Spin-Orbit and Zeeman Effects on the Electronic Properties of Single Quantum Rings: Applied Magnetic Field and Topological Defects.

Within the framework of effective mass theory, we investigate the effects of spin-orbit interaction (SOI) and Zeeman splitting on the electronic properties of an electron confined in GaAs single quantum rings. Energies and envelope wavefunctions in the system are determined by solving the Schrödinger equation via the finite element method. First, we consider an inversely quadratic model potential to describe electron confining profiles in a single quantum ring. The study also analyzes the influence of applied electric and magnetic fields. Solutions for eigenstates are then used to evaluate the linear inter-state light absorption coefficient through the corresponding resonant transition energies and electric dipole matrix moment elements, assuming circular polarization for the incident radiation. Results show that both SOI effects and Zeeman splitting reduce the absorption intensity for the considered transitions compared to the case when these interactions are absent. In addition, the magnitude and position of the resonant peaks have non-monotonic behavior with external magnetic fields. Secondly, we investigate the electronic and optical properties of the electron confined in the quantum ring with a topological defect in the structure; the results show that the crossings in the energy curves as a function of the magnetic field are eliminated, and, therefore, an improvement in transition energies occurs. In addition, the dipole matrix moments present a non-oscillatory behavior compared to the case when a topological defect is not considered.

Optical Properties in a ZnS/CdS/ZnS Core/Shell/Shell Spherical Quantum Dot: Electric and Magnetic Field and Donor Impurity Effects.

A theoretical analysis of optical properties in a ZnS/CdS/ZnS core/shell/shell spherical quantum dot was carried out within the effective mass approximation. The corresponding Schrödinger equation was solved using the finite element method via the 2D axis-symmetric module of COMSOL-Multiphysics software. Calculations included variations of internal dot radius, the application of electric and magnetic fields (both oriented along z-direction), as well as the presence of on-center donor impurity. Reported optical properties are the absorption and relative refractive index change coefficients. These quantities are related to transitions between the ground and first excited states, with linearly polarized incident radiation along the z-axis. It is found that transition energy decreases with the growth of internal radius, thus causing the red-shift of resonant peaks. The same happens when the external magnetic field increases. When the strength of applied electric field is increased, the opposite effect is observed, since there is a blue-shift of resonances. However, dipole matrix moments decrease drastically with the increase of the electric field, leading to a reduction in amplitude of optical responses. At the moment impurity effects are activated, a decrease in the value of the energies is noted, significantly affecting the ground state, which is more evident for small internal radius. This is reflected in an increase in transition energies.

Tb3+-Tb3+ cross-relaxation study under novel experimental technique: Simultaneous laser excitation at UV-Vis.

Tb3+ doped GeO2-Na2O glasses have been fabricated by conventional melt quenching technique using 0.3, 1, 3, and 5 %mol of terbium ions. The optical properties were studied by means of steady-state photoluminescence (excitation and emission spectra), and emission decay time. Under excitation of 355 nm and as the concentration of dopant increases, the glasses show an enhancement of the emission intensity from 5D4 level accompanied by a decrease on the emission intensity from 5D3 level. This phenomenon can be attributed to an energy transfer process that occurs through cross-relaxation mechanisms between Tb3+ ions. The aim of this study is to report an experimental technique to study the cross-relaxation of 5D3 level decay curves of Tb3+ ions under simultaneous temporal and spatial pulsed excitation using UV and visible light (355 nm + 488 nm), allowing to limit the occurrence of cross-relaxation mechanisms and increase luminescent efficiency. Upon simultaneous UV + Vis excitation, the emission from 5D3 level in enhanced, as the energy of the 488 nm pulse is increased. Additionally, the energy transfer efficiency between Tb3+ ions was analyzed with the Inokuti-Hirayama (IH) model, as function of the excitation pulse energy at 488 nm, keeping fixed the energy of the 355 nm pulse, determining a dipole-dipole interaction as the dominant interaction mechanism.

Deep photothermal effect induced by stereotactic laser beams in highly scattering media.

Plasmonic photothermal therapy (PPTT), as an increasingly studied treatment alternative, has been widely regarded mostly as a surface tissue treatment choice. Although some techniques have been implemented for interstitial tumors, these involve some grade of invasiveness, as the outer skin is usually broken to introduce light-delivering optical fibers or even catheters. In this work, we present a potential non-invasive strategy using the stereotactic approach, long employed in radiosurgery, by converging multiple near infrared laser beams for PPTT in tissue-equivalent optical phantoms that enclose small gel spheres and simulate interstitial tissue impregnated with plasmonic nanoparticles. The real-time in-depth monitoring of temperature increase is realized by an infrared camera face-on mounted over the phantom. Our results show that a significant reduction in the surface heating can be achieved with this configuration while remarkably increasing the interstitial reach of PPTT, assuring a ∼6∘C temperature increase for the simulated tumors at 10 mm depth and ∼4∘C at 15 mm depth and opening up new possibilities for future clinical applications.

Phosphorene and phosphorene oxides as a toxic gas sensor materials: a theoretical study.

A systematic study of the adsorption of several harmful gases (CO2, NO, SO2, NH3y H2S) onto black phosphorene and three different black phosphorene oxides (BPO) is carried out through density functional theory calculations. In general, it is shown that BPOs are more suitable adsorbents than pure black phosphorene. Smaller values of adsorption energy correspond to CO2molecules, whilst those exhibiting larger ones are NH3, H2S, NO y SO2. It is found that SO2shows the greater difference in electronic charge transfer as well as the longer time of recovery among all species, being an electron acceptor molecule. Besides, it is revealed that physisorption induces changes of different order in the electronic, magnetic and optical responses of phosphorene systems involved. Greater changes in the electronic structure are produced in the case of NO adsorption. In that case, semiconductor nature and magnetization features of black phosphorene band structure become significantly modified. Moreover, a notorious effect of an externally applied electric field on the molecule adsorption onto BPOs has been detected. In accordance, adsorption energy changes with the applied electric field direction, in such a way that the higher value is favored through an upwards-directed orientation of NO y SO2adsorbates. Results presented could help to enhancing the understanding of BPOs as possible candidates for applications in gas sensing.

Electronic structure of vertically coupled quantum dot-ring heterostructures under applied electromagnetic probes. A finite-element approach.

We theoretically investigate the electron and hole states in a semiconductor quantum dot-quantum ring coupled structure, inspired by the recent experimental report by Elborg and collaborators (2017). The finite element method constitutes the numerical technique used to solve the three-dimensional effective mass equation within the parabolic band approximation, including the effects of externally applied electric and magnetic fields. Initially, the features of conduction electron states in the proposed system appear discussed in detail, under different geometrical configurations and values of the intensity of the aforementioned electromagnetic probes. In the second part, the properties of an electron-hole pair confined within the very kind of structure reported in the reference above are investigated via a model that tries to reproduce as close as possible the developed profile. In accordance, we report on the energies of confined electron and hole, affected by the influence of an external electric field, revealing the possibility of field-induced separate spatial localization, which may result in an indirect exciton configuration. In relation with this fact, we present a preliminary analysis of such phenomenon via the calculation of the Coulomb integral.

Merging Mie solutions and the radiative transport equation to measure optical properties of scattering particles in optical phantoms.

We present a new method to calculate the complex refractive index of spherical scatterers in a novel optical phantom developed by using homemade monodisperse silica nanospheres embedded into a polyester resin matrix and an ethanol-water mixture for applications in diffuse imaging. The spherical geometry of these nanoparticles makes them suitable for direct comparison between the values of the absorption and reduced scattering coefficients (µa and µs', respectively) obtained by the diffusion approximation solution to the transport equation from scattering measurements and those obtained by the Mie solution to Maxwell's equations. The values of the optical properties can be obtained by measuring, using an ultrafast detector, the time-resolved intensity distribution profiles of diffuse light transmitted through a thick slab of the silica nanosphere phantom, and by fitting them to the time-dependent diffusion approximation solution to the transport equation. These values can also be obtained by Mie solutions for spherical particles when their physical properties and size are known. By using scanning electron microscopy, we measured the size of these nanospheres, and the numerical results of µa and µs' can then be inferred by calculating the absorption and scattering efficiencies. Then we propose a numerical interval for the imaginary part of the complex refractive index of SiO2 nanospheres, ns, which is estimated by fixing the fitted values of µa and µs', using the known value of the real part of ns, and finding the corresponding value of Im(ns) that matches the optical parameters obtained by both methods finding values close to those reported for silica glass. This opens the possibility of producing optical phantoms with scattering and absorption properties that can be predicted and designed from precise knowledge of the physical characteristics of their constituents from a microscopic point of view.

Pyramidal core-shell quantum dot under applied electric and magnetic fields.

We have theoretically investigated the electronic states in a core/shell pyramidal quantum dot with GaAs core embedded in AlGaAs matrix. This system has a quite similar recent experimental realization through a cone/shell structure [Phys. Status Solidi-RRL 13, 1800245 (2018)]. The research has been performed within the effective mass approximation taking into account position-dependent effective masses and the presence of external electric and magnetic fields. For the numerical solution of the resulting three-dimensional partial differential equation we have used a finite element method. A detailed study of the conduction band states wave functions and their associated energy levels is presented, with the analysis of the effect of the geometry and the external probes. The calculation of the non-permanent electric polarization via the off-diagonal intraband dipole moment matrix elements allows to consider the related optical response by evaluating the coefficients of light absorption and relative refractive index changes, under different applied magnetic field configurations.

Donor impurity energy and optical absorption in spherical sector quantum dots.

The properties of the conduction band energy states of an electron interacting with a donor impurity center in spherical sector-shaped GaAs-Al0.3Ga0.7As quantum dots are theoretically investigated. The study is performed within the framework of the effective mass approximation through the numerical solution of the 3D Schrödinger equation for the envelope function via the finite element method. The modifications undergone by the spectrum due to the changes in the conical structure geometry (radius and apical angle) as well as in the position of the donor atom are discussed. With the information regarding electron states the linear optical absorption coefficient associated with transition between confined energy levels is evaluated and its features are discussed. The comparison of results obtained within the considered model with available experimental data in GaAs truncated-whisker-like quantum dots shows very good agreement. Besides, our simulation leads to identify the lowest energy photoluminescence peak as donor-related, instead of being associated to acceptor atoms, as claimed after experimental measurement (Hiruma et al. (1995) [14]). Also, a checking of our numerical approach is performed by comparing with analytical solutions to the problem of a spherical cone-shaped GaN with infinite confinement and donor impurity located at the cone apex. Coincidence is found to be remarkable.

Electronic states in GaAs-(Al,Ga)As eccentric quantum rings under nonresonant intense laser and magnetic fields.

The features of the electron energy spectrum in eccentric two-dimensional GaAs-AlGaAs quantum rings of circular shape are theoretically investigated taking into account the effect of externally applied magnetic and intense laser fields. Analytical expressions for the laser-dressed confining potential in this kind of quantum ring geometry are reported for the first time. Finite element method is used to solve the resulting single-particle effective mass two-dimensional partial differential equation. It is shown that the allowed level spectrum is greatly influence by the external probe as well as by the breaking of geometric symmetry related to the changes in eccentricity. In presence of an intense laser field, the conduction band confining profile suffers strong modifications along the structure, with an additional contribution to symmetry breaking. These modifications of electronic quantum states reflect in the intraband optical absorption. Accordingly, the features of the intraband transitions are discussed in detail, revealing the significant influence of the magnetic field strength and laser field intensity and polarization, together with eccentricity, in the allowing of ground-to-excited states transitions and their corresponding intensities.

Salud Cardiovascular En Población Migrante Ecuatoriana En Madrid (España). ¿Debemos Preocuparnos? / Cardiovascular Health In An Ecuadorian Migrant Population To Madrid (Spain). Should We Worry?

RESUMEN Antecedentes: La comunidad ecuatoriana es la tercera comunidad extranjera más numerosa en España. Sin embargo, es poco lo que se conoce acerca de su estado de salud cardiovascular (CV) y si los efectos de la migración han causado un detrimento en dicho estado. Métodos: Con el objetivo de conocer la salud CV en una población ecuatoriana de migrantes en Madrid, se realizó un estudio transversal no aleatorizado en el que se incluyeron personas de nacionalidad ecuatoriana, mayores de 25 años, residentes en Madrid desde hace un año o más. Se realizaron encuestas, mediante el uso de cuestionarios previamente validados, para determinar el estado de salud CV de la población, así como el grado de distress psicológico. Resultados: Se incluyeron 165 participantes (68,5% mujeres), con edad promedio de 49 años. El 86,1% de la población estudiada presentó salud cardiovascular pobre y 13,9% intermedia, sin diferencias significativas según el sexo. No hubo individuos que cumplan las 7 variables con valores ideales. Las mujeres presentaron puntuaciones más altas en el cuestionario DASS-21 en comparación a los hombres (p<0,05). Conclusión: En la población migrante ecuatoriana residente en Madrid, más del 85% presentó una salud CV pobre, y ninguno presentó una salud CV ideal. Los factores de riesgo más prevalentes en dicha población fueron pobre actividad física, sobrepeso/obesidad y malos hábitos dietéticos. Se requieren más estudios para identificar la situación real de riesgo CV de la población migrante ecuatoriana. Probablemente, a medio-largo plazo, será necesario implementar políticas de salud especialmente dirigidas a los migrantes.

ABSTRACT Background: The Ecuadorian community is the third largest foreign community in Spain. However, little is known about their cardiovascular (CV) health status and whether the effects of migration have caused a detriment in that state. Methods: With the aim of knowing the CV health in an Ecuadorian population of migrants in Madrid, a non-randomized, cross-sectional study was carried out, which included people of Ecuadorian nationality, older than 25 years, living in Madrid for a year or more. Surveys were conducted through the use of previously validated questionnaires, to determine the health status of the population, as well as the degree of neuro-physiological distress. Results: We included 165 participants (68.5% women), with an average age of 49 years. Of these, 86.1% presented poor cardiovascular health and 13.9% intermediate, without significant differences according to sex. There were no individuals that met the 7 variables consistent with and ideal CV status. Women had higher scores on the DASS-21 questionnaire compared to men (p <0.05). Conclusion: In the Ecuadorian migrant population living in Madrid, more than 85% had poor CV health, and none had an ideal CV health. Most prevalent risk factors in this population were poor physical activity, overweight/obesity and poor dietary habits. More studies are required to identify the real situation of CV risk in the Ecuadorian migrant population. Probably, in the medium-long term, it will be necessary to implement health policies especially addressed to migrants.

Low intensity sonosynthesis of iron carbide@iron oxide core-shell nanoparticles.

Here we demonstrate a simple method for the organic sonosynthesis of stable Iron Carbide@Iron Oxide core-shell nanoparticles (ICIONPs) stabilized by oleic acid surface modification. This robust synthesis route is based on the sonochemistry reaction of organometallic precursor like Fe(CO)5 in octanol using low intensity ultrasonic bath. As obtained, nanoparticles diameter sizes were measured around 6.38 nm ±â€¯1.34 with a hydrodynamic diameter around 25 nm and an estimated polydispersity of 0.27. Core-Shell structure of nanoparticles was confirmed using HR-TEM and XPS characterization tools in which a core made up of iron carbide (Fe3C) and a shell of magnetite (γ-Fe2O3) was found. The overall nanoparticle presented ferromagnetic behavior at 4 K by SQUID. With these characteristics, the ICIONPs can be potentially used in various applications such as theranostic agent due to their properties obtained from the iron oxides and iron carbide phases.

Effects of Geometry on the Electronic Properties of Semiconductor Elliptical Quantum Rings.

The electronic states in GaAs-AlxGa1-xAs elliptically-shaped quantum rings are theoretically investigated through the numerical solution of the effective mass band equation via the finite element method. The results are obtained for different sizes and geometries, including the possibility of a number of hill-shaped deformations that play the role of either connected or isolated quantum dots (hills), depending on the configuration chosen. The quantum ring transversal section is assumed to exhibit three different geometrical symmetries - squared, triangular and parabolic. The behavior of the allowed confined states as functions of the cross-section shape, the ring dimensions, and the number of hills-like structures are discussed in detail. The effective energy bandgap (photoluminescence peak with electron-hole correlation) is reported as well, as a function of the Al molar fraction.

Comparison of spatially and temporally resolved diffuse transillumination measurement systems for extraction of optical properties of scattering media.

This paper discusses the main differences between two different methods for determining the optical properties of tissue optical phantoms by fitting the spatial and temporal intensity distribution functions to the diffusion approximation theory. The consistency in the values of the optical properties is verified by changing the width of the recipient containing the turbid medium; as the optical properties are an intrinsic value of the scattering medium, independently of the recipient width, the stability in these values for different widths implies a better measurement system for the acquisition of the optical properties. It is shown that the temporal fitting method presents higher stability than the spatial fitting method; this is probably due to the addition of the time of flight parameter into the diffusion theory.

Enhanced conversion efficiency in Si solar cells employing photoluminescent down-shifting CdSe/CdS core/shell quantum dots.

Silicon solar cells have captured a large portion of the total market of photovoltaic devices mostly due to their relatively high efficiency. However, Silicon exhibits limitations in ultraviolet absorption because high-energy photons are absorbed at the surface of the solar cell, in the heavily doped region, and the photo-generated electron-hole pairs need to diffuse into the junction region, resulting in significant carrier recombination. One of the alternatives to improve the absorption range involves the use of down-shifting nano-structures able to interact with the aforementioned high energy photons. Here, as a proof of concept, we use downshifting CdSe/CdS quantum dots to improve the performance of a silicon solar cell. The incorporation of these nanostructures triggered improvements in the short circuit current density (Jsc, from 32.5 to 37.0 mA/cm2). This improvement led to a ∼13% increase in the power conversion efficiency (PCE), from 12.0 to 13.5%. Our results demonstrate that the application of down-shifting materials is a viable strategy to improve the efficiency of Silicon solar cells with mass-compatible techniques that could serve to promote their widespread utilization.

Characterization of the synergistic interaction between Beauveria bassiana strain GHA and Bacillus thuringiensis morrisoni strain tenebrionis applied against Colorado potato beetle larvae.

Studies were undertaken to further characterize the previously identified synergistic activity of Bacillus thuringiensis- and Beauveria bassiana-based biopesticides against Colorado potato beetle (CPB). A flowable concentrate of B. thuringiensis morrisoni strain tenebrionis (Bt) (Novodor® FC) and a wettable powder of B. bassiana strain GHA (Bb) (Mycotrol® 22WP) were applied against CPB larval populations infesting potato in field plots. Novodor FC and an oil-dispersion formulation of Bb (Mycotrol ES) were applied against second-instar CPB larvae on potted potato plants in greenhouse tests under low relative humidity (RH), variable-temperature conditions. Each pathogen was applied alone and in combination (tank-mixed) with the other pathogen. In the field tests, each biopesticide was also combined with the spray-carrier (formulation without active ingredient) of the other pathogen. Results from the greenhouse tests showed that under warm, dry conditions, low activity of Mycotrol was counterbalanced by high activity of the Novodor, and under cool, somewhat more humid conditions, low Novodor activity was balanced by high activity of Mycotrol, with the result being a constant level of synergism (CPB mortality ca. 20 percentage points higher than predicted by independent action). Similar levels of synergism were observed under the markedly different conditions of the field and greenhouse environments, and the synergism was confirmed as arising from interaction of the two micobes, as the Bt spray carrier had no significant effect on efficacy of the Mycotrol product and the Bb spray carrier had no effect on the efficacy of Novodor. The great capacity of these two control agents to act in concert to control CPB is well documented (the fast-acting, toxic Bt acting to protect potato crops from defoliation and the slow-acting Bb reducing survival to the adult stage). These finding further underscore the strong complementary action of these agents applied jointly against CPB.

Electron Raman Scattering and Raman Gain in Pyramidal Semiconductor Quantum Dots.

The Raman scattering related with conduction band states in semiconductor pyramidal quantum dots is theoretically investigated. The electron Raman differential cross section and Raman gain coefficient are calculated making use of analytically determined quantum states. The energy spectrum is obtained within the effective mass approximation. The features of the Raman differential cross section are discussed in terms of their dependence on the changes of the quantum dot geometry. The variation of the Raman gain coefficient as a function of the quantum dot size and shape is also analyzed.

Effects of Hydrostatic Pressure and Electric Field on the Electron-Related Optical Properties in GaAs Multiple Quantum Well.

The properties of the electronic structure of a finite-barrier semiconductor multiple quantum well are investigated taking into account the effects of the application of a static electric field and hydrostatic pressure. With the information of the allowed quasi-stationary energy states, the coefficients of linear and nonlinear optical absorption and of the relative refractive index change associated to transitions between allowed subbands are calculated with the use of a two-level scheme for the density matrix equation of motion and the rotating wave approximation. It is noticed that the hydrostatic pressure enhances the amplitude of the nonlinear contribution to the optical response of the multiple quantum well, whilst the linear one becomes reduced. Besides, the calculated coefficients are blueshifted due to the increasing of the applied electric field, and shows systematically dependence upon the hydrostatic pressure. The comparison of these results with those related with the consideration of a stationary spectrum of states in the heterostructure-obtained by placing infinite confining barriers at a conveniently far distance-shows essential differences in the pressure-induced effects in the sense of resonant frequency shifting as well as in the variation of the amplitudes of the optical responses.

Donor Impurity States in Semiconductor Zincblende Nitride Quantum Systems as a Source of Nonlinear Optical Response.

The optical absorption and the optical rectification coefficients associated to hydrogenic impurity interstate transitions in zincblende GaN-based nanostructures of the quantum wire type are investigated. The system is assumed to have cylindrical shape and the influence of external tuning probes such as hydrostatic pressure and static electric fields is particularly taken into account. The electron states are obtained within the effective mass approximation, via the exact diagonalization of the donor-impurity Hamiltonian with parabolic confinement. The nonlinear optical coefficients are calculated using a nonperturbative solution of the density-matrix Bloch equation. Our results show that the resonance-related features of the optical response become shifted in the frequency range of the incident radiation due to the effect of the hydrostatic pressure, the strength of the applied field and the change in the impurity center position.