106 research outputs found
PAHs and star formation in the HII regions of nearby galaxies M83 and M33
We present mid-infrared (MIR) spectra of HII regions within star-forming
galaxies M83 and M33. Their emission features are compared with Galactic and
extragalactic HII regions, HII-type galaxies, starburst galaxies, and
Seyfert/LINER type galaxies. Our main results are as follows: (i) the M33 and
M83 HII regions lie in between Seyfert/LINER galaxies and HII-type galaxies in
the 7.7/11.3 - 6.2/11.3 plane, while the different sub-samples exhibiting
different 7.7/6.2 ratios; (ii) Using the NASA Ames PAH IR Spectroscopic
database, we demonstrate that the 6.2/7.7 ratio does not effectively track PAH
size, but the 11.3/3.3 PAH ratio does; (iii) variations on the 17 m PAH
band depends on object type; however, there is no dependence on metallicity for
both extragalactic HII regions and galaxies; (iv) the PAH/VSG intensity ratio
decreases with the hardness of the radiation field and galactocentric radius
(Rg), yet the ionization alone cannot account for the variation seen in all of
our sources; (v) the relative strength of PAH features does not change
significantly with increasing radiation hardness, as measured through the
[NeIII]/[NeII] ratio and the ionization index; (vi) We present PAH SFR
calibrations based on the tight correlation between the 6.2, 7.7, and 11.3
m PAH luminosities with the 24 m luminosity and the combination of
the 24 m and H luminosity; (vii) Based on the total luminosity
from PAH and FIR emission, we argue that extragalactic HII regions are more
suitable templates in modeling and interpreting the large scale properties of
galaxies compared to Galactic HII regions.Comment: 26 pages, 24 figures, 6 tables. Accepted for publication in MNRA
Polycyclic Aromatic Hydrocarbon Size Tracers
We examine the dependence of polycyclic aromatic hydrocarbon (PAH) band
intensity ratios as a function of the average number of carbon atoms and assess
their effectiveness as tracers for PAH size, utilising the data, models, and
tools provided by the NASA Ames PAH Infrared Spectroscopic Database. To achieve
this, we used spectra from mixtures of PAHs of different ionisation fractions,
following a size distribution. Our work, congruent with earlier findings, shows
that band ratios that include the 3.3 m PAH band provide the best PAH
size tracers for small-to-intermediate sized PAHs. In addition, we find that
band ratios that include the sum of the 15-20 m PAH features
(I) and the 6.2 or 7.7 m bands also serve as good
tracers for PAH size in the case of small-to-intermediate sized PAHs, for
objects under a similar PAH size distribution as with the presented models. For
different PAH size distributions, the application of a scaling factor to the
I/I ratio can provide estimates for the size of the
small-to-intermediate PAH population within sources. Employment of the
I/I and I/I ratios can be
of particular interest for JWST observations limited only to 5-28
m MIRI(-MRS) coverage.Comment: 8 pages, 5 figures; Accepted for publication in MNRA
On the interaction between the island divertor heat fluxes, the scrape-off layer radial electric field and the edge turbulence in Wendelstein 7-X plasmas
The formation of the radial electric field, E-r in the scrape-off layer (SOL) has been experimentally studied for attached divertor conditions in stellarator W7-X. The main objective of this study is to test the validity in a complex three-dimensional (3D) island divertor of simple models, typically developed in tokamaks, relating E-r in the SOL to the sheath potential drop gradient at the target. Additionally, we investigate the effect of the edge E-r shear on the reduction of density fluctuation amplitude, a well-established phenomenon according to the existing bibliography. The main diagnostic for measurements in the SOL is a V-band Doppler reflectometer that can provide the measurement of the E-r and density fluctuations with good spatial resolution. 3D measurements of divertor parameters have been carried out using infrared cameras, with the exponential decay length of the divertor heat flux (lambda(q)) resulting in a suitable proxy for the model-relevant lambda(T), the exponential decay length of the temperature at the divertor. In the investigated attached regimes, it is shown for the first time that the formation of the E-r in the SOL depends on parameters at the divertor, following a E-r proportional to T-e/lambda(q) qualitatively similar to that found in a tokamak. Then, from the analyzed plasmas, the observed E-r shear at the edge is linked to a moderate local reduction of the amplitude of density fluctuations
Comparison of the Impact of Ga-68-DOTATATE and F-18-FDG PET/CT on Clinical Management in Patients with Neuroendocrine Tumors
This study aimed to assess the clinical impact of 68Ga-DOTATATE and 18F-fluorodeoxyglucose
with respect to the management plan and to evaluate the prognostic value of both tracers.
Methods: A total of 104 patients (55 males, 49 females; median age 58 years, range 20–90) with
histopathologically proven neuroendocrine tumors (NETs) underwent both 68Ga-DOTATATE
and 18F-FDG PET/CT. Twenty-eight patients (26.9%) had poorly differentiated (PD) and 76
(73.1%), well-differentiated tumors. PET/CT results and SUVs were compared with prognostic
factors such as pathologic grading (G1, G2, G3), chromogranin A, and proliferation index
(Ki67).
Results: 68Ga-DOTATATE and 18F-FDG PET/CT findings were discordant in 65 (62.5%) and
concordant in 39 (37.5%) pts. PET/CT results changed the therapeutic plan in 84 (80.8%) pts. In
22 (21.1%) pts decision making was based on 18F-FDG findings, in 32 (30.8%) on findings with
both radiotracers, and in 50 (48.1%) on 68Ga-DOTATATE findings. The most frequent
management decision based on 18F-FDG was initiation of chemotherapy (10 pts, 47.6%). The
most common treatment decision due to 68Ga-DOTATATE was initiation of peptide receptor
radionuclide therapy (14 pts, 27.4%). In 11/28 (39.2%) pts with PD NETs the management
decision was based only on 18F-FDG results. For 68Ga-DOTATATE, SUVmax was higher for G1
and lower for G3 tumors (p=0.012). However, no significant differences in 18F-FDG-derived
SUVs were observed between different tumor grades (p=0.38). Mann-Whitney test showed
significant differences in 68Ga-DOTATATE SUVmax between tumors with Ki<5% and tumors
with Ki>5% (p=0.004), without significance differences in 18F-FDG SUVmax. Log-rank analysis
showed statistically significant differences in survival for patients with bone vs soft tissue or no
metastasis for both 18F-FDG (p=0.037) and 68Ga-DOTATATE (p=0.047). Overall survival was
found to decline rapidly with increasing histological grade (p=0.001), with estimated survival of
91 months for G1, 59 months for G2, and 48 months for G3.
Conclusion: 18F-FDG PET/CT had no clinical impact in G1 NETs and moderate impact in G2
NETs. However in PD NETs, 18F-FDG PET/CT plays a significant clinical role in combination
with 68Ga-DOTATATE. 68Ga DOTATATE SUVmax values relate to tumor grade and Ki67 index
and can be used prognostically
On the interaction between the island divertor heat fluxes, the scrape-off layer radial electric field and the edge turbulence in Wendelstein 7-X plasmas
A far-ultraviolet-driven photoevaporation flow observed in a protoplanetary disk.
Most low-mass stars form in stellar clusters that also contain massive stars, which are sources of far-ultraviolet (FUV) radiation. Theoretical models predict that this FUV radiation produces photodissociation regions (PDRs) on the surfaces of protoplanetary disks around low-mass stars, which affects planet formation within the disks. We report James Webb Space Telescope and Atacama Large Millimeter Array observations of a FUV-irradiated protoplanetary disk in the Orion Nebula. Emission lines are detected from the PDR; modeling their kinematics and excitation allowed us to constrain the physical conditions within the gas. We quantified the mass-loss rate induced by the FUV irradiation and found that it is sufficient to remove gas from the disk in less than a million years. This is rapid enough to affect giant planet formation in the disk
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