2,044 research outputs found
Evaluation of Specific Symptoms of Bacterial Vaginosis Among Pregnant Women
Objective: Identification of the symptoms of bacterial vaginosis (BV) in pregnancy might be rational in order to identify a possible BV-associated group at risk of preterm delivery
A Spherical Model for "Starless" Cores of Magnetic Molecular Clouds and Dynamical Effects of Dust Grains
In the standard picture of isolated star formation, dense ``starless'' cores
are formed out of magnetic molecular clouds due to ambipolar diffusion. Under
the simplest spherical geometry, I demonstrate that ``starless'' cores formed
this way naturally exhibit a large scale inward motion, whose size and speed
are comparable to those detected recently by Taffala et al. and Williams et al.
in ``starless'' core L1544. My model clouds have a relatively low mass (of
order 10 ) and low field strength (of order 10 G) to begin with.
They evolve into a density profile with a central plateau surrounded by a
power-law envelope, as found previously. The density in the envelope decreases
with radius more steeply than those found by Mouschovias and collaborators for
the more strongly magnetized, disk-like clouds.
At high enough densities, dust grains become dynamically important by greatly
enhancing the coupling between magnetic field and the neutral cloud matter. The
trapping of magnetic flux associated with the enhanced coupling leads, in the
spherical geometry, to a rapid assemblage of mass by the central protostar,
which exacerbates the so-called ``luminosity problem'' in star formation.Comment: 27 pages, 4 figures, accepted by Ap
Prenatal antidepressant exposure and child behavioural outcomes at 7 years of age: a study within the Danish National Birth Cohort
Objective: To investigate the impact of prenatal antidepressant exposure on behavioural problems in children at 7 years of age. Design: Nationwide population-based study. Setting: Danish National Birth Cohort. Population: A cohort of 49 178 pregnant women recruited between 1996 and 2002. Methods: Data obtained from computer-assisted telephone interviews twice during pregnancy were used to identify children born to: (i) depressed women who took antidepressants during pregnancy (n = 210); (ii) depressed women who did not take any antidepressants during pregnancy (n = 231); and (iii) healthy women who were not depressed (n = 48 737). Childhood behavioural problems at 7 years of age were examined using the validated Danish parent-report version of the Strengths and Difficulties Questionnaire (SDQ). Main outcome measures: SDQ scores. Results: No associations were observed between prenatal antidepressant exposure and abnormal SDQ scores for overall problem behaviour (adjusted relative risk, aRR 1.00; 95% confidence interval, 95% CI 0.49–2.05), hyperactivity/inattention (aRR 0.99; 95% CI 0.56–1.75), or peer problems (aRR 1.04; 95% CI 0.57–1.91). Although prenatal antidepressant exposure appeared to be associated with abnormal SDQ scores on the subscales of emotional symptoms (aRR 1.68; 95% CI 1.18–2.38) and conduct problems (aRR 1.58; 95% CI 1.03–2.42), these associations were significantly attenuated following adjustment for antenatal mood status (aRR 1.20; 95% CI 0.85–1.70 and aRR 1.19; 95% CI 0.77 1.83, respectively). Untreated prenatal depression was associated with an increased risk of all behavioural outcomes evaluated, compared with unexposed children, with significant attenuation following adjustment for antenatal mood status. Conclusions: The results of this study suggest that independent of maternal illness, prenatal antidepressant exposure is not associated with an increased risk of behavioural problems in children at 7 years of age.LE Grzeskowiak, JL Morrison, TB Henrikse, BH Bech, C Obel, J Olsen, LH Pederse
Rotation and X-ray emission from protostars
The ASCA satellite has recently detected variable hard X-ray emission from
two Class I protostars in the rho Oph cloud, YLW15 (IRS43) and WL6, with a
characteristic time scale ~20h. In YLW15, the X-ray emission is in the form of
quasi-periodic energetic flares, which we explain in terms of strong magnetic
shearing and reconnection between the central star and the accretion disk. In
WL6, X-ray flaring is rotationally modulated, and appears to be more like the
solar-type magnetic activity ubiquitous on T Tauri stars. We find that YLW15 is
a fast rotator (near break-up), while WL6 rotates with a significantly longer
period. We derive a mass M_\star ~ 2 M_\odot and \simlt 0.4 M_\odot for the
central stars of YLW15 and WL6 respectively. On the long term, the interactions
between the star and the disk results in magnetic braking and angular momentum
loss of the star. On time scales t_{br} ~ a few 10^5 yrs, i.e., of the same
order as the estimated duration of the Class~I protostar stage. Close to the
birthline there must be a mass-rotation relation, t_{br} \simpropto M_\star,
such that stars with M_\star \simgt 1-2 M_\odot are fast rotators, while their
lower-mass counterparts have had the time to spin down. The rapid rotation and
strong star-disk magnetic interactions of YLW15 also naturally explain the
observation of X-ray ``superflares''. In the case of YLW15, and perhaps also of
other protostars, a hot coronal wind (T~10^6 K) may be responsible for the VLA
thermal radio emission. This paper thus proposes the first clues to the
rotation status and evolution of protostars.Comment: 13 pages with 6 figures. To be published in ApJ (April 10, 2000 Part
1 issue
Constraints on the Formation and Evolution of Circumstellar Disks in Rotating Magnetized Cloud Cores
We use magnetic collapse models to place some constraints on the formation
and angular momentum evolution of circumstellar disks which are embedded in
magnetized cloud cores. Previous models have shown that the early evolution of
a magnetized cloud core is governed by ambipolar diffusion and magnetic
braking, and that the core takes the form of a nonequilibrium flattened
envelope which ultimately collapses dynamically to form a protostar. In this
paper, we focus on the inner centrifugally-supported disk, which is formed only
after a central protostar exists, and grows by dynamical accretion from the
flattened envelope. We estimate a centrifugal radius for the collapse of mass
shells within a rotating, magnetized cloud core. The centrifugal radius of the
inner disk is related to its mass through the two important parameters
characterizing the background medium: the background rotation rate \Omb and
the background magnetic field strength \Bref. We also revisit the issue of
how rapidly mass is deposited onto the disk (the mass accretion rate) and use
several recent models to comment upon the likely outcome in magnetized cores.
Our model predicts that a significant centrifugal disk (much larger than a
stellar radius) will be present in the very early (Class 0) stage of
protostellar evolution. Additionally, we derive an upper limit for the disk
radius as it evolves due to internal torques, under the assumption that the
star-disk system conserves its mass and angular momentum even while most of the
mass is transferred to a central star.Comment: 23 pages, 1 figure, aastex, to appear in the Astrophysical Journal
(10 Dec 1998
High-Mass Proto-Stellar Candidates - II : Density structure from dust continuum and CS emission
We present a detailed 1.2 mm continuum and CS spectral line study of a large
sample of 69 massive star forming regions in very early stages of evolution,
most of them prior to building up an ultracompact HII region. The continuum
data show a zoo of different morphologies and give detailed information on the
spatial distributions, the masses, column densities and average densities of
the whole sample. Fitting the radial intensity profiles shows that three
parameters are needed to describe the spatial distribution of the sources:
constant emission from the center out to a few arcsec radius followed by a
first power law intensity distribution which steepens further outside into a
second power law distribution. The mean inner power law intensity index mi
(I~r^(-mi)) is 1.2 corresponding to density indices p (n~r^(-p)) of 1.6. In
total the density distribution of our massive star formations sites seem to be
not too different from their low-mass counterparts, but we show that setting
tight constrains on the density indices is very difficult and subject to many
possible errors. The local densities we derive from CS calculations are higher
(up to one order of magnitude) than the mean densities we find via the
mm-continuum. Such inhomogeneous density distribution reflects most likely the
ubiquitous phenomenon of clumping and fragmentation in molecular clouds.
Linewidth-mass relations show a departure from virial equilibrium in the stages
of strongly collapsing cores.Comment: 15 pages, 13 jpeg-figures. Astrophysical Journal, in pres
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