158 research outputs found
Rotation of rigid Venus: a complete precession-nutation model
Context: With the increasing knowledge of the terrestrial planets due to
recent space probes it is possible to model their rotation with increasing
accuracy. Despite that fact, an accurate determination of Venus precession and
nutation is lacking.
Aims : Although Venus rotation has been studied in several aspects, a full
and precise analytical model of its precession-nutation motion remains to be
constructed. We propose to determine this motion with up-to-date physical
parameters of the planet
Methods: We adopt a theoritical framework already used for a precise
precession-nutation model of the Earth, based on a Hamiltonian formulation,
canonical equations and an accurate development of the perturbing function due
to the Sun.
Results: After integrating the disturbing function and applying the canonical
equations, we can evaluate the precession constant and the
coefficients of nutation, both in longitude and in obliquity. We get
, corresponding to a precession period of
years. This result, based on recent estimations of the Venus
moment of inertia is significantly different from previous estimations. The
largest nutation coefficient in longitude with an argument (where
is the longitude of the Sun) has a 2"19 amplitude and a 112.35 d
period. We show that the coefficients of nutation of Venus due to its
triaxiality are of the same order of amplitude as these values due to its
dynamical flattening, unlike of the Earth, for which they are negligible.Comment: 14 pages, figures, published in A&
A precise modeling of Phoebe's rotation
Although the rotation of some Saturn's satellites in spin-orbit has already
been studied by several authors, this is not the case of the rotation of
Phoebe, which has the particularity of being non resonant. The purpose of the
paper is to determine for the first time and with precision its
precession-nutation motion. We adopt an Hamiltonian formalism of the motion of
rotation of rigid celestial body set up by Kinoshita (1977) based on Andoyer
variables and canonical equations. First we calculate Phoebe's obliquity at
J2000,0 from available astronomical data as well as the gravitational
perturbation due to Saturn on Phoebe rotational motion. Then we carry out a
numerical integration and we compare our results for the precession rate and
the nutation coefficients with pure analytical model. Our results for Phoebe
obliquity (23{\deg}95) and Phoebe precession rate (5580".65/cy) are very close
to the respective values for the Earth. Moreover the amplitudes of the
nutations (26" peak to peak for the nutaton in longitude and 8" for the
nutation in obliquity) are of the same order as the respective amplitudes for
the Earth. We give complete tables of nutation, obtained from a FFT analysis
starting from the numerical signals. We show that a pure analytical model of
the nutation is not accurate due to the fact that Phoebe orbital elements e, M
and Ls are far from having a simple linear behaviour. The precession and
nutation of Phoebe have been calculated for the first time in this paper. We
should keep on the study in the future by studying the additional gravitational
effects of the Sun, of the large satellites as Titan, as well as Saturn
dynamical ellipticity.Comment: 11 pages,15 figures, accepted for publication in A&
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
About the various contributions in Venus rotation rate and LOD
% context heading (optional) {Thanks to the Venus Express Mission, new data
on the properties of Venus could be obtained in particular concerning its
rotation.} % aims heading (mandatory) {In view of these upcoming results, the
purpose of this paper is to determine and compare the major physical processes
influencing the rotation of Venus, and more particularly the angular rotation
rate.} % methods heading (mandatory) {Applying models already used for the
Earth, the effect of the triaxiality of a rigid Venus on its period of rotation
are computed. Then the variations of Venus rotation caused by the elasticity,
the atmosphere and the core of the planet are evaluated.} % results heading
(mandatory) {Although the largest irregularities of the rotation rate of the
Earth at short time scales are caused by its atmosphere and elastic
deformations, we show that the Venus ones are dominated by the tidal torque
exerted by the Sun on its solid body. Indeed, as Venus has a slow rotation,
these effects have a large amplitude of 2 minutes of time (mn). These
variations of the rotation rate are larger than the one induced by atmospheric
wind variations that can reach 25-50 seconds of time (s), depending on the
simulation used. The variations due to the core effects which vary with its
size between 3 and 20s are smaller. Compared to these effects, the influence of
the elastic deformation cause by the zonal tidal potential is negligible.} %
conclusions heading (optional), leave it empty if necessary {As the variations
of the rotation of Venus reported here are of the order 3mn peak to peak, they
should influence past, present and future observations providing further
constraints on the planet internal structure and atmosphere.}Comment: 12 pages, 10 figures, Accepted in A&
La dysenterie des agneaux existe en France (Entérotoxémie des Agneaux nouveau-nés ou à la mamelle)
Personalised therapy in follicular lymphoma - is the dial turning?
Follicular lymphoma is the most common indolent lymphoma accounting for approximately 20%–25% of all new non-Hodgkin lymphoma diagnoses in western countries. Whilst outcomes are mostly favorable, the spectrum of clinical phenotypes includes high-risk groups with significantly inferior outcomes. This review discusses recent updates in risk stratification and treatment approaches from upfront treatment for limited and advanced stage follicular lymphoma to the growing options for relapsed, refractory disease with perspectives on how to approach this from a personalized lens. Notable gaps remain on how one can precisely and prospectively select optimal treatment for patients based on varying risks, with an anticipation that an increased understanding of the biology of these different phenotypes and increasing refinement of imaging- and biomarker-based tools will, in time, allow these gaps to be closed
A Stochastic Multi-scale Approach for Numerical Modeling of Complex Materials - Application to Uniaxial Cyclic Response of Concrete
In complex materials, numerous intertwined phenomena underlie the overall
response at macroscale. These phenomena can pertain to different engineering
fields (mechanical , chemical, electrical), occur at different scales, can
appear as uncertain, and are nonlinear. Interacting with complex materials thus
calls for developing nonlinear computational approaches where multi-scale
techniques that grasp key phenomena at the relevant scale need to be mingled
with stochastic methods accounting for uncertainties. In this chapter, we
develop such a computational approach for modeling the mechanical response of a
representative volume of concrete in uniaxial cyclic loading. A mesoscale is
defined such that it represents an equivalent heterogeneous medium: nonlinear
local response is modeled in the framework of Thermodynamics with Internal
Variables; spatial variability of the local response is represented by
correlated random vector fields generated with the Spectral Representation
Method. Macroscale response is recovered through standard ho-mogenization
procedure from Micromechanics and shows salient features of the uniaxial cyclic
response of concrete that are not explicitly modeled at mesoscale.Comment: Computational Methods for Solids and Fluids, 41, Springer
International Publishing, pp.123-160, 2016, Computational Methods in Applied
Sciences, 978-3-319-27994-
Charge-radius change and nuclear moments in the heavy tin isotopes from laser spectroscopy: Charge radius of Sn
NESTER ACCLaser spectroscopy measurements have been carried out on the neutron-rich tin isotopes with the COMPLIS experimental setup. Using the optical transition, hyperfine spectra of Sn and were recorded for the first time. The nuclear moments and the mean square charge radius variation (\delta, the absolute charge radii of these isotopes were deduced in particular that of the doubly magic Sn nucleus. The comparison of the results with several mean-field-type calculations have shown that dynamical effects play an important role in the tin isotopes
Release properties of UC and molten U targets
The release properties of UC and molten U thick targets associated with a Nier- Bernas ion source have been studied. Two experimental methods are used to extract the release time. Results are presented and discussed for Kr, Cd, I and Xe
High yield of surveillance in patients diagnosed with constitutional mismatch repair deficiency
BackgroundConstitutional mismatch repair deficiency (CMMRD) is a rare autosomal recessively inherited syndrome that is caused by biallelic pathogenic variants of the mismatch repair genes. It is characterised by the development of multiple tumours in the first and second decade of life including brain, gastrointestinal and haematological tumours often resulting in early death. In order to improve the prognosis of these patients, the European collaborative group 'care for CMMRD' developed a surveillance programme in 2014 and established a registry of patients with CMMRD in Paris. The aim of the study was to evaluate the outcome of this programme. MethodsTwenty-two patients with a definitive diagnosis of CMMRD and with at least one follow-up study were selected from the registry. Medical data on the outcome of surveillance were collected from these patients. ResultsDuring a mean follow-up of 4 years, the programme detected eight malignant tumours including three brain tumours, three upper gastrointestinal cancers and two colorectal cancers. Most tumours could successfully be treated. In addition, many adenomas were detected in the duodenum, and colorectum and subsequently removed. Seven patients developed a symptomatic malignancy, including two brain tumours, one small bowel cancer and four haematological malignancies. At the end of the follow-up, 16 out of 22 patients (73%) who participated in the surveillance programme were still alive. ConclusionThe study suggests a beneficial effect of surveillance of the digestive tract and brains.Cellular mechanisms in basic and clinical gastroenterology and hepatolog
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