Fractal Analysis of Strain-Induced Microstructures in Metals

The deformation of materials is a key topic for different industrial sectors. The correlation between specific thermomechanical processes, like extrusion, rolling or additive manufacturing, and the resultant material’s microstructure, is particularly interesting. In these thermomechanical processes, the microstructure of the materials depends mainly on the applied stress, the magnitude of strain achieved in a given time period, and the temperature. In the case of metals and alloys, plastic deformation can be described microscopically based on the dynamics of a huge population of moving dislocations. Plasticity is characterized at the mesoscale by the avalanche-like collective behavior of dislocations, which is a typical case of self-organized systems. Dislocations are organized into cells named grains or subgrains that greatly influence the mechanical behavior of metals and alloys. The existence of these fractal structures of dislocations in metals is well established. However, it is very complex to conduct a fractal analysis of these microstructures. This is actually done by looking for a compromise between a detailed description of the complex fractal microstructure and the development of a practical procedure that avoids unaffordable extensive characterization in a different time and spatial scales. Several cases will be described considering different alloys and experimental conditions

Influence of the processing route on the mechanical properties at high temperatures of Mg-Ni-Y-RE alloys containing LPSO-phases

The mechanical properties at high temperatures of two Mg-Ni-Y-RE alloys prepared by conventional or powder metallurgy routes have been evaluated. All alloys exhibit high-strength up to 250°C but their strength depends more on the composition of the alloy rather than on the processing route. High strength of the alloys arises from their fine grain size but there is an additional contribution of load transfer from the magnesium matrix towards the second phases in the alloys processed by the conventional route while additional hardening in the alloys prepared by powder metallurgy is due to Orowan mechanism. Above 250°C, the strength drops to very low values but all alloys exhibit high elongations and grain boundary sliding is the controlling mechanism. Grain boundary sliding also induces cracking of the coarse second phases into smaller pieces during the initial stages of plastic deformation of conventionally processed alloys

Passivity-based control of islanded microgrids with unknown power loads

In this paper, the control problem of microgrids (MGs)operating in islanded mode is approached from a passivity-based control perspective. A control scheme is proposed that, relying only on local measurements for the power converters included in the network representation, achieves both voltage regulation and power balance in the network through the generation of grid-forming and grid-following nodes. From the mathematical perspective, the importance of the contribution lies in the feature that, exploiting a port-controlled Hamiltonian representation of the MG, the closed-loop system’s stability properties are formally proved using arguments from the theory of non-linear dynamical systems. Fundamental for this achievement is the decomposition of the system into subsystems that require a control law and another whose variables can evolve in a free way. From the practical viewpoint, the advantage of the proposed controller lies in the feature that the power demanded by the loads is satisfied without neither computing its specific value nor solving the non-linear algebraic equations given by the power flow, avoiding the computational burden associated with this task. The usefulness of the scheme is illustrated via a numerical simulation that includes practical considerations.Universidad Tecnológica de Bolíva

Modificaciones fisarias en la rata tras enclavijamiento: estudio comparativo entre implantes plásticos y metálicos

El presente trabajo se efectuó para estudiar las modificaciones locales inducidas por implantes que atraviesan el cartílago de crecimiento. Se utilizaron 20 ratas macho de 5 semanas de edad. A través de una incisión parapatelar externa se insertó una aguja de Kirschner en el fémur derecho y una de plástico en el izquierdo, ambas de 1 mm de diámetro, atravesando la placa fisaria distal. Cinco animales por grupo fueron sacrificados al cabo de 1,2,8 y 16 semanas. Tras denudar los fémures de partes blandas, su extremidad distal fue procesada para estudio histológico, histomorfométrico e histoquímico. Los resultados demuestran que desde la segunda semana la fisis tuvo mayor altura en los fémures con implante metálico, aunque las diferencias no fueron estadísticamente significativas. No se apreciaron diferencias histológicas remarcables entre las placas fisarias con uno u otro implante a lo largo del estudio. La captación de azul alcián fue asimismo similar, salvo en la decimosexta semana en que fue marcadamente menor alrededor de los implantes metálicos. Se concluye que la naturaleza del implante condiciona las modificaciones fisarias inducida por éste.A study is made of the local changes induced by implants transversing growth cartilage. Twenty 5-week-old rats were used. A Kirschner needl e 1 mm. of diameter was introduced through an external parapatellar incision into the right femur, while a plastic needle of the same dimensions was passed into the left femur. Both needles wer e advanced until the distal physeal plates wer e pierced. The rats wer e sacrificed in groups of 5 after 1,2,8 and 16 weeks. After soft tissue removal, the distal femoral ends were processed for histological, histomorphometric and histochemical study. After the second week the physeal portions wer e taller in the femurs that received metal implants, although the differences were not statistically significant. No important histological differences wer e noted between the physeal plates corresponding to either implant during the study; alcian blue uptake was likewise similar, with the sole exception of the 16th week, during which uptake was markedly less intense around the metal implants. To conclude, implant type is seen to condition the physeal change s induced

Construcción de un sistema inteligente de rehabilitación motriz para extremidades superiores basado en algoritmos de control y monitoreo

El presente trabajo de titulación denominado construcción de un sistema inteligente de rehabilitación motriz para extremidades superiores basado en algoritmos de control y monitoreo, tiene como objetivo permitir realizar una rehabilitación adecuada mediante ejercicios regenerativos, que fomente la auto rehabilitación desde la comodidad de su hogar, contando siempre con un control permanente de un especialista. El desarrollo del trabajo de investigación estuvo contemplado como primera instancia en una identificación y revisión bibliográfica sobre las medidas antropométricas, así como el desarrollo de un protocolo de rehabilitación definido para el proceso de rehabilitación de miembros superiores, posteriormente se realizó la generación de un modelo original para la asistencia al proceso de rehabilitación mediante el software Solidworks, se realizó la selección del hardware y software adecuados para la implementación de un sistema de control y un interfaz hombre máquina (HMI) para manipulación del equipo, luego se realizó la implementación del equipo de asistencia al proceso de rehabilitación, finalizando con la validación del equipo mediante pruebas de funcionamiento obteniendo valores porcentuales para los ángulos positivos con carga, con un error del 9.63% y sin carga un error del 4%, donde se muestra porcentajes admisibles en cada repetición de los distintos grados de libertad en los diferentes niveles, concluyendo con la obtención de resultados numéricos y gráficos de comparación para una validez y aceptación adecuada del prototipo. Se refleja un porcentaje mínimo de error para los ángulos negativos (sin carga - con carga), sobre todo en el grado de libertad correspondiente al codo, debido a que no es factible movimientos de recuperación menores a cero grados. Se recomienda realizar pruebas en personas de otras localidades para obtener mejores datos para ser analizados, de la misma manera, realizar simulación de cada una de las partes que conforman la estructura externa del prototipo utilizando otro software de simulación.The present degree work, called construction of an inteligent motor rehabilitatión system for upper limbs base on control and monitoring algorithms, aims to allow adequate rehabilitation through regenerative exercises, which promotes self-rehabilitation from the comfort of your home, always under the continuous control of a specialist. The development of the research work was contemplated as a first instance in an identification and literature review on anthropometric measurement, as well as the development of a rehabilitation protocol defined for the rehabilitation process of upper limbs, then the generation of an original model for the assistance to the rehabilitation process using SolidWorks software, the selection of appropriate hardware and software for the implementation of a control system and a human machine interface (HMI) for handling the equipment was performed. Then, the implementation of the equipment to assist the rehabilitation process was performed, ending with the validation of the equipment through functional tests obtaining percentage values for the positive angles with load, with an error of 9.63% and without load an error of 4%, where admissible percentages are shown in each repetition of the different degrees of freedom in different levels, concluding with the obtaining of numerical results and comparison graphs for an adequate validity and acceptance of the prototype. A minimun percentage of error is reflected for the negative angles (without load – with load), especially in the degree of freedom corresponding to the elbow, due to the fact that recovery movements of less than zero degrees are not feasible. It is recommended to perform tests on people from other locations to obtain better data to be analyzed, in the same way, to perform simulation of each of the parts that make up the external structure of the prototype using other simulation software

Detection of capsinoids by ESI-mass analysis

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Influence of Fruit Ripening on the Total and Individual Capsaicinoids and Capsiate Content in Naga Jolokia Peppers (Capsicum chinense Jacq.)

"Naga Jolokia" (Capsicum chinense Jacq.) is a hot pepper variety native to India which has received the attention of the global scientific community due to its high capsaicinoid concentration. The present study evaluated the influence of fruit ripening on the total and individual capsaicinoids, as well as capsiate content. The aim was to determine the optimal moment to harvest the peppers depending on their pungent properties. Ultrasound-assisted extraction (UAE) using methanol as the extraction solvent and reverse-phase ultra-high-performance liquid chromatography (UHPLC-photodiode array (PDA)) were employed. Capsaicinoids gradually accumulated in the peppers from the moment they started growing until they reached a maximum concentration (7.99 +/- 0.11 mg g(-1) of fresh weight (FW)) at 33 days postanthesis (dpa). For this reason, based on its content of pungent compounds, as it is one of the main attributes of this variety, the optimal time for collection would be on day 33. From then on, there was a sharp decrease (96.35% of the total concentration) due to the peroxidase enzymes. The evolution of the principal capsaicinoids in "Naga Jolokia" peppers had a different behavior with respect to literature reports. After this investigation, these changes in content can be attributed to each pepper genotype. Capsiate content reached it maximum value at 19 dpa (0.27 +/- 0.01 mg g(-1) of FW). Then, there was a gradual drop due to the activities of different peroxidases. Given the important biological activity of capsaicinoids and capsinoids, the information described here allows for determining the ideal time to harvest "Naga Jolokia" peppers

Apoyo familiar y docente percibido:

Using the data from the First Survey of Human Development in Children and Adolescents held in Chile in 2017, the perception that students have of the classroom, school and family to which they belong is analyzed, as new indicators of educational quality. Highlights the high perceived value of the family and teacher support. Parents and teachers are positioned as positive figures for the student as they provide emotional comfort and foster environments of respect and opportunities for expression, being elementary components for the sense of well-being, generation of learning conditions and development of prosocial behaviors. Results that emphasize the necessary family-school imbrication for future strategies of educational improvement.Utilizando los datos de la Primera Encuesta de Desarrollo Humano en Niños, Niñas y Adolescentes realizada en Chile en el año 2017, se analiza la percepción que los estudiantes tienen del aula, colegio y familia a la cual pertenecen, en tanto constituyen nuevos indicadores de la calidad educativa. Al respecto, destaca la alta valoración en relación con el apoyo familiar y docente percibido. Los padres y los profesores se posicionan como figuras positivas para el alumno al brindar confort emocional y propiciar ambientes de respeto y oportunidades de expresión, que son componentes elementales para la sensación de bienestar, generación de condiciones para el aprendizaje y desarrollo de conductas prosociales. Los resultados enfatizan la necesaria imbricación familia-escuela para futuras estrategias de mejoramiento educativo