Abstract
We present the localization and host galaxies of one repeating and two apparently nonrepeating fast radio bursts (FRBs). FRB 20180301A was detected and localized with the Karl G. Jansky Very ...Large Array to a star-forming galaxy at
z
= 0.3304. FRB20191228A and FRB20200906A were detected and localized by the Australian Square Kilometre Array Pathfinder to host galaxies at
z
= 0.2430 and
z
= 0.3688, respectively. We combine these with 13 other well-localized FRBs in the literature, and analyze the host galaxy properties. We find no significant differences in the host properties of repeating and apparently nonrepeating FRBs. FRB hosts are moderately star forming, with masses slightly offset from the star-forming main sequence. Star formation and low-ionization nuclear emission-line region emission are major sources of ionization in FRB host galaxies, with the former dominant in repeating FRB hosts. FRB hosts do not track stellar mass and star formation as seen in field galaxies (more than 95% confidence). FRBs are rare in massive red galaxies, suggesting that progenitor formation channels are not solely dominated by delayed channels which lag star formation by gigayears. The global properties of FRB hosts are indistinguishable from core-collapse supernovae and short gamma-ray bursts hosts, and the spatial offset (from galaxy centers) of FRBs is mostly inconsistent with that of the Galactic neutron star population (95% confidence). The spatial offsets of FRBs (normalized to the galaxy effective radius) also differ from those of globular clusters in late- and early-type galaxies with 95% confidence.
Nanotubular shaped α-MnO2/graphene oxide nanocomposites were synthesized via a simple, cost and time efficient hydrothermal method. The growth of hollow structured MnO2 nanotubes preferentially ...occurred along the 001 direction as evidenced from the morphological and structural characterizations. The tunnels of α-MnO2 nanotubes easily accommodated the molecular oxygen and exhibited excellent catalytic activity towards the oxygen reduction reaction over the rod structure and was further enhanced with the effective carbon support graphene oxide. The MnO2 nanotubes/graphene oxide nanocomposite modified electrode exhibited a maximum power density of 3359 mW m(-2) which is 7.8 fold higher than that of unmodified electrode and comparable with the Pt/C modified electrode. The microbial fuel cell equipped with MnO2 nanotubes/graphene oxide nanocomposite modified cathode exhibited quick start up and excellent durability over the studied electrodes and is attributed to the high surface area and number of active sites. These findings not only provide the fundamental studies on carbon supported low-dimensional transition-metal oxides but also open up the new possibilities of their applications in green energy devices.
We study the physical properties of a homogeneous sample of 157 optically thick absorption line systems at redshifts ~1.8-4.4, selected from a high-dispersion spectroscopic survey of Lyman limit ...systems (LLSs). By means of multiple ionization models and Bayesian techniques, we derive the posterior probability distribution functions for the density, metallicity, temperature and dust content of the absorbing gas. We find that z > 2 LLSs are highly ionized with ionization parameters between -3 ... log U ... -2, depending on the H I column density. LLSs are characterized by low temperatures (T < 5 x 10... K) and reside in dust-poor environments. Between z ~ 2.5-3.5, ~80 per cent of the LLSs have physical densities between n... ~ 10... -10... cm... for the assumed UV background, but we caution that a degeneracy between the ionization parameter and the intensity of the radiation field prevents robust inference on the density and sizes of LLSs. Conversely, metallicity estimates are less sensitive to the assumptions behind ionization corrections. LLSs at z > 2 are characterized by a broad unimodal distribution over > 4 orders of magnitude, with a peak at log Z/Z... ~ -2. LLSs are metal poor, significantly less enriched than DLAs, with ~70 per cent of the metallicity PDF below log Z/Z... less than or equal to -1.5. The median metallicity of super LLSs with log... greater than or equal to 19 rapidly evolves with redshift, with a 10-fold increase between z ~ 2.1-3.6 (~1.5 Gyr). Based on this sample, we find that LLSs at z = 2.5-3.5 account for ~15 per cent of all the metals produced by UV-selected galaxies. The implications for theories of cold gas accretion and metal ejection from galaxies are also discussed. (ProQuest: ... denotes formulae/symbols omitted.)
Chronic inflammation is often associated with the development of tissue fibrosis, but how mesenchymal cell responses dictate pathological fibrosis versus resolution and healing remains unclear. ...Defining stromal heterogeneity and identifying molecular circuits driving extracellular matrix deposition and remodeling stands to illuminate the relationship between inflammation, fibrosis, and healing. We performed single-cell RNA-sequencing of colon-derived stromal cells and identified distinct classes of fibroblasts with gene signatures that are differentially regulated by chronic inflammation, including IL-11-producing inflammatory fibroblasts. We further identify a transcriptional program associated with trans-differentiation of mucosa-associated fibroblasts and define a functional gene signature associated with matrix deposition and remodeling in the inflamed colon. Our analysis supports a critical role for the metalloprotease Adamdec1 at the interface between tissue remodeling and healing during colitis, demonstrating its requirement for colon epithelial integrity. These findings provide mechanistic insight into how inflammation perturbs stromal cell behaviors to drive fibroblastic responses controlling mucosal matrix remodeling and healing.
We measure the effective optical depth of He II Lyalpha absorption tau sub(eff,HeII) at 2.3 < z< 3.5 in 17 UV-transmitting quasars observed with UV spectrographs on the Hubble Space Telescope. The ...median tau sub(eff,HeII) values increase gradually from 1.95 at z= 2.7 to 5.17 at z= 3.4, but with a strong sightline-to-sightline variance. Many Asymptotically = to35 comoving Mpc regions of the z> 3 intergalactic medium (IGM) remain transmissive (tau sub(eff,HeII)< 4), and the gradual trend with redshift appears consistent with density evolution of a fully reionized IGM. These modest optical depths imply average He II fractions of x sub(eff,HeII)< 0.01 and He II ionizing photon mean free paths of Asymptotically = to50 comoving Mpc at zAsymptotically = to 3.4, thus requiring that a substantial volume of the helium in the universe was already doubly ionized at early times; this stands in conflict with current models of He II reionization driven by luminous quasars. Along 10 sightlines we measure the coeval H I Lyalpha effective optical depths, allowing us to study the density dependence of tau sub(eff,HeII) at z~ 3. We establish that the dependence of tau sub(eff,HeII) on increasing tau sub(eff,HeI) is significantly shallower than expected from simple models of an IGM reionized in He ii. This requires higher He ii photoionization rates in overdense regions or underdense regions being not in photoionization equilibrium. Moreover, there are very large fluctuations in tau sub(eff,HeII) at all tau sub(eff,HeI) which greatly exceed the expectations from these simple models. These data present a distinct challenge to scenarios of He II reionization-an IGM where He ii appears to be predominantly ionized at zAsymptotically = to 3.4, and with a radiation field strength that may be correlated with the density field, but exhibits large fluctuations at all densities.
In the current cosmological model, only the three lightest elements were created in the first few minutes after the Big Bang; all other elements were produced later in stars. To date, however, heavy ...elements have been observed in all astro physical environments. We report the detection of two gas clouds with no discernible elements heavier than hydrogen. These systems exhibit the lowest heavy-element abundance in the early universe, and thus are potential fuel for the most metal-poor halo stars. The detection of deuterium in one system at the level predicted by primordial nucleosynthesis provides a direct confirmation of the standard cosmological model. The composition of these clouds further implies that the transport of heavy elements from galaxies to their surroundings is highly inhomogeneous.
CRISPR-Cas9 is a versatile genome editing technology for studying the functions of genetic elements. To broadly enable the application of Cas9 in vivo, we established a Cre-dependent Cas9 knockin ...mouse. We demonstrated in vivo as well as ex vivo genome editing using adeno-associated virus (AAV)-, lentivirus-, or particle-mediated delivery of guide RNA in neurons, immune cells, and endothelial cells. Using these mice, we simultaneously modeled the dynamics of KRAS, p53, and LKB1, the top three significantly mutated genes in lung adenocarcinoma. Delivery of a single AAV vector in the lung generated loss-of-function mutations in p53 and Lkb1, as well as homology-directed repair-mediated KrasG12D mutations, leading to macroscopic tumors of adenocarcinoma pathology. Together, these results suggest that Cas9 mice empower a wide range of biological and disease modeling applications.
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•Generation of mouse lines with Cre-dependent and constitutive Cas9 expression•Viral/nonviral delivery of sgRNA to the brain, vasculature, immune cells, and lung•Modeling of competition between gain- and loss-of-function mutations in lung cancer•A convenient platform for achieving efficient genome editing in vivo
Viral and nonviral delivery of sgRNAs in CRISPR-Cas9 knockin mice enables diverse genome engineering applications in biology and disease modeling.
All galaxies once passed through a hyperluminous quasar phase powered by accretion onto a supermassive black hole. But because these episodes are brief, quasars are rare objects typically separated ...by cosmological distances. In a survey for Lyman-α emission at redshift z ≈ 2, we discovered a physical association of four quasars embedded in a giant nebula. Located within a substantial overdensity of galaxies, this system is probably the progenitor of a massive galaxy cluster. The chance probability of finding a quadruple quasar is estimated to be ∼10–7, implying a physical connection between Lyman-α nebulae and the locations of rare protoclusters. Our findings imply that the most massive structures in the distant universe have a tremendous supply (≃1011 solar masses) of cool dense (volume density ≃ 1 cm–3) gas, which is in conflict with current cosmological simulations.
Recently, substantial advances in the understanding of the molecular pathogenesis of inflammatory bowel disease (IBD) have been made owing to three related lines of investigation. First, IBD has been ...found to be the most tractable of complex disorders for discovering susceptibility genes, and these have shown the importance of epithelial barrier function, and innate and adaptive immunity in disease pathogenesis. Second, efforts directed towards the identification of environmental factors implicate commensal bacteria (or their products), rather than conventional pathogens, as drivers of dysregulated immunity and IBD. Third, murine models, which exhibit many of the features of ulcerative colitis and seem to be bacteria-driven, have helped unravel the pathogenesis/mucosal immunopathology of IBD.
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