782 research outputs found
Scaling Model of Annihilation-Diffusion Kinetics for Charged Particles with Long-Range Interactions
We propose the general scaling model for the diffusio n-annihilation reaction
with long-range power-law i
nteractions. The presented scaling arguments lead to the finding of three
different regimes, dep ending on the space dimensionality d and the long-range
force power e xponent n. The obtained kinetic phase diagram agrees well with
existing simulation data and approximate theoretical results.Comment: RevTEX, 7 pages, no figures, accepted to Physical Review
Spatial Organization in the Reaction A + B --> inert for Particles with a Drift
We describe the spatial structure of particles in the (one dimensional)
two-species annihilation reaction A + B --> 0, where both species have a
uniform drift in the same direction and like species have a hard core
exclusion. For the case of equal initial concentration, at long times, there
are three relevant length scales: the typical distance between similar
(neighboring) particles, the typical distance between dissimilar (neighboring)
particles, and the typical size of a cluster of one type of particles. These
length scales are found to be generically different than that found for
particles without a drift.Comment: 10 pp of gzipped uuencoded postscrip
Asymptotic behavior of A + B --> inert for particles with a drift
We consider the asymptotic behavior of the (one dimensional) two-species
annihilation reaction A + B --> 0, where both species have a uniform drift in
the same direction and like species have a hard core exclusion. Extensive
numerical simulations show that starting with an initially random distribution
of A's and B's at equal concentration the density decays like t^{-1/3} for long
times. This process is thus in a different universality class from the cases
without drift or with drift in different directions for the different species.Comment: LaTeX, 6pp including 3 figures in LaTeX picture mod
A Novel Approach for Ellipsoidal Outer-Approximation of the Intersection Region of Ellipses in the Plane
In this paper, a novel technique for tight outer-approximation of the
intersection region of a finite number of ellipses in 2-dimensional (2D) space
is proposed. First, the vertices of a tight polygon that contains the convex
intersection of the ellipses are found in an efficient manner. To do so, the
intersection points of the ellipses that fall on the boundary of the
intersection region are determined, and a set of points is generated on the
elliptic arcs connecting every two neighbouring intersection points. By finding
the tangent lines to the ellipses at the extended set of points, a set of
half-planes is obtained, whose intersection forms a polygon. To find the
polygon more efficiently, the points are given an order and the intersection of
the half-planes corresponding to every two neighbouring points is calculated.
If the polygon is convex and bounded, these calculated points together with the
initially obtained intersection points will form its vertices. If the polygon
is non-convex or unbounded, we can detect this situation and then generate
additional discrete points only on the elliptical arc segment causing the
issue, and restart the algorithm to obtain a bounded and convex polygon.
Finally, the smallest area ellipse that contains the vertices of the polygon is
obtained by solving a convex optimization problem. Through numerical
experiments, it is illustrated that the proposed technique returns a tighter
outer-approximation of the intersection of multiple ellipses, compared to
conventional techniques, with only slightly higher computational cost
Ellipsometric measurements by use of photon pairs generated by spontaneous parametric down-conversion
We present a novel interferometric technique for performing ellipsometric
measurements. This technique relies on the use of a non-classical optical
source, namely, polarization-entangled twin photons generated by spontaneous
parametric down-conversion from a nonlinear crystal, in conjunction with a
coincidence-detection scheme. Ellipsometric measurements acquired with this
scheme are absolute; i.e., they do not require source and detector calibration.Comment: 10 pages, accepted for publication in Optics Letter
Wheat-derived arabinoxylan oligosaccharides with prebiotic effect increase satietogenic gut peptides and reduce metabolic endotoxemia in diet-induced obese mice
BACKGROUND: Alterations in the composition of gut microbiota -known as dysbiosis- have been proposed to contribute to the development of obesity, thereby supporting the potential interest of nutrients acting on the gut microbes to produce beneficial effect on host energetic metabolism. Non-digestible fermentable carbohydrates present in cereals may be interesting nutrients able to influence the gut microbiota composition.OBJECTIVE AND DESIGN: The aim of the present study was to test the prebiotic potency of arabinoxylan oligosaccharides (AXOS) prepared from wheat bran in a nutritional model of obesity, associated with a low-grade chronic systemic inflammation. Mice were fed either a control diet or a high fat (HF) diet, or a HF diet supplemented with AXOS during 8 weeks.RESULTS: AXOS supplementation induced caecal and colon enlargement associated with an important bifidogenic effect. It increased the level of circulating satietogenic peptides produced by the colon (peptide YY and glucagon-like peptide-1), and coherently counteracted HF-induced body weight gain and fat mass development. HF-induced hyperinsulinemia and the Homeostasis Model Assessment of insulin resistance were decreased upon AXOS feeding. In addition, AXOS reduced HF-induced metabolic endotoxemia, macrophage infiltration (mRNA of F4/80) in the adipose tissue and interleukin 6 (IL6) in the plasma. The tight junction proteins (zonula occludens 1 and claudin 3) altered upon HF feeding were upregulated by AXOS treatment suggesting that the lower inflammatory tone was associated with the improvement of gut barrier function.CONCLUSION: Together, these findings suggest that specific non-digestible carbohydrates produced from cereals such as AXOS constitute a promising prebiotic nutrient in the control of obesity and related metabolic disorders.</p
Self-Consistent Model of Annihilation-Diffusion Reaction with Long-Range Interactions
We introduce coarse-grained hydrodynamic equations of motion for
diffusion-annihilation system with a power-law long-range interaction. By
taking into account fluctuations of the conserved order parameter - charge
density - we derive an analytically solvable approximation for the nonconserved
order parameter - total particle density. Asymptotic solutions are obtained for
the case of random Gaussian initial conditions and for system dimensionality . Large-t, intermediate-t and small-t asymptotics were calculated and
compared with existing scaling theories, exact results and simulation data.Comment: 22 pages, RevTEX, 1 PostScript figur
Heavy Dynamical Fermions in Lattice QCD
It is expected that the only effect of heavy dynamical fermions in QCD is to
renormalize the gauge coupling. We derive a simple expression for the shift in
the gauge coupling induced by flavors of heavy fermions. We compare this
formula to the shift in the gauge coupling at which the
confinement-deconfinement phase transition occurs (at fixed lattice size) from
numerical simulations as a function of quark mass and . We find remarkable
agreement with our expression down to a fairly light quark mass. However,
simulations with eight heavy flavors and two light flavors show that the eight
flavors do more than just shift the gauge coupling. We observe
confinement-deconfinement transitions at induced by a large number of
heavy quarks. We comment on the relevance of our results to contemporary
simulations of QCD which include dynamical fermions.Comment: COLO-HEP-311, 26 pages and 6 postscript figures; file is a shar file
and all macros are (hopefully) include
Reaction Diffusion and Ballistic Annihilation Near an Impenetrable Boundary
The behavior of the single-species reaction process is examined
near an impenetrable boundary, representing the flask containing the reactants.
Two types of dynamics are considered for the reactants: diffusive and ballistic
propagation. It is shown that the effect of the boundary is quite different in
both cases: diffusion-reaction leads to a density excess, whereas ballistic
annihilation exhibits a density deficit, and in both cases the effect is not
localized at the boundary but penetrates into the system. The field-theoretic
renormalization group is used to obtain the universal properties of the density
excess in two dimensions and below for the reaction-diffusion system. In one
dimension the excess decays with the same exponent as the bulk and is found by
an exact solution. In two dimensions the excess is marginally less relevant
than the bulk decay and the density profile is again found exactly for late
times from the RG-improved field theory. The results obtained for the diffusive
case are relevant for Mg or Cd doping in the TMMC crystal's
exciton coalescence process and also imply a surprising result for the dynamic
magnetization in the critical one-dimensional Ising model with a fixed spin.
For the case of ballistic reactants, a model is introduced and solved exactly
in one dimension. The density-deficit profile is obtained, as is the density of
left and right moving reactants near the impenetrable boundary.Comment: to appear in J. Phys.
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