Vol. 67 No. 4 Jul-Aug (2021): Revista Mexicana de Física

This work describes a visualization technique that allows to register and analyze flow inside a Submerged Entry Nozzle (SEN) model. The internal flow has a swirling pattern that produces characteristic flow conditions that can be used in efficiently supplying liquid steel from the tundish to the mold in the continuous casting process. The visualization method is a first step in analyzing the characteristics of the internal flow and hence in designing new SENs. A LED light source is employed to illuminate the SEN which reduces the reflections in the images. To enhance visualizations and measurements, a transparent cell consisting of a cubic volume with reduced dimensions was used to capture images from the high-speed camera and to record the flow pattern within the SEN. The SEN model consists of a vertical, constant diameter tube with two rounded exit ports located at the bottom with a downward angle of 15° each. The working fluid is water and reaches Re=10,000 within the cell. We also use the laser illuminated Particle Imaging Velocimetry (PIV) to calculate the velocity of fluid within the SEN and close to the exit ports. We confirm previously reported formation of three vortexes that interact with each other altering the swirl motion of the exit flow. Experimental results were compared with numerical simulations. The comparisons contribute to the validation of findings of Computational Fluid Dynamics (CFD) and Smoothed-Particle Hydrodynamics (SPH) results. Qualitative and quantitative similarities were found. Both physical and numerical results display a high turbulent flow behavior at the lower zone of the SEN. Experimental and numerical methods may be used together as a development method to measure and evaluate the characteristics of the flow behavior inside and outside the SEN model in order to design a better SEN to increase the quality of the steel slab.

This paper investigates exact voyaging (2 + 1) dimensional Heisenberg ferromagnetic spin chain solutions with conformable fractional derivatives, an important family of nonlinear equations from Schrödinger (NLSE) for the construction of hyperbolic, trigonometric and complex function solutions. The detailed rational sine-cosine system and rational sinh-cosh system were used to locate dim, special and periodic wave solutions successfully. These findings suggest that the proposed approaches may be useful to investigate a range of solutions inside a repository of applied sciences and engineering, with success, quality, and trust. In addition, graphical representations and physical expresses of such solutions are represented by a set of the required values of the parameters involved. The methods are essentially adequate and can be extended to different dynamic models that create the nonlinear processes in today’s research.

Investigation of the Ginzburg-Landau equation (GLE) was done to secure new chirped bright, dark periodic and singular function solutions. For this, we used the traveling wave hypothesis and the chirp component. From there it was pointed out the constraint relation to the dierent arbitrary parameters of the GLE. Thereafter, we employed the improved sub-ODE method to handle the nonlinear ordinary differential equation (NODE). It was highlighted the virtue of the used analytical method via new chirped solitary waves. In our knowledge, these results are new, and will be helpful to explain physical phenomenons.

One of the greatest challenges of science is to understand the current accelerated expansion of the Universe. In this work we show that by considering the quantum nature of the gravitational field, its wavelength can be associated to an effective Compton mass. We propose that this mass can be interpreted as dark energy, with a Compton wavelength given by the size of the observable Universe, implying that the dark energy varies depending on this size. If we do so, we find that: 1.- Even without any free constant for dark energy, the evolution of the Hubble parameter is exactly the same as for the LCDM model, so this model has the same predictions as LCDM. 2.- The density rate of the dark energy is ΩΛ = 0.69 which is a very similar value as the one found by the Planck satellite ΩΛ = 0.684. 3.- The dark energy has this value because it corresponds to the actual size of the radius of the Universe, thus the coincidence problem has a very natural explanation. 4.- It is possible to find also a natural explanation to why observations inferred from the local distance ladder find the value H0 = 73 km/s/Mpc for the Hubble constant, we show that if we take the variability of the dark energy into account they should measure H0 = 67.3 km/s/Mpc as well. 5.- In this model the inflationary period contains a natural successful graceful exit.

In this study, we investigate the analytical solutions of the modified Benjamin Bona Mahony and Sharma-Tosso-Olver equations, which are defined with Atangana conformable fractional derivative, using the modified exponential function method. Analytical solutions of the modified Benjamin Bona Mahony and Sharma-Tosso-Olver equations were obtained by using the modified exponential function method. Two, three-dimensional and contour graphics are used to understand the physical interpretations of the resulting analytical solutions to the mathematical model. When all these results and graphs are analzyed, it has been shown that the modified exponential function method is an effective method for obtaining analytical solutions for all other nonlinear fractional partial differential equations containing conformable fractional derivatives of Atangana.

We investigate modulation analysis and optical solitons of perturbed nonlinear Schrodinger equation (PNLSE). The PNLSE has terms of cubic nonlinearity and self-steepening and spatio-temporal dispersion (STD). Proposed model has been studied by [14, 15] without self-steepening term. The presence of the STD and self-steepening can help to compensate the low GVD to the model. Bright and dark solitary waves, trigonometric, periodic and singular optical solitons are obtained by some expansion methods including exponential and sinh-Gordon. Obtained results will hold a significant place in the field of nonlinear optical fibers, where solitons are used to codify data.

A nonlinear model of Brownian motion is developed in a three-dimensional quantum vacuum defined by a variable quantum vacuum energy density corresponding to processes of creation/annihilation of virtual particles. In this model, the polarization of the quantum vacuum determined by a perturbative fluctuation of the quantum vacuum energy density associated with a fluctuating viscosity, which mimics the action of dark matter, emerges as the fundamental entity which generates the Brownian motion.

The flavor changing neutral current decay $h\to\tau\mu$ is studied in a renormalizable scalar leptoquark
model with no proton decay. Analytical expressions for the one-loop level contributions of a scalar leptoquark
to the decay width of the process $h\to\tau\mu$ are presented. We find a viable model parameter space via
the current constraints on the muon ($g-2$), the decay $\tau\to\mu\gamma$, the LHC Higgs boson data and
the direct leptoquark searches at the LHC. Then, we evaluate branching ratio of the decay $h\to\tau\mu$
induced by leptoquarks; we find that it is of the order of $10^{-8}-10^{-7}$ ($10^{-8}$; $10^{-9}-10^{-8}$)
for a scalar leptoquark mass equal to $m_{\Omega_{5/3}}=1$ TeV ($m_{\Omega_{5/3}}=2$;
$m_{\Omega_{5/3}}=10$ TeV). Finally, we evaluate the number of events produced at future hadron
colliders from both the $h\to\tau\mu$ decay and the potential Standard Model background finding a potential
evidence for the $h\to\tau\mu$ decay.

In the present work, the density functional theory (DFT) was performed for the investigation of the structural, electronic and optical properties of the Zn_1-xCd_xSe_yTe_1-y quaternary alloys using the full potential linearized augmented plane wave (FP-LAPW) method. For the calculations of the structural properties we have used the Perdew-Burke-Ernzerhof generalized gradient approximation (GGA-PBEsol). On other hand, the electronic properties have been computed within the local density approximation (LDA) in adding to the Tran-Blaha modified Becker-Johnson (TB-mBJ) approach. Our results indicate that the lattice constant, as well as the bulk modulus and the energy gap for the Zn_1-xCd_xSe_yTe_1-y quaternary show almost linear variations on the concentration x (0.125≤x≤0.875). In addition, the simulated band structures for the

Zn_1-xCd_xSe_yTe_1-y quaternary exhibits a direct-gap for all concentrations. Moreover, low bowing parameters are observed. Also, some interesting optical properties such as dielectric constant, refractive index, extinction coefficient, absorption coefficient and reflectivity have been calculated by using the TB-mBJ method.  The results of our computations shows that the

Zn_1-xCd_xSe_yTe_1-y quaternary alloy is a promissing candidate for optoelectronic applications. It is noteworthy that the present work is the first theoretical study of the quaternary of interest using the FP-LAPW calculations.

The structural and electronic properties of  and semiconductor detectors at various concentrations x = 0, 0.25, 0.5, 0.75 and 1 of Selenium (Se) were determined by using the full potential-linearized augmented plane wave (FP-LAPW) based on the density functional theory (DFT). The compositional dependence of such properties was analysed and discussed. The concentration dependence of lattice parameter and bulk modulus show nonlinearity. All the investigated alloys have a direct bandgap (Γ-Γ) which decreasesnonlinearly with increase in Se concentration. On the other hand, Geant4 simulations have been performed for studying the absolute and full-energy peak detection efficiencies and energy resolution at 1.5”×1.5” of these alloys as semiconductor detectors in the 511-1332 keV gamma-ray energy range. Ours findings are in a good agreement with the available theoretical and experimental data. We hope that our results serve as are reference for future theoretical and experimental researches.

Using first-principles calculations based on density functional theory, structural, elastic, electronic and thermoelectric properties of laves phase LaCo₂ intermetallic compound with prototype MgCu₂ are stated in this paper. The optimized lattice constant by structural optimization is found to be rationally compatible with the experimental lattice constant.  The Generalized Gradient Approximation (GGA) +Hubbard model was incorporated to evaluate the exact electronic structure. Elastic properties such as, elastic constants, bulk modulus B, shear modulus G, Young’s modulus E, and Poisson ratio ν have been determined using the Voigt–Reuss– Hill approximation. The ductility nature appears in both values of Cauchy pressure and Pugh’s ratio. The band structures and the Cauchy pressure show that the material behaves as metallic. In addition, semi-classical Boltzmann theory is used to verify the applicability of the material for thermoelectric applications. Calculations depict that the spin-up/down transport coefficients are temperature-dependent. It has been found that LaCo₂ has a high Seebeck coefficient and therefore a large power factor.

In this work, the fabrication of zinc oxide thin film transistors (ZnO TFTs) on plastic substrates by High-frequency Ultrasonic Spray Pyrolysis
at Low Temperature is presented. The maximum fabrication temperature was 200±C. Spin-on glass was used as gate insulator. Polyethylene
terephthalate is used as plastic substrate. The ZnO TFTs exhibit an electron mobility of 1.25 cm2/Vs and a threshold voltage of 10.5 V,
while the on/off current ratio was of 104. In addition, the trap density in active layer and at the insulator/semiconductor interface is extracted.
Moreover, Metal-Insulator-Metal capacitors were fabricated on plastic and characterized in order to evaluate the gate insulator

Convergent beam diffraction (CBED) patterns of nanoparticles are possible. CBED of triangular prismatic shaped Au nanoparticle with focus on diffraction pattern symmetry and forbidden reflections observed along [111] and [112] zone axes are reported in this work. It is well known that the CBED patterns of nanoparticles of 30 nm or less in size only show bright kinematical discs. The dynamic contrast with Kikuchi and sharp HOLZ lines within the bright discs, as observed in CBED of volumetric materials, is well observed in particles larger of 500 nm in size. In addition, it is shown that the 1/3[422] and 1/2[311] weak forbidden reflections observed in the [111] and [112] electron diffraction patterns of these particles do not modify the symmetry of the CBED patterns, but they disappear as the size of the particle increases. The symmetry of the CBED patterns are always observed in concordance with the space group Fm3m (No. 225) of the Au unit cell. The possible explanations for observing forbidden reflections are the incomplete ABC stacking due to surface termination and the stacking faults in the fcc structure.

The alpha-transfer reaction 28Si(20Ne,16O)32S at 52.3 and 70 MeV is examined by using the double-folding (DF) based on the optical model. The real part is obtained for ten different density distributions of 20Ne projectile. For the imaginary part, the Woods-Saxon potential is used. The obtained results are compared with the experimental data of alpha-transfer reaction as well as the literature results. It is seen that the results are in good agreement with the data, and are better than the literature results.

In this paper, we discuss the fixed time synchronization of a class of chaotic systems based on the backstepping control with disturbances. A new and important fixed time stability theorem is presented. The upper bound estimate formulas of the settling time are also given which are different from the existing results in the literature. Based on the new fixed time stability theorem, a novel saturation controller for the fixed time synchronization a class of chaotic systems is proposed via the backstepping method. Finally, the new chaotic system is taken as an example to illustrate the applicability of the obtained theory.

A study on the epidemiologic Susceptible-Infected-Recovered (SIR) model is presented using free particle dynamics. The study is performed using a computational model consisting of randomly allocated particles in a closed domain which are free to move inrandom directions with the ability to collide into each other. The transmission rules for the particle–particle interactions are based on the main viral infection mechanisms, resulting in real–time results of the number of susceptible, infected, and recovered particles within a population of N= 200 particles. The results are qualitatively compared with a differential equation SIR model in terms of the transmission rate β, recovery rate γ, and the basic reproductive number R0, yielding overall good results. The effect of the particle density ρ on R0 is also studied to analyze how an infectious disease spreads over different types of populations. The versatility of the proposed free–particle–dynamics SIR model allows to simulate different scenarios, such as social distancing, commonly referredto as quarantine, no social distancing measures, and a mixture of the former and the latter. It is found that by implementing early relaxation of social distancing measures before the number of infected particles reaches zero, could lead to subsequent outbreaks such as the particular events observed in different countries due to the ongoing COVID–19 health crisis