313 research outputs found
Rain, power laws, and advection
Localized rain events have been found to follow power-law size and duration
distributions over several decades, suggesting parallels between precipitation
and seismic activity [O. Peters et al., PRL 88, 018701 (2002)]. Similar power
laws are generated by treating rain as a passive tracer undergoing advection in
a velocity field generated by a two-dimensional system of point vortices.Comment: 7 pages, 4 figure
Sand stirred by chaotic advection
We study the spatial structure of a granular material, N particles subject to
inelastic mutual collisions, when it is stirred by a bidimensional smooth
chaotic flow. A simple dynamical model is introduced where four different time
scales are explicitly considered: i) the Stokes time, accounting for the
inertia of the particles, ii) the mean collision time among the grains, iii)
the typical time scale of the flow, and iv) the inverse of the Lyapunov
exponent of the chaotic flow, which gives a typical time for the separation of
two initially close parcels of fluid. Depending on the relative values of these
different times a complex scenario appears for the long-time steady spatial
distribution of particles, where clusters of particles may or not appear.Comment: 4 pages, 3 figure
Vortex Images and q-Elementary Functions
In the present paper problem of vortex images in annular domain between two
coaxial cylinders is solved by the q-elementary functions. We show that all
images are determined completely as poles of the q-logarithmic function, where
dimensionless parameter is given by square ratio of the
cylinder radii. Resulting solution for the complex potential is represented in
terms of the Jackson q-exponential function. By composing pairs of q-exponents
to the first Jacobi theta function and conformal mapping to a rectangular
domain we link our solution with result of Johnson and McDonald. We found that
one vortex cannot remain at rest except at the geometric mean distance, but
must orbit the cylinders with constant angular velocity related to q-harmonic
series. Vortex images in two particular geometries in the limit
are studied.Comment: 17 page
Reversal of loss of bone mass in old mice treated with mefloquine
Aging is accompanied by imbalanced bone remodeling, elevated osteocyte apoptosis, and decreased bone mass and mechanical properties; and improved pharmacologic approaches to counteract bone deterioration with aging are needed. We examined herein the effect of mefloquine, a drug used to treat malaria and systemic lupus erythematosus and shown to ameliorate bone loss in glucocorticoid-treated patients, on bone mass and mechanical properties in young and old mice. Young 3.5-month-old and old 21-month-old female C57BL/6 mice received daily injections of 5 mg/kg/day mefloquine for 14 days. Aging resulted in the expected changes in bone volume and mechanical properties. In old mice mefloquine administration reversed the lower vertebral cancellous bone volume and bone formation; and had modest effects on cortical bone volume, thickness, and moment of inertia. Mefloquine administration did not change the levels of the circulating bone formation markers P1NP or alkaline phosphatase, whereas levels of the resorption marker CTX showed trends towards increase with mefloquine treatment. In addition, and as expected, aging bones exhibited an accumulation of active caspase3-expressing osteocytes and higher expression of apoptosis-related genes compared to young mice, which were not altered by mefloquine administration at either age. In young animals, mefloquine induced higher periosteal bone formation, but lower endocortical bone formation. Further, osteoclast numbers were higher on the endocortical bone surface and circulating CTX levels were increased, in mefloquine- compared to vehicle-treated young mice. Consistent with this, addition of mefloquine to bone marrow cells isolated from young mice led to increased osteoclastic gene expression and a tendency towards increased osteoclast numbers in vitro. Taken together our findings identify the age and bone-site specific skeletal effects of mefloquine. Further, our results highlight a beneficial effect of mefloquine administration on vertebral cancellous bone mass in old animals, raising the possibility of using this pharmacologic inhibitor to preserve skeletal health with aging
Computational Method for Phase Space Transport with Applications to Lobe Dynamics and Rate of Escape
Lobe dynamics and escape from a potential well are general frameworks
introduced to study phase space transport in chaotic dynamical systems. While
the former approach studies how regions of phase space are transported by
reducing the flow to a two-dimensional map, the latter approach studies the
phase space structures that lead to critical events by crossing periodic orbit
around saddles. Both of these frameworks require computation with curves
represented by millions of points-computing intersection points between these
curves and area bounded by the segments of these curves-for quantifying the
transport and escape rate. We present a theory for computing these intersection
points and the area bounded between the segments of these curves based on a
classification of the intersection points using equivalence class. We also
present an alternate theory for curves with nontransverse intersections and a
method to increase the density of points on the curves for locating the
intersection points accurately.The numerical implementation of the theory
presented herein is available as an open source software called Lober. We used
this package to demonstrate the application of the theory to lobe dynamics that
arises in fluid mechanics, and rate of escape from a potential well that arises
in ship dynamics.Comment: 33 pages, 17 figure
Smooth-filamental transition of active tracer fields stirred by chaotic advection
The spatial distribution of interacting chemical fields is investigated in
the non-diffusive limit. The evolution of fluid parcels is described by
independent dynamical systems driven by chaotic advection. The distribution can
be filamental or smooth depending on the relative strength of the dispersion
due to chaotic advection and the stability of the chemical dynamics. We give
the condition for the smooth-filamental transition and relate the H\"older
exponent of the filamental structure to the Lyapunov exponents. Theoretical
findings are illustrated by numerical experiments.Comment: 4 pages, 3 figure
Jets, Stickiness and Anomalous Transport
Dynamical and statistical properties of the vortex and passive particle
advection in chaotic flows generated by four and sixteen point vortices are
investigated. General transport properties of these flows are found anomalous
and exhibit a superdiffusive behavior with typical second moment exponent (\mu
\sim 1.75). The origin of this anomaly is traced back to the presence of
coherent structures within the flow, the vortex cores and the region far from
where vortices are located. In the vicinity of these regions stickiness is
observed and the motion of tracers is quasi-ballistic. The chaotic nature of
the underlying flow dictates the choice for thorough analysis of transport
properties. Passive tracer motion is analyzed by measuring the mutual relative
evolution of two nearby tracers. Some tracers travel in each other vicinity for
relatively large times. This is related to an hidden order for the tracers
which we call jets. Jets are localized and found in sticky regions. Their
structure is analyzed and found to be formed of a nested sets of jets within
jets. The analysis of the jet trapping time statistics shows a quantitative
agreement with the observed transport exponent.Comment: 17 pages, 17 figure
O(1/N_f) Corrections to the Thirring Model in 2<d<4
The Thirring model, that is, a relativistic field theory of fermions with a
contact interaction between vector currents, is studied for dimensionalities
2<d<4 using the 1/N_f expansion, where N_f is the number of fermion species.
The model is found to have no ultraviolet divergences at leading order provided
a regularization respecting current conservation is used. Explicit O(1/N_f)
corrections are computed, and the model shown to be renormalizable at this
order in the massless limit; renormalizability appears to hold to all orders
due to a special case of Weinberg's theorem. This implies there is a universal
amplitude for four particle scattering in the asymptotic regime. Comparisons
are made with both the Gross-Neveu model and QED.Comment: 22 pages in plain TeX, with 7 figs included using psfig.tex (Minor
conceptual changes - algebra unaffected
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