429 research outputs found
Latent Stochastic Differential Equations for Modeling Quasar Variability and Inferring Black Hole Properties
Active galactic nuclei (AGN) are believed to be powered by the accretion of
matter around supermassive black holes at the centers of galaxies. The
variability of an AGN's brightness over time can reveal important information
about the physical properties of the underlying black hole. The temporal
variability is believed to follow a stochastic process, often represented as a
damped random walk described by a stochastic differential equation (SDE). With
upcoming wide-field surveys set to observe 100 million AGN in multiple bandpass
filters, there is a need for efficient and automated modeling techniques that
can handle the large volume of data. Latent SDEs are well-suited for modeling
AGN time series data, as they can explicitly capture the underlying stochastic
dynamics. In this work, we modify latent SDEs to jointly reconstruct the
unobserved portions of multivariate AGN light curves and infer their physical
properties such as the black hole mass. Our model is trained on a realistic
physics-based simulation of ten-year AGN light curves, and we demonstrate its
ability to fit AGN light curves even in the presence of long seasonal gaps and
irregular sampling across different bands, outperforming a multi-output
Gaussian process regression baseline.Comment: 10 pages, 5 figures, accepted at the ICLR 2023 Workshop on Physics
for Machine Learnin
Exploring the disk-jet connection from the properties of narrow line regions in powerful young radio-loud AGNs
We investigate the optical emission-line flux ratios of narrow-line regions,
in order to determine whether the formation of AGN jets requires specific
accretion conditions. We find that bright compact radio galaxies, which are
powerful radio galaxies in the early stage of the jet activity, exhibit
systematically larger flux ratios of [O{\sc i}]6300/[O{\sc
iii}]5007 and smaller flux ratios of [O{\sc iii}]5007/[O{\sc
iii}]4363 than radio-quiet (RQ) Seyfert 2 galaxies. Comparing the
observed line ratios with photoionization models, it is found that the
difference in the flux ratio of low- to high-ionization lines (e.g., [O{\sc
i}]6300/[O{\sc iii}]5007) can be well understood by the
difference in the spectral energy distribution (SED) of ionizing sources.
Powerful young radio-loud (YRL) AGNs favor SED without a strong big blue bump,
i.e., a radiatively inefficient accretion flow (RIAF), while RQ AGNs are
consistent with the models adopting SED with a strong big blue bump, i.e., a
geometrically thin, optically thick disk. These findings imply that the
formation of powerful AGN jets requires the accretion disk with harder ionizing
SED (i.e., a RIAF). We discuss the obscuring structure of YRL AGNs as a
plausible origin of the difference in flux ratios of [O{\sc iii}]5007/[O{\sc iii}]4363.Comment: 17 pages, 8 figures, accepted for publication in Ap
Constructing Impactful Machine Learning Research for Astronomy: Best Practices for Researchers and Reviewers
Machine learning has rapidly become a tool of choice for the astronomical
community. It is being applied across a wide range of wavelengths and problems,
from the classification of transients to neural network emulators of
cosmological simulations, and is shifting paradigms about how we generate and
report scientific results. At the same time, this class of method comes with
its own set of best practices, challenges, and drawbacks, which, at present,
are often reported on incompletely in the astrophysical literature. With this
paper, we aim to provide a primer to the astronomical community, including
authors, reviewers, and editors, on how to implement machine learning models
and report their results in a way that ensures the accuracy of the results,
reproducibility of the findings, and usefulness of the method.Comment: 14 pages, 3 figures; submitted to the Bulletin of the American
Astronomical Societ
Diagnostic and Therapeutic Problems of Pulmonary Tuberculosis in Elderly Patients
To identify differences in the clinical, radiologic, and microbiologic features of pulmonary tuberculosis (TB) in the young (<64 yr) and elderly (≥65 yr), we performed a retrospective analysis of the medical charts and chest radiographs of 207 young and 119 elderly pulmonary TB patients. Hemoptysis and a febrile sense were more frequent in the young, whereas weakness, dyspnea, anorexia, and mental change were more frequent in the elderly. Elderly patients showed higher frequencies of cardiovascular and chronic lung diseases, whereas the young showed a higher proportion of underlying liver disease. In addition, chest radiography showed a significantly higher frequency of mid or lower lung involvement by TB lesions in the elderly (10.6% vs. 22.7%, p<0.05). Lesions were frequently misdiagnosed as pneumonia or lung cancer in the elderly. However, there was no difference between these two groups in terms of sputum acid-fast bacilli positivity. The elderly showed a higher frequency of adverse drug reactions (18.5% vs. 40.7%, p<0.05), and higher TB-related mortality (1.3% vs. 11.1%, p<0.05). In conclusion this study showed that young and elderly pulmonary TB patients have similar microbiologic features; however, the elderly showed higher frequencies of atypical clinical and radiologic presentations, adverse drug reactions, and higher TB-related mortality
Climate change may drive cave spiders to extinction
Subterranean ecosystems present ideal opportunities to study mechanisms underlying responses to changes in climate because species within them are often adapted to a largely constant temperature. We have characterized the thermal conditions of caves in the Western Alps, and relate these hypogean climate data to the occurrence of Troglohyphantes troglobiontic spiders (Araneae, Linyphiidae). Our data indicate that present distributions reflect Pleistocence glaciation events and also point to specific responses as a consequence of changes in temperature. Constant temperatures recorded inside caves provide an approximation of the mean annual temperature outside, thus we extend the results to a regional scale. Ecological niche modeling is used to predict habitat suitability both in the Pleistocene and under future global warming scenarios. These analyses point toward a future decline in habitat suitability for subterranean spiders and the potential extinction of the most restricted endemic species
Differential Effects of Concomitant Use of Vitamins C and E on Trophoblast Apoptosis and Autophagy between Normoxia and Hypoxia-Reoxygenation
Concomitant supplementation of vitamins C and E during pregnancy has been reportedly associated with low birth weight, the premature rupture of membranes and fetal loss or perinatal death in women at risk for preeclampsia; however, the cause is unknown. We surmise that hypoxia-reoxygenation (HR) within the intervillous space due to abnormal placentation is the mechanism and hypothesize that concomitant administration of aforementioned vitamin antioxidants detrimentally affects trophoblast cells during HR.Using villous explants, concomitant administration of 50 microM of vitamins C and E was observed to reduce apoptotic and autophagic changes in the trophoblast layer at normoxia (8% oxygen) but to cause more prominent apoptosis and autophagy during HR. Furthermore, increased levels of Bcl-2 and Bcl-xL in association with a decrease in the autophagy-related protein LC3-II were noted in cytotrophoblastic cells treated with vitamins C and E under standard culture conditions. In contrast, vitamin treatment decreased Bcl-2 and Bcl-xL as well as increased mitochondrial Bak and cytosolic LC3-II in cytotrophoblasts subjected to HR.Our results indicate that concomitant administration of vitamins C and E has differential effects on the changes of apoptosis, autophagy and the expression of Bcl-2 family of proteins in the trophoblasts between normoxia and HR. These changes may probably lead to the impairment of placental function and suboptimal growth of the fetus
Galaxy pairs in the Sloan Digital Sky Survey - IV: Interactions trigger AGN
Galaxy-galaxy interactions are predicted to cause gas inflows leading to
enhanced nuclear star formation. In this paper we test the further prediction
that the gas inflows lead to enhanced accretion onto the central supermassive
black hole, triggering activity in the nucleus. Based on a sample of 11,060
SDSS galaxies with a close companion (rp < 80 kpc, Delta V < 200 km/s), we
classify AGN based either on emission line ratios or on spectral classification
as a quasar. The AGN fraction in the close pairs sample is compared to a
control sample of 110,600 mass- and redshift-matched control galaxies with no
nearby companion. We find a clear increase in the AGN fraction in close pairs
of galaxies with projected separations < 40 kpc by up to a factor of 2.5
relative to the control sample (although the enhancement depends on the chosen
S/N cut of the sample). The increase in AGN fraction is strongest in equal mass
galaxy pairings, and weakest in the lower mass component of an unequal mass
pairing. The increased AGN fraction at small separations is accompanied by an
enhancement in the number of `composite' galaxies whose spectra are the result
of photoionization by both AGN and stars. Our results indicate that AGN
activity occurs (at least in some cases) well before final coalescence and
concurrently with ongoing star formation. Finally, we find a marked increase at
small projected separations of the fraction of pairs in which BOTH galaxies
harbour AGN. We demonstrate that the fraction of double AGN exceeds the
expected random fraction, indicating that some pairs undergo correlated nuclear
activity. Taken together with complimentary studies, we favour an
interpretation where interactions trigger AGN, but are not the only cause of
nuclear activity.Comment: Accepted for publication in MNRA
Detection methods predict differences in biology and survival in breast cancer patients
BackgroundThe aim of this study was to measure the biological characteristics involved in tumorigenesis and the progression of breast cancer in symptomatic and screen-detected carcinomas to identify possible differences.MethodsFor this purpose, we evaluated clinical-pathological parameters and proliferative and apoptotic activities in a series of 130 symptomatic and 161 screen-detected tumors.ResultsAfter adjustment for the smaller size of the screen-detected carcinomas compared with symptomatic cancers, those detected in the screening program presented longer disease-free survival (RR = 0.43, CI = 0.19-0.96) and had high estrogen and progesterone receptor concentrations more often than did symptomatic cancers (OR = 3.38, CI = 1.72-6.63 and OR = 3.44, CI = 1.94-6.10, respectively). Furthermore, the expression of bcl-2, a marker of good prognosis in breast cancer, was higher and HER2/neu expression was lower in screen-detected cancers than in symptomatic cancers (OR = 1.77, CI = 1.01-3.23 and OR = 0.64, CI = 0.40-0.98, respectively). However, when comparing prevalent vs incident screen-detected carcinomas, prevalent tumors were larger (OR = 2.84, CI = 1.05-7.69), were less likely to be HER2/neu positive (OR = 0.22, CI = 0.08-0.61) and presented lower Ki67 expression (OR = 0.36, CI = 0.17-0.77). In addition, incident tumors presented a shorter survival time than did prevalent ones (RR = 4.88, CI = 1.12-21.19).ConclusionsIncident carcinomas include a variety of screen-detected carcinomas that exhibit differences in biology and prognosis relative to prevalent carcinomas. The detection method is important and should be taken into account when making therapy decisions
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