25,952 research outputs found
Determination of bone mineral mass in vivo
Radiographic equipment incorporates two radiation sources, generating high-energy and low-energy beams. Recording equipment measures amount of radiation that has penetrated limb. Data are fed into computer that determines mass of the examined bone
Temporal fluctuations in the differential rotation of cool active stars
This paper reports positive detections of surface differential rotation on
two rapidly rotating cool stars at several epochs, by using stellar surface
features (both cool spots and magnetic regions) as tracers of the large scale
latitudinal shear that distorts the convective envelope in this type of stars.
We also report definite evidence that this differential rotation is different
when estimated from cool spots or magnetic regions, and that it undergoes
temporal fluctuations of potentially large amplitude on a time scale of a few
years. We consider these results as further evidence that the dynamo processes
operating in these stars are distributed throughout the convective zone rather
than being confined at its base as in the Sun. By comparing our observations
with two very simple models of the differential rotation within the convective
zone, we obtain evidence that the internal rotation velocity field of the stars
we investigated is not like that of the Sun, and may resemble that we expect
for rapid rotators. We speculate that the changes in differential rotation
result from the dynamo processes (and from the underlying magnetic cycle) that
periodically converts magnetic energy into kinetic energy and vice versa. We
emphasise that the technique outlined in this paper corresponds to the first
practical method for investigating the large scale rotation velocity field
within convective zones of cool active stars, and offers several advantages
over asteroseismology for this particular purpose and this specific stellar
class.Comment: 14 pages, 4 figure
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Kinosternon integrum
Number of Pages: 6Integrative BiologyGeological Science
Magnetic activity on AB Doradus: Temporal evolution of starspots and differential rotation from 1988 to 1994
Surface brightness maps for the young K0 dwarf AB Doradus are reconstructed
from archival data sets for epochs spanning 1988 to 1994. By using the
signal-to-noise enhancement technique of Least-Squares Deconvolution, our
results show a greatly increased resolution of spot features than obtained in
previously published surface brightness reconstructions. These images show that
for the exception of epoch 1988.96, the starspot distributions are dominated by
a long-lived polar cap, and short-lived low to high latitude features. The
fragmented polar cap at epoch 1988.96 could indicate a change in the nature of
the dynamo in the star. For the first time we measure differential rotation for
epochs with sufficient phase coverage (1992.05, 1993.89, 1994.87). These
measurements show variations on a timescale of at least one year, with the
strongest surface differential rotation ever measured for AB Dor occurring in
1994.86. In conjunction with previous investigations, our results represent the
first long-term analysis of the temporal evolution of differential rotation on
active stars.Comment: accepted by MNRAS 18 pages 18 figure
Mashing up Visual Languages and Web Mash-ups
Research on web mashups and visual languages
share an interest in human-centered computing. Both
research communities are concerned with supporting
programming by everyday, technically inexpert users.
Visual programming environments have been a focus for
both communities, and we believe that there is much to
be gained by further discussion between these research
communities. In this paper we explore some connections
between web mashups and visual languages, and try to
identify what each might be able to learn from the other.
Our goal is to establish a framework for a dialog
between the communities, and to promote the exchange
of ideas and our respective understandings of humancentered
computing.published or submitted for publicationis peer reviewe
Recommended from our members
Compressed intramolecular dispersion interactions.
The feasibility of the compression of localized virtual orbitals is explored in the context of intramolecular long-range dispersion interactions. Singular value decomposition (SVD) of coupled cluster doubles amplitudes associated with the dispersion interactions is analyzed for a number of long-chain systems, including saturated and unsaturated hydrocarbons and a silane chain. Further decomposition of the most important amplitudes obtained from these SVDs allows for the analysis of the dispersion-specific virtual orbitals that are naturally localized. Consistent with previous work on intermolecular dispersion interactions in dimers, it is found that three important geminals arise and account for the majority of dispersion interactions at the long range, even in the many body intramolecular case. Furthermore, it is shown that as few as three localized virtual orbitals per occupied orbital can be enough to capture all pairwise long-range dispersion interactions within a molecule
Rotationally Modulated X-ray Emission from T Tauri Stars
We have modelled the rotational modulation of X-ray emission from T Tauri
stars assuming that they have isothermal, magnetically confined coronae. By
extrapolating surface magnetograms we find that T Tauri coronae are compact and
clumpy, such that rotational modulation arises from X-ray emitting regions
being eclipsed as the star rotates. Emitting regions are close to the stellar
surface and inhomogeneously distributed about the star. However some regions of
the stellar surface, which contain wind bearing open field lines, are dark in
X-rays. From simulated X-ray light curves, obtained using stellar parameters
from the Chandra Orion Ultradeep Project, we calculate X-ray periods and make
comparisons with optically determined rotation periods. We find that X-ray
periods are typically equal to, or are half of, the optical periods. Further,
we find that X-ray periods are dependent upon the stellar inclination, but that
the ratio of X-ray to optical period is independent of stellar mass and radius.Comment: 10 pages, 8 figures, accepted for publication in MNRA
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