A systematic overview on the subject of assembly sequencing is presented. Sequencing lies at the core of assembly planning, and variants include finding a feasible sequence—respecting the precedence constraints between the assembly operations—, or determining an optimal one according to one or several operational criteria. The different ways of representing the space of feasible assembly sequences are described, as well as the search and optimization algorithms that can be used. Geometry plays a fundamental role in devising the precedence constraints between assembly operations, and this is the subject of the second part of the survey, which treats also motion in contact in the context of the actual performance of assembly operations.
Node placement problems have been long investigated in the optimization field due to numerous applications in facility location, logistics, services, etc. Such problems are attracting again the attention of researchers now from the networking domain, and more especially from Wireless Mesh Networks (WMNs) field. Indeed, the placement of mesh routers nodes appears to be crucial for the performance and operability of WMNs, in terms of network connectivity and stability. However, node placement problems are known for their hardness in solving them to optimality, and therefore heuristics methods are approached to near-optimally solve such problems. In this work we evaluate the performance of different heuristic methods in order to judge on their suitability of solving mesh router nodes problem. We have selected methods from two different families, namely, local search methods (Hill Climbing and Simulated Annealing) and population-based methods (Genetic Algorithms). The former are known for their capability to exploit the solution space by constructing a path of visited solutions, while the later methods use a population of individuals aiming to largely explore the solution space. In both cases, a bi-objective optimization consisting in the maximization of the size of the giant component in the mesh routers network (for measuring network connectivity) and that of user coverage are considered. In the experimental evaluation, we have used a benchmark of instances—varying from small to large size—generated using different distributions of mesh node clients (Uniform, Normal, Exponential and Weibull).
Java 2 Micro Edition (J2ME) technology has been designed to bring a common framework of development for mobile devices. This can bring the Java development approach of "develop once run everywhere" to the Mobile application emerging market. Combined with the widespread of the support for this platform among the park of mobile devices, all of this makes J2ME a suitable option for mobile application development. However, J2ME has been designed to run in small devices, that's why the APIs (Application Programming Interface) implemented are very limited and kept to the strictly necessary. This decision has let out all the structured data persistence management, like object serialization, and the relational database access; neither to store data inside the mobile device nor to access a remote host. This paper presents J2MEMicroDB, an Open Source development that implements Object Serialization, local relational database engine and a remote database access protocol that allows the access to any JDBC database. In the design and implementation of J2MEMicroDB specific requirements and limitation of Mobile devices have been considered. Even some performance improvements have been developed, like BTree indexing structures which improves significantly the efficiency, as the cross-platform presented benchmarking proves.