Vol. 70 No. 2 Mar-Apr (2024): Revista Mexicana de Física

Dynamics of a two-level system in the superposition of two dephasing environments with Ohmic-like spectral density is studied when considering initial system-environment correlations. The quantum system and one environment are treated as whole thermal equilibrium state, while the other environment is at thermal equilibrium state alone. Which environment the system interacts with is determined by an ancillary two-level system. When the system interacts with mixture of two sub-Ohmic environments, initial correlations can make the mixed dynamics non-Markovian. For two identical sub-Ohmic environments, if performing the projective measurement on the ancillary two-level system at the special time points, whatever the initial state of the system is, the coherence can be enhanced. For two different environments with βħω₀/2>>, we get the approximate expression about the coherence of the system when measuring the ancillary two-level system.

We performed first-principle calculations to investigate the structural, electronic, and magnetic properties of ZnS and ZnSe binary compounds, Zn_0.5Cr_0.5S and Zn_0.5Cr_0.5Se DMS alloys and (ZnS)₂/Zn_0.5Cr_0.5Se and (ZnSe)₂/Zn_0.5Cr_0.5S superlattices in the wurtzite structure using the full potential linear muffin–tin orbital  (FP-LMTO) method. Features such as lattice constant, modulus of compressibility and its first derivative, spin-polarized band structures, total and local or partial electronic densities of states and magnetic properties were calculated. The electronic structure shows that Zn_0.5Cr_0.5S and Zn_0.5Cr_0.5Se DMS alloys and (ZnS)₂/Zn_0.5Cr_0.5Se and (ZnSe)₂/Zn_0.5Cr_0.5S superlattices are half-metallic ferromagnetic with 100% complete spin polarization. The total magnetic moments calculated show the same integer value of 4 µB, which confirms the ferromagnetic half-metallic behavior of these compounds. We found that the ferromagnetic state is stabilized by the p-d exchange associated with the double-exchange mechanism. Zn_0.5Cr_0.5S and Zn_0.5Cr_0.5Se DMS alloys and (ZnS)₂/Zn_0.5Cr_0.5Se and (ZnSe)₂/Zn_0.5Cr_0.5S  superlattices are shown to be promising new candidates for applications in the fields of spintronics.

In this work, we theoretically investigate the propagation length of plasmon waves in graphene layer under uniform strain surrounded by two dielectric media of dielectric constants ε1 and ε2, respectively. The plasmon losses (plasmon damping), plasmon propagation length and the penetration depth of the electric field associates with the charge fluctuations can be controlled by varying the direction and the strength of the applied strain and the direction of the plasmon wave propagation with respect to the direction of the applied strain. Because strain induces anisotropy in graphene optical conductivity, the strain-dependent orientation plays an important role to manipulate the direction and variations of the graphene plasmon energy, which may be useful to tune graphene properties in plasmonic devices to enhance light-matter interaction.

In this work the design and manufacture of a prototype of an ozone measuring device is presented. One of the goals of this design is to develop an easy and fast way to manufacture these kind of devices, that might also be used for other gases. The method used to measure the ozone is the Beer´s Lamberth Law. Readily available materials are used. An UV LED was used as a source, and a photodiode as a detector. For the air-light interaction an absorption cell was necessary, it was made of Polylactic Acid and manufactured in a 3D printer. In the microcontroller the operational amplifiers and the signal processors were implemented in a PSoC 5. Good performance of all components, both electronic and 3D printed, was observed. Measurements were achieved in a range of 0 to 100 ppm with an accuracy of ± 5 ppm.

En este trabajo se presenta el diseño y la fabricación de un prototipo para medición de ozono, en el cual se utilizan materiales de fácil adquisición. El propósito de este diseño es proporcionar una alternativa robusta y menos costosa de fabricar un dispositivo de medición de ozono que puede ser extendida a otros gases. El método de medición se basa en la Ley De Beer-Lamberth. Se utiliza un LED (light-emitting diode) UV como fuente y un fotodiodo como detector de luz. La muestra de aire interactúa con la luz en el interior de una celda de absorción, fabricada en una impresora 3D usando como material PLA (Polylactic Acid). La amplificación y el procesamiento de la señal, se realizaron mediante una tarjeta electrónica PSoC (Programable System on Chip). Se observó un buen comportamiento de todos los componentes, tanto electrónicos como impresos 3D. Se lograron realizar mediciones en un rango de 0 a 100 ppm con una exactitud de ± 5 ppm.

We study the KH₂PO₄ (KDP) /Ca₁₀(PO₄)₆(OH)₂ (HA) biocomposite to evaluate its electrical conductivity. It was prepared by manual grinding on a 1:3 molar ratio. Studies by X-ray powder diffraction and Raman spectroscopy show a variation in the volume of the unit cell between KDP and HA and the disappearance of bands associated with KDP. Impedance spectroscopy was studied over a range of temperatures (25-80 ºC) and frequencies from 10 Hz to 1 MHz. It was found that the bulk resistance of the composite is higher in pure KDP. Using the Jonscher empirical expression suggest that the ionic hopping conduction mechanism is responsible for the conductivity behavior with hopping frequency of 1.21 x10⁴ Rad at 80ºC. 

For over five decades, ultra-high molecular weight polyethylene (UHMWPE) has been the standard material for total knee replacements (TKR). Zero wear of the UHMWPE would be ideal; however, due to the natural knee movements, wear damage to the UHMWPE articulating surface is inevitable. The generated wear debris results in joint mechanical instability, reduced joint mobility, increased pain, and implant loosening. Because of these issues, the research on the materials in TKRs has increased their survival rate for up to 20 years; however, in younger patients, the durability of the UHMWPE component decreases due to increased physical activity. Hence there is a constant need for highly wear-resistant tribological pairs for TKRs. Carbon-based materials have an excellent balance between lubricating and mechanical properties and have shown great promise in tribological applications. This study used self-lubricating cubic titanium carbide (c-TiC) and multiwalled carbon nanotubes (MWCNTs) to improve the UHMWPE wear resistance further. The combination of carbon-based materials decreased the material loss by about 41.7 % compared to the UHMWPE vs. bare steel ball tribological pair. The improvement, attributed to the c-TiC self-lubricating coating surface, is close to 5 %. Cold flow and burnishing were the predominant wear mechanisms observed in all the systems; more subtle wear processes were detected for the sliding couple with c-TiC self-lubricating coating. Meanwhile, polymer delamination and micrometer-sized debris formation were the main wear mechanisms in the UHMWPE-MWCNT vs. bare steel ball system. The adhesion work obtained from the electronic structure calculations shows a more significant interfacial interaction of the CNTs on the c-TiC surface. This interaction can be associated with the layer formation that protects the surface from wear and friction.

Si-g-LDPE (Silane-grafted LDPE) is the based material of silane-crosslinked polyethylene (Si-XLPE) nominated to be used in renewable energy (photovoltaic) structures for the reason of its good behavior under weathering circumstances. The present study has an attempt to follow up the cross-linking process of Si-g-LDPE under cyclic accelerated weathering aging and to track its photo and thermo-oxidative degradation at both microscopic and macroscopic scales. The realized experiments consist to carry out cyclic accelerated weathering aging of 1152 hours, using QUV chamber, on films of Si-g-LDPE. The process of cross-linking is checked by using Hot-Set-Test measurements and Fourier Transform Infrared (FTIR) spectroscopy. Evolution of mechanical properties and carbonyl index are used as relevant precursors of photo and thermo-oxidation degradation. Additional information on the microstructural changes (crystallinity) and on the optical properties is gained by using X-ray difractometry and UV-visible measurements. Our findings lead to a result that Si-g-LDPE has a big ability to crosslink under cyclic weathering aging. The elastic behavior of the material was enhanced gradually with increasing aging time. The elastic behavior enhancement is a consequence of crosslink network density increase. FTIR results support perfectly the Hot-Set-Test results by the increase of single or multi-siloxane linkages absorption bands. These linkages modify the digital fingerprint of the material. Our results ascertained also that we can relate the elongation at break and tensile strength changes to the changes in the carbonyl index. Both characteristics are related to the photo and thermo-oxidation degradation. Photo-oxidation degradation leads to the decrease of mechanical properties and to the increase of carbonyl index. An abrupt and sharp increase at the beginning of aging in the crystallinity of the material followed by a level-off state was observed. Finally, the optical properties (band gaps, Urbach energy and dielectric constant) are greatly affected by the weathering aging process.

The Au/GaN/GaAs Schottky diode is a fundamental electronic component with versatile applications. In this study we delve into the parameter estimation of Au/GaN/GaAs Schottky diodes using the Grey Wolf Optimizer (GWO) algorithm. Our research encompasses experimental procedures, mathematical modeling, and optimization techniques to extract critical electrical parameters, including the ideality factor (n), Schottky barrier height (φbn), and series resistance (RS). The primary aim is to enhance our comprehension of the behavior of Au/GaN/GaAs Schottky diodes and showcase the effectiveness of GWO in achieving precise parameter estimates. These diodes, featuring metal-semiconductor junctions, play pivotal roles in electronics, necessitating accurate parameter determination for optimized functionality. The effectiveness of the GWO algorithm was examined through a comparative analysis, employing analytical techniques pioneered by Cheung and Cheung. This study sought to assess the algorithm’s performance and accuracy in parameter estimation for Au/GaN/GaAs Schottky diodes, providing valuable insights into its practical applicability in electronic device characterization and optimization. Keywords: Schottky diodes, Grey Wolf Optimization, Electrical measurement. Parameter estimation, Gan, GaAs

Graphite acts as an electrical conductor due to the delocalization of electrons between the surfaces. Graphene oxide (GO) is produced by using graphite via the Hummers method. Reduced GO (rGO) is a form of GO where the oxygen content has been reduced due to chemical, thermal, and other processes. In this study, we have produced a prototype of capacitors containing the synthesized rGO with variation of the rGO mass, i.e.: 0 g., 0,2 g; and 0,8 g. Than we compare the capacitance values obtained from the capacitors using a multitester. Characterizations of the rGO are conducted using XRD, UV-Vis, and FTIR. The results of the UV-Vis test show peak at a wavelength of 300 nm indicating absorption of rGO. The XRD test shows a transition from GO to rGO in an amorphous phase. Finally, the FTIR tests produce transmittance bands from the functional groups of CO₂, CO, and OH. This paper shows that the capacitance values of the capacitor using rGO material is greater than using graphite material. It means that rGO is capable of storing more charges than graphite. The highest capacitance value is obtained for the capacitor with 0.2 g rGO, i.e.: 165,02 µF.

In this work we study the pressure of the quark-gluon plasma (QGP) in the presence of a weak magnetic field, using a minimally enhanced model of a weakly interacting gas of quasi-particles in a thermal bath. We include the magnetic field effects through the quark mass that has been modified using a recently proposed thermo-magnetic coupling. This thermo-magnetic coupling emerges form the quark-gluon vertex in the HTL approximation [1]. We use Lattice QCD [2] data, to constrain the thermo-magnetic bag function of the quasi-particle model and provide an estimate of the thermo-magnetic vacuum energy density. We then compute the transverse pressure of the system and compare with similar results from the literature. We find that the inverse magnetic catalysis already built within this thermo-magnetic coupling allows a robust description of this Lattice QCD data for the pressure of the QGP in the presence of a weak magnetic field. The extension to the thermal quasi-particle model we have introduced here, makes it easier to pursue further phenomenological studies that require simulations with an EoS that has integrable quasi-particle thermodynamic variables which have the general features of lattice data in the weak magnetic field regime.

We propose a surface plasmon resonance (SPR) sensor based on multilayer films with silver (Ag) and gold (Au) interfaces coated with a thin layer of zirconium oxide (ZrO2) in Kretschmann configuration. A dielectric layer of ZrO2 acts as the prism coating and the second layer is deposited after the metal film in the dielectric/metal/dielectric (DMD) system. In order to achieve the best design for the sensor, the dependence of the sensitivity on the angle of incidence and the thickness of the alternating layer is comprehensively explored. The polarization change results are shown with the angles Ψ and ∆ which are the traditional ellipsometry measurement angles of the optical properties of the DMD system. The advantage of Ag/ZrO2 multilayers over Au and Au/ZrO2 for SPR refractive index detection in terms of sensitivity, as well as the Ag/ZrO2 interface offers the possibility of studies with promising features for SPR users to generalize this type of interface. The proposed DMD sensor is expected to find application in biochemical sensing due to its resolution.

In the present paper, we propose to make an optical diagnosis by laser interferometry to determine experimentally the density of neutral particles in a coronal discharge bathing in a gaseous medium N2. We are particularly interested in the measurement of variation of the optical path and therefore of the index of refraction which allows us to highlight the variation of the density of the neutrals in the discharge, and using a computer treatment (Pearce method) the refractive index of the medium is calculated to determine the spatial distribution of density and temperature (radial and axial) at the core of the corona discharge in two different situations (positive and negative). This optical diagnosis also allowed us to quantitatively determine the phenomenon of depopulation of neutral particles. These quantitative and experimental results are interesting because they allow a good correlation between the theoretical results obtained so far

For the first time, the adopted stochastic form of the perturbed Biswas-Milovic equation with cubic-quintic-septic law having spatio-temporal and chromatic dispersion in the presence of multiplicative white noise in Ito sense was presented and examined. The Biswas-Milovic equation ˆ models numerous physical phenomena occurring in optical fiber. We analyzed the optical soliton solutions of the stochastic model with the aid of a subversion of the new extended auxiliary equation method. Furthermore, we investigated the evaluation of the noise impacts and the effects of some model parameters on the dynamics of the generated soliton. Finally, graphical depictions of the derived soliton types were represented for some solution functions. The stochastic model and the derived results will contribute to the comprehension of the nonlinear dynamics of pulse propagation in optical fibers which has great importance for the advancement of optical communication engineering.

In this work, we describe two alternative methods for solving the ill-conditioned inverse problem that allows estimating the particle size distribution (PSD) from turbidimetry measurements. The first method uses the inverse Penrose matrix to solve the inverse problem in its discrete form. The second method consists of replacing an ill-posed problem with a collection of well-posed problems, penalizing the norm of the solution, and it is known as the Tikhonov regularization. Both methods are used to solve a synthetic application of the inverse problem by solving the direct problem using a theoretical expression of the distribution of particles sizes function f(D) and considering soft industrial latex particles (NBR), with average particle diameters of: 80.4, 82.8, 83.6, and 84.5 nm; and three illumination wavelengths in the UV-Vis region: 300, 450, and 600 nm. The estimated solution obtained by the inverse Penrose matrix is different from the original solution due to the inverse problem is ill-conditioned. In contrast, when using Tikhonov’s regularization, the estimate obtained is close to the original solution, which proves that the particle size distribution is adequate.

In a classic small tokamak, the magnetic confinement is achieved by toroidal coils that fit into a donut-shape mechanical structure. To facilitate their handling and maintenance as well as the access to various auxiliaries components, their design has evolved toward a modular configuration. For such demountable design, it is important to guarantee the electrical continuity of the winding of the coil across the modular parts through electrical contacts. The resulting joints rely on pressure and specific materials to transfer high current densities at a good mechanical stability and manageable losses. In the present work, a prototype of a circular demountable toroidal field coil (CDTFC) was designed and built to test some technical choices to be used in the final coils of a table-top tokamak referred to as TPM-1U. For this small tokamak, the magnet wires to wind the toroidal coils should be able to handle large pulsed currents in the tens of thousands of Amperes whereas the coil joints should handle a peak current density of at least 75 kA/cm2. The case study here is the TPM-U1 table-top tokamak. Its conceptual design is recalled and mechanical and magnetic details of the demountable coil prototype are provided. For the experimental test, the contacts were slightly pressed using a custom-made contact assembly and current pulses between 4 kA and 8 kA were fed
to the coil prototype. The degradation of the joint was visually estimated by assessing the amount of micro-melting, plastic deformation and oxidation appearing at the interface between the materials in contact. It is shown that the selected AWG-04 magnet wire is appropriate for carrying kiloAmpere range pulsed currents and that the CuBe contacts are able to withstand current densities larger than the specification, up to 263 kA/cm2, under low contact pressures of a few mega-Pascal simplifying their handling. Some technical choices have been probed on a prototype coil yielding a generic sequence of tasks to build and test mechanically and electromagnetically demountable coils and their joints.

This work presents a study of ceramics with the (K_0.44Na_0.52Li_0.04)_0.97La_0.01Nb_0.9Ta_0.1O₃ composition through their Raman spectra. In the previous studies [1], this particular composition has shown good permittivity and piezoelectric parameter values that justify a deeper investigation. Two sets of samples of these ceramic compounds were prepared using different methods. The first set was prepared using a classical solid-state reaction of oxides and carbonates, as described in Ref. 2. The second set was prepared using the NaNbO₃ as a precursor. The Raman spectra of the samples obtained by the direct ceramic method consisted of 4 modes. In contrast, the spectra of the samples obtained using the precursor showed a shift of the wavenumber of the A_1g(ν1) mode peak towards lower values and consisted of six modes with the appearance of two additional IR modes, F_1u(ν3) and F_2g(ν4). Notably, the use of the precursor preparation route led to important improvements resulting in a more straightforward method than that of Saito et al. [3].