Flux reversal in a simple random walk model on a fluctuating symmetric lattice

A rather simple random walk model on a one-dimensional lattice is put forward. The lattice as a whole switches randomly between two possible states which are spatially symmetric. Both lattice states are identical, but translated by one site with respect to each other, and consist of infinite arrays of absorbing sites separated by two non-absorbing sites. Exact explicit expressions for the long-time velocity and the effective diffusion coefficient are obtained and discussed. In particular, it is shown that the direction of the steady motion can be reversed by conveniently varying the values of either the mean residence times in the lattice states or the transition rates to the absorbing and non-absorbing sites.Comment: 6 pages, 3 Figures, (to appear in Physical Review E

Directed motion of spheres induced by unbiased driving forces in viscous fluids beyond the Stokes' law regime

The emergence of directed motion is investigated in a system consisting of a sphere immersed in a viscous fluid and subjected to time-periodic forces of zero average. The directed motion arises from the combined action of a nonlinear drag force and the applied driving forces, in the absence of any periodic substrate potential. Necessary conditions for the existence of such directed motion are obtained and an analytical expression for the average terminal velocity is derived within the adiabatic approximation. Special attention is paid to the case of two mutually perpendicular forces with sinusoidal time dependence, one with twice the period of the other. It is shown that, although neither of these two forces induces directed motion when acting separately, when added together, the resultant force generates directed motion along the direction of the force with the shortest period. The dependence of the average terminal velocity on the system parameters is analyzed numerically and compared with that obtained using the adiabatic approximation. Among other results, it is found that, for appropriate parameter values, the direction of the average terminal velocity can be reversed by varying the forcing strength. Furthermore, certain aspects of the observed phenomenology are explained by means of symmetry arguments

La capilla de San Juan en el edificio gótico de la Universidad de Valladolid: datos para su estudio

Es muy escaso el conocimiento que poseemos sobre el antiguo edificio gótico de la Universidad de Valladolid. Apenas unas viejas fotografías y los datos del momento en el que se procedió a su derribo, arrojan un poco de luz. Algunos datos dispersos por la bibliografía contribuyen a que nos hagamos una idea de como pudo ser el edificio que albergó la institución universitaria vallisoletana antes del siglo XX. Un pleito que tuvo lugar en la Real Chancillería de Valladolid a comienzos del siglo XVI aporta nuevos datos sobre la autoría y realización de la capilla universitaria.We know very few things about the ancient gothic building of the University of Valladolid. Only a few old photographs and some information from the time when the building was demolished, shed a little light. Certain data scattered throughout the bibliography al so help us to imagine how the building that was home to the University before the 20th century was. A litigation which took place in the Royal Chancellery of Valladolid at the beginning of the 16th century provides fresh data about the authorship and building process of the University chapel

Juan II de Aragón y las artes suntuarias

Producción CientíficaA la muerte de Juan II de Aragón, se realizó inventario de sus posesiones. Entre los objetos se destacaron especialmente un interesante conjunto de tapices y piezas de plata y oro, procedentes en su mayoría de su capilla. Muchos de estos objetos se vendieron y empeñaron para hacer frente a los gastos de la casa real y pagar a sus oficiales. Sin embargo, lejos de ser algo excepcional, esta actitud hacia las artes era común a finales del siglo XV. Por encima de apreciaciones estéticas, importaba más el valor económico de las obras. En este trabajo repasamos algunas de las posesiones del rey aragonés y reflexionamos acerca de su relación con las artes.After the death of John II of Aragon, an inventory of his possessions was made. Among the objects, were especially highlighted an interesting set of tapestries and pieces of silver and gold, most of them from his chapel. Many of these items were sold and pawned to pay the expenses of the royal household and its officers. However, far from being exceptional, this attitude towards the arts was common at the end of the fifteenth century. Over aesthetic appreciation, the economic value of the pieces was more important. This paper reviews some of the possessions of the Aragonese king and reflects about his relationship with the arts.Ministerio del Economía y Competitividad (project HAR2013-41053-P

El "Templo de la Fama": una arquitectura efímera para la proclamación de Fernando VII en Valladolid

En plena ocupación francesa, Valladolid fue el escenario de la proclamación del monarca Fernando VII en octubre de 1808. Para la ocasión se erigió en la Plaza Mayor una arquitectura efímera denominada Templo de la Fama, que sería reutilizada en dos ocasiones más, para festejar la onomástica de José Bonaparte en 1809 y con motivo de la entrada que este realizó en la ciudad en 1811. Damos a conocer nuevos datos sobre su uso y su decoración, para la que se usó retardatariamente la Emblemática de siglos anteriores.During the French occupation, Valladolid was the scene of the proclamation of the king Ferdinand VII in October 1808. For the occasion an ephemeral architecture denominated Hall of Fame was built in the Plaza Mayor. It was reused in two more occasions, to celebrate the onomastics of Joseph Bonaparte in 1809 and due to his entry in the city in 1811. We present what its decoration consisted in and some facts about its use

Martín Alderete, pintor, y la cofradía de la Vera Cruz de Santibáñez de Valcorba (Valladolid)

Damos a conocer la noticia de un contrato entre la cofradía de la Vera Cruz de Santibáñez de Valcorba (Valladolid) y el pintor Martín Alderete. Se trata de la realización de un crucificado de bulto destinado a los desfiles procesionales de la cofradía y que podría relacionarse con el que hoy ocupa el ático del retablo de la iglesia parroquial de la localidad.We present a document that shows a contract between the brotherhood of the True Cross of Santibáñez de Valcorba (Valladolid) and the painter Martín Alderete, about a sculpture of the crucified Christ for the brotherhood's processions and that could be put in relation with the one that is situated on the top of the main altar piece of the parish church of the village

Overdamped Deterministic Ratchets Driven By Multifrequency Forces

We investigate a dissipative, deterministic ratchet model in the overdamped regime driven by a {\it rectangular force}. Extensive numerical calculations are presented in a diagram depicting the drift velocity as a function of a wide range of the driving parameter values. We also present some theoretical considerations which explain some features of the mentioned diagram. In particular, we proof the existence of regions in the driving parameter space with bounded particle motion possessing zero current. Moreover, we present an explicit analytical expression for the drift velocity in the adiabatic limit.Comment: 12 pages, 6 figure

Comment on "Soliton ratchets induced by excitation of internal modes"

Very recently Willis et al. [Phys. Rev. E {\bf 69}, 056612 (2004)] have used a collective variable theory to explain the appearance of a nonzero energy current in an ac driven, damped sine-Gordon equation. In this comment, we prove rigorously that the time-averaged energy current in an ac driven nonlinear Klein-Gordon system is strictly zero.Comment: 3 pages, 1 figure, Submitted to Phys. Rev.