219 research outputs found
Deriving Bounds on the Size of Spatial Areas
Many application domains such as surveillance, environmental monitoring or sensor-data processing need upper and lower bounds on areas that are covered by a certain feature. For example, a smart-city infrastructure might need bounds on the size of an area polluted with fine-dust, to re-route combustion-engine traffic. Obtaining such bounds is challenging, because in almost any real-world application, information about the region of interest is incomplete, e.g., the database of sensor data contains only a limited number of samples. Existing approaches cannot provide upper and lower bounds or depend on restrictive assumptions, e.g., the area must be convex. Our approach in turn is based on the natural assumption that it is possible to specify a minimal diameter for the feature in question. Given this assumption, we formally derive bounds on the area size, and we provide algorithms that compute these bounds from a database of sensor data, based on geometrical considerations. We evaluate our algorithms both with a real-world case study and with synthetic data
Clinical trial updates and hotline sessions presented at the European Society of Cardiology Congress 2008
This article summarizes the results of a number of clinical trials in the field of cardiovascular medicine which were presented during the Hotline and Clinical Trial Update Sessions at the annual meeting of the European Society of Cardiology, held in Munich, Germany, from 30th August to 3rd September 2008. The data were presented by leading experts in the field with relevant positions in the trials. It is important to note that unpublished reports should be considered as preliminary data, as the analysis may change in the final publications. The comprehensive summaries have been generated from the oral presentation and the webcasts of the European Society of Cardiology and should provide the readers with the most comprehensive information on diagnostic and therapeutic developments in cardiovascular medicine
Can rotation explain the multiple main sequence turn-offs of Magellanic Cloud star clusters?
Many intermediate age star clusters in the Magellanic Clouds present multiple
main sequence turn-offs (MMSTO), which challenge the classical idea that star
formation in such objects took place over short timescales. It has been
recently suggested that the presence of fast rotators among main sequence stars
could be the cause of such features (Bastian & de Mink 2009), hence relaxing
the need for extended periods of star formation. In this letter, we compute
evolutionary tracks and isochrones of models with and without rotation. We find
that, for the same age and input physics, both kinds of models present
turn-offs with an almost identical position in the colour-magnitude diagrams.
As a consequence, a dispersion of rotational velocities in coeval ensembles of
stars could not explain the presence of MMSTOs. We construct several synthetic
colour-magnitude diagrams for the different kinds of tracks and combinations of
them. The models that best reproduce the morphology of observed MMSTOs are
clearly those assuming a significant spread in the stellar ages - as long as
~400 Myr - added to a moderate amount of convective core overshooting. Only
these models produce the detailed "golf club" shape of observed MMSTOs. A
spread in rotational velocities alone cannot do anything similar. We also
discuss models involving a mixture of stars with and without overshooting, as
an additional scenario to producing MMSTOs with coeval populations. We find
that they produce turn-offs with a varying extension in the CMD direction
perpendicular to the lower main sequence, which are clearly not present in
observed MMSTOs.Comment: To appear in MNRAS Letters. Figs. 2 and 3 are in colou
Effect of Recombination Catalyst Loading in PEMWE Membranes on Anodic Hydrogen Content Reduction
Integrating platinum-based recombination catalysts into proton exchange membrane water electrolysis systems effectively reduces the anodic hydrogen content. We studied the effect of the platinum loading of an interlayer close to the anode within the membrane on the anodic hydrogen in oxygen content. For the investigated Pt-loadings between 1 μgPt cm−2 and 140 μgPt cm−2, the results revealed that for a 110 μm membrane, 7 μgPt cm−2 were sufficient to allow a safe operation at cathode pressures up to 10 bar. A further increase of the Pt-loading did not significantly improve the reduction of the anodic hydrogen in oxygen content
Communication - Proving the Importance of Pt-Interlayer Position in PEMWE Membranes for the Effective Reduction of the Anodic Hydrogen Content
Gas crossover through the membrane poses a significant challenge to proton exchange membrane water electrolysers. This work investigates the influence of the position of platinum-based recombination interlayers integrated in the membrane on the anodic hydrogen in oxygen content. The results show that all interlayer positions reduce the anodic hydrogen content without performance losses compared to the reference without interlayer. However, an interlayer positioned closer to the anode is more effective than closer to the cathode. Further, the effect of the interlayer is more pronounced with increasing anode pressure. © 2021 The Author(s). Published on behalf of The Electrochemical Society by IOP Publishing Limited
Turbulent Convection in Stellar Interiors. II. The Velocity Field
We analyze stellar convection with the aid of 3D hydrodynamic simulations,
introducing the turbulent cascade into our theoretical analysis. We devise
closures of the Reynolds-decomposed mean field equations by simple physical
modeling of the simulations (we relate temperature and density fluctuations via
coefficients); the procedure (CABS, Convection Algorithms Based on Simulations)
is terrestrially testable and is amenable to systematic improvement. We develop
a turbulent kinetic energy equation which contains both nonlocal and time
dependent terms, and is appropriate if the convective transit time is shorter
than the evolutionary time scale. The interpretation of mixing-length theory
(MLT) as generally used in astrophysics is incorrect; MLT forces the mixing
length to be an imposed constant. Direct tests show that the damping associated
with the flow is that suggested by Kolmogorov. The eddy size is approximately
the depth of the convection zone, and this dissipation length corresponds to
the "mixing length". New terms involving local heating by turbulent dissipation
should appear in the stellar evolution equations. The enthalpy flux
("convective luminosity") is directly connected to the buoyant acceleration,
and hence the velocity scale. MLT tends to systematically underestimate this
velocity scale. Quantitative comparison with a variety of 3D simulations
reveals a previously recognized consistency. Examples of application to stellar
evolution will be presented in subsequent papers in this series.Comment: 47 pages, 7 figures, accepted by Ap
Effects of face masks on performance and cardiorespiratory response in well-trained athletes
Background
During the COVID-19 pandemic, compulsory masks became an integral part of outdoor sports such as jogging in crowded areas (e.g. city parks) as well as indoor sports in gyms and sports centers. This study, therefore, aimed to investigate the effects of medical face masks on performance and cardiorespiratory parameters in athletes.
Methods
In a randomized, cross-over design, 16 well-trained athletes (age 27 ± 7 years, peak oxygen consumption 56.2 ± 5.6 ml kg−1 min−1, maximum performance 5.1 ± 0.5 Watt kg−1) underwent three stepwise incremental exercise tests to exhaustion without mask (NM), with surgical mask (SM) and FFP2 mask (FFP2). Cardiorespiratory and metabolic responses were monitored by spiroergometry and blood lactate (BLa) testing throughout the tests.
Results
There was a large effect of masks on performance with a significant reduction of maximum performance with SM (355 ± 41 Watt) and FFP2 (364 ± 43 Watt) compared to NM (377 ± 40 Watt), respectively (p < 0.001; ηp2 = 0.50). A large interaction effect with a reduction of both oxygen consumption (p < 0.001; ηp2 = 0.34) and minute ventilation (p < 0.001; ηp2 = 0.39) was observed. At the termination of the test with SM 11 of 16 subjects reported acute dyspnea from the suction of the wet and deformed mask. No difference in performance was observed at the individual anaerobic threshold (p = 0.90).
Conclusion
Both SM and to a lesser extent FFP2 were associated with reduced maximum performance, minute ventilation, and oxygen consumption. For strenuous anaerobic exercise, an FFP2 mask may be preferred over an SM
Clinical trial updates and hotline sessions presented at the European Society of Cardiology Congress 2008
This article summarizes the results of a number of clinical trials in the field of cardiovascular medicine which were presented during the Hotline and Clinical Trial Update Sessions at the annual meeting of the European Society of Cardiology, held in Munich, Germany, from 30th August to 3rd September 2008. The data were presented by leading experts in the field with relevant positions in the trials. It is important to note that unpublished reports should be considered as preliminary data, as the analysis may change in the final publications. The comprehensive summaries have been generated from the oral presentation and the webcasts of the European Society of Cardiology and should provide the readers with the most comprehensive information on diagnostic and therapeutic developments in cardiovascular medicine
A Comprehensive Spectroscopic Analysis of DB White Dwarfs
We present a detailed analysis of 108 helium-line (DB) white dwarfs based on
model atmosphere fits to high signal-to-noise optical spectroscopy. We derive a
mean mass of 0.67 Mo for our sample, with a dispersion of only 0.09 Mo. White
dwarfs also showing hydrogen lines, the DBA stars, comprise 44% of our sample,
and their mass distribution appears similar to that of DB stars. As in our
previous investigation, we find no evidence for the existence of low-mass (M <
0.5 Mo) DB white dwarfs. We derive a luminosity function based on a subset of
DB white dwarfs identified in the Palomar-Green survey. We show that 20% of all
white dwarfs in the temperature range of interest are DB stars, although the
fraction drops to half this value above Teff ~ 20,000 K. We also show that the
persistence of DB stars with no hydrogen features at low temperatures is
difficult to reconcile with a scenario involving accretion from the
interstellar medium, often invoked to account for the observed hydrogen
abundances in DBA stars. We present evidence for the existence of two different
evolutionary channels that produce DB white dwarfs: the standard model where DA
stars are transformed into DB stars through the convective dilution of a thin
hydrogen layer, and a second channel where DB stars retain a helium-atmosphere
throughout their evolution. We finally demonstrate that the instability strip
of pulsating V777 Her white dwarfs contains no nonvariables, if the hydrogen
content of these stars is properly accounted for.Comment: 74 pages including 30 figures, accepted for publication in the
Astrophysical Journa
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