12,055 research outputs found
Effect of the curing time on the numerical modelling of the behaviour of a chemically stabilised soft soil
The ability of the Modified Cam Clay (MCC) model combined with the Von Mises (VM) model, considering the effect of curing time on the enhancement of the mechanical properties of a chemically stabilised soft soil is examined. The evolution of the strength and stiffness over time is based on the results of undrained compressive strength (UCS) tests carried out for different curing times (from 28 days to 360 days). Initially, the MCC/VM models associated with the effect of curing time are validated by CIU triaxial tests, for curing times of 28 and 90 days. Finally, the behaviour of an embankment built on a soft soil reinforced with deep mixing columns is predicted based on the previously validated models. The results show that the increase of curing time of the DMCs slightly decreases the settlement obtained with a curing time of 28 days
Dynamical stability analysis of the HD202206 system and constraints to the planetary orbits
Long-term precise Doppler measurements with the CORALIE spectrograph revealed
the presence of two massive companions to the solar-type star HD202206.
Although the three-body fit of the system is unstable, it was shown that a 5:1
mean motion resonance exists close to the best fit, where the system is stable.
We present here an extensive dynamical study of the HD202206 system aiming at
constraining the inclinations of the two known companions, from which we derive
possible ranges of value for the companion masses.
We study the long term stability of the system in a small neighborhood of the
best fit using Laskar's frequency map analysis. We also introduce a numerical
method based on frequency analysis to determine the center of libration mode
inside a mean motion resonance.
We find that acceptable coplanar configurations are limited to inclinations
to the line of sight between 30 and 90 degrees. This limits the masses of both
companions to roughly twice the minimum. Non coplanar configurations are
possible for a wide range of mutual inclinations from 0 to 90 degrees, although
configurations seem to be favored. We also confirm the
5:1 mean motion resonance to be most likely. In the coplanar edge-on case, we
provide a very good stable solution in the resonance, whose does not
differ significantly from the best fit. Using our method to determine the
center of libration, we further refine this solution to obtain an orbit with a
very low amplitude of libration, as we expect dissipative effects to have
dampened the libration.Comment: 14 pages, 18 figure
Corrections to the Boltzmann mean free path in disordered systems with finite size scatterers
The mean free path is an essential characteristic length in disordered
systems. In microscopic calculations, it is usually approximated by the
classical value of the elastic mean free path. It corresponds to the Boltzmann
mean free path when only isotropic scattering is considered, but it is
different for anisotropic scattering. In this paper, we work out the
corrections to the so called Boltzmann mean free path due to multiple
scattering effects on finite size scatterers, in the s-wave approximation, ie.
when the elastic mean free path is equivalent to the Boltzmann mean free path.
The main result is the expression for the mean free path expanded in powers of
the perturbative parameter given by the scatterer density.Comment: 12 page
Accurate free and forced rotational motions of rigid Venus
% context :The precise and accurate modelling of a terrestrial planet like
Venus is an exciting and challenging topic, all the more interesting since it
can be compared with that of the Earth for which such a modelling has already
been achieved at the milliarcsecond level % aims: We want to complete a
previous study (Cottereau and Souchay, 2009), by determining at the
milliarcsecond level the polhody, i.e. the torque-free motion of the axis of
angular momentum of a rigid Venus in a body-fixed frame, as well as the
nutation of its third axis of figure in space, which is fundamental from an
observational point of view. results :In a first part we have computed the
polhody, i.e. the respective free rotational motion of the axis of angular
momentum of Venus with respect to a body-fixed frame. We have shown that this
motion is highly elliptical, with a very long period of 525 cy to be compared
with 430 d for the Earth. This is due to the very small dynamical flattening of
Venus in comparison with our planet. In a second part we have computed
precisely the Oppolzer terms which allow to represent the motion in space of
the third Venus figure axis with respect to Venus angular momentum axis, under
the influence of the solar gravitational torque. We have determined the
corresponding tables of coefficients of nutation of the third figure axis both
in longitude and in obliquity due to the Sun, which are of the same order of
amplitude as for the Earth. We have shown that the coefficients of nutation for
the third figure axis are significantly different from those of the angular
momentum axis on the contrary of the Earth. Our analytical results have been
validated by a numerical integration which revealed the indirect planetary
effects.Comment: 14 pages, 11 figures, accepted for publication in section 11.
Celestial mechanics and astrometry of Astronomy and Astrophysics (27/02/2010
Ab-initio study of the relation between electric polarization and electric field gradients in ferroelectrics
The hyperfine interaction between the quadrupole moment of atomic nuclei and
the electric field gradient (EFG) provides information on the electronic charge
distribution close to a given atomic site. In ferroelectric materials, the loss
of inversion symmetry of the electronic charge distribution is necessary for
the appearance of the electric polarization. We present first-principles
density functional theory calculations of ferroelectrics such as BaTiO3, KNbO3,
PbTiO3 and other oxides with perovskite structures, by focusing on both EFG
tensors and polarization. We analyze the EFG tensor properties such as
orientation and correlation between components and their link with electric
polarization. This work supports previous studies of ferroelectric materials
where a relation between EFG tensors and polarization was observed, which may
be exploited to study ferroelectric order when standard techniques to measure
polarization are not easily applied.Comment: 9 pages, 6 figures, 5 tables, corrected typos, as published in Phys.
Rev.
Recommended from our members
Analgesic interpatient variability of remifentanil assessed through pupillary dilation reflex
info:eu-repo/semantics/publishedVersio
Intrapatient variability of the pupillary pain index to remifentanil
info:eu-repo/semantics/publishedVersio
Portuguese primary and secondary education in times of COVID-19 pandemic: An exploratory study on teacher training and challenges
The discussion about the use of digital technologies in education is not new. However, the COVID-19 pandemic and the total closure of schools around the world, that forced millions of
students to attend their classes from home, has demonstrated the importance of this discussion. It has highlighted the need to revisit debates about the interactions between technology and education, and the added value of digital resources to enhance the educational process. This article, based on an exploratory analysis, aims to understand how the transition from face-to-face to digital was accomplished in Portuguese primary and secondary education, namely regarding teacher training and the difficulties experienced during the emergency remote education period. The data analysed in this article were collected through an online questionnaire, disseminated through online social networks, and answered by 136 Portuguese primary and secondary education teachers. The questions focused on this article were open-ended, and the information collected was analysed using content analysis methodology. The results show how teachers have been forced to modify their pedagogical work, the importance of training, and the inherent challenges and critical reflections associated with the process, as well as the opportunities presented in a post-pandemic educational reality.info:eu-repo/semantics/publishedVersio
- …