111 research outputs found
Air pollution modelling using a graphics processing unit with CUDA
The Graphics Processing Unit (GPU) is a powerful tool for parallel computing.
In the past years the performance and capabilities of GPUs have increased, and
the Compute Unified Device Architecture (CUDA) - a parallel computing
architecture - has been developed by NVIDIA to utilize this performance in
general purpose computations. Here we show for the first time a possible
application of GPU for environmental studies serving as a basement for decision
making strategies. A stochastic Lagrangian particle model has been developed on
CUDA to estimate the transport and the transformation of the radionuclides from
a single point source during an accidental release. Our results show that
parallel implementation achieves typical acceleration values in the order of
80-120 times compared to CPU using a single-threaded implementation on a 2.33
GHz desktop computer. Only very small differences have been found between the
results obtained from GPU and CPU simulations, which are comparable with the
effect of stochastic transport phenomena in atmosphere. The relatively high
speedup with no additional costs to maintain this parallel architecture could
result in a wide usage of GPU for diversified environmental applications in the
near future.Comment: 5 figure
Thermomechanische Resistenz und chemische Beständigkeit spektral selektiver Mehrschichtsysteme für die Architekturverglasung
Die vorliegende Arbeit verfolgt das Ziel der Entwicklung neuer, hochresistenter Sonnen- und Wärmeschutzschichten für Architekturglas zur optimalen Kontrolle des Gesamtenergiedurch-lassgrades (g-Wert) bei Gebäudeverglasung. Das Ziel hoher Resistenz bezieht sich dabei auf den Erhalt der Schichteigenschaften bei Wärmebehandlung (Temperung, thermisches Vor-spannen), korrosivem Angriff (Glas- und Schichtkorrosion) und mechanischer Belastung (Handling und Reinigung). Mittels systematischer Analyse einer Reihe von Defekten bei Sonnen- und Wärmeschutzschichten, die gezielt durch Wärmebehandlung, Korrosionstest und mechanische Belastung herbeigeführt werden, erfolgt die Verknüpfung zwischen Schädi-gungsursache und -wirkung. Auf Basis der resultierenden Ergebnisse und mit dem Verständnis der schädigenden Prozesse werden Modellbeschichtungen hergestellt, hinsichtlich ihrer Resistenz und Materialeigenschaften untersucht und eine Verbindung zwischen Stabilitätsmerkmalen wie Temperatur, Abrieb- und Feuchtebeständigkeit und materialspezifischen Eigenschaften wie Struktur, Eigenspannungen und Elastizität hergestellt. Im Ergebnis dienen die gewonnenen Erkenntnisse als methodische Grundlage und erster Entwicklungsansatz hin zu Beschichtungen höherer Resistenz
Dust is forming along the red giant branch of 47 TUC
We present additional evidence that dust is really forming along the red
giant branch (RGB) of 47 Tuc at luminosities ranging from above the horizontal
branch to the RGB-tip (Origlia et al. 2007). The presence of dust had been
inferred from an infrared excess in the (K-8) color, with K measured from high
spatial resolution ground based near-IR photometry and "8" referring to
Spitzer-IRAC 8 micron photometry. We show how (K-8) is a far more sensitive
diagnostic for detecting tiny circumstellar envelopes around warm giants than
colors using only the Spitzer-IRAC bands, for example the (3.6-8) color used by
Boyer et al. (2010). In addition, we also show high resolution HST-ACS I band
images of the giant stars which have (K-8) color excess. These images clearly
demonstrate that Boyer et al (2010) statement that our detections of color
excess associated with stars below the RGB-tip arise from blends and artefacts
is simply not valid.Comment: 12 pages, 4 figure
Gamma-Ray Burst Spectral Correlations: Photospheric and Injection Effects
We present a physical framework that can account for most of the observed
spectral properties of the prompt gamma-ray burst emission. This includes the
variety of spectral shapes, shape evolutions, and spectral correlations between
flux and spectral peak, within bursts described by Borgonovo & Ryde, and among
bursts described by Amati/Ghirlanda. In our proposed model the spectral peak is
given by the photospheric emission from a relativistic outflow for which the
horizon length is much smaller than the radial width. The observed duration of
the thermal flash will be given by the radial light-crossing time. This then
gives that the typical emission site is at ~10e11 cm from the center, with a
Lorentz factor of ~300. This emission is accompanied by non-thermal emission
from dissipation locations outside the photosphere. The relative strength of
these two components depend on injection effects at the central engine leading
to varying relative location of the saturation and photospheric radii. The
total emission can then reproduce the observed variety. The spectral
correlations are found by assuming that the amount of energy dissipated depends
non-linearly on the averaged particle density. Beside the spectral correlations
this also gives a description of how the relative strength of the thermal
component varies with temperature within a burst.Comment: ApJ accepted, acknowledgement adde
VLBI and Archival VLA and WSRT Observations of the GRB 030329 Radio Afterglow
We present VLBI and archival Karl G. Jansky Very Large Array (VLA) and
Westerbork Synthesis Radio Telescope (WSRT) observations of the radio afterglow
from the gamma-ray burst (GRB) of 2003 March 29 (GRB 030329) taken between 672
and 2032 days after the burst. The EVLA and WSRT data suggest a simple power
law decay in the flux at 5 GHz, with no clear signature of any rebrightening
from the counter jet. We report an unresolved source at day 2032 of size
mas, which we use in conjunction with the expansion rate of the
burst to argue for the presence of a uniform, ISM-like circumburst medium.
We develop a semi-analytic method to model gamma-ray burst afterglows, and
apply it to the 5 GHz light curve to perform burst calorimetry. A limit of mas yr is placed on the proper motion, supporting the standard
afterglow model for gamma-ray bursts.Comment: 24 pages, 5 figure
An Observed Correlation Between Thermal and Non-Thermal Emission in Gamma-Ray Bursts
Recent observations by the Gamma-ray Space Telescope have confirmed
the existence of thermal and non-thermal components in the prompt photon
spectra of some Gamma-ray bursts (GRBs). Through an analysis of six bright
Fermi GRBs, we have discovered a correlation between the observed photospheric
and non-thermal -ray emission components of several GRBs using a
physical model that has previously been shown to be a good fit to the Fermi
data. From the spectral parameters of these fits we find that the
characteristic energies, and , of these two components are
correlated via the relation which varies from
GRB to GRB. We present an interpretation in which the value of index
indicates whether the jet is dominated by kinetic or magnetic energy. To date,
this jet composition parameter has been assumed in the modeling of GRB outflows
rather than derived from the data
Very Metal-poor Stars in the Outer Galactic Bulge Found by the Apogee Survey
Despite its importance for understanding the nature of early stellar
generations and for constraining Galactic bulge formation models, at present
little is known about the metal-poor stellar content of the central Milky Way.
This is a consequence of the great distances involved and intervening dust
obscuration, which challenge optical studies. However, the Apache Point
Observatory Galactic Evolution Experiment (APOGEE), a wide-area, multifiber,
high-resolution spectroscopic survey within Sloan Digital Sky Survey III
(SDSS-III), is exploring the chemistry of all Galactic stellar populations at
infrared wavelengths, with particular emphasis on the disk and the bulge. An
automated spectral analysis of data on 2,403 giant stars in twelve fields in
the bulge obtained during APOGEE commissioning yielded five stars with low
metallicity([Fe/H]), including two that are very metal-poor
[Fe/H] by bulge standards.
Luminosity-based distance estimates place the five stars within the outer
bulge, where other 1,246 of the analyzed stars may reside. A manual reanalysis
of the spectra verifies the low metallicities, and finds these stars to be
enhanced in the -elements O, Mg, and Si without significant
-pattern differences with other local halo or metal-weak thick-disk
stars of similar metallicity, or even with other more metal-rich bulge stars.
While neither the kinematics nor chemistry of these stars can yet definitively
determine which, if any, are truly bulge members, rather than denizens of other
populations co-located with the bulge, the newly-identified stars reveal that
the chemistry of metal-poor stars in the central Galaxy resembles that of
metal-weak thick-disk stars at similar metallicity.Comment: 6 pages, 3 figures, 2 table
Crystallisation Kinetics of a β
LZSA (Li2O-ZrO2-SiO2-Al2O3) glass ceramic system has shown high potential to obtain LTCC laminate tapes at low sintering temperature (<1000°C) for several applications, such as screen-printed electronic components. Furthermore, LZSA glass ceramics offer interesting mechanical, chemical, and thermal properties, which make LZSA also a potential candidate for fabricating multilayered structures processed by Laminated Objects Manufacturing (LOM) technology. The crystallization kinetics of an LZSA glass ceramic with a composition of 16.9Li2O⋅5.0ZrO2⋅65.1SiO2⋅8.6Al2O3 was investigated using nonisothermal methods by differential thermal analysis and scanning electronic microscopy. Apparent activation energy for crystallization was found to be in the 274–292 kJ⋅mol−1 range, and an Avrami parameter n of 1 was obtained that is compared very favorably with SEM observations
Tracing chemical evolution over the extent of the Milky Way's Disk with APOGEE Red Clump Stars
We employ the first two years of data from the near-infrared, high-resolution
SDSS-III/APOGEE spectroscopic survey to investigate the distribution of
metallicity and alpha-element abundances of stars over a large part of the
Milky Way disk. Using a sample of ~10,000 kinematically-unbiased red-clump
stars with ~5% distance accuracy as tracers, the [alpha/Fe] vs. [Fe/H]
distribution of this sample exhibits a bimodality in [alpha/Fe] at intermediate
metallicities, -0.9<[Fe/H]<-0.2, but at higher metallicities ([Fe/H]=+0.2) the
two sequences smoothly merge. We investigate the effects of the APOGEE
selection function and volume filling fraction and find that these have little
qualitative impact on the alpha-element abundance patterns. The described
abundance pattern is found throughout the range 5<R<11 kpc and 0<|Z|<2 kpc
across the Galaxy. The [alpha/Fe] trend of the high-alpha sequence is
surprisingly constant throughout the Galaxy, with little variation from region
to region (~10%). Using simple galactic chemical evolution models we derive an
average star formation efficiency (SFE) in the high-alpha sequence of ~4.5E-10
1/yr, which is quite close to the nearly-constant value found in
molecular-gas-dominated regions of nearby spirals. This result suggests that
the early evolution of the Milky Way disk was characterized by stars that
shared a similar star formation history and were formed in a well-mixed,
turbulent, and molecular-dominated ISM with a gas consumption timescale (1/SFE)
of ~2 Gyr. Finally, while the two alpha-element sequences in the inner Galaxy
can be explained by a single chemical evolutionary track this cannot hold in
the outer Galaxy, requiring instead a mix of two or more populations with
distinct enrichment histories.Comment: 18 pages, 17 figures. Accepted for publication in Ap
Risk of diabetes and the impact on preexisting diabetes in patients with lymphoma treated with steroid-containing immunochemotherapy
First-line treatments for lymphomas often include high doses of prednisolone, but the risks of new-onset diabetes mellitus (DM) or worsening of preexisting DM following treatment with cyclic high dose corticosteroids is unknown. This cohort study matched non-Hodgkin lymphoma (NHL) patients treated with steroid-containing immunochemotherapy (ie, R-CHOP[-like] and R-CVP) between 2002 and 2015 to individuals from the Danish population to investigate the risks of new-onset DM. For patients with preexisting DM, the risks of insulin dependency and anthracycline-associated cardiovascular diseases (CVDs) were assessed. In total, 5672 NHL patients and 28 360 matched comparators were included. Time-varying incidence rate ratios (IRRs) showed increased risk of DM in the first year after treatment compared with matched comparators, with the highest IRR being 2.7. The absolute risks were higher among patients in the first 2 years, but the difference was clinically insignificant. NHL patients with preexisting DM had increased risks of insulin prescriptions with 0.5-, 5-, and 10-year cumulative risk differences of insulin treatment of 15.3, 11.8, and 6.0 percentage units as compared with the DM comparators. In a landmark analysis at 1 year, DM patients with lymphoma had decreased risks of insulin dependency compared with comparators. Time-varying IRRs showed a higher CVD risk for NHL patients with DM as compared with comparators in the first year after treatment. NHL patients treated with steroid-containing immunochemotherapy regimens have a clinically insignificant increased risk of DM in the first year following treatment, and patients with preexisting DM have a temporary increased risk of insulin prescriptions and CVD
- …