基于格子Boltzmann方法的疏水表面润湿性数值模拟

润湿性对固体表面上液体的各种动力学行为具有重要影响,疏水表面的特殊润湿性是其在减阻、降噪、防污等领域有着广泛应用前景的根本原因。基于Shan-Chen模型的格子Boltzmann方法对疏水表面润湿性进行数值模拟,获得了材料属性和微形貌对疏水表面润湿性的影响规律。研究表明,要使疏水表面处于Cassie-Baxter润湿状态,微形貌高度必须大于某一临界值,而当疏水表面一旦处于Cassie-Baxter润湿状态后,继续增加微形貌高度也不会提高其疏水性能;疏水表面的表观接触角随气液界面分数先增大后减小,且存在一个最佳的气液界面分数使表观接触角达到最大。     

某边坡钢筋混凝土格构梁锚索复合结构验收试验

介绍了某边坡工程锚索的设计参数及施工工艺,对该边坡钢筋混凝土格构梁锚索复合结构进行了验收试验,并阐明了具体的试验程序,指出在最大验收试验荷载作用下,受检锚索变形稳定,满足变形要求。     

基于随机桥过程的窄带信道多径衰落仿真研究

将多径分量仿真为随机射线的传播,其轨迹描述为随机桥过程的样本。研究随机射线在渗流网格中扩散的物理规律,以改进物理散射约束,使之有足够样本用于场强时延分布建模。通过实验,模拟不同波长的波束在不同散射体密度的渗流网格内的扩散,得出信道的相干带宽、误码率和场强的统计特征,验证了信号的多径衰落统计特征与相应的随机射线扩散程度有关,随机射线模型能够较大概率地仿真信号多径衰落的特性。     

Nickel-Based Single-Crystal Superalloys (Ni,Co)-Al-(Ta,Ti)-(Cr,Mo, W) Designed by Cluster-Plus-Glue-Atom Model and Their 1000 h Long-Term Ageing Behavior at 900 degrees CEI北大核心CSCD

It has been pointed out recently that the compositions of industrial alloys are originated from cluster-plus-glue-atom structure units in solid solutions. Specifically for nickel-based superalloys, after properly grouping the alloying elements into Al, Ni-like ((Ni) over bar, including Ni, Co, Fe, Re, Ru and Ir), gamma '- forming Cr-like ((Cr) over bar (gamma '), including Ta, Ti, V, Nb), and gamma-forming Cr-like ((Cr) over bar;(gamma), including Cr, Mo and W), the optimal formula for single-crystal superalloys has been established [Al-(Ni) over bar (12)] (Al-1(Cr) over bar (gamma ')(0.5)(Cr) over bar (gamma)(1.5)). In this work, the first generation single-crystal superalloys were investigated on the basis of the proposed formula, by using (Ni) over bar=(Ni and Co), (Cr) over bar (gamma ')=(Ta and Ti), and (Cr) over bar (gamma)=(Cr, Mo and W). Two series of alloys were designed, formulated respectively as group A: [Al-Ni11Co1] (Al1TaxTi0.5-xCr1W0.25Mo0.25), with x=0, 0.25 and 0.5 (the corresponding mass fractions of Ta and Ti are respectively 0Ta-2.65Ti, 4.82Ta-1.26Ti and 9,32Ta-0Ti), and group B: [Al-Ni12-yCo gamma](Al1Ta0.25Ti0.25Cr1W0.25MO0.25), with y=1.5, 1.75, 2 and 2.5 (the corresponding mass fractions of Co are respectively 9.43Co, 11Co, 12.57Co and 15.71Co). The single-crystal superalloys were prepared using selector technique. And then they underwent the following tests of incipient melting, standard heat treatment and 1000 h long term ageing at 900 degrees C. It is found that: (1) In group A, with increasing Ta content (decreasing Ti), all the incipient melting temperatures are increased to above 1330 degrees C, and to the highest value is between 1335 degrees C and 1340 degrees C for alloy 9.32Ta-0Ti; the gamma(')gamma(') lattice negative misfits after standard heat treatment are reduced from -0.262% (0Ta-2.65Ti) to -0.247% (9.32Ta-0Ti); the gamma(') coarsening tendency after long-term ageing is deduced, and alloy 9.32Ta-0Ti has the lowest coarsening rate (K=5.6x10(-5) mu(3)/h). (2) In group B, the Co content does not influence the incipient melting temperature (always above 1330 degrees C) and the coarsening rate of gamma(') after long-term ageing. The major role of Co is to increase the mean size of the gamma(') precipitates to about 0.55 pm and the gamma(') volume fraction to about 69% after the standard heat treatment. These two groups of alloys have their gamma(') coarsening rates approaching the level of third-generation single-crystal superalloys (K approximate to(2.08 similar to 3.82)*10(-5) mu m(3)/h).     

Pore-scale modeling of competition and cooperation of multispecies biofilms for nutrients in changing environments

In this article, we developed a pore-scale model of integrated lattice Boltzmann method and cellular automata to investigate competitive growth of aerobic nitrite and ammonium oxidizers in a bioreactor. The results showed that inlet nutrient concentrations have significant effects on maximum biofilm concentration, ratio of microorganisms' concentrations, growth pattern, and time. The local availability of oxygen could control the competition, resulting in different growth patterns. The coexistence of ammonium and nitrite in same inlet zone increased not only the biofilm concentration (7%) but also the ratio of microorganisms' concentrations (36%). Although this coexistence decreased the total biofilm concentration in some cases, it increased the growth rate about 25%. Changes of the maximum biomass concentration could change biofilm concentration of about 40% and microorganisms' concentrations ratio of about 30%. This framework provides a powerful tool to improve our understanding of dynamic interdependency of many complex microbial consortia systems with environments.     

The fracture process in quasi‐brittle materials simulated using a lattice dynamical model

The damage process in quasi‐brittle materials is characterized by the evolution of a micro‐crack field, followed by the joining of micro‐cracks, stress localization and crack instability. In network models, masses are lumped at nodal points which are interconnected by one‐dimensional elements with a bilinear constitutive relation, considering the energy consistency during the simulated process. In order to replicate the material imperfections, to render a realistic behaviour in damage localization, the model has not only random elastic and rupture properties, but also a geometric perturbation. In the present paper 2D plates with different levels of brittleness are simulated. The numerical results are presented in terms of global stress vs strain diagram, final network configuration, energy balance during the process and as geometric damage evolution. Therefore, the predictive potential of the lattice discrete element model to capture fracture processes in quasi‐brittle materials is demonstrated.     

Mesoscopic approach for steady‐state free convection in a diamond array

The purpose of the present paper is testing an in‐house efficiency algorithm based on lattice Boltzmann method (LBM) and using it to resolve the obtained coupled nondimensional governing equations to analyze two‐dimensional free convection inside a cold outer cavity subjected to a heated cylindrical diamond array. Steady state or oscillatory results are obtained using the Bhatnagar‐Gross‐Krook collision model associated to the thermal LBM. Both the velocity and temperature fields are solved using the D2Q9 models. With different Rayleigh numbers (Ra), the tested free convection can either achieve to steady state or oscillatory. We extended our in house Fortran 90 code using curved boundary conditions and implemented them into a cavity with a diamond array. The numerical simulations were done using distinct Ra (10⁶ and 10 ⁷) and distances between the four neighboring circular cylinders aligned in a diamond array. The effects of several physical parameters, including Ra and position of the hot body array on flow and heat transfer characteristics are investigated. The obtained results are highlighted in the form of streamlines, isotherms, and velocities plots. We show in this paper the stability and the efficiency of the LBM to deal with a complex geometry and its ability to reach suitable convergence criteria for high Ra (10 ⁶ and 10 ⁷). The numerical results indicate that LBM can simulate numerical problems with a high Ra reaching a steady state where we can depict the change of the flow pattern and enhancement of the heat transfer in the presence of heated diamond array.     

Influence of Ag on TCR and MR of La0.7(Ca0.27Sr0.03)MnO3:Ag0.2 ceramics subjected to cross magnetic fields

In this account, polycrystalline La_0.7(Ca_0.27Sr_0.03)MnO₃:Ag_0.2 (LCSMO:Ag) ceramics were synthesized by the sol-gel method followed by solid-state doping. The Ag amounts doped into grain boundary and cell lattice could be adjusted by changing the sintering temperature from 1000 °C to 1500 °C. The temperature coefficient of resistivity (TCR) and magnetoresistance (MR) of the obtained LCSMO:Ag ceramics were tested under cross magnetic field with directions parallel and perpendicular to the flat of bulk. The difference between TCR and MR values reached their maxima at sintering temperature of 1450 °C, meaning that degree of lattice distortion reached maximum value. The combined data from X-ray diffraction (XRD) and scanning electron microscopy (SEM) demonstrated that Ag was doped into the grain boundary and lattice cell, and Ag played an important role during the process. The influence of Ag-doping on TCR and MR suggested that degree of lattice distortion can be adjusted by doping, leading to change in isotropic ceramics into anisotropic ceramics without damage. Application of parallel magnetic fields shifted the application temperature to room temperature, and response sensitivity of the ceramics to magnetic field further increased. Overall, these findings look promising for future applications in photoelectric and magnetic devices.     

Knowledge structures in a knowledge base

Rough set theory is a useful tool for dealing with imprecise knowledge. One of the advantages of rough set theory is the fact that an unknown target concept can be approximately characterized by existing knowledge structures in a knowledge base. This paper explores knowledge structures in a knowledge base. Knowledge structures in a knowledge base are firstly described by means of set vectors and relationships between knowledge structures divided into four classes. Then, properties of knowledge structures are discussed. Finally, group, lattice, mapping, and soft characterizations of knowledge structures are given.