Magnetic induction maps in a magnetized spherical Couette flow experiment

The DTS experiment is a spherical Couette flow experiment with an imposed dipolar magnetic field. Liquid sodium is used as a working fluid. In a series of measurement campaigns, we have obtained data on the mean axisymmetric velocity, the mean induced magnetic field and electric potentials. All these quantities are coupled through the induction equation. In particular, a strong omega-eff ect is produced by di fferential rotation within the fluid shell, inducing a significant azimuthal magnetic field. Taking advantage of the simple spherical geometry of the experiment, I expand the azimuthal and meridional fields into Legendre polynomials and derive the expressions that relate all measurements to the radial functions of the velocity field for each harmonic degree. For small magnetic Reynolds numbers Rm the relations are linear, and the azimuthal and meridional equations decouple. Selecting a set of measurements for a given rotation frequency of the inner sphere (Rm = 9.4), I invert simultaneously the velocity and the magnetic data and thus reconstruct both the azimuthal and the meridional fields within the fluid shell. The results demonstrate the good internal consistency of the measurements, and indicate that turbulent non-axisymmetric fluctuations do not contribute significantly to the axisymmetric magnetic induction.Comment: soumis au Comptes Rendus Physiqu

Magnetic induction and diffusion mechanisms in a liquid sodium spherical Couette experiment

We present a reconstruction of the mean axisymmetric azimuthal and meridional flows in the DTS liquid sodium experiment. The experimental device sets a spherical Couette flow enclosed between two concentric spherical shells where the inner sphere holds a strong dipolar magnet, which acts as a magnetic propeller when rotated. Measurements of the mean velocity, mean induced magnetic field and mean electric potentials have been acquired inside and outside the fluid for an inner sphere rotation rate of 9 Hz (Rm 28). Using the induction equation to relate all measured quantities to the mean flow, we develop a nonlinear least square inversion procedure to reconstruct a fully coherent solution of the mean velocity field. We also include in our inversion the response of the fluid layer to the non-axisymmetric time-dependent magnetic field that results from deviations of the imposed magnetic field from an axial dipole. The mean azimuthal velocity field we obtain shows super-rotation in an inner region close to the inner sphere where the Lorentz force dominates, which contrasts with an outer geostrophic region governed by the Coriolis force, but where the magnetic torque remains the driver. The meridional circulation is strongly hindered by the presence of both the Lorentz and the Coriolis forces. Nevertheless, it contributes to a significant part of the induced magnetic energy. Our approach sets the scene for evaluating the contribution of velocity and magnetic fluctuations to the mean magnetic field, a key question for dynamo mechanisms

Couplings in parametrically excited inclined cables systems

Cables in stayed bridges are subjected to important dynamic solicitations for which dynamic model are now well established. Due to their design, such structures highlight resonance phenomena and instabilities frequently observed. Nevertheless, some structures exhibit important vibration amplitudes that can not be explained simply. Measurement recently performed on a bridge point a coupling of the cable with the deck or the pillar. The present paper suggests to consider the deck flexibility coupled to the nonlinear dynamic of the inclined cable. Results of previous study are used. The retained nonlinear model of the cable include two degrees of freedom for the in-plane motion. Considering the bridge mass and deck rigidity adds one DOF, assumed linear in a first approach. The excitation is created on the deck, which produce an external force(such as the wind or the car traffic for example). An experimental set-up uses a specific device in order to highlight expected coupling phenomena on the parametric instabilities. It is composed of a flexible blade which represents the deck, and an inclined cable. Both elements are linked to a mass forced to move vertically, and which represent the anchor point and the equivalent mass of a section of the deck. Therefore, the cable has a given initial static tension. An electrodynamic shaker applies a force close to blade clumping. The transmitted force from the shaker to the structure is measured thanks to a piezo-electric sensor. The instantaneous cable tension is measured via a Shape force sensor. And a high resolution laser sensor captures without contact the in-plane motion of the cable. Analytically, the multiple scales method is applied to solve the nonlinear equations of motion. In-plane vibration of the cable and stability in the vicinity of the primary resonance w1 and sub-harmonic resonance 2w1 are computed. The competition between the behaviour at 2w1 and w2 are of particular interest, as it is observed experimentally

Combinatorial Search for new mixed electronic ionic materials for SOFC Cathode Applications

In order to lower SOFC operating temperature between the range of 500 and 800°C, research has been focussed on finding alternative cathode materials, as it is where the highest area specific resistivity in the ceramic cell is exhibited. There is a constant requirement for novel high performance mixed conducting oxides for a variety of applications including cathodes for solid oxide fuel cells and as oxygen separation membranes. The conventional method of approaching this problem is by synthesising oxide compositions obtained from consideration of crystal structure and chemistry. One consequence of this is that synthesis is limited to a few chosen compositions because of the time consuming nature of the synthesis process. A way round this is the use of combinatorial methods to explore much wider ranges of compositions based upon rational choices of starting compositions. An interdisciplinary project was launched to use an ink jet based robot system, LUSI (London University Search Instrument), in order to synthesise combinatorial arrays of ceramic dot samples (2mm dia 500μm high) suitable for measurement of oxygen transport. More information on the robot and the project can be found on the related project web page www.foxd.org. The aim is to use oxygen 18 isotopic exchange with an array together with high resolution SIMS to identify materials with a high degree of exchange with oxygen gas at a given temperature. The first part of this programme was aimed at producing arrays of materials for which the transport properties are well known and to this end we have started with the perovskite materials with the general formula La1-xSrxCo1-yMnyO3, for which we have enough previous information to verify that the experimental protocols are correct. This study was followed by the study of a less known composition space with the general formula La1-xSrxCo1-y-zMnyFezO3. Quality synthesis of automated ink-jet printed samples has been carried out and composition (Induced Couple Plasma Mass Spectrometry), structure determination (X-ray diffraction and Raman Spectrometry) and oxygen content (Thermogravimetric and Catalysis Temperature-programmed Desorption) have been characterised systematically over the full range of compositions prior to performing the isotopic exchange procedure. Isotopic exchange procedures have been written, and tested on one composition. A new diffusion algorithm has been coded to take into account the shape of the combinatorial samples. Design of a new high-throughput technique has been created and this technique has been tested to identify new SOFC cathode materials. A first systematic study has been carried out over the full range of composition of general formula La1-xSrxCo1-y-zMnyFezO3. An automated production of thick-film perovskites has been achieved to a certain extent: composition, phase and oxygen non stoichiometry have been characterised over the full composition of the La0.8Sr0.2Co1-y-zMnyFezO3 pseudo-ternary solid solution. The isotopic exchange technique has been carried out on the La0.8Sr0.2MnO3 and La0.8Sr0.2CoO3 samples

Hydrodynamics and Metzner-Otto correlation in stirred vessels for yield stress fluids

This paper investigates the hydrodynamics and power consumption in laminar stirred vessel flowusing numerical computation. The Metzner–Otto correlation was established for mixing in power-law fluids. This paper focuses on its application to yield stress fluids. Distributions of shear rates and their link to power consumption for helical and anchor agitators are discussed. Insight is sought from the analytical formula for Taylor–Couette flows. Laws are established for Bingham, Herschel-Bulkley and Casson fluids and reveal similar results. Fully or partially sheared flow situations with plug regions are considered. Depending on the fluid model, the concept is valid or constitutes a satisfactory approximation for fully sheared flows. When the flow is partially sheared, the expression depends on the Bingham number and the concept must be adapted. The results of the numerical simulations are interpreted in the light of this analysis and results from the literature

Phosphate handling by the rat nephron during saline diuresis

Phosphate handling by the rat nephron during saline diuresis. Inorganic phosphate handling by the nephron was investigated using renal micropuncture techniques in fasted rats undergoing sustained saline diuresis and in controls. The early distal and the late accessible proximal convolutions of the same nephron were micropunctured. Despite the presence of decreased fractional volume reabsorption at the end of the proximal tubule during saline diuresis, the tubular fluid to plasma phosphate ratio was unaffected. Fractional phosphate delivery at this site was not significantly higher. Fractional phosphate delivery at the early distal and late proximal segments of the same nephron were significantly correlated in both groups. The slopes of the regression lines were not different. The delivery of phosphate to the early distal tubule, for a given value of delivery from the late proximal, was lower during saline diuresis. Mean fractional phosphate reabsorption between the late proximal and the early distal tubules was twice as high during saline diuresis as in controls. This observation may account for the decreased fractional phosphate excretion in ureteral urine observed in fasting animals. Clearance studies indicated a different behavior between fed and fasted rats undergoing saline diuresis. Fractional phosphate excretion increased in the former and decreased in the latter

Fractal Dimension of Particle Showers Measured in a Highly Granular Calorimeter

We explore the fractal nature of particle showers using Monte-Carlo simulation. We define the fractal dimension of showers measured in a high granularity calorimeter designed for a future lepton collider. The shower fractal dimension reveals detailed information of the spatial configuration of the shower. %the information hidden in the details of shower spatial configuration, It is found to be characteristic of the type of interaction and highly sensitive to the nature of the incident particle. Using the shower fractal dimension, we demonstrate a particle identification algorithm that can efficiently separate electromagnetic showers, hadronic showers and non-showering tracks. We also find a logarithmic dependence of the shower fractal dimension on the particle energy.Comment: 4 pages, 5 figure