602 research outputs found

    Control of fluorescence in quantum emitter and metallic nanoshell hybrids for medical applications

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    We study the light emission from quantum emitter and double metallic nanoshell hybrid systems. Quantum emitters act as local sources which transmit their light efficiently due to a double nanoshell near field. The double nanoshell consists a dielectric core and two outer nanoshells

    The impact of a large object with Jupiter in July 2009

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    On 2009 July 19, we observed a single, large impact on Jupiter at a planetocentric latitude of 55^{\circ}S. This and the Shoemaker-Levy 9 (SL9) impacts on Jupiter in 1994 are the only planetary-scale impacts ever observed. The 2009 impact had an entry trajectory opposite and with a lower incidence angle than that of SL9. Comparison of the initial aerosol cloud debris properties, spanning 4,800 km east-west and 2,500 km north-south, with those produced by the SL9 fragments, and dynamical calculations of pre-impact orbit, indicate that the impactor was most probably an icy body with a size of 0.5-1 km. The collision rate of events of this magnitude may be five to ten times more frequent than previously thought. The search for unpredicted impacts, such as the current one, could be best performed in 890-nm and K (2.03-2.36 {\mu}m) filters in strong gaseous absorption, where the high-altitude aerosols are more reflective than Jupiter's primary cloud.Comment: 15 pages, 5 figure

    Symmetry-projected variational approach for ground and excited states of the two-dimensional Hubbard model

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    We present a symmetry-projected configuration mixing scheme to describe ground and excited states, with well defined quantum numbers, of the two-dimensional Hubbard model with nearestneighbor hopping and periodic boundary conditions. Results for the half-filled 2{\times}4, 4{\times}4, and 6{\times}6 lattices, as well as doped 4 {\times} 4 systems, compare well with available results, both exact and from other state-of-the-art approximations. We report spectral functions and density of states obtained from a well-controlled ansatz for the (Ne {\pm} 1)-electron system. Symmetry projected methods have been widely used for the many-body nuclear physics problem but have received little attention in the solid state community. Given their relatively low (mean-field) computational cost and the high quality of results here reported, we believe that they deserve further scrutiny

    The Holographic Dual of 2+1 Dimensional QFTs with N=1 SUSY and Massive Fundamental Flavours

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    The Maldacena Nastase solution is generalised to include massive fundamental matter through the addition of a flavour profile. This gives a holographic dual to N=1 SYM-CS with massive fundamental matter with a singularity free IR. We study this solution in some detail confirming confinement and asymptotic freedom. A recently proposed solution generating technique is then applied which results in a new type-IIA supergravity solution. In a certain limit the geometry of this solution is asymptotically AdS_4X Y, where Y is the metric at the base of the Bryant-Salamon G_2 cone, which has topology S^3XS^3.Comment: 31 pages plus appendices, 6 figures. v3: Typos corrected, version to appear in JHE

    Parity-Violating Hydrodynamics in 2+1 Dimensions

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    We study relativistic hydrodynamics of normal fluids in two spatial dimensions. When the microscopic theory breaks parity, extra transport coefficients appear in the hydrodynamic regime, including the Hall viscosity, and the anomalous Hall conductivity. In this work we classify all the transport coefficients in first order hydrodynamics. We then use properties of response functions and the positivity of entropy production to restrict the possible coefficients in the constitutive relations. All the parity-breaking transport coefficients are dissipationless, and some of them are related to the thermodynamic response to an external magnetic field and to vorticity. In addition, we give a holographic example of a strongly interacting relativistic fluid where the parity-violating transport coefficients are computable.Comment: 39+1 page

    Zero Sound in Strange Metallic Holography

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    One way to model the strange metal phase of certain materials is via a holographic description in terms of probe D-branes in a Lifshitz spacetime, characterised by a dynamical exponent z. The background geometry is dual to a strongly-interacting quantum critical theory while the probe D-branes are dual to a finite density of charge carriers that can exhibit the characteristic properties of strange metals. We compute holographically the low-frequency and low-momentum form of the charge density and current retarded Green's functions in these systems for massless charge carriers. The results reveal a quasi-particle excitation when z<2, which in analogy with Landau Fermi liquids we call zero sound. The real part of the dispersion relation depends on momentum k linearly, while the imaginary part goes as k^2/z. When z is greater than or equal to 2 the zero sound is not a well-defined quasi-particle. We also compute the frequency-dependent conductivity in arbitrary spacetime dimensions. Using that as a measure of the charge current spectral function, we find that the zero sound appears only when the spectral function consists of a single delta function at zero frequency.Comment: 20 pages, v2 minor corrections, extended discussion in sections 5 and 6, added one footnote and four references, version published in JHE

    Quantum Griffiths effects and smeared phase transitions in metals: theory and experiment

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    In this paper, we review theoretical and experimental research on rare region effects at quantum phase transitions in disordered itinerant electron systems. After summarizing a few basic concepts about phase transitions in the presence of quenched randomness, we introduce the idea of rare regions and discuss their importance. We then analyze in detail the different phenomena that can arise at magnetic quantum phase transitions in disordered metals, including quantum Griffiths singularities, smeared phase transitions, and cluster-glass formation. For each scenario, we discuss the resulting phase diagram and summarize the behavior of various observables. We then review several recent experiments that provide examples of these rare region phenomena. We conclude by discussing limitations of current approaches and open questions.Comment: 31 pages, 7 eps figures included, v2: discussion of the dissipative Ising chain fixed, references added, v3: final version as publishe

    Mining the Herschel-astrophysical terahertz large area survey : Submillimetre-selected blazars in equatorial fields

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    The Herschel-Astrophysical Terahertz Large Area Survey (H-ATLAS) provides an unprecedented opportunity to search for blazars at sub-mm wavelengths. We cross-matched the Faint Images of the Radio Sky at Twenty-cm (FIRST) radio source catalogue with the 11 655 sources brighter than 35 mJy at 500 μm in the ∼135 deg2 of the sky covered by the H-ATLAS equatorial fields at 9h and 15h, plus half of the field at 12h. We found that 379 of the H-ATLAS sources have a FIRST counterpart within 10 arcsec, including eight catalogued blazars (plus one known blazar that was found at the edge of one of the H-ATLAS maps). To search for additional blazar candidates we have devised new diagnostic diagrams and found that known blazars occupy a region of the log(S500μm/S350μm) versus log(S500μm/S1.4 GHz) plane separated from that of sub-mm sources with radio emission powered by star formation, but shared with radio galaxies and steep-spectrum radio quasars. Using this diagnostic we have selected 12 further possible candidates that turn out to be scattered in the (r-z) versus (u-r) plane or in the Wide-Field Infrared Survey Explorer colour-colour diagram, where known blazars are concentrated in well defined strips. This suggests that the majority of them are not blazars. Based on an inspection of all the available photometric data, including unpublished VISTA Kilo-degree Infrared Galaxy survey photometry and new radio observations, we found that the spectral energy distributions (SEDs) of only one out of the 12 newly selected sources are compatible with being synchrotron dominated at least up to 500 μm, i.e. with being a blazar. Another object may consist of a faint blazar nucleus inside a bright star-forming galaxy. The possibility that some blazar hosts are endowed with active star formation is supported by our analysis of the SEDs of Planck Early Release Compact Source Catalogue blazars detected at both 545 and 857 GHz. The estimated rest-frame synchrotron peak frequencies of H-ATLAS blazars are in the range 11.5 ≤ log (νpeak, Hz) ≤ 13.7, implying that these objects are low synchrotron peak. Six of them also show evidence of an ultraviolet excess that can be attributed to emission from the accretion disc. Allowing for the possibility of misidentifications and of contamination of the 500 μm flux density by the dusty torus or by the host galaxy, we estimate that there are seven or eight pure synchrotron sources brighter than S500μm = 35 mJy over the studied area, a result that sets important constraints on blazar evolutionary models.Peer reviewe

    El Servicio de Validación de Copernicus EMS como vector de mejora de la cartografía de emergencias basada en Sentinel

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    [EN] The Copernicus Emergency Management Service (CEMS) is coordinated by the European Commission and “provides all actors involved in the management of natural disasters, man-made emergency situations, and humanitarian crises with timely and accurate geo-spatial information derived from satellite remote sensing and complemented by available in situ or open data sources”. It includes two components, Early Warning and Monitoring and Mapping. The latter provides on demand geo-spatial information derived from satellite imagery during all phases of the disaster management cycle. It includes 3 systems, Rapid Mapping (RM), Risk and Recovery Mapping (RRM), and a Validation Service. RM provides geospatial information immediately after a disaster to assess its impact; RRM in the prevention, preparation and reconstruction phases; and the Validation Service is in charge of validating and verifying the products generated by both, and of collecting and analyzing users’ feedback. The wide spectrum of activities framed in the Validation Service has allowed it to become a vector to improve the Mapping component through the testing of new methodologies, data input type, or approach for the creation of emergency cartography in the frame of the CEMS. The present paper introduces the main investigation lines based on Sentinel-1 and 2 for flood and fire monitoring that could be implemented in the CEMS services taking into consideration the characteristics of the Mapping component in terms of products to create and time constraints. The applicability of Sentinel-1 for flood monitoring based on the backscattering, the MultiTemporal Coherence (MTC), and dual polarization; and for burnt area delineation based on MTC was studied, while Sentinel-2 was used for burnt area delineation based on vegetation indices. Results indicate that proposed methodologies might be appropriate for the creation of crisis information products in large areas, due to the relative easy and fast implementation compared to classic photo interpretation, although further applicability analyses should be carried out.[ES] El Servicio de Gestión de Emergencias de Copernicus (CEMS), está coordinado por la Comisión Europea y “provee de información geoespacial precisa y oportuna derivada de la teledetección satelital y completada por fuentes de datos disponibles in situ o abiertas a todos los actores involucrados en la gestión de emergencias, bien sean derivadas de desastres naturales o producidos por el hombre, o de crisis humanitarias”. El servicio tiene dos componentes, uno de alerta temprana y monitoreo y otro de creación de mapas. El servicio de mapeo se encarga de proveer, bajo demanda, a los diferentes agentes de emergencias de información geoespacial derivada de imágenes de satélite en todas las fases de la gestión de emergencias, consta de 3 sistemas, Rapid Mapping (RM), Risk and Recovery Mapping (RRM), y Validation. RM aporta información inmediatamente después de un desastre para evaluar su impacto; RRM en las fases de prevención, preparación y reconstrucción; y la Validación se encarga de validar y verificar los productos generados por ambos, y de recoger y analizar los comentarios de los usuarios. El amplio espectro de actividades enmarcadas en él le ha permitido ser vector de mejora de los servicios de mapeo de emergencias mediante el testeo de nuevas metodologías, tipos de datos, o enfoques para la creación de cartografías de emergencias en el marco de CEMS. El presente artículo describe las principales líneas de investigación en el uso de datos Sentinel-1 y 2 para la monitorización de inundaciones e incendios, que se podrían implementar en el futuro en el marco de CEMS. La aplicabilidad de Sentinel-1 para el monitoreo de inundaciones basado en la retrodispersión, la coherencia multitemporal (MTC) y la polarización dual; y se estudió la delimitación del área quemada basada en MTC. Sentinel-2 se usó para delimitar áreas quemadas en base a índices de vegetación. Los resultados indican que las metodologías propuestas podrían ser apropiadas para la creación de productos de información de crisis en grandes áreas, debido a la implementación relativamente fácil y rápida en comparación con la fotointerpretación clásica, aunque deberían realizarse más análisis para su aplicación en el marco de CEMS.The authors gratefully acknowledge the contribution of Massimiliano Rossi and Antigoni Maistrali for the preparation of the materials analysed in this work.Donezar-Hoyos, U.; Albizua-Huarte, L.; Amezketa-Lizarraga, E.; Barinagarrementeria-Arrese, I.; Ciriza, R.; De Blas-Corral, T.; Larrañaga-Urien, A.... (2020). The Copernicus EMS Validation service as a vector for improving the emergency mapping based on Sentinel data. Revista de Teledetección. 0(56):23-34. https://doi.org/10.4995/raet.2020.13770OJS233405
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