Obtención de cemento eco-eficiente a base de ceniza procedente de caldera de lecho fluidizado

El objetivo principal de este trabajo ha sido la valorización de una ceniza procedente de un combustor de lecho fluidizado de biomasa forestal (CCBF) para su posible empleo como adición puzolánica con el fin de obtener un material base cemento más ecoeficiente. Esta ceniza es un residuo procedente de un combustor que es alimentado fundamentalmente por restos de corteza de eucalipto para la fabricación de pasta de papel, originando toneladas de dichas cenizas. La ceniza CCBF tiene importantes contenidos en SiO2, CaO, Al2O3 y K2O, como componentes mayoritarios. Estos óxidos la hacen atractiva para el campo de los materiales de construcción. Para su valorización se somete a la ceniza a un tratamiento hidrotermal (TH) durante un periodo de 4h a dos temperaturas (150 y 200ºC) en contacto con dos medios, agua desmineralizada y una disolución de NaOH 1M, en ambos casos se ha empleado una relación líquido/sólido de 10. Los cambios que se producen en la fase sólida resultante del TH se analizan mediante diferentes técnicas de caracterización Después del TH, se identifica, como fase predominante, la fase tipo tobermorita, precursora del gel C-S-H. La obtención de dicha fase, se optimiza durante el TH a 200ºC, temperatura en la que desapareen prácticamente la fase cuarzo y disminuye la de calcita, lo que favorece la formación de las fases tobermorita por incorporación de iones calcio y silicio, a su estructura. Previa a la incorporación de la ceniza a la matriz de cemento es necesario determinar su activididad puzolánica. Por ello, se ha estudiado la actividad puzolánica de la ceniza CCBF y de la ceniza CCBF activada hidrotermalmente (200ºC/4h). Para determinar esta activiad se ha empleado en ambos casos el método de la disolución saturada de cal, desarrollado en el Instituto Ciencias de la Construcción “Eduardo Torroja”. En ambas cenizas, CCBF y CCBF-200º/4h, se alcanzan valores de cal fijada a los 28 días, de 52,1 y 98,2% respectivamente. Debido a la alta actividad puzolánica que presentan, se procedió a una sustitución parcial de cemento Portland por ambas cenizas, en porcentajes del 0, 10 y 20% del cemento por ceniza, según la EN 196-3. Para evaluar el efecto de las mismas, se fabricaron probetas de 1x1x6cm, las cuales se sometieron a pruebas de resistencia mecánica a compresión a diferentes edades de hidratación (2, 7 y 28 días). Se pudo observar como con la adición de ambos tipos de ceniza mejoraba hasta un 30% la resistencia mecánica a los 28 días en relación a la referencia (0%), obteniendo mayores resistencias en ambos casos (CCBF y CCBF-200ºC-4h) con el 10% de sustitució

Self-Averaging in the Three Dimensional Site Diluted Heisenberg Model at the critical point

We study the self-averaging properties of the three dimensional site diluted Heisenberg model. The Harris criterion \cite{critharris} states that disorder is irrelevant since the specific heat critical exponent of the pure model is negative. According with some analytical approaches \cite{harris}, this implies that the susceptibility should be self-averaging at the critical temperature ($R_\chi=0$). We have checked this theoretical prediction for a large range of dilution (including strong dilution) at critically and we have found that the introduction of scaling corrections is crucial in order to obtain self-averageness in this model. Finally we have computed critical exponents and cumulants which compare very well with those of the pure model supporting the Universality predicted by the Harris criterion.Comment: 11 pages, 11 figures, 14 tables. New analysis (scaling corrections in the g2=0 scenario) and new numerical simulations. Title and conclusions chang

Short term fluctuations of zooplankton abundance during autumn circulation in two reservoirs with contrasting trophic state

Zooplankton community in the reservoirs of Maranhao and Santa Luzia (Portugal) were studied during the autumn stratification breakdown and the weeks before it. The results from water transparency, chlorophyll-a and total phosphorus concentrations, calanoid to cyclopoid copepods ratio and zooplankton abundance confirm the different trophic state of both studied reservoirs: mesotrophic-eutrophic (Maranhao) and oligotrophic-mesotrophic (Santa Luzia), as previous studies have reported. Using Copidodiaptomus numidicus to compare both studied reservoirs, we found higher egg production rates in Maranhao than in Santa Luzia. Nevertheless, no relationship was ever found between zooplankton (abundance or egg production rate) and environmental variables (temperature and chlorophyll-a), which may suggest that wide and complex range of factors, abiotic as much as biotic, are involved in zooplankton dynamics during the autumn circulation period.La comunidad zooplanctónica de los embalses de Maranhao y Santa Luzia (Portugal) fue estudiada durante la ruptura de la estratificación otoñal y las semanas previas. Los resultados de transparencia del agua, concentración de clorofila-a y concentración de fósforo total, así como la razón entre copépodos calanoides y ciclopoides y la abundancia de zooplancton confirman el diferente estado trófico entre ambos embalses: mesotrófico-eutrófico (Maranhao) y oligotrófico-mesotrófico (Santa Luzia), como estudios previos habían mostrado. Utilizando al copépodo Copidodiaptomus numidicus para comparar ambos embalses, se ha observado una mayor tasa de producción de huevos en Maranhao que en Santa Luzia. Sin embargo, en ningún caso se ha encontrado una relación entre el zooplancton (abundancia o tasa de producción de huevos) y las variables ambientales (temperatura y concentración de clorofila-a), por lo que se sugiere que una amplia y compleja gama de factores, tanto bióticos como abióticos, deben de estar involucrados en la dinámica del zooplancton durante el periodo de circulación otoñal

FtsZ of filamentous, heterocyst-forming cyanobacteria has a conserved N-Terminal peptide required for normal FtsZ polymerization and cell division

Filamentous cyanobacteria grow by intercalary cell division, which should involve distinct steps compared to those producing separate daughter cells. The N-terminal region of FtsZ is highly conserved in the clade of filamentous cyanobacteria capable of cell differentiation. A derivative of the model strain Anabaena sp. PCC 7120 expressing only an FtsZ lacking the amino acids 2-51 of the N-terminal peptide (1N-FtsZ) could not be segregated. Strain CSL110 expresses both 1N-FtsZ, from the endogenous ftsZ gene promoter, and the native FtsZ from a synthetic regulated promoter. Under conditions of 1N-FtsZ predominance, cells of strain CSL110 progressively enlarge, reflecting reduced cell division, and show instances of asymmetric cell division and aberrant Z-structures notably differing from the Z-ring formed by FtsZ in the wild type. In bacterial 2-hybrid assays FtsZ interacted with 1N-FtsZ. However, 1N-FtsZ-GFP appeared impaired for incorporation into Z-rings when expressed together with FtsZ. FtsZ, but not 1N-FtsZ, interacted with the essential protein SepF. Both FtsZ and 1N-FtsZ polymerize in vitro exhibiting comparable GTPase activities. However, filaments of FtsZ show a distinct curling forming toroids, whereas 1N-FtsZ form thick bundles of straight filaments. Thus, the N-terminal FtsZ sequence appears to contribute to a distinct FtsZ polymerization mode that is essential for cell division and division plane location in Anabaena.Agencia Estatal de Investigación BFU2013-44686-P BFU2016-77097-

Harmonic states for the free particle

Different families of states, which are solutions of the time-dependent free Schr\"odinger equation, are imported from the harmonic oscillator using the Quantum Arnold Transformation introduced in a previous paper. Among them, infinite series of states are given that are normalizable, expand the whole space of solutions, are spatially multi-localized and are eigenstates of a suitably defined number operator. Associated with these states new sets of coherent and squeezed states for the free particle are defined representing traveling, squeezed, multi-localized wave packets. These states are also constructed in higher dimensions, leading to the quantum mechanical version of the Hermite-Gauss and Laguerre-Gauss states of paraxial wave optics. Some applications of these new families of states and procedures to experimentally realize and manipulate them are outlined.Comment: 21 pages, 3 figures. Title changed, content added, references adde

Scaling behavior of the Heisenberg model in three dimensions

We report on extensive numerical simulations of the three-dimensional Heisenberg model and its analysis through finite-size scaling of Lee-Yang zeros. Besides the critical regime, we also investigate scaling in the ferromagnetic phase. We show that, in this case of broken symmetry, the corrections to scaling contain information on the Goldstone modes. We present a comprehensive Lee-Yang analysis, including the density of zeros and confirm recent numerical estimates for critical exponents.Comment: 19 pages, 9 figure

Implementación de una red MODBUS/TCP

En este artículo se describe el desarrollo de un sistema que permite la supervisión, mando y adquisición de datos de diversos controladores de procesos desde cualquier computador conectado a internet, pasando por diversos medios físicos (Ethernet, RS232 y RS485) y protocolos de comunicación (Modbus/TCP, Modbus y protocolos ASCII). Se presentan los conceptos básicos del protocolo Modbus/TCP. Esta aplicación particular soluciona un problema del laboratorio de automática de la Universidad del Valle

Computational Delay Models to Estimate the Delay of Floating Cubes in CMOS Circuits

The verification of the timing requirements of large VLSI circuits is generally performed by using simulation or timing analysis on each combinational block of the circuit. A key factor in timing analysis is the election of the delay model type. Pin-to-pin delay models are usually employed, but their application is limited in timing analysis when dealing with floating mode or complex gates. This paper does not introduce a delay model but a delay model type called Transistor Path Delay Model (TPDM). This new type of delay model is specially useful for timing analysis in floating mode, since it is not required to know the whole input sequence to apply it, and can manage complex CMOS gates. An algorithm to get upper bounds on the stabilization time of each gate output using TPDM is also introduced

An in-depth view of the microscopic dynamics of Ising spin glasses at fixed temperature

Using the dedicated computer Janus, we follow the nonequilibrium dynamics of the Ising spin glass in three dimensions for eleven orders of magnitude. The use of integral estimators for the coherence and correlation lengths allows us to study dynamic heterogeneities and the presence of a replicon mode and to obtain safe bounds on the Edwards-Anderson order parameter below the critical temperature. We obtain good agreement with experimental determinations of the temperature-dependent decay exponents for the thermoremanent magnetization. This magnitude is observed to scale with the much harder to measure coherence length, a potentially useful result for experimentalists. The exponents for energy relaxation display a linear dependence on temperature and reasonable extrapolations to the critical point. We conclude examining the time growth of the coherence length, with a comparison of critical and activated dynamics.Comment: 38 pages, 26 figure

Superhydrophobic Cerium-Based Coatings on Al-Mg Alloys and Aluminized Steel

Aluminum-magnesium (Al-Mg) alloy and aluminum-coated steel (aluminized steel) are typically used for the manufacturing of baking trays and molds. For these applications, these materials must be modified to develop release and hydrophobic properties. With this aim, the bare substrates are typically coated with low-surface energy materials such as fluoropolymers, elastomers, or sol-gel layers. In this work, some alternative strategies to prepare these functional surfaces are presented. We used three-step processes involving (i) micro-texturing, (ii) nano layer deposition through immersion and electrodeposition, and (iii) hydrophobization. The raw substrates were sanded or sandblasted at the micro scale, accordingly. Texturization at the nano scale was achieved with a cerium layer formed by electrodeposition or solution immersion. The cerium layers were hydrophobized with fatty acids. The wetting properties of the samples were studied with tilting-plate and bouncing drop methods. We measured the surface roughness of the samples by contact profiling and analyzed their surface morphology using a field emission scanning electron microscope (FESEM). The elemental chemical composition of the samples was analyzed by energy-dispersive X-ray spectroscopy (EDX). The wettability results indicated that the best performance for the Al-Mg substrates was reached by sandblasting and later immersion in a cerium nitrate solution. For aluminized steel substrates, the best results were obtained with both electrodeposition and immersion methods using a cerium chloride solution