Scielo RSS <![CDATA[Revista mexicana de física]]> vol. 63 num. 3 lang. es <![CDATA[SciELO Logo]]> <![CDATA[Solutions of the Helmholtz equation given by solutions of the eikonal equation]]> Abstract We find the form of the refractive index such that a solution, S, of the eikonal equation yields an exact solution, exp⁡(i 𝑘 0 𝑆), of the corresponding Helmholtz equation.<hr/>Resumen Hallamos la forma del índice de refracción tal que una solución, 𝑆, de la ecuación iconal produce una solución exacta, exp⁡(i 𝑘 0 𝑆), de la ecuación de Helmholtz correspondiente. <![CDATA[Nambu-Goto action and classical rebits in any signature and in higher dimensions]]> Abstract We perform an extension of the relation between the Nambu-Goto action and classical rebits. Of course, the Cayley hyperdeterminant is the key mathematical tool in such generalization. Using the Wick rotation, we find that in four dimensions such a relation can be established no only with the signature (2+2) but also with any signature. We generalize our result to a curved space-time of (2 2n +2 2n )-dimensions and (2 2n+1 +2 2n+1 )-dimensions. <![CDATA[Extension of a factorization method of nonlinear second order ODE’s with variable coefficients]]> Abstract The factorization of nonlinear second-order differential equations proposed by Rosu and Cornejo-Pérez in 2005 is extended to equations containing quadratic and cubic forms in the first derivative. A few illustrative examples encountered in physics are provided.<hr/>Resumen La factorización de ecuaciones diferenciales de segundo orden no lineales propuesta por Rosu y Cornejo-Pérez en 2005 se extiende a ecuaciones con potencias cuadráticas y cúbicas en la primera derivada. Se proporcionan algunos ejemplos físicos ilustrativos. <![CDATA[Gaussian superlattice in GaAs/GaInNAs solar cells]]> Abstract We present a new type of photovoltaic device where Gaussian superlattice is inserted in the i-region of a GaAs/GaInNAs p-i-n solar cell. A theoretical model is developed to study the performance of these devices. We establish a new criterion to calculate miniband widths in superlattice heterostructures in the presence of electric field. By optimizing miniband width, the spectral response of the cell in the energy region below the absorption edge of host material is significantly enhanced. Our results show that these devices could reach higher conversion efficiencies than the single-gap solar cell. <![CDATA[Analyses of 𝛑 ± nucleus elastic scattering data at 𝐓 𝛑 =𝟓𝟎 MeV using a suggested scaling method]]> Abstract The data for elastically scattered charged pions from few nuclei, namely 16 O, 28 Si, 30 Si, 32 S, 34 S, 40 Ca, 43 Ca, 56 Fe, 58 Ni, 64 Ni and 90 Zr have been analyzed by obtained potentials using a suggested scaling procedure. Originally the π ± - 12 C elastic scattering data at 50 MeV was nicely fitted by a parameterized simple local optical potential extracted from available phase shifts using inverse scattering theory. The potential parameters of the π ± - 12 C systems were scaled to π ± - 16 O systems and then successively to other few systems covering the scattering of charged pions from target nuclei and isotopes, namely π ± - 28 Si, 30 Si, π ± - 32 S, 34 S, π ± - 40 Ca, 48 Ca, π ± - 56 Fe, π ± - 58 Ni, 64 Ni and π ± - 90 Zr. For all these systems, the obtained scaled potentials showed a remarkable success in explaining the available elastic scattering data at 50 MeV. For the first time, simple scaling relations are well established, and are used in explaining successfully the elastic differential and integral cross sections. This motivates using the scaling procedure to predict pion-nucleus potentials capable of explaining measured angular distributions for the scattering of charged pions off other target nuclei, and few isotopes, at energies in the low energy region. <![CDATA[The retrieval of ozone’s absorption coefficient in the stratosphere]]> Abstract This study modifies the Monte Carlo Multilayer (MCML) algorithm to simulate the propagation of light while using an authentic model of the atmosphere as a proposal. The modified algorithm determines the diffuse reflectance as the coefficients of absorption and/or scattering change. Hence, spectral curves of diffuse reflectance are obtained from the simulations and are adjusted with the trigonometric series using the Fourier expansion. The absorption coefficient of the ozone in the stratosphere is retrieved in terms of Fourier’s coefficients. <![CDATA[Una revisión de los métodos para estimar el exponente de Hurst y la dimensión fractal en series de precipitación y temperatura]]> Resumen Este artículo presenta una revisión del estado del arte de los métodos fundamentados en la geometría fractal que han sido utilizados para estimar la dimensión fractal y/o el exponente de Hurst; así como un análisis de sus parámetros de entrada, ventajas y desventajas. Posteriormente se presenta una sección de aplicaciones, en donde se realizó un compilado de los resultados de investigaciones que aplican los métodos anteriores para analizar la estructura de series de precipitación y temperatura en diversas regiones del planeta. Además, se analiza la relación entre los resultados de las investigaciones consultadas y las características climáticas de la región correspondiente; encontrando que el exponente de Hurst de precipitación y temperatura permite caracterizar la precipitación promedio anual y temperatura promedio anual. Finalmente, se presenta un mapa global de la localización de las investigaciones realizadas donde pueden apreciarse las mayores concentraciones de este tipo de investigación en Europa y Medio Oriente. Las series de precipitación y temperatura con comportamiento antipersistente se concentran cerca del Ecuador. Sin embargo, aún se requiere desarrollar investigaciones en diversas regiones del mundo para lograr obtener información suficiente que permitan realizar inferencias de la estructura de series de precipitación y temperatura.<hr/>Abstract This paper presents a review of the state of the art of methods with fractal geometry foundation that have been used to estimate the fractal dimension and/or Hurst exponent; as well as an analysis of their parameters, advantages and disadvantages. Subsequently an applications section is presented, where a results compilation of researches using these methods to analyze rainfall and temperature series’ structure across the world is shown. Furthermore, a relationship analysis between the consulted researches results and climatic characteristics of the corresponding region is performed; showing that rainfall and temperature series´ Hurst exponent values can characterize average annual rainfall and average annual temperature. Finally, a global map displaying the location of the conducted researches is presented, where the higher concentration corresponds to Europe and Middle East. Rainfall and temperature series that display antipersistent behavior are registered near the equator line. However, a lot of research is needed in other regions of the world in order to obtain enough information to make inferences about rainfall and temperature series’ structure. <![CDATA[Improved performance of the cryptographic key distillation protocol of an FSO/CV-QKD system on a turbulent channel using an adaptive LDPC encoder]]> Abstract In this paper, a dynamical and adaptive LDPC coding scheme is proposed in order to improve the performance of the cryptographic key distillation protocol of an FSO/CV-QKD system considering the atmospheric turbulence levels that may be present in the classic channel. In this scheme, the Generator and Parity-check matrices of the encoder are modified according to the Rytov variance values estimated in the classical channel in order to improve the final secret key rate of the QKD system. The simulation results show that the final secret key was incremented 87.5 Kbps (from 52.5 Kbps to 140 Kbps) using the adaptive code rate; meaning that the information encrypted and transmitted is increased. In addition, the use of the dynamical encoder avoids the drastically reduction of the final secret key rate when the conditions of the classical channel are considered. Our proposal might be implemented based on the use of high-speed FPGA’s and DSP’s commercially available. <![CDATA[Asymptotic structure of spacetime and the Newman-Penrose formalism: a brief review]]> Abstract A brief review about the Newman-Penrose formalism and the asymptotic structure of the spacetime is given. The goal of this review is to describe the latest developments in these topics and make a summary of the most important articles published by Newman and collaborators. Additionally, we discuss some aspects of this approach, and we compute the spin coefficients and the Weyl scalars for a general stationary axisymmetric spacetimes in a tetrad basis different from that defined by the principal null geodesic directions. <![CDATA[The solution of the Schrödinger equation obtained fromthe solution of the Heisenberg equations]]> Abstract It is shown that the knowledge of the solution of the Heisenberg equations for a given Hamiltonian allows us to find the corresponding propagator up to a time-dependent phase factor, which gives the solution of the Schrödinger equation.<hr/>Resumen Se muestra que el conocimiento de la solución de las ecuaciones de Heisenberg para un hamiltoniano dado nos permite hallar el propagador correspondiente hasta un factor de fase dependiente del tiempo, el cual da la solución de la ecuación de Schrödinger. <![CDATA[Radiative corrections to the magnetic moment of a charged lepton at finite temperature from the photon-photino pair in SUSY standard model]]> Absract Within the context of the Supersymmetric Standard Model of Electroweak Unification, we compute the radiative virtual corrections, at finite temperature, to the magnetic dipole moment of a charged lepton coming from the virtual photon-photino and lepton-slepton pairs. We show that the corrections from the virtual photon-photino vanish in the limit of exact supersymmetry. <![CDATA[Diffusion Monte Carlo study of actinide monohydrides and monofluorides]]> Abstract Ground state total energies, bond lengths, bond dissociation energies, and dipole moments for early actinide monohydrides and monofluorides have been calculated by using the diffusion Monte Carlo (DMC) method with LC-BLYP functional. The calculated results are compared with previous theoretical calculations at various levels of theory. Our results show that the DMC method employing LC-BLYP functional at the optimal value of the range separation parameter is capable of providing a reasonable description of early actinide containing molecules and their bonding properties.