Chromatic coupling in LHC and its correction

The geometrical optical aberrations dominate the dynamic aperture in LHC and were therefore much studied. It turned out however that a large second order chromaticity was observed for some possible configurations of the field errors in the dipoles. It is shown here to be explained by a momentum dependent betatron coupling excited by the skew sextupolar component of the dipole field. This coupling is tune dependent and increases to unacceptable values when the LHC working point is moved towards the diagonal at a position which is operational in existing machines. The numerical results are exactly predicted using canonical perturbation theory. This knowledge is used to design a simple and optimal correction system which consists in tilting some focusing sextupoles in the arcs

Documenting some Uses of the Isidore Platform

The availability of millions of digital resources, and of the means for processing, analysing, signalling, and exposing them, should make it possible to facilitate the emergence of new research objects and new questions. After a brief description of Isidore, this paper proposes first results in observing the Isidore platform because it presents all the basic materials a researcher needs: publications, blogs, websites and conference calendars. Then we discuss how facets proposed by Isidore are currently being used and finally we propose some issues which are being studie

La mesure des angles au BNM-LNE : création d'une nouvelle référence de mesure angulaire

The object of this article is to present the angular reference plate developed by the BNM-LNE. After having presented the angular standards we draw the purposes to reach for an angular reference instrument. The principle of two encoders' errors elimination is presented with the solution carried out to free itself from under sampling defaults inherent to this measuring principle. Presentation of the assessment of uncertainties and its result of a standard uncertainty of ± 0.04" for the measurement of angular polygons are validated by the participation at the comparative survey EUROMET 37

Patient-specific simulation of stent-graft deployment within an abdominal aortic aneurysm

In this study, finite element analysis is used to simulate the surgical deployment procedure of a bifurcated stent-graft on a real patient's arterial geometry. The stent-graft is modeled using realistic constitutive properties for both the stent and most importantly for the graft. The arterial geometry is obtained from pre-operative imaging exam. The obtained results are in good agreement with the post-operative imaging data. As the whole computational time was reduced to less than 2 hours, this study constitutes an essential step towards predictive planning simulations of aneurysmal endovascular surger

Vegetation patch effects on flow resistance at channel scale

International audienceThanks to a specific experimental design in a controlled channel, this paper aimed at quantifying how patches of four different ditches plant species affect integrated flow resistance parameters, the Manning coefficient. These plants, frequently encountered in the farmland ditches and irrigation channels of the south of France, were selected according to a large range of hydrophilic requirements, flexibility and branching complexity related to the plant blockage factor. Eight different spatial patches (regular, random, lateral or central patches) of each plant with crescent or similar plant densities were implanted at the bottom of a controlled channel where the water levels and water velocities were measured for three different discharges in steady and unsteady flow conditions. Resistance parameters (Manning parameters) were then estimated from the total head-loss, or from flow propagation velocity in the channel thanks to inversion of an hydrodynamic model. These experiments allow us to test the significance effect of channel vegetation patches and densities on flow resistance parameters at the reach scale

Ensuring Public Access to Green Spaces in Urban Densification: The Role of Planning and Property Rights

Implementing densification while ensuring green space accessibility is a crucial planning challenge. The powerful role of private for-profit actors densification projects mean that green spaces are at risk of being co-opted by private interests and transformed into club goods. Using a new-institutionalist approach, we analyse the implementation of densification and urban greening based on two case-studies in Switzerland and the Netherlands. We ask what planning strategies are successful in ensuring public access to green spaces in private-led densification. To counteract club formation, planners need to restrict property rights, actively monitor implementation of planning objectives, and ensure an open physical design

Z calibration of the LNE ultra precision coordinate measuring machine

The Laboratoire National de Métrologie et d’Essais (LNE) has developed an innovative ultra precision coordinate measuring machine [1,2] traceable to the national length standard. This machine can be equipped with different kinds of sensors and is dedicated to the measurement with nanometer uncertainties of features, standards and in more general way three-dimensional objects. The measuring range is 300 mm x 300 mm x 50 μm. The objective in term of uncertainty is to reach 30 nm in X and Y directions for a 300 mm displacement and about few nanometers for the 50 μm vertical displacement. For the geometric calibration of this machine, dedicated procedures have been developed. The present paper will focus more specifically on the one used for the Z calibration