1,593 research outputs found
Dynamic hysteresis from zigzag domain walls
We investigate dynamic hysteresis in ferromagnetic thin films with zigzag
domain walls. We introduce a discrete model describing the motion of a wall in
a disordered ferromagnet with in-plane magnetization, driven by an external
magnetic field, considering the effects of dipolar interactions and anisotropy.
We analyze the effects of external field frequency and temperature on the
coercive field by Monte Carlo simulations, and find a good agreement with the
experimental data reported in literature for Fe/GaAs films. This implies that
dynamic hysteresis in this case can be explained by a single propagating domain
wall model without invoking domain nucleation.Comment: 10 pages, 13 figures; minor modifications and two figures adde
GASP IV: A muse view of extreme ram-pressure stripping in the plane of the sky: the case of jellyfish galaxy JO204
In the context of the GAs Stripping Phenomena in galaxies with Muse (GASP)
survey, we present the characterization of JO204, a jellyfish galaxy in A957, a
relatively low-mass cluster with . This galaxy
shows a tail of ionized gas that extends up to 30 kpc from the main body in the
opposite direction of the cluster center. No gas emission is detected in the
galaxy outer disk, suggesting that gas stripping is proceeding outside-in. The
stellar component is distributed as a regular disk galaxy; the stellar
kinematics shows a symmetric rotation curve with a maximum radial velocity of
200km/s out to 20 kpc from the galaxy center. The radial velocity of the gas
component in the central part of the disk follows the distribution of the
stellar component; the gas kinematics in the tail retains the rotation of the
galaxy disk, indicating that JO204 is moving at high speed in the intracluster
medium. Both the emission and radial velocity maps of the gas and stellar
components indicate ram-pressure as the most likely primary mechanism for gas
stripping, as expected given that JO204 is close to the cluster center and it
is likely at the first infall in the cluster. The spatially resolved star
formation history of JO204 provides evidence that the onset of ram-pressure
stripping occurred in the last 500 Myr, quenching the star formation activity
in the outer disk, where the gas has been already completely stripped. Our
conclusions are supported by a set of hydrodynamic simulations.Comment: accepted for publication in Ap
GASP XIX: AGN and their outflows at the center of jellyfish galaxies
The GASP survey, based on MUSE data, is unveiling the properties of the gas
in the so-called "jellyfish" galaxies: these are cluster galaxies with
spectacular evidence of gas stripping by ram pressure. In a previous paper, we
selected the seven GASP galaxies with the most extended tentacles of ionized
gas, and based on individual diagnostic diagrams concluded that at least five
of them present clear evidence for an Active Galactic Nucleus. Here we present
a more detailed analysis of the emission lines properties in these galaxies.
Our comparison of several emission line ratios with both AGN and shock models
show that photoionization by the AGN is the dominant ionization mechanism. This
conclusion is strengthened by the analysis of luminosities, the
presence of nuclear iron coronal lines and extended ( kpc) emission line
regions ionized by the AGN in some of these galaxies. From emission line
profiles, we find the presence of outflows in four galaxies, and derive mass
outflow rates, timescales and kinetic energy of the outflows.Comment: 20 pages, 10 Figure
Improved photocatalytic properties of doped titanium-based nanometric oxides
Photocatalysis is considered one of the most promising technologies for applications in the environmental field especially in the abatement of water-soluble organic pollutants. In this field, titanium dioxide nanoparticles have drawn much attention recently; however, the use of this oxide presents some limitation since it allows to obtain high photoresponse and degradation efficiency only under UV light irradiation, that represents the 3 to 4% of the solar radiation, so preventing its environmental large-scale applications under diffuse daylight. In this work the photocatalytic efficiencyoftitanium-based oxides systems containing alkaline earth metals such as barium and strontium, prepared by a simple sol-gel method was investigated, evaluating the degradation of methylene blue as model compound under UV and visible light irradiation. The results were compared with those obtained with Degussa P25 titanium dioxide. The achieved degradation percentage of methylene blue are very promising showing that under visible light irradiation it is possible to obtain a maximum dye removal percentage ~ 50 % higher than that obtained with the Degussa P25
GASP. XVI. Does cosmic web enhancement turn on star formation in galaxies?
Galaxy filaments are a peculiar environment, and their impact on the galaxy
properties is still controversial. Exploiting the data from the GAs Stripping
Phenomena in galaxies with MUSE (GASP), we provide the first characterisation
of the spatially resolved properties of galaxies embedded in filaments in the
local Universe. The four galaxies we focus on show peculiar ionised gas
distributions: Halpha clouds have been observed beyond four times the effective
radius. The gas kinematics, metallicity map and the ratios of emission line
fluxes confirm that they do belong to the galaxy gas disk, the analysis of
their spectra shows that very weak stellar continuum is associated to them.
Similarly, the star formation history and luminosity weighted age maps point to
a recent formation of such clouds. The clouds are powered by star formation,
and are characterised by intermediate values of dust absorption. We hypothesise
a scenario in which the observed features are due to "Cosmic Web Enhancement":
we are most likely witnessing galaxies passing through or flowing within
filaments that assist the gas cooling and increase the extent of the star
formation in the densest regions in the circumgalactic gas. Targeted
simulations are mandatory to better understand this phenomenon.Comment: MNRAS in press, 18 pages, 12 figure
Enhanced star formation in both disks and ram pressure stripped tails of GASP jellyfish galaxies
Exploiting the data from the GAs Stripping Phenomena in galaxies with MUSE
(GASP) program, we compare the integrated Star Formation Rate- Mass relation
(SFR-M_ast) relation of 42 cluster galaxies undergoing ram pressure stripping
("stripping galaxies") to that of 32 field and cluster undisturbed galaxies.
Theoretical predictions have so far led to contradictory conclusions about
whether ram pressure can enhance the star formation in the gas disks and tails
or not and until now a statistically significant observed sample of stripping
galaxies was lacking. We find that stripping galaxies occupy the upper envelope
of the control sample SFR-M_ast relation, showing a systematic enhancement of
the SFR at any given mass. The star formation enhancement occurs in the disk
(0.2 dex), and additional star formation takes place in the tails. Our results
suggest that strong ram pressure stripping events can moderately enhance the
star formation also in the disk prior to gas removal.Comment: ApJL in pres
Levels of disability in the older population of England: Comparing binary and ordinal classifications.
BACKGROUND: Recent studies suggest the importance of distinguishing severity levels of disability. Nevertheless, there is not yet a consensus with regards to an optimal classification. OBJECTIVE: Our study seeks to advance the existing binary definitions towards categorical/ordinal manifestations of disability. METHODS: We define disability according to the WHO's International Classification of Functioning, Disability and Health (ICF) using data collected at the baseline wave of the English Longitudinal Study of Aging, a longitudinal study of the non-institutionalized population, living in England. First, we identify cut-off points in the continuous disability score derived from ICF to distinguish disabled from no-disabled participants. Then, we fit latent class models to the same data to find the optimal number of disability classes according to: (i) model fit indicators; (ii) estimated probabilities of each disability item; (iii) association of the predicted disability classes with observed health and mortality. RESULTS: According to the binary classification criteria, about 32% of both men and women are classified disabled. No optimal number of classes emerged from the latent class models according to model fit indicators. However, the other two criteria suggest that the best-fitting model of disability severity has four classes. CONCLUSIONS: Our findings contribute to the debate on the usefulness and relevance of adopting a finer categorization of disability, by showing that binary indicators of disability averaged the burden of disability and masked the very strong effect experienced by individuals having severe disability, and were not informative for low levels of disability
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