针叶树材纵向气体渗透的三维流阻网络

气体在木材中的渗透是通过木材内的孔隙通道进行 ,而木材内的孔隙结构非常复杂 ,在纵向、径向、弦向的连接特性均不相同。以往关于针叶树材气体渗透的模型或理论 ,只考虑针叶树材内气体渗透通道在 1个或 2个方向上的连接。本文根据针叶树材管胞流阻和管胞在纵向、径向、弦向的连接特性 ,建立了一个描述针叶树材纵向气体渗透性的三维流阻网络 ,并运用重正化变换求解出流阻网络的流阻 ,计算了针叶树材气体纵向渗透系数。所得马尾松木材气体纵向渗透系数计算值与其测量结果进行比较 ,两者十分吻合 。

Surface nanostructure modification of Al substrates by N^+ ion implantation and their corrosion inhibition

The influence of implantation of N+ions of different energies on the nanostructure of7049Al substrates and the corrosioninhibition of produced Al samples in a3.5%NaCl solution was studied.The X-ray diffraction(XRD)results confirmed the formationof AlN as a result of N+ion implantation.The atomic force microscope(AFM)results showed that grains of larger scale are formedby increasing N+energy which can be due to heat accumulation in the sample during implantation causing higher rate of diffusion inthe sample,hence decreasing the number of defects.Corrosion resistance of the samples was studied by the electrochemicalimpedance spectroscopy(EIS)measurements.Results showed that corrosion resistance of implanted Al increases with increasing N+ion energy.The equivalent circuits for the N+implanted Al samples with different energies were obtained,using the EIS data whichshowed strong dependence of the equivalent circuit elements on the surface morphology of the samples.Finally,the relationshipbetween corrosion inhibition and equivalent circuit elements was investigated.

A General Study on Equivalent Resistance of Three-Terminal Ladder Network

In view of the application importance of resistance network in modern science and technology, this paper presents the basic structure of a three terminals ladder shaped resistance network, for which, to study in- depth the equivalent resistance, carry out network analysis by applying virtual current method and construct a model of two elements three orders differential equation. Based on different marginal conditions, two general adaptive rules for the three-terminal ladder shaped inlet resistance, as well as two ultimate rules for the equiva- lent resistance of three-terminal infinite ladder shaped were given.

Effects of temperature variation on Li_xFe PO_4/C(0

Li Fe PO4/C was prepared via solid state reaction and characterized with X-ray powder diffraction and charge–discharge test. As-prepared Li Fe PO4/C has a triphylite structure and exhibits an excellent rate capability and capacity retention. Electrochemical impedance spectroscopy(EIS) was applied to investigate LixFe PO4/C(0<x<1) electrode on temperature variation. The valid equivalent circuit for EIS fitting was determined which contains an intercalation capacitance for Li+ ion accumulation and consumption in the electrode reaction. The surface layer impedance needs to be included in the equivalent circuit when Li Fe PO4/C is deeply delithiated at a relatively high temperature. EIS examination indicates that a temperature rise leads to a better reversibility, lower charge transfer resistance, higher exchange current density J0 and greater Li+ ion diffusion coefficient for the LixFe PO4/C electrode process. The Li+ ion concentration in LixFe PO4/C is potential to impact the Li+ ion diffusion coefficient, and a decrease in the former results in an increase in the latter.

Constructal optimization of cylindrical heat sources with forced convection based on entransy dissipation rate minimization

Based on constructal theory and entransy theory,the optimal designs of constant-and variable-cross-sectional cylindrical heat sources are carried out by taking dimensionless equivalent resistance minimization as optimization objective.The effects of the cylindrical height,the cylindrical shape and the ratio of thermal conductivity of the fin to that of the heat source are analyzed.The results show that when the volume of the heat source is fixed,there exists an optimal ratio of the center-to-centre distance of the fin and the heat source to the cylinder radius which leads to the minimum dimensionless equivalent thermal resistance.With the increase in the height of the cylindrical heat source and the ratio of thermal conductivity,the minimum dimensionless equivalent thermal resistance decreases gradually.For the heat source model with inverted variable-cross-sectional cylinder,there exist an optimal ratio of the center-to-centre distance of the fin and the heat source to the cylinder radius and an optimal radius ratio of the smaller and bigger circles of the cylindrical fin which lead to a double minimum dimensionless equivalent thermal resistance.Therefore,the heat transfer performance of the cylindrical heat source is improved by adopting the cylindrical model with variable-cross-section.The optimal constructs of the cylindrical heat source based on the minimizations of dimensionless maximum thermal resistance and dimensionless equivalent thermal resistance are different.When the thermal security is ensured,the optimal construct of the cylindrical heat source based on minimum equivalent thermal resistance can provide a new alternative scheme for the practical design of heat source.The results obtained herein enrich the work of constructal theory and entransy theory in the optimal design field of the heat sources,and they can provide some guidelines for the designs of practical heat source systems.