Vol. 65 No. 1 Jan-Jun (2019): Revista Mexicana de Física E

To model wealth distributions there exist models based on the Boltzmann-Gibbs distribution (BGD), which is obtained by simulating binary economic interactions or exchanges that are similar to particle collisions in physics with conserved
energy (or money in econophysics). Also, BGD can be reproduced by numerical simulations of diffusion for many particles which experience energy fluctuations. This latter case is analogous to non-interacting pollen particles performing Brownian motion. In order to decrease inequality, we also modify the energy-conserved diffusion by taxing the richest agent. In all cases, we calculate the corresponding Gini inequality index and the time evolution of the entropy to show the stability of the statistical distributions.

General Relativity describes gravity in geometrical terms. This suggests that quantising such theory is the same as quantising geometry. The subject can therefore be called quantum geometry and one may think that mathematicians are responsible of this subject. Unfortunately most mathematicians are not aware of this beautiful area of study. Here we give a basic introduction to what quantum geometry means to a community working in a theory known as loop quantum gravity. It is directed towards graduate or upper students of physics and mathematics. We do it so from a point of view of a mathematician.

Tchebycheff Polynomials are obtained thorough linear algebra methods. A matrix
corresponding to the Tchebycheff differential operator is found and its eigenvalues are obtained. The elements of the eigenvectors obtained corresponds to the Tchebycheff polynomials.

1,- RESUMEN

 

Este trabajo muestra el diseño de una sensible y versátil alarma sísmica basada en elementos de bajo costo o desechos, sustentada en principios y fenómenos físicos básicos tales como: Principio de inducción electromagnética de Faraday, momento angular, amplificador operacional, retraso de pulso, movimientos sísmicos, etc. El sensor de la alarma es una poderosa bobina móvil proveniente de un disco duro de computador, la señal es magnificada por un amplificador operacional µA741 y el pulso de alerta tiene duración ajustada por un circuito integrado “timer” µA 555.

 

 

 

ABSTRACT

This work shows the design of a sensitive and versatile seismic alarm using low-cost items or waste. The design is based on basic principles and physical phenomena such as: electromagnetic induction of Faraday, operational amplifier, angular momentum, delay of pulse, seismic movements, etc. The alarm sensor consist of a powerful mobile coil from a computer hard drive, the signas is amplfied by an oprational amplifier µA741, and the audible pulse has a duration that is programable by an integrated circuit (timer) µA 555.

From the first observations made by Slipher, our understanding and interpretation of the cosmological redshift was evolving until reaching the current consensus, through the expanding universe and the emergence of modern physical cosmology within the framework of General Relativity. The redshift is one of the most basic concepts of astronomy, and is one of the few observational parameters that can be measured directly. To refer to the temporal evolution of objects or cosmic structures in the universe, we often do so indistinctly through cosmic time or cosmological redshift. But repeatedly this connection ends up generating confusion not only among popular science communicators but also within the professional astronomical community. In this article, we will make a pedagogical approach to the link between cosmic time and cosmological redshift, and we will also clarify several common misunderstandings around this relation.

We present an analogy between the one dimensional Poisson equation in inhomogeneous media and the Dirac equation in one space dimension with a Lorentz scalar potential for zero energy. We illustrate how the zero energy state in the Jackiw-Rebbi model can be implemented in a simple one dimensional electrostatic setting by using an inhomogeneous electric permittivity and an infinite charged sheet. Our approach provides a novel insight into the Jackiw-Rebbi zero energy state and provides a helpful way to visualize and teach this important quantum field theory model using basic electrostatics.

Las estrellas Cefeidas han sido de gran relevancia para la determinación de distancias tanto en la Galaxia como a escala cosmológica. Debido a que, hasta el momento, la mayor parte de las Cefeidas cercanas observadas se encuentran en la vecindad solar, se juzga pertinente un estudio probabilístico sobre su distribución, no solo en la vecindad solar sino también en toda la Vía Láctea, pues deben estar jugando un papel importante para mantener la estructura de nuestra Galaxia. Partiendo de 187 Cefeidas observadas en la Vía Láctea, se presenta una función de densidad de probabilidad normal que sirvió para elaborar un modelo en tres dimensiones que permite encontrar la zona de más alta concentración de Cefeidas y de paso, con ella, predecir la existencia de Cefeidas en zonas ceranas a toda la Galaxia. Asmismo, se da a conocer una segunda distribución de probabilidad, normal también, pero en la vecindad del eje galáctico, a fin de elaborar otro modelo que permita predecir la existencia de estrellas Cefeidas dentro de la Vía Láctea y en la vecindad del sol.

ABSTRACT

The Cepheid stars have been very relevant for the determination of
distances both in the Galaxy and also at cosmological scale. Because, so far, most of the nearby observed Cepheids are in the solar neighborhood, a probabilistic study about their distribution in the solar neighborhood and in the whole Milky Way is pertinent, since they must be playing an important role for keeping the structure of our Galaxy. Starting from the in the Milky Way already 187 observed Cepheids, a normal probability density function for their distribution in the Galaxy is presented, which is used to carry out a model which allows to find the high concentration zone of Cepheids and, in turn, with it, to predict the existence of Cepheids in the neighborhood of the Galaxy. A second model has been done, in order to prognosticate the existence of Cepheids within the milky way and in the neigborhood of the sun.

The educational model (Science, Technology, Engineering and Mathematics) proposes among its activities the development of the skills that students must acquire from initial levels. This article consists of the fact that this pedagogical construct can determine, through interdisci- plinary collaborative projects, professional skills for the development of I + D + i activities for the estimation of the electric demand in marginal rural and urban areas of the Guayaquil canton. The model promotes some learning strategies in the
students of the basic level of Industrial Engineering at the University of Guayaquil from the emotional, experiential and collaborative point of view in non-formal envi- ronments. To assess the model, a mixed type of research was carried out that took a heterogeneous sample of 83 volunteer subjects, all of them aged between 18 and 25 years. An ad hoc questionnaire of learning strategies was used in which each learning cycle selected an item mode admitted a triple response. The first one refers to the skills offered by the (Science, Technology, Engineering and Mathematics) model perceived from the student’s own personal experience. The second dimension referred to the motivational learning strategies and finally, the degree of acceptance of the didactic model. The application of this model demonstrates the development of the effective dimension of technology to work collaboratively and the acceptance of the construct. (Science, Technology, Engineering and
Mathematics) as a means for training university students in I + D + i

El modelo educativo STEM (Ciencia, Tecnología, Ingeniería y Matemáticas) propone entre sus actividades el desarrollo de las habilidades que debe adquirir los estudiantes desde niveles iniciales. Este artículo consiste en que este constructo pedagógico puede determinar, a través de proyectos colaborativos interdisciplinarios, habilidades profesionales para el desarrollo de actividades I + D + i para la estimación de la demanda eléctrica en zonas rurales y urbanas marginales del cantón Guayaquil . El modelo promueve algunas estrategias de aprendizaje en los estudiantes del nivel básico de la Ingeniería Industrial de la Universidad de Guayaquil desde el punto de vista emocional, experiencial y colaborativo en ambientes no formales. Para la valoración del modelo, se realizó una investigación de tipo mixta que tomó una muestra heterogénea de 83 sujetos voluntarios, todos ellos con edades comprendidas entre 18 y 25 años. Se utilizó un cuestionario ad hoc de estrategias de aprendizaje en el que cada ciclo de aprendizaje seleccionaba un modo de ítem admitía una triple respuesta. La primera se refiere a las habilidades que ofrece el modelo STEM percibida desde la propia experiencia personal del estudiante. La segunda dimensión hizo referencia a las estrategias de aprendizaje motivacional y por último, el grado de aceptación del modelo didáctico. La aplicación de este modelo demuestra el desarrollo de la dimensión efectiva de la tecnología para trabajar colaborativamente y la aceptación del constructo. STEM como medio para la capacitación de estudiantes universitarios en actividades I + D + i.

El calentamiento global antropogénico es un fenómeno físico que se ha ido incrementando, generando efectos negativos que están afectando cada vez más a los ecosistemas terrestres. En este trabajo se instruye al lector en los fundamentos y procesos físicos básicos que lo producen, dándole elementos confiables para tomar mejores decisiones y coadyuvar a la disminución de los efectos nocivos. La secuencia didáctica propuesta, conduce lógicamente a la conclusión de que la civilización atraviesa por una crísis climática grave, la cual obliga a los países y al habitante común a hacer  una reflexión profunda sobre su responsabilidad en dicho fenómeno y a utilizar herramientas analíticas para apreciar avances o retrocesos en la implementación de estrategias a nivel internacional para enfrentar el problema.

Anthropogenic global warming is a physical phenomenon that has been increasing, generating negative effects that are affecting terrestrial ecosystems. In this work, the reader is instructed in the foundations and basic physical processes that produce providing reliable elements to make better decisions and contribute to the reduction of harmful effects. The didactic sequence proposed, logically leads to the conclusion that civilization is going through a severe climate crisis, which forces countries and the common inhabitant to make a profound reflection on their responsibility in this phenomenon and to use analytical tools to appreciate progress or setbacks in the implementation of strategies at an international level to face the problem.

We present a simple low-cost electronic circuit that is able to show two different dynamical regimens with oscillations of voltages and with constant values of them. This device is designed as a negative feedback three-node network inspired in the genetic repressilator. The circuit's behavior is modeled by a system of differential equations which is studied in several different ways by applying the dynamical system formalism, making numerical simulations and constructing and measuring it experimentally. We find that the most important characteristics of the Hopf bifurcation can be found and controlled. Particularly, a resistor value plays the role of the bifurcation parameter, which can be easily varied experimentally. As a result, this system can be employed to introduce many aspects of a research in a real physical system and it enables us to study one of the most important kinds of bifurcation.

Earth's magnetosphere, beyond protecting the ozone layer, is a natural phenomena which allows to study the interaction between charged particles from solar activity and electromagnetic fields. In this paper we studied trajectories of charged particles interacting with a constant dipole magnetic field as first approach of the Earth's magnetosphere using different initial conditions. As a result of this interaction there is a formation of well defined radiation regions by a confinement of charged particles around the lines of the magnetic field. These regions, called Van Allen radiation belts, are described by classical electrodynamics and appear naturally in the numerical modeling done in this work.

After reviewing how the Dirac delta contributions to the electrostatic and magnetostatic fields of a point electric dipole and a point magnetic dipole are usually introduced, we present an alternative procedure for obtaining these terms based on a regularization prescription similar to that used in the computation of the transverse and longitudinal delta functions. We think this method may be useful for the students in other analogous calculations.

En este trabajo se presentan las principales aportaciones de Leonhard Euler a la mecánica, que van desde la invaluable transcripción de la mecánica newtoniana al lenguaje del cálculo diferencial e integral, hasta su peculiar interpretación, en términos de la impenetrabilidad, de la Tercera Ley de Newton, pasando por su profunda valoración del concepto de inercia y su aportación relativa a plantear la Segunda Ley de Newton en coordenadas cartesianas.

 

In this work it is presented the Leonhard Euler more important contributions to mechanics, from the invaluable transcriptions of the newtonian mechanics to integral and diferential calculus, up to his peculiar interpretation of the Newton’s Third Law in terms of the impenetrability, going through his profound evaluation about the inertia concept and his great idea to pose the Newton’s Second Law in cartesians coordinates.

En este artículo se discute la pregunta: ¿Cómo sabemos que los átomos existen? Esto a partir de un análisis físico y filosófico de algunas de las pruebas y argumentos históricamente más relevantes, incluyendo, en orden cronológico: 1) la Ley de las proporciones definidas o Ley de Proust, 2) La Teoría Cinética de los Gases, 3) El Movimiento Browniano y las 4) imágenes de microscopio de efecto túnel. La discusión filosófica se centra en los argumentos de realismo y anti-realismo científico, así como en diversos argumentos metodológicos, por ejemplo: ¿Debemos confiar en una afirmación sobre la naturaleza solamente porque es parte de una teoría científica empíricamente exitosa? Pocas personas pueden exponer dudas razonables sobre la existencia o no, de átomos y este artículo presenta algunas de las aristas más destacadas de esta relevante discusión científica, histórica y filosófica.

 

In this article the question: How do we know atoms exist? Is discussed. This is done starting from a physical and philosophical analysis of some of the most relevant historical evidences and arguments. In chronological order they are: 1) The Law of Definite Proportions or Proust’s Law, 2) The Kinetic Theory of Gases, 3) The Brownian Motion and, 4) Images taken by STM (Scanning Tunneling Microscope). The philosophical discussion is focused on arguments regarding scientific realism and anti-realism, as well as on methodological
arguments, for example: i) Should we believe a statement about nature only because it follows from an empirically successful scientific theory? And ii) If the scientific theories are designed to achieve empirical success and mathematical adequacy. Why should be strange that sometimes they have
huge empirical evidence and sometimes not? Very few people can provide reasonable doubts about the existence (or non-existence) of atoms and this article present some of the most prominent issues of this important scientific,
historic and philosophical discussion.