玉米淀粉与丙烯酸接枝共聚合成高吸水树脂

高吸水性树指是七十年代迅速发展起来的一种新型功能高分子材料,由于它吸水速度快且能吸收自身重量数百倍乃至上千倍的水,吸水膨胀后生成的凝胶在加压条件下不易将水析出,而在周围环境缺水的条件下,又可将水缓慢释放出来,因此在农业、园林、医药卫生、沙漠治理、通信电缆等领域具有广泛的用途。近年来,随着高吸水树脂应用范围的不断拓展,其需求量迅速增加,平均年增长率高达30—40％。高吸水树脂根据合成原料的不同,主要分为合成树脂类、纤维素类和淀粉类,合成树脂类生产工艺简单,具有优良的吸水保水能力,但难于降解;纤维素类虽然可降解,但吸水率较低;淀粉类由于原料来源广泛,价格低廉,在自然界中可生物降解,对环境友好,成为吸水树脂领域的研究重点。我国在进行高吸水树脂的研究方面起步较晚,     

Bistabercarpamines A and B,first vobasinyl-chippiine-type bisindole alkaloid from Tabernaemontana corymbosa

Two novel dimeric monoterpene indole alkaloids, bistabercarpamines A (1) and B (2) possessing unprecedented bis-vobasinyl-chippiine-type skeleton, were isolated from the leaves of Tabernaemontana corymbosa. The structures were elucidated on the basis of spectroscopic data, and the absolute configurations of these isolates were determined by CD excition chirality method. Bistabercarpamine A (1) exhibited moderate cell growth inhibitory activity against HepG-2 cells with IC₅₀ of 38.14 ± 1.1 μM.     

The testing of stress-sensitivity in heteroepitaxy GaN/Si by Raman spectroscopy

In this paper the stress-sensitive features of hexagonal-GaN (H-GaN) and cubic-Si (C-Si) were investigeted. The H-GaN films have been grown on Si (1 1 1) substrates by metal-organic chemical vapor deposition (MOCVD). The Raman peaks of GaN E₂ (high) and Si (TO) have a blueshift when applying displacement-loadings which parallel the (0 0 0 2) plane of H-GaN. According to the relationship between stress changing and Raman peak shifts, the values of compressive stress in both materials were larger with increasing the displacement-loadings. The stress-sensitivity of H-GaN up to 93.5 MPa/μm which higher than C-Si which testing is 467.9 MPa/μm and the nonlinear error σ of GaN films is 0.1639 and Si is 0.0698. The measurement has a great significance to deeply research the piezoelectric polarization of H-GaN in future. This finding is important for the understanding and application of nitride semiconductors.     

The structural properties of Al doped ZnO films depending on the thickness and their effect on the electrical properties

In this study, the structural and electrical properties of AZO films with different film thickness deposited by r.f. magnetron sputtering were interpreted in relation with film growth process. The result shows that the grain size increases during film growth, which is accompanied by decrease of compressive stress, indicating the enhancement of crystallinity. The relationship between grain size and compressive stress follows the same tendency for the samples regardless of deposition temperature, which implies the strong dependencies between the grain size and the compressive stress. The XPS analysis shows that the defects such as chemisorbed oxygen and segregated Al₂O₃ cluster at grain boundary are reduced with increase of film thickness or deposition temperature, leading to increase of carrier concentration and mobility. The mobility increase is accompanied by grain size increase and compressive stress reduction, indicating the influences of grain boundary and crystallinity on the mobility.     

Electric Field-induced dynamical evolution of spiral wave in the regular networks of Hodgkin-Huxley neurons

An additional gradient force is often used to simulate the polarization effect induced by the external field in the reaction-diffusion systems. The polarization effect of weak electric field on the regular networks of Hodgkin-Huxley neurons is measured by imposing an additive term V_E on physiological membrane potential at the cellular level, and the dynamical evolution of spiral wave subjected to the external electric field is investigated. A statistical variable is defined to study the dynamical evolution of spiral wave due to polarization effect. In the numerical simulation, 40000 neurons placed in the 200 × 200 square array with nearest neighbor connection type. It is found that spiral wave encounters death and the networks become homogeneous when the intensity of electric field exceeds the critical value, otherwise, spiral wave keeps alive completely. On the other hand, breakup of spiral wave occurs as the intensity of electric field exceeds the critical value in the presence of weak channel noise, otherwise, spiral wave keeps robustness to the external field completely. The critical value can be detected from the abrupt changes in the curve for factors of synchronization vs. control parameter, a smaller factor of synchronization is detected when the spiral wave keeps alive.     

DFT and TD-DFT study on structure and properties of organic dye sensitizer TA-St-CA

The geometry, electronic structure, polarizability and hyperpolarizability of organic dye sensitizer TA-St-CA, which contains a π-conjugated oligo-phenylenevinylene unit with an electron donor–acceptor moiety, was studied using density functional theory (DFT), and the electronic absorption spectrum was investigated via time-dependent DFT (TD-DFT) with several hybrid functionals. The calculated geometry indicates that the strong conjugated effects are formed in the dye. The TD-DFT results show that the hybrid functional PBE1PBE and MPW1PW91 are more suitable than B3LYP for calculating electronic absorption spectra. The features of electronic absorption spectra were assigned on account of the qualitative agreement between the experiment and the calculations. The absorption bands in visible and near-UV region are related to photoinduced electron transfer processes, and the diphenylaniline group is major chromophore that contributed to the sensitization, and the interfacial electron transfer are electron injection processes from the excited dyes to the semiconductor conduction band. Compared with the similar dye D5, the good performance of TA-St-CA in dye-sensitized solar cells may be resulted from the higher energy level of the lowest unoccupied molecular orbital and the larger oscillator strengths for the most excited states with intramolecular electron transfer character.     

NHC triggered cascade metal-free synthesis of 2,3-diarylated indoles under solvent-free conditions

A new cascade strategy to the synthesis of 2,3-diarylated indoles via the metal-free reaction of aryl aldehyde and aryl amine triggered by N-heterocyclic carbene (NHC) under solvent-free conditions, has been disclosed. The protocol has the advantages of easy work-up, high yields, wide application scope, and an environmentally benign procedure compared with the reported methods.