11,239 research outputs found
Addendum to "Coherent Lagrangian vortices: The black holes of turbulence"
In Haller and Beron-Vera (2013) we developed a variational principle for the
detection of coherent Lagrangian vortex boundaries. The solutions of this
variational principle turn out to be closed null-geodesics of the Lorentzian
metric associated with a generalized Green-Lagrange strain tensor family. This
metric interpretation implies a mathematical analogy between coherent
Lagrangian vortex boundaries and photon spheres in general relativity. Here we
give an improved discussion on this analogy.Comment: Revised 27 June 201
Closing the Sanitation Gap: The Case for Better Public Funding of Sanitation and Hygiene
Slow progress is being made towards the achievement of the Millennium Development Goal for sanitation despite the fact that investments in sanitation have significant health, educational and economic benefits. More action is needed to improve the quality and accountability of service delivery. This report presents and summarises all the latest information on benefits and costs of sanitation and lays out proposals for government and donor action to address the problem
Coherent Lagrangian vortices: The black holes of turbulence
We introduce a simple variational principle for coherent material vortices in
two-dimensional turbulence. Vortex boundaries are sought as closed stationary
curves of the averaged Lagrangian strain. Solutions to this problem turn out to
be mathematically equivalent to photon spheres around black holes in cosmology.
The fluidic photon spheres satisfy explicit differential equations whose
outermost limit cycles are optimal Lagrangian vortex boundaries. As an
application, we uncover super-coherent material eddies in the South Atlantic,
which yield specific Lagrangian transport estimates for Agulhas rings.Comment: To appear in JFM Rapid
Response of St. Augustinegrass to Fluridone in Irrigation Water
Research has shown that aquatic weeds, particularly hydrilla
(
Hydrilla verticillata
, (L.F.) Royle), can be controlled with
exposure of 8 to 12 weeks with concentrations of 10 to 15
ppb of fluridone (1-methyl-3-phenyl-5-[3-trifluoromethyl)
phenyl]-4(1
H
)- pyridinone) (Haller et al. 1990 and Fox et
al. 1994). Fluridone label recommendations restrict the use
of the treated waters for irrigation of turf or newly seeded
crops and seed beds for 30 days following the last application
of the herbicide. The objective of this
research was to determine the effects of 10 weeks of irrigation
with fluridone containing water on a common Florida
residential turfgrass
Precision Measurements of Stretching and Compression in Fluid Mixing
The mixing of an impurity into a flowing fluid is an important process in
many areas of science, including geophysical processes, chemical reactors, and
microfluidic devices. In some cases, for example periodic flows, the concepts
of nonlinear dynamics provide a deep theoretical basis for understanding
mixing. Unfortunately, the building blocks of this theory, i.e. the fixed
points and invariant manifolds of the associated Poincare map, have remained
inaccessible to direct experimental study, thus limiting the insight that could
be obtained. Using precision measurements of tracer particle trajectories in a
two-dimensional fluid flow producing chaotic mixing, we directly measure the
time-dependent stretching and compression fields. These quantities, previously
available only numerically, attain local maxima along lines coinciding with the
stable and unstable manifolds, thus revealing the dynamical structures that
control mixing. Contours or level sets of a passive impurity field are found to
be aligned parallel to the lines of large compression (unstable manifolds) at
each instant. This connection appears to persist as the onset of turbulence is
approached.Comment: 5 pages, 5 figure
Quantum Gauge Equivalence in QED
We discuss gauge transformations in QED coupled to a charged spinor field,
and examine whether we can gauge-transform the entire formulation of the theory
from one gauge to another, so that not only the gauge and spinor fields, but
also the forms of the operator-valued Hamiltonians are transformed. The
discussion includes the covariant gauge, in which the gauge condition and
Gauss's law are not primary constraints on operator-valued quantities; it also
includes the Coulomb gauge, and the spatial axial gauge, in which the
constraints are imposed on operator-valued fields by applying the
Dirac-Bergmann procedure. We show how to transform the covariant, Coulomb and
spatial axial gauges to what we call
``common form,'' in which all particle excitation modes have identical
properties. We also show that, once that common form has been reached, QED in
different gauges has a common time-evolution operator that defines
time-translation for states that represent systems of electrons and photons.
By combining gauge transformations with changes of representation from
standard to common form, the entire apparatus of a gauge theory can be
transformed from one gauge to another.Comment: Contribution for a special issue of Foundations of Physics honoring
Fritz Rohrlich; edited by Larry P. Horwitz, Tel-Aviv University, and Alwyn
van der Merwe, University of Denver (Plenum Publishing, New York); 40 pages,
REVTEX, Preprint UCONN-93-3, 1 figure available upon request from author
Analysis of low-temperature direct-condensing vapor-chamber fin and conducting fin radiators
Analysis of flat, direct-condensing finned-tube space radiator with vapor chamber, and central fin tube geometries for low temperature Rankine space power electric generating syste
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