14 research outputs found
Centrifugal Barrier and Super-Keplerian Rotation in Protostellar Disk Formation
With the advent of ALMA, it is now possible to observationally constrain how
disks form around deeply embedded protostars. In particular, the recent ALMA
C3H2 line observations of the nearby protostar L1527 have been interpreted as
evidence for the so-called "centrifugal barrier," where the protostellar
envelope infall is gradually decelerated to a stop by the centrifugal force in
a region of super-Keplerian rotation. To test the concept of centrifugal
barrier, which was originally based on angular momentum conserving-collapse of
a rotating test particle around a fixed point mass, we carry out simple
axisymmetric hydrodynamic simulations of protostellar disk formation including
a minimum set of ingredients: self-gravity, rotation, and a prescribed
viscosity that enables the disk to accrete. We find that a super-Keplerian
region can indeed exist when the viscosity is relatively large but, unlike the
classic picture of centrifugal barrier, the infalling envelope material is not
decelerated solely by the centrifugal force. The region has more specific
angular momentum than its surrounding envelope material, which points to an
origin in outward angular momentum transport in the disk (subject to the
constraint of disk expansion by the infalling envelope), rather than the
spin-up of the envelope material envisioned in the classic picture as it falls
closer to the center in order to conserve angular momentum. For smaller
viscosities, the super-Keplerian rotation is weaker or non-existing. We
conclude that, despite the existence of super-Keplerian rotation in some
parameter regime, the classic picture of centrifugal barrier is not supported
by our simulations
How negative feedback and the ambient environment limit the influence of recombination in common envelope evolution
We perform 3D hydrodynamical simulations to study recombination and
ionization during the common envelope (CE) phase of binary evolution, and
develop techniques to track the ionic transitions in time and space. We
simulate the interaction of a red giant branch primary and a
companion modeled as a particle. We compare a run employing a
tabulated equation of state (EOS) that accounts for ionization and
recombination, with a run employing an ideal gas EOS. During the first half of
the simulations, per cent more mass is unbound in the tabulated EOS
run due to the release of recombination energy, but by simulation end the
difference has become negligible. We explain this as being a consequence of (i)
the tabulated EOS run experiences a shallower inspiral and hence smaller
orbital energy release at late times because recombination energy release
expands the envelope and reduces drag, and (ii) collision and mixing between
expanding envelope gas, ejecta and circumstellar ambient gas assists in
unbinding the envelope, but does so less efficiently in the tabulated EOS run
where some of the energy transferred to bound envelope gas is used for
ionization. The rate of mass unbinding is approximately constant in the last
half of the simulations and the orbital separation steadily decreases at late
times. A simple linear extrapolation predicts a CE phase duration of
, after which the envelope would be unbound.Comment: Submitted to MNRA
Metabolomics and network analysis uncovered profound inflammation-associated alterations in hepatitis B virus-related cirrhosis patients with early hepatocellular carcinoma
Patients with hepatitis B virus (HBV)-related liver cirrhosis (LC) are at high risk for hepatocellular carcinoma (HCC). Limitations in the early detection of HCC give rise to poor survival in this high-risk population. Here, we performed comprehensive metabolomics on health individuals and HBV-related LC patients with and without early HCC. Compared to non-HCC patients (N = 108) and health controls (N = 80), we found that patients with early HCC (N = 224) exhibited a specific plasma metabolome map dominated by lipid alterations, including lysophosphatidylcholines, lysophosphatidic acids and bile acids. Pathway and function network analyses indicated that these metabolite alterations were closely associated with inflammation responses. Using multivariate regression and machine learning approaches, we identified a five-metabolite combination that showed significant performances in differentiating early-HCC from non-HCC than α-fetoprotein (area under the curve values, 0.981 versus 0.613). At metabolomic levels, this work provides additional insights of metabolic dysfunction related to HCC progressions and demonstrates the plasma metabolites might be measured to identify early HCC in patients with HBV-related LC
Vertically stratified methane, nitrogen and sulphur cycling and coupling mechanisms in mangrove sediment microbiomes
Abstract Background Mangrove ecosystems are considered as hot spots of biogeochemical cycling, yet the diversity, function and coupling mechanism of microbially driven biogeochemical cycling along the sediment depth of mangrove wetlands remain elusive. Here we investigated the vertical profile of methane (CH4), nitrogen (N) and sulphur (S) cycling genes/pathways and their potential coupling mechanisms using metagenome sequencing approaches. Results Our results showed that the metabolic pathways involved in CH4, N and S cycling were mainly shaped by pH and acid volatile sulphide (AVS) along a sediment depth, and AVS was a critical electron donor impacting mangrove sediment S oxidation and denitrification. Gene families involved in S oxidation and denitrification significantly (P < 0.05) decreased along the sediment depth and could be coupled by S-driven denitrifiers, such as Burkholderiaceae and Sulfurifustis in the surface sediment (0–15 cm). Interestingly, all S-driven denitrifier metagenome-assembled genomes (MAGs) appeared to be incomplete denitrifiers with nitrate/nitrite/nitric oxide reductases (Nar/Nir/Nor) but without nitrous oxide reductase (Nos), suggesting such sulphide-utilizing groups might be an important contributor to N2O production in the surface mangrove sediment. Gene families involved in methanogenesis and S reduction significantly (P < 0.05) increased along the sediment depth. Based on both network and MAG analyses, sulphate-reducing bacteria (SRB) might develop syntrophic relationships with anaerobic CH4 oxidizers (ANMEs) by direct electron transfer or zero-valent sulphur, which would pull forward the co-existence of methanogens and SRB in the middle and deep layer sediments. Conclusions In addition to offering a perspective on the vertical distribution of microbially driven CH4, N and S cycling genes/pathways, this study emphasizes the important role of S-driven denitrifiers on N2O emissions and various possible coupling mechanisms of ANMEs and SRB along the mangrove sediment depth. The exploration of potential coupling mechanisms provides novel insights into future synthetic microbial community construction and analysis. This study also has important implications for predicting ecosystem functions within the context of environmental and global change. Video Abstrac