可调谐半导体激光吸收光谱技术的调制参量影响及优化选择

为获得较好的谐波信号,完成不同测量目的,以DFB-760.77nm波长处氧气监测为例,通过改变扫描锯齿信号和调制正弦信号的频率和幅值,讨论了调制参量对二次谐波信号峰-峰值、对称性、谐波信号展宽和信号完整性等判别依据的影响和变化.结果表明:Sinmulink模拟值和实验值相关性较高,当正弦调制信号和锯齿扫描信号频率比值为1 000倍时,可以获得较好的二次谐波信号.该研究为实验系统中调制参量的选取和调制度及系统准确度、稳定性、重复性等性能的优化提供了一定帮助.     

A semi-analytical method for free vibration of straight orthotropic beams with rectangular cross-sections

On the basis of the two-dimensional elasticity equations with orthotropy, a semi-analytical method is proposed to analyze free vibration of straight beams with rectangular cross-sections. To this end, the state space method is combined with the differential quadrature method so that state equations with respect to state variables at discrete points are derived. The frequency equation for free vibration of straight orthotropic beams is then formulated. Numerical results are presented and compared with that available in the literature. The present method can be used to analyze either shallow or deep orthotropic beams with arbitrary end conditions.     

3D Dendritic Nanostructure of Silver‐Array: Preparation,Growth Mechanism and Application in Nitrate Sensor

A 3D dendritic nanostructure of silver‐array (DSA) was prepared via electrodeposition on an interdigitated array (IDA) microelectrode. For preparation of this nanostructure, the optimal parameters such as deposition potential, deposition time, the electrode bandwidth and gap size were systematically investigated. It was found that the edge effect of the IDA microelectrode is a key factor for controlling the 3D dendritic growth of silver. Furthermore, the formation of the 3D dendritic morphology was discussed from the aspect of electrochemical nucleation theory and nonequilibrium growth dynamics to give a deep understanding of its growth mechanism. For its potential practical application, we showed that the as‐prepared 3D DSA nanomaterial exhibited high electrocatalytic reduction ability to nitrate in neutral solution and excellent performance for nitrate determination. An amperometric nitrate microsensor based on the 3D DSA was obtained.     

Development and validation of a custom panel including 183 Y-SNPs for Chinese Y-chromosomal haplogroups dissection using a MALDI-TOF MS system

Y-chromosome SNP haplogroups exhibit geographic structuring in many populations around the world. Therefore, Y-chromosome haplogroups have been widely used to infer paternal biogeographical ancestry and high-resolution paternal lineage classification. In the present study, we designed a customized panel containing 183 Y-SNPs based on previous studies and evaluated the genotyping performance and repeatability, concordance, sensitivity, and ability of analysing case-type samples using a MALDI-TOF MS platform. The average call rate for duplicate typing of any one SNP in the panel was 97.0%. In the concordance and accuracy study, the results of haplogroup designation obtained from MALDI-TOF MS platform were fully consistent with those obtained from the next-generation sequencing (NGS) platform. The optimal amount of template DNA in the PCR seemed to be 10 ng. However, if less DNA (≥156.25 pg) was available, it was still possible to obtain meaningful haplogroup information. For the application part, this panel could be applied for the detection of blood, semen, and buccal swabs samples. Particularly, blood stain on FTA card samples could be dissected by direct PCR amplification on the MALDI-TOF MS platform. Besides, 371 unrelated male individuals from four Chinese ethnic groups (Han, Hui, Mongolian, and Kazak) were detected using this panel. Total 78 terminal haplogroups were found and the haplogroup diversity was 0.933576. The results demonstrate that this panel could be an accurate, fast, and cost-effective method for database construction where the amount of sample material is less of a concern and when the cost of the assay is taken into consideration.     

A density functional theory study on the atmospheric reaction of CH3O2 with HS: Mechanism and kinetics

The reaction mechanism of CH₃O₂ and HS was systematically investigated by density functional theory (DFT). Six singlet pathways and seven triplet ones are located on the potential surface (PES). The result indicates that the main products are CH₃O and HSO both on the singlet and triplet PES, different from the CH₃O₂ + OH reaction. Moreover, deformation density (ρ_def) and atoms in molecules (AIM) analyses were carried out to further uncover the nature of chemical bonding evolution in the primary pathways. Furthermore, reaction rate constants were calculated in the temperature range from 200 to 1000 K using the transition state theory with the Wigner and Eckart tunneling corrections. Our results can shed light on the title reaction and offer instructions for analogous atmospheric reactions, as well as experimental research in the future.     

Urea-Induced Dissociation of Nerve Growth Factor from Venom of Chinese Cobra by SEC

The urea-induced dissociation of nerve growth factor from venom of Chinese cobra (_cNGF) was studied by intrinsic fluorescence emission spectra, SEC, urea-gradient polyacrylamide gel electrophoresis, assays of biological activity and thermodynamic parameters. The results showed that when urea concentration was lower than or equal to 4.0 mol L^?1 or higher than or equal to 8.0 mol L^?1, _cNGF existed only in native homodimer form or monomer form, respectively; whereas when urea concentration was higher than 4.0 mol L^?1 and lower than 8.0 mol L^?1, they existed simultaneously in the native homodimer and monomer forms and the former decreased, while the latter increased with the increase in urea concentration. Based on the association–dissociation equilibrium between _cNGF and urea molecules, an equation, which includes two characteristic dissociation parameters K and ?m, was presented to describe the urea-induced dissociation process of _cNGF. As the reaction temperature increased from 15 to 35 °C, positive enthalpy and entropy changes were observed, and the parameter K increased from 2.72 × 10^?13 to 5.18 × 10^?12 (L mol^?1), while the parameters ?m and ?G, respectively, decreased from 10.18 to 8.42 and from ?10.27 to ?18.67 (kJ mol^?1), which means that the urea-induced dissociation of _cNGF was spontaneous and entropy-driven and the higher temperature was favorable for the dissociation process. Using the procedures and equations mentioned in the paper, the urea-induced dissociation of _cNGF is first comprehensively described. Furthermore, this work presents a useful method for people to study the dissociation of dimer or multimer proteins induced by denaturants, inducers, pH, etc.     

The Adsorption and Simulated Separation of Light Hydrocarbons in Isoreticular Metal–Organic Frameworks Based on Dendritic Ligands with Different Aliphatic Side Chains

Three isoreticular metal–organic frameworks, JUC‐100, JUC‐103 and JUC‐106, were synthesized by connecting six‐node dendritic ligands to a [Zn₄O(CO₂)₆] cluster. JUC‐103 and JUC‐106 have additional methyl and ethyl groups, respectively, in the pores with respect to JUC‐100. The uptake measurements of the three MOFs for CH₄, C₂H₄, C₂H₆ and C₃H₈ were carried out. At 298 K, 1 atm, JUC‐103 has relatively high CH₄ uptake, but JUC‐100 is the best at 273 K, 1 atm. JUC‐100 and JUC‐103 have similar C₂H₄ absorption ability. In addition, JUC‐100 has the best absorption capacity for C₂H₆ and C₃H₈. These results suggest that high surface area and appropriate pore size are important factors for gas uptake. Furthermore, ideal adsorbed solution theory (IAST) analyses show that all three MOFs have good C₃H₈/CH₄ and C₂H₆/CH₄ selectivities for an equimolar quaternary CH₄/C₂H₄/C₂H₆/C₃H₈ gas mixture maintained at isothermal conditions at 298 K, and JUC‐106 has the best C₂H₆/CH₄ selectivity. The breakthrough simulations indicate that all three MOFs have good capability for separating C2 hydrocarbons from C3 hydrocarbons. The pulse chromatographic simulations also indicate that all three MOFs are able to separate CH₄/C₂H₄/C₂H₆/C₃H₈ mixture into three different fractions of C1, C2 and C3 hydrocarbons.     

A Green Procedure for the Oxidation of Benzyl Halides to Aromatic Aldehydes or Ketones in Aqueous Media

Green oxidation of benzyl halides to the corresponding aldehydes or ketones was achieved in aqueous media using trimethylamine N-oxide generated in situ from trimethylamine and H₂O₂. The yield of the reaction was excellent and the workup was simple.     

A molecular dynamics study on permeability of gases through parylene AF8 membranes

The amorphous and crystalline poly‐p‐xylylene (parylene) AF8 membranes are constructed by a novel computational technique, that is, a combined method of NVT + NPT‐molecular dynamics (MD) and gradually reduce the size. The related permeation properties are calculated using Grand Canonical Monte Carlo (GCMC) and NVT‐MD methods. The results show that amorphous and crystalline parylene AF8 membranes have different permeation properties. Compared with amorphous parylene AF8 area, crystalline parylene AF8 membranes provide less walking paths of gases. In parylene AF8 membranes, gases walk front and back among the stable sites for holding the minimal energy. Furthermore, gases walk just along the y axis of crystalline cell, however, randomly in amorphous area. The corresponding permeability coefficients approach the experimental data. Copyright © 2011 John Wiley & Sons, Ltd.