24,310 research outputs found
Verifying the mass-metallicity relation in damped Lyman-alpha selected galaxies at 0.1<z<3.2
A scaling relation has recently been suggested to combine the galaxy
mass-metallicity (MZ) relation with metallicities of damped Lyman-alpha systems
(DLAs) in quasar spectra. Based on this relation the stellar masses of the
absorbing galaxies can be predicted. We test this prediction by measuring the
stellar masses of 12 galaxies in confirmed DLA absorber - galaxy pairs in the
redshift range 0.1<z<3.2. We find an excellent agreement between the predicted
and measured stellar masses over three orders of magnitude, and we determine
the average offset = 0.44+/-0.10 between absorption
and emission metallicities. We further test if could depend on the
impact parameter and find a correlation at the 5.5sigma level. The impact
parameter dependence of the metallicity corresponds to an average metallicity
difference of -0.022+/-0.004 dex/kpc. By including this metallicity vs. impact
parameter correlation in the prescription instead of , the scatter
reduces to 0.39 dex in log M*. We provide a prescription how to calculate the
stellar mass (M*,DLA) of the galaxy when both the DLA metallicity and DLA
galaxy impact parameter is known. We demonstrate that DLA galaxies follow the
MZ relation for luminosity-selected galaxies at z=0.7 and z=2.2 when we include
a correction for the correlation between impact parameter and metallicity.Comment: 15 pages, 6 figures. Major revision. Accepted for publication in
MNRA
Transitions in non-conserving models of Self-Organized Criticality
We investigate a random--neighbours version of the two dimensional
non-conserving earthquake model of Olami, Feder and Christensen [Phys. Rev.
Lett. {\bf 68}, 1244 (1992)]. We show both analytically and numerically that
criticality can be expected even in the presence of dissipation. As the
critical level of conservation, , is approached, the cut--off of the
avalanche size distribution scales as . The
transition from non-SOC to SOC behaviour is controlled by the average branching
ratio of an avalanche, which can thus be regarded as an order
parameter of the system. The relevance of the results are discussed in
connection to the nearest-neighbours OFC model (in particular we analyse the
relevance of synchronization in the latter).Comment: 8 pages in latex format; 5 figures available upon reques
Correlations and invariance of seismicity under renormalization-group transformations
The effect of transformations analogous to those of the real-space
renormalization group are analyzed for the temporal occurrence of earthquakes.
The distribution of recurrence times turns out to be invariant under such
transformations, for which the role of the correlations between the magnitudes
and the recurrence times are fundamental. A general form for the distribution
is derived imposing only the self-similarity of the process, which also yields
a scaling relation between the Gutenberg-Richter b-value, the exponent
characterizing the correlations, and the recurrence-time exponent. This
approach puts the study of the structure of seismicity in the context of
critical phenomena.Comment: Short paper. I'll be grateful to get some feedbac
What Fraction of Boron-8 Solar Neutrinos arrive at the Earth as a nu_2 mass eigenstate?
We calculate the fraction of B^8 solar neutrinos that arrive at the Earth as
a nu_2 mass eigenstate as a function of the neutrino energy. Weighting this
fraction with the B^8 neutrino energy spectrum and the energy dependence of the
cross section for the charged current interaction on deuteron with a threshold
on the kinetic energy of the recoil electrons of 5.5 MeV, we find that the
integrated weighted fraction of nu_2's to be 91 \pm 2 % at the 95% CL. This
energy weighting procedure corresponds to the charged current response of the
Sudbury Neutrino Observatory (SNO). We have used SNO's current best fit values
for the solar mass squared difference and the mixing angle, obtained by
combining the data from all solar neutrino experiments and the reactor data
from KamLAND. The uncertainty on the nu_2 fraction comes primarily from the
uncertainty on the solar delta m^2 rather than from the uncertainty on the
solar mixing angle or the Standard Solar Model. Similar results for the
Super-Kamiokande experiment are also given. We extend this analysis to three
neutrinos and discuss how to extract the modulus of the Maki-Nakagawa-Sakata
mixing matrix element U_{e2} as well as place a lower bound on the electron
number density in the solar B^8 neutrino production region.Comment: 23 pages, 8 postscript figures, latex. Dedicated to the memory of
John Bahcall who championed solar neutrinos for many lonely year
PReS-FINAL-2027: Cerebral demyelination and optic neuritis during treatment with eternacept and methotrexate
Boundary effects in a random neighbor model of earthquakes
We introduce spatial inhomogeneities (boundaries) in a random neighbor
version of the Olami, Feder and Christensen model [Phys. Rev. Lett. 68, 1244
(1992)] and study the distributions of avalanches starting both from the bulk
and from the boundaries of the system. Because of their clear geophysical
interpretation, two different boundary conditions have been considered (named
free and open, respectively). In both cases the bulk distribution is described
by the exponent . Boundary distributions are instead
characterized by two different exponents and , for free and open boundary conditions, respectively. These
exponents indicate that the mean-field behavior of this model is correctly
described by a recently proposed inhomogeneous form of critical branching
process.Comment: 6 pages, 2 figures ; to appear on PR
Surfaces Meeting Porous Sets in Positive Measure
Let n>2 and X be a Banach space of dimension strictly greater than n. We show
there exists a directionally porous set P in X for which the set of C^1
surfaces of dimension n meeting P in positive measure is not meager. If X is
separable this leads to a decomposition of X into a countable union of
directionally porous sets and a set which is null on residually many C^1
surfaces of dimension n. This is of interest in the study of certain classes of
null sets used to investigate differentiability of Lipschitz functions on
Banach spaces
The response of thermoluminescence dosimeters to monoenergetic photons of energies between 15 keV and 100 keV
Avoiding convergence in cooperative coevolution with novelty search
Cooperative coevolution is an approach for evolving solutions composed of coadapted components. Previous research
has shown, however, that cooperative coevolutionary algorithms are biased towards stability: they tend to converge
prematurely to equilibrium states, instead of converging to
optimal or near-optimal solutions. In single-population evolutionary algorithms, novelty search has been shown capable of avoiding premature convergence to local optima —
a pathology similar to convergence to equilibrium states.
In this study, we demonstrate how novelty search can be
applied to cooperative coevolution by proposing two new
algorithms. The first algorithm promotes behavioural novelty at the team level (NS-T), while the second promotes
novelty at the individual agent level (NS-I). The proposed
algorithms are evaluated in two popular multiagent tasks:
predator-prey pursuit and keepaway soccer. An analysis
of the explored collaboration space shows that (i) fitnessbased evolution tends to quickly converge to poor equilibrium states, (ii) NS-I almost never reaches any equilibrium
state due to constant change in the individual populations,
while (iii) NS-T explores a variety of equilibrium states in
each evolutionary run and thus significantly outperforms
both fitness-based evolution and NS-I.info:eu-repo/semantics/acceptedVersio
- …