Vol. 70 No. 3 May-Jun (2024): Revista Mexicana de Física

In the present work, we have carried out a comparative study of the effects of uniaxial stress and spatial dielectric functions on the density of impurity states (DOIS) of shallow donor impurities in a GaAs  quantum well dot of circular cross-section. Using a trial wave function in the effective mass approximation, we carried out calculations for a range of binding energies of hydrogenic (dielectric constant) and non-hydrogenic (spatial dielectric functions) donors for various applied uniaxial stress and for different uniaxial lengths of the quantum dot. Our results show that, for a constant axial length of the quantum dot and constant uniaxial stress, the DOIS for the donor impurity is markedly enhanced for the non-hydrogenic donor impurity over that for purely hydrogenic donor impurity. At constant axial length, the applied uniaxial stress enhances the DOIS in both cases. The density of impurity states has also been studied for a constant applied uniaxial stress for different axial lengths of the quantum dot. Here, again, the DOIS increases with increasing axial length of the quantum dot. In fact, the enhanced DOIS is observed throughout the range of binding energies considered. These results show that not only does the DOIS vary with the applied uniaxial stress and spatial dielectric functions they are also different for various axial lengths of the quantum dot. These findings indicate that is  important to take into account the effect of applied uniaxial stress and spatial dielectric functions when performing experimental studies of electronic, optical and transport properties of such nanostructures as quantum dots.

Ab initio calculation of the structural, electronic and optical properties of half-Heusler MgYGa alloy are reported using the FP-LAPW approach of the Density Functional Theory. Generalized Gradient Approximation was used as the exchange and correlation potential for investigating these properties. Structural properties of MgYGa alloy, such as the lattice constants, bulk modulus and pressure derivative of the bulk module have been studied. Electronic properties were investigated by calculating and analyzing the electronic band structure, partial and total density of states graphs for the MgYGa compound. We have found that MgYGa compound has a metallic character. The investigation of optical properties indicates a great interaction between the compound and the incident light.

We present a no-go theorem for spherically symmetric configurations of two charged fluid species in equilibrium. The fluid species are assumed to be dusts, that is, perfect fluids without pressure, and the equilibrium can be attained for a single dust from the balance of electrostatic repulsion and gravitational attraction. We show that this is impossible for two dust species unless both of them are indistinguishable in terms of their electric charge density to matter density ratio. The result is obtained in the main three theories of mechanics, that is, in Newtonian Mechanics, in Special Relativity and in General Relativity. In particular, as charged dust solutions have been used to study the possibility of black hole mimickers, this result shows that such mimickers can not be constructed unless the underlying charged particle has the correct charge to mass ratio.

For the Einstein-Maxwell equation system, with perfect fluid in a static and spherically symmetrical spacetime, we report an analytical internal solution which is obtained by imposing the Karmarkar condition, the behaviour of the solution is such that the density and pressures are monotonically decreasing functions while the electric field function is a monotonically increasing function that is adequate to represent compact objects. In particular we have these characteristics for the observational values of mass (1.29 ± 0.05) M_⊙ and radius (8.831 ± 0.09) km of the star SMC X-4. We will analyze the two extremes the one of minimum compactness u_min = 0.20523 (M = 1.24 M_⊙, R = 8.921 km) and the one of maximum compactness u_max = 0.22635 (M = 1.34 M_⊙, R = 8.741 km), resulting that the electric charge Qumin ∈ [1.5279, 1.8498]10²⁰C and Qu_max ∈ [1.6899, 1.9986]10²⁰C respectively, implying that the case with higher compactness has a higher electric charge. Also in a graphic manner, it is shown that the causality condition is satisfied and that the solution is stable against infinitesimal radial adiabatic perturbation and also in regards to the Harrison-Novikov-Zeldovich criteria

The Nikiforov-Uvarov method is an efficient technique for solving of heavy diquark systems. It has been used to derive analytic-exact energy eigenvalues and eigenfunctions in fractional forms, which are useful in describing such systems. The potentials employed include the Cornell potential, harmonic potential, and spin-spin interaction; have been updated with respect to previous studies. Mass spectra of heavy pentaquarks were also calculated using this method. Compared to previous studies, the present results exhibit good experimental data agreement and are improved. We deduce that the fractional models contribute greatly to the heavy pentaquark masses.

Some current energy transfer modules and magnetic stimulation systems with vortex fields are mostly composed of a Rodin coil. It has been hypothesized that the most significant changes in the biological system stimulated with vortex magnetic fields are related to the type of field lines and its magnetic field gradient. Therefore, characterizing the vortex magnetic field produced inside this coil and defining the behavior of the field gradient is necessary to take full advantage of its efficiency. The theoretical Biot-Savart law for this coil geometry is discussed in this work, and the magnetic induction lines are characterized. Magnetic field modeling is done with the finite element method; the above processes are correlated with the register of the magnetic field of the Rodin performed with a three-dimensional magnetometer. Furthermore, the results obtained with Rodin coil stimulation are compared with those obtained with Helmholtz coil stimulation of a similar biological system. The effect is widely evident in the first case.

This investigation aims to improve the properties of 304 L stainless steel (SS) substrates for use in corrosion, mechanical, and biomedical applications by depositing ZnO thin films. The ultrasonic spraying technique was used to prepare ZnO thin films with depositional times of 1, 4, and 9 minutes. XRD and Raman studied the surface characteristics of ZnO samples. XRD analysis revealed a hexagonal structure with an average crystallite size of 22 nm for ZnO. Indentation nano measurements indicated an increase in the hardness of the films examined. To determine the type of conductivity and estimate the charge carrier density, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and Mott-Schottky analysis were performed. The thin film deposited for 9 minutes was found to be the most effective in improving corrosion resistance.

An experimentally calibrated numerical model was employed to examine the vibroacoustic impact of the arching profile in a violin soundbox, a study unattainable through experimental means alone. The finite element method successfully modeled the soundbox using the material properties of an actual violin, albeit with a simplified representation of the coupling with the air in the cavity and the forces from the strings. Achieving agreement with the real counterpart necessitated careful adjustment of the modal damping in the simulation. Damped models of violins are infrequently encountered. The impulse response of the soundbox model was obtained through the calculation of thousands of substeps induced by forced vibration. To streamline the time-domain analysis, the superimposed method was implemented instead of the more commonly used full option, resulting in a significant reduction in computational time. Additionally, synthetic musical notes, accounting for how the force of the strings is transmitted through the bridge, were employed as input to the soundbox model. Subsequently, the impulse responses were convolved with the synthetic notes to generate sounds. Through these procedures, the violin’s performance was assessed as the height of the arching profile of the plates was adjusted. The results demonstrated that higher arching profiles led to a general increase in the resonant frequencies of the violin, perceptible in the sound generated by the model.

The solid material's wettability behavior is determined by the contact angle value. The wettability of materials is critical in the coating, lubricating, and insulating industries. In high-tech industries including corrosion resistance, water-oil separation, medical material production, implant technology, and friction reduction, the contact angle is very important. A new method called the full angle method was used to measure the contact angle and compared with current methods. The wettability behavior of plexiglass, which is employed in a variety of applications ranging from lighting to decorating, and industrial designs to accessory production, was explored in this study. The measurement of the contact angle was done by dropping 1.8 M (molar) of saltwater over the plexiglass materials. In order to examine the effect of evaporation on the contact angle, changes in contact angle, height and baseline were investigated depending on the waiting time. 

A Monte Carlo simulation algorithm to investigate the measurement of the average prompt neutron multiplicity as a function of pre-neutron mass, ν(A), for fragments from the spontaneous fission of 252Cf is presented. The input data consist of experimental measurements of the kinetic energy and mass distributions obtained by Göök et al., and the values of ν(A) calculated using the FIFRELIN model by Piau et al., νth(A). We analyze the output curve, νsim(A), obtained by simulation of the 2E technique, which should ideally match νth(A). However, we find that νsim(A) exhibits a maximum value at A≈122, close to mass symmetry, while νth(A) has a maximum at A≈118. Additionally, we observe that νsim(A) > νth(A) for A< 90 and A> 169, respectively. We attribute this discrepancy to inaccuracies in the relationship between provisional mass and the pre-neutron mass used in the 2E technique for data processing in each fission event.

The angular distributions of the elastic and inelastic scattering cross sections of alpha projectiles on different heavy ion target nuclei including ¹²C, ¹⁶O, ²⁴Mg, ²⁸Si and ⁴⁰Ca at energy of 130 MeV have been studied using two different microscopic real potentials generated by the energy density functional (EDF) theory, and single folding cluster model as well as phenomenological Woods-Saxon potentials. A new parameterization was considered for the first time by EDF and to make the normalization coefficient tend to unity, it is necessary to consider correction to the calculated real potential. Coupled channel calculations for various low-lying states were performed, and the best fit values for the deformation length with the above models were extracted by fitting the inelastic scattering cross section and compared to previous work values. The total reaction cross section, as well as the real and imaginary volume integrals, have been studied.

Our main goal is to find the locus of images formed as a result of an inferior mirage. To achieve our goal we show, at first, that, provided the beam entering a detection system has a small aperture, the image of a point object formed by that system in a vertical plane passing through the object is a point, regardless of whether the image formed by an optical system previously traversed by the beam has generated a non-point image of the object. Secondly, we show that the different images formed by the detection system, as its position relative to the object varies, are located on the caustic curve corresponding to the previously traversed optical system. Next, we have found the analytical expressions of the caustic curves corresponding to two particular cases, one of them being the inferior mirages. These expressions have been found by means of the Legendre antitransform of the asymptotic lines to the paths of light rays reaching the detector. For the case of inferior mirages, we have studied in detail the locus of the images in each vertical plane passing through the object as a function of the position of the object relative to the ground, its position relative to the detector, and the atmospheric conditions. Finally, we get somewhat into the matter of the images position as they would be seen by a casual observer of an inferior mirage.

We study the atom-field interaction at finite temperature and in the dispersive regime. We show that the master equation for this sytem may be solved with the use of superoperator techniques. We calculate the linear entropy in case the field is initially in a coherent state and the atom in a superposition of its ground and excited states.

In this work we propose to qualitatively test the quality of a concave parabolic mirror by means of the Ronchi interferometric test using substructured gratings to increase the sharpness of the fringes. The substructured gratings are designed considering that the grating period is divided into several stripes of equal width that can be transparent or opaque; the transmission coefficients of the stripes along the grating period are not periodic, but a previously chosen binary sequence. Equations were derived to obtain the corresponding intensity profiles and an analysis of these profiles was performed for different sequences and positions of the substructured gratings with respect to the test mirror. It was experimentally verified that the fringes are sharper at the Rayleigh distance inside and outside the mirror focus.

El estado de polarización de la luz normalmente se mide determinando los parámetros de Stokes. Varios autores han propuesto formas alternativas de obtener estos parámetros. Sin embargo, la esencia del método ha prevalecido. En este trabajo se propone un método de extremos, que consiste en medir intensidades máximas y mínimas. El procedimiento consta de cuatro medidas directas para obtener el estado de polarización de la luz, sin necesidad de utilizar los parámetros de Stokes. Se ofrece una representación matemática alternativa de la polarización elíptica, basada en parámetros que representan directamente la inclinación de la elipse y la relación entre sus semiejes. Se muestran resultados experimentales que se comparan favorablemente con el método tradicional.  

The polarization state of light is normally measured by determining the Stokes parameters. Several authors have proposed alternative ways to obtain these parameters. However the essence of the method has prevailed. In this work, a method of extremes is proposed, which consists of measuring maximum and minimum intensities. The procedure consists of four direct measurements to obtain the polarization state of the light, without the need to use the Stokes parameters. An alternative mathematical representation of the elliptical polarization is offered, based on parameters that directly represent the inclination of the ellipse and the relationship between its semi-axes. Experimental results that compare favorably with the traditional method are shown.

The (3+1)-dimensional new negative-order-KdV-CBS model is investigated in this study. The suggested model combines the Korteweg-de Vries (KdV) and Calogero-Bogoyavlenskii-Schiff (CBS) equations. This research provides multiple soliton solutions and traveling wave solutions for the KdV-CBS model. Multiple exp-function methods have been used for extracting soliton solutions. For this aim, the extended sinh-Gordon equation expansion approach was selected to get traveling wave solutions. The findings are graphically examined by selecting appropriate values for arbitrary parameters.

Some new different kinds of one-soliton solutions for various forms of Boussinesq-type equations are presented in this
paper to describe the nonlinear wave phenomena in coastal and ocean areas such as tsunami waves. These one-soliton
solutions include bright, dark, and singular ones. The property of each solution in coastal and ocean engineering is
explained.

This paper explores the effects of numerical algorithms on global magnetohydrodynamics simulations of solar wind (SW) in the inner heliosphere. To do so, we use sunRunner3D, a 3-D magnetohydrodynamics model that employs the boundary conditions generated by CORHEL and the PLUTO code to compute the plasma properties of the SW with the ideal magnetohydrodynamics approximation up to 1.1 AU in the inner heliosphere. Mainly, we define three different combinations of numerical algorithms based on their diffusion level. This diffusion level is related to the way of solving the magnetohydrodynamics equations using the finite volume formulation, and, therefore, we set in terms of the divergence-free condition methods, Riemann solvers, variable reconstruction schemes, limiters, and time-steeping algorithms. According to the simulation results, we demonstrate that sunRunner3D reproduces global features of Corotating Interaction Regions observed by Earth-based spacecraft for a set of Carrington rotations that cover a period that lays in the late declining phase of solar cycle 24, independently of the numerical algorithms. Moreover, statistical analyses between models and in-situ measurements show reasonable agreement with the observations, and remarkably, the high diffusive method matches better with in-situ data than low diffusive methods.

In this paper, we present an extension of the plane-wave method (PWM) to compute the complex band structure of thermal wave crystals (TWCs). The structural periodicity of TWC allows the possibility to manipulate non-Fourier heat via wave interference. While the Cattaneo-Vernotte (CV) heat conduction theory accurately models oscillatory wave-like propagation of heat in TWCs, obtaining an eigenvalue equation for frequency using the CV wave equation is not possible. To overcome this limitation, we propose a novel approach that solves a complex eigenvalue equation for the Bloch wave vectors

Monte Carlo simulations of simple Lennard Jones fluids confined in different geometries, sphere, cylinder and slit-like pores are conducted to study the vapour-liquid transition. Phase diagrams, in the temperature-density (T-ρ) and pressure-temperature (P-T) are obtained. For each geometry the coexistence lines are plotted from the clapeyron equation of each systems and a P −T equation is proposed in terms of the critical temperature which works for all the systems. Additionally, the transition latent heat is also evaluated, from the enthalpy calculation obtained directly from the simulation data, and the fluid structure from density profiles.