Radiative Transfer in a Low-Density Ablative Material Under Arcjet Flow Conditions

2020 ◽  
Vol 34 (1) ◽  
pp. 181-192
Author(s):  
Bernard O. Owiti ◽  
Takeharu Sakai ◽  
Yuichi Ishida
Keyword(s):  
Radiative Transfer ◽  
Low Density ◽  
Flow Conditions

Mechanical degradation of low density polyethylene under flow conditions

1978 ◽  
Vol 20 (11) ◽  
pp. 2740-2744 ◽  
Author(s):  
V.M. Gol'dberg ◽  
B.V. Yarlykov ◽  
N.G. Paverman ◽  
Ye.I. Berezina ◽  
M.S. Akutin ◽  
...  
Keyword(s):  
Low Density Polyethylene ◽  
Mechanical Degradation ◽  
Low Density ◽  
Flow Conditions

scholarly journals A multi-scale exploration of a massive young stellar object

2019 ◽  
Vol 625 ◽  
pp. A44 ◽  
Author(s):  
A. J. Frost ◽  
R. D. Oudmaijer ◽  
W. J. de Wit ◽  
S. L. Lumsden
Keyword(s):  
Radiative Transfer ◽  
Spectral Energy Distribution ◽  
Young Stellar Objects ◽  
Radiative Transfer Model ◽  
Spectral Energy ◽  
Absorption Feature ◽  
Transfer Model ◽  
Mass Star ◽  
Low Density ◽  
Circumstellar Environments

Context. The rarity of young massive stars combined with the fact that they are often deeply embedded has limited the understanding of the formation of stars larger than 8 M⊙. Ground based mid-infrared (IR) interferometry is one way of securing the spatial resolution required to probe the circumstellar environments of massive young stellar objects (MYSOs). Given that the spatial-frequency coverage of such observations is often incomplete, direct-imaging can be supplementary to such a dataset. By consolidating these observations with modelling, the features of a massive protostellar environment can be constrained. Aims. This paper aims to detail the physical characteristics of the protostellar environment of the MYSO G305.20+0.21 at three size-scales by fitting one 2.5D radiative transfer model to three different types of observations simultaneously, providing an extensive view of the accreting regions of the MYSO. Methods. Interferometry, imaging and a multi-wavelength spectral energy distribution (SED) are combined to study G305.20+0.21. The high-resolution observations were obtained using the Very Large Telescope’s MIDI and VISIR instruments, producing visibilities in the N-band and near-diffraction-limited imaging in the Q-band respectively. By fitting simulated observables, derived from the radiative transfer model, to our observations the properties of the MYSO are constrained. Results. The VISIR image shows elongation at 100 mas scales and also displays a degree of asymmetry. From the simulated observables derived from the radiative transfer model output we find that a central protostar with a luminosity of ~5 × 104 L⊙ surrounded by a low-density bipolar cavity, a flared 1 M⊙ disk and an envelope is sufficient to fit all three types of observational data for G305.20+0.21. The weak silicate absorption feature within the SED requires low-density envelope cavities to be successfully fit and is an atypical characteristic in comparison to previously studied MYSOs. Conclusions. The fact that the presence of a dusty disk provides the best fit to the MIDI visibilities implies that this MYSO is following a scaled-up version of the low-mass star formation process. The low density, low extinction environment implies the object is a more evolved MYSO and this combined with large inner radius of the disk suggests that it could be an example of a transitional disk around an MYSO.

scholarly journals Assessing the Potential of the DART Model to Discrete Return LiDAR Simulation—Application to Fuel Type Mapping

2021 ◽  
Vol 13 (3) ◽  
pp. 342
Author(s):  
Sergio Revilla ◽  
María Teresa Lamelas ◽  
Darío Domingo ◽  
Juan de la Riva ◽  
Raquel Montorio ◽  
...  
Keyword(s):  
Support Vector Machine ◽  
Radiative Transfer ◽  
Laser Scanning ◽  
Diversity Index ◽  
Classification Model ◽  
Support Vector ◽  
Low Density ◽  
Fuel Type ◽  
Machine Method ◽  
Type Classification

Fuel type is one of the key factors for analyzing the potential of fire ignition and propagation in agricultural and forest environments. The increase of three-dimensional datasets provided by active sensors, such as LiDAR (Light Detection and Ranging), has improved the classification of fuel types through empirical modelling. Empirical methods are site and sensor specific while Radiative Transfer Models (RTM) approaches provide broader universality. The aim of this work is to analyze the suitability of Discrete Anisotropic Radiative Transfer (DART) model to replicate low density small-footprint Airborne Laser Scanning (ALS) measurements and subsequent fuel type classification. Field data measured in 104 plots are used as ground truth to simulate LiDAR response based on the sensor and flight characteristics of low-density ALS data captured by the Spanish National Plan for Aerial Orthophotography (PNOA) in two different dates (2011 and 2016). The accuracy assessment of the DART simulations is performed using Spearman rank correlation coefficients between the simulated metrics and the ALS-PNOA ones. The results show that 32% of the computed metrics overpassed a correlation value of 0.80 between simulated and ALS-PNOA metrics in 2011 and 28% in 2016. The highest correlations were related to high height percentiles, canopy variability metrics as for example standard deviation and Rumple diversity index, reaching correlation values over 0.94. Two metric selection approaches and Support Vector Machine classification method with variants were compared to classify fuel types. The best-fitted classification model, trained with the DART simulated sample and validated with ALS-PNOA data, was obtained using Support Vector Machine method with radial kernel. The overall accuracy of the classification after validation was 88% and 91% for the 2011 and 2016 years, respectively. The use of DART demonstrates its value for simulating generalizable 3D data for fuel type classification providing relevant information for forest managers in fire prevention and extinction.

Dispersion Studies of Agglomerates in Steady and Dynamic Flows of Polymeric Materials

2002 ◽  
Vol 75 (1) ◽  
pp. 119-132 ◽  
Author(s):  
P. Levresse ◽  
I. Manas-Zloczower ◽  
D. L. Feke
Keyword(s):  
Shear Flow ◽  
Polymeric Materials ◽  
Oscillatory Shear ◽  
Hydrodynamic Dispersion ◽  
Low Density ◽  
Flow Conditions ◽  
Erosion Rates ◽  
Oscillatory Shear Flow ◽  
Steady Shear Flow ◽  
Dynamic Flows

Abstract The hydrodynamic dispersion of spherical calcium carbonate agglomerates was studied under both steady and oscillatory shear-flow conditions. For a given intensity of steady shear flow, erosion rates were strongly influenced by the cohesive strength of the agglomerates with less cohesive, low-density agglomerates exhibiting faster erosion than high-density agglomerates. The dispersion kinetics were also affected by the extent of matrix infiltration within the agglomerate, with more infiltration resulting in reduced erosion rates. Experiments conducted in oscillatory shear flow fields provided new insights on local mechanisms of erosion.

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