1,401 research outputs found
Buoyancy and g-modes in young superfluid neutron stars
We consider the local dynamics of a realistic neutron star core, including
composition gradients, superfluidity and thermal effects. The main focus is on
the gravity g-modes, which are supported by composition stratification and
thermal gradients. We derive the equations that govern this problem in full
detail, paying particular attention to the input that needs to be provided
through the equation of state and distinguishing between normal and superfluid
regions. The analysis highlights a number of key issues that should be kept in
mind whenever equation of state data is compiled from nuclear physics for use
in neutron star calculations. We provide explicit results for a particular
stellar model and a specific nucleonic equation of state, making use of cooling
simulations to show how the local wave spectrum evolves as the star ages. Our
results show that the composition gradient is effectively dominated by the
muons whenever they are present. When the star cools below the superfluid
transition, the support for g-modes at lower densities (where there are no
muons) is entirely thermal. We confirm the recent suggestion that the g-modes
in this region may be unstable, but our results indicate that this instability
will be weak and would only be present for a brief period of the star's life.
Our analysis accounts for the presence of thermal excitations encoded in
entrainment between the entropy and the superfluid component. Finally, we
discuss the complete spectrum, including the normal sound waves and, in
superfluid regions, the second sound.Comment: 29 pages, 9 figures, submitted to MNRA
The relevance of ambipolar diffusion for neutron star evolution
We study ambipolar diffusion in strongly magnetised neutron stars, with
special focus on the effects of neutrino reaction rates and the impact of a
superfluid/superconducting transition in the neutron star core. For
axisymmetric magnetic field configurations, we determine the deviation from
equilibrium induced by the magnetic force and calculate the velocity of
the slow, quasi-stationary, ambipolar drift. We study the temperature
dependence of the velocity pattern and clearly identify the transition to a
predominantly solenoidal flow. For stars without superconducting/superfluid
constituents and with a mixed poloidal-toroidal magnetic field of typical
magnetar strength, we find that ambipolar diffusion proceeds fast enough to
have a significant impact on the magnetic field evolution only at low core
temperatures, K. The ambipolar diffusion timescale
becomes appreciably shorter when fast neutrino reactions are present, because
the possibility to balance part of the magnetic force with pressure gradients
is reduced. We also find short ambipolar diffusion timescales in the case of
superconducting cores for K, due to the reduced interaction
between protons and neutrons. In the most favourable scenario, with fast
neutrino reactions and superconducting cores, ambipolar diffusion results in
advection velocities of several km/kyr. This velocity can substantially
reorganize magnetic fields in magnetar cores, in a way that can only be
confirmed by dynamical simulations.Comment: 14 pages, 11 figures, version accepted for publication in MNRA
Towards asteroseismology of core-collapse supernovae with gravitational-wave observations - I. Cowling approximation
Gravitational waves from core-collapse supernovae are produced by the
excitation of different oscillation modes in the proto-neutron star (PNS) and
its surroundings, including the shock. In this work we study the relationship
between the post-bounce oscillation spectrum of the PNS-shock system and the
characteristic frequencies observed in gravitational-wave signals from
core-collapse simulations. This is a fundamental first step in order to develop
a procedure to infer astrophysical parameters of the PNS formed in
core-collapse supernovae. Our method combines information from the oscillation
spectrum of the PNS, obtained through linear-perturbation analysis in general
relativity of a background physical system, with information from the
gravitational-wave spectrum of the corresponding non-linear, core-collapse
simulation. Using results from the simulation of the collapse of a 35
presupernova progenitor we show that both types of spectra are
indeed related and we are able to identify the modes of oscillation of the PNS,
namely g-modes, p-modes, hybrid modes, and standing-accretion-shock-instability
(SASI) modes, obtaining a remarkably close correspondence with the
time-frequency distribution of the gravitational-wave modes. The analysis
presented in this paper provides a proof-of-concept that asteroseismology is
indeed possible in the core-collapse scenario, and it may serve as a basis for
future work on PNS parameter inference based on gravitational-wave
observations
Quasi-periodic oscillations in superfluid, relativistic magnetars with nuclear pasta phases
We study the torsional magneto-elastic oscillations of relativistic superfluid magnetars and explore the effects of a phase transition in the crust–core interface (nuclear pasta) which results in a weaker elastic response. Exploring various models with different extension of nuclear pasta phases, we find that the differences in the oscillation spectrum present in purely elastic modes (weak magnetic field) are smeared out with increasing strength of the magnetic field. For magnetar conditions, the main characteristic and features of models without nuclear pasta are preserved. We find, in general, two classes of magneto-elastic oscillations which exhibit a different oscillation pattern. For Bp 5 × 1014 G. We do not find any evidence of fundamental pure crustal modes in the low-frequency range (below 200 Hz) for Bp ≥ 1014 G.AP acknowledges support from the European Union under the Marie Sklodowska Curie Actions Individual Fellowship, grant agreement no 656370. This work is supported in part by the Spanish MINECO grant AYA2015-66899-C2-2-P, the programme PROMETEOII-2014-069 (Generalitat Valenciana), and by the NewCompstarCOST action MP1304
Mito-nuclear coevolution and phylogenetic artifacts: the case of bivalve mollusks
Mito‐nuclear phylogenetic discordance in Bivalvia is well known. In particular, the monophyly of Amarsipobranchia (Heterodonta + Pteriomorphia), retrieved from mitochondrial markers, contrasts with the monophyly of Heteroconchia (Heterodonta + Palaeoheterodonta), retrieved from nuclear markers. However, since oxidative phosphorylation nuclear markers support the Amarsipobranchia hypothesis instead of the Heteroconchia one, interacting subunits of the mitochondrial complexes ought to share the same phylogenetic signal notwithstanding the genomic source, which is different from the signal obtained from other nuclear markers. This may be a clue of coevolution between nuclear and mitochondrial genes. In this work we inferred the phylogenetic signal from mitochondrial and nuclear oxidative phosphorylation markers exploiting different phylogenetic approaches and added two more datasets for comparison: genes of the glycolytic pathway and genes related to the biogenesis of regulative small noncoding RNAs. All trees inferred from mitochondrial and nuclear subunits of the mitochondrial complexes support the monophyly of Amarsipobranchia, regardless of the phylogenetic pipeline. However, not every single marker agrees with this topology: this is clearly visible in nuclear subunits that do not directly interact with the mitochondrial counterparts. Overall, our data support the hypothesis of a coevolution between nuclear and mitochondrial genes for the oxidative phosphorylation. Moreover, we suggest a relationship between mitochondrial topology and different nucleotide composition between clades, which could be associated to the highly variable gene arrangement in Bivalvia
Identification and localization of the bilitranslocase homologue in white grape berries (Vitis vinifera L.) during ripening
A homologue of the mammalian bilirubin transporter bilitranslocase (BTL) (TCDB 2.A.65.1.1), able to perform an apparent secondary active transport of flavonoids, has previously been found in carnation petals and red grape berries. In the present work, a BTL homologue was also shown in white berries from Vitis vinifera L. cv. Tocai/Friulano, using anti-sequence antibodies specific for rat liver BTL. This transporter, similarly to what found in red grape, was localized in the first layers of the epidermal tissue and in the vascular bundle cells of the mesocarp. In addition, a strong immunochemical reaction was detected in the placental tissue and particularly in peripheral integuments of the seed. The protein was expressed during the last maturation stages in both skin and pulp tissues and exhibited an apparent molecular mass of c. 31 kDa. Furthermore, the transport activity of such a carrier, measured as bromosulphophthalein (BSP) uptake, was detected in berry pulp microsomes, where it was inhibited by specific anti-BTL antibodies. The BTL homologue activity exhibited higher values, for both Km and Vmax, than those found in the red cultivar. Moreover, two non-pigmented flavonoids, such as quercetin (a flavonol) and eriodictyol (a flavanone), inhibited the uptake of BSP in an uncompetitive manner. Such results strengthen the hypothesis that this BTL homologue acts as a carrier involved also in the membrane transport of colourless flavonoids and demonstrate the presence of such a carrier in different organs and tissues
Fiber Bragg Grating sensors for deformation monitoring of GEM foils in HEP detectors
Fiber Bragg Grating (FBG) sensors have been so far mainly used in high energy
physics (HEP) as high precision positioning and re-positioning sensors and as
low cost, easy to mount, radiation hard and low space- consuming temperature
and humidity devices. FBGs are also commonly used for very precise strain
measurements. In this work we present a novel use of FBGs as flatness and
mechanical tensioning sensors applied to the wide Gas Electron Multiplier (GEM)
foils of the GE1/1 chambers of the Compact Muon Solenoid (CMS) experiment at
Large Hadron Collider (LHC) of CERN. A network of FBG sensors has been used to
determine the optimal mechanical tension applied and to characterize the
mechanical stress applied to the foils. The preliminary results of the test
performed on a full size GE1/1 final prototype and possible future developments
will be discussed.Comment: Four pages, seven figures. Presented by Michele Caponero at IWASI
2015, Gallipoli (Italy
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Time-resolved connectome of the five-factor model of personality
Abstract: The human brain is characterized by highly dynamic patterns of functional connectivity. However, it is unknown whether this time-variant ‘connectome’ is related to the individual differences in the behavioural and cognitive traits described in the five-factor model of personality. To answer this question, inter-network time-variant connectivity was computed in n = 818 healthy people via a dynamical conditional correlation model. Next, network dynamicity was quantified throughout an ad-hoc measure (T-index) and the generalizability of the multi-variate associations between personality traits and network dynamicity was assessed using a train/test split approach. Conscientiousness, reflecting enhanced cognitive and emotional control, was the sole trait linked to stationary connectivity across several circuits such as the default mode and prefronto-parietal network. The stationarity in the ‘communication’ across large-scale networks offers a mechanistic description of the capacity of conscientious people to ‘protect’ non-immediate goals against interference over-time. This study informs future research aiming at developing more realistic models of the brain dynamics mediating personality differences
Eco-friendly gas mixtures for Resistive Plate Chambers based on Tetrafluoropropene and Helium
Due to the recent restrictions deriving from the application of the Kyoto
protocol, the main components of the gas mixtures presently used in the
Resistive Plate Chambers systems of the LHC experiments will be most probably
phased out of production in the coming years. Identifying possible replacements
with the adequate characteristics requires an intense R&D, which was recently
started, also in collaborations across the various experiments. Possible
candidates have been proposed and are thoroughly investigated. Some tests on
one of the most promising candidate - HFO-1234ze, an allotropic form of
tetrafluoropropane- have already been reported. Here an innovative approach,
based on the use of Helium, to solve the problems related to the too elevate
operating voltage of HFO-1234ze based gas mixtures, is discussed and the
relative first results are shown.Comment: 9 pages, 6 figures, 1 tabl
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