157 research outputs found
Gamma-Ray Bursts from tidally spun-up Wolf-Rayet stars?
The collapsar model requires rapidly rotating Wolf-Rayet stars as progenitors
of long gamma-ray bursts. However, Galactic Wolf-Rayet stars rapidly lose
angular momentum due to their intense stellar winds. We investigate whether the
tidal interaction of a Wolf-Rayet star with a compact object in a binary system
can spin up the Wolf-Rayet star enough to produce a collapsar. We compute the
evolution of close Wolf-Rayet binaries, including tidal angular momentum
exchange, differential rotation of the Wolf-Rayet star, internal magnetic
fields, stellar wind mass loss, and mass transfer. The Wolf-Rayet companion is
approximated as a point mass. We then employ a population synthesis code to
infer the occurrence rates of the various relevant binary evolution channels.
We find that the simple scenario -- i.e., the Wolf-Rayet star being tidally
spun up and producing a collapsar -- does not occur at solar metallicity and
may only occur with low probability at low metallicity. It is limited by the
widening of the binary orbit induced by the strong Wolf-Rayet wind or by the
radius evolution of the Wolf-Rayet star that most often leads to a binary
merger. The tidal effects enhance the merger rate of Wolf-Rayet stars with
black holes such that it becomes comparable to the occurrence rate of long
gamma-ray bursts.Comment: 9 pages, 11 figures, accepted for publication in A&
Gravitational wave detection using pulsars: status of the Parkes Pulsar Timing Array project
The first direct detection of gravitational waves may be made through
observations of pulsars. The principal aim of pulsar timing array projects
being carried out worldwide is to detect ultra-low frequency gravitational
waves (f ~ 10^-9 to 10^-8 Hz). Such waves are expected to be caused by
coalescing supermassive binary black holes in the cores of merged galaxies. It
is also possible that a detectable signal could have been produced in the
inflationary era or by cosmic strings. In this paper we review the current
status of the Parkes Pulsar Timing Array project (the only such project in the
Southern hemisphere) and compare the pulsar timing technique with other forms
of gravitational-wave detection such as ground- and space-based interferometer
systems.Comment: Accepted for publication in PAS
Cygnus X-3 and the problem of the missing Wolf-Rayet X-ray binaries
Wetensch. publicatieFaculteit der Wiskunde en Natuurwetenschappe
The Sensitivity of the Parkes Pulsar Timing Array to Individual Sources of Gravitational Waves
We present the sensitivity of the Parkes Pulsar Timing Array to gravitational
waves emitted by individual super-massive black-hole binary systems in the
early phases of coalescing at the cores of merged galaxies. Our analysis
includes a detailed study of the effects of fitting a pulsar timing model to
non-white timing residuals. Pulsar timing is sensitive at nanoHertz frequencies
and hence complementary to LIGO and LISA. We place a sky-averaged constraint on
the merger rate of nearby () black-hole binaries in the early phases
of coalescence with a chirp mass of 10^{10}\,\rmn{M}_\odot of less than one
merger every seven years. The prospects for future gravitational-wave astronomy
of this type with the proposed Square Kilometre Array telescope are discussed.Comment: fixed error in equation (4). [13 pages, 6 figures, 1 table, published
in MNRAS
Diagnostic DNA Methylation Biomarkers for Renal Cell Carcinoma:A Systematic Review
CONTEXT: The 5-yr survival of early-stage renal cell carcinoma (RCC) is approximately 93%, but once metastasised, the 5-yr survival plummets to 12%, indicating that early RCC detection is crucial to improvement in survival. DNA methylation biomarkers have been suggested to be of potential diagnostic value; however, their current state of clinical translation is unclear and a comprehensive overview is lacking. OBJECTIVE: To systematically review and summarise all literature regarding diagnostic DNA methylation biomarkers for RCC. EVIDENCE ACQUISITION: We performed a systematic literature review of PubMed, EMBASE, Medline, and Google Scholar up to January 2019, according to the Preferred Reporting Items for Systematic Review and Meta-Analysis of Diagnostic Test Accuracy Studies (PRISMA-DTA) guidelines. Included studies were scored according to the Standards for Reporting of Diagnostic Accuracy Studies (STARD) criteria. Forest plots were generated to summarise diagnostic performance of all biomarkers. Level of evidence (LoE) and potential risk of bias were determined for all included studies. EVIDENCE SYNTHESIS: After selection, 19 articles reporting on 44 diagnostic DNA methylation biomarkers and 11 multimarker panels were included; however, only 15 biomarkers were independently validated. STARD scores varied from 4 to 13 out of 23 points, with a median of 10 points. Large variation in subgroups, methods, and primer locations was observed. None of the reported biomarkers exceeded LoE III, and the majority of studies reported inadequately. CONCLUSIONS: None of the reported biomarkers exceeded LoE III, indicating their limited clinical utility. Moreover, study reproducibility and further development of these RCC biomarkers are greatly hampered by inadequate reporting. PATIENT SUMMARY: In this report, we reviewed whether specific biomarkers could be used to diagnose the most common form of kidney cancer. We conclude that due to limited evidence and reporting inconsistencies, none of these biomarkers can be used in clinical practice, and further development towards clinical use is hindered
CATT voor de boomkwekerij - pilotproeven met sierheesterstek en vaste planten laten kansen voor de toekomst zien
In dit project hebben we het perspectief voor CATT-behandelingen (Controlled Atmosphere Temperature Treatment) voor boomkwekerijgewassen onderzocht. Deze methode combineert een CA-behandeling (gewijzigde luchtsamenstelling door aanpassing van CO2-en O2-condities) met een temperatuurbehandeling. Hiervoor wordt het plantmateriaal gedurende een bepaalde periode in een gasdichte cel bewaard. CATT-behandelingen zijn een duurzame vorm van plaagbestrijding omdat er geen chemische middelen aan te pas komen en omdat er geringe kans is op resistentieontwikkeling van de plaagorganismen. Bovendien kan deze methode zeer snel in praktijk worden geïmplementeerd omdat deze geen wettelijke toelating behoeft. Zo zijn in korte tijd CATT-behandelingen ontwikkeld voor het bestrijden van plagen in aardbei, die nu succesvol in praktijk worden toegepast. In dit project hebben we twee sierheesters in de stekfase (Buxus sempervirens en Ilex altaclerensis) en vier soorten vaste planten in de winterbewaring (Astilbe japonica, Geranium sanguineum, Phlox paniculata, Paeonia officinalis) behandeld en vergeleken met onbehandelde controles
Placing limits on the stochastic gravitational-wave background using European Pulsar Timing Array data
Direct detection of low-frequency gravitational waves (
Hz) is the main goal of pulsar timing array (PTA) projects. One of the main
targets for the PTAs is to measure the stochastic background of gravitational
waves (GWB) whose characteristic strain is expected to approximately follow a
power-law of the form , where is the
gravitational-wave frequency. In this paper we use the current data from the
European PTA to determine an upper limit on the GWB amplitude as a function
of the unknown spectral slope with a Bayesian algorithm, by modelling
the GWB as a random Gaussian process. For the case , which is
expected if the GWB is produced by supermassive black-hole binaries, we obtain
a 95% confidence upper limit on of , which is 1.8 times
lower than the 95% confidence GWB limit obtained by the Parkes PTA in 2006. Our
approach to the data analysis incorporates the multi-telescope nature of the
European PTA and thus can serve as a useful template for future
intercontinental PTA collaborations.Comment: 14 pages, 8 figures, 3 tables, mnras accepte
Cygnus X-3 and the problem of the missing Wolf-Rayet X-ray binaries
Cygnus X-3 is a strong X-ray source (L_X about 10^38 erg/s) which is thought
to consist of a compact object, accreting matter from a helium star. We find
analytically that the estimated ranges of mass-loss rate and orbital-period
derivative for Cyg X-3 are consistent with two models: i) the system is
detached and the mass loss from the system comes from the stellar wind of a
massive helium star, of which only a fraction that allows for the observed
X-ray luminosity is accreted, or ii) the system is semidetached and a
Roche-lobe-overflowing low- or moderate-mass helium donor transfers mass to the
compact object, followed by ejection of its excess over the Eddington rate from
the system. These analytical results appear to be consistent with evolutionary
calculations. By means of population synthesis we find that currently in the
Galaxy there may exist ~1 X-ray binary with a black hole that accretes from a
>~ 7 MSun Wolf-Rayet star and ~1 X-ray binary in which a neutron star accretes
matter from a Roche-lobe-overflowing helium star with mass <~ 1.5 MSun. Cyg X-3
is probably one of these systems.Comment: 12 pages, 6 figures, accepted by A&
A precise mass measurement of the intermediate-mass binary pulsar PSR J1802-2124
PSR J1802-2124 is a 12.6-ms pulsar in a 16.8-hour binary orbit with a
relatively massive white dwarf (WD) companion. These properties make it a
member of the intermediate-mass class of binary pulsar (IMBP) systems. We have
been timing this pulsar since its discovery in 2002. Concentrated observations
at the Green Bank Telescope, augmented with data from the Parkes and Nancay
observatories, have allowed us to determine the general relativistic Shapiro
delay. This has yielded pulsar and white dwarf mass measurements of 1.24(11)
and 0.78(4) solar masses (68% confidence), respectively. The low mass of the
pulsar, the high mass of the WD companion, the short orbital period, and the
pulsar spin period may be explained by the system having gone through a
common-envelope phase in its evolution. We argue that selection effects may
contribute to the relatively small number of known IMBPs.Comment: 9 pages, 4 figures, 3 tables, accepted for publication in the
Astrophysical Journa
Probing dust grain evolution in IM Lupi's circumstellar disc. Multi-wavelength observations and modelling of the dust disc
We present a panchromatic study, involving a multiple technique approach, of
the circumstellar disc surrounding the T Tauri star IM Lupi (Sz 82). We have
undertaken a comprehensive observational study of IM Lupi using photometry,
spectroscopy, millimetre interferometry and multi-wavelength imaging. For the
first time, the disc is resolved from optical and near-infrared wavelengths in
scattered light, to the millimetre regime in thermal emission. Our data-set, in
conjunction with existing photometric data, provides an extensive coverage of
the spectral energy distribution, including a detailed spectrum of the silicate
emission bands. We have performed a simultaneous modelling of the various
observations, using the radiative transfer code MCFOST, and analysed a grid of
models over a large fraction of the parameter space via Bayesian inference. We
have constructed a model that can reproduce all of the observations of the
disc. Our analysis illustrates the importance of combining a wide range of
observations in order to fully constrain the disc model, with each observation
providing a strong constraint only on some aspects of the disc structure and
dust content. Quantitative evidence of dust evolution in the disc is obtained:
grain growth up to millimetre-sized particles, vertical stratification of dust
grains with micrometric grains close to the disc surface and larger grains
which have settled towards the disc midplane, and possibly the formation of
fluffy aggregates and/or ice mantles around grains.Comment: 20 pages, 13 figures. Accepted for publication in A&
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