Oxidative dehydrogenation of ethane over Co–BaCO3 catalysts using CO2 as oxidant: effects of Co promoter

Co–BaCO₃ catalysts exhibited high catalytic performance for oxidative dehydrogenation of ethane (ODE) using CO₂ as oxidant. The maximal formation rate of C₂H₄ was 0.264 mmol · min⁻¹ · (g · cat.)⁻¹ (48.0% C₂H₆ conversion, 92.2% C₂H₄ selectivity, 44.3% C₂H₄ yield) on 7 wt% Co–BaCO₃ catalyst at 650 °C and 6000 ml. (g · cat.)⁻¹. h⁻¹. Co–BaCO₃ catalysts were comparatively characterized by XRF, N₂ isotherm adsorption-desorption, XRD, H₂-TPR and LRs. It was found that Co⁴⁺–O species were active sites on these catalysts in ODE with CO₂. The redox cycle of Co–O species played an important role on the catalytic performance of Co–BaCO₃ catalysts. On the other hand, the co-operation of BaCO₃ and BaCoO₃ was considered to be one of possible reasons for the high catalytic activity of these catalysts.     

Synthesis, isolation, spectroscopic and electrochemical characterization of some calcium-containing metallofullerenes

A few Ca-containing mono-metallofullerenes, i.e. Ca@C₇₆, Ca@C₈₈, Ca@C₉₀ (I, II), were synthesized by an improved DC arc discharge method and isolated by a multi-stage HPLC method for the first time. These isomer-separated metallofullerenes were characterized by LD-TOF MS and UV-vis-NIR spectrometry. Their HOMO-LUMO band gaps and possible molecular geometries are discussed according to the absorption spectra in this report. In addition, the cyclic and differential pulse voltammetry of Ca@C₇₆ was conducted in MeCN/C₆H₅CH₃ (1:4 v/v). The voltammograms of Ca@C₈₂ (II, III) and Ca@C₈₄ (II) were also recorded. Their electrochemical behaviors are discussed compared with those of corresponding ytterbium metallofullerenes. The features of the Ca metallofullerenes’ electronic structures are also discussed.     

Study of different effect on foaming process of biodegradable bionolle in supercritical carbon dioxide

Microcellular foaming of biodegradable Bionolle in supercritical CO₂ has been produced. The effects of a series of variable factors, such as saturation temperature, saturation pressure, and depressurization time and step on the foam structures and density, were studied through measurement of density and SEM observation. The experimental results show that higher saturation temperatures lead to an increase in bulk densities; and different depressurization time and step result in different product cell morphology. In addition, at some saturation temperature, the orientation of the cells can be found in the product morphology. XRD experimental results show that the foaming treatment with SC CO₂ increased the crystallinity of Bionolle. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2901–2906, 2006     

提纯乙型脑炎细胞培养疫苗的研究

应用截留分子量10万的超滤系统,将地鼠肾细胞乙型脑炎疫苗浓缩10～20倍,再以差速离心法提纯。所得提纯乙脑疫苗免疫原性及抗原效价均比原制苗明显提高,达到日本提纯苗的水平。经人体接种反应和效果观察表明,提纯苗反应轻微,血凝抗体4倍增长率占100%,GMT258.9,与常规苗相比有非常显著差异。     

传统民本论与现代民主的异同

分析了中国传统的民本思想与现代民主思想在权利主体、价值目的、实现方式和经济基础方面存在的本质区别和在重视人民作用、反对统治者专权、专利方面存在的一致性。发展当代中国的民主,应积极培育民众政治参与意识,清除官本位思想,加强法制建设,大力发展市场经济。     

Molten salts/ceramic-foam matrix composites by melt infiltration method as energy storage material

A new type of high temperature energy storage material was obtained through the melt infiltration method, using compounding SiC ceramic foam as matrix and Na₂SO₄ as phase change material. The resulting composite material was measured by XRD, SEM, TG-DSC methods. The experimental results indicate that the composite is composed of silicon carbide, sodium sulfate and square quartz, and no chemical reactions occurs between Na₂SO₄ and SiC matrix. Na₂SO₄ has a good bonding with the SiC ceramic foam matrix. As the composite material is characterized by high thermal energy storage density and high thermal conductivity, it is suit for energy storage under high temperature. Funded by the “863” Hi-Tech Research and Development Program of China (2008AA05Z418)     

农村政治学的个案研究方法述评

政治学者进入农村,首选的就是个案研究.从数量来看,可分为单个案和多个案;从时间来看,可分为共时和历时;从范围来看.可分为特殊性和普遍性.在中国本土政治学者进入农村之前,社会学者、人类学者和海外学者早已在农村收获了丰富的理论成果,起步较晚的本土学者一方面学习借鉴了他们的研究方法,另一方面又发展出具有自身学科特色的研究方法.     

A nonlinear control method for the electromagnetic suspension system of the maglev train

To deal with the inherent nonlinearity and open-loop instability of the electromagnetic suspension (EMS) system, a new nonlinear control method is proposed. The simulation results show that, for a PID controller, the overshoot of the system response to an airgap step disturbance is about 3 mm, and the transient time is 6 s; however, for the proposed nonlinear controller, there is no overshoot and transient time within 2 s. The proposed method has a faster response and stronger robustness. With a designed bi-DSP suspension controller, this nonlinear control method was implemented on the Shanghai Urban Maglev Test Line (SUMTL) to validate its effectiveness and feasibility.

     

Discrimination for ablative control mechanism in solid-propellant rocket nozzle

The ablation in solid-propellant rocket nozzle is a coupling process resulted by chemistry, heat and mass transfer. Based on the heat and mass transfer theory, the aero-thermo-dynamic, and thermo-chemical kinetics, the thermal-chemical ablation model is established. Simulations are completed on the heat flow field and chemical ablation in the nozzle with different concentrations, frequency factors and activation energy of H2. The calculation results show that the concentration and the activation energy of H...     

Transitions from solid to liquid in isotactic polystyrene studied by thermal analysis and X-ray scattering

A three-phase model, comprising mobile amorphous fraction (MAF), rigid amorphous fraction (RAF) and crystalline fraction (C), has been applied to interpret the thermal transitions and structure of cold-crystallized isotactic polystyrene (iPS) from below the glass transition temperature, T_g, to above the melting point. Quenched amorphous iPS films were isothermally crystallized at different temperatures for 12 h. The fraction of crystalline phase, ?_c, was measured by differential scanning calorimetry (DSC), wide angle X-ray scattering and Fourier Transform infrared spectroscopy. The fraction of the mobile amorphous phase, ?_MAF, was obtained from the heat capacity increment at the glass transition temperature. In the three-phase model, the fraction of the rigid amorphous phase, ?_RAF, was found from 1−?_MAF−?_c. Specific heat capacity measurements by standard DSC confirm that the experimental baseline heat capacity conforms to a three-phase model for temperatures ranging from below T_g, up to the relaxation of RAF. The relaxation of RAF appears as a sigmoidal change in heat capacity accompanied by excess enthalpy, in which solid-like RAF is converted to an identical amount of liquid-like MAF.At temperatures above the relaxation of RAF, either one or two major crystal melting endotherms are observed in standard DSC, dependent upon crystallization temperature. However, using quasi-isothermal temperature modulated DSC, we always observed two reversing melting endotherms. The effects of annealing on iPS structure during the quasi-isothermal measurement were assessed using small angle X-ray scattering (SAXS). Combining the DSC and SAXS results, a model for the melting of iPS lamellae at low heating rates is presented.