952 research outputs found
A simulator and flight study of yaw coupling in turning maneuvers of large transport aircraft
Piloted simulator study of yaw coupling in turning maneuvers of supersonic transport compared with flight test data on large variable stability jet transpor
Flight investigation of methods for implementing noise-abatement landing approaches
Flight tests and simulation of steep noise reducing landing approaches with jet transpor
Improved age constraints for the AB Dor quadruple system - The binary nature of AB Dor B
We present resolved NACO photometry of the close binary AB Dor B in H- and
Ks-band. AB Dor B is itself known to be a wide binary companion to AB Dor A,
which in turn has a very low-mass close companion named AB Dor C. These four
known components make up the young and dynamically interesting system AB Dor,
which will likely become a benchmark system for calibrating theoretical
pre-main sequence evolutionary mass tracks for low-mass stars. However, for
this purpose the actual age has to be known, and this subject has been a matter
of discussion in the recent scientific literature. We compare our resolved
photometry of AB Dor Ba and Bb with theoretical and empirical isochrones in
order to constrain the age of the system. This leads to an age estimate of
about 50 to 100 Myr. We discuss the implications of such an age range for the
case of AB Dor C, and compare with other results in the literature.Comment: 7 pages, 6 figures, accepted for publication in A&
Systematic review of fatty acid composition of human milk from mothers of preterm compared to full-term infants
Background: Fatty acid composition of human milk serves as guidance for the composition of infant formulae. The aim of the study was to systematically review data on the fatty acid composition of human milk of mothers of preterm compared to full-term infants. Methods: An electronic literature search was performed in English (Medline and Medscape) and German (SpringerLink) databases and via the Google utility. Fatty acid compositional data for preterm and fullterm human milk were converted to differences between means and 95% confidence intervals. Results: We identified five relevant studies publishing direct comparison of fatty acid composition of preterm versus full-term human milk. There were no significant differences between the values of the principal saturated and monounsaturated fatty acids. In three independent studies covering three different time points of lactation, however, docosahexaenoic acid (DHA) values were significantly higher in milk of mothers of preterm as compared to those of full-term infants, with an extent of difference considered nutritionally relevant. Conclusion: Higher DHA values in preterm than in full-term human milk underlines the importance of using own mother's milk for feeding preterm babies and raises the question whether DHA contents in preterm formulae should be higher than in formulae for full-term infants. Copyright (c) 2008 S. Karger AG, Basel
A critique of neo-mercantilist analyses of Icelandic political economy and crisis
Iceland’s journey from rags to riches in the 20th century is related, in the dominant discourse, to its gaining independence in 1944. This discourse played a significant role in both the legitimation of the finance-dominated growth model in the 1990s and 2000s and in the latter’s defence as it came under scrutiny before its collapse in October 2008. It is therefore ironic – or perhaps, in some sense, logical – to find dominant analyses of the crisis arising from the neo-mercantilist tradition. Drawing on Marxist critiques of neo-mercantilism, we challenge these interventions and thus seek to redress the neglect of social struggle in the dominant discourse
High-Resolution Spectroscopy of Some Very Active Southern Stars
We have obtained high-resolution echelle spectra of 18 solar-type stars that
an earlier survey showed to have very high levels of Ca II H and K emission.
Most of these stars belong to close binary systems, but 5 remain as probable
single stars or well-separated binaries that are younger than the Pleiades on
the basis of their lithium abundances and H-alpha emission. Three of these
probable single stars also lie more than 1 magnitude above the main sequence in
a color-magnitude diagram, and appear to have ages of 10 to 15 Myr. Two of
them, HD 202917 and HD 222259, also appear to have a kinematical association
with the pre-main sequence multiple system HD 98800.Comment: 25 figures, 3 table
ESR, raman and conductivity studies on fractionated poly(2-methoxyaniline-5-sulfonic acid)
Synthesis methods used to produce poly(2-methoxyaniline-5-sulfonic acid) (PMAS), a water soluble, self-doped conducting polymer, have been shown to form two distinctly different polymer fractions with molecular weights of approximately 2 kDa and 8 -10 kDa. The low molecular weight (LMWT) PMAS fraction is redox inactive and non-conducting while the high molecular weight (HMWT) PMAS is electro-active with electrical conductivities of 0.94 0.05 S cm-1. Previous investigations have illustrated the different photochemical and electrochemical properties of these fractions, but have not correlated these properties with the structural and electronic interactions that drive them. Incomplete purification of the PMAS mixture, typically via bag dialysis, has been shown to result in a mixture of approximately 50:50 HMWT:LMWT PMAS with electrical conductivity significantly lower at approximately 0.10 to 0.26 S cm-1. The difference between the electrical conductivities of these fractions has been investigated by the controlled addition of the non-conducting LMWT PMAS fraction into the HMWT PMAS composite film with the subsequent electronic properties investigated by solid-state ESR and Raman spectroscopies. These studies illustrate strong electronic intereactions of the insulating LMWT PMAS with the emeraldine salt HMWT PMAS to substantially alter the population of the electronic charge carriers in the conducting polymer. ESR studies on these mixtures, when compared to HMWT PMAS, exhibited a lower level of electron spin in the presence of LMWT PMAS indicative of the the formation of low spin bipolarons without a change the oxidation state of the conducting HMWT fraction
On the dynamics of the ABDoradus system
We present an astrometric analysis of the binary systems ABDorA /ABDorC and
ABDorBa / ABDorBb. These two systems of well-known late-type stars are
gravitationally associated and they constitute the quadruple ABDoradus system.
From the astrometric data available at different wavelengths, we report: (i)
a determination of the orbit of ABDorC, the very low mass companion to ABDorA,
which confirms the mass estimate of 0.090Msun reported in previous works; (ii)
a measurement of the parallax of ABDorBa, which unambiguously confirms the
long-suspected physical association between this star and ABDorA; and (iii)
evidence of orbital motion of ABDorBa around ABDorA, which places an upper
bound of 0.4Msun on the mass of the pair ABDorBa / ABDorBb (50% probability).
Further astrometric monitoring of the system at all possible wavelengths would
determine with extraordinary precision the dynamical mass of its four
components.Comment: 7 pages, 4 figure
Molecular evolution of HoxA13 and the multiple origins of limbless morphologies in amphibians and reptiles
Developmental processes and their results, morphological characters, are inherited through transmission of genes regulating development. While there is ample evidence that cis-regulatory elements tend to be modular, with sequence segments dedicated to different roles, the situation for proteins is less clear, being particularly complex for transcription factors with multiple functions. Some motifs mediating protein-protein interactions may be exclusive to particular developmental roles, but it is also possible that motifs are mostly shared among different processes. Here we focus on HoxA13, a protein essential for limb development. We asked whether the HoxA13 amino acid sequence evolved similarly in three limbless clades: Gymnophiona, Amphisbaenia and Serpentes. We explored variation in ω (dN/dS) using a maximum-likelihood framework and HoxA13sequences from 47 species. Comparisons of evolutionary models provided low ω global values and no evidence that HoxA13 experienced relaxed selection in limbless clades. Branch-site models failed to detect evidence for positive selection acting on any site along branches of Amphisbaena and Gymnophiona, while three sites were identified in Serpentes. Examination of alignments did not reveal consistent sequence differences between limbed and limbless species. We conclude that HoxA13 has no modules exclusive to limb development, which may be explained by its involvement in multiple developmental processes
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