1,427 research outputs found
Orientational transitions in a nematic confined by competing surfaces
The effect of confinement on the orientational structure of a nematic liquid
crystal model has been investigated by using a version of density-functional
theory (DFT). We have focused on the case of a nematic confined by opposing
flat surfaces, in slab geometry (slit pore), which favor planar molecular
alignment (parallel to the surface) and homeotropic alignment (perpendicular to
the surface), respectively. The spatial dependence of the tilt angle of the
director with respect to the surface normal has been studied, as well as the
tensorial order parameter describing the molecular order around the director.
For a pore of given width, we find that, for weak surface fields, the alignment
of the nematic director is perpendicular to the surface in a region next to the
surface favoring homeotropic alignment, and parallel along the rest of the
pore, with a interface separating these regions (S phase). For strong surface
fields, the director is distorted uniformly, the tilt angle exhibiting a linear
dependence with the distance normal to the surface (L phase). Our calculations
reveal the existence of a first-order transition between the two director
configurations, which is driven by changes in the surface field strength, and
also by changes in the pore width. In the latter case the transition occurs,
for a given surface field, between the S phase for narrow pores and the L phase
for wider pores. A link between the L-S transition and the anchoring transition
observed for the semi-infinite case is proposed. We also provide calculations
with a phenomenological approach that yields the same main result that DFT in
the scale length where this is valid.Comment: submitted to PR
La bóveda tabicada como mejora higiénica y económica en la construcción militar de acuartelamientos. El Cuartel de la Puerta de la Carne (Sevilla)
Las fuentes documentales para el estudio de la historia de la construcción militar de los siglos XVIII y XIX
Influencia de las infiltraciones en la rehabilitación energética de la envolvente. El caso del plan de actuaciones en el parque público residencial de Andalucía
The present study presents the research on the energy retrofit of the building envelope of 615 social housing that are part of the sustainable construction plans for the public housing stock of Andalusia (southern Spain). The analysis provides a new assessment of the relationship between the air-tightness and the energy demand for air conditioning of dwellings in warm climate. Both magnitudes offer a parallelism in the results, with average values of 21.45% decrease in air changes rate and 21.82% decrease in demand. To this end, during the implementation of interventions, tests of infiltrations have been developed in dwellings. The measured air permeability are used as input in a process of energy modeling under different approaches, differentiating the controlled air leakages (ventilation) and the uncontrolled or unnecessary ones (infiltration). The results show the behavior of buildings after refurbishment and energy savings by air leakage can be quantified in each case.El presente estudio presenta la investigación sobre la rehabilitación energética de la envolvente en una muestra de 615 viviendas sociales, incluidas dentro de los planes de construcción sostenible para el parque público residencial de Andalucía. Se evalúa de forma novedosa la relación entre las tasas de renovación de aire exterior y la demanda de climatización de viviendas en clima cálido. Ambas magnitudes ofrecen un paralelismo en los resultados, con valores promedio de 21,45% de disminución de tasa de renovación y un 21,82% de disminución en la demanda. Para ello, durante la ejecución de las intervenciones se ha desarrollado un muestreo de infiltraciones en viviendas. Las permeabilidades medidas se utilizan como parámetros de entrada en un proceso de modelizaciones energéticas bajo diferentes hipótesis, diferenciando la entrada de aire controlada o necesaria (ventilación) y la incontrolada o innecesaria (infiltraciones). Los resultados permiten visualizar el comportamiento de los edificios rehabilitados, cuantificando el ahorro energético como consecuencia de las infiltraciones para cada caso
Bacterial community composition and optical signature of DOM shape empirical leucine-to-carbon conversion factors in north-eastern Atlantic waters (0-4000 m)
Oral communicationMicrobial heterotrophic activity is a major process regulating the flux
of dissolved organic matter (DOM) in the ocean. DOM quantity and
quality strongly influence its microbial utilization and fate in the
ocean. In order to broaden the vertical resolution of leucine-to-carbon
conversion factors (CFs), needed for converting substrate
incorporation into biomass production by heterotrophic bacteria, nine
dilution experiments were performed in the north Atlantic. We found a
very consistent depth-stratification in empirical CFs values from
epipelagic to bathypelagic waters (3.95 ± 0.05 to 0.90 ±
0.51 kg C mol Leu-1). Our results demonstrated that the
customarily used CF of 1.55 kg C mol Leu-1 in oceanic
waters leads to an underestimation of prokaryotic heterotrophic
production in epi- and mesopelagic waters, while it causes a severe
overestimation in bathypelagic waters. Pearson correlations showed
that CFs were related not only to hydrographic variables but also
to specific phylogenetic groups and DOM quality and quantity
indicators. Furthermore, a multiple linear regression model predicting
CFs from relatively simple hydrographic and optical spectroscopic
measurements is provided. Taken together, our results suggest that
differences in CFs throughout the water column might be mostly
associated to the quality of DOM affecting the response of particular
phylogenetic groups.ASL
Evaluation of the GEXCAT software in the design and correction of multiple choice exams: preliminary data
Resúmenes IV Congreso VetDoc de Docencia Veterinaria, León 2017 (6-7 de Julio)[ES] El sistema de evaluación continua propuesto por el Plan Bolonia supone un incremento de la carga de trabajo del profesor universitario (Pagani y González, 2002). Los exámenes tipo test son una opción, sobre todo en el caso de asignaturas con un elevado número de créditos. Permiten una pronta corrección y se puede aumentar el número de evaluaciones, mejorando los resultados de los alumnos, lo que aumenta su motivación (Escolano et al., 2014). Para que los alumnos no se copien convienen preparar varios modelos de exámenes, aunque esto complica la corrección, facilitando el error humano. Para evitar tal situación se han creado programas informáticos. El programa privativo de Gestión de Exámenes y Corrección Automática de Tests, GEXCAT (Innocan, 2017), es una herramienta que ayuda en la preparación y corrección de exámenes tipo test, con la ventaja de utilizar hojas DINA4 y un escáner básico. Permite generar exámenes de tipo test tanto en formato electrónico como en papel. Barajando tanto las preguntas como las respuestas puede llegar a generar hasta nueve modelos de examen. Además, las preguntas pueden ser clasificadas por nivel de dificultad. El programa proporciona las correcciones casi instantáneamente, pudiendo exportar las calificaciones en formato Excel, enviar los resultados a los alumnos vía email y gestionar eficazmente las evaluaciones continuas
Parallel evolution of vgsc mutations at domains IS6, IIS6 and IIIS6 in pyrethroid resistant Aedes aegypti from Mexico
Aedes aegypti is the primary urban mosquito vector of viruses causing dengue, Zika and chikungunya fevers –for which vaccines and efective pharmaceuticals are still lacking. Current strategies to suppress arbovirus outbreaks include removal of larval-breeding sites and insecticide treatment of larval and adult populations. Insecticidal control of Ae. aegypti is challenging, due to a recent rapid global increase in knockdown-resistance (kdr) to pyrethroid insecticides. Widespread, heavy use of pyrethroid spacesprays has created an immense selection pressure for kdr, which is primarily under the control of the voltage-gated sodium channel gene (vgsc). To date, eleven replacements in vgsc have been discovered, published and shown to be associated with pyrethroid resistance to varying degrees. In Mexico, F1,534C and V1,016I have co-evolved in the last 16 years across Ae. aegypti populations. Recently, a novel replacement V410L was identifed in Brazil and its efect on vgsc was confrmed by electrophysiology. Herein, we screened V410L in 25 Ae. aegypti historical collections from Mexico, the frst heterozygote appeared in 2002 and frequencies have increased in the last 16 years alongside V1,016I and F1,534C. Knowledge of the specifc vgsc replacements and their interaction to confer resistance is essential to predict and to develop strategies for resistance management
First Jurassic brittlestar from Neuquén Basin, Argentina
Articulated fossil ophiuroids from South America were reported for the Devonian, Cretaceous, Eocene, and Miocene. Here
we report the first Jurassic record of an articulated ophiuroid from the Sierra Chacaicó Formation (early Pliensbachian–
Sinemurian) in Neuquén Basin, Argentina, and discuss the taphonomic processes that allowed its preservation. The Sierra
Chacaicó Formation represents the onset of the Early Jurassic extensive marine transgression in the basin. The basal
section comprises shoreface and offshore Gilbert-type delta system, which was affected by hyperpycnal discharges. The
middle and upper sections are represented by offshore deposits, affected by storms and eroded by hyperpycnal channel-levee
systems. The ophiuroid specimen was found in levels of massive, fine, tuffaceous sandstone beds and covered
by coarse sandstone containing a large amount of plant debris and organic matter. It was preserved articulated, with a
complete disc and almost complete arms. Based on the microstructure of the spine-bearing lateral arm plates, the ophiuroid
is assigned to Sinosura, an extinct genus of the family Ophioleucidae, widespread in the Lower Jurassic deposits
of Europe but previously unknown from other parts of the world. The posture of the ophiuroid, with one arm curved
distally and extended in one direction and the other four arms symmetrically oriented in the opposite direction, suggests
a walking or escape movement frozen in time. This implies that the ophiuroid was buried alive by sediment thick enough
to prevent successful escape. The taphonomic and sedimentologic evidence indicates that the fossil material was found in
hyperpycnal deposits accumulated in offshore positions, which carried a high concentration of sediment in suspension
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