Hidden Brønsted acid catalysis: pathways of accidental or deliberate generation of triflic acid from metal triflates

The generation of a hidden Br?nsted acid as a true catalytic species in hydroalkoxylation reactions from metal precatalysts has been clarified in case studies. The mechanism of triflic acid (CF(3)SO(3)H or HOTf) generation starting either from AgOTf in 1,2-dichloroethane (DCE) or from a Cp*RuCl(2)/AgOTf/phosphane combination in toluene has been elucidated. The deliberate and controlled generation of HOTf from AgOTf and cocatalytic amounts of tert-butyl chloride in the cold or from AgOTf in DCE at elevated temperatures results in a hidden Br?nsted acid catalyst useful for mechanistic control experiments or for synthetic applications.     

A robust near infrared luminescent ytterbium metal-organic framework for sensing of small molecules

The first near-infrared luminescent ytterbium metal-organic framework has been realized for the highly selective and sensitive sensing of small molecules.     

Two copper(II) complexes with 4-benzoylpyridine ligand: synthesis, crystal structure and luminescent properties

Two new copper(II) complexes Cu(NCS)2(4-Bzpy)2 (1) and Cu(NO3)2(4-Bzpy)4 (2) (4-Bzpy=4-benzoylpyridine) have been synthesized and characterized by IR, UV, elemental analysis and X-ray crystallography. Cu(II) atom has a square planar environment for 1 and an distorted octahedral environment for 2, respectively. In solid state there are C-H?π interactions and C-H?S hydrogen bonds between adjacent molecules in complex 1. The molecule of complex 2 is further connected by multiform π-π interactions, C-H?π interactions and C-H?O hydrogen bonds to form a three-dimensional supramolecular structure. The luminescent properties of the complexes 1 and 2 were both investigated in H2O solution and in solid state at room temperature, respectively.     

A new flavonoid glycoside from Vaccaria hispanica

A profiling analysis for the methanol extract of the seeds of Vaccaria hispanica (Mill.) Rauschert was performed using a HPLC-ESI-MS technique. Five compounds were identified according to their retention times, UV spectroscopic and MS features, and by comparison with literature data. Among them, a new flavonoid glycoside, named vaccarin H, was isolated and the structure determined by spectral and chemical analysis as isovitexin 2"-O-alpha-L-arabinopyranosyl-4'-O-(6"-O-dihydroferuloyl)-3-beta-glucopyranoside.     

ON THE NUMBER OF LIMIT CYCLES OF A POLYNOMIAL DIFFERENTIAL SYSTEM

In this paper, we employ qualitative analysis and methods of bifurcation theory to study the maximum number of limit cycles for a polynomial system with center in global bifurcation.     

Manipulating backbone structure with various conjugated spacers to enhance photovoltaic performance of D–A-type two-dimensional copolymers

A class of low band-gap two-dimensional conjugated polymers of PBDTT-FQ, PBDTT-TQ, PBDTT-BTQ and PBDTT-TTQ was designed and synthesized, which contains the same di(alkylthiophene)-substituted benzo[1,2-b:4,5-b′]dithiophene (BDTT) and 6,7-difluoroquinoxaline (Q) units, as well as various conjugated spacers of furan, thiophene, bithiophene and thieno[3,2-b]thiophene in the main chain. Significant effect of the varied spacers between the BDTT and Q units on the thermal, optical, electrochemical and photovoltaic properties was investigated and observed for these two-dimensional copolymers in the polymer solar cells. The maximum power conversion efficiency of 5.9% with a short circuit current of 13.7 mA/cm² and a fill factor of 0.56 was obtained for the PBDTT-TQ with thiophene spacer in the bulk hetero-junction PSCs using [6,6]-phenyl-C₇₁-butyric acid methyl ester as acceptor.     

Feedback control variables to restrain the Babesiosis disease

In this paper, we complete the study of the dynamics of a recognized continuous‐time model for the Babesiosis disease. The local and global asymptotic stability of the endemic state are established theoretically and experimentally. In addition, to restrain the disease in the original model when the endemic state exists, we propose and study the continuous model with feedback controls. The global stability of the boundary‐equilibrium point of this model is analyzed by means of rigorous mathematical methods. As an important consequence of this result, we propose a strategy to select feedback control variables in order to restrain the disease in the original model. This strategy allows us to make the disease vanish completely. In other words, the feedback controls are specially effective for restraining disease in the model. The validity of the established theoretical result is supported by a set of numerical simulations.     

Simple numerical methods of second- and third-order convergence for solving a fully third-order nonlinear boundary value problem

Numerical Algorithms - In this paper, we consider a fully third-order nonlinear boundary value problem that is of great interest of many researchers. First, we establish the existence and...     

Properties of the defect mode in one-dimensional ferroelectric Si/C60 photonic crystals

In the present paper, a novel photonic crystal (PC) defect mode is designed by inserting a ferroelectric material layer (LiNbO₃) into Si/C₆₀ one-dimensional PCs. The band structure of the ferroelectric PCs is numerically analyzed by the transfer matrix method (TMM). The width of the photonic band gap increases by 80 nm and a defect mode appears at a central wavelength of 680 nm when a 150 nm LiNbO₃ layer is inserted into the Si/C₆₀ PC structure. The defect mode in the band gap shifts linearly with the change in electric field. The defect mode shifts by 11.2 nm toward shorter wavelengths when the thin film is subjected to a DC voltage of 1 KV.     

基于红外热像仪的温压弹爆炸温度场测试

复杂的野外环境大大影响了红外热像仪对爆炸温度场的测量精度.从理论角度分析了影响测温精度的因素,提出相关的改进措施.温压弹爆炸测试现场使用野外标准黑体对红外热像仪进行实地定标,准确采集到温压弹的爆炸过程,并提取到相关数据.利用MATLAB软件平台对实验所得数据进行处理,进而得到爆炸火球表面的温度场分布信息:爆炸火球的最高温度2881℃;1000℃及其以上温度场持续时间为1300 ms;1000℃及其以上温度场最大散布范围为12.61 m.测试现场同时设置了CCD高速相机进行可见光波段的测试,测试结果表明,测试数据具有很高的精确性和可靠性.