Search results for "astronomía"
showing 10 items of 247 documents
Space-like (vs. time-like) collinear limits in QCD: Is factorization violated?
2012
We consider the singular behaviour of QCD scattering amplitudes in kinematical configurations where two or more momenta of the external partons become collinear. At the tree level, this behaviour is known to be controlled by factorization formulae in which the singular collinear factor is universal (process independent). We show that this strict (process-independent) factorization is not valid at one-loop and higher-loop orders in the case of the collinear limit in space-like regions (e.g., collinear radiation from initial-state partons). We introduce a generalized version of all-order collinear factorization, in which the space-like singular factors retain some dependence on the momentum a…
Double collinear splitting amplitudes at next-to-leading order
2013
We compute the next-to-leading order (NLO) QCD corrections to the $1 \to 2$ splitting amplitudes in different dimensional regularization (DREG) schemes. Besides recovering previously known results, we explore new DREG schemes and analyze their consistency by comparing the divergent structure with the expected behavior predicted by Catani's formula. Through the introduction of scalar-gluons, we show the relation among splittings matrices computed using different schemes. Also, we extended this analysis to cover the double collinear limit of scattering amplitudes in the context of QCD+QED.
Triple collinear splitting functions at NLO for scattering processes with photons
2014
We present splitting functions in the triple collinear limit at next-to-leading order. The computation was performed in the context of massless QCD+QED, considering only processes which include at least one photon. Through the comparison of the IR divergent structure of splitting amplitudes with the expected known behavior, we were able to check our results. Besides that we implemented some consistency checks based on symmetry arguments and cross-checked the results among them. Studying photon-started processes, we obtained very compact results.
Aportaciones al cálculo de la latitud en la náutica española de principios del siglo XVII contenidas en el manuscrito de Diego Ramírez de Arellano &l…
2013
In 1620, was named chief pilot of the Casa de Contratación de Sevilla Diego Ramírez de Arellano, author of a manuscript entitled Reconocimiento de los estrechos de Magallanes y San Vicente, con algunas cosas curiosas de navegación. He had participated in the reconnaissance mission referred by the title of the manuscript, and in that book developed same methods and tools for a nautical understood scientifically, and even used a methodology close to modern science, as in refuting the theory about Figueiredo of the linear relationship between longitude and magnetic variation of the needle navigation. This article is based on some conclusions that can get an analysis of the manuscript. It focus…
Alimentación y salud en la Valencia medieval. Teorías y prácticas
2013
The aim of this article is to provide an initial survey about the relationship between food habits and health in a Mediterranean city during the Late Middle Ages, by comparing medical treatises, gastronomic recipes and the archival sources that tell us about the actual expenses in food. Through this comparison, and by using accounting records of aristocratic houses, merchant enterprises, convents and hospitals, we can observe the dietary guidelines that were applied, and their concordance with the galenic principles of University medicine. Moreover, we attempt to assess what were the key factors in the evolution of these theories’ guidelines, and how they were probably rather a way to appro…
Long-term X-ray variability of the microquasar system LS 5039/RX J1826.2−1450
2003
We report on the results of the spectral and timing analysis of a BeppoSAX observation of the microquasar system LS 5039/RX J1826.2-1450. The source was found in a low-flux state with Fx(1-10 keV)= 4.7 x 10^{-12} erg cm^{-2} s^{-1}, which represents almost one order of magnitude lower than a previous RXTE observation 2.5 years before. The 0.1--10 keV spectrum is described by an absorbed power-law continuum with photon-number spectral index Gamma=1.8+-0.2 and hydrogen column density of NH=1.0^{+0.4}_{-0.3} x 10^{22} cm^{-2}. According to the orbital parameters of the system the BeppoSAX observation covers the time of an X-ray eclipse should one occur. However, the 1.6-10 keV light curve does…
Cycles of time in the Iberian culture: the astronomical orientation of the temple of El Tossal de Sant Miquel de Llíria
2006
We present an archaeoastronomical study of the temple of the Iberian settlement of El Tossal de Sant Miquel de Llíria (València). We find that the major axis of the building is oriented very close to the east-west cardinal axis. The entrance of the temple is pointing towards an outstanding mountain on the eastern horizon, where the sunrise around the equinoxes takes place. On the other hand, the absence of other constructions just in front of the cultic building seems to support the inference that the astronomical relation was intentional, because it would permit the observation of the sunrise from the temple. The existence of other nearby Iberian sanctuaries showing similar relations with …
Cycles of time in the Iberian culture: the astronomical orientation of the temple of El Tossal de Sant Miquel de Llíria
2006
We present an archaeoastronomical study of the temple of the Iberian settlement of El Tossal de Sant Miquel de Llíria (València). We find that the major axis of the building is oriented very close to the east-west cardinal axis. The entrance of the temple is pointing towards an outstanding mountain on the eastern horizon, where the sunrise around the equinoxes takes place. On the other hand, the absence of other constructions just in front of the cultic building seems to support the inference that the astronomical relation was intentional, because it would permit the observation of the sunrise from the temple. The existence of other nearby Iberian sanctuaries showing similar relations with …
In-situ high-pressure x-ray diffraction study of zinc ferrite nanoparticles
2016
We have studied the high-pressure structural behavior of zinc ferrite (ZnFe2O4) nanoparticles by powder X-ray diffraction measurements up to 47 GPa. We found that the cubic spinel structure of ZnFe2O4 remains up to 33 GPa and a phase transition is induced beyond this pressure. The high-pressure phase is indexed to an orthorhombic CaMn2O4-type structure. Upon decompression the low- and high-pressure phases coexist. The compressibility of both structures was also investigated. We have observed that the lattice parameters of the high-pressure phase behave anisotropically upon compression. Further, we predict possible phase transition around 55 GPa. For comparison, we also studied the compressi…
Unveiling the nature of six HMXBs through IR spectroscopy
2008
The International Gamma-Ray Astrophyiscs Laboratory (INTEGRAL) is discovering a large number of new hard X-ray sources, many of them being HMXBs. The identification and spectral characterization of their optical/infrared counterparts is a necessary step to undertake detailed study of these systems. In particular, the determination of the spectral type is crucial in the case of the new class of Supergiant Fast X-ray Transients (SFXTs), which show X-ray properties common to other objects. We used the ESO/NTT SofI spectrograph to observe proposed IR counterparts to HMXBs, obtaining Ks medium resolution spectra (R = 1320) with a S/N >= 100. We classified them through comparison with publishe…