We present Atacama Large Millimeter Array 850 m continuum observations of the Orion Nebula Cluster that provide the highest angular resolution (∼0 1 40 au) and deepest sensitivity (∼0.1 mJy) of the ...region to date. We mosaicked a field containing ∼225 optical or near-IR-identified young stars, ∼60 of which are also optically identified "proplyds." We detect continuum emission at 850 m toward ∼80% of the proplyd sample, and ∼50% of the larger sample of previously identified cluster members. Detected objects have fluxes of ∼0.5-80 mJy. We remove submillimeter flux due to free-free emission in some objects, leaving a sample of sources detected in dust emission. Under standard assumptions of isothermal, optically thin disks, submillimeter fluxes correspond to dust masses of ∼0.5-80 Earth masses. We measure the distribution of disk sizes, and find that disks in this region are particularly compact. Such compact disks are likely to be significantly optically thick. The distributions of submillimeter flux and inferred disk size indicate smaller, lower-flux disks than in lower-density star-forming regions of similar age. Measured disk flux is correlated weakly with stellar mass, contrary to studies in other star-forming regions that found steeper correlations. We find a correlation between disk flux and distance from the massive star θ1 Ori C, suggesting that disk properties in this region are influenced strongly by the rich cluster environment.
Superelastic conducting fibers with improved properties and functionalities are needed for diverse applications. Here we report the fabrication of highly stretchable (up to 1320%) sheath-core ...conducting fibers created by wrapping carbon nanotube sheets oriented in the fiber direction on stretched rubber fiber cores. The resulting structure exhibited distinct short- and long-period sheath buckling that occurred reversibly out of phase in the axial and belt directions, enabling a resistance change of less than 5% for a 1000% stretch. By including other rubber and carbon nanotube sheath layers, we demonstrated strain sensors generating an 860% capacitance change and electrically powered torsional muscles operating reversibly by a coupled tension-to-torsion actuation mechanism. Using theory, we quantitatively explain the complementary effects of an increase in muscle length and a large positive Poisson's ratio on torsional actuation and electronic properties.
The detection of non-technical losses (NTL) is a very important economic issue for power utilities. Diverse machine learning strategies have been proposed to support electric power companies tackling ...this problem. Methods performance is often measured using standard cost-insensitive metrics, such as the accuracy, true positive ratio, AUC, or F1. In contrast, we propose to design a NTL detection solution that maximizes the effective economic return. To that end, both the income recovered and the inspection cost are considered. Furthermore, the proposed framework can be used to design the infrastructure of the division in charge of performing customers inspections. Then, assisting not only short term decisions, e.g., which customer should be inspected first, but also the elaboration of long term strategies, e.g., planning of NTL company budget. The problem is formulated in a Bayesian risk framework. Experimental validation is presented using a large dataset of real users from the Uruguayan utility. The results obtained show that the proposed method can boost companies profit and provide a highly efficient and realistic countermeasure to NTL. Moreover, the proposed pipeline is general and can be easily adapted to other practical problems.
We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of 1.1 mm dust continuum and CO 2-1 emission toward six dense cores within the Ophiuchus molecular cloud. We detect ...compact, subarcsecond continuum structures toward three targets, two of which (Oph A N6 and SM1) are located in the Ophiuchus A ridge. Two targets, SM1 and GSS 30, contain two compact sources within the ALMA primary beam. We argue that several of the compact structures are small (R 80 au) accretion disks around young protostars, based on their resolved, elongated structures, coincident radio and X-ray detections, or bipolar outflow detections. While CO line wings extend to 10-20 km s−1 for the more evolved sources GSS 30 IRS3 and IRS1, CO emission toward other sources, where detected, only extends a few km s−1 from the cloud vLSR. The dust spectral index toward the compact objects suggests either that the disks are optically thick at 1.1 mm or that significant grain growth has already occurred. We identify, for the first time, a single compact continuum source (R ∼ 100 au) toward N6 embedded within a larger continuum structure. SM1N is extended in the continuum but is highly centrally concentrated, with a density profile that follows a r−1.3 power law within 200 au and additional structure suggested by the uv-data. Both N6 and SM1N show no clear bipolar outflows with velocities greater than a few km s−1 from the cloud velocity. These sources are candidates to be the youngest protostars or first hydrostatic cores in the Ophiuchus molecular cloud.
Cross-beam energy transfer (CBET) results from two-beam energy exchange via seeded stimulated Brillouin scattering, which detrimentally reduces ablation pressure and implosion velocity in ...direct-drive inertial confinement fusion. Mitigating CBET is demonstrated for the first time in inertial-confinement implosions at the National Ignition Facility by detuning the laser-source wavelengths (±2.3 Å UV) of the interacting beams. We show that, in polar direct-drive, wavelength detuning increases the equatorial region velocity experimentally by 16% and alters the in-flight shell morphology. These experimental observations are consistent with design predictions of radiation-hydrodynamic simulations that indicate a 10% increase in the average ablation pressure.
Nitrous oxide (N2O) is a potent greenhouse gas and is produced in the soil by nitrification and denitrification processes. These processes are catalysed by a number of key enzymes from microbial ...communities in the soil. In grazed pasture soils, most of the N2O is emitted from nitrogen (N) returned in animal excreta deposited during outdoor grazing, particularly in the urine. The nitrification inhibitor, dicyandiamide (DCD), has been used to mitigate N2O emissions from grazed pasture soils. However, how the nitrifying and denitrifying communities and N2O emissions are affected by the urine and DCD applications under contrasting soil moisture conditions in grazed pasture soils is poorly understood. Here we report a laboratory incubation study to determine the impact of soil moisture status in combination with animal urine and DCD applications on the abundance of ammonia oxidizer (AO) and denitrifier functional genes, and N2O emissions from a grazed pasture soil. The soil used was a Horotiu silt loam (Typic Udivitrand) developed from volcanic ash. The treatments included three soil moisture contents: 60%, 100% and 130% field capacity (FC), each with Control, Urine and Urine + DCD treatments. The incubation temperature was 12 °C to simulate New Zealand autumn/winter soil temperatures (when DCD is used). Results showed that soil moisture significantly increased N2O emissions from the urine treated soil, with total N2O emissions at 100% and 130% FC being 9 and 400 times that at 60% FC, respectively. Soil moisture content also significantly affected the growth of ammonia oxidiser and denitrifier communities, with the functional genes increasing with increased soil moisture content. The application of urine significantly increased the abundance of AOB amoA, nirK and nosZ (clades I and II) genes, but decreased the abundance of AOA amoA and narG genes at 130% FC. DCD was highly effective in inhibiting the growth of AOB communities, and reducing N2O emissions at 100% and 130% FC. The abundance of nirK gene was also reduced by DCD at 130% FC, but this was, most likely, a reflection of changes in AOB populations, bearing the majority of the nirK gene detected in this study. DCD did not affect the other denitrifier genes studied. Total N2O emissions were significantly related to the abundance of AOB (R2 = 0.94, p < 0.001) and nirK genes (R2 = 0.57, p < 0.05), but not to the other genes studied. These results suggest that soil moisture has a major influence on ammonia oxidizing and denitrifying microbial communities in urine treated soils and that this affects the N2O emissions. Ammonia oxidizers are able to grow under very wet soil conditions, probably in part due to the growth of AOB communities that also carry the nirK gene.
•Soil moisture status affected the growth of ammonia oxidiser and denitrifier communities.•The application of urine significantly increased the abundance of AOB amoA, nirK and nosZ (clades I and II) genes.•Animal urine decreased the abundance of AOA amoA and narG genes.•The abundance of AOB and nirK gene was reduced by the nitrification inhibitor dicyandiamide.•N2O emissions were related to the abundance of AOB and nirK genes but not to the other genes studied.
We present a catalogue of dense cores in a ∼4° × 2° field of the Taurus star-forming region, inclusive of the L1495 cloud, derived from Herschel SPIRE and PACS observations in the 70 μm, 160 μm, 250 ...μm, 350 μm, and 500 μm continuum bands. Estimates of mean dust temperature and total mass are derived using modified blackbody fits to the spectral energy distributions. We detect 525 starless cores of which ∼10–20 per cent are gravitationally bound and therefore presumably prestellar. Our census of unbound objects is ∼85 per cent complete for M > 0.015 M⊙ in low-density regions (A
V ≲ 5 mag), while the bound (prestellar) subset is ∼85 per cent complete for M > 0.1 M⊙ overall. The prestellar core mass function (CMF) is consistent with lognormal form, resembling the stellar system initial mass function, as has been reported previously. All of the inferred prestellar cores lie on filamentary structures whose column densities exceed the expected threshold for filamentary collapse, in agreement with previous reports. Unlike the prestellar CMF, the unbound starless CMF is not lognormal, but instead is consistent with a power-law form below 0.3 M⊙ and shows no evidence for a low-mass turnover. It resembles previously reported mass distributions for CO clumps at low masses (M ≲ 0.3 M⊙). The volume density PDF, however, is accurately lognormal except at high densities. It is consistent with the effects of self-gravity on magnetized supersonic turbulence. The only significant deviation from lognormality is a high-density tail which can be attributed unambiguously to prestellar cores.
ABSTRACT
Filaments are crucial intermediaries in the star formation process. Recent observations of filaments show that (i) a number of them are non-singular entities, and rather a bundle of velocity ...coherent fibres, and (ii) while a majority of filaments spawn cores narrower than their natal filaments, some cores are broader. We explore these issues by developing hydrodynamic simulations of an initially sub-critical individual filament that is allowed to accrete gas from its neighbourhood and evolves under self-gravity. Results obtained here support the idea that fibres form naturally during the filament formation process. We further argue that the ambient environment, i.e. the magnitude of external pressure, and not the filament linemass alone, has bearing upon the morphology of its evolution. We observe that a filament is susceptible to the sausage-type instability irrespective of the external pressure. The fragments, however, are pinched in a filament experiencing pressure comparable to that in the Solar neighbourhood (∼104 K cm−3). By contrast, fragments are broad and spherical – having density profiles similar to that of a stable Bonnor–Ebert sphere – when the filament experiences a higher pressure, typically ≥105 K cm−3, but ≤106 K cm−3). The filament tends to rupture at even higher external pressure (≥107 K cm−3). These observations collectively mean that star formation is less efficient with increasing external pressure.
We develop and apply a Hessian-based filament detection algorithm to submillimetre continuum observations of Orion A North. The resultant filament radial density profiles are fitted with ...beam-convolved line-of-sight Plummer-profiles using Markov chain Monte Carlo techniques. The posterior distribution of the radial decay parameter demonstrates that the majority of filaments exhibit p = 1.5–3, with a mode at p = 2.2, suggesting deviation from the Ostriker p = 4 isothermal, equilibrium, self-gravitating cylinder. The spatial distribution of young stellar objects relative to the high column density filaments is investigated, yielding a lower limit on the star-forming age of the integral-shaped filament ∼1.4 Myr. Additionally, inferred lifetimes of filaments are examined which suggest long-term filament accretion, varying rates of star formation, or both. Theoretical filament stability measures are determined with the aid of HARP C18O J = 3–2 observations and indicate that the majority of filaments are gravitationally subcritical, despite the presence of young protostars. The results from this investigation are consistent with the one-dimensional accretion flow filament model recently observed in numerical simulations.
ABSTRACT Filamentary structures are ubiquitous in molecular clouds, and have been recently argued to play an important role in regulating the size and mass of embedded clumps through fragmentation ...and mass accretion. Here, we reveal the dynamical state and fragmentation of filamentary molecular gas associated with the Serpens South protocluster through analysis of wide ( ) observations of NH3 (1, 1) and (2, 2) inversion transitions with the Green Bank Telescope. Detailed modeling of the NH3 lines reveals that the kinematics of the cluster and surrounding filaments are complex. We identify hierarchical structure using a dendrogram analysis of the NH3 emission. The distance between neighbor structures that are embedded within the same parent structure is generally greater than expected from a spherical Jeans analysis, and is in better agreement with cylindrical fragmentation models. The NH3 line width-size relation is flat, and average gas motions are sub- or trans-sonic over all physical scales observed. Subsonic regions extend far beyond the typical 0.1 pc scale previously identified in star-forming cores. As a result, we find a strong trend of decreasing virial parameter with increasing structure mass in Serpens South. Extremely low virial parameters on the largest scales probed by our data suggest that the previously observed, ordered magnetic field is insufficient to support the region against collapse, in agreement with large radial infall motions previously measured toward some of the filaments. A more complex magnetic field configuration in the dense gas, however, may be able to support the filaments.
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