5,448 research outputs found
Topology and excited state multiplicity as controlling factors in the carbazole-photosensitized CPD formation and repair
Photosensitized thyminethymine (ThyThy) formation and repair can be mediated by carbazole (Cbz). The former occurs from the Cbz triplet excited state via energy transfer, while the latter takes place from the singlet excited state via electron transfer. Here, fundamental insight is provided into the role of the topology and excited state multiplicity, as factors governing the balance between both processes. This has been achieved upon designing and synthesizing different isomers of trifunctional systems containing one Cbz and two Thy units covalently linked to the rigid skeleton of the natural deoxycholic acid. The results shown here prove that the Cbz photosensitized dimerization is not counterbalanced by repair when the latter, instead of operating through-space, has to proceed through-bond. © 2022 The Authors. Published by American Chemical Society
The impact of a large object with Jupiter in July 2009
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
Portland cement pastes analysed by synchrotron and laboratory X-ray imaging
Portland Cement (PC) is the most used construction material and the derived building materials have very complex hierarchical microstructures. Quantitative characterization of their microstructures is of paramount importance for assessing the performance and durability of the final products.
As cement performance is controlled by its phase composition and microstructure, in particular, the pore network plays a critical role in the mechanical properties and durability. The chemical and hydration changes in PC binders affect their performances mainly because of the binding properties of the main component, the so-called C-S-H gel. Here, we analyse porosity in PC pastes using laboratory and synchrotron X-ray micro-tomography with different water to cement mass ratios (w/c) after 28 days of hydration. Monochromatic synchrotron X-ray microtomography is used for reference and the main aim is determining volume percentage of different components with focus on porosity. It will be shown, as expected, that higher amount of water (that increases fluidity of pastes) results in higher porosities at 28 days of hydration. Therefore, in the histogram and tomograms more pores, hydrated materials, and less anhydrous materials would appear with increasing w/c (see Figure 1).
The excellent spatial resolution (and slightly better contrast) of synchrotron experiments serve as reference for data analysis. Despite 0.2-0.3 m voxel-sizes in all the used experimental setups (see Figure 2), the laboratory tomograms show some limitations that will be discussed. In this work, a two-steps approach is followed. Firstly, we will report the analysis of the histograms by classifying in the three types of components based on grey-levels: i) pores, ii) hydrated components; and iii) unreacted cement phases. Secondly, segmented pore contribution will be further analyzed and the results from laboratory tomograms will be compared with the reference values derived from synchrotron data.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech
Formation of monopoles and domain walls after brane inflation
We study cosmological defect formation after brane inflation. The
cosmological defects are corresponding to the branes that have less than three
spacial dimensions in the uncompactified spacetime. Contrary to the previous
arguments, production of monopoles and domain walls are not always negligible.
Monopoles and domain walls are formed by the branes extended between mother
branes.Comment: 27pages, 7 figures, many comments, footnotes and reviews are added,
to appear in JHE
Branonium
We study the bound states of brane/antibrane systems by examining the motion
of a probe antibrane moving in the background fields of N source branes. The
classical system resembles the point-particle central force problem, and the
orbits can be solved by quadrature. Generically the antibrane has orbits which
are not closed on themselves. An important special case occurs for some
Dp-branes moving in three transverse dimensions, in which case the orbits may
be obtained in closed form, giving the standard conic sections but with a
nonstandard time evolution along the orbit. Somewhat surprisingly, in this case
the resulting elliptical orbits are exact solutions, and do not simply apply in
the limit of asymptotically-large separation or non-relativistic velocities.
The orbits eventually decay through the radiation of massless modes into the
bulk and onto the branes, and we estimate this decay time. Applications of
these orbits to cosmology are discussed in a companion paper.Comment: 34 pages, LaTeX, 4 figures, uses JHEP
Paleofitogeografía de los pinares en las montañas periféricas de la cuenca del Duero
En las dos últimas décadas se han obtenido numerosos resultados procedentes de diferentes trabajos paleobotánicos (Cuaternario final) realizados en los territorios montanos periféricos de la depresión del Duero. Las metodologías empleadas han sido diversas y tienen que ver con los diferentes tipos de yacimientos y de muestras biológicas seleccionadas para su estudio; entre ellas destacan las técnicas de microscopía óptica para la identificación de maderas subfósiles, la morfología comparada de macrorrestos y los estudios dendrocronológicos en árboles longevos y maderas subfósiles. En esta comunicación se reúnen y resumen los trabajos más importantes, haciéndose una síntesis de las conclusiones obtenidas en los trabajos paleofitogeográficos realizados hasta el momento; se hace hincapié en la información proporcionada por los macrorrestos (maderas, estróbilos) así como por la recogida en los registros dendrocronológicos (con extensión a la dendroecología). Otro de los objetivos de la comunicación es la síntesis de las conclusiones obtenidas en los trabajos paleofitogeográficos realizados hasta el momento. Uno de esos resultados es que el comportamiento de los pinares a lo largo del Holoceno presenta diferentes modalidades en cada una de las cordilleras que bordean la cuenca del Duero; desde casos con marcada estabilidad a otros en que se muestran variaciones temporales apreciables (con patrones de heterogeneidad en función de un eje N-S y/o O-E
Towards the improvement of methane production in CO2 photoreduction using Bi2WO6/TiO2 heterostructures
Russelite bismuth tungstate (Bi2WO6) has been widely reported for the photocatalytic degradation and mineralization of a myriad of pollutants as well as organic compounds. These materials present perovskite-like structure with hierarchical morphologies, which confers excellent optoelectronic properties as potentials candidates for photocatalytic solar fuels production. Here, we propose the development of Bi2WO6/TiO2 heterojunctions for CO2 photoreduction, as a promising solution to produce fuels, alleviate global warming and tackle fossil fuel shortage. Our results show an improvement of the photocatalytic activity of the heterojunctions compared to the pristine semiconductors. Near Ambient Pressure X-ray Photoelectron Spectroscopy (NAP-XPS) experiments reveals a preferential CO2 adsorption over TiO2. On the other hand, transient absorption spectroscopy measurements show that the charge transfer pathway in Bi2WO6/TiO2 hybrids leads to longer-lived photogenerated carriers in spatially separated redox active sites, which favor the reduction of CO2 into highly electron demanding fuels and chemicals, such as CH4 and C2H6Financial support has been received from the European Research
Council (ERC), through HYMAP project (grant agreement No. 648319),
under the European Union's Horizon 2020 research and innovation
program, as well as from the Marie Sklodowska-Curie grant agreement
No. 754382. L.C. acknowledges funding from the project ARMONIA
(PID2020–119125RJ-I00) funded by MCIN/AEI/10.13039/
501100011033. Financial support has also been received from AEIMINECO/FEDER (Nympha Project, PID2019–106315RB-I00), "Comunidad de Madrid" regional government, and the European Structural
Funds (FotoArt-CM project, S2018/NMT-4367). Authors also acknowledge financial support from the grant PLEC2021–007906 funded by MCIN/AEI/10.13039/501100011033 and the "European Union
NextGenerationEU/PRTR"
Nuclear parton distributions at next to leading order
We perform a next to leading order QCD global analysis of nuclear deep
inelastic scattering and Drell-Yan data using the convolution approach to
parameterize nuclear parton densities. We find both a significant improvement
in the agreement with data compared to previous extractions, and substantial
differences in the scale dependence of nuclear effects compared to leading
order analyses.Comment: 9 pages, 10 figure
Análisis de la dosis glandular media (DGM) y dosis a tiroides (DTHY) en la mastografía
La mastografía analógica es una imagen por rayos X de las glándulas mamarias, cuyo objetivo principal es detectar el cáncer de mama. De acuerdo con Sechopoulos et al.1 se ha determinado que no hay un riesgo de cáncer de tiroides al realizarse la mastografía. Sin embargo, los nódulos tiroideos en las mujeres tie-nen una prevalencia de 67% y han sido una de las preocupaciones, en cuanto a la seguridad al realizarse la mastografía. Por ello, el objetivo del presente traba-jo es determinar el riesgo radiológico. Al comparar la dosis glandular media (DGM), con la dosis en tiroides (DThy) de las mujeres que se realizan la mastografía para la detección de cáncer de mama en las proyec-ciones: cráneo caudal (CC) y medio lateral oblicua (MLO)
- …