472 research outputs found
Effect of the number of vortices on the torque scaling in Taylor-Couette flow
Torque measurements in Taylor-Couette flow, with large radius ratio and large
aspect ratio, over a range of velocities up to a Reynolds number of 24 000 are
presented. Following a specific procedure, nine states with distinct number of
vortices along the axis were found and the aspect ratio of the vortices were
measured. The relationship between the speed and the torque for a given number
of vortices is reported. In the turbulent Taylor vortex flow regime, at
relatively high Reynolds number, a change in behaviour is observed
corresponding to intersections of the torque-speed curves for different states.
Before each intersection, the torque for a state with larger number of vortices
is higher. After each intersection, the torque for a state with larger number
of vortices is lower. The exponent, from the scaling laws of the torque, always
depends on the aspect ratio of the vortices. When the Reynolds number is
rescaled using the mean aspect ratio of the vortices, only a partial collapse
of the exponent data is found.Comment: 11 pages, 6 figure
Spinors in Higher Dimensional and Locally Anisotropic Spaces
The theory of spinors is developed for locally anisotropic (la) spaces, in
brief la-spaces, which in general are modeled as vector bundles provided with
nonlinear and distinguished connections and metric structures (such la-spaces
contain as particular cases the Lagrange, Finsler and, for trivial nonlinear
connections, Kaluza-Klein spaces). The la-spinor differential geometry is
constructed. The distinguished spinor connections are studied and compared with
similar ones on la-spaces. We derive the la-spinor expressions of curvatures
and torsions and analyze the conditions when the distinguished torsion and
nonmetricity tensors can be generated from distinguished spinor connections.
The dynamical equations for gravitational and matter field la-interactions are
formulated.Comment: 54 pages, Revtex, an extension of the paper published in J. Math.
Phys. 37 (1996), 508--52
Matrix exponential via Clifford algebras
We use isomorphism between matrix algebras and simple orthogonal
Clifford algebras \cl(Q) to compute matrix exponential of a real,
complex, and quaternionic matrix A. The isomorphic image in
\cl(Q), where the quadratic form has a suitable signature is
exponentiated modulo a minimal polynomial of using Clifford exponential.
Elements of \cl(Q) are treated as symbolic multivariate polynomials in
Grassmann monomials. Computations in \cl(Q) are performed with a Maple
package `CLIFFORD'. Three examples of matrix exponentiation are given
Mixing of dust aerosols into a mesoscale convective system: Generation, filtering and possible feedbacks on ice anvils
International audienceDuring the second Specific Observing Period (SOP) of the African Monsoon Multidisplinary Analyses (AMMA) campaign, several intense mesoscale convective systems (MCS) developed over Niger. An examination of a particular convective storm simulated with a mesoscale model near Banizoumbou, Niger, on 1 July, 2006, shows that this MCS generates a strong emission of dust particles at the leading edge of its density current. A fraction of these dust aerosols are uplifted by the convective core of the system and redistributed by aqueous processes. Aerosol impaction scavenging is the main process by which particles are deposited within the mesoscale convective system. However, small particles (smaller than 1 ÎĽm) that are not efficiently scavenged, are able to reach the upper troposphere at a concentration of 6 particles per cm3. This suggests that deep convection over semi-arid regions is able to create its own ice nuclei in high concentrations. This leads to the question: can deep convection over semi-arid regions affect particular ice properties such as ice anvil extension or induce possible feedbacks of dust on precipitation through ice sedimentation
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