3,590 research outputs found
On the scattering length of the K^- d system
Multiple-scattering approximations to Faddeev calculations of the K^- d
scattering length are reviewed and compared with published Kbar-N-N pi-Y-N
fully reactive Faddeev calculations. A new multiple-scattering approximation
which goes beyond the `fixed-center' assumption for the nucleons is proposed,
aiming at accuracies of 5-10%. A precise value of the K^- d scattering length
from the measurement of the K^- d 1s atomic level shift and width, planned by
the DEAR/SIDDHARTA collaboration, plus a precise value for the K^- p scattering
length by improving the K^- p atom measurements, are essential for extracting
the K^- n scattering length, for resolving persistent puzzles in low-energy
Kbar-N phenomenology and for extrapolating into Kbar-nuclear systems.Comment: Invited talk at MESON 2006, Krakow, June 2006. To be published in
International Journal of Modern Physics A. Requires use of ws-ijmpa.cl
Kleinberg Navigation in Fractal Small World Networks
We study the Kleinberg problem of navigation in Small World networks when the
underlying lattice is a fractal consisting of N>>1 nodes. Our extensive
numerical simulations confirm the prediction that most efficient navigation is
attained when the length r of long-range links is taken from the distribution
P(r)~r^{-alpha}, where alpha=d_f, the fractal dimension of the underlying
lattice. We find finite-size corrections to the exponent alpha, proportional to
1/(ln N)^2
Designer Nets from Local Strategies
We propose a local strategy for constructing scale-free networks of arbitrary
degree distributions, based on the redirection method of Krapivsky and Redner
[Phys. Rev. E 63, 066123 (2001)]. Our method includes a set of external
parameters that can be tuned at will to match detailed behavior at small degree
k, in addition to the scale-free power-law tail signature at large k. The
choice of parameters determines other network characteristics, such as the
degree of clustering. The method is local in that addition of a new node
requires knowledge of only the immediate environs of the (randomly selected)
node to which it is attached. (Global strategies require information on finite
fractions of the growing net.
Real-time dynamics in Quantum Impurity Systems: A Time-dependent Numerical Renormalization Group Approach
We develop a general approach to the nonequilibrium dynamics of quantum
impurity systems for arbitrary coupling strength. The numerical renormalization
group is used to generate a complete basis set necessary for the correct
description of the time evolution. We benchmark our method with the exact
analytical solution for the resonant-level model. As a first application, we
investigate the equilibration of a quantum dot subject to a sudden change of
the gate voltage and external magnetic field. Two distinct relaxation times are
identified for the spin and charge dynamics.Comment: 5 pages, 5 figure
The scientific heritage of Richard Henry Dalitz, FRS (1925-2006)
Professor Richard H. Dalitz passed away on January 13, 2006. He was almost 81
years old and his outstanding contributions are intimately connected to some of
the major breakthroughs of the 20th century in particle and nuclear physics.
These outstanding contributions go beyond the Dalitz Plot, Dalitz Pair and CDD
poles that bear his name. He pioneered the theoretical study of strange baryon
resonances, of baryon spectroscopy in the quark model, and of hypernuclei, to
all of which he made lasting contributions. His formulation of the
" puzzle" led to the discovery that parity is not a symmetry of
the weak interactions. A brief scientific evaluation of Dalitz's major
contributions to particle and nuclear physics is hereby presented, followed by
the first comprehensive list of his scientific publications, as assembled from
several sources. The list is divided into two categories: the first, main part
comprises Dalitz's research papers and reviews, including topics in the history
of particle physics, biographies and reminiscences; the second part lists book
reviews, public lectures and obituaries authored by Dalitz, and books edited by
him. This provides the first necessary step towards a more systematic research
of the Dalitz heritage in modern physics.
The present 2016 edition updates the original 2006 edition, published in
Nucl. Phys. A 771 (2006) 2-7, doi:10.1016/j.nuclphysa.2006.03.007, and 8-25,
doi:10.1016/j.nuclphysa.2006.03.008, by including for the first time a dozen or
so of publications, found recently in a list submitted to the Royal Society by
Dalitz in 2004, that escaped our attention in the original version.Comment: updates the original edition by including several publications,
mostly in category III, that were unknown to us in 200
Diffusion-Limited Coalescence with Finite Reaction Rates in One Dimension
We study the diffusion-limited process in one dimension, with
finite reaction rates. We develop an approximation scheme based on the method
of Inter-Particle Distribution Functions (IPDF), which was formerly used for
the exact solution of the same process with infinite reaction rate. The
approximation becomes exact in the very early time regime (or the
reaction-controlled limit) and in the long time (diffusion-controlled)
asymptotic limit. For the intermediate time regime, we obtain a simple
interpolative behavior between these two limits. We also study the coalescence
process (with finite reaction rates) with the back reaction , and in
the presence of particle input. In each of these cases the system reaches a
non-trivial steady state with a finite concentration of particles. Theoretical
predictions for the concentration time dependence and for the IPDF are compared
to computer simulations. P. A. C. S. Numbers: 82.20.Mj 02.50.+s 05.40.+j
05.70.LnComment: 13 pages (and 4 figures), plain TeX, SISSA-94-0
Percolation in Hierarchical Scale-Free Nets
We study the percolation phase transition in hierarchical scale-free nets.
Depending on the method of construction, the nets can be fractal or small-world
(the diameter grows either algebraically or logarithmically with the net size),
assortative or disassortative (a measure of the tendency of like-degree nodes
to be connected to one another), or possess various degrees of clustering. The
percolation phase transition can be analyzed exactly in all these cases, due to
the self-similar structure of the hierarchical nets. We find different types of
criticality, illustrating the crucial effect of other structural properties
besides the scale-free degree distribution of the nets.Comment: 9 Pages, 11 figures. References added and minor corrections to
manuscript. In pres
Facilitated diffusion of proteins on chromatin
We present a theoretical model of facilitated diffusion of proteins in the
cell nucleus. This model, which takes into account the successive
binding/unbinding events of proteins to DNA, relies on a fractal description of
the chromatin which has been recently evidenced experimentally. Facilitated
diffusion is shown quantitatively to be favorable for a fast localization of a
target locus by a transcription factor, and even to enable the minimization of
the search time by tuning the affinity of the transcription factor with DNA.
This study shows the robustness of the facilitated diffusion mechanism, invoked
so far only for linear conformations of DNA.Comment: 4 pages, 4 figures, accepted versio
A Method of Intervals for the Study of Diffusion-Limited Annihilation, A + A --> 0
We introduce a method of intervals for the analysis of diffusion-limited
annihilation, A+A -> 0, on the line. The method leads to manageable diffusion
equations whose interpretation is intuitively clear. As an example, we treat
the following cases: (a) annihilation in the infinite line and in infinite
(discrete) chains; (b) annihilation with input of single particles, adjacent
particle pairs, and particle pairs separated by a given distance; (c)
annihilation, A+A -> 0, along with the birth reaction A -> 3A, on finite rings,
with and without diffusion.Comment: RevTeX, 13 pages, 4 figures, 1 table. References Added, and some
other minor changes, to conform with final for
Hybrid method for simulating front propagation in reaction-diffusion systems
We study the propagation of pulled fronts in the
microscopic reaction-diffusion process using Monte Carlo (MC) simulations. In
the mean field approximation the process is described by the deterministic
Fisher-Kolmogorov-Petrovsky-Piscounov (FKPP) equation. In particular we
concentrate on the corrections to the deterministic behavior due to the number
of particles per site . By means of a new hybrid simulation scheme, we
manage to reach large macroscopic values of which allows us to show
the importance in the dynamics of microscopic pulled fronts of the interplay of
microscopic fluctuations and their macroscopic relaxation.Comment: 5 pages, 4 figure
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