388 research outputs found
Filaments in Galactic Winds Driven by Young Stellar Clusters
The starburst galaxy M82 shows a system of H-emitting filaments which
extend to each side of the galactic disk. We model these filaments as the
result of the interaction between the winds from a distribution of Super
Stellar Clusters (SSCs). We first derive the condition necessary for producing
a radiative interaction between the cluster winds (a condition which is met by
the SSC distribution of M82). We then compute 3D simulations for SSC wind
distributions which satisfy the condition for a radiative interaction, and also
for distributions which do not satisfy this condition. We find that the highly
radiative models, that result from the interaction of high metallicity cluster
winds, produce a structure of H emitting filaments, which qualitatively
agrees with the observations of the M82, while the non-radiative SSC wind
interaction models do not produce filamentary structures. Therefore, our
criterion for radiative interactions (which depends on the mass loss rate and
the terminal velocity of the SSC winds, and the mean separation between SSCs)
can be used to predict whether or not an observed galaxy should have associated
H emitting filaments.Comment: 10 pages, 6 Figures. ApJ Accepted, August 7, 200
A cross-sectional observational study of the vitamin D status in children with chronic kidney disease at Charlotte Maxeke Johannesburg academic hospital
A research report submitted to the Faculty of Health Sciences, University of
the Witwatersrand, Johannesburg, in partial fulfillment of the requirements
for
the degree in Masters of Medicine in Paediatrics (MMed)
Johannesburg, May 2015Introduction
Vitamin D has numerous important functions in the human body. There is limited
data available regarding vitamin D status in children with Chronic Kidney Disease
(CKD) in South Africa.
Objectives
To determine the vitamin D status, as well as factors that affect it, in children with
CKD in Johannesburg, South Africa.
Methods
A cross-sectional observational study was performed on 69 patients who attended
the Renal Outpatient Clinic, and required routine phlebotomy, at Charlotte Maxeke
Johannesburg Academic Hospital, Division of Paediatric Nephrology, between
20/08/2013 and 20/05/2014.
Results
71% (n=49) of patients in our study sample were vitamin D sufficient. Significant
factors that influenced vitamin D status included albumin levels and the presence
of Nephrotic syndrome with relapse.
There was a statistically significant positive correlation between albumin and
vitamin D (p=0.00). As albumin levels increased so did the vitamin D levels.
Patients with Nephrotic Syndrome with relapse had significantly lower vitamin D
levels compared to patients with Nephrotic Syndrome in remission (p=0.00).
Conclusion
The majority of children with Chronic Kidney Disease in Johannesburg, South
Africa, are vitamin D sufficient. This is reassuring as it implies that there is no need
for routine vitamin D supplementation in this sample of children. However patients,
especially those with nephrotic syndrome with relapse, still need to be screened
for vitamin D deficiency and insufficiency and supplemented if necessary.MT201
Radiation from matter entrainment in astrophysical jets: the AGN case
Jets are found in a variety of astrophysical sources, from young stellar
objects to active galactic nuclei. In all the cases the jet propagates with a
supersonic velocity through the external medium, which can be inhomogeneous,
and inhomogeneities could penetrate into the jet. The interaction of the jet
material with an obstacle produces a bow shock in the jet in which particles
can be accelerated up to relativistic energies and emit high-energy photons. In
this work, we explore the active galactic nuclei scenario, focusing on the
dynamical and radiative consequences of the interaction at different jet
heights. We find that the produced high-energy emission could be detectable by
the current gamma-ray telescopes. In general, the jet-clump interactions are a
possible mechanism to produce (steady or flaring) high-energy emission in many
astrophysical sources in which jets are present.Comment: 4 pages, 2 figures. Accepted for publication in the Proceedings of
the 275 IAU Symposium: "Jets at all Scales", held in Buenos Aires, September
13-17, 201
The X-ray Luminosities of HH Objects
The recent detection of X-ray emission from HH 2 and HH 154 with the Chandra
and XMM-Newton satellites (respectively) have opened up an interesting, new
observational possibility in the field of Herbig-Haro objects. In order to be
able to plan further X-ray observations of other HH objects, it is now of
interest to be able to estimate their X-ray luminosities in order to choose
which objects to observe. This paper describes a simple, analytic model for
predicting the X-ray luminosity of a bow shock from the parameters of the flow
(i.e., the size of the bow shock, its velocity, and the pre-shock density). The
accuracy of the analytic model is analyzed through a comparison with the
predictions obtained from axisymmetric, gasdynamic simulations of the leading
working surface of an HH jet. We find that our analytic model reproduces the
observed X-ray luminosities of HH 2 and HH 154, and we propose that HH~80/81 is
a good candidate for future observations with Chandra.Comment: 10 pages (8 text, 2 figures
The Kinematics of HH 34 from HST Images with a Nine-year Time Baseline
We study archival HST [S II] 6716+30 and Hα images of the HH 34 outflow, taken in 1998.71 and in 2007.83. The ~9 yr time baseline and the high angular resolution of these observations allow us to carry out a detailed proper-motion study. We determine the proper motions of the substructure of the HH 34S bow shock (from the [S II] and Hα frames) and of the aligned knots within ~30'' from the outflow source (only from the [S II] frames). We find that the present-day motions of the knots along the HH 34 jet are approximately ballistic, and that these motions directly imply the formation of a major mass concentration in ~900 yr, at a position similar to the one of the present-day HH 34S bow shock. In other words, we find that the knots along the HH 34 jet will merge to form a more massive structure, possibly resembling HH 34S
Numerical Modeling of Eta Carinae Bipolar Outflows
In this paper, we present two-dimensional gas dynamic simulations of the
formation and evolution of the eta-Car bipolar outflows. Adopting the
interacting nonspherical winds model, we have carried out high-resolution
numerical simulations, which include explicitly computed time-dependent
radiative cooling, for different possible scenarios of the colliding winds. In
our simulations, we consider different degrees of non-spherical symmetry for
the pre-outburst wind and the great eruption of the 1840s presented by the
eta-Car wind. From these models, we obtain important differences in the shape
and kinematical properties of the Homunculus structure. In particular, we find
an appropriate combination of the wind parameters (that control the degree of
non-spherical symmetry) and obtain numerical experiments that best match both
the observed morphology and the expansion velocity of the eta-Car bipolar
shell. In addition, our numerical simulations show the formation of a bipolar
nebula embedded within the Homunculus (the little Homunculus) developed from a
secondary eruptive event suffered by the star in the 1890s, and also the
development of tenuous, high velocity ejections in the equatorial region that
result from the impact of the eruptive wind of the 1840s with the pre-outburst
wind and that could explain some of the high speed features observed in the
equatorial ejecta. The models were, however, unable to produce equatorial
ejections associated to the second eruptive event.Comment: 33 pages, 9 figures, accepted by the Astrophysical Journa
Collimated Outflow Formation via Binary Stars. 3-D Simulations of AGB Wind and Disk Wind Interactions
We present three-dimensional hydrodynamic simulations of the interaction of a
slow wind from an asymptotic giant branch(AGB) star and a jet blown by an
orbiting companion. The jet or "Collimated Fast Wind" is assumed to originate
from an accretion disk which forms via Bondi accretion of the AGB wind or Roche
lobe overflow. We present two distinct regimes in the wind-jet interaction
determined by the ratio of the AGB wind to jet momentum flux. Our results show
that when the wind momentum flux overwhelms the flux in the jet a more
dis-ordered outflow outflow results with the jet assuming a corkscrew pattern
and multiple shock structures driven into the AGB wind. In the opposite regime
the jet dominates and will drive a highly collimated narrow waisted outflow. We
compare our results with scenarios described by Soker & Rappaport (2000) and
extrapolate the structures observed in PNe and Symbiotic stars.Comment: 22 pages, 8 figures, submitted to Ap
Mental health problems: Are they or are they not a risk factor for dropout from drug treatment? A systematic review of the evidence
Background: A sizeable number of recent studies investigating whether clients with substance misuse and mental health problems (dual diagnosis clients) are at heightened risk of dropout from drug treatment have been published. It is timely that their findings are brought together in a comprehensive review of the current evidence.
Aims: The aim of the review is to examine whether dually diagnosed clients are less likely to be retained in drug treatment than clients without mental health problems, and, if so, whether this varies for clients diagnosed with different types of mental health problems.
Methods: The review considers peer-reviewed research published after 1 January 1990, which was located using the literature databases Medline and PsycInfo. Predefined search terms were used. Further papers were identified from the bibliographies of relevant publications.
Findings: 58 studies (84% from the USA) met the inclusion criteria for the review. The findings suggest that for most clients, having a past history of mental health problems does not influence the likelihood of being retained in drug treatment. The body of evidence regarding concurrent mental health problems is contradictory. On the whole, the majority of studies suggest that neither presence nor severity of depressive, anxiety, or other Axis-I disorders is related to retention, but these findings are not entirely unequivocal, as a few studies report strong positive or negative associations between depression and anxiety disorders and retention. Few researchers looked separately at psychotic spectrum disorders hence no conclusions could be drawn. The presence of most personality disorders also did not appear to affect treatment tenure, with the exception of antisocial personality disorder, for which the evidence points towards a greater risk of dropout.
Conclusions: The balance of evidence suggests that, overall, dual diagnosis clients with Axis-I disorders who seek treatment in drug treatment services are retained as well as clients without dual diagnosis. Subgroups of clients who appear more vulnerable to premature dropout include those with antisocial personality disorder. Methodological shortcomings of the reviewed studies and resulting implications for this review and future research are discussed
Magnetic Field Effects on the Structure and Evolution of Overdense Radiatively Cooling Jets
We investigate the effect of magnetic fields on the propagation dynamics and
morphology of overdense, radiatively cooling, supermagnetosonic jets, with the
help of fully three-dimensional SPMHD simulations. Evaluated for a set of
parameters which are mainly suitable for protostellar jets (with density ratios
between the jet and the ambient medium 3-10, and ambient Mach number ~ 24),
these simulations are also compared with baseline non-magnetic and adiabatic
calculations. We find that, after amplification by compression and
re-orientation in nonparallel shocks at the working surface, the magnetic field
that is carried backward with the shocked gas into the cocoon improves the jet
collimation relative to the purely hydrodynamic (HD) systems. Low-amplitude,
approximately equally spaced internal shocks (which are absent in the HD
systems) are produced by MHD K-H reflection pinch modes. The longitudinal field
geometry also excites non-axisymmetric helical modes which cause some beam
wiggling. The strength and amount of these modes are, however, reduced (by ~
twice) in the presence of radiative cooling relative to the adiabatic cases.
Besides, a large density ratio between the jet and the ambient medium also
reduces, in general, the number of the internal shocks. As a consequence, the
weakness of the induced internal shocks makes it doubtful that the magnetic
pinches could produce by themselves the bright knots observed in the overdense,
radiatively cooling protostellar jets.Comment: To appear in ApJ; 36 pages + 16 (gif) figures. PostScript files of
figures are available at http://www.iagusp.usp.br/preprints/preprint.htm
Novos registros de Aleyrodidae (Hemiptera) no estado de Roraima, Brasil.
Registra pela primeira vez a ocorrĂȘncia de seis espĂ©cies de Aleyrodidae e respectivas plantas hospedeiras no Estado de Roraima. Dentre os registros constam Aleurocanthus woglumi Ashby, praga quarentenĂĄria presente no Brasil (A2) e alguns inimigos naturais
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