2,286 research outputs found
A system for online beam emittance measurements and proton beam characterization
A system for online measurement of the transverse beam emittance was
developed. It is named PrOBaM (4-Profiler Online Beam
Emittance Measurement) and was conceived to measure the emittance in a fast and
efficient way using the multiple beam profiler method. The core of the system
is constituted by four consecutive UniBEaM profilers, which are based on silica
fibers passing across the beam. The PrOBaM system was
deployed for characterization studies of the 18~MeV proton beam produced by the
IBA Cyclone 18 MeV cyclotron at Bern University Hospital (Inselspital). The
machine serves daily radioisotope production and multi-disciplinary research,
which is carried out with a specifically conceived Beam Transport Line (BTL).
The transverse RMS beam emittance of the cyclotron was measured as a function
of several machine parameters, such as the magnetic field, RF peak voltage, and
azimuthal angle of the stripper. The beam emittance was also measured using the
method based on the quadrupole strength variation. The results obtained with
both techniques were compared and a good agreement was found. In order to
characterize the longitudinal dynamics, the proton energy distribution was
measured. For this purpose, a method was developed based on aluminum absorbers
of different thicknesses, a UniBEaM detector, and a Faraday cup. The results
were an input for a simulation of the BTL developed in the MAD-X software. This
tool allows machine parameters to be tuned online and the beam characteristics
to be optimized for specific applications.Comment: published in Journal of Instrumentatio
A Window On The Earliest Star Formation: Extreme Photoionization Conditions of a High-Ionization, Low-Metallicity Lensed Galaxy at z~2
We report new observations of SL2SJ021737-051329, a lens system consisting of
a bright arc at z=1.84435, magnified ~17x by a massive galaxy at z=0.65.
SL2SJ0217 is a low-mass (M <10^9 M*), low-metallicity (Z~1/20 Z*) galaxy, with
extreme star-forming conditions that produce strong nebular UV emission lines
in the absence of any apparent outflows. Here we present several notable
features from rest-frame UV Keck/LRIS spectroscopy: (1) Very strong narrow
emission lines are measured for CIV 1548,1550, HeII 1640, OIII] 1661,1666,
SiIII] 1883,1892, and CIII] 1907,1909. (2) Double-peaked LyA emission is
observed with a dominant blue peak and centered near the systemic velocity. (3)
The low- and high-ionization absorption features indicate very little or no
outflowing gas along the sightline to the lensed galaxy. The relative emission
line strengths can be reproduced with a very high-ionization, low-metallicity
starburst with binaries, with the exception of He \ii, which indicates an
additional ionization source is needed. We rule out large contributions from
AGN and shocks to the photoionization budget, suggesting that the emission
features requiring the hardest radiation field likely result from extreme
stellar populations that are beyond the capabilities of current models.
Therefore, SL2S0217 serves as a template for the extreme conditions that are
important for reionization and thought to be more common in the early Universe.Comment: 28 pages, 16 figures, 8 tables, re-submitted to ApJ, comments welcom
UHECR observations and lensing in the magnetic field of the Virgo cluster
We discuss how lensing by magnetic fields in galaxy clusters affects
ultrahigh energy cosmic ray (UHECR) observations. As specific example, we use
Virgo together with the cluster magnetic fields obtained earlier in a
constrained simulation of structure formation including MHD processes. We find
that, if M87 is the single source of UHECRs from Virgo, the emitted flux is
strongly anisotropic in the most interesting energy range, (50-100)EeV, and
differs from the average value by a factor five or more for a significant
fraction of observers. Since magnetic lensing is energy dependent, the external
energy spectrum as seen by different observers varies strongly too. These
anisotropies are averaged out in the case that all active galactic nuclei in
Virgo emit UHECRs. In both cases, the anisotropies of the emitted UHECR flux
may introduce an important bias in the interpretation of UHECR data like, e.g.,
the determination of the source density n_s and the source energy spectrum of
UHECRs.Comment: 12 pages, 15 eps figures; v2: extended discussion of modifications in
external energy spectrum, matches version to be publishe
GZK photons as UHECR above 10 eV
"GZK photons" are produced by extragalactic nucleons through the resonant
photoproduction of pions. We present the expected range of the GZK photon
fraction of UHECR, assuming a particular UHECR spectrum and primary nucleons,
and compare it with the minimal photon fraction predicted by Top-Down models.Comment: Talk given at TAUP2005, Sept. 10-14 2005, Zaragoza (Spain); 3 pages,
2 figure
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Inducible interleukin-1 gene expression in human vascular smooth muscle cells.
Interleukin-1 (IL-1) mediates many components of generalized host response to injury and may also contribute to local vascular pathology during immune or inflammatory responses. Because altered function of smooth muscle cells (SMC) accompanies certain vascular diseases, we tested whether SMC themselves might produce this hormone. Unstimulated SMC contain little or no IL-1 mRNA. However, exposure to bacterial endotoxin caused accumulation of IL-1 mRNA in SMC cultured from human vessels. Endotoxin maximally increased IL-1 beta mRNA in SMC after 4-6 h. The lowest effective concentration of endotoxin was 10 pg/ml. 10 ng/ml produced maximal increases in IL-1 beta mRNA. Interleukin-1 alpha mRNA was detected when SMC were incubated with endotoxin under "superinduction" conditions with cycloheximide. Endotoxin-stimulated SMC also released biologically functional IL-1, measured as thymocyte costimulation activity inhibitable by anti-IL-1 antibody. Thus, human SMC can express IL-1 beta and IL-1 alpha genes, or very similar ones, and secrete biologically active product in response to a pathological stimulus. Endogenous local production of this inflammatory mediator by the blood vessel wall's major cell type could play an important early role in the pathogenesis of vasculitis and arteriosclerosis
The Sloan Lens ACS Survey. IX. Colors, Lensing and Stellar Masses of Early-type Galaxies
We present the current photometric dataset for the Sloan Lens ACS (SLACS)
Survey, including HST photometry from ACS, WFPC2, and NICMOS. These data have
enabled the confirmation of an additional 15 grade `A' (certain) lens systems,
bringing the number of SLACS grade `A' lenses to 85; including 13 grade `B'
(likely) systems, SLACS has identified nearly 100 lenses and lens candidates.
Approximately 80% of the grade `A' systems have elliptical morphologies while
~10% show spiral structure; the remaining lenses have lenticular morphologies.
Spectroscopic redshifts for the lens and source are available for every system,
making SLACS the largest homogeneous dataset of galaxy-scale lenses to date. We
have developed a novel Bayesian stellar population analysis code to determine
robust stellar masses with accurate error estimates. We apply this code to
deep, high-resolution HST imaging and determine stellar masses with typical
statistical errors of 0.1 dex; we find that these stellar masses are unbiased
compared to estimates obtained using SDSS photometry, provided that informative
priors are used. The stellar masses range from 10^10.5 to 10^11.8 M and
the typical stellar mass fraction within the Einstein radius is 0.4, assuming a
Chabrier IMF. The ensemble properties of the SLACS lens galaxies, e.g. stellar
masses and projected ellipticities, appear to be indistinguishable from other
SDSS galaxies with similar stellar velocity dispersions. This further supports
that SLACS lenses are representative of the overall population of massive
early-type galaxies with M* >~ 10^11 M, and are therefore an ideal
dataset to investigate the kpc-scale distribution of luminous and dark matter
in galaxies out to z ~ 0.5.Comment: 20 pages, 18 figures, 5 tables, published in Ap
Disentangling Baryons and Dark Matter in the Spiral Gravitational Lens B1933+503
Measuring the relative mass contributions of luminous and dark matter in
spiral galaxies is important for understanding their formation and evolution.
The combination of a galaxy rotation curve and strong lensing is a powerful way
to break the disk-halo degeneracy that is inherent in each of the methods
individually. We present an analysis of the 10-image radio spiral lens
B1933+503 at z_l=0.755, incorporating (1) new global VLBI observations, (2) new
adaptive-optics assisted K-band imaging, (3) new spectroscopic observations for
the lens galaxy rotation curve and the source redshift. We construct a
three-dimensionally axisymmetric mass distribution with 3 components: an
exponential profile for the disk, a point mass for the bulge, and an NFW
profile for the halo. The mass model is simultaneously fitted to the kinematics
and the lensing data. The NFW halo needs to be oblate with a flattening of
a/c=0.33^{+0.07}_{-0.05} to be consistent with the radio data. This suggests
that baryons are effective at making the halos oblate near the center. The
lensing and kinematics analysis probe the inner ~10 kpc of the galaxy, and we
obtain a lower limit on the halo scale radius of 16 kpc (95% CI). The dark
matter mass fraction inside a sphere with a radius of 2.2 disk scale lengths is
f_{DM,2.2}=0.43^{+0.10}_{-0.09}. The contribution of the disk to the total
circular velocity at 2.2 disk scale lengths is 0.76^{+0.05}_{-0.06}, suggesting
that the disk is marginally submaximal. The stellar mass of the disk from our
modeling is log_{10}(M_{*}/M_{sun}) = 11.06^{+0.09}_{-0.11} assuming that the
cold gas contributes ~20% to the total disk mass. In comparison to the stellar
masses estimated from stellar population synthesis models, the stellar initial
mass function of Chabrier is preferred to that of Salpeter by a probability
factor of 7.2.Comment: 16 pages, 13 figures, minor revisions based on referee's comments,
accepted for publication in Ap
Active Galactic Nuclei and Transformation of Dark Matter into Visible Matter
The hypothesis that dark matter is converted into visible particles in active
galactic nuclei is investigated. If dark matter consists of stable superheavy
neutral particles and active galactic nuclei are rotating black holes, then,
due to the Penrose process, superheavy particles can decay into unstable
particles with larger mass, whose decay into quarks and leptons leads to events
in cosmic rays observed by the Auger group. Similar processes of decay of
superheavy particles of dark matter into visible matter occurred in the early
Universe. Numerical estimates of the processes in active galactic nuclei and in
the early Universe are given.Comment: 5 pages, LaTeX; v2: one reference added, published versio
A Search for Correlation of Ultra-High Energy Cosmic Rays with IRAS-PSCz and 2MASS-6dF Galaxies
We study the arrival directions of 69 ultra-high energy cosmic rays (UHECRs)
observed at the Pierre Auger Observatory (PAO) with energies exceeding 55 EeV.
We investigate whether the UHECRs exhibit the anisotropy signal expected if the
primary particles are protons that originate in galaxies in the local universe,
or in sources correlated with these galaxies. We cross-correlate the UHECR
arrival directions with the positions of IRAS-PSCz and 2MASS-6dF galaxies
taking into account particle energy losses during propagation. This is the
first time that the 6dF survey is used in a search for the sources of UHECRs
and the first time that the PSCz survey is used with the full 69 PAO events.
The observed cross-correlation signal is larger for the PAO UHECRs than for 94%
(98%) of realisations from an isotropic distribution when cross-correlated with
the PSCz (6dF). On the other hand the observed cross-correlation signal is
lower than that expected from 85% of realisations, had the UHECRs originated in
galaxies in either survey. The observed cross-correlation signal does exceed
that expected by 50% of the realisations if the UHECRs are randomly deflected
by intervening magnetic fields by 5 degrees or more. We propose a new method of
analysing the expected anisotropy signal, by dividing the predicted UHECR
source distribution into equal predicted flux radial shells, which can help
localise and constrain the properties of UHECR sources. We find that the 69 PAO
events are consistent with isotropy in the nearest of three shells we define,
whereas there is weak evidence for correlation with the predicted source
distribution in the two more distant shells in which the galaxy distribution is
less anisotropic.Comment: 23 pages, version published in JCA
Search for single sources of ultra high energy cosmic rays on the sky
In this paper, we suggest a new way to identify single bright sources of
Ultra High Energy Cosmic Rays (UHECR) on the sky, on top of background. We look
for doublets of events at the highest energies, E > 6 x 10^19 eV, and identify
low energy tails, which are deflected by the Galactic Magnetic Field (GMF). For
the sources which are detected, we can recover their angular positions on the
sky within one degree from the real ones in 68% of cases. The reconstruction of
the deflection power of the regular GMF is strongly affected by the value of
the turbulent GMF. For typical values of 4 microG near the Earth, one can
reconstruct the deflection power with 25% precision in 68% of cases.Comment: 20 pages, 10 figures. Corresponds to the version published in JCA
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