Nachweis der Existenz nicht-isomorpher Gruppen von gleicher Situation der Untergruppen

Ohne Zusammenfassung     

Optimizing routes and stock

This work is motivated by a problem proposed to the authors by a bakery company in Northern Spain. The objective is to design the daily routes over the week in order to minimize the total traveled distance. For reducing this total distance, some flexibility in the dates of delivery is introduced, which will cause a stock. Therefore, we study the problem under the bi-objective perspective, “minimizing” simultaneously the total traveled distance and the stock. A bi-objective mixed-integer linear model for the problem is formulated and two methodologies of solution are presented. The first one is based on a series of linked variable neighborhood searches and the second one is based on NSGA-II provided of specific operators. Numerical results showing the obtained estimated Pareto front in both cases are presented.     

Metaheuristics for the linear ordering problem with cumulative costs

The linear ordering problem with cumulative costs (LOPCC) is a variant of the well-known linear ordering problem, in which a cumulative propagation makes the objective function highly non-linear. The LOPCC has been recently introduced in the context of mobile-phone telecommunications. In this paper we propose two metaheuristic methods for this NP-hard problem. The first one is based on the GRASP methodology, while the second one implements an Iterated Greedy-Strategic Oscillation procedure. We also propose a post-processing based on Path Relinking to obtain improved outcomes. We compare our methods with the state-of-the-art procedures on a set of 218 previously reported instances. The comparison favors the Iterated Greedy - Strategic Oscillation with the Path Relinking post-processing, which is able to identify 87 new best objective function values.     

基于变长度染色体混沌遗传算法的专用交通道优化

大型运动会要求主办方在规定时间内将相关人员从运动员村运送至指定比赛场馆.基于大城市日趋严重的交通拥堵,为满足运送时间的要求,通常在城市公共交通网络中设置专用交通道.但专用交通道的设置会对城市公共交通产生影响,最小化其对城市公共交通影响是专用交通道优化问题的关键.针对此类问题,在给出了改进的混合整数规划模型的基础上,提出了基于问题特性的变长度染色体混沌遗传算法,包括变长度染色体编码、混沌个体初始化、交叉操作、变异操作、适应度函数的计算和不可行解的惩罚、修复策略等.最后,以经典算例和随机生成算例对算法有效性进行了验证.     

Two improved formulations for the minimum latency problem

In network problems, latency is associated with the metric used to evaluate the length of the path from a root vertex to each vertex in the network. In this work we are dealing with two applications or variations of the minimum latency problem known as the repairman problem and the deliveryman problem. We have developed two integer formulations for the minimum latency problem and compared them with other two formulations from the literature for the time-dependent traveling salesman problem. The present work highlights the similarities and differences between the different formulations. In addition, we discuss the convenience of including a set of constraints in order to reduce the computation time needed to reach the optimal solution. We have carried out extensive computational experimentation on asymmetrical instances, since they provide the characteristics of the deliveryman and repairman problems in a better way.     

Secants of Lagrangian Grassmannians

We study the dimensions of secant varieties of Grassmannian of Lagrangian subspaces in a symplectic vector space. We calculate these dimensions for third and fourth secant varieties. Our result is obtained by providing a normal form for four general points on such a Grassmannian and by explicitly calculating the tangent spaces at these four points.     

Type-II Matrices Attached to Conference Graphs

We determine the Nomura algebras of the type-II matrices belonging to the Bose-Mesner algebra of a conference graph.     

Quantum mechanic glimpse into peptide bond formation within the ribosome shed light on origin of life

This article describes a rare, however extremely pleasing, scientific study originated by Prof. Louis Massa during a friendly discussion, which yielded an insightful understanding of one of the two major ribosome functions, namely peptide bond formation. It demonstrates how elaborate, creative approach to the investigation of the location of the actual reaction of the formation of peptide bonds within the ribosomal active site was incorporated into scholarly argumentation on major issues concerning origin of life, including the question: what was first, the genetic code or its products?