Vol. 68 No. 4 Jul-Aug (2022): Revista Mexicana de Física

In this article, we review the dynamics of charge carriers in graphene and related 2D systems from a quantum field theoretical point of view. By allowing the electromagnetic fields to propagate throughout space and constraining fermions to move on a 2D manifold, the effective theory of such systems becomes a non-local version of quantum electrodynamics (QED) dubbed in literature pseudo or reduced QED. We review some aspects of the theory assuming the coupling arbitrary in strength. In particular, we focus on the chiral symmetry breaking scenarios and the analytical structure of the fermion propagator in vacuum and under the influence of external agents like a heat bath, in the presence of a Chern-Simons term, anisotropy and in curved space. We briefly discuss the major advances and some new results on this field.

We develop a formalism which provides a new view for the transformation of spherically symmetric metrics, regarding cosmological and Kruskal type metrics. Our analysis begins with some general relevant dynamical metrics in cosmology, and prove that they all can be transformed to a unique static form. We extend the formalism to obtain generalized Kruskal type coordinates in cosmology and black hole theory. This extended formalism provides a novel mechanism to obtain suitable coordinate charts associated with spherically symmetric metrics. In particular, we obtain explicitly new Kruskal type coordinates for extremal Reissner-Nordström and Schwarzschild-de-Sitter metrics, as well for an extension of the de-Sitter metric.

We show that the gravitational waves measurements have raised the opportunity to measure $H_0$ with dark sirens to within 2$\sigma$, the accuracy required to resolve the \hubble tension. There are two principal reasons for our results: (1) upgrades to GW LIGO-Virgo transient catalogues GWTC-1 and GWTC-2 enhance their sensitive with only 10\% of contamination fraction, and (2) new dark sirens should help to constrain our dynamical EoS. In conjunction, sensitivity upgrades and a new dark energy model will facilitate an accurate inference of the \hubble constant $H_0$ to better with an $\pm 0.077$ error in comparison to the LIGO dark siren with $+14.0$/$-7.0$, which would further solidify the role of dark sirens in late dark energy for precision cosmology in the future.

In this paper, we consider a Caputo space-time fractional Schrodinger equation for the delta potential. To solve the equation, we use the ¨ joint Laplace and Fourier transforms on the spatial and time coordinates, respectively. After applying the integral transformations, we use the special initial and boundary physical conditions obtained by trial and error; these special initial conditions involve considering the initial spatial wave function in terms of the Mittag-Leffler function. Consequently, using the fractional calculus, we obtain the wave functions and corresponding eigenvalues. Finally, to verify the solution, we recover the standard case corresponding to α → 1 and β → 1.

The lepton sector is studied within a flavored non-renormalizable model where the S3 ⊗ Z2 flavor symmetry controls the masses and mixings. In this work, the effective neutrino as well as the charged lepton mass matrices are hierarchical and these have (under a benchmark in the charged sector) a kind of Fritzsch textures that accommodate the mixing angles in good agreement with the last experimental data. The model favors the normal hierarchy, this also predicts consistent values for the CP-violating phase and the |mee| effective Majorana neutrino mass rate. Along with this, the branching ratio for the lepton flavor violation process, µ → eγ, is below the current bound.

In this paper, we discussed the probability distribution of exponential and non-exponential tunneling ionization of atoms, taking into account that the tunneling is not instantaneous, but requires a very short time interval. Also, it was investigated how different laser beam profiles affect the probability distribution. These physical situations are analyzed for the valence electron of potassium atom exposed to a strong laser field in a wide range of intensities (10¹² -10¹⁵  W/cm²). We use ADK theory formalism to compute probability distributions. The results demonstrate that the probability distribution in the non-exponential mode has a significantly lower value than in the exponential mode, calculated under the same conditions. We showed that various laser beam profiles on these probability distributions produce different tunneling time intervals.

In this paper, the electron backscattering coefficient for normally incident beams with energy up to 30 keV impinging on thin film targets is stochastically modeled using a Monte Carlo simulation.Accordingly, a generalized model describing the realisticbackscattering behaviortaking into account both the atomic number and the thickness for energy up to 30keV is proposed. The obtained results are compared to the experimental and theoretical data, where an excellent agreement is achieved. Moreover, the usefulness of the proposed model as a probe for investigating the electrons backscattered behavior of several materials is thoroughly discussed. It is revealed that the developedmodel allowsidentifying the critical thickness of thin film exhibiting the same electron backscattering behavior as that of a semi-infinite solid, which contributes to an accurate assessment of surface properties of various thin-films.The use of our empirical model enables reducing the simulation time as compared to that of complicated Monte Carlo time consuming simulation.Therefore, the presented model can be implemented to accurately determinatethe electron backscattering coefficient of various thin-film materials with dissimilar thicknesses, making it appropriate for surface analysis applications.

3-dimensions (3D) printing technology is a type of additive manufacturing (AM) that is on the rise and works by manufacturing components by the deposition of a thermoplastic layer upon layer. In this paper, we explore the use of AM to print a novel fused deposition modeling-based 3D printing electrochemical cell from a non-commercially available composite of PLA/PTFE polymer filament for corrosion applications within materials science. To validate the 3D printed cell, a galvanic series and cyclic voltammetry to aluminum in Hank’s solution was done, and a corrosion resistance study was conducted by using the electrochemical impedance spectroscopy (EIS) and anodic and cathodic polarization (Tafel) techniques to a virgin and a boride ASTM F-73 alloy as working electrode. The results show the possibility of replacing commercial electrochemical cells with 3D printed ones without any compromise on quality of the experiment. Also, this inexpensive and simple instrument design is both, adaptable and sensitive for a wide range of laboratory electrochemical applications.

Inhibition efficiencies (IE) process in polyvinylpyrrolidone (PVP) which is influenced by independent factors, concentration and size of PVP, temperature, time of immersion, and perchloric acid concentration was investigated in this paper. The relationship between factors and their responses is established by the concept of response surface methodology (RSM) explicitly through regression statistical analysis and probabilistic analysis is used in this work. The concept is a combination of mathematical and statistical techniques allowing the modeling and problems analysis by experimental design. In this study, the results based on statistical analysis showed that the quadratic models for the inhibition efficiencies (IE) were significant at the value of probability P < 0.0001 and the coefficient of multiple regressions R²=0.9997, for further validation of the model, R²_Adj=0.9993 indicated a good model. The observed experimental values were in good agreement with predicted ones and the model was
highly significant with Q²= 0.9884. The optimal conditions of inhibition efficiencies (IE) obtained are 104.301% for a concentration of 3.55×10−3 mol/L, temperature of 20.15°C, immersion time of 2h, size of PVP 58000 g/mol, and acid concentration of 0.5 mol/L.

We report on the magnetization of core-shells nanoparticles. Magnetic nanoparticles with a core of magnetite of 13 nm diameter covered with a shell of dopamine (1.1 nm thickness) are studied through vibrating sample magnetometer (VSM), Monte Carlo (MC) computer simulations, and analytical equations. All parameters involved in the theoretical analysis are experimentally determined, namely, the magnetic moment, temperature, magnetic field, core diameter, shell thickness, magnetic anisotropy, and particle concentration. The dependence of the magnetization with the magnetic field obtained through VSM and MC shows a 1% discrepancy in the magnetic saturation and up to 40% in the initial magnetic susceptibility. However, the dependence of the magnetization with the temperature obtained by MC indicates that the MNPs obey the Curie law above a critical temperature of 100 K, and dipolar interactions play an important role in the interval 20 < T < 100 K. That critical temperature is very close to the blocking temperature measured following the zero-field-cooled and zero-cooled protocols, where the dipolar interactions between MNPs become significant. Further analysis shows a Langevin-like behavior for both experimental and theoretical magnetizations. 

Basal and squamous cell carcinoma is currently treated mainly by surgery. In search of non-invasive treatments, the topical treatment with ¹⁸⁸Re was developed, which has shown satisfactory therapeutic results. However, there are currently only two-dimensional descriptions of the absorbed dose distribution in the target region, which limits the information regarding to the absorbed dose (D) imparted to surrounding healthy tissue. Methodology. The simulation scenario was a cream containing a uniformly distributed 188Re, a mylar plastic sheet, and a voxel type phantom representing the skin with a volume of ​​2X2X0.1 cm3 and a voxel size of 100 µm per side. The isodose surfaces, as well as the curves in the sagittal and transverse sections, were analyzed to describe the dose distribution. Results and Conclusion. The Homogeneity Index reveals how homogeneity decreases as depth increases. Tables are reported with the irradiation time necessary to deliver a 50 Gy radiation dose in a 250-750 µm depth range. With the therapeutic configuration described in this work, which is the one used in clinical practice, it was found that it is possible to give a treatment to a depth of 250-650 µm without exceeding the limit of absorbed dose recommended for the epidermis, which is exceeded if the prescribed radiation dose is reached at a depth of 750 µm.

A brain-machine interface (BMI), is a device or experimental setup that receives a brain signal, classifies it, and then uses it as a computer command. Even if large amounts of work exist in the field, there is not a consensus on which kind of learning methodology (deep learning, convolutional networks, AI, etc.) and/or type of algorithms in each methodology, are best to run BMIs. The aim of this work was to build a low-cost, portable, easy-to-use and a reliable BMI based on Motor Imagery Electro-encephalography. To this end, different algorithms were compared to find the one that best satisfied such conditions. In this study, motor imagery EEG signals, from both PhysioNet public data and from our own laboratory obtained using an Emotiv headset, were classified with four machine learning algorithms. These algorithms were: Common spatial patterns combined with linear discriminant analysis, Deep neural network, convolutional neural network and finally Riemannian minimum distance to mean. The mean accuracy for each method was 78%, 66%, 60% and 80% respectively. The best results were obtained for the baseline vs Motor Imagery comparison. With global-training public data, an accuracy between 86.4% and 99.9% was achieved. With global-training lab data, the accuracy was above 99% for Common Spatial Patterns and Riemannian cases. For lab data, the classification/prediction computing time per event were 8.3 ms, 18.1 ms, 62 ms and 9.9 ms, respectively. In the discussion a comparison between the results presented here and state-of-the-art of methodologies and algorithms for BMIs can be found. We concluded that Common spatial patterns and Riemannian minimum distance to mean, algorithms resulted in fast (computing time) and effective (success rate) tools for their implementation as deep learning algorithms in BMIs.

We aim to reach an analytic expression that describes the path of light rays through the Earth’s atmosphere in the particular situation in which an inferior mirage is occurring. To achieve our goal, we assume an exponential refractive index profile close to the ground, as suggested by empirical and theoretical studies on the state of air when an inferior mirage is taking place. We consider a parallel-plane atmosphere and assume that the laws of geometric optics apply. Since Fermat’s principle holds, we solve the Euler’s equation and, from the solution we obtain an analytic expression that describes the ray paths in a plane perpendicular to the ground. Given that we focus on the particular case of inferior mirages, we were able to find a very simple and easy-to-use expression to describe the ray paths, allowing us to extract additional valuable information with minimal computational effort. We take advantage of it to impose a limit to the thickness of the air layer next to the ground where appropriate conditions exist to bend the rays upwards, and produce an inferior mirage.

In this present paper, the effect of fractional analysis on magnetic curves is researched. A magnetic field is defined by the property that its divergence is zero in a three dimensional Riemannian manifold. We investigate the trajectories of the magnetic fields called as t-magnetic, n-magnetic and b-magnetic curves according to fractional derivative and integral. As it is known, there are not many studies on a geometric interpretation of fractional calculus. When examining the effect of fractional analysis on a magnetic curve, the conformable fractional derivative that best fits the algebraic structure of differential geometry derivative is used. This effect is examined with the help of examples consistent with the theory and visualized for different values of the conformable fractional derivative. The difference of this study from others is the use of conformable fractional derivatives and integrals in calculations. Fractional calculus has applications in many fields such as physics, engineering, mathematical biology, fluid mechanics, signal processing, etc. Fractional derivatives and integrals have become an extremely important and new mathematical method in solving various problems in many sciences.

Sales per capita (per number of employees) of the two thousand Forbes Magazine top publicly-traded companies (G-2000) for years 2015, 2020 and 2021 are statistically analyzed. Employing an econophysical model, the sales distributions per capita for the three years exhibit a two-class structure: a Pareto power law in the higher part and exponential in the lower part resembling a Boltzmann-Gibbs distribution. This distribution is consistent with income distributions around the world as if a fraction of a firms' wealth goes to its employees in the form of wages and salaries. We highlight some changes in sales between 2020 and 2021 on selected industries that had the biggest negative and positive impacts partially due to the COVID-19 pandemic.

The calibrations of the full-energy peak efficiency, energy, and energy resolution are the main factors for successful quantitative gamma-ray analysis. The first purpose of this work is to present the calibration factors for 2"x2" ScintiPack Model 296 NaI(Tl). The detector was irradiated with radioactive sources ( 137 Cs, 60 Co, 152 Eu point sources, and 241 Am, 22 Na cylinder-shaped sources) that emit photons at different energies from 59 keV to 1408 keV. The detector efficiency was also evaluated using Geant4 based GATE simulation. The analytical equations for efficiency calibration were found out with their parameters. Since the results obtained from the experimental and simulation were compatible with each other and with literature results, then the simulation model was modified into the novel scintillation detector systems such as; LaBr₃, GAGG(Ce), and SrI₂ .

Experimental angular distributions for the weakly bound ^9,10Be nuclei elastically scattered from ²⁰⁸Pb target at various energies are investigated using phenomenological and microscopic potentials. The considered data in this study is: ⁹Be+²⁰⁸Pb in the energy range of 37.0–75.0 MeV and ¹⁰Be+²⁰⁸Pb in the energy range of 38.4–43.9 MeV. The performed analysis reflects the nature and peculiarities of the considered projectiles. For the ⁹Be+²⁰⁸Pb nuclear system, the data showed a typical Fresnel diffraction scattering pattern and the Coulomb rainbow phenomenon is well presented due to the interference between partial waves refracted by the Coulomb and nuclear potentials. The ⁷Li+d and ⁹Be+n cluster structures of ⁹Be and ¹⁰Be, respectively are studied. The extracted renormalization factors for the real part of potential constructed on the basis of double folding as well as cluster folding could reflect the nature of the loosely bound projectiles.

In the present work, we have calculated the radiative transfer, it means the radiative energy that escapes from a plasma formed from a mixture of Argon−Helium. The computations take into account several pressures between 1 ≤ p ≤ 100 atm in the temperature T wide range of 5000 − 30 000 K. In the case of the plasmas is supposed to be in local thermodynamic equilibrium. Where the contributions have been treated separately in the calculation: atomic emission lines self-absorbed and not self-absorbed, continuum (radiative attachment, radiative recombination and radius). The results show that a large part of radiation is absorbed at the first crossed millimeter and also the contribution of resonance lines is very important. These are the lines which are strongly absorbed.

A low-pressure ethanol and methanol discharge produced by a DC electric field was studied experimentally, analyzing the disruptive voltage between parallel electrodes with a circular geometry as function of pressure and distance according with the Paschen’s law, this states that the breakdown voltage is a function of the product of gas pressure and distance following the relationship: VB = f(pd). Detailed knowledge of the minimum breakdown voltage required to initiate the ethanol–methanol discharge will be useful to providing important information for future experiments and applications. In this experiment, a cylindrical chamber was used to generate a glow discharge of the ethanol (CH3CH2OH), methanol (CH3OH), and 50% mixture, over a pressure range of 0.07–5.00 Torr. Optical emission spectroscopy was performed in the wavelength range of 200–900 nm. The Paschen curves, measured experimentally for ethanol and methanol are presented, taking in account the coefficient obtained using the variation in Paschen’s law as a function of the distance and radius of the electrodes (d/r).

Semiconductors with wide bandgap are crucial for optoelectronic devices and energy applications owing to their electron confinement, high optical transparency and tunable electrical conductivity. Therefore, in this study, the quantum confinement effect of the energy bandgap of chalcogenide semiconductor nanocrystals such as ZnS, ZnSe, ZnTe, SnS, SnSe and SnTe are studied based on the Brus model using the effective mass approximation, the hyperbolic band model and the cohesive energy model. The obtained results indicate that the value of energy bandgap differs from the bulk crystals related to the quantum confinement effect. These verdicts confirm the quantum confinement effects of materials and their potential applications in optoelectronic devices. Theoretical findings are compared with its valid experimental data.

Light scattering due to the interaction of photons and acoustic waves present in a dilute inert gas is analyzed through the use of irreversible thermodynamics. The dispersion relation, which governs the dynamics of the density uctuation of the gas allows the establishment of a simple criterion for the corresponding Rayleigh-Brillouin spectrum to be observed. The criterion here proposed allows a clear physical interpretation and suggests generalizations for other interesting physical scenarios.