4,049 research outputs found
On the influence of statistics on the determination of the mean value of the depth of shower maximum for ultra high energy cosmic ray showers
The chemical composition of ultra high energy cosmic rays is still uncertain.
The latest results obtained by the Pierre Auger Observatory and the HiRes
Collaboration, concerning the measurement of the mean value and the
fluctuations of the atmospheric depth at which the showers reach the maximum
development, Xmax, are inconsistent. From comparison with air shower
simulations it can be seen that, while the Auger data may be interpreted as a
gradual transition to heavy nuclei for energies larger than ~ 2-3x10^18 eV, the
HiRes data are consistent with a composition dominated by protons. In Ref. [1]
it is suggested that a possible explanation of the observed deviation of the
mean value of Xmax from the proton expectation, observed by Auger, could
originate in a statistical bias arising from the approximated exponential shape
of the Xmax distribution, combined with the decrease of the number of events as
a function of primary energy. In this paper we consider a better description of
the Xmax distribution and show that the possible bias in the Auger data is at
least one order of magnitude smaller than the one obtained when assuming an
exponential distribution. Therefore, we conclude that the deviation of the
Auger data from the proton expectation is unlikely explained by such
statistical effect.Comment: To be published in Journal of Physics G: Nuclear and Particle Physic
Minority-carrier characteristics of InGaAs metal-oxide-semiconductor structures using atomic-layer-deposited A12O3 gate dielectric
Atomic layer depositio
Nonextensive hydrodynamics for relativistic heavy-ion collisions
The nonextensive one-dimensional version of a hydrodynamical model for
multiparticle production processes is proposed and discussed. It is based on
nonextensive statistics assumed in the form proposed by Tsallis and
characterized by a nonextensivity parameter . In this formulation the
parameter characterizes some specific form of local equilibrium which is
characteristic for the nonextensive thermodynamics and which replaces the usual
local thermal equilibrium assumption of the usual hydrodynamical models. We
argue that there is correspondence between the perfect nonextensive
hydrodynamics and the usual dissipative hydrodynamics. It leads to simple
expression for dissipative entropy current and allows for predictions for the
ratio of bulk and shear viscosities to entropy density, and ,
to be made.Comment: Final version accepted for publication in Phys. Rev.
Regional calibration of the Pitman model for the Okavango River
This paper reports on the application of a monthly rainfall-runoff model for the Okavango River Basin. Streamflow is mainly generated in Angola where the Cuito and Cubango rivers arise. They then join and cross the Namibia/Angola border, flowing into the Okavango wetland in Botswana. The model is a modified version of the Pitman model, including more explicit ground and surface water interactions. Significant limitations in access to climatological data, and lack of sufficiently long records of observed flow for the eastern sub-basins represent great challenges to model calibration. The majority of the runoff is generated in the wetter headwater tributaries, while the lower sub-basins are dominated by channel loss processes with very little incremental flow contributions, even during wet years. The western tributaries show significantly higher seasonal variation in flow, compared to the baseflow dominated eastern tributaries: observations that are consistent with their geological differences. The basin was sub-divided into 24 sub-basins, of which 18 have gauging stations at their outlet. Satisfactory simulations were achieved with sub-basin parameter value differences that correspond to the spatial variability in basin physiographic characteristics. The limited length of historical rainfall and river discharge data over Angola precluded the use of a split sample calibration/validation test. However, satellite generated rainfall data, revised to reflect the same frequency characteristics as the historical rainfall data, were used to validate the model against the available downstream flow data during the 1990s. The overall conclusion is that the model, in spite of the limited data access, adequately represents the hydrological response of the basin and that it can be used to assess the impact of future development scenarios
Estimating the inelasticity with the information theory approach
Using the information theory approach, in both its extensive and nonextensive
versions, we estimate the inelasticity parameter of hadronic reactions
together with its distribution and energy dependence from and
data. We find that the inelasticity remains essentially constant in energy
except for a variation around , as was originally expected.Comment: 14 pages, 8 figures. Misprints correcte
Nonextensive statistical effects in the quark-gluon plasma formation at relativistic heavy-ion collisions energies
We investigate the relativistic equation of state of hadronic matter and
quark-gluon plasma at finite temperature and baryon density in the framework of
the non-extensive statistical mechanics, characterized by power-law quantum
distributions. We impose the Gibbs conditions on the global conservation of
baryon number, electric charge and strangeness number. For the hadronic phase,
we study an extended relativistic mean-field theoretical model with the
inclusion of strange particles (hyperons and mesons). For the quark sector, we
employ an extended MIT-Bag model. In this context we focus on the relevance of
non-extensive effects in the presence of strange matter.Comment: 12 pages, 5 figure
Nonextensive thermal sources of cosmic rays?
The energy spectrum of cosmic rays (CR) exhibits power-like behavior with a
very characteristic "knee" structure. We consider a possibility that such a
spectrum could be generated by some specific nonstatistical temperature
fluctuations in the source of CR with the "knee" structure reflecting an abrupt
change of the pattern of such fluctuations. This would result in a generalized
nonextensive statistical model for the production of CR. The possible physical
mechanisms leading to these effects are discussed together with the resulting
chemical composition of the CR, which follows the experimentally observed
abundance of nuclei.Comment: 16 pages, 3 figures, rewritten and updated version, to be published
in Centr. Eur. J. Phy
Magnetized strangelets at finite temperature
The main properties of magnetized strangelets, namely, their energy per
baryon, radius and electric charge, are studied. Temperature effects are also
taken into account in order to study their stability compared to the 56Fe
isotope and non-magnetized strangelets using the liquid drop model. Massive
quarks are considered with the aim to have a more realistic description for
strangelets in the astrophysical context and the environment of heavy ion
colliders, playing also an important role in the thermodynamical quantities of
the quark gas. It is concluded that the presence of a magnetic field tends to
stabilize more the strangelets, even when temperature effects are taken into
account. Magnetized strangelets in a paired superconductor phase (magnetized
color flavor locked phase) are also discussed. It is shown that they are more
stable than ordinary magnetized strangelets for typical gap values of the order
of O(100) MeV.Comment: 10 pages, 10 figures, discussion extended, new references adde
Equivalence of volume and temperature fluctuations in power-law ensembles
Relativistic particle production often requires the use of Tsallis statistics
to account for the apparently power-like behavior of transverse momenta
observed in the data even at a few GeV/c. In such an approach this behavior is
attributed to some specific intrinsic fluctuations of the temperature in
the hadronizing system and is fully accounted by the nonextensivity parameter
. On the other hand, it was recently shown that similar power-law spectra
can also be obtained by introducing some specific volume fluctuations,
apparently without invoking the introduction of Tsallis statistics. We
demonstrate that, in fact, when the total energy is kept constant, these volume
fluctuations are equivalent to temperature fluctuations and can be derived from
them. In addition, we show that fluctuations leading to multiparticle power-law
Tsallis distributions introduce specific correlations between the considered
particles. We then propose a possible way to distinguish the fluctuations in
each event from those occurring from event-to-event. This could have
applications in the analysis of high density events at LHC (and especially in
ALICE).Comment: Revised version with new figure, footnotes and references adde
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