22,315 research outputs found
What makes red quasars red? Observational evidence for dust extinction from line ratio analysis
Red quasars are very red in the optical through near-infrared (NIR)
wavelengths, which is possibly due to dust extinction in their host galaxies as
expected in a scenario in which red quasars are an intermediate population
between merger-driven star-forming galaxies and unobscured type 1 quasars.
However, alternative mechanisms also exist to explain their red colors: (i) an
intrinsically red continuum; (ii) an unusual high covering factor of the hot
dust component, that is, , where
the is the luminosity from the hot dust component and the
is the bolometric luminosity; and (iii) a moderate viewing
angle. In order to investigate why red quasars are red, we studied optical and
NIR spectra of 20 red quasars at 0.3 and 0.7, where the usage of the NIR
spectra allowed us to look into red quasar properties in ways that are little
affected by dust extinction. The Paschen to Balmer line ratios were derived for
13 red quasars and the values were found to be 10 times higher than
unobscured type 1 quasars, suggesting a heavy dust extinction with
mag. Furthermore, the Paschen to Balmer line ratios of red quasars are
difficult to explain with plausible physical conditions without adopting the
concept of the dust extinction. The of red quasars are similar
to, or marginally higher than, those of unobscured type 1 quasars. The
Eddington ratios, computed for 19 out of 20 red quasars, are higher than those
of unobscured type 1 quasars (by factors of ), and hence the moderate
viewing angle scenario is disfavored. Consequently, these results strongly
suggest the dust extinction that is connected to an enhanced nuclear activity
as the origin of the red color of red quasars, which is consistent with the
merger-driven quasar evolution scenario.Comment: 14 pages, 13 figures, Accepted for publication in A&
A monolithic and flexible fluoropolymer film microreactor for organic synthesis applications
A photocurable and viscous fluoropolymer with chemical stability is a highly desirable material for fabrication of microchemical devices. Lack of a reliable fabrication method, however, limits actual applications for organic reactions. Herein, we report fabrication of a monolithic and flexible fluoropolymer film microreactor and its use as a new microfluidic platform. The fabrication involves facile soft lithography techniques that enable partial curing of thin laminates, which can be readily bonded by conformal contact without any external forces. We demonstrate fabrication of various functional channels (similar to 300 mu m thick) such as those embedded with either a herringbone micromixer pattern or a droplet generator. Organic reactions under strongly acidic and basic conditions can be carried out in this film microreactor even at elevated temperature with excellent reproducibility. In particular, the transparent film microreactor with good deformability could be wrapped around a light-emitting lamp for close contact with the light source for efficient photochemical reactions with visible light, which demonstrates easy integration with optical components for functional miniaturized systems.open1112Ysciescopu
Prediction of monthly Arctic sea ice concentrations using satellite and reanalysis data based on convolutional neural networks
Changes in Arctic sea ice affect atmospheric circulation, ocean current, and polar ecosystems. There have been unprecedented decreases in the amount of Arctic sea ice due to global warming. In this study, a novel 1-month sea ice concentration (SIC) prediction model is proposed, with eight predictors using a deep-learning approach, convolutional neural networks (CNNs). This monthly SIC prediction model based on CNNs is shown to perform better predictions (mean absolute error - MAE - of 2.28 %, anomaly correlation coefficient - ACC - of 0.98, root-mean-square error - RMSE - of 5.76 %, normalized RMSE - nRMSE - of 16.15 %, and NSE - Nash-Sutcliffe efficiency - of 0.97) than a random-forest-based (RF-based) model (MAE of 2.45 %, ACC of 0.98, RMSE of 6.61 %, nRMSE of 18.64 %, and NSE of 0.96) and the persistence model based on the monthly trend (MAE of 4.31 %, ACC of 0.95, RMSE of 10.54 %, nRMSE of 29.17 %, and NSE of 0.89) through hindcast validations. The spatio-temporal analysis also confirmed the superiority of the CNN model. The CNN model showed good SIC prediction results in extreme cases that recorded unforeseen sea ice plummets in 2007 and 2012 with RMSEs of less than 5.0 %. This study also examined the importance of the input variables through a sensitivity analysis. In both the CNN and RF models, the variables of past SICs were identified as the most sensitive factor in predicting SICs. For both models, the SIC-related variables generally contributed more to predict SICs over ice-covered areas, while other meteorological and oceanographic variables were more sensitive to the prediction of SICs in marginal ice zones. The proposed 1-month SIC prediction model provides valuable information which can be used in various applications, such as Arctic shipping-route planning, management of the fishing industry, and long-term sea ice forecasting and dynamics
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