A New Amperometric Hydrazine Sensor Based on Prussian Blue/Single‐walled Carbon Nanotube Nanocomposites

A slow reaction process has been successfully used to synthesize Prussian blue/single‐walled carbon nanotubes (PB/SWNTs) nanocomposites. Electrochemical and surface characterization by cyclic voltammetry (CV), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV‐vis absorption spectroscopy, Fourier transform infrared (FTIR) spectroscopy and X‐ray diffraction (XRD) confirmed the presence of PB nanocrystallites on SWNTs. PB/SWNTs modified glassy carbon electrode (GCE) exhibits efficient electron transfer ability and high electrochemical response towards hydrazine. The fabricated hydrazine sensor showed a wide linear range of 2.0×10^?6–6.0×10^?3 M with a response time less than 4 s and a detection limit of 0.5 μM. PB/SWNTs modified electrochemical sensors are promising candidates for cost‐effective in the hydrazine assays.     

Investigation of cross-polarized heterodyne technique for measuring refractive index and thickness of glass panels

A new mathematical model of cross-polarized heterodyning is proposed for measuring glass panels. An optical system is presented for obtaining relative thickness variation and difference distribution of refractive indices simultaneously, and the dual-balanced coherent demodulation technique is used. The experiment results show that the transmittance of light beam can be less than 0.5% when the vibration amplitude of the glass panels is equal to 5 mm. It takes about 200 s to scan the whole glass sample with size of 1430 × 1360 mm². The resolution of the thickness variation is 0.3 μm, and the lateral sampling resolution is 1 mm.     

Determination of nicotine in mainstream smoke on the single puff level by liquid-phase microextraction coupled to matrix-assisted laser desorption/ionization Fourier transform mass spectrometry

A method coupling liquid-phase microextraction with matrix-assisted laser desorption/ionization Fourier transform mass spectrometry (LPME/MALDI-FTMS) was developed to measure the content of nicotine in mainstream smoke at the single puff level. Glycerol was utilized as a matrix additive in the sample preparation to improve the homogeneity of analyte distribution in a sample spot. Good repeatability of the MALDI-MS signal (RSD <9%) was achieved by the method. Selective LPME facilitated the separation and purification of basic components from cigarette smoke. The LPME device was coupled to a smoking machine, and each puff of one cigarette could be gathered by this modified machine. The amount of nicotine in the mainstream smoke was measured at the single puff level by LPME/MALDI-FTMS. The method was simple and selective and was sufficiently sensitive to detect nicotine in each puff of one cigarette. The method thus offered an alternative approach to the study of the formation mechanism of cigarette smoke constituents.     

Structural relationships in small molecule interactions governing gas-phase enantioselectivity and zwitterionic formation

Gas-phase zwitterionic amino acids were formed in complexes of underivatized beta-cyclodextrin through reactions with a neutral base, n-propylamine. The reaction was performed in the analyzer cell of an electrospray ionization-Fourier transform mass spectrometer. Most of the natural amino acids were studied with three cyclodextrin hosts including alpha-, beta-, and gamma-cyclodextrin to understand better the structural features that lead to the stabilization of the zwitterionic complexes. Molecular dynamics calculations were performed to provide insight into the structural features of the complexes. The rate constants of the reactions were obtained through kinetic plots. Examination of both L- and D-enantiomers of the amino acid showed that the reaction was enantioselective. The reaction was then employed to analyze mixtures of Glu enantiomers naturally occurring in the bacteria Bacillus licheniformis.     

Highly active Au(I) catalyst for the intramolecular exo-hydrofunctionalization of allenes with carbon, nitrogen, and oxygen nucleophiles

Reaction of benzyl (2,2-diphenyl-4,5-hexadienyl)carbamate (4) with a catalytic 1:1 mixture of Au[P(t-Bu)2(o-biphenyl)]Cl (2) and AgOTf (5 mol %) in dioxane at 25 degrees C for 45 min led to isolation of benzyl 4,4-diphenyl-2-vinylpyrrolidine-1-carboxylate (5) in 95% yield. The Au(I)-catalyzed intramolecular hydroamination of N-allenyl carbamates tolerated substitution at the alkyl and allenyl carbon atoms and was effective for the formation of piperidine derivatives. gamma-Hydroxy and delta-hydroxy allenes also underwent Au-catalyzed intramolecular hydroalkoxylation within minutes at room temperature to form the corresponding oxygen heterocycles in good yield with high exo-selectivity. 2-Allenyl indoles underwent Au-catalyzed intramolecular hydroarylation within minutes at room temperature to form 4-vinyl tetrahydrocarbazoles in good yield. Au-catalyzed cyclization of N-allenyl carbamates, allenyl alcohols, and 2-allenyl indoles that possessed an axially chiral allenyl moiety occurred with transfer of chirality from the allenyl moiety to the newly formed stereogenic tetrahedral carbon atom.     

Shape versus inverse-shape selective adsorption of alkane isomers in carbon nanotubes

Simulation results are reported for the adsorption of pure pentane (C5) isomers and their ternary mixture in a series of open-ended armchair-type (m,m) single-walled carbon nanotubes (SWNTs). Inverse-shape selective adsorption occurs in the order of nC5or=iC5>neoC5 as a result of the configurational entropy effect. In smaller SWNTs, depending on the diameter, only nC5 adsorbs, or no adsorption at all occurs. The entropy effects are found to lead to a large adsorptive separation among the C5 isomers from their mixture. Using the ideal-adsorbed-solution theory with data on the adsorption of only the pure isomers, we predict mixture adsorption. The agreement between predictions and simulations deteriorates with decreasing diameter of the SWNT.     

Tri-iterative least-square method for bearing estimation in MIMO radar

In this paper, we introduce a novel tri-iterative least-square (TI-LS) method for bearing estimation in multiple-input multiple-output (MIMO) radar system. The TI-LS iteratively finds two steering matrices associated with the transmit and receive arrays, and the target's bearing can be easily obtained based on prior knowledge of the transmit and receive array manifolds. Furthermore, by jointly using the information from the transmit and receive array responses, angular estimation accuracy can be significantly improved. Numerical examples are presented to illustrate the excellent angular estimation accuracy and computational efficiency of this new method.     

非结构网格FVTD中二次函数重构技术用于电磁计算

提出了一种适用于非结构网格下格子中心型时域有限体积方法的基于最小平方法的二次函数重构技术以取代以往采用的线性重构技术,包括插值模板的选择和重构函数的确定.通过对典型的电磁场本征值问题及散射问题的计算验证,表明了文中方法较以往方法大大改善了算法的耗散性,提高精度的同时可以显著地减少CPU时间和存储量.     

基于IEEE 1588的时钟同步技术在分布式系统中的应用

为实现分布式系统高精度同步数据采集及实时控制,提出一种基于IEEE 1588协议的分布式系统时钟同步方法。通过分析影响同步精度的因素,采用FPGA设计时间戳生成器,并且采用晶振频率补偿时钟解决时间戳的精确获取和从时钟相对主时钟的频率纠偏等问题。     

镍、金掺杂n型硅材料的NTC和电学特性

Silicon materials compensated by deep level impurities such as nickel and gold have negative temperature coefficient （NTC） characteristics. In this work, n-type silicon wafers are smeared by nickel chloride ethanol solution and gold chloric acid ethanol solution, and subsequently put in the opening environment to heat. The electrical resistance and B-value of the thermistors made by this silicon material are measured and analyzed. When the silicon surface concentration of gold atoms is 2 × 10-6 mol/cm2, the uniformity of the single-crystal silicon material is optimal. When the diffusion temperature is between 900 and 1000 ℃, a material with high B-value and low electrical resistivity is obtained. The B-T and R-T change laws calculated by the theory of semiconductor deep level energy are basically consistent with the experimental results.