La influencia del factor dimensión en la pertenencia a centrales de compra por parte del pequeño comercio

[ES] Desde hace varios años, el pequeño comercio en España y en otros países europeos viene enfrentándose a un entorno de creciente concurrencia, con la irrupción de nuevas formas comerciales más integradas vertical u horizontalmente, y mejor preparadas para competir en precio y variedad. Ante este hecho, las centrales de compra se ofrecen como una alternativa tendente a acortar distancias en estas dos cuestiones, a la vez que buscan la prestación de ciertos servicios que ayuden al pequeño comerciante a gestionar más eficaz y eficientemente su negocio.

Some Results on Fixed and Best Proximity Points of Precyclic Self-Mappings

12 p.

Best Proximity Points of Generalized Semicyclic Impulsive Self-Mappings: Applications to Impulsive Differential and Difference Equations

This paper is devoted to the study of convergence properties of distances between points and the existence and uniqueness of best proximity and fixed points of the so-called semicyclic impulsive self-mappings on the union of a number of nonempty subsets in metric spaces. The convergences of distances between consecutive iterated points are studied in metric spaces, while those associated with convergence to best proximity points are set in uniformly convex Banach spaces which are simultaneously complete metric spaces. The concept of semicyclic self-mappings generalizes the well-known one of cyclic ones in the sense that the iterated sequences built through such mappings are allowed to have images located in the same subset as their pre-image. The self-mappings under study might be in the most general case impulsive in the sense that they are composite mappings consisting of two self-mappings, and one of them is eventually discontinuous. Thus, the developed formalism can be applied to the study of stability of a class of impulsive differential equations and that of their discrete counterparts. Some application examples to impulsive differential equations are also given.

An R package for permutations, Mallows and Generalized Mallows models

[EN]Probability models on permutations associate a probability value to each of the permutations on n items. This paper considers two popular probability models, the Mallows model and the Generalized Mallows model. We describe methods for making inference, sampling and learning such distributions, some of which are novel in the literature. This paper also describes operations for permutations, with special attention in those related with the Kendall and Cayley distances and the random generation of permutations. These operations are of key importance for the efficient computation of the operations on distributions. These algorithms are implemented in the associated R package. Moreover, the internal code is written in C++.

The cross layer RMPA handover: a reliable mobility pattern aware handover strategy for broadband wireless communication in a high-speed railway domain

Enhancing the handover process in broadband wireless communication deployment has traditionally motivated many research initiatives. In a high-speed railway domain, the challenge is even greater. Owing to the long distances covered, the mobile node gets involved in a compulsory sequence of handover processes. Consequently, poor performance during the execution of these handover processes significantly degrades the global end-to-end performance. This article proposes a new handover strategy for the railway domain: the RMPA handover, a Reliable Mobility Pattern Aware IEEE 802.16 handover strategy "customized" for a high-speed mobility scenario. The stringent high mobility feature is balanced with three other positive features in a high-speed context: mobility pattern awareness, different sources for location discovery techniques, and a previously known traffic data profile. To the best of the authors' knowledge, there is no IEEE 802.16 handover scheme that simultaneously covers the optimization of the handover process itself and the efficient timing of the handover process. Our strategy covers both areas of research while providing a cost-effective and standards-based solution. To schedule the handover process efficiently, the RMPA strategy makes use of a context aware handover policy; that is, a handover policy based on the mobile node mobility pattern, the time required to perform the handover, the neighboring network conditions, the data traffic profile, the received power signal, and current location and speed information of the train. Our proposal merges all these variables in a cross layer interaction in the handover policy engine. It also enhances the handover process itself by establishing the values for the set of handover configuration parameters and mechanisms of the handover process. RMPA is a cost-effective strategy because compatibility with standards-based equipment is guaranteed. The major contributions of the RMPA handover are in areas that have been left open to the handover designer's discretion. Our simulation analysis validates the RMPA handover decision rules and design choices. Our results supporting a high-demand video application in the uplink stream show a significant improvement in the end-to-end quality of service parameters, including end-to-end delay (22%) and jitter (80%), when compared with a policy based on signal-to-noise-ratio information.

Polymer-Optical-Fiber Lasers and Amplifiers Doped with Organic Dyes

Polymer optical fibers (POFs) doped with organic dyes can be used to make efficient lasers and amplifiers due to the high gains achievable in short distances. This paper analyzes the peculiarities of light amplification in POFs through some experimental data and a computational model capable of carrying out both power and spectral analyses. We investigate the emission spectral shifts and widths and on the optimum signal wavelength and pump power as functions of the fiber length, the fiber numerical aperture and the radial distribution of the dopant. Analyses for both step-index and graded-index POFs have been done.

Extending Distance-based Ranking Models In Estimation of Distribution Algorithms

Recently, probability models on rankings have been proposed in the field of estimation of distribution algorithms in order to solve permutation-based combinatorial optimisation problems. Particularly, distance-based ranking models, such as Mallows and Generalized Mallows under the Kendall’s-t distance, have demonstrated their validity when solving this type of problems. Nevertheless, there are still many trends that deserve further study. In this paper, we extend the use of distance-based ranking models in the framework of EDAs by introducing new distance metrics such as Cayley and Ulam. In order to analyse the performance of the Mallows and Generalized Mallows EDAs under the Kendall, Cayley and Ulam distances, we run them on a benchmark of 120 instances from four well known permutation problems. The conducted experiments showed that there is not just one metric that performs the best in all the problems. However, the statistical test pointed out that Mallows-Ulam EDA is the most stable algorithm among the studied proposals.

Métodos para obtener el coeficiente de concentración de tensiones para fatiga

[ES]Existen diferentes propuestas para obtener el coeficiente de concentración de tensiones para el análisis de fatiga: Neuber, Peterson, distancia crítica, corrección de modelo de elementos finitos, etc. En este trabajo se trata de estudiar los principales y compararlos entre ellos de forma sistemática utilizando como referencia piezas con entallas de geometría sencilla y extrayendo conclusiones útiles para diseño y análisis mecánico.

Handover en LTE basado en distancia en plataforma de simulación

[ES]Mejorar el proceso de handover en el despliegue de comunicaciones inalámbricas de banda ancha tradicionalmente ha motivado muchas iniciativas de investigación. En el dominio de los ferrocarriles de alta velocidad, el reto es incluso mayor. Debido a las largas distancias que se cubren, el nodo móvil se ve envuelto en una secuencia obligatoria de procesos de handover. Consecuentemente, un rendimiento pobre en la ejecución de esos procesos de handover degrada significativamente el rendimiento global extremo a extremo. Este documento propone una nueva estrategia de handover para el dominio de los ferrocarriles: un algoritmo de decisión para LTE basado en distancia en lugar de en potencia. La decisión de realizar el handover se realiza cuando un eNB candidato se encuentra más cerca del UE que el eNB fuente. Adicionalmente, cabe la posibilidad de retrasar esa decisión mediante un umbral. Asimismo, se añade una nueva función al modelo de LTE de la plataforma de simulación empleada en la verificación de este modelo. Este mecanismo de decisión introduce un retardo menor en los procesos de handover y, en consecuencia, la calidad extremo-a-extremo aumenta.

Análisis comparativo de cuatro soluciones de forjado

[ES]Se trata de realizar el cálculo de un forjado mediante cuatro soluciones constructivas diferentes, nervios in situ, viguetas prefabricadas, prelosas y placas alveolares. Se quiere establecer cuál es la solución más adecuada para diferentes distancias entre apoyos. Para ello se harán dos estudios con diferentes herramientas informáticas, Excel y CYPE.

Study and comparison of four forest structures on Mt. Chortiatis (northern Greece)

EL proyecto estudia y analiza la estructura de cuatro bosques en el monte Chortiatis, Grecia.

How central are clients in sexual networks created by commercial sex?

Sex workers are traditionally considered important vectors of transmission of sexually transmitted infections (STI). The role of clients is commonly overlooked, partially due to the lack of evidence on clients' position in the sexual network created by commercial sex. Contrasting the diffusion importance of sex workers and their clients in the map of their sexual encounters in two Web-mediated communities, we find that from diffusion perspective, clients are as important as sex workers. Their diffusion importance is closely linked to the geography of the sexual encounters: as a result of different movement patterns, travelling clients shorten network distances between distant network neighborhoods and thus facilitate contagion among them more than sex workers, and find themselves more often in the core of the network by which they could contribute to the persistence of STIs in the community. These findings position clients into the set of the key actors and highlight the role of human mobility in the transmission of STIs in commercial sexual networks.

Properties of convergence of a class of iterative processes generated by sequences of self-mappings with applications to switched dynamic systems

This article investigates the convergence properties of iterative processes involving sequences of self-mappings of metric or Banach spaces. Such sequences are built from a set of primary self-mappings which are either expansive or non-expansive self-mappings and some of the non-expansive ones can be contractive including the case of strict contractions. The sequences are built subject to switching laws which select each active self-mapping on a certain activation interval in such a way that essential properties of boundedness and convergence of distances and iterated sequences are guaranteed. Applications to the important problem of stability of dynamic switched systems are also given.

Results on proximal and generalized weak proximal contractions including the case of iteration-dependent range sets

This paper presents some further results on proximal and asymptotic proximal contractions and on a class of generalized weak proximal contractions in metric spaces. The generalizations are stated for non-self-mappings of the forms for and , or , subject to and , such that converges uniformly to T, and the distances are iteration-dependent, where , , and are non-empty subsets of X, for , where is a metric space, provided that the set-theoretic limit of the sequences of closed sets and exist as and that the countable infinite unions of the closed sets are closed. The convergence of the sequences in the domain and the image sets of the non-self-mapping, as well as the existence and uniqueness of the best proximity points, are also investigated if the metric space is complete. Two application examples are also given, being concerned, respectively, with the solutions through pseudo-inverses of both compatible and incompatible linear algebraic systems and with the parametrical

Thermal stability and crystallochemical analysis for CoII based coordination polymers with TPP and TPPS porphyrins

Artículo CrystEngComm 2013