628 research outputs found
Critical Phenomena in Neutron Stars I: Linearly Unstable Nonrotating Models
We consider the evolution in full general relativity of a family of linearly
unstable isolated spherical neutron stars under the effects of very small,
perturbations as induced by the truncation error. Using a simple ideal-fluid
equation of state we find that this system exhibits a type-I critical
behaviour, thus confirming the conclusions reached by Liebling et al. [1] for
rotating magnetized stars. Exploiting the relative simplicity of our system, we
are able carry out a more in-depth study providing solid evidences of the
criticality of this phenomenon and also to give a simple interpretation of the
putative critical solution as a spherical solution with the unstable mode being
the fundamental F-mode. Hence for any choice of the polytropic constant, the
critical solution will distinguish the set of subcritical models migrating to
the stable branch of the models of equilibrium from the set of subcritical
models collapsing to a black hole. Finally, we study how the dynamics changes
when the numerically perturbation is replaced by a finite-size, resolution
independent velocity perturbation and show that in such cases a nearly-critical
solution can be changed into either a sub or supercritical. The work reported
here also lays the basis for the analysis carried in a companion paper, where
the critical behaviour in the the head-on collision of two neutron stars is
instead considered [2].Comment: 15 pages, 9 figure
Cardiomyopathy of ruminants induced by the litter of poultry fed on rations containing the ionophore antibiotic, maduramicin. 1. Epidemiology, clinical signs and clinical pathology
The epidemiological, clinical and clinical pathological findings in 20 cattle and 4 sheep from 15 outbreaks of poultry litter toxicity in South Africa over the past 6 years are documented. In 6 outbreaks, the litter emanated from batteries where maduramicin had been incorporated into rations of broilers. According to circumstantial evidence the litter involved in the 9 other outbreaks was also derived from broilers which had been fed on rations containing an ionophore. The litter was fed ad libitum to the affected stock or constituted 30-80% by volume of their rations. The principal sign manifested was sudden mortality of up to 70% of the herd or flock, usually within 20-40 days of commencement of
feeding of poultry litter. A few cattle developed signs of congestive heart failure, and stiffness was commonly seen in sheep.
In a dosing trial with poultry litter involving 1 steer and 6 sheep, the steer and a sheep died suddenly and a second sheep was destroyed in extremis. Tachycardia and/or cardiac arrythmia were recorded in 5 sheep, and the activity of aspartate transaminase (AST) and/or lactate dehydrogenase (LD) in the sera of 4 was elevated.
Since the cardiac lesions in field cases were similar to those of ionophore poisoning and broiler rations containing maduramicin was a common factor in several outbreaks, toxic litter from some of these outbreaks were tested for the presence of this compound. Analysis by high performance liquid chromatography of litter from 2 specimens of outbreaks revealed that they contained 2,5ppm and 6,1ppm maduramicin. Sheep in a trial fed rations incorporating c 2,5ppm and 5ppm maduramicin, developed clinical signs and lesions consistent with those of the field cases.The articles have been scanned in colour with a HP Scanjet 5590; 600dpi.
Adobe Acrobat XI Pro was used to OCR the text and also for the merging and conversion to the final presentation PDF-format.mn201
Cardiomyopathy of ruminants induced by the litter of poultry fed on rations containing the ionophore antibiotic, maduramicin. II. Macropathology and histopathology
This report contains an account of the gross and histopathological lesions of 20 cattle and four sheep in 15 field
outbreaks of poultry litter toxicity, one steer fed ad lib. and six sheep dosed with toxic poultry litter, and ten sheep
fed experimental rations containing c 2,5 ppm and 5 ppm maduramicin.
The principle macroscopic lesions in most cattle that died in field outbreaks were indicative of congestive heart
failure. The lesions in sheep were similar, but generally milder. Cardiac dilatation was observed in both sheep and
cattle. Microscopically, the cardiac lesions were more pronounced in cattle and comprised varying degrees of
atrophy, hypertrophy, degeneration, necrosis of myocardial fibres, and interstitial fibrosis. Skeletal muscle lesions
were usually more severe in sheep, particularly in the muscles of the hindquarters which appeared pale, oedematous
and mottled.
One of the sheep in the poultry litter dosing trial developed signs of congestive heart failure and the hearts of two
others were dilated. Extensive hypertrophy and atrophy of myocardial fibres were evident in the steer fed ad lib.
with this material. As in field cases, the myocardial lesions of the sheep were less severe than those of the steer.
Mild cardiac dilatation was present in four of the seven sheep in the maduramicin feeding trial. Diffuse hypertrophy
of myocardial nuclei was present in all seven cases, myocardial fibre atrophy in six, multifocal fibrosis and necrosis
in six and two cases, respectively, and focal endocardial thickening in two. The skeletal muscles revealed granular
degeneration and foci of necrosis and regeneration.
The cardiac and skeletal lesions in the field outbreaks, poultry litter feeding trials and maduramicin feeding trials,
were highly comparable. This suggests that this form of poultry litter intoxication is a chronic form of ionophore
toxicity, the pathology of which is characterized by a dilated cardiomyopathy with congestive heart failure and mild
(cattle) to severe (sheep) skeletal muscle lesions.The articles have been scanned in colour with a HP Scanjet 5590; 600dpi.
Adobe Acrobat XI Pro was used to OCR the text and also for the merging and conversion to the final presentation PDF-format.mn201
The quest for companions to post-common envelope binaries: I. Searching a sample of stars from the CSS and SDSS
As part of an ongoing collaboration between student groups at high schools
and professional astronomers, we have searched for the presence of
circum-binary planets in a bona-fide unbiased sample of twelve post-common
envelope binaries (PCEBs) from the Catalina Sky Survey (CSS) and the Sloan
Digital Sky Survey (SDSS). Although the present ephemerides are significantly
more accurate than previous ones, we find no clear evidence for orbital period
variations between 2005 and 2011 or during the 2011 observing season. The
sparse long-term coverage still permits O-C variations with a period of years
and an amplitude of tens of seconds, as found in other systems. Our
observations provide the basis for future inferences about the frequency with
which planet-sized or brown-dwarf companions have either formed in these
evolved systems or survived the common envelope (CE) phase.Comment: accepted by A&
A direct image of the obscuring disk surrounding an active galactic nucleus
Active galactic nuclei (AGN) are generally accepted to be powered by the
release of gravitational energy in a compact accretion disk surrounding a
massive black hole. Such disks are also necessary to collimate powerful radio
jets seen in some AGN. The unifying classification schemes for AGN further
propose that differences in their appearance can be attributed to the opacity
of the accreting material, which may obstruct our view of the central region of
some systems. The popular model for the obscuring medium is a parsec-scale disk
of dense molecular gas, although evidence for such disks has been mostly
indirect, as their angular size is much smaller than the resolution of
conventional telescopes. Here we report the first direct images of a pc-scale
disk of ionised gas within the nucleus of NGC 1068, the archetype of obscured
AGN. The disk is viewed nearly edge-on, and individual clouds within the
ionised disk are opaque to high-energy radiation, consistent with the unifying
classification scheme. In projection, the disk and AGN axes align, from which
we infer that the ionised gas disk traces the outer regions of the long-sought
inner accretion disk.Comment: 14 pages, LaTeX, PSfig, to appear in Nature. also available at
http://hethp.mpe-garching.mpg.de/Preprint
Response rates in postal surveys of healthcare professionals between 1996 and 2005: An observational study
<p>Abstract</p> <p>Background</p> <p>Postal surveys are a frequently used method of data collection in health services research. Low response rates increase the potential for bias and threaten study validity. The objectives of this study were to estimate current response rates, to assess whether response rates are falling, to explore factors that might enhance response rates and to examine the potential for non-response bias in surveys mailed to healthcare professionals.</p> <p>Methods</p> <p>A random sample of postal or electronic surveys of healthcare workers (1996-2005) was identified from Medline, Embase or Psycinfo databases or Biomed Central. Outcome measures were survey response rate and non response analysis. Multilevel, multivariable logistic regression examined the relationship between response rate and publication type, healthcare profession, country and number of survey participants, questionnaire length and use of reminders.</p> <p>Results</p> <p>The analysis included 350 studies. Average response rate in doctors was 57.5% (95%CI: 55.2% to 59.8%) and significantly lower than the estimate for the prior 10 year period. Response rates were higher when reminders were sent (adjusted OR 1.3; 95%CI 1.1-1.6) but only half the studies did this. Response rates were also higher in studies with fewer than 1000 participants and in countries other than US, Canada, Australia and New Zealand. They were not significantly affected by publication type or healthcare profession (p > 0.05). Only 17% of studies attempted assessment of possible non-response bias.</p> <p>Conclusion</p> <p>Response rates to postal surveys of healthcare professionals are low and probably declining, almost certainly leading to unknown levels of bias. To improve the informativeness of postal survey findings, researchers should routinely consider the use of reminders and assess potential for non-response bias.</p
The Interaction of 3C401 with the Surrounding Intracluster Medium
We present an observation of the radio-galaxy 3C401 and the surrounding
intracluster medium (ICM) of its host galaxy cluster by the Chandra X-ray
Observatory. This luminous radio-galaxy is notable in that it has
characteristics intermediate between the FRI and FRII morphologies. We clearly
detect point-like emission coincident with the radio-core of 3C401, although
the spatial resolution of even Chandra is only 2kpc at the distance of 3C401
(z=0.201) and so the possibility remains that this is a dense (and rapidly
cooling) thermal gaseous core in the center of the ICM atmosphere. Strong
departures from spherical symmetry in the central 10-20kpc of the ICM clearly
suggest interaction between the ICM and the radio-lobes of 3C401. A central
X-ray bar probably results from the evacuation of two ICM cavities by the
expanding radio lobes. Beyond these central regions, the cluster possesses a
flatter profile than many clusters of comparable mass suggesting the importance
of ICM heating and entropy injection by 3C401. We detect an interesting
cross-like structure in the ICM on 100kpc scales. We speculate that this could
be a radio-galaxy induced disturbance corresponding to a time when 3C401 was
substantially more powerful. A particularly exciting possibility is that this
cross-like structure corresponds to a large scale global g-mode oscillation
excited by a past outburst of 3C401.Comment: 7 pages, 5 postscript figures. Accepted for publication in MNRA
Three little pieces for computer and relativity
Numerical relativity has made big strides over the last decade. A number of
problems that have plagued the field for years have now been mostly solved.
This progress has transformed numerical relativity into a powerful tool to
explore fundamental problems in physics and astrophysics, and I present here
three representative examples. These "three little pieces" reflect a personal
choice and describe work that I am particularly familiar with. However, many
more examples could be made.Comment: 42 pages, 11 figures. Plenary talk at "Relativity and Gravitation:
100 Years after Einstein in Prague", June 25 - 29, 2012, Prague, Czech
Republic. To appear in the Proceedings (Edition Open Access). Collects
results appeared in journal articles [72,73, 122-124
On the nature of the FBS blue stellar objects and the completeness of the Bright Quasar Survey. II
In Paper I (Mickaelian et al. 1999), we compared the surface density of QSOs
in the Bright Quasar Survey (BQS) and in the First Byurakan Survey (FBS) and
concluded that the completeness of the BQS is of the order of 70% rather than
30-50% as suggested by several authors. A number of new observations recently
became available, allowing a re-evaluation of this completeness. We now obtain
a surface density of QSOs brighter than B = 16.16 in a subarea of the FBS
covering ~2250 deg^2, equal to 0.012 deg^-2 (26 QSOs), implying a completeness
of 53+/-10%.Comment: LaTeX 2e, 11 pages, 3 tables and 3 figures (included in text). To
appear in Astrophysics. Uses a modified aaspp4.sty (my_aaspp4.sty), included
in packag
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