296 research outputs found
Infrared Study of Fullerene Planetary Nebulae
We present a study of 16 PNe where fullerenes have been detected in their
Spitzer spectra. This large sample of objects offers an unique opportunity to
test conditions of fullerene formation and survival under different metallicity
environments as we are analyzing five sources in our own Galaxy, four in the
LMC, and seven in the SMC. Among the 16 PNe under study, we present the first
detection of C60 (possibly also C70) fullerenes in the PN M 1-60 as well as of
the unusual 6.6, 9.8, and 20 um features (possible planar C24) in the PN K
3-54. Although selection effects in the original samples of PNe observed with
Spitzer may play a potentially significant role in the statistics, we find that
the detection rate of fullerenes in C-rich PNe increases with decreasing
metallicity (5% in the Galaxy, 20% in the LMC, and 44% in the SMC). CLOUDY
photoionization modeling matches the observed IR fluxes with central stars that
display a rather narrow range in effective temperature (30,000-45,000 K),
suggesting a common evolutionary status of the objects and similar fullerene
formation conditions. The observed C60 intensity ratios in the Galactic sources
confirm our previous finding in the MCs that the fullerene emission is not
excited by the UV radiation from the central star. CLOUDY models also show that
line- and wind-blanketed model atmospheres can explain many of the observed
[NeIII]/[NeII] ratios by photoionization suggesting that possibly the UV
radiation from the central star, and not shocks, are triggering the
decomposition of the circumstellar dust grains. With the data at hand, we
suggest that the most likely explanation for the formation of fullerenes and
graphene precursors in PNe is that these molecular species are built from the
photo-chemical processing of a carbonaceous compound with a mixture of aromatic
and aliphatic structures similar to that of HAC dust.Comment: Accepted for publication in ApJ (43 pages, 11 figures, and 4 tables).
Small changes to fit the proof-corrected article to be published in Ap
Active galactic nuclei synapses: X-ray versus optical classifications using artificial neural networks
(Abridged) Many classes of active galactic nuclei (AGN) have been defined
entirely throughout optical wavelengths while the X-ray spectra have been very
useful to investigate their inner regions. However, optical and X-ray results
show many discrepancies that have not been fully understood yet. The aim of
this paper is to study the "synapses" between the X-ray and optical
classifications.
For the first time, the new EFLUXER task allowed us to analyse broad band
X-ray spectra of emission line nuclei (ELN) without any prior spectral fitting
using artificial neural networks (ANNs). Our sample comprises 162 XMM-Newton/pn
spectra of 90 local ELN in the Palomar sample. It includes starbursts (SB),
transition objects (T2), LINERs (L1.8 and L2), and Seyferts (S1, S1.8, and S2).
The ANNs are 90% efficient at classifying the trained classes S1, S1.8, and
SB. The S1 and S1.8 classes show a wide range of S1- and S1.8-like components.
We suggest that this is related to a large degree of obscuration at X-rays. The
S1, S1.8, S2, L1.8, L2/T2/SB-AGN (SB with indications of AGN), and SB classes
have similar average X-ray spectra within each class, but these average spectra
can be distinguished from class to class. The S2 (L1.8) class is linked to the
S1.8 (S1) class with larger SB-like component than the S1.8 (S1) class. The L2,
T2, and SB-AGN classes conform a class in the X-rays similar to the S2 class
albeit with larger fractions of SB-like component. This SB-like component is
the contribution of the star-formation in the host galaxy, which is large when
the AGN is weak. An AGN-like component seems to be present in the vast majority
of the ELN, attending to the non-negligible fraction of S1-like or S1.8-like
component. This trained ANN could be used to infer optical properties from
X-ray spectra in surveys like eRosita.Comment: 15 pages, 7 figures, accepted for publication in A&A. Appendix B only
in the full version of the paper here:
https://dl.dropboxusercontent.com/u/3484086/AGNSynapsis_OGM_online.pd
Bicriteria food packaging process optimization in double-layered upright and diagonal multihead weighers
[EN] Double-layered multihead weighing machines contain twice the number of hoppers as present in a simple machine with the same number of heads, which enables additional objective optimization possibilities considering the increased number of combinations among hoppers. This research study deals with bicriteria optimization for double-layered upright and diagonal machines using brute force as the optimization criteria. One of the optimization objectives is related to the target weight; the target weight must be at least and as close as possible to the weight to pack. Furthermore, this study also aims to minimize the time for which a certain portion of a product remains in the hopper while waiting to be selected for package formation. This time is known as priority and is measured based on the number of iterations or the number of packages produced by the machine while the hopper waits to be discharged. For these purposes, Different strategies were tested for both machines, which simultaneously optimize the target weight and the priority of the hoppers, showing the reduction of the extraction of the process in addition to reducing the costs of excess product and its reprocessing.We express our gratitude for the support from Universidad Simon Bolivar, Colombia, and Universitat Politecnica de Valencia.Garcia-Jimenez, R.; García-Díaz, JC.; Pulido-Rojano, AD. (2023). Bicriteria food packaging process optimization in double-layered upright and diagonal multihead weighers. Journal of Computational and Applied Mathematics. 428:1-10. https://doi.org/10.1016/j.cam.2023.11516811042
Packaging Process Optimization in MultiheadWeighers with Double-Layered Upright and Diagonal Systems
[EN] In multihead weighers, packaging processes seek to find the best combination of passage hoppers whose product content provides a total package weight as close as possible to its (nominal) label weight. The weighing hoppers arranged in these machines dispense the product quantity that each package contains through computer algorithms designed and executed for this purpose. For its part, in the packaging process for double-layered multihead weighers, all hoppers are arranged in two levels. The first layer comprises a group of weighing hoppers, and the second comprises a set of booster hoppers placed uprightly or diagonally to each weighing hopper based on design of the machine. In both processes, the initial machine configuration is the same; however, the hopper selection algorithm works differently. This paper proposes a new packaging process optimization algorithm for double-layer upright and diagonal machines, wherein the hopper subset combined has previously been defined, and the packaging weight is expressed as actual values. As part of its validation, product filling strategies were implemented for weighing hoppers to assess the algorithm in different scenarios. Results from the process performance metrics prove that the new algorithm improves processes by reducing variability. In addition, results reveal that some machine configurations were also able to improve their operation.We express our gratitude for the support from Universidad Simon Bolivar, and Universitat Politecnica de Valencia.Garcia-Jimenez, R.; García-Díaz, JC.; Pulido-Rojano, ADJ. (2021). Packaging Process Optimization in MultiheadWeighers with
Double-Layered Upright and Diagonal Systems. Mathematics. 9(9):1-20. https://doi.org/10.3390/math9091039S1209
The formation of fullerenes: clues from new C60, C70, and (possible) planar C24 detections in Magellanic Cloud Planetary Nebulae
We present ten new Spitzer detections of fullerenes in Magellanic Cloud
Planetary Nebulae, including the first extragalactic detections of the C70
molecule. These new fullerene detections together with the most recent
laboratory data permit us to report an accurate determination of the C60 and
C70 abundances in space. Also, we report evidence for the possible detection of
planar C24 in some of our fullerene sources, as indicated by the detection of
very unusual emission features coincident with the strongest transitions of
this molecule at ~6.6, 9.8, and 20 um. The infrared spectra display a complex
mix of aliphatic and aromatic species such as hydrogenated amorphous carbon
grains (HACs), PAH clusters, fullerenes, and small dehydrogenated carbon
clusters (possible planar C24). The coexistence of such a variety of molecular
species supports the idea that fullerenes are formed from the decomposition of
HACs. We propose that fullerenes are formed from the destruction of HACs,
possibly as a consequence of shocks driven by the fast stellar winds, which can
sometimes be very strong in transition sources and young PNe. This is supported
by the fact that many of our fullerene-detected PNe show altered [NeIII]/[NeII]
ratios suggestive of shocks as well as P-Cygni profiles in their UV lines
indicative of recently enhanced mass loss.Comment: Accepted for publication in The Astrophysical Journal Letters (16
pages, 2 Tables and 3 figures
Revealing the mid-infrared emission structure of IRAS 16594-4656 and IRAS 07027-7934
TIMMI2 diffraction-limited mid-infrared images of a multipolar
proto-planetary nebula IRAS 16594-4656 and a young [WC] elliptical planetary
nebula IRAS 07027-7934 are presented. Their dust shells are for the first time
resolved (only marginally in the case of IRAS 07027-7934) by applying the
Lucy-Richardson deconvolution algorithm to the data, taken under exceptionally
good seeing conditions (<0.5"). IRAS 16594-4656 exhibits a two-peaked
morphology at 8.6, 11.5 and 11.7 microns which is mainly attributed to emission
from PAHs. Our observations suggest that the central star is surrounded by a
toroidal structure observed edge-on with a radius of 0.4" (~640 AU at an
assumed distance of 1.6 kpc) with its polar axis at P.A.~80 degrees, coincident
with the orientation defined by only one of the bipolar outflows identified in
the HST optical images. We suggest that the material expelled from the central
source is currently being collimated in this direction and that the multiple
outflow formation has not been coeval. IRAS 07027-7934 shows a bright,
marginally extended emission (FWHM=0.3") in the mid-infrared with a slightly
elongated shape along the N-S direction, consistent with the morphology
detected by HST in the near-infrared. The mid-infrared emission is interpreted
as the result of the combined contribution of small, highly ionized PAHs and
relatively hot dust continuum. We propose that IRAS 07027-7934 may have
recently experienced a thermal pulse (likely at the end of the AGB) which has
produced a radical change in the chemistry of its central star.Comment: 35 pages, 8 figures (figures 1, 2, 4 and 6 are in low resolution)
accepted for publication in Ap
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