57 research outputs found
Light bosons and photospheric solutions to the solar abundance problem
It is well known that current spectroscopic determinations of the chemical
composition of the Sun are starkly at odds with the metallicity implied by
helioseismology. We investigate whether the discrepancy may be due to
conversion of photons to a new light boson in the solar photosphere. We examine
the impact of particles with axion-like interactions with the photon on the
inferred photospheric abundances, showing that resonant axion-photon conversion
is not possible in the region of the solar atmosphere in which line-formation
occurs. Although non-resonant conversion in the line-forming regions can in
principle impact derived abundances, constraints from axion-photon conversion
experiments rule out the couplings necessary for these effects to be
detectable. We show that this extends to hidden photons and chameleons (which
would exhibit similar phenomenological behaviour), ruling out known theories of
new light bosons as photospheric solutions to the solar abundance problem.Comment: 11 pages, PDFLaTeX. v2: Major revision. Inclusion of refractive index
effect on photon-ALP conversion strengthens our conclusion that such an
effect cannot explain the solar abundance problem with a coupling allowed by
experimental axion-like particle searches. We now include a discussion of
chameleons and hidden photons, with similar conclusion
New Results on Standard Solar Models
We describe the current status of solar modelling and focus on the problems
originated with the introduction of solar abundance determinations with low CNO
abundance values. We use models computed with solar abundance compilations
obtained during the last decade, including the newest published abundances by
Asplund and collaborators. Results presented here make focus both on
helioseismic properties and the models as well as in the neutrino fluxes
predictions. We also discuss changes in radiative opacities to restore
agreement between helioseismology, solar models, and solar abundances and show
the effect of such modifications on solar neutrino fluxes.Comment: 9 pages. Review talk presented at "Synergies between solar and
stellar modelling", Rome, June 2009. To be published by Astrophysics and
Space Scienc
Mutation of pescadillo Disrupts Oligodendrocyte Formation in Zebrafish
Background: In vertebrates, the myelin sheath is essential for efficient propagation of action potentials along the axon shaft. Oligodendrocytes are the cells of the central nervous system that create myelin sheaths. During embryogenesis, ventral neural tube precursors give rise to oligodendrocyte progenitor cells, which divide and migrate throughout the central nervous system. This study aimed to investigate mechanisms that regulate oligodendrocyte progenitor cell formation. Methodology/Principal Findings: By conducting a mutagenesis screen in transgenic zebrafish, we identified a mutation, designated vu166, by an apparent reduction in the number of oligodendrocyte progenitor cells in the dorsal spinal cord. We subsequently determined that vu166 is an allele of pescadillo, a gene known to play a role in ribosome biogenesis and cell proliferation. We found that pescadillo function is required for both the proper number of oligodendrocyte progenitors to form, by regulating cell cycle progression, and for normal levels of myelin gene expression. Conclusions/Significance: Our data provide evidence that neural precursors require pes function to progress through th
The effect of membrane curvature on the conformation of antimicrobial peptides: implications for binding and the mechanism of action
Short cationic antimicrobial peptides (AMPs) are believed to act either by inducing transmembrane pores or disrupting membranes in a detergent-like manner. For example, the antimicrobial peptides aurein 1.2, citropin 1.1, maculatin 1.1 and caerin 1.1, despite being closely related, appear to act by fundamentally different mechanisms depending on their length. Using molecular dynamics simulations, the structural properties of these four peptides have been examined in solution as well as in a variety of membrane environments. It is shown that each of the peptides has a strong preference for binding to regions of high membrane curvature and that the structure of the peptides is dependent on the degree of local curvature. This suggests that the shorter peptides aurein 1.2 and citropin 1.1 act via a detergent-like mechanism because they can induce high local, but not long-range curvature, whereas the longer peptides maculatin 1.1 and caerin 1.1 require longer range curvature to fold and thus bind to and stabilize transmembrane pores
TESS and ESPRESSO discover a super-Earth and a mini-Neptune orbiting the K-dwarf TOI-238
The number of super-Earth and mini-Neptune planet discoveries has increased
significantly in the last two decades thanks to transit and radial velocity
surveys. When it is possible to apply both techniques, we can characterise the
internal composition of exoplanets, which in turn provides unique insights on
their architecture, formation and evolution.
We performed a combined photometric and radial velocity analysis of TOI-238
(TYC 6398-132-1), which has one short-orbit super-Earth planet candidate
announced by NASA's TESS team. We aim to confirm its planetary nature using
radial velocities taken with the ESPRESSO and HARPS spectrographs, to measure
its mass and to detect the presence of other possible planetary companions. We
carried out a joint analysis by including Gaussian processes and Keplerian
orbits to account for the stellar activity and planetary signals
simultaneously.
We detected the signal induced by TOI-238 b in the radial velocity
time-series, and the presence of a second transiting planet, TOI-238 c, whose
signal appears in RV and TESS data. TOI-238 b is a planet with a radius of
1.402 R and a mass of 3.40
M. It orbits at a separation of 0.02118 0.00038 AU of its host
star, with an orbital period of 1.2730988 0.0000029 days, and has an
equilibrium temperature of 1311 28 K. TOI-238 c has a radius of 2.18
0.18 R and a mass of 6.7 1.1 M. It orbits at a
separation of 0.0749 0.0013 AU of its host star, with an orbital period
of 8.465652 0.000031 days, and has an equilibrium temperature of 696
15 K. The mass and radius of planet b are fully consistent with an
Earth-like composition, making it likely a rocky super-Earth. Planet c could be
a water-rich planet or a rocky planet with a small H-He atmosphere.Comment: 33 pages, 31 figures, 5 tables. Accepted for publication at A&
Computational Identification of Uncharacterized Cruzain Binding Sites
Chagas disease, caused by the unicellular parasite Trypanosoma cruzi, claims 50,000 lives annually and is the leading cause of infectious myocarditis in the world. As current antichagastic therapies like nifurtimox and benznidazole are highly toxic, ineffective at parasite eradication, and subject to increasing resistance, novel therapeutics are urgently needed. Cruzain, the major cysteine protease of Trypanosoma cruzi, is one attractive drug target. In the current work, molecular dynamics simulations and a sequence alignment of a non-redundant, unbiased set of peptidase C1 family members are used to identify uncharacterized cruzain binding sites. The two sites identified may serve as targets for future pharmacological intervention
Perspectives in Global Helioseismology, and the Road Ahead
We review the impact of global helioseismology on key questions concerning
the internal structure and dynamics of the Sun, and consider the exciting
challenges the field faces as it enters a fourth decade of science
exploitation. We do so with an eye on the past, looking at the perspectives
global helioseismology offered in its earlier phases, in particular the
mid-to-late 1970s and the 1980s. We look at how modern, higher-quality, longer
datasets coupled with new developments in analysis, have altered, refined, and
changed some of those perspectives, and opened others that were not previously
available for study. We finish by discussing outstanding challenges and
questions for the field.Comment: Invited review; to appear in Solar Physics (24 pages, 6 figures
Autoantibodies against type I IFNs in patients with life-threatening COVID-19
Interindividual clinical variability in the course of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection is vast. We report that at least 101 of 987 patients with life-threatening coronavirus disease 2019 (COVID-19) pneumonia had neutralizing immunoglobulin G (IgG) autoantibodies (auto-Abs) against interferon-w (IFN-w) (13 patients), against the 13 types of IFN-a (36), or against both (52) at the onset of critical disease; a few also had auto-Abs against the other three type I IFNs. The auto-Abs neutralize the ability of the corresponding type I IFNs to block SARS-CoV-2 infection in vitro. These auto-Abs were not found in 663 individuals with asymptomatic or mild SARS-CoV-2 infection and were present in only 4 of 1227 healthy individuals. Patients with auto-Abs were aged 25 to 87 years and 95 of the 101 were men. A B cell autoimmune phenocopy of inborn errors of type I IFN immunity accounts for life-threatening COVID-19 pneumonia in at least 2.6% of women and 12.5% of men
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