843 research outputs found
A long trail behind the planetary nebula HFG1 (PK 136+05) and its precataclysmic binary central star V664 Cas
A deep wide-field image in the light of the Halpha+[N II] emission lines, of
the planetary nebula HFG1 which surrounds the precataclysmic binary system V664
Cas, has revealed a tail of emission at least 20' long, at a position angle of
316deg. Evidence is presented which suggests that this is an ~10^5 y old trail
of shocked material, left behind V664 Cas as it ejects matter whilst ploughing
through its local interstellar media at anywhere between 29 and 59 km/s
depending on its distance from the Sun.Comment: 3 pages, 1 figure, accepted for publication in MNRA
Observations of stratospheric aerosols associated with the El Chichon eruption
Lidar observations of aerosols were carried out at Aberystwyth between Nov. 1982 and Dec. 1985 using a frequency doubled and frequency tripled Nd/Yag laser and a receiver incorporating a 1 m diameter in a Newtonian telescope configuration. In analyses of the experimental data attention is paid to the magnitude of the coefficient relating extinction and backscatter, the choice being related to the possible presence of aerosols in the upper troposphere and the atmospheric densities employed in the normalisation procedure. The aerosol loading showed marked day to day changes in early months and an overall decay was apparent only after April 1983, this decay being consistent with an e sup -1 time of about 7 months. The general decay was accompanied by a lowering of the layer but layers of aerosols were shown intermittently at heights above the main layer in winter months. The height variations of photon counts corrected for range, or of aerosol backscatter ratio, showed clear signatures of the tropopause. A strong correlation was found between the heights of the tropopause identified from the lidar measurements and from radiosonde-borne temperature measurements. A notable feature of the observations is the appearance of very sharp height gradients of backscatter ratio which seem to be produced by differential advection
Numerical simulation of CO2 dispersion from punctures and ruptures of buried high-pressure dense phase CO2 pipelines with experimental validation
Carbon capture and storage (CCS) presents an option for significantly reducing the amount of carbon dioxide (CO2) released into the atmosphere and mitigating the effects of climate change. Pipelines are considered to be the most likely method for transporting captured CO2 and their safe operation is of paramount importance as their contents are likely to be in the region of several thousand tonnes and CO2 poses a number of concerns upon release due to its unusual physical properties. To this end, National Grid initiated the COOLTRANS (CO2 Liquid Pipeline Transportation) research programme to consider the pipeline transportation of high-pressure dense phase CO2. Part of this work involved the development of a mathematical model for predicting the dispersion of pure CO2 following the venting, puncture, or rupture, of such a transportation pipeline during normal operational conditions. In this paper, we describe the use of a computational fluid dynamic (CFD) tool that can be used to numerically simulate the near-field sonic dispersion from such releases, above and below ground. The model is shown to qualitatively and quantitatively reproduce observed experimental results. Validated flows at the top of the crater formed by below ground releases presented here for a range of scenarios provide the basis for developing robust source conditions for use in CFD studies of far-field dispersion, and for use with pragmatic quantified risk assessment (QRA) models
Health improvement and health promotion education of undergraduate radiographers in a Scottish HEI.
Health Professionals (AHPs) (including radiographers) have been identified as a key workforce to improve and promote the health and wellbeing of the UK population by 'making every contact count (MECC)'
It's a wonderful tail: the mass loss history of Mira
Recent observations of the Mira AB binary system have revealed a surrounding
arc-like structure and a stream of material stretching 2 degrees away in
opposition to the arc. The alignment of the proper motion vector and the
arc-like structure shows the structures to be a bow shock and accompanying
tail. We have successfully hydrodynamically modelled the bow shock and tail as
the interaction between the asymptotic giant branch (AGB) wind launched from
Mira A and the surrounding interstellar medium. Our simulations show that the
wake behind the bow shock is turbulent: this forms periodic density variations
in the tail similar to those observed. We investigate the possiblity of
mass-loss variations, but find that these have limited effect on the tail
structure. The tail is estimated to be approximately 450,000 years old, and is
moving with a velocity close to that of Mira itself. We suggest that the
duration of the high mass-loss phase on the AGB may have been underestimated.
Finally, both the tail curvature and the rebrightening at large distance can be
qualitatively understood if Mira recently entered the Local Bubble. This is
estimated to have occured 17 pc downstream from its current location.Comment: 12 pages, 3 colour figures, accepted by ApJ Part II (Letters
Faraday Rotation in the Tail of the Planetary Nebula DeHt 5
We present 1420 MHz polarization images of a 5x5 degree region around the
planetary nebula (PN) DeHt 5. The images reveal narrow Faraday-rotation
structures on the visible disk of DeHt 5, as well as two wider, tail-like,
structures "behind" DeHt 5. Though DeHt 5 is an old PN known to be interacting
with the interstellar medium (ISM), a tail has not previously been identified
for this object. The innermost tail is approximately 3 pc long and runs away
from the north-east edge of DeHt 5 in a direction roughly opposite that of the
sky-projected space velocity of the white dwarf central star, WD 2218+706. We
believe this tail to be the signature of ionized material ram-pressure stripped
and deposited downstream during a >74,000 yr interaction between DeHt 5 and the
ISM. We estimate the rotation measure (RM) through the inner tail to be -15 +/-
5 rad/m^2, and, using a realistic estimate for the line-of-sight component of
the ISM magnetic field around DeHt 5, derive an electron density in the inner
tail of n_e = 3.6 +/- 1.8 cm^-3. Assuming the material is fully ionized, we
estimate a total mass in the inner tail of 0.68 +/- 0.33 solar masses, and
predict that 0.49 +/- 0.33 solar masses was added during the PN-ISM
interaction. The outermost tail consists of a series of three roughly circular
components, which have a collective length of approximately 11.0 pc. This tail
is less conspicuous than the inner tail, and may be the signature of the
earlier interaction between the WD 2218+706 asymptotic giant branch (AGB)
progenitor and the ISM. The results for the inner and outer tails are
consistent with hydrodynamic simulations, and may have implications for the PN
missing-mass problem as well as for models which describe the impact of the
deaths of intermediate-mass stars on the ISM.Comment: 30 pages (single-column preprint format), 5 figures. Accepted for
publication in the Astrophysical Journa
Uterine spiral artery remodeling involves endothelial apoptosis induced by extravillous trophoblasts through Fas/FasL interactions.
Objective— Invasion of uterine spiral arteries by extravillous trophoblasts in the first trimester of pregnancy results in loss of endothelial and musculoelastic layers. This remodeling is crucial for an adequate blood supply to the fetus with a failure to remodel implicated in the etiology of the hypertensive disorder preeclampsia. The mechanism by which trophoblasts induce this key process is unknown. This study gives the first insights into the potential mechanisms involved.
Methods and Results— Spiral arteries were dissected from nonplacental bed biopsies obtained at Caesarean section, and a novel model was used to mimic in vivo events. Arteries were cultured with trophoblasts in the lumen, and apoptotic changes in the endothelial layer were detected after 20 hours, leading to loss of endothelium by 96 hours. In vitro, coculture experiments showed that trophoblasts stimulated apoptosis of primary decidual endothelial cells and an endothelial cell line. This was blocked by caspase inhibition and NOK2, a FasL blocking antibody. NOK2 also abrogated trophoblast-induced endothelial apoptosis in the vessel model.
Conclusions— Extravillous trophoblast induction of endothelial apoptosis is a possible mechanism by which the endothelium is removed, and vascular remodeling may occur in uterine spiral arteries. Fas/FasL interactions have an important role in trophoblast-induced endothelial apoptosis
Comparison of Numerical Predictions with CO2 Pipeline Release Datasets of Relevance to Carbon Capture and Storage Applications
Predicting the correct multi-phase fluid flow behaviour during the discharge process in the near-field of sonic CO2 jets is of particular importance in assessing the risks associated with transport aspects of carbon capture and storage schemes, given the very different hazard profiles of CO2 in the gaseous and solid states. In this paper, we apply our state-of-the-art mathematical model implemented in an efficient computational method to available data. Compared to previous applications, an improved equation of state is used. We also compare to all the available data, rather than just subsets as previously, and demonstrate both the improved performance of the fluid flow model and the variation between the available datasets. The condensed phase fraction at the vent, puncture or rupture release point is revealed to be of key importance in understanding the near-field dispersion of sonic CO2
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