5,133 research outputs found
Sobre el género Gratiola L. (Scrophulariaceae) en el norte de Marruecos y Andalucía.
La preparación de las síntesis del género Gratiola para Flora iberica y BIOGEO ha propiciado la consulta y revisión de materiales del herbario marroquíes, andaluces y de otras procedencias
Dynamics and Kinetic Roughening of Interfaces in Two-Dimensional Forced Wetting
We consider the dynamics and kinetic roughening of wetting fronts in the case
of forced wetting driven by a constant mass flux into a 2D disordered medium.
We employ a coarse-grained phase field model with local conservation of
density, which has been developed earlier for spontaneous imbibition driven by
a capillary forces. The forced flow creates interfaces that propagate at a
constant average velocity. We first derive a linearized equation of motion for
the interface fluctuations using projection methods. From this we extract a
time-independent crossover length , which separates two regimes of
dissipative behavior and governs the kinetic roughening of the interfaces by
giving an upper cutoff for the extent of the fluctuations. By numerically
integrating the phase field model, we find that the interfaces are superrough
with a roughness exponent of , a growth exponent of
, and as a function of the
velocity. These results are in good agreement with recent experiments on
Hele-Shaw cells. We also make a direct numerical comparison between the
solutions of the full phase field model and the corresponding linearized
interface equation. Good agreement is found in spatial correlations, while the
temporal correlations in the two models are somewhat different.Comment: 9 pages, 4 figures, submitted to Eur.Phys.J.
Remarks on Bootstrap Percolation in Metric Networks
We examine bootstrap percolation in d-dimensional, directed metric graphs in
the context of recent measurements of firing dynamics in 2D neuronal cultures.
There are two regimes, depending on the graph size N. Large metric graphs are
ignited by the occurrence of critical nuclei, which initially occupy an
infinitesimal fraction, f_* -> 0, of the graph and then explode throughout a
finite fraction. Smaller metric graphs are effectively random in the sense that
their ignition requires the initial ignition of a finite, unlocalized fraction
of the graph, f_* >0. The crossover between the two regimes is at a size N_*
which scales exponentially with the connectivity range \lambda like_* \sim
\exp\lambda^d. The neuronal cultures are finite metric graphs of size N \simeq
10^5-10^6, which, for the parameters of the experiment, is effectively random
since N<< N_*. This explains the seeming contradiction in the observed finite
f_* in these cultures. Finally, we discuss the dynamics of the firing front
Evolucao da erosividade das chuvas na Bacia do Alto Taquari.
O assoreamento do rio Taquari constitui hoje um dos mais graves e discutidos problemas de impacto ambiental e socio economicos do Pantanal. Apesar do rio Taquari, historicamente, transportar grande quantidade de sedimento, a partir do final da decada de 70 esse processo foi intensificado com a expansao da atividade agropecuaria na Bacia do Alto Taquari (BAT). Outro fator importante no aumento do aporte de sedimento para o Pantanal pode estar relacionado a mudanca no regime pluviometrico na BAT. O calculo do indice mensal de erosividade da chuva foi efetuado para dois periodos: de 1969/70 a 1972/73 (periodo 1) e de 1973/74 A 1987/88 (periodo 2), utilizando o metodo de Lombardi Neto. Foram selecionadas cinco estacoes pluviometricas localizadas na BAT que tinham pelo menos cinco anos de registro de dados de chuva no periodo 1. Analisou-se, tambem, as medias mensais de precipitacao para os mesmos periodos. Os resultados das analises estatisticas evidenciaram um aumento significativo no regime pluviometrico e consequentemente na erosividade das chuvas na BAT, entre o periodo de 1969-70/1973-74 para o periodo de 1974-75/1987-88.bitstream/item/37427/1/BP25.pd
Reading Remediation Program for Struggling Readers: An Impact Study
One of the most important aspects of education is reading, which is essential to progress in a literate
society. It is important then to speed up reading through reading programs. Reading remediation is a
supplemental reading program that focuses on correct phonological processes. The study established
the value of reading remediation as a tool for helping struggling readers in grade 2 to learn more
effectively. In particular, it sought to ascertain how the program had affected a child's reading ability
before and after its implementation. The experimental pretest-posttest research design was used for
this investigation. Microsoft Excel was utilized to simplify the statistical computation of the data.
Results showed that the respondents' performance ratings in the pretest were poor, but they were
good in the post-test, indicating that there is an improvement in performance after giving struggling
readers reading remediation. Therefore, the Reading Remediation is a useful tool for improving
learning for the struggling grade 2 readers of Sevilla Elementary School
Anomalous Roughening in Experiments of Interfaces in Hele-Shaw Flows with Strong Quenched Disorder
We report experimental evidences of anomalous kinetic roughening in the
stable displacement of an oil-air interface in a Hele-Shaw cell with strong
quenched disorder. The disorder consists on a random modulation of the gap
spacing transverse to the growth direction (tracks). We have performed
experiments varying average interface velocity and gap spacing, and measured
the scaling exponents. We have obtained beta=0.50, beta*=0.25, alpha=1.0,
alpha_l=0.5, and z=2. When there is no fluid injection, the interface is driven
solely by capillary forces, and a higher value of beta around beta=0.65 is
measured. The presence of multiscaling and the particular morphology of the
interfaces, characterized by high slopes that follow a L\'evy distribution,
confirms the existence of anomalous scaling. From a detailed study of the
motion of the oil--air interface we show that the anomaly is a consequence of
different local velocities over tracks plus the coupling in the motion between
neighboring tracks. The anomaly disappears at high interface velocities, weak
capillary forces, or when the disorder is not sufficiently persistent in the
growth direction. We have also observed the absence of scaling when the
disorder is very strong or when a regular modulation of the gap spacing is
introduced.Comment: 14 pages, 17 figure
Probing the Dark Dimension with Auger data
[Abridged] By combining swampland conjectures with observational data, it was
recently noted that our universe could stretch off in an asymptotic region of
the string landscape of vacua. In this framework, the cosmological hierarchy
problem can be resolved by the addition of one mesoscopic (dark) dimension of
size . The Planck scale of
the higher dimensional theory, , is tantalizingly close to the energy
above which the TA and Auger collaborations found conclusive evidence for a
sharp cutoff of the flux of UHECRs. It was recently suggested that since
physics becomes strongly coupled to gravity beyond , universal
features deep-rooted in the dark dimension could control the energy cutoff of
the source spectra. Conversely, in the absence of phenomena inborn within the
dark dimension, we would expect a high variance of the cosmic ray maximum
energy characterizing the source spectra, reflecting the many different
properties inherent to the most commonly assumed UHECR accelerators. A recent
analysis of Auger and TA data exposed strong evidence for a correlation between
UHECRs and nearby starburst galaxies, with a global significance post-trial of
. Since these galaxies are in our cosmic backyard, the flux
attenuation factor due to cosmic ray interactions en route to Earth turns out
to be negligible. This implies that for each source, the shape of the observed
spectrum should roughly match the emission spectrum, providing a unique testing
ground for the dark dimension hypothesis. Using Auger data, we carry out a
maximum likelihood analysis to characterize the shape of the UHECR emission
from the galaxies dominating the anisotropy signal. We show that the observed
spectra could be universal only if .Comment: 17 pages, 3 figure
Monitoramento do comportamento do rio Paraguai no Pantanal Sul-Mato-grossense-2008/2009.
Este trabalho visa dar continuidade ao programa de monitoramento do comportamento do rio Paraguai que é feito anualmente pela Embrapa Pantanal.bitstream/CPAP-2010/57313/1/COT80.pd
Precise Modeling of the Exoplanet Host Star and CoRoT Main Target HD 52265
This paper presents a detailed and precise study of the characteristics of
the Exoplanet Host Star and CoRoT main target HD 52265, as derived from
asteroseismic studies. The results are compared with previous estimates, with a
comprehensive summary and discussion. The basic method is similar to that
previously used by the Toulouse group for solar-type stars. Models are computed
with various initial chemical compositions and the computed p-mode frequencies
are compared with the observed ones. All models include atomic diffusion and
the importance of radiative accelerations is discussed. Several tests are used,
including the usual frequency combinations and the fits of the \'echelle
diagrams. The possible surface effects are introduced and discussed. Automatic
codes are also used to find the best model for this star (SEEK, AMP) and their
results are compared with that obtained with the detailed method. We find
precise results for the mass, radius and age of this star, as well as its
effective temperature and luminosity. We also give an estimate of the initial
helium abundance. These results are important for the characterization of the
star-planet system.Comment: 9 pages, 6 figures, 7 tables, to be published in Astronomy and
Astrophysic
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