A rapid,sensitive, and widely applicable method for quantitative analysis of underivatized amino acids in different biological matrices by UHPLC‐MS/MS

A rapid, sensitive, and widely applicable method for the simultaneous quantitative analysis of 20 underivatized amino acids in different biological matrices, including serum, plasma, and tissue homogenates, using ultra high performance liquid chromatography with tandem mass spectrometry was developed and validated. Only 4 µL of serum, plasma, or tissue homogenate was extracted with 996 µL of solution (1.7 mM ammonium formate in 85% acetonitrile containing 0.1% formic acid) containing 100 ng/mL phenylalanine‐d5 as an internal standard without any further derivatization step. In addition, the matrix effects were small because a large volume of extraction solution was used. The total run time including reequilibration was 13 min. The results of linearity, accuracy, repeatability, precision, limits of detection, limits of quantification, and sample stability were sufficient to allow the measurement of the amino acids in different biological matrices. We conclude that our method is rapid, sensitive, and widely applicable and represents an improvement over other currently available technologies.     

Application of amino‐based chitosan cyclodextrin derivatives for the extraction of catechins in green tea with high‐performance liquid chromatography

Chitosan derivatives have been studied widely, but poor solubility in water restricts their applications. In this study, four types of amine‐based chitosan derivatives were prepared and modified further with beta‐cyclodextrin. The sequential microextraction of catechins ((+)‐catechin and (?)‐epigallocatechin gallate) from green tea powder by an optimized solid‐phase extraction method using these four derivatives was investigated. The optimal conditions for the extraction of catechins were 60°C for a 40 min extraction period. The purity and amount of each catechin were determined by high‐performance liquid chromatography. The different amines strengthened the extraction capacity of chitosan. Among the four types of amines, ethylene diamine grafted chitosan beta‐cyclodextrin had the highest extraction capacity to catechins. Therefore, this material was used in the extraction assay, and the standard curves of (+)‐catechin and (?)‐epigallocatechin gallate were linear over the concentration range, 0.25–500 µg/mL, after assaying five data points in duplicate. Solid‐phase extraction with the amino‐based chitosan beta‐cyclodextrin system is a new application of chitosan, which has potential applications in the extraction of bioactive compounds from plant materials or the removal of different impurities from specific extracts.     

Cationic starch as a precursor to prepare porous activated carbon for application in supercapacitor electrodes

Three activated carbons (ACs) for the electrodes of supercapacitor were prepared from cationic starch using KOH, ZnCl₂ and ZnCl₂/CO₂ activation. The BET surface area, pore volume and pore size distribution of the ACs were evaluated using density functional theory method, based on N₂ adsorption isotherms at 77 K. The surface morphology was characterized with SEM. Their electrochemical performance in prototype capacitors was determined by galvanostatic charge/discharge characteristics and cyclic voltammetry, and compared with that of a commercial AC, which was especially prepared for use in supercapacitors. The KOH-activated starch AC presented higher BET surface area (3332 m² g⁻¹) and larger pore volume (1.585 cm³ g⁻¹) than those of the others, and had a different surface morphology. When used for the electrodes of supercapacitors, it exhibited excellent capacitance characteristics in 30 wt% KOH aqueous electrolytes and showed a high specific capacitance of 238 F g⁻¹ at 370 mA g⁻¹, which was nearly twice that of the commercial AC.     

Independent measurement of the total active 8B solar neutrino flux using an array of 3He proportional counters at the Sudbury Neutrino Observatory

The Sudbury Neutrino Observatory (SNO) used an array of 3He proportional counters to measure the rate of neutral-current interactions in heavy water and precisely determined the total active (nu_x) 8B solar neutrino flux. This technique is independent of previous methods employed by SNO. The total flux is found to be 5.54_-0.31;+0.33(stat)-0.34+0.36(syst)x10(6) cm(-2) s(-1), in agreement with previous measurements and standard solar models. A global analysis of solar and reactor neutrino results yields Deltam2=7.59_-0.21;+0.19x10(-5) eV2 and theta=34.4_-1.2;+1.3 degrees. The uncertainty on the mixing angle has been reduced from SNO's previous results.     

Arbitrary pulse shaping based on intensity-only modulation in the frequency domain

We propose a novel technique to implement arbitrary pulse shaping of an ultrashort pulse by intensity-only modulation in the frequency domain. The intensity-only modulation is realized by nonuniformly spaced sampling in the frequency domain. By properly designing the sampling function, multiple pulses in the time domain will be generated with one of which being the desired waveform. The desired waveform is then selected by a time window. Both the optical amplitude and phase distributions of the output waveform can be controlled. Theoretical analysis is presented. An example showing the generation of a rectangular pulse is provided.     

Superhydrophobic surfaces prepared from water glass and non-fluorinated alkylsilane on cotton substrates

Superhydrophobic surfaces have been successfully prepared by sol-gel method using water glass as starting material. Such surfaces were obtained first by dip-coating the silica hydrosols prepared via hydrolysis and condensation of water glass onto cotton substrates, then the surface of the silica coating was modified with a non-fluoro compound, hexadecyltrimethoxysilane (HDTMS), to gain a thin film through self-assembly, superhydrophobicity with a water contact angle higher than 151° can be achieved. The morphology and surface roughness were characterized by SEM and AFM.     

In-situ control of different oxygen fugacity experimental study on the electrical conductivity of lherzolite at high temperature and high pressure

At pressure 1.0-4.0 GPa and temperature 1073-1423 K and under the control of oxygen fugacity (Mo+MoO₂, Fe+FeO and Ni+NiO), a YJ-3000t multi-anvil solid high-temperature and high-pressure apparatus and Solartron-1260 impedance/Gain-Phase analyzer were employed to analyze the electrical conductivity of lherzolite. The experimental results showed that: (1) within the range of the selected frequencies (10³-10⁶ Hz), either as viewed from the relationship between the real or imaginary part of complex impedance and the frequency, or from the relationship between modulus, phase angle and frequency, it can be seen clearly that the complex impedance has a strong dependence on frequency; (2) with the rise of temperature (T), the electrical conductivity (σ) increased, and Lg σ and 1/T follows the Arrhenius relationship; (3) with the rise of pressure, the electrical conductivity decreased, and activation enthalpy and temperature-independent pre-exponential factor decreased as well. And the activation energy and activation bulk volume of the main charge carrier in the lherzolite have been obtained for the first time, which are 1.68±0.02 eV and 0.04±0.01 cm³/mol, respectively; (4) under the given pressure and temperature, the electrical conductivity tends to increase with increasing oxygen fugacity, and under the given pressure, the activation enthalpy and pre-exponential factor tend to decrease with the rise of oxygen fugacity; (5) at 2.0 GPa and the control of the three solid buffers, Mo+MoO₂, Fe+FeO and Ni+NiO, the exponential factors of electrical conductivity variation range with oxygen fugacity are , and the theoretical model for the relationship between the electrical conductivity of lherzolite and the oxygen fugacity under high pressure has been established for the first time; (6) the electrical conduction mechanism of small polarons provides a reasonable explanation to the variation of conductivity of lherzolite with oxygen fugacity.     

Room-temperature all-semiconducting sub-10-nm graphene nanoribbon field-effect transistors

Sub-10 nm wide graphene nanoribbon field-effect transistors (GNRFETs) are studied systematically. All sub-10 nm GNRs afforded semiconducting FETs without exception, with Ion/Ioff ratio up to 10(6) and on-state current density as high as approximately 2000 microA/microm. We estimated carrier mobility approximately 200 cm2/V s and scattering mean free path approximately 10 nm in sub-10 nm GNRs. Scattering mechanisms by edges, acoustic phonon, and defects are discussed. The sub-10 nm GNRFETs are comparable to small diameter (d< or = approximately 1.2 nm) carbon nanotube FETs with Pd contacts in on-state current density and Ion/Ioff ratio, but have the advantage of producing all-semiconducting devices.     

基于标准互相关函数的图像分辨率自动标定方法

理想规则图像特征经标准互相关函数匹配后,相似函数C*(x)可用确定的解析式Z(x)表达.但是对于含噪声图像,相似函数C(x)较之C*(x)发生了变化,但存在"零相似不变性".将此原理应与于显微视觉中图像物面分辨率的在线标定,推导了矩形图像特征的一维相似函数解析式Z(x);求解C(x)=0作为Z(x)的近似,并给出了具体标定算法;通过仿真图像实验,给出标定算法的正确度在0.1～0.2 pixel;最后,将标定算法应用于可连续变焦的微对准装配系统,实测算法的精密度可达为0.08 pixel.实验结果表明,基于"零相似不变性"的标定算法是具有实用性的亚像素标定方法.～290nm波长激发下,310～390nm范围内产生荧光光谱,峰位波长在350nm,最佳激励波长为250nm;采用垂直偏振片(起偏角为0°)起偏照射样品,发现偏振荧光峰位不变,荧光峰强度随检偏角的增大而呈明显的线性递减关系.由实验数据计算得到荧光偏振度为0.783,表明分子具有一定确定取向;另外,分析认为酸性橙Ⅱ产生荧光,是由于分子中含有苯环和萘环结构吸收紫外光能量,以及氮键在光子作用下形成顺式异构体的激发单线态后,两者发射的光子所致.整个结果对酸性橙Ⅱ在食品中的违禁使用检测、特性表征、以及分子规律的更深入研究,有一定的参考价值.