Vol. 68 No. 2 Mar-Apr (2022): Revista Mexicana de Física

Crisis in coronavirus times requires understanding the effects on society and establishing efficient mechanisms to prevent infections. The disinfection of personal protection equipment by UVC light remains a key opportunity area. Therefore, this letter presents the main drawbacks and challenges on the fabrication of deep ultraviolet LEDs based on III-nitrides, such as the substrate selection, dislocation reduction, the increase of external quantum efficiency, enhancement of the radiative recombination in the active region, the complications to reach high Al content in AlGaN-based UVC LED avoiding the reduction of the p-doping, replacing the p-GaN contact layer by p-AlGaN without hindering the deposition of ohmic contacts. Furthermore, the cubic phase is suggested as a promising candidate for AlGaN UVC-LEDs applications as is discussed in this work.

The energy levels of the Schrödinger equation under the Eckart-Hellmann potential (EHP) energy function are studied by the Nikiforov-Uvarov-Functional Analysis (NUFA) method. We obtained the analytic solution of the energy spectra and the wave function in closed form with the help of Greene-Aldrich approximation. The numerical bound states energy for various screening parameters at different quantum states and vibrational energies of EHP for CuLi, TiH, VH, and TiC diatomic molecules were computed. Four exceptional cases of this potential were achieved. To test the accuracy of our results, we computed the bound states energy eigenvalues of Hellmann potential which are in excellent agreement with the report of other researchers.

Sample of the quaternary phase CuAlGeSe₄, a member of the I-III-IV--VI₄ semiconductor system, was synthesized by the melt and annealing technique and analyzed using X-ray powder diffraction data. The indexing and refinement of the pattern indicate that this compound crystallizes in the tetragonal system, space group I (Nº82) with unit cell parameters: a = 5.5646(3) Å, c = 10.682(2) Å, V = 330.77(5) ų. The space group was established from a cationic and anionic distribution analysis in the tetragonal space groups: I2d (Nº 122), I2m (Nº 121), and I (Nº 82), for an ordered structure in this material. The Rietveld refinement, performed with the starting model: Cu 2c, Al 2b, Ge 2d, 2a, and Se 8g, converged to R_exp= 7.2%, R_P = 7.4%, R_wp = 9.6%, and χ² = 1.7.

Inspired by the physics of the Miyake - Narikiyo model (MN) for superconductivity in the γ sheet of Sr2RuO4, we set out to investigate numerically the behavior caused by a non-magnetic disorder in the imaginary part of the elastic scattering matrix for an anisotropic tight-binding model. We perform simulations by going from the Unitary to the Born scattering limit, varying the parameter c which is inverse to the strength of the impurity potential. It is found that the unitary and intermedia limits persist for different orders of magnitude in simulating the disorder concentration. Subsequently and in order to find the MN tiny gap, we perform a numerical study of the unitary limit as a function of disorder concentration, to find the tiny anomalous gap.

In this article, we utilize the generalized full nonlinearity perturbed complex Fokas-Lenells model (GFLM) which is a general dynamics representation of modern electronic communications "Internet blogs, Facebook communication and Twitter comments". The modified simple equation method (MSEM) has been applied effectively to generate closed form solution. On the other hand, the Riccati-Bernoulli Sub-ODE method (RPSOM) which reduces the steps of calculation has been applied perfectly to achieve accurate solution to this equation. We established the solutions achieved by these distinct manners in same vein and parallel.

In this paper, the tunnelling of a particle through a potential barrier is investigated in the presence of a time-dependent perturbation. The latter is attributed to the process of the energy measurement of the scattered particle. The time-dependent Schrödinger equation of the model is exactly solved. The probability density inside the barrier is calculated from the obtained wave function, proving that the tunnelling dynamics is determined not only by the transmitted and reflected waves but also by their interference. Furthermore, the interference term is time-dependent and contribute to the scattering process duration. The tunnelling time is calculated as the time needed to get the probability density inside the barrier to zero. This is the minimum duration of the measurement process before detecting the particle beyond the barrier. Based on this, a new method of estimating the tunnelling time by energy experimental measuring is proposed.

This paper deals with the application of a novel variable-order and constant-order fractional derivative without singular kernel of Atangana-Koca type to describe the fractional viscoelastic models, namely, fractional Maxwell model, fractional Kelvin-Voigt model, fractional Zener model and fractional Poynting-Thomson model. For each fractional viscoelastic model, the stress relaxation modulus and creep compliance are derived analytically under the variable-order and constant-order fractional derivative without singular kernel. Our results show that the relaxation modulus and creep compliance exhibit viscoelastic behaviors producing temporal fractality at different scales. For each viscoelastic model, the stress relaxation modulus and creep compliance are derived analytically under novel variable-order and constant-order fractional derivative with no singular kernel.

In this work we explore the thermodynamic aspects of dark energy for late future time universe in two different scenarios: as a perfect fluid with constant and variable equation of state parameter; and as dissipative fluid described by a barotropic equation of state with bulk viscosity in the framework of the Eckart theory and the full Israel-Stewart theory.
We explore cosmological solutions for a flat, homogeneous and isotropic universe; and we assume the late future time behavior when the dark energy dominates the cosmic evolution.
When modeled as a perfect fluid with a dynamical equation of state, $p=w(a)\rho$, the dark energy has an energy density, temperature and entropy well defined and an interesting result is that there is no entropy production even though been dynamical.
For dissipative dark energy, in the Eckart theory two cases are studied: $\xi=const.$ and $\xi =(\beta/\sqrt{3}) \rho^{1/2}$; it is found that the entropy grows exponentially for the first case and as a power-law for the second.
In the Israel-Stewart theory we consider a $\xi =\xi_0 \rho^{1/2}$ and a relaxation time $\tau = \xi/\rho$; an analytical Big Rip solution is obtained with a power-law entropy.
In all cases is obtained a power-law relation between temperature and energy density.
In order to maintain the second law of thermodynamics theoretical constraints for the equation of state are found in the different dark energy models studied.
A barotropic dark fluid with $w<-1$ is thermodynamically difficult to support, but the overall effect of bulk viscosity in certain cases allows a phantom regime without thermodynamic anomalies.

In a previous work [1] it was shown that by considering the quantum nature of the gravitational field mediator, it is possible to introduce the momentum energy of the graviton into the Einstein equations as an effective cosmological constant. The Compton Mass Dark Energy (CMaDE) model proposes that this momentum can be interpreted as dark energy, with a Compton wavelength given by the size of the observable universe RH, implying that the dark energy varies depending on this size. The main result of this previous work is the existence of an effective cosmological constant Λ = 2π²/λ² that varies very slowly, being λ = (c/H₀)R_H the graviton Compton wavelength. In the present work we use that the dark energy density rate is given by Ω_Λ = 2π²/3/R_H² , it only has the curvature Ω_k as a free constant and depends exclusively on the radiation rate Ω_r. Using Ω_r = 9.54×10−5, the theoretical prediction for a flat universe of the dark energy rate is Ω_Λ = 0.6922. We perform a general study for a non-flat universe, using the Planck data and a modified version of the CLASS code we find an excellent concordance with the Cosmic Microwave Background and Mass Power Spectrum profiles, provided that the Hubble parameter today is H₀ = 72.6 km/s/Mpc for an universe with curvature Ω_k = −0.003. We conclude that the CMaDE model provides a natural explanation for the accelerated expansion and the coincidence problem of the universe.

We consider non-autonomous systems of ordinary differential equations that can be expressed in Hamiltonian form in terms of two different coordinate systems, not related by a canonical transformation. We show that the relationship between these coordinate systems leads to a, possibly time-dependent, tensor field, $S^{\alpha}_{\beta}$, whose eigenvalues are constants of motion. We prove that if the Nijenhuis torsion tensor of $S^{\alpha}_{\beta}$ is equal to zero then the eigenvalues of $S^{\alpha}_{\beta}$ are in involution, and that these eigenvalues may be in involution even if the Nijenhuis tensor is not zero.

This paper introduces the fractal model of the nonlinear Schrodinger equation with quadratic-cubic nonlinearity in magneto-optic waveguides that has many applications in fiber optics. He's variational approach and Painleve technique are used to attain soliton solutions of the governing system. Thus bright and kink solitons are retrieved. The constraint conditions that ensure the existence of these solitons arise naturally from the model's solution structure. The fractal parameter eect on these solitons is portrayed by 2D and 3D graphical illustrations. These techniques may be very useful and ecient gadgets for solving nonlinear fractal dierential equations that emerge in mathematical physics.

In this paper, we firstly review the quasi uniformly accelerated motion (QUAM) with Fermi derivative by cold plasma in Heisenberg space. We define new quasi uniformly accelerated potential electric energy of quasi normal magnetic biharmonic particles and some Lorentz fields. Moreover, we design the new relationship between the quasi uniformly accelerated motion and the Fermi parallel transportation in cold plasma. Also, we collect new physical geometric designs for a quasi uniformly accelerated motion of normal magnetic biharmonic particles in Heisenberg space. Finally, we construct quasi uniformly accelerated potential electric energy with respect to its electric field and some quasi curvatures.

Process optimization of multiphase chemical and/or photochemical reactor means a challenge not only at laboratory scale but also while scaling-up is intended towards industrial applications. Using computational tools, such as Computational Fluid Dynamics, is essential to assess transport limitations of the heterogeneous process to verify the kinetic regime while the reaction and the reactor engineering are studied. Computational Fluid Dynamics, together with Genetic Algorithms, has been currently applied to verify fluid behavior and turbulence. The latter device has been self-designed and is planned to be constructed for CO₂ reduction. The results of the Computational Fluid Dynamics simulations are presented and discussed, in order to optimize reactor operation of a multi-inlet vortex photoreactor. By considering the catalytic particle features, the residence time distribution in the multi-inlet photoreactor has been verified and optimized.

In this paper, we investigate the new approximate bound state solution of deformed Klein--Gordon, Dirac and Schr\"{o}dinger equations in the symmetries of extended relativistic quantum mechanics ERQM and extended nonrelativistic quantum mechanics ENRQM have been obtained with a newly proposed potential called improved Hellmann-generalized Morse potential (IHGMP, for short). To the best of our knowledge, this problem is examined in literature in the usual RQM and NRQM with Hellmann-generalized Morse potential. The potential is a superposition of Hellmann potential, generalized Morse or Deng-Fan potential, and some other exponential terms. By employing the improved approximation to deal with the centrifugal term, Bopp's shift and standard perturbation theory method. The new approximate analytical energy shift and the corrections of bound state energy
eigenvalues in ERQM and ENRQM are obtained for some selected diatomic molecules such as (HCl, LiH, H2, ScH, TiH, VH, CrH, CuLi, TiC, NiC, ScN and ScF). The new values that we get appeared sensitive to the quantum numbers $% \left( j,l,s,m\right) $, the potential depths of the improved Hellmann-generalized Morse potential ($a,b$), the range of the potential $%\alpha $, the dissociation energy $D_{e}$, the equilibrium bond length $%r_{e} $, and noncommutativity parameters$\left( \Theta ,\sigma ,\chi \right)$ . We have highlighted three physical phenomena that automatically generate a result of the topological properties of noncommutativity, the first physical phenomena are the perturbative spin-orbit coupling, the second the magnetic induction while the third corresponds to the rotational proper phenomena. In both relativistic and nonrelativistic problems, we show that
the corrections on the spectrum energy are smaller than the main energy in the ordinary cases of quantum field theory and quantum mechanics. In the new symmetries of NCQM, it is not possible to get the exact analytical solutions for $l=0$ and $l\neq 0$, the approximate solutions are available. Four special cases, i.e., l wave are investigated in the context of deformed Klien-Gordon and Schr\"{o}dinger theories. The relativistic energy equations and the new nonrelativistic energy for some potentials such as improved Hellmann potential and improved generalized Morse potential have also been obtained by varying some potential parameters. We have clearly shown that the Schr\"{o}dinger and Klein Gordon equations in the new symmetries can
physically describe each of the two Dirac equations and the Duffin--Kemmer equation under the effect of IHGMP.

In this study, a new and cost-effective contact angle measurement system has been developed. As direct application of this easy-to-use measuring system, the wettability behavior of acrylic polymers was analyzed by dropping a saline solution of 2.4 M on acrylic materials, where contact angle measurements were made.

In this study, the structure of Ag₅₀Pd₅₀ alloy was investigated with temperature dependent in-situ X-ray diffraction, residual resistometry, and differential scanning calorimetry (DSC) as well as differential thermal analysis (DTA) techniques. Isochronal annealing experiment was performed to determine the impact of ordering on the residual electrical resistivity. The residual resistivity curve shows a sharp minimum near 250 °C indicating the on-set of ordering. The in-situ X-ray diffraction data taken for a well annealed sample shows no super lattice reflections over the investigated temperature range but the lattice parameter determined from this data shows an abrupt decrease in its value at 250 °C showing an order-disorder phase transformation (ODPT). The diffraction pattern of a sample annealed at 230 °C shows splitting of the high angle 511 fundamental reflection due to the tetragonal distortion. The peak intensity and c/a ratios are found to be 1:1.94 and 1.0028, respectively. A similar phase change was also observed during a DSC experiment around 250 °C on this alloy. The existence of these anomalies may be attributed to L1_o - FCC type order-disorder phase transformation at this temperature.

We report on a functional Fabry-Perot mode interferometer and its application for absolute displacement sensing. The proposed device consists of two well-cleaved tips of standard optical fibers that were introduced into a microcapillary glass with an inner diameter of 125.5 um, one tip was stuck to the capillary by the application of an electric arc from a standard splice machine, while the other tip was free to be longitudinally moved. The transmission spectrum of the interferometric device exhibited an interferometric pattern due to the re ections of the fundamental mode on the two partial re ecting tip surfaces of the standard optical bers. The period and the intensity level of the interference pattern depend strongly on the separation between the optical ber tips caused by the displacement of the free optical fiber tip. This dependence allows for the use
of either period or intensity changes for length displacement sensing interrogation. For the period interrogation, the length can be accurately calculated and measured by taking the Fast Fourier Transform (FFT) of the detected interference pattern. For intensity interrogation, a simple photodetector can be used to determine the distance that separates the optical fiber tips.

We present the study of the behavior of the electromagnetic field propagating in the ultra-small core photonic crystal fiber (PCF) beyond its fundamental mode cut-off. We first use plane waves expansion (PWE) method to find necessary parameters and then involve finite-difference time-domain (FDTD) method accelerated with graphic processing unit (GPU) for long-range light propagation simulation. The confinement losses beyond $\lambda = 1200 nm$ achieves tens of dB/cm which can be lowered significantly by increasing the number of cladding rings.

We compare the thermal lens (TLS) and the optical transmission (OT) spectroscopy techniques to monitor the kinetic of a photocatalytic reaction. For this, an OT measurement facility was added to a TLS set-up. The TLS was implemented in a microspatial configuration named thermal lens microscopy (TLM). Methylene blue (MB) in Water solutions were used as test samples within a concentration range in which both techniques show good sensibility. Within this range, the limit of detection obtained by TLM was about one order of magnitude lower than that achieved by OT. The methylene blue concentration evolution with photocatalytic reaction time was measured with both techniques, showing a good agreement between their results. A ZnO thin film deposited on a glass substrate by the spray pyrolysis technique was used as catalyst, and the reaction was induced by UV-violet light.

In this work, we used the First-principles method Fplapw based on density functional theory (DFT) to study the thermal and optical properties of Half-Heusler compounds VFeSb and NbFeSb. These materials are characterized with a small and narrow band gap semiconductors close to the fermi level; following the electron number and other structural properties of these materials have a high performance thermoelectric .In our calculations, we will use the structural and electronic properties for our materials already calculated in previous publications. The modified Becke–Johnson exchange potential (mBJ)-LDA approach was also used. Optical properties such as complex dielectric function, refractive index, reflectivity, energy loss function for incident photon energy up to 30eV have been predicted. We also analyze the influence of the pressure and temperature on the primitive cell volume, heat capacity, volume expansion coefficient, and Debye temperature of the Half-Heusler compounds.

Mediante detectores de trazas tipo CR-39 se determinó la dosis equivalente ambiental H*(10) por neutrones rápidos y térmicos en un acelerador Varian Clinac 2300 que opera en el rango de 6-18 MV. Mediciones preliminares fueron efectuadas ante una fuente moderada de neutrones 252Cf para obtener la respuesta del detector según el rango de energía. Se obtuvieron valores de tasa de densidad de trazas, flujo y dosis equivalente ambiental H*(10) por neutrones rápidos y térmicos en la mesa de tratamiento del recinto. Se determinó que la dosis equivalente ambiental H*(10) por unidad de dosis Gy en el isocentro (IC) es de 162 ± 11 μSv/Gy a una distancia de 13 cm del IC. Se presentan igualmente valores de flujo y tasa de densidad de trazas en el cabezal del acelerador.