114 research outputs found
Coronagraph particulate measurements. Skylab flight experiment T025
Major results of the Skylab T025 Coronagraph experiment designed to monitor the particulate contamination about the spacecraft and to study the earth's atmospheric aerosol distribution are presented. A model for comet outbursts based on the properties of amorphous ice and ground based narrow-band and white light photography of comet Kohoutek ten days to perihelion are included. The effect of atmospheric refraction on the analysis of the T025 atmospheric data was also investigated
Soft-x-ray fluorescence study of the quasi-one-dimensional Heisenberg antiferromagnet tetraphenylverdazyl
Soft-x-ray fluorescence measurements have been performed on a single crystal of the organic antiferromagnet 2,4,6-triphenylverdazyl. Resonant and nonresonant C Kα and N Kα (2p → 1s transition) x-ray emission spectra (XES) were measured and compared with x-ray photoelectron valence band spectra and deMon density-functional theory calculations. It is shown that intramolecular interactions are much stronger than intermolecular ones and give the main contribution to the formation of C 2p density of states. We present evidence of a delocalization of unpaired N 2p electrons over the verdazyl ring. The excitation energy dependence of C Kα and N Kα XES observed below the C 1s and N 1s thresholds, respectively, is discussed in terms of symmetry selective resonant inelastic x-ray scattering
Radiation pressure and pulsation effects on the Roche lobe
Several observational pieces of evidence indicate that specific evolutionary
channels which involve Roche lobe overflow are not correctly accounted for by
the classical Roche model. We generalize the concept of Roche lobe in the
presence of extra forces (caused by radiation pressure or pulsations). By
computing the distortion of the equipotential surfaces, we are able to evaluate
the impact of these perturbing forces on the stability of Roche-lobe overflow
(RLOF). Radiative forces are parametrized through the constant reduction factor
that they impose on the gravitational force from the radiating star (neglecting
any shielding in case of large optical thickness). Forces imparted by
pulsations are derived from the velocity profile of the wind that they trigger.
We provide analytical expressions to compute the generalized Roche radius.
Depending on the extra force, the Roche-lobe radius may either stay unchanged,
become smaller, or even become meaningless (in the presence of a radiatively-
or pulsation-driven wind). There is little impact on the RLOF stability.Comment: 11 pages, 13 Postscript figure
Vaccine effectiveness of the pneumococcal Haemophilus influenzae protein D conjugate vaccine (PHiD-CV10) against clinically suspected invasive pneumococcal disease: a cluster-randomised trial
Mass Transfer by Stellar Wind
I review the process of mass transfer in a binary system through a stellar
wind, with an emphasis on systems containing a red giant. I show how wind
accretion in a binary system is different from the usually assumed Bondi-Hoyle
approximation, first as far as the flow's structure is concerned, but most
importantly, also for the mass accretion and specific angular momentum loss.
This has important implications on the evolution of the orbital parameters. I
also discuss the impact of wind accretion, on the chemical pollution and change
in spin of the accreting star. The last section deals with observations and
covers systems that most likely went through wind mass transfer: barium and
related stars, symbiotic stars and central stars of planetary nebulae (CSPN).
The most recent observations of cool CSPN progenitors of barium stars, as well
as of carbon-rich post-common envelope systems, are providing unique
constraints on the mass transfer processes.Comment: Chapter 7, in Ecology of Blue Straggler Stars, H.M.J. Boffin, G.
Carraro & G. Beccari (Eds), Astrophysics and Space Science Library, Springe
Post-AGB stars with hot circumstellar dust: binarity of the low-amplitude pulsators
While the first binary post-AGB stars were serendipitously discovered, the
distinct characteristics of their Spectral Energy Distribution (SED) allowed us
to launch a more systematic search for binaries. We selected post-AGB objects
which show a broad dust excess often starting already at H or K, pointing to
the presence of a gravitationally bound dusty disc in the system. We started a
very extensive multi-wavelength study of those systems and here we report on
our radial velocity and photometric monitoring results for six stars of early F
type, which are pulsators of small amplitude. To determine the radial velocity
of low signal-to-noise time-series, we constructed dedicated auto-correlation
masks. The radial velocity variations were subjected to detailed analysis to
differentiate between pulsational variability and variability due to orbital
motion. Finally orbital minimalisation was performed to constrain the orbital
elements. All of the six objects are binaries, with orbital periods ranging
from 120 to 1800 days. Five systems have non-circular orbits. The mass
functions range from 0.004 to 0.57 solar mass and the companions are likely
unevolved objects of (very) low initial mass. We argue that these binaries must
have been subject to severe binary interaction when the primary was a cool
supergiant. Although the origin of the circumstellar disc is not well
understood, the disc is generally believed to be formed during this strong
interaction phase. The eccentric orbits of these highly evolved objects remain
poorly understood. With the measured orbits and mass functions we conclude that
the circumbinary discs seem to have a major impact on the evolution of a
significant fraction of binary systems.Comment: 13 pages, 15 figures, accepted for Astronomy and Astrophysic
The decline and rise of neighbourhoods: the importance of neighbourhood governance
There is a substantial literature on the explanation of neighbourhood change. Most of this literature concentrates on identifying factors and developments behind processes of decline. This paper reviews the literature, focusing on the identification of patterns of neighbourhood change, and argues that the concept of neighbourhood governance is a missing link in attempts to explain these patterns. Including neighbourhood governance in the explanations of neighbourhood change and decline will produce better explanatory models and, finally, a better view about what is actually steering neighbourhood change
Влияние интенсивности механической активации на структуру гексагонального нитрида бора
Изучено влияние интенсивности механической активации на микроструктуру и свойства гексагонального нитрида бора (hBN).Вивчено вплив інтенсивності механічної активації на мікроструктуру і властивості гексагонального нітриду бору (hBN).The mechanical activation intensity effect on the microstructure and properties of hexagonal boron nitride (hBN) has been studied
Do pneumococcal conjugate vaccines provide any cross-protection against serotype 19A?
<p>Abstract</p> <p>Background</p> <p>Introduction of the 7-valent pneumococcal conjugate vaccine (7vCRM) in several countries has led to a rapid, significant drop in vaccine-type invasive pneumococcal disease (IPD) in immunized children. In the United States and some other countries with high antibiotic use, a subsequent rise in serotype 19A IPD has been taken to indicate that the 19F conjugate in the vaccine provides no cross-protection against the immunologically related 19A.</p> <p>Discussion</p> <p>We systematically assessed the clinical efficacy and effectiveness of 19F-containing vaccines against 19A disease or nasopharyngeal carriage by searching English-language articles in the electronic databases PubMed, Current contents, Scopus, and Embase from 1985 to 2008. The vaccine efficacy and effectiveness point estimates were consistently positive for modest protection against 19A IPD and acute otitis media (AOM). However, statistical significance was not reached in any individual study. No consistent impact of 7vCRM on 19A nasopharyngeal colonization could be detected. These findings are discussed in context of immunogenicity analyses indicating that 7vCRM induces functionally active anti-19A antibodies after the booster dose, and that other 19F-containing vaccine formulations may elicit higher levels of such antibodies after both primary and booster doses.</p> <p>Summary</p> <p>Taken together, these results suggest that 19F-conjugates can provide some protection against 19A disease. The magnitude of this protection in a given setting will likely depend on several factors. These include the anti-19A immunogenicity of the specific vaccine formulation, the number of doses of that formulation needed to elicit the response, and the burden of 19A disease that occurs after those doses. It is possible that a modest protective effect may be obscured by the presence of countervailing selection pressures (such as high antibiotic use) that favor an increase in colonization with antibiotic-non-susceptible strains of 19A.</p
The Evolution of Compact Binary Star Systems
We review the formation and evolution of compact binary stars consisting of
white dwarfs (WDs), neutron stars (NSs), and black holes (BHs). Binary NSs and
BHs are thought to be the primary astrophysical sources of gravitational waves
(GWs) within the frequency band of ground-based detectors, while compact
binaries of WDs are important sources of GWs at lower frequencies to be covered
by space interferometers (LISA). Major uncertainties in the current
understanding of properties of NSs and BHs most relevant to the GW studies are
discussed, including the treatment of the natal kicks which compact stellar
remnants acquire during the core collapse of massive stars and the common
envelope phase of binary evolution. We discuss the coalescence rates of binary
NSs and BHs and prospects for their detections, the formation and evolution of
binary WDs and their observational manifestations. Special attention is given
to AM CVn-stars -- compact binaries in which the Roche lobe is filled by
another WD or a low-mass partially degenerate helium-star, as these stars are
thought to be the best LISA verification binary GW sources.Comment: 105 pages, 18 figure
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