2,287 research outputs found
Ages and abundances in large-scale stellar disks of nearby S0 galaxies
By undertaking deep long-slit spectroscopy with the focal reducer SCORPIO of
the Russian 6m telescope, we studied stellar population properties and their
variation with radius in 15 nearby S0 galaxies sampling a wide range of
luminosities and environments. For the large-scale stellar disks of S0s, we
have measured SSP-equivalent metallicities ranging from the solar one down to
[Z/H]=-0.4 - -0.7, rather high magnesium-to-iron ratios, [Mg/Fe] > +0.2, and
mostly old SSP-equivalent ages. Nine of 15 (60%) galaxies have large-scale
stellar disks older than 10 Gyr, and among those we find all the galaxies which
reside in denser environments. The isolated galaxies may have intermediate-age
stellar disks which are 7-9 Gyr old. Only two galaxies of our sample, NGC 4111
and NGC 7332, reveal SSP-equivalent ages of their disks of 2-3 Gyrs. Just these
two young disks appear to be thin, while the other, older disks have scale
heights typical for thick stellar disks. The stellar populations in the bulges
at radii of 0.5r_eff are on the contrary more metal-rich than the solar
metallicity, with the ages homogeneously distributed between 2 and 15 Gyr,
being almost always younger than the disks. We conclude that S0 galaxies could
not form in groups at z=0.4 as is thought now; a new scenario of the general
evolution of disk galaxies is proposed instead.Comment: Accepted to the MNRA
Validity of abundances derived from spaxel spectra of the MaNGA survey
We measured the emission lines in the spaxel spectra of MaNGA galaxies in
order to determine the abundance distributions therein. It has been suggested
that the strength of the low-ionization lines, R_2, N_2, and S_2 may be
increased (relative to Balmer lines) in (some) spaxel spectra of the MaNGA
survey due to a contribution of the radiation of the diffuse ionized gas.
Consequently, the abundances derived from the spaxel spectra through
strong-line methods may suffer from large errors. We examined this expectation
by comparing the behaviour of the line intensities and the abundances estimated
through different calibrations for slit spectra of HII regions in nearby
galaxies, for fibre spectra from the SDSS, and for spaxel spectra of the MaNGA
survey. We found that the S_2 strength is increased significantly in the fibre
and spaxel spectra. The mean enhancement changes with metallicity and can be as
large as a factor of 2. The mean distortion of R_2 and N_2 is less than a
factor of 1.3. This suggests that Kaufmann et al.'s demarcation line between
AGNs and HII regions in the BPT diagram is a useful criterion to reject spectra
with significantly distorted strengths of the N_2 and R_2 lines. We find that
the three-dimensional R calibration, which uses the N_2 and R_2 lines, produces
reliable abundances in the MaNGA galaxies. The one-dimensional N2 calibration
produces either reliable or wrong abundances depending on whether excitation
and N/O abundance ratio in the target region (spaxel) are close to or differ
from those parameters in the calibrating points located close to the
calibration relation. We then determined abundance distributions within the
optical radii in the discs of 47 MaNGA galaxies. The optical radii of the
galaxies were estimated from the surface brightness profiles constructed based
on the MaNGA observations.Comment: 19 pages, 15 figures, accepted for publication in A&
Restoration of hand function with long-term paired associative stimulation after chronic incomplete tetraplegia: a case study
INTRODUCTION: This case study explores the gains in hand function in an individual with a chronic spinal cord injury (SCI). The intervention was long-term paired associative simulation (PAS). We aimed to provide PAS until full recovery of hand muscle strength occurred, or until improvements ceased. CASE PRESENTATION: A 46-year-old man with traumatic C7 AIS B tetraplegia was administered PAS three times per week. After 24 weeks, PAS was combined with concomitant motor training of the remaining weak hand muscles. Outcome measures included the manual muscle test (MMT), motor-evoked potentials (MEPs), F-responses, hand functional tests, and the spinal cord independence measure (SCIM). DISCUSSION: After 47 weeks of PAS the subject had improved self-care and indoor mobility and was able to perform complex motor tasks (SCIM score improved from 40 to 56). His left hand regained maximum MMT score (total 75; increase of score from baseline condition 19); the effect remained stable in the 32-week follow up. In the right-hand muscles, MMT scores of 4-5 were observed in follow up (total 71; increase from baseline 48). Improved values were also observed in other outcomes. This is the first demonstration of long-term PAS restoring muscle strength corresponding to MMT scores of 4-5 in an individual with chronic SCI. The effect persisted for several months, indicating that PAS induces stable plastic changes in the corticospinal pathway.Peer reviewe
Thermodynamics of Two - Band Superconductors: The Case of MgB
Thermodynamic properties of the multiband superconductor MgB have often
been described using a simple sum of the standard BCS expressions corresponding
to - and -bands. Although, it is \textit{a priori} not clear if
this approach is working always adequately, in particular in cases of strong
interband scattering. Here we compare the often used approach of a sum of two
independent bands using BCS-like -model expressions for the specific
heat, entropy and free energy to the solution of the full Eliashberg equations.
The superconducting energy gaps, the free energy, the entropy and the heat
capacity for varying interband scattering rates are calculated within the
framework of two-band Eliashberg theory. We obtain good agreement between the
phenomenological two-band -model with the Eliashberg results, which
delivers for the first time the theoretical verification to use the
-model as a useful tool for a reliable analysis of heat capacity data.
For the thermodynamic potential and the entropy we demonstrate that only the
sum over the contributions of the two bands has physical meaning.Comment: 27 pages, 10 figures, 1 table, submitted to Phys. Rev.
Spectral distribution in the reflection of parametric X-rays
The parametric X-ray radiation (PXR) spectra are measured on condition when the angular size of PXR cone is smaller than the angular resolution of the experiment. The PXR is generated under interaction of 50GeV proton beam with silicon crystal in Bragg geometry. The comparison of experimental data with results of developed theoretical model is presented and discusse
The oxygen isotope effect in the ab-plane reflectance of underdoped YBa_2Cu_3O_{7-delta}
We have measured the effect of oxygen isotope substitution on the ab-plane
reflectance of underdoped YBCO. The frequency shift of the transverse optic
phonons due to the substitution of O-16 by O-18 yields an isotope effect of the
expected magnitude for copper-oxygen stretching modes with alpha=0.5 +- 0.1.
The reflectance shoulder at 400 - 500 cm^-1 shows a much smaller exponent of
alpha=0.1 +- 0.1 in the normal state and alpha=0.23+- 0.1 in the
superconducting state. These observations suggest that the shoulder is of
electronic origin and not due to a phonon mode as has been suggested recently.Comment: 4 pages 2 figure
Theory of the Optical Conductivity in the Cuprate Superconductors
We present a study of the normal state optical conductivity in the cuprate
superconductors using the nearly antiferromagnetic Fermi liquid (NAFL)
description of the magnetic interaction between their planar quasiparticles. We
find that the highly anisotropic scattering rate in different regions of the
Brillouin zone, both as a function of frequency and temperature, a benchmark of
NAFL theory, leads to an average relaxation rate of the Marginal Fermi Liquid
form for overdoped and optimally doped systems, as well as for underdoped
systems at high temperatures. We carry out numerical calculations of the
optical conductivity for several compounds for which the input spin fluctuation
parameters are known. Our results, which are in agreement with experiment on
both overdoped and optimally doped systems, show that NAFL theory explains the
anomalous optical behavior found in these cuprate superconductors.Comment: REVTEX file, 8 PostScript figure
Infrared and optical properties of pure and cobalt-doped LuNi_2B_2C
We present optical conductivity data for Lu(NiCo)BC over
a wide range of frequencies and temperatures for x=0 and x=0.09. Both materials
show evidence of being good Drude metals with the infrared data in reasonable
agreement with dc resistivity measurements at low frequencies. An absorption
threshold is seen at approximately 700 cm-1. In the cobalt-doped material we
see a superconducting gap in the conductivity spectrum with an absorption onset
at 24 +/- 2 cm-1 = 3.9$ +/- 0.4 k_BT_c suggestive of weak to moderately strong
coupling. The pure material is in the clean limit and no gap can be seen. We
discuss the data in terms of the electron-phonon interaction and find that it
can be fit below 600 cm-1 with a plasma frequency of 3.3 eV and an
electron-phonon coupling constant lambda_{tr}=0.33 using an alpha^{2}F(omega)
spectrum fit to the resistivity.Comment: 10 pages with 10 embedded figures, submitted to PR
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