such as type and volume of extraction and dispersive solvent, extraction time, ultrasonic time, and centrifuging time) were evaluated. Under the optimum condition, good linearity was obtained in a range of 0.00059–1.52 mg L⁻¹ for all analytes with the correlation coefficient (r²) > 0.999. Intra-assay and inter-assay precision evaluated as the relative standard deviation (RSD) were less than 3.4 and 8.9%. The recoveries of six pyrethroids at three spiked levels were in the range of 86.2–109.3% with RSD of less than 8.7%. The enrichment factors for the six pyrethroids were ranged from 767 to 1033 folds.     

3-Hydroxymethylglutaryl flavonol glycosides from a Mongolian and Tibetan medicine, Oxytropis racemosa

Three new flavonol 3-O-glycosides, rhamnetin 3-O-[(S)-3-hydroxy-3-methyl-glutaroyl(1→6)]-β-D-glucopyranoside (1), rhamnocitrin 3-O-[(S)-3-hydroxy-3-methylglutaroyl(1→6)]-β-D-glucopyranoside (2), and isorhamnetin 3-O-[(S)-3-hydroxy-3-methylglutaroyl(1→6)]-α-L-rhamnopyranosyl(1→2)-β-D-glucopyranoside (3), along with 13 known compounds, were isolated from Oxytropis racemosa TURCZ. Their structures were deduced by means of spectroscopic methods and chemical evidence. 2 and 6 showed cytotoxic activities against HCT-8 (IC?? 6.38 μM) and A549 (IC?? 5.20 μM), respectively.     

Unusual buffer action of free-standing nanoscopically confined water

The acid–base properties of nanoscopic water confined in the black soap films (BSFs), which were prepared from aqueous solutions of sodium dodecylsulphate (SDS) with the dye neutral red (NR) as a pH probe, were investigated using a combination of UV–vis and FTIR spectroscopy. For the SDS micellar solutions at pH 1.0–9.5 adjusted with HCl/NaOH solutions and at pH 9.4 with ammonium buffered solution, the aqueous core thicknesses in the corresponding BSFs ranged from 2.7 to 6.2 nm, and the nanoscopically confined water exhibits unusual buffer action resistant not only to acidic/alkaline solutions but also to standard buffer solution. In the heavily water-depleted confined zones, it is most likely that charge pairs in proton-transfer reactions could not be formed effectively and proton transfer was prohibited in the absence of sufficient solvating ability. Theoretical analyzes indicated that the buffer action of the nanoscopic water originated from the confinement effect of two charged surfaces of the BSFs. These results might inspire deeper understanding and further studies of biobuffering, enzyme superactivity, acid-catalyzed reactions, and Nafion fuel cell membranes.     

低于1×10-6/℃的低压CMOS带隙基准电流源

提出了一种新颖的CMOS带隙基准电流源的二阶曲率补偿技术,通过增加一个运算跨导放大器(OTA),使带隙基准参考电路的电流特性与理论分析相符合,实现低温度系数(TC)的参考电流。该电路采用SMIC0.13μm标准CMOS工艺,可在1.2 V的电源电压下工作,有效面积为0.045 mm2。仿真结果表明,在-40～85℃温度范围内参考电流的温度系数为0.5×10-6/℃;当电源电压为1.1 V时,电路依然可以正常工作,电源电压调整率为1 mV/V。     

基于微多普勒分析的弹道目标识别技术研究

目标微动产生的微多普勒特征,通常被认为是目标独有的特征,可用于确定目标的性质,实现对目标的检测、识别与分类。文中在对微动目标微多普勒分析的基础上,建立了导弹与诱饵的数学模型,采用短时傅里叶变换的方法对回波信号进行微多普勒特征提取,仿真分析了导弹与诱饵的微多普勒特征,通过研究其时频分布特点的差异成功的识别出了真假目标,从而为弹道导弹与重诱饵的识别提供了一个新的有效方法。     

硅单结晶体管γ射线辐照电阻变化规律研究

对在γ射线辐照条件下的单结晶体管基区阻值进行了多点测量和实时监测。结果发现：单结晶体管基区电阻值随γ射线辐照剂量的增加,具有先减小后增大的规律。对比国内外相关实验结果,从7射线与物质作用微观分析,证明位移效应是单结晶体管基区电阻在γ射线辐照下的主要效应,但它较电离效应具有一定滞后性。     

Silica‐Coated Manganese Oxide Nanoparticles as a Platform for Targeted Magnetic Resonance and Fluorescence Imaging of Cancer Cells

Monodisperse silica‐coated manganese oxide nanoparticles (NPs) with a diameter of ～35 nm are synthesized and are aminated through silanization. The amine‐functionalized core–shell NPs enable the covalent conjugation of a fluorescent dye, Rhodamine B isothiocyanate (RBITC), and folate (FA) onto their surface. The formed Mn₃O₄@SiO₂(RBITC)–FA core–shell nanocomposites are water‐dispersible, stable, and biocompatible when the Mn concentration is below 50 µg mL^?1 as confirmed by a cytotoxicity assay. Relaxivity measurements show that the core–shell NPs have a T₁ relaxivity (r₁) of 0.50 mM ^?1 s^?1 on the 0.5 T scanner and 0.47 mM ^?1 s^?1 on the 3.0 T scanner, suggesting the possibility of using the particles as a T₁ contrast agent. Combined flow cytometry, confocal microscopy, and magnetic resonance imaging studies show that the Mn₃O₄@SiO₂(RBITC)–FA nanocomposites can specifically target cancer cells overexpressing FA receptors (FARs). Findings from this study suggest that the silica‐coated Mn₃O₄ core–shell NPs could be used as a platform for bimodal imaging (both magnetic resonance and fluorescence) in various biological systems.     

基于磨粒运动轨迹的硅片化学机械抛光材料去率研究

硅片化学机械抛光（CMP）是机械作用与化学作用相结合的技术,硅片表面的化学反应层主要是由抛光液中磨料的机械作用去除,磨粒对硅片表面的摩擦和划擦对硅片表面材料的去除起着重要作用。磨粒在硅片表面上的划痕长度直接影响硅片表面的材料去除率。本文首先在实验结果的基础上分析了硅片CMP过程中磨粒的分布形式,然后根据运动学和接触力学理论,分析了硅片、磨粒及抛光垫三者之间的运动关系,根据磨粒在硅片表面上的运动轨迹长度,得出了材料去除率与抛光速度之间的关系,该分析结果与实验结果一致,研究结果可为进一步理解硅片CMP的材料去除机理提供理论指导。     

Simulation of carrier transport in heterostructures using the 2D self-consistent full-band ensemble Monte Carlo method

We demonstrate a two-dimensional(2D) full-band ensemble Monte-Carlo simulator for heterostructures, which deals with carrier transport in two different semiconductor materials simultaneously as well as at the boundary by solving self-consistently the 2D Poisson and Boltzmann transport equations(BTE).The infrastructure of this simulator,including the energy bands obtained from the empirical pseudo potential method,various scattering mechanics employed,and the appropriate treatment of the carrier transport...     

Fast computation of wideband RCS using characteristic basis function method and asymptotic waveform evaluation technique

The Asymptotic Waveform Evaluation (AWE) technique is an extrapolation method that provides a reduced-order model of linear system and has already been successfully used to analyze wideband electromagnetic scattering problems. As the number of unknowns increases, the size of Method Of Moments (MOM) impedance matrix grows very rapidly, so it is a prohibitive task for the computation of wideband Radar Cross Section (RCS) from electrically large object or multi-objects using the traditional AWE technique that needs to solve directly matrix inversion. In this paper, an AWE technique based on the Characteristic Basis Function (CBF) method, which can reduce the matrix size to a manageable size for direct matrix inversion, is proposed to analyze electromagnetic scattering from multi-objects over a given frequency band. Numerical examples are presented to illustrate the computational accuracy and efficiency of the proposed method.