Vol. 66 No. 4 Jul-Aug (2020): Revista Mexicana de Física

We present our experimental setup to produce ultracold strongly correlated fermionic superfluids made of a two-component spin-mixture of 6Li atoms. Employing standard cooling techniques, we achieve quantum degeneracy in a single-beam optical dipole trap. Our setup is capable of generating spin-balanced samples at temperatures as low as T/TF = 0.1 containing up to 5 × 10^4 atomic pairs. We can access different superfluid regimes by tuning the interparticle interactions close to a broad magnetic Feshbach resonance. In particular, we are able to explore the crossover from the molecular Bose-Einstein condensate (BEC) to the Bardeen-Cooper-Schrieffer (BCS) superfluid regimes. In the near future, we plan to study different collective excitations in these superfluid samples.

This paper studies optical soliton perturbation that appears with Kerr law nonlinearity having spatio-temporal dispersion. The numerical scheme adopted is the variational iteration method. The perturbation terms are of Hamiltonian type and stem from inter-modal dispersion, self-steepening and nonlinear dispersion. Both bright and dark solitons are taken into consideration.

In this paper we consider the Coulomb’s law with deviation. We use the Dunkl derivative to derive the deformed Gauss law for the electric field and the electrostatic potential
which gives a new deformed electrostatics called a Dunkl-deformed electrostatics. We
modify the Dunkl derivative for the electric field for multi sources or continuous charge
distribution. We discuss some examples of the Dunkl-deformed electrostatics.

We explicitly show that the groups of $2 \times 2$ unitary matrices with determinant equal to 1 whose entries are double or dual numbers are homomorphic to ${\rm SO}(2,1)$ or to the group of rigid motions of the Euclidean plane, respectively, and we introduce the corresponding two-component spinors. We show that with the aid of the double numbers we can find generating functions for separable solutions of the Laplace equation in the $(2 + 1)$ Minkowski space, which contain special functions that also appear in the solution of the Laplace equation in the three-dimensional Euclidean space, in spheroidal and toroidal coordinates.

In this study the tachyon-like Dirac equation, formulated by Chodos to describe superluminal neutrino, is solved. The analytical solutions are Gaussian wave packets obtained using the envelope method. It is shown that the superluminal neutrino behaves like a pseudo-tachyon, namely a particle with subluminal velocity and pure imaginary mass that fulfils the energy-momentum relation typical of classical tachyons. The obtained results are used to prove that the trembling motion of the particle position around the median, known as Zitterbewegung, also takes place for the superluminal neutrino, even if the oscillation velocity is always lower than the speed of light. Finally, the pseudo-tachyon wave packet is used to calculate the probability of oscillation between mass states, obtaining a formula analogous to the one obtained for the ordinary neutrino. This suggest that in the experiments concerning neutrino oscillation is not possible to distinguish tachyonic neutrinos from ordinary ones.

We firstly discuss the geometric phase rotation for an electromagnetic wave traveling along the optical fiber in Minkowski space. We define two types of novel geometric phases associated with the evolution of the polarization vectors in the normal and binormal directions along the optical fiber by identifying the normal-Rytov parallel transportation law and binormal-Rytov parallel transportation law and derive their relationships with the new types of Fermi-Walker transportation law in Minkowski space. Then we describe a novel approach of solving Maxwell's equations in terms of electromagnetic field vectors and geometric quantities associated with the curved path characterizing the path uniform optical fiber by using the traveling wave transformation method. Finally, we investigate that electromagnetic wave propagation along the uniform optical fiber admits an interesting family of Maxwellian evolution equation having numerous physical and geometric applications for anholonomic coordinate system in Minkowski space

In this work, we investigate the Lagrangians and potentials for two coupled damped Duffing oscillators both directionally and bi-directionally. We show that, although it is not always possible to define a potential in dissipative systems, the potential of our model can be defined if the damping coefficient has a logarithmic derivative form. It is possible to apply these results to the analysis of the dynamics of complex networks based on three-node motif configurations. As an example, we study numerically the dynamics for one of the thirteen different possible configurations. Here, the phenomenon of synchronization is observed in terms of the coupling parameter.

We compute the gluon polarization tensor in a thermo-magnetic environment in the
strong magnetic field limit at zero and high temperature. The magnetic field effects are introduced using Schwinger's proper time method. Thermal effects are computed in the HTL approximation. At zero temperature, we reproduce the well-known result whereby for a non-vanishing quark mass, the polarization tensor reduces to the parallel structure and its coefficient develops an imaginary part corresponding to the threshold for quark-antiquark pair production. This coefficient is infrared finite and simplifies considerably when the quark mass vanishes. Keeping always the field strength as the largest energy scale, in the high temperature regime we analyze two complementary hierarchies of scales: $q^2<< m_f^2<< T^2$ and $m_f^2<< q^2<< T^2$. In the latter, we show that the polarization tensor is infrared finite as $m_f$ goes to zero. In the former, we discuss the thermal corrections to the magnetic Debye mass.

Este trabajo presenta la configuración y montaje de un equipo empleado para la cuantificar el coeficiente magnetoeléctrico dinámico (α) de compuestos cerámicos multiferroicos. En particular, se analizan las propiedades magnetoeléctricas de los compuestos de composición Bi_0.5(Na_0.8K_0.2)_0.5TiO₃-Ni_0.5Co_0.5Fe₂O₄ (BNKT-NCF). En el método dinámico, la señal magnetoeléctrica (ME) es registrada midiendo el potencial eléctrico a través de la muestra bajo un campo magnético continuo y variable en presencia de un campo magnético de CA. Los elementos de medición constan de un sistema de polarización (eléctrico y magnético), para polarizar la cerámica magnetoeléctrica, y un lock-in para generar la señal alterna y filtrar el ruido. Además, dada la baja señal ME es necesario un blindaje adecuado y una sección fina de electrodos junto al amplificador tipo lock-in. El rendimiento de los dispositivos fabricados resulta satisfactorio para realizar la medición dinámica del efecto ME para materiales magnetoeléctricos basados en cerámicos multiferroicos.

Particle detectors based on the response of sensitive material (plastic scintillator, saturated gas, etc.) usually need characterization and test procedures before final installation. Cosmic ray particles are normally used to perform those preliminary tests which includes a detailed inspection of the readout electronics and a data acquisition to obtain a charge distribution of cosmic ray detection.

The Data Processing Interface is implemented in an FPGA (ALTERA family), designed to test the acquisition of digitized signals from light sensors, fotomultipliers (PMTs)  and Avalanche photodiodes (APDs) are the most common ones. The architecture is based on a medium density FPGA that continuously reads the data coming from a 10-bit, 40MHz ADC. Input data is stored in a dual port memory designed to search for valid pulses and compress them by removing data below a programmable voltage threshold. The Interface can produce two types of data packets, non-Zero packets and empty packets. Data in non-zero packets are compressed with a lossless technique and they are marked with a start of data, time stamp, valid data and data size information for reconstruction purposes. Empty events are generated when the maximum waiting time for a valid pulse is exceeded and information is added to preserve the time continuity.

Lightweight composite materials are the gold standard in aeronautical and aerospace applications due to their strength and low mass. To carry higher payloads and decrease launching costs, nanosatellites lightweight. Additionally, nanosatellites must also resist high thermal radiation loads while working in orbit. Polymer-based composite materials maintain low mass and added reinforcing ceramic fillers contributes to increasing radiation resistance, thus producing composites that meet both requirements. In this work, the effects of γ-alumina (Al₂O₃) and zinc oxide (ZnO) micro- and nanoparticles on the thermal properties and degradation kinetics of epoxy-based composites were investigated. The effective thermal conductivity improved up to 17.8 % for epoxy/γ-Al₂O₃ and 27.4 % for epoxy/ZnO. The effective thermal diffusivity values show a monotonic decreasing behavior as a function of the particle concentration for the epoxy/γ-Al₂O₃ composites; for the epoxy/ZnO composites, no correlation on the effective thermal diffusivity values with the ZnO-content was observed. Both oxide-based ceramic fillers increase the thermal stability of epoxy up to 250 °C; however, γ-Al₂O₃ decreased the maxima decomposition temperature of the epoxy matrix by 6°C. Zinc oxide did not affect the maxima decomposition temperature but decreased the activation energy of epoxy by ~ 45 %. These results provide a feasible manufacturing method for epoxy-based composite materials (i.e. nanosatellites) where efficient heat transfer, heat resistance, and low mass are required.

Serrated GaN nanowires were synthesized on sapphire substrate by chemical vapor deposition. Copper nanowires were synthesized by liquid-phase reduction method. The surface morphology of GaN and copper nanowires was observed by scanning electron microscopy. An UV detector based on GaN nanowires was prepared with copper nanowires as electrode. The results show that the device is a photoconductive detector. The detector has different response under different wavelength light illumination and has the maximum response under 365nm ultraviolet light. Photocurrent–time characteristics show the detector has good stability over time.

Laboratory scale studies of tribological properties of nitride coatings are useful in predicting their protective wear behavior in cutting tools for industrial scale applications. Main aim of this research is to determinate optical and tribo-mechanical properties in multilayer coatings of metal-ceramic assigned as coatings A and B. These coatings were deposited by DC magnetron sputtering on carbon steel AISI 1060 using buffer adhesion layers of W, Ti/W/WN and TiN/TiN respectively. For to determinate molecules interactions of materials were analysed by means of Raman and FTR spectroscopies. The nanohardness, tribological and adhesion behaviour were studied by nanoindentation, pin on disk and a tribometer. The hardness and behaviour tribological, were obtained by Nano-indentation, pin on disk, and scratch test using a tribometer. FTIR and Raman analysis shown the formation of Ti metallic ion and WO₃ mainly in both coatings. The hardness of coatings shown a slight improvement compared with the substrate. However, for industrial application this property should be increase. The behaviour of COF does not presented improvement. The mass loss and wear rate were high significantly due to the formation of cracks on surface coatings. Scratch analysis, it found three wear mechanics determined by the presence of irregular borders with sharp shadow, semicircle detachment in coatings and coatings detachment in the central track as the load increased.

Green sulfur bacteria is a photosynthetic organism whose light-harvesting complex accommodates a pigment-protein complex called Fenna-Matthews-Olson (FMO). The FMO complex sustains quantum coherence and quantum correlations between the electronic states of spatially separated pigment molecules as energy moves with nearly a 100% quantum efficiency to the reaction center. We present a method based on the quantum uncertainty associated to local measurements to quantify discord-like quantum correlations between two subsystems where one is a qubit and the other is a qudit. We implement the method by calculating local quantum uncertainty (LQU), concurrence, and coherence between subsystems of pure and mixed states represented by the eigenstates and by the thermal equilibrium state determined by the FMO Hamiltonian. Three partitions of the seven chromophores network define the subsystems: one chromophore with six chromophores, pairs of chromophores, and one chromophore with two chromophores. Implementation of the LQU approach allows us to characterize quantum correlations that had not been studied before, identify the most quantum correlated subsets of chromophores, and determine that, in the strongest associations of chromophores, the LQU is a monotonically increasing function of the coherence.

Aqueous alkanolamines solutions are widely used in petroleum refineries to remove acid gases from hydrotreated streams. The knowledge of physical properties in this kind of solutions is useful for the correct design, operation, and control of sweetening processes. Due to the above, we carried out a study on the density of the ternary mixture: 2-Amino-2-Methyl-1-Propanol (AMP) + Diethanolamine (DEA) + Water (H₂O). Density was measured by means of the vibrating tube method with an uncertainty of 2×10^-4 g·cm^-3.  The experimental data was obtained in the entire concentration range, temperatures from 303.15 to 333.15 K, and pressure of 101.3 kPa. In addition, the following three prediction methods were tested to estimate the density of the blend: mixing rule, polynomial correlation, and excess molar volume. The best prediction was obtained by means of the excess molar volume through the Redlich-Kister and Cibulka equations, where an average absolute deviation (AAD) of 0.02%, correlation coefficient (R) of 0.9999, and standard deviation (<s>) of 3×10^-4 g·cm^-3 were obtained.

At the end of December of 2019, a new type of coronavirus, now called COVID-19 started spreading in Wuhan, China and later throughout the world. Due to the global emergency state the World Health Organization declared and the need to know more about the danger Mexico is in, we worked on analyzing the risk of the COVID-19 importation to Mexico through the Air Transportation Network with a multilayer network approach. Based on the data obtained from the public data bases of OpenFlights, we created a multiplex network in which nodes represented airports, flights represented links, and airlines represented layers. We then simulated the propagation of the coronavirus using an unbiased random walk model with probability p=1 of infection once the random walker steps in a certain airport. We found the COVID-19 spread behavior the first month is anomalous (subdiffusion) and later behaves as a normal diffusion. We also found the risk of importing the virus to Mexico increases linearly over time and after approximately one year, there is almost a 90% probability of being infected. However, it is important to mention this high risk is due to contagions by people from other countries (not China) which have already confirmed cases of coronavirus. We concluded the risk of importing the COVID-19 to Mexico is almost ineludible over time unless effective medical interventions are imposed.