Optimal design of water distribution networks by a discrete state transition algorithm

In this study it is demonstrated that, with respect to model formulation, the number of linear and nonlinear equations involved in water distribution networks can be reduced to the number of closed simple loops. Regarding the optimization technique, a discrete state transition algorithm (STA) is introduced to solve several cases of water distribution networks. Firstly, the focus is on a parametric study of the ‘restoration probability and risk probability’ in the dynamic STA. To deal effectively with head pressure constraints, the influence is then investigated of the penalty coefficient and search enforcement on the performance of the algorithm. Based on the experience gained from training the Two-Loop network problem, a discrete STA has successfully achieved the best known solutions for the Hanoi, triple Hanoi and New York network problems.     

Availability and cost-centered preventive maintenance scheduling of continuous operating series systems using multi-objective genetic algorithm: A case study

This article presents a multi-objective (maximization of availability and minimization of maintenance cost) preventive maintenance (PM) scheduling model for a continuous operating series system (COSS) which do not provide an off-working period for PM. The objective functions are optimized by using a Multi-Objective Genetic Algorithm (MOGA). The effectiveness of the model is demonstrated through a coal-fired boiler-tube. The case study shows that the model can improve the availability along with profound reduction of the maintenance cost, i.e., increases the profit of the plant.     

Molecular dynamics simulation study on the structure II clathrate-hydrates of methane + cyclic organic compounds

The ternary structure II (sII) clathrates of methane + cyclic organic compounds (COCs) are studied using molecular dynamics (MD) simulations. The results show that the COC guest molecules have a stabilizing effect on the clathrate-hydrate and stability of the unit cell decreases upon replacing more COC guest molecules in the large cages by CH₄ molecules which is confirmed by the comparison of radial distribution functions and unit cell volumes of the different occupancy cases. The maximum methane storage capacity for sII in the presence of tetrahydropyran, cyclobutanone, and cyclohexane are 11.9, 10.5, and 9.6 wt% of methane gas, respectively.     

High porous yttria-stabilized zirconia with aligned pore channels: Morphology directionality influence on heat transfer

High porous yttria stabilized zirconia with unidirectionally aligned channels is used in engineering applications with extremely low thermal conductivity. This property is strongly influenced by microstructure features such as pore volume fraction, pore size distribution, random porous microstructure and pore morphology directionality. Although several models are reported in the available literature, but their analytical formulas are formalised for homogeneous structures or they are based on proportion between solid and fluid phases. These differences from real microstructures cause significant computational errors especially when thermal conductivity changes as the function of the measurement direction (parallel or perpendicular). In this context, the application of an intermingled fractal unit's procedure capable of reproducing porous microstructure as well as predicting thermal conductivity has been proposed. The results are in agreement with experimental ones measured for parallel and perpendicular directions and suggest improving the formalisation of fractal modelling in order to obtain an instrument of microstructure design.     

Application of A4F-MALS for the Characterization of Polymers Prepared by Emulsion Polymerization: Comparison of the Molecular Structure of Styrene-Acrylate and Methyl Methacrylate-Acrylate Copolymers

In this paper, organic asymmetric flow field flow fractionation coupled to a multi-angle light scattering detector is presented as a very efficient tool for the characterization of copolymers prepared by emulsion polymerization. The molar mass distribution and the extent of branching of styrene–acrylate copolymers have been compared with corresponding copolymers of methyl methacrylate. It has been found that the presence of acrylate monomer results in the increase of molar mass and formation of branched macromolecules due to intermolecular chain transfer to polymer similarly as in case of methyl methacrylate–acrylate copolymers. However, the effect is far less pronounced.     

Measurement of unsaturated shear strength parameters of silty sand and its correlation with unconfined compressive strength

Compressive strength and direct shear testing parameters on unsaturated soil are often used in analysis and design of several geotechnical infrastructures. Rarely, any attempt has been made to quantify shear strength of unsaturated soil under different net normal stress conditions. The objectives of this study are to quantify shear strength parameters of unsaturated silty sand and to establish a simple correlation of it with unconfined compressive strength. Consolidated drained direct shear tests and unconfined compressive strength tests were performed to determine shear strength of unsaturated completely decomposed granite (CDG) soil. To interpret this, a series of typical soil water characteristic curves (SWCC) of CDG soil under different net normal stresses were also measured. Experimental results show that the unsaturated shear strength significantly increases with increase in net normal stress and matric suction. A new model for prediction of unconfined compression strength of unsaturated soil from shear strength and initial suction was proposed. The predictions from newly proposed model were found to be consistent with the measured unconfined compressive strength. This correlation can be useful in economical and rapid design/analysis of geotechnical infrastructure.     

底部加热的复合多孔介质热-流耦合场非线性特性

针对非线性流动传热受底部加热模型骨架的影响及分叉、震荡点的非线性解析解难求的问题,采用数值模拟及实验的方法对底部加热的复合多孔介质热流耦合传热过程进行数值求解和温度测试。构建底部加热的复合多孔介质热-流耦合传热的三维模型;采用SIMPLE算法对控制方程组进行QUICK格式离散求解,并在底部加热实验台上对测点进行温度采集。在小Ra工况下,揭示了复合多孔介质内存在热流分布分层特性及确定了非线性分叉、震荡解的特征值。数值结果表明:热流场分布对初始场依赖敏感,低Ra情况下三维腔体内热流场表现出稳定的二维性质;与单层多孔介质相比,复合多孔介质内存在热流分布分层的非线性特性;非线性分叉、震荡点对应的临界Ra依赖复合多孔介质骨架高度比,高度比越大(强导热、高阻力多孔介质区所占高度越大),静态分叉及震荡所对应的临界Ra越小,越早表现出分叉、震荡等非线性特性;改变复合多孔介质内高度比可以重新优化热流场分布,实现削弱或强化传热。     

The Biodiversity and Climate Change Virtual Laboratory: Where ecology meets big data

Advances in computing power and infrastructure, increases in the number and size of ecological and environmental datasets, and the number and type of data collection methods, are revolutionizing the field of Ecology. To integrate these advances, virtual laboratories offer a unique tool to facilitate, expedite, and accelerate research into the impacts of climate change on biodiversity. We introduce the uniquely cloud-based Biodiversity and Climate Change Virtual Laboratory (BCCVL), which provides access to numerous species distribution modelling tools; a large and growing collection of biological, climate, and other environmental datasets; and a variety of experiment types to conduct research into the impact of climate change on biodiversity.Users can upload and share datasets, potentially increasing collaboration, cross-fertilisation of ideas, and innovation among the user community. Feedback confirms that the BCCVL's goals of lowering the technical requirements for species distribution modelling, and reducing time spent on such research, are being met.     

关于算子形式的Bohr不等式的推广

采用算子论中的方法和技巧,研究了Bohr不等式的有界线性算子形式的推广,并且给出一些算子不等式,这样对文[4-5]中的结果进行了推广.进一步研究了Bohr不等式在算子范数上的性质,推广了文[6]中的相关结果.     

Simulation of granular packing of particles with different size distributions

The study of granular matter composed of spherical particles is of interest in manufacturing, material, and metallurgy. The viscoelastic and frictional contacts between the particles are the cause of forming the agglomeration. We present a numerical simulation for particles packing with three different kinds of size distributions: monosize, bimodal, and Gaussian, using distinct element method (DEM). The particles are initially put randomly but without any overlap, and then fall down due to the gravity force and collide with neighbor particles. Because of the dissipative factors of viscoelastic collision and frictional force, all the particles finally come together to form an agglomeration. Coordination number, porosity, radial distribution function, and force distribution are calculated for different size distributions. It is demonstrated that particle size distribution does affect the granular packing structure.