263 research outputs found
A discrete chemo-dynamical model of the dwarf spheroidal galaxy Sculptor: mass profile, velocity anisotropy and internal rotation
We present a new discrete chemo-dynamical axisymmetric modeling technique,
which we apply to the dwarf spheroidal galaxy Sculptor. The major improvement
over previous Jeans models is that realistic chemical distributions are
included directly in the dynamical modelling of the discrete data. This avoids
loss of information due to spatial binning and eliminates the need for hard
cuts to remove contaminants and to separate stars based on their chemical
properties. Using a combined likelihood in position, metallicity and
kinematics, we find that our models naturally separate Sculptor stars into a
metal-rich and a metal-poor population. Allowing for non-spherical symmetry,
our approach provides a central slope of the dark matter density of . The metal-rich population is nearly isotropic (with
) while the metal-poor population is tangentially
anisotropic (with ) around the half light radius
of kpc. A weak internal rotation of the metal-rich population is
revealed with . We run tests using mock data
to show that a discrete dataset with stars is required to
distinguish between a core () and cusp (), and to
constrain the possible internal rotation to better than confidence
with our model. We conclude that our discrete chemo-dynamical modelling
technique provides a flexible and powerful tool to robustly constrain the
internal dynamics of multiple populations, and the total mass distribution in a
stellar system.Comment: Accepted by MNRA
Regional libraries online project : Survey
The Library and Information Service of Western Australia (LISWA) implemented their Regional Libraries Online Project in 1997 to provide public Internet access to 11 regional libraries in Western Australia. This report highlights major trends and issues that arose during the implementation of the project..
Microstructural and Chemical Characterization of a Purple Pigment from a Faiyum Mummy Portrait
Results are presented from analyses that were conducted to explain the presence of chromium, detected noninvasively using energy-dispersive X-ray fluorescence (XRF), in the unusually large (2-3mm diameter) rough gem-like purple pigment particles in the paint used for a Faiyum mummy portrait. An approximately 50 μm diameter particle of the chromium-containing purple pigment was extracted from the Portrait of a Bearded Man, dated to Roman Imperial Egypt in the second century, circa 170-180 CE, accession #32.6 in the Walters Art Museum collection. The particle was characterized using energy-dispersive X-ray fluorescence analysis, electron microscopy, diffraction, and atom probe tomography. It is demonstrated that the purple pigment particle is a heterogeneous organic pigment, specifically, a lake pigment likely derived from either plant or insect matter, which contains minor percentages of both transition metals and alkali / alkali earth metals, with nanometer-scale crystallites of lead carbonates and sulfates. The analyses revealed for the first time the nanoscale microstructure and stratigraphy in an ancient lake pigment. Results suggest that similarities with respect to time period and place of production may be developed among unprovenienced Faiyum mummy portraits to help localize workshops or artists, using analyses focused on lake pigments to characterize specifically metal-based mordants
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Being an Athlete or Being a Girl: Selective Identities among Fictional Female Athletes Who Play with the Boys
This article examines the experiences of female protagonists who join all-male teams in recently published middle grade and young adult sports fiction. Two frames of analysis, identity and intersectionality, are applied in examining the question of how female protagonists navigate girlhood identities given their nontraditional sports participation on historically male teams. Findings suggest that as the fictional female athletes move into male-dominated spaces, they must reconceptualize their identities within either/or binaries that reaffirm gendered expectations and that these binaries ignore the complicated multiplicity of identities and their associated privileges and oppressions.</p
The central mass and mass-to-light profile of the Galactic globular cluster M15
We analyze line-of-sight velocity and proper motion data of stars in the
Galactic globular cluster M15 using a new method to fit dynamical models to
discrete kinematic data. Our fitting method maximizes the likelihood for
individual stars and, as such, does not suffer the same loss of spatial and
velocity information incurred when spatially binning data or measuring velocity
moments. In this paper, we show that the radial variation in M15 of the
mass-to-light ratio is consistent with previous estimates and theoretical
predictions, which verifies our method. Our best-fitting axisymmetric Jeans
models do include a central dark mass of , which
can be explained by a high concentration of stellar remnants at the cluster
center. This paper shows that, from a technical point of view and with current
computing power, spatial binning of data is no longer necessary. This not only
leads to more accurate fits, but also avoids biased mass estimates due to the
loss of resolution. Furthermore, we find that the mass concentration in M15 is
significantly higher than previously measured, and is in close agreement with
theoretical predictions for core-collapsed globular clusters without a central
intermediate-mass black hole.Comment: Accepted by MNRAS; 8 pages, 7 figure
Total mass slopes and enclosed mass constrained by globular cluster system dynamics
The goal of this work is to probe the total mass distribution of early-type
galaxies with globular clusters (GCs) as kinematic tracers, by constraining the
parameters of the profile with a flexible modelling approach. To that end, we
leverage the extended spatial distribution of GCs from the SLUGGS survey
() in combination with
discrete dynamical modelling. We use discrete Jeans anisotropic modelling in
cylindrical coordinates to determine the velocity moments at the location of
the GCs in our sample. We use a Bayesian framework to determine the best-fit
parameters of the total mass density profile and orbital properties of the GC
systems. We find that the orbital properties (anisotropy and rotation of the
dispersion-dominated GC systems) minimally impact the measurements of the inner
slope and enclosed mass, while a strong presence of dynamically-distinct
subpopulations or low numbers of kinematic tracers can bias the results. Owing
to the large spatial extent of the tracers our method is sensitive to the
intrinsic inner slope of the total mass profile and we find for 12 galaxies with robust measurements. To compare our
results with literature values we fit a single power-law profile to the
resulting total mass density. In the radial range 0.1-4~ our
measured slope has a value of
and is in good agreement with the literature.Comment: 17 pages, 13 Figures, 8 Tables, Accepted for publication in A&
Gene Combination Transfer to Block Autoimmune Damage in Transplanted Islets of Langerhans
Islet transplantation therapy would be applicable to a
wider range of diabetic patients if donor islet acceptance
and protection were possible without systemic immunosuppression
of the recipient. To this aim, gene transfer
to isolated donor islets ex vivo is one method that has
shown promise. This study examines the combined effect of
selected immunomodulatory and anti-inflammatory genes
known to extend the functional viability of pancreatic islet
grafts in an autoimmune system. These genes, indoleamine
2,3-dioxygenase (IDO), manganese superoxide dismutase
(MnSOD), and interleukin (IL)-1 receptor antagonist protein
(IRAP), were transferred to isolated NOD donor islets
ex vivo then transplanted to NODscid recipients and evaluated
in vivo after diabetogenic T-cell challenge. The length
of time the recipient remained euglycemic was used to measure
the ability of the transgenes to protect the graft from
autoimmune destruction. Although the results of these cotransfections
gave little evidence of a synergistic relationship,
they were useful to show that gene combinations can be used to more efficiently protect islet grafts from diabetogenic
T cells
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