https://uvadoc.uva.es/handle/10324/1310 Dpto. Física Teórica, Atómica y Óptica - Artículos de revista 2026-04-12T19:44:47Z https://uvadoc.uva.es/handle/10324/83967 Having in mind the significance of parity (reflection) in various areas of physics, the single-mode and two-mode Wigner algebras are considered adding to them a reflection operator. The associated deformed 𝑠𝑙(2, 𝑅) algebra, 𝑠𝑙𝜈(2, 𝑅) and the deformed 𝑠𝑜(3) algebra, 𝑠𝑜𝜈(3), are constructed for the widely used Jordan-Schwinger and Holstein-Primakoff realizations, commenting on various aspects and ingredients of the formalism for both single-mode and two-mode cases. Finally, due to its potential application in the study of qubit and qutrit systems, the parity-deformed 𝑠𝑜𝜈(3) representation is analyzed based on the isomorphy of 𝑠𝑜(3) and 𝑠𝑢(2). Related applications are discussed as well. 2026-01-01T00:00:00Z https://uvadoc.uva.es/handle/10324/83943 We analyze two-dimensional systems related to the Helmholtz equation that allow separation of variables in both polar and parabolic coordinates. We pay special attention to the symmetry algebras involved in the separation of variables. We show how the modification of symmetry operators can lead from purely geometric symmetries to other dynamical ones, that is, from free systems to interacting systems, with the addition of potentials, which in our case are of two types: Kepler–Coulomb and Makarov. We also calculate the spectrum and associated eigenfunctions of the corresponding quantum mechanical systems, and we present a discussion of naturally separable classical systems, including the analysis of different types of trajectories. A discussion of the global properties of polar and parabolic coordinates is included, the relevance of which is demonstrated in the spectral and classical properties of these systems. 2026-01-01T00:00:00Z https://uvadoc.uva.es/handle/10324/83907 The lead-rich liquid lithium–lead eutectic alloy, Li17Pb83, is one of the candidates to be used in breeding blanket modules of future fusion reactors where tritium breeding is essential to provide the necessary fuel for fusion. It has several properties that favour its use, such as the breeding capacity of Li, the neutron multiplication capacity of Pb, the ease of circulation for off-site tritium recovery, and the capability to, at least partly, refrigerate the system. It is therefore important to understand the properties of the tritium generated in the breeding reactions, and its effects on the hosting liquid. The same applies to helium nuclei that are generated in a 1:1 ratio to tritium in the breeding reactions. We have performed first principles molecular dynamics simulations to study the structural changes observed in liquid Li17Pb83 when tritium or helium is added. In one set of simulations we have made calculations for several amounts of tritium, with molar concentrations ranging from 0.20 to 0.03, without any He atoms. In the other set of simulations we have included helium atoms with molar concentration 0.11, and no tritium. Tritium atoms are found to bind preferentially with Li, modifying substantially the Li–Li correlation functions. We also observe the presence of long-lasting di-tritium molecules when tritium concentration is not too low, which also tend to bind to Li atoms. The velocity autocorrelation functions of tritium, Li and Pb are evaluated, and analysed in order to obtain the corresponding vibrational properties of the different species. Helium atoms tend to aggregate together forming a cluster whose characteristics are reported, together with the correlation functions of He atoms with Li and Pb. The motion of He atoms within this cluster is found to be sub-diffusive, while an estimate of He mobility outside the aggregate is also given. 2026-01-01T00:00:00Z https://uvadoc.uva.es/handle/10324/83870 The imaging platform developed at the High Energy Density-Helmholtz International Beamline for Extreme Fields (HED-HiBEF) instrument at the European X-ray Free Electron Laser (XFEL) and its applications to HED and fusion related research are presented. The platform combines the XFEL beam with the high-intensity short-pulse laser ReLaX and the high-energy nanosecond-pulse laser DiPOLE-100X. The spatial resolution is better than 500 nm and the temporal resolution of the order of 50 fs. The influence of the XFEL source in the x-ray imaging method is discussed. Free-propagation x-ray phase contrast imaging and Talbot-Lau imaging setups are shown. We show examples of blast waves and converging cylindrical shocks in aluminum, resonant absorption measurements of specific charged states in copper with ReLaX and planar shocks in polystyrene material generated by DiPOLE-100X. For the first time, we show the application of Talbot-Lau interferometry to convergent cylindrical shocks as well as resonant absorption processes. We also discuss the possibilities introduced by combining this imaging platform with a kJ-class laser. 2026-01-01T00:00:00Z https://uvadoc.uva.es/handle/10324/83304 Purpose: To assess the reproducibility of retinal nerve fiber layer (RNFL) measurements and the variability of the probabilistic classification algorithm in normal, hypertensive and glaucomatous eyes using Stratus optical coherence tomography (OCT). Methods: Forty-nine eyes (13 normal, 17 ocular hypertensive [OHT] and 19 glaucomatous) of 49 subjects were included in this study. RNFL was determined with Stratus OCT using the standard protocol RNFL thickness 3.4. Three different images of each eye were taken consecutively during the same session. To evaluate OCT reproducibility, coefficient of variation (COV) and intraclass correlation coefficient (ICC) were calculated for average thickness (AvgT), superior average thickness (Savg), and inferior average thickness (Iavg) parameters. The variability of the results of the probabilistic classification algorithm, based on the OCT normative database, was also analyzed. The percentage of eyes with changes in the category assigned was calculated for each group. Results: The 50th percentile of COV was 2.96%, 4.00%, and 4.31% for AvgT, Savg, and Iavg, respectively. Glaucoma group presented the largest COV for all three parameters (3.87%, 5.55%, 7.82%). ICC were greater than 0.75 for almost all measures (except from the inferior thickness parameter in the normal group; ICC = 0.64, 95% CI 0.334–0.857). Regarding the probabilistic classification algorithm for the three parameters (AvgT, Savg, Iavg), the percentage of eyes without color-code category changes among the three images was as follows: normal group, 100%, 84.6% and 92%; OHT group, 89.5%, 52.7%, 79%; and Glaucoma group, 82%, 70.6%, and 76.5%, respectively. A probabilistic category switch from pathologic to normal or vice versa was observed in three eyes (15.8%) of the glaucomatous group for the Savg parameter and in two eyes of the OHT group: one eye (5,9%) for the AvgT and one eye (5.9%) for the Savg parameter. Conclusions: OCT RNFL measurements showed a good reproducibility in normal, OHT, and glaucoma eyes. The probabilistic classification for the three main parameters showed certain variability, especially in glaucoma group and OHT group. Therefore, one isolated category result should be interpreted with caution before clinical classification of the patient. 2009-01-01T00:00:00Z https://uvadoc.uva.es/handle/10324/83303 Purpose: To validate the use of noncontact scanning slit pachymetry and OCT pachymetry measurements without contact lens (CL) removal, to determine corneal swelling variations during extended wear (EW). Methods: Central corneal thickness (CCT) was measured with ultrasonic (US) pachymetry, noncontact scanning slit pachymetry (Orbscan II; Bausch & Lomb, Tampa, FL), and optical coherence tomography (OCT) 1 week before the wearing of CLs and during 1 week of EW. High-Dk (lotrafilcon A) and low-Dk (etafilcon A) soft CLs were randomly fitted for EW in the right and left eyes of 20 subjects with normal ocular health. Orbscan and OCT were also performed without CL removal after 3 and 7 days of wear. Results: CCT measured with Orbscan and OCT showed a high correlation with US pachymetry. There were corneas with edema and without edema. Bland-Altman analysis showed a high level of agreement between Orbscan and OCT, with and without CL removal and with US pachymetry. High repeatability of Orbscan (r 2 = 0.000) and OCT (r 2 = 0.001) measurements without CL removal was also found. Etafilcon A lenses induced significantly higher corneal swelling than did lotrafilcon A lenses measured with Orbscan and OCT. Conclusions: Orbscan and OCT are accurate, noninvasive, and reproducible techniques for evaluation of CCT without CL removal. OCT has more accuracy and repeatability than does Orbscan. Both techniques allowed for measurement throughout the study period of the CCT differences induced by CL wear. 2007-01-01T00:00:00Z https://uvadoc.uva.es/handle/10324/82856 We performed density-functional-theoretical calculations to investigate the adsorption of two stable nanoclusters corresponding to (TiO2)N with N = 3 and 5 supported on three different type of substrates: graphene, silver and gold. For each of these surfaces we consider three textures: pristine, with a single vacancy and with a Co atom as impurity. In the case of the defects (vacancy or impurity) they act as possible anchors for the adsorption of the cluster. The proposed particles present flat configurations in their respective free standing putative ground states, so they can accommodate themselves as parallel, perpendicular or inclined with respect to the surface producing different isomers: only the four lowest energy isomers for each particle (N = 3 or 5), each surface and each texture are reported and analyzed. Density Functional Theory calculations by means of the SIESTA package are done in a thorough way covering a large number of the possible configurations. Reported parameters are: adsorption energy, assisted binding energy (binding energy in the presence of the substrate), and the main different interatomic distances presented in the adsorption. A comparison with some previous theoretical results on related systems is done. Possible extensions of this work are commented. 2021-03-01T00:00:00Z https://uvadoc.uva.es/handle/10324/82703 Because of the lack of a net magnetic moment, antiferromagnets possess a unique robustness to external magnetic fields and are thus predicted to play an important role in future magnetic technologies. However, this robustness also makes them quite difficult to control, and the development of novel methods to manipulate these systems with external stimuli is a fundamental goal of antiferromagnetic spintronics. In this work, we report evidence for a metastable reorientation of the order parameter in an antiferromagnetic semiconductor triggered by an ultrafast quench of the equilibrium order via photoexcitation above the band gap. The metastable state forms less than 10 ps after the excitation pulse, and persists for longer than 150 ps before decaying to the ground state via thermal fluctuations. Importantly, this transition cannot be induced thermodynamically, and requires the system to be driven out of equilibrium. Broadly speaking, this phenomenology is ultimately the result of large magnetoelastic coupling in combination with a relatively low symmetry of the magnetic ground state. Since neither of these properties are particularly uncommon in magnetic materials, the observations presented here imply a generic path toward novel device technology enabled by ultrafast dynamics in antiferromagnets. 2025-01-01T00:00:00Z https://uvadoc.uva.es/handle/10324/82702 Iron ilmenene is a new two-dimensional material that has recently been exfoliated from the naturally occurring iron titanate found in ilmenite ore, a material that is abundant on the earth's surface. In this work, we theoretically investigate the structural, electronic and magnetic properties of 2D transition-metal-based ilmenene-like titanates. The study of magnetic order reveals that these ilmenenes usually present intrinsic antiferromagnetic coupling between the 3d magnetic metals decorating both sides of the Ti–O layer. Furthermore, the ilmenenes based on late 3d brass metals, such as CuTiO3 and ZnTiO3, become ferromagnetic and spin compensated, respectively. Our calculations which include spin–orbit coupling reveal that the magnetic ilmenenes have large magnetocrystalline anisotropy energies when the 3d shell departs from being either filled or half-filled, with their spin orientation being out-of-plane for elements below half-filling of 3d states and in-plane above. These interesting magnetic properties of ilmenenes make them useful for future spintronic applications because they could be synthesized as already realized in the iron case. 2023-01-01T00:00:00Z https://uvadoc.uva.es/handle/10324/82689 We performed two-dimensional simulations of turbulent laser-plasma instabilities in the presence and absence of external magnetic fields using the Laser Plasma Simulation Environment (LPSE) code. The results demonstrate that, in the presence of a magnetic field, the transition from ballistic to gyrating electron motion enhances the energy transfer from electron plasma waves to the electron population. Although stronger magnetic fields produce a larger population of hot electrons, these electrons tend to remain confined near the quarter-critical density, where the instabilities also localize, thereby reducing the potential for hot electron transport deeper into the target. Additionally, we present a scaling analysis that quantifies hot electron generation as a function of plasma electron temperature, density scale length, and applied magnetic field strength. These findings may have important applications for controlling hot electron flux and mitigating preheat in inertial confinement fusion targets. 2026-01-01T00:00:00Z https://uvadoc.uva.es/handle/10324/82683 The substitution of rare earths in M-type hexaferrites has attracted attention in the past decade due to their ability to modify the crystal structure and magnetic properties. However, achieving rare earth incorporation in the M-type structure is extremely challenging because they often create secondary phases during the sintering process. This study analyzes the effect of rare earth substitution on the magnetic properties of M-type hexaferrites, examining 312 samples reported in the last decade. We focus on the effects of rare earth substitution on the magnetic properties, including magnetization to saturation, remanence magnetization, coercive field, remanence squareness ratio and maximum energy product. Moreover, different fabrication routes and sintering parameters such as heating time and temperature were considered in the analysis. The results are presented in a comprehensive table showcasing the progress that rare earth-substituted hexaferrites have made in the last decade. This review provides insights into the correlations between experimental factors and synthesis parameters with purity, structural variations and the magnetic properties resulted from the rare-earths substitution. This review aims to elucidate the connections between synthesis parameters and experimental factors, with the resulting purity, structural variations, and magnetic properties of M-type hexaferrites substituted using rare-earths. In addition, a critical perspective is presented about the challenges and potential of substituted hexaferrites in the next-generation of magnetic ceramics. 2025-01-01T00:00:00Z https://uvadoc.uva.es/handle/10324/82295 Atmospheric water vapor, a greenhouse gas, is increasing in the Arctic. It is a scientific challenge to understand the causes for this increase and determine adaptation and mitigation actions to confront its climatic effects. During the last decades, spatial and temporal coverage of water vapor satellite observations increased notably, and reanalysis water vapor estimates have steadily improved. However, the scarce spatial and temporal coverage in the Arctic of integrated water vapor (IWV) surface‐based observations limits the representativeness of satellite observations and reanalysis estimate validations. Recently, we validated sun photometer IWV (IWVsp) observations with IWV from radiosondes in the Arctic. Here, we compare the hourly means of IWVsp from 13 Arctic AERONET stations and the IWV from ERA‐5 and MERRA‐2 reanalyses. The comparison is conducted at hourly timescale for individual stations for two Arctic regions and for the whole Arctic. The comparison showed a moist bias of IWV from reanalyses with respect to IWVsp. The individual station wise pattern shows slightly better accuracy and precision for ERA5 than for MERRA‐2 also evident at the selected subregional scale. The differences of IWV from ERA5 and MERRA‐2 and IWVsp show no dependence on IWVsp nor the solar zenith angle. This study corroborates that IWVsp may be used for validations of satellite IWV observations and IWV reanalyses products. 2025-01-01T00:00:00Z https://uvadoc.uva.es/handle/10324/82294 This paper explores the influence of the presence of clouds on sky radiances. It also analyses their impact on the retrieval of aerosol properties when using an inversion algorithm whose radiative transfer model (RTM) is designed for cloud-free atmospheres. For that, synthetic observations are simulated for 9 partially cloudy skies and for their equivalent cloud-free skies, considering 16 different aerosol scenarios. A parameter named cloud enhancement factor (CEF) has been used to determine the modifications induced in the sky radiances by each partially cloudy scenario with respect to the cloud-free sky. This parameter indicates that the sky radiances remaining after applying a cloud-screening are affected by the presence of clouds. In general, they show en-hancements between 0 and 20 % with respect to the cloud-free radiances, depending on the cloudy conditions and the scattering angle. The synthetic observations used as input for the retrieval of aerosol properties are the ones required by the inversion strategy used, GRASPpac: the aerosol optical depth (AOD) and sky radiances at 4 different wavelengths together with the ceilometer range corrected signal (RCS). In partially cloudy scenarios with low CEFs, the aerosol properties do not present significant changes with respect to the cloud-free conditions. However, for partially cloudy scenarios with higher CEFs, a clear differentiation between the aerosol optical properties retrieved with and without clouds is observed. In these scenarios, the precision of the retrieval is similar for both conditions, but the accuracy is lower for the cloudy conditions. In particular, under partially cloudy conditions, it is observed an overestimation of the real refractive index (RRI) and the single scattering albedo (SSA) between 0.05 and 0.06 and between 0.03 and 0.06 respectively, and an underestimation of the asymmetry factor (g) and the imaginary refractive index (IRI) of about -0.02 and - 0.005, respectively. These values slightly vary with the aerosol load and wavelength for the RRI and SSA. The effects on the size distribution parameters are very small, concluding that the impact of clouds is noticeable in the optical properties but not so much in the microphysical part. 2025-01-01T00:00:00Z https://uvadoc.uva.es/handle/10324/82292 This study explores the potential to retrieve aerosol properties with the GRASP algorithm (Generalized Retrieval of Atmosphere and Surface Properties) using as input measurements of zenith sky radiance (ZSR), which are sky radiance values measured in the zenith direction, recorded at four wavelengths by a ZEN-R52 radiometer. To this end, the ZSR measured at 440, 500, 675 and 870 nm by a ZEN-R52 (ZSRZEN), installed in Valladolid (Spain), is em-ployed. This instrument is calibrated by intercomparing the signal of each channel with coincident ZSR values simulated (ZSRSIM) at the same wavelengths with a radiative trans-fer model (RTM). These simulations are carried out using the GRASP forward module as RTM and the aerosol infor-mation from a co-located CE318 photometer belonging to AERONET (AErosol RObotic NETwork) as input. The dark signal and the signal dependence on temperature are char-acterized and included in the calibration process. The uncertainties for each channel are quantified by an intercomparison aerosol optical depth (AOD) values in general overestimate the reference ones by 0.03, 0.02, 0.02 and 0.01 for 440, 500, 675 and 870 nm, respectively. The calibrated ZSRZEN measurements, recorded during 2.5 years at Valladolid, are inverted by the GRASP-ZEN strategy to retrieve some aerosol properties like AOD. The retrieved AOD shows a high correlation with respect to independent values obtained from a co-located AERONET CE318 photometer, with determination coefficients (r2) of 0.86, 0.85, 0.79 and 0.72 for 440, 500, 675 and 870 nm, respectively, and finding uncertainties between 0.02 and 0.03 with respect to the AERONET values. Finally, the retrieval of other aerosol properties, like aerosol volume concentration for total, fine and coarse modes (VCT, VCF and VCC, respectively), is also explored. The comparison against independent values from AERONET presents r2 values of 0.57, 0.56 and 0.66 and uncertainties of 0.009, 0.016 and 0.02 μm3 μm-2 for VCT, VCF and VCC, respectively. 2023-01-01T00:00:00Z https://uvadoc.uva.es/handle/10324/82281 Durante el verano de 2018 se realizaron en Longyearbyen (archipiélago de Svalbard) más de 70 perfiles verticales de aerosoles y variables meteorológicas mediante un sistema de globo cautivo equipado con instrumentación para medir carbono negro equivalente (eBC), nanopartículas (NP) y parámetros atmosféricos básicos. El resultado principal es la creación de un conjunto de datos homogéneo de perfiles verticales de eBC, NP, temperatura, humedad relativa y presión, útil para futuros estudios de modelización de la contaminación en el Ártico. Las concentraciones medias de eBC y NP fueron similares por debajo y por encima de 500 m. Los perfiles tomados durante inversión térmica, condiciones asociadas a advecciones cálidas desde Escandinavia que favorecen la acumulación de contaminantes locales en la capa límite atmosférica del Ártico, muestran valores más altos tanto de eBC como de NP. Estas observaciones en globo se complementaron con medidas continuas en superficie. Se corroboran los datos más elevados en presencia de inversión térmica, analizando los datos 2h antes del lanzamiento de cada globo. En paralelo, se registraron datos de las propiedades ópticas del aerosol en columna para el análisis en profundidad de dos casos estudios relacionados con alta polución durante la campaña de medidas. Durante estos episodios, que se extendieron por todo el archipiélago, se detectaron valores altos de espesor óptico de aerosoles (AOD) en tres estaciones de medida: Longyearbyen, Ny-Ålesund y Barentsburg, separadas más de 100 km. Se muestra para estos casos una prevalencia de partículas pequeñas, siendo más abundantes aquellas con un radio efectivo inferior a 0.5 μm. 2022-01-01T00:00:00Z https://uvadoc.uva.es/handle/10324/82279 En este trabajo se analiza cómo identificar episodios de Alta Turbiedad Atmosférica (HAT, de su siglas en inglés High Atmospheric Turbidity), un aspecto esencial para la monitorización global de aerosoles. 2020-01-01T00:00:00Z