51 research outputs found
Space Science on the Space Shuttle: Plans and Prospects
An overview is given of current planning for use of the Space Shuttle and Spacelab for carrying out NASA\u27s program in Space Science. Major categories of use will be: (1) As a launch and service vehicle; (2) As an experiment platform for carrying out passive observations; (3) As a component in active and controlled experiments in space; (4) As a manned orbiting laboratory for carrying out investigations requiring hands-on access to equipment and samples. Examples of each type of use are given. Some of the multi-user facility instruments which are planned for early development (Solar Optical Telescope, Shuttle Infrared Telescope Facility, Chemical Release Module, Life Sciences Laboratory Equipment) are described. Payloads to be carried on the early missions (Orbital Flight Test, Spacelab 1 and Spacelab 2) are discussed with particular emphasis orr the unique capabilities of Shuttle/Spacelab to be demonstrated by these missions
Vida doméstica en Cuba durante los años 50
El artículo presenta los resultados de un estudio exploratorio realizado en la localidad habanera de Bejucal en 1997, como parte de las investigaciones sobre historia de la familia en Cuba que realiza el Centro de Investigación y Desarrollo de la Cultura Cubana Juan Marinello, de La Habana. En él se pretende caracterizar las costumbres familiares de los diversos grupos sociales y demostrar la idoneidad de las fuentes orales para reconstruir el pasado reciente.The article shows the results of an exploratory study carried out in the Havana locality of Bejucal in the year 1997. It is part of a research work about family history in Cuba which is being conducted by the «Centro de Investigación y Desarrollo de la Cultura Cubana Juan Marinello» in Havana. The objectives of the investigation are to characterize family customs of various social groups and to show the validity of oral sources in the reconstruction of recent past
Bright OB stars in the Galaxy.II. Wind variability in O supergiants as traced by H-alpha
We investigate the line-profile variability (lpv) of H-alpha for a large
sample of O-type supergiants. We used the Temporal Variance Spectrum (TVS)
analysis, developed by Fullerton et al 1996 and modified by us to take into
account the effects of wind emission. By means of a comparative analysis we put
a number of constraints on the properties of the variability as a function of
stellar and wind parameters. The results of our analysis show that all the
stars in the sample show evidence of significant lpv in H-alpha, mostly
dominated by processes in the wind. The variations occur between zero and 0.3
v_inf (i.e., below ~1.5 R_star), in good agreement with the results from
similar studies. A comparison between observations and line-profile simulations
indicates that for stars with intermediate wind densities the H-alpha
variability can be explained by simple models, consisting of coherent or broken
shells (blobs) uniformly distributed over the wind volume, with an intrinsic
scatter in the maximum density contrast of about a factor of two. For stars at
lower and higher wind densities, on the other hand, we found certain
inconsistencies between observations and our predictions, most importantly
concerning the mean amplitude and the symmetry properties of the TVS. This
disagreement might be explained with the presence of coherent large-scale
structures, partly confined in a volume close to the star. Interpreted in terms
of a variable mass-loss rate, the observed variations of H-alpha indicate
changes of 4% with respect to the mean value of M_dot for stars with stronger
winds and of 16% for stars with weaker winds. The effect of these variations on
the corresponding wind momenta is rather insignificant (<0.16 dex), increasing
the local scatter without affecting the Wind Momentum Luminosity Relationship.Comment: 22 pages, 11 figures. Accepted by Astronomy and Astrophysic
User-definable resource bounds analysis for logic programs
We present a static analysis that infers both upper and lower bounds on the usage that a logic program makes of a set of user-definable resources. The inferred bounds will in general be functions of input data sizes. A resource in our approach is a quite general, user-defined notion which associates a basic cost function with elementary operations. The analysis then derives the related (upper- and lower-bound) resource usage functions for all predicates in the program. We also present an assertion
language which is used to define both such resources and resourcerelated properties that the system can then check based on the results of the analysis. We have performed some preliminary experiments with some concrete resources such as execution steps, bytes sent or received by an application, number of files left open, number of accesses to a datábase, number of calis to a procedure, number of asserts/retracts, etc. Applications of our analysis include resource consumption verification and debugging (including for mobile code), resource control in parallel/distributed computing, and resource-oriented specialization
Large-scale wind structures in OB supergiants: a search for rotationally modulated H\alpha variability
We present the results of a long-term monitoring campaign of the H\alpha line
in a sample of bright OB-supergiants (O7.5-B9) that aims at detecting
rotationally modulated changes potentially related to the existence of
large-scale wind structures. A total of 22 objects were monitor ed during 36
nights spread over 6 months in 2001-2002. Coordinated broad-band photometric
observations were also obtained for some targets. Conspicuous evidence for
variability in H\alpha is found for the stars displaying a feature contaminated
by wind emission. Most changes take place on a daily time-scale, although
hourly variations are also occasionally detected. Convincing evidence for a
cyclical pattern of variability in H\alpha has been found in 2 stars: HD 14134
and HD 42087 (periodic signals are also detected in other stars, but
independent confirmation is required). Rotational modulation is suggested from
the similarity between the observed recurrence time-scales (in the range 13-25
days) and estimated periods of stellar rotation. We call attention to the
atypical case of HD 14134 which exhibits a clear 12.8-d periodicity both in the
photometric and in the spectroscopic data sets. This places this object among a
handful of early-type stars where one may observe a clear link between extended
wind structures and photospheric disturbances. Further modelling may test the
hypothesis that azimuthally-extended wind streams are responsible for the
patterns of spectral variability in our target stars.Comment: 18 pages, accepted for publication in MNRA
On the nature of the galactic early-B hypergiants
Despite their importance to a number of astrophysical fields, the lifecycles
of very massive stars are still poorly defined. In order to address this
shortcoming, we present a detailed quantitative study of the physical
properties of four early-B hypergiants (BHGs); Cyg OB2 #12, zeta Sco, HD190603
and BP Cru. These are combined with an analysis of their long-term
spectroscopic and photometric behaviour in order to determine their
evolutionary status. The long-term datasets revealed that they are remarkably
stable over long periods (>40yr), with the possible exception of zeta Sco prior
to the 20th century, in contrast to the typical excursions that characterise
luminous blue variables (LBVs). Zeta Sco, HD190603 and BP Cru possess physical
properties intermediate between B supergiants and LBVs; we therefore suggest
that BHGs are the immediate descendants and progenitors (respectively) of such
stars (for initial masses in the range ~30-60Msun). In contrast, while the wind
properties of Cyg OB2 #12 are consistent with this hypothesis, the combination
of extreme luminosity and spectroscopic mass (~110Msun) and comparatively low
temperature means it cannot be accommodated in such a scheme. Likewise, despite
its co-location with several LBVs above the Humphreys-Davidson (HD) limit, the
lack of long term variability and its unevolved chemistry apparently excludes
such an identification. Since such massive stars are not expected to evolve to
such cool temperatures, the properties of Cyg OB2 #12 are difficult to
understand under current evolutionary paradigms. [ABRIDGED]Comment: 36 pages, 19 figures (of which 17 pages are online supplemental
material). Accepted for publication in Astronomy and Astrophysic
Bright OB stars in the Galaxy - III. Constraints on the radial stratification of the clumping factor in hot star winds from a combined Halpha, IR and radio analysis
Recent results strongly challenge the canonical picture of massive star
winds: various evidence indicates that currently accepted mass-loss rates,
Mdot, may need to be revised downwards significantly. This is because the most
commonly used mass-loss diagnostics are affected by ``clumping'' (small-scale
density inhomogeneities), influencing our interpretation of observed spectra
and fluxes. Such downward revisions would have dramatic consequences for the
evolution of, and feedback from, massive stars, and thus robust determinations
of the clumping properties and mass-loss rates are urgently needed. Here, we
present a first attempt to constrain the radial stratification of the so-called
clumping factor. To this end, we have analyzed a sample of 19 Galactic O-type
supergiants/giants, by combining data for Halpha, IR, mm and radio fluxes, and
using appropriate analysis methods. Clumping has been included into our
analysis in the ``conventional'' way, by assuming the inter-clump matter to be
void. Because (almost) all our diagnostics depends on the square of density, we
cannot derive absolute clumping factors, but only factors normalized to a
certain minimum. This minimum was usually found to be located in the outermost,
radio-emitting region, i.e., the radio mass-loss rates are the lowest ones,
compared to Mdot derived from Halpha and the IR. The radio rates agree well
with those predicted by theory, but are only upper limits, due to unknown
clumping in the outer wind. Our most important result concerns a (physical)
difference between denser and thinner winds: for denser winds, the innermost
region is more strongly clumped than the outermost one (with a normalized
clumping factor of 4.1+/-1.4), whereas thinner winds have similar clumping
properties in the inner and outer regions.Comment: 40 pages, 17 figures, accepted by A&
Crustal structures of the Rhinegraben and the Massif Central grabens: An experimental approach
International audienceTwo of the most improtant segments of the west European Rift, the Rhinegraben and the Massif Central grabens, show in plan and cross section a very different crustal structure
Quantitative Spectroscopy of BA-type Supergiants
Luminous BA-SGs allow topics ranging from NLTE physics and the evolution of
massive stars to the chemical evolution of galaxies and cosmology to be
addressed. A hybrid NLTE technique for the quantitative spectroscopy of BA-SGs
is discussed. Thorough tests and first applications of the spectrum synthesis
method are presented for four bright Galactic objects. Stellar parameters are
derived from spectroscopic indicators. The internal accuracy of the method
allows the 1sigma-uncertainties to be reduced to <1-2% in Teff and to
0.05-0.10dex in log g. Elemental abundances are determined for over 20 chemical
species, with many of the astrophysically most interesting in NLTE. The NLTE
computations reduce random errors and remove systematic trends in the analysis.
Inappropriate LTE analyses tend to systematically underestimate iron group
abundances and overestimate the light and alpha-process element abundances by
up to factors of 2-3 on the mean. Contrary to common assumptions, significant
NLTE abundance corrections of ~0.3dex can be found even for the weakest lines.
NLTE abundance uncertainties amount to typically 0.05-0.10dex (random) and
\~0.10dex (systematic 1sigma-errors). Near-solar abundances are derived for the
heavier elements, and patterns indicative of mixing with nuclear-processed
matter for the light elements. These imply a blue-loop scenario for Eta Leo,
while the other three objects appear to have evolved directly from the main
sequence. In the most ambitious computations several ten-thousand spectral
lines are accounted for, permitting the accurate reproduction of the entire
observed spectra from the visual to NIR. This prerequisite for the quantitative
interpretation of medium-resolution spectra opens up BA-SGs as versatile tools
for extragalactic stellar astronomy beyond the Local Group. (abridged)Comment: 36 pages, 18 figures, accepted for publication in A&
Difusão e territórios diocesanos no Brasil: 1551-1930.
Entre o início da colonização portuguesa e 1930, a constituição dos territórios diocesanos católicos no Brasil resultou de um complexo processo de difusão espacial, no qual participaram a dimensão do país, o processo de seu povoamento e as necessidades e vicissitudes da Igreja Católica. Dois períodos podem ser identificados, 1551-1854 e 1890-1930. O primeiro período é marcado pela dependência da Igreja Católica à Coroa Portuguesa e por uma superficial apropriação e controle dos 12 territórios diocesanos dispersos por 8,5 milhões de Km2. O segundo período associa-se a separação entre Igreja e Estado e a criação de 68 novas dioceses, distribuídas pelo país, embora concentradas nas regiões Sudeste e Nordeste. As estratégias da Igreja Católica variaram segundo diferentes lógicas. Contudo, a apropriação e controle ainda é superficial. O resultado disto foi o desenvolvimento de um catolicismo popular, que domina o Brasil
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