Vol. 69 No. 5 Sep-Oct (2023): Revista Mexicana de Física

We study the quantum-mechanical problem of scattering caused by a localized obstacle that breaks spatial and temporal reversibility. Accordingly, we follow Maxwell's prescription to achieve a violation of the second law of thermodynamics by means of a momentum-dependent interaction in the Hamiltonian, resulting in what is known as Maxwell's demon. We obtain the energy-dependent Green's function analytically, as well as its meromorphic structure. The poles lead directly to the solution of the evolution problem, in the spirit of M. Moshinsky's work published in the 1950s. Symmetric initial conditions are evolved in this way, showing important differences between classical and wave-like irreversibility in terms of collapses and revivals of wave packets. Our setting can be generalized to other wave operators, e.g. electromagnetic cavities in a classical regime.

Topological insulators are novel quantum material states with insulating bulk band gaps and topologically protected metallic surface states that have been extensively studied owing to their intriguing properties for spintronic and quantum-computing applications. The structural, mechanical, electronic, thermal, and optical properties of inverse Heusler compounds La2RuPb and, Sc2 RuPb in two Hg2CuTi, Cu2 MnAltype structures were calculated using the full potential linear muffin-tin orbital simulation methodology as implemented in the computer code,which is based on density functional theory.We employed the local-density approximation for the exchange and correlation potential (XC) terms. Consequently, the optical characteristics of La2 RuPb, Sc2 RuPb and elastic constants Cij and their corresponding elastic moduli were computed for the first time. According to our structural calculations, La2 RuPb is more stable in its Hg2 CuTi-type structure than Sc2 RuPb in its Cu2 MnAl-type structure. However, the mechanical characteristics demonstrate their stability in the final stages of elastic deformation.

We present a simplified model of a boat to study its rotational dynamics, which is a significant criterion for the development of navigation systems. The stability of a floating body can be examined by means of rotational potential energy, which depends solely on the boat’s gravity center and a point called the metacentric height. Typically, this geometric point is a function of the body’s orientation in relation to the fluid surface, and the estimation of its value can often be ambiguous. This paper presents an alternative method for calculating the metacentric height using a vectorial approach, as well as a general definition of rotational potential energy applicable to this type of problem. The potential energy facilitates the determination of stable and unstable equilibrium directions as a function of the boat’s relative density and orientation.

We show that it is possible to define, e.g., the z-component of the linear momentum of the system formed by a charged particle and a magnetic field if and only if the magnetic field is invariant under translations along the z-axis. Similarly, it is possible to define the z-component of the angular momentum of the system formed by a charged particle and a magnetic field if and only if the magnetic field is invariant under rotations about the z-axis.

In this work, we present a stable algorithm for the inverse problem of identifying cortical sources from electroencephalographic measurements on the scalp. This inverse problem is ill-posed due to the numerical instability it presents, i.e., small changes in the measurements can produce large variations in the location of the sources. A boundary value problem is used to find correlations between the sources and measurements. In the case in which the head is modeled using two concentric spheres. We use spherical harmonics to find the solution to the inverse source cortical problem. To handle the numerical instability of this problem, we use the Tikhonov regularization method and a cut-off of the harmonic expansion series. From numerical tests, we found these parameters with which we get good approximations. Finally, we illustrate the algorithm proposed with synthetic examples

We present explicit examples of generalizations in relativistic quantum mechanics. First of all, we discuss the generalized spin-1/2 equations for neutrinos. They have been obtained by means of the Gersten-Sakurai method for derivations of arbitrary-spin relativistic equations. Possible physical consequences are discussed. Next, it is easy to check that both Dirac algebraic equations Det(ˆp − m) = 0 and Det(ˆp + m) = 0 for u− and v− 4-spinors have solutions with p0 = ±Ep = ± p p2 + m2. The same is true for higher-spin equations. Meanwhile, every book considers the equality p0 = Ep for both u− and v− spinors of the (1/2, 0) ⊕ (0, 1/2) representation, thus applying the DiracFeynman-Stueckelberg procedure for elimination of the negative-energy solutions. The recent Ziino works (and, independently, the articles of several others) show that the Fock space can be doubled. We re-consider this possibility on the quantum field level for both S = 1/2 and higher spin particles. The third example is: we postulate the non-commutativity of 4-momenta, and we derive the mass splitting in the Dirac equation. The applications are discussed.

The present work analyzes the sintering conditions for ∼ 3 mm inner diameter hollow iron spheres, sintered for manufacturing composite structures. Optimal sintering variables were investigated modifying temperature from 700 to 1200◦C, while times were between 1 and 3 h. Results showed that packing of the spheres increased with time and temperature: at 700◦C sintering was not enough; at temperatures from 800◦ to 1000◦C spheres were well sintered with porosity between them; while at higher temperatures were completely packed. Densities ranged from 0.6 gcm−3 to a maximum of 1.1 gcm−3 for spheres 100% packed, where it was observed a sphere-to-polyhedron shape transformation, with maximum values of penetration (0.39 mm) and sintering neck width (1.42 mm). Complete packing of the Fe particles of the sphere walls was also observed. The use of Design of Experiments made possible to establish correlations between sintering variables and characteristics such as neck width, penetration, porosity and packing. These results could be used as a starting point for the adequate selection of the sintering conditions of hollow Fe spheres for manufacturing hollow composite structures, taking into account not only the characteristics of the sintered hollow spheres but also of the Fe particles forming their walls.

The influence of Al and Zn by 10 wt.% as alloying elements on the electrochemical corrosion behaviour of Cu-based alloy in 0.1 M NaCl solution is examined. Results from both electrochemical impedance spectroscopy method and potentiodynamic techniques indicate that the corrosion occurred at a higher rate for Zn and Al added alloys than pure Cu, where Zn added alloy shows the worst corrosion performance. Copper forms stable a protective layer of Cu₂O, and CuO, as a result, has a lower corrosion rate. In case of Al and Zn added alloys, dealloying, as well as dissolution of additional Al₂O₃ and ZnO are responsible for higher corrosion rates, respectively. The surfaces are investigated by optical and scanning electron microscopy. Phases of different intermetallics within the Cu matrix are identified in the etched optical micrographs of the experimental alloys. The optical images after corrosion depict layers of oxides on the surfaces where the Zn-added alloys are highly affected, followed by Al-added alloys and pure Cu. Increased amounts of internal damage to the surface of the Zn-added alloy are visible in the SEM images. The EDX spectrum not only supports the presence of oxide layers but also claims that Zn-containing particles are dissolved at a greater rate than Al.

This work brings Raman and Fourier transform infrared (FTIR) spectroscopy as a proposal for a vibrational characterization of Carapa Guianensis Aublet essential oil in natura and polymerized and of magnetic nanoemulsion. Calculation of computational chemistry based on the method density functional theory with B3LYP functional and 6-311+G(d,p) base set parameters was used to obtain theoretical frequencies and vibrational signatures of the oleic acid molecule. Results of Raman and Fourier transform infrared spectroscopy confirm bands of Carapa Guianensis Aublet essential oil present in polymerized oil and magnetic nanoemulsion studied. The density functional theory method shows that the bands 1099 cm^-1, 1714 cm^-1 and 1812 cm^-1 explain the presence of vibrational modes of oleic acid in the samples. The density functional theory brought good conformation to the chosen molecule.

In this article, we examine the structure, electronic, optical, and magnetic properties of ZnTe before and after doping with the transition metal Mn. The ab initio calculations of this compound were performed using the full potential linearized extended full potential planar waveform (FP-LAPW) in the context of density functional theory (DFT) implemented in the Wien2K code. The potential for exchange and correlation was addressed by the GGA approximation. The electronic properties show that the ZnTe material exhibits semiconductor behavior before doping and it becomes semimetal after doping. The findings attained by Monte Carlo simulations display that the ZnMnTe material goes from an antiferromagnetic phase to the paramagnetic phase at the Neel temperature value T_N =159.31 K.

Pure ZnO, Ag doped ZnO and Ag-Fe co-doped ZnOwere preparedusing thermal evaporation.  XRD analysis confirms that all layers present a hexagonal wurtzite structure; however, there is a small shift in the peaks position due to thedistortion of the film’s lattice. Scanning Electron Microscopy (SEM) analysis reveals the morphological variation of the film’s surfaces due to the doping. Pure ZnO and Ag:ZnO films have a nanostructured surface, however, Ag-Fe:ZnO films showed a smooth surface without any nanoparticles. Raman analysis showed the presence of A₁(LO), E₂(high) andlocal vibrational modes (LVMs) for all layers. Ultraviolet–visible spectroscopy (UV-VIS) analysis shows that the films have a good transparency and the bandgapdecreases with ZnO doping from 3.80 eVto 3.78 eV and 3.70 eV,for pure ZnO, Ag:ZnO and Ag-Fe:ZnO films, respectively. The electrical properties confirm the semiconductor nature of ZnO films with a resistivity around 1.4 Ω.cm, and with Ag and Ag-Fe doping, the films behave like conductors with 1.4´10^-4Ω.cm and 1.4´10^-3Ω.cm, respectively. These results make the Ag:ZnO and Ag-Fe ZnO thin films good materials for photovoltaic application.

In this paper, an exhaustive investigation was carried out on the compound double Perovskite Ba₂GdReO₆ including its structural, electronic, magnetic and thermoelectric properties. This study is based on the density functional theory (DFT) and more explicitly on the full potential linearized augmented plane wave (FP-LAPW), in the context of different approximations as exchange and correlation potential such as: The generalized gradient approximation (GGA) and its corollary the Becke – Johnson approach modified by Trans-Blaha (TB - mBJ) for a better approximation of the gap, and the GGA + U approach (where U is the Hubbard correction term). After an analysis of the results obtained, it turns out that the double perovskite material Ba₂GdReO₆ is a ferromagnetic material and has a half-metallic character, moreover, this compound has an integral magnetic moment of 9µB, which is in accordance with the rule of Slater-Pauling. From the study of the thermoelectric properties consisting in plotting curves of different parameters such as: the Seebeck coefficient (S), electrical conductivity per relaxation time (σ/τ), the electronic thermal conductivity per relaxation time ( /τ)  and the merit factor (ZT) as a function of temperature, based on the GGA+U approximation, which is most suitable for the study of this compound, it emerges that the double pérovskite Ba₂GdReO₆ presents thermoelectric performances in medium to high temperature ranges, in view of the high values ​​of the Seebeck coefficient and those of the electrical conductivity as well as a value close to unity for the merit factor, therefore, this compound can be used for thermoelectric applications in this range of temperatures (medium to high).

The extraction of circadian cycles from experimental data can be interpreted as a specific case of time-series or signal analysis, but chrono- biology and time-series analysis appear to have developed according to separate paths. Whereas some techniques such as continuous (CWT) and discrete wavelet analysis (DWT) are used frequently in rhythmobiology, other specialized methdos such as digital filters, nonlinear mode decomposition (NMD), singular spectrum analysis (SSA), empirical mode decomposition (EMD), ensemble empirical mode decomposition (EEMD) and complete ensemble empirical model decomposition with adaptive noise (CEEMDAN) have only occasionally been applied. No studies are available that compare the applicability between a wide variety of different methods or for different variables, and this is the purpose of the present contribution. These methods improve the goodness-of-fit of the circadian cycle with respect to the standard approach of cosinor analysis. They have the additional advantage of being able to quantify the day-to-day variability of the circadian parameters of mesor, amplitude, period and acrophase around their average values, with potential clinical applications to distinguish between healthy and unhealthy populations. Finally, the circadian parameters are interpreted within the context of homeostatic regulation with distinctive statistics for regulated and effector variables.

The angular distribution of the 26Mg(3H,2H)27Mg reaction at 36 MeV incident energy is reanalyzed by using the distorted wave Born approximation (DWBA) method. Four forms of the optical model potentials such as temperature dependent and temperature independent density distributions, different nuclear potentials, and different nucleon-nucleon interactions
are used to determine the effect on the 26Mg(3H,2H)27Mg transfer reaction of the entrance channel. These analyses display the similarities and differences of all the approaches which are discussed in this work, and provide alternative density, alternative nuclear potential and alternative nucleon-nucleon interactions.

In this paper, we provide a theoretical prediction about the likelihood of producing high-order modes using, as far as we know, the simplest mode converter. The mode converter is a simple discontinuous waveguide for which reflection and transmission have recently been reported. As a result of the scattering of the fundamental guided mode (TE₀), we have found that the high-order mode excitation is highly dependent on the position of the discontinuity. On the one hand, we discovered that in the presence of a discontinuity in the propagation direction, only even modes (TE₀ and TE₂) are excited, skipping the odd mode (TE₁). When a lateral shift is considered, however, both even and odd higher-order modes (TE₁ and TE₂) are generated. Furthermore, after some lateral shifting, we found that only the pure TE₂ mode is propagated.

A new class of repulsive bound-electron pairs have been found in a Peierls lattice within the Hubbard model for energies E < 0 despite U > 0. These new repulsive bound-electron pairs have a high degree of localization as both the correlation energy U and the tS/tL hopping ratio increases. In order to study electronic correlation in Peierls lattices, our previous real space mapping method has also been extended to the so called generalized mapping method which is briefly presented here. In this paper, we concentrate our attention to discuss in detail the two-particle problem within a repulsive Hubbard model for the one-dimensional Peierls lattice.

In recent years, the hybrid perovskite CH₃NH₃PbI₃ has been widely studied because of its potential application in the fabrication of high efficiency solar cells. The main challenge is to avoid destabilization of this compound under working conditions. Indeed, the MAPbI₃ begins to decompose into the precursor phases, a few hours or days after being formed. We reported a stability monitoring of doped compounds CH₃NH₃Pb_0.9Sn_0.1I₂.8Cl_0.2 and CH₃NH₃Pb_0.75Sn_0.25I_2.5Cl_0.5 obtained as films from solutions of the precursors in N-N dimethylformamide on chemically treated glass substrates. The monitoring was carried out using X-Ray diffraction and absorbance measurements in the UV-Vis region. The tetragonal symmetry initially determined for the three compounds, remains almost unaltered for CH₃NH₃Pb_0.75Sn_0.25I_2.5Cl_0.5 even after 600 days, under environmental conditions. The bandgap value for this doped perovskite is 1.44 eV.

In this research, both the standard molar enthalpy of formation in the crystalline phase and in the gas phase of 3-methylglutaric anhydride was calculated from experimental data. The temperature and enthalpy of fusion, as well as the molar heat capacity in solid phase was calculated by differential scanning calorimetry; the molar enthalpy of sublimation at 298.15 K by the Knudsen effusion method, the molar enthalpy of vaporization at 298.15 K by thermogravimetric analysis, and the standard massic combustion energy by combustion adiabatic calorimetry. Since 3,3-dimethylglutaric anhydride presented crystal transitions (with endothermic points at 352.76 K, 356.98 K and 397.15 K), some of its thermochemical properties were estimated from the functional group-contribution methods proposed by Benson, Gani and Naef and from application of Machine Learning based models.