10,057 research outputs found
Loss and reappearance of gap junctions in regenerating liver
Changes in intercellular junctional morphology associated with rat liver regeneration were examined in a freeze-fracture study. After a two-thirds partial hepatectomy, both gap junctions and zonulae occludentes were drastically altered. Between 0 and 20 h after partial hepatectomy, the junctions appeared virtually unchanged. 28 h after partial hepatectomy, however, the large gap junctions usually located close to the bile canaliculi and the small gap junctions enmeshed within the strands of the zonulae occudentes completely disappeared. Although the zonulae occludentes bordering the bile canaliculi apparently remained intact, numerous strands could now be found oriented perpendicular to the canaliculi. In some instances, the membrane outside the canaliculi was extensively filled with isolated junctional strands, often forming very complex configurations. About 40 h after partial hepatectomy, very many small gap junctions reappeared in close association with the zonulae occludentes. Subsequently, gap junctions increased in size and decreased in number until about 48 h after partial hepatectomy when gap junctions were indistinguishable in size and number from those of control animals. The zonulae occludentes were again predominantly located around the canalicular margins. These studies provide further evidence for the growth of gap junctions by the accretion of particles and of small gap junctions to form large maculae
A quick-retrieval high-speed digital framing camera
A new high-speed digital framing camera is described. The design is built around a rotating polygon mirror that provides a framing rate of 24 000 frames/s. The camera electronics digitizes an image into a 32×104 grid of pixels, where the second dimension of the grid can be varied and is determined by the 8 bit computer-aided measurement and control digitizer sampling rate. Available digitizer memory provides for 314 frames at this horizontal resolution. The advantages over other available high-speed framing cameras are (1) low cost of the system provided the digitizers are available, (2) rapid retrieval of a recorded event, and (3) the ease with which the system can be used. Sample results from an application in high-power arc photography are given to illustrate the system's spatial and temporal resolution
The Atmosphere Explorer and the shuttle glow
Recent analyses of the Atmosphere Explorer data are discussed in which it is demonstrated that the satellite glows have two components, one at high altitudes which is consistent with excitation in single collisions of atmospheric oxygen atoms with the vehicle surface and the other at low altitudes which is consistent with double collisions of nitrogen molecules. Contrary to an earlier suggestion, the low-altitude data are not consistent with collisions of oxygen molecules. The separation of the two components strengthens the conclusion that the high-altitude glow arises from vibrationally excited OH molecules produced by a formation mechanism that is different from that leading to the normal atmospheric OH airglow. The spectrum is consistent with association of oxygen and hydrogen atoms at sites on the surface into the vibrational levels of OH. The low-altitude glow is consistent with the green mechanism but there are difficulties with it. The shuttle glows are different and have the spectral appearance of emission from NO2. The characteristics of the shuttle glows and the satellite glows will be contrasted and a tentative resolution of the differences in the Atmosphere Explorer and shuttle glows will be offered
Stratifying and predicting patterns of neighbourhood change and gentrification ‐ an urban analytics approach
While recent debates have widely acknowledged gentrification’s varied manifestations, success in enumerating and disentangling the process and its defining features from other forms of neighbourhood change at-scale and across entire cities, has remained largely elusive. This paper addresses this gap and employs a novel, open and reproducible urban analytics approach to systematically examine the past and future trajectories of neighbourhood change using London, England, as a case-study example. Using suites of datasets relating to population, house prices and built environment development, the nature of gentrification’s mutations and its spatial patterns are extracted through a multi-stage data dimensionality reduction and classification methodology. Machine Learning is subsequently adopted to model gentrification’s observed trends and predict its future frontiers with interactive visualisation methods offering new insights into gentrification’s projected dynamics and geographies
Star Formation in Cluster Galaxies at 0.2<z<0.55
The rest frame equivalent width of the [OII]3727 emission line, W(OII), has
been measured for cluster and field galaxies in the CNOC redshift survey of
rich clusters at 0.2<z<0.55. Emission lines of any strength in cluster galaxies
at all distances from the cluster centre, out to 2R_{200}, are less common than
in field galaxies. The mean W(OII) in cluster galaxies more luminous than
M_r^k<-18.5 + 5\log h (q_o=0.1) is 3.8 \pm 0.3 A (where the uncertainty is the
1 sigma error in the mean), significantly less than the field galaxy mean of
11.2 \pm 0.3 A. For the innermost cluster members (R<0.3R_{200}), the mean
W(OII) is only 0.3 \pm 0.4 A. Thus, it appears that neither the infall process
nor internal tides in the cluster induce detectable excess star formation in
cluster galaxies relative to the field. The colour-radius relation of the
sample is unable to fully account for the lack of cluster galaxies with
W(OII)>10 A, as expected in a model of cluster formation in which star
formation is truncated upon infall. Evidence of supressed star formation
relative to the field is present in the whole cluster sample, out to 2 R_{200},
so the mechanism responsible for the differential evolution must be acting at a
large distance from the cluster centre, and not just in the core. The mean star
formation rate in the cluster galaxies with the strongest emission corresponds
to an increase in the total stellar mass of less than about 4% if the star
formation is due to a secondary burst lasting 0.1 Gyr.Comment: aasms4 latex, 3 postscript figures, accepted for publication in ApJ
Letters. Also available at http://astrowww.phys.uvic.ca/~balogh
The age and abundance structure of the stellar populations in the central sub-kpc of the Milky Way
The four main findings about the age and abundance structure of the Milky Way
bulge based on microlensed dwarf and subgiant stars are: (1) a wide metallicity
distribution with distinct peaks at [Fe/H]=-1.09, -0.63, -0.20, +0.12, +0.41;
(2) a high fraction of intermediate-age to young stars where at [Fe/H]>0 more
than 35 % are younger than 8 Gyr, (3) several episodes of significant star
formation in the bulge 3, 6, 8, and 11 Gyr ago; (4) the `knee' in the
alpha-element abundance trends of the sub-solar metallicity bulge appears to be
located at a slightly higher [Fe/H] (about 0.05 to 0.1 dex) than in the local
thick disk.Comment: 4 pages, contributed talk at the IAU Symposium 334 "Rediscovering our
Galaxy" in Potsdam, July 10-14, 201
MOA-2011-BLG-293Lb: First Microlensing Planet possibly in the Habitable Zone
We used Keck adaptive optics observations to identify the first planet
discovered by microlensing to lie in or near the habitable zone, i.e., at
projected separation AU from its host, being the highest microlensing mass definitely identified.
The planet has a mass , and could in principle
have habitable moons. This is also the first planet to be identified as being
in the Galactic bulge with good confidence: kpc. The
planet/host masses and distance were previously not known, but only estimated
using Bayesian priors based on a Galactic model (Yee et al. 2012). These
estimates had suggested that the planet might be a super-Jupiter orbiting an M
dwarf, a very rare class of planets. We obtained high-resolution images
using Keck adaptive optics to detect the lens and so test this hypothesis. We
clearly detect light from a G dwarf at the position of the event, and exclude
all interpretations other than that this is the lens with high confidence
(95%), using a new astrometric technique. The calibrated magnitude of the
planet host star is . We infer the following probabilities
for the three possible orbital configurations of the gas giant planet: 53% to
be in the habitable zone, 35% to be near the habitable zone, and 12% to be
beyond the snow line, depending on the atmospherical conditions and the
uncertainties on the semimajor axis.Comment: Accepted by ApJ, 21 pages, 4 figure
The dynamics of z~1 clusters of galaxies from the GCLASS survey
We constrain the internal dynamics of a stack of 10 clusters from the GCLASS
survey at 0.87<z<1.34. We determine the stack cluster mass profile M(r) using
the MAMPOSSt algorithm of Mamon et al., the velocity anisotropy profile beta(r)
from the inversion of the Jeans equation, and the pseudo-phase-space density
profiles Q(r) and Qr(r), obtained from the ratio between the mass density
profile and the third power of the (total and, respectively, radial) velocity
dispersion profiles of cluster galaxies. Several M(r) models are statistically
acceptable for the stack cluster (Burkert, Einasto, Hernquist, NFW). The total
mass distribution has a concentration c=r200/r-2=4.0-0.6+1.0, in agreement with
theoretical expectations, and is less concentrated than the cluster
stellar-mass distribution. The stack cluster beta(r) is similar for passive and
star-forming galaxies and indicates isotropic galaxy orbits near the cluster
center and increasingly radially elongated with increasing cluster-centric
distance. Q(r) and Qr(r) are almost power-law relations with slopes similar to
those predicted from numerical simulations of dark matter halos. Combined with
results obtained for lower-z clusters we determine the dynamical evolution of
galaxy clusters, and compare it with theoretical predictions. We discuss
possible physical mechanisms responsible for the differential evolution of
total and stellar mass concentrations, and of passive and star-forming galaxy
orbits [abridged].Comment: 12 pages, 7 figures. Version accepted for publication in A&A after
minor modification
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