Insight into the dynamics of low temperature dielectric relaxation of ordinary perovskite ferroelectrics

The temperature dependence of the dielectric response of ordinary ferroelectric materials exhibits a frequency-independent anomalous peak as a manifestation of the ferroelectric to paraelectric phase transition. A second anomaly in the permittivity has been reported in different ferroelectric perovskite-type systems at low temperatures, often at cryogenic temperatures. This anomaly manifests as a frequency-dependent local maximum, which exhibits similar characteristics to that observed in relaxor ferroelectrics around their phase transition. The origin of this unexpected behavior is still controversial. In order to clarify this phenomenon, a model-free route solution is developed in this work. Our findings reveal the same critical linear pattern/glass-like freezing behavior previously observed for glass-forming systems. Contrary to current thought, our results suggest that a critical-like dynamic parameterization could provide a more appropriate solution than the conventional Vogel–Fulcher–Tammann equation. The implemented methodology may open a new pathway for analyzing relaxation phenomena in other functional materials like relaxor ferroics.Postprint (published version

The generalized Vogel-Fulcher-Tamman equation for describing the dynamics of relaxor ferroelectrics

Relaxor ferroelectrics (RF) are outstanding materials owing to their extraordinary dielectric, electromechanical, and electro-optical properties. Although their massive applications, they remain to be one of the most puzzling solid-state materials because understanding their structural local order and relaxation dynamics is being a long-term challenge in materials science. The so-called Vogel-Fulcher-Tamman (VFT) relation has been extensively used to parameterize the relaxation dynamics in RF, although no microscopic description has been firmly established for such empirical relation. Here, we show that VFT equation is not always a proper approach for describing the dielectric relaxation in RF. Based on the Adam-Gibbs model and the Grüneisen temperature index, a more general equation to disentangle the relaxation kinetic is proposed. This approach allows to a new formulation for the configurational entropy leading to a local structural heterogeneity related order parameter for RF. A new pathway to disentangle relaxation phenomena in other relaxor ferroics could have opened.Postprint (published version

Unfolding kinetic fragility in relaxor ferroelectrics

The fragility parameter is one of the most important material constants that is extensively used in glass science, playing a central role in the enhancement of the understanding the glass formation process of disordered systems. Although fragility has been widely used, this concept has never been precisely defined and evaluated in relaxor ferroelectrics. Here, we have filled up this scientific gap. Based on a generalized Vogel-Fulcher-Tammann equation, the fragility parameter is introduced for relaxor ferroelectrics. The new formulation has been quantitatively assessed by combining dielectric spectroscopy and pyroelectric measurements on canonical relaxors. A clear correlation between the fragility and a new local structural heterogeneity related order parameter elucidates new information about the ferroelectric order of relaxor ferroelectrics. A new pathway to disentangle relaxation phenomena in other relaxor ferroics could have opened.Peer ReviewedPostprint (author's final draft

Evidence for a dynamics crossover and its implication on the freezing temperature determination of relaxor ferroelectrics

Relaxor ferroelectrics are characterized by a broadened and dispersive permittivity peak in their temperature-dependent dielectric spectra. Although several models have been proposed to explain the nature of these materials, understanding their relaxation dynamics still remains open and requires additional theoretical and experimental explanations. Particularly, a precise determination of the freezing temperature still remains controversial because the influence of dynamic ruptures at temperatures approaching the freezing states (dynamic crossovers) has never evaluated before. In this paper, a model-free approach for describing the super-Arrhenius behaviour in glassy systems is validated for relaxor ferroelectrics. As a result, a predicted dynamic change at a specific temperature (crossover temperature) is evidenced by a derivative-based representation of the relaxation time data. The Stickel function is suggested as a more straightforward but model-dependent method for obtaining the dynamic crossover temperature. Furthermore, the divergence (freezing) temperature is obtained on the basis of the Grüneisen-style activation energy temperature index without assuming any model equation for parameterizing the relaxation data. The influence of the dynamic change occurrences on the freezing temperature determination is also considered, showing that the dynamic crossover temperature determination is a key factor for a proper finding of the freezing temperature in relaxor ferroelectrics.Postprint (author's final draft

Desempeño escolar y acompañamiento familiar: una mirada desde las configuraciones familiares emergentes en el Municipio de Sabaneta

Maestría en Educación y Desarrollo Humano, Facultad de Ciencias Sociales y Humanas.Los resultados de la investigación, servirán en primer lugar, para aportar a derribar el mito de los determinismos sociales y las brechas que se crean por los mismos. En segundo lugar, podrá usarse como referente para la comprensión del municipio de Sabaneta, como entidad territorial certificada en educación, que puede realizar acciones acertadas con ocasión de los resultados e intervenir en cualquiera de las instituciones educativas de la localidad. En tercer lugar, podrá servir como referente para la elaboración de nuevos trabajos de investigación que permitan ampliar la comprensión del ya entramado mundo de las configuraciones familiares, entendiendo que estas no son estáticas, sino dinámicas de acuerdo con la realidad

Propuesta de diseño de 520 metros lineales de adoquinado en sector de zona franca siglo xxi, municipio de masaya para un periodo de serviciabilidad de 20 años (2018-2038)

La ciudad de Masaya localizada a 29 kilómetros de la capital Managua, por sus características físicas geográficas presenta una topográfica irregular identificándose sitios vulnerables que son objeto de inundaciones, por tanto, la municipalidad ha planificado en el plan de operación anual realizar proyectos que resuelvan de forma inmediata y económica esta problemática. Por otra parte, el gobierno de Nicaragua a través del ministerio de transporte e infraestructura (MTI) y las Alcaldías municipales ha implementado en los últimos ocho años el programa “calles para el pueblo” proyectos viales en todo el territorio nacional que pretenden dar respuesta a la estropeada red vial de nuestras ciudades y así de esa forma mejorar las condiciones de vida socioeconómicas de la población

Estudio de los efectos producidos por las condiciones de transformación en la viscosidad del Polietilentereftalato (PET) reciclado.

Se estudió el efecto producido por las condiciones de transformación en la viscosidad del polietilentereftalato reciclado. Para ello, se realizó una simulación del procesado en un plastómetro para la determinación del Índice de Fluidez, sobre la base de un diseño de experimentos factorial 22. Como variables independientes se tomaron la temperatura y tiempo de retención del polímero dentro de la cámara de procesamiento, mientras que como variable respuesta se evaluó la viscosidad intrínseca del polietilentereftalato. Mediante un análisis de regresión lineal del diseño experimental se logró obtener por primera vez la ecuación del modelo ajustado para la viscosidad intrínseca, sobre la que los dos factores estudiados (tiempo y temperatura) así como la interacción entre ellos presentaron un efecto significativo con un nivel de confianza de 95 %. En todos los casos ocurrió una disminución de la viscosidad del polietilentereftalato reciclado, encontrándose la mayor incidencia con un 30 % al incrementar la temperatura de 260 a 280 °C. De cara a un proceso de reciclado, se recomienda mantener un perfil de temperaturas que no supere los 260 °C y tiempos de residencia igual o menores a 10 min.The effect produced by the processing conditions on the viscosity of recycled polyethylene terephthalate was studied. For this, a simulation of the processing was carried out using a melt flow index plastometer, based on a factorial design of experiments 22. The temperature and the retention time of the polymer inside the processing chamber were selected as independent factors, while the intrinsic viscosity of the polyethylene terephtalate was the response variable. Through a linear regression analysis of the experimental design, it was possible to obtain for the first time the equation of the model adjusted for intrinsic viscosity, on which the two factors studied (time and temperature) as well as the interaction between them presented a significant effect with a level 95% confidence. In all cases, there was a decrease in the viscosity of the recycled polyethylene terephthalate, with the highest incidence being 30% when the temperature increased from 260 to 280 °C. For a recycling process, it is recommended to maintain a temperature profile that does not exceed 260 °C and residence times equal to or less than 10 min

Study of the effects produced by the transformation conditions on the viscosity of recycled polyethylenterephthalate (pet)

Se estudió el efecto producido por las condiciones de transformación en la viscosidad del polietilentereftalato reciclado. Para ello, se realizó una simulación del procesado en un plastómetro para la determinación del Índice de Fluidez, sobre la base de un diseño de experimentos factorial 2^2. Como variables independientes se tomaron la temperatura y tiempo de retención del polímero dentro de la cámara de procesamiento, mientras que como variable respuesta se evaluó la viscosidad intrínseca del polietilentereftalato. Mediante un análisis de regresión lineal del diseño experimental se logró obtener por primera vez la ecuación del modelo ajustado para la viscosidad intrínseca, sobre la que los dos factores estudiados (tiempo y temperatura) así como la interacción entre ellos presentaron un efecto significativo con un nivel de confianza de 95 %. En todos los casos ocurrió una disminución de la viscosidad del polietilentereftalato reciclado, encontrándose la mayor incidencia con un 30 % al incrementar la temperatura de 260 a 280 °C. De cara a un proceso de reciclado, se recomienda mantener un perfil de temperaturas que no supere los 260 °C y tiempos de residencia igual o menores a 10 min.The effect produced by the processing conditions on the viscosity of recycled polyethylene terephthalate was studied. For this, a simulation of the processing was carried out using a melt flow index plastometer, based on a factorial design of experiments 22 . The temperature and the retention time of the polymer inside the processing chamber were selected as independent factors, while the intrinsic viscosity of the polyethylene terephtalate was the response variable. Through a linear regression analysis of the experimental design, it was possible to obtain for the first time the equation of the model adjusted for intrinsic viscosity, on which the two factors studied (time and temperature) as well as the interaction between them presented a significant effect with a level of 95% confidence. In all cases, there was a decrease in the viscosity of the recycled polyethylene terephthalate, with the highest incidence being 30% when the temperature increased from 260 to 280 °C. For a recycling process, it is recommended to maintain a temperature profile that does not exceed 260 °C and residence times equal to or less than 10 min.Fil: Velázquez Infante, Julio Cesar. Universidad de Holguin.; CubaFil: Vega García, Arles. Universidad de Holguin.; CubaFil: Esquivel Figueredo, Rosalia de la Caridad. Universidad de Holguin.; Cuba. Universidad Nacional de Córdoba. Instituto de Investigación y Desarrollo en Ingeniería de Procesos y Química Aplicada. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigación y Desarrollo en Ingeniería de Procesos y Química Aplicada; ArgentinaFil: Bárcenas Martínez, Sandra. Universidad de Holguin.; CubaFil: Martínez Hung, Hassan. Universidad de Oriente.; Cub

Investigating mutations in the genes GDF9 and BMP15 in Pelibuey sheep through the amplification-refractory mutation system with tetra-primers

Single Nucleotide Polymorphisms (SNP) or mutations are variations with a broad distribution in the genome and, as part of genetic studies, SNP allow the identification of allelic variants related to characteristics of economic importance in sheep production. However, the identification of SNP and their genotypes through sequencing is expensive, as it requires specialized materials and equipment. The objective of this study was to identify polymorphisms and their genotypes in the growth differentiation factor 9 (GDF9) and bone morphogenetic protein 15 (BMP15) genes in Pelibuey sheep using the tetra-primer amplification-refractory mutation system through polymerase chain reaction (T-ARMS-PCR). DNA extraction and amplification of BMP15 and GDF9 were conducted from blood samples contained in WhatmanTM FTATM cards from 60 multiparous Pelibuey ewes with reproductive records. The T-ARMS-PCR methodology allowed the identification of wild-type genotypes and mutated homozygous genotypes in polymorphisms G4 and G6 of GDF9, whereas mutations in the BMP15 gene were not found. These results were confirmed by sequencing. In conclusion, the T-ARMS-PCR methodology allowed the identification of mutated and wild-type genotypes in SNP G4 and G6 of GDF9, although no mutations were found in BMP15 in Pelibuey sheep. This technique was found to be reliable, rapid, and easily applied to identify polymorphic genotypes

Contribución a la familia Braconidae (Hymenoptera: Ichneumonoidea) del estado de Aguascalientes

Braconidae es la segunda familia de Hymenoptera con mayor diversidad en el mundo, e incluye parasitoides de insectos y de otros artrópodos. Para Aguascalientes, hasta 2017, sólo se conocían siete subfamilias, ocho géneros y cuatro especies. En el presente trabajo se recolectaron 608 adultos de Braconidae correspondientes a 18 subfamilias, 44 géneros, tres especies y 107 morfoespecies, obtenidos en 111 localidades de los once municipios; de las cuales, 11 subfamilias, 39 géneros y tres especies corresponden a nuevos registros para la entidad. Este trabajo permitió incrementar el registro a 18 subfamilias, 47 géneros y siete especies de Braconidae para el estado de Aguascalientes. La mayoría de los géneros son cosmopolitas y las especies son Neárticas y Neotropicales. Los géneros más abundantes fueron Opius, Aphidius, Trioxys y Aleiodes.Braconidae is the second most diverse Hymenoptera family in the world, which includes parasitoids of insects and other arthropods. Until 2017, only seven subfamilies, eight genera and four species were known in Aguascalientes. In this research, 608 adults of Braconidae family, corresponding to 18 subfamilies, 44 genera, three species and 107 morphospecies, were obtained in 111 localities of eleven municipalities; from those, 11 subfamilies, 39 genera and three species are new records for the state. This work allowed increasing the registry to 18 subfamilies, 47 genera and seven species of Braconidae for the State of Aguascalientes. Most genera are cosmopolitan, and the species are Nearctic and Neotropical. The most abundant genera were Opius, Aphidius, Trioxys and Aleiodes