Review of road surface photometry methods and devices – Proposal for new measurement geometries

Specifications concerning road lighting and photometry of road surfaces were established more than 50 years ago. Road lighting design and road marking visibility were developed for vehicle driving. The observation distance defined by standards corresponds to interurban applications; however, within Europe these areas do not tend to be lit. The objective of the SURFACE project is to propose new geometries for the photometric characterisation of pavements, both adapted to different urban travel modes and new lighting technologies. This article reviews the available guidelines, standards, measuring devices and literature regarding geometries and road lighting applications, and presents the project SURFACE analysis and proposal. The SURFACE consortium recommends adding several new angles for different driving conditions and road users; 2.29 degrees for urban environments and consistency with road marking standard, and 1 degrees for extra-urban environment and consistency with previous geometries. A 5 degrees angle, corresponding to 17-m viewing distance, could be an interesting compromise, suitable for urban driving at low speed, cycling and for scooters. The angles of 10 degrees and 20 degrees are under consideration for describing the boundary between diffuse and specular behaviour

Les pratiques de l’enseignant concepteur instrumentées via les tablettes numériques

International audienc

Local velocity measurements in heterogeneous and time-dependent flows of a micellar solution

We present and discuss the results of pointwise velocity measurements performed on a viscoelastic micellar solution made of cetyltrimethylammonium bromide and sodium salicylate in water, respectively, at the concentrations of 50 and 100 mmol. The sample is contained in a Couette device and subjected to flow in the strain controlled mode. This particular solution shows shear banding and, in a narrow range of shear rates at the right end of the stress plateau, apparent shear thickening occurs. Time-dependent recordings of the shear stress in this range reveal that the flow has become unstable and that large sustained oscillations of the shear stress and of the first normal stresses difference emerge and grow in the flow. Local pointwise velocity measurements clearly reveal a velocity profile typical of shear banding when the imposed shear rate belongs to the plateau, but also important wall slip in the entire range of velocity gradients investigated. In the oscillations regime, the velocity is recorded as a function of time at a fixed point close to the rotor of the Couette device. The time-dependent velocity profile reveals random fluctuations but, from time to time, sharp decreases much larger than the standard deviation are observed. An attempt is made to correlate these strong variations with the stress oscillations and a correlation coefficient r is computed. However, the small value found for the coefficient r does not allow us to draw a final conclusion as concerns the correlation between stress oscillations and velocity fast decreases

Temporal oscillations of the shear stress and scattered light in a shear-banding-shear-thickening micellar solution

The results of optical and rheological experiments performed on a viscoelastic solution (cetyltrimethylammonium bromide + sodium salicylate in water) are reported. The flow curve has a horizontal plateau extending between two critical shear rates characteristic of heterogeneous flows formed by two layers of fluid with different viscosities. These two bands which also have different optical anisotropy are clearly seen by direct observation in polarized light. At the end of the plateau, apparent shear thickening is observed in a narrow range of shear rates; in phase oscillations of the shear stress and of the first normal stress difference are recorded in a shearing device operating under controlled strain. The direct observation of the annular gap of a Couette cell in a direction perpendicular to a plane containing the vorticity shows that the turbidity of the whole sample also undergoes time dependent variations with the same period as the shear stress. However no banding is observed during the oscillations and the flow remains homogeneous

Observation of a finite-time singularity in needle propagation in Hele-Shaw cells

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Observation of a finite-time singularity in needle propagation in Hele-Shaw cells

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Dynamic light scattering from lyotropic lamellar phases subjected to a flow field

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Dynamic light scattering from lyotropic lamellar phases subjected to a flow field

International audienceno abstrac

Bistability in non-Newtonian flow: Rheology of lyotropic liquid crystals

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