Industrial and Tramp Ship Routing Problems: Closing the Gap for Real-Scale Instances

Recent studies in maritime logistics have introduced a general ship routing problem and a benchmark suite based on real shipping segments, considering pickups and deliveries, cargo selection, ship-dependent starting locations, travel times and costs, time windows, and incompatibility constraints, among other features. Together, these characteristics pose considerable challenges for exact and heuristic methods, and some cases with as few as 18 cargoes remain unsolved. To face this challenge, we propose an exact branch-and-price (B&P) algorithm and a hybrid metaheuristic. Our exact method generates elementary routes, but exploits decremental state-space relaxation to speed up column generation, heuristic strong branching, as well as advanced preprocessing and route enumeration techniques. Our metaheuristic is a sophisticated extension of the unified hybrid genetic search. It exploits a set-partitioning phase and uses problem-tailored variation operators to efficiently handle all the problem characteristics. As shown in our experimental analyses, the B&P optimally solves 239/240 existing instances within one hour. Scalability experiments on even larger problems demonstrate that it can optimally solve problems with around 60 ships and 200 cargoes (i.e., 400 pickup and delivery services) and find optimality gaps below 1.04% on the largest cases with up to 260 cargoes. The hybrid metaheuristic outperforms all previous heuristics and produces near-optimal solutions within minutes. These results are noteworthy, since these instances are comparable in size with the largest problems routinely solved by shipping companies

New algorithm for distributed frequency assignments in IEEE 802.11

The continuous growth of IEEE 802.11 wireless local area networks (WLAN) brings the benefit of a high speed wireless access to packet networks, such as Internet. But it also entails the successive appearance of new unresolved problems. One of these problems consists in the degradation of the performance observed by the users when there is a great number of radio networks coexisting in the same area. In densely populated zones it is not strange to find WLANs of different nature (private, public, etc.) sharing a scarce resource as it is the radio spectrum. This problem can be mitigated with an appropriate channel allocation. In this paper we present an algorithm for the frequency assignment problem (FAP) in IEEE 802.11, based on classical graph colouring but adding the objective of reducing interferences among overlapping cells, and thus improving the global throughput performance. An accurate evaluation of interferences is obtained not only measuring power levels, but also being aware of traffic load. Important performance improvements have been observed on a real scenario

The Vehicle Routing Problem with Service Level Constraints

We consider a vehicle routing problem which seeks to minimize cost subject to service level constraints on several groups of deliveries. This problem captures some essential challenges faced by a logistics provider which operates transportation services for a limited number of partners and should respect contractual obligations on service levels. The problem also generalizes several important classes of vehicle routing problems with profits. To solve it, we propose a compact mathematical formulation, a branch-and-price algorithm, and a hybrid genetic algorithm with population management, which relies on problem-tailored solution representation, crossover and local search operators, as well as an adaptive penalization mechanism establishing a good balance between service levels and costs. Our computational experiments show that the proposed heuristic returns very high-quality solutions for this difficult problem, matches all optimal solutions found for small and medium-scale benchmark instances, and improves upon existing algorithms for two important special cases: the vehicle routing problem with private fleet and common carrier, and the capacitated profitable tour problem. The branch-and-price algorithm also produces new optimal solutions for all three problems

Communication, power, and transgression in the "global society of information"

Alertando sobre los efectos ideológicos del nuevo determinismo “globalista” imperante en la reflexión sociológica sobre el “impacto” de las nuevas tecnologías de la información y la co-municación, este artículo constituye un análisis crítico-deconstructivo de las directas implicaciones de las mismas en el despliegue de los nuevos poderes constituyentes de nuestra “sociedad global de (control) informacional”. La aplicación de referentes teóricos procedentes del enfoque sistémico-cibernético de “segundo orden”, de la “teoría del caos” y de la “pragmática” de la comunicación humana sirve, pues, para la definición de un nuevo paradigma relacional del poder basado en la generación dinámica del orden social por fluctuaciones. Desde ahí, se apunta hacia una nueva teoría transgresora de la comunicación atenta a la actual estructura de los “Medios Globales” como productores y transmisores de complejidad reducida; y como conformadores de unas relaciones sociales basadas en los principios de la “no-reciprocidad”, la “espectacularización”, la “desmovilización”, la “mercantilización”, la “anticipación”, la “desmemorización” y la “deslocalización”. La estrategia de resistencia propuesta finalmente -inspirada en una nueva racionalidad hermenéutica de naturaleza transcultural- se enfocará hacia la búsqueda nuevos espacios de sociabilidad -verdaderamente recíprocos y transitivos- en los que sea posible la proyección abierta y plural de una subjetividad realizada “en” y “a través” de la alteridad.Mindful of the ideological effects of the current “globalist” determinism in sociological reflection on the “impact” of new information and communication technologies, this article represents a critical deconstruction of their direct implications in the display of the new powers that shape our “global society of information control”. The application of theoretical referents coming from the cyber-systemic, “second order” approach, from the “theory of chaos”, and from the “pragmatics” of human communication, serves to define a new relational paradigm of power based on the dynamic generation of social order through fluctuations. This points the way to a new transgressive theory of communication attentive to the current structure of the “Global Media” as producers and transmitters of reduced complexity who conform to social structures based on the principles of “non-reciprocity”, “spectacularization”, “demobilization”, “mercantilization”,”anticipation”, “de-memorization” and “de-localization”. The strategy of resistance strategy proposed here is inspired by a new hermeneutical rationality that is transcultural in nature and will focus on the search for new spaces for sociability -both reciprocal and transitive- where the open and plural projection of a subjectivity realized “in” and “through” otherness might be possible

A modular CMOS analog fuzzy controller

The low/medium precision required for many fuzzy applications makes analog circuits natural candidates to design fuzzy chips with optimum speed/power figures. This paper presents a sixteen rules-two inputs analog fuzzy controller in a CMOS 1 /spl mu/m single-poly technology based on building blocks implementations previously proposed by the authors (1995). However, such building blocks are rearranged here to get a highly modular architecture organized from two high level blocks: the label block and the rule block. In addition, sharing of membership function circuits allows a compact design with low area and power consumption and its highly modular architecture will permit to increase the number of inputs and rules in future chips with hardly design effort. The paper includes measurements from a silicon prototype of the controller

CMOS design of adaptive fuzzy ASICs using mixed-signal circuits

Analog circuits are natural candidates to design fuzzy chips with optimum speed/power figures for precision up to about 1%. This paper presents a methodology and circuit blocks to realize fuzzy controllers in the form of analog CMOS chips. These chips can be made to adapt their function through electrical control. The proposed design methodology emphasizes modularity and simplicity at the circuit level - prerequisites to increasing processor complexity and operation speed. The paper include measurements from a silicon prototype of a fuzzy controller chip in CMOS 1.5 /spl mu/m single-poly technology