19,438 research outputs found
Multiwavelength analysis of the young open cluster NGC 2362
We present a multiwavelength analysis of the young open cluster NGC 2362.
UBVRcIc CCD photometric observations, together with available data in the
Chandra data base, near infrared data from the Two Micron All Sky Survey
(2MASS), and recently published Halpha spectroscopy were used to get
information about the evolutionary stage of the cluster and the main physical
properties of its stellar content. Cluster membership is estimated for every
individual star by means of ZAMS and isochrone fitting. The cluster is
confirmed to host a richly populated pre-main sequence (PMS), and to contain a
large amount of X-ray emitting stars, which reach from the PMS members of GK
spectral type, up to the most luminous OB type main sequence (MS) members. The
PMS cluster members show no significant age spread, and the comparison to both
PMS and post-MS isochrones suggests a younger age for the more massive MS than
for lower mass PMS members. The analysis allows to asses the validity of
currently used pre-main sequence evolutionary models, and supports the
suggestion of a well defined positive correlation of the X-ray emission from
PMS stars with their bolometric luminosity. Clear differences are found on the
other hand, between the X-ray activity properties of MS and PMS cluster
members, both in the relation between X-ray luminosity and bolometric
luminosity, and in spectral properties as well.Comment: 1 gzipped file: 1 tex file with 9 pages text. 5 ps files with
figures. Submitted to Astrophysical Journa
The luminosity function of Palomar 5 and its tidal tails
We present the main sequence luminosity function of the tidally disrupted
globular cluster Palomar 5 and its tidal tails. For this work we analyzed
imaging data obtained with the Wide Field Camera at the INT (La Palma) and data
from the Wide Field Imager at the MPG/ESO 2.2 m telescope at La Silla down to a
limiting magnitude of approximately 24.5 mag in B. Our results indicate that
preferentially fainter stars were removed from the cluster so that the LF of
the cluster's main body exhibits a significant degree of flattening compared to
other GCs. This is attributed to its advanced dynamical evolution. The LF of
the tails is, in turn, enhanced with faint, low-mass stars, which we interpret
as a consequence of mass segregation in the cluster.Comment: 4 pages, 3 figures, to be published in the proceedings of the
conference "Satellites and tidal streams" held at La Palma, Canary Islands,
May 26 - 30, 200
Comprehensive theory of the relative phase in atom-field interactions
We explore the role played by the quantum relative phase in a well-known
model of atom-field interaction, namely, the Dicke model. We introduce an
appropriate polar decomposition of the atom-field relative amplitudes that
leads to a truly Hermitian relative-phase operator, whose eigenstates correctly
describe the phase properties, as we demonstrate by studying the positive
operator-valued measure derived from it. We find the probability distribution
for this relative phase and, by resorting to a numerical procedure, we study
its time evolution.Comment: 20 pages, 4 figures, submitted to Phys. Rev.
Supersymmetry and Electroweak Breaking in the Interval
Hypermultiplets are considered in the five-dimensional interval where all
fields are continuous and the boundary conditions are dynamically obtained from
the action principle. The orbifold boundary conditions are obtained as
particular cases. We can interpret the Scherk-Schwarz supersymmetry breaking as
a misalignment of boundary conditions while a new source of supersymmetry
breaking corresponding to a mismatch of different boundary parameters is
identified. The latter can be viewed as coming from boundary supersymmetry
breaking masses for hyperscalars and the nature of the corresponding
supersymmetry breaking parameter is analyzed. For some regions of the parameter
space where supersymmetry is broken (either by Scherk-Schwarz boundary
conditions or by boundary hyperscalar masses) electroweak symmetry breaking can
be triggered at the tree level.Comment: 28 pages, 5 figure
Thanks, but no thanks: women's avoidance of help-seeking in the context of a dependency-related stereotype
The stereotype that women are dependent on men is a commonly verbalized, potentially damaging aspect of benevolent sexism. We investigated how women may use behavioral disconfirmation of the personal applicability of the stereotype to negotiate such sexism. In an experiment (N = 86), we manipulated female college studentsâ awareness that women may be stereotyped by men as dependent. We then placed participants in a situation where they needed help. Women made aware of the dependency stereotype (compared to controls who were not) were less willing to seek help. They also displayed a stronger negative correlation between help-seeking and post help-seeking affect - such that the more help they sought, the worse they felt. We discuss the relevance of these findings for research concerning womenâs help-seeking and their management of sexist stereotyping in everyday interaction. We also consider the implications of our results for those working in domains such as healthcare, teaching and counseling, where interaction with individuals in need and requiring help is common
Evaluation of mechanical properties of composite materials made from recycled fly ash and polymers
In this article evaluates the mechanical properties of composite materials based on fly ash and Coal-fired power plants Termozipa combined with the stretch film (stretch film), linear low density polyethylene post-consumer and partially thermoplastic polymer, crystalline Industrial post. Mixtures were obtained by varying the content of fly ash, 0 to 50 % by weight in each of the three polymeric materials, within a machine type Brabender mixer. The mechanical properties evaluated were: tensile strength, Shore D hardness, and energy absorption, the results obtained indicate that in all cases, as fly ash is added, the mechanical properties increase.En el presente artĂculo se evalĂşan las propiedades mecĂĄnicas de los materiales compuestos basados en cenizas volantes de carbĂłn de la central termoelĂŠctrica de Termozipa combinadas con los pelĂcula extensible (Stretch film), polietilenos de baja densidad lineal de pos-consumo y polĂmero termoplĂĄstico parcialmente cristalino pos- industrial. Se obtuvieron mezclas variando el contenido de cenizas volantes de 0 a 50 % en peso en cada uno de los tres materiales polimĂŠricos, dentro de una mĂĄquina mezcladora tipo Brabender. Las propiedades mecĂĄnicas evaluadas fueron: resistencia a la tracciĂłn, dureza Shore D, y absorciĂłn de energĂa. Los resultados obtenidos indican que en todos los casos a medida que se agrega ceniza volante las propiedades mecĂĄnicas aumentan
Pre-main sequence stars in open clusters. I. The DAY-I catalogue
We present the project we are carrying out at present, the search for and
characterisation of pre-main sequence (PMS) stars among the members of Galactic
young clusters. The observations of 10 southern clusters, nine of them located
in the Carina-Sagittarius spiral arm of the Milky Way are presented. We aim at
listing candidate PMS member stars in young clusters. The catalogued stars will
serve as a basis for future spectroscopic studies of individual objects to
determine the properties of stellar formation in the last phases before the
main sequence stage. Properties such as the presence of residual envelopes or
disks, age spread among PMS members, and the possible presence of several
episodes of star formation in the clusters, are to be addressed.
Multicolour photometry in the UBVRcIc system has been obtained for 10
southern young clusters in the fourth Galactic quadrant, located between
Galactic longitudes l=238 and l=310. For six clusters in the sample, the
observations presented here provide the first published study based on CCD
photometry. A quantitative comparison is performed with post-MS isochrones, and
PMS isochrones from three different evolutionary models are used in the
photometric membership analysis for possible PMS stars. The observations
produce photometric indices in the Johnson-Cousins photometric systems for a
total of 26962 stars. Matching with the 2MASS data base provides astrometric
calibration for all stars, and JHK 2MASS indices for 60 per cent of them.
Post-MS cluster ages range from 4 to 60 Myr, whereas the photometric membership
analysis assigns PMS membership to a total of 842 stars, covering an age range
between 1 and 10 Myr. A catalogue, named DAY-I, with the information on the PMS
candidate members has been ellaborated.Comment: 15 pages, 10 figures. Accepted in Astronomy and Astrophysics:
30.1.200
PADAMOT : project overview report
Background and relevance to radioactive waste management
International consensus confirms that placing radioactive wastes and spent nuclear fuel deep
underground in a geological repository is the generally preferred option for their long-term
management and disposal. This strategy provides a number of advantages compared to leaving it
on or near the Earthâs surface. These advantages come about because, for a well chosen site, the
geosphere can provide:
⢠a physical barrier that can negate or buffer against the effects of surface dominated natural
disruptive processes such as deep weathering, glaciation, river and marine erosion or
flooding, asteroid/comet impact and earthquake shaking etc.
⢠long and slow groundwater return pathways from the facility to the biosphere along which
retardation, dilution and dispersion processes may operate to reduce radionuclide
concentration in the groundwater.
⢠a stable, and benign geochemical environment to maximise the longevity of the engineered
barriers such as the waste containers and backfill in the facility.
⢠a natural radiation shield around the wastes.
⢠a mechanically stable environment in which the facility can be constructed and will
afterwards be protected.
⢠an environment which reduces the likelihood of the repository being disturbed by inadvertent
human intrusion such as land use changes, construction projects, drilling, quarrying and
mining etc.
⢠protection against the effects of deliberate human activities such as vandalism, terrorism and
war etc.
However, safety considerations for storing and disposing of long-lived radioactive wastes must
take into account various scenarios that might affect the ability of the geosphere to provide the
functionality listed above. Therefore, in order to provide confidence in the ability of a repository
to perform within the deep geological setting at a particular site, a demonstration of geosphere
âstabilityâ needs to be made. Stability is defined here to be the capacity of a geological and
hydrogeological system to minimise the impact of external influences on the repository
environment, or at least to account for them in a manner that would allow their impacts to be
evaluated and accounted for in any safety assessments.
A repository should be sited where the deep geosphere is a stable host in which the engineered
containment can continue to perform according to design and in which the surrounding
hydrogeological, geomechanical and geochemical environment will continue to operate as a
natural barrier to radionuclide movement towards the biosphere. However, over the long periods
of time during which long-lived radioactive wastes will pose a hazard, environmental change at
the surface has the potential to disrupt the stability of the geosphere and therefore the causes of
environmental change and their potential consequences need to be evaluated.
As noted above, environmental change can include processes such as deep weathering,
glaciation, river and marine erosion. It can also lead to changes in groundwater boundary
conditions through alternating recharge/discharge relationships. One of the key drivers for
environmental change is climate variability. The question then arises, how can geosphere stability be assessed with respect to changes in climate? Key issues raised in connection with
this are:
⢠What evidence is there that 'going underground' eliminates the extreme conditions that
storage on the surface would be subjected to in the long term?
⢠How can the additional stability and safety of the deep geosphere be demonstrated with
evidence from the natural system?
As a corollary to this, the capacity of repository sites deep underground in stable rock masses to
mitigate potential impacts of future climate change on groundwater conditions therefore needs to
be tested and demonstrated. To date, generic scenarios for groundwater evolution relating to
climate change are currently weakly constrained by data and process understanding. Hence, the
possibility of site-specific changes of groundwater conditions in the future can only be assessed
and demonstrated by studying groundwater evolution in the past. Stability of groundwater
conditions in the past is an indication of future stability, though both the climatic and geological
contexts must be taken into account in making such an assertion
Physical parameters of pre-main sequence stars in open clusters
Our aims are twofold: To determine the physical parameters of PMS members in
young open clusters (YOCs), and to check and compare the performances of
different model isochrones.
We compare UBVRI photometric observations of YOCs to theoretical isochrones
in the photometric diagrams. The comparison simultaneously provides membership
assignments for MS and PMS stars, and estimates for the masses, ages, and
spatial distribution of the candidate members.
The relations found between the different cluster parameters show that the
procedure applied to assign cluster membership, and to measure physical
parameters for the selected members, is well founded.Comment: 11 pages, 8 figures. Accepted for publication in Astronomy and
Astrophysics (17.5.2011
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