Domain coarsening in viscous sintering as a result of topological pore evolution

The microstructure evolution in 3D was studied by X-ray microtomography to reveal the relation between topology of pore networks and characteristic length in viscous sintering. The mean intercept length was defined from solid/pore interface for characterizing the length of solid phase and pore phase. The increase of the characteristic length with densification was termed as domain coarsening. The topological pore evolution was analyzed by using genus. The characteristic length increased with decreasing genus in the intermediate stage. The domain coarsening takes place as a natural consequence of pore evolution in viscous sintering, i.e., the decrease of total surface area concurrent with the topological transformations.     

Topology optimization for crashworthiness of thin-walled structures under axial crash considering nonlinear plastic buckling and locations of plastic hinges

Although topology optimization is established for linear static problems, more effort is required for solving nonlinear plastic problems. A new topology optimization approach with equivalent static loads (ESLs) is suggested to find the optimum topologies and locations of plastic hinges of thin-walled crash boxes by considering crash-induced deformation, the main crash energy-absorbing mechanism. Together with finite element method crashworthiness analyses, considering all nonlinearities with rate-dependent plasticity, the method was developed using an appropriate time-incremental scheme of ESLs without removing any high values of loads. Analyses show that the crash boxes with optimum topologies have energy-absorbing capabilities equivalent to the original structure. The proposed method is evaluated for two crashes: a crash box at low speed and a double cell subjected to high-speed collision. The results indicate that this method captures nonlinear crushing behaviours and accurate locations of plastic hinges where, if proper reinforcements are made, energy absorption can be enhanced.     

Optimal PMU placement considering topology constraints

A new optimization algorithm for optimal PMU configuration based on combination of graph theory and genetic algorithm is proposed. According to four topology reconstruction rules and three PMU configuration rules based on the graphic relationships between PMUs, constraints of PMU placement are put forward through topology constraint analysis, which dramatically limits the feasible solution space, thereby enhancing the algorithm speed. Meanwhile, an improved genetic algorithm based on serial number coding is presented to avoid infeasible solutions and improve the overall optimization performance. New corresponding crossover and mutation operator is also created. Examples show that the proposed algorithm performs very well and is highly valuable to large-scale networks.     

Three-phased clustered topology formation for Aeronautical Ad-Hoc Networks

In-Flight Internet Connectivity (IFC) has become one of the crucial needs of passengers with technological improvements. The Aeronautical Ad-hoc Networks (AANETs) have been proposed by establishing air-to-air (A2A) links between aircraft to satisfy this need. However, the unstructured aircraft topology caused by their ultra-dynamic characteristics reduces the longevity of A2A links in AANET. This shorter longevity decreases the stability of AANET by accelerating the connection establishment/termination procedures between aircraft. Additionally, the shorter link longevity affects the packet transfer delay and the delivery ratio of AANET. To the best of our knowledge, these three challenges are not investigated simultaneously under one topology management model. This paper proposes a three-phased topology formation model for AANETs to increase the stability and packet delivery ratio in AANET with a shorter packet transfer delay. The first phase corresponds to the aircraft clustering formation, and here, we aim to increase the AANET stability by creating spatially correlated clusters. The second phase consists of the A2A link determination for reducing the packet transfer delay. Finally, the cluster head selection increases the packet delivery ratio in AANET. According to our simulations, we see that the stability and packet delivery ratio of AANET topology are roughly improved 35% and 31% with a 28% delay reduction compared to the methods in the literature.     

Topology management techniques for tolerating node failures in wireless sensor networks: A survey

In wireless sensor networks (WSNs) nodes often operate unattended in a collaborative manner to perform some tasks. In many applications, the network is deployed in harsh environments such as battlefield where the nodes are susceptible to damage. In addition, nodes may fail due to energy depletion and breakdown in the onboard electronics. The failure of nodes may leave some areas uncovered and degrade the fidelity of the collected data. However, the most serious consequence is when the network gets partitioned into disjoint segments. Losing network connectivity has a very negative effect on the applications since it prevents data exchange and hinders coordination among some nodes. Therefore, restoring the overall network connectivity is very crucial. Given the resource-constrained setup, the recovery should impose the least overhead and performance impact. This paper focuses on network topology management techniques for tolerating/handling node failures in WSNs. Two broad categories based on reactive and proactive methods have been identified for classifying the existing techniques. Considering these categories, a thorough analysis and comparison of all the recent works have been provided. Finally, the paper is concluded by outlining open issues that warrant additional research.     

岩体质量的可拓学评价方法在边坡工程中的应用

可拓工程评价方法是在解决矛盾问题的过程中，既可利用物元的可拓性确定定性因素，又可利用可拓集合论，通过关联函数可取负值这一特点进行定量计算，使评价方法能较全面地分析对象属于集合的程度，较好地解决了岩体质量评价中定性与定量因素综合评价的问题。     

一种射影变换的图形图像纠正原理

由于各种因素的影响,地形图会发生不规则变形,因此,必须对其进行纠正.为此提出了一种射影变换纠正法,叙述了其纠正方法和纠正原理,并总结了其优点.     

新乡土建筑的一次诠释--关于天台博物馆的对谈

本文记录了支文军与王路关于天台博物馆的对话,讨论了相关的传统与创新、本土性与国际性、地域与环境、空间与形态、材料与形式等问题,以及对当代新乡土建筑的一些思考。     

Grey filter functions for suppression of grey-scale elements

To solve the problem of the presence of grey-scale material in optimization results and improve convergence efficiency during the optimization procedure caused by those intermediate densities, three kinds of simpler filter functions were proposed for the variable density method according to S-curve models. First, the feasible range for the parameters of the filter functions was determined by studying Messerschmitt–Bölkow–Blohm beam with the solid isotropic micro-structure with the penalization (SIMP) method. Then, the filter functions were applied to three classic examples to verify their validity and feasibility. The results showed that higher convergence efficiency, clearer structure boundaries, and better feasible solutions were obtained compared with that without the filter function. Finally, the filter functions were also compared with one existing method to demonstrate its effectiveness and validity.