Ion acceleration at dipolarization fronts associated with the interchange instability in Earth’s magnetotail

Science China Technological Sciences - It has been confirmed that dipolarization fronts (DFs) are the result of the interchange instability in the Earth’s magnetotail. In this paper, we use a...     

中国近代时期重要建筑家（二）

~~中国近代时期重要建筑家(二)@赖德霖 @王浩娱 @袁雪平 @司春娟     

Simulation of three-dimensional nonideal MHD flow at low magnetic Reynolds number

A numerical procedure based on a five-wave model associated with non-ideal, low magnetic Reynolds number magnetohydrodynamic (MHD) flows was developed. It is composed of an entropy conditioned scheme for solving the non-homogeneous Navier-Stokes equations, in conjunction with an SOR method for solving the elliptic equation governing the electrical potential of flow field. To validate the developed procedure, two different test cases were used which included MHD Rayleigh problem and MHD Hartmann problem. The simulations were performed under the assumption of low magnetic Reynolds number. The simulated results were found to be in good agreement with the closed form analytical solutions deduced in the present study, showing that the present algorithm could simulate engineering MHD flow at low magnetic Reynolds number effectively. In the end, a flow field between a pair of segmented electrodes in a three dimensional MHD channel was simulated using the present algorithm with and without including Hall effects. Without the introduction of Hall effects, no distortion was observed in the current and potential lines. By taking the Hall effects into account, the potential lines distorted and clustered at the upstream and downstream edges of the cathode and anode, respectively.     

Microbial fuel cell performance with non-Pt cathode catalysts

Various cathode catalysts prepared from metal porphyrines and phthalocyanines were examined for their oxygen reduction activity in neutral pH media. Electrochemical studies were carried out with metal tetramethoxyphenylporphyrin (TMPP), CoTMPP and FeCoTMPP, and metal phthalocyanine (Pc), FePc, CoPc and FeCuPc, supported on Ketjenblack (KJB) carbon. Iron phthalocyanine supported on KJB (FePc-KJB) carbon demonstrated higher activity towards oxygen reduction than Pt in neutral media. The effect of carbon substrate was investigated by evaluating FePc on Vulcan XC carbon (FePcVC) versus Ketjenblack carbon. FePc-KJB showed higher activity than FePcVC suggesting the catalyst activity could be improved by using carbon substrate with a higher surface area. With FePc-KJB as the MFC cathode catalyst, a power density of 634 mW m⁻² was achieved in 50 mM phosphate buffer medium at pH 7, which was higher than that obtained using the precious-metal Pt cathode (593 mW m⁻²). Under optimum operating conditions (i.e. using a high surface area carbon brush anode and 200 mM PBM as the supporting electrolyte with 1 g L⁻¹ acetate as the substrate), the power density was increased to 2011 mW m⁻². This high power output indicates that MFCs with low cost metal macrocycles catalysts is promising in further practical applications.     

Simulation of three-dimensional nonideal MHD flow at high magnetic Reynolds number

A conservative TVD scheme is adopted to solve the equations governing the three-dimensional flow of a nonideal compressible conducting fluid in a magnetic field.The eight-wave equations for magnetohydrodynamics(MHD) are proved to be a non-strict hyperbolic system,therefore it is difficult to develop its eigenstructure.Powell developed a new set of equations which cannot be numerically simulated by conservative TVD scheme directly due to its non-conservative form.A conservative TVD scheme augmented with a ne...     

次模函数近似算法求最小弱顶点覆盖

求给定无向图的最小弱顶点覆盖是一个NP困难问题,只能通过研究此问题的近似算法来求解.本文从基本圈出发,定义了一个次模函数,利用次模函数理论来得到一个最小弱顶点覆盖问题的近似解,且近似度为1+ln(d-1),其中d为图的顶点最大度.     

Polymer complexation for functional fibers

Polymer complex is a polymer association of different polymers with good miscibility resulting from the relatively strong intermolecular interactions or stereo match effect between polymer chains. Polymer complexes have been utilized in various fields, such as food, biomedical, cosmetic, and pharmacy. Fiber is one of the most important material forms, and shaping polymer complex into fiber will further extend its applications. This review briefly introduces the fundamentals of polymer complex, and then demonstrates the main approaches to produce polymer complex fibers(PCFs). Followed by, the modification of fibers with polymer complexes is presented. Finally, the applications of PCFs and the polymer complex modified fibers are provided, and the prospect of polymer complexation for fibers is discussed properly.     

多效精馏优化设计的研究进展

综述了多效精馏优化设计的研究进展，总结了早期多效精馏的优化数学模型及其解法，与近年来考虑了时间和控制对系统影响的新的优化设计动态模型。介绍了序贯和联立两种优化设计方法，用以识别系统操作瓶颈，得到节能效果更佳的多效精馏系统，通过实例比较，联立法比序贯法的节能效果更佳。最后展望了多效精馏优化设计的发展方向。