117 research outputs found
Investigating comammox Nitrospira in rapid sand filters via metagenomics and single-cell genomics
Metagenomics and single-cell genomics reveal high abundance of comammox Nitrospira in a rapid gravity sand filter treating groundwater
Effective kaon energy from a novel chiral SU(3) model
A new chiral SU(3) Lagrangian is proposed to describe the properties of kaons and anti-kaons in the nuclear medium. The saturation properties of nuclear matter are reproduced as well as the results of the Dirac-Brückner theory. After introducing the coupling between the omega meson and the kaon, our results for effective kaon and anti-kaon energy are quite similar as calculated in the one-boson-exchange model
Kaon effective mass and energy from a novel chiral SU(3)-symmetric Lagrangian
A new chiral SU(3) Lagrangian is proposed to describe the properties of kaons
and antikaons in the nuclear medium, the ground state of dense matter and the
kaon-nuclear interactions consistently.
The saturation properties of nuclear matter are reproduced as well as the
results of the Dirac-Br\"{u}ckner theory. Our numerical results show that the
kaon effective mass might be changed only moderately in the nuclear medium due
to the highly non-linear density effects. After taking into account the
coupling between the omega meson and the kaon, we obtain similar results for
the effective kaon and antikaon energies as calculated in the
one-boson-exchange model while in our model the parameters of the kaon-nuclear
interactions are constrained by the SU(3) chiral symmetry.Comment: 13 pages, Latex, 3 PostScript figures included; replaced by the
revised version, to appear in Phys. Rev.
Nuclei in a chiral SU(3) model
Nuclei can be described satisfactorily in a nonlinear chiral SU(3)-framework,
even with standard potentials of the linear -model. The condensate
value of the strange scalar meson is found to be important for the properties
of nuclei even without adding hyperons. By neglecting terms which couple the
strange to the nonstrange condensate one can reduce the model to a Walecka
model structure embedded in SU(3). We discuss inherent problems with chiral
SU(3) models regarding hyperon optical potentials.Comment: 25 pages, RevTe
Neutrinoless double-beta decay with three or four neutrino mixing
Considering the scheme with mixing of three neutrinos and a mass hierarchy
that can accommodate the results of solar and atmospheric neutrino experiments,
it is shown that the results of solar neutrino experiments imply a lower bound
for the effective Majorana mass in neutrinoless double-beta decay, under the
natural assumptions that massive neutrinos are Majorana particles and there are
no unlikely fine-tuned cancellations among the contributions of the different
neutrino masses. Considering the four-neutrino schemes that can accommodate
also the results of the LSND experiment, it is shown that only one of them is
compatible with the results of neutrinoless double-beta decay experiments and
with the measurement of the abundances of primordial elements produced in
Big-Bang Nucleosynthesis. It is shown that in this scheme, under the
assumptions that massive neutrinos are Majorana particles and there are no
cancellations among the contributions of the different neutrino masses, the
results of the LSND experiment imply a lower bound for the effective Majorana
mass in neutrinoless double-beta decay.Comment: 18 pages including 2 figures, RevTe
Viral entry and escape from antibody-mediated neutralization influence hepatitis C virus reinfection in liver transplantation
End-stage liver disease caused by chronic hepatitis C virus (HCV) infection is a leading cause for liver transplantation (LT). Due to viral evasion from host immune responses and the absence of preventive antiviral strategies, reinfection of the graft is universal. The mechanisms by which the virus evades host immunity to reinfect the liver graft are unknown. In a longitudinal analysis of six HCV-infected patients undergoing LT, we demonstrate that HCV variants reinfecting the liver graft were characterized by efficient entry and poor neutralization by antibodies present in pretransplant serum compared with variants not detected after transplantation. Monoclonal antibodies directed against HCV envelope glycoproteins or a cellular entry factor efficiently cross-neutralized infection of human hepatocytes by patient-derived viral isolates that were resistant to autologous host-neutralizing responses. These findings provide significant insights into the molecular mechanisms of viral evasion during HCV reinfection and suggest that viral entry is a viable target for prevention of HCV reinfection of the liver graft
Dark Energy Survey identification of a low-mass active galactic nucleus at redshift 0.823 from optical variability
We report the identification of a low-mass active galactic nucleus (AGN), DES J0218−0430, in a redshift z = 0.823 galaxy in the Dark Energy Survey (DES) Supernova field. We select DES J0218−0430 as an AGN candidate by characterizing its long-term optical variability alone based on DES optical broad-band light curves spanning over 6 yr. An archival optical spectrum from the fourth phase of the Sloan Digital Sky Survey shows both broad Mg II and broad H β lines, confirming its nature as a broad-line AGN. Archival XMM–Newton X-ray observations suggest an intrinsic hard X-ray luminosity of L2−12keV≈7.6±0.4×1043 erg s−1, which exceeds those of the most X-ray luminous starburst galaxies, in support of an AGN driving the optical variability. Based on the broad H β from SDSS spectrum, we estimate a virial black hole (BH) mass of M• ≈ 106.43–106.72 M⊙ (with the error denoting the systematic uncertainty from different calibrations), consistent with the estimation from OzDES, making it the lowest mass AGN with redshift > 0.4 detected in optical. We estimate the host galaxy stellar mass to be M* ≈ 1010.5 ± 0.3 M⊙ based on modelling the multiwavelength spectral energy distribution. DES J0218−0430 extends the M•–M* relation observed in luminous AGNs at z ∼ 1 to masses lower than being probed by previous work. Our work demonstrates the feasibility of using optical variability to identify low-mass AGNs at higher redshift in deeper synoptic surveys with direct implications for the upcoming Legacy Survey of Space and Time at Vera C. Rubin Observatory
An X-Ray-Selected Sample of Candidate Black Holes in Dwarf Galaxies
We present a sample of hard X-ray-selected candidate black holes (BHs) in 19 dwarf galaxies. BH candidates are identified by cross-matching a parent sample of ~44,000 local dwarf galaxies (M* = 3 × 10 9 M☉, z < 0.055) with the Chandra Source Catalog and subsequently analyzing the original X-ray data products for matched sources. Of the 19 dwarf galaxies in our sample, eight have X-ray detections reported here for the first time. We find a total of 43 point-like hard X-ray sources with individual luminosities L2-10 keV ~ 10 37 - 10 40 erg s-1. Hard X-ray luminosities in this range can be attained by stellar-mass X-ray binaries (XRBs) and by massive BHs accreting at low Eddington ratio. We place an upper limit of 53% (10/19) on the fraction of galaxies in our sample hosting a detectable hard X-ray source consistent with the optical nucleus, although the galaxy center is poorly defined in many of our objects. We also find that 42% (8/19) of the galaxies in our sample exhibit statistically significant enhanced hard X-ray emission relative to the expected galaxy-wide contribution from low-mass and high-mass XRBs, based on the [data] star formation rate relation defined by more massive and luminous systems. For the majority of these X-ray-enhanced dwarf galaxies, the excess emission is consistent with (but not necessarily due to) a nuclear X-ray source. Follow-up observations are necessary to distinguish between stellar-mass XRBs and active galactic nuclei powered by more massive BHs. In any case, our results support the notion that X-ray-emitting BHs in low-mass dwarf galaxies may have had an appreciable impact on reionization in the early universe
The X-ray properties of million solar mass black holes
We present new Chandra X-ray observations of seven low-mass black holes (~1e6
Msun) accreting at low Eddington ratios between -2.0<log L/Ledd<-1.5. We
compare the X-ray properties of these seven low-mass active galactic nuclei
(AGN) to a total of 73 other low-mass AGN in the literature with published
Chandra observations (with Eddington ratios extending from -2.0<log
L/Ledd<-0.1). We do not find any statistical differences between low- and
high-Eddington ratio low-mass AGN in the distributions of their X-ray to
ultraviolet luminosity ratios (aox), or in their X-ray spectral shapes.
Furthermore, the aox distribution of low-L/Ledd AGN displays an X-ray weak tail
that is also observed within high-L/Ledd objects. Our results indicate that
between -2<log L/Ledd<-0.1, there is no systematic change in the structure of
the accretion flow for active galaxies hosting 1e6 Msun black holes. We examine
the accuracy of current bolometric luminosity estimates for our low-L/Ledd
objects with new Chandra observations, and it is plausible that their Eddington
ratios could be underestimated by up to an order of magnitude. If so, then in
analogy with weak emission line quasars, we suggest that accretion from a
geometrically thick, radiatively inefficient `slim disk' could explain their
diverse properties in aox. Alternatively, if current Eddington ratios are in
fact correct (or overestimated), then the X-ray weak tail would imply that
there is diversity in disk/corona couplings among individual low-mass objects.
Finally, we conclude by noting that the aox distribution for low-mass black
holes may have favorable consequences for the epoch of cosmic reionization
being driven by AGN.Comment: 14 pages, 6 figures, 6 tables. Accepted for publication in Ap
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