9,710 research outputs found
Bar-induced central star formation as revealed by integral field spectroscopy from CALIFA
We investigate the recent star formation history (SFH) in the inner region of
57 nearly face-on spiral galaxies selected from the Calar Alto Legacy Integral
Field Area (CALIFA) survey. For each galaxy we use the integral field
spectroscopy from CALIFA to obtain two-dimensional maps and radial profiles of
three parameters that are sensitive indicators of the recent SFH: the 4000\AA\
break (D(4000)), and the equivalent width of H absorption
(EW(H)) and H emission (EW(H)). We have also
performed photometric decomposition of bulge/bar/disk components based on SDSS
optical image. We identify a class of 17 "turnover" galaxies whose central
region present significant drop in D(4000), and most of them
correspondingly show a central upturn in EW(H) and EW(H).
This indicates that the central region of the turnover galaxies has experienced
star formation in the past 1-2 Gyr, which makes the bulge younger and more
star-forming than surrounding regions. We find almost all (15/17) the turnover
galaxies are barred, while only half of the barred galaxies in our sample
(15/32) are classified as a turnover galaxy. This finding provides strong
evidence in support of the theoretical expectation that the bar may drive gas
from the disc inward to trigger star formation in galaxy center, an important
channel for the growth/rejuvenation of pseudobulges in disc galaxies.Comment: 19 pages, 10 figures, ApJ accepte
Signatures of strong correlation effects in RIXS on Cuprates
Recently, spin excitations in doped cuprates are measured using the resonant
inelastic X-ray scattering (RIXS). The paramagnon dispersions show the large
hardening effect in the electron-doped systems and seemingly
doping-independence in the hole-doped systems, with the energy scales
comparable to that of the antiferromagnetic magnons. This anomalous hardening
effect was partially explained by using the strong coupling t-J model but with
a three-site term(Nature communications 5, 3314 (2014)). However we show that
hardening effect is a signature of strong coupling physics even without
including this extra term. By considering the t-t'-t"-J model and using the
Slave-Boson (SB) mean field theory, we obtain, via the spin-spin
susceptibility, the spin excitations in qualitative agreement with the
experiments. These anomalies is mainly due to the doping-dependent bandwidth.
We further discuss the interplay between particle-hole-like and paramagnon-like
excitations in the RIXS measurements.Comment: 7 pages, 6 figure
The peculiar filamentary HI structure of NGC 6145
In this paper, we report the peculiar HI morphology of the cluster spiral
galaxy NGC 6145, which has a 150 kpc HI filament on one side that is nearly
parallel to its major axis. This filament is made up of several HI clouds and
the diffuse HI gas between them, with no optical counterparts. We compare its
HI distribution with other one-sided HI distributions in the literature, and
find that the overall HI distribution is very different from the typical tidal
and ram-pressure stripped HI shape, and its morphology is inconsistent with
being a pure accretion event. Only about 30% of the total HI gas is anchored on
the stellar disk, while most of HI gas forms the filament in the west. At a
projected distance of 122 kpc, we find a massive elliptical companion (NGC
6146) with extended radio emission, whose axis points to an HI gap in NGC 6145.
The velocity of the HI filament shows an overall light-of- sight motion of 80
to 180 km/s with respect to NGC 6145. Using the long-slit spectra of NGC 6145
along its major stellar axis, we find that some outer regions show enhanced
star formation, while in contrast, almost no star formation activities are
found in its center (less than 2 kpc). Pure accretion, tidal or ram-pressure
stripping is not likely to produce the observed HI filament. An alternative
explanation is the jet-stripping from NGC 6146, although direct evidence for a
jet-cold gas interaction has not been found.Comment: 12 pages, 6 figures; Accepted for publication in A
On the Universal Approximation Property of Deep Fully Convolutional Neural Networks
We study the approximation of shift-invariant or equivariant functions by
deep fully convolutional networks from the dynamical systems perspective. We
prove that deep residual fully convolutional networks and their
continuous-layer counterpart can achieve universal approximation of these
symmetric functions at constant channel width. Moreover, we show that the same
can be achieved by non-residual variants with at least 2 channels in each layer
and convolutional kernel size of at least 2. In addition, we show that these
requirements are necessary, in the sense that networks with fewer channels or
smaller kernels fail to be universal approximators
Progressive amorphization of GeSbTe phase-change material under electron beam irradiation
Fast and reversible phase transitions in chalcogenide phase-change materials
(PCMs), in particular, Ge-Sb-Te compounds, are not only of fundamental
interests, but also make PCMs based random access memory (PRAM) a leading
candidate for non-volatile memory and neuromorphic computing devices. To RESET
the memory cell, crystalline Ge-Sb-Te has to undergo phase transitions firstly
to a liquid state and then to an amorphous state, corresponding to an abrupt
change in electrical resistance. In this work, we demonstrate a progressive
amorphization process in GeSb2Te4 thin films under electron beam irradiation on
transmission electron microscope (TEM). Melting is shown to be completely
absent by the in situ TEM experiments. The progressive amorphization process
resembles closely the cumulative crystallization process that accompanies a
continuous change in electrical resistance. Our work suggests that if
displacement forces can be implemented properly, it should be possible to
emulate symmetric neuronal dynamics by using PCMs
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