VLBI measurement of the secular aberration drift

While analyzing decades of very long baseline interferometry (VLBI) data, we detected the secular aberration drift of the extragalatic radio source proper motions caused by the rotation of the Solar System barycenter around the Galactic center. Our results agree with the predicted estimate to be 4-6 micro arcseconds per year ({\mu}as/yr) towards {\alpha} = 266\circ and {\delta} = -29\circ. In addition, we tried to detect the quadrupole systematics of the velocity field. The analysis method consisted of three steps. First, we analyzed geodetic and astrometric VLBI data to produce radio source coordinate time series. Second, we fitted proper motions of 555 sources with long observational histories over the period 1990-2010 to their respective coordinate time series. Finally, we fitted vector spherical harmonic components of degrees 1 and 2 to the proper motion field. Within the error bars, the magnitude and the direction of the dipole component agree with predictions. The dipole vector has an amplitude of 6.4 \pm 1.5 {\mu}as/yr and is directed towards equatorial coordinates {\alpha} = 263\circ and {\delta} = -20\circ. The quadrupole component has not been detected. The primordial gravitational wave density, integrated over a range of frequencies less than 10-9 Hz, has a limit of 0.0042 h-2 where h is the normalized Hubble constant is H0/(100 km s-1)

Secular Aberration Drift and IAU Definition of ICRS

The gravitational attraction of the Galactic centre leads to the centrifugal acceleration of the Solar system barycentre. It results in secular aberration drift which displaces the position of the distant radio sources. The effect should be accounted for in high-precision astrometric reductions as well as by the corresponding update of the ICRS definition.Comment: 6 page

Estimation of the strain field from full-field displacement noisy data. Comparing finite elements global least squares and polynomial diffuse approximation

International audienceIn this study, the issue of reconstructing strain fields from corrupted full-field displacement data is addressed. Two approaches are proposed, a global one based on Finite Element Approximation (FEA) and a local one based on Diffuse Approximation (DA). Both approaches are compared on a case study which is supposed difficult (open-hole tensile test). DA provides more stable results, but is more CPU time consuming. Eventually, it is proposed to monitor locally the filtering effect of both approaches, the prospects being an impending improvement of the reconstruction for both approaches

Sources documentaires et histoire administrative de l’Orient romain tardif, ive‑viie siècles

Programme de l’année 2010-2011 : I. Inscriptions de l’Antiquité tardive (suite). — II. Recherches sur les Novelles de Justin II

Sources documentaires et histoire administrative de l’Orient romain tardif, ive-viie siècles

Programme de l’année 2007-2008 : I. Inscriptions de l’Antiquité tardive. — II. Forums impériaux, colonnes et statues de Constantinople. — III. Recherches sur les Novelles de Justinien (suite)

Sources documentaires et histoire administrative de l’Orient romain tardif, ive-viie siècles

Programme de l’année 2006-2007 : I. Inscriptions de l’Antiquité tardive.— II. Recherches sur les Novelles de Justinien (suite)

Sources documentaires et histoire administrative de l’orient romain tardif, ive-viie siècles

Programme de l’année 2008-2009 : I. Documents pour l’histoire des institutions municipales au VIe siècle. — II. Recherches sur les Novelles de Justinien (suite)

Sources documentaires et histoire administrative de l’Orient romain tardif, ive‑viie siècles

Programme de l’année 2010-2011 : I. Inscriptions de l’Antiquité tardive (suite). — II. Recherches sur les Novelles de Justin II