Russian Doll Renormalization Group and Superconductivity

We show that an extension of the standard BCS Hamiltonian leads to an infinite number of condensates with different energy gaps and self-similar properties, described by a cyclic RG flow of the BCS coupling constant which returns to its original value after a finite RG time.Comment: 4 pages, 2 figs, RevTex

The Matrix Product Approach to Quantum Spin Ladders

We present a manifestly rotational invariant formulation of the matrix product method valid for spin chains and ladders. We apply it to 2 legged spin ladders with spins 1/2, 1 and 3/2 and different magnetic structures labelled by the exchange coupling constants, which can be ferromagnetic or antiferromagnetic along the legs and the rungs of the ladder We compute ground state energy densities, correlation lengths and string order parameters. We present numerical evidence of the duality properties of the 3 different non ferromagnetic spin 1/2 ladders. We show that the long range topological order characteristic of isolated spin 1 chains is broken by the interchain coupling. The string order correlation function decays exponentially with a finite correlation length that we compute. A physical picture of the spin 1 ladder is given in terms of a collection of resonating spin 1 chains. Finally for ladders with spin equal or greater than 3/2 we define a class of AKLT states whose matrix product coefficients are given by 9-j symbols.Comment: REVTEX file, 16 pages, 12 figures, 6 Table

The many levels pairing Hamiltonian for two pairs

We address the problem of two pairs of fermions living on an arbitrary number of single particle levels of a potential well (mean field) and interacting through a pairing force. The associated solutions of the Richardson's equations are classified in terms of a number $v_l$, which reduces to the seniority $v$ in the limit of large values of the pairing strength $G$ and yields the number of pairs not developing a collective behaviour, their energy remaining finite in the $G\to\infty$ limit. We express analytically, through the moments of the single particle levels distribution, the collective mode energy and the two critical values $G_{\rm cr}^{+}$ and $G_{\rm cr}^{-}$ of the coupling which can exist on a single particle level with no pair degeneracy. Notably $G_{\rm cr}^{+}$ and $G_{\rm cr}^{-}$ merge when the number of single particle levels goes to infinity, where they coincide with the $G_{\rm cr}$ (when it exists) of a one pair system, not envisioned by the Richardson theory. In correspondence of $G_{\rm cr}$ the system undergoes a transition from a mean field to a pairing dominated regime. We finally explore the behaviour of the excitation energies, wave functions and pair transfer amplitudes finding out that the former, for $G>G_{\rm cr}^{-}$, come close to the BCS predictions, whereas the latter display a divergence at $G_{\rm cr}$, signaling the onset of a long range off-diagonal order in the system.Comment: 35 pages, 6 figures, 2 tables, to be published in EPJ

Characterization of wind-blown sediment transport with height in a highly mobile dune (SW Spain)

The Valdevaqueros dune is located at one of the windiest points of Europe, where the frequent occurrence of strong easterly winds has generated a highly mobile dune. Several rotating cup anemometers in vertical array and a self-designed vertical sand trap, were placed to retain the drift sands at different heights over the surface in order to determine theoretical and actual sand transport rates in the Valdevaqueros dune system. General results show that 90% of the wind-blown sand is transported within the first 20cm above the dune crest surface. Theoretical transport rates based on different empirical formulae were 0.33 to 0.78 times the in-situ sand transport rate detected, which was 2.08·10-2kgm-1s-1 under moderate wind power (mean speed ranging from 8.4 to 17.9ms-1). Analysis of different statistical grain-size parameters helped to understand sand transport distribution at different heights

Coste de la limpieza “cotidiana” de playas

Más de 90.000 buques mercantes al año cruzan el Estrecho de Gibraltar de los que aproximadamente un 5% son petroleros. Ello, conjuntamente con la existencia de varios puertos con refinerías y polígonos industriales petroquímicos y la práctica del bunkering para aprovisionamiento de combustible, hace a la costa gaditana un punto de riesgo para la contaminación por hidrocarburos (Carmona et al., 2009). La Demarcación de Costas de Andalucía-Atlántico (DCAA), dependiente del Ministerio de Agricultura, Alimentación y Medio Ambiente, ha realizado en numerosas ocasiones la limpieza de su litoral debido a la polución producida por ese tipo de vertidos (Carmona et al., 2012), existiendo ya alguna bibliografía sobre cómo abordar la retirada de alquitrán y otros derivados similares de las playas (e.g. DGC 2005, CEPRECO 2006a, CEPRECO 2006b). Sin embargo, además de la fracción no volátil de los hidrocarburos, existe otro tipo de desechos, naturales y/o antrópicos, que llegan a nuestras playas y que, debido sobre todo al carácter turístico de nuestro litoral, deben ser recogidos. Por ley, esta limpieza corresponde a las autoridades locales. No obstante, debido a la escasez de su presupuesto, los municipios suelen atender prioritariamente a la limpieza de las playas más urbanas y de máxima utilización. Es por este motivo que, dentro de un espíritu de colaboración entre Administraciones, la DCAA, mediante su partida de conservación y mantenimiento, ha apoyado las tareas de los Ayuntamientos, reforzando la labor municipal en las playas más concurridas y limpiando aquellas que son menos visitadas ya sea por su lejanía del casco urbano o por su escasez de servicios. En esta ponencia se presentarán los medios humanos y materiales con los que se cuenta para esta tarea, aportando cifras de toneladas de basura retiradas y coste del trabajo, junto con una comparación superficial con los datos de otros organismos y alguna sugerencia de posibles mejoras de la productividad

Fluid Overload in Peritoneal Dialysis

The prevalence of end-stage renal disease (ESRD) has increased globally to 10% due to diabetes mellitus, hypertension, and stroke. When chronic kidney disease (CKD) maintenance therapy fails, patients require renal replacement therapy (RRT) to survive, such as peritoneal dialysis (PD), hemodialysis, and renal transplantation. The most common therapy in Mexico is PD because it is a feasible, low-cost, and easy-to-perform procedure; however, fluid overload is a frequent condition in patients with this RRT modality. The usual adverse comorbidities in patients with PD are cardiovascular diseases (CVD) associated to atherosclerosis, uremia, inflammation, and oxidative stress. Fluid overload is intimately associated to hypertension, left ventricular hypertrophy, heart failure, and worsening of kidney failure, leading to increased hospital admissions, higher cardiovascular mortality, and reduced life expectancy. Two main pathologies are involved in the deterioration of both heart and kidney functions, namely, cardiorenal syndrome and uremic cardiomyopathy. Along with these phenomena, patients in PD with rapid peritoneal transport have reduced ultrafiltration, increased glucose absorption, and albumin loss in the dialysate, which lead to overhydration, hypertension, dyslipidemia, and malnutrition. This review focuses on the clinical, physiological, and biochemical mechanisms involved in fluid overload of patients with CKD undergoing PD

Different behaviour and management of two littoral dunes in southern Spain

The north-western coast of Cadiz (Spain) presents a variety of coastal engineering and coastal management problems whose solution is not an easy task due to the complexity of the parameters involved. Two cases of dune zone management in this a rea are described in this paper. Punta Candor beach, a very popular recreational area in Rota municipality, experiences one of the highest dune erosion rates in Spain of more than 1 m/yr. In order to address this coastal degradation, the Atlantic Andalusian Coastal District has performed beach and dune restoration planning, described in this paper as an example of sustainable coastal management. The Valdevaqueros dune area also represents animportant recreational zone. However, after the Spanish Shore Act was approved in 1988, sand extraction was prohibited, and the system began to lose stability resulting in landward dune invasion. As in the previous case, an integrated study of the management alternatives is also presented for the Valdevaqueros dune area, considering all of the problems involved: dune degradation, invasion of the Punta Paloma road by the mobile dunes, excessive recreational pressure on the dune area and adjacent lagoon, parking lot resettlements, and undesirable land use in the surroundings. In particular, a cost-benefit analysis for the different alternatives was carried out regarding the road-dune interaction