3,333 research outputs found
Extremely High Energy Neutrinos and their Detection
We discuss in some detail the production of extremely high energy (EHE)
neutrinos with energies above 10^18 eV. The most certain process for producing
such neutrinos results from photopion production by EHE cosmic rays in the
cosmic background photon field. However, using assumptions for the EHE cosmic
ray source evolution which are consistent with results from the deep QSO survey
in the radio and X-ray range, the resultant flux of neutrinos from this process
is not strong enough for plausible detection. A measurable flux of EHE
neutrinos may be present, however, if the highest energy cosmic rays which have
recently been detected well beyond 10^20 eV are the result of the annihilation
of topological defects which formed in the early universe. Neutrinos resulting
from such decays reach energies of the grand unification (GUT) scale, and
collisions of superhigh energy neutrinos with the cosmic background neutrinos
initiate neutrino cascading which enhances the EHE neutrino flux at Earth. We
have calculated the neutrino flux including this cascading effect for either
massless or massive neutrinos and we find that these fluxes are conceivably
detectable by air fluorescence detectors now in development. The
neutrino-induced showers would be recognized by their starting deep in the
atmosphere. We evaluate the feasibility of detecting EHE neutrinos this way
using air fluorescence air shower detectors and derive the expected event rate.
Other processes for producing deeply penetrating air showers constitute a
negligible background.Comment: 33 pages, including 12 eps figures, LaTe
A Comparison of Cosmic Ray Composition Measurements at the Highest Energies
In recent years the Fly's Eye and Akeno groups have presented analyses of the
cosmic ray mass composition at energies above 10^17 eV. While the analysis of
the Fly's Eye group points to a likely change in mass composition from heavy to
light at energies above 10^18 eV, the Akeno analysis favours an unchanging
composition. However, the two groups base their conclusions on simulations
using quite different hadronic models. Here we present a comparison of the
experiments using the same hadronic model and find that the agreement between
the experiments is much improved. Under this model, both experiments measure a
composition rich in iron around 10^17 eV which becomes lighter at higher
energies. However, the agreement is not complete, which indicates scope for
improvement of the interaction model, or perhaps the need for a re-examination
of the experimental results.Comment: 15 pages, uses epsfig.sty with 6 figures. Submitted to Astroparticle
Physics, 25th January 1998. This is a revised version (21st May 1998) which
addresses some referee comments, and which clarifies discussions of our
result
Comparison of AGASA data with CORSIKA simulation
An interpretation of AGASA (Akeno Giant Air Shower Array) data by comparing
the experimental results with the simulated ones by CORSIKA (COsmic Ray
SImulation for KASCADE) has been made. General features of the electromagnetic
component and low energy muons observed by AGASA can be well reproduced by
CORSIKA. The form of the lateral distribution of charged particles agrees well
with the experimental one between a few hundred metres and 2000 m from the
core, irrespective of the hadronic interaction model studied and the primary
composition (proton or iron). It does not depend on the primary energy between
10^17.5 and 10^20 eV as the experiment shows. If we evaluate the particle
density measured by scintillators of 5 cm thickness at 600 m from the core
(S_0(600), suffix 0 denotes the vertically incident shower) by taking into
account the similar conditions as in the experiment, the conversion relation
from S_0(600) to the primary energy is expressed as E [eV] = 2.15 x 10^17 x
S_0(600)^1.015, within 10% uncertainty among the models and composition used,
which suggests the present AGASA conversion factor is the lower limit. Though
the form of the muon lateral distribution fits well to the experiment within
1000 m from the core, the absolute values change with hadronic interaction
model and primary composition. The slope of the rho_mu(600) (muon density above
1 GeV at 600 m from the core) vs. S_0(600) relation in experiment is flatter
than that in simulation of any hadronic model and primary composition. Since
the experimental slope is constant from 10^15 eV to 10^19 eV, we need to study
this relation in a wide primary energy range to infer the rate of change of
chemical composition with energy. keywords: cosmic ray, extensive air shower,
simulation, primary energy estimation PACS number ; 96.40.De, 96.40.PqComment: 30 pages, 15 figures, accepted by Astroparticle Physics at 6. Dec
199
Inhibition of TRPA1 channel activity in sensory neurons by the glial cell line-derived neurotrophic factor family member, artemin
<p>Abstract</p> <p>Background</p> <p>The transient receptor potential (TRP) channel subtype A1 (TRPA1) is known to be expressed on sensory neurons and respond to changes in temperature, pH and local application of certain noxious chemicals such as allyl isothiocyanate (AITC). Artemin is a neuronal survival and differentiation factor and belongs to the glial cell line-derived neurotrophic factor (GDNF) family. Both TRPA1 and artemin have been reported to be involved in pathological pain initiation and maintenance. In the present study, using whole-cell patch clamp recording technique, <it>in situ </it>hybridization and behavioral analyses, we examined the functional interaction between TRPA1 and artemin.</p> <p>Results</p> <p>We found that 85.8 ± 1.9% of TRPA1-expressing neurons also expressed GDNF family receptor alpha 3 (GFR α3), and 87.5 ± 4.1% of GFRα3-expressing neurons were TRPA1-positive. In whole-cell patch clamp analysis, a short-term treatment of 100 ng/ml artemin significantly suppressed the AITC-induced TRPA1 currents. A concentration-response curve of AITC resulting from the effect of artemin showed that this inhibition did not change EC<sub>50 </sub>but did lower the AITC-induced maximum response. In addition, pre-treatment of artemin significantly suppressed the number of paw lifts induced by intraplantar injection of AITC, as well as the formalin-induced pain behaviors.</p> <p>Conclusions</p> <p>These findings that a short-term application of artemin inhibits the TRPA1 channel's activity and the sequential pain behaviors suggest a role of artemin in regulation of sensory neurons.</p
Stripe-Like Inhomogeneities, Spectroscopies, Pairing, and Coherence in the High-Tc Cuprates
It is found that the carriers of the high-T_c cuprates are polaron-like
"stripons" carrying charge and located in stripe-like inhomogeneities,
"quasi-electrons" carrying charge and spin, and "svivons" carrying spin and
lattice distortion. This is shown to result in the observed anomalous
spectroscopic properties of the cuprates. The AF/stripe-like inhomogeneities
result from the Bose condensation of the svivon field, and the speed of their
dynamics is determined by the width of the double-svivon neutron-resonance
peak. Pairing results from transitions between pair states of stripons and
quasi-electrons through the exchange of svivons. The obtained pairing symmetry
is of the d_{x^2-y^2} type; however, sign reversal through the charged stripes
results in features not characteristic of this symmetry. The phase diagram is
determined by a pairing and a coherence line, associated with a Mott
transition, and the pseudogap state corresponds to incoherent pairing.Comment: 13 pages, 8 figures; version including recent references, to be
published in J. Phys. Chem. Solid
Astrophysical sources of high energy neutrinos
Several high energy, >100 GeV, neutrino telescopes are currently operating or
under construction. Their main motivation is the extension of the horizon of
neutrino astronomy to cosmological scales. We show that general, model
independent, arguments imply that ~1 Gton detectors are required to detect
cosmic high energy neutrino sources. Predictions of models of some of the
leading candidate sources, gamma-ray bursts and micro-quasars, are discussed,
and the question of what can be learned from neutrino observations is
addressed.Comment: Invited talk, Neutrino 2002 (Munich
Aqua[2-(2-pyridyl)-1,8-naphthyridine-κ2 N 1,N 2](2,2′:6′,2′′-terpyridine-κ3 N,N′,N′′)ruthenium(II) bis(hexafluoridophosphate) acetone sesquisolvate
The asymmetric unit of the title compound, [Ru(C13H9N3)(C15H11N3)(H2O)](PF6)2·1.5C3H6O, consists of two crystallographically independent RuII complexes. Each complex is approximately octahedral with the RuII atom bound by an N,N′-coordinated 2-(2-pyridyl)-1,8-naphthyridine (pynp) ligand, a meridional 2,2′:6′,2′′-terpyridine (tpy) ligand and one aqua ligand. The tpy ligand is coordinated in a planar tridentate fashion with the central N atom closest to the RuII atom. The aqua ligand is trans to the pyridine N atom of pynp. The long Ru—O distances [2.150 (5) and 2.138 (5) Å] are typical for aqua ligands in polypyridyl ruthenium complexes. In the crystal, both intramolecular O—H⋯N and intermolecular O—H⋯O hydrogen bonds are observed
Extension of the Cosmic-Ray Energy Spectrum Beyond the Predicted Greisen-Zatsepin-Kuz'min Cutoff
The cosmic-ray energy spectrum above 10^{18.5} eV is reported using the
updated data set of the Akeno Giant Air Shower Array (AGASA) from February 1990
to October 1997. The energy spectrum extends beyond 10^{20} eV and the energy
gap between the highest energy event and the others is being filled up with
recently observed events. The spectral shape suggests the absence of the 2.7 K
cutoff in the energy spectrum or a possible presence of a new component beyond
the 2.7 K cutoff.Comment: to be published in PRL, 3 figures, REVTEX forma
Atomic Dark Matter
We propose that dark matter is dominantly comprised of atomic bound states.
We build a simple model and map the parameter space that results in the early
universe formation of hydrogen-like dark atoms. We find that atomic dark matter
has interesting implications for cosmology as well as direct detection:
Protohalo formation can be suppressed below for weak scale dark matter due to Ion-Radiation interactions in the
dark sector. Moreover, weak-scale dark atoms can accommodate hyperfine
splittings of order 100 \kev, consistent with the inelastic dark matter
interpretation of the DAMA data while naturally evading direct detection
bounds.Comment: 17 pages, 3 figure
The Extremely High Energy Cosmic Rays
Experimental results from Haverah Park, Yakutsk, AGASA and Fly's Eye are
reviewed. All these experiments work in the energy range above 0.1 EeV. The
'dip' structure around 3 EeV in the energy spectrum is well established by all
the experiments, though the exact position differs slightly. Fly's Eye and
Yakutsk results on the chemical composition indicate that the cosmic rays are
getting lighter over the energy range from 0.1 EeV to 10 EeV, but the exact
fraction is hadronic interaction model dependent, as indicated by the AGASA
analysis. The arrival directions of cosmic rays are largely isotropic, but
interesting features may be starting to emerge. Most of the experimental
results can best be explained with the scenario that an extragalactic component
gradually takes over a galactic population as energy increases and cosmic rays
at the highest energies are dominated by particles coming from extragalactic
space. However, identification of the extragalactic sources has not yet been
successful because of limited statistics and the resolution of the data.Comment: The review paper including 21 figures. 39 pages: To be published in
Journal of Physics
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