477 research outputs found
Multimeson production in pp interactions as a background for eta and eta' decays
Multimeson production in pp interactions comprises important background for
eta, omega and eta' mesons production experiments and for the studies of their
decays planned with WASA detector at COSY. The available information about the
reactions is summarized and the need for efforts to describe the processes is
stressed.Comment: Proceedings of MENU07 Conference Julich, Germany 200
Red giants from the Pennsylvania - Torun Planet Search
The main goal of the Pennsylvania - Torun Planet Search (PTPS) is detection
and characterization of planets around evolved stars using the high-accuracy
radial velocity (RV) technique. The project is performed with the 9.2 m
Hobby-Eberly Telescope. To determine stellar parameters and evolutionary status
for targets observed within the survey complete spectral analysis of all
objects is required. In this paper we present the atmospheric parameters
(effective temperatures, surface gravities, microturbulent velocities and
metallicities) of a subsample of Red Giant Clump stars using strictly
spectroscopic methods based on analysis of equivalent widths of Fe I and Fe II
lines. It is shown that our spectroscopic approach brings reliable and
consistent results.Comment: 3 pages, 2 figures, proceeding of the conference "New Technologies
for Probing the Diversity of Brown Dwarfs and Exoplanets" (Shangai, China,
July 19-24, 2009), to appear in EPJ Web of Conference
The Penn State - Toru\'n Planet Search: target characteristics and recent results
More than 450 stars hosting planets are known today but only approximately 30
planetary systems were discovered around stars beyond the Main Sequence. The
Penn State-Toru\'n Planet Search, putting an emphasis on extending studies of
planetary system formation and evolution to intermediate-mass stars, is
oriented towards the discoveries of substellar-mass companions to a large
sample of evolved stars using high-precision radial velocity technique. We
present the recent status of our survey and detailed characteristic for ~350
late type giant stars, i.e. the new results of radial velocity analysis and
stellar fundamental parameters obtained with extensive spectroscopic method.
Moreover, in the future we will make an attempt to perform the statistical
study of our sample and searching the correlations between the existence of
substellar objects and stellar atmospheric parameters according to previous
works which investigated the planetary companion impact on the evolution of the
host stars.Comment: 7 pages, 5 figures, proceeding of the conference "Planetary Systems
beyond the Main Sequence" (Bamberg, Germany, August 11-14, 2010) edited by S.
Schuh, H. Drechsel and U. Heber, AIP Conference Series, part of
PlanetsbeyondMS/2010 proceedings http://arxiv.org/html/1011.660
CERTAIN MODIFICATIONS OF AITKEN'S ACCELERATOR FOR SLOWLY CONVERGENT SEQUENCES
The paper presents three modifications of the Aitken accelerator for slowly or irregularly
convergent sequences. The first proposal, based on backward extension of a sequence,
is particularly useful if a small number of regular sequence terms is known. The next
two procedures - integral exponential and hyperbolic - can be applied to sequences with
irregular or disturbed convergence. Numerical examples show essential error reduction of
the limit of sequences under consideration
Planets Around the K-Giants BD+20 274 and HD 219415
We present the discovery of planet-mass companions to two giant stars by the
ongoing Penn State- Toru\'n Planet Search (PTPS) conducted with the 9.2 m
Hobby-Eberly Telescope. The less massive of these stars, K5-giant BD+20 274,
has a 4.2 MJ minimum mass planet orbiting the star at a 578-day period and a
more distant, likely stellar-mass companion. The best currently available model
of the planet orbiting the K0-giant HD 219415 points to a Jupiter-mass
companion in a 5.7-year, eccentric orbit around the star, making it the longest
period planet yet detected by our survey. This planet has an amplitude of
\sim18 m/s, comparable to the median radial velocity (RV) "jitter", typical of
giant stars.Comment: 5 figures, 13 pages, accepted by the Astrophysical Journal. arXiv
admin note: substantial text overlap with arXiv:1110.164
Cluster analysis of the impact of air back-trajectories on aerosol optical properties at Hornsund, Spitsbergen
In this paper, spectra of aerosol optical thickness from the AERONET (AErosol RObotic NETwork) station at Hornsund in the southern part of Spitsbergen were employed to study the impact of air mass history on aerosol optical thickness for wavelength λ=500 nm – AOT(500) – and the Ångström exponent. Backward trajectories computed, using the NOAA HYSPLIT model, were used to trace air history. It was found that in spring, the changes in AOT values over the Hornsund station were strongly influenced by air mass trajectories 8 days or longer in duration, arriving both in the free troposphere and at an altitude of 1 km above sea level. Nevertheless, free tropospheric advection was dominant. AOT variability in summer was best explained by the local direction and speed of advection (1-day trajectories) and was dominated by the effectiveness of cleansing processes. During the ASTAR 2007 campaign, the aerosols near Hornsund displayed low AOT values ranging from 0.06 to 0.09, which is lower than the mean AOT(500) for spring seasons from 2005 to 2007 (0.110±0.007; mean ± standard deviation of mean). 9 April 2007 with AOT(500)=0.147 was exceptional. The back-trajectories belonged to clusters with low and average cluster mean AOT. Apart from the maximum AOT of 9 April 2007, the observed AOT values were close to or lower than the means for the clusters to which they belonged
Excitonic fine structure and binding energies of excitonic complexes in single InAs quantum dashes
P.M., J.M. and G. S. acknowledge support from the grant of National Science Centre of Poland No. 2011/02/A/ST3/00152 (Maestro), whereas M.Z. acknowledges support from the Polish National Science Centre under grant No. 2015/18/E/ST3/005 (Sonata Bis). The experiments have partially been performed within the Wroclaw University of Science and Technology laboratory infrastructure financed by the Polish Ministry of Science and Higher Education Grant No. 6167/IA/119/2012.The fundamental electronic and optical properties of elongated InAs nanostructures embedded in quaternary InGaAlAs barrier are investigated by means of high-resolution optical spectroscopy and many-body atomistic tight-binding theory. These wire-like shaped self-assembled nanostructures are known as quantum dashes and are typically formed during the molecular beam epitaxial growth on InP substrates. In this work we study properties of excitonic complexes confined in quantum dashes emitting in a broad spectral range from below 1.2 to 1.55 μm. We find peculiar trends for the biexciton and negative trion binding energies, with pronounced trion binding in smaller size quantum dashes. These experimental findings are then compared and qualitatively explained by atomistic theory. The theoretical analysis shows a fundamental role of correlation effects for the absolute values of excitonic binding energies. Eventually, we determine the bright exciton fine structure splitting (FSS), where both the experiment and theory predict a broad distribution of the splitting varying from below 50 to almost 180 μeV. We identify several key factors determining the FSS values in such nanostructures including quantum dash size variation and composition fluctuations.PostprintPeer reviewe
System Response Kernel Calculation for List-mode Reconstruction in Strip PET Detector
Reconstruction of the image in Positron Emission Tomographs (PET) requires
the knowledge of the system response kernel which describes the contribution of
each pixel (voxel) to each tube of response (TOR). This is especially important
in list-mode reconstruction systems, where an efficient analytical
approximation of such function is required. In this contribution, we present a
derivation of the system response kernel for a novel 2D strip PET.Comment: 10 pages, 2 figures; Presented at Symposium on applied nuclear
physics and innovative technologies, Cracow, 03-06 June 201
Application of Compressive Sensing Theory for the Reconstruction of Signals in Plastic Scintillators
Compressive Sensing theory says that it is possible to reconstruct a measured
signal if an enough sparse representation of this signal exists in comparison
to the number of random measurements. This theory was applied to reconstruct
signals from measurements of plastic scintillators. Sparse representation of
obtained signals was found using SVD transform.Comment: 7 pages, 3 figures; Presented at Symposium on applied nuclear physics
and innovative technologies, Cracow, 03-06 June 201
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