386 research outputs found
Star Formation in Extreme Environments: The Effects of Cosmic Rays and Mechanical Heating
Context: Molecular data of extreme environments, such as Arp 220, but also
NGC 253, show evidence for extremely high cosmic ray (CR) rates (10^3-10^4 *
Milky Way) and mechanical heating from supernova driven turbulence.
Aims: The consequences of high CR rates and mechanical heating on the
chemistry in clouds are explored.
Methods: PDR model predictions are made for low, n=10^3, and high, n=10^5.5
cm^-3, density clouds using well-tested chemistry and radiation transfer codes.
Column densities of relevant species are discussed, and special attention is
given to water related species. Fluxes are shown for fine-structure lines of O,
C+, C, and N+, and molecular lines of CO, HCN, HNC, and HCO+. A comparison is
made to an X-ray dominated region model.
Results: Fine-structure lines of [CII], [CI], and [OI] are remarkably similar
for different mechanical heating and CR rates, when already exposed to large
amounts of UV. HCN and H2O abundances are boosted for very high mechanical
heating rates, while ionized species are relatively unaffected. OH+ and H2O+
are enhanced for very high CR rates zeta > 5 * 10^-14 s^-1. A combination of
OH+, OH, H2O+, H2O, and H3O+ trace the CR rates, and are able to distinguish
between enhanced cosmic rays and X-rays.Comment: 13 pages, 8 figures, A&A accepte
Local bone metabolism during the consolidation process of spinal interbody fusion
INTRODUCTION: Although computed tomography (CT) can identify the presence of eventual bony bridges following lumbar interbody fusion (LIF) surgery, it does not provide information on the ongoing formation process of new bony structures. 18F sodium fluoride (18F-NaF) positron emission tomography (PET) could be used as complementary modality to add information on the bone metabolism at the fusion site. However, it remains unknown how bone metabolism in the operated segment changes early after surgery in uncompromised situations. This study aimed to quantify the changes in local bone metabolism during consolidation of LIF. MATERIALS AND METHODS: Six skeletally mature sheep underwent LIF surgery. 18F-NaF PET/CT scanning was performed 6 and 12 weeks postoperatively to quantify the bone volume and metabolism in the operated segment. Bone metabolism was expressed as a function of bone volume. RESULTS: Early in the fusion process, bone metabolism was increased at the endplates of the operated vertebrae. In a next phase, bone metabolism increased in the center of the interbody region, peaked, and declined to an equilibrium state. During the entire postoperative time period of 12 weeks, bone metabolism in the interbody region was higher than that of a reference site in the spinal column. CONCLUSION: Following LIF surgery, there is a rapid increase in bone metabolism at the vertebral endplates that develops towards the center of the interbody region. Knowing the local bone metabolism during uncompromised consolidation of spinal interbody fusion might enable identification of impaired bone formation early after LIF surgery using 18F-NaF PET/CT scanning
Probing X-ray irradiation in the nucleus of NGC 1068 with observations of high-J lines of dense gas tracers
With the incorporation of high-J molecular lines, we aim to constrain the
physical conditions of the dense gas in the central region of the Seyfert 2
galaxy NGC 1068 and to determine signatures of the AGN or the starburst
contribution.
We used the James Clerk Maxwell Telescope to observe the J=4-3 transition of
HCN, HNC, and HCO+, as well as the CN N_J=2_{5/2}-1_{3/2} and
N_J=3_{5/2}-2_{5/2}, in NGC 1068.
We estimate the excitation conditions of HCN, HNC, and CN, based on the line
intensity ratios and radiative transfer models.
We find that the bulk emission of HCN, HNC, CN, and the high-J HCO+ emerge
from dense gas n(H_2)>=10^5 cm^-3). However, the low-J HCO+ lines (dominating
the HCO+ column density) trace less dense (n(H_2)<10^5 cm^-3) and colder
(T_K30 K) gas than
the other molecules.
The HCO+ J=4-3 line intensity, compared with the lower transition lines and
with the HCN J=4-3 line, support the influence of a local XDR environment. The
estimated N(CN)/N(HCN)~1-4 column density ratios are indicative of an XDR/AGN
environment with a possible contribution of grain-surface chemistry induced by
X-rays or shocks.Comment: Main text: 8 pages, 5 tables, 1 figure. Appendix: 7 pages, 1 table, 8
figures. Accepted for publication in A&
Twitter Flood Mapping Scripts: First Release
The increasing number and severity of floods, driven by phenomena
such as urbanization, deforestation, subsidence and climate change, create a
growing need for accurate and timely flood maps. In this paper we present and
evaluate a method to create deterministic and probabilistic flood maps from
Twitter messages that mention locations of flooding. A deterministic flood
map created for the December 2015 flood in the city of York (UK) showed good
performance (F(2)â=ââŻ0.69; a statistic ranging from 0 to 1,
with 1Â expressing a perfect fit with validation data). The probabilistic
flood maps we created showed that, in the York case study, the uncertainty in
flood extent was mainly induced by errors in the precise locations of flood
observations as derived from Twitter data. Errors in the terrain elevation
data or in the parameters of the applied algorithm contributed less to flood
extent uncertainty. Although these maps tended to overestimate the actual
probability of flooding, they gave a reasonable representation of flood
extent uncertainty in the area. This study illustrates that inherently
uncertain data from social media can be used to derive information about
flooding
Extended warm and dense gas towards W49A: starburst conditions in our Galaxy?
The star formation rates in starburst galaxies are orders of magnitude higher
than in local star-forming regions, and the origin of this difference is not
well understood. We use sub-mm spectral line maps to characterize the physical
conditions of the molecular gas in the luminous Galactic star-forming region
W49A and compare them with the conditions in starburst galaxies. We probe the
temperature and density structure of W49A using H_2CO and HCN line ratios over
a 2'x2' (6.6x6.6 pc) field with an angular resolution of 15" (~0.8 pc) provided
by the JCMT Spectral Legacy Survey. We analyze the rotation diagrams of lines
with multiple transitions with corrections for optical depth and beam dilution,
and estimate excitation temperatures and column densities. Comparing the
observed line intensity ratios with non-LTE radiative transfer models, our
results reveal an extended region (about 1'x1', equivalent to ~3x3 pc at the
distance of W49A) of warm (> 100 K) and dense (>10^5 cm^-3) molecular gas, with
a mass of 2x10^4 - 2x10^5 M_Sun (by applying abundances derived for other
regions of massive star-formation). These temperatures and densities in W49A
are comparable to those found in clouds near the center of the Milky Way and in
starburst galaxies. The highly excited gas is likely to be heated via shocks
from the stellar winds of embedded, O-type stars or alternatively due to UV
irradiation, or possibly a combination of these two processes. Cosmic rays,
X-ray irradiation and gas-grain collisional heating are less likely to be the
source of the heating in the case of W49A.Comment: Accepted for publication in A&A; 11 pages, 9 figure
Are Dutch dental students and dental-care providers competent prescribers of drugs?
Dental students and dental-care providers should be able to prescribe drugs safely and effectively. As it is unknown whether this is the case, we assessed and compared the prescribing competence of dental students and dental-care providers in the Netherlands. In 2017, all Dutch final-year dental students and a random sample of all qualified general dental practitioners and dental specialists (oral and maxillofacial surgeons and orthodontists) were invited to complete validated prescribing knowledge-assessment and skills-assessment instruments. The knowledge assessment comprised 40 multiple-choice questions covering important drug topics. The skills assessment comprised three common clinical case scenarios. For the knowledge assessment, the response rates were 26 (20%) dental students, 28 (8%) general dental practitioners, and 19 (19%) dental specialists, and for the skills assessment the response rates were 14 (11%) dental students, eight (2%) general dental practitioners, and eight (8%) dental specialists. Dental specialists had higher knowledge scores (78% correct answers) than either dental practitioners (69% correct answers) or dental students (69% correct answers). A substantial proportion of all three groups made inappropriate treatment choices (35%-49%) and prescribing errors (47%-70%). Although there were some differences, dental students and dental-care providers in the Netherlands lack prescribing competence, which is probably because of poor prescribing education during under- and postgraduate dental training. Educational interventions are urgently needed
Excitation of the molecular gas in the nuclear region of M82
We present high resolution HIFI spectroscopy of the nucleus of the
archetypical starburst galaxy M82. Six 12CO lines, 2 13CO lines and 4
fine-structure lines are detected. Besides showing the effects of the overall
velocity structure of the nuclear region, the line profiles also indicate the
presence of multiple components with different optical depths, temperatures and
densities in the observing beam. The data have been interpreted using a grid of
PDR models. It is found that the majority of the molecular gas is in low
density (n=10^3.5 cm^-3) clouds, with column densities of N_H=10^21.5 cm^-2 and
a relatively low UV radiation field (GO = 10^2). The remaining gas is
predominantly found in clouds with higher densities (n=10^5 cm^-3) and
radiation fields (GO = 10^2.75), but somewhat lower column densities
(N_H=10^21.2 cm^-2). The highest J CO lines are dominated by a small (1%
relative surface filling) component, with an even higher density (n=10^6 cm^-3)
and UV field (GO = 10^3.25). These results show the strength of multi-component
modeling for the interpretation of the integrated properties of galaxies.Comment: Accepted for publication in A&A Letter
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