Hormigón autocompactante con nano adiciones y fibras

El hormigón autocompactante se puede definir como aquel hormigón que bajo la acción de su propio peso, es capaz de fluir y rellenar toda la superficie de un molde, pasando a través de zonas densamente armadas, sin la necesidad de algún mecanismo de compactación o vibración. Este hormigón se fabrica con los mismos componentes que un hormigón convencional pero variando ciertos aspectos de la composición con un incremento de áridos finos, una disminución de áridos grueso, incorporación del filler y aditivos como el superplastificante y el agente modificador de viscosidad. Finalmente se obtendrá un hormigón con alto contenido de finos, mayor volumen de pasta, alto contenido de adiciones y aditivos. Teniendo en cuenta lo antes expresado el hormigón autocompactante debe cumplir con unas propiedades en estado fresco como lo es la capacidad de relleno, capacidad de paso y resistencia a la segregación. Al cumplir con estas propiedades obtendremos la principal propiedad de estos hormigones que es la autocompactabilidad. Se puede decir que en estado endurecido el hormigón autocompactante tiende a comportarse muy similar al hormigón convencional, pero apreciando una mejoría en el aspecto de la durabilidad y una mayor deformaciones endógenas por el alto contenido de pasta. En este Trabajo Fin de Máster se realizó una campaña experimental para estudiar el efecto de las nano adiciones y fibras en un hormigón autocompactante (HACNF), siendo esto expresado el objetivo fundamental. Las nano adiciones utilizadas fueron nano alúmina (Al₂O₃) y nano sílice (SiO₂) y las fibras que se incorporaron para reforzar fueron fibras de acero y fibras de poliolefina. Para poder caracterizar el HACNF en estado fresco se realizaron dos ensayos los cuales fueron el ensayo de escurrimiento y el ensayo de embudo en V. Las propiedades en estado endurecido se midieron mediante los ensayos de resistencia a compresión, resistencia a tracción indirecta, módulo de elasticidad, profundidad de penetración de agua bajo presión y resistencia a flexo-tracción. Los resultados obtenidos fueron satisfactorios y acorde con lo establecido en la norma.

Plant β-diversity i in human-altered forest ecosystems: the importance of the structural, spatial, and topographical characteristics of stands in patterning plant species assemblages

An understanding of spatial patterns of plant species diversity and the factors that drive those patterns is critical for the development of appropriate biodiversity management in forest ecosystems. We studied the spatial organization of plants species in human- modified and managed oak forests (primarily, Quercus faginea) in the Central Pre- Pyrenees, Spain. To test whether plant community assemblages varied non-randomly across the spatial scales, we used multiplicative diversity partitioning based on a nested hierarchical design of three increasingly coarser spatial scales (transect, stand, region). To quantify the importance of the structural, spatial, and topographical characteristics of stands in patterning plant species assemblages and identify the determinants of plant diversity patterns, we used canonical ordination. We observed a high contribution of ˟-diversity to total -diversity and found ˟-diversity to be higher and ˞-diversity to be lower than expected by random distributions of individuals at different spatial scales. Results, however, partly depended on the weighting of rare and abundant species. Variables expressing the historical management intensities of the stand such as mean stand age, the abundance of the dominant tree species (Q. faginea), age structure of the stand, and stand size were the main factors that explained the compositional variation in plant communities. The results indicate that (1) the structural, spatial, and topographical characteristics of the forest stands have the greatest effect on diversity patterns, (2) forests in landscapes that have different land use histories are environmentally heterogeneous and, therefore, can experience high levels of compositional differentiation, even at local scales (e.g., within the same stand). Maintaining habitat heterogeneity at multiple spatial scales should be considered in the development of management plans for enhancing plant diversity and related functions in human-altered forests

Morteros de cemento con nano-adiciones de sílice, hierro y alúmina

A lo largo de los últimos años, la ingeniería de la construcción ha seguido una tendencia creciente en lo que se refiere a la exigencia de altas prestaciones en los materiales empleados en obra, siendo el hormigón el material por excelencia. Es bien conocido que la capacidad de mejora de las prestaciones de los materiales está estrechamente ligada al desarrollo tecnológico existente en ese tiempo. En la actualidad, de entre todos los avances tecnológicos, cabe destacar la nanotecnología, ciencia que trabaja con elementos de tamaño 109 y que en los últimos años está siendo el motor de las investigaciones en el campo de la construcción. De entre todas las nano-adiciones existentes cabe destacar la nano-sílice, estudiada por numerosos investigadores y que goza de un gran número de artículos científicos. En cambio, existen otras nano-adiciones que no han tenido tanta aceptación o se encuentran en un segundo plano, como son la nano-hierro y la nano-alúmina. Es por tanto objeto de este Trabajo Fin de Máster: estudiar el efecto de la incorporación en diferentes proporciones de nano-adiciones de sílice, hierro y alúmina a un mortero de cemento convencional, mediante una campaña experimental realizada en el seno del Departamento de Ingeniería de la Construcción de la ETSICCP de la Universidad Politécnica de Madrid.

Morteros de cemento con nano-adiciones de hierro y sílice

Cada vez más, el hormigón tiene unas aplicaciones estructurales que demandan unos requisitos de resistencia y durabilidad difíciles de alcanzar siguiendo dosificaciones convencionales. Este contexto, de una mayor exigencia y desempeño del hormigón, es el epicentro de numerosas investigaciones que persiguen mejorar las características de los hormigones a través del uso de adiciones. Dentro de este marco de investigación, los últimos avances se encuentran vinculados al desarrollo de la nanotecnología, concretamente al uso de adiciones de tamaño nanométrico. La presente investigación queda enmarcada dentro de un Trabajo Fin de Máster y persigue la evaluación de los efectos a nivel microestructural y macroestructural del efecto de adiciones de tamaño nanométrico de hierro y sílice en proporciones variables a morteros de cemento. Para ver estas posibles mejoras, se comparará cuantitativamente con un mortero convencional de referencia. Para poder realizar dicha evaluación, se realizará una campaña experimental que incluye ensayos de resistencia, porosimetría, análisis térmico diferencial y resistividad. Una vez realizados los ensayos se ha procedido a analizar los resultados y a partir de ellos se han obtenido conclusiones acerca del desempeño de las nano adiciones en la matriz cementícia, así como de sus efectos en términos de resistencia y durabilidad principalmente. Finalmente, y dado que la investigación se encuentra acotada en el tiempo al ser un proyecto final de máster, se proponen unas líneas de investigación futuras con el fin de poder profundizar más en los procesos microestructurales que rigen el comportamiento de estas partículas en la matriz cementícia y con el propósito también de poder explicar resultados que no hayan podido quedar suficientemente resueltos a través del presente trabajo.

1D and 2D neutral particle patterning by dielectrophoretic forces on z-cut Fe:LiNbO3 crystals

1D and 2D patterning of uncharged micro- and nanoparticles via dielectrophoretic forces on photovoltaic z-cut Fe:LiNbO3 have been investigated for the first time. The technique has been successfully applied with dielectric micro-particles of CaCO3 (diameter d = 1-3 μm) and metal nanoparticles of Al (d = 70 nm). At difference with previous experiments in x- and y-cut, the obtained patterns locally reproduce the light distribution with high fidelity. A simple model is provided to analyse the trapping process. The results show the remarkably good capabilities of this geometry for high quality 2D light-induced dielectrophoretic patterning overcoming the important limitations presented by previous configurations.

Comparative theoretical analysis between parallel and perpendicular geometries for 2D particle patterning in photovoltaic ferroelectric substrates

This paper describes the dielectrophoretic potential created by the evanescent electric field acting on a particle near a photovoltaic crystal surface depending on the crystal cut. This electric field is obtained from the steady state solution of the Kukhtarev equations for the photovoltaic effect, where the diffusion term has been disregarded. First, the space charge field generated by a small, square, light spot where d _ l (being d a side of the square and l the crystal thickness) is studied. The surface charge density generated in both geometries is calculated and compared as their relation determines the different properties of the dielectrophoretic potential for both cuts. The shape of the dielectrophoretic potential is obtained and compared for several distances to the sample. Afterwards other light patterns are studied by the superposition of square spots, and the resulting trapping profiles are analysed. Finally the surface charge densities and trapping profiles for different d/l relations are studied.

Comparison of push-in and push-out tests for measuring interfacial shear strength in nano-reinforced composite materials

The influence of the carbon nanotubes (CNTs) content on the fiber/matrix interfacial shear strength (IFSS) in glass/fiber epoxy composites was measured by means of push-in and push-out tests. Both experimental methodologies provided equivalent values of the IFSS for each material. It was found that the dispersion of CNTs increased in IFSS by 19% in average with respect to the composite without CNTs. This improvement was reached with 0.3 wt.% of CNTs and increasing the CNT content up to 0.8 wt.% did not improve the interface strength.

Effect of nano-Si2O and nano-Al2O3 on cement mortars for use in agriculture and livestock production

The effect of nano-silica, nano-alumina and binary combinations on surface hardness, resistance to abrasion and freeze-thaw cycle resistance in cement mortars was investigated. The Vickers hardness, the Los Angeles coefficient (LA) and the loss of mass in each of the freeze–thaw cycles to which the samples were subjected were measured. Four cement mortars CEM I 52.5R were prepared, one as control, and the other three with the additions: 5% nano-Si, 5% nano-Al and mix 2.5% n-Si and 2.5% n-Al. Mortars were tested at 7, 28 and 90 d of curing to determine compression strength, total porosity and pore distribution by mercury intrusion porosimetry (MIP) and the relationship between the CSH gel and Portlandite total by thermal gravimetric analysis (TGA). The capillary suction coefficient and an analysis by a scanning electron microscope (SEM) was made. There was a large increase in Vickers surface hardness for 5% n-Si mortar and a slight increase in resistance to abrasion. No significant difference was found between the mortars with nano-particles, whose LA was about 10.8, classifying them as materials with good resistance to abrasion. The microstructure shows that the addition of n-Si in mortars refines their porous matrix, increases the amount of hydrated gels and generates significant changes in both Portlandite and Ettringite. This produced a significant improvement in freeze–thaw cycle resistance. The effect of n-Al on mortar was null or negative with respect to freeze–thaw cycle resistance.

Abnormal skeletal patterning in embryos lacking a single Cbp allele: A partial similarity with Rubinstein–Taybi syndrome

CBP is a transcriptional coactivator required by many transcription factors for transactivation. Rubinstein–Taybi syndrome, which is an autosomal dominant syndrome characterized by abnormal pattern formation, has been shown to be associated with mutations in the Cbp gene. Furthermore, Drosophila CBP is required in hedgehog signaling for the expression of decapentapleigic, the Drosophila homologue of bone morphogenetic protein. However, no direct evidence exists to indicate that loss of one copy of the mammalian Cbp gene affects pattern formation. Here, we show that various abnormalities occur at high frequency in the skeletal system of heterozygous Cbp-deficient mice resulting from a C57BL/6-CBA × BALB/c cross. In support of a conserved signaling pathway for pattern formation in insects and mammals, the expression of Bmp7 was found to be reduced in the heterozygous mutants. The frequency of the different abnormalities was significantly lower in a C57BL/6-CBA background, suggesting that the genetic background is an important determinant of the variability and severity of the anomalies seen in Rubinstein–Taybi syndrome patients.

TectoRNA: modular assembly units for the construction of RNA nano-objects

Structural information on complex biological RNA molecules can be exploited to design tectoRNAs or artificial modular RNA units that can self-assemble through tertiary interactions thereby forming nanoscale RNA objects. The selective interactions of hairpin tetraloops with their receptors can be used to mediate tectoRNA assembly. Here we report on the modulation of the specificity and the strength of tectoRNA assembly (in the nanomolar to micromolar range) by variation of the length of the RNA subunits, the nature of their interacting motifs and the degree of flexibility of linker regions incorporated into the molecules. The association is also dependent on the concentration of magnesium. Monitoring of tectoRNA assembly by lead(II) cleavage protection indicates that some degree of structural flexibility is required for optimal binding. With tectoRNAs one can compare the binding affinities of different tertiary motifs and quantify the strength of individual interactions. Furthermore, in analogy to the synthons used in organic chemistry to synthesize more complex organic compounds, tectoRNAs form the basic assembly units for constructing complex RNA structures on the nanometer scale. Thus, tectoRNA provides a means for constructing molecular scaffoldings that organize functional modules in three-dimensional space for a wide range of applications.

CA1-specific N-methyl-d-aspartate receptor knockout mice are deficient in solving a nonspatial transverse patterning task

In both humans and animals, the hippocampus is critical to memory across modalities of information (e.g., spatial and nonspatial memory) and plays a critical role in the organization and flexible expression of memories. Recent studies have advanced our understanding of cellular basis of hippocampal function, showing that N-methyl-d-aspartate (NMDA) receptors in area CA1 are required in both the spatial and nonspatial domains of learning. Here we examined whether CA1 NMDA receptors are specifically required for the acquisition and flexible expression of nonspatial memory. Mice lacking CA1 NMDA receptors were impaired in solving a transverse patterning problem that required the simultaneous acquisition of three overlapping odor discriminations, and their impairment was related to an abnormal strategy by which they failed to adequately sample and compare the critical odor stimuli. By contrast, they performed normally, and used normal stimulus sampling strategies, in the concurrent learning of three nonoverlapping concurrent odor discriminations. These results suggest that CA1 NMDA receptors play a crucial role in the encoding and flexible expression of stimulus relations in nonspatial memory.

Polaris, a Protein Involved in Left-Right Axis Patterning, Localizes to Basal Bodies and Cilia

Mutations in Tg737 cause a wide spectrum of phenotypes, including random left-right axis specification, polycystic kidney disease, liver and pancreatic defects, hydrocephalus, and skeletal patterning abnormalities. To further assess the biological function of Tg737 and its role in the mutant pathology, we identified the cell population expressing Tg737 and determined the subcellular localization of its protein product called Polaris. Tg737 expression is associated with cells possessing either motile or immotile cilia and sperm. Similarly, Polaris concentrated just below the apical membrane in the region of the basal bodies and within the cilia or flagellar axoneme. The data suggest that Polaris functions in a ciliogenic pathway or in cilia maintenance, a role supported by the loss of cilia on the ependymal cell layer in ventricles of Tg737orpk brains and by the lack of node cilia in Tg737Δ2-3βGal mutants.

Activation of a protease cascade involved in patterning the Drosophila embryo

Dorsoventral patterning of the Drosophila embryo is initiated by a ventralizing signal. Production of this signal requires the serine proteases Gastrulation Defective (GD), Snake, and Easter, which genetic studies suggest act sequentially in a cascade that is activated locally in response to a ventral cue provided by the pipe gene. Here, we demonstrate biochemically that GD activates Snake, which in turn activates Easter. We also provide evidence that GD zymogen cleavage is important for triggering this cascade but is not spatially localized by pipe. Our results suggest that a broadly, rather than locally, activated protease cascade produces the ventralizing signal, so a distinct downstream step in this cascade must be spatially regulated to restrict signaling to the ventral side of the embryo.

Vascular patterning defects associated with expression of activated Notch4 in embryonic endothelium

Notch proteins function as receptors for membrane-bound ligands (Jagged and Delta-like) to regulate cell-fate determination. We have investigated the role of Notch signaling in embryonic endothelium of the mouse by expressing an activated form of the Notch4 protein in vasculature under the regulation of the Flk1 (VEGFR) locus. Expression of activated Notch4 results in a growth and developmental delay and embryonic lethality at about 10 days postcoitum. The extent of the developing vasculature in mutant embryos was restricted, fewer small vessels were seen, and vascular networks were disorganized. The brain periphery of mutant embryos contained large dilated vessels with evidence of compromised vessel-wall integrity and large areas of necrosis; yolk-sac vasculature was abnormal. Expression of an activated form of Notch4 in embryonic vasculature leads to abnormal vessel structure and patterning, implicating the Notch pathway in phases of vascular development associated with vessel patterning and remodeling.

Patterning of the mammalian cochlea

The mammalian cochlea is sophisticated in its function and highly organized in its structure. Although the anatomy of this sense organ has been well documented, the molecular mechanisms underlying its development have remained elusive. Information generated from mutant and knockout mice in recent years has increased our understanding of cochlear development and physiology. This article discusses factors important for the development of the inner ear and summarizes cochlear phenotypes of mutant and knockout mice, particularly Otx and Otx2. We also present data on gross development of the mouse cochlea.