1,592 research outputs found
Grain growth in the envelopes and disks of Class I protostars
We present new 3 mm ATCA data of two Class I Young Stellar Objects in the
Ophiucus star forming region: Elias29 and WL12. For our analysis we compare
them with archival 1.1 mm SMA data. In the (u,v) plane the two sources present
a similar behavior: a nearly constant non-zero emission at long baselines,
which suggests the presence of an unresolved component and an increase of the
fluxes at short baselines, related to the presence of an extended envelope. Our
data analysis leads to unusually low values of the spectral index , which may indicate that mm-sized dust grains have already formed
both in the envelopes and in the disk-like structures at such early stages. To
explore the possible scenarios for the interpretation of the sources we perform
a radiative transfer modeling using a Monte Carlo code, in order to take into
account possible deviations from the Rayleigh-Jeans and optically thin regimes.
Comparison between the model outputs and the observations indicates that dust
grains may form aggregates up to millimeter size already in the inner regions
of the envelopes of Class I YSOs. Moreover, we conclude that the embedded
disk-like structures in our two Class Is are probably very compact, in
particular in the case of WL12, with outer radii down to tens of AU.Comment: 12 pages, 8 figures, Accepted for publication in A&
Relationship between tremor and volcanic activity during the Southeast Crater eruption on Mount Etna in early 2000
The Southeast Crater of Mount Etna (Italy) was characterized by a violent eruptive
activity between 26 January and 24 June 2000. This activity produced 64 lava fountain
episodes with repose periods from 3 hours to 10 days. We estimated a volume of about
15–20 106 m3 lava and at least 2–3 106 m3 of tephra. We compared the
paroxysmal volcanic activity to its associated seismic signature: The high number of
events highlighted a strict correlation between tremor and volcanic activity. Seismic and
volcanic characteristics, such as the frequency of occurrence, the duration of lava
fountains and the associated tremor energy, suggested the subdivision of the studied
period into two stages separated by the 20 February event. Combining volcanic with
seismic data, we observed some useful relationships among lava fountain height,
sustained column height and Reduced Displacement; in addition, we found that the entire
episode was well correlated with the duration of the amplitude increase. Computing the
tremor energy linked to each event, the total energy associated with lava fountains
episodes results in 76% of the energy released during the whole period. Finally, the
different ratios among the overall spectral amplitude of the seismic signals of the stations
located at different altitudes suggested to us the elaboration of a simple qualitative model
to explain the dynamic behavior of the tremor source during the whole episode
Serum creatine kinase isoenzymes in children with osteogenesis imperfecta
This study evaluates serum creatine kinase isoenzyme
activity in children with osteogenesis imperfecta to determine
its usefulness as a biochemical marker during treatment
with bisphosphonate. The changes of creatine kinase
(CK) isoenzyme activity during and after discontinuation therapy
were observed. These results could be useful in addressing
over-treatment risk prevention.
Introduction The brain isoenzyme of creatine kinase (CKbb)
is highly expressed in mature osteoclasts during osteoclastogenesis,
thus plays an important role in bone resorption. We
previously identified high serum CKbb levels in 18 children
with osteogenesis imperfect (OI) type 1 treated for 1 year with
bisphosphonate (neridronate). In the present study, serum CK
isoenzymes were evaluated in the same children with continuous
versus discontinued neridronate treatment over a further
2-year follow-up period.
Methods This study included 18 children with OI type 1, 12
with continued (group A) and 6 with ceased (group B)
neridronate treatment. Auxological data, serum biochemical
markers of bone metabolism, bone mineral density z-score,
and serum total CK and isoenzyme activities were determined
in both groups.
Results Serum CKbb was progressively and significantly increased
in group A (p < 0.004) but rapidly decreased to undetectable
levels in group B. In both groups, the cardiac muscle
creatine kinase isoenzyme (CKmb) showed a marked decrease,
while serum C-terminal telopeptide (CTx) levels were
almost unchanged.
Conclusions This study provides evidence of the cumulative
effect of neridronate administration in increasing serum CKbb
levels and the reversible effect after its discontinuation. This
approach could be employed for verifying the usefulness of
serum CKbb as a biochemical marker in patients receiving
prolonged bisphosphonate treatment. Moreover, the decreased
serum CKmb levels suggest a systemic effect of these drugs
Model Equation for the Dynamics of Wrinkled Shockwaves: Comparison with DNS and Experiments
International audienceA model equation for the dynamics and the geometry of the wrinkled front of shock waves, obtained for strong shocks in the Newtonian limit, is tested by comparison with direct numerical simulations and a shock tube experiment
ALMA 870 m continuum observations of HD 100546. Evidence of a giant planet on a wide orbit
This paper reports on a new analysis of archival ALMA m dust
continuum observations. Along with the previously observed bright inner ring
(au), two addition substructures are evident in the new
continuum image: a wide dust gap, au, and a faint outer ring
ranging from au to au and whose presence was
formerly postulated in low-angular-resolution ALMA cycle 0 observations but
never before observed. Notably, the dust emission of the outer ring is not
homogeneous, and it shows two prominent azimuthal asymmetries that resemble an
eccentric ring with eccentricity . The characteristic double-ring
dust structure of HD 100546 is likely produced by the interaction of the disk
with multiple giant protoplanets. This paper includes new
smoothed-particle-hydrodynamic simulations with two giant protoplanets, one
inside of the inner dust cavity and one in the dust gap. The simulations
qualitatively reproduce the observations, and the final masses and orbital
distances of the two planets in the simulations are 3.1 at 15 au and
8.5 at 110 au, respectively. The massive outer protoplanet
substantially perturbs the disk surface density distribution and gas dynamics,
producing multiple spiral arms both inward and outward of its orbit. This can
explain the observed perturbed gas dynamics inward of 100 au as revealed by
ALMA observations of CO.
Finally, the reduced dust surface density in the au dust gap
can nicely clarify the origin of the previously detected HO gas and ice
emission.Comment: Accepted for publicatio
ALMA Observations of the Young Substellar Binary System 2M1207
We present ALMA observations of the 2M1207 system, a young binary made of a
brown dwarf with a planetary-mass companion at a projected separation of about
40 au. We detect emission from dust continuum at 0.89 mm and from the rotational transition of CO from a very compact disk around the young brown
dwarf. The small radius found for this brown dwarf disk may be due to
truncation from the tidal interaction with the planetary-mass companion. Under
the assumption of optically thin dust emission, we estimated a dust mass of 0.1
for the 2M1207A disk, and a 3 upper limit of for dust surrounding 2M1207b, which is the tightest upper
limit obtained so far for the mass of dust particles surrounding a young
planetary-mass companion. We discuss the impact of this and other
non-detections of young planetary-mass companions for models of planet
formation, which predict the presence of circum-planetary material surrounding
these objects.Comment: 10 pages, 6 figures, accepted for publication in A
Long-lived Dust Rings around HD 169142
Recent Atacama Large Millimeter/submillimeter Array (ALMA) observations of the protoplanetary disk around HD 169142 reveal a peculiar structure made of concentric dusty rings: a main ring at similar to 20 au, a triple system of rings at similar to 55-75 au in millimetric continuum emission, and a perturbed gas surface density from the (CO)-C-12,(CO)-C-13, and (CO)-O-18 (J = 2-1) surface brightness profile. In this Letter, we perform 3D numerical simulations and radiative transfer modeling exploring the possibility that two giant planets interacting with the disk and orbiting in resonant locking can be responsible for the origin of the observed dust inner rings structure. We find that in this configuration the dust structure is actually long lived while the gas mass of the disk is accreted onto the star and the giant planets, emptying the inner region. In addition, we also find that the innermost planet is located at the inner edge of the dust ring, and can accrete mass from the disk, generating a signature in the dust ring shape that can be observed in mm ALMA observations
The time evolution of dusty protoplanetary disc radii: Observed and physical radii differ
Proto-planetary disc surveys conducted with ALMA are measuring disc radii in
multiple star forming regions. The disc radius is a fundamental quantity to
diagnose whether discs undergo viscous spreading, discriminating between
viscosity or angular momentum removal by winds as drivers of disc evolution.
Observationally, however, the sub-mm continuum emission is dominated by the
dust, which also drifts inwards, complicating the picture. In this paper we
investigate, using theoretical models of dust grain growth and radial drift,
how the radii of dusty viscous proto-planetary discs evolve with time. Despite
the existence of a sharp outer edge in the dust distribution, we find that the
radius enclosing most of the dust increases with time, closely
following the evolution of the gas radius. This behaviour arises because,
although dust initially grows and drifts rapidly onto the star, the residual
dust retained on Myr timescales is relatively well coupled to the gas.
Observing the expansion of the dust disc requires using definitions based on
high fractions of the disc (e.g. 95 per cent) and very long
integrations with ALMA, because the dust grains in the outer part of the disc
are small and have a low sub-mm opacity. We show that existing surveys lack the
sensitivity to detect viscous spreading. The disc radii they measure do not
trace the mass radius or the sharp outer edge in the dust distribution, but the
outer limit of where the grains have significant sub-mm opacity. We predict
that these observed radii should shrink with time
On the millimetre continuum flux–radius correlation of proto-planetary discs
A correlation between proto-planetary disc radii and sub-mm fluxes has been
recently reported. In this Letter we show that the correlation is a sensitive
probe of grain growth processes. Using models of grain growth and drift, we
have shown in a companion paper that the observed disc radii trace where the
dust grains are large enough to have a significant sub-mm opacity. We show that
the observed correlation emerges naturally if the maximum grain size is set by
radial drift, implying relatively low values of the viscous parameter
. In this case the relation has an almost universal
normalisation, while if the grain size is set by fragmentation the flux at a
given radius depends on the dust-to-gas ratio. We highlight two observational
consequences of the fact that radial drift limits the grain size. The first is
that the dust masses measured from the sub-mm could be overestimated by a
factor of a few. The second is that the correlation should be present also at
longer wavelengths (e.g. 3mm), with a normalisation factor that scales as the
square of the observing frequency as in the optically thick case
Dynamical and spectral properties of complex networks
Dynamical properties of complex networks are related to the spectral
properties of the Laplacian matrix that describes the pattern of connectivity
of the network. In particular we compute the synchronization time for different
types of networks and different dynamics. We show that the main dependence of
the synchronization time is on the smallest nonzero eigenvalue of the Laplacian
matrix, in contrast to other proposals in terms of the spectrum of the
adjacency matrix. Then, this topological property becomes the most relevant for
the dynamics.Comment: 14 pages, 5 figures, to be published in New Journal of Physic
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