1,538 research outputs found
HST color-magnitude diagrams of 74 galactic globular clusters in the HST F439W and F555W bands
We present the complete photometric database and the color-magnitude diagrams
for 74 Galactic globular clusters observed with the HST/WFPC2 camera in the
F439W and F555W bands. A detailed discussion of the various reduction steps is
also presented, and of the procedures to transform instrumental magnitudes into
both the HST F439W and F555W flight system and the standard Johnson B and V
systems. We also describe the artificial star experiments which have been
performed to derive the star count completeness in all the relevant branches of
the color magnitude diagram. The entire photometric database and the
completeness function will be made available on the Web immediately after the
publication of the present paper.Comment: 21 pages, 77 figures. High resolution version of this paper can be
retrived at http://dipastro.pd.astro.it/globular
Dust remobilization in fusion plasmas under steady state conditions
The first combined experimental and theoretical studies of dust
remobilization by plasma forces are reported. The main theoretical aspects of
remobilization in fusion devices under steady state conditions are analyzed. In
particular, the dominant role of adhesive forces is highlighted and generic
remobilization conditions - direct lift-up, sliding, rolling - are formulated.
A novel experimental technique is proposed, based on controlled adhesion of
dust grains on tungsten samples combined with detailed mapping of the dust
deposition profile prior and post plasma exposure. Proof-of-principle
experiments in the TEXTOR tokamak and the EXTRAP-T2R reversed-field pinch are
presented. The versatile environment of the linear device Pilot-PSI allowed for
experiments with different magnetic field topologies and varying plasma
conditions that were complemented with camera observations.Comment: 16 pages, 11 figures, 3 table
The MODEST questions: challenges and future directions in stellar cluster research
We present a review of some of the current major challenges in stellar
cluster research, including young clusters, globular clusters, and galactic
nuclei. Topics considered include: primordial mass segregation and runaway
mergers, expulsion of gas from clusters, the production of stellar exotica seen
in some clusters (eg blue stragglers and extreme horizontal--branch stars),
binary populations within clusters, the black--hole population within stellar
clusters, the final parsec problem, stellar dynamics around a massive black
hole, and stellar collisions. The Modest Questions posed here are the outcome
of discussions which took place at the Modest-6A workshop held in Lund, Sweden,
in December, 2005. Modest-6A was organised as part of the activities of the
Modest Collaboration (see www.manybody.org for further details)Comment: 24 pages, no figures, accepted for publication in New Astronom
A priori and a posteriori analysis of the flow around a rectangular cylinder
The definition of a correct mesh resolution and modelling approach for the Large Eddy Simulation (LES) of the flow around a rectangular cylinder is recognized to be a rather elusive problem as shown by the large scatter of LES results present in the literature. In the present work, we aim at assessing this issue by performing an a priori analysis of Direct Numerical Simulation (DNS) data of the flow. This approach allows us to measure the ability of the LES field on reproducing the main flow features as a function of the resolution employed. Based on these results, we define a mesh resolution which maximize the opposite needs of reducing the computational costs and of adequately resolving the flow dynamics. The effectiveness of the resolution method proposed is then verified by means of an a posteriori analysis of actual LES data obtained by means of the implicit LES approach given by the numerical properties of the Discontinuous Galerkin spatial discretization technique. The present work represents a first step towards a best practice for LES of separating and reattaching flows
The RESEARCH project. Soil-related hazards and archaeological heritage in the challenge of climate change
Archaeological Heritage, naturally endangered by environmental processes and anthropogenic pressures, is today increasingly at risk, because of intense human activities and climate change, and their impact on atmosphere and soil. European research is increasingly dedicated to the development of good practices for monitoring archaeological sites and their preservation. One of the running projects about these topics is RESEARCH (Remote Sensing techniques for Archaeology; H2020-MSCA-RISE, grant agreement: 823987), started in 2018 and ending in 2022. RESEARCH aims at testing risk assessment methodology using an integrated system of documentation and research in the fields of archaeology and environmental studies. It will introduce a strategy and select the most efficient tools for the harmonization of different data, criteria, and indicators in order to produce an effective risk assessment. These will be used to assess and monitor the impact of soil erosion, land movement, and land-use change on tangible archaeological heritage assets. As a final product, the Project addresses the development of a multi-task thematic platform, combining advanced remote sensing technologies with GIS application. The demonstration and validation of the Platform will be conducted on six case studies located in Italy, Greece, Cyprus, and Poland, and variously affected by the threats considered by the Project. In the frame of RISE (Research and Innovation Staff Exchange), RESEARCH will coordinate the existing expertise and research efforts of seven beneficiaries into a synergetic plan of collaborations and exchanges of personnel (Ph.D. students and research staff), to offer a comprehensive transfer of knowledge and training environment for the researchers in the specific area. This paper aims at illustrating the results of the activities conducted during the first year of the Project, which consisted in developing an effective risk assessment methodology for soil-related threats affecting archaeological heritage, and defining the scientific requirements and the user requirements of the Platform. The activities have been conducted in synergy with all the Partners and were supported by the possibility of staff exchange allowed by the funding frame MSCA-RISE
Photometric metallicity for 694233 Galactic giant stars from Gaia DR3 synthetic Stromgren photometry. Metallicity distribution functions of halo sub-structures
We use the calibrations by Calamida et al. and by Hilker et al., and the
standardised synthetic photometry in the v, b, and y Stromgren passbands from
Gaia DR3 BP/RP spectra, to obtain photometric metallicities for a selected
sample of 694233 old Galactic giant stars having |b|>20.0 and parallax
uncertainties lower than 10%. The zero point of both sets of photometric
metallicities has been shifted to to ensure optimal match with the
spectroscopic [Fe/H] values for 44785 stars in common with APOGEE DR17,
focusing on the metallicity range where they provide the highest accuracy. The
metallicities derived in this way from the Calamida et al. calibration display
a typical accuracy of ~0.1 dex and 1 sigma precision ~0.2 dex in the range -2.2
<=[Fe/H]<= -0.4, while they show a systematic trend with [Fe/H] at higher
metallicity, beyond the applicability range of the relation. Those derived from
the Hilker et al. calibration display, in general, worse precision, and lower
accuracy in the metal-poor regime, but have a median accuracy < 0.05 dex for
[Fe/H]>= -0.8. These results are confirmed and, consequently, the metallicities
validated, by comparison with large sets of spectroscopic metallicities from
various surveys. The newly obtained metallicities are used to derive
metallicity distributions for several previously identified sub-structures in
the Galactic halo with an unprecedented number of stars. The catalogue
including both sets of metallicities and the associated uncertainties is made
publicly available.Comment: Accepted for publication by Astronomy & Astrophysics. Latex. 20
pages, 21 color figures. The catalogue will be publicly available at CDS. In
the meanwhile it is available upon request to the first autho
Is Eriophyes mali Nalepa present in Italy?
In the last few years, blistering symptoms were observed on apple plants in commercial orchards. Blisters are commonly found on apple leaves as well as on small fruits. This symptom is compatible with that described for apple blister mites belonging to the genus Eriophyes (Eriophyidae). To assess the identity of the etiological agent, leaf blisters and buds of symptomatic apple and, as a control, pear plants were examined under the dissection microscope and eriophyoid mites were collected. Specimens were examined using both molecular and morphological approaches. The analysis of sequences confirmed that eriophyoid mites collected from symptomatic apple and pear plants are genetically different. Our analyses highlight a complex scenario inside the genus Eriophyes that is worth to be studied in more detai
Relative Frequencies of Blue Stragglers in Galactic Globular Clusters: Constraints for the Formation Mechanisms
We discuss the main properties of the Galactic globular cluster (GC) blue
straggler stars (BSS), as inferred from our new catalog containing nearly 3000
BSS. The catalog has been extracted from the photometrically homogeneous V vs.
(B-V) color-magnitude diagrams (CMD) of 56 GCs, based on WFPC2 images of their
central cores. In our analysis we used consistent relative distances based on
the same photometry and calibration. The number of BSS has been normalized to
obtain relative frequencies (F_{BSS}) and specific densities (N_S) using
different stellar populations extracted from the CMD. The cluster F_{BSS} is
significantly smaller than the relative frequency of field BSS. We find a
significant anti-correlation between the BSS relative frequency in a cluster
and its total absolute luminosity (mass). There is no statistically significant
trend between the BSS frequency and the expected collision rate. F_{BSS} does
not depend on other cluster parameters, apart from a mild dependence on the
central density. PCC clusters act like normal clusters as far as the BSS
frequency is concerned. We also show that the BSS luminosity function for the
most luminous clusters is significantly different, with a brighter peak and
extending to brighter luminosities than in the less luminous clusters. These
results imply that the efficiency of BSS production mechanisms and their
relative importance vary with the cluster mass.Comment: 12 pages, 3 figures. accepted for publication in ApJ
Diffusion bonding effects on the adhesion of tungsten dust on tungsten surfaces
Abstract High temperature excursions have the potential to strongly enhance the room temperature adhesion of tokamak dust. Planar tungsten substrates containing adhered nearly monodisperse spherical tungsten dust have been exposed to linear plasmas and vacuum furnaces. Prolonged thermal treatments of varying peak temperature and constant duration were followed by room temperature adhesion measurements with the electrostatic detachment method. Adhesive forces have been observed to strongly depend on the thermal pre-history, greatly increasing above a threshold temperature. Adhesive forces have been measured up to an order of magnitude larger than those of untreated samples. This enhancement has been attributed to atomic diffusion that slowly eliminates the omnipresent nanometer-scale surface roughness, ultimately switching the dominant interaction from long-range weak van der Waals forces to short-range strong metallic bonding
Catechols: a new class of carbonic anhydrase inhibitors
Catechols adopt a peculiar binding mode to the CA active site which involves both the zinc bound water molecule and the "deep water"
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