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"Yu, B"
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A peculiar low-luminosity short gamma-ray burst from a double neutron star merger progenitor
Double neutron star (DNS) merger events are promising candidates of short gamma-ray burst (sGRB) progenitors as well as high-frequency gravitational wave (GW) emitters. On August 17, 2017, such a coinciding event was detected by both the LIGO-Virgo gravitational wave detector network as GW170817 and Gamma-Ray Monitor on board NASA’s
Fermi
Space Telescope as GRB 170817A. Here, we show that the fluence and spectral peak energy of this sGRB fall into the lower portion of the distributions of known sGRBs. Its peak isotropic luminosity is abnormally low. The estimated event rate density above this luminosity is at least
19
0
-
160
+
440
Gpc
−3
yr
−1
, which is close to but still below the DNS merger event rate density. This event likely originates from a structured jet viewed from a large viewing angle. There are similar faint soft GRBs in the
Fermi
archival data, a small fraction of which might belong to this new population of nearby, low-luminosity sGRBs.
A short-duration gamma-ray burst was detected along with a double neutron start merger gravitational wave by LIGO-Virgo on August 17th 2017. Here, the authors show that the fluence and spectral peak energy of this event fall into the lower portion of the distribution of known short-duration gamma-ray bursts.
Journal Article
Gut microbiota Turicibacter strains differentially modify bile acids and host lipids
Bacteria from the
Turicibacter
genus are prominent members of the mammalian gut microbiota and correlate with alterations in dietary fat and body weight, but the specific connections between these symbionts and host physiology are poorly understood. To address this knowledge gap, we characterize a diverse set of mouse- and human-derived
Turicibacter
isolates, and find they group into clades that differ in their transformations of specific bile acids. We identify
Turicibacter
bile salt hydrolases that confer strain-specific differences in bile deconjugation. Using male and female gnotobiotic mice, we find colonization with individual
Turicibacter
strains leads to changes in host bile acid profiles, generally aligning with those produced in vitro. Further, colonizing mice with another bacterium exogenously expressing bile-modifying genes from
Turicibacter
strains decreases serum cholesterol, triglycerides, and adipose tissue mass. This identifies genes that enable
Turicibacter
strains to modify host bile acids and lipid metabolism, and positions
Turicibacter
bacteria as modulators of host fat biology.
Mechanisms by which the gut microbiota affects its host are a main research focus. Here, Lynch et al. characterize bile acid modifications performed by a prevalent bacterial taxon from the gut, the genus
Turicibacter
, and found they broadly altered host lipids, connecting
Turicibacter
functions and host physiology.
Journal Article
Observations of atmospheric mercury in China: a critical review
China presently contributes the largest amount of anthropogenic mercury (Hg) emission into the atmosphere in the world. Over the past decade, numerous studies have been conducted to characterize the concentration and forms of atmospheric Hg in China, which provide insights into the spatial and temporal distributions of atmospheric Hg through ground-based measurements at widely diverse geographical locations and during cruise and flight campaigns. In this paper, we present a comprehensive review of the state of understanding in atmospheric Hg in China. Gaseous elemental mercury (GEM) and particulate-bound mercury (PBM) measured at the remote sites in China are substantially elevated compared to the background values in the Northern Hemisphere. In Chinese urban areas, the highly elevated GEM, PBM and gaseous oxidized mercury (GOM) were mainly derived from local anthropogenic Hg emissions, whereas regional anthropogenic emissions and long-range transport from domestic source regions are the primary causes of the elevated GEM and PBM concentrations at remote sites. Using 7–9 years of continuous observations at a remote site and an urban site, a slight increase in atmospheric GEM (2.4–2.5 % yr−1) was identified (paired samples test: p < 0.01), which is in agreement with the increasing domestic anthropogenic emissions. Anthropogenic GEM emission quantity in China estimated through the observed GEM / CO concentration ratios ranged from 632 to 1138 t annually over the past decade, 2–3 times larger than published values using emission activity data. Modeling results and filed measurements show dry deposition is the predominant process for removing Hg from the atmosphere, 2.5–9.0 times larger than wet deposition, due to the elevated atmospheric GEM and PBM concentrations that facilitate dry deposition to terrestrial landscapes. Further studies to reconcile the observed and simulated Hg concentrations, to understand the impact of domestic emission reduction on Hg concentration and deposition and to delineate the role of Hg emission and deposition of China in the global Hg biogeochemical cycle, are needed.
Journal Article
Universal superconducting precursor in three classes of unconventional superconductors
A pivotal challenge posed by unconventional superconductors is to unravel how superconductivity emerges upon cooling from the generally complex normal state. Here, we use nonlinear magnetic response, a probe that is uniquely sensitive to the superconducting precursor, to uncover remarkable universal behaviour in three distinct classes of oxide superconductors: strontium titanate, strontium ruthenate, and the cuprate high-
T
c
materials. We find unusual exponential temperature dependence of the diamagnetic response above the transition temperature
T
c
, with a characteristic temperature scale that strongly varies with
T
c
. We correlate this scale with the sensitivity of
T
c
to local stress and show that it is influenced by intentionally-induced structural disorder. The universal behaviour is therefore caused by intrinsic, self-organized structural inhomogeneity, inherent to the oxides’ perovskite-based structure. The prevalence of such inhomogeneity has far-reaching implications for the interpretation of electronic properties of perovskite-related oxides in general.
The understanding of how superconductivity emerges from a complex normal state remains elusive in unconventional superconductors. Here, Pelc et al. report exponential temperature dependence of the diamagnetic response in the normal state with a characteristic temperature scale, universally existing in three classes of oxide superconductors.
Journal Article
Gut microbiota utilize immunoglobulin A for mucosal colonization
Microbial communities in the gut can be highly individual. What engenders this specificity? The gut characteristically produces gram quantities of immunoglobulin A (IgA) antibody, which is presumed to protect the gut from pathogen attack. Donaldson et al. engineered strains of Bacteroides fragilis , a common human commensal, to modify its surface capsule, which affects its ability to colonize the germ-free mouse gut. Capsule changes altered the capacity of IgA to bind to the different mutants. It seems that this commensal species exploits IgA sticking power specifically to give it a competitive edge and to promote its establishment in the gut. Science , this issue p. 795 Bacteroides fragilis modifies its surface to induce an immunoglobulin A response that promotes stable mucosal association and colonization resistance. The immune system responds vigorously to microbial infection while permitting lifelong colonization by the microbiome. Mechanisms that facilitate the establishment and stability of the gut microbiota remain poorly described. We found that a regulatory system in the prominent human commensal Bacteroides fragilis modulates its surface architecture to invite binding of immunoglobulin A (IgA) in mice. Specific immune recognition facilitated bacterial adherence to cultured intestinal epithelial cells and intimate association with the gut mucosal surface in vivo. The IgA response was required for B. fragilis (and other commensal species) to occupy a defined mucosal niche that mediates stable colonization of the gut through exclusion of exogenous competitors. Therefore, in addition to its role in pathogen clearance, we propose that IgA responses can be co-opted by the microbiome to engender robust host-microbial symbiosis.
Journal Article
Chiral Selectors in Capillary Electrophoresis: Trends during 2017–2018
Chiral separation is an important process in the chemical and pharmaceutical industries. From the analytical chemistry perspective, chiral separation is required for assessing the fit-for-purpose and the safety of chemical products. Capillary electrophoresis, in the electrokinetic chromatography mode is an established analytical technique for chiral separations. A water-soluble chiral selector is typically used. This review therefore examines the use of various chiral selectors in electrokinetic chromatography during 2017–2018. The chiral selectors were both low and high (macromolecules) molecular mass molecules as well as molecular aggregates (supramolecules). There were 58 papers found by search in Scopus, indicating continuous and active activity in this research area. The macromolecules were sugar-, amino acid-, and nucleic acid-based polymers. The supramolecules were bile salt micelles. The low molecular mass selectors were mainly ionic liquids and complexes with a central ion. A majority of the papers were on the use or preparation of sugar-based macromolecules, e.g., native or derivatised cyclodextrins. Studies to explain chiral recognition of macromolecular and supramolecular chiral selectors were mainly done by molecular modelling and nuclear magnetic resonance spectroscopy. Demonstrations were predominantly on drug analysis for the separation of racemates.
Journal Article
Modelling human blastocysts by reprogramming fibroblasts into iBlastoids
Human pluripotent and trophoblast stem cells have been essential alternatives to blastocysts for understanding early human development
1
–
4
. However, these simple culture systems lack the complexity to adequately model the spatiotemporal cellular and molecular dynamics that occur during early embryonic development. Here we describe the reprogramming of fibroblasts into in vitro three-dimensional models of the human blastocyst, termed iBlastoids. Characterization of iBlastoids shows that they model the overall architecture of blastocysts, presenting an inner cell mass-like structure, with epiblast- and primitive endoderm-like cells, a blastocoel-like cavity and a trophectoderm-like outer layer of cells. Single-cell transcriptomics further confirmed the presence of epiblast-, primitive endoderm-, and trophectoderm-like cells. Moreover, iBlastoids can give rise to pluripotent and trophoblast stem cells and are capable of modelling, in vitro, several aspects of the early stage of implantation. In summary, we have developed a scalable and tractable system to model human blastocyst biology; we envision that this will facilitate the study of early human development and the effects of gene mutations and toxins during early embryogenesis, as well as aiding in the development of new therapies associated with in vitro fertilization.
Human fibroblasts are reprogrammed to generate blastocyst-like structures called iBlastoids, which recapitulate aspects of embryo implantation.
Journal Article