993 research outputs found
Heavy-tailed distributions in fatal traffic accidents: role of human activities
Human activities can play a crucial role in the statistical properties of
observables in many complex systems such as social, technological and economic
systems. We demonstrate this by looking into the heavy-tailed distributions of
observables in fatal plane and car accidents. Their origin is examined and can
be understood as stochastic processes that are related to human activities.
Simple mathematical models are proposed to illustrate such processes and
compared with empirical results obtained from existing databanks.Comment: 10 pages, 5 figure
Scaling and correlations in the dynamics of forest-fire occurrence
Forest-fire waiting times, defined as the time between successive events
above a certain size in a given region, are calculated for Italy. The
probability densities of the waiting times are found to verify a scaling law,
despite that fact that the distribution of fire sizes is not a power law. The
meaning of such behavior in terms of the possible self-similarity of the
process in a nonstationary system is discussed. We find that the scaling law
arises as a consequence of the stationarity of fire sizes and the existence of
a non-trivial ``instantaneous'' scaling law, sustained by the correlations of
the process.Comment: Not a long paper, but many figures (but no large size in kb
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Temperature trends at the Mauna Loa observatory, Hawaii
Observations at the Mauna Loa Observatory, Hawaii, established the systematic increase of anthropogenic CO2 in the atmosphere. For the same reasons that this site provides excellent globally averaged CO2 data, it may provide temperature data with global significance. Here, we examine hourly temperature records, averaged annually for 1977-2006, to determine linear trends as a function of time of day. For night-time data (22:00 to 06:00 LST (local standard time)) there is a near-uniform warming of 0.040 degrees C yr(-1). During the day, the linear trend shows a slight cooling of -0.014 degrees C yr(-1) at 12:00 LST (noon). Overall, at Mauna Loa Observatory, there is a mean warming trend of 0.021 degrees C yr(-1). The dominance of night-time warming results in a relatively large annual decrease in the diurnal temperature range (DTR) of -0.050 degrees C yr(-1) over the period 1977-2006. These trends are consistent with the observed increases in the concentrations of CO2 and its role as a greenhouse gas (demonstrated here by first-order radiative forcing calculations), and indicate the possible relevance of the Mauna Loa temperature measurements to global warming.</p
Portugueses Gaúchos: socio-political transnationalism, integration and identities in the River Plate Region
Através da análise de entrevistas com emigrantes portugueses e os seus descendentes na região platina, o artigo explora as relações entre integração e participação em associações de emigrantes, e como elas se inter-relacionam com a identidade colectiva na sociedade de recepção. Examinamos o papel das associações de emigrantes na construção e reforço dos símbolos, referências e identidades nacionais, e como simultaneamente facilitam a integração. Sugerimos que a activação de identidades do país de origem não tem efeitos etnicizantes; pelo contrário, funciona como recurso efectivo da integração, promovendo as redes sociais abertas
Inverse spectral problems for Dirac operators with summable matrix-valued potentials
We consider the direct and inverse spectral problems for Dirac operators on
with matrix-valued potentials whose entries belong to ,
. We give a complete description of the spectral data
(eigenvalues and suitably introduced norming matrices) for the operators under
consideration and suggest a method for reconstructing the potential from the
corresponding spectral data.Comment: 32 page
Avalanche Statistics of Driven Granular Slides in a Miniature Mound
We examine avalanche statistics of rain- and vibration-driven granular slides
in miniature sand mounds. A crossover from power-law to non power-law
avalanche-size statistics is demonstrated as a generic driving rate is
increased. For slowly-driven mounds, the tail of the avalanche-size
distribution is a power-law with exponent , reasonably close to
the value previously reported for landslide volumes. The interevent occurrence
times are also analyzed for slowly-driven mounds; its distribution exhibits a
power-law with exponent .Comment: 4 pages, 3 figures, 1 tabl
Non-characteristic Half-lives in Radioactive Decay
Half-lives of radionuclides span more than 50 orders of magnitude. We
characterize the probability distribution of this broad-range data set at the
same time that explore a method for fitting power-laws and testing
goodness-of-fit. It is found that the procedure proposed recently by Clauset et
al. [SIAM Rev. 51, 661 (2009)] does not perform well as it rejects the
power-law hypothesis even for power-law synthetic data. In contrast, we
establish the existence of a power-law exponent with a value around 1.1 for the
half-life density, which can be explained by the sharp relationship between
decay rate and released energy, for different disintegration types. For the
case of alpha emission, this relationship constitutes an original mechanism of
power-law generation
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