2,604 research outputs found
Long-range epidemic spreading in a random environment
Modeling long-range epidemic spreading in a random environment, we consider a
quenched disordered, -dimensional contact process with infection rates
decaying with the distance as . We study the dynamical behavior
of the model at and below the epidemic threshold by a variant of the
strong-disorder renormalization group method and by Monte Carlo simulations in
one and two spatial dimensions. Starting from a single infected site, the
average survival probability is found to decay as up to
multiplicative logarithmic corrections. Below the epidemic threshold, a
Griffiths phase emerges, where the dynamical exponent varies continuously
with the control parameter and tends to as the threshold is
approached. At the threshold, the spatial extension of the infected cluster (in
surviving trials) is found to grow as with a
multiplicative logarithmic correction, and the average number of infected sites
in surviving trials is found to increase as with
in one dimension.Comment: 12 pages, 6 figure
Cross sections of proton-induced reactions on 152Gd, 155Gd and 159Tb with emphasis on the production of selected Tb radionuclides
Cross sections are presented for various Dy, Tb and Gd radionuclides produced in the proton bombardment
of 159Tb as well as for the reactions 152Gd(p,4n)149Tb and 155Gd(p,4n)152Tb up to 66 MeV. The
experimental excitation functions are compared with theoretical predictions by means of the geometrydependent
hybrid (GDH) model as implemented in the code ALICE/ASH, as well as with values from the
TENDL-2012 library and previous literature experimental data, where available. Physical yields have been
derived for the production of some of the medically important radioterbiums, namely 149Tb (radionuclide
therapy), 152Tb (PET) and 155Tb (SPECT). The indirect production of high-purity 155Tb via the decay of
its precursor 155Dy is reported. The possibility of a large-scale production facility based on a commercial
70 MeV cyclotron is also discussed
Universality class of fiber bundles with strong heterogeneities
We study the effect of strong heterogeneities on the fracture of disordered
materials using a fiber bundle model. The bundle is composed of two subsets of
fibers, i.e. a fraction 0<\alpha<1 of fibers is unbreakable, while the
remaining 1-\alpha fraction is characterized by a distribution of breaking
thresholds. Assuming global load sharing, we show analytically that there
exists a critical fraction of the components \alpha_c which separates two
qualitatively different regimes of the system: below \alpha_c the burst size
distribution is a power law with the usual exponent \tau=5/2, while above
\alpha_c the exponent switches to a lower value \tau=9/4 and a cutoff function
occurs with a diverging characteristic size. Analyzing the macroscopic response
of the system we demonstrate that the transition is conditioned to disorder
distributions where the constitutive curve has a single maximum and an
inflexion point defining a novel universality class of breakdown phenomena
Lattice study of the Coleman--Weinberg mass in the SU(2)-Higgs model
Radiative symmetry breaking is a well known phenomenon in perturbation
theory. We study the problem in a non-perturbative framework, i.e. lattice
simulations. The example of the bosonic sector of the SU(2)-Higgs model is
considered. We determine the minimal scalar mass which turns out to be higher
than the mass value given by 1-loop continuum perturbation theory.Comment: Contribution to ICHEP-02, Amsterdam, 24-31 July 2002, 2 pages, 1
figur
Anderson transition and multifractals in the spectrum of the Dirac operator of Quantum Chromodynamics at high temperature
We investigate the Anderson transition found in the spectrum of the Dirac
operator of Quantum Chromodynamics (QCD) at high temperature, studying the
properties of the critical quark eigenfunctions. Applying multifractal
finite-size scaling we determine the critical point and the critical exponent
of the transition, finding agreement with previous results, and with available
results for the unitary Anderson model. We estimate several multifractal
exponents, finding also in this case agreement with a recent determination for
the unitary Anderson model. Our results confirm the presence of a true Anderson
localization-delocalization transition in the spectrum of the quark Dirac
operator at high-temperature, and further support that it belongs to the 3D
unitary Anderson model class.Comment: 10 pages, 6 figure
Anderson localization through Polyakov loops: lattice evidence and Random matrix model
We investigate low-lying fermion modes in SU(2) gauge theory at temperatures
above the phase transition. Both staggered and overlap spectra reveal
transitions from chaotic (random matrix) to integrable (Poissonian) behavior
accompanied by an increasing localization of the eigenmodes. We show that the
latter are trapped by local Polyakov loop fluctuations. Islands of such "wrong"
Polyakov loops can therefore be viewed as defects leading to Anderson
localization in gauge theories. We find strong similarities in the spatial
profile of these localized staggered and overlap eigenmodes. We discuss
possible interpretations of this finding and present a sparse random matrix
model that reproduces these features.Comment: 11 pages, 23 plots in 11 figures; some comments and references added,
some axis labels corrected; journal versio
Comparing the performance of stellar variability filters for the detection of planetary transits
We have developed a new method to improve the transit detection of
Earth-sized planets in front of solar-like stars by fitting stellar
microvariability by means of a spot model. A large Monte Carlo numerical
experiment has been designed to test the performance of our approach in
comparison with other variability filters and fitting techniques for stars of
different magnitudes and planets of different radius and orbital period, as
observed by the space missions CoRoT and Kepler. Here we report on the results
of this experiment.Comment: 4 pages, 3 postscript figures, Transiting Planets Proceeding IAU
Symposium No.253, 200
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