7,292 research outputs found
Are there any stable magnetic fields in barotropic stars?
We construct barotropic stellar equilibria, containing magnetic fields with
both poloidal and toroidal field components. We extend earlier results by
exploring the effect of different magnetic field and current distributions. Our
results suggest that the boundary treatment plays a major role in whether the
poloidal or toroidal field component is globally dominant. Using time
evolutions we provide the first stability test for mixed poloidal-toroidal
fields in barotropic stars, finding that all these fields suffer instabilities
due to one of the field components: these are localised around the pole for
toroidal-dominated equilibria and in the closed-field line region for
poloidal-dominated equilibria. Rotation provides only partial stabilisation.
There appears to be very limited scope for the existence of stable magnetic
fields in barotropic stars. We discuss what additional physics from real stars
may allow for stable fields.Comment: 16 pages, 11 figures. Some minor revision from v1, including a new
figure; results unchanged. Now published in MNRA
Interaction between U/UO2 bilayers and hydrogen studied by in-situ X-ray diffraction
This paper reports experiments investigating the reaction of H with
uranium metal-oxide bilayers. The bilayers consist of 100 nm of
epitaxial -U (grown on a Nb buffer deposited on sapphire) with a
UO overlayer of thicknesses of between 20 and 80 nm. The oxides were made
either by depositing via reactive magnetron sputtering, or allowing the uranium
metal to oxidise in air at room temperature. The bilayers were exposed to
hydrogen, with sample temperatures between 80 and 200 C, and monitored via
in-situ x-ray diffraction and complimentary experiments conducted using
Scanning Transmission Electron Microscopy - Electron Energy Loss Spectroscopy
(STEM-EELS). Small partial pressures of H caused rapid consumption of the
U metal and lead to changes in the intensity and position of the diffraction
peaks from both the UO overlayers and the U metal. There is an
orientational dependence in the rate of U consumption. From changes in the
lattice parameter we deduce that hydrogen enters both the oxide and metal
layers, contracting the oxide and expanding the metal. The air-grown oxide
overlayers appear to hinder the H-reaction up to a threshold dose, but
then on heating from 80 to 140 C the consumption is more rapid than for the
as-deposited overlayers. STEM-EELS establishes that the U-hydride layer lies at
the oxide-metal interface, and that the initial formation is at defects or
grain boundaries, and involves the formation of amorphous and/or
nanocrystalline UH. This explains why no diffraction peaks from UH
are observed. {\textcopyright British Crown Owned Copyright 2017/AWE}Comment: Submitted for peer revie
Inflammatory Mediators of Hepatic Steatosis
Nonalcoholic fatty liver disease (NAFLD) is rapidly becoming a world-wide public health problem. NAFLD represents a spectrum of disease ranging from “simple steatosis”, which is considered relatively benign, to nonalcoholic steatohepatitis and to NAFLD-associated cirrhosis and end-stage liver disease. The etiology of NAFLD and its progression is complex and remains incompletely understood. The progression of the disease involves many factors. Apart from the two hits, the accumulation of TG and the development of fibrosis and necroinflammatory processes, exit numerous molecules associated with these two hits. Among them we can highlight the pro-inflammatory molecules and adiponectins. This review focuses on the growing evidence from both experimental and human studies suggesting a central role of cytokines in the pathogenesis of NAFLD. We review the role of cytokines as key regulators of insulin sensitivity and hepatic lipid overloading, liver injury and inflammation, and fibrosis with an emphasis on potential therapeutic implications
Twisted magnetar magnetospheres
Magnetar magnetospheres are strongly twisted, and are able to power sudden
energetic events through the rapid release of stored electromagnetic energy. In
this paper, we investigate twisted relativistic force-free axisymmetric
magnetospheres of rotating neutron stars. We obtain numerical solutions of such
configurations using the method of simultaneous relaxation for the magnetic
field inside and outside the light-cylinder. We introduce a toroidal magnetic
field in the region of closed field-lines that is associated with a poloidal
electric current distribution in that region, and explore various mathematical
expressions for that distribution. We find that, by increasing the twist, a
larger fraction of magnetic field-lines crosses the light-cylinder and opens up
to infinity, thus increasing the size of the polar caps and enhancing the
spin-down rate. We also find that, for moderately to strongly twisted
magnetospheres, the region of closed field-lines ends at some distance inside
the light-cylinder. We discuss the implications of these solutions on the
variation of magnetar spin-down rates, moding and nulling of pulsars, the
relation between the angular shear and the twist and the overall shape of the
magnetosphere.Comment: Accepted by MNRA
Nature of non-magnetic strongly-correlated state in delta-plutonium
Ab-initio relativistic dynamical mean-field theory is applied to resolve the
long-standing controversy between theory and experiment in the "simple"
face-centered cubic phase of plutonium called delta-Pu. In agreement with
experiment, neither static nor dynamical magnetic moments are predicted. In
addition, the quasiparticle density of states reproduces not only the peak
close to the Fermi level, which explains the large coefficient of electronic
specific heat, but also main 5f features observed in photoelectron
spectroscopy.Comment: 9 pages, 3 figure
Electronic structure of the muonium center as a shallow donor in ZnO
The electronic structure and the location of muonium centers (Mu) in
single-crystalline ZnO were determined for the first time. Two species of Mu
centers with extremely small hyperfine parameters have been observed below 40
K. Both Mu centers have an axial-symmetric hyperfine structure along with a
[0001] axis, indicating that they are located at the AB_{O,//} and BC_{//}
sites. It is inferred from their small ionization energy (~6 meV and 50 meV)
and hyperfine parameters (~10^{-4} times the vacuum value) that these centers
behave as shallow donors, strongly suggesting that hydrogen is one of the
primary origins of n type conductivity in as-grown ZnO.Comment: 4 pages, 4 figures, submitted to PR
An experimental and numerical investigation into damage mechanisms in tapered laminates under tensile loading
Through-thickness thickness reductions in laminated composites are essential for weight and aerodynamic efficiency, but they can also be the site of damage initiation. Tensile failure mechanisms of modestly tapered laminates, loaded via gripping their thick and thin ends, and a severely tapered laminate, loaded by contact at its tapered section, were investigated via experiments and high-fidelity finite element modelling. The primary failure mode is by delamination, initiated from a terminated ply in the tapered region, which is quite sensitive to a small delamination defect at a ply drop location. Experimental measurements and FE predictions correlate very well in all cases for both location and load. In the severely tapered case, the contact stress influences the delamination and so a fibre failure criterion also needs to be considered, including both the fibre direction tensile stress and its interaction with through-thickness direct and shear stresses imposed by the contact
Nebulized Delivery of the MAPKAP Kinase 2 Peptide Inhibitor MMI-0100 Protects Against Ischemia-Induced Systolic Dysfunction
Acute myocardial infarction (AMI) results in systolic dysfunction, myocarditis and fibrotic remodeling, which causes irreversible pathological remodeling of the heart. Associated cell death and inflammation cause cytokine release, which activates the p38 MAPK signaling pathway to propagate damaging signals via MAPKAP kinase 2 (MK2). Previously we showed that intraperitoneal injection of a cell permeable peptide inhibitor of MK2, MMI-0100, protects against fibrosis, apoptosis and systolic dysfunction in a mouse model of AMI induced by left-anterior descending coronary artery (LAD) ligation. Here we tested a new route of administration of MMI-0100: inhalation of nebulized peptide. When given within 30 min of AMI and daily for 2 weeks thereafter, both inhaled and injected MMI-0100 improved cardiac function as measured by conscious echocardiography. Limited fibrosis was observed after 2 weeks by Massons trichrome staining, suggesting that MMI-0100 protects the heart prior to the formation of significant fibrosis. These results support a nebulized route of administration of MMI-0100 can protect the myocardium from ischemic damage
Ambipolar diffusion in superfluid neutron stars
In this paper we reconsider the problem of magnetic field diffusion in
neutron star cores. We model the star as consisting of a mixture of neutrons,
protons and electrons, and allow for particle reactions and binary collisions
between species. Our analysis is in much the same spirit as that of Goldreich &
Reisenegger (1992), and we content ourselves with rough estimates of magnetic
diffusion timescales, rather than solving accurately for some particular field
geometry. However, our work improves upon previous treatments in one crucial
respect: we allow for superfluidity in the neutron star matter. We find that
the consequent mutual friction force, coupling the neutrons and charged
particles, together with the suppression of particles collisions and reactions,
drastically affect the ambipolar magnetic field diffusion timescale. In
particular, the addition of superfluidity means that it is unlikely that there
is ambipolar diffusion in magnetar cores on the timescale of the lifetimes of
these objects, contradicting an assumption often made in the modelling of the
flaring activity commonly observed in magnetars. Our work suggests that if a
decaying magnetic field is indeed the cause of magnetar activity, the field
evolution is likely to take place outside of the core, and might represent
Hall/Ohmic diffusion in the stellar crust, or else that a mechanism other than
standard ambipolar diffusion is active, e.g. flux expulsion due to the
interaction between neutron vortices and magnetic fluxtubes.Comment: Paper changed to incorporate comments from referee. To appear in
MNRA
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