Vol. 68 No. 1 Jan-Feb (2022): Revista Mexicana de Física

The entropy generation analysis of a thermal process is capable of determining the efficiency of that process and is therefore helpful to optimize the thermal system operating under various conditions. There are several ingredients upon which the phenomenon of entropy generation can depend, such as the nature of flow and the fluid, the assumed conditions, and the material properties of the working fluid. However, the dependence of entropy generation phenomenon upon such properties has so far not been fully realized, in view of the existing literature. On the other hand, based upon the existing studies, it has been established that the non-uniform concentration of nanoparticles in the base fluid does cause to enhance the heat transfer rate. Therefore, it is logical to investigate the entropy production under the impact of non-homogenous distribution of nanoparticles. Based upon this fact the aim of current study is to explore a comprehensive detail about the influence of non-homogeneous nanoparticles concentration on entropy production phenomenon by considering a laminar viscous flow past a moving continuous flat plate. Non-uniform concentration is considered in the nanofluid modeling in which the Brownian and thermophoretic diffusions are considered which impart significant effects on velocity and temperature profiles. An exact self-similar solution to this problem is observed to be possible and is reported. The effects of various controlling physical parameters such as Brinkman number, Schmidt number, Prandtl number, diffusion parameter, and concentration parameter on both local as well as total entropy generation number and Bejan number are elaborated by several graphs and Tables. The obtained results reveal a significant impact of all aforementioned parameters on entropy generation characteristics. It is observed that by a 20% increase in nanoparticles concentration the total entropy generation is increased up to 67% for a set of fixed values of remaining parameters.

‎In this paper‎, ‎different types of soliton solutions of the modified equal width wave (MEW) equation with beta time derivative are obtained by implementing the two different methods named as‎: ‎extended Jacobi's elliptic expansion function method and Kudryashov method‎. ‎The dark‎, ‎bright‎, ‎singular and other solitons are achieved‎. ‎The obtained soliton solutions are verified through MATHEMATICA‎. ‎At the end‎, ‎the results are also explained through graphs‎. ‎These soliton solutions suggest that these two methods are effective‎, ‎straight forward and reliable as compare to other methods‎. ‎The obtained results can be used in describing the substantial understanding of the studious structures as well as others related non-linear physical structures‎.

From a previous paper where we proposed a description of general relativity within the gravito-electromagnetic limit, we propose an alternative modified gravitational theory. As in the former version, we analyze the vector and tensor equations of motion, the gravitational continuity equation, the conservation of the energy, the energy-momentum tensor, the field tensor, and the constraints concerning these fields. The Lagrangian formulation is also exhibited as an unified and simple formulation that will be useful for future investigation.

In this work, we construct solitary wave solutions of a nonlinear evolution equation in the physical phenomena of waves;
namely the time-fractional fifth-order Sawada-Kotera equation and the (4+1)-dimensional space-time fractional Fokas
equation by Kudryashov method with a new function. As a result, new types of exact analytical solutions are obtained.
Here the fractional derivative is described in beta sense.

 

The exotic particles such as the pentaquarks are to strengthen understanding of important interactions and the principle of QCD in which pentaquarks contain two heavy- valence quarks. The structure of two bodies including an antiquark and two-diquark is introduced. A new potential for quark interaction is suggested which includes the logarithm potential, the linear potential, and the spin-spin interaction. The suggested potential is included in the framework of spinless of Bethe-Salpeter equation. A comparison with other works is presented which provides a good description of pentaquarks.

We investigate the connection between the London superconductor and a mesoscopic RLC circuit in both classical and quantum contexts. We show that mathematical framework to describe the dynamics of these two dierent systems is identical. Based on the Lewis-Riesenfeld invariant method together with the Fock states, we solve the time-dependent Schrodinger equation for this problem and evaluate some of its important physical properties, such as coherent states, expectation values of the charge and magnetic ux, their quantum uctuations and the corresponding uncertainty principle.

The quaternary alloy (CuIn)₂NbTe₅ was synthesized by solid-state reaction using the melt and annealing technique. The thermal analysis shows that this compound melts at 1026 K. The present alloy is isotypic with Cu₂FeIn₂Se₅ and crystallizes in the space group P2c (Nº 112), with unit cell parameters a = 6.1964(2) Å, c = 12.4761(4) Å, c/a = 2.01, V = 479.02(3) ų. (CuIn)₂NbTe₅, belonging to the system (CuInSe₂)_1-x(FeSe)_x with x= ⅓, is a new adamantane compound with a P-chalcopyrite structure. This structure is characterized by a double alternation of anions-cations layers according to the Te-Te : Nb-In-Nb-In : Cu-In-Cu-In : Te-Te sequence, along the 010 direction.

The two-variable Black-Scholes equation is used to study the option exercise price of two different currencies. Due to the complexity of dealing with several variables, reduction methods have been implemented to deal with these problems. This paper proposes an alternative reduction by using the so-called Zwanzig projection method to one-dimension, successfully developed to study the diffusion in confined systems. In this case, the option price depends on the stock price and the exchange rate between currencies. We assume that the exchange rate between currencies will depend on the stock price through some model that bounds such dependence, which somehow influences the final option price.
As a result, we find a projected one-dimensional Black-Scholes equation similar to the so-called Fick-Jacobs equation for diffusion on channels. This equation is an effective Black-Scholes equation with two different interest rates, whose solution gives rise to a modified Black-Scholes formula. The properties of this solution are shown and were graphically compared with previously found solutions, showing that the corresponding difference is bounded.

The classical master-slave configuration allows synchronizing pairs of unidirectionally coupled systems in a relatively easy manner. However, it has been found that this scheme has a limitation: for certain systems including those with chaotic dynamics this scheme fails to induce synchronization. In this work a modified master-slave scheme, based on combining elastic and dissipative couplings is presented. We focuses on a possible solution for this limitation by illustrating our method employing the va der Pol and Dung oscillators and analyzing three dierent ways of coupling. We obtain, synchronization in both oscillators.

The adiabatic effects of electron-positron pair-production on the dynamical instability of very-massive stars is investigated from stellar progenitors of carbon-oxygen cores within the range of 64 M < MCO < 133 M  both with and without rotation. At a very high temperature and relatively low density; the production of electron-positron pairs in the centres of massive stars leads the adiabatic index to below 4/3. The adiabatic quantities are evaluated by constructing a model into a thermodynamically consistent electron-positron equation of state (EoS) table. It is observed that the adiabatic indices in the instability regions of the rotating models are fundamentally positive with central temperature and density. Similarly, the mass of the oxygen core within the instability region has accelerated the adiabatic indices in order to compress the star, while the mass loss and adiabatic index in the non-rotating model exponentially decay. In the rotating models, a small amount of heat is required to increase the central temperature for the end fate of the massive stars. The dynamic of most of the adiabatic quantities show a similar pattern for all the rotating models. The non-rotating model may not be suitable for inducing the instability. Many adiabatic quantities have shown great effects on the dynamical instability of the massive stars due to electron-positron pair-production in their centres. The results of this work would be useful for better understanding of the end fate of very-massive stars.

This article analyzes and compares the two algorithms for the numerical solutions of the fractional isothermal chemical equations (FICEs) based on mass action kinetics for autocatalytic feedback, involving the conversion of a reactant in the Liouville-Caputo sense. The first method is based upon the spectral collocation method (SCM), where the properties of Legendre polynomials are utilized to reduce the FICEs to a set of algebraic equations. We then use the well-known method like Newton-Raphson method (NRM) to solve the set of algebraic equations. The second method is based upon the properties of Newton polynomial interpolation (NPI) and the fundamental theorem of fractional calculus. We utilize these methods to construct the numerical solutions of the FICEs. The accuracy and effectiveness of these methods is satisfied graphically by combining the numerical results and plotting the absolute error. Also, the absolute errors are tabulated, and a good agreement
found in all cases.

The ASTM A-36 steel is the main alloy, used in the metal-mechanical industry. In the present study, the effect of boron-carbon coating on the hardness and corrosion resistance of the steel ASTM A-36 was reported. Boronizing thermochemical treatment was carried out at 950 °C for 4 h followed by the carburizing process at 930 °C for 6 h. The corrosion study was conducted using the polarization technique (Tafel) and electrochemical impedance spectroscopy (EIS), which employed a fused deposition modeling-based 3D printing electrochemical cell made of polylactic acid (PLA). A commercial platinum foil and an Ag/AgCl (3.5 M KCl) electrode were used as the counter and reference electrode, respectively. The working electrode used an area of 1 cm² of the sample. Optical microscopic analysis shown that borides formed on the surface of steels has a saw-tooth morphology and a uniform coating with a thickness of about 60 µm in both samples. The carburizing over boride promoted the formation of coatings on the outermost layer of the samples with a thickness of about 17 µm over the boride layer. Boride formation was verified by X-ray diffraction (XRD) analysis indicating only the formation of the Fe₂B phase. Results showed that boride samples exhibited inferior corrosion resistance compared to original samples, but after carburizing, an outer layer was formed, with the hardness and corrosion resistance like that of the original sample.

Since they have become indispensable in various technological applications and a powerful
source for generating energy in thermoelectric devices, Lithium-based alloys symbolize the topic
of many experimental and theoretical reports. Hence, LiAlX(X = C, Si, Ge, Sn) materials represent
the main research in this study. Different interesting properties such as the effect of pressure on
the band gap as well as the elastic parameters and the thermoelectric efficiency of these materials
were investigated using the full potential linearized augmented plane wave (FP-LAPW) method.
LiAlX alloys were found to be semiconducting with indirect band gaps. When studying the
mechanical properties, we found that LiAlC alloy is stable against a wide range of pressure
changes (90 GPa), while the rest three systems preserve their mechanical stability in a moderate
respectively range of 40, 50 and 30 GPa, respectively. The semiconducting band gap for each
possible transition have been calculated in a range of different pressures using both GGA and
mBJ-GGA approximations. The results ended up revealing a decaying trend of the indirect gap
along Г-X direction with the increase of pressure. High values of the power factor were achieved
and a large figure of merit (almost 0.7 for all systems) was calculated at 600K, which makes
these Li-based alloys very auspicious in the thermoelectric field applications.

Using a Monte Carlo method, we simulate the measurement, by the 2E technique, of the average prompt neutron multiplicity as a function of the mass of fragments from the thermal neutron-induced fission of 239Pu. The input data for the simulation, associated with the primary fragment mass (A), consist of the yield (Y), the distribution of the total kinetic energy characterized by its average ((TKE) ̅) and its standard deviation (σ_TKE), the average prompt neutron multiplicity (ν ̅_s, a sawtooth approach of experimental data), and the slope of neutron multiplicity against total kinetic energy (dν_s/d<TKE>). The output data, associated with the simulated as the fragment mass measured by the 2E technique (µ), consist of the yield (y), the distribution of the total kinetic energy characterized by its average ((tke) ̅) and its standard deviation (σ_tke), and the average prompt neutron multiplicity (ν ̅_µ). In the mass regions A≈115 and A>150, ν ̅_µ is higher than ν ̅_s. This result suggests that, in those mass regions, the 2E experimental values associated with the average neutron multiplicity are overestimated, referred to the corresponding to the primary fragments.

Classic phase retrieval techniques use intensity patterns to obtain typical aberrations such as coma or astigmatism. However, the patterns obtained with the Transport of Intensity Equation techniques have not been studied yet. In this work, we propose a method to obtain intensity distributions of some aberration wavefronts. It is expected that this characterization method may facilitate new testing strategies in optical workshops.

Human mobility is an important factor in the propagation of infectious diseases. In particular, the spatial spread of a disease is a consequence of human mobility. On the other hand, the control strategies based on mobility restrictions are generally unpopular and costly. These  high social and economic costs make it very important to design global protocols where the cost is minimized and eects maximized. In this work, we calculate the percolation threshold of the spread in a network of a disease. In particular, we found the number of roads to close and regions to isolate in the Puebla State, Mexico, to avoid the global spread of COVID-19.  Computational simulations taking into account the proposed strategy show a potential reduction of 94% of infections. This methodology can be used in broader and dierent areas to help in the design of health policies.