Vol. 69 No. 1 Jan-Feb (2023): Revista Mexicana de Física

In this paper, we present a theoretical study of scattering cross sections for positron impact of electronic states of hydrogen molecule (H₂) using the scaling Born positron (SBP) approach. Cross sections to low-lying electronic states, B¹∑⁺_u, C¹П_u, B´¹ ∑⁺_u, and D¹П_u are investigated. In an earlier theoretical effort [J.L.S.Lino, Rev. Mex. Fisica 62 (2016) 596], an application of the SBP approach for the X¹∑⁺_g - > B¹∑⁺_u electronic excitation of the H₂ molecule, gave cross sections with reasonable qualitative agreement with experimental data [J.P.Sullivan et. al., Phys.Rev.Lett.87,073201 (2001)]. However, recent studies for the excitation of the B¹∑⁺_u state by positron impact showed that this electronic state still demand of a refined degree of description of the quality of the cross sections (Weiss et. al., Eur. Phys. J. D (2018) 72). The purpose of this work was to reexamine the B¹∑⁺_u state and verify the quality of the numerical convergence of SBP method and extend the investigation to other states. The possibility to estimate a indirect contribution of multichannel effects ( three states considering the ground X¹, B¹∑⁺_u and E,F¹∑⁺_u state) are introduced within the SBP context. For the first time, integral cross sections to these new states using the SBP approach are reported. In the absence of the experimental data and theoretical developments, comparisons are made with analogous electron scattering.

It is known that the standard and the inverted harmonic oscillator are different. Replacing thus ω by ±iω in the regular oscillator is necessary going to give the inverted oscillator H^{r}. This replacement would lead to anti- PT-symmetric harmonic oscillator Hamiltonian (∓iH^{os}). The pseudo-hermiticity relation has been used here to relate the anti-PT-symmetric harmonic Hamiltonian to the inverted oscillator. By using a simple algebra, we introduce the ladder operators describing the inverted harmonic oscillator to reproduce the analytical solutions.We construct the inverted coherent states which minimize the quantum mechanical uncertainty between the position and the momentum. This paper is dedicated to the memory of Omar Djemli and Nouredinne Mebarki who died due to covid 19.

This paper aims to present a group of compounds Dy₂M₂O₇ (with M = Hf, Ce and Zr) which could be an alternative having the same function as TiO₂. Based on our studies and those reported in the literature, we will discuss in detail the roles and the functional mechanism of the catalysts. The results show that Zr₂Dy₂O₇ is the best candidate to be a photo-catalyst: it has a band gap close to 2.2 eV, and a good absorption in visible range compared to the other compound having absorption in UV. The quantum efficiency of Zr₂Dy₂O₇   reaches up to 3%, and the limit of conduction band and valence band are localized in potential redox zone. Doping with Cerium gives another energy level, which allows having other optical transitions and improving the absorption and reaching the quantum efficiency to 4% in a visible range.

We determine the operators associated to the index of degeneration of Landau's levels for the Landau's gauge and symmetric gauge of the magnetic field, with the non separable eigenvalue solution obtained for a charged particle in a flat box under a magnetic field perpendicular to flat motion.

In this work, the influences of biaxial compressive and tensile strains on optical gain and threshold current density are investigated theoretically as a function of the side lengths of the quantum box in the GaN/Al_0.2Ga_0.8N structure by using a model based on the density matrix theory of semiconductor lasers with relaxation broadening. For various side lengths of the quantum box, we compare the spectra gain curves of compressive, tensile-strained, and unstrained structures of the GaN/Al_0.2Ga_0.8N cubic quantum-dot (QD) laser. The dependence of peak optical gain on carrier density and the modal gain on current density is plotted too for all cases. The results reveal that many enhancements can be made to the laser structure by introducing -0.5% compressive strain: a higher value of optical gain of 18421 cm^-1  at  L=60A, a lower value of transparency of carrier density of N_tr=0.13*10¨¨¹⁹ cm^-3and transparency current density of J_tr=26.9 A/cm  and a lower threshold current density of J_th= 78.87 A/cm²  at L=100 A.

The purpose of this work is to perform a CFD study of the free shock separation (FSS) in an overexpanded nozzle. The original contraction profile of the nozzle was numerically replaced by a set of curves, where the overall length was identical with the test-rig. For the baseline case, the static pressure and the separation location exhibited a good agreement with the experimental measurements, provided by the DLR. The Error-function contraction profile has revealed a relative displacement of 1.38% on the separation location in the core flow direction. In this case, there was an increase in the thrust coefficient, that has been improved up to 1.7% in comparison with the baseline nozzle design.

Overdamping is a regime in which friction is sufficiently large that the motion either decays to its equilibrium position or it crosses the equilibrium position exactly once before returning monotonically towards the equilibrium position. The phenomena of overdamping has been studied classically and quantum mechanically only for the case of the linear damped harmonic oscillator. Here we study the classical and quantum dynamics of a family of over-damped non linear systems. The main objective of this paper is to find a Lagrangian and Hamiltonian framework to study over-damped non linear systems and to show that a quantum mechanical description can be developed in the momentum representation. Our results reduce to the well known solution of the linear damped harmonic oscillator when the non linear part is set to zero.

It is shown that in some examples of classical mechanics, the complex, double and dual numbers are useful in the search of symmetries of the equations of motion. As a byproduct, we obtain non-standard Lagrangians for the systems under consideration.

A black-hole solution in four time and four space dimensions ((4+4)-dimensions) is developed. It is emphasized that such a solution establishes a duality relation between the (1+3) and the (3+1) black-holes, which are part of the (4+4)-world. Moreover, it is found that a cosmological constant of the (1+3)-world is dual to the cosmological constant in the (3+1)-world.

Manganese (II) acetates tetrahydrate, zinc dihydrate and anhydrous zirconium, processed by freeze-drying, were heat-treated in free atmosphere at different temperatures and times, generating the main oxides of these metals. These acetates were structurally characterized by scanning electron microscopy (SEM), thermogravimetry (TG), differential scanning calorimetry (DSC) and, along with all the oxides generated, by X-ray diffraction (XRD). Calculations obtained from TG data showed that manganese acetate lost two waters after freeze-drying, also confirmed by X-ray data and that the same phenomenon may be occurring for zinc acetate. The results indicate that exothermic events occurred at lower temperatures for freeze-dried acetates, which may be related to the high surface area of the material, and consequent greater reactivity. The total decomposition temperatures of the acetates in the ZnO and ZrO₂ semiconducting oxides and the manganese oxides Mn₂O₃ and Me₃O₄, with excellent crystallization, were obtained.

TM (TM = Sn, Al) doped and co-doped CdO thin films were deposited by spray pyrolysis technique on glass substrate at temperature 350 ˚C. The effect of TM doping and co-doping on the structural, morphological, optical, and electrical properties of CdO thin films was investigated. The obtained films are crystallized in the cubic structure and oriented along the preferential (111) crystallographic plane. The average optical transmittance reaches 79% in the visible range for Sn doped CdO films and 74% for Al-Sn co-doped films. The gap values of the obtained samples are between 2.29 and 2.49 eV. All the deposited films exhibit n-type conductivity with a low electrical resistivity of 7.85.10^-4 Ω.cm obtained for Al doped CdO films.

Many of the known examples of half-metallic ferromagnets HMF are oxides, sulfides, or Heusler alloys have attracted some interest for their potential use in spintronics. In order to achieve such understanding we have performed an ab-initio calculations with spin polarization using plane-wave pseudo potential technique based on the density-functional theory (DFT), the exchange-correlation potential was treated with the generalized gradient approximation (PBE-GGA), whereas for the treatment of on-site electron-electron correlations the PBE-GGA+U approximation (where U is the Hubbard Coulomb energy term) are applied for the calculation of the structural, electronic, elastic and magnetic properties of Pd₂PrX (X=Cl, F). The results showed that for Pd₂PrCl and Pd₂PrF, Hg₂CuTi-type structure is energetically more stable than Cu2MnAl-type structure at the equilibrium volume. Electronically, Pd₂PrCl and Pd₂PrF exhibit half-metallicity with small band gaps of 0.06 and 0.25eV respectively with GGA-PBE+U in the spin-down channels whereas spin-up channels are conducting. The calculated total magnetic moment of 2.00 μB per formula unit is very close to integer value and agree well with the Slater-Pauling rules ( M_tot=34-Z_tot), where the magnetic moment is basically carried by Pr atoms. However, the elastic properties show that Pd₂PrX (X=Cl, F) compounds are ductile and anisotropic according to the analysis of B/G and Cauchy’s pressure. The Thermodynamic properties were also analyzed using the quasi-harmonic Debye model. Both the compounds are found structurally stable.

The primary goal of this study is to investigate the effect of different exchange-correlation functionals on the optoelectronic and elastic properties of the Ag₂O chalcogenide compound. For the electronic structures and optical spectra, the Tran-Blaha modified Becke-Johnson approach combined with GGA and with GGA+U (mBJ-GGA-PBEsol and mBJ-GGA-PBEsol+U, respectively) was used. The available theoretical and experimental data for the bandgap energy were reported to determine whether there is a correlation with our results. The electronic structure revealed that our compound is a direct semiconductor at the R-symmetry point with a bandgap of 1.22 eV, which this value agrees well with the experimental values for the first time. The elastic constants were also evaluated using the IRelast package, which revealed that the compound was mechanically stable. Finally, the optical response was systematically studied, and it was found that Ag₂O exhibited excellent optical efficiency.

In this paper the continuity equation for Wigner-Dunkl-Schrodinger equation is studied. Some properties of ¨ ν-deformed functions related to Dunkl derivative are also studied. Based on these, the step potential and Ramsauer-Townsend effect are discussed in Wigner-Dunkl quantum mechanics

The magnetic dipole and electric quadrupole moments for some Boron isotopes were calculated using the shell model taking into account the effect of the two-body effective interactions and the single-particle potentials. These isotopes are; (8 5)B(2 +), (1 50)B(3 +), (1 51)B((3/2)−), ( 1 52)B(1 +) and (1 53)B((3/2)−). Also, the elastic and inelastic longitudinal and transverse electron scattering form factors are calculated for 10B and 11B, for which there are available experimental data. The one-body transition density matrix elements (OBDM) were calculated using the two-body effective interactions; PWT, PEWT, PKUO and CKIHE, which are carried out in the p-shell model space. Skyrme interaction was implemented to generate the single-particle matrix elements with Hartree-Fock approximation and compared with those of harmonic-oscillator and Wood-Saxon potentials. All the evaluated results were compared with available experimental data. The present work has led us to conclude that the shell model calculations with Skyrme type interaction give a good tool for nuclear structure studies. All signs for the experimental electromagnetic moments data are reproduced correctly. The longitudinal and transverse form factors for positive and negative parity states are fairly well reproduced when using a suitable model space.

In recent years, the discussion about using marijuana to treat some specific diseases has been the reason for several studies to determine how Cannabis could affect or benefit the human body, such as chronic pain. However, the legal status of marijuana in different parts of the world remains a problem when conducting experiments for academic purposes. In this way, algorithms based on molecular dynamics are of great help to study the change in the physical properties of membranes, which is our first defense barrier, in the presence of external agents. Here we used equilibrium molecular dynamics to study the interactions of a DPPC/DPPG monolayer membrane with CBD and THC, these two molecules being one of the main components of Cannabis, and compare the interactions with morphine and lidocaine which are drugs with well-known anesthetic properties. We also used the umbrella sampling method to determine the variations of the potential of mean forces as every single drug crosses the membrane obtaining an approximation of the hydration free energy, we obtained a value of 57 kJ mol^-1 for CBD and 5 kJ mol^-1 for THC; values reported for the first time using molecular dynamics.

Within the framework of the effective mass approximation, a detailed investigation of the effects of an external (DC) electric field on the electronic and optical properties of a multi-layer cylindrical ZnS/ZnO quantum dot with fixed height and radius respectively at 10 nm and 5 nm, while modeling the ZnO wells using a parabolic potential. Numerical results were carried out using the Finite Difference Method (FDM), in order to compute the confinement energies, probability densities, expectation value for the potential describing a (DC) electric field for both the ground state and first excited state, and finishes by deducing the transition energy, transition dipole moment (TDM) and the absorption coefficient (AC) while taking into account multiple layer thickness configurations as we vary the electric field strength $F$. The results shows that varying the (DC) electric field strength does has an noticeable impact on the electronic and optical properties while all other inputs are kept unchanged.

In this paper we present the discrete thermodynamics where the inverse temperature is not continuous but discrete. We construct the discrete analogue of Boltzmann factor based on the discrete inverse temperature lattice. We study the discrete thermodynamics related to the discrete analogue of Boltzmann factor. We also discuss the superstatistics for the discrete inverse temperature.

In this work a 1D slightly doped n-type Silicon layer is considered. Irreversible thermodynamics transport equations are used to obtain the spatial particle distribution in isothermal stationary state. The excess particle transport is studied in low injection regime and quasineutrality condition. The material is subjected to Dirichlet-Neumann (N-D) conditions at the boundaries. We wonder if an asymmetry of the particle flux exists when the boundary conditions are inverted. We find that the asymmetry does exist and a rectification factor may reach the value 0.35. We conclude that particle flux rectification seems to be featuring the particle transport in slightly non-homogeneously doped semiconductor when the excess hole concentration is smaller than the equilibrium hole concentration