Revestimientos y acabados superficiales en construcciones con tierra contemporáneas

Earth construction is in increasing demand in some areas of building activity, which means a need for technical solutions to maintain and preserve the properties of earth walls. Like earth wall construction techniques themselves, materials used for rendering (plastering, painting, panelling, etc) have evolved in a way that allows us to find formal solutions suitable for every architectural situation. This paper deals with the special features of each rendering technique available in contemporary construction, from renderings permitting earth wall textures and finish to be appreciated, to plasters from different materials. Special attention will be focused on clay plasters, which are more appreciated due to its natural characteristics and compatibility with the base wall. The explanations are supported by different examples of buildings where these techniques have been used during the last two decades.La creciente demanda para la construcción de muros de tierra en algunos ámbitos del sector de la edificación conlleva la necesidad de plantear soluciones constructivas que permitan el adecuado mantenimiento de las prestaciones de dichos muros. Al igual que las propias técnicas para la construcción de los muros, los materiales utilizados para su revestimiento y protección han evolucionado permitiendo una gran variedad de soluciones formales acordes a cada situación. En este artículo se pretende hacer una revisión sobre las particularidades de las diferentes posibilidades que se presentan en el panorama de la construcción actual: desde los revestimientos que permitan mantener a la vista los acabados de los muros de tierra a los revocos de distinta naturaleza, con especial incidencia en aquellos que utilizan la propia tierra como material base, siendo los más apropiados a priori por su natural compatibilidad con el soporte. La explicación se acompañará de ejemplos ilustrativos de la aplicación de dichas técnicas en edificios construidos durante las dos últimas décadas

Development of Clay Plasters Containing Thermoregulating Microcapsules for Indoor Walls

This work shows the technical feasibility of incorporating phase change materials (PCMs) into clay plastering mortars to improve the thermal properties of the building envelopes. Due to the absence of regulated and internationally agreed-upon norms for clay mortars containing thermoregulating microcapsules (MPCMs), two tests following UNE-EN-998-1:2010 and UNE-EN-1015, were designed to provide the greatest similarity to its final application. Three different dosages 5, 10, and 15 wt% of MPCM relative to the dried mortar weight were used. Fresh mortars were physically characterized to determine its consistency, apparent density, period of workability and open time, and occluded air content. Physical and mechanical characteristics were determined for hardened mortar. The thermal characteristics of the specimens were analysed by using a differential scanning calorimetry, obtaining their apparent specific heat capacities and the enthalpy curves. Building simulation software is a fundamental tool for designing buildings with almost zero energy consumption. In this study, three identical architectural models were simulated. The reference building had inner coatings of clay-based mortar, mortar with 15% added material, and a conventional gypsum mortar. These buildings were subjected to the same exposure and radiation conditions, which allowed the result to be compared to evaluate the effect of incorporating the PCM

Hippocampal Dendritic Spines Modifications Induced by Perinatal Asphyxia

Perinatal asphyxia (PA) affects the synaptic function and morphological organization. In previous works, we have shown neuronal and synaptic changes in rat neostriatum subjected to hypoxia leading to long-term ubi-protein accumulation. Since F-actin is highly concentrated in dendritic spines, modifications in its organization could be related with alterations induced by hypoxia in the central nervous system (CNS). In the present study, we investigate the effects of PA on the actin cytoskeleton of hippocampal postsynaptic densities (PSD) in 4-month-old rats. PSD showed an increment in their thickness and in the level of ubiquitination. Correlative fluorescence-electron microscopy photooxidation showed a decrease in the number of F-actin-stained spines in hippocampal excitatory synapses subjected to PA. Although Western Blot analysis also showed a slight decrease in β-actin in PSD in PA animals, the difference was not significant. Taken together, this data suggests that long-term actin cytoskeleton might have role in PSD alterations which would be a spread phenomenon induced by PA

Phase diagram of S=1/2 XXZ chain with NNN interaction

We study the ground state properties of one-dimensional XXZ model with next-nearest neighbor coupling alpha and anisotropy Delta. We find the direct transition between the ferromagnetic phase and the spontaneously dimerized phase. This is surprising, because the ferromagnetic phase is classical, whereas the dimer phase is a purely quantum and nonmagnetic phase. We also discuss the effect of bond alternation which arises in realistic systems due to lattice distortion. Our results mean that the direct transition between the ferromagnetic and spin-Peierls phase occur.Comment: 4 pages, 2 eps figure

Finite Temperature DMRG Investigation of the Spin-Peierls Transition in CuGeO3_3

We present a numerical study of thermodynamical properties of dimerized frustrated Heisenberg chains down to extremely low temperatures with applications to CuGeO$_3$. A variant of the finite temperature density matrix renormalization group (DMRG) allows the study of the dimerized phase previously unaccessible to ab initio calculations. We investigate static dimerized systems as well as the instability of the quantum chain towards lattice dimerization. The crossover from a quadratic response in the free energy to the distortion field at finite temperature to nonanalytic behavior at zero temperature is studied quantitatively. Various physical quantities are derived and compared with experimental data for CuGeO$_3$ such as magnetic dimerization, critical temperature, susceptibility and entropy.Comment: LaTeX, 5 pages, 5 eps figures include

La técnica del tapial en la Comunidad Autónoma de Madrid. Aplicación de nuevos materiales para la consolidación de muros de tapia

The use of earth as a building material is spread in a great part of the architectural heritage of the Autonomous Community of Madrid, especially in the southern region, it appears in different usages and building methods like rammed earth, adobe or filled wood frame structures. The need of maintenance and preservation of this heritage justify the convenience of research on new techniques and materials applicable to restoration works. This paper aims to offer a view on the particularities of rammed earth (tapial), predominant in this region, and show the studies carried out on the architectural heritage as well as the targets, methodology and results of the research works developed to analyze the use of new products to consolidate rammed earth walls. The work has been carried out conjunctly by members of the Department of Construction of the Polytechnic University of Madrid and the ONGD Interaction.La Comunidad Autónoma de Madrid, especialmente en su mitad meridional, conserva un amplio patrimonio de edificios construidos con tierra, con ejemplos de distintas técnicas como la tapia, adobe o los entramados de madera rellenos. La necesidad de conservación y mantenimiento de este patrimonio justifica la conveniencia de investigaciones sobre nuevas técnicas y procedimientos constructivos aplicables en trabajos de restauración y rehabilitación. En este articulo se pretende dar una visión general sobre las particularidades de la técnica del tapial, predominante en nuestra región, y exponer los estudios realizados sobre el patrimonio existente así como los objetivos, metodología y resultado de la investigación desarrollada para analizar la aplicación de nuevos productos en la consolidación de muros de tapia, realizada conjuntamente por el Departamento de Construcción y Tecnología Arquitectónicas de la Escuela Técnica Superior de Arquitectura de Madrid y la ONGD Inter-Acción

Phase diagram of an asymmetric spin ladder

We investigate an asymmetric zig-zag spin ladder with different exchange integrals on both legs using bosonization and renormalization group. When the leg exchange integrals and frustration both are sufficiently small, renormalization group analysis shows that the Heisenberg critical point flows to an intermediate-coupling fixed point with gapless excitations and a vanishing spin velocity. When they are large, a spin gap opens and a dimer liquid is realized. Here, we find a continuous manifold of Hamiltonians with dimer product ground states, interpolating between the Majumdar-Ghosh and sawtooth spin-chain model.Comment: 4 pages, 2 EPS figures, to be published in PR

Spontaneous plaquette dimerization in the J1−J2J_1-J_2 Heisenberg model

We investigate the non magnetic phase of the spin-half frustrated Heisenberg antiferromagnet on the square lattice using exact diagonalization (up to 36 sites) and quantum Monte Carlo techniques (up to 144 sites). The spin gap and the susceptibilities for the most important crystal symmetry breaking operators are computed. A genuine and somehow unexpected `plaquette RVB', with spontaneously broken translation symmetry and no broken rotation symmetry, comes out from our numerical simulations as the most plausible ground state for $J_2/J_1 \simeq 0.5$.Comment: 4 pages, 5 postscript figure

Group versus Individualised Minimum Velocity Thresholds in the Prediction of Maximal Strength in Trained Female Athletes

This study examined the accuracy of di erent velocity-based methods in the prediction of bench press and squat one-repetition maximum (1RM) in female athletes. Seventeen trained females (age 17.8 1.3 years) performed an incremental loading test to 1RM on bench press and squat with the mean velocity being recorded. The 1RM was estimated from the load–velocity relationship using the multiple- (8 loads) and two-point (2 loads) methods and group and individual minimum velocity thresholds (MVT). No significant e ect of method, MVT or interaction was observed for the two exercises (p > 0.05). For bench press and squat, all prediction methods demonstrated very large to nearly perfect correlations with respect to the actual 1RM (r range = 0.76 to 0.97). The absolute error (range = 2.1 to 3.8 kg) for bench press demonstrated low errors that were independent of the method and MVT used. For squat, the favorable group MVT errors for the multiple- and two-point methods (absolute error = 7.8 and 9.7 kg, respectively) were greater than the individual MVT errors (absolute error = 4.9 and 6.3 kg, respectively). The 1RM can be accurately predicted from the load–velocity relationship in trained females, with the two-point method o ering a quick and less fatiguing alternative to the multiple-point method