Vol. 70 No. 4 Jul-Aug (2024): Revista Mexicana de Física

The quantization of the electron orbits in the Bohr atom is revisited. The toroidal electron model, in which electron charge is described by Schwinger electromagnetic wave orbiting the electron mass, offers a natural explanation for the orbit quantization. As a consequence, the four Bohr postulates can be directly derived from the toroidal electron structure. A physical meaning for the Rydberg constant is also proposed.

The mass attenuation coefficient (MAC) for different sulphate compounds can be estimated by using the Energy Dispersive X-ray Fluorescence (EDXRF), also known as X-ray Fluorescence (XRF) technique. The X-ray photons emitted have different energies depending on incident photon energy, atomic weight, and molecular structure of tested material. The excitation energy of the gamma rays source with 59.53 keV was obtained by using 241Am (40 µci). The (MAC) for sulphate compounds of a different element (Fe, Ni, Cu, Zn) have been calculated by measuring the intensity difference for kα in pure elements and their compounds. The determined results showed that the maximum value for (µm) was in FeSO₄. These results are consistent with the theoretical value obtained by the XCOM software in addition to investigating the wide energy response of photon interaction with the introduced compounds using the FLUKA Monte Carlo simulation software. The mass attenuation coefficient (MAC) of these compounds is numerically evaluated in the energy range 0.015-15 MeV using the FLAIR code. The computed (µm) is used to generate significant radiation protection factors such as the linear attenuation coefficient (LAC), half-layer value (HVL), effective (Zeff), and equivalent (Zeq) atomic number. For studying the shielding effectiveness and efficiency, for fast and thermal neutron radiation, the removal cross-section Ʃ_R was given.

We study the Su-Schrieffer-Hegger model, perhaps the simplest realization of a topological insulator, in the presence of an embedded impurity superlattice. We consider the impact of the said impurity by changing the hopping amplitudes between them and their nearest neighbors in the topological boundaries and the edge state localization in the chain of atoms. Within a tight-binding approach and through a topolectrical circuit simulation, we consider three different impurity-hopping amplitudes. We found a relaxation of the condition between hopping parameters for the topologically trivial and non-trivial phase boundary and a more profound edge state localization given by the impurity position within the supercell.

Using the density functional theory (DFT) and the spectral limited maximum efficiency (SLME) model, we thoroughly evaluate the material MA₂GeI₄ as a prospective absorber for photovoltaic applications. This material belongs to the family of layered material organic-inorganic Ruddlesden-Popper perovskites, which have attracted interest due to their stability. Our first-principles calculations show that MA₂GeI₄ has a direct bandgap that is suitable for light absorption at 1.37 eV. To understand the source of its exceptional optical properties, the electronic structure, density of states, and optical properties were examined. Also, we used the SLME model to estimate the MA₂GeI₄ solar cell efficiency. The latter was found to be about 32.6% power conversion efficiency. The material’s excellent absorption and promising photovoltaic properties contribute to its high efficiency, even when quantum confinement occurs between layers. We found that MA₂GeI₄ is a potential absorber material for solar applications, demonstrating both good absorption characteristics and advantageous electrical properties. This discovery lays the path for additional experimental investigation of MA₂GeI₄ based solar cell.

Two exact different solutions to the Telegraph equation in three-dimensional space are obtained in terms of Airy functions. As a result, these solutions unveil a distinctive propagation pattern along a coordinate that resembles a speed-cone-like coordinate of the system. This unique characteristic leads to effective Schr¨ödinger-like equations, amenable to exact solutions through Airy functions.

Cobimaximal mixing predicts π/4 and 3π/2 for the atmospheric angle and the Dirac CP-violating phase, respectively. These values are in tension with the neutrino global fits. If this pattern was behind the lepton mixings, then it would have to be broken. In that case, in this paper, we explore the S₃ flavor symmetry within the B − L gauge model where the aforementioned scheme comes from the neutrino sector but the charged lepton contribution breaks the well known predictions so the mixing observables as well as the m_ee mass can be accommodated quite well according to the available data. Notably, the predicted regions for the Dirac CP-violating phase would allow us to test the model in future experiments.

Partiendo de la teoría de masa efectiva y el modelo de Thomas-Fermi (TF) se ha establecido el perfil de potencial para un sistema tipo delta-dopado simple en Arseniuro de Galio (GaAs) tipo n. Resolviendo la ecuación de Schrödinger asociada al sistema, se han calculado los autovalores y las autofunciones del perfil de potencial, determinando así su estructura electrónica. Con ayuda de la teoría de Matriz Densidad se ha determinado el cambio en el índice de refracción (CIR) lineal y no lineal del sistema. De tal manera que, añadiendo un término de desorden en el sistema (ζ), es posible calcular numéricamente los cambios en la estructura electrónica y las propiedades ópticas no lineales. Se ha determinado que con valores de ζ alrededor del 10% asociado a la densidad de impurezas (N_2D), el cambio en el índice de refracción lineal y no lineal no sufre cambios significativos. Por otro lado, cuando se incrementa el desorden en la densidad de impurezas introducidas en el material semiconductor, el comportamiento de la propiedad óptica se pierde por completo. Finalmente, notamos que al introducir desorden en la intensidad del laser, la propiedad óptica no sufre cambios. El presente estudio teórico podría predecir el efecto del desorden estructural sobre el comportamiento del CIR en los dispositivos basados en delta dopados al momento de su síntesis.

Starting from effective mass theory and the Thomas-Fermi (TF) model, the potential profile for a simple delta-doped system in n-type Gallium Arsenide (GaAs) has been established. By solving the Schrödinger equation associated with the system, the eigenvalues and eigenfunctions of the potential profile have been calculated, thus determining its electronic structure. So, with the Density Matrix theory, the change in the linear and nonlinear refractive index (CRI) of the system have been determined. In By introducing a disorder term in the system (ζ), it is possible to calculate numerically the changes in the electronic structure and nonlinear optical properties. Here, it has been determined that with ζ values around 10% associated with the density of impurities (N_2D), the change in the linear and nonlinear refractive index does not undergo significant changes. On the other hand, On the other hand, as the disorder in the impurity density introduced into the semiconductor material increases, the optical property behavior is completely lost. Finally, we note that when introducing a disorder term in the laser intensity, the optical properties do not change significantly. This theoretical study could predict the effect of structural disorder on the behavior of CRI in delta-doped devices during their synthesis.

We investigated the electronic, elastic, and magnetic properties of the hypothetical half- Heusler alloys with Niobium base atom, XNbSn with (X= Cr, Mn, Co, Fe, V) uses the full-potential (linearized) augmented plane-wave and local-orbitals [FP-(L)APW + lo] basis set in the WIEN2K ab-initio package based on density functional theory (DFT). We investigated the elastic constants, Shear modulus, young modulus, and bulk modulus of these alloys under different pressures (0, 20, 40, and 80 GPa). We predicted that CoNbSn behaves as a semiconductor with a direct energy gap of 0.99 eV, while the other half- Heusler alloys show a metallic behavior. CoNbSn keeps its semiconductor behavior under higher pressures up to 80 GPa. Both of VNbSn and CrNbSn have a high value of magnetic moments of 2.158 and 3.002 µB respectively. All XNbSn alloys are stable mechanically at different pressures according to the Born-Huang conditions. CoNbSn, FeNbSn, CrNbSn, and MnNbSn behave as a ductile material at ambient pressure.

This study presents a novel methodology framework for simulating and optimizing reaction kinetics in natural convection microfluidic devices. The approach involves coupling heat and mass transfer, fluid flow, and chemistry. Visual and regression analyses are performed to evaluate the impact of different operational parameters on reaction speed, aiming to improve microfluidic natural convection systems. The methodology was applied to a practical example of a Polymerase Chain Reaction triangular microfluidic glass device that utilizes natural convection for the required reactions. The findings showed that the fluid flow velocity is significant in determining the reaction speed, which can be controlled by adjusting the temperature cycling differences and the inner diameter of the device. Despite challenges posed by the fluid flow direction, the best reaction times achieved ranged from 18 to 21 minutes. Due to its computational efficiency, the developed methodology allows simulations to be conducted on mid-range computers. Also, the visual and regression analyses offer insights into improving a specific device by measuring the influence of several parameters. Then, the methodology is convenient for selecting the best conditions before developing an experiment.

This study aims to explore the potential of olive leaves nanoparticles (OLNPs) in scavenging free radicals, particularly 2,2-diphenyl-1- picryl-hydrazyl-hydrate (DPPH), and their capability to mitigate the effects of ionizing radiation. The in vitro assessment of antioxidant activity revealed promising results for OLNPs, exhibiting effective DPPH scavenging within a concentration range of 0.00002 to 0.0001 g/l. Additionally, the natural nanoparticles demonstrated significant antioxidant capacity, suggesting their potential as radical scavengers against free radical-induced damages. Characterization of OLNPs was conducted using UV-Visible absorption spectroscopy, revealing surface Plasmon resonance absorption peaks around 287 nm. Furthermore, atomic force microscopy was employed to determine the morphology and size of the OLNPs, indicating an average diameter of 65 nm.

In the present text we construct velocity-dependent or equivalently energy-dependent potential (EDP) to an energy-independent nonlocal potential (EIP) of rank-1 by Taylor series method. The phase shifts for the nucleon-nucleon and alpha-nucleon systems are computed for these two potentials by exploiting the variable phase method and the Fredholm determinant, respectively. The velocity-dependent potential is found to be superior to central nonlocal interaction in generating the scattering phase shifts up to high energy region.

We study the possible existence of bound states of three Ω_bbb baryons. We consider only S wave interactions and we start from recent lattice QCD results which give a strongly attractive potential between two Ω_bbb baryons in the ¹S0 channel. We analyze different scenarios. At baryonic level, the Ω_bbbΩ_bbb interaction could be understood to be basically spin-independent, so that the two contributing channels, ¹S₀ and ⁵S₂, would have a very similar interaction. This baryonic analysis leads to the existence of bound states in the three-body system. At the quark level, repulsive effects would appear in the ⁵S₂ channel, making it more repulsive than the ¹S₀ channel. We study the effect of such repulsion.

This paper presents a numerical analysis of the impact of grooving the Nd doped YAG rod on the sunlight-pumped lasers performance. The study analyzes laser systems that utilize side-exciting and end-side-exciting approaches to activate both grooved and non-grooved Nd doped YAG laser rods. The effects of the rod surface groove on the performance of the sunlight-pumped-lasers are thoroughly examined using ZEMAX^© and LASCAD^© software. To excite the grooved and non-grooved Nd doped YAG rods alternately, a ring-array sunlight flux concentrator is employed. Moreover, in the side-exciting technique, the head of the laser system contains a rectangular light guide of an extremely transparent glass made from fusing silica and an excitation cavity with a V-shaped configuration, housing the Nd doped YAG rod. This exciting method with a grooved laser rod resulted in a 13.70% increase in laser power and a 28.20% reduction in stress intensity compared to the non-grooved rod. In the end-side-exciting technique, the head of the laser system comprises an aspheric lens made of a fused silica glass and a conical-shaped excitation cavity, accommodating the Nd doped YAG rod. Results indicate that using grooved laser rod in this exciting system did not lead to an amelioration in output laser power. However, this technique enhanced the stress intensity by a reduction of 35.03%.

This paper is based on finding soliton solutions to fractional Kaup-Boussinesq (FKB) system. The fractional derivatives such as β-derivative and truncated M-fractional derivative are used in this study. The unified approach, generalized projective riccati equations method (GPREM) and improved tan (φ(ζ)/2)-expansion approaches are efficiently used for obtaining bright soliton, dark soliton, singular soliton, periodic soliton, dark-singular combo soliton and dark-bright combo soliton. The numerical simulations are also carried out by 3D and 2D, graphs of some of the obtained solutions to discuss the fractional effects.

The effect of a non-unitary transformation on an initial Hermitian operator is studied. The initial (Hermitian) optical system is a Glauber-Fock optical lattice. The resulting non-Hermitian Hamiltonian models an anisotropic (Glauber-Fock) waveguide array of the Hatano-Nelson-type. Several cases are analyzed and exact analytical solutions for both the Hermitian and non-Hermitian Schrödinger problems are given, as they are simply connected. Indeed, such transformation can be regarded as a non-unitary Supersymmetric transformation and the resulting non-Hermitian Hamiltonian can be considered as representing an open system that interchanges energy with the environment.

The study of carbon-based nanostructured materials is a highly active research field, that has made significant progress in the study of twodimensional materials and nanotechnology. The interest in these materials is mainly attributed to the fascinating properties they exhibit, as seen in the case of graphene as a 2D material, as well as emergence on numerous novel 2D materials and their heterostructures. Additionally, there is important interest in systems such as 2D quantum dots. Therefore, this work focuses on the systematic study of graphene quantum dots of various sizes, all within the framework of first-principles density functional theory. We started with the simplest graphene quantum dot (GQD) structure, benzene (C6H6), which consist of six carbon atoms passivated with hydrogen atoms. We then increased its size by adding more aromatic rings, resulting in the following GQD configurations: C₂₄H₁₂, C₅₄H₁₈, C₉₆H₂₄, C₁₅₀H₃₀ and C₂₁₆H₃₆. We report the density of states (DOS) and the imaginary part of the dielectric function (ε2) for the system, analyzing both the pristine configuration and the effect of both single and double (boron, nitrogen and silicon, denoted as Sa). The double substitutional atom study was done considering random, ortho-, meta-, and para-director positions just for the C₉₄H₂₄S_a2 GQD. In general, we can conclude that as the GQD increases in size, the HOMO-LUMO energy decreases. Furthermore, it is observed that boron and nitrogen exhibit their expected n-, and p-type doping characteristics, but this differs between single and double Sa substitutions. Additionally, the imaginary part of the dielectric function is highly sensitive to the positions of single and double substitutional atoms, as well as the polarization of incident light. Therefore, we suggest that these differences can be used to clearly determinate the type of substitutional atoms and their positions from optical measurements.

In this work we designed an experimental setup based on a double coil and an electromagnet to measure the magnetoelectric effect of a PZT/Ni_50.5Mn_27.9Ga_21.6/PZT laminate composite, made of a bulk single crystal of Ni_50.5Mn_27.9Ga_21.6 shape memory alloy. The shape memory alloy showed a martensitic transformation at 298 K, a Curie temperature at 368 K and room temperature magnetization of 2.87 u_B/f.u. Strain response was found to be between 3% and 4% for magnetic fields greater than or equal to 4 kOe. As for the magnetoelectric effect, the induced voltages were moderate, increasing linearly with the frequency. There was a slight change in the magnetoelectric response with the DC applied magnetic field. For low frequencies, the magnetoelectric voltage was on the order of 10 mV and for higher frequencies about 50 mV. The best magnetoelectric coefficient (215 mV/cmOe) was obtained under an AC field of 1 Oe and a static magnetic field of 7 kOe.

Green diesel is a potential biofuel that offers certain advantages over traditional fossil diesel, such as low environmental pollution and no sulfur. However, there is little information available regarding the density and viscosity of green diesel, which is crucial for the quality control of biofuels and their performance in engines. In this study, the properties of green diesel produced from palm and soybean oils hydrotreatment were investigated, and models were developed to predict the physical properties of green diesel and n-alkanes. The experimental measurements had uncertainties of 1×10^-4 g/cm³ and 1×10^-2 mPa s in density and viscosity, respectively. The models were found to be in good agreement with the experimental values. The study highlights the importance of density and viscosity for quality control and engine performance of biofuels. The developed models for predicting the physical properties of green diesel and n-alkanes can be useful for quality control and optimization of biofuel production processes. The findings can be useful for researchers, engineers, and policymakers working in the field of biofuels and renewable energy. Further research is needed to explore the applicability of the developed models to other types of biofuels and to investigate the environmental and economic sustainability of green diesel production.