Limit on Lorentz-Invariance- and CPT-Violating Neutron Spin Interactions Using a 3He-129Xe Comagnetometer

We performed a search for a Lorentz-invariance- and CPT-violating coupling of the 3He and [Formula: see text]Xe nuclear spins to posited background fields. Our experimental approach is to measure the free precession of nuclear spin polarized 3He and [Formula: see text]Xe atoms using SQUIDs as detectors. As the laboratory reference frame rotates with respect to distant stars, we look for a sidereal modulation of the Larmor frequencies of the co-located spin samples. As a result we obtain an upper limit on the equatorial component of the background field [Formula: see text] GeV (68% C.L.). This experiment is currently the most precise test of spin anisotropy due to the excellent long spin-coherence time.

Time-dependent force acting on a particle moving arbitrarily in a rotating flow, at small Reynolds and Taylor numbers

The arbitrary motion of a solid sphere released in a solid-body rotating fluid is investigated theoretically in the limit of small Reynolds and Taylor numbers. The angular velocity of the fluid is assumed to be constant and under the premise that Ta1/2 ≫ Re, the simplicity of the unperturbed flow enables us to calculate analytically the force acting on a particle moving with a harmonic slip velocity (by means of matched asymptotic expansions), when both inertia and unsteady effects are taken into account. Subsequently, these single-frequency results are used in order to determine the temporal expression of the force acting on an arbitrarily moving sphere, since the problem under study is linear. This force is first determined in a co-rotating reference frame and takes the form of two convolution products involving the particle acceleration and the particle velocity. For convenience, the corresponding expression of this force is also derived in the laboratory reference frame, and the particle motion equation obtained is thereafter illustrated by dealing with two practical situations, where unsteady and inertia effects must be taken into account to predict the particle dynamics accurately.

Experimental studies of wakes behind circularly capped bubbles

The wake behind a circularly capped bubble rising in fluids of different viscosity has been experimentally investigated using aspirin powder for flow visualization and high-speed photography synchronized with pressure-time measurements to measure the pressure field. The bubble plus its primary wake with a cusped tail is observed to contain symmetric pressure minima within the primary wake. Adjacent to the boundary wake is a free shear layer which contains large-scale vortices generated near the bubble rim that remain essentially stationary to an observer in the laboratory reference frame. The change in wake geometry and the transition to an ellipsoidal bubble shape as fluid viscosity increases is documented.The airfoil shape of the boundary of the circularly capped bubble and its closed primary wake is modelled using a Joukowski transformation in which the Joukowski constant is adjusted to match the experimental and potential-flow pressures along the bubble cap. The model successfully predicts the frontal pressure field, and the wake size and shape. The Davies & Taylor bubble-cap boundary condition is also verified.

Radial Pump Impeller Measurements Using a Laser Doppler Velocimeter

A shrouded fully transparent radial pump impeller with thin backswept blades has been tested using a laser doppler velocimeter. Two components of the velocity were measured relative to the laboratory reference frame in a plane perpendicular to the axis of rotation. The velocity distribution is presented relative to the blades at different radii and different flow rates over the whole blade passage. The results show that the flow is essentially unsteady and, at low flow rate, highly influenced by viscous effects. A comparison between the experimental data and a potential flow theory shows good agreement at high flow rates.