Vol. 68 No. 3 May-Jun (2022): Revista Mexicana de Física

A theoretical and experimental study of a falling metal drop which interacts with a perpendicular non-localized magnetic field is addressed. As the metal drops traverses the magnetic field, it suffers a braking due to induced electromagnetic effects. An analytical solution for the velocity of the falling drop is obtained thought a balance of forces which affect its motion. A numerical solution from the incompressible Navier-Stokes equations for two phase flows is also obtained. A numerical model for the solution of the incompresible Navier-Stokes for two-phase flows is also implemented. This model is based in the fron-tracking/finite volume method. The simulation allows observe a more detailed dynamics such as the deformation of the drop. Both the theoretical and numerical results validate the experimental data obtained through the Particle Image Velocimetry.

The linear and nonlinear optical properties of CuIn1−xGaxSe2 free standing nanowire have been studied by employing the compact-density matrix formalism and the effective mass approximation. Considering the system under the effect of the polarization vector of the incident light in both cases perpendicular and parallel to the axis of the nanowire, the systematic theoretical investigation contains results with all possible combinations of the involved parameters, such as incident light intensity, relaxation time, nanowire radius and Ga concentration. Our results show that in the case of the polarization vector perpendicular to the nanowire axis, the linear and nonlinear absorption coefficient and refractive index changes can be controlled by changing the nanowire radius, and the effect of Ga concentration is clearly apparent. In contrast, polarization along the nanowire axis allows for a very large absorption coefficient and control of the optical properties through the height, but minimal effect on the transition energy. The increase of the relaxation time as well as the intensity of the incident light has a major role in the nonlinearity effects, while the Ga concentration and the size of the structure influence the amplitude and the transition energy shift.

In this work the self-assembling of InAs quantum dots (QDs) within asymmetric barriers of (Al)GaAs is studied via reflection high energy electron diffraction (RHEED). A comparative study between the AlGaAs/InAs/GaAs interfaces and its mirror-like heterostructure GaAs/InAs/AlGaAs showed significant differences in the self-assembling and capping of the QDs. The critical thickness of InAs QDs results was proven to be larger when it is grown on AlGaAs alloys, compared with the deposition on GaAs layers. This change is explained by the reduced mobility of In atoms on the Al-containing surfaces, for which the QDs density is increased due to the strain relieve. Through the in-situ analysis of diffusion parameters, it is concluded that the mobility of In atoms decreases the mass transport of 2D and 3D precursors that conduces to the self-assembling of the QDs nanoislands, modifying the rate at which the QDs are formed. Further, during the first stages of QDs capping it is observed that the III-V materials intermixing plays a predominant role. The nanoislands are less affected when are covered by AlGaAs in comparison with the GaAs capping, preserving the QDs morphology and avoiding materials alloying. By following the RHEED intensity behavior during the QDs capping, a model was proposed to obtain quantitative parameters for the smoothing process. High resolution x ray diffraction (HRXRD) measurements show the composition of sharp interfaces for the AlGaAs/InAs/GaAs heterostructure. Lastly, numerical simulations were performed to evaluate the strain changes using the experimental information as input data.

Linear response methods allow studying magnetic susceptibility relaxation in isotropic colloidal magnetic fluids. We show a relationship between the susceptibility of macroscopic magnetization at thermal equilibrium and the diffusion constant of a tracer particle. The comparison of the predicted frequency-dependent susceptibility with computer simulations shows their agreement. Besides, at a low concentration of particles, it has the expected Debye behavior. However, the initial susceptibility yields only the qualitative trends of the existing experiments at a low volume fraction of particles and its temperature dependence.

The present research evaluates commercial aluminum alloys 319 (AA319) and modified series by Ni additions on microstructure and mechanical properties through x-ray diffraction, electron microscopy, hardness, and tensile tests. All AA319+X%Ni compositions (x = 0.5,1, 2) improved both hardness and UTS at room temperature, T6, over-aging, and high-temperature conditions. UTS obtained an improvement of around 30% to AA319 + 1%N i and AA319+2%Ni relatives to unmodified reference from T6 and high-temperature conditions. In addition, Ni increased remarkably the number of θ 0-Al2Cu pairs and reduced their thickness within the aluminum matrix compared to commercial alloy. The synthesis methodology is also adaptable to the current aluminum casting industry, creating the material in ingots and finished products.

Pollycrystalline CdTe thin films deposited in large areas present some difficulties, such as non-uniformity over the entire area. It is well known that the ratio between the thickness and grain size of CdTe thin films is approximately one. In contrast, the pin holes in CdTe should be minimized.  CdS thin films as window materials must guarantee a uniform transparent film free of pinholes to avoid short-circuiting in the photovoltaic device. In this work, CdTe and CdS thin films are reported in areas of 40 cm² with optimal physical properties for potential application on solar cells. CdTe mini-modules were fabricated using CdTe and CdS layers obtained and characterized under outdoor conditions. The current-voltage measurements were performed under different charge and solar irradiance conditions.

Superhydrophobic surfaces are highly desired for several applications due to their exceptional properties such as self-cleaning, anti-icing, anti-friction and others. Such surfaces can be prepared via numerous methods including plasma technology [1-7]. Among plasma technology methods used to prepare these surfaces, the plasma enhanced chemical vapor deposition method, which provides the advantages of low cost, simple processing, and easy to form micro-nano structure.

In this work, a treatment of surface paper for improving hydrophobicity using a PECVD technique was realized, paper substrates was treated by CH₄ plasma , the substrates were held on a grounded substrate, with time variation of 5, 10, 15 and 20 min, while pressure and power have been kept constant at 8.10^-2 and 100 W respectively.

After deposition we proceeded to carry out structural and morphological characterization of the treated surfaces, by (SEM), AFM, FTIR and then through contact angle measurements. It is found that all layers are hydrophobic and super-hydrophobic. Except the layers treated for 10 minutes which are hydrophobic with a contact angle equal to 137.7° , the layers treated for 05, 15 and 20 minutes show superhydrophobic surfaces with a contact angles equal to 153.8°, , 149.2° and 156◦ respectively.

The concept of a Magnetic Resonance Imaging (MRI) device is based on the emission of radio waves produced by the protons of the hydrogen atoms in water molecules when placed in a constant magnetic field after they interact with a pulsed radio frequency (RF) current. When the RF field is turned on, the protons are brought to a spin excited state. When the RF field is turned off, the MRI sensors are able to detect the energy released as the protons realign their spins with the magnetic field. In this work we provide a simple model to describe the basic physical mechanism responsible for the operation of MRI devices. We model the water molecule in terms of a central force problem, where the protons move around the (unstructured) doubly negatively charged oxygen atom. First, we employ an analytical treatment to obtain the system's wave function as well as its energy levels, which we show are degenerate. Next, the energy levels from the water molecule are studied in the presence of a uniform external magnetic field. As a result, they get shifted and the degeneration is lifted. We provide numerical results for a magnetic field strength commonly used in MRI devices.

Using different potentials based on phenomenological, semi microscopic, and microscopic models, we investigated the reaction dynamics induced by the weakly bound ⁶Li ions on a heavy mass target ²⁰⁸Pb at sixteen energy sets ranging from 25 MeV to 210 MeV. The ⁶Li cluster nature and its dissociation into a core (α-particle) and a valence particle (deuteron) orbiting this core was taken into consideration using the cluster folding model (CFM). The new version of Sao Paulo potential (SPP2) is also used to investigate ⁶Li+²⁰⁸Pb data. In order to reproduce the experimental data, the strength of real part of potential created using SPP and CFM should be reduced by ~ 49 % and 62 %, respectively. The data could be well reproduced using non-renormalized real cluster folding potential, if an additional dynamical polarization potential (DPP) of repulsive real surface form is introduced. The observed reduction in the strength of the real double folded and cluster folding potentials is due to the break-up effect of ⁶Li.

In this study, a lot of fusion experimental data are theoretically analyzed by using ten different density distributions of the 19F nucleus. The real potentials are obtained by means of the double folding model while the imaginary potentials are accepted as the Woods-Saxon potential. The theoretical results are compared with the results calculated over one-dimensional Wong formula as well as the experimental data. Thus, alternative density distributions are proposed for the analysis of the experimental data of the 19F fusion reactions. Additionally, the barrier positions and heights of all the analyzed fusion reactions are calculated for all the density distributions and new analytical expressions for these results are derived. Finally, new pocket formulas giving the imaginary potential depths for fusion cross-section calculations with 19F are obtained for the first time.

microscopic folded potentials for both the real central and the spin-orbit (SO). For the imaginary central, we used surface Woods-Saxon (WS) potential. We aimed to test the microscopic SO potential based on the M3Y effective nucleon-nucleon (NN) interaction for the light system p+$^9$Be. The present calculation showed that the microscopic SO potential is satisfactory reproduce $A_y$ above 8 MeV and qualitatively reproduced $A_y$ below 8 MeV. In addition, we found that the calculated real central potentials are successfully reproduced the $d\sigma/d\Omega$ for all the considered energies. From the present analysis, we excepted that the present microscopic SO potential could reproduce successfully the $A_y$ for p+nucleus as the incident proton energy increases above 10 MeV.

We study the electronic, optic and transport properties of both bulk materials ErN and Er0.125Ga0.875N, where crystallize in zinc-blind and wurtzite structure respectively which are materials involved form a quantum well devices.Based on density functional theory, by applying the full-potential linearized augmented plane-wave method with spin orbit coupling effect. The
analysis of the electronic properties show that the ErN and Er0.125Ga0.875N has a band gap at 0.79 and 3.38eV respectively. on the other hand, the technology makes possible to stack these materials for a quantum well heterostructure of Er0.125Ga0.875N/ErN.The optical properties such as optical coefficients, refractive index and extinction coefficient are discussed in detail. The transport properties of alloys are investigated using the semi-classical Boltzmann theory as implemented in the BoltzTraP code in conjunction with ab initio electronic structure calculations. Our result shows that Er doping of wide band gap semiconductors is could be a potential candidate for quantum wells devices.

We study the diffraction of a monochromatic electromagnetic plane wave by a dielectric&metal-core/metal-shell nanoparticle surrounded by a dielectric medium. This problem was solved by using generalized Mie’s theory and both the scattering cross section and the square module of the electric field were calculated as a function of shell thickness. Numerically, the first particles studied were gold-core/silver-shell nanoparticles and their inverse configuration. The gold-core/silver-shell particle presented more variation of their optical properties. The second particles were vacuum-core/metal-shell surrounded by vacuum, symmetric configurations. In this case, the dispersive Drude dielectric function for the metal was used, and a comparative study between the positions of the resonance frequencies obtained from quasi-static limit and electrodynamic theory was performed. Thus, consequently the formula obtained from the quasi-static limit can be used to calculate the positions of the resonance frequencies instead of the electrodynamic theory, when the external radius is smaller than 20 nm.

We present our recently-built experimental setup designed to generate near-infrared and narrow-band correlated photon pairs by inducingfour-wave mixing in a cold gas of ⁸⁷Rb atoms confined in a magneto-optical trap. The experimental setup and its automation and control approach are described in detail. A characterization of the optical density of the atomic ensemble as well as the basic statistical measurements of the generated light are reported. The non-classical nature of the photons pairs is confirmed by observing a violation of Cauchy-Schwarz inequality by a factor of 5.6 × 10 ⁵ in a Hanbury Brown – Twiss interferometer. A 1/e coherence time for the heralded, idler photons of 4.4 ± 0.1 ns is estimated from our observations. We are able to achieve a value of 10⁴ s⁻¹pair-detection-rate, which results in a spectral brightness of 280 (MHz s)⁻¹. The combination of high brightness and narrow-band spectrum makes this photon-pair source a viable tool in fundamental studies of quantum states and opens the door to use them in quantum technologies.

In this paper, the amplitude and phase characteristics of internal reflection of gold nanofilms are investigated using polarization modulation of electromagnetic radiation in the Kretschmann geometry, an excited wavelength of the SPR at 633 nm is considered. The numerical results that are presented in this work are based on the substrate, the variation of the thickness of the dielectric and the type of plasmonic material using gold (Ag), through the ellipsometry parameters Ψ and ∆.

Many natural composite materials contain systems of partially oriented thin low-resistivity inclusions (for example, water-saturated microcracks in a double porosity sedimentary formation). We have calculated the components of the electrical conductivity tensor of such materials as a function of crack density. The results were obtained for thin ellipsoidal inclusions with conductivity (electrical or thermal) much larger than the matrix conductivity. To calculate the effective conductivity, we have used the effective field method (EFM). We have obtained the explicit expressions for the effective parameters of inhomogeneous materials. The application of the EFM allows one to describe the influence of the peculiarities in the spatial distribution of inclusions on the effective properties of the medium. General explicit expressions, obtained in this work, are illustrated by calculation examples for inclusions, homogeneously distributed in the sector [-Beta, Beta], where Beta is the disorientation angle, and some continuous angle distribution functions. The calculations have shown that the spatial distribution of the crack-like inclusions strongly affects the conductive properties of the effective medium and the symmetry of their tensor.

The performance of today's quantum computers are affected by noise. This effect can be analyzed in the result of simple quantum algorithms in real quantum computers. The noise can be characterized as a decoherence error or a systematic error, the last could be corrected by a unitary rotation.
In this article we propose two methods to model a systematic error, in the Quantum Fourier Transform algorithm (QFT). The first method uses the isotropic index presented in ``  [1] and needs to reconstruct the density matrix of the experimental state, while the second method, although less general, only needs to reconstruct the reduced density matrices for each qubit.
In both methods, a unitary transformation is proposed, which approximates the experimental result to the expected theoretical state. As an example, the QFT algorithm is analyzed for two qubit states, in quantum IBM Q computer ibmq\_santiago.

In Mexico there are 28 public and private universities in which Physics, Engineering Physics and related degrees are taught. Although the websites of the different universities mention the different employment options that a physicist can have, there is no study about the job opportunities of Physicists and Engineering Physicists in Mexico. In this paper we present the results of an online survey addressed to Physics and Engineering Physics graduates who completed their bachelor’s degree in Mexico and who were active in the labor market, with the aim of knowing the labor field of Mexican physicists. In addition to employment, information about their salaries, sex, their highest degree of studies and their perception of the level of personal fulfillment in the professional field was obtained. The information gathered can be used to form a guide for students and recent graduates to learn about the different employment options available to broaden their vision on job prospects for physicists in Mexico.

The hybrid atoms-cell site entanglement in a one-dimensional Su-Schrieffer-Heeger (SSH) topological insulator with first and second neighbor hopping in space representation of finite chains is analyzed. The geometrical phase is calculated by the Resta electric polarization and the entanglement in the atomic basis by the Schmidt number. A relation between entanglement and the topological phase transitions (TPT) is given since the Schmidt number has local critical points of maximal entangled (ME) states in the singularities of the geometrical phase. States with second neighbors have higher entanglement than first-neighbors hopping. The general conditions to produce ME hybrid Bell states and the localization-entanglement relation are given.

We present a theoretical framework to study equilibrium configurations of filaments within a spinor representation of curves. The curve representing the filament is described by a unit two-component spinor field and its charge conjugate satisfying two-dimensional equations coupled by the curvature and torsion. The spinor field replaces the Frenet-Serret frame, whereas its structure equations replace the Frenet-Serret equations. Employing this spinorial description of curves, we derive the Euler-Lagrange equations of curves whose energies depend on their curvature and torsion. We analyze the conservation laws of the spinors representing the balance of the forces and torques along the filament. We illustrate this framework by applying these results to the Euler Elastica, whose bending energy is quadratic in the curvature.

In this paper, switched linear systems are considered and dwell and average dwell time for their global asymptotic stability is examined. Dwell and average dwell time are determined based on the condition number for the global asymptotic stability of switched linear differential systems. Numerical examples which show the effect of the results obtained are given with the new dwell and average dwell times.

In this paper we investigate the Fokas-Lenells (FL)   equation via the -expansion method. To convert this nonlinear model into ODEs, we utilize an intelligible wave transformation. The solutions show that considered method fit well for Fokas-Lenells equation with complex structure. The achieved soliton solutions will give stretch study for this model and all related phenomena’s. With the view of the results, new improvements can happen for applications of the model.