3,532 research outputs found
The Spin Evolution of Fast-Rotating, Magnetized Super-Chandrasekhar White Dwarfs in the Aftermath of White Dwarf Mergers
The evolution of the remnant of the merger of two white dwarfs is still an
open problem. Furthermore, few studies have addressed the case in which the
remnant is a magnetic white dwarf with a mass larger than the Chandrasekhar
limiting mass. Angular momentum losses might bring the remnant of the merger to
the physical conditions suitable for developing a thermonuclear explosion.
Alternatively, the remnant may be prone to gravitational or rotational
instabilities, depending on the initial conditions reached after the
coalescence. Dipole magnetic braking is one of the mechanisms that can drive
such losses of angular momentum. However, the timescale on which these losses
occur depend on several parameters, like the strength of the magnetic field. In
addition, the coalescence leaves a surrounding Keplerian disk that can be
accreted by the newly formed white dwarf. Here we compute the post-merger
evolution of a super-Chandrasekhar magnetized white dwarf taking into account
all the relevant physical processes. These include magnetic torques acting on
the star, accretion from the Keplerian disk, the threading of the magnetic
field lines through the disk, as well as the thermal evolution of the white
dwarf core. We find that the central remnant can reach the conditions suitable
to develop a thermonuclear explosion before other instabilities (such as the
inverse beta-decay instability or the secular axisymmetric instability) are
reached, which would instead lead to gravitational collapse of the magnetized
remnant.Comment: Accepted for publication in The Astrophysical Journa
Overexpression of chloroplast-targeted ferrochelatase 1 results in a genomes uncoupled chloroplast-to-nucleus retrograde signalling phenotype.
Chloroplast development requires communication between the progenitor plastids and the nucleus, where most of the genes encoding chloroplast proteins reside. Retrograde signals from the chloroplast to the nucleus control the expression of many of these genes, but the signalling pathway is poorly understood. Tetrapyrroles have been strongly implicated as mediators of this signal with the current hypothesis being that haem produced by the activity of ferrochelatase 1 (FC1) is required to promote nuclear gene expression. We have tested this hypothesis by overexpressing FC1 and specifically targeting it to either chloroplasts or mitochondria, two possible locations for this enzyme. Our results show that targeting of FC1 to chloroplasts results in increased expression of the nuclear-encoded chloroplast genes GUN4, CA1, HEMA1, LHCB2.1, CHLH after treatment with Norflurazon (NF) and that this increase correlates to FC1 gene expression and haem production measured by feedback inhibition of protochlorophyllide synthesis. Targeting FC1 to mitochondria did not enhance the expression of nuclear-encoded chloroplast genes after NF treatment. The overexpression of FC1 also increased nuclear gene expression in the absence of NF treatment, demonstrating that this pathway is operational in the absence of a stress treatment. Our results therefore support the hypothesis that haem synthesis is a promotive chloroplast-to-nucleus retrograde signal. However, not all FC1 overexpression lines enhanced nuclear gene expression, suggesting there is still a lot we do not understand about the role of FC1 in this signalling pathway. This article is part of the theme issue 'Retrograde signalling from endosymbiotic organelles'.BBRS
Effect of low temperature nitriding of 100Cr6 substrates on TiN coatings deposited by IBAD
CNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOIn this paper we studied the influence of pre-treating the surface of 100Cr6 steel by ion beam nitriding at low temperature (380 degrees C) on the surface topography and wear resistance of thin TiN coatings deposited by reactive ion beam assisted deposition. The specimens were characterized by grazing incidence X-ray diffraction, scanning electron microscopy and atomic force microscopy. The wear resistance of the TiN-coated specimens was evaluated by means of ball on disc tests. The results showed that application of a preliminary ion beam nitriding treatment slightly increased the surface roughness but improved the wear resistance of the 100Cr6 steel due to the formation of a diffusion zone containing the gamma'-Fe4N nitride combined with the TiN coating.In this paper we studied the influence of pre-treating the surface of 100Cr6 steel by ion beam nitriding at low temperature (380 degrees C) on the surface topography and wear resistance of thin TiN coatings deposited by reactive ion beam assisted deposition. The specimens were characterized by grazing incidence X-ray diffraction, scanning electron microscopy and atomic force microscopy. The wear resistance of the TiN-coated specimens was evaluated by means of ball on disc tests. The results showed that application of a preliminary ion beam nitriding treatment slightly increased the surface roughness but improved the wear resistance of the 100Cr6 steel due to the formation of a diffusion zone containing the gamma'-Fe4N nitride combined with the TiN coating.1815458CNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOSem informaçãoThis work was supported by the NanoCom Network Project, 7th Framework Program – IRSES – Project Nr. 247524. SSV, FA and HP are CNPq fellows
The afterglow and kilonova of the short GRB 160821B
GRB 160821B is a short duration gamma-ray burst (GRB) detected and localized
by the Neil Gehrels Swift Observatory in the outskirts of a spiral galaxy at
z=0.1613, at a projected physical offset of 16 kpc from the galaxy's center. We
present X-ray, optical/nIR and radio observations of its counterpart and model
them with two distinct components of emission: a standard afterglow, arising
from the interaction of the relativistic jet with the surrounding medium, and a
kilonova, powered by the radioactive decay of the sub-relativistic ejecta.
Broadband modeling of the afterglow data reveals a weak reverse shock
propagating backward into the jet, and a likely jet-break at 3.5 d. This is
consistent with a structured jet seen slightly off-axis while expanding into a
low-density medium. Analysis of the kilonova properties suggests a rapid
evolution toward red colors, similar to AT2017gfo, and a low nIR luminosity,
possibly due to the presence of a long-lived neutron star. The global
properties of the environment, the inferred low mass (M_ej < 0.006 Msun) and
velocities (v > 0.05 c) of lanthanide-rich ejecta are consistent with a binary
neutron star merger progenitor.Comment: 14 pages, 6 figures, MNRAS, in press. Moderate revision, added Figure
5 and X-ray data to Table
Removal of nutrients and pesticides from agricultural runoff using microalgae and cyanobacteria
The use of pesticides in agriculture has ensured the production of different crops. However, pesticides have become an emerging public health problem for Latin American countries due to their excessive use, inadequate application, toxic characteristics, and minimal residue control. The current project evaluates the ability of two strains of algae (Chlorella and Scenedesmus sp.) and one cyanobacteria (Hapalosyphon sp.) to remove excess pesticides and other nutrients present in runoff water from rice production. Different concentrations of wastewater and carbon sources (Na2CO3 and NaHCO3 ) were evaluated. According to the results, all three strains can be grown in wastewater without dilution (100%), with a biomass concentration comparable to a synthetic medium. All three strains significantly reduced the concentration of NO3 and PO4 (95 and 85%, respectively), with no difference between Na2CO3 or NaHCO3 . Finally, Chlorella sp. obtained the highest removal efficiency of the pesticide (Chlorpyrifos), followed by Scenedesmus and Hapalosyphon sp. (100, 75, and 50%, respectively). This work shows that it is possible to use this type of waste as an alternative source of nutrients to obtain biomass and metabolites of interest, such as lipids and carbohydrates, to produce biofuels
An analysis of the psychosocial backgrounds of Youths (13–18) Who-Pose-Sexual-Risk to children
© 2016, © The Author(s) 2016. Summary: Social workers had expressed concern to their Local Safeguarding Children Board (LSCB) about male Youths (13–18)-Who-Pose-Sexual-Risk (YWPSR) to children, leading to this study of 36 social-history protocols, completed by the youths’ social workers, that identified the presence of research-based factors of YWPSR who then go on to become adult child sex offenders. To ensure total confidentiality, no actual case-record data were available to the authors, ensuring the LSCB, social workers and their clients remain totally anonymous. While a small sample poses methodological difficulties, the authors believe the data is worthy of consideration as a pilot study for a larger project that might highlight the potential areas for early intervention. Findings: Key findings were: 29 (80%) of 36 YWPSR were < 14 when first showing inappropriate sexual behaviour, whilst 25% were known to have been sexually abused themselves, mostly < 11 years and 47% were either currently or had been, Looked-After-Children, with 42% having been Excluded-from-School of who 36% had learning difficulties. Their level of disturbance is shown by 11% having made a suicide attempt and they being formally charges for sex offences against children, which was significantly higher than that found in the adult general population. Finally 66% suffered from low self-esteem, were socially isolated and had poor peer relationships; reflected in the high level of problems at school. Application: Such young people pose a challenge for all concerned and an evidence-based debate is required to explore how to prevent further unacceptable behaviour and thereby protect vulnerable children
The Sensitivity of HAWC to High-Mass Dark Matter Annihilations
The High Altitude Water Cherenkov (HAWC) observatory is a wide field-of-view
detector sensitive to gamma rays of 100 GeV to a few hundred TeV. Located in
central Mexico at 19 degrees North latitude and 4100 m above sea level, HAWC
will observe gamma rays and cosmic rays with an array of water Cherenkov
detectors. The full HAWC array is scheduled to be operational in Spring 2015.
In this paper, we study the HAWC sensitivity to the gamma-ray signatures of
high-mass (multi- TeV) dark matter annihilation. The HAWC observatory will be
sensitive to diverse searches for dark matter annihilation, including
annihilation from extended dark matter sources, the diffuse gamma-ray emission
from dark matter annihilation, and gamma-ray emission from non-luminous dark
matter subhalos. Here we consider the HAWC sensitivity to a subset of these
sources, including dwarf galaxies, the M31 galaxy, the Virgo cluster, and the
Galactic center. We simulate the HAWC response to gamma rays from these sources
in several well-motivated dark matter annihilation channels. If no gamma-ray
excess is observed, we show the limits HAWC can place on the dark matter
cross-section from these sources. In particular, in the case of dark matter
annihilation into gauge bosons, HAWC will be able to detect a narrow range of
dark matter masses to cross-sections below thermal. HAWC should also be
sensitive to non-thermal cross-sections for masses up to nearly 1000 TeV. The
constraints placed by HAWC on the dark matter cross-section from known sources
should be competitive with current limits in the mass range where HAWC has
similar sensitivity. HAWC can additionally explore higher dark matter masses
than are currently constrained.Comment: 15 pages, 4 figures, version to be published in PR
Control of magnetic anisotropy by orbital hybridization in (La0.67Sr0.33MnO3)n/(SrTiO3)n superlattice
The asymmetry of chemical nature at the hetero-structural interface offers an
unique opportunity to design desirable electronic structure by controlling
charge transfer and orbital hybridization across the interface. However, the
control of hetero-interface remains a daunting task. Here, we report the
modulation of interfacial coupling of (La0.67Sr0.33MnO3)n/(SrTiO3)n
superlattices by manipulating the periodic thickness with n unit cells of
SrTiO3 and n unit cells La0.67Sr0.33MnO3. The easy axis of magnetic anisotropy
rotates from in-plane (n = 10) to out-of-plane (n = 2) orientation at 150 K.
Transmission electron microscopy reveals enlarged tetragonal ratio > 1 with
breaking of volume conservation around the (La0.67Sr0.33MnO3)n/(SrTiO3)n
interface, and electronic charge transfer from Mn to Ti 3d orbitals across the
interface. Orbital hybridization accompanying the charge transfer results in
preferred occupancy of 3d3z2-r2 orbital at the interface, which induces a
stronger electronic hopping integral along the out-of-plane direction and
corresponding out-of-plane magnetic easy axis for n = 2. We demonstrate that
interfacial orbital hybridization in superlattices of strongly correlated
oxides may be a promising approach to tailor electronic and magnetic properties
in device applications
Understanding the Nature of the Optical Emission in Gamma-Ray Bursts: Analysis from TAROT, COATLI, and RATIR Observations
We collected the optical light curve data of 227 gamma-ray bursts (GRBs)
observed with the TAROT, COATLI, and RATIR telescopes. These consist of 133
detections and 94 upper limits. We constructed average light curves in the
observer and rest frames in both X-rays (from {\itshape Swift}/XRT) and in the
optical. Our analysis focused on investigating the observational and intrinsic
properties of GRBs. Specifically, we examined observational properties, such as
the optical brightness function of the GRBs at seconds after the
trigger, as well as the temporal slope of the afterglow. We also estimated the
redshift distribution for the GRBs within our sample. Of the 227 GRBs analysed,
we found that 116 had a measured redshift. Based on these data, we calculated a
local rate of Gpc yr for these events with . To
explore the intrinsic properties of GRBs, we examined the average X-ray and
optical light curves in the rest frame. We use the {\scshape afterglowpy}
library to generate synthetic curves to constrain the parameters typical of the
bright GRB jet, such as energy (~erg), opening angle (~rad), and density (
cm). Furthermore, we analyse microphysical parameters, including the
fraction of thermal energy in accelerated electrons
() and in the magnetic field
(), and the power-law index of the
population of non-thermal electrons ().Comment: Resubmitted to MNRAS after minor revision, 13 pages and 9 figure
Total dairy consumption in relation to overweight and obesity in children and adolescents: A systematic review and meta-analysis
A systematic review and meta-analysis of cross-sectional and prospective cohort studies was conducted to assess the associations between total dairy consumption and its different subtypes with the prevalence and incidence of overweight, obesity, and overweight/obesity in children and adolescents. A literature search was conducted in Medline through PUBMED and Cochrane Library databases until October 18, 2021. Articles reporting the risk estimates as odd ratios (OR), risk ratios (RR), or hazard ratios and their corresponding 95% confidence interval (CI) for the association between dairy product consumption and the risk of overweight and/or obesity were included. In the meta-analysis from cross-sectional studies, results showed an inverse association between total dairy consumption and obesity prevalence (OR (95% CI): 0.66 (0.48–0.91). No significant associations were found between milk or yogurt and obesity prevalence risk. Regarding prospective studies, total milk consumption was positively associated with overweight prevalence (OR (95% CI): 1.13 (1.01–1.26)) and incidence (RR (95%CI): 1.17 (1.01–1.35)) risk. Evidence from pooled analysis of cross-sectional studies suggested an inverse association between total dairy consumption and obesity. However, there is limited and no conclusive evidence to confirm an inverse relationship from pooled analysis of prospective studies in children and adolescents
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