3,663 research outputs found
Investigation of a direction sensitive sapphire detector stack at the 5 GeV electron beam at DESY-II
Extremely radiation hard sensors are needed in particle physics experiments
to instrument the region near the beam pipe. Examples are beam halo and beam
loss monitors at the Large Hadron Collider, FLASH or XFEL. Currently artificial
diamond sensors are widely used. In this paper single crystal sapphire sensors
are considered as a promising alternative. Industrially grown sapphire wafers
are available in large sizes, are of low cost and, like diamond sensors, can be
operated without cooling. Here we present results of an irradiation study done
with sapphire sensors in a high intensity low energy electron beam. Then, a
multichannel direction-sensitive sapphire detector stack is described. It
comprises 8 sapphire plates of 1 cm^2 size and 525 micro m thickness,
metallized on both sides, and apposed to form a stack. Each second metal layer
is supplied with a bias voltage, and the layers in between are connected to
charge-sensitive preamplifiers. The performance of the detector was studied in
a 5 GeV electron beam. The charge collection efficiency measured as a function
of the bias voltage rises with the voltage, reaching about 10 % at 950 V. The
signal size obtained from electrons crossing the stack at this voltage is about
22000 e, where e is the unit charge.
The signal size is measured as a function of the hit position, showing
variations of up to 20 % in the direction perpendicular to the beam and to the
electric field. The measurement of the signal size as a function of the
coordinate parallel to the electric field confirms the prediction that mainly
electrons contribute to the signal. Also evidence for the presence of a
polarisation field was observed.Comment: 13 pages, 7 figures, 3 table
The outer crust of non-accreting cold neutron stars
The properties of the outer crust of non-accreting cold neutron stars are
studied by using modern nuclear data and theoretical mass tables updating in
particular the classic work of Baym, Pethick and Sutherland. Experimental data
from the atomic mass table from Audi, Wapstra, and Thibault of 2003 is used and
a thorough comparison of many modern theoretical nuclear models, relativistic
and non-relativistic ones, is performed for the first time. In addition, the
influences of pairing and deformation are investigated. State-of-the-art
theoretical nuclear mass tables are compared in order to check their
differences concerning the neutron dripline, magic neutron numbers, the
equation of state, and the sequence of neutron-rich nuclei up to the dripline
in the outer crust of non-accreting cold neutron stars.Comment: 20 pages, 10 figures, accepted for publication in Phys. Rev.
Dynamic changes in host-virus interactions associated with colony founding and social environment in fire ant queens (Solenopsis invicta)
Funding Information US Department of Agriculture AFRI Award. Grant Number: 2009‐35302‐05301 Marie Curie International Incoming Fellowship. Grant Number: FP7‐PEOPLE‐2013‐IIF‐625487Peer reviewedPublisher PD
The rapidly oscillating Ap star HD 99563 and its distorted dipole pulsation mode
We undertook a time-series photometric multi-site campaign for the rapidly
oscillating Ap star HD 99563 and also acquired mean light observations over two
seasons. The pulsations of the star, that show flatter light maxima than
minima, can be described with a frequency quintuplet centred on 1557.653
microHertz and some first harmonics of these. The amplitude of the pulsation is
modulated with the rotation period of the star that we determine with 2.91179
+/- 0.00007 d from the analysis of the stellar pulsation spectrum and of the
mean light data. We break the distorted oscillation mode up into its pure
spherical harmonic components and find it is dominated by the l=1 pulsation,
and also has a notable l=3 contribution, with weak l=0 and 2 components. The
geometrical configuration of the star allows one to see both pulsation poles
for about the same amount of time; HD 99563 is only the fourth roAp star for
which both pulsation poles are seen and only the third where the distortion of
the pulsation modes was modelled. We point out that HD 99563 is very similar to
the well-studied roAp star HR 3831. Finally, we note that the visual companion
of HD 99563 is located in the Delta Scuti instability strip and may thus show
pulsation. We show that if the companion was physical, the roAp star would be a
2.03 solar mass object, seen at a rotational inclination of 44 degrees, which
then predicts a magnetic obliquity of 86.4 degrees.Comment: 10 pages, 6 figures, accepted for publication by MNRA
Extragalactic Globular Clusters in the Near-Infrared: V. IC 4051 and NGC 3311
We present the results of combined optical and near-infrared photometry for
the globular cluster systems of the giant ellipticals IC 4051 and NGC 3311. We
use the reduced age-metallicity degeneracy in (V-I) vs.(V-H) color-color
diagrams to derive the cumulative age distribution within the red
sub-population of globular clusters and to search for age sub-populations. The
age distribution is then compared to the one determined for simulated globular
cluster systems in order to set constraints on the relative age and size of
these globular cluster sub-populations. In both galaxies we find a significant
fraction of globular clusters with ages between 2- 5 Gyr. We also investigate
the metallicity distribution in both systems. Small number statistics prevent
us from making any definite statements concerning NGC 3311, but we find that
the derived metallicity distribution of the IC 4051 clusters strongly depends
on the assumed age distribution. Based on our most likely result that finds a
large number of young/intermediate age clusters (~2 Gyr) within the selected
globular cluster sample, we find metallicity peaks at -0.2 for the old
clusters and +0.8 for the young clusters. Only few very metal poor clusters are
found. However, the metallicity distribution within the young/intermediate
globular cluster population is significantly affected by our choice of the
applied Single Stellar Population model. The mean metallicity of the second
generation of globular clusters changes from the above mentioned and extremely
high +0.8 dex to +0.2 dex. Note that the model dependency becomes less severe
with an increasing age of the cluster population.Comment: 21 pages, 21 figures, A&A, accepte
Extinction ratios in the inner Galaxy as revealed by the VVV survey
Accepted for publication in ApJ Letters, 10 pages, 3 Figures, 2 Tables © 2017 The American Astronomical Society. All rights reserved.Interstellar extinction towards the Galactic Center is large and significantly differential. Its reddening and dimming effects in red clump stars in the Galactic Bulge can be exploited to better constrain the extinction law towards the innermost Galaxy. By virtue of a deep and complete catalog of more than 30 million objets at and obtained from VVV survey observations, we apply the red clump method to infer the selective-to-total extinction ratios in the , , , and broadband near-infrared filters. The measured values are smaller than previously reported, and are not constant, with mean values, e.g., and . We also obtain a ratio :::: of 7.74:5.38:3.30:1.88:1.0, implying extinction towards the Galactic Center to follow a distribution as a function of wavelength steeper than previously reported, consistent with a power law in the near-infrared.Peer reviewedFinal Accepted Versio
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