Ingenieria en Tecnologia Automotriz

Introduccion. Aluminio: El aluminio es un elemento químico, de símbolo Al y número atómico 13. Se trata de un metal no ferromagnético. Es el tercer elemento más común encontrado en la corteza terrestre. Los compuestos de aluminio forman el 8% de la corteza de la tierra y se encuentran presentes en la mayoría de las rocas, de la vegetación y de los animales. Este metal posee una combinación de propiedades que lo hacen muy útil en ingeniería de materiales, tales como su baja densidad(2.700 kg/m 3) y su alta resistencia a la corrosión. Mediante aleaciones adecuadas se puede aumentar sensiblemente su resistencia mecánica (hasta los 690 MPa). Es buen conductor de la electricidad y del calor, se mecaniza con facilidad y es muy barato. Por todo ello es desde mediados del siglo XX el metal que más se utiliza después del acero. El aluminio es un elemento muy abundante en la naturaleza, sólo aventajado por el silicio y el oxígeno. Se trata de un metal ligero, con una densidad de 2700 kg/m 3 , y con un bajo punto de fusión (660 °C). Su color es blanco y refleja bien la radiación electromagnética del espectro visible y el térmico. Es buen conductor eléctrico (entre 35 y 38 m/(Ω mm 2)) y térmico (80 a 230 W/(m·K)). Características mecánicas Mecánicamente es un material blando y maleable. En estado puro tiene un límite de resistencia en tracción.Todo ello le hace adecuado para la fabricación de cables eléctricos y láminas delgadas, pero no como elemento estructural. Para mejorar estas propiedades se alea con otros metales, lo que permite realizar sobre él operaciones de fundición y forja, así como la extrusión del material. También de esta forma se utiliza como soldadura. Características químicas La capa de valencia del aluminio está poblada por tres electrones, por lo que su estado normal de oxidación es III. Esto hace que reaccione con el Oxígeno de la atmósfera formando con rapidez una fina capa gris mate de alúmina Al 2 O 3 , que recubre el material, aislándolo de ulteriores corrosiones. Esta capa puede disolverse con ácido cítrico. A pesar de ello es tan estable que se usa con frecuencia para extraer otros metales de sus óxidos. Por lo demás, el aluminio se disuelve en ácidos ybases.Reacciona con facilidad con el ácido clorhídrico y el hidróxido sódico.

Based on the 3+1 formalism for the formulation of an arbitrary reference frame and using the concept of electric and magnetic Weyl’s tensors, profound analogies between gravitational and electromagnetic field, its invariants, and specifically, among the energy-momentum field tensor in electromagnetic theory and Bel-Robinson’s (BR) or “super-energy” tensor in gravitation are established and discussed. In order to do that, original expressions for Weyl’s and BR’s tensors in terms of quasi-electric and quasi-magnetic fields were obtained. Furthermore, some theoretical consequences on the implications of the development of those analogies are outlined within the context of the yet to be directly proven experimental reality of gravitational waves.

A computational simulation of the formation of an ion beam extracted from a magnetically confined ECR plasma is made. First simulation stage consists in calculating of the electrostatic field produced by an extraction system. The extraction system is composed of three cylindrically hollow symmetrical electrodes and its respective shielding box. For the purpose of calculating the extraction and focalization electrostatic field, a finite differences algorithm that solves Laplace equation within the ion propagation volume and allows studying the dependency of the electrostatic field on the geometrical configuration of the extraction system is developed. Second stage consists in calculating the electric and magnetic fields due to extracted ions themselves by solving Poisson equation using the fast Fourier transform (FFT) technique based on a high order difference approximation with identity expansion (HODIE) scheme. Finally, an algorithm based on Boris integration scheme to calculate ion trajectories with the objective of simulating the movement on an ion beam due to the field generated by electrodes and beam itself is developed. Based upon results obtained, the search for an optimized ion extraction system from a 14 GHz ECR ion source is begun. Preliminary configurations are obtained and shown.

It is proposed that thanks to its profound philosophical roots, semiotics could be employed as a heuristic tool in philosophy of science. It is remarked that this possibility has been only slightly explored within relevant academic spheres, at least from a conscious and explicit intellectual perspective. This is manifested as a pitiful circumstance, since clear and explicit semiotics-based studies in philosophy of science are scarce, while noticeable semiotics-based studies, though non-explicit and probably even unconscious with respect of their authorship, permeate the fundamental intellectual discussion on scientific epistemology, to the point that it seems possible to state that some of them are part of the classical references on the matter without being recognized as such. Within the prospective heuristic context of semiotics on philosophy of science examples of both types of works are briefly discussed.

Se propone que la semiótica estructural, gracias a sus profundas raíces filosóficas,
podría ser empleada como herramienta de trabajo de naturaleza heurística en filosofía
de la ciencia; sin embargo, se anota que esta posibilidad ha sido poco explorada en
ambientes académicos, llamados a tomarla en cuenta, al menos partiendo desde
una perspectiva intelectual explícita y plenamente consciente; esto es una lástima,
puesto que estudios con claro y explícito fundamento semiótico en temáticas propias
de la filosofía de la ciencia escasean, mientras que estudios con claro trasfondo
semiótico, si bien inexplícito y muy seguramente inconsciente para sus autores,
permean la discusión de principio en epistemología científica hasta el punto que
resulta posible afirmar que algunos de ellos forman parte de las referencias clásicas para los estudiosos en la materia sin ser reconocidos como tales. Ejemplos de ambos
tipos de trabajos son referenciados y brevemente discutidos.

A harmonically-driven, incompressible, electrically conducting, and viscous magnetohydrodynamic flow through a thin walled duct of rectangular cross section interacting with a uniform magnetic field transverse to its motion direction is numerically investigated. Spectral collocation method is used to solve the Navier-Stokes equation under the inductionless approximation for the magnetic field in the gradient formulation for the problem. Flow is considered fully developed in the direction perpendicular to the applied external magnetic field, laminar in regime, and feasible to be core-side-layer approximated. Flow structure and key features are numerically inquired regarding prospective alternating power generation applications in a liquid metal magnetodydrodynamic generator rectangular channel configuration. It is found that in the side layer and its vicinity the emerging flow structures/patterns depend mainly on the Hartmann number and oscillatory interaction parameter ratio. Formulation developed and tested with these calculations admits implementation of a generator configuration by means of load resistance attachment and walls conductivity optimization.

A harmonically-driven, incompressible, electrically conducting, and viscous liquid metal magnetohydrodynamic flow through a thin walled duct of rectangular cross section interacting with a uniform magnetic field traverse to its motion direction is numerically investigated. Chebyshev spectral collocation method is used to solve the Navier-Stokes equation under the inductionless approximation for the magnetic field in the gradient formulation for the electric field. Flow is considered fully developed in the direction perpendicular to the applied magnetic field and laminar in regime. Validation of numerical calculations respect to analytical calculations is established. Flow structure and key magnetohydrodynamic features regarding eventual alternating power generation application in a rectangular channel liquid metal magnetohydrodynamic generator setup are numerically inquired. Influence of pertinent parameters such as Hartmann number, oscillatory interaction parameter and wall conductance ratio on magnetohydrodynamic flow characteristics is illustrated. Particularly, it is found that in the side layer and its vicinity the emerging flow structures/patterns depend mainly on the Hartmann number and oscillatory interaction parameter ratio, while the situation for the Hartmann layer and its vicinity is less eventful. A similar feature has been discussed in the literature for the steady liquid metal flow case and served as rationale for developing the composite core-side-layer approximation to study the magnetohydrodynamics of liquid metal flows usable in direct power generation. In this study that approximation is not considered and the analysis is performed on liquid metal oscillatory (i., e., unsteady) flows usable in alternating power generation. Conversely, in terms of prospective practical applicability the formulation developed and tested with these calculations admits the implementation of a load resistance and walls conductivity optimization. That means that besides representing a numerical study on the magnetohydrodynamics of the oscillatory flow under consideration, absent in the literature for the parametric ranges reported, the formulation presently implemented can also be applicable to study the performance of an alternating liquid metal magnetohydrodynamic generator in the rectangular channel configuration.

The performance characterization of a liquid metal magnetohydrodynamic alternate generator is numerically investigated via its electric isotropic efficiency. The model consists of a harmonically driven liquid metal oscillatory flow confined to a thin-walled closed rectangular duct interacting with a uniform magnetic field transverse to its motion and attached to a load resistance. Spectral collocation method is used to solve the properly boundary-conditioned Navier-Stokes equation under inductionless approximation for the magnetic field with implementation of gradient formulation for the electric field. Flow is considered fully developed in the direction perpendicular to the applied uniform magnetic field (i.e., motion direction), incompressible, viscous, and laminar in regime. Currently, there are neither purely analytical or experimental results on this problem, but ours were cross-referenced with those from a one-dimensional analytical model as close as possible to it, finding reasonable correspondence. Dimensional estimates on the power production of prospective mesoscale devices having in mind household application are provided for different liquid metals as well.

At present, the possibility of communicating or expressing oneself through an electronic medium is very wide: most users of computers and mobile devices use email, social networks, chats and other tools. One of the problems that has arisen with this form of communication is excess, such as plagiarism, false identity, intimidating notes, and others. The attribution of authorship of texts (AAT) is responsible for answering the question of who is the author of a text, giving some previous examples of that author (training set). A useful process within the AAT is the identification of gender or sex (male, female) and that has been studied by several authors, but mainly for English. The present work proposes a computational model based on lexical characteristics (n-grams) for the identification of the genre for short texts in Spanish. Tests were made with a corpus of text messages on social networks and blogs, obtaining promising results.

Due to its nutritional and economic value, the tomato is considered one of the main vegetables in terms of production and consumption in the world. For this reason, an important case study is the fruit maturation parametrized by its mass loss in this study. This process develops in the fruit mainly after harvest. Since that parameter affects the economic value of the crop, the scientific community has been progressively approaching the issue. However, there is no a state-of-the-art practical model allowing the prediction of the tomato fruit mass loss yet. This study proposes a prediction model for tomato mass loss in a continuous and definite time-frame using regression methods. The model is based on a combination of adjustment methods such as least squares polynomial regression leading to error estimation, and cross validation techniques. Experimental results from a 50 fruit of tomato sample studied over a 54 days period were compared to results from the model using a second-order polynomial approach found to provide optimal data fit with a resulting efficiency of ~97%. The model also allows the design of precise logistic strategies centered on post-harvest tomato mass loss prediction usable by producers, distributors, and consumers.

Within the Natural Language Processing (NLP), it has been considered that the syntactic analysis task represents a high computational cost, so its application to various tasks has been limited. One of these is the attribution of authorship of texts (AAT), which is responsible for answering the question of who is the author of a text, giving some previous examples of that

This work proposes an optimization tool based on genetic algorithms for the inverse design of photonic crystals. Based on target reflectance, the algorithm generates a population of chromosomes where the genes represent the thickness of a layer of a photonic crystal. Each layer is independent of another. Therefore, the sequence obtained is a disordered configuration. In the genetic algorithm, two dielectric materials are first selected to generate the population. Throughout the simulation, the chromosomes are evaluated, crossed over, and mutated to find the best-fitted one based on an error function. The target reflectance was a perfect mirror in the visible region. As a result, it was found that obtaining photonic crystal configurations with a specific stop band with disordered arrangements is possible. The genetic information of the best-fitted individuals (layer sequence, optical response, and error) is stored in an h5 format. This method of generating artificial one-dimensional ...

El estrés académico es la reacción normal que tiene el estudiante frente a las diversas exigencias y demandas a las que se enfrenta en la Universidad, tales como pruebas, exámenes, trabajos, presentaciones, etc. Esta reacción lo activa y lo moviliza para responder con eficacia y conseguir nuestras metas y objetivos. Sin embargo, en ocasiones, puede tener demasiadas exigencias al mismo tiempo, lo que puede agudizar la respuesta y disminuir su rendimiento.

Neoplasms of the peripheral nerve sheath represent essential clinical manifestations of the syndromes known as the neurofibromatoses. Although involvement of multiple organ systems, including skin, central nervous system and skeleton, may also be conspicuous, peripheral nerve neoplasia is often the most important and frequent cause of morbidity in these patients. Clinical characteristics of neurofibromatosis type 1 (NF1) and neurofibromatosis type 2 (NF2) have been extensively described and studied during the last century, and the identification of mutations in the NF1 and NF2 genes by contemporary molecular techniques have created a separate multidisciplinary field in genetic medicine. In schwannomatosis, the most recent addition to the neurofibromatosis group, peripheral nervous system involvement is the exclusive (or almost exclusive) clinical manifestation. Although the majority of cases of schwannomatosis are sporadic, approximately a third occur in families and a subset of these has recently been associated with germline mutations in the tumor suppressor gene SMARCB1/INI1. Other curious syndromes that involve the peripheral nervous system are associated with predominant endocrine manifestations, and include Carney Complex and MEN2b, secondary to inactivating mutations in the PRKAR1A gene in a subset, and activating mutations in RET respectively. In this review, we provide a concise update on the diagnostic criteria, pathology and molecular pathogenesis of these enigmatic syndromes in relation to peripheral nerve sheath neoplasia.