149 research outputs found
A dearth of short-period massive binaries in the young massive star forming region M17: Evidence for a large orbital separation at birth?
The formation of massive stars remains poorly understood and little is known
about their birth multiplicity properties. Here, we investigate the strikingly
low radial-velocity dispersion measured for a sample of 11 massive pre- and
near-main-sequence stars (sigma_rv = 5.6 +/- 0.2 km/s) in the young massive
star forming region M17 to obtain first constraints on the multiplicity
properties of young massive stellar objects. Methods: We compute the RV
dispersion of synthetic populations of massive stars for various multiplicity
properties and we compare the simulated sigma_rv distributions to the observed
value. We specifically investigate two scenarios: a low binary fraction and a
dearth of short-period binary systems. Results: Simulated populations with low
binary fractions (f_bin = 0.12_{-0.09}^{+0.16}) or with truncated period
distributions (P_cutoff > 9 months) are able to reproduce the low sigma_rv
observed within their 68%-confidence intervals. Parent populations with f_bin >
0.42 or P_cutoff < 47 d can however be rejected at the 5%-significance level.
Both constraints are contrast with the high binary fraction and plethora of
short-period systems found in few Myr-old, OB-type populations. To explain the
difference, the first scenario requires a variation of the outcome of the
massive star formation process. In the the second scenario, compact binaries
must form later on, and the cut-off period may be related to physical
length-scales representative of the bloated pre-main-sequence stellar radii or
of their accretion disks. Conclusions: If the obtained constraints are
representative of the overall properties of massive young stellar objects, our
results may provide support to a formation process in which binaries are
initially formed at larger separations, then harden or migrate to produce the
typical (untruncated) power-law period distribution observed in few Myr-old OB
binaries.Comment: 5 pages; Accepted for publication in Astronomy and Astrophysics
Letter
Uso da espectroscopia e tomografia de ressonância magnética para monitorar o amadurecimento e fatores de qualidade em manga e mamão.
bitstream/CNPDIA/10365/1/CT35_2000.pd
Detrusor Arreflexia as an End Stage of Neurogenic Bladder in HAM/TSP?
The HTLV-1 virus is a known agent involved in the development of HAM/TSP. Past studies have typically observed patients with autonomic dysfunction consisting of detrusor overactivity and detrusor-sphincter dyssynergia, with the occasional observation of underactive detrusor or detrusor arreflexia. However, studies have not yet evaluated the progression of neurogenic bladder over time. In this paper, we describe a HAM/TSP patient with the initial development of overactive detrusor, and subsequent development of detrusor arreflexia. Given a paucity of studies characterizing the effects of HTLV-1 on the autonomic nervous system, particularly aspects controlling continence, this patient's clinical course may represent one type of end point for patients with HAM/TSP and neurogenic bladder. Further cohort or case-series studies, with particular emphasis on the progression of neurogenic bladder, are needed to evaluate the significance of this described case in relation to typical disease progression patterns
Diffuse interstellar bands in the HII region M17: Insights into their relation with the total-to-selective visual extinction
Diffuse interstellar bands (DIBs) are broad absorption features measured in
sightlines probing the diffuse interstellar medium. Although large
carbon-bearing molecules have been proposed as the carriers producing DIBs,
their identity remains unknown. The sight line to the young massive
star-forming region M17 shows anomalous extinction in the sense that the
total-to-selective extinction parameter differs significantly from the average
Galactic value and may reach values . Given the high values,
we investigate whether the DIBs in sight lines towards young OB stars in M17
show a peculiar behaviour. We measure the properties of the most prominent DIBs
in M17 and study these as a function of and . The DIB strengths
in M17 concur with the observed relations between DIB equivalent width and
reddening in Galactic sight lines. For several DIBs we discover a
linear relation between the normalised DIB strength EW/ and
. These trends suggest two groups: (i) a group of ten moderately
strong DIBs that show a sensitivity to changes in that is modest and
proportional to DIB strength, and (ii) a group of four very strong DIBs that
react sensitively and to a similar degree to changes in , but in a way
that does not appear to depend on DIB strength. The DIB behaviour as a function
of reddening is not peculiar in sight lines to M17. Also, we do not detect
anomalous DIB profiles as seen in Her 36. DIBs are stronger, per unit visual
extinction, in sight lines characterised by a smaller value of (large
fraction of small dust particles). New relations between extinction normalised
DIB strengths, EW/, and support the idea that DIB carriers and
interstellar dust are connected. Given the distinct behaviour of two groups of
DIBs, different types of carriers do not necessarily relate to the dust grains
in a similar way.Comment: Abstract has been shortened. Accepted for publication in A&A. 14
pages, 7 pages of appendix, 28 figure
Massive pre-main-sequence stars in M17: and overtone CO bandhead emission and the thermal infrared
Recently much progress has been made in probing the embedded stages of
massive star formation, pointing to formation scenarios akin to a scaled up
version of low-mass star formation. However, the latest stages of massive star
formation have rarely been observed. Using 1st and 2nd overtone CO bandhead
emission and near- to mid-infrared photometry we aim to characterize the
remnant formation disks around 5 unique pre-main-sequence (PMS) stars with
masses , that have constrained stellar parameters thanks to
their detectable photospheres. We seek to understand this emission and the
disks it originates from in the context of the evolutionary stage of the
studied sources. We use an analytic LTE disk model to fit the CO bandhead and
the dust emission, found to originate in different disk regions. For the first
time we modeled the 2nd overtone emission. Furthermore, we fit continuum
normalized bandheads and show the importance of this in constraining the
emission region. We also include in our models as an additional
probe of the young nature of the studied objects. We find that the CO emission
originates in a narrow region close to the star (<1 AU) and under very similar
disk conditions (temperatures and densities) for the different objects. This is
consistent with previous modeling of this emission in a diverse range of young
stellar objects. We discuss these results in the context of the positions of
these PMS stars in the Hertzsprung-Russel diagram and the CO emission's
association with early age and high accretion rates in (massive) young stellar
objects. We conclude that, considering their mass range and for the fact that
their photospheres are detected, the M17 PMS stars are observed in a relatively
early formation stage. They are therefore excellent candidates for longer
wavelength studies to further constrain the end stages of massive star
formation.Comment: 21 pages, 12 figure
Spectroscopic variability of massive pre-main-sequence stars in M17
It is a challenge to study the formation process of massive stars: their
formation time is short, they are few, often deeply embedded, and at relatively
large distances. Our strategy is to study the outcome of the star formation
process and to look for signatures remnant of the formation. We have access to
a unique sample of (massive) pre-main-sequence (PMS) stars in the giant HII
region M17, showing a photosphere and circumstellar disk. The aim is to
determine the variability properties of the hot gaseous disks to understand the
physical origin of the emission lines and identify dominant physical processes
in these disks. We have obtained multiple-epoch (4-5 epochs) VLT/X-shooter
spectra of six young stars in M17 covering about a decade. Using stacked
spectra we update the spectral classification and identify circumstellar
features. With the temporal variance method (TVS) we determine the extent and
amplitude of the spectral line variations. The double-peaked emission lines in
the PMS stars with gaseous disks are used to determine peak-to-peak velocities,
V/R-ratios and the radial velocity of the systems. We identify many disk
features, under which a new detection of CO bandhead and CI emission. In three
of the stars we detect spectral variability, mainly in lines originating in the
circumstellar disk, in a velocity range up to 320 km/s. In two PMS stars the
ratio between the blue and red peaks shows a correlation with the peak-to-peak
velocity, possibly explained by a spiral-arm structure in the disk. The PMS
stars with variability are at similar positions in the HRD but show significant
differences in disk lines and variability. The extent and timescale of the
variability differs for each star and per line (sets). We find indications for
an accretion flow, slow disk winds and/or disk structures in the hot gaseous
inner disk as the cause of the variability in these PMS stars.Comment: 27 pages, 24 figures, accepted for publication in Astronomy and
Astrophysics, abstract abbreviate
COMPARISON of DATA AVAILABILITY and QUALITY for PHARMACOECONOMIC ANALYSIS in BRAZIL VERSUS the UNITED STATES and EUROPEAN UNION: the CASES of DIABETES & HYPERTENSION
Axia Bio Consulting, São Paulo, BrazilI3 Innovus, Medford, MA USAUniversidade Federal de São Paulo, São Paulo, BrazilNovartis Biociencias SA, São Paulo, BrazilNovartis Pharma AG, Basel, SwitzerlandUniversidade Federal de São Paulo, São Paulo, BrazilWeb of Scienc
Characterizing water fingering phenomena in soils using magnetic resonance imaging and multifractal theory
Abstract. The study of water movement in soils is of fundamental\ud
importance in hydrologic science. It is generally\ud
accepted that in most soils, water and solutes flow through\ud
unsaturated zones via preferential paths or fingers. This\ud
paper combines magnetic resonance imaging (MRI) with\ud
both fractal and multifractal theory to characterize preferential\ud
flow in three dimensions. A cubic double-layer column\ud
filled with fine and coarse textured sand was placed\ud
into a 500 gauss MRI system. Water infiltration through\ud
the column (0.15×0.15×0.15m3) was recorded in steady\ud
state conditions. Twelve sections with a voxel volume\ud
0.1×0.1×10mm3 each were obtained and characterized using\ud
fractal and multifractal theory. The MRI system provided\ud
a detailed description of the preferential flow under steady\ud
state conditions and was also useful in understanding the dynamics\ud
of the formation of the fingers. The f ( ) multifractal\ud
spectrum was very sensitive to the variation encountered\ud
at each horizontally-oriented slice of the column and provided\ud
a suitable characterization of the dynamics of the process\ud
identifying four spatial domains. In conclusion, MRI\ud
and fractal and multifractal analysis were able to characterize\ud
and describe the preferential flow process in soils. Used\ud
together, the two methods provide a good alternative to study\ud
flow transport phenomena in soils and in porous media.CIDA-Canada through the ALTAGRO ProjectFAPESP (07/58561-7
Endometrial Cancer Presenting as Acute Urinary Retention: a Case Report and Review of the Literature
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