Search results for "consultancy"
showing 10 items of 62 documents
Aminoacid zwitterions in solution : Geometric, energetic, and vibrational analysis using density functional theory-continuum model calculations
1998
Glycine and alanine aminoacids chemistry in solution is explored using a hybrid three parameters density functional (B3PW91) together with a continuum model. Geometries, energies, and vibrational spectra of glycine and alanine zwitterions are studied at the B3PW91/6-31+G∗∗ level and the results compared with those obtained at the HF and MP2/6-31+G∗∗ levels. Solvents effects are incorporated by means of an ellipsoidal cavity model with a multipolar expansion (up to sixth order) of the solute’s electrostatic potential. Our results confirm the validity of the B3PW91 functional for studying aminoacid chemistry in solution. Taking into account the more favorable scaling behavior of density funct…
The origin of the auditor’s income and audit quality : the Spanish case
2022
Estudios previos señalan la existencia de una relación entre la especialización del auditor y la calidad de la auditoría. A partir de esta idea, cuanto más importante sea la actividad de auditoría en el total del negocio de la firma auditora y mayor especialización exista en dicha actividad, el auditor firmante adoptará una postura más conservadora en la emisión de su informe. Utilizando la materialidad cuantitativa como subrogado de la calidad, se examina el efecto que los honorarios por otros servicios distintos a los de auditoría y el peso de los socios firmantes en la firma tienen sobre la cifra de materialidad. Partiendo de la materialidad real utilizada en cada uno de los encargos com…
Continuum elastic sphere vibrations as a model for low-lying optical modes in icosahedral quasicrystals
2004
The nearly dispersionless, so-called "optical" vibrational modes observed by inelastic neutron scattering from icosahedral Al-Pd-Mn and Zn-Mg-Y quasicrystals are found to correspond well to modes of a continuum elastic sphere that has the same diameter as the corresponding icosahedral basic units of the quasicrystal. When the sphere is considered as free, most of the experimentally found modes can be accounted for, in both systems. Taking into account the mechanical connection between the clusters and the remainder of the quasicrystal allows a complete assignment of all optical modes in the case of Al-Pd-Mn. This approach provides support to the relevance of clusters in the vibrational prop…
Supercontinuum generation with 532 nm quasi-continuum pulses in photonic crystal fibre tapers
2007
We report experimental results on supercontinuum generation in PCF tapers using quasi-continuous pump pulses of 7 ns duration at 532 nm. SC generation in normal and anomalous dispersion regimes are presented. Introduction Supercontinuum generation (SC) in photonic crystal fibres (PCF), fibre tapers, and PCF tapers has been demonstrated in the past with pump pulses of fs, ps, and tenths of ns duration [1-2]. Here, we present experimental results on SC generation in PCF tapers using quasi-continuous pump pulses of 7 ns duration at 532 nm. Fabrication of the PCF tapers The PCF from which the tapers were made, was a large-air-hole PCF ("cobweb" PCF) with two rings of air holes around a solid si…
ELDAR, a new method to identify AGN in multi-filter surveys: the ALHAMBRA test case
2017
We present ELDAR, a new method that exploits the potential of medium- and narrow-band filter surveys to securely identify active galactic nuclei (AGN) and determine their redshifts. Our methodology improves on traditional approaches by looking for AGN emission lines expected to be identified against the continuum, thanks to the width of the filters. To assess its performance, we apply ELDAR to the data of the ALHAMBRA (Advance Large Homogeneous Area Medium Band Redshift Astronomical) survey, which covered an effective area of 2.38 deg2 with 20 contiguous medium-band optical filters down to F814W ≃ 24.5. Using two different configurations of ELDAR in which we require the detection of at lea…
A simple scheme for the direct calculation of ionization potentials with coupled-cluster theory that exploits established excitation energy methods
1999
Vertical ionization potentials can be obtained from existing computer programs for the high-level treatment of excited states by simply including a continuum orbital in the basis set. Exploiting this feature easily allows final state energies for ionized states to be calculated at several previously untested levels of theory that go beyond the equation-of-motion coupled-cluster singles and doubles model. Values obtained for N2, CO, and F2 with the most theoretically complete approximations studied here (those based on the CCSDT-3 and CC3 parametrizations of the neutral ground state) are in excellent agreement with experiment when a large basis set is used.
Spectral analysis of the low-mass X-ray pulsar 4U 1822-371: Reflection component in a high-inclination system
2021
Context. The X-ray source 4U 1822-371 is an eclipsing low-mass X-ray binary and X-ray pulsar, hosting a NS that shows periodic pulsations in the X-ray band with a period of 0.59 s. The inclination angle of the system is so high (80–85°) that in principle, it should be hard to observe both the direct thermal emission of the central object and the reflection component of the spectrum because they are hidden by the outer edge of the accretion disc. Despite the number of studies carried out on this source, many aspects such as the geometry of the system, its luminosity, and its spectral features are still debated. Aims. Assuming that the source accretes at the Eddington limit, the analysis perf…
Magneto-elastic oscillations of neutron stars: exploring different magnetic field configurations
2012
We study magneto-elastic oscillations of highly magnetized neutron stars (magnetars) which have been proposed as an explanation for the quasi-periodic oscillations (QPOs) appearing in the decaying tail of the giant flares of soft gamma-ray repeaters (SGRs). We extend previous studies by investigating various magnetic field configurations, computing the Alfv��n spectrum in each case and performing magneto-elastic simulations for a selected number of models. By identifying the observed frequencies of 28 Hz (SGR 1900+14) and 30 Hz (SGR 1806-20) with the fundamental Alfv��n QPOs, we estimate the required surface magnetic field strength. For the magnetic field configurations investigated (dipole…
Radio emission of SN1993J. The complete picture: II. Simultaneous fit of expansion and radio light curves
2010
We report on a simultaneous modelling of the expansion and radio light curves of SN1993J. We have developed a simulation code capable of generating synthetic expansion and radio light curves of supernovae by taking into consideration the evolution of the expanding shock, magnetic fields, and relativistic electrons, as well as the finite sensitivity of the interferometric arrays used in the observations. Our software successfully fits all the available radio data of SN 1993J with an standard emission model for supernovae extended with some physical considerations, as an evolution in the opacity of the ejecta material, a radial drop of the magnetic fields inside the radiating region, and a ch…
Testing Rate Dependent corrections on timing mode EPIC-pn spectra of the accreting Neutron Star GX 13+1
2014
When the EPIC-pn instrument on board XMM-Newton is operated in Timing mode, high count rates (>100 cts/s) of bright sources may affect the calibration of the energy scale, resulting in a modification of the real spectral shape. The corrections related to this effect are then strongly important in the study of the spectral properties. Tests of these calibrations are more suitable in sources which spectra are characterised by a large number of discrete features. Therefore, in this work, we carried out a spectral analysis of the accreting Neutron Star GX 13+1, which is a dipping source with several narrow absorption lines and a broad emission line in its spectrum. We tested two different co…