6,599 research outputs found
Detailed Abundances for the Old Population near the Galactic Center: I. Metallicity distribution of the Nuclear Star Cluster
We report the first high spectral resolution study of 17 M giants
kinematically confirmed to lie within a few parsecs of the Galactic Center,
using R=24,000 spectroscopy from Keck/NIRSPEC and a new linelist for the
infrared K band. We consider their luminosities and kinematics, which classify
these stars as members of the older stellar population and the central cluster.
We find a median metallicity of =-0.16 and a large spread from
approximately -0.3 to +0.3 (quartiles). We find that the highest metallicities
are [Fe/H]<+0.6, with most of the stars being at or below the Solar iron
abundance. The abundances and the abundance distribution strongly resembles
that of the Galactic bulge rather than disk or halo; in our small sample we
find no statistical evidence for a dependence of velocity dispersion on
metallicity.Comment: 18 pages, 14 figures, accepted for publication in A
Musical feedback system Jymmin leads to enhanced physical endurance in the elderly: A feasibility study
Background and objectives: Active music-making in combination with physical exercise has evoked several positive effects in users of different age groups. These include enhanced mood, muscular effectivity, pain threshold, and decreased perceived exertion. The present study tested the applicability of this musical feedback system, called Jymmin®, in combination with strength-endurance exercises in a population of healthy older adults. Research design and methods: Sixteen healthy, physically inactive older adults (5 males, 11 females) at the mean age of 70 years performed physical exercise in two conditions: A conventional work-out while listening passively music and a Jymmin® work-out, where musical sounds were created with one's work-out movements. According to the hypothesis that strength-endurance is increased during musical feedback exercise, parameters relating to strength-endurance were assessed, including exercise duration, number of repetitions, perceived exertion (RPE), and participants' mental state (Multidimensional Mood State Questionnaire; MDMQ). Results: Results show that participants exercised significantly longer while doing Jymmin® (Mdn = 248.75 s) as compared to the conventional work-out (Mdn = 182.73 s), (Z = 3.408, p = 0.001). The RPE did not differ between conventional work-out and the Jymmin® condition, even though participants worked out significantly longer during the Jymmin® condition (Mdn = 14.50; Z = −0.905; p = 0.366). The results of the MDMQ showed no significant differences between both conditions (Z = −1.037; p = 0.300). Discussion and implications: Results show that participants could work out longer while showing the same perceived exertion, relating to increased physical endurance. Music feedback work-out encouraged a greater degree of isometric contractions (muscle actively held at fixed length) and, therefore, less repetitions in this condition. In addition to the previously described effect on muscle effectivity, this non-stereotypic contraction pattern during music feedback training may have enhanced endurance in participants supporting them to better proportion energetic reserves during training (pacing)
Quantum phase transitions in a resonant-level model with dissipation: Renormalization-group studies
We study a spinless level that hybridizes with a fermionic band and is also
coupled via its charge to a dissipative bosonic bath. We consider the general
case of a power-law hybridization function \Gamma(\w)\propto |\w|^r with
, and a bosonic bath spectral function B(\w)\propto \w^s with . For and , this Bose-Fermi quantum impurity
model features a continuous zero-temperature transition between a delocalized
phase, with tunneling between the impurity level and the band, and a localized
phase, in which dissipation suppresses tunneling in the low-energy limit. The
phase diagram and the critical behavior of the model are elucidated using
perturbative and numerical renormalization-group techniques, between which
there is excellent agreement in the appropriate regimes. For this model's
critical properties coincide with those of the spin-boson and Ising Bose-Fermi
Kondo models, as expected from bosonization.Comment: 14 pages, 14 eps figure
Metallicities of M Dwarf Planet Hosts from Spectral Synthesis
We present the first spectroscopic metallicities of three M dwarfs with known
or candidate planetary mass companions. We have analyzed high resolution, high
signal-to-noise spectra of these stars which we obtained at McDonald
Observatory. Our analysis technique is based on spectral synthesis of atomic
and molecular features using recently revised cool-star model atmospheres and
spectrum synthesis code. The technique has been shown to yield results
consistent with the analyses of solar-type stars and allows measurements of M
dwarf [M/H] values to 0.12 dex precision. From our analysis, we find [M/H] =
-0.12, -0.32, and -0.33 for GJ 876, GJ 436, and GJ 581 respectively. These
three M dwarf planet hosts have sub-solar metallicities, a surprising departure
from the trend observed in FGK-type stars. This study is the first part of our
ongoing work to determine the metallicities of the M dwarfs included in the
McDonald Observatory planet search program.Comment: 13 pages, 2 figures, accepted for publication in ApJ
Electric and heat transport in a charge two-channel Kondo device
Motivated by the experimental realization of a multi-channel charge Kondo
device [Iftikhar et al., Nature 526, 233 (2015)], we study generic charge and
heat transport properties of the charge two-channel Kondo model. We present a
comprehensive discussion of the out-of-equilibrium and time-dependent charge
transport, as well as thermal transport within linear response theory. The
transport properties are calculated at, and also in the vicinity of, the
exactly solvable Emery-Kivelson point, which has the form of a Majorana fermion
resonant level model. We focus on regimes where our solution gives exact
results for the physical quantum dot device, and highlight new predictions
relevant to future experiments.Comment: 57 pages, 8 figure
GASP II. A MUSE view of extreme ram-pressure stripping along the line of sight: kinematics of the jellyfish galaxy JO201
This paper presents a spatially-resolved kinematic study of the jellyfish
galaxy JO201, one of the most spectacular cases of ram-pressure stripping (RPS)
in the GASP (GAs Stripping Phenomena in Galaxies with MUSE) survey. By studying
the environment of JO201, we find that it is moving through the dense
intra-cluster medium of Abell 85 at supersonic speeds along our line of sight,
and that it is likely accompanied by a small group of galaxies. Given the
density of the intra-cluster medium and the galaxy's mass, projected position
and velocity within the cluster, we estimate that JO201 must so far have lost
~50% of its gas during infall via RPS. The MUSE data indeed reveal a smooth
stellar disk, accompanied by large projected tails of ionised (Halpha) gas,
composed of kinematically cold (velocity dispersion <40km/s) star-forming knots
and very warm (>100km/s) diffuse emission which extend out to at least ~50 kpc
from the galaxy centre. The ionised Halpha-emitting gas in the disk rotates
with the stars out to ~6 kpc but in the disk outskirts becomes increasingly
redshifted with respect to the (undisturbed) stellar disk. The observed
disturbances are consistent with the presence of gas trailing behind the
stellar component, resulting from intense face-on RPS happening along the line
of sight. Our kinematic analysis is consistent with the estimated fraction of
lost gas, and reveals that stripping of the disk happens outside-in, causing
shock heating and gas compression in the stripped tails.Comment: ApJ, revised version after referee comments, 15 pages, 16 figures.
The interactive version of Figure 9 can be viewed at
web.oapd.inaf.it/gasp/publications.htm
The Physics of Kondo Impurities in Graphene
This article summarizes our understanding of the Kondo effect in graphene,
primarily from a theoretical perspective. We shall describe different ways to
create magnetic moments in graphene, either by adatom deposition or via
defects. For dilute moments, the theoretical description is in terms of
effective Anderson or Kondo impurity models coupled to graphene's Dirac
electrons. We shall discuss in detail the physics of these models, including
their quantum phase transitions and the effect of carrier doping, and confront
this with existing experimental data. Finally, we point out connections to
other quantum impurity problems, e.g., in unconventional superconductors,
topological insulators, and quantum spin liquids.Comment: 27 pages, 8 figs. Review article prepared for Rep. Prog. Phys. ("key
issues" section). (v2) Final version as publishe
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