2,812 research outputs found
Secondary vortices in swirling flow
Twisted tapes are used to induce swirling flow and improve mixing. The flow
induced by a 180 degree twisted tape with length (pitch) 60 mm and diameter
25.4 mm in a circular pipe was investigated using Laser Doppler Velocimetry
(LDV) measurements. Tangential velocity profiles downstream of the twisted tape
swirler were measured at multiple locations along the pipe axis, across the
horizontal diameter of the pipe. The profiles showed an unexpected transition
along the pipe axis from regular swirling flow to an apparent counter-rotation
near the pipe axis, and then reverting back to regular swirling flow. Injecting
fine air bubbles into the flow showed the existence of two co-rotating helical
vortices superimposed over the main swirling flow. The close proximity of the
two co-rotating vortices creates the local reversing flow at the pipe
centerline. The secondary vortices are analyzed with high speed camera videos
and numerical simulations.Comment: 2 videos include
Topological restrictions for circle actions and harmonic morphisms
Let be a compact oriented smooth manifold which admits a smooth circle
action with isolated fixed points which are isolated as singularities as well.
Then all the Pontryagin numbers of are zero and its Euler number is
nonnegative and even. In particular, has signature zero. Since a
non-constant harmonic morphism with one-dimensional fibres gives rise to a
circle action we have the following applications: (i) many compact manifolds,
for example , surfaces, () where
is the closed surface of genus can never be the domain of a
non-constant harmonic morphism with one-dimensional fibres whatever metrics we
put on them; (ii) let be a compact orientable four-manifold and
a non-constant harmonic morphism. Suppose that one of
the following assertions holds: (1) is half-conformally flat and its
scalar curvature is zero, (2) is Einstein and half-conformally flat,
(3) is Hermitian-Einstein. Then, up to homotheties and Riemannian
coverings, is the canonical projection between flat tori.Comment: 18 pages; Minor corrections to Proposition 3.1 and small changes in
Theorem 2.8, proof of Theorem 3.3 and Remark 3.
Quantum States of Neutrons in Magnetic Thin Films
We have studied experimentally and theoretically the interaction of polarized
neutrons with magnetic thin films and magnetic multilayers. In particular, we
have analyzed the behavior of the critical edges for total external reflection
in both cases. For a single film we have observed experimentally and
theoretically a simple behavior: the critical edges remain fixed and the
intensity varies according to the angle between the polarization axis and the
magnetization vector inside the film. For the multilayer case we find that the
critical edges for spin up and spin down polarized neutrons move towards each
other as a function of the angle between the magnetization vectors in adjacent
ferromagnetic films. Although the results for multilayers and single thick
layers appear to be different, in fact the same spinor method explains both
results. An interpretation of the critical edges behavior for the multilyers as
a superposition of ferromagnetic and antifferomagnetic states is given.Comment: 6 pages, 5 figure
SQCD Vacua and Geometrical Engineering
We consider the geometrical engineering constructions for the N = 1 SQCD
vacua recently proposed by Giveon and Kutasov. After one T-duality, the
geometries with wrapped D5 branes become N = 1 brane configurations with NS
branes and D4 branes. The field theories encoded by the geometries contain
extra massive adjoint fields for the flavor group. After performing a flop, the
geometries contain branes, antibranes and branes wrapped on non-holomorphic
cycles. The various tachyon condensations between pairs of wrapped D5 branes
and anti D5 branes together with deformations of the cycles give rise to a
variety of supersymmetric and metastable non-supersymmetric vacua.Comment: 21 Pages, Latex, 8 Figure
Training Induced Positive Exchange Bias in NiFe/IrMn Bilayers
Positive exchange bias has been observed in the
NiFe/IrMn bilayer system via soft x-ray resonant
magnetic scattering. After field cooling of the system through the blocking
temperature of the antiferromagnet, an initial conventional negative exchange
bias is removed after training i. e. successive magnetization reversals,
resulting in a positive exchange bias for a temperature range down to 30 K
below the blocking temperature (450 K). This new manifestation of magnetic
training is discussed in terms of metastable magnetic disorder at the
magnetically frustrated interface during magnetization reversal.Comment: 4 pages, 3 figure
Neutron resonances in planar waveguides
Results of experimental investigations of a neutron resonances width in
planar waveguides using the time-of-flight reflectometer REMUR of the IBR-2
pulsed reactor are reported and comparison with theoretical calculations is
presented. The intensity of the neutron microbeam emitted from the waveguide
edge was registered as a function of the neutron wavelength and the incident
beam angular divergence. The possible applications of this method for the
investigations of layered nanostructures are discussed
Well-posedness of the fully coupled quasi-static thermo-poro-elastic equations with nonlinear convective transport
This paper is concerned with the analysis of the quasi-static
thermo-poroelastic model. This model is nonlinear and includes thermal effects
compared to the classical quasi-static poroelastic model (also known as Biot's
model). It consists of a momentum balance equation, a mass balance equation,
and an energy balance equation, fully coupled and nonlinear due to a convective
transport term in the energy balance equation. The aim of this article is to
investigate, in the context of mixed formulations, the existence and uniqueness
of a weak solution to this model problem. The primary variables in these
formulations are the fluid pressure, temperature and elastic displacement as
well as the Darcy flux, heat flux and total stress. The well-posedness of a
linearized formulation is addressed first through the use of a Galerkin method
and suitable a priori estimates. This is used next to study the well-posedness
of an iterative solution procedure for the full nonlinear problem. A
convergence proof for this algorithm is then inferred by a contraction of
successive difference functions of the iterates using suitable norms.Comment: 22 page
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