898 research outputs found
Highly Ionized High Velocity Clouds: Intergalactic Gas in the Local Group or Distant Gas in the Galactic Halo?
We have recently identified several high velocity (V < -100 km/s) clouds in
the directions of Mrk 509 and PKS 2155-304 that have unusual ionization
properties. The clouds exhibit strong C IV absorption with little or no
detectable low ion (C II, Si II) absorption or H I 21cm emission. As the
closest known analog to the outer diffuse halos of damped Ly-alpha absorbers
and the low H I column density metal line absorption systems seen in the
spectra of high redshift quasars, these "C IV-HVCs" present unique
opportunities for relating the conditions within the Milky Way halo and nearby
intergalactic gas to the properties of galactic halos at higher redshift.
The C IV-HVCs have ionization properties consistent with photoionization by
extragalactic background radiation, though some contribution by collisional
ionization within a hot plasma cannot be ruled out. The clouds are probably low
density [n(H) ~ 10^-4 cm^-3], large [greater than several kiloparsecs], and
mostly ionized [n(HI)/n(H) ~ 10^-3] regions located well beyond the neutral gas
layer of the Galaxy. The presence of weak H I-HVCs detected through 21cm
emission near both sight lines indicates that the C IV-HVCs trace the extended,
ionized, low density regions of the H I-HVCs. Several lines of evidence,
including very low thermal pressures (P/k ~ 2 cm^-3 K), favor a location for
the C IV-HVCs in the Local Group or very distant Galactic halo.Comment: AASTEX manuscript and tables, 55 pages, 8 postscript figures.
Astrophysical Journal, in pres
Quantifying Beta-Galactosylceramide Kinetics in Cerebrospinal Fluid of Healthy Subjects Using Deuterium Labeling
Nonlinear Dynamics of the Perceived Pitch of Complex Sounds
We apply results from nonlinear dynamics to an old problem in acoustical
physics: the mechanism of the perception of the pitch of sounds, especially the
sounds known as complex tones that are important for music and speech
intelligibility
Lovelock theories, holography and the fate of the viscosity bound
We consider Lovelock theories of gravity in the context of AdS/CFT. We show
that, for these theories, causality violation on a black hole background can
occur well in the interior of the geometry, thus posing more stringent
constraints than were previously found in the literature. Also, we find that
instabilities of the geometry can appear for certain parameter values at any
point in the geometry, as well in the bulk as close to the horizon. These new
sources of causality violation and instability should be related to CFT
features that do not depend on the UV behavior. They solve a puzzle found
previously concerning unphysical negative values for the shear viscosity that
are not ruled out solely by causality restrictions. We find that, contrary to
previous expectations, causality violation is not always related to positivity
of energy. Furthermore, we compute the bound for the shear viscosity to entropy
density ratio of supersymmetric conformal field theories from d=4 till d=10 -
i.e., up to quartic Lovelock theory -, and find that it behaves smoothly as a
function of d. We propose an approximate formula that nicely fits these values
and has a nice asymptotic behavior when d goes to infinity for any Lovelock
gravity. We discuss in some detail the latter limit. We finally argue that it
is possible to obtain increasingly lower values for the shear viscosity to
entropy density ratio by the inclusion of more Lovelock terms.Comment: 42 pages, 17 figures, JHEP3.cls. v2: reference adde
Evaluation of a psychoeducational intervention for adolescents with inflammatory bowel disease
OBJECTIVES: Inflammatory bowel disease (IBD), comprising Crohn's disease, ulcerative colitis, and indeterminate colitis, often has its onset in adolescence. The aim of this study was to evaluate whether a psychoeducational group intervention (aiming to enhance information seeking and giving about the disease, relaxation, social competence, and positive thinking) can strengthen the coping efforts of adolescents with IBD and have a positive effect on their Health-Related Quality of Life (HRQoL). METHODS: Adolescent IBD patients from the Emma Children's Hospital AMC and adolescent members of the Crohn and Ulcerative Colitis Association in The Netherlands, were invited to participate in The intervention study. Using reliable and valid self-report instruments the adolescent's coping styles, feelings of competence, and HRQoL were assessed before and 6-8 months after the intervention. The parents were asked to fill in the Child Behavior Check List. Linear regression analyses were performed to test whether group participation was predictive of the outcome measures while correcting for the first measurement occasion and sex. RESULTS AND CONCLUSION: Forty patients responded positively to invitation to the intervention. Eighteen adolescents, however, lived too far away to attend and served as a control group. Twenty-two children were enrolled and attended in groups of four to six children in six group sessions, supervised by two psychologists. The intervention seemed to have a positive effect on: coping (predictive control, P<0.01), feelings of competence (global self-worth, P<0.05 and physical appearance, P<0.01), and HRQoL (body image, P<0.05). These results give good reason to continue this intervention study with a larger population. © 2009 Lippincott Williams & Wilkins, Inc
Iron abundances of B-type post-Asymptotic Giant Branch stars in globular clusters: Barnard 29 in M 13 and ROA 5701 in omega Cen
High resolution optical and ultraviolet spectra of two B-type post-Asymptotic
Giant Branch (post-AGB) stars in globular clusters, Barnard 29 in M 13 and ROA
5701 in omega Cen, have been analysed using model atmosphere techniques. The
optical spectra have been obtained with FEROS on the ESO 2.2-m telescope and
the 2d-Coud\'e spectrograph on the 2.7-m McDonald telescope, while the
ultraviolet observations are from the GHRS on the HST. Abundances of light
elements (C, N, O, Mg, Al and S) plus Fe have been determined from the optical
spectra, while the ultraviolet data provide additional Fe abundance estimates
from Fe III absorption lines in the 1875-1900 {\AA} wavelength region. A
general metal underabundance relative to young B-type stars is found for both
Barnard 29 and ROA 5701. These results are consistent with the metallicities of
the respective clusters, as well as with previous studies of the objects. The
derived abundance patterns suggest that the stars have not undergone a gas-dust
separation, contrary to previous suggestions, although they may have evolved
from the AGB before the onset of the third dredge-up. However, the Fe
abundances derived from the HST spectra are lower than those expected from the
metallicities of the respective clusters, by 0.5 dex for Barnard 29 and 0.8 dex
for ROA 5701. A similar systematic underabundance is also found for other
B-type stars in environments of known metallicity, such as the Magellanic
Clouds. These results indicate that the Fe III ultraviolet lines may yield
abundance values which are systematically too low by typically 0.6 dex and
hence such estimates should be treated with caution.Comment: 15 pages, 3 figures. Accepted for publication in MNRA
Quantifying Beta‐Galactosylceramide Kinetics in Cerebrospinal Fluid of Healthy Subjects Using Deuterium Labeling
Therapeutics promoting myelin synthesis may enhance recovery in demyelinating diseases, such as multiple sclerosis. However, no suitable method exists to quantify myelination. The turnover of galactosylceramide (myelin component) is indicative of myelination in mice, but its turnover has not been determined in humans. Here, six healthy subjects consumed 120 mL 70% D2 O daily for 70 days to label galactosylceramide. We then used mass spectrometry and compartmental modeling to quantify the turnover rate of galactosylceramide in cerebrospinal fluid. Maximum deuterium enrichment of body water ranged from 1.5-3.9%, whereas that of galactosylceramide was much lower: 0.05-0.14%. This suggests a slow turnover rate, which was confirmed by the model-estimated galactosylceramide turnover rate of 0.00168 day-1 , which corresponds to a half-life of 413 days. Additional studies in patients with multiple sclerosis are needed to investigate whether galactosylceramide turnover could be used as an outcome measure in clinical trials with remyelination therapies.PharmacologyAnalytical BioScience
Infall Times for Milky Way Satellites From Their Present-Day Kinematics
We analyze subhalos in the Via Lactea II (VL2) cosmological simulation to
look for correlations among their infall times and z = 0 dynamical properties.
We find that the present day orbital energy is tightly correlated with the time
at which subhalos last crossed into the virial radius. This energy-infall
correlation provides a means to infer infall times for Milky Way satellite
galaxies. Assuming that the Milky Way's assembly can be modeled by VL2, we show
that the infall times of some satellites are well constrained given only their
Galactocentric positions and line-of-sight velocities. The constraints sharpen
for satellites with proper motion measurements. We find that Carina, Ursa
Minor, and Sculptor were all accreted early, more than 8 Gyr ago. Five other
dwarfs, including Sextans and Segue 1, are also probable early accreters,
though with larger uncertainties. On the other extreme, Leo T is just falling
into the Milky Way for the first time while Leo I fell in \sim 2 Gyr ago and is
now climbing out of the Milky Way's potential after its first perigalacticon.
The energies of several other dwarfs, including Fornax and Hercules, point to
intermediate infall times, 2 - 8 Gyr ago. We compare our infall time estimates
to published star formation histories and find hints of a dichotomy between
ultrafaint and classical dwarfs. The classical dwarfs appear to have quenched
star formation after infall but the ultrafaint dwarfs tend to be quenched long
before infall, at least for the cases in which our uncertainties allow us to
discern differences. Our analysis suggests that the Large Magellanic Cloud
crossed inside the Milky Way virial radius recently, within the last \sim 4
billion years.Comment: 15 pages, 7 figures, all figures include colors, submitted for
publication in MNRA
A participatory physical and psychosocial intervention for balancing the demands and resources among industrial workers (PIPPI): study protocol of a cluster-randomized controlled trial
Background: Need for recovery and work ability are strongly associated with high employee turnover, well-being and sickness absence. However, scientific knowledge on effective interventions to improve work ability and decrease need for recovery is scarce. Thus, the present study aims to describe the background, design and protocol of a cluster randomized controlled trial evaluating the effectiveness of an intervention to reduce need for recovery and improve work ability among industrial workers. Methods/Design: A two-year cluster randomized controlled design will be utilized, in which controls will also receive the intervention in year two. More than 400 workers from three companies in Denmark will be aimed to be cluster randomized into intervention and control groups with at least 200 workers (at least 9 work teams) in each group. An organizational resources audit and subsequent action planning workshop will be carried out to map the existing resources and act upon initiatives not functioning as intended. Workshops will be conducted to train leaders and health and safety representatives in supporting and facilitating the intervention activities. Group and individual level participatory visual mapping sessions will be carried out allowing team members to discuss current physical and psychosocial work demands and resources, and develop action plans to minimize strain and if possible, optimize the resources. At all levels, the intervention will be integrated into the existing organization of work schedules. An extensive process and effect evaluation on need for recovery and work ability will be carried out via questionnaires, observations, interviews and organizational data assessed at several time points throughout the intervention period. Discussion: This study primarily aims to develop, implement and evaluate an intervention based on the abovementioned features which may improve the work environment, available resources and health of industrial workers, and hence their need for recovery and work ability
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