Inhomogeneous soliton ratchets under two ac forces

We extend our previous work on soliton ratchet devices [L. Morales-Molina et al., Eur. Phys. J. B 37, 79 (2004)] to consider the joint effect of two ac forces including non-harmonic drivings, as proposed for particle ratchets by Savele'v et al. [Europhys. Lett. 67}, 179 (2004); Phys. Rev. E {\bf 70} 066109 (2004)]. Current reversals due to the interplay between the phases, frequencies and amplitudes of the harmonics are obtained. An analysis of the effect of the damping coefficient on the dynamics is presented. We show that solitons give rise to non-trivial differences in the phenomenology reported for particle systems that arise from their extended character. A comparison with soliton ratchets in homogeneous systems with biharmonic forces is also presented. This ratchet device may be an ideal candidate for Josephson junction ratchets with intrinsic large damping

Ratchet behavior in nonlinear Klein-Gordon systems with point-like inhomogeneities

We investigate the ratchet dynamics of nonlinear Klein-Gordon kinks in a periodic, asymmetric lattice of point-like inhomogeneities. We explain the underlying rectification mechanism within a collective coordinate framework, which shows that such system behaves as a rocking ratchet for point particles. Careful attention is given to the kink width dynamics and its role in the transport. We also analyze the robustness of our kink rocking ratchet in the presence of noise. We show that the noise activates unidirectional motion in a parameter range where such motion is not observed in the noiseless case. This is subsequently corroborated by the collective variable theory. An explanation for this new phenomenom is given

Current and entanglement in a Bose-Hubbard lattice

We study the generation of entanglement for interacting cold atoms in an optical lattice. The entanglement is generated by managing the interaction between two distinct atomic species. It is found that the current of one of the species can be used as a good indicator of entanglement generation. The thermalization process between the species is also shown to be closely related to the evolution of the current.Comment: 10 pages, 5 figure

Optimization of soliton ratchets in inhomogeneous sine-Gordon systems

Unidirectional motion of solitons can take place, although the applied force has zero average in time, when the spatial symmetry is broken by introducing a potential $V(x)$, which consists of periodically repeated cells with each cell containing an asymmetric array of strongly localized inhomogeneities at positions $x_{i}$. A collective coordinate approach shows that the positions, heights and widths of the inhomogeneities (in that order) are the crucial parameters so as to obtain an optimal effective potential $U_{opt}$ that yields a maximal average soliton velocity. $U_{opt}$ essentially exhibits two features: double peaks consisting of a positive and a negative peak, and long flat regions between the double peaks. Such a potential can be obtained by choosing inhomogeneities with opposite signs (e.g., microresistors and microshorts in the case of long Josephson junctions) that are positioned close to each other, while the distance between each peak pair is rather large. These results of the collective variables theory are confirmed by full simulations for the inhomogeneous sine-Gordon system

Resonant ratcheting of a Bose-Einstein condensate

We study the rectification process of interacting quantum particles in a periodic potential exposed to the action of an external ac driving. The breaking of spatio-temporal symmetries leads to directed motion already in the absence of interactions. A hallmark of quantum ratcheting is the appearance of resonant enhancement of the current (Europhys. Lett. 79 (2007) 10007 and Phys. Rev. A 75 (2007) 063424). Here we study the fate of these resonances within a Gross-Pitaevskii equation which describes a mean field interaction between many particles. We find, that the resonance is i) not destroyed by interactions, ii) shifting its location with increasing interaction strength. We trace the Floquet states of the linear equations into the nonlinear domain, and show that the resonance gives rise to an instability and thus to the appearance of new nonlinear Floquet states, whose transport properties differ strongly as compared to the case of noninteracting particles

Shared Resources in Industrial Districts: Information, know-how and institutions in the Spanish tile industry

The aim of this paper is to measure the effect of shared resources on individual firm performance. Using the Industrial District as a definition of the interorganizational context, we propose a model that includes a set of factors that are associated with the endowment of external resources, that is, collective information and know-how, and involvement in local institutions. In order to illustrate the theoretical argumentation, we develop an empirical study using a one hundred-firm sample from the Spanish Ceramic Tile industry in order to search for a statistical association between resource variables and performance of the firms. Finally, findings of the paper suggest that in order to increase performance firms must develop a distinct capacity so as to be able to shape and exploit shared or collective resource

Internal mode mechanism for collective energy transport in extended systems

We study directed energy transport in homogeneous nonlinear extended systems in the presence of homogeneous ac forces and dissipation. We show that the mechanism responsible for unidirectional motion of topological excitations is the coupling of their internal and translation degrees of freedom. Our results lead to a selection rule for the existence of such motion based on resonances that explains earlier symmetry analysis of this phenomenon. The direction of motion is found to depend both on the initial and the relative phases of the two harmonic drivings, even in the presence of noise.Comment: Final version, to appear in Physical Review Letter

Efficiency and Innovation in Sub-Networks of Companies. A Study of the Spanish Ceramics District

La homogeneidad dentro del distrito industrial frente a las empresas externas se ha asumido tradicionalmente en la literatura. Sin embargo, nuestro trabajo sugiere que los distritos muestran un cierto grado de heterogeneidad. Así puede, atendiendo a variables relacionales, hablarse de la existencia de una core network y de una periphery network. A partir de un método cuantitativo se pretende investigar, para el caso del distrito industrial de la cerámica de Castellón (españa), la existencia de diferencias significativas en eficiencia técnica e innovación entre estos dos grupos de empresas. La confirmación de la heterogeneidad interna concita nuevas líneas de trabajo en el campo de los distritos industriales.Homogeneity in the industrial district with respect to outside companies has traditionally been an assumption in the literature. However, this paper suggests that districts show a certain degree of heterogeneity. Thus, based on relational variables, two different networks can be referred to: Core and Periphery. These groups of firms vary in terms of behavior and performance. Using quantitative methods, this research explores the existence of significant differences in technical efficiency and innovation between the two groups of firms in the spanish ceramic tile industrial district. Findings confirming internal heterogeneity suggest new lines of research in this field.L'homogénéité à l'intérieur du district industriel face aux entreprises externes a traditionnellement été assumée dans la littérature. Cependant, notre travail suggère que les districts montrent un certain degré d'hétérogénéité. Il est donc possible, tenant compte de variables relationnelles, de considérer l'existence de core network et de periphery network. À partir d'une méthode quantitative, on prétend faire une recherche, pour le cas du district industriel de céramique de Castellón (espagne), sur l'existence de différences significatives en efficacité technique et en innovation entre ces deux groupes d'entreprises. La confirmation de l'hétérogénéité interne incite à ouvrir de nouvelles lignes de travail dans le champ des districts industriels.A homogeneidade dentro do setor industrial ante as empresas externas vem sendo assumido tradicionalmente na literatura. Contudo, nosso trabalho sugere que os setores mostram um grau de heterogeneidade. Assim, atendendo a variáveis relacionais, pode-se falar da existência de uma core network e de uma periphery network. A partir de um método quantitativo, pretende-se pesquisar, para o caso do setor industrial da cerâmica de Castellón (espanha), a existência de diferenças significativas em eficiência técnica e inovação entre estes dois grupos de empresas. A confirmação da heterogeneidade interna concita novas linhas de trabalhos no campo dos setores industriais.Esta investigación ha sido financiada por el Ministerio de Educación y Ciencia, Plan Nacional de I+D+i (2007-2010), proyecto “El Distrito Industrial: el impacto del Capital Social sobre la Gestión de la Cadena de Suministro” (SEJ2007-62876/ECON

Mexico’s Tradition and Culture Entering the Digital Age: The Mexican Cultural Heritage Repository Project

Mexico is a country with a vast and extraordinary cultural heritage, which is the result of a rich history of cultural exchange, syncretism and transculturation. This rich culture has been materialized through the consolidation of a long and prestigious museum tradition, which at the same time is sadly characterized by an endemic lack of technological resources rather than professional skills. As a result, we have found that Mexican museums produce very heterogeneous forms of documentation, which are often not even managed using information technologies. Furthermore, most museums deploy ad hoc solutions that directly limit the usefulness and value of the documentation process itself. In response, the recently founded Mexican Ministry of Culture is undertaking the development of the Mexican cultural heritage data model (Modelo de Datos México), which is aimed at contributing to the cultural heritage domain of our country through the correct characterization and documentation of its cultural objects. It is the first documented experience in Mexico of a large-scale data model inspired by CIDOC-CRM, which is complemented by a set of terminological tools that attempt to capture the singularities and idiosyncrasies of the Mexican cultural sector. In the present paper, we will describe the motivations and decisions made so far to optimize the data model to the Mexican reality and the development of the project that will define a set of local terminologies built on the expertise of linguists, information architects, developers and especially, museum professionals.This research was funded by the Secretaría de Cultura of Mexico