232 research outputs found
TO THE QUESTION ABOUT THE REASONS DESTOCKING FISHIN THE CASPIAN SEA
Aim. To identify the reasons for the decline of fish stocks in the Caspian sea. Location. The Caspian sea. Methods. When adverse effects of multiple abiotic factors, the other part indicates the important role of fisheries. How fair this point of view will try to answer in this paper. Consider long-term changes in the average water temperature in the Northern Caspian sea. Results. Considered abiotic and biological factors ( prey base) productivity of the Northern Caspian sea could cause catastrophic ( tenfold) reduction of fish stocks. Evidence of this is shown in table. 2 which shows that external factors do not provide a clear correlation with the yield of fish, more important are the internal factors related to the impact of fishing. Main conclusions. You should pay very close attention to human factors and in particular on the volume of catch, location and time fishing and more time to assess how rational our modern craft
The background from single electromagnetic subcascades for a stereo system of air Cherenkov telescopes
The MAGIC experiment, a very large Imaging Air Cherenkov Telescope (IACT)
with sensitivity to low energy (E < 100 GeV) VHE gamma rays, has been operated
since 2004. It has been found that the gamma/hadron separation in IACTs becomes
much more difficult below 100 GeV [Albert et al 2008] A system of two large
telescopes may eventually be triggered by hadronic events containing Cherenkov
light from only one electromagnetic subcascade or two gamma subcascades, which
are products of the single pi^0 decay. This is a possible reason for the
deterioration of the experiment's sensitivity below 100 GeV. In this paper a
system of two MAGIC telescopes working in stereoscopic mode is studied using
Monte Carlo simulations. The detected images have similar shapes to that of
primary gamma-rays and they have small sizes (mainly below 400 photoelectrons
(p.e.)) which correspond to an energy of primary gamma-rays below 100 GeV. The
background from single or two electromagnetic subcascdes is concentrated at
energies below 200 GeV. Finally the number of background events is compared to
the number of VHE gamma-ray excess events from the Crab Nebula. The
investigated background survives simple cuts for sizes below 250 p.e. and thus
the experiment's sensitivity deteriorates at lower energies.Comment: 15 pages, 7 figures, published in Journ.of Phys.
On Active Galactic Nuclei as Sources of Ultra-High Energy Cosmic Rays
We measure the correlation between sky coordinates of the Swift BAT catalogue
of active galactic nuclei with the arrival directions of the highest energy
cosmic rays detected by the Auger Observatory. The statistically complete, hard
X-ray catalogue helps to distinguish between AGN and other source candidates
that follow the distribution of local large-scale structure. The positions of
the full catalogue are marginally uncorrelated with the cosmic ray arrival
directions, but when weighted by their hard X-ray flux, AGN within 100 Mpc are
correlated at a significance level of 98 per cent. This correlation sharply
decreases for sources beyond ~100 Mpc, suggestive of a GZK suppression. We
discuss the implications for determining the mechanism that accelerates
particles to these extreme energies in excess of 10^19 eV.Comment: 5 pages, 2 figures. Accepted for publication in MNRA
Diffusive propagation of cosmic rays from supernova remnants in the Galaxy. I: spectrum and chemical composition
In this paper we investigate the effect of stochasticity in the spatial and
temporal distribution of supernova remnants on the spectrum and chemical
composition of cosmic rays observed at Earth. The calculations are carried out
for different choices of the diffusion coefficient D(E) experienced by cosmic
rays during propagation in the Galaxy. In particular, at high energies we
assume that D(E)\sim E^{\delta}, with and being the
reference scenarios. The large scale distribution of supernova remnants in the
Galaxy is modeled following the distribution of pulsars, with and without
accounting for the spiral structure of the Galaxy. We find that the stochastic
fluctuations induced by the spatial and temporal distribution of supernovae,
together with the effect of spallation of nuclei, lead to mild but sensible
violations of the simple, leaky-box-inspired rule that the spectrum observed at
Earth is with , where
is the slope of the cosmic ray injection spectrum at the sources. Spallation of
nuclei, even with the small rates appropriate for He, may account for slight
differences in spectral slopes between different nuclei, providing a possible
explanation for the recent CREAM observations. For we find that
the slope of the proton and helium spectra are and
respectively at energies above 1 TeV (to be compared with the measured values
of and ). For the hardening of the He
spectra is not observed. We also comment on the effect of time dependence of
the escape of cosmic rays from supernova remnants, and of a possible clustering
of the sources in superbubbles. In a second paper we will discuss the
implications of these different scenarios for the anisotropy of cosmic rays.Comment: 28 pages, To appear in JCA
Limits to the energy resolution of a single Air Cherenkov Telescope at low energies
The photon density on the ground is a fundamental quantity in all experiments
based on Cherenkov light measurements, e.g. in the Imaging Air Cherenkov
Telescopes (IACT). IACT's are commonly and successfully used in order to search
and study Very High Energy (VHE) gamma-ray sources. Difficulties with
separating primary photons from primary hadrons (mostly protons) in Cherenkov
experiments become larger at lower energies. I have calculated longitudinal and
lateral density distributions and their fluctuations at low energies basing on
Monte Carlo simulations (for vertical gamma cascades and protonic showers) to
check the influence of the detector parameters on the possible measurement.
Relative density fluctuations are significantly higher in proton than in photon
induced showers. Taking into account the limited detector field of view (FOV)
implies the changes of these calculated distributions for both types of primary
particles and causes an enlargement in relative fluctuations. Absorption due to
Rayleigh and Mie scattering has an impact on mean values but does not change
relative fluctuations. The total number of Cherenkov photons is more sensitive
to the observation height in gamma cascades than in proton showers at low
primary energies. The relative fluctuations of the density do not depend on the
reflector size in the investigated size range (from 240 m^2 up to 960 m^2).
This implies that a single telescope with a mirror area larger than that of the
MAGIC telescope cannot achieve better energy resolution than estimated and
presented in this paper. The correlations between longitudinal and lateral
distributions are much more pronounced for primary gamma-ray than for primary
proton showers.Comment: 21 pages, 11 figures, accepted for publication in Journal of Physics
Parametrizations of Inclusive Cross Sections for Pion Production in Proton-Proton Collisions
Accurate knowledge of cross sections for pion production in proton-proton
collisions finds wide application in particle physics, astrophysics, cosmic ray
physics and space radiation problems, especially in situations where an
incident proton is transported through some medium, and one requires knowledge
of the output particle spectrum given the input spectrum. In such cases
accurate parametrizations of the cross sections are desired. In this paper we
review much of the experimental data and compare to a wide variety of different
cross section parametrizations. In so doing, we provide parametrizations of
neutral and charged pion cross sections which provide a very accurate
description of the experimental data. Lorentz invariant differential cross
sections, spectral distributions and total cross section parametrizations are
presented.Comment: 32 pages with 15 figures. Published in Physical Review D62, 094030.
File includes 6 tex files. The main file is paper.tex which has include
statements refering to the rest. figures are in graphs.di
The Particle Physics Reach of High-Energy Neutrino Astronomy
We discuss the prospects for high-energy neutrino astronomy to study particle
physics in the energy regime comparable to and beyond that obtainable at the
current and planned colliders. We describe the various signatures of
high-energy cosmic neutrinos expected in both neutrino telescopes and air
shower experiments and discuss these measurements within the context of
theoretical models with a quantum gravity or string scale near a TeV,
supersymmetry and scenarios with interactions induced by electroweak
instantons. We attempt to access the particle physics reach of these
experiments.Comment: Mini-review article for New Journal of Physics, "Focus on Neutrinos"
issue. 27 pages, 11 figure
Upper Bounds on the Neutrino-Nucleon Inelastic Cross Section
Extraterrestrial neutrinos can initiate deeply developing air showers, and
those that traverse the atmosphere unscathed may produce cascades in the ice or
water. Up to now, no such events have been observed. This can be translated
into upper limits on the diffuse neutrino flux. On the other hand, the
observation of cosmic rays with primary energies > 10^{10} GeV suggests that
there is a guaranteed flux of cosmogenic neutrinos, arising from the decay of
charged pions (and their muon daughters) produced in proton interactions with
the cosmic microwave background. In this work, armed with these cosmogenic
neutrinos and the increased exposure of neutrino telescopes we bring up-to-date
model-independent upper bounds on the neutrino-nucleon inelastic cross section.
Uncertainties in the cosmogenic neutrino flux are discussed and taken into
account in our analysis. The prospects for improving these bounds with the
Pierre Auger Observatory are also estimated. The unprecedented statistics to be
collected by this experiment in 6 yr of operation will probe the
neutrino-nucleon inelastic cross section at the level of Standard Model
predictions.Comment: To be published in JCA
Measurement of the Cosmic Ray Energy Spectrum and Composition from 10^{17} to 10^{18.3} eV Using a Hybrid Fluorescence Technique
We study the spectrum and average mass composition of cosmic rays with
primary energies between 10^{17} eV and 10^{18} eV using a hybrid detector
consisting of the High Resolution Fly's Eye (HiRes) prototype and the MIA muon
array. Measurements have been made of the change in the depth of shower maximum
as a function of energy. A complete Monte Carlo simulation of the detector
response and comparisons with shower simulations leads to the conclusion that
the cosmic ray intensity is changing f rom a heavier to a lighter composition
in this energy range. The spectrum is consistent with earlier Fly's Eye
measurements and supports the previously found steepening near 4 \times 10^{17}
eV .Comment: 39 pages, 15 figures, in revtex4 epsf style, submited to AP
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