1,354,144 research outputs found
Heading to Class in Brunengo Building
No full textA student heads to class in one of the Brunengo Building's several classroomsA student heads to class in one of the Brunengo Building's several classroom
Heading to Class in Brunengo Building
No full textA student heads to class in one of the Brunengo Building's several classroom
Engineered poly(vinylidene fluoride) based composites containing inorganic inclusions as materials for energy-related applications: process-structure-properties correlations
No full textIn recent years the continuous and rapid development of the electronic industry together with the need for more efficient electric energy harvesting have notably increased the demand for: (i) high dielectric constant and breakdown strength materials for high energy density capacitors and (ii) piezoelectric flexible materials, with the ability to bend into diverse shapes, for powering low-power portable devices and self-powered electronic systems.
Polymer-based composites and nanocomposites with inclusions of a ceramic active phase are very attractive for these applications because they combine materials with different characteristics, allowing the possibility to tune and optimize the dielectric and piezoelectric properties in the ensuing composite systems. In particular, many parameters can affect the material performance: (i) the nature of the polymer matrix and active component; (ii) the phases connectivity; (iii) the filler concentration, shape and dimensions; (iv) the filler/matrix interactions; (v) the preparation technique and processing. All this variability expands the possible applications of polymer-composites for energy-related purposes but also increases the difficulty in realistically predicting their ultimate properties. The design of polymer composites thus requires a rational selection of components, good interface engineering and proper processing optimization. To achieve this, a thorough comprehension of the process-structure-properties correlations is very important.
This is the principal aim of this thesis work, which focus on the preparation of poly(vinylidene fluoride) homopolymer (PVDF) or poly(vinylidene fluoride-co-hexafluoropropylene) copolymer (PVDF-HFP) based composites with 0-3 connectivity containing different perovskite fillers, namely, BaTiO3 (BT), Pb(Zr,Ti)O3 (PZT) and Na0.5Bi0.5TiO3 - BaTiO3 (BNBT). The filler particles were used as prepared or properly surface modified and several techniques were employed for the composites preparation (i.e., solvent casting, melt blending, hot-pressing, compression moulding).
Initially, a study of the neat polymer matrices was performed, by using, for the first time in literature, the compression moulding technique to tune the polymorphism of PVDF. A principal component analysis was performed on the infrared spectra of the moulded films to validate the equation usually employed for determining the electroactive phase amount (FEA) then multiple linear regression was applied to better understand how the processing parameters affect the FEA value. A double-step procedure was proven fundamental in inducing the formation of PVDF β phase and improving the dielectric properties of the ensuing polymer films.
After this preparatory investigation, the study of the process-structure-properties correlations was extended to PVDF-based composites, addressing three main issues: (i) the influence of processing on the ultimate properties of the prepared samples; (ii) the influence of particles dimensions and surface modification on the dielectric behaviour of the composite materials; (iii) the response of flexible piezoelectric composites.
The preparation technique affects the microstructure at different levels, but it was found that not always a flawless particles dispersion necessary leads to the best final performance of the composite. Whereas, a proper moulding method, by affecting the polymorphism of the polymer matrix and the compactness of the film, can improve significantly the dielectric response.
The presence of an inorganic shell around BT particles allows a modulation of the effective permittivity of the composites; if intrinsic factors (i.e., the permittivity of the components) prevail on extrinsic ones (i.e., interfacial polarization), the composites response can be predicted by FEM calculations. However, in these conditions, the reduction in the dielectric constant compensates for the increase of the breakdown strength promoted by the shell and, as a whole, the stored energy decreases.
It is worth noting that the composites containing core-shell particles are characterized by low tunability, a condition which is important for application as dielectric capacitors.
The functionalization of the ceramic particles with the tested coupling agents, despite decreasing to a certain extent the dielectric permittivity of the ensuing composites (due to the intrinsic low permittivity of the silane moieties), increases the maximum electric field, thus leading to an energy recovering capability comparable or slightly higher than that of the composite containing pristine BT particles.
The dielectric response of the composites is affected by the particles dimensions even though the films containing pristine BT and those containing TiO2-coated particles exhibit a different trend of dielectric permittivity with filler size; this suggests a not negligible contribution of the interfaces, which varies with the method of particles synthesis.
As concerns the piezoelectric composites, the piezoelectric coefficient (d33), in general, increases if the filler dimensions increase significantly. The higher response of the samples containing sintered and crushed PZT or BNBT particles (with respect to simply calcined powders) probably derived from the higher particles connectivity inside the agglomerates, which in turn leads to higher local stresses inside the material. As far as we know, the piezoelectric properties of composites made of fluorinated polymer matrices and BNBT filler had not been studied yet. The obtained d33 are in line with those of many flexible lead-free composites made with particles different from BNBT, suggesting the potentiality of these composites in the field of energy harvesting.
As principal achievements, I obtained: (i) an alternative and smart method to tune the polymorphism of PVDF homopolymer and its copolymers, by exploiting a simple and easily-scalable processing technique; (ii) solvent-free fabrication of polymer-based composites with dielectric properties improved by the moulding process; (iii) a better comprehension about the role of the interfaces, useful to tune the final performance of the dielectric composites; (iv) flexible lead-free polymer-based composites with a good piezoelectric response for potential application as safe energy harvesting devices
Chitosan-based electrospun membranes: Effects of solution viscosity, coagulant and crosslinker
No full textChitosan-based membranes were prepared via electrospinning technique using a low concentrated acetic acid solution as solvent and poly(ethylene oxide) as co-spinning agent. Different solutions were rheologically characterized and increasing the solution viscosity was found to correspond to a better-defined morphology. The membranes were first subjected to a coagulation process with different baths in order to stabilize chitosan and the mats were found not able to withstand a strongly basic environment. Subsequently, a physical and a chemical crosslinking approach were separately optimized to obtain stable mats whose composition was assessed via thermogravimetric and spectroscopic techniques, proving in both cases the elimination of the co-spinning agent. Above all, the ionically crosslinked mats represent a class of extremely promising biomedical products being probably highly biocompatible and characterized by thin and homogenous nanofibers with a diameter of 200 nm, thus showing the ideal structure to foster cell viability
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Investigation of the Mechanical and Dynamic-Mechanical Properties of Electrospun Polyvinylpyrrolidone Membranes: A Design of Experiment Approach
No full textPolyvinylpyrrolidone electrospun membranes characterized by randomly, partially, or
almost completely oriented nanofibers are prepared using a drum collector in static (i.e., 0 rpm) or
rotating (i.e., 250 rpm or 500 rpm) configuration. Besides a progressive alignment alongside the
tangential speed direction, the nanofibers show a dimension increasing with the collector rotating
speed in the range 410–570 nm. A novel design of experiment approach based on a face-centred
central composite design is employed to describe membrane mechanical properties using the
computation of mathematical models and their visualization via response surface methodology. The
results demonstrate the anisotropic nature of the fibre-oriented membranes with Young’s modulus
values of 165 MPa and 71 MPa parallelly and perpendicularly to the alignment direction,
respectively. Above all, the proposed approach is proved to be a promising tool from an industrial
point of view to prepare electrospun membranes with a tailored mechanical response by simply
controlling the collector speed
“Efecto local y sistémico de los bifosfonatos en la reparación ósea peri-implantaría en un modelo experimental”
No full textFil: Brunengo, Ignacio. Universidad Nacional de Córdoba. Facultad de Odontología; Argentina.La oseointegración es la conexión firme, estable y duradera entre un implante sujeto a carga y el tejido óseo que lo rodea. El éxito de esta conexión depende de factores biológicos y sistémicos, como así también de las características del implante y su superficie. Objetivo: Estudiar el efecto de Alendronato y Pamidronato sobre la interfaz del implante y el tejido óseo peri-implante. Materiales y métodos: Se utilizaron 52 ratas Wistar macho de 180 ± 20g de p.c. Se siguieron las normas establecidas por SECyT para el uso y cuidado de animales. Se diseñó un implante de Ti cp clase V. Se realizó la caracterización superficial. Los animales fueron divididos en 3 grupos de 16 y 4 animales conformaron el grupo control 0hs. Se les administró semanalmente, por vía subcutánea en el miembro izquierdo, en la zona cercana a la intervención quirúrgica; 0,3 ml/100 g de pc de solución salina (Grupo Control); 0,5 mg de Alendronato/Kg de pc (Grupo AL) y 0,6 mg de Pamidronato/Kg de pc (Grupo PA). La cirugía se realizó con una incisión longitudinal en la tibia. Con una fresa número 6 y a rotación manual, se realizó una cavidad, se colocó el implante. Se posicionaron los planos y se suturó con hilo reabsorbible. A las 0, 15, 30, 60, 90 días se realizó la eutanasia. En cada tiempo experimental se obtuvieron muestras de sangre para realizar la medición de valores de fosfatasa alcalina; se obtuvieron radiografías de ambas tibias con radiovisiógrafo y posteriormente las tibias fueron procesadas e incluídas en resina acrílica. Se realizaron cortes por desgaste transversales al eje mayor de la tibia. Se realizó la evaluación histológica e histomorfométrica en los distintos tiempos experimentales. Se evaluó área de tejido óseo peri-implante y porcentaje de superficie ósea en contacto con el implante. Se realizó análisis de Varianza (ANOVA) a dos criterios de clasificación para los datos obtenidos de FA y de radiovisiógrafo. Los datos histomorfométricos se analizaron con test t de Student (p<0,05). Resultados: Estudios bioquímicos, FA mostró diferencias significativas entre los grupos experimentales AL y PA con respecto al grupo SF. En el estudio radiográfico, tanto en diferencia de intensidad como en zona radial, el grupo AL expresó los valores más elevados vs grupo tibias homólogas no habiendo diferencias estadísticamente significativas. Evaluación histológica: se evidenció la formación de tejido óseo de tipo laminar oseointegrado en todos los grupos a los 15, 30, 60 y 90 días, sin evidencias de necrosis o proceso inflamatorio. En relación a los resultados histomorfométricos los grupos Al y PA, no optimizaron el porcentaje de tejido óseo en contacto con la superficie del implante. Conclusiones: Podemos concluir en base a los resultados obtenidos que la administración semanal de AL o PA tuvo efectos sobre el proceso reparativo peri-implante, sin optimizar la oseointegración. El marcador bioquímico FA, la evaluación con RVG y la histomorfometría fueron métodos de evaluación óptimos ene ste modelo experimental. La correlación de los resultados permitirían proponer la valoración clínica de los implantes por medio de RVG.2023-02-01Fil: Brunengo, Ignacio. Universidad Nacional de Córdoba. Facultad de Odontología; Argentina
Variations on the Author
No full text“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Un estudio de las gramáticas de género en una organización del sector salud del Conurbano Sur, durante los años 2008 - 2015
No full textEsta investigación se concentra en analizar los procesos de selección de personal, los sistemas de promoción, las remuneraciones, las trayectorias profesionales y las instancias de capacitación según los rasgos que adquiere la división sexual del trabajo en una organización del sector salud del Conurbano Sur, durante los años 2008 - 2015. Asimismo, se analizarán las representaciones y estereotipos de género presentes en los/as responsables de las áreas de recursos humanos en cuanto a la gestión de la fuerza de trabajo. En términos metodológicos, este estudio se inscribe en el paradigma interpretativo de las ciencias sociales. La pregunta que guía esta investigación se enfoca en analizar cómo se manifiestan las gramáticas de género en las relaciones laborales en una organización pública del sector salud altamente feminizada. Por tal motivo, este trabajo retoma las técnicas provenientes de la investigación cuantitativa y de la cualitativa ya que el objetivo general del trabajo es describir, comprender e interpretar los fenómenos a través de las percepciones y significados producidos por las experiencias de los actores y actrices. De acuerdo al plan de estudios vigente, este trabajo integrador final se presenta para optar por el título de Licenciatura en Relaciones del Trabajo en la Universidad Nacional Arturo Jauretche (UNAJ).Fil: Brunengo, Andrea Paola. Universidad Nacional Arturo Jauretche. Instituto de Ciencias Sociales y Administración; Argentina.Fil: Partenio, Florencia. Universidad Nacional Arturo Jauretche. Instituto de Ciencias Sociales y Administración; Argentina
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