Stability and bifurcation of a two-dimension discrete neural network model with multi-delays

A two-dimension discrete neural network model with multi-delays is obtained using Euler method. Furthermore, the linear stability of the model is studied. It is found that there exists Hopf bifurcations when the delay passes a sequence of critical values. Using the normal form method and the center manifold theorem, the explicit formulas which determine the direction of the Hopf bifurcations and the stability of bifurcating periodic solutions are derived. Finally, computer simulations are performed to support the theoretical predictions.     

Ab initio potential energy surface and quantum dynamics for the H + CH4 → H2 + CH3 reaction

A new full-dimensional potential energy surface for the title reaction has been constructed using the modified Shepard interpolation scheme. Energies and derivatives were calculated using the UCCSD(T) method with aug-cc-pVTZ and 6-311++G(3df,2pd) basis sets, respectively. A total number of 30,000 data points were selected from a huge number of molecular configurations sampled by trajectory method. Quantum dynamical calculations showed that the potential energy surface is well converged for the number of data points for collision energy up to 2.5 eV. Total reaction probabilities and integral cross sections were calculated on the present surface, as well as on the ZBB3 and EG-2008 surfaces for the title reaction. Satisfactory agreements were achieved between the present and the ZBB3 potential energy surfaces, indicating we are approaching the final stage to obtain a global potential energy surface of quantitative accuracy for this benchmark polyatomic system. Our calculations also showed that the EG-2008 surface is less accurate than the present and ZBB3 surfaces, particularly in high energy region.     

Synthesis of 2H-indazoles by the [3 + 2] dipolar cycloaddition of sydnones with arynes

A rapid and efficient synthesis of 2H-indazoles has been developed using a [3 + 2] dipolar cycloaddition of sydnones and arynes. A series of 2H-indazoles have been prepared in good to excellent yields using this protocol, and subsequent Pd-catalyzed coupling reactions can be applied to the halogenated products to generate a structurally diverse library of indazoles.     

Selectivity control in alkylidene carbene-mediated C-H insertion and allene formation

Regioselectivity of alkylidene carbene-mediated C-H insertion was explored utilizing electronic, conformational, steric, and stereoelectronic effects. Relying on these factors, highly regio- and chemoselective carbene insertion reaction of C-H bonds in different environments could be obtained. The observed selectivity clearly indicates that an electronic effect plays a more important role than steric effect. In general, C-H bonds in conformationally rigid cyclic environments are less reactive than those in acyclic systems toward carbene insertion, and in this situation, a competing intermolecular reaction between alkylidene carbene and trimethylsilyldiazomethane led to the formation of allenylsilanes. The formation of allenylsilane becomes more favorable as the concentration of reaction becomes higher, as well as the C-H bonds undergoing insertion becomes electronically and conformationally deactivated.     

Asymmetric syntheses of (R)-4-halo-6,6a,7,8,9,10-hexahydro-5H-pyrazino[1,2-a][1,n]naphthyridines,important 5-HT2C agonist precursors

Asymmetric syntheses of N-protected (R)-4-halo-6,6a,7,8,9,10-hexahydro-5H-pyrazino[1,2-a][1,n]naphthyridines, advanced intermediates for the synthesis of highly potent and selective 5-HT_2C agonists, are described. The key transformation involves ring opening of N-protected bicyclic sulfamidate (R)-hexahydro-3H-pyrazino[1,2-c][1,2,3]oxathiazine 1,1-dioxide with (4-halo-2-fluoropyridin-3-yl)lithiums or (3-bromo-5-fluoropyridin-4-yl)lithium. In situ hydrolyses of the resultant sulfamic acids and subsequent intramolecular nucleophilic aromatic substitutions (S_NAr) produce the enantiopure tricycles. The two step procedure represents new methodology for the stereoselective syntheses of tetrahydronaphthyridines.     

Synthesis of silica microcoils by catalyst-free carbothermic method

Amorphous silica microcoils were prepared by catalyst-free carbothermal route. The lengths of them could reach as long as several hundreds of micrometers. From the morphological perspective, the microcoils could be grouped into two categories: one type was formed from an individual microwire, whereas the other type consisted of two intertwined microwires. The silica microcoils were formed spontaneously in a conventional vapor-solid growth process and the competition between the fluctuation of the pressure and the growth inertia was invoked to explain the formation of the coiled morphology. The photoluminescence (PL) spectrum of the product showed two bands centered at 416 nm and 438 nm under excitation at 320 nm.     

内生无限平面网格上基于策略互动的均衡网络结构及吸收集

在内生网络环境下,基于局中人的策略互动研究了均衡网络的结构特性,以及局中人策略选择的倾向性. 在动态进程的同一阶段,规定所有局中人同时进行策略更新,研究了网络生成的连接费用、互动支付等参数之间的相互关系及其对均衡结构或吸收集的影响. 主要贡献是将网络的内生性与无限网格上的策略互动联系在一起,得出不同连接费用水平之下的均衡结构、吸收集的准确特征.     

Identification and treatment approach for spectral baseline distortion in processing of gas analysis online by Fourier transform infrared spectroscopy

Addressing the problem of baseline drift or distortion in Fourier transform infrared spectra when analyzing gas continuously at scene, a novel and simple method is proposed to identify and treat spectral baseline drift. Firstly, the spectral baseline was corrected with the common approach followed by standard gas analysis. Then, absorbance of analytes was reconstructed and reduced from the corrected spectrum. Finally, a Fourier transform was performed with the difference spectrum, and the first four-line strengths were used as feature variables to determine if baseline distortion occurred. In the end of this paper, this approach has been applied in the field of wellhead gas logging with Fourier transform infrared. The application results showed that all the spikes had been removed from the raw logging curves, confirming that this approach could be used to identify spectral baseline distortion accurately.