Scielo RSS <![CDATA[Revista mexicana de física]]> vol. 62 num. 2 lang. es <![CDATA[SciELO Logo]]> <![CDATA[<b>Deformation of an elastic cylindrical tube filled with water and a dry granular material</b>]]> The deformation of a vertical thin-walled tube filled with a liquid or a non-cohesive granular material is investigated theoretically and experimentally. Experiments using latex tubes filled with water or spherical glass beads have been conducted and the results were compared to theoretical results derived from the Janssen model. The results obtained suggest that soft elastic tubes could provide a simple and convenient means to investigate the forces that arise within different materials. <![CDATA[<b>Simulación molecular de isotermas de adsorción para hidratos simples de metano y dióxido de carbono</b>]]> En este trabajo se calcula el número de hidratación y la fracción de ocupación de los gases metano y dióxido de carbono en las cavidades de los hidratos simples tipo I. Los cálculos se obtuvieron utilizando simulaciones Monte Carlo. Los resultados se comparan con datos experimentales y los obtenidos aplicando la teoría de van der Waals y Platteeuw, la cual combina la termodinámica estadística con la teoría clásica de adsorción. Los números de hidratación calculados con ambas metodologías están dentro del rango de los valores experimentales para los dos hidratos. Para el hidrato de metano los resultados de las simulaciones Monte Carlo concuerdan en la tendencia observada con los calculados con la teoría de van der Waals y Platteeuw. En el caso del hidrato de dióxido de carbono la ocupación del gas en las cavidades del hidrato alcanza dos valores límite a diferentes presiones lo cual se puede deber a que se llenan primero las cavidades grandes y luego las cavidades más pequeñas al aumentar la presión.<hr/>In this work the hydration number and fractional cage occupancy of simple methane and carbon dioxide sI clathrate hydrates are calculated by Monte Carlo simulations. The results are compared with experimental data and those obtained by applying the theory of van der Waals and Platteeuw, which combined statistical thermodynamics with the classical theory of adsorption. The hydration numbers estimated from both methodologies are within the range of experimental values for the two hydrates. The fractional cage occupancy obtained by Monte Carlo simulations for methane hydrate agrees on the trend with those calculated using the theory of van der Waals and Platteeuw. In the case of carbon dioxide hydrate, the occupation of cavities reaches two plateaus in pressure that may be due to that large cages are occupied first and then, when the pressure increases the small cages begin to be occupied. <![CDATA[<b>A SUSY <i>SU</i>(6) GUT model with pseudo-Goldstone Higgs doublets</b>]]> We present a novel way of realizing the pseudo-Nambu-Goldstone boson mechanism at all orders in perturbation theory, for the doublet-triplet splitting in supersymmetric grand unified theories. The global symmetries of the Higgs sector are attributed to a non-vectorlike Higgs content, which is consistent with unbroken supersymmetry in a scenario with flat extra dimensions and branes. We also show how in such a model one can naturally obtain a realistic pattern for the Standard Model fermion masses and mixings.<hr/>Presentamos un modelo que genera el mecanismo de pseudo-Nambu-Goldstone a todo orden en teoría de perturbaciones para el problema de corrimiento de doblete-triplete en teorías supersimétricas de gran unificación. Las simetrías globales del sector de Higgs son atribuidas al contenido no vectorial de Higgs, el cual es consistente con supersimetría no rota en un escenario de dimensiones extra planas y branas. Además, mostramos como en este modelo uno puede obtener un patrón realístico de las masas y mezclas de fermiones del Modelo Estándar. <![CDATA[<b>Tribological performance evaluation of coated steels with TiNbCN subjected to tribo-chemical wear in Ringer's solution</b>]]> With the aim of generating solutions against the deterioration of the joint prostheses, it was studied the tribo-corrosive behavior of titanium niobium carbonitride (TiNbCN) deposited on stainless steel AISI 316 LVM using the technique of magnetron sputtering physical vapor deposition. The tests were performed in a balanced saline solution (Ringer's solution) which represents the characteristics of the body fluids, using an equipment where the micro-abrasive wear is generated by the contact of micro particles in the system; the micro-abrasion-corrosion mechanism is described by means of the incorporation of an electrochemical cell consisting of three electrodes. Both the substrate and the coating, were subjected to micro-abrasive wear simultaneously with the electrochemical tests of Tafel polarization curves and electrochemical impedance spectroscopy (EIS); subsequently of the tests, the specimens were analyzed by optical microscopy and scanning electron microscopy characterizing the surface morphology. It was observed that the coating presents an increase in its corrosion and wear resistance with the presence of a simulated biological fluid. <![CDATA[<b>Optical band gap energy and urbach tail of CdS</b>: <b>Pb2+ thin films</b>]]> PbS-doped CdS nanomaterials were successfully synthetized using chemical bath. Transmittance measurements were used to estimate the optical band gap energy. Tailing in the band gap was observed and found to obey Urbach rule. The diffraction X-ray (XRD) show that the size of cristallites is in the ~33 nm to 12 nm range. The peaks belonging to primary phase are identified at 20 = 26.5° and 20 = 26.00° corresponding to CdS and PbS respectively. Thus, a shift in maximum intensity peak from 20 = 26.4° to 28.2° is clear indication of possible transformation of cubic to hexagonal phase. Also peaks at 20 = 13.57°, 15.9° correspond to lead perchlorate thiourea. The effects on films thickness and substrate doping on the band gap energy and the width on tail were investigated. Increasing doping give rise to a shift in optical absorption edge ~0.4 eV <![CDATA[<b>Improving the optical and crystalline properties on CdS thin films growth on small and large area by using CBD technique</b>]]> CdS polycrystalline thin films have been used as window layer in solar cells; the optical and crystalline quality of the CdS-partner plays an important role in the photovoltaic device performance. CdS thin films were deposited by using Chemical Bath Deposition (CBD). The SnO2 :F substrates used were chemically treated with HCl (0.1M) and others were thermally annealed in different atmospheres (Ar y O2). The physical properties of CdS thin films were influenced by the HCl treatment, position, size and the substrates movement inside the reaction beaker. The CdS samples were deposited in áreas of 4 cm², 50 cm² and 100 cm². Finaly CdS thin films with thickness of 35-300 nm with good optical and crystalline quality on a uniform morphology were obtained. Transmittance values were obtained for all samples about 85-90% with an average of gap energy of 2.5 eV.<hr/>Las películas delgadas policristalinas de CdS han sido usadas como el material ventana en celdas solares; la calidad (óptica y cristalina de la película delgada de CdS juega un papel muy importante en el desempeño del dispositivo fotovoltaíco. Películas delgadas de CdS fueron depositadas utilizando la técnica de bario químico (DBQ). Los substratos de SnO2 :F utilizados fueron tratados químicamente con HCl (0.1M) y algunos otros fueron térmicamente recocidos en diferentes atmosferas (Ar and O2). Observamos que las propiedades físicas de las películas delgadas de CdS se ven influenciadas por el tratamiento con HCl, la posición, el tamaño y el movimiento del substrato dentro del vaso reactor. Las muestras de CdS se depositaron en áreas de 4 cm², 50 cm² and 100 cm². Finalmente se obtivieron películas delgadas con espesores de 35 - 300 nm con buena calidad óptica y cristalina en una morfología uniforme. Los Los valores de transmitancia en las muestras obtenidas se encuentran entre un 85 y 90% con una brecha prohibida de energía promedio de 2.5 eV. <![CDATA[<b>Symmetries of the hamiltonian operator and constants of motion</b>]]> It is shown that, in the framework of non-relativistic quantum mechanics, any conserved Hermitian operator (which may depend explicitly on the time) is the generator of a one-parameter group of unitary symmetries of the Hamiltonian and that, conversely, any one-parameter family of unitary symmetries of the Hamiltonian is generated by a conserved Hermitian operator.<hr/>Se muestra que, en el marco de la mecánica cuántica no relativista, cualquier operador hermitiano conservado (el cual puede depender explícitamente del tiempo) es el generador de un grupo uniparamétrico de simetrías unitarias del hamiltoniano y que, recíprocamente, cualquier familia uniparamétrica de simetrías unitarias del hamiltoniano es generada por un operador hermitiano conservado. <![CDATA[<b>Electro chemical characterization of V<i><sub>X</sub></i>Nb<i><sub>Y</sub></i>C<i><sub>Z</sub></i>/Bi<i><sub>X</sub></i>Ti<i><sub>Y</sub></i>O<i><sub>Z</sub></i> coatings produced through thermo-reactive diffusion and the sputtering technique</b>]]> We present an experimental study of the structural evolution of a bilayer V X NbY C Z /Bix TiY O Z coating produced via thermo-reactive diffusion (TRD) and the RF sputtering process on D2 steel substrate. The TRD treatments were carried out in a molten mixture consisting of borax, ferro-niobium, ferro-vanadium, and aluminum, at 1313 K for 3 hours, using a resistance-heating furnace. BiX TiY O Z coatings were deposited using RF magnetron sputtering on TRD coatings, in order to carry out a study of the corrosion behavior of this compound. The crystallographic structure of the coatings was determined via X-ray diffraction (XRD), the corrosion resistance was analyzed through the po-tentiodynamic polarization test (Tafel Extrapolation) and electrochemical impedance spectroscopic analysis (EIS). XRD patterns showed that the ternary coating (VNbC2) was preferentially oriented along the [200] direction with a cubic-centered face structure, and the BiX TiY O Z coatings were amorphous. The electrochemical studies showed that the resistance corrosion of the coatings increased with respect to the bare substrate, and that polarization resistance in the bilayer coatings increased with respect to the ternary coatings, suggesting that the titanate has anticorrosive barrier effects. <![CDATA[<b>Electrical circuits described by a fractional derivative with regular Kernel</b>]]> In this paper we presented the electrical circuits LC, RC, RL and RLC using a novel fractional derivative with regular kernel called Caputo-Fabrizio fractional derivative. The fractional equations in the time domain considers derivatives of order (0; 1], the analysis is performed in the frequency domain and the conversion in the time domain is performed using the numerical inverse Laplace transform algorithm; furthermore, analytical solutions are presented for these circuits considering different source terms introduced in the fractional equation. The numerical results for different values of the fractional order γ exhibits fluctuations or fractality of time in different scales and the existence of heterogeneities in the electrical components causing irreversible dissipative effects. The classical behaviors are recovered when the order of the temporal derivative is equal to 1 and the system exhibit the Markovian nature. <![CDATA[<b>Fractional drude model of electrons in a metal</b>]]> In the present work we analyse the behaviour of electrons in a metal placed into uniform electric field, E, from its fractional differential equation. We show that the velocity and the current density of the electrons not only depend on the time t, but also on the order of the fractional differential equation γ, the Drude model is a particular case. This fact could have interesting consequences in the study of electrical properties of metals. <![CDATA[<b>First principles study of the effects of disorder in the Sr<sub>2</sub>FeMoO<sub>6</sub> perovskite</b>]]> First principles calculations were done in the double perovskite Sr2FeMoO6 regarding the effects of cationic disorder and electronic correlation in the ground-state properties such as spin polarization and magnetic saturation. We used the Generalized Gradient Approximation (GGA) method including a U Hubbard term. Results with 25% of disorder, where Fe-O-Fe and Mo-O-Mo configurations frequently occur, are shown. We found that disorder breaks down the half-metallic ferromagnetic behavior. We also calculated a magnetic saturation decrease from 4.0jtB per formula unit to 2.22jtB in accord with neutron magnetic scattering experiments. <![CDATA[<b>Entropy production</b>: <b>evolution criteria, robustness and fractal dimension</b>]]> It was proved through Rossler model, where the funnel case is more robust tan spiral chaos, the entropy production per unit time is a Lyapunov's function on the space of the control system parameters. It was established the conjecture of entropy production fractal dimension. The current theoretical framework will hopefully provide a better understanding of the relationship between thermodynamics and nonlinear dynamics and contribute to unify theses through complex systems theory. <![CDATA[<b>Characterization of thermal rectification in asymmetrical-structured materials with inhomogeneous mass distribution</b>]]> We study the asymmetrical heat flux present in a one-dimensional, two-segment, nearest-neighbor anharmonic oscillator system subjected to the influence of a temperature gradient for two different mass distributions. For a small system size the largest asymmetry in the heat flux is obtained for the case wherein one segment has larger mass values than the other one, the lowest with the already considered uniform mass distribution, and an intermediate one with a linear mass gradient along the system length. These results are also obtained in the largest system size limit, wherewith it was observed that the heat flux increases as the system size does so for the case of the two segments with dissimilar mass value.<hr/>En este trabajo estudiamos el flujo de calor asimétrico presente en un sistema unidimensional de osciladores anarmónicos acoplados a primeros vecinos, compuesto de dos segmentos diferentes y sujeto a la influencia de un gradiente de temperatura para el caso de dos distribuciones de masa distintas. Para tamaños de sistema pequeños la mayor asimetría en el flujo de calor se obtiene para el caso en el cual uno de los segmentos tiene mayor masa que el otro, la menor para el caso ya conocido de masa uniforme y un caso intermedio para un gradiente de masa a lo largo de toda la longitud del sistema. Estos resultados se mantienen para tamaños de sistema grandes, con los cuales se observa que el flujo de calor se incrementa conforme también lo hace el tamaño del sistema para el caso de los dos segmentos con diferente masa. <![CDATA[<b>Use of self-friction polynomials in standard convention and auxiliary functions for construction of One-Range addition theorems for noninteger slater type orbitals</b>]]> Using L(Pi*) -self-friction polynomials (L(Pi*)-SFPs), complete orthonormal sets of ψ(Pi*)-SF exponential type orbitals ψ(Pi*)-SFETOs) in standard convention and Qq-integer auxiliary functions (Qq-IAFs) introduced by the author, the combined one- and two-center one-range addition theorems for x-noninteger Slater type orbitals (x-NISTOs) are established, where Pi* = 2l + 2 - α* and α* is SF quantum number. As an application, the one-center atomic nuclear attraction integrals of x-NISTOs and V-noninteger Coulombic potential (V-NICPs) are calculated. The obtained formulas can be useful especially in the electronic structure calculations of atoms, molecules and solids. <![CDATA[<b>Diseño y caracterización de un enfriador de átomos de tipo "desacelerador Zeeman"</b>]]> Nosotros presentamos un método que utiliza simultaneamente dos modelos matemáticos, con el objetivo de optimizar el diseño de un desacelerador Zeeman, con miras a la implementación de átomos ultrafríos a la física del estado sólido. Proponemos la implementación novedosa de una simulación por medio de elementos finitos con la cual es posible predecir con mucha precisión el perfil de intensidad del campo magnético generado por el diseño realizado. Al poder predecir el comportamiento del desacelerador Zeeman se adquiere un mayor control, a partir del cual es posible optimizar las diferentes variables experimentales. El método propuesto es aplicado para el diseño y construcción de un desacelerador Zeeman solenoidal de tipo "Spin Flip" para átomos de estroncio. El perfil de intensidades de campo magnético generado por el desacelerador Zeeman construido concuerda con el perfil de intensidades de campo magnético necesario para el enfriamiento de átomos de estroncio y tiene además la ventaja que la intensidad de campo magnético tiende a cero en los extremos. Ambas condiciones permiten incrementar la cantidad de átomos enfriados y atrapados.<hr/>We report on an investigation of a method that applies simultaneously two different mathematical models in order to optimize the design of a Zeeman Slower towards the implementation of ultra cold atoms in solid state physics. We introduce the implementation of a finite element simulation that allows us to predict with great accuracy the magnetic field intensity profile generated by the proposed design. Through the prediction of the behavior of the Zeeman Slower a greater control is acquired, which allows the optimization of the different experimental variables. We applied the method in the design of a multilayer solenoidal "Spin-Flip" Zeeman Slower for strontium atoms. The magnetic intensity profile generated by the Zeeman Slower is in agreement with the magnetic field strength profile necessary for the atom cooling and tends to zero in both end sides. The latter terms are essential in order to optimize the amount of trapped and cooled atoms.