Vol. 70 No. 1 Jan-Feb (2024): Revista Mexicana de Física

In this work, we focused on solving the space-time fractional diffusion equation with an application on the intrinsic arsenic diffusion in germanium. At first we have treated the differential equation in a semi-infinite medium by using Caputo-Fabrizio fractional derivative. We have introduced the Laplace transform to solve this type of equations. Secondly, Based on the obtained solution, we have simulated an profile of arsenic diffusion in germanium under intrinsic conditions. Accurate simulations have been achieved showing that the fractional derivative orders affect on the estimation of the diffusion coefficient, where increasing the time fractional derivative order α reduces the value of the diffusion coefficient, while increasing the space fractional derivative order β increases the value of the diffusion coefficient.

The doped dodecylbenzene sulfonic acid (DBSA) with polypyrrole (PPy) and also incorporated an increasing concentration of Y₂O₃ to obtain the composites of PPy-DBSA-Y₂O₃ via chemical polymerization technique. The PPy-DBSA-Y₂O₃ composites formation were confirmed by interaction between PPy-DBSA and Y₂O₃-particles utilizing Raman spectroscopy. Thermal stability of PPy-DBSA- Y₂O₃ composites was improved as enhanced the load of Y₂O₃-particles. The increase in DC conductivity by mixing Y₂O₃ into PPy-DBSA at all temperatures showed the three-dimensional Mott’s variable range hopping model. Density of localized states, hopping dimension as well as activation energy are computed and found to be affected due to the presence of Y₂O₃ in DBSA-PPy. The ESR of Y₂O₃ (~12 Ω), PPy (~11.80 Ω), PPy-DBSA (~11.30 Ω) and PPy-DBSA-8%Y₂O₃ composite (~9.50 Ω). EIS results confirm that the PPy-DBSA-8% Y₂O₃ composite with a low value of impedance gives a maximum value of electrical conductivity.

This work focuses on knowing the physical, environmental and population effects from the impact of an asteroid occurring in the Mexican territory. The work consists of the adaptation of routines product of previous works in the literature to generate a numerical code written in PyThon that allowed modeling this kind of phenomenon. Firstly, a map of the superficial densities of the Mexican territory has been developed with a resolution of $0.5^\circ$ of longitude by $0.5^\circ$ of latitude of the Earth. The map allows us to find the value of surface density in a specific geological area of the country. Once the surface density value was obtained, it is established as the value of the impact site (target). The model requires using fixed parameters, such as the diameter of the body, its density or mass, the angle of incidence and the density value at the impact site. The output, provides the impact velocity, as well as the energy released, diameter and depth of the crater, the magnitude of the earthquake as well as the damage on the surface. We studied the Chicxulub asteroid event in two hypothetical scenarios. Firstly, the atmospheric density profile was modified, allowing the calculation of a new value for the impact velocity. Secondly, we assume that the object hits with a fraction of the initial mass, and with this the impact velocity and its effects were recalculated for three different targets. They were used to calculate the infrastructure damage they would cause if the impact could occur today. Finally, the results obtained by our model were compared with the literature, showing that they are consistent with the observational data. Models such as this one contribute to having tools for the attention towards the prevention of this kind of event that in the context of the study risks from the space are necessary in Mexico.

In this article, we study the mass spectra, Regge trajectories and decay properties of heavy-flavour mesons $Q\bar{Q}$ $(Q=c,b)$ within a non-relativistic quark model. The spin hyperfine interaction is used to get the prediction for the heavy-meson masses for radial and orbital excitations. By using the radial and orbital excitations, we construct Regge trajectories for the heavy-mesons in the $(J,M^2)$ and $(n,M^2)$ plane and find their slopes and intercepts. We have computed leptonic, photonic and gluonic decay widths of heavy flavour mesons with and without QCD correction factor. We have compared our results of masses as well as decay widths with other theoretical and lattice QCD predictions for each states. Moreover, the known experimental results are also reasonably close to our predicted results.

Pandemic by SARS-CoV-2 has revealed the importance of disinfection methods due to pathogens of medical importance being detectable and infective after several hours on contaminated surfaces, including medical devices. The aim of this work was to design, construction, and validation of a UVC light irradiation system in the short wavelength region (200 to 320 nm). We studied the effective of the system through in vitro disinfection to eliminate pathogens such as SARS-CoV-2, ESKAPE bacteria and fungi in biofilm and planktonic forms. Doses of 0.25 J/cm2 (10 s of exposure to UVC light), 100% death of ESKAPE bacteria and fungi in planktonic form was observed. Through biofilm formation induction assays of these microorganisms showed resistance to treatment with UV light; however, their viability was not detected after 20 s of exposure (via confocal microscopy). For SARS-CoV-2, 100% reduction was reached after 120 s of exposure. This evidence shows the need to employ emerging methods of disinfection of surfaces and medical devices since these are potential vehicles for transmitting pathogens. The advantages of using UV light as an emergent disinfection method in the era of COVID-19 are discussed.

The purpose of this research was to evaluate the Grunwald-Letnikov definition of fractional order derivatives for determining the fractional derivative of ESR signals from UHMWPE free radicals using the fitted Gaussian distribution method. Specifically, the study focused on analyzing two long-lasting oxygen-induced residual radicals di- or tri-enyls with a carbon center radical (R1) and the oxygen-containing radical (R2). The impact of the derivative order on ESR spectral parameters, such as the Landé g-factor and peak-to-peak separation, was analyzed, and new spectral parameters were established for both radicals. The samples were measured in an ESR tube using ESR power saturation techniques at room temperature. Following the measurements, the fitted Gaussian distribution of the ESR signals was used to determine the fractional derivative using the Grunwald-Letnikov definition. Two estimators (I and II) were developed for both radicals, and their values were found to be 9.19 and 4.27 for Radical R1 and 11.51 and 2060.62 for Radical R2. Our results showed that the fractional derivative approach provided accurate and reliable estimations for the radicals. This method can be easily implemented for various ESR signals and can be useful in many applications, including materials science and biomedical research. The accuracy and reliability of our estimators were confirmed by comparing them with the results obtained from the conventional method. Our findings have important implications for materials science and biomedical research, where ESR signals are widely used. This method can help researchers to obtain more accurate and reliable estimations of radicals, which can ultimately lead to more accurate and reliable conclusions in their studies. Additional research is required to assess the effectiveness of this approach on various ESR signals and to investigate its potential use in other fields of study.

The aim of this study is to propose a methodology to actively control the vibration of functionally graded plates, with the help of piezoelectric actuators and sensors. The study relays on the classical plate theory to analytically formulate the governing equation of motion, which is then expanded to derive a space state equation of the model. The material properties of the FG plate are assumed to vary along the thickness direction. In order to improve the damping effectiveness, the location of the piezoelectric sensors and actuators is optimally determined using the H2 norm. The necessary control voltage was determined based on optimal LQR and LQG controllers.

In this work we analyzed the structural, electronic, and optical properties of a set of silicon nanowires oriented in different directions, using the density functional theory. Structural optimization was performed in order to relax the atomic coordinates and cell parameters, after which the electronic band structure and density of states were obtained. Simultaneously, we computed the imaginary part of the dielectric function using the elements of the dipolar matrix. Furthermore, we related the transitions between the Van Hove singularities in the density of states with peaks in the absorption spectra, thus identifying relationships among them, which could be used to characterize the density of states by means of the absorption spectrum. The results showed that the electronic and optical properties depend on the diameter and orientation of the nanowires.

Piezoelectric materials have nonlinear effects that can be used in 5G and IoT technologies. However, since most nonlinear problems in this area do not have analytic solutions, FEM simulations are an essential design tool. In this study, we have developed a stress-charge formulation for non-linear piezoelectric materials compatible with commonly used simulation tools in industry and research. FEM simulation results for AlN with three nonlinear phenomena are presented: variation of effective electrical permittivity, shift of the effective elasticity constants, and enhancement of electromechanical coupling factor. These simulations were conducted with the same material parameters, having great agreement with recent and important experimental results. The simulations allow us to deduce the values of the components of the high-order tensors for the first time as qr_331 = qr_333 = −1600 and g_333 = −80N/V m. The maximum percent errors obtained for the simulations of the
effective electrical permittivity and effective elasticity constants were 0.1% and 1.77%, respectively.

To perform electro-catalytic oxidation of alcohols in an alkaline media, zinc oxide (ZnO) thin films were effectively deposited on indium tin oxide (ITO) substrates using the pulsed electrodeposition (PE) method in a zinc nitrate aqueous solution. Analyses of microstructural, photoelectrochemical, and optical characteristics of ZnO thin films were performed as a function of pulsed electrodeposition parameters. XRD analysis was applied to determine structural properties, and SEM and AFM analysis were used to investigate morphological characteristics. X-ray diffraction analyses revealed that the produced films were polycrystalline and had a (002) preferentially oriented, hexagonal wurtzite structure. The morphology of ZnO has improved in the direction of nanorod films, as evidenced by scanning electron microscopy (SEM) and atomic force microscopy (AFM) images. UV transmittance data was used using Tauc's relationship to determine the film's bandgap to be 3.26 eV. The photocurrent response shows that ZnO films have high values, at 305.17 A/cm2, and good optical characteristics. The electrocatalytic oxidation of methanol was finally evaluated on the films. After being optimized in the pulsed electrodeposition mode, ZnO thin film characteristics and methanol electrocatalytic oxidation both saw substantial improvements.

CH₃CH₂OH-N₂ plasma mixture was used to synthesize cuprous oxide (Cu₂O) micro-particles in a pulsed DC sputtering system, using a ethanol pressure of 1.5 Torr and a current of 400 mA at a frequency of 30 kHz. The plasma mixture was used successfully to obtain the micro-particles of Cu₂O using a copper (Cu) target and a stainless steel substrate. The Cu₂O products are characterized by the scanning electron microscope (SEM), the results show that the morphology of the Cu₂O microparticles have a spherical shape which are randomly distributed on the stainless steel substrate. Raman results show that from the CH₃CH₂OH-N₂ plasma mixture it is possible to obtain one of the Cu oxidation phases which corresponds to Cu₂O due to the fact that within the sample analyzed by means of Raman it is possible to observe only the peaks that correspond to the Cu₂O phase. The analysis by energy dispersive spectroscopy (EDS) serves to determine the stoichiometric balance present in the substrate, from which the presence of the characteristic peaks of stainless steel was confirmed, along with the characteristic peaks of Cu and O which exhibit an atomic ratio of 2:1 respectively. Atomic force microscopy (AFM) was used to again determine the morphology of the microparticles, finding a spherical morphology. In addition, the value of roughness and grain size was determined, finding values of 20 nm and 45 nm respectively. The images 3-D show the presence of peaks and valleys within the substrate and an non-homogeneous distribution of spherical micro-particles on the surface of the stainless steel.

The combination of Fourier Optics and Artificial Intelligence has driven significant advances in image processing and modeling of optical systems, with the UNet architecture being the main protagonist. However, the DeepLabV3+ network has recently shown promising performance in detecting transfer opens. In this study, we investigate the effectiveness of DeepLabV3+ in identifying transfer apertures in light propagation models and compare its performance with that of UNet. The results reveal that DeepLabV3+ outperforms UNet in terms of accuracy and robustness in identifying transfer apertures, even in the presence of noise and aperture shape variations.

Este artículo investiga el efecto de niveles cercanos no resonantes en las líneas espectrales de los átomos que interactúan con un campo electromagnético. Específicamente, examinamos el efecto AC Stark que ocurre cuando la frecuencia del campo coincide con la frecuencia de transición entre dos niveles más bajos y el campo tiene un número promedio pequeño de fotones (|α| 2 < 4). Nuestra investigación demuestra que los cambios en la forma de la línea espectral se pueden utilizar para distinguir entre los estados de gato de Schrödinger con fases opuestas en π, a saber, los estados |αi + |−αi y |αi − |−αi. Descriptores: Estados gato de Schrödinger; efecto AC stark; formas de las líneas; espectrales, modelo de Jaynes-Cummings.

This article investigates the effect of near non-resonant levels on the spectral lines of atoms interacting with an electromagnetic field. Specifically, we examine the AC Stark effect that occurs when the field frequency matches the transition frequency between two lower levels and the field has a small average number of photons (|α| 2 < 4). Our research demonstrates that the changes in spectral line shape can be used to distinguish between Schrödinger cat states with opposite phases in π, namely, the states |αi + |−αi and |αi − |−αi.

The coherent superposition of states in degenerate quantum systems is investigated using detuned laser pulses in which the Rabi frequencies are time-dependent, and the pulse area is zero. In this study, a quantum system with an arbitrary number of degenerate states in the ground set as well as an arbitrary number of degenerate states in the exciting set is considered. We assume that all states in the ground set are coupled to the excited states using laser pulses such that the pulse area of Rabi frequency is zero, and all of them have the same time dependence. It is also assumed that all laser pulses are in a non-resonant condition with Bohr transitions, and all detunings are the same. We will show that by applying the appropriate temporal dependence for the pulses and the appropriate rate for the detunings, the population can be transferred from an arbitrary superposition from the ground states to a desired superposition from the excited states.

In this study, we synthesized magnetite nanoparticles through a modified coprecipitation route and subsequently coated them directly with Curcuma longa extract. The resulting nanoparticles were then dispersed in distilled water to create a nanofluid. The particle size distribution ranged between 9 to 18 nm according to Transmission Electron Microscopy and Dynamic Light Scattering. The nanofluid’s thermal parameters were obtained by photothermal techniques, obtaining their thermal diffusivity, effusivity, conductivity, and heat capacity per unit volume. The Thermal Wave Resonator Cavity was employed to measure the thermal diffusivity, while the Inverse Photopyroelectric photothermal technique was used to determine the effusivity value. The obtained thermal parameters were close to the carrier liquid (distilled water), being a preliminary study that can be analyzed to improve the heat transfer application in other suspension fluids.

The resonances of a loop pierced by a magnetic field are analized in terms of the scattering matrix phase, the Wigner delay time and its relation to Poisson’s kernel. Except for specific values of the magnetic flux, the resonances appear overlapped by pairs due to the broken degeneracy. Although it is well known that the Poisson kernel describes how the phase is distributed in the Argand plane, we demonstrate that Poisson’s kernel coincides with the reciprocal of the Wigner delay time, thus providing a novel interpretation of this quantity. The distribution of the Wigner delay time is also determined, it exhibits explicitly the effect of the magnetic flux, contrary to what happens to the distribution of the phase.