钐配合物有序分子膜的激光诱导荧光研究

用Langmuir-Blodgett(LB)膜方法组装了可发红色荧光的钐配合物有序分子膜。用时间分辨技术得到了其激光诱导荧光光谱,并分析了荧光光谱的精细结构,计算了有序分子膜中钐离子的能级常数,测定了配合物中心离子的荧光寿命,从分子内及分子间能量转移机理上研究了分子存在状态、膜中组分对钐配合物荧光寿命及能级常数的影响。     

Room-temperature ferromagnetism in CuO sol-gel powders and films

Both CuO nanopowders and thin films prepared by sol-gel method exhibit room-temperature ferromagnetism (FM), even though CuO bulk presents a paramagnetism (PM) at room temperature above its antiferromagnetic Néel temperature. For CuO nanopowders at room temperature, FM likely occurs at surfaces of nanograins, while PM may remain in the inner of grains. The vacuum annealing greatly enhances room-temperature FM, and the air reheating after vacuum annealing reduces FM again, indicating that the observed FM in CuO sol-gel powders and thin films are connected with oxygen vacancies. The room-temperature FM of CuO nanograins decreases with an increase of grain size, possibly due to the decrease of oxygen vacancy concentrations at surfaces of nanograins.     

Adsorption of CO on the O2 pre-adsorbed LaFeO3 (0 1 0) surface: A density functional theory study

The adsorption of CO molecule on the O₂ pre-adsorbed LaFeO₃ (0 1 0) surface has been investigated using a density functional theory calculation. The calculated results show that the most appropriate reaction occurs between the CO and the pre-adsorbed O₂. After CO adsorption, the bonding mechanism between Fe site and the pre-adsorbed O₂ is not modified, and the HOMO–LUMO energy gap of the M1 mode is narrowed, which is caused by the redistribution of electron density in the surface.     

Gas-sensing properties of perovskite La0.875Ba0.125FeO3 nanocrystalline powders

La_0.875Ba_0.125FeO₃ nanocrystalline powders have been prepared by a sol-gel method. The structure, conductance and gas-sensing properties were investigated. La_0.875Ba_0.125FeO₃ crystallizes as a perovskite phase with the orthorhombic structure. The La_0.875Ba_0.125FeO₃ based sensor shows good sensitivity and selectivity to alcohol gas. The highest sensitivity to 500 ppm alcohol gas reached was 58 at 170 °C. The adsorption of O₂ on the La_0.875Ba_0.125FeO₃ (0 1 0) surface was studied with the first-principles calculation based on the density functional theory. The results show that the surface states are near the Fermi energy level and that the Fe ion plays an important role in the process of oxygen adsorption, which affects the gas-sensing properties.     

Detecting direct associations in a network by information theoretic approaches

Detecting direct associations or inferring networks based on the observed data is an important issue in many fields, including biology, physics, engineering and social studies. In this work, we focus on the information theoretic approaches in the network reconstruction or the direct association detection, in particular,for biological networks. We not only review the traditional approaches or measurements on the associations among the observed variables, such as correlation coefficient, mutual information and conditional mutual information(CMI), but also summarize recently developed theories and methods. The new theoretic works include:information geometry to give a unified framework in detecting causality/association, the partial independence to alleviate the singularity of CMI, and multiscale analysis of CMI to avoid the underestimation issue of CMI.The new methods include part mutual information(PMI) and partial associations(PA), which improve the old measurements in avoiding both overestimation and underestimation. All those theories and methods make important contributions as major advances in the development of network inference.     

H<Subscript>2</Subscript>-Sensing Characteristics of Nanocrystalline La<Subscript>0.8</Subscript>Pb<Subscript>0.2</Subscript>FeO<Subscript>3</Subscript> Prepared by Sol–Gel Method

Nanocrystalline La_0.8Pb_0.2FeO₃ has been prepared by the sol-gel method. XRD patterns show that the nanocrystalline La_0.8Pb_0.2FeO₃ is a perovskite phase with the orthorhombic structure and its mean crystallite size is about 19 nm. The influence of Pb ions which replaced the La ions on A-sites can be directly observed from the electrical and sensing properties to H₂ gas. The conductance of La_0.8Pb_0.2FeO₃-based sensor is considerably higher than that of LaFeO₃-based sensor, and Pb-doping can enhance the sensitivity to H₂ gas. An empirical relationship of with α = 0.668 was obtained.