1,471 research outputs found
Ultra-compact binaries: relevance and role of Utrecht
We present a short overview of the formation and evolution of ultra-compact
binaries. They are relevant to a surprisingly large number of astrophysical
phenomena (binary interactions, mass transfer stability, explosive phenomena
such as type Ia supernovae and gravitational waves).Comment: To appear in proceedings of "370 years of astronomy in Utrecht",
Noordwijkerhout, The Netherlands, April 2-5, 2012 (ASP Conference Series
Biomarkers, Models and Mechanisms of Intestinal Fibrosis
Chronic intestinal inflammation in Crohn’s disease (CD) frequently causes complications such as fibrosis or fistulae. Intestinal fibrosis is characterized by excessive deposition of collagens and causing stenosis and finally intestinal obstruction. Fistulae on the other hand are characterized by a relative decrease in deposition of collagens due to persistent inflammation. Despite advances in treatment with anti-inflammatory drugs, the incidence of fibrosis and fistulae remains high. Repetitive endoscopic dilatation of stenosis, or surgery for fibrosis or fistulae are so far the only therapeutic options. Furthermore, currently no serological biomarkers are available to detect the presence of intestinal fibrosis or fistulae. The development of drugs against intestinal fibrosis/fistulae is being hampered by the lack of insight in the underlying mechanism and by the lack of translational models that can predict drug efficacy in humans. We describe a novel translational ex vivo model for intestinal fibrosis, which could bridge the gap between pre-clinical and clinical research to evaluate the efficacy of anti-fibrotic drugs in man. In addition, pH sensing receptor ovarian cancer G-protein coupled receptor-1 was confirmed to be part of the mechanism of inducing intestinal fibrosis and may be a target for CD-associated fibrosis. Furthermore, we propose targets to inhibit intestinal fibrosis and existing drugs acting on these targets, based on increased mRNA expression of enzymes involved in the post-translational collagen processing of intestinal fibrosis affected tissue. Finally, we provide evidence for the use of serological markers related to turnover of extra cellular matrix to detect the presence of penetrating CD
Formation of the planet around the millisecond pulsar J1719-1438
Context. Recently the discovery of PSR J1719-1438, a 5.8 ms pulsar with a
companion in a 2.2 hr orbit, was reported. The combination of this orbital
period and the very low mass function is unique. The discoverers, Bailes et
al., proposed an ultracompact X-ray binary (UCXB) as the progenitor system.
However, the standard UCXB scenario would not produce this system as the time
required to reach this orbital period exceeds the current estimate of the age
of the Universe. The detached state of the system aggravates the problem. Aims.
We want to understand the evolutionary history of PSR J1719-1438, and determine
under which circumstances it could have evolved from an UCXB. Methods. We model
UCXB evolution varying the donor size and investigate the effect of a wind mass
loss from the donor, and compare the results with the observed characteristics
of PSR J1719-1438. Results. An UCXB can reach a 2.2 hr orbit within the age of
the Universe, provided that 1) the millisecond pulsar can significantly heat
and expand the donor by pulsar irradiation, or 2) the system loses extra
orbital angular momentum, e.g. via a fast wind from the donor. Conclusions. The
most likely scenario for the formation of PSR J1719-1438 is UCXB evolution
driven by angular momentum loss via the usual gravitational wave emission,
which is enhanced by angular momentum loss via a donor wind of ~3x10^-13
Msun/yr. Depending on the size of the donor during the evolution, the companion
presently probably has a mass of ~1-3 Jupiter masses, making it a very low mass
white dwarf as proposed by Bailes et al. Its composition can be either helium
or carbon-oxygen. A helium white dwarf companion makes the long (for an UCXB)
orbital period easier to explain, but the required inclination makes it a
priori less likely than a carbon-oxygen white dwarf.Comment: 5 pages, 4 figures. Accepted for publication in Astronomy and
Astrophysics. v2: Updated a referenc
The Influence of Video Interaction Guidance on the Quality of Parental Bonding towards and Interaction with the Premature Infant
Developing a parent-infant bond and interaction can be more challenging for parents of a preterm born infant. This study wants to shed light on the influence of video interaction guidance (VIG) on the quality of parental bonding towards and interaction with the premature infant
The Making of Argumentation Theory: A Pragma-dialectical View
In ‘The making of argumentation theory’ van Eemeren and van Haaften describe the contributions made to the five components of a full-fledged research program of argumentation theory by four prominent approaches to the discipline: formal dialectics, rhetoric/pragmalinguistics, informal logic, and pragma-dialectics. Most of these approaches do not contribute to all components, but to some in particular. Starting from the pragma-dialectical view of the relationship between dialectical reasonableness and rhetorical effectiveness – the crucial issue in argumentation theory – van Eemeren and van Haaften explain the positions taken by representatives from the approaches discussed and indicate where they differ from the pragma-dialectical approach. It transpires that approaches focusing on dialectical reasonableness are, next to pragma-dialectics, formal dialectics and informal logic; approaches focusing on rhetorical effectiveness are, next to pragma-dialectics, rhetoric and pragmalinguistics, and the informal logician Tindale. When it comes to the relationship between dialectical reasonableness and rhetorical effectiveness, some interest in it is shown in rhetoric and pragmalinguistics, but only in pragma-dialectics and in Tindale’s work is it a real focus. The main difference between Tindale’s view and the pragma-dialectical view is that in pragma-dialectics the decisive role in deciding about reasonableness is assigned to a code of conduct for reasonable argumentative discourse and in Tindale’s approach this role is assigned to Tindale’s interpretation of the Perelmanian universal audience.</p
Population synthesis of classical low-mass X-ray binaries in the Galactic Bulge
Aims. We model the present-day population of 'classical' low-mass X-ray
binaries (LMXBs) with neutron star accretors, which have hydrogen-rich donor
stars. Their population is compared with that of hydrogen-deficient LMXBs,
known as ultracompact X-ray binaries (UCXBs). We model the observable LMXB
population and compare it to observations. Methods. We combine the binary
population synthesis code SeBa with detailed LMXB evolutionary tracks to model
the size and properties of the present-day LMXB population in the Galactic
Bulge. Whether sources are persistent or transient, and what their
instantaneous X-ray luminosities are, is predicted using the thermal-viscous
disk instability model. Results. We find a population of ~2.1 x 10^3 LMXBs with
neutron star accretors. Of these about 15 - 40 are expected to be persistent
(depending on model assumptions), with luminosities higher than 10^35 erg s^-1.
About 7 - 20 transient sources are expected to be in outburst at any given
time. Within a factor of two these numbers are consistent with the observed
population of bright LMXBs in the Bulge. This gives credence to our prediction
of the existence of a population of ~1.6 x 10^3 LMXBs with low donor masses
that have gone through the period minimum, and have present-day mass transfer
rates below 10^-11 Msun yr^-1. Conclusions. Even though the observed population
of hydrogen-rich LMXBs in the Bulge is larger than the observed population of
(hydrogen-deficient) UCXBs, the latter have a higher formation rate. While
UCXBs may dominate the total LMXB population at the present, the majority would
be very faint, or may have become detached and produced millisecond radio
pulsars. In that case UCXBs would contribute significantly more to the
formation of millisecond radio pulsars than hydrogen-rich LMXBs. [abridged]Comment: 8 pages, 10 figures. Accepted for publication in Astronomy and
Astrophysics. v2: minor language correction
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