69 research outputs found
The Modified Weighted Slab Technique: Models and Results
In an attempt to understand the source and propagation of galactic cosmic
rays we have employed the Modified Weighted Slab technique along with recent
values of the relevant cross sections to compute primary to secondary ratios
including B/C and Sub-Fe/Fe for different galactic propagation models. The
models that we have considered are the disk-halo diffusion model, the dynamical
halo wind model, the turbulent diffusion model and a model with minimal
reacceleration. The modified weighted slab technique will be briefly discussed
and a more detailed description of the models will be given. We will also
discuss the impact that the various models have on the problem of anisotropy at
high energy and discuss what properties of a particular model bear on this
issue.Comment: LaTeX - AASTEX format, Submitted to ApJ, 8 figures, 20 page
The Galactic positron flux and dark matter substructures
In this paper we calculate the Galactic positron flux from dark matter
annihilation in the frame of supersymmetry, taking the enhancement of the flux
by existence of dark matter substructures into account. The propagation of
positrons in the Galactic magnetic field is solved in a realistic numerical
model GALPROP. The secondary positron flux is recalculated in the GLAPROP
model. The total positron flux from secondary products and dark matter
annihilation can fit the HEAT data well when taking a cuspy density profile of
the substructures.Comment: 16 pages, 10 figures, accepted by JCA
Secondary antiprotons and propagation of cosmic rays in the Galaxy and heliosphere
High-energy collisions of cosmic-ray nuclei with interstellar gas are
believed to be the mechanism producing the majority of cosmic ray antiprotons.
Due to the kinematics of the process they are created with a nonzero momentum;
the characteristic spectral shape with a maximum at ~2 GeV and a sharp decrease
towards lower energies makes antiprotons a unique probe of models for particle
propagation in the Galaxy and modulation in the heliosphere. On the other hand,
accurate calculation of the secondary antiproton flux provides a ``background''
for searches for exotic signals from the annihilation of supersymmetric
particles and primordial black hole evaporation. Recently new data with large
statistics on both low and high energy antiproton fluxes have become available
which allow such tests to be performed. We use our propagation code GALPROP to
calculate interstellar cosmic-ray propagation for a variety of models. We show
that there is no simple model capable of accurately describing the whole
variety of data: boron/carbon and sub-iron/iron ratios, spectra of protons,
helium, antiprotons, positrons, electrons, and diffuse gamma rays. We find that
only a model with a break in the diffusion coefficient plus convection can
reproduce measurements of cosmic-ray species, and the reproduction of primaries
(p, He) can be further improved by introducing a break in the primary injection
spectra. For our best-fit model we make predictions of proton and antiproton
fluxes near the Earth for different modulation levels and magnetic polarity
using a steady-state drift model of propagation in the heliosphere.Comment: Many Updates, 20 pages, 15 ps-figures, emulateapj5.sty. To be
published in ApJ v.564 January 10, 2002 issue. More details can be found at
http://www.gamma.mpe-garching.mpg.de/~aws/aws.htm
Ubiquitin D is correlated with colon cancer progression and predicts recurrence for stage II-III disease after curative surgery
Uncertainties of Cosmic Ray Spectra and Detectability of Antiproton mSUGRA Contributions With PAMELA
We studied the variation of and top of the atmosphere spectra
due to the parameters uncertainties of the Milky Way geometry, propagation
models and cross sections. We used the B/C data and Galprop code for the
propagation analysis. We also derived the uncertainty bands for subFe/Fe ratio,
H and He. Finally, we considered a neutralino induced component in the
antiproton flux in the mSUGRA framework. PAMELA expectations for positrons and
antiprotons are calculated. We studied in details the possibility of
disentanglement of an eventual signal component in the antiproton spectra in a
clumpy halo scenario: minimal values of clumpiness factors necessary to
disentangle the signal from the background without violating the quality of the
antiproton data fit are found. There are also given examples of total spectra
in comparison with existing experimental data and an example of PAMELA
prediction for the total spectra. The main result of this work is that for the
diffusion and convection background model PAMELA will be able to disentangle an
eventual supersymmetric signal even for small clumpiness factors.Comment: 26 pages, 27 eps figures. Final JCAP accepted versio
Cosmic Ray Diffusion from the Galactic Spiral Arms, Iron Meteorites, and a possible climatic connection?
We construct a Galactic cosmic ray (CR) diffusion model while considering
that CR sources reside predominantly in the Galactic spiral arms. We find that
the CR flux (CRF) reaching the solar system should periodically increase each
crossing of a Galactic spiral arm. We search for this signal in the CR exposure
age record of Iron meteorites and confirm this prediction. We then check the
hypothesis that climate, and in particular the temperature, is affected by the
CRF to the extent that glaciations can be induced or completely hindered by
possible climatic variations. We find that although the geological evidence for
the occurrence of IAEs in the past Eon is not unequivocal, it appears to have a
nontrivial correlation with the spiral arm crossings--agreeing in period and
phase. Thus, a better timing study of glaciations could either confirm this
result as an explanation to the occurrence of IAEs or refute a CRF climatic
connection.Comment: 4 Journal pages, 2 figures, revtex4. Appearing today in Phys Rev Let
Emulsification and Other Physicochemical Changes in Polydimethylsiloxanes in Contact with Model Systems Representing Eyeball Tissue, Human Blood Serum and Collagen
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