589 research outputs found
Chronic Midsubstance Patellar Tendon and Retinacular Rupture: Primary Repair Enhancement Using Bioinductive Implant Augmentation
Midsubstance tears of the patellar tendon are uncommon and present a difficult injury to treat. If left untreated, these can be debilitating injuries for patients and leave them with an overall lack of function in the injured extremity. Compared to a proximal or distal patellar tendon rupture, midsubstance tears rely on tendon-to-tendon healing instead of bone to tendon healing. Given this situation, specific preoperative planning and the use of a bioinductive scaffolding allows surgeons to enhance the overall construct, while promoting a beneficial healing environment. Although the addition of bioinductive implants has grown in popularity for upper extremity injuries, few cases describe its use in the lower extremity setting. Here, we present a case of midsubstance patellar tendon repair, as well as a medial and lateral retinacular repair using a structural biological implant with Type I collagen for augmentation to enhance our overall final construct
The SONYC survey: Towards a complete census of brown dwarfs in star forming regions
SONYC, short for "Substellar Objects in Nearby Young Clusters", is a survey
program to provide a census of the substellar population in nearby star forming
regions. We have conducted deep optical and near-infrared photometry in five
young regions (NGC1333, rho Ophiuchi, Chamaeleon-I, Upper Sco, and Lupus-3),
combined with proper motions, and followed by extensive spectroscopic campaigns
with Subaru and VLT, in which we have obtained more than 700 spectra of
candidate low-mass objects. We have identified and characterized more than 60
new substellar objects, among them a handful of objects with masses close to,
or below the Deuterium burning limit. Through SONYC and surveys by other
groups, the substellar IMF is now well characterized down to ~ 5 - 10 MJup, and
we find that the ratio of the number of stars with respect to brown dwarfs lies
between 2 and 6. A comprehensive survey of NGC 1333 reveals that, down to
~5MJup, free-floating objects with planetary masses are 20-50 times less
numerous than stars, i.e. their total contribution to the mass budget of the
clusters can be neglected.Comment: to appear in the proceedings of the conference 'Brown dwarfs come of
age', May 20-24 2013, Memorie della Societa Astronomica Italian
Multiscale modeling of acoustic shielding materials
It is very important to protect high-tech systems from acoustic excitation when operating in a noisy environment. Some passive absorbing materials such as acoustic foams can improve the performance which depends on the interaction of the acoustic wave and the microstructure of the foam
Lack of PAH emission toward low-mass embedded young stellar objects
PAHs have been detected toward molecular clouds and some young stars with
disks, but have not yet been associated with embedded young stars. We present a
sensitive mid-IR spectroscopic survey of PAH features toward a sample of
low-mass embedded YSOs. The aim is to put constraints on the PAH abundance in
the embedded phase of star formation using radiative transfer modeling.
VLT-ISAAC L-band spectra for 39 sources and Spitzer IRS spectra for 53
sources are presented. Line intensities are compared to recent surveys of
Herbig Ae/Be and T Tauri stars. The radiative transfer codes RADMC and RADICAL
are used to model the PAH emission from embedded YSOs consisting of a PMS star
with a circumstellar disk embedded in an envelope. The dependence of the PAH
feature on PAH abundance, stellar radiation field, inclination and the
extinction by the surrounding envelope is studied.
The 3.3 micron PAH feature is undetected for the majority of the sample
(97%), with typical upper limits of 5E-16 W/m^2. Compact 11.2 micron PAH
emission is seen directly towards 1 out of the 53 Spitzer Short-High spectra,
for a source that is borderline embedded. For all 12 sources with both VLT and
Spitzer spectra, no PAH features are detected in either. In total, PAH features
are detected toward at most 1 out of 63 (candidate) embedded protostars (<~
2%), even lower than observed for class II T Tauri stars with disks (11-14%).
Assuming typical class I stellar and envelope parameters, the absence of PAHs
emission is most likely explained by the absence of emitting carriers through a
PAH abundance at least an order of magnitude lower than in molecular clouds but
similar to that found in disks. Thus, most PAHs likely enter the protoplanetary
disks frozen out in icy layers on dust grains and/or in coagulated form.Comment: 13 pages, 9 figures, accepted for publication in A&
Spatially extended PAHs in circumstellar disks around T Tauri and Herbig Ae stars
Our aim is to determine the presence and location of the emission from
polycyclic aromatic hydrocarbons (PAHs) towards low and intermediate mass young
stars with disks using large aperture telescopes.
VLT-VISIR N-band spectra and VLT-ISAAC and VLT-NACO L-band spectra of 29
sources are presented, spectrally resolving the 3.3, 8.6, 11.2, and 12.6 micron
PAH features. Spatial-extent profiles of the features and the continuum
emission are derived and used to associate the PAH emission with the disks. The
results are discussed in the context of recent PAH-emission disk models.
The 3.3, 8.6, and 11.2 micron PAH features are detected toward a small
fraction of the T Tauri stars, with typical upper limits between 1E-15 and
5E-17 W/m^2. All 11.2 micron detections from a previous Spitzer survey are
confirmed with (tentative) 3.3 micron detections, and both the 8.6 and the 11.2
micron features are detected in all PAH sources. For 6 detections, the spatial
extent of the PAH features is confined to scales typically smaller than
0.12-0.34'', consistent with the radii of 12-60 AU disks at their distances
(typically 150 pc). For 3 additional sources, WL 16, HD 100546, and TY CrA, one
or more of the PAH features are more extended than the hot dust continuum of
the disk, whereas for Oph IRS 48, the size of the resolved PAH emission is
confirmed as smaller than for the large grains. For HD 100546, the 3.3 micron
emission is confined to a small radial extent of 12 +- 3 AU, most likely
associated with the outer rim of the gap in this disk. Gaps with radii out to
10-30 AU may also affect the observed PAH extent for other sources. For both
Herbig Ae and T Tauri stars, the small measured extents of the 8.6 and 11.2
micron features are consistent with larger (>= 100 carbon atoms) PAHs.Comment: 14 pages, 17 figures, accepted for publication in A&
Dust sedimentation in protoplanetary disks with polycyclic aromatic hydrocarbons
Context. Dust sedimentation is known to affect the infrared spectra and images of disks. In particular the far-infrared emission may be reduced by strong sedimentation. However, dust grains of different sizes sediment to different depths in the disk. Spectral features of one species may thus be enhanced, while those of other species may be suppressed.
Aims. Polycyclic aromatic hydrocarbons (PAHs) are among the smallest βdust grainsβ. We investigate how the presence of PAHs in
protoplanetary disks affects the diskβs spectral energy distribution (SED) and feature strengths when the thermal (large) grains are
allowed to sediment.
Methods. We calculate the vertical distribution of dust grains for both the PAH βdustβ and the thermal dust grains.We include vertical
settling and vertical mixing via turbulence. The results are inserted into a Monte-Carlo radiative transfer code to compute the SEDs.
Results. For high turbulence the sedimentation barely affects the spectrum. For low turbulence, however, the PAHs still stay well-mixed
in the diskβs surface layer, while the 0.1 ΞΌm size grains sediment deep into the disk. This strongly enhances the PAH features
relative to the continuum (by factors of 2 to 10), while the far-infrared flux is reduced. This predicts that sources with weak far-infrared
flux have stronger PAH features, which is β at least among Herbig Ae stars β opposite to what is observed, suggesting that
sedimentation is not the only factor responsible for the weak mid- to far-infrared excess in some disks. We speculate that coagulation
might be a solution, reducing both the mid- to far-infrared flux and the PAH features
Cold Disks: Spitzer Spectroscopy of Disks around Young Stars with Large Gaps
We have identified four circumstellar disks with a deficit of dust emission
from their inner 15-50 AU. All four stars have F-G spectral type, and were
uncovered as part of the Spitzer Space Telescope ``Cores to Disks'' Legacy
Program Infrared Spectrograph (IRS) first look survey of ~100 pre-main sequence
stars. Modeling of the spectral energy distributions indicates a reduction in
dust density by factors of 100-1000 from disk radii between ~0.4 and 15-50 AU,
but with massive gas-rich disks at larger radii. This large contrast between
the inner and outer disk has led us to use the term `cold disks' to distinguish
these unusual systems. However, hot dust [0.02-0.2 Mmoon] is still present
close to the central star (R ~0.8 AU). We introduce the 30/13 micron, flux
density ratio as a new diagnostic for identifying cold disks. The mechanisms
for dust clearing over such large gaps are discussed. Though rare, cold disks
are likely in transition from an optically thick to an optically thin state,
and so offer excellent laboratories for the study of planet formation.Comment: 13 pages, 3 figures, accepted to ApJ
C2D Spitzer-IRS spectra of disks around T Tauri stars: IV. Crystalline silicates
Aims. Dust grains in the planet-forming regions around young stars are expected to be heavily processed due to coagulation, fragmentation, and crystallization. This paper focuses on the crystalline silicate dust grains in protoplanetary disks for a statistically significant number of TTauri stars (96).
Methods. As part of the cores to disks (c2d) legacy program, we obtained more than a hundred Spitzer/IRS spectra of TTauri stars, over a spectral range of 5-35 ΞΌm where many silicate amorphous and crystalline solid-state features are present. At these wavelengths, observations probe the upper layers of accretion disks up to distances of a dozen AU from the central object.
Results. More than 3/4 of our objects show at least one crystalline silicate emission feature that can be essentially attributed to Mg-rich silicates. The Fe-rich crystalline silicates are largely absent in the c2d IRS spectra. The strength and detection frequency of the crystalline features seen at Ξ» > 20 ΞΌm correlate with each other, while they are largely uncorrelated with the observational properties of the amorphous silicate 10 ΞΌm feature. This supports the idea that the IRS spectra essentially probe two independent disk regions: a warm zone (β€1 AU) emitting at ~ 10 ΞΌm and a much colder region emitting at Ξ» > 20 ΞΌm (β€10 AU). We identify a crystallinity paradox, as the long-wavelength (Ξ» > 20 m) crystalline silicate features are detected 3.5 times more frequently (~55% vs. ~15%) than the crystalline features arising from much warmer disk regions (Ξ» ~ 10 ΞΌm). This suggests that the disk has an inhomogeneous dust composition within ~10 AU. The analysis of the shape and strength of both the amorphous 10 ΞΌm feature and the crystalline feature around 23 ΞΌm provides evidence for the prevalence of ΞΌm-sized (amorphous and crystalline) grains in upper layers of disks.
Conclusions. The abundant crystalline silicates found far from their presumed formation regions suggest efficient outward radial transport mechanisms in the disks around TTauri stars. The presence of ΞΌm-sized grains in disk atmospheres, despite the short timescales for settling to the midplane, suggests efficient (turbulent) vertical diffusion, probably accompanied by grain-grain fragmentation to balance the expected efficient growth. In this scenario, the depletion of submicron-sized grains in the upper layers of the disks points toward removal mechanisms such as stellar winds or radiation pressure
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