Microstructure and magnetic properties of Co(Cr)/Ti(Cr)/ZnO films prepared by laser ablation on Si substrates

High-quality Co(Cr)(50–66 nm)/Ti(Cr)(25–30 nm)/ZnO(165–225 nm) films were grown on Si substrates by the pulsed-laser deposition technique at 450–500°C. The microstructure of the films and their magnetic properties were investigated by X-ray diffraction, transmission electron microscopy and a vibrating sample magnetometer. It was found that the Co(Cr)/Ti(Cr)/ZnO thin films had a highly preferential c-axis direction normal to the surface of the substrate, and the ZnO sublayer had columnar structures in the growth direction. The interface of the multi-layer films is smooth without interface reaction. The as-produced films had in-plane easy magnetization. It indicates that the enhancements of the magnetic properties of the films are mainly ascribed to the grain structure and multi-domain state of the Co-alloy layer, which can be controlled by the ZnO sublayer.     

LC Separation and Determination of Five Diester-Diterpenoid Alkaloids in the Unprocessed and Processed Aconite Roots

A reliable liquid chromatographic method with photodiode array detector (DAD) was developed and validated for simultaneous separation and determination of five diester-diterpenoid alkaloids in the aconite roots. The separation was successfully performed on a Zorbax Extend-C₁₈ column with a mobile phase gradient prepared from methanol and ammonia solution at a flow rate of 1.0 mL min^?1. Good linearity (r > 0.999) was observed over the concentration ranges investigated, and intra-day and inter-day precision were high. The mean recoveries of five components ranged from 90.45 to 102.63% and relative standard deviations were always <5%. The validated method was successfully used for simultaneous determination of the five diester-diterpenoid alkaloids of unprocessed and processed aconite roots. The quantitative method provided a scientific basis for safety assurance and clinical application of aconite roots.     

Universal relation for size dependent thermodynamic properties of metallic nanoparticles

The previous model on surface free energy has been extended to calculate size dependent thermodynamic properties (i.e., melting temperature, melting enthalpy, melting entropy, evaporation temperature, Curie temperature, Debye temperature and specific heat capacity) of nanoparticles. According to the quantitative calculation of size effects on the calculated thermodynamic properties, it is found that most thermodynamic properties of nanoparticles vary linearly with 1/D as a first approximation. In other words, the size dependent thermodynamic properties P(n) have the form of P(n) = P(b)(1 -K/D), in which P(b) is the corresponding bulk value and K is the material constant. This may be regarded as a scaling law for most of the size dependent thermodynamic properties for different materials. The present predictions are consistent literature values.     

Sm(CobalFexCu0.049Zr0.024)7.5(x=0.102～0.282)的结构和磁性能

采用XRD,AFM等检测方法研究了Fe含量对Sm（CobalFexCu0.049Zr0.024）7.5（x=0.102-0.282）的磁性能和显微结构的影响。结果表明,磁体的Br先随Fe含量的增加而增加,在x=0.239时达最大值1.099 T,进一步增加Fe含量由于FeCo软磁性相的形成而导致Br下降。当Fe含量由x=0.239增加至0.282时,Hci由最大值1660.3 kA·m^-1迅速降低至979.1kA·m^-1。Fe含量对磁体的相结构没有显著的影响,主要由2∶17R相、1∶5相和2∶17H相构成。但当Fe含量x〈0.197时,Sm（CobalFexCu0.049Zr0.024）7.5的胞状组织未发生显著变化,平均尺寸约为80nm;当Fe含量x〉0.197时,胞状结构发生长大,均匀性变差,胞状结构的变化导致矫顽力的温度稳定性随Fe含量的增高而大幅降低;当x=0.282时,磁体在500℃下的Hci只有114 kA·m^-1,磁通不可逆损失达-36.7%。     

大肠杆菌氧化还原辅因子代谢工程

NAD⁺、NADP⁺、NADH、NADPH等四类烟酰胺类辅因子也被称为氧化还原辅因子,是维持细胞氧化还原平衡,驱动胞内许多分解与合成反应的重要分子。近年来,辅因子在生物转化系统中的作用受到研究者的重视,氧化还原辅因子更成为人们关注的重点。文章综述了大肠杆菌（Escherichia coli, E. coli）氧化还原辅因子代谢工程研究的最新进展,重点总结最近发展的氧化还原辅因子代谢工程策略,讨论不同代谢工程策略对细胞氧化还原辅因子水平的影响及其在生物合成中的应用,并展望了辅因子代谢工程未来发展方向。     

LC Separation and Determination of Five Diester-Diterpenoid Alkaloids in the Unprocessed and Processed Aconite Roots

A reliable liquid chromatographic method with photodiode array detector (DAD) was developed and validated for simultaneous separation and determination of five diester-diterpenoid alkaloids in the aconite roots. The separation was successfully performed on a Zorbax Extend-C₁₈ column with a mobile phase gradient prepared from methanol and ammonia solution at a flow rate of 1.0 mL min⁻¹. Good linearity (r > 0.999) was observed over the concentration ranges investigated, and intra-day and inter-day precision were high. The mean recoveries of five components ranged from 90.45 to 102.63% and relative standard deviations were always <5%. The validated method was successfully used for simultaneous determination of the five diester-diterpenoid alkaloids of unprocessed and processed aconite roots. The quantitative method provided a scientific basis for safety assurance and clinical application of aconite roots.

     

Modeling size effects on the surface free energy of metallic nanoparticles and nanocavities

Based on the rigorous consideration of the bond broken rule and surface relaxation, a model for the size-dependent surface free energy of face-centered-cubic nanoparticles and nanocavities is presented, where the surface relaxation is calculated by the BOLS relationship. It is found that the surface free energy of nanoparticles and nanocavities represents a reverse size effect-the surface free energy of nanoparticles decreases with the decrease of particle size while it rises with the shrinkage of cavities. The size effect on the surface free energy of nanoparticles and nanocavities is not evident in large size ranges, while it becomes more and more distinct with decreasing size, especially for sizes smaller than 10 nm. The present predictions are in good agreement with the available literature data.     

Ablation properties of carbon/carbon composites with tungsten carbide

The ablation properties and morphologies of carbon/carbon (C/C) composites with tungsten carbide (WC) filaments were investigated by ablation test on an arc heater and scanning electron microscopy. And the results were compared with those without tungsten carbide (WC) filaments tested under the same conditions. It shows that there is a big difference between C/C composites with and without WC filaments on both macroscopic and microscopic ablation morphologies and the ablation rates of the former are higher than the latter. It is found that the ablation process of C/C composites with WC filaments includes oxidation of carbon fibers, carbon matrices and WC, melting of WC and WO₃, and denudation of WC, WO₃ and C/C composites. Oxidation and melting of WC leads to the formation of holes in z directional carbon fiber bundles, which increases the coarseness of the ablation surfaces of the composites, speeds up ablation and leads to the higher ablation rate. Moreover, it is further found that the molten WC and WO₃ cannot form a continuous film on the ablation surface to prevent further ablation of C/C composites.     

The effect of compound addition Dy2O3 and Sn on the structure and properties of NdFeNbB magnets

NdFeNbB with the additions of Dy₂O₃ and Sn permanent magnets have been attained by means of powder-blending technique, and their magnetic properties, temperature performance and microstructure were studied in this paper. The addition of just 2.0 wt% Dy₂O₃ or 0.3 wt% Sn proved to be very effective in improving the permanent magnetic properties of NdFeNbB magnets. Dy₂O₃ additions result in the increase in the H_ci and temperature dependence due to the increase of T_c, formation of (NdDy)-rich phase and grain refinement of Φ phase. This improvement of the coercivity stability of the magnets from the addition of Sn is attributed to the smoothing effect of the Sn addition at the grain boundaries. The magnetic properties, the temperature dependence and Curie temperature of NdFeNbB with Dy₂O₃ and Sn combined addition were found to be considerably improved. From the X-ray diffraction, SEM-EDAX studies and the thermo-magnetic study, the improved properties due to the solution of Dy and Sn to the Φ phase, the reduced N_eff and the smaller Φ phase.