Universidad Nacional Experimental Marítima del Caribe

Este artículo presenta las producciones de diseño y construcción de un robot de limpieza, elaboradas por estudiantes de tercer año de la educación media general venezolana, en el contexto de un ciclo de Alfabetización Matemática. Se asume la Alfabetización Matemática como un proceso social y educativo que forma al ciudadano y le da poder para ir a comprender su realidad, al mismo tiempo que transforma el acto educativo en uno más humano, democrático y Liberador, abordando integralmente la problemática de la enseñanza de las Matemáticas. La experiencia se guía por los principios de la investigación acción, participativa y transformadora, dejando en evidencia los conocimientos de los estudiantes sobre la geometría espacial en el diseño del robot, la lógica proposicional de los circuitos eléctricos para su funcionamiento, las leyes del movimiento y circuitos eléctricos. Esto ejemplifica cómo las experiencias de Alfabetización Matemática, partiendo de los intereses de los estudiantes, conllevan a contextos matemáticos que se interconectan. Además, observa una transformación en sus subjetividades con respecto al trabajo y aprendizaje en equipo.

Mathematical modeling within the framework of the general theory of relativity has been used to explain the behavior and structure of massive objects as neutron stars, quasars, black holes, pulsars and white dwarfs and requires finding the exact solutions of the Einstein-Maxwell system. In this paper we study the effects induced by fluctuations of local anisotropy in a new family of anisotropic solutions depending on a parameter α, whose value α=2 provides a radial pressure having the same functional dependence on the radial coordinate as the Schwarzschild solution. It is shown the effect the functional dependence on the radial coordinate has in the occurrence of cracking within the sphere when anisotropy fluctuations are allowed.

The general theory of relativity has allowed a better understanding of the structure of universe. One of the fundamentals problems in the general relativity is finding exact solutions of the Einstein-Maxwell field equations. Some solutions found applications in astrophysics, cosmology and more recently in the developments inspired by string theory. In this paper, we presented a compact object model in the framework of Einstein-Gauss-Bonnet gravity (EGB) with a linear equation of state considering a metric potential proposed for Buchdahl (1959). The new obtained models satisfy all physical requirements of a physically reasonable stellar object. We analyzed the effect of the Gauss-Bonnet coupling constant α on the main physical characteristics of the model. We checked that the radial pressure, energy density and anisotropy are well defined and are regular in the interior of the star and are dependent of the values of the coupling constant.

The main interest of the current research study is, on the one hand, to increase heat transfer of the base and mixture fluids by using hybrid nanoparticles. By considering two types of boundary conditions such as insulated and convective tips, to explore numerically and analytically the simultaneous impacts of the thermal radiative and free convective flow of hybrid nanofluid via a moving porous longitudinal fin. This investigation employs Darcy’s model and the mixture base fluid H2O (50%)–C2H6O2 (50%). The governing equations have been solved by utilizing Runge–Kutta–Fehlberg 4th–5th order technique (RKFT45) with shooting-scheme and analytically via Duan–Rach Approach (DRA). It is found that the nondimensional temperature θ ( η ) is a decreasing function of a wet porous number m 2 and convective parameter Nc for both insulated and convective tips, and as an increasing function of ambient temperature θ a , Peclet number Pe and power index n. It is also found that the thermal profile θ ( η ) presents a decrease for all considered shape factors in the cases of insulated and convective tips boundary conditions. Computational results and those obtainable in the previous works have been used to verify and strengthen the results gained by the analytical DRA technique.

This work presents a tracking method that is easy to design and implement. In particular, it is considered the tracking of a predefined trajectory whose temporal derivatives are known. This anticipated information of the desired reference signal allows, by employing a guaranteed dominant pole placement criterion, the formulation of a control law that uses the conventional feedback error compensation together with the anticipated knowledge of the derivatives of the reference signal. This provides substantial improvements in the closed-loop behavior of the system, impossible to achieve using only the feedback compensation. A numerical example, the steering of a ship and a real application, the control of a rotary flexible joint, show the effectiveness of the proposed method.

We perform an analytic investigation of the stability of line-driven disk winds, independent of hydrodynamic simulations. Our motive is to determine whether or not line-driven disk winds can account for the wide/broad UV resonance absorption lines seen in cataclysmic variables (CVs) and quasi-stellar objects (QSOs). In both CVs and QSOs observations generally indicate that the absorption arising in the outflowing winds has a steady velocity structure on time scales exceeding years (for CVs) and decades (for QSOs). However, published results from hydrodynamic simulations of line-driven disk winds are mixed, with some researchers claiming that the models are inherently unsteady, while other models produce steady winds. The analytic investigation presented here shows that if the accretion disk is steady, then the line-driven disk wind emanating from it can also be steady. In particular, we show that a gravitational force initially increasing along the wind streamline, which is characteristic of disk winds, does not imply an unsteady wind. The steady nature of line-driven disk winds is consistent with the 1D streamline disk-wind models of Murray and collaborators and the 2.5D time-dependent models of Pereyra and collaborators. This paper emphasizes the underlying physics behind the steady nature of line-driven disk winds using mathematically simple models that mimic the disk environment