5,650 research outputs found
The Origin of the Brightest Cluster Galaxies
Most clusters and groups of galaxies contain a giant elliptical galaxy in
their centres which far outshines and outweighs normal ellipticals. The origin
of these brightest cluster galaxies is intimately related to the collapse and
formation of the cluster. Using an N-body simulation of a cluster of galaxies
in a hierarchical cosmological model, we show that galaxy merging naturally
produces a massive, central galaxy with surface brightness and velocity
dispersion profiles similar to observed BCG's. To enhance the resolution of the
simulation, 100 dark halos at are replaced with self-consistent
disk+bulge+halo galaxy models following a Tully-Fisher relation using 100000
particles for the 20 largest galaxies and 10000 particles for the remaining
ones. This technique allows us to analyze the stellar and dark matter
components independently. The central galaxy forms through the merger of
several massive galaxies along a filament early in the cluster's history.
Galactic cannibalism of smaller galaxies through dynamical friction over a
Hubble time only accounts for a small fraction of the accreted mass. The galaxy
is a flattened, triaxial object whose long axis aligns with the primordial
filament and the long axis of the cluster galaxy distribution agreeing with
observed trends for galaxy-cluster alignment.Comment: Revised and accepted in ApJ, 25 pages, 10 figures, online version
available at http://www.cita.utoronto.ca/~dubinski/bcg
Decentralised Learning MACs for Collision-free Access in WLANs
By combining the features of CSMA and TDMA, fully decentralised WLAN MAC
schemes have recently been proposed that converge to collision-free schedules.
In this paper we describe a MAC with optimal long-run throughput that is almost
decentralised. We then design two \changed{schemes} that are practically
realisable, decentralised approximations of this optimal scheme and operate
with different amounts of sensing information. We achieve this by (1)
introducing learning algorithms that can substantially speed up convergence to
collision free operation; (2) developing a decentralised schedule length
adaptation scheme that provides long-run fair (uniform) access to the medium
while maintaining collision-free access for arbitrary numbers of stations
The blazar-like radio structure of the TeV source IC310
Context. The radio galaxy IC310 in the Perseus cluster has recently been
detected in the gamma-ray regime at GeV and TeV energies. The TeV emission
shows time variability and an extraordinarily hard spectrum, even harder than
the spectrum of the similar nearby gamma-ray emitting radio galaxy M87.
Aims. High-resolution studies of the radio morphology help to constrain the
geometry of the jet on sub-pc scales and to find out where the high-energy
emission might come from.
Methods. We analyzed May 2011 VLBA data of IC310 at a wavelength of 3.6 cm,
revealing the parsec-scale radio structure of this source. We compared our
findings with more information available from contemporary single-dish flux
density measurements with the 100-m Effelsberg radio telescope.
Results. We have detected a one-sided core-jet structure with blazar-like,
beamed radio emission oriented along the same position angle as the kiloparsec
scale radio structure observed in the past by connected interferometers.
Doppler-boosting favoritism is consistent with an angle of theta < 38 degrees
between the jet axis and the line-of-sight, i.e., very likely within the
boundary dividing low-luminosity radio galaxies and BL Lac objects in unified
schemes.
Conclusions. The stability of the jet orientation from parsec to kiloparsec
scales in IC310 argues against its classification as a headtail radio galaxy;
i.e., there is no indication of an interaction with the intracluster medium
that would determine the direction of the tail. IC310 seems to represent a
low-luminosity FRI radio galaxy at a borderline angle to reveal its BL Lac-type
central engine.Comment: 5 pages, 3 figures (1 color); A&A, accepte
Magnetic Pulse Welding of the “Tube – Plug” Pair of STS410 Steel
The research was focused on the magnetic pulse welding (MPW) of 12.5% Cr steel
STS410. The experiments were performed in the tube-plug geometry (both details were
made of the same steel). Magnetic pulse unit consisted of pulsed current generator (PCG)
loaded to a single-turn coil. Magnetic field amplitude of 40 T was generated in the coil
during experiments. The amplitude of pulsed current reached 750 kA.
The effects of energy storage capacity, charging voltage, and end plug shape were
studied. The welded samples were investigated by optical microscopy. The optimal
velocities of impact and contact front motion were evaluated as 300 m/s and 3-3.5 km/s,
respectively.
The paper includes the leakage test results as well. To date, the joints with a helium
leak rate of 10-9 mbar·l·s-1 have been produced
Arts on prescription for community‐dwelling older people with a range of health and wellness needs
Published evidence for the role of participatory art in supporting health and well‐being is growing. The Arts on Prescription model is one vehicle by which participatory art can be delivered. Much of the focus of Arts on Prescription has been on the provision of creative activities for people with mental health needs. This Arts on Prescription program, however, targeted community‐dwelling older people with a wide range of health and wellness needs. Older people were referred to the program by their healthcare practitioner.
Professional artists led courses in visual arts, photography, dance and movement, drama, singing, or music. Classes were held weekly for 8–10 weeks, with six to eight participants per class, and culminated with a showing of work or a performance. Program evaluation involved pre‐ and postcourse questionnaires, and focus groups and individual interviews. Evaluation data on 127 participants aged 65 years and older were available for analysis. We found that Arts on Prescription had a positive impact on participants.
Quantitative findings revealed a statistically significant improvement in the Warwick–Edinburgh Mental Well‐being Scale(WEMWBS) as well as a statistically significant increase in the level of self‐reported creativity and frequency of creative activities.
Qualitative findings indicated that the program provided challenging artistic activities which created a sense of purpose and direction, enabled personal growth and achievement, and empowered participants, in a setting which fostered the development of meaningful relationships with others.
This evaluation adds to the evidence base in support of Arts on Prescription by expanding the application of the model to older people with a diverse range of health and wellness needs
The Specific Heat of a Ferromagnetic Film.
We analyze the specific heat for the vector model on a -dimensional
film geometry of thickness using ``environmentally friendly''
renormalization. We consider periodic, Dirichlet and antiperiodic boundary
conditions, deriving expressions for the specific heat and an effective
specific heat exponent, \alpha\ef. In the case of , for , by
matching to the exact exponent of the two dimensional Ising model we capture
the crossover for \xi_L\ra\infty between power law behaviour in the limit
{L\over\xi_L}\ra\infty and logarithmic behaviour in the limit
{L\over\xi_L}\ra0 for fixed , where is the correlation length in
the transverse dimensions.Comment: 21 pages of Plain TeX. Postscript figures available upon request from
[email protected]
Sorting live stem cells based on Sox2 mRNA expression.
PMCID: PMC3507951This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.While cell sorting usually relies on cell-surface protein markers, molecular beacons (MBs) offer the potential to sort cells based on the presence of any expressed mRNA and in principle could be extremely useful to sort rare cell populations from primary isolates. We show here how stem cells can be purified from mixed cell populations by sorting based on MBs. Specifically, we designed molecular beacons targeting Sox2, a well-known stem cell marker for murine embryonic (mES) and neural stem cells (NSC). One of our designed molecular beacons displayed an increase in fluorescence compared to a nonspecific molecular beacon both in vitro and in vivo when tested in mES and NSCs. We sorted Sox2-MB(+)SSEA1(+) cells from a mixed population of 4-day retinoic acid-treated mES cells and effectively isolated live undifferentiated stem cells. Additionally, Sox2-MB(+) cells isolated from primary mouse brains were sorted and generated neurospheres with higher efficiency than Sox2-MB(-) cells. These results demonstrate the utility of MBs for stem cell sorting in an mRNA-specific manner
Screening for Diabetes and Pre-Diabetes With Proposed A1C-Based Diagnostic Criteria
OBJECTIVE — An International Expert Committee (IEC) and the American Diabetes Asso-ciation (ADA) proposed diagnostic criteria for diabetes and pre-diabetes based on A1C levels. We hypothesized that screening for diabetes and pre-diabetes with A1C measurements would differ from using oral glucose tolerance tests (OGTT). RESEARCH DESIGN AND METHODS — We compared pre-diabetes, dysglycemia (diabetes or pre-diabetes), and diabetes identified by the proposed criteria (A1C 6.5 % for diabetes and 6.0–6.4 % [IEC] or 5.7–6.4 % [ADA] for high risk/pre-diabetes) with standard OGTT diagnoses in three datasets. Non-Hispanic white or black adults without known diabetes who had A1C and 75-g OGTT measurements were included from the prospective Screening for Impaired Glucose Tolerance study (n 1,581), and from the National Health and Nutrition Examination Survey (NHANES) III (n 2014), and NHANES 2005–2006 (n 1,111). RESULTS — OGTTs revealed pre-diabetes in 35.8 % and diabetes in 5.2 % of combined study subjects. A1C provided receiver operating characteristic (ROC) curve areas for diabetes of 0.79– 0.83, but ROC curve areas were 0.70 for dysglycemia or pre-diabetes. The proposed criteria missed 70 % of individuals with diabetes, 71–84 % with dysglycemia, and 82–94 % with pre
Cold gas outflows from the Small Magellanic Cloud traced with ASKAP
Feedback from massive stars plays a critical role in the evolution of the
Universe by driving powerful outflows from galaxies that enrich the
intergalactic medium and regulate star formation. An important source of
outflows may be the most numerous galaxies in the Universe: dwarf galaxies.
With small gravitational potential wells, these galaxies easily lose their
star-forming material in the presence of intense stellar feedback. Here, we
show that the nearby dwarf galaxy, the Small Magellanic Cloud (SMC), has atomic
hydrogen outflows extending at least 2 kiloparsecs (kpc) from the star-forming
bar of the galaxy. The outflows are cold, , and may have formed
during a period of active star formation million years (Myr) ago. The
total mass of atomic gas in the outflow is solar masses, , or % of the total atomic gas of the galaxy. The inferred
mass flux in atomic gas alone, , is up to an order of magnitude greater than the star
formation rate. We suggest that most of the observed outflow will be stripped
from the SMC through its interaction with its companion, the Large Magellanic
Cloud (LMC), and the Milky Way, feeding the Magellanic Stream of hydrogen
encircling the Milky Way.Comment: Published in Nature Astronomy, 29 October 2018,
http://dx.doi.org/10.1038/s41550-018-0608-
Exploring Halo Substructure with Giant Stars III: First Results from the Grid Giant Star Survey and Discovery of a Possible Nearby Sagittarius Tidal Structure in Virgo
We describe first results of a spectroscopic probe of selected fields from
the Grid Giant Star Survey. Multifiber spectroscopy of several hundred stars in
a strip of eleven fields along delta approximately -17^{circ}, in the range 12
<~ alpha <~ 17 hours, reveals a group of 8 giants that have kinematical
characteristics differing from the main field population, but that as a group
maintain coherent, smoothly varying distances and radial velocities with
position across the fields. Moreover, these stars have roughly the same
abundance, according to their MgH+Mgb absorption line strengths. Photometric
parallaxes place these stars in a semi-loop structure, arcing in a contiguous
distribution between 5.7 and 7.9 kpc from the Galactic center. The spatial,
kinematical, and abundance coherence of these stars suggests that they are part
of a diffuse stream of tidal debris, and one roughly consistent with a wrapped,
leading tidal arm of the Sagittarius dwarf spheroidal galaxy.Comment: 8 pages including 4 figures. Accepted for publication in ApJ
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