scholarly journals Chemical modelling of dust–gas chemistry within AGB outflows – II. Effect of the dust-grain size distribution

2020 ◽  
Vol 495 (2) ◽  
pp. 1650-1665 ◽  
Author(s):  
M Van de Sande ◽  
C Walsh ◽  
T Danilovich
Keyword(s):  
Grain Size ◽  
Size Distribution ◽  
Gas Phase ◽  
Surface Area ◽  
Grain Size Distribution ◽  
Agb Stars ◽  
Gas Chemistry ◽  
Starting Point ◽  
Dust Grain ◽  
Grain Surface

ABSTRACT Asymptotic giant branch (AGB) stars are, together with supernovae, the main contributors of stellar dust to the interstellar medium (ISM). Dust grains formed by AGB stars are thought to be large. However, as dust nucleation and growth within their outflows are still not understood, the dust-grain size distribution (GSD) is unknown. This is an important uncertainty regarding our knowledge of the chemical and physical history of interstellar dust, as AGB dust forms ${\sim} 70{{\ \rm per\ cent}}$ of the starting point of its evolution. We expand on our chemical kinetics model, which uniquely includes a comprehensive dust–gas chemistry. The GSD is now allowed to deviate from the commonly assumed canonical Mathis, Rumpl & Nordsieck distribution. We find that the specific GSD can significantly influence the dust–gas chemistry within the outflow. Our results show that the level of depletion of gas-phase species depends on the average grain surface area of the GSD. Gas-phase abundance profiles and their possible depletions can be retrieved from observations of molecular emission lines when using a range of transitions. Because of degeneracies within the prescription of GSD, specific parameters cannot be retrieved, only (a lower limit to) the average grain surface area. None the less, this can discriminate between dust composed of predominantly large or small grains. We show that when combined with other observables such as the spectral energy distribution and polarized light, depletion levels from molecular gas-phase abundance profiles can constrain the elusive GSD of the dust delivered to the ISM by AGB outflows.

scholarly journals Texture of Polar Firn for Remote Sensing

1987 ◽  
Vol 9 ◽  
pp. 1-4 ◽  
Author(s):  
R.B. Alley
Keyword(s):  
Remote Sensing ◽  
Grain Size ◽  
Size Distribution ◽  
Grain Size Distribution ◽  
Anisotropic Medium ◽  
Preferred Orientation ◽  
Remotely Sensed Data ◽  
Horizontal Orientation ◽  
Prolate Spheroids ◽  
Grain Surface

Knowledge of the texture of polar firn is necessary for interpretation of remotely sensed data. We find that dry polar firn is an irregularly stratified, anisotropic medium. Grains in firn may be approximated as prolate spheroids with average axial ratios as high as 1.2 or greater and with a preferred orientation of long axes clustered around the vertical. Such elongate grains are preferentially bonded near their ends into vertical columns, so that grain bonds show a preferred horizontal orientation. The grain-size distribution is similar in most firn and the normalized distribution is stationary in time, but the distribution is somewhat different in depth hoar. Fluctuations of firn properties are large near any depth, but decrease with increasing depth. With increasing depth, anisotropy of surfaces decreases, bond size relative to grain size decreases slightly, and number of bonds per grain and fraction of total grain surface in bonds increase. Grain size increases linearly with age below 2 to 5 m, but increases more rapidly in shallower firn.

Influence of Composition and Grain Size Distribution on the Properties of Limestone and Dolomite Asphalt Fillers

2012 ◽  
Vol 729 ◽  
pp. 344-349 ◽  
Author(s):  
Róbert Géber ◽  
István Kocserha ◽  
László A. Gömze
Keyword(s):  
Grain Size ◽  
Specific Surface ◽  
Size Distribution ◽  
Surface Area ◽  
Grain Size Distribution ◽  
Research Work ◽  
Road Construction ◽  
Asphalt Pavements ◽  
Coarse Grains ◽  
Mineral Fillers

The aim of the present research work is to examine the influence of mineral composition and grain size distribution on the properties of limestone and dolomite mineral fillers used in Hungarian road construction. Since these properties fundamentally define the features of asphalt pavements, our research goals were assigned accordingly. Different fractions of two mineral fillers (limestone from Alsózsolca and dolomite from Pilisvörösvár) were compared. We have observed deviations in the grain size distribution of some fractions of fillers that were free of contaminations. While limestone consists of a great amount of fines and a relatively small amount of coarse grains, in case of dolomite it is the opposite, that is, small amount of fines and greater amount of coarse grains. The decrease of the grain size of fractions resulted in a slight increase of specific surface area of fillers. We have observed that by the decrease of the grain size of fillers, the hydrophilic coefficient has also decreased. The increasing presence of fines however, resulted in the decrease of the hydrophilic coefficient.

Dynamic evolution of debris flow grain composition

2021 ◽  
Author(s):  
Yong Li
Keyword(s):  
Grain Size ◽  
Debris Flow ◽  
Specific Surface ◽  
Size Distribution ◽  
Surface Area ◽  
Grain Size Distribution ◽  
Specific Surface Area ◽  
Grain Composition ◽  
Negative Power ◽  
Dynamic Rotation

<p>Debris flow is composed of solid grains of different sizes. the characteristics of grain size distribution reflect the movement mode and dynamic conditions of the fluid, and have different effects on the movement of debris flow. Due to the high variability of debris flow materials, the granular interaction is bound to affect the fluid properties. The grain size distribution (GSD) of debris flow satisfies the formula: P(D)=CD<sup>-μ</sup>exp(-D/D<sub>c</sub>), where, GSD parameters μ and D<sub>c</sub> can comprehensively reflect the change of grain composition. with μ reflecting the structure and variation characteristics of fine grains, and D<sub>c</sub> reflecting the range of grain size. Field surveys in various regions indicate that the GSD parameters are distinct in materials of flow, source, and deposition. The GSD parameters of source soil and deposition soil are random and discrete, while the GSD parameters of fluid samples show obvious negative power function form: D<sub>c</sub>= aμ<sup>b</sup> (Figure 1). This shows that the grain composition of debris flow contains some dynamic information. In this paper, we use natural soil materials in a typical debris flow valley to conduct a series dynamically mixing and rotating experiments to simulate the flow evolution, and explore the change of grains under the action of dynamics and the effect of grain adjustment on the mobility of debris flow. The results show that the GSD shows a significant regularity after dynamic rotation. The specific performance is that μ and D<sub>c</sub> change from the initial random discrete state to negative power correlation (Figure 2), and the appearance of this correlation corresponds to the best mobility of debris flow. At the same time, the Malvern laser grain size analyzer was used to analyze the specific surface area of fine grains (<0.20 mm) in the dynamic rotation experiment. The results show that with the increase of dynamic time, the specific surface area increases according to power law, and when the time reaches about 100 minutes, the growth slows down, and the specific surface area changes little. The experimental results are helpful for a deep understanding of the dynamics of debris flow.</p>

scholarly journals Evolution of grain size distribution in galactic discs

2020 ◽  
Vol 636 ◽  
pp. A18 ◽  
Author(s):  
M. Relaño ◽  
U. Lisenfeld ◽  
K.-C. Hou ◽  
I. De Looze ◽  
J. M. Vílchez ◽  
...  
Keyword(s):  
Grain Size ◽  
Size Distribution ◽  
Grain Size Distribution ◽  
Radial Distribution ◽  
Molecular Gas ◽  
Evolutionary Stage ◽  
Dust Grains ◽  
Cosmological Simulations ◽  
Dust Grain ◽  
Dust Evolution

Context. Dust is formed out of stellar material and it is constantly affected by different mechanisms occurring in the interstellar medium. Depending on their size, the behaviour of dust grains vary under these mechanisms and, therefore, the dust grain size distribution evolves as part of the dust evolution itself. Following how the grain size distribution evolves is a difficult computing task that has only recently become the subject of consideration. Smoothed particle hydrodynamic (SPH) simulations of a single galaxy, together with cosmological simulations, are producing the first predictions of the evolution of dust grain size distribution. Aims. We compare, for the first time, the evolution of the dust grain size distribution as predicted by SPH simulations and results from observations. We are able to validate not only the predictions of the evolution of the small-to-large grain mass ratio (DS/DL) within a galaxy, but we also provide observational constraints for recent cosmological simulations that include the grain size distribution in the dust evolution framework. Methods. We selected a sample of three spiral galaxies with different masses: M 101, NGC 628, and M 33. We fitted the dust spectral energy distribution across the disc of each object and derived the abundance of the different grain types included in the dust model. We analysed how the radial distribution of the relative abundance of the different grain size populations changes over the whole disc within each galaxy. The DS/DL ratio as a function of the galactocentric distance and metallicity is directly compared to what has been predicted by the SPH simulations. Results. We find a good agreement between the observed radial distribution of DS/DL and what was obtained from the SPH simulations of a single galaxy. The comparison agrees with the expected evolutionary stage of each galaxy. We show that the central parts of NGC 628 at a high metallicity and with a high molecular gas fraction are mainly affected not only by accretion, but also by the coagulation of dust grains. The centre of M 33, having a lower metallicity and lower molecular gas fraction, presents an increase in the DS/DL ratio, demonstrating that shattering is very effective for creating a large fraction of small grains. Finally, the observational results provided by our galaxies confirm the general relations predicted by the cosmological simulations based on the two-grain size approximation. However, we also present evidence that the simulations could be overestimating the amount of large grains in high massive galaxies.

scholarly journals Texture of Polar Firn for Remote Sensing

1987 ◽  
Vol 9 ◽  
pp. 1-4 ◽  
Author(s):  
R.B. Alley
Keyword(s):  
Remote Sensing ◽  
Grain Size ◽  
Size Distribution ◽  
Grain Size Distribution ◽  
Anisotropic Medium ◽  
Preferred Orientation ◽  
Remotely Sensed Data ◽  
Horizontal Orientation ◽  
Prolate Spheroids ◽  
Grain Surface

Knowledge of the texture of polar firn is necessary for interpretation of remotely sensed data. We find that dry polar firn is an irregularly stratified, anisotropic medium. Grains in firn may be approximated as prolate spheroids with average axial ratios as high as 1.2 or greater and with a preferred orientation of long axes clustered around the vertical. Such elongate grains are preferentially bonded near their ends into vertical columns, so that grain bonds show a preferred horizontal orientation. The grain-size distribution is similar in most firn and the normalized distribution is stationary in time, but the distribution is somewhat different in depth hoar. Fluctuations of firn properties are large near any depth, but decrease with increasing depth. With increasing depth, anisotropy of surfaces decreases, bond size relative to grain size decreases slightly, and number of bonds per grain and fraction of total grain surface in bonds increase. Grain size increases linearly with age below 2 to 5 m, but increases more rapidly in shallower firn.

scholarly journals Texture of Polar Firn for Remote Sensing

1987 ◽  
Vol 9 ◽  
pp. 1-4 ◽  
Author(s):  
R.B. Alley
Keyword(s):  
Remote Sensing ◽  
Grain Size ◽  
Size Distribution ◽  
Grain Size Distribution ◽  
Anisotropic Medium ◽  
Preferred Orientation ◽  
Remotely Sensed Data ◽  
Horizontal Orientation ◽  
Prolate Spheroids ◽  
Grain Surface

Knowledge of the texture of polar firn is necessary for interpretation of remotely sensed data. We find that dry polar firn is an irregularly stratified, anisotropic medium. Grains in firn may be approximated as prolate spheroids with average axial ratios as high as 1.2 or greater and with a preferred orientation of long axes clustered around the vertical. Such elongate grains are preferentially bonded near their ends into vertical columns, so that grain bonds show a preferred horizontal orientation. The grain-size distribution is similar in most firn and the normalized distribution is stationary in time, but the distribution is somewhat different in depth hoar. Fluctuations of firn properties are large near any depth, but decrease with increasing depth. With increasing depth, anisotropy of surfaces decreases, bond size relative to grain size decreases slightly, and number of bonds per grain and fraction of total grain surface in bonds increase. Grain size increases linearly with age below 2 to 5 m, but increases more rapidly in shallower firn.

A Model for the Changing Pore Structure and Dust Grain Size Distribution in a Porous Comet Nucleus

Icarus ◽  
1997 ◽  
Vol 126 (2) ◽  
pp. 342-350 ◽  
Author(s):  
Yossi Shoshani ◽  
Eyal Heifetz ◽  
Dina Prialnik ◽  
Morris Podolak
Keyword(s):  
Grain Size ◽  
Pore Structure ◽  
Size Distribution ◽  
Grain Size Distribution ◽  
Comet Nucleus ◽  
Dust Grain
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