341 research outputs found
On the origin of magnetoresistance in SrFeMoO
We report detailed magnetization () and magnetoresistance () studies
on a series of SrFeMoO samples with independent control on anti-site
defect and grain boundary densities. These results, exhibiting a switching-like
behavior of with , establish that the is controlled by the
magnetic polarization of grain boundary regions, rather than of the grains
within a resonant tunnelling mechanism.Comment: 4 pages, 4 figure
Decoding the spectra of SDSS early-type galaxies: New indicators of age and recent star formation
(Abridged) We apply Principal Component Analysis (PCA) to a sample of
early-type galaxies from the Sloan Digital Sky Survey (SDSS) in order to infer
differences in their star formation histories. Out of the first few principal
components (PC), we study four which give information about stellar populations
and velocity dispersion. We construct two parameters (eta and zeta) as linear
combinations of PC1 and PC2. We find zeta to be most sensitive to recent
episodes of star formation, and eta to be strongly dependent on the average age
of the stellar populations. The distribution of the eta component of the
composites appear to be indistinguishable between high and low density regions,
whereas the distribution of zeta parameters have a significant skew towards
lower values for galaxies in low density regions. This result suggests that
galaxies in lower density environments are less likely to present weak episodes
of recent star formation. In contrast, a significant number of galaxies from
our high density subsample -- which includes clusters (both outer regions and
centres) and groups -- underwent small but detectable recent star formation at
high metallicity, in agreement with recent estimates targeting elliptical
galaxies in Hickson Compact Groups and in the field (Ferreras et al.).Comment: 19 pages, 12 figures. Accepted for publication in MNRA
Local analogues of high-redshift star-forming galaxies: integral field spectroscopy of green peas
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society. ©: 2017 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.We use integral field spectroscopy, from the SWIFT and Palm3K instruments, to perform a spatially-resolved spectroscopic analysis of four nearby highly star-forming `green pea' (GP) galaxies, that are likely analogues of star-forming systems at z~2.5-3. By studying emission-line maps in H, [NII]6548,6584 and [SII]6716,6731, we explore the kinematic morphology of these systems and constrain properties such as gas-phase metallicities, electron densities and gas-ionization mechanisms. Two of our GPs are rotationally-supported while the others are dispersion-dominated systems. The rotationally-supported galaxies both show evidence for recent or ongoing mergers. However, given that these systems have intact disks, these interactions are likely to have low mass ratios (i.e. minor mergers), suggesting that the minor-merger process may be partly responsible for the high SFRs seen in these GPs. Nevertheless, the fact that the other two GPs appear morphologically undisturbed suggests that mergers (including minor mergers) are not necessary for driving the high star formation rates in such galaxies. We show that the GPs are metal-poor systems (25-40 per cent of solar) and that the gas ionization is not driven by AGN in any of our systems, indicating that AGN activity is not co-eval with star formation in these starbursting galaxies.Peer reviewedFinal Published versio
The Morphological Changes in the Vestibular Sensory Epithelia Following Electrical Stimulation
The morphological changes of the vestibular sensory epithelia of the guinea pig following electrical stimulation were investigated using scanning electron microscope.
Positive and negative square wave pulse stimulation was given through a silver ball electrode placed on the round window membrane for one hour. The current intensities used were 100, 200 and 300 A.
While the direct current stimulation at intensities of 100 or 200 A did not cause any significant changes, severe damage of the utricular macula and the ampullar crista of the lateral semicircular canal was observed at 300 A. The degenerative changes such as fusion of sensory hairs, protrusion of the cuticular plate and loss of sensory cells were found on both the utricle and the semicircular canal. In the most severely damaged area, the sensory epithelial surface was badly torn apart.
In the clinical application of direct current to the inner ear for relieving tinnitus, special attention should be paid to the vestibular organ
The elliptical colour-magnitude relation as a discriminant between the monolithic and merger paradigms: the importance of progenitor bias
The colour-magnitude relation (CMR) of cluster ellipticals has been widely
used to constrain their star formation histories (SFHs) and to discriminate
between the monolithic and merger paradigms of elliptical galaxy formation. We
investigate the elliptical CMR predicted in the merger paradigm by using a LCDM
hierarchical merger model. We first highlight sections of the literature which
indicate that the traditional use of fixed apertures to derive colours gives a
distorted view of the CMR due to the presence of colour gradients in galaxies.
Fixed aperture observations make the CMR steeper and tighter than it really is.
We then show that the star formation history (SFH) of cluster ellipticals
predicted by the model is quasi-monolithic, with over 95 percent of the total
stellar mass formed before a redshift of 1. The quasi-monolithic SFH produces a
predicted CMR that agrees well at all redshifts with its observed counterpart
once the fixed aperture effect is removed. More importantly, we present
arguments to show that the elliptical-only CMR can be used to constrain the
SFHs of present-day cluster ellipticals only if we believe a priori in the
monolithic collapse model. It is not a meaningful tool for constraining the SFH
in the merger paradigm, because a progressively larger fraction of the
progenitor set of present-day cluster ellipticals is contained in late-type
star forming systems at higher redshift, which cannot be ignored when deriving
the SFHs. Hence, the elliptical-only CMR is not a useful discriminant between
the two competing theories of elliptical galaxy evolution.Comment: replaced with accepted versio
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