557 research outputs found
Crowded-Field Astrometry with the Space Interferometry Mission - I. Estimating the Single-Measurement Astrometric Bias Arising from Confusion
The accuracy of position measurements on stellar targets with the future
Space Interferometry Mission (SIM) will be limited not only by photon noise and
by the properties of the instrument (design, stability, etc.) and the overall
measurement program (observing strategy, reduction methods, etc.), but also by
the presence of other "confusing" stars in the field of view (FOV). We use a
simple "phasor" model as an aid to understanding the main effects of this
"confusion bias" in single observations with SIM. This analytic model has been
implemented numerically in a computer code and applied to a selection of
typical SIM target fields drawn from some of the Key Projects already accepted
for the Mission. We expect that less than 1% of all SIM targets will be
vulnerable to confusion bias; we show that for the present SIM design,
confusion may be a concern if the surface density of field stars exceeds 0.4
star/arcsec^2. We have developed a software tool as an aid to ascertaining the
possible presence of confusion bias in single observations of any arbitrary
field. Some a priori knowledge of the locations and spectral energy
distributions of the few brightest stars in the FOV is helpful in establishing
the possible presence of confusion bias, but the information is in general not
likely to be available with sufficient accuracy to permit its removal. We
discuss several ways of reducing the likelihood of confusion bias in crowded
fields. Finally, several limitations of the present semi-analytic approach are
reviewed, and their effects on the present results are estimated. The simple
model presented here provides a good physical understanding of how confusion
arises in a single SIM observation, and has sufficient precision to establish
the likelihood of a bias in most cases.Comment: 28 pages, 20 figures, 1 table; to appear in December 2007 issue of
PAS
Atmospheric radiation model for water surfaces
An atmospheric correction model was extended to account for various atmospheric radiation components in remotely sensed data. Components such as the atmospheric path radiance which results from singly scattered sky radiation specularly reflected by the water surface are considered. A component which is referred to as the virtual Sun path radiance, i.e. the singly scattered path radiance which results from the solar radiation which is specularly reflected by the water surface is also considered. These atmospheric radiation components are coded into a computer program for the analysis of multispectral remote sensor data over the Great Lakes of the United States. The user must know certain parameters, such as the visibility or spectral optical thickness of the atmosphere and the geometry of the sensor with respect to the Sun and the target elements under investigation
Neurosequential Model of Therapeutics in a Therapeutic Preschool: Implications for Work with Children with Complex Neuropsychiatric Problems
The two studies presented examine the use of the Neurosequential Model of Therapeutics on the social-emotional development and behavior of 28 children participating in a therapeutic preschool program. Results from these studies indicate that the use of the Neurosequential Model of Therapeutics approach to determine the nature, timing, and “dose” of developmentally appropriate activities and interventions within the context of a therapeutic preschool did improve the social-emotional development of the participating children. Interventions and activities were provided in the context of Filial Play Therapy as part of the therapeutic preschool environment. Six-month and 12-month follow-ups suggest gains in social-emotional development and behavior were retained. Implications for future use are discussed
A Networks-Science Investigation into the Epic Poems of Ossian
In 1760 James Macpherson published the first volume of a series of epic poems
which he claimed to have translated into English from ancient Scottish-Gaelic
sources. The poems, which purported to have been composed by a third-century
bard named Ossian, quickly achieved wide international acclaim. They invited
comparisons with major works of the epic tradition, including Homer's Iliad and
Odyssey, and effected a profound influence on the emergent Romantic period in
literature and the arts. However, the work also provoked one of the most famous
literary controversies of all time, colouring the reception of the poetry to
this day. The authenticity of the poems was questioned by some scholars, while
others protested that they misappropriated material from Irish mythological
sources. Recent years have seen a growing critical interest in Ossian,
initiated by revisionist and counter-revisionist scholarship and by the
two-hundred-and-fiftieth anniversary of the first collected edition of the
poems in 1765. Here we investigate Ossian from a networks-science point of
view. We compare the connectivity structures underlying the societies described
in the Ossianic narratives with those of ancient Greek and Irish sources.
Despite attempts, from the outset, to position Ossian alongside the Homeric
epics and to distance it from Irish sources, our results indicate significant
network-structural differences between Macpherson's text and those of Homer.
They also show a strong similarity between Ossianic networks and those of the
narratives known as Acallam na Sen\'orach (Colloquy of the Ancients) from the
Fenian Cycle of Irish mythology.Comment: Accepted for publication in Advances in Complex system
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