Artículos de Investigación

Permanent URI for this collection

Browse

Recent Submissions

Now showing 1 - 20 of 734
  • Item
    Applications of Hybrid Metal-Dielectric Nanostructures: State of the Art
    (Wiley, 2022-04-01) Barreda, Ángela; Vitale, Francesco; Minovich, Alexander E.; Ronning, Carsten; Staude, Isabelle
    Enhancing the light-matter interactions is important for many different applications like sensing, surface enhanced spectroscopies, solar energy harvesting, and for quantum effects such as nonlinear frequency generation or spontaneous and stimulated emission. Hybrid metal-dielectric nanostructures have shown extraordinary performance in this respect, demonstrating their superiority with respect to bare metallic or high refractive index dielectric nanostructures. Such hybrid nanostructures can combine the best of two worlds: strong confinement of the electromagnetic energy by metallic structures and high scattering directivity and low losses of the dielectric ones. In this review, following a general overview of the properties of metal-dielectric nanostructures, some of their most relevant applications including directional scattering, sensing, surface enhanced Raman spectroscopy, absorption enhancement, fluorescence and quantum dot emission enhancement, nonlinear effects, as well as lasing, are summarized.
  • Publication
    Simultaneous desalination and consolidation treatment through the application of electrokinetic techniques
    (Elsevier, 2023-12-08) Feijoo, J.; Gómez Villalba, Luz Stella; Fort, R.; Rabanal Jiménez, María Eugenia; Comunidad de Madrid
    The vast majority of building materials that are heavily affected by salts require desalination and subsequent consolidation treatments. This double intervention entails a risk associated with the loss of material due to continuous contact with the affected surface. This study evaluates the effectiveness of an electrokinetic process of simultaneous desalination-consolidation of two types of stones (dolostone and limestone). The results show that it is possible to reduce the salts up to percentages of 100% and at the same time to fill the pores and fractures with insoluble compounds compatible with the materials to be treated, such as calcium-magnesium carbonates.
  • Item
    Investigation of dipole emission near a dielectric metasurface using a dual-tip scanning near-field optical microscope
    (De Gruyter, 2021-12-01) Abbasirad, Najmeh; Barreda, Ángela; Arslan, Dennis; Steinert, Michael; Fasold, Stefan; Rockstuhl, Carsten; Staude, Isabelle; Setzpfandt, Frank; Pertsch, Thomas; European Commission
    A wide variety of near-field optical phenomena are described by the interaction of dipole radiation with a nanophotonic system. The electromagnetic field due to the dipole excitation is associated with the Green’s function. It is of great interest to investigate the dipole interaction with a photonic system and measure the near-field Green’s function and the quantities it describes, e.g., the local and cross density of optical states. However, measuring the near-field Green’s function requires a point-source excitation and simultaneous near-field detection below the diffraction limit. Conventional single-tip near-field optical microscope (SNOM) provides either a point source excitation or amplitude and phase detection with subwavelength spatial resolution. The automated dual-tip SNOM, composed of two tips, has overcome the experimental challenges for simultaneous near-field excitation and detection. Here, we investigate the dipole emission in the near-field of a dielectric metasurface using the automated dual-tip SNOM. We have analyzed the near-field pattern and directional mode propagation depending on the position of the dipole emission relative to the metasurface. This study is one further step toward measuring the dyadic Green’s function and related quantities such as cross density of optical states in complex nanophotonic systems for both visible and near-infrared spectra.
  • Item
    Metal, dielectric and hybrid nanoantennas for enhancing the emission of single quantum dots: A comparative study
    (Elsevier, 2021-12-01) Barreda, Ángela; Hell, S.; Weissflog, M. A.; Minovich, A.; Pertsch, T.; Staude, Isabelle
    The confinement of electromagnetic energy to subwavelength volumes through nanoscale antennas can be used to enhance the spontaneous emission of quantum emitters. With this aim, different configura- tions of metallic and high refractive index dielectric nanoparticles have been explored. Here, we carry out a comparative analysis of planar metallic, high refractive index dielectric, and hybrid nanoantennas considering three different parameters: the Purcell factor enhancement, radiation efficiency, and directionality properties. We focus our study on different geometries and material combinations of a dimer of cylinders. A dimer made of two gold nanocylinders is the most promising candidate for improving the spontaneous emission. While most previous works have paid attention to the redirection of the scattered emission in the nanoparticle plane, our proposed nanostructure of two large gold cylinders ( R = λ/ 4) emits most of the radiation upwards. This effect is due to the strong quadrupolar electric contribution to the resonant mode. With the aim to further improve the directionality properties, additional silicon nanocylinders are used as directors of the scattered radiation, increasing the directivity by a factor of 2.4 with respect to the gold dimer without directors. All in all, a hybrid structure composed of a gold dimer and silicon nanoparticles is proposed to enhance the spontaneous emission of a single quantum dot and to govern its emission pattern. The results shown in this work could be useful in fluorescence enhance- ment or in quantum photonics. They are particularly interesting for the development of single-photon sources based on quantum dots and other nanoscale emitters.
  • Publication
    Untangling connections between challenges in the adoption of learning analytics in higher education
    (Springer, 2022-04-01) Alzahrani, Asma; Tsai, Yi-Shan; Iqbal, Sehrish; Moreno Marcos, Pedro Manuel; Scheffel, Maren; Drachsler, Hendrik; Delgado Kloos, Carlos; Aljohani, Naif; Gasevic, Dragan
    Potential benefits of learning analytics (LA) for improving students performance, predicting students success, and enhancing teaching and learning practice have increasingly been recognized in higher education. However, the adoption of LA in higher education institutions (HEIs) to date remains sporadic and predominantly small in scale due to several socio-technical challenges. To better understand why HEIs struggle to scale LA adoption, it is needed to untangle adoption challenges and their related factors. This paper presents the findings of a study that sought to investigate the associations of adoption factors with challenges HEIs face in the adoption of LA and how these associations are compared among HEIs at different scopes of adoption. The study was based on a series of semi-structured interviews with senior managers in HEIs. The interview data were thematically analysed to identify the main challenges in LA adoption. The connections between challenges and other factors related to LA adoption were analysed using epistemic network analysis (ENA). From senior managers viewpoints, ethical issues of informed consent and resistance culture had the strongest links with challenges of learning analytic adoption in HEI; this was especially true for those institutions that had not adopted LA or who were in the initial phase of adoption (i.e., preparing for or partially implementing LA). By contrast, among HEIs that had fully adopted LA, the main challenges were found to be associated with centralized leadership, gaps in the analytic capabilities, external stakeholders, and evaluations of technology. Based on the results, we discuss implications for LA strategy that can be useful for institutions at various stages of LA adoption, from early stages of interest to the full adoption phase.
  • Item
    Stability of laminar flames on upper and lower inclined fuel surfaces
    (Elsevier, 2021-03-01) Hakes, Raquel; Coenen, Wilfried; Sánchez, Antonio L.; Gollner, Michael J.; Williams, Forman A.
    Experiments have found substantial morphological differences between buoyancy-driven flames developing on the upper and lower surfaces of inclined burning plates. These differences cannot be explained on the basis of existing analytical solutions of steady semi-infinite flames, which provide identical descriptions for the top and bottom configurations. To investigate the potential role of flame instabilities in the experimentally observed flow differences, a temporal linear stability analysis is performed here. The problem is formulated in the limit of infinitely fast reaction, taking into account the non-unity Lewis number of the fuel vapor. The stability analysis incorporates non-parallel effects of the base flow and considers separately spanwise traveling waves and Görtler-like streamwise vortices. The solution to the stability eigenvalue problem determines the downstream location at which the flow becomes unstable, characterized by a critical value of the relevant Grashof number, whose value varies with the plate inclination angle. The results for the flame formed on the underside of the fuel surface indicate that instabilities emerge farther downstream than they do for a flame developing over the top of the fuel surface, in agreement with experimental observations. Increased buoyancy-induced vorticity production is reasoned to be responsible for the augmented instability tendency of topside flames.
  • Item
    Numerical description of axisymmetric blue whirls over liquid-fuel pools
    (Elsevier, 2021-01-01) Carpio, Jaime; Coenen, Wilfried; Sánchez, Antonio L.; Oran, Elaine; Williams, Forman A.; Ministerio de Ciencia, Innovación y Universidades (España)
    This numerical investigation is focused on determining the structures of blue whirls, recently found to occur in laboratory investigations of fire whirls when the circulation becomes sufficiently large to produce a vortex breakdown that drastically shortens the fire whirl and correspondingly reduces residence times, so that the yellow flames turn blue. The computations address axisymmetric configurations for round pools of liquid fuels flush with and at the center of a larger solid horizontal disc, at the outer edge of which vanes of adjustable angles cause the entrained air to enter with a controllable azimuthal component of velocity. The nondimensionlized conservation equations employed include realistic Lewis numbers with temperature-dependent transport coefficients and a one-step chemical-kinetic approximation that correctly reproduces laminar burning velocities. Buoyancy and radiant energy transport from the flames to the liquid surface are both taken into account, the latter being found to be essential for the blue whirl. Along with the vaporization-equilibrium and energy-conservation boundary conditions at the fuel surface, inflow boundary conditions are provided by a recently developed solution for the boundary-layer flow over the solid disc, while zero-gradient outflow conditions are applied above the whirl. Controlling nondimensional parameters, besides Reynolds, Damköhler, and Froude numbers, are a ratio of radiant to convective energy flux and a ratio of azimuthal to inward radial flow velocity in the boundary layer at the edge of the disc. The computed conditions for the onset of the blue whirl, as well as the computed structure of the whirl itself, bear close resemblance to what was found experimentally.
  • Item
    Modelling and direct numerical simulation of flow and solute dispersion in the spinal subarachnoid space
    (Elsevier, 2021-06-01) Gutiérrez Montes, Cándido; Coenen, Wilfried; Lawrence, Jenna J.; Martínez Bazán, C.; Sánchez, A. L.; Lasheras, J. C.; Junta de Andalucía; Comunidad de Madrid; Ministerio de Economía, Comercio y Empresa (España)
    The motion of the cerebrospinal fluid in the spinal subarachnoid space, a slender annular canal surrounding the spinal cord, exhibits an oscillatory velocity component driven by the pressure oscillations induced by the cardiac and respiratory cycles. A time-averaged transport equation has been recently proposed for describing solute transport along the canal, circumventing the need to compute the concentration fluctuations resulting from this fast oscillatory motion. The accuracy and limitations of this time-averaged description are tested here by means of comparisons with results of direct numerical simulations spanning hundreds of oscillation cycles, as needed to generate significant dispersion of the solute. The comparisons between the numerical results and the predictions of the analytical model include velocity fields and quantifications of transient solute-dispersion events for selected values of the flow parameters and two different idealized, canonical geometries of the spinal canal. The comparisons clearly demonstrate the accuracy of the time-averaged description of the analytical model, which is seen to provide a good fidelity at a fraction of the computational cost involved in the direct numerical simulations. The variations of canal eccentricity along the spinal canal are found to play an important role in the dynamics of the solute transport, leading to the emergence of closed recirculating Lagrangian vortices that may hinder solute dispersion along the canal, as revealed by both direct numerical simulations and time-averaged results.
  • Item
    Evaluation of systemic gentamicin as translational readthrough therapy for a patient with epidermolysis bullosa simplex with muscular dystrophy owing to PLEC1 pathogenic nonsense variants
    (American Medical Association, 2022-03-02) Martínez Santamaría, Lucía; Maseda, Rocío; Arriba Pérez, María del Carmen de; Membrilla, Javier A.; Iglesias Sigüenza, Alberto; Mascia, Javier; García Díez, Marta; Quintana, Lucía; Esteban Rodríguez, Isabel; Hernández Fernández, Carlos Pelayo; Illera Esteban, Nuria; Duarte González, Blanca; Guerrero Aspizúa, Sara; Woodley, David T.; Río Nechaevsky, Marcela del; Lucas, Raúl de; Larcher Laguzzi, Fernando; Escámez Toledano, María José
    Importance: Epidermolysis bullosa simplex with muscular dystrophy (EBS-MD) is an autosomal recessive disorder caused by pathogenic variants in PLEC1, which encodes plectin. It is characterized by mild mucocutaneous fragility and blistering and muscle weakness. Translational readthrough-inducing drugs, such as repurposed aminoglycoside antibiotics, may represent a valuable therapeutic alternative for untreatable rare diseases caused by nonsense variants. Objective: To evaluate whether systemic gentamicin, at a dose of 7.5 mg/kg/d for 14 consecutive days, is clinically beneficial in a patient with EBS-MD. Design, Setting, and Participants: A single patient in Madrid, Spain, received 2 treatment courses with gentamicin on July 2019 and February 2020 with a follow-up period of 120 and 150 days, respectively. Results: In this case report of a woman in her 30s with EBS-MD, before gentamicin treatment, the patient had mucocutaneous involvement, skeletal and respiratory muscle weakness, and myalgia that negatively affected her quality of life. Outcomes were evaluated with extensive laboratory tests and clinical scales. No nephrotoxic or ototoxic effects were detected after intravenous gentamicin administration. Gentamicin treatment was followed by plectin expression in the skin for at least 5 months. Although minimal changes were noted in skeletal muscle function (as measured by the Hammersmith functional motor scale and its expanded version: 6/40 to 7/40 and from 10/66 to 11/66, respectively) and respiratory musculature (maximal inspiratory and expiratory pressures D0 vs D16, MIP: 2.86 vs 3.63 KPa and MEP: 2.93 vs 4.63 KPa), myalgia disappeared (VAS dropped from 6 to 0), and quality of life improved (EuroQoL-5D-3L pain and anxiety dropped from 2 to 1). Conclusions and Relevance: The findings of this single case report suggest that gentamicin treatment may help suppress PLEC1 premature termination codons and induce plectin expression in EBS-MD primary keratinocytes and skin. Our study suggests that gentamicin may play an important role in treating EBS-MD owing to nonsense variants.
  • Item
    Radiationless anapole states in on-chip photonics
    (Springer Nature, 2021-10-04) Díaz Escobar, Evelyn; Bauer, Thomas; Pinilla Cienfuegos, Elena; Barreda, Ángela; Griol, Amadeu; Kuipers, L.; Martínez, Alejandro; European Commission; Generalitat Valenciana; Ministerio de Ciencia, Innovación y Universidades (España)
    High-index nanoparticles are known to support radiationless states called anapoles, where dipolar and toroidal moments interfere to inhibit scattering to the far field. In order to exploit the striking properties arising from these interference conditions in photonic integrated circuits, the particles must be driven in-plane via integrated waveguides. Here, we address the excitation of electric anapole states in silicon disks when excited on-chip at telecom wavelengths. In contrast to normal illumination, we find that the anapole condition—identified by a strong reduction of the scattering—does not overlap with the near-field energy maximum, an observation attributed to retardation effects. We experimentally verify the two distinct spectral regions in individual disks illuminated in-plane from closely placed waveguide terminations via far-field and near-field measurements. Our finding has important consequences concerning the use of anapole states and interference effects of other Mie-type resonances in high-index nanoparticles for building complex photonic integrated circuitry.
  • Publication
    The Wars of others: the effect of the Russian invasion of Ukraine on Spanish nationalism
    (The University of Chicago Press, 2024-01-17) Balcells, Laia; Tellez, Juan F.; Villamil Fernández, Francisco
    Wars can produce drastic changes in the attitudes and behavior of the citizens of the countries involved in the fighting. Yet such conflicts also have important security and economic implications for uninvolved, third-party states. How do the wars of others shape domestic public attitudes? We explore this question by analyzing the effect of the February 2022 Russian invasion of Ukraine on Spanish nationalism. Exploiting a natural experiment in Spain, we show that the Russian invasion caused a general increase in the salience of Spanish national identification, but not at the expense of regional or substate national identities. We also find an activation effect on electoral participation and increased support for taxation. Our study illuminates pathways through which international conflicts can affect domestic politics in third-party states.
  • Publication
    The SHEILA Framework: Informing Institutional Strategies and Policy Processes of Learning Analytics
    (Soc Learning Analytics Research-Solar, 2018-12-11) Tsai, Yi-Shan; Moreno Marcos, Pedro Manuel; Jivet, Ioana; Scheffel, Maren; Tammets, Kairit; Kollom, Kaire; Gasevic, Dragan; European Commission
    This paper introduces a learning analytics policy and strategy framework developed by a cross-European research project team - SHEILA1 (Supporting Higher Education to Integrate Learning Analytics), based on interviews with 78 senior managers from 51 European higher education institutions across 16 countries. The framework was developed adapting the RAPID Outcome Mapping Approach (ROMA), which is designed to develop effective strategies and evidence-based policy in complex environments. This paper presents four case studies to illustrate the development process of the SHEILA framework and how it can be used iteratively to inform strategic planning and policy processes in real world environments, particularly for large-scale implementation in higher education contexts. To this end, the selected cases were analyzed at two stages, each a year apart, to investigate the progression of adoption approaches that were followed to solve existing challenges, and identify new challenges that could be addressed by following the SHEILA framework.
  • Publication
    El crimen organizado: especial consideración a Iberoamérica
    (Universidad Rey Juan Carlos, 2017-02-01) Zafra Espinosa De Los Monteros, Maria Rocio
    El mundo globalizado en el que vivimos, nos ha reportado enorme beneficios pero también ha conllevado el crecimiento y expansión de la delincuencia organizada transnacional. Este tipo de delincuencia, cada vez es más sofisticada, ha logradoincorporarse a las instituciones públicas. Ello le permite actuar desde el Estado para la búsqueda de impunidad y para dotar de apariencia de legalidad los beneficios obtenidos con el crimen. Lamentablemente, Iberoamérica es en una de las regiones más afectadas por esta situación en la que se está trabajando para su evitación creando unidades de transparencia. Tradicionalmente, los entramados criminales que venían actuando en el territorio de un solo Estado, se han expandido logrando la hermandad con otras organizaciones, logrando la transnacionalización de sus acciones criminales. Ante esta situación, la acción de un solo Estado es insuficiente frente a una actividad criminal organizada que sobrepasa las fronteras. Es necesario que se supere el concepto de soberanía y los diferentes países aúnen esfuerzos para la cooperación con el fin de acabar con esta lacra social. En este sentido, tanto los convenios bilaterales como los acuerdos firmados por las organizaciones internacionales iberoamericanas así como con las organizaciones europeas de cooperación son imprescindibles.
  • Publication
    Repercusión de las métricas de audiencia online en la comercialización publicitaria del producto informativo
    (Tec de Ecuador, 2017) Aguado Guadalupe, María Guadalupe de la Cruz
    El presente artículo analiza la repercusión de las métricas de audiencia online en lacomercialización publicitaria del producto informativo. Se observa en qué medida elconocimiento de dados sobre el comportamiento de los usuarios con respecto a los mediosdigitales influye en la delimitación y valoración de soportes, en las relaciones medioanunciantesy en los riesgos que han de asumir los medios de cara a la publicidad. Pararealizar el análisis se abordan los factores considerados en las métricas de audiencia, asícomo los cambios en los sistemas de contratación publicitaria y en los criterios deremuneración por parte de los anunciantes. Se observa un gran giro con respecto a lasprácticas tradicionales de comercialización del producto informativo, así como laasunción de mayores riesgos para los medios en las negociaciones publicitarias.
  • Publication
    Análisis de la evolución histórica de la razón de masculinidad al nacer en España
    (2023-06-01) Sánchez Barricarte, Jesús Javier
    Presentamos un análisis de la razón de masculinidad al nacer en España desde finales del siglo xix hasta la actualidad. Se hace una explotación muy detallada para el período 1975-2019 sobre la base de más de 20 millones de fichas de nacimientos. Además de constatar la escasa fiabilidad de los registros de los nacimientos en las primeras décadas del siglo xx, hemos determinado que, al contrario de lo generalmente aceptado, esta ratio no es constante. Nuestros datos muestran que la edad y la raza de los progenitores, el orden de nacimiento, el estado civil de las madres y la intensidad de la radiación solar tienen una clara influencia en dicho indicador.
  • Publication
    Relationship between historical developments in the percentages of low birthweight and fetal mortality in Spain
    (Elsevier, 2023-01-02) Sánchez Barricarte, Jesús Javier; Sánchez-Arlegui, Amaia; Agencia Estatal de Investigación (España)
    Objective To document the differences in low birthweight in different population subgroups and to analyze its possible relationship with fetal mortality rates in Spain. Method We used the microdata on live births and stillbirths since 1975 to 2020 from the Spanish National Statistics Institute to examine differentials in delivering a low birthweight controlling for different sociodemographic variables and to determine the relationship between low birthweight and fetal mortality. No statistical analysis was necessary beyond the calculation of percentages and rates. Results The data at our disposal for Spain confirm the historical increase in the incidence of low birthweight and allow us to link trends in low birthweight with a decrease in the fetal mortality rate. When fetal mortality is high, the incidence of low birthweight is low, given that a natural selection effect takes place. Conclusions The surprising historical increase in the incidence of low birthweight in Spain can be explained by the improvement in mortality rates. As more fetuses of lower gestational age are born alive, cases of low birthweight also increase.
  • Publication
    Factors influencing the sex ratio at birth in the United States from a historical perspective
    (Cambridge University Press, 2023-01-16) Sánchez Barricarte, Jesús Javier; Agencia Estatal de Investigación (España)
    Many of the studies on the sex ratio at birth (SRB) are based on a small number of cases over a short period of time. Taking a multivariate approach to a dataset consisting of nearly 199 million birth records in the United States from 1968 to 2019, we present a detailed analysis of several possible factors that might affect the sex ratio at birth (SRB) and its patterns of variation. We found that race/ethnicity is the variable with the strongest influence on this index. Parental age, birth order and solar radiation also have a bearing on the SRB, albeit only to a moderate degree. The historical evolution of the SRB among Black and American Indian and Alaska Native populations remains unexplained.
  • Publication
    Análisis de la actuación reciente de las Cortes Generales. Dos apuntes críticos
    (Congreso de los Diputados, 2023-12-01) Baamonde Gómez, Laura
    Nuestras Cortes Generales corren el riesgo de caer en una deriva «suicida» en términos no sólo de credibilidad y percepción social, sino también en atención a la relevancia sustancial de las atribuciones que le son propias. Se observa una progresiva pérdida de centralidad parlamentaria en el desempeño práctico del esquema de reparto del poder diseñado por el constituyente. Para ilustrar esta impresión se analizan dos fenómenos en relación con el ejercicio de las funciones parlamentarias: uno de tipo abusivo; otro de repliegue o abdicación. Se realiza una reflexión crítica a propósito de ambos que culmina con la propuesta de dos líneas de reconducción de la situación con la finalidad última de revitalizar la institución representativa, cuya reivindicación sigue siendo necesaria como condición de supervivencia del Estado social y democrático de Derecho.
  • Publication
    Sentencias del Tribunal Constitucional dictadas durante el primer cuatrimestre de 2023
    (Centro de Estudios Políticos y Constitucionales, 2023-09-21) Elvira Perales, Ascensión; Espinosa Díaz, Ana; Gómez Lugo, Yolanda; Baamonde Gómez, Laura; Carranza Galaico, Gonzalo Gabriel
  • Publication
    Sentencias dictadas durante el tercer cuatrimestre de 2022
    (Centro de Estudios Políticos y Constitucionales, 2023-04-30) Elvira Perales, Ascensión; Espinosa Díaz, Ana; Gómez Lugo, Yolanda; Baamonde Gómez, Laura; Carranza Galaico, Gonzalo Gabriel