1,467 research outputs found
Fermionic Mach-Zehnder interferometer subject to a quantum bath
We study fermions in a Mach-Zehnder interferometer, subject to a
quantum-mechanical environment leading to inelastic scattering, decoherence,
renormalization effects, and time-dependent conductance fluctuations. Both the
loss of interference contrast as well as the shot noise are calculated, using
equations of motion and leading order perturbation theory. The full dependence
of the shot-noise correction on setup parameters, voltage, temperature and the
bath spectrum is presented. We find an interesting contribution due to
correlations between the fluctuating renormalized phase shift and the output
current, discuss the limiting behaviours at low and high voltages, and compare
with simpler models of dephasing.Comment: 5 pages, 3 figure
A panoramic view of the Milky Way analogue NGC 891
Recent panoramic observations of the dominant spiral galaxies of the Local
Group have revolutionized our view of how these galaxies assemble their mass.
However, it remains completely unclear whether the properties of the outer
regions of the Local Group large spirals are typical. Here, we present the
first panoramic view of a spiral galaxy beyond the Local Group, based on the
largest, contiguous, ground-based imaging survey to date resolving the stellar
halo of the nearest prime analogue of the Milky Way, NGC 891 (D~10 Mpc). The
low surface brightness outskirts of this galaxy are populated by multiple,
coherent, and vast substructures over the 90kpc * 90kpc extent of the survey.
These include a giant stream, the first to be resolved into stars beyond the
Local Group using ground-based facilities, that loops around the parent galaxy
up to distances of ~50kpc. The bulge and the disk of the galaxy are found to be
surrounded by a previously undetected large, flat and thick cocoon-like stellar
structure at vertical and radial distances of up to ~15kpc and ~40kpc
respectively.Comment: 2 figures, Apj Letter, in pres
SDSS-IV MaNGA: bulge-disc decomposition of IFU data cubes (BUDDI)
With the availability of large integral field unit (IFU) spectral surveys of nearby galaxies, there is now the potential to extract spectral information from across the bulges and discs of galaxies in a systematic way. This information can address questions such as how these components built up with time, how galaxies evolve and whether their evolution depends on other properties of the galaxy such as its mass or environment. We present bulgeādisc decomposition of IFU data cubes (buddi), a new approach to fit the two-dimensional light profiles of galaxies as a function of wavelength to extract the spectral properties of these galaxiesā discs and bulges. The fitting is carried out using galfitm, a modified form of galfit which can fit multiwaveband images simultaneously. The benefit of this technique over traditional multiwaveband fits is that the stellar populations of each component can be constrained using knowledge over the whole image and spectrum available. The decomposition has been developed using commissioning data from the Sloan Digital Sky Survey-IV Mapping Nearby Galaxies at APO (MaNGA) survey with redshifts z 22 arcsec, but can be applied to any IFU data of a nearby galaxy with similar or better spatial resolution and coverage. We present an overview of the fitting process, the results from our tests, and we finish with example stellar population analyses of early-type galaxies from the MaNGA survey to give an indication of the scientific potential of applying bulgeādisc decomposition to IFU data
Intervention for mixed receptive-expressive language impairment : a review
Children with receptive-expressive language impairment (RELI), also referred to as 'receptive language disorder' or 'mixed receptive-expressive disorder',2 form a subset of those with speech, language, and communication needs who commonly have problems understanding both spoken and written language; they have particular difficulties in comprehending vocabulary and grammar and inferring meaning. They will have problems with expressive language and some will also have difficulties in pragmatics, i.e. the use of language in social contexts
The Structure of the Sagittarius Stellar Stream as Traced by Blue Horizontal Branch Stars
We use a sample of blue horizontal branch (BHB) stars from the Sloan Digital
Sky Survey Data Release 7 to explore the structure of the tidal tails from the
Sagittarius Dwarf Galaxy. We use a method yielding BHB star candidates with up
to ~70% purity from photometry alone. The resulting sample has a distance
precision of roughly 5% and can probe distances in excess of 100 kpc. Using
this sample, we identify a possible extension to the trailing arm at distances
of 60-80 kpc from the Sun with an estimated significance of at least 3.8 sigma.
Current models predict that a distant `returning' segment of the debris stream
should exist, but place it substantially closer to the Sun where no debris is
observed in our data. Exploiting the distance precision of our tracers, we
estimate the mean line-of-sight thickness of the leading arm to be ~3 kpc, and
show that the two `bifurcated' branches of the debris stream differ by only 1-2
kpc in distance. With a spectroscopic very pure BHB star subsample, we estimate
the velocity dispersion in the leading arm, 37 km s^-1, which is in reasonable
agreement with models of Sgr disruption. We finally present a sample of
high-probability Sgr BHB stars in the leading arm of Sgr, selected to have
distances and velocities consistent with Sgr membership, to allow further
study.Comment: Astrophysical Journal, in press. 17 pages, 15 figure
Stellar Population Variations in the Milky Way's Stellar Halo
If the stellar halos of disk galaxies are built up from the disruption of
dwarf galaxies, models predict highly structured variations in the stellar
populations within these halos. We test this prediction by studying the ratio
of blue horizontal branch stars (BHB stars; more abundant in old, metal-poor
populations) to main-sequence turn-off stars (MSTO stars; a feature of all
populations) in the stellar halo of the Milky Way using data from the Sloan
Digital Sky Survey. We develop and apply an improved technique to select BHB
stars using ugr color information alone, yielding a sample of ~9000 g<18
candidates where ~70% of them are BHB stars. We map the BHB/MSTO ratio across
~1/4 of the sky at the distance resolution permitted by the absolute magnitude
distribution of MSTO stars. We find large variations of BHB/MSTO star ratio in
the stellar halo. Previously identified, stream-like halo structures have
distinctive BHB/MSTO ratios, indicating different ages/metallicities. Some halo
features, e.g., the low-latitude structure, appear to be almost completely
devoid of BHB stars, whereas other structures appear to be rich in BHB stars.
The Sagittarius tidal stream shows an apparent variation in BHB/MSTO ratio
along its extent, which we interpret in terms of population gradients within
the progenitor dwarf galaxy. Our detection of coherent stellar population
variations between different stellar halo substructures provides yet more
support to cosmologically motivated models for stellar halo growth.Comment: Astronomical Journal, in press. 10 pages, 5 color figures. Much
better printed in colo
The Northern wraps of the Sagittarius Stream as traced by Red Clump stars: distances, intrinsic widths and stellar densities
We trace the tidal Stream of the Sagittarius dwarf spheroidal galaxy (Sgr
dSph) using Red Clump stars from the catalog of the Sloan Digital Sky Survey -
Data Release 6, in the range 150{\deg} < RA < 220{\deg}, corresponding to the
range of orbital azimuth 220{\deg} < Lambda < 290{\deg}. Substructures along
the line of sight are identified as significant peaks in the differential star
count profiles (SCP) of candidate Red Clump stars. A proper modeling of the
SCPs allows us to obtain: (a) <10% accurate, purely differential distances with
respect to the main body of Sgr, (b) estimates of the FWHM along the line of
sight, and (c) estimates of the local density, for each detected substructure.
In the range 255{\deg} < Lambda < 290{\deg} we cleanly and continuously trace
various coherent structures that can be ascribed to the Stream, in particular:
the well known northern portion of the leading arm, running from d~43 kpc at
Lambda ~ 290{\deg} to d ~ 30 kpc at Lambda ~ 255{\deg}, and a more nearby
coherent series of detections lying at constant distance d ~ 25 kpc, that can
be identified with a wrap of the trailing arm. The latter structure, predicted
by several models of the disruption of Sgr dSph, was never traced before;
comparison with existing models indicates that the difference in distance
between these portions of the leading and trailing arms may provide a powerful
tool to discriminate between theoretical models assuming different shapes of
the Galactic potential. A further, more distant wrap in the same portion of the
sky is detected only along a couple of lines of sight.[abridged]Comment: 31 pages, 28 figures, accepted for publication in the Astrophysical
Journal, a version with figures at full resolution can be downloaded at the
following URL: http://www.bo.astro.it/SGR
Constraining the Milky Way potential with a 6-D phase-space map of the GD-1 stellar stream
The narrow GD-1 stream of stars, spanning 60 deg on the sky at a distance of
~10 kpc from the Sun and ~15 kpc from the Galactic center, is presumed to be
debris from a tidally disrupted star cluster that traces out a test-particle
orbit in the Milky Way halo. We combine SDSS photometry, USNO-B astrometry, and
SDSS and Calar Alto spectroscopy to construct a complete, empirical
6-dimensional phase-space map of the stream. We find that an eccentric orbit in
a flattened isothermal potential describes this phase-space map well. Even
after marginalizing over the stream orbital parameters and the distance from
the Sun to the Galactic center, the orbital fit to GD-1 places strong
constraints on the circular velocity at the Sun's radius V_c=224 \pm 13 km/s
and total potential flattening q_\Phi=0.87^{+0.07}_{-0.04}. When we drop any
informative priors on V_c the GD-1 constraint becomes V_c=221 \pm 18 km/s. Our
6-D map of GD-1 therefore yields the best current constraint on V_c and the
only strong constraint on q_\Phi at Galactocentric radii near R~15 kpc. Much,
if not all, of the total potential flattening may be attributed to the mass in
the stellar disk, so the GD-1 constraints on the flattening of the halo itself
are weak: q_{\Phi,halo}>0.89 at 90% confidence. The greatest uncertainty in the
6-D map and the orbital analysis stems from the photometric distances, which
will be obviated by Gaia.Comment: 16 pages, 18 figures; accepted to ApJ; full resolution version is
available at http://www.ast.cam.ac.uk/~koposov/files/gd1_fullres.pd
Randomised Controlled Trial of Unsolicited Occupational Therapy in Community-Dwelling Elderly People: The LOTIS Trial
OBJECTIVE: The objective of this trial, the Leiden 85-Plus Occupational Therapy Intervention Study (LOTIS), was to assess whether unsolicited occupational therapy, as compared to no therapy, can decelerate the increase in disability in high-risk elderly people. DESIGN: This was a randomised controlled trial with 2-y follow-up. SETTING: The study took place in the municipality of Leiden in the Netherlands. PARTICIPANTS: The participants were 402 community-dwelling 85-y-old people, with a Mini-Mental State Examination score of >18 points at baseline. INTERVENTIONS: Participants in the intervention group were visited by an occupational therapist who provided training and education about assistive devices that were already present and who gave recommendations and information about procedures, possibilities, and costs of assistive devices and community-based services. Control participants were not visited by an occupational therapist. OUTCOME MEASURES: The primary outcome measure was the score achieved on the Groningen Activity Restriction Scale. Secondary outcome measures included self-evaluations of well-being and feelings of loneliness. RESULTS: The participants were evenly divided between the two groups: 202 participants were allocated to the intervention group and 200 participants to the control group. Of the 202 participants randomised to occupational therapy, 55 participants declined the proposed intervention. An occupational therapist indicated that of the remaining 147 participants, 66 (45%) needed an occupational therapy intervention. A total of 44 new assistive devices and five community-based services were implemented. During follow-up there was a progressive increase in disability in the intervention group (mean annual increase, 2.0 points; SE 0.2; p < 0.001) and control group (mean annual increase, 2.1 points; SE 0.2; p < 0.001). The increase in disability was not significantly different between study groups (0.08 points; 95% CI, ā1.1ā1.2; p = 0.75). There was also no difference between study groups for any of the secondary outcome measures. CONCLUSION: Unsolicited occupational therapy in high-risk elderly participants does not decelerate the increase in disability over time
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