Vol. 69 No. 6 Nov-Dec (2023): Revista Mexicana de Física

Shannon entropy (SE) for hydrogen isoelectronic sequence is calculated through numerical simulation. Fast and accurate Numerov method is applied for the computation of the wavefunctions used for the evaluation of Shannon entropy. The reliability of this approach is verified by the excellent comparison with the available literature results. It is observed that Shannon entropy values diminish with an increment in atomic number (Z). Additionally, previously unexplored Shannon entropy behaviour for a variety of higher excited orbitals is investigated. It is found that Shannon entropy exhibits an interesting behavior of increasing and decreasing nature with principal quantum number n and orbital quantum number l, respectively. Benchmark values for Shannon information entropy are established for the ground and excited states as a signature of localization and delocalization of electron density. This will further contribute to the diagnostics of spectroscopic data and atomic system complexity.

This is to investigate the structural, mechanical, electronic and optical properties of half-Heusler KZnN and KZnP compounds. The ab initio method based on density functional theory is employed. The study of structural properties has allowed us to verify the cubic structure type I that is the most stable among the three possible atomic arrangements for the two half-Heusler compounds. The mechanical stability is checked, since the calculated elastic constants obey the stability criteria of cubic. Our calculations have demonstrated that KZnN is a ductile material that is considerably stiffer than KZnP, which exhibits brittleness. The obtained results for the electronic properties with mBJ-GGA approximation reveal a semiconductor behavior with a band gap along Γ as estimated at 0.3 eV and 0.9 eV for KZnN and KZnP compounds, respectively. In addition, the optical properties have been studied by analyzing the variation of different parameters such as dielectric function, refractive index, reflectivity, absorption coefficient and conductance as a function of photon’s energy for a wide range; 0 - 40 eV. The origin of peaks in the optical spectra is determined in terms of calculated energy band structures. This work has predicted strong absorption in the ultraviolet field.

The structural and vibrational properties of 4-(benzenesulfonyl)-morpholine, C₁₀H₁₃NO₃S, have been studied using multinuclear (¹H and ¹³C) NMR, IR and Raman spectroscopy techniques at pressures up to 3.2 GPa, as well as molecular modeling and vibrational mode assignment using DFT calculations with B3LYP functional and 6-31G (d,p) basis set and potential energy distribution (PED). Experimental and calculated spectra were compared and showed good accuracy. The sample was subjected to high pressure in the range of 0 to 3.2 GPa. The pressure measurements suggest a conformational transition for values around 0.7, 1.7 and 2.5 GPa, which was observed in some spectral regions, mainly in the high energy vibrational bands.

The large eddy simulation approach was used to perform a numerical simulation of a flow around a helical segmented-fin tube bundle. This work focuses on the study of turbulence and the effect of segment depth on it. The simulation was conducted in an area away from the boundaries of the tube bundle, where the flow is fully-developed, and the use of periodic boundary conditions is possible. The computer-aided design of the helical segmented-fin tube geometry is incorporated into the computational grid from the immersed boundary technique. The Reynolds stress tensor was used to analyze the anisotropic state of turbulence. This flow is characterized by an anisotropic state generated by a flow with a preferential direction. A transfer of momentum in the inter-segment space and contiguous zones was observed. This intersegment flow generates a less anisotropic state of turbulence. This study aimed to understand a possible transformation of heat transfer with marginal geometrical changes and pressure drop increases.

Quantum Field Theory (QFT) is used to describe the physics of particles in terms of their fundamental constituents. The Light-Front Field Theory (LFFT), introduced by Paul Dirac in 1949 [1], is an alternative approach to solve some of the problems that arise in quantum field theory. The LFFT is similar to the Equal Time Quantum Field Theory (EQT), however, some particularities are not, such as the loss of covariance in the light-front. Pion electromagnetic form factor is studied in this work at lower and higher momentum transfer regions to explore the constituent quark models and the differences among these and other models. The electromagnetic current is calculated with both the “plus” and “minus” components in the light-front approach. The results are compared with other models, as well as with experimental data.

The deformed Klein-Gordonequation has been solved in three-dimensional extended relativistic quantum mechanics (3D-ERQM) symmetries for the improved modified Yukawa-Kratzer potential (IMYKP) model under the influence of the deformation space-space symmetries. The new relativistic energy eigenvalues were calculated using the parametric Bopp’s shift method and standard perturbation theory in addition to the approximation scheme suggested by Greene and Aldrich for the inverse square terms. The new relativistic energy eigenvalues of (LiH, HCl, CO and H2) molecules under the IMYKP model it was shown to be sensitive to the atomic quantum numbers (j, l, s, m), mixed potential depths (V0, De, re), the screening parameter’s inverse α and noncommutativity parameters (Θ,τ ,χ). In addition, we analyzed the nonrelativistic energy values by applying the well-known transmission rules known in the literature. In addition, we studied many special cases useful to researchers in the framework of the new extended symmetries, such as the improved modified Kratzer potential, the improved generalized Kratzer potential, the improved Kratzer potential, the improved modified Kratzer plus screened Coulomb potential, the improved Hellmann potential, the improved Yukawa potential, and improved inversely square Yukawa potential. We noticed that these particular results are identical to our previous work and other known works in the literature. The study is further extended to calculate the mass spectra of mesons of charmonium (cc) and bottomonium (bb) within the framework of the IMYKP model in three-dimensional extended non-relativistic quantum mechanics (3D-ENRQM) symmetries.

The structural, electronic, optical, and thermoelectric properties of the niobium new halide double perovskites Cs₂GeNbX₆ (X = Cl, Br, I) were investigated using a density functional theory method. The generalized gradient approximation (GGA) method is used to project the exchange-correlation potential. The tolerance factor and optimizing total energy define the structure's stability. The magnetic moments of our compounds are high, more than 3μ_B. The compounds have direct narrow band gaps of 0.69, 0.46, and 0.26 eV, respectively, for Cs₂GeNbCl₆, Cs₂GeNbBr₆, and Cs₂GeNbI₆, as determined by band structure calculations. This is ideal for investigating these compounds for use in solar cells. In addition, the investigated compounds were investigated in terms of optical absorption, refractive index, and dielectric constants for energy range 0–12 eV, ensuring absorption in infrared, visible, and ultraviolet regions. This was done in order to study optical characteristics. The investigated compounds are excellent candidates for harvest solar cell applications due to their maximum visible absorption. They are also good candidates for thermoelectric applications due to their Seebeck coefficient, lattice thermal, electric conductivities and figure of merit (ZT) addressed by Boltzmann theory.

This study investigates the corrosion potential of ASTM A-36 steel after slide burnishing using different applied forces. Turned samples of ASTM A-36 steel were subjected to slide burnishing surface treatment. The burnishing process was carried out with forces of 150 N, 300 N, and 450 N, at a travel speed of 100 mm/min. The effects of burnishing on the chemical composition of the material were analyzed using Grazing Incidence X-ray Diffraction and X-ray photoelectron spectroscopy, which indicated no changes in the chemical composition of the material. Corrosion potential measurements were performed using the Tafel test. The results showed that as the burnishing force increased, the corrosion potential shifted to lower values. Additionally, roughness analysis suggested that the change in corrosion potential was attributed to plastic deformation caused by the burnishing process. The increased mechanical work exerted on the material during burnishing may be the underlying reason for the observed shift towards lower corrosion potentials with higher applied forces.

This study aims to determine the effect of the concentration of Carbon Dots on the bandwidth of the Carbon Dots luminescence spectrum. Carbon Dots are produced by ultrasonification method and characterized using UV-Vis spectroscopy, photoluminescence (PL) spectroscopy, scanning electron microscopy (SEM), electron dispersive X-Ray spectroscopy (EDX), X-ray diffraction (XRD), and particle size analyzer (PSA). Measurement of the bandwidth of the Carbon Dots fluorescence spectrum for various concentrations was carried out by irradiating the Carbon Dots sample using a laser with a wavelength of 405 nm and looking at the spectrum of light emitted using a Kirchoff-Bunsen spectroscope.The characterization results show that the resulting Carbon Dots have a light absorption peak at a wavelength of 303 nm, a light wave emission peak at a wavelength of 508.87 nm, the surface structure of the Carbon Dots is in the form of a porous layer, the presence of the dominance of carbon and oxygen atoms in Carbon Dots, an amorphous Carbon Dots structure is observed, and the smallest measured Carbon Dots particle size is 1.12 nm. The results show that increasing the concentration of Carbon Dots causes a tendency to increase the bandwidth of orange, green and blue light spectra emitted by the particles, and in the red color there was no significant effect of increasing the concentration of Carbon Dots on the spectrum. However, increasing the concentration of Carbon Dots actually causes a narrowing of the yellow and violet color spectra.

In the present research, a supervised learning classification methodology is proposed to identify post-COVID conditions. Image processing and deep learning methods were employed to analyze a data set provided by the High Specialty Medical Unit No.1 of the Mexican Institute of Social Security (T1-IMSS) of Leon, Guanajuato, Mexico, of Mexican patients infected with COVID-19. The dataset is classified into post-COVID findings and no post-COVID findings. A deep neural network of 50 hidden layers is used to extract regions of interest, with properties that can potentially be related to computer-aided medical diagnosis. Different patterns were found in the post-COVID computed tomography scans: pulmonary fibrosis, ground glass pattern, etc. The efficiency of the proposed method was 97% precision using the cross-validation classification scenario. This result allows to provide an auxiliary tool in medical diagnosis, through computer-aided diagnosis. This model provides an automatic and objective estimation of post-COVID conditions of Mexican patients, facilitating the expert interpretation during the COVID-19 pandemic.

The phase function method/variable phase approach to potential scattering is exploited to calculate the phase shifts for nucleon-nucleon systems in low and intermediate energy regions by representing nuclear part of the interaction by the Hellmann potential while the electromagnetic part by the Coulomb one.  In addition, the differential and total scattering cross sections are estimated with our phase parameters. Results reproduced by the concerned potential are in good agreement with the previous works in the literature.

The radioactivity concentration for shrimp and sea bass retrieved from the Mexican Pacific Ocean and the Gulf of Mexico is reported in this work. The activity of 40K and 208Tl was determined with gamma spectroscopy using a High Purity Germanium detector. Overall, the radioactivity concentration of samples from the Mexican Pacific Ocean is higher than from the Gulf of Mexico. The 40K concentration measured for shrimp is 575 ± 14 Bq/kg (Pacific) and 443 ± 10 Bq/kg (Gulf), while the activity for sea bass is 753 ± 18 Bq/kg (Pacific) and 502 ± 14 Bq/kg (Gulf). Similarly, the measured concentration of 208Tl for shrimp and sea bass is 0.75 ± 0.03 and 1.09 ± 0.05 Bq/kg (Pacific), respectively, and 0.51 ± 0.02 and 0.85 ± 0.04 Bq/kg (Gulf), respectively. No other natural radionuclides or radiation contaminants were observed with significant activity. This is the first comparison of radioactivity concentration in fish and shellfish between the two main Mexican marine ecosystems.

In this study, we research the behavior of a linearly-polarized light wave in optical fiber and the rotation of the polarization plane through the alternative moving frame { N,C,W } in Minkowski 3-space. Then Berry’s phase equations are discussed for electromagnetic curves in the { C } and { W } directions along an optic fiber via alternative moving frame in Minkowski 3-space. Moreover, electromagnetic curve’s { C } and { W } Rytov parallel transportation laws are defined. Finally, we examine the electromagnetic curve’s Maxwellian evolution by Maxwell’s equation.

Nano optical crescent patch antenna for Terahertz applications using Graphene is designed in this paper. The antenna is designed at 7.28 THZ with several substrates material as PTFE (²r = 2.1), polymide (²r = 3.5), RO3003 (²r = 3), RO4003 (²r = 3.4) and Arlon AD (²r = 2.5). Graphene is the material patch used with different properties such as chemical potential µc = 0.2 eV, relaxation time τ = 1 ps and thickness of 60 nm to achieve a high gain and bandwidth. We obtained a very good performance of crescent antenna at 7.28 THZ with −37.962 dB, 7.124 dBi, 1.767 THZ of return loss, gain and bandwidth respectively which is very satisfactory for terahertz transmission between [0.1-10] THZ.

In the present work, we analyze the different regions that are configured in a vertical plane for the visualization of the inferior mirage phenomenon. To achieve our goal, we take advantage of a methodology that we have previously developed to analytically obtain the path taken by any ray emerging from a point object, explicitly considering the atmosphere’s behavior near the surface. By means of this procedure we have reached analytical expressions, dependent on measurable temperature values, to delimit the observation regions in which it would be possible to see only objects, only images, both simultaneously, or none of them. From the expressions obtained, we study how these regions are distributed under different atmospheric conditions. The results obtained show that our methodology allow to predict the position (distance from the object and height from the ground) at which an observer should be located to observe the phenomenon, knowing the values of the air temperature at three different heights in the microlayer.

Nowadays, when calibrating spectrocolorimeters, the uncertainties are calculated based on the premise that the obtained measurements have a Gaussian distribution, but there is no certainty that the latter is completely true. The aim of this work is to show that, when measuring reference materials with different spectrocolorimeters, most of the results do not have, for all the points in the visible spectrum of the spectral curve, a Gaussian distribution. Also, this distribution is not present in measurements of the chromatic coordinates of these materials. These measurements were performed with two integrating sphere spectrocolorimeters; a Minolta 2600d r (portable) and a Gretag Macbeth 7000 r (bench) equipment, under the same measurement parameters and conditions of repeatability, as well as controlled environmental conditions, i.e., 20 ± 1 ◦C. Since a Gaussian distribution is needed to use parametric statistics to calculate the combined uncertainties and consequently, the expanded ones, the statistical method currently used is erroneous. Thus, parametric statistics should not be used to calculate the spectrocolorimeters’ uncertainties.

In this paper, we consider a Weyl pair under the effect of an external uniform magnetic field in a monolayer medium without considering any charge-charge interaction between the particles. Choosing the interaction of the particles with the magnetic field in the symmetric gauge we seek for an analytical solution of the corresponding form of a one-time fully-covariant two-body Dirac equation derived from quantum electrodynamics via the action principle. As it is usual with two-body problems, we separate the relative motion and center of mass motion coordinates. Assuming the center of mass is at rest, we derive a matrix equation in terms of the relative motion coordinates without considering any group theoretical method. This equation gives a wave equation in exactly soluble form and accordingly we obtain the spinor components and complete energy eigen-states (in closed form) for such a spinless composite structure. Our results not only give exact Landau levels for such a Weyl pair in a monolayer medium but also show the considered system behaves as a two-dimensional harmonic oscillator. Furthermore, our findings give exactly the excited states of a Weyl particle under the effect of uniform external magnetic field in a monolayer graphene sheet and there is no imprint to distinguish these modes from each other. This means that the performed experiments based on Landau levels for a monolayer graphene sheet may actually involve many-body effects. Our results provide a suitable basis to analyze the associated thermal quantities and accordingly we discuss the thermal properties by determining free energy, total energy, entropy and specific heat for the composite system in question.