Motility of Swimming Bacteria Hydrodynamics and Statistics

The present work contains original research on the field of biophysics, specifically the study of swimming bacteria. Swimming microorganisms can be modeled as active particles moving at low Reynolds number (Re ≪ 1) and subject to different sources of noise. The term “active” means that they are self-propelled, while Re ≪ 1 implies that their motion is dominated by viscous stresses, therefore relying on non-reciprocal deformations in time, in order to achieve movement. Noise arises from thermal fluctuations and the inherent stochasticity of their propelling machinery, as a result, bacteria follow random trajectories. Nevertheless, bacteria have evolved to display a number of strategies to overcome randomness and achieve directed locomotion, known as “taxis”. Here, we explore the mechanisms involved in the propulsion and navigation of swimming bacteria, using low Reynolds number flow techniques and random walks. First, we introduce the physical principles that govern the dynamics of a low Reynolds number swimmer. We pay special attention to the random walk model for the description of the swimming trajectories, since it allows to quantify motility in terms of statistical measures, such as diffusivity and drift velocity, which can be measured experimentally. After a general discussion of the model, we demonstrate its use by applying it to the dynamics of bacteria-driven microswimmers, which are active particles that use bacteria as a propulsion mechanism. We show in particular, that the diffusivity of such particles increases with the square of their size and that the microswimmers inherit the chemotactic capabilities from the bacteria that propel them. These results are in agreement with experiments and can be useful to improve the design of these artificial microswimmers. Next, we investigate the motility properties of Spiroplasma melliferum, which is special among bacteria, as it can swim without flagella. Instead, Spiroplasma can switch the handedness of its helical body and in the process, the helical domains rotate generating propulsion. Based on experimental observations, we develop a hydrodynamic model to describe Spiroplasma motility. We obtain expressions for the total linear and angular displacements of the cell body per swimming stroke. Observing that the cell body does not reorient at the end of one period, we define an effective swimming speed and a hydrodynamic efficiency. Then, we show that the helical shape that maximises speed and efficiency has a pitch angle close to that of Spiroplasma, φ ≃ 35◦, in agreement with experimental observations and with previous numerical simulations. Finally, we explore the dynamics of a low Reynolds number swimmer crossing a viscosity gradient. This is a work in collaboration with experimental groups in the National University of Mexico (UNAM) and Brown University. The experiments aim to shed light on the dynamics of the bacterium Helicobacter pylori, which inhabits the human gut and is capable of penetrating the mucus layer that protects the stomach. Experimentally, a magnetic swimmer is immersed in a stratified solution of miscible fluids with different viscosities. The swimmer consists of a helical tail and a cylindrical head that rotate at a fixed rate due to the action of an external magnetic field. As the swimmer advances, it accelerates or slows down, depending on its orientation with respect to the gradient. In general, the experimental results show that it is harder for a pusher-like swimmer to swim up the gradient, whereas for a puller-like swimmer it is the opposite. We rationalize this mathematically by assuming that the forces acting on the swimmer depend on the local viscosity that it experiences. This allows us to calculate the swimming speed as a function of the swimmer’s position along the gradient. The predictions of the model are in good agreement with the experimental observations. The results also suggest that viscotaxis is possible without viscoreceptors, and in fact governed solely by the motility pattern of the swimmer. Together, the results presented in this thesis contribute to the understanding of bacterial motility and low Reynolds number swimmers in general. Furthermore, these results may be useful for future developments in biophysics, including applications to targeted drug delivery and microrobotics.European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement 682754 to Eric Lauga

Implementación de paneles solares para minimizar el consumo de energía eléctrica en viviendas de Guayaquil.

El presente proyecto de investigación determina la factibilidad económica para la comercialización de paneles solares en la ciudad de Guayaquil. Las elevadas temperaturas han contribuidos para que sea una realidad la implementación de dichos instrumentos, necesarios en la vida cotidiana de cada persona que habita en la cuidad. En el capítulo 1 se reconocerán las teorías que ayuden a solventar el estudio de la investigación en proceso, con ello se identificarán los escenarios existentes y sus implicaciones con relación al trabajo. En el capítulo 2 se mostrarán los estudios realizados y sus respectivos resultados, basados en deducciones realizadas posterior a los métodos de investigación aplicados, dentro de ella se identificarán las posibles ventajas y desventajas de la investigación. En el capítulo 3 se analizarán los resultados y si realizara su respectivo resumen de las encuestas y entrevistas con los datos elaborados del capítulo anterior. En el capítulo 4 se realizará un análisis a los resultados obtenidos dentro del capítulo anterior y esto permitirá realizar un comparativo con otras investigaciones En el capítulo 5 se pone en marcha la propuesta de la investigación reflejando las mejoras considerables que mostrara la aplicación de los paneles solares en la ciudad de Guayaquil. Se realiza la recomendación y conclusiones de la investigación, así como los pasos a seguir posterior a la implementaciónThis research project determines the economic feasibility for the commercialization of solar panels in the city of Guayaquil. The high temperatures have contributed to make the implementation of these instruments, necessary in the daily life of every person living in the city, a reality. Chapter 1 will recognize theories that help solve the study of research in process, which will identify the existing scenarios and their implications in relation to work. Chapter 2 will show the studies carried out and their respective results, based on deductions made after the applied research methods, within which it will identify the possible advantages and disadvantages of the research. Chapter 3 will analyze the results and if you make your respective summary of the surveys and interviews with the data elaborated in the previous chapter. In chapter 4 an analysis will be made to the results obtained within the previous chapter and this will allow to make a comparative with other investigations. Chapter 5 sets out the research proposal, reflecting the considerable improvements in the application of solar panels in the city of Guayaquil. The recommendation and conclusions of the research are made, as well as the steps to follow after the implementatio

“TRASPASOS ENTRE AFORES EN EL SISTEMA PENSIONARIO EN MÉXICO 2011-2016: UN ANÁLISIS BIMESTRAL CON CADENAS DE MARKOV”

En 2015, se publicaron modificaciones regulatorias a diversos aspectos operativos del Sistema de Ahorro para el Retiro (Boletín CUO y Boletín Circular Agentes Promotores) con el fin de garantizar mejores prácticas comerciales y proveer mayor calidad de los servicios proporcionados por las Afores. VI Los cambios a la Circular Única Operativa (CUO) y a la Circular de Agentes Promotores plantean por primera vez la digitalización del SAR a través de la creación de expedientes electrónicos (tanto de los ahorradores como de los Agentes Promotores), y por tanto, la migración a un esquema de mayor seguridad en el manejo de datos personales y optimización de costos para los trabajadores y para las Afores. En este sentido, las modificaciones al marco normativo incluyen también ajustes en un tema central del SAR: un Nuevo Modelo de Traspasos (CONSAR, 2015) que ayudará a fortalecer la toma de decisiones de los ahorradores en este rubro. Gran parte de los traspasos son producto de la actividad comercial generada por los Agentes Promotores sin que necesariamente sean los trabajadores quienes estén buscando el cambio (CONSAR, 2015), por ello, fue que se modificó la CUO, una de las columnas normativas del Sistema de Ahorro para Retiro, con dos fines centrales: fomentar mayor participación y racionalidad de los ahorradores que desean cambiar de Afore para que elijan una mejor opción y garantizar que los Agentes Promotores se conduzcan con las mejores prácticas (CONSAR, 2015). Al cierre de diciembre del 2014 el Sistema de Ahorro para el Retiro registró 2’436,697 traspasos (la cifra más alta en los últimos 5 años) por un monto de 313,501.5 millones de pesos equivalentes al 13.4% del total de los recursos administrados por las AFORE (CONSAR, 2015)

Importance of molecular interactions in colloidal dispersions

We review briefly the concept of colloidal dispersions, their general properties and some of their most important applications, as well as the basic molecular interactions that give rise to their properties in equilibrium. Similarly, we revisit Brownian motion and hydrodynamic interactions associated with the concept of viscosity of colloidal dispersion. It is argued that the use of modern research tools, such as computer simulations, allows one to predict accurately some macroscopically measurable properties by solving relatively simple models of molecular interactions for a large number of particles. Lastly, as a case study, we report the prediction of rheological properties of polymer brushes using state of the art, coarse grained computer simulations, which are in excellent agreement with experiments.Comment: 8 pages, 10 figure

Implications of Message Length and Delay in Undergraduate Online Discussions

This study aimed at verifying the association of message length and delay in university online discussions with academic achievement and students' influence on their classmates. Forums in Moodle were designed, and asynchronous online discussions with first-year undergraduate students of Educational Sciences were conducted. We gained word count from the learning management system, the weekly delay in posting a message to the forum was regarded, and we assumed the students' grades to know their academic success. To obtain an indicator of influence, we conducted a social network analysis from the interactions that emerged from the online discussions. Then, we calculated the eigenvector centrality of each student once the debate had been completed. Results showed a low monotonic association between grades and the message words or the delay in posting. There was a slight trend to achieve more eigenvector centrality since students took more time to send a message and when messages were more synthetic. However, we did not obtain values in the coefficients that would allow us to infer a relevant association. The level of correlation detected for the grades was significant and, above all, regarding eigenvector centrality. We discussed the limitations of this study, the need for more research, and the implications for educational practice.El objetivo de este estudio fue comprobar la relación de la extensión y la demora de los mensajes en discusiones en línea con la influencia entre estudiantes y el rendimiento académico en la universidad. Se diseñaron foros en Moodle y se llevaron a cabo discusiones asíncronas en línea con estudiantes de primer año de Ciencias de la Educación. Obtuvimos el recuento de palabras desde el sistema de gestión del aprendizaje, consideramos el retraso semanal para publicar mensajes en el foro y tomamos las calificaciones de los estudiantes para conocer su éxito académico. Para obtener un indicador de influencia, llevamos a cabo un análisis de redes sociales a partir de las interacciones en los debates. Después calculamos la centralidad de vector propio para cada estudiante, una vez finalizado el debate. Los resultados mostraron una correlación monotónica baja entre las notas y la extensión de los mensajes o el retraso en publicarlos. Hubo una ligera tendencia a conseguir más centralidad de vector propio a medida que se tardaba más en enviar un mensaje y cuando los mensajes eran más sintéticos. Sin embargo, no hubo valores en los coeficientes que permitieran inferir una asociación sustantiva. El nivel de correlación detectado para las calificaciones fue significativo, sobre todo para la centralidad del vector propio. Discutimos las limitaciones del estudio, la necesidad de más investigación y las implicaciones para la práctica educativa

Characterization of nanostructured SnO2 films deposited by reactive DC-magnetron sputtering

Nanostructured tin oxide thin films were deposited on silicon and glass slides substrates by reactive DC-Magnetron sputtering using a tin target in a mixture of argon and oxygen gases. The substrate temperature was varied in the range from 53 to 243 oC, keeping the other deposition parameters constant. The tin oxide films were characterized by: Scanning Electron Microscopy, Energy Dispersive Spectrometry, X Ray Diffraction, microRaman spectroscopy and UV-VIS spectroscopy. It was found that the substrate temperature has an effect mainly on the structural, morphological and optical properties of the thin films. At 53 and 90 oC the tetragonal crystalline phase was obtained while a mixture of crystalline phases (o-SnO2 and t-SnO2) was obtained at 148, 185 and 243 oC

Los derechos sucesorios a favor del cónyuge supérstite en segundas nupcias contraídas de buena fe

La presente investigación tuvo por finalidad regular derechos sucesorios, en el Código Civil Peruano, al cónyuge supérstite que ha contraído matrimonio de buena fe en segundas nupcias, con el objetivo de cautelar la dignidad del consorte afectado con la declaratoria de nulidad del aparente matrimonio. Para lograr ello, se trabajó con una muestra constituida por 3 Jueces Especializados, 2 Jueces de Paz Letrado y 60 abogados con conocimiento en Derecho Familia o Sucesiones delICAL, utilizando un diseño de investigación cuantitativo, de tipo aplicada descriptivay nivel explicativo; así mismo, como técnica de recolección de datos la encuesta y como instrumento el cuestionario, aplicándose el Método Kuder-Richardson (KR20)para la obtención de la confiabilidad. Por otro lado, se obtuvo como resultado, que el 63.1% de la muestra encuestada consideró, que se protege la institución familiar a través de una regulación normativa en la que se reconozca derechos sucesorios al cónyuge putativo; mientras que, el 36.9% restante, respondió lo contrario; pudiéndose comprobar la hipótesis planteada, siendo necesario que el Código Civil regule expresamente derechos sucesorios a favor del cónyuge supérstite, en el caso de un matrimonio putativo, a fin de proteger a la prole y las relaciones jurídicas generadas con terceros

α-FAPbI3 powder presynthesized by microwave irradiation for photovoltaic applications

The development of up-scalable and high-throughput methodologies to fabricate high-efficiency lead halide perovskite solar cells (PSCs) based on α-phase formamidinium lead iodide (FAPbI3) is one of the main challenges of making solar energy economical. In this context, PSCs based on α-phase formamidinium lead iodide (FAPbI3) are receiving special attention as this perovskite has the highest theoretical photoconversion efficiency (PCE). This manuscript reports an easy, fast and environmentally-friendly way to prepare α-FAPbI3 black powders by a microwave-assisted synthesis and their application in solar cells. The α-FAPbI3 powders consist of micrometric particles that can be stored for weeks in a closed vial at ambient conditions. This technique presents an enormous potential for upscaling FAPbI3 powders synthesis prerequisite necessary for large scale commercialization. The performance of the presynthesized FAPbI3-based solar cell was comparable with that of PSCs fabricated with the conventional procedure from precursors solutions, leading to a maximum PCE value of 18.15%, with an VOC=1.07 V, a Jsc=24.28 mA/cm2 and an FF=70%. The presynthesized FAPbI3-based solar cell was further modified through the addition of methylammonium chloride (MACl) in order to study the generality of the approach. The optical band gap for the presynthesized perovskite shifted from ∼1.43 eV to ∼1.55 eV with the MACl addition (30 mol%), indicating the formation of a mixed methylammonium and formamidinium based perovskite material (MAFAPbI3). In addition, the incorporation of MACl led to an increase in the grain size and the disappearance of the residual δ-phase perovskite, thus improving the efficiency of the final device.Funding for open access charge: CRUE-Universitat Jaume