Context.
A key piece of information to understand the origin and role of protoplanetary disk substructures is their dust content. In particular, disk substructures associated with gas pressure bumps ...can work as dust traps, accumulating grains and reaching the necessary conditions to trigger the streaming instability.
Aims.
In order to shed some light on the origin and role that disk substructures play in planet formation, we aim to characterize the dust content of substructures in the disk of TW Hya.
Methods.
We present Atacama Large Millimeter Array (ALMA) observations of TW Hya at 3.1 mm with ~50 milliarcsecond resolution. These new data were combined with archival high angular resolution ALMA observations at 0.87, 1.3, and 2.1 mm. We analyze these multiwavelength data to infer a disk radial profile of the dust surface density, maximum particle size, and slope of the particle size distribution.
Results.
Most previously known annular substructures in the disk of TW Hya are resolved at the four wavelengths. Inside the inner 3 au cavity, the 2.1 and 3.1 mm images show a compact source of free–free emission, likely associated with an ionized jet. Our multiwavelength analysis of the dust emission shows that the maximum particle size in the disk of TW Hya is >1 mm. The inner 20 au are completely optically thick at all four bands, which results in the data tracing different disk heights at different wavelengths. Coupled with the effects of dust settling, this prevents the derivation of accurate density and grain size estimates in these regions. At
r
> 20 au, we find evidence of the accumulation of large dust particles at the position of the bright rings, indicating that these are working as dust traps. The total dust mass in the disk is between 250 and 330
M
⊕
, which represents a gas-to-dust mass ratio between 50 and 70. Our mass measurement is a factor of 4.5–5.9 higher than the mass that one would estimate using the typical assumptions of large demographic surveys.
Conclusions.
Our results indicate that the ring substructures in TW Hya are ideal locations to trigger the streaming instability and form new generations of planetesimals.
Full text
Available for:
FMFMET, NUK, UL, UM, UPUK
Display omitted
Absorbable medical devices must be developed in order to have an appropriate degradation rate in agreement with the healing rate of bone in the implantation site. In this work, ...biodegradable composites formed by a polylactic acid matrix reinforced with 10%wt. magnesium microparticles were processed and their in vitro degradation investigated during 28days. A joint analysis of the amount of H2 released, the changes in pH in buffered (PBS) and non-buffered media (distilled water), the variations in mass, microstructure and the mechanical performance of the specimens was developed. The main aim was to elucidate the relevance of Mg particles shape on tailoring the degradation kinetics of these novel composites. The results show that the shape of the Mg reinforcing particles plays a crucial role in the degradation rate of PLA/Mg composites, with spherical particles promoting a lower degradation rate than irregular particles. This fact is only partially due to the smaller surface area to volume ratio of the spherical particles. Irregular particles promote a faster formation of cracks and, therefore, an increasingly faster degradation of the polymeric matrix. In every case, the amount of H2 released by the composites was well below that released by monolithic Mg. The pH of PBS during degradation remained always within 7.2 and 7.4. PLA/Mg reinforced with spherical particles retains more than 90% of its mechanical properties after 7days of immersion and more than 60% after 28days.
The increasing demand for temporary orthopaedic implants is the driving force to seek new strategies to decrease costs and simultaneously improve patients comfort as well as simplify surgical procedures. Resorbable medical devices must be developed in order to have an appropriate degradation rate in agreement with the healing rate of bone. We are presenting for the first time results of the degradation kinetics of a new material based on polylactic acid reinforced with 10%wt. Mg microparticles. This work analyzes the relevance of Mg particle shape (irregular and spherical) on tailoring the degradation behaviour of these composites. Conclusions withdrawn from this study help to customize bioabsorbable materials in order to meet the requirements for a specific application and patient.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Our understanding of protoplanetary disks is rapidly departing from the classical view of a smooth, axisymmetric disk. This is in part thanks to the high angular resolution that (sub)millimeter ...observations can provide. Here, we present the combined results of Atacama Large Millimeter/submillimeter Array (ALMA) (0.9 mm) and Very Large Array (VLA) (7 mm) dust continuum observations toward the protoplanetary disk around the solar analog GM Aur. Both images clearly resolve the ∼35 au inner cavity. The ALMA observations also reveal a fainter disk that extends up to ∼250 au. We model our observations using two approaches: an analytical fit to the observed deprojected visibilities, and a physical disk model that fits the spectral energy distribution as well as the VLA and ALMA observations. Despite not being evident in the deconvolved images, the VLA and ALMA visibilities can only be fitted with two bright rings of radii ∼40 and ∼80 au. Our physical model indicates that this morphology is the result of an accumulation or trapping of large dust grains, probably due to the presence of two pressure bumps in the disk. Even though alternative mechanisms cannot be discarded, the multiple rings suggest that forming planets may have cleared at least two gaps in the disk. Finally, our analysis suggests that the inner cavity might display different sizes at 0.9 and 7 mm. This discrepancy could be caused by the presence of free-free emission close to the star at 7 mm, or by a more compact accumulation of the large dust grains at the edge of the cavity.
We present a detailed multiwavelength characterization of the multi-ring disk of HD 169142. We report new Atacama Large Millimeter/submillimeter Array (ALMA) observations at 3 mm and analyze them ...together with archival 0.89 and 1.3 mm data. Our observations resolve three out of the four rings in the disk previously seen in high-resolution ALMA data. A simple parametric model is used to estimate the radial profile of the dust optical depth, temperature, density, and particle size distribution. We find that the multiple ring features of the disk are produced by annular accumulations of large particles, probably associated with gas pressure bumps. Our model indicates that the maximum dust grain size in the rings is ∼1 cm, with slightly flatter power-law size distributions than the interstellar medium-like size distribution (p ∼ 3.5) found in the gaps. In particular, the inner ring (∼26 au) is associated with a strong and narrow buildup of dust particles that could harbor the necessary conditions to trigger the streaming instability. According to our analysis, the snowlines of the most important volatiles do not coincide with the observed substructures. We explore different ring formation mechanisms and find that planet-disk interactions are the most likely scenario to explain the main features of HD 169142. Overall, our multiwavelength analysis provides some of the first unambiguous evidence of the presence of radial dust traps in the rings of HD 169142. A similar analysis in a larger sample of disks could provide key insights on the impact that disk substructures have on the dust evolution and planet formation processes.
This work deals with the mechanical characterization by depth-sensing indentation (DSI) of PLLA and PLDA composites reinforced with micro-particles of Mg (up to 15wt%), which is a challenging task ...since the indented volume must provide information of the bulk composite, i.e. contain enough reinforcement particles. The composites were fabricated by combining hot extrusion and compression moulding. Physico-chemical characterization by TGA and DSC indicates that Mg anticipates the thermal degradation of the polymers but does not compromise their stability during processing. Especial emphasis is devoted to determine the effect of strain rate and Mg content on mechanical behavior, thus important information about the visco-elastic behavior and time-dependent response of the composites is obtained. Relevant for the intended application is that Mg addition increases the elastic modulus and hardness of the polymeric matrices and induces a higher resistance to flow. The elastic modulus obtained by DSI experiments shows good agreement with that obtained by uniaxial compression tests. The results indicate that DSI experiments are a reliable method to calculate the modulus of polymeric composites reinforced with micro-particles. Taking into consideration the mechanical properties results, PLA/Mg composite could be used as substitute for biodegradable monolithic polymeric implants already in the market for orthopedics (freeform meshes, mini plates, screws, pins, …), craniomaxillofacial, or spine.
Display omitted
•PLLA and PLDA composites were reinforced with micro-particles of Mg.•Mg does not compromise the polymer stability during thermoplastic processing.•Mg increases elastic modulus, hardness and resistance to flow of polymers.•Depth-sensing indentation was used to calculate their mechanical properties.•Depth sensing analysis correlates well with uniaxial compression data.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
ABSTRACT
The massive star-forming region W75N (B) is thought to host a cluster of massive protostars (VLA 1, VLA 2, and VLA 3) undergoing different evolutionary stages. In this work, we present radio ...continuum data with the highest sensitivity and angular resolution obtained to date in this region, using the VLA-A and covering a wide range of frequencies (4–48 GHz), which allowed us to study the morphology and the nature of the emission of the different radio continuum sources. We also performed complementary studies with multi-epoch Very Large Array (VLA) data and Atacama Large Millimeter Array (ALMA) archive data at 1.3 mm wavelength. We find that VLA 1 is driving a thermal radio jet at scales of ≈0.1 arcsec (≈130 au), but also shows signs of an incipient hypercompact H ii region at scales of ≲1 arcsec (≲1300 au). VLA 3 is also driving a thermal radio jet at scales of a few tenths of arcsec (few hundred of au). We conclude that this jet is shock exciting the radio continuum sources Bc and VLA 4 (obscured Herbig–Haro objects), which show proper motions moving outward from VLA 3 at velocities of ≈112–118 km s−1. We have also detected three new weak radio continuum sources, two of them associated with millimetre continuum cores observed with ALMA, suggesting that these two sources are also embedded young stellar objects in this massive star-forming region.
Centimeter continuum observations of protostellar jets have revealed knots of shocked gas where the flux density decreases with frequency. This spectrum is characteristic of nonthermal synchrotron ...radiation and implies both magnetic fields and relativistic electrons in protostellar jets. Here, we report on one of the few detections of a nonthermal jet driven by a young massive star in the star-forming region G035.02+0.35. We made use of the NSF’s Karl G. Jansky Very Large Array (VLA) to observe this region at
C
,
K
u
, and
K
bands with the A- and B-array configurations, and obtained sensitive radio continuum maps down to an rms of 10
μ
Jy beam
−1
. These observations allow for a detailed spectral index analysis of the radio continuum emission in the region, which we interpret as a protostellar jet with a number of knots aligned with extended 4.5
μ
m emission. Two knots clearly emit nonthermal radiation and are found at similar distances, of approximately 10 000 au, at each side of the central young star, from which they expand at velocities of several hundred km s
−1
. We estimate both the mechanical force and the magnetic field associated with the radio jet, and infer a lower limit of 0.4 × 10
−4
M
⊙
yr
−1
km s
−1
and values in the range 0.7–1.3 mG.
Full text
Available for:
FMFMET, NUK, UL, UM, UPUK
This work aims to develop polymer/magnesium composites as new biodegradable and bioresorbable materials for osteosynthesis implants. The polymeric matrix will benefit from the higher strength and ...modulus of the Mg particles, whereas Mg will benefit from the surrounded protective polymeric matrix that will control its degradation rate. To provide a proof of concept a set of specimens were processed by combining solvent casting of PLLA (poly-l-lactic acid) loaded with 30wt% of Mg particles and further molding by compression. Mechanical characterization reveals that reinforcing the polymer matrix with Mg particles improves its mechanical properties (hardness up to 340MPa and yield strength up to 100MPa). Interestingly, Young's modulus determined by ultramicroindentation increases up to 8GPa. From the DSC analysis it follows that the unloaded and loaded polymer has similar crystallinity, which indicates that the improvement in mechanical properties is purely the effect of particle reinforcement.
Display omitted
► We develop novel PLLA/Mg composites as biodegradable and bioresorbable materials. ► With Mg particles improves yield strength and elastic modulus of PLLA. ► Mg slightly decreases the glass transition temperature of PLLA. ► Mg does not induce crystal nucleation during cooling from the melt
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Aims. We seek to study the physical properties of the ionized jet emission in the vicinity of an O-type young stellar object (YSO) and to estimate the efficiency of the transfer of energy and ...momentum from small- to large-scale outflows. Methods. We conducted Karl G. Jansky Very Large Array (VLA) observations, at both 22 and 45GHz, of compact and faint radio continuum emission in the high-mass star-forming region G023.01-00.41 with an angular resolution between 0". 3 and 0". 1 and a thermal rms on the order of 10mu Jybeam super(-1). Results. We discovered a collimated thermal (bremsstrahlung) jet emission with a radio luminosity (L sub(rad)) of 24mJykpc super(2) at 45GHz in the inner 1000AU from an O-type YSO. The radio thermal jet has an opening angle of 44degrees and carries a momentum rate of 8 x 10 super(-3)M sub(middot in circle)yr super(-1)kms super(- 1). By combining the new data with previous observations of the molecular outflow and water maser shocks, we can trace the outflow emission from its driving source through the molecular clump across more than two orders of magnitude in length (500AU-0.2pc). We find that the momentum-transfer efficiency between the inner jet emission and the extended outflow of entrained ambient gas is near unity. This result suggests that the large-scale flow is swept up by the mechanical force of radio jet emission, which originates from within 1000AU of the high-mass YSO.
Full text
Available for:
FMFMET, NUK, UL, UM, UPUK
ABSTRACT We report Atacama Large Millimeter/submillimeter Array (ALMA) observations of a one-sided, high-velocity (∼80 km s−1) CO(J = 2 → 1 ) jet powered by the intermediate-mass protostellar source ...Serpens SMM1-a. The highly collimated molecular jet is flanked at the base by a wide-angle cavity; the walls of the cavity can be seen in both 4 cm free-free emission detected by the Very Large Array and 1.3 mm thermal dust emission detected by ALMA. This is the first time that ionization of an outflow cavity has been directly detected via free-free emission in a very young, embedded Class 0 protostellar source that is still powering a molecular jet. The cavity walls are ionized either by UV photons escaping from the accreting protostellar source or by the precessing molecular jet impacting the walls. These observations suggest that ionized outflow cavities may be common in Class 0 protostellar sources, shedding further light on the radiation, outflow, and jet environments in the youngest, most embedded forming stars.