1,949 research outputs found
VLT spectroscopy of globular clusters in the Sombrero galaxy
We have obtained intermediate-resolution VLT spectroscopy of 75 globular
cluster candidates around the Sa galaxy M104 (NGC4594). Fifty-seven candidates
out to ~ 40 kpc in the halo of the galaxy were confirmed to be bona-fide
globular clusters, 27 of which are new. A first analysis of the velocities
provides only marginal evidence for rotation of the cluster system. From Hbeta
line strengths, almost all of the clusters in our sample have ages that are
consistent, within the errors, with Milky Way globular clusters. Only a few
clusters may be 1-2 Gyr old, and bulge and halo clusters appear coeval. The
absorption line indices follow the correlations established for the Milky Way
clusters. Metallicities are derived based upon new empirical calibrations with
Galactic globular clusters taking into account the non-linear behavior of some
indices (e.g., Mg2). Our sample of globular clusters in NGC4594 spans a
metallicity range of -2.13 < [Fe/H] < +0.26 dex, and the median metallicity of
the system is [Fe/H] = -0.85. Thus, our data provide evidence that some of the
clusters have super-solar metallicity. Overall, the abundance distribution of
the cluster system is consistent with a bimodal distribution with peaks at
[Fe/H] ~- 1.7 and -0.7. However, the radial change in the metallicity
distribution of clusters may not be straightforwardly explained by a varying
mixture of two sub-populations of red and blue clusters.Comment: 6 pages (incl. 4 figures) to appear in the proceedings of the ESO
workshop "Extragalactic Globular Cluster Systems", ESO Astrophysics Symp.,
Garching bei Muenchen (Germany), ed. Kissler-Patig M., Springer-Verlag:
Heidelber
Design Oriented Aerodynamic Modelling of Wind Turbine Performance
The development of a wind turbine aerodynamics model using a Boundary Integral Equation model (BIEM) is presented. The methodology is valid to study inviscid unsteady flows around three dimensional bodies of arbitrary shape and arbitrarily moving with respect to the incoming flow. The extension of this methodology to study viscosity effects in turbine blade flow at high angle of attack is addressed and an approach to determine aerodynamic loads over a wide range of turbine operating conditions is proposed. Numerical applications considering a selected test cases from the NREL experimental dataset are presented. Finally, the application of the proposed turbine aerodynamics model into a multi-disciplinary study including aeroelasticity of pylon-turbine assembly and aeroacoustics modelling of induced noise is briefly described
Comparison between 1-D and grey-box models of a SOFC
Solid Oxide Fuel Cells (SOFCs) have shown unique performance in terms of greater electrical efficiency and thermochemical integrity with the power systems compared to gas turbines and internal combustion engines. Nonetheless, simple and reliable models still must be defined. In this paper, a comparison between a grey-box model and a 1-D model of a SOFC is performed to understand the impact of the heat transfer inside the cell on the internal temperature distribution of the solid electrolyte. Hence, a significant internal temperature peak of the solid electrolyte is observed for a known difference between anode and cathode inlet temperatures. Indeed, it highlights the difference between the 1-D model and the grey-box model regarding the thermal conditioning of the SOFC. Therefore, the results of this study can be used to investigate the reliability of the thermal results of box models in system-level simulations
Spectroscopy of very hot plasma in non-flaring parts of a solar limb active region: spatial and temporal properties
In this work we investigate the thermal structure of an off-limb active
region in various non-flaring areas, as it provides key information on the way
these structures are heated. In particular, we concentrate in the very hot
component (>3 MK) as it is a crucial element to discriminate between different
heating mechanisms. We present an analysis using Fe and Ca emission lines from
both SOHO/SUMER and HINODE/EIS. A dataset covering all ionization stages from
Fe X to Fe XIX has been used for the thermal analysis (both DEM and EM). Ca XIV
is used for the SUMER-EIS radiometric cross-calibration.
We show how the very hot plasma is present and persistent almost everywhere
in the core of the limb AR. The off-limb AR is clearly structured in Fe XVIII.
Almost everywhere, the EM analysis reveals plasma at 10 MK (visible in Fe XIX
emission) which is down to 0.1% of EM of the main 3 MK plasma. We estimate the
power law index of the hot tail of the EM to be between -8.5 and -4.4. However,
we leave an open question on the possible existence of a small minor peak at
around 10 MK. The absence in some part of the AR of Fe XIX and Fe XXIII lines
(which fall into our spectral range) enables us to determine an upper limit on
the EM at such temperatures. Our results include a new Ca XIV 943.59 \AA~
atomic model
Remote light source for silicon photonic transceivers in mobile fronthaul applications
The design and experimental characterisation of a depolarised light source for feeding a remote transceiver based on silicon photonics are presented. Since the transceiver only works in TE mode, the source is designed to deliver, over up to 10 km standard single-mode fibre links, a continuous-wave light with almost constant power along this polarisation direction, whatever be the random polarisation rotation because of the fibre link. The depolarised light source is realised by combining the output of two independent distributed feedback lasers, having orthogonal polarisation and controlled frequency difference. The transmission performance and stability of the remote light source are successfully tested
Patterns of Italian high school and university students’ attitudes towards physics: an analysis based on semiotic-cultural perspective
The purpose of this study was to analyse Italian high school and university students’ attitudes towards physics using the Semiotic Cultural Psychological Theory (SCPT). In the SCPT framework, attitudes represent how individuals interpret their experience through the mediation of generalized meaning with which they are identified. A view-of-physics questionnaire was used as an instrument to collect data with 1603 high school and university students. Data were analysed through multiple correspondence analysis and cluster analysis. We identified four generalized meanings of physics: (a) interesting and important for society; (b) a quite interesting, but badly taught subject at school and not completely useful for society; (c) difficult to study and irrelevant for society; and (d) a fascinating and protective niche from society. The identified generalized meanings are significantly correlated to the choice to study physics at undergraduate level and to the choice of attending physics-related activities in high school. Implications for research are discussed
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