Three-dimensional effects on extended states in disordered models of polymers

We study electronic transport properties of disordered polymers in the presence of both uncorrelated and short-range correlated impurities. In our procedure, the actual physical potential acting upon the electrons is replaced by a set of nonlocal separable potentials, leading to a Schr\"odinger equation that is exactly solvable in the momentum representation. We then show that the reflection coefficient of a pair of impurities placed at neighboring sites (dimer defect) vanishes for a particular resonant energy. When there is a finite number of such defects randomly distributed over the whole lattice, we find that the transmission coefficient is almost unity for states close to the resonant energy, and that those states present a very large localization length. Multifractal analysis techniques applied to very long systems demonstrate that these states are truly extended in the thermodynamic limit. These results reinforce the possibility to verify experimentally theoretical predictions about absence of localization in quasi-one-dimensional disordered systems.Comment: 16 pages, REVTeX 3.0, 5 figures on request from FDA ([email protected]). Submitted to Phys. Rev. B. MA/UC3M/09/9

Delocalization in Continuous Disordered Systems

Continuous One-dimensional models supporting extended states are studied. These delocalized statesoccur at well defined values of the energy and are consequences of simple statistical correlation rules. We explicitly study alloys of delta-barrier potentials as well as alloys and liquids of quantum well as.The divergence of the localization length is studied and a critical exponent 2/3 is found for the delta-barrier case, whereas for the quantum wells we find an exponent of 2 or 2/3 depending on the well's parameters. These results support the idea that correlations between random scattering sequences break Anderson localization. We further calculate the conductance of disordered superlattices. At the peak transmission the relative fluctuations of the transmission coefficient are vanishing.Comment: 8 page

Propagation of Rayleighs waves in cracked media

Este trabajo está enfocado a la obtención de resultados numéricos que permitan la detección y caracterización de grietas sub-superficiales en sólidos mediante la incidencia de ondas elásticas de Rayleigh. Los resultados se obtienen a partir de ecuaciones integrales de frontera, que pertenecen al campo de la elastodinámica. Una vez que se aplican las condiciones de frontera se obtiene un sistema de ecuaciones integrales del tipo Fredholm de segunda especie y orden cero, el cual es resuelto mediante eliminación gaussiana. El método que se emplea para la discretización de dichas ecuaciones es conocido como «método indirecto de elementos frontera», el cual puede ser visto como una derivación del teorema clásico de Somigliana. A partir de los análisis realizados en el dominio de la frecuencia emergen picos de resonancia que permiten inferir la presencia de grietas mediante los cocientes espectrales. Se analizaron varios modelos de medios agrietados donde se pretende evidenciar la gran utilidad que presenta el uso de los cocientes espectrales para identificar grietas. Se estudiaron los efectos de la orientación y la localización de las grietas. Los resultados obtenidos presentan buena concordancia con los publicados previamente.This work is focused on the finding of numerical results for detection and characterization of sub-surface cracks in solids under the incidence of Rayleighs elastic waves. The results are obtained from boundary integral equations, which belong to the field of dynamics of elasticity. Once applied the boundary conditions, a system of Fredholms integral equations of second kind and zero order is obtained, which is solved using Gaussian elimination. The method that is used for the solution of such integral equations is known as the Indirect Boundary Element Method, which can be seen as a derivation of the Somiglianas classic theorem. On the basis of the analysis made in the frequency domain, resonance peaks emerge and allow us to infer the presence of cracks through the spectral ratios. Several models of cracked media were analyzed, where analyses reveal the great utility that displays the use of spectral ratios to identify cracks. We studied the effects of orientation and location of cracks. The results show good agreement with the previously published.Peer Reviewe

Delocalization of states in two component superlattices with correlated disorder

Electron and phonon states in two different models of intentionally disordered superlattices are studied analytically as well as numerically. The localization length is calculated exactly and we found that it diverges for particular energies or frequencies, suggesting the existence of delocalized states for both electrons and phonons. Numerical calculations for the transmission coefficient support the existence of these delocalized states.Comment: RevTeX, 12 pages, 2 PS figures adde

SLUG in cancer development

The SNAIL-related zinc-finger transcription factor, SLUG (SNAI2), is critical for the normal development of neural crest-derived cells and loss-of-function SLUG mutations have been proven to contribute to piebaldism and Waardenburg syndrome type 2 in a dose-dependent fashion. While aberrant induction of SLUG has been documented in cancer cells, relatively little is known about the consequences of SLUG overexpression in malignancy. To investigate the potential role of SLUG overexpression in development and in cancer, we generated mice carrying a tetracycline-repressible Slug transgene. These mice were morphologically normal at birth, and developed mesenchymal tumours (leukaemia and sarcomas) in almost all cases examined. Suppression of the Slug transgene did not rescue the malignant phenotype. Furthermore, the BCR–ABL oncogene, which induces Slug expression in leukaemic cells, did not induce leukaemia in Slug-deficient mice, implicating Slug in BCR–ABL leukaemogenesis in vivo. Overall, the findings indicate that while Slug overexpression is not sufficient to cause overt morphogenetic defects in mice, they demonstrate a specific and critical role for Slug in the pathogenesis of mesenchymal tumours.Research in our group is supported by MEyC (BIO2000-0453-P4-02, SAF2003- 01103and FIT-010000-2004-157), Junta de Castilla y León (CSI06/03), ADE de Castilla y León (04/04/SA/0001), FIS (PI020138, G03/179, and G03/136) and USALCIBASA project. MPC is a recipient of an MCyT fellowship and MSM is supported by Fundación Cientíica de la AECC.Peer reviewe

Spectrophotometric analysis of GRB afterglow extinction curves with X-shooter

In this work we use gamma-ray burst (GRB) afterglow spectra observed with the VLT/X-shooter spectrograph to measure rest-frame extinction in GRB lines-of-sight by modeling the broadband near-infrared (NIR) to X-ray afterglow spectral energy distributions (SEDs). Our sample consists of nine Swift GRBs, eight of them belonging to the long-duration and one to the short-duration class. Dust is modeled using the average extinction curves of the Milky Way and the two Magellanic Clouds. We derive the rest-frame extinction of the entire sample, which fall in the range $0 \lesssim {\it A}_{\rm V} \lesssim 1.2$. Moreover, the SMC extinction curve is the preferred extinction curve template for the majority of our sample, a result which is in agreement with those commonly observed in GRB lines-of-sights. In one analysed case (GRB 120119A), the common extinction curve templates fail to reproduce the observed extinction. To illustrate the advantage of using the high-quality X-shooter afterglow SEDs over the photometric SEDs, we repeat the modeling using the broadband SEDs with the NIR-to-UV photometric measurements instead of the spectra. The main result is that the spectroscopic data, thanks to a combination of excellent resolution and coverage of the blue part of the SED, are more successful in constraining the extinction curves and therefore the dust properties in GRB hosts with respect to photometric measurements. In all cases but one the extinction curve of one template is preferred over the others. We show that the modeled values of the extinction and the spectral slope, obtained through spectroscopic and photometric SED analysis, can differ significantly for individual events. Finally we stress that, regardless of the resolution of the optical-to-NIR data, the SED modeling gives reliable results only when the fit is performed on a SED covering a broader spectral region.Comment: 17 pages, 7 figures, 4 tables, accepted for publication in Astronomy & Astrophysic

Mobility Edge in Aperiodic Kronig-Penney Potentials with Correlated Disorder: Perturbative Approach

It is shown that a non-periodic Kronig-Penney model exhibits mobility edges if the positions of the scatterers are correlated at long distances. An analytical expression for the energy-dependent localization length is derived for weak disorder in terms of the real-space correlators defining the structural disorder in these systems. We also present an algorithm to construct a non-periodic but correlated sequence exhibiting desired mobility edges. This result could be used to construct window filters in electronic, acoustic, or photonic non-periodic structures.Comment: RevTex, 4 pages including 2 Postscript figure

Dynamic equivalence between atomic and colloidal liquids

We show that the kinetic-theoretical self-diffusion coefficient of an atomic fluid plays the same role as the short-time self-diffusion coefficient D_S in a colloidal liquid, in the sense that the dynamic properties of the former, at times much longer than the mean free time, and properly scaled with D_S, will indistinguishable from those of a colloidal liquid with the same interaction potential. One important consequence of such dynamic equivalence is that the ratio D_L/ D_S of the long-time to the short-time self-diffusion coefficients must then be the same for both, an atomic and a colloidal system characterized by the same inter-particle interactions. This naturally extends to atomic fluids a well-known dynamic criterion for freezing of colloidal liquids[Phys. Rev. Lett. 70, 1557 (1993)]. We corroborate these predictions by comparing molecular and Brownian dynamics simulations on (soft- and hard-sphere) model systems, representative of what we may refer to as the "hard-sphere" dynamic universality class

Diagnóstico de producción en ganado lechero en pastoreo de un grupo ganadero de validación y transferencia de tecnología

The regionalization of framing issues for producers Livestock Group of Validation and Technology Transfer (GGAVATT) from San Jose Miahuatlán Veracruz, Mexico, under the current production of native grass prairie with mainly during the months of higher temperature have a poor performance and thus milk production declines which promotes a great use of concentrated feeds which causes an increase in production cost and less use to them. For this purpose we made a diagnosis of current conditions GGAVATT production, yielding information that helps us source and compared to determine precisely what the effect of applying the proposed alternative. We propose an alternative implementation of pastures with improved pastures needed to produce a greater amount of forage per unit area especially in the colder months.La regionalización de la problemática encuadrando a los productores del Grupo Ganadero de Validación y Transferencia de Tecnología (GGAVATT) de San José Miahuatlán Veracruz, México, bajo la actual situación de producción de praderas básicamente con gramas nativas que durante los meses de menor frío tienen un pobre desempeño y por ende la producción de leche se deteriora lo cual promueve una gran utilización de alimentos concentrados lo que provoca un incremento en el costo de producción y una menor utilidad para estos. Para dicho propósito se realizó un diagnóstico de las condiciones actuales de producción del GGAVATT, arrojando información que nos sirve de partida y de comparación para determinar con precisión cuál es el efecto de aplicar la alternativa propuesta. Se plantea como alternativa la implantación de praderas con pastos mejorados que permitan producir una mayor cantidad de forrajes por unidad de superficie sobre todo en los meses de menor temperatura

Gram-negative prosthetic joint infection: outcome of a debridement, antibiotics and implant retention approach. A large multicentre study

AbstractWe aim to evaluate the epidemiology and outcome of gram-negative prosthetic joint infection (GN-PJI) treated with debridement, antibiotics and implant retention (DAIR), identify factors predictive of failure, and determine the impact of ciprofloxacin use on prognosis. We performed a retrospective, multicentre, observational study of GN-PJI diagnosed from 2003 through to 2010 in 16 Spanish hospitals. We define failure as persistence or reappearance of the inflammatory joint signs during follow-up, leading to unplanned surgery or repeat debridement >30 days from the index surgery related death, or suppressive antimicrobial therapy. Parameters predicting failure were analysed with a Cox regression model. A total of 242 patients (33% men; median age 76 years, interquartile range (IQR) 68–81) with 242 episodes of GN-PJI were studied. The implants included 150 (62%) hip, 85 (35%) knee, five (2%) shoulder and two (1%) elbow prostheses. There were 189 (78%) acute infections. Causative microorganisms were Enterobacteriaceae in 78%, Pseudomonas spp. in 20%, and other gram-negative bacilli in 2%. Overall, 19% of isolates were ciprofloxacin resistant. DAIR was used in 174 (72%) cases, with an overall success rate of 68%, which increased to 79% after a median of 25 months' follow-up in ciprofloxacin-susceptible GN-PJIs treated with ciprofloxacin. Ciprofloxacin treatment exhibited an independent protective effect (adjusted hazard ratio (aHR) 0.23; 95% CI, 0.13–0.40; p <0.001), whereas chronic renal impairment predicted failure (aHR, 2.56; 95% CI, 1.14–5.77; p 0.0232). Our results confirm a 79% success rate in ciprofloxacin-susceptible GN-PJI treated with debridement, ciprofloxacin and implant retention. New therapeutic strategies are needed for ciprofloxacin-resistant PJI