489 research outputs found
Loss of mass and stability of galaxies in MOND
The self-binding energy and stability of a galaxy in MOND-based gravity are
curiously decreasing functions of its center of mass acceleration towards
neighbouring mass concentrations. A tentative indication of this breaking of
the Strong Equivalence Principle in field galaxies is the RAVE-observed escape
speed in the Milky Way. Another consequence is that satellites of field
galaxies will move on nearly Keplerian orbits at large radii (100 - 500 kpc),
with a declining speed below the asymptotically constant naive MOND prediction.
But consequences of an environment-sensitive gravity are even more severe in
clusters, where member galaxies accelerate fast: no more Dark-Halo-like
potential is present to support galaxies, meaning that extended axisymmetric
disks of gas and stars are likely unstable. These predicted reappearance of
asymptotic Keplerian velocity curves and disappearance of "stereotypic
galaxies" in clusters are falsifiable with targeted surveys.Comment: 4 pages, 2 figures, ApJ Letter
Resolving the timing problem of the globular clusters orbiting the Fornax dwarf galaxy
We re-investigate the old problem of the survival of the five globular
clusters orbiting the Fornax dwarf galaxy in both standard and modified
Newtonian dynamics. For the first time in the history of the topic, we use
accurate mass models for the Fornax dwarf, obtained through Jeans modelling of
the recently published line of sight velocity dispersion data, and we are also
not resigned to circular orbits for the globular clusters. Previously conceived
problems stem from fixing the starting distances of the globulars to be less
than half the tidal radius. We relax this constraint since there is absolutely
no evidence for it and show that the dark matter paradigm, with either cusped
or cored dark matter profiles, has no trouble sustaining the orbits of the two
least massive globular clusters for a Hubble time almost regardless of their
initial distance from Fornax. The three most massive globulars can remain in
orbit as long as their starting distances are marginally outside the tidal
radius. The outlook for modified Newtonian dynamics is also not nearly as bleak
as previously reported. Although dynamical friction inside the tidal radius is
far stronger in MOND, outside dynamical friction is negligible due to the
absence of stars. This allows highly radial orbits to survive, but more
importantly circular orbits at distances more than 85% of Fornax's tidal radius
to survive indefinitely. The probability of the globular clusters being on
circular orbits at this distance compared with their current projected
distances is discussed and shown to be plausible. Finally, if we ignore the
presence of the most massive globular (giving it a large line of sight
distance) we demonstrate that the remaining four globulars can survive within
the tidal radius for the Hubble time with perfectly sensible orbits.Comment: 8 pages, 10 figures, 1 table, MNRAS in pres
Admission to hospital following head injury in England: Incidence and socio-economic associations
BACKGROUND:
Head injury in England is common. Evidence suggests that socio-economic factors may cause variation in incidence, and this variation may affect planning for services to meet the needs of those who have sustained a head injury.
METHODS:
Socio-economic data were obtained from the UK Office for National Statistics and merged with Hospital Episodes Statistics obtained from the Department of Health. All patients admitted for head injury with ICD-10 codes S00.0–S09.9 during 2001–2 and 2002–3 were included and collated at the level of the extant Health Authorities (HA) for 2002, and Primary Care Trust (PCT) for 2003. Incidence was determined, and cluster analysis and multiple regression analysis were used to look at patterns and associations.
Results: 112,718 patients were admitted during 2001–2 giving a hospitalised incidence rate for England of 229 per 100,000. This rate varied across the English HA's ranging from 91–419 per 100,000. The rate remained unchanged for 2002–3 with a similar magnitude of variation across PCT's. Three clusters of HA's were identified from the 2001–2 data; those typical of London, those of the Shire counties, and those of Other Urban authorities. Socio-economic factors were found to account for a high proportion of the variance in incidence for 2001–2. The same pattern emerged for 2002–3 at the PCT level. The use of public transport for travel to work is associated with a
decreased incidence and lifestyle indicators, such as the numbers of young unemployed, increase the incidence.
CONCLUSION:
Head injury incidence in England varies by a factor of 4.6 across HA's and PCT's.
Planning head injury related services at the local level thus needs to be based on local incidence
figures rather than regional or national estimates. Socio-economic factors are shown to be
associated with admission, including travel to work patterns and lifestyle indicators, which suggests
that incidence is amenable to policy initiatives at the macro level as well as preventive programmes
targeted at key groups
Kinematic deprojection and mass inversion of spherical systems of known velocity anisotropy
Traditionally, the mass / velocity anisotropy degeneracy (MAD) inherent in
the spherical, stationary, non-streaming Jeans equation has been handled by
assuming a mass profile and fitting models to the observed kinematical data.
Here, the opposite approach is considered: the equation of anisotropic
kinematic projection is inverted for known arbitrary anisotropy to yield the
space radial velocity dispersion profile in terms of an integral involving the
radial profiles of anisotropy and isotropic dynamical pressure. Then, through
the Jeans equation, the mass profile is derived in terms of double integrals of
observable quantities. Single integral formulas for both deprojection and mass
inversion are provided for several simple anisotropy models (isotropic, radial,
circular, general constant, Osipkov-Merritt, Mamon-Lokas and
Diemand-Moore-Stadel). Tests of the mass inversion on NFW models with these
anisotropy models yield accurate results in the case of perfect observational
data, and typically better than 70% (in 4 cases out of 5) accurate mass
profiles for the sampling errors expected from current observational data on
clusters of galaxies. For the NFW model with mildly increasing radial
anisotropy, the mass is found to be insensitive to the adopted anisotropy
profile at 7 scale radii and to the adopted anisotropy radius at 3 scale radii.
This anisotropic mass inversion method is a useful complementary tool to
analyze the mass and anisotropy profiles of spherical systems. It provides the
practical means to lift the MAD in quasi-spherical systems such as globular
clusters, round dwarf spheroidal and elliptical galaxies, as well as groups and
clusters of galaxies, when the anisotropy of the tracer is expected to be
linearly related to the slope of its density.Comment: Accepted in MNRAS. 19 pages. Minor changes from previous version:
Table 1 of nomenclature, some math simplifications, paragraph in Discussion
on alternative deprojection method by deconvolution. 19 pages. 6 figure
Altered splicing of the BIN1 muscle-specific exon in humans and dogs with highly progressive centronuclear myopathy
Amphiphysin 2, encoded by BIN1, is a key factor for membrane sensing and remodelling in different cell types. Homozygous BIN1 mutations in ubiquitously expressed exons are associated with autosomal recessive centronuclear myopathy (CNM), a mildly progressive muscle disorder typically showing abnormal nuclear centralization on biopsies. In addition, misregulation of BIN1 splicing partially accounts for the muscle defects in myotonic dystrophy (DM). However, the muscle-specific function of amphiphysin 2 and its pathogenicity in both muscle disorders are not well understood. In this study we identified and characterized the first mutation affecting the splicing of the muscle-specific BIN1 exon 11 in a consanguineous family with rapidly progressive and ultimately fatal centronuclear myopathy. In parallel, we discovered a mutation in the same BIN1 exon 11 acceptor splice site as the genetic cause of the canine Inherited Myopathy of Great Danes (IMGD). Analysis of RNA from patient muscle demonstrated complete skipping of exon 11 and BIN1 constructs without exon 11 were unable to promote membrane tubulation in differentiated myotubes. Comparative immunofluorescence and ultrastructural analyses of patient and canine biopsies revealed common structural defects, emphasizing the importance of amphiphysin 2 in membrane remodelling and maintenance of the skeletal muscle triad. Our data demonstrate that the alteration of the muscle-specific function of amphiphysin 2 is a common pathomechanism for centronuclear myopathy, myotonic dystrophy, and IMGD. The IMGD dog is the first faithful model for human BIN1-related CNM and represents a mammalian model available for preclinical trials of potential therapies
On the central stellar mass density and the inside-out growth of early-type galaxies
[Abridged] In this paper we derive the central stellar mass density within a
fixed radius and the effective stellar mass density within the effective radius
for a complete sample of 34 ETGs morphologically selected at 0.9<z_{spec}<2 and
compare them with those derived for a sample of ~900 local ETGs in the same
mass range. We find that the central stellar mass density of high-z ETGs spans
just an order of magnitude and it is similar to the one of local ETGs as
actually found in previous studies.However, we find that the effective stellar
mass density of high-z ETGs spans three orders of magnitude, exactly as the
local ETGs and that it is similar to the effective stellar mass density of
local ETGs showing that it has not changed since z~1.5, in the last 9-10 Gyr.
Thus, the wide spread of the effective stellar mass density observed up to
z~1.5 must originate earlier, at z>2. Also, we show that the small scatter of
the central mass density of ETGs compared to the large scatter of the effective
mass density is simply a peculiar feature of the Sersic profile hence,
independent of redshift and of any assembly history experienced by galaxies.
Thus, it has no connection with the possible inside-out growth of ETGs.
Finally, we find a tight correlation between the central stellar mass density
and the total stellar mass of ETGs in the sense that the central mass density
increases with mass as M^{~0.6}. This implies that the fraction of the central
stellar mass of ETGs decreases with the mass of the galaxy. These correlations
are valid for the whole population of ETGs considered independently of their
redshift suggesting that they originate in the early-phases of their formation.Comment: 11 pages, 6 figures. Accepted for publication in MNRAS (MNRAS
version
Interbreed variation in serum serotonin (5-hydroxytryptamine) concentration in updates healthy dogs
Introduction: Serotonin (5-hydroxytryptamine [5-HT]) has several biological functions. In different species, excessive 5-HT has been linked to valvular lesions, similar to those seen in dogs with myxomatous mitral valve disease. Previous studies suggest higher 5-HT in healthy Cavalier King Charles Spaniels (CKCSs), a breed highly affected by myxomatous mitral valve disease, compared to other breeds. Objective: To investigate potential interbreed variation in serum 5-HT in healthy dogs. Animals: 483 healthy dogs of nine breeds aged 1-7 years. Methods: Dogs were examined at five European centers. Absence of cardiovascular, organ-related, or systemic diseases was ensured by thorough clinical investigations including echocardiography. Serum was frozen and later analyzed by enzyme-linked immunosorbent assay (ELISA). Results: Median 5-HT concentration was 252.5 (interquartile range = 145.5-390.6) ng/mL. Overall breed difference was found (p Conclusions: Interbreed variation in serum 5-HT concentration was found in healthy dogs aged 1-7 years. These differences should be taken into account when designing clinical studies. (C) 2018 Elsevier B.V. All rights reserved.Peer reviewe
HACD1, a regulator of membrane composition and fluidity, promotes myoblast fusion and skeletal muscle growth
The reduced diameter of skeletal myofibres is a hallmark of several congenital myopathies, yet the underlying cellular and molecular mechanisms remain elusive. In this study, we investigate the role of HACD1/PTPLA, which is involved in the elongation of the very long chain fatty acids, in muscle fibre formation. In humans and dogs, HACD1 deficiency leads to a congenital myopathy with fibre size disproportion associated with a generalized muscle weakness. Through analysis of HACD1-deficient Labradors, Hacd1-knockout mice, and Hacd1-deficient myoblasts, we provide evidence that HACD1 promotes myoblast fusion during muscle development and regeneration. We further demonstrate that in normal differentiating myoblasts, expression of the catalytically active HACD1 isoform, which is encoded by a muscle-enriched splice variant, yields decreased lysophosphatidylcholine content, a potent inhibitor of myoblast fusion, and increased concentrations of ≥C18 and monounsaturated fatty acids of phospholipids. These lipid modifications correlate with a reduction in plasma membrane rigidity. In conclusion, we propose that fusion impairment constitutes a novel, non-exclusive pathological mechanism operating in congenital myopathies and reveal that HACD1 is a key regulator of a lipid-dependent muscle fibre growth mechanism
X-ray Group and cluster mass profiles in MOND: Unexplained mass on the group scale
Although very successful in explaining the observed conspiracy between the
baryonic distribution and the gravitational field in spiral galaxies without
resorting to dark matter (DM), the modified Newtonian dynamics (MOND) paradigm
still requires DM in X-ray bright systems. Here, to get a handle on the
distribution and importance of this DM, and thus on its possible form, we
deconstruct the mass profiles of 26 X-ray emitting systems in MOND, with
temperatures ranging from 0.5 to 9 keV. Initially we compute the MOND dynamical
mass as a function of radius, then subtract the known gas mass along with a
component of galaxies which includes the cD galaxy with . Next we test
the compatibility of the required DM with ordinary massive neutrinos at the
experimental limit of detection ( eV), with density given by the
Tremaine-Gunn limit. Even by considering that the neutrino density stays
constant and maximal within the central 100 or 150 kpc (which is the absolute
upper limit of a possible neutrino contribution there), we show that these
neutrinos can never account for the required DM within this region. The natural
corollary of this finding is that, whereas clusters (T \ga 3 keV) might have
most of their mass accounted for if ordinary neutrinos have a 2 eV mass, groups
(T \lsim 2 keV) cannot be explained by a 2 eV neutrino contribution. This
means that, for instance, cluster baryonic dark matter (CBDM, Milgrom 2007) or
even sterile neutrinos would present a more satisfactory solution to the
problem of missing mass in MOND X-ray emitting systems.Comment: 13 pages, 8 figures, 1 table, accepted in MNRA
Results from PAMELA, ATIC and FERMI : Pulsars or Dark Matter ?
It is well known that the dark matter dominates the dynamics of galaxies and
clusters of galaxies. Its constituents remain a mystery despite an assiduous
search for them over the past three decades. Recent results from the
satellite-based PAMELA experiment detect an excess in the positron fraction at
energies between 10-100 GeV in the secondary cosmic ray spectrum. Other
experiments namely ATIC, HESS and FERMI show an excess in the total electron
(\ps + \el) spectrum for energies greater 100 GeV. These excesses in the
positron fraction as well as the electron spectrum could arise in local
astrophysical processes like pulsars, or can be attributed to the annihilation
of the dark matter particles. The second possibility gives clues to the
possible candidates for the dark matter in galaxies and other astrophysical
systems. In this article, we give a report of these exciting developments.Comment: 27 Pages, extensively revised and significantly extended, to appear
in Pramana as topical revie
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