Full Wave Logging In An Irregular Borehole

We present a boundary integral equation formulation for the problem of wave propagation in a borehole of irregular cross-section. The method consists in representing the wave field diffracted at the borehole-rock interface by the radiation from a distribution of surface sources applied along the borehole wall. The wave field in the borehole fluid and in the elastic rock are then expressed using the discrete wavenumber method. The application of the boundary conditions at discretized locations along the borehole wall leads to a linear system of equations. The inversion of this system yields the required source distribution. We have used the method to investigate the effect of changes in borehole diameter on the pressure wave field inside the borehole. The results show that when the change is smooth, the records obtained ahead of the discontinuity location are not affected by its presence. In the case of a steep variation, however, a significant amount of the Stoneley wave energy is reflected. When the borehole diameter is different at the source and at the receiver levels, the microseismograms obtained are somewhat of an average between the ones that would be recorded in boreholes of constant radius equal to the radius at the source and at the receiver. The presence of small-scale fluctuations in borehole diameter reduces the amplitude of the Stoneley wave and decreases its velocity and the pseudo-Rayleigh wave velocity.Massachusetts Institute of Technology. Full Waveform Acoustic Logging ConsortiumSociete Nationale Elf Aquitain

Watershed of a Continuous Function

Special issue on Mathematical Morphology.International audienceThe notion of watershed, used in morphological segmentation, has only a digital definition. In this paper, we propose to extend this definition to the continuous plane. Using this continuous definition, we present the watershed differences with classical edge detectors. We then exhibit a metric in the plane for which the watershed is a skeleton by influence zones and show the lower semicontinuous behaviour of the associated skeleton. This theoretical approach suggests an algorithm for solving the eikonal equation: ‖∇ƒ‖ = g. Finally, we end with some new watershed algorithms, which present the advantage of allowing the use of markers and/or anchor points, thus opening the way towards grey-tone skeletons

Economic Orientation and Local Employment Growth in the Living Basins of Market Towns and Small Cities,

An analysis of the way in which the main economic activities combine locally highlights the growing presence in rural employment of economic activities designed to satisfy the needs of local people, activities which constitute the basis of a residential economy. Agriculture and the sectors directly linked to it are now relatively insignificant and have been overtaken by the industrial sectors. Thus, while in 1980 only a third of the living basins centred around a market town or small city had more residential jobs than agricultural and industrial jobs, in 1999 more than half were in this position. During the period, basins with a residential economy experienced more favourable economic development than basins with a more industrial or agricultural character. Furthermore, all other things being equal, employment growth was more marked in basins close to large urban centres, the local demographic dynamic having a positive influence on the development of economic activity.Industry Location, Local Employment Dynamics, Rural Development

Datation des calcites et des grès de Fontainebleau : une remise à plat de l'âge des silicifications des terrains tertiaires du Bassin.de Paris

National audienceLa mise en lumière du rôle des périodes froides dans les mécanismes de précipitation de la silice permet de proposer un modèle de silicification unique, homogène et cohérent pour toutes les silicifications du Bassin de Paris : grès, calcaires silicifiés et meumières. Ce modèle doit être envisagé bien au-delà du Bassin de Paris, nombre de silicifications des formations tertiaires d’Europe, d’Amérique du nord et de régions altitudinales plus méridionales ( ?) méritent d’être revisitées avec un œil neuf

Optimal Hemodialysis Prescription: Do Children Need More Than a Urea Dialysis Dose?

When prescribing hemodialysis in children, the clinician should first establish an adequate regimen, before seeking to optimize the treatment (Fischbach et al. 2005). A complete dialysis dose should consist of a urea dialysis dose and a determined convective volume. Intensified and more frequent dialysis regimens should not be considered exclusively as rescue therapy. Interestingly, a recent single-center study demonstrated that frequent on-line HDF provides an optimal dialysis prescription, both in terms of blood pressure control (and therefore avoidance of left ventricular hypertrophy), and catch-up growth, that is, no malnutrition or cachexia and less resistance to growth hormone. Nevertheless, this one-center experience would benefit from a prospective randomized study