507 research outputs found
The provision of education and training for healthcare professionals through the medium of the internet
This paper describes a new initiative to provide Internet based courses to student and professional occupational therapists in four centres in the UK, Belgium the Netherlands and Sweden. The basis of this collaborative Occupational Therapy Internet School (OTIS) is the concept of the “Virtual College”. This comprises the design and implementation of a sophisticated Internet-based system through which courses can be managed, prepared and delivered online in an effective fashion, and where students can communicate both with the staff and their peers. The aim is to support and facilitate the whole range of educational activities within a remote electronic environment. A major feature of the course organisation is the adoption of a problem-based approach in which students will collaborate internationally to propose effective intervention in given case study scenarios.
The paper outlines the rationale for OTIS, the content and structure of the courseware, the technical specification of the system and evaluation criteria. In addition to the more conventional web-based learning facilities generally offered, a number of agent-based approaches are being adopted to assist in the management of the course by ensuring the proper delivery of course materials and to assist the functioning of project groups. </p
Xenotransplantation of adult hippocampal neural progenitors into the developing zebrafish for assessment of stem cell plasticity
Adult stem cells are considered multipotent, restricted to differentiate into a few tissue-specific cell types. With the advent of technologies which can dedifferentiate and transdifferentiate cell types, assumptions about the process of cell fate determination must be reconsidered, including the role of extrinsic versus intrinsic factors. To determine the plasticity of adult neural progenitors, rat hippocampal progenitor cells were xenotransplanted into embryonic zebrafish. These animals allow for easy detection of transplanted cells due to their external development and transparency at early stages. Adult neural progenitors were observed throughout the zebrafish for the duration of the experiment (at least five days post-transplantation). While the majority of transplanted cells were observed in the central nervous system, a large percentage of cells were located in superficial tissues. However, approximately one-third of these cells retained neural morphology and expression of the neuronal marker, Class III β-tubulin, indicating that the transplanted adult neural progenitors did not adapt alternate fates. A very small subset of cells demonstrated unique, non-neural flattened morphology, suggesting that adult neural progenitors may exhibit plasticity in this model, though at a very low rate. These findings demonstrate that the developing zebrafish may be an efficient model to explore plasticity of a variety of adult stem cell types and the role of external factors on cell fate
S986 in M67: A Totally-Eclipsing Binary at the Cluster Turnoff
We have discovered that the star S986 in the old open cluster M67 has
detectable total eclipses of depth 0.08 mag for the primary eclipse and 0.011
mag for the secondary eclipse (in I only). We confirm the detection of a third
star in spectra contributing 11.5% +/- 1.5% of the total light in V band. The
radial velocity of the third star indicates that it is a cluster member, but it
is unclear whether it is physically associated with the eclipsing binary. Using
spectroscopic and photometric data, we deconvolve the photometry of the three
stars, and find that the primary star in the eclipsing binary is significantly
hotter than the turnoff. The two most likely explanations are that the primary
star is in a rapid phase of evolution near core hydrogen exhaustion (associated
with the turnoff gap in M67's color-magnitude diagram), or that it is a blue
straggler created during a stellar collision earlier in the cluster's history.
Our detection of Li in the primary star tightly constrains possible formation
mechanisms in the blue straggler explanation. Because S986 is often used to
constrain tidal dissipation models, this may imply that the strength of tidal
effects is underestimated.Comment: 27 pages, 8 figures, accepted for A
Modelling Collision Products of Triple-Star Mergers
In dense stellar clusters, binary-single and binary-binary encounters can
ultimately lead to collisions involving two or more stars. A comprehensive
survey of multi-star collisions would need to explore an enormous amount of
parameter space, but here we focus on a number of representative cases
involving low-mass main-sequence stars. Using both Smoothed Particle
Hydrodynamics (SPH) calculations and a much faster fluid sorting software
package (MMAS), we study scenarios in which a newly formed product from an
initial collision collides with a third parent star. By varying the order in
which the parent stars collide, as well as the orbital parameters of the
collision trajectories, we investigate how factors such as shock heating affect
the chemical composition and structure profiles of the collision product. Our
simulations and models indicate that the distribution of most chemical elements
within the final product is not significantly affected by the order in which
the stars collide, the direction of approach of the third parent star, or the
periastron separations of the collisions. We find that the sizes of the
products, and hence their collisional cross sections for subsequent encounters,
are sensitive to the order and geometry of the collisions. For the cases that
we consider, the radius of the product formed in the first (single-single star)
collision ranges anywhere from roughly 2 to 30 times the sum of the radii of
its parent stars. The final product formed in our triple-star collisions can
easily be as large or larger than a typical red giant. We therefore expect the
collisional cross section of a newly formed product to be greatly enhanced over
that of a thermally relaxed star of the same mass.Comment: 20 pages, submitted to MNRA
Composition Mixing during Blue Straggler Formation and Evolution
We use smoothed-particle hydrodynamics to examine differences between direct
collisions of single stars and binary star mergers in their roles as possible
blue straggler star formation mechanisms. We find in all cases that core helium
in the progenitor stars is largely retained in the core of the remnant, almost
independent of the type of interaction or the central concentration of the
progenitor stars.
We have also modelled the subsequent evolution of the hydrostatic remnants,
including mass loss and energy input from the hydrodynamical interaction. The
combination of the hydrodynamical and hydrostatic models enables us to predict
that little mixing will occur during the merger of two globular cluster stars
of equal mass. In contrast to the results of Proctor Sills, Bailyn, & Demarque
(1995), we find that neither completely mixed nor unmixed models can match the
absolute colors of observed blue stragglers in NGC 6397 at all luminosity
levels. We also find that the color distribution is probably the crucial test
for explanations of BSS formation - if stellar collisions or mergers are the
correct mechanisms, a large fraction of the lifetime of the straggler must be
spent away from the main sequence. This constraint appears to rule out the
possibility of completely mixed models. For NGC 6397, unmixed models predict
blue straggler lifetimes ranging from about 0.1 to 4 Gyr, while completely
mixed models predict a range from about 0.6 to 4 Gyr.Comment: AASTeX, 28 pg., accepted for ApJ, also available at
http://ucowww.ucsc.edu/~erics/bspaper.htm
Time-Series Photometry of M67: W UMa Systems, Blue Stragglers, and Related Systems
We present an analysis of over 2200 V images taken on 14 nights at the Mt.
Laguna 1 m telescope of the open cluster M67. Our observations overlap but
extend beyond the field analyzed by Gilliland et al. (1991), and complement
data recently published by van den Berg et al. (2002) and Stassun et al.
(2002). We show variability in the light curves of all 4 of the known W UMa
variables on timescales ranging from a day to decades (for AH Cnc). We have
modeled the light curve of AH Cnc, and the total eclipses allow us to determine
q = 0.16 +0.03/-0.02 and i = 86 +4/-8 degrees. The position of this system near
the turnoff of M67 makes it useful for constraining the turnoff mass for the
cluster. We have also detected two unusual features in the light curve of AH
Cnc that may be caused by prominences. We have also monitored cluster blue
stragglers for variability, and we present evidence hinting at low level
variations in the stragglers S752, S968, and S1263, and we place limits on the
variability of a number of other cluster blue stragglers. Finally, we provide
photometry of the sub-subgiant branch star S1063 showing variability on
timescales similar to the orbital period, while the ``red straggler'' S1040
shows evidence of an unexplained drop in brightness at phases corresponding to
the passage of the white dwarf in front of the giant.Comment: 44 pages, 16 figures, AASTeX, accepted for A
Adult neural stem cell plasticity
Stem cells derived from adult tissues have long been considered multipotent, able to differentiate into a limited number of cell types found in their tissue of origin. Embryonic stem cells, in contrast, are pluripotent, which may differentiate into almost all cell types. With the ability to create induced pluripotent stem cells from somatic cells now available, the properties of multipotent stem cells are being re-evaluated. If adult cells may be reverted to pluripotent stem cells, can multipotent stem cells also be manipulated towards pluripotency? Advancements in biotechnology now allow for better methods to investigate stem cell plasticity, such as the relative influence of external versus intrinsic factors on cell fate. Recent studies indicate that adult neural stem cells (NSCs) demonstrate greater plasticity under certain conditions, resulting in the derivation of a variety of cell types including muscle, hematopoietic, and epithelial cells. This suggests that NSCs may provide a potential source of rare cell types for clinical application as an alternative to embryonic stem cells. Producing rare cell types from NSCs rather than embryonic stem cells avoids the ethical issues surrounding the use of this cell type. Further, NSCs may be an advantageous source compared to induced pluripotent stem cells, which are difficult to create, expensive, and time-consuming to develop.
Adult NSCs have the ability to form neurons, astrocytes, and oligodendrocytes in vitro. More recently, evidence has arisen which indicates adult NSCs may have extended plasticity. Studies have demonstrated differentiation into cell types of all three germ layers through a variety of methods
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