Bonding evolution with sintering temperature in low alloyed steels with chromium

At present, high performance PM steels for automotive applications follow a processing route that comprises die compaction of water-atomized powder, followed by sintering and secondary treatments, and finishing operations. This study examines Cr-alloyed sintered steels with two level of alloying. In chromium-alloyed steels, the surface oxide on the powder is of critical importance for developing the bonding between the particles during sintering. Reduction of this oxide depends mainly on three factors: temperature, dew point of the atmosphere, and carbothermic reduction provided by the added graphite. The transformation of the initial surface oxide evolves sequence as temperature increases during sintering, depending on the oxide composition. Carbothermic reduction is supposed to be the controlling mechanism, even when sintering in hydrogen-containing atmospheres. The effect of carbothermic reduction can be monitored by investigating the behavior of the specimens under tensile testing, and studying the resultant fracture surfaces

La altura como factor asociado a mortalidad en pacientes COVID-19 en el Perú

Determinar si la altura es un factor asociado a mortalidad en pacientes COVID-19 en el territorio peruano. Materiales y métodos: Estudio observacional de casos y controles analítico de base de datos secundaria. Se midió la asociación de la altura y la mortalidad mediante Chi cuadrado X2 de Pearson y análisis multivariado con regresión logística simple y múltiple controlando las variables edad, sexo, severidad y comorbilidades con IC 95%. Resultados: Se analizaron los datos de 616 382 pacientes durante la segunda ola en 26 regiones del Perú (47,7% de sexo femenino y 52,3% de sexo masculino) siendo la edad promedio 42,7 ± 18,2 años. La comorbilidad más frecuente fue la enfermedad cardiovascular (4,5%) y el síntoma más frecuente fue la tos (65,2 %). Las tasas de mortalidad más altas se registraron en las macrorregiones de Lima/Callao y Norte con 157 y 131/100 000 respectivamente. En el análisis bivariado la edad, sexo, grado de severidad y comorbilidades fueron significativas (p<0,001; IC 95%) por lo que entraron al análisis multivariado de regresión logística múltiple, donde se observa que residir entre 2 000-3 000 y 4 000-5 000 m s.n.m. tiene un 62% y 32 % menos probabilidad de muerte en comparación con la población que reside a menos de 1000 m s.n.m.; IC 95% OR: 0,38 (0,36 - 0,40) y OR 0,68 (0,59 - 0,80) respectivamente. En la regresión logística simple los paciente que viven entre 2 000-3 000 m s.n.m. tienen 68% menos probabilidad de morir respecto a la población que vive a menos de 1 000 m.s.n.m. OR: 0,32 (IC 95% 0,31 - 0,34). Conclusión: En la población peruana residir a más de 1 000 m s.n.m y 2 300 m s.n.m constituye un factor de protección frente a la muerte por COVID-19.To determine whether altitude is a factor associated with mortality in COVID-19 patients in Peru. Materials and methods: Observational case-control study analyzing secondary database. We measured association with Chi-square X2 and multivariate analysis with simple and multiple logistic regression controlling for age, sex, severity and comorbidities (95%CI). Results: We analyzed data from 616382 patients during the second wave in 26 regions of Peru (47.7% female and 52.3% male) with an average age of 42.7 ± 18.2 years. The most frequent comorbidity was cardiovascular disease (4.5%), the most frequent symptom was cough (65.2%). The highest mortality rates were recorded in the macro-regions of Lima/Callao and the North with 157 and 131/100 000 respectively. In the bivariate analysis, age, sex, degree of severity and comorbidities were significant (p<0.001; 95% CI) and therefore entered the multivariate analysis of multiple logistic regression, where it was observed that residing between 2 000-3 000 and 4 000-5 000 m asl has a 62% and 32% lower probability of death compared to the population residing at less than 1 000 m asl; 95%CI OR: 0.38 (0.36-0.40) and OR 0.68 (0.59-0.80) respectively. In the simple logistic regression, patients living between 2 000-3 000 m asl were 68% less likely to die compared to the population living below 1000 m asl OR: 0.32 (CI 95% 0.31-0.34). Conclusion: In the Peruvian population, residing above 1 000 m asl and 2 300 m asl is a protective factor against death from COVID-19.Tesi

Study of the optimal approach and detection phases for missions to small asteroids

Nowadays, small asteroids are catching the space community’s attention and interest. Instead of planning expensive missions to planets, missions to small asteroids (<100m) are of interest both because of their lower costs and scientific value. Small asteroids are extremely faint objects that are serendipitously discovered while they are extremely close to the Earth. After a period of only a few days, a newly discovered small object moves far enough from the Earth so that its brightness falls below the detectability threshold of current telescopes. If the length of time that the asteroid has been visible from Earth is not long enough, the uncertainty on its ephemerides may still be high. When a transfer is planned, the spacecraft is sent to a blind point since the asteroid cannot be seen from Earth. It becomes visible only the last days of the rendezvous trajectory. To ensure the meeting between the spacecraft and the object, only asteroids with very accurate ephemerides are targeted. The aim of the project is to gain an insight into optimal approach trajectories in order to ensure that a small object is detected or, failing a total certainty, maximizing the probability to detect it during the close approach. With this aim, the relative motion dynamics in the Hill coordinate frame will be studied and Matlab simulations will be performe

Examination of the community food environment and the drivers affecting and impacting obesogenicity in a deprived urban neighbourhood in Scotland

Introduction: The condition of obesity has been classified as a pandemic , given that it is negatively impacted health in almost every country in the world (1). Scotland has one of the worst obesity records in the world and one of the highest rates of all OECD countries (2). Scottish men and women in the most deprived areas had higher rates of obesity in 2016 in comparison with less deprived areas (3,4). Its alarming increasing trend year on year and the magnitude of the level of obesity over the last 30 years, coupled with the causality network which appears to be rooted in health inequities has been made obesity a titan challenge of the 21st century (1,5,6). No country in the world has reversed the challenge of obesity. The community food environment has been identified as one of the environmental causes of obesity (7–9). The high presence and accessibility of less healthy food sources appears to determine an increased availability of high-energy dense food, and the lower presence and accessibility of healthier food outlets also decreases the availability and shopping possibilities for more nutritious products (7–9). Both scenarios encourage a more frequent consumption of obesogenic food, promoting a rapid and sustained weight increase in all age groups, but especially among adults and elders (6,7,10). This thesis is the first study in Scotland that has mapped a complete foodscape or food map in a deprived neighbourhood and identify some key contributors that promote obesity. Methodology and methods: the study was conducted in a Scottish urban neighbourhood, which is low-income with high levels of poverty and obesity and poor dietary patterns. Data collection made use of a combination of different databases and approaches, including ethnographic fieldwork and online validation. Predominance, proximity and density of all type food sources, and healthier and less healthy food sources were calculated, using the Quantum Geographic Information System (QGIS) software. Food sources were categorised using 15-point classification tool, proposed by Lake et al (11). Accessibility to these sources was assessed separately for general stores and healthier and less healthy categories. Results: Findings reported a wide range of outlet types and confirmed an obesogenic food environment in the neighbourhood. Food sources related to deprivation were also present, such as food banks, whereas others such as organic food outlets which are related to more affluent areas were absent. A set of ready-made food at a low price, easy to collect or delivery at home preparations was present in over 30% of the establishments and are described in the thesis. These preparations were highly popular among the residents, and almost all the menu options were served in extra-large portions. The food outlets’ showcases were often in a deteriorated state with a preponderance of special cheap offers. Most of the establishments had a small sit-in area, while promotion of food delivery and takeaway was high. A higher proportion of less healthy food sources (27.7%) than healthy food sources (5.5%) were present within the neighbourhood. Less healthy food sources, such as fast-food outlets, takeaways, and convenience stores, were highly accessible and offered a wide range of high-energy dense foods. This scenario is known as food swamp. On the opposite side, the few healthier food sources, such as supermarkets, and fruit and vegetable stores, were located further away from households than the less healthy food sources. This scenario is known as a food desert, and alongside a food swamp, they confirmed that the geographical area mapped, anonymised to Whitewood has a highly obesogenic food environment. This environment appeared to be encouraging unhealthy eating patterns among residents and people working and studying in the area. Conclusions: This complete food exposure mapping showed for the first time in an area of intense deprivation, the features of a low-income food environment. Regarding the obesogenic characteristics of the food environment, results resonated with previous investigations. The presence of a food swamp and a food desert and the high accessibility of less healthy food in comparison with healthier establishments, is a scenario described previously in literature in other countries, including the US and Canada (12,13). According to Glanz et al. and Story et al. there are common drivers related to deprivation that influence a less healthy food shopping behaviour among residents, contributing to the weight gain process (7,8,14). Although the obesity causality network is hugely complex and several determinants can potentially influence eating patterns, the community food environments quality and accessibility may be part of the factors that encourage inhabitants to eat less healthy food regularly. Obesity causes are potentiated by health inequities, and there is an urgent need to tackle the obesity problem from the roots, using a multilevel approach (5,6,15). Intervening within the food environments in deprived neighbourhoods is part of the Scottish government new food policy; however, more articulated initiatives are needed to fight against obesity, starting from tackling the roots of poverty (16,17)

El paisaje fundacional de Tecomatlán: El mito de la Víbora Tlán a partir de la tradición oral y las prácticas festivas en San Miguel Tecomatlán, Tenancingo, Estado de México

Esta investigación se enfoca a la riqueza de cultura inmaterial en la tradición oral en San Miguel Tecomatlán, Estado de México, la cual ha sido trasmitida por generaciones, y en la que destaca particularmente la historia de “La Víbora Tlán y San Miguel”, la cual otorga fundamento y justifica la razón de ser y permanecer del “pueblo”, tomado este último, como el conjunto de vida tradicional practicada de manera secular por un grupo reconocido entre sí de pobladores que realizan actividades comunes, identificados en un territorio históricamente construido

Desarrollo de nuevos aceros sinterizados de alta resistencia aleados mecánicamente con Nb

En aceros estructurales, la reducción del tamaño de grano es el único mecanismo que permite un aumento significativo tanto de la resistencia como de la tenacidad del material. Este criterio ha sido utilizado con éxito en los aceros microaleados, en los que la acción conjunta de tratamientos termomecánicos con la incorporación en la composición de pequeñas cantidades de elementos de microaleación conduce a una microestructura muy fina que proporciona una excelente combinación de propiedades. La posibilidad de microalear mediante técnicas pulvimetalúrgicas no se ha explorado completamente debido a ciertas dificultades técnicas, como la imposibilidad de realizar tratamientos termomecánicos durante un ciclo de sinterización convencional, la dificultad de distribuir uniformemente en la microestructura cantidades tan pequeñas de aleantes, la elevada afinidad por el oxígeno de los elementos de microaleación o la necesidad de que estos reaccionen durante el ciclo de sinterización para formar una distribución de carburos eficaz para controlar el crecimiento de grano. En este trabajo de investigación se estudia la posibilidad de desarrollar nuevos aceros sinterizados de alta resistencia aleados con niobio, aplicando el concepto de afino de grano desarrollado en los aceros microaleados. De entre los elementos de microaleación, el niobio es el que posee un mayor potencial para el control del crecimiento de grano en aceros sinterizados. En los aceros microaleados ha demostrado ser eficaz para inhibir el crecimiento de grano austenítico y retrasar la recristalización de la austenita en forma de carburos o carbonitruros. Además, estando en solución sólida, es uno de los elementos de aleación que produce una mayor reducción de la movilidad de los bordes de grano en aceros mediante solute drag. Mediante el empleo de la molienda mecánica como técnica de aleación se obtienen polvos prealeados nanoestructurados en los que el niobio se puede incorporar de forma elemental o directamente como carburos. De esta manera se posibilita la comparación de los dos mecanismos de control del crecimiento de grano planteados (particle pinning y solute drag) durante la sinterización. Así mismo, el uso de técnicas de sinterización asistidas por presión (hot pressing, SPS) permite la obtención de un material completamente denso utilizando menores tiempos y temperaturas de sinterización, lo cual conlleva un control adicional del tamaño de grano. Esta tesis doctoral abarca todo el proceso de diseño de un nuevo material, desde la elección de composiciones y fabricación del polvo prealeado mediante aleación mecánica hasta la evaluación y validación de los materiales sinterizados. -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------Grain refining is the only strengthening mechanism in structural steels that increases both yield strength and toughness. This concept have been applied successfully in microalloyed steels, in which the use of thermomechanical treatmens and the addition of small quantities of microalloying elements lead to a very fine microstructure that provides a great combination of properties. Microalloying in sintered steels have not been fully explored since it involves some difficulties, like the absence of thermomechanical treatments in a conventional sintering process, the high oxygen affinity of the microalloying elements or the need to ensure a good distribution of the microalloying elements in such small quantity. Besides, the sintering process itself, as a diffusive process, requires temperature and time enough to consolidate properly the material, leading to a quite large microstructure. This work studies the development of new high strength sintered steels alloyed with niobium, and applies the concept of grain refining implemented in microalloyed steels. Niobium is the microalloying element with a higher potential to control the grain growth of steels. In microalloyed steels, niobium have proven to inhibit the grain growth and the recrystallization of austenite in the form of carbides or carbonitrides by particle pinning. But also in solid solution is one of the alloying elements of steels that provides a stronger effect in the grain boundary mobility by solute or impurity drag. Mechanical alloying allows to distribute uniformly the alloying elements in a nanostructured iron powder. Through this technique niobium can be incorporated in elemental form or directly as niobium carbide, providing the possibility to compare both mechanisms to control grain growth (particle pinning and solute drag). In addition to that, the use of special consolidation techniques, like pressure assisted sintering (hot pressing, SPS), allows to reduce the sintering temperatures and times, which helps to moderate the grain growth during sintering. This thesis involves the whole process of design of a new material, from the choice of the composition and the production of the prealloyed powder by mechanical alloying, to the evaluation and validation of the sintered materials

Teaching aids to increase the learning process in the nursing career from the University Seats.

Se realizó un estudio de  desarrollo de tipo cualitativo retrospectivo encaminado a la confección de distintos medios de enseñanza  para que sean usados en las unidades universitarias de salud de manzanillo con el objetivo de mejorar la calidad del desarrollo de las conferencias  impartidas por los profesores de estos centros docentes. En estas sedes no existen estos medios de enseñanza para desarrollar las actividades docentes con calidad. La elaboración de estos medios ayudará a mejorar la calidad de las conferencias impartidas por los profesores de las asignaturas medico quirúrgico, morfología y otras en dichos centros. Se utilizó la técnica de Papier Maché  y fue realizado por los autores de este trabajo en horas extras, que con gran amor dedican a su sentido de profesional. El método empírico empleado fue la observación por la cual se detectó que no existen estos medios didácticos para el proceso enseñanza aprendizaje.It was performed a qualitative-retrospective research to elaborate a set of different  teaching aids to be used at the university health seats in Manzanillo with the objective to improve the quality of the development of conferences given by the teachers of these teaching centers. In these places the students cannot count on teaching aids to perform the teaching activities with the required quality. The elboration of these aids will help to improve the quality of the conferences from the clinical surgical morphology and some other subjects.The Papier Mache technique was applied and it was developed by the authors of this work in extra hours. The empirical method applied was the obervation through which it was perceived that the didactic methods do not exist for the teaching learning process in the aforementioned centers

3D Visual Tracking of an Articulated Robot in Precision Automated Tasks

Abstract: The most compelling requirements for visual tracking systems are a high detection accuracy and an adequate processing speed. However, the combination between the two requirements in real world applications is very challenging due to the fact that more accurate tracking tasks often require longer processing times, while quicker responses for the tracking system are more prone to errors, therefore a trade-off between accuracy and speed, and vice versa is required. This paper aims to achieve the two requirements together by implementing an accurate and time efficient tracking system. In this paper, an eye-to-hand visual system that has the ability to automatically track a moving target is introduced. An enhanced Circular Hough Transform (CHT) is employed for estimating the trajectory of a spherical target in three dimensions, the colour feature of the target was carefully selected by using a new colour selection process, the process relies on the use of a colour segmentation method (Delta E) with the CHT algorithm for finding the proper colour of the tracked target, the target was attached to the six degree of freedom (DOF) robot end-effector that performs a pick-and-place task. A cooperation of two Eye-to Hand cameras with their image Averaging filters are used for obtaining clear and steady images. This paper also examines a new technique for generating and controlling the observation search window in order to increase the computational speed of the tracking system, the techniques is named Controllable Region of interest based on Circular Hough Transform (CRCHT). Moreover, a new mathematical formula is introduced for updating the depth information of the vision system during the object tracking process. For more reliable and accurate tracking, a simplex optimization technique was employed for the calculation of the parameters for camera to robotic transformation matrix. The results obtained show the applicability of the proposed approach to track the moving robot with an overall tracking error of 0.25 mm. Also, the effectiveness of CRCHT technique in saving up to 60% of the overall time required for image processing