10,750 research outputs found
Location and sizes of forsterite grains in protoplanetary disks: interpretation from the Herschel DIGIT programme
The spectra of protoplanetary disks contain mid- and far- infrared emission
features produced by forsterite dust grains. The spectral features contain
information about the forsterite temperature, chemical composition and grain
size. We aim to characterize how the 23 and 69 micron features can be used to
constrain the physical locations of forsterite in disks. We check for
consistency between two independent forsterite temperature measurements: the
23/69 feature strength ratio and the shape of the 69 micron band. We performed
radiative transfer modeling to study the effect of disk properties to the
forsterite spectral features. Temperature-dependent forsterite opacities were
considered in self-consistent models to compute forsterite emission from
protoplanetary disks. Modelling grids are presented to study the effects of
grain size, disk gaps, radial mixing and optical depth to the forsterite
features. Independent temperature estimates derived from the 23/69 feature
strength ratio and the 69 micron band shape are most inconsistent for HD141569
and Oph IRS 48. A case study of the disk of HD141569 shows two solutions to fit
the forsterite spectrum. A model with T ~ 40 K, iron-rich (~0-1 % Fe) and 1
micron forsterite grains, and a model with warmer (T ~ 100 K), iron-free, and
larger (10 micron) grains. We find that for disks with low upper limits of the
69 micron feature (most notably in flat, self-shadowed disks), the forsterite
must be hot, and thus close to the star. We find no correlation between disk
gaps and the presence or absence of forsterite features. We argue that the 69
micron feature of the evolved transitional disks HD141569 and Oph IRS 48 is
most likely a tracer of larger (i.e. ~10 micron) forsterite grains.Comment: Accepted for publication in A&A. 14 pages, 9 figure
Micron-sized forsterite grains in the pre-planetary nebula of IRAS 17150-3224 - Searching for clues on the mysterious evolution of massive AGB stars
We study the grain properties and location of the forsterite crystals in the
circumstellar environment of the pre-planetary nebula (PPN) IRAS 17150-3224 in
order to learn more about the as yet poorly understood evolutionary phase prior
to the PPN. We use the best-fit model for IRAS 17150-3224 of Meixner et al.
(2002) and add forsterite to this model. We investigate different spatial
distributions and grain sizes of the forsterite crystals in the circumstellar
environment. We compare the spectral bands of forsterite in the mid-infrared
and at 69 micrometre in radiative transport models to those in ISO-SWS and
Herschel/PACS observations. We can reproduce the non-detection of the
mid-infrared bands and the detection of the 69 micrometre feature with models
where the forsterite is distributed in the whole outflow, in the superwind
region, or in the AGB-wind region emitted previous to the superwind, but we
cannot discriminate between these three models. To reproduce the observed
spectral bands with these three models, the forsterite crystals need to be
dominated by a grain size population of 2 micrometre up to 6 micrometre. We
hypothesise that the large forsterite crystals were formed after the superwind
phase of IRAS 17150-3224, where the star developed an as yet unknown hyperwind
with an extremely high mass-loss rate (10^-3 Msol/yr). The high densities of
such a hyperwind could be responsible for the efficient grain growth of both
amorphous and crystalline dust in the outflow. Several mechanisms are discussed
that might explain the lower-limit of 2 micrometre found for the forsterite
grains, but none are satisfactory. Among the mechanisms explored is a possible
selection effect due to radiation pressure based on photon scattering on
micron-sized grains.Comment: Accepted by A&
Scaling of spontaneous rotation with temperature and plasma current in tokamaks
Using theoretical arguments, a simple scaling law for the size of the
intrinsic rotation observed in tokamaks in the absence of momentum injection is
found: the velocity generated in the core of a tokamak must be proportional to
the ion temperature difference in the core divided by the plasma current,
independent of the size of the device. The constant of proportionality is of
the order of . When the
intrinsic rotation profile is hollow, i.e. it is counter-current in the core of
the tokamak and co-current in the edge, the scaling law presented in this
Letter fits the data remarkably well for several tokamaks of vastly different
size and heated by different mechanisms.Comment: 5 pages, 3 figure
Patient Safety in Interventional Radiology: A CIRSE IR Checklist
Interventional radiology (IR) is an invasive speciality with the potential for complications as with other invasive specialities. The World Health Organization (WHO) produced a surgical safety checklist to decrease the morbidity and mortality associated with surgery. The Cardiovascular and Interventional Society of Europe (CIRSE) set up a task force to produce a checklist for IR. Use of the checklist will, we hope, reduce the incidence of complications after IR procedures. It has been modified from the WHO surgical safety checklist and the RAD PASS from Holland
Global assessment of nitrogen deposition effects on terrestrial plant diversity : a synthesis
Atmospheric nitrogen (N) deposition is it recognized threat to plant diversity ill temperate and northern parts of Europe and North America. This paper assesses evidence from field experiments for N deposition effects and thresholds for terrestrial plant diversity protection across a latitudinal range of main categories of ecosystems. from arctic and boreal systems to tropical forests. Current thinking on the mechanisms of N deposition effects on plant diversity, the global distribution of G200 ecoregions, and current and future (2030) estimates of atmospheric N-deposition rates are then used to identify the risks to plant diversity in all major ecosystem types now and in the future. This synthesis paper clearly shows that N accumulation is the main driver of changes to species composition across the whole range of different ecosystem types by driving the competitive interactions that lead to composition change and/or making conditions unfavorable for some species. Other effects such its direct toxicity of nitrogen gases and aerosols long-term negative effects of increased ammonium and ammonia availability, soil-mediated effects of acidification, and secondary stress and disturbance are more ecosystem, and site-specific and often play a supporting role. N deposition effects in mediterranean ecosystems have now been identified, leading to a first estimate of an effect threshold. Importantly, ecosystems thought of as not N limited, such as tropical and subtropical systems, may be more vulnerable in the regeneration phase. in situations where heterogeneity in N availability is reduced by atmospheric N deposition, on sandy soils, or in montane areas. Critical loads are effect thresholds for N deposition. and the critical load concept has helped European governments make progress toward reducing N loads on sensitive ecosystems. More needs to be done in Europe and North America. especially for the more sensitive ecosystem types. including several ecosystems of high conservation importance. The results of this assessment Show that the Vulnerable regions outside Europe and North America which have not received enough attention are ecoregions in eastern and Southern Asia (China, India), an important part of the mediterranean ecoregion (California, southern Europe). and in the coming decades several subtropical and tropical parts of Latin America and Africa. Reductions in plant diversity by increased atmospheric N deposition may be more widespread than first thought, and more targeted Studies are required in low background areas, especially in the G200 ecoregions
Evidence on continuous flow peritoneal dialysis: A review
Clinical application of continuous flow peritoneal dialysis (CFPD) has been explored since the 1960s, but despite anticipated clinical benefits, CFPD has failed to gain a foothold in clinical practice, among others due to the typical use of two catheters (or a dual-lumen catheter) and large dialysate volumes required per treatment. Novel systems applying CFPD via the existing single-lumen catheter using rapid dialysate cycling may solve one of these hurdles. Novel on-demand peritoneal dialysate generation systems and sorbent-based peritoneal dialysate regeneration systems may considerably reduce the storage space for peritoneal dialysate and/or the required dialysate volume. This review provides an overview of current evidence on CFPD in vivo. The available (pre)clinical evidence on CFPD is limited to case reports/series with inherently nonuniform study procedures, or studies with a small sample size, short follow-up, and no hard endpoints. Small solute clearance appears to be higher in CFPD compared to conventional PD, in particular at dialysate flows ≥100 mL/min using two single-lumen catheters or a double-lumen catheter. Results of CFPD using rapid cycling via a single-lumen catheter are too preliminary to draw any conclusions. Continuous addition of glucose to dialysate with CFPD appears to be effective in reducing the maximum intraperitoneal glucose concentration while increasing ultrafiltration efficiency (mL/g absorbed glucose). Patient tolerance may be an issue since abdominal discomfort and sterile peritonitis were reported with continuous circulation of the peritoneal dialysate. Thus, well-designed clinical trials of longer duration and larger sample size, in particular applying CFPD via the existing catheter, are urgently required
The Question of Low-Lying Intruder States in and Neighboring Nuclei
The presence of not yet detected intruder states in e.g. a
intruder at 9 excitation would affect the shape of the -delayed alpha spectra of and . In order to test the
plausibility of this assumption, shell model calculations with up to excitations in (and up to excitations in
) were performed. With the above restrictions on the model spaces, the
calculations did not yield any low-lying intruder state in . Another
approach -the simple deformed oscillator model with self-consistent frequencies
and volume conservation gives an intruder state in which is lower in
energy than the above shell model results, but its energy is still considerably
higher than 9 .Comment: 16 pages (RevTeX), 1 PS figure. To appear in Phys. Rev.
Field-Dependent Tilt and Birefringence of Electroclinic Liquid Crystals: Theory and Experiment
An unresolved issue in the theory of liquid crystals is the molecular basis
of the electroclinic effect in the smectic-A phase. Recent x-ray scattering
experiments suggest that, in a class of siloxane-containing liquid crystals, an
electric field changes a state of disordered molecular tilt in random
directions into a state of ordered tilt in one direction. To investigate this
issue, we measure the optical tilt and birefringence of these liquid crystals
as functions of field and temperature, and we develop a theory for the
distribution of molecular orientations under a field. Comparison of theory and
experiment confirms that these materials have a disordered distribution of
molecular tilt directions that is aligned by an electric field, giving a large
electroclinic effect. It also shows that the net dipole moment of a correlated
volume of molecules, a key parameter in the theory, scales as a power law near
the smectic-A--smectic-C transition.Comment: 18 pages, including 9 postscript figures, uses REVTeX 3.0 and
epsf.st
Status of the XMM-Newton cross-calibration with SASv6.5.0
Further achievements of the XMM-Newton cross-calibration - XMM internal as
well as with other X-ray missions - are presented. We explain the major changes
in the new version SASv6.5 of the XMM-Newton science analysis system. The
current status of the cross-calibration of the three EPIC cameras is shown.
Using a large sample of blazars, the pn energy redistribution at low energy
could be further calibrated, correcting the overestimation of fluxes in the
lowest energy regime. In the central CCDs of the MOSs, patches were identified
at the bore-sight positions, leading to an underestimation of the low energy
fluxes. The further improvement in the understanding of the cameras resulted in
a good agreement of the EPIC instruments down to lowest energies. The latest
release of the SAS software package already includes corrections for both
effects as shown in several examples of different types of sources. Finally the
XMM internal cross-calibration is completed by the presentation of the current
cross-calibration status between EPIC and RGS instruments. Major efforts have
been made in cross-calibrations with other X-ray missions, most importantly
with Chandra, of course, but also with currently observing satellites like
Swift.Comment: 6 pages, 23 figures. To appear in the proceedings of "The X-Ray
Universe 2005" conference, 2005 Sept 26-30, El Escorial, Madrid, Spai
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