6,623 research outputs found
Passive Evolution: Are the Faint Blue Galaxy Counts Produced by a Population of Eternally Young Galaxies?
A constant age population of blue galaxies, postulated in the model of
Gronwall & Koo (1995), seems to provide an attractive explanation of the excess
of very blue galaxies in the deep galaxy counts. Such a population may be
generated by a set of galaxies with cycling star formation rates, or at the
other extreme, be maintained by the continual formation of new galaxies which
fade after they reach the age specified in the Gronwall and Koo model. For both
of these hypotheses, we have calculated the luminosity functions including the
respective selection criteria, the redshift distributions, and the number
counts in the B_J and K bands. We find a substantial excess in the number of
galaxies at low redshift (0 < z < 0.05) over that observed in the CFH redshift
survey (Lilly et al. 1995) and at the faint end of the Las Campanas luminosity
function (Lin et al. 1996). Passive or mild evolution fails to account for the
deep galaxy counts because of the implications for low redshift determinations
of the I-selected redshift distribution and the r-selected luminosity function
in samples where the faded counterparts of the star-forming galaxies would be
detectable.Comment: 11 pages, LaTeX type (aaspp4.sty), 3 Postscript figures, submitted to
ApJ Letter
Catch-up growth strategies differ between body structures: interactions between age and structure-specific growth in wild nestling Alpine swifts
1. Little is known on the occurrence and magnitude of faster than normal (catch-up) growth in response to periods of undernutrition in the wild, and the extent to which different body structures compensate and over what timescales is poorly understood.
2. We investigated catch-up growth in nestling Alpine Swifts, Apus melba, by comparing nestling growth trajectories in response to a naturally occurring 1-week period of inclement weather and undernutrition with growth of nestlings reared in a good year.
3. In response to undernutrition, nestlings exhibited a hierarchy of tissues preservation and compensation, with body mass being restored quickly after the end of the period of undernutrition, acceleration of skeletal growth occurring later in development, and compensation in wing length occurring mostly due to a prolongation of growth and delayed fledging.
4. The effect of undernutrition and subsequent catch-up growth was age-dependent, with older nestlings being more resilient to undernutrition, and in turn having less need to compensate later in the development.
5. This shows that young in a free-living bird population can compensate in body mass and body size for a naturally occurring period of undernutrition, and that the timing and extent of compensation varies with age and between body structures
A ring galaxy at z=1 lensed by the cluster Abell 370
We present a study of a very peculiar object found in the field of the
cluster-lens Abell 370. This object displays, in HST imaging, a spectacular
morphology comparable to nearby ring-galaxies. From spectroscopic observations
at the CFHT, we measured a redshift of based on the identification of
[O ii] 3727 \AA and [Ne v] 3426 \AA emission lines. These emission lines are
typical of starburst galaxies hosting a central active nucleus and are in good
agreement with the assumption that this object is a ring-galaxy. This object is
also detected with ISO in the LW2 and LW3 filters, and the mid Infra-Red (MIR)
flux ratio favors a Seyfert 1 type. The shape of the ring is gravitationally
distorted by the cluster-lens, and most particularly by a nearby cluster
elliptical galaxy. Using the cluster mass model, we can compute its intrinsic
shape. Requiring that the outer ring follows an ellipse we put constraints on
the M/L ratio of the nearby galaxy and derive a magnification factor of 2.5
0.2. The absolute luminosities of the source are then $L_B = 1.3 \
10^{12} L_{B \odot}\nu_\nu \simeq 4. 10^{10}_\odot$ in the
mid-IR.Comment: 5 pages, 5 figures, uses aa.cls, accepted to A&A Letters. Minor
changes, Figure 1 revisited and typos adde
Gamma-ray bursts and X-ray melting of material as a potential source of chondrules and planets
The intense radiation from a gamma-ray burst (GRB) is shown to be capable of
melting stony material at distances up to 300 light years which subsequently
cool to form chondrules. These conditions were created in the laboratory for
the first time when millimeter sized pellets were placed in a vacuum chamber in
the white synchrotron beam at the European Synchrotron Radiation Facility
(ESRF). The pellets were rapidly heated in the X-ray and gamma-ray furnace to
above 1400 C melted and cooled. This process heats from the inside unlike
normal furnaces. The melted spherical samples were examined with a range of
techniques and found to have microstructural properties similar to the
chondrules that come from meteorites. This experiment demonstrates that GRBs
can melt precursor material to form chondrules that may subsequently influence
the formation of planets. This work extends the field of laboratory
astrophysics to include high power synchrotron sources.Comment: 8 pages, 10 figures. Proceedings of the 5th INTEGRAL Workshop, Munich
16-20 February 2004. High resolution figures available at
http://bermuda.ucd.ie/%7Esmcbreen/papers/duggan_01.pd
Renal replacement modality and stroke risk in end-stage renal disease—a national registry study
Background:
The risk of stroke in end-stage renal disease (ESRD) on renal replacement therapy (RRT) is up to 10-fold greater than the general population. However, whether this increased risk differs by RRT modality is unclear.
Methods:
We used data contained in the Scottish Renal Registry and the Scottish Stroke Care Audit to identify stroke in all adult patients who commenced RRT for ESRD from 2005 to 2013. Incidence rate was calculated and regression analyses were performed to identify variables associated with stroke. We explored the effect of RRT modality at initiation and cumulative dialysis exposure by time-dependent regression analysis, using transplant recipients as the reference group.
Results:
A total of 4957 patients commenced RRT for ESRD. Median age was 64.5 years, 41.5% were female and 277 patients suffered a stroke (incidence rate was 18.6/1000 patient-years). Patients who had stroke were older, had higher blood pressure and were more likely to be female and have diabetes. On multivariable regression older age, female sex, diabetes and higher serum phosphate were associated with risk of stroke. RRT modality at initiation was not. On time-dependent analysis, haemodialysis (HD) exposure was independently associated with increased risk of stroke.
Conclusions:
In patients with ESRD who initiate RRT, HD use independently increases risk of stroke compared with transplantation. Use of peritoneal dialysis did not increase risk on adjusted analysis
Pressure Sensitive Skin for Prosthetic Hands:2D Contact Location Determination Using Output Connections from a Single Side
The human hand is a vital component of our interaction with the environment, containing a large number of sensory receptors. The loss of a hand is, therefore, a serious and debilitating injury. Surveys have shown that 98% of users of upper limb prostheses desire to feel the level of force they apply through their prosthetic hands. Developments in tactile sensors have yielded many functional electronic skins. However, their complexity remains a barrier to their use in commercial prosthetic hands. This paper introduces a new design of a simple, flexible pressure sensor using carbon fibre tows as both the sensor and the electrodes. The design results in a dynamic pressure range of 0.35 to 280 kPa in a 25-by-25 mm prototype.</p
The First Detections of the Extragalactic Background Light at 3000, 5500, and 8000A (III): Cosmological Implications
(Abridged) We have used HST WFPC2 and ground-based spectroscopy to measure
the integrated extragalactic background light (EBL) at optical wavelengths. We
have also computed the integrated light from individual galaxy counts in the
images used to measure the EBL and in the Hubble Deep Field. We find that the
flux in galaxies as measured by standard galaxy photometry methods has
generally been underestimated by about 50%. Further, we find that the total
flux in individually detected galaxies is a factor of 2 to 3 less than the EBL
at 3000--8000A. We show that a significant fraction of the EBL may come from
normal galaxies at z<4, which are simply undetectable as a result of
K-corrections and cosmological surface brightness dimming. This is consistent
with recent redshift surveys at z<4. In the context of some simple models, we
discuss the constraints placed by the EBL on the evolution of the luminosity
density at z>1. Based on our optical EBL and published UV and IR EBL
measurements, we estimate that the total EBL from 0.1--1000 microns is 100+/-20
nW/m^2/sr. If the total EBL were produced entirely by stellar nucleosynthesis,
then we estimate that the total baryonic mass processed through stars is
Omega_* = 0.0062 (+/- 0.0022) h^{-2}, which corresponds to 0.33+/-0.12 Omega_B
for currently favored values of the baryon density. This estimate is smaller by
roughly 7% if 7 h_{0.7} nW/m^2/sr of the total EBL comes from accretion onto
central black holes. This estimate of Omega_* suggests that the universe has
been enriched to a total metal mass of 0.21(+/-0.13) Z_sun Omega_B. Our
estimate is consistent with other measurements of the cumulative metal mass
fraction of stars, stellar remnants, and the intracluster medium of galaxy
clusters in the local universe.Comment: Accepted for publication in ApJ, 20 pages using emulateapj.sty,
version with higher resolution figures available at
http://www.astro.lsa.umich.edu/~rab/publications.html or at
http://nedwww.ipac.caltech.edu/level5/Sept01/Bernstein3/frames.htm
Changing care culture through focusing on a ‘neglected’ equality issue – outcomes from a project aimed at improving care for LGBT people in care homes
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