114 research outputs found
Thermoplasmatales and Methanogens: Potential Association with the Crenarchaeol Production in Chinese Soils
Crenarchaeol is a unique isoprenoid glycerol dibiphytanyl glycerol tetraether (iGDGT) lipid, which is only identified in cultures of ammonia-oxidizing Thaumarchaeota. However, the taxonomic origins of crenarchaeol have been debated recently. The archaeal populations, other than Thaumarchaeota, may have associations with the production of crenarchaeol in ecosystems characterized by non-thaumarchaeotal microorganisms. To this end, we investigated 47 surface soils from upland and wetland soils and rice fields and another three surface sediments from river banks. The goal was to examine the archaeal community compositions in comparison with patterns of iGDGTs in four fractional forms (intact polar-, core-, monoglycosidic- and diglycosidic-lipid fractions) along gradients of environments. The DistLM analysis identified that Group I.1b Thaumarchaeota were mainly responsible for changes in crenarchaeol in the overall soil samples; however, Thermoplasmatales may also contribute to it. This is further supported by the comparison of crenarchaeol between samples characterized by methanogens, Thermoplasmatales or Group I.1b Thaumarchaeota, which suggests that the former two may contribute to the crenarchaeol pool. Last, when samples containing enhanced abundance of Thermoplasmatales and methanogens were considered, crenarchaeol was observed to correlate positively with Thermoplasmatales and archaeol, respectively. Collectively, our data suggest that the crenarchaeol production is mainly derived from Thaumarchaeota and partly associated with uncultured representatives of Thermoplasmatales and archaeol-producing methanogens in soil environments that may be in favor of their growth. Our finding supports the notion that Thaumarchaeota may not be the sole source of crenarchaeol in the natural environment, which may have implication for the evolution of lipid synthesis among different types of archaea
Robust Facial Expression Recognition with Convolutional Visual Transformers
Facial Expression Recognition (FER) in the wild is extremely challenging due
to occlusions, variant head poses, face deformation and motion blur under
unconstrained conditions. Although substantial progresses have been made in
automatic FER in the past few decades, previous studies are mainly designed for
lab-controlled FER. Real-world occlusions, variant head poses and other issues
definitely increase the difficulty of FER on account of these
information-deficient regions and complex backgrounds. Different from previous
pure CNNs based methods, we argue that it is feasible and practical to
translate facial images into sequences of visual words and perform expression
recognition from a global perspective. Therefore, we propose Convolutional
Visual Transformers to tackle FER in the wild by two main steps. First, we
propose an attentional selective fusion (ASF) for leveraging the feature maps
generated by two-branch CNNs. The ASF captures discriminative information by
fusing multiple features with global-local attention. The fused feature maps
are then flattened and projected into sequences of visual words. Second,
inspired by the success of Transformers in natural language processing, we
propose to model relationships between these visual words with global
self-attention. The proposed method are evaluated on three public in-the-wild
facial expression datasets (RAF-DB, FERPlus and AffectNet). Under the same
settings, extensive experiments demonstrate that our method shows superior
performance over other methods, setting new state of the art on RAF-DB with
88.14%, FERPlus with 88.81% and AffectNet with 61.85%. We also conduct
cross-dataset evaluation on CK+ show the generalization capability of the
proposed method
Thermoplasmatales and Methanogens: Potential Association with the Crenarchaeol Production in Chinese Soils
Crenarchaeol is a unique isoprenoid glycerol dibiphytanyl glycerol tetraether (iGDGT) lipid, which is only identified in cultures of ammonia-oxidizing Thaumarchaeota. However, the taxonomic origins of crenarchaeol have been debated recently. The archaeal populations, other than Thaumarchaeota, may have associations with the production of crenarchaeol in ecosystems characterized by non-thaumarchaeotal microorganisms. To this end, we investigated 47 surface soils from upland and wetland soils and rice fields and another three surface sediments from river banks. The goal was to examine the archaeal community compositions in comparison with patterns of iGDGTs in four fractional forms (intact polar-, core-, monoglycosidic- and diglycosidic-lipid fractions) along gradients of environments. The DistLM analysis identified that Group I.1b Thaumarchaeota were mainly responsible for changes in crenarchaeol in the overall soil samples; however, Thermoplasmatales may also contribute to it. This is further supported by the comparison of crenarchaeol between samples characterized by methanogens, Thermoplasmatales or Group I.1b Thaumarchaeota, which suggests that the former two may contribute to the crenarchaeol pool. Last, when samples containing enhanced abundance of Thermoplasmatales and methanogens were considered, crenarchaeol was observed to correlate positively with Thermoplasmatales and archaeol, respectively. Collectively, our data suggest that the crenarchaeol production is mainly derived from Thaumarchaeota and partly associated with uncultured representatives of Thermoplasmatales and archaeol-producing methanogens in soil environments that may be in favor of their growth. Our finding supports the notion that Thaumarchaeota may not be the sole source of crenarchaeol in the natural environment, which may have implication for the evolution of lipid synthesis among different types of archaea
Exploring Reionization-Era Quasars IV: Discovery of Six New Quasars with DES, VHS and unWISE Photometry
This is the fourth paper in a series of publications aiming at discovering
quasars at the epoch of reionization. In this paper, we expand our search for
quasars to the footprint of the Dark Energy Survey (DES) Data Release
One (DR1), covering deg of new area. We select quasar
candidates using deep optical, near-infrared (near-IR) and mid-IR photometric
data from the DES DR1, the VISTA Hemisphere Survey (VHS), the VISTA Kilo-degree
Infrared Galaxy (VIKING) survey, the UKIRT InfraRed Deep Sky Surveys -- Large
Area Survey (ULAS) and the unblurred coadds from the Wide-field Infrared Survey
Explore () images (unWISE). The inclusion of DES and unWISE photometry
allows the search to reach 1 magnitude fainter, comparing to our quasar survey in the northern sky (Wang et al. 2018). We report
the initial discovery and spectroscopic confirmation of six new luminous
quasars at , including an object at , the fourth quasar yet
known at , from a small fraction of candidates observed thus far. Based on
the recent measurement of quasar luminosity function using the
quasar sample from our survey in the northern sky, we estimate that there will
be 55 quasars at at in the full DES
footprint.Comment: 8 pages, 3 figures, submitted to A
An Escaping Outflow in a Galaxy with an Intermediate-mass Black Hole
While in massive galaxies active galactic nuclei (AGN) feedback plays an
important role, the role of AGN feedback is still under debate in dwarf
galaxies. With well spatially resolved data obtained from the Multi-Unit
Spectroscopic Explorer (MUSE), we identify a spatially extended () and fast () AGN-driven outflow in a
dwarf galaxy: SDSS J022849.51-090153.8 with that host an intermediate-mass black hole of and . Through the
measurement of the rotation curve, we estimate the escape velocity of the halo
and the ratio of the outflow velocity to the halo escape velocity to be
, indicating that the outflow is capable of escaping not only the
galaxy disk but the halo. The outflow size of our AGN is found to be larger
than AGN in massive galaxies at the given AGN [O III] luminosity, while the
size of the photo-ionized narrow-line region is comparable. These results
suggest the important role of AGN feedback through outflows in dwarf galaxies
when their central intermediate-mass black holes accrete at high-Eddington
ratios.Comment: 12 pages, 2 tables, 12 figures, accepted for publication in MNRA
Chandra Detection of Three X-ray Bright Quasars at z>5
We report Chandra detection of three UV bright radio quiet quasars at
. We have collected a sufficient number of photons to extract an
X-ray spectrum of each quasar to measure their basic X-ray properties, such as
the X-ray flux, power law photon index (), and optical-to-X-ray
spectral slope (). J074749+115352 at is the X-ray
brightest radio-quiet quasar at . It may have a short timescale variation
(on a timescale of in the observer's frame, or
in the rest frame) which is however largely embedded in the statistical noise.
We extract phase folded spectra of this quasar. There are two distinguishable
states: a "high soft" state with an average X-ray flux times of the
"low hard" state, and a significantly steeper X-ray spectral slope
( vs ). We also compare the
three quasars detected in this paper to other quasar samples. We find that
J074749+115352, with a SMBH mass of and an Eddington ratio of , is extraordinarily X-ray bright. It has an average
and a 2-10 keV bolometric correction factor of
, both significantly depart from some
well defined scaling relations. We compare of the three quasars to
other samples at different redshifts, and do not find any significant redshift
evolution based on the limited sample of quasars with reliable
measurements of the X-ray spectral properties.Comment: 12 pages, 5 figures, 2 tables, accepted for publication by Ap
Ultra-luminous quasars at redshift from SkyMapper
The most luminous quasars at high redshift harbour the fastest-growing and
most massive black holes in the early Universe. They are exceedingly rare and
hard to find. Here, we present our search for the most luminous quasars in the
redshift range from to using data from SkyMapper, Gaia and WISE. We
use colours to select likely high-redshift quasars and reduce the stellar
contamination of the candidate set with parallax and proper motion data. In
12,500~deg of Southern sky, we find 92 candidates brighter than
. Spectroscopic follow-up has revealed 21 quasars at (16 of
which are within ), as well as several red quasars, BAL quasars and
objects with unusual spectra, which we tentatively label OFeLoBALQSOs at
redshifts of to . This work lifts the number of known bright
quasars in the Southern hemisphere from 10 to 26 and brings the
total number of quasars known at and to 42.Comment: Submitted to MNRAS, 10 page
Quantifying the Escape of Ly α at z ≈ 5–6: A Census of Ly α Escape Fraction with H α -emitting Galaxies Spectroscopically Confirmed by JWST and VLT/MUSE
The James Webb Space Telescope provides an unprecedented opportunity for unbiased surveys of Hα-emitting galaxies at z > 4 with the NIRCam's wide-field slitless spectroscopy (WFSS). In this work, we present a census of Lyα escape fraction (f esc,Lyα ) of 165 star-forming galaxies at z = 4.9–6.3, utilizing their Hα emission directly measured from FRESCO NIRCam/WFSS data. We search for Lyα emission of each Hα-emitting galaxy in the Very Large Telescope/MUSE data. The overall f esc,Lyα measured by stacking is 0.090 ± 0.006. We find that f esc,Lyα displays a strong dependence on the observed UV slope (β obs) and E(B − V), such that the bluest galaxies (β obs ∼ −2.5) have the largest escape fractions (f esc,Lyα ≈ 0.6), indicative of the crucial role of dust and gas in modulating the escape of Lyα photons. f esc,Lyα is less well related to other parameters, including the UV luminosity and stellar mass, and the variation in f esc,Lyα with them can be explained by their underlying coupling with E(B − V) or β obs. Our results suggest a tentative decline in f esc,Lyα at z ≳ 5, implying increasing intergalactic medium attenuation toward higher redshift. Furthermore, the dependence of f esc,Lyα on β obs is proportional to that of the ionizing photon escape fraction (f esc,LyC), indicating that the escape of Lyα and ionizing photon may be regulated by similar physical processes. With f esc,Lyα as a proxy to f esc,LyC, we infer that UV-faint (M UV > −16) galaxies contribute >70% of the total ionizing emissivity at z = 5–6. If these relations hold during the epoch of reionization, UV-faint galaxies can contribute the majority of UV photon budget to reionize the Universe
- …