1,751 research outputs found
Tomography of Collisionless Stellar Systems
In this paper the concept of tomography of a collisionless stellar system of
general shape is introduced, and a generalization of the Projected Virial
Theorem is obtained. Applying the tomographic procedure we then derive a new
family of virial equations which coincides with the already known ones for
spherically symmetric systems. This result is obtained without any use of
explicit expressions for the line-of-sight velocity dispersion, or spherical
coordinate system.Comment: BAP-06-1994-016-OAB. 7 pages, postscript file. In press on Celestial
Mechanic
Pattern and degree of left ventricular remodeling following a tailored surgical approach for hypertrophic obstructive cardiomyopathy.
Background The role of a tailored surgical approach for hypertrophic cardiomyopathy (HCM) on regional ventricular remodelling remains unknown. The aims of this study were to evaluate the pattern, extent and functional impact of regional ventricular remodelling after a tailored surgical approach. Methods From 2005 to 2008, 44 patients with obstructive HCM underwent tailored surgical intervention. Of those, 14 were ineligible for cardiac magnetic resonance (CMR) studies. From the remainder, 14 unselected patients (42±12 years) underwent pre- and post-operative CMR studies at a median 12 months post-operatively (range 4-37 months). Regional changes in left ventricular (LV) thickness as well as global LV function following surgery were assessed using CMR Tools (London, UK). Results Pre-operative mean echocardiographic septal thickness was 21±4 mm and mean LV outflow gradient was 69±32 mmHg. Following surgery, there was a significant degree of regional regression of LV thickness in all segments of the LV, ranging from 16% in the antero-lateral midventricular segment to 41% in the anterior basal segment. Wall thickening was significantly increased in basal segments but showed no significant change in the midventricular or apical segments. Globally, mean indexed LV mass decreased significantly after surgery (120±29g/m2 versus 154±36g/m2; p<0.001). There was a trend for increased indexed LV end-diastolic volume (70±13 mL versus 65±11 mL; p=0.16) with a normalization of LV ejection fraction (68±7% versus 75±9%; p<0.01). Conclusion Following a tailored surgical relief of outflow obstruction for HCM, there is a marked regional reverse LV remodelling. These changes could have a significant impact on overall ventricular dynamics and function
The origin of polar ring galaxies: evidence for galaxy formation by cold accretion
Polar ring galaxies are flattened stellar systems with an extended ring of
gas and stars rotating in a plane almost perpendicular to the central galaxy.
We show that their formation can occur naturally in a hierarchical universe
where most low mass galaxies are assembled through the accretion of cold gas
infalling along megaparsec scale filamentary structures. Within a large
cosmological hydrodynamical simulation we find a system that closely resembles
the classic polar ring galaxy NGC 4650A. How galaxies acquire their gas is a
major uncertainty in models of galaxy formation and recent theoretical work has
argued that cold accretion plays a major role. This idea is supported by our
numerical simulations and the fact that polar ring galaxies are typically low
mass systems.Comment: 4 pages, 5 figures, stability of the ring discussed, minor changes to
match the accepted version by ApJL. A preprint with high-resolution figures
is available at http://krone.physik.unizh.ch/~andrea/PolarRing/PolarRing.p
Evaluation of Prebiotic and Probiotic Effects on the Intestinal Gut Microbiota and Histology of Atlantic salmon (Salmo salar L.)
In the present study the impact on gut microbiology and indigenous gut histology of Atlantic salmon (Salmo salar L.) was investigated following feeding of a control and a prebiotic (EWOS prebiosal®) diet and ex vivo exposure to saline or the probiotic bacterium Carnobacterium divergens. The results showed that ex vivo exposure of C. divergens at 108 CFU ml-¹ did not cause cell damage to the intestine tract of Atlantic salmon. Furthermore, prior provision of dietary prebiotic elevated the ability of C. divergens to adhere to the epithelium or mucus layer in the proximal intestine, where culturable heterotrophic bacterial levels (which were identified as C. divergens) were elevated by 234% compared to the control. This effect was not apparent in the distal intestine. The ability of isolated carnobacteria from the ex vivo experiment to inhibit growth of two fish pathogenic bacteria (Yersinia rückeri and Aeromonas salmonicida ssp. salmonicida) was assessed. Extracellular products from all 11 of the isolated carnobacteria strains, plus the type strain Carnobacterium inhibens CCUG 31728, inhibited the in vitro growth of Y. rückeri. However, only extracellular products from C. divergens isolate 57 inhibited the growth of A. salmonicidapublishedVersio
The Distribution of Bar and Spiral Strengths in Disk Galaxies
The distribution of bar strengths in disk galaxies is a fundamental property
of the galaxy population that has only begun to be explored. We have applied
the bar/spiral separation method of Buta, Block, and Knapen to derive the
distribution of maximum relative gravitational bar torques, Q_b, for 147 spiral
galaxies in the statistically well-defined Ohio State University Bright Galaxy
Survey (OSUBGS) sample. Our goal is to examine the properties of bars as
independently as possible of their associated spirals. We find that the
distribution of bar strength declines smoothly with increasing Q_b, with more
than 40% of the sample having Q_b <= 0.1. In the context of recurrent bar
formation, this suggests that strongly-barred states are relatively short-lived
compared to weakly-barred or non-barred states. We do not find compelling
evidence for a bimodal distribution of bar strengths. Instead, the distribution
is fairly smooth in the range 0.0 <= Q_b < 0.8. Our analysis also provides a
first look at spiral strengths Q_s in the OSU sample, based on the same torque
indicator. We are able to verify a possible weak correlation between Q_s and
Q_b, in the sense that galaxies with the strongest bars tend also to have
strong spirals.Comment: Accepted for publication in the Astronomical Journal, August 2005
issue (LaTex, 23 pages + 11 figures, uses aastex.cls
Testing the nature of S0 galaxies using planetary nebula kinematics in NGC 1023
We investigate the manner in which lenticular galaxies are formed by studying
their stellar kinematics: an S0 formed from a fading spiral galaxy should
display similar cold outer disc kinematics to its progenitor, while an S0
formed in a minor merger should be more dominated by random motions. In a pilot
study to attempt to distinguish between these scenarios, we have measured the
planetary nebula (PN) kinematics of the nearby S0 system NGC 1023. Using the
Planetary Nebula Spectrograph, we have detected and measured the line-of-sight
velocities of 204 candidate PNe in the field of this galaxy. Out to
intermediate radii, the system displays the kinematics of a normal
rotationally-supported disc system. After correction of its rotational
velocities for asymmetric drift, the galaxy lies just below the spiral galaxy
Tully-Fisher relation, as one would expect for a fading system. However, at
larger radii the kinematics undergo a gradual but major transition to random
motion with little rotation. This transition does not seem to reflect a change
in the viewing geometry or the presence of a distinct halo component, since the
number counts of PNe follow the same simple exponential decline as the stellar
continuum with the same projected disc ellipticity out to large radii. The
galaxy's small companion, NGC 1023A, does not seem to be large enough to have
caused the observed modification either. This combination of properties would
seem to indicate a complex evolutionary history in either the transition to
form an S0 or in the past life of the spiral galaxy from which the S0 formed.
More data sets of this type from both spirals and S0s are needed in order to
definitively determine the relationship between these types of system.Comment: Accepted for publication in MNRAS. Version with full resolution
figure 1 can be found at
http://www.nottingham.ac.uk/~ppzmrm/N1023_PNS.accepted.pd
Recommended from our members
Sixteen years of bathymetry and waves at San Diego beaches.
Sustained, quantitative observations of nearshore waves and sand levels are essential for testing beach evolution models, but comprehensive datasets are relatively rare. We document beach profiles and concurrent waves monitored at three southern California beaches during 2001-2016. The beaches include offshore reefs, lagoon mouths, hard substrates, and cobble and sandy (medium-grained) sediments. The data span two energetic El Niño winters and four beach nourishments. Quarterly surveys of 165 total cross-shore transects (all sites) at 100 m alongshore spacing were made from the backbeach to 8 m depth. Monthly surveys of the subaerial beach were obtained at alongshore-oriented transects. The resulting dataset consists of (1) raw sand elevation data, (2) gridded elevations, (3) interpolated elevation maps with error estimates, (4) beach widths, subaerial and total sand volumes, (5) locations of hard substrate and beach nourishments, (6) water levels from a NOAA tide gauge (7) wave conditions from a buoy-driven regional wave model, and (8) time periods and reaches with alongshore uniform bathymetry, suitable for testing 1-dimensional beach profile change models
Dark-Matter Content of Early-Type Galaxies with Planetary Nebulae
We examine the dark matter properties of nearby early-type galaxies using
planetary nebulae (PNe) as mass probes. We have designed a specialised
instrument, the Planetary Nebula Spectrograph (PN.S) operating at the William
Herschel telescope, with the purpose of measuring PN velocities with best
efficiency. The primary scientific objective of this custom-built instrument is
the study of the PN kinematics in 12 ordinary round galaxies. Preliminary
results showing a dearth of dark matter in ordinary galaxies (Romanowsky et al.
2003) are now confirmed by the first complete PN.S datasets. On the other hand
early-type galaxies with a "regular" dark matter content are starting to be
observed among the brighter PN.S target sample, thus confirming a correlation
between the global dark-to-luminous mass virial ratio (f_DM=M_DM/M_star) and
the galaxy luminosity and mass.Comment: 5 pages, 2 figures. To appear in the proceedings of the IAU Symposium
244 "Dark Galaxies and Lost Baryons", Cardiff 25-29 June 2007, eds. J.I.
Davies & M.J. Disne
Differential requirements for actin during yeast and mammalian endocytosis
Key features of clathrin-mediated endocytosis have been conserved across evolution. However, endocytosis in Saccharomyces cerevisiae is completely dependent on a functional actin cytoskeleton, whereas actin appears to be less critical in mammalian cell endocytosis. We reveal that the fundamental requirement for actin in the early stages of yeast endocytosis is to provide a strong framework to support the force generation needed to direct the invaginating plasma membrane into the cell against turgor pressure. By providing osmotic support, pressure differences across the plasma membrane were removed and this reduced the requirement for actin-bundling proteins in normal endocytosis. Conversely, increased turgor pressure in specific yeast mutants correlated with a decreased rate of endocytic patch invagination
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