1,810 research outputs found
Annona muricata (graviola): toxic or therapeutic
This paper examines annona muricata (graviola): toxic or therapeutic
Cyclic and Long-term Variation of Sunspot Magnetic Fields
Measurements from the Mount Wilson Observatory (MWO) are used to study the
long-term variations of sunspot field strengths from 1920 to 1958. Following a
modified approach similar to that in Pevtsov et al. (2011), for each observing
week we select a single sunspot with the strongest field strength measured that
week and then compute monthly averages of these weekly maximum field strengths.
The data show the solar cycle variation of the peak field strengths with an
amplitude of about 500-700 gauss (G), but no statistically significant
long-term trends. Next, we use the sunspot observations from the Royal
Greenwich Observatory (RGO) to establish a relationship between the sunspot
areas and the sunspot field strengths for Cycles 15-19. This relationship is
then used to create a proxy of peak magnetic field strength based on sunspot
areas from the RGO and the USAF/NOAA network for the period from 1874 to early
2012. Over this interval, the magnetic field proxy shows a clear solar cycle
variation with an amplitude of 500-700 G and a weaker long-term trend. From
1874 to around 1920, the mean value of magnetic field proxy increases by about
300-350 G, and, following a broad maximum in 1920-1960, it decreases by about
300 G. Using the proxy for the magnetic field strength as the reference, we
scale the MWO field measurements to the measurements of the magnetic fields in
Pevtsov et al. (2011) to construct a combined data set of maximum sunspot field
strengths extending from 1920 to early 2012. This combined data set shows
strong solar cycle variations and no significant long-term trend (linear fit to
the data yields a slope of 0.8 G year). On the other hand, the
peak sunspot field strengths observed at the minimum of the solar cycle show a
gradual decline over the last three minima (corresponding to cycles 21-23) with
a mean downward trend of 15 G year
A reinterpretation of Volcano Ranch lateral distribution measurements to infer the mass composition of cosmic rays
In the course of its operation, the Volcano Ranch array collected data on the
lateral distribution of showers produced by cosmic rays at energies above
{\rm eV}. From these data very precise measurements of the steepness
of the lateral distribution function, characterized by the parameter,
were made. The current availability of sophisticated hadronic interaction
models has prompted a reinterpretation of the measurements. We use the
interaction models {\sc qgsjet} and {\sc sibyll} in the {\sc aires} Monte Carlo
code to generate showers together with {\sc geant4} to simulate the response of
the detectors to ground particles. As part of an effort to estimate the primary
mass composition of cosmic rays at this energy range, we present the results of
our preliminary analysis of the distribution of .Comment: 4 pages, 5 figures Talk presented at the XII International Symposium
on Very High Energy Cosmic Ray Interactions, CERN 2002. To be published in
Nucl. Phys. B (Proc. Suppl.
Mass Composition of Cosmic Rays in the Range 2 x 10^17 - 3 x 10^18 Measured with Haverah Park Array
At the Haverah Park Array a number of air shower observables were measured
that are relevant to the determination of the mass composition of cosmic rays.
In this paper we discuss measurements of the risetime of signals in large area
water-Cherenkov detectors and of the lateral distribution function of the
water-Cherenkov signal. The former are used to demonstrate that the CORSIKA
code, using the QGSJET98 model, gives an adequate description of the data with
a low sensitivity, in this energy range, to assumptions about primary mass. By
contrast the lateral distribution is sufficiently well measured that there is
mass sensitivity. We argue that in the range 0.2-1.0 EeV the data are well
represented with a bi-modal composition of 34+-2 % protons and the rest iron.
We also discuss the systematic errors induced by the choice of hadronic model.Comment: 16 pages, 13 figures. Accepted for publication in Astroparticle
Physic
The Importance of Slow-roll Corrections During Multi-field Inflation
We re-examine the importance of slow-roll corrections during the evolution of
cosmological perturbations in models of multi-field inflation. We find that in
many instances the presence of light degrees of freedom leads to situations in
which next to leading order slow-roll corrections become significant. Examples
where we expect such corrections to be crucial include models in which modes
exit the Hubble radius while the inflationary trajectory undergoes an abrupt
turn in field space, or during a phase transition. We illustrate this with two
examples -- hybrid inflation and double quadratic inflation. Utilizing both
analytic estimates and full numerical results, we find that corrections can be
as large as 20%. Our results have implications for many existing models in the
literature, as these corrections must be included to obtain accurate
observational predictions -- particularly given the level of accuracy expected
from CMB experiments such as PlanckComment: v1: 21 pages, 3 figures, 1 appendix. v2: clarifications to
{\S}{\S}2.1, 3.1 and 4, {\S}5.3 added, references added, results unchanged.
Matches published version in JCA
Random Mass Dirac Fermions in Doped Spin-Peierls and Spin-Ladder systems: One-Particle Properties and Boundary Effects
Quasi-one-dimensional spin-Peierls and spin-ladder systems are characterized
by a gap in the spin-excitation spectrum, which can be modeled at low energies
by that of Dirac fermions with a mass. In the presence of disorder these
systems can still be described by a Dirac fermion model, but with a random
mass. Some peculiar properties, like the Dyson singularity in the density of
states, are well known and attributed to creation of low-energy states due to
the disorder. We take one step further and study single-particle correlations
by means of Berezinskii's diagram technique. We find that, at low energy
, the single-particle Green function decays in real space like
. It follows that at these energies the
correlations in the disordered system are strong -- even stronger than in the
pure system without the gap. Additionally, we study the effects of boundaries
on the local density of states. We find that the latter is logarithmically (in
the energy) enhanced close to the boundary. This enhancement decays into the
bulk as and the density of states saturates to its bulk value on
the scale . This scale is different from
the Thouless localization length . We
also discuss some implications of these results for the spin systems and their
relation to the investigations based on real-space renormalization group
approach.Comment: 26 pages, LaTex, 9 PS figures include
Brane Gas Cosmology, M-theory and Little String Theory
We generalize the Brane Gas Cosmological Scenario to M-theory degrees of
freedom, namely and branes. Without brane intersections, the
Brandenberger Vafa(BV) arguments applied to M-theory degrees of freedom
generically predict a large 6 dimensional spacetime. We show that intersections
of and branes can instead lead to a large 4 dimensional spacetime.
One dimensional intersections in 11D is related to (2,0) little strings (LST)
on NS5 branes in type IIA. The gas regime of membranes in M-theory corresponds
to the thermodynamics of LST obtained from holography. We propose a mechanism
whereby LST living on the worldvolume of NS5 (M5)-branes wrapping a five
dimensional torus, annihilate most efficiently in 3+1 dimensions leading to a
large 3+1 dimensional spacetime. We also show that this picture is consistent
with the gas approximation in M-theory.Comment: 8 page
Slavnov-Taylor identities in Coulomb gauge Yang-Mills theory
The Slavnov-Taylor identities of Coulomb gauge Yang-Mills theory are derived
from the (standard, second order) functional formalism. It is shown how these
identities form closed sets from which one can in principle fully determine the
Green's functions involving the temporal component of the gauge field without
approximation, given appropriate input.Comment: 20 pages, no figure
The rate of cosmic ray showers at large zenith angles: a step towards the detection of ultra-high energy neutrinos by the Pierre Auger Observatory
It is anticipated that the Pierre Auger Observatory can be used to detect
cosmic neutrinos of >10^19 eV that arrive at very large zenith angles. However
showers created by neutrino interactions close to the detector must be picked
out against a background of similar events initiated by cosmic ray nuclei. As a
step towards understanding this background, we have made the first detailed
analysis of air showers recorded at Haverah Park (an array which used similar
detectors to those planned for the Auger Observatory) with zenith angles above
60 degs. We find that the differential shower rate from 60 degs to 80 degs. can
be predicted accurately when we adopt the known primary energy spectrum above
10^17 eV and assume the QGSJET model and proton primaries. Details of the
calculation are given.Comment: 22 pages, 12 figures, to appear in Astroparticle Physic
Cluster Analysis of Extremely High Energy Cosmic Rays in the Northern Sky
The arrival directions of extremely high energy cosmic rays (EHECR) above
eV, observed by four surface array experiments in the northern
hemisphere,are examined for coincidences from similar directions in the sky.
The total number of cosmic rays is 92.A significant number of double
coincidences (doublet) and triple coincidences (triplet) are observed on the
supergalactic plane within the experimental angular resolution. The chance
probability of such multiplets from a uniform distribution is less than 1 % if
we consider a restricted region within of the supergalactic
plane. Though there is still a possibility of chance coincidence, the present
results on small angle clustering along the supergalactic plane may be
important in interpreting EHECR enigma. An independent set of data is required
to check our claims.Comment: 9 pages, 6 tables, 8 figures. submitted to Astroparticle Physic
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