Mineral dust is an important component of the climate system, interacting with radiation, clouds, and biogeochemical systems and impacting atmospheric circulation, air quality, aviation, and solar ...energy generation. These impacts are sensitive to dust particle size distribution (PSD), yet models struggle or even fail to represent coarse (diameter (d) 2.5 µm) and giant (d20 µm) dust particles and the evolution of the PSD with transport. Here we examine three state-of-the-art airborne observational datasets, all of which measured the full size range of dust (d=0.1 to 100 µm) at different stages during transport with consistent instrumentation. We quantify the presence and evolution of coarse and giant particles and their contribution to optical properties using airborne observations over the Sahara (from the Fennec field campaign) and in the Saharan Air Layer (SAL) over the tropical eastern Atlantic (from the AER-D field campaign).
The light scattered from dust grains in debris disks is typically modeled as compact spheres using the Lorenz-Mie theory or as porous spheres by incorporating an effective medium theory. In this work ...we examine the effect of incorporating a more realistic particle morphology on estimated radiation-pressure blowout sizes. To calculate the scattering and absorption cross-sections of irregularly shaped dust grains, we use the discrete dipole approximation. These cross-sections are necessary to calculate the β-ratio, which determines whether dust grains can remain gravitationally bound to their star. We calculate blowout sizes for a range of stellar spectral types corresponding with stars known to host debris disks. As with compact spheres, more luminous stars blow out larger irregularly shaped dust grains. We also find that dust grain composition influences blowout size such that absorptive grains are more readily removed from the disk. Moreover, the difference between blowout sizes calculated assuming spherical particles versus particle morphologies more representative of real dust particles is compositionally dependent as well, with blowout size estimates diverging further for transparent grains. We find that the blowout sizes calculated have a strong dependence on the particle model used, with differences in the blowout size calculated being as large as an order of magnitude for particles of similar porosities.
We present initial observations of the interstellar body 2I/(2019 Q4) Borisov taken to determine its nature prior to the perihelion in 2019 December. Images from the Nordic Optical Telescope show a ...prominent, morphologically stable dust coma and tail. The dust cross-section within 15,000 km of the nucleus averages 130 km2 (assuming geometric albedo 0.1) and increases by about 1% per day. If sustained, this rate indicates that the comet has been active for ∼100 days prior to the observations. Cometary activity thus started in 2019 June, at which time C/Borisov was at ∼4.5 au from the Sun, a typical distance for the onset of water ice sublimation in comets. The dust optical colors, B − V = 0.80 0.05, V − R = 0.47 0.03 and R− I = 0.49 0.05, are identical to those of a sample of (solar system) long-period comets. The colors are similar to those of 1I/(2017 U1) 'Oumuamua, indicating a lack of the ultrared matter that is common in the Kuiper Belt, on both interstellar objects. The effective size of the dust particles is estimated as = 100 m, based on the length of the dust tail and the 100 day lifetime. With this size, the ejected dust mass is of order 1.3 × 107 kg and the current dust mass loss rate ∼2 kg s−1. We set an upper limit to the nucleus radius using photometry at rn ≤3.8 km (again for albedo 0.1) and we use a statistical argument to show that the nucleus must be much smaller, likely a few hundred meters in radius.
Here, the nonlinear convective transport of non-Newtonian fluids embedded with dust particles over a stretched surface is investigated. The silent features of non-Newtonian fluid are considered by ...Casson and Carreau fluid models. The heat transfer mechanism involves the influences of a magnetic dipole, nonlinear radiative heat and non-uniform heat source/sink. The convective condition is also retained at the boundary. The non-linear partial differential equations that model the transport phenomenon was transformed, non-dimensionalized and parameterized. The subsequent boundary value problems were computed numerically for distinct pertinent parameters using Runge–Kutta based shooting techniques. The present results are validated with the existing literature by direct comparison. The heat transfer rate in Casson/Carreau fluid phase is significantly higher than that of dust phase.
•Casson parameter β has opposite effects on velocity and temperature profiles.•The nonlinear convection parameter increases the momentum boundary layer thickness.•The dimensionless temperature increases with rise in thermal radiation.•The skin friction coefficient and the local Nusselt number increases by increasing values of λ.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Mg alloy waste dust can react with water to produce hydrogen in the production of Mg alloy products, which has the possibility to lead to fires or explosions. Firstly, from the perspective of safety ...management, this paper systematically studies the impact of the difference of hydrogen evolution amount of magnesium based alloy waste dust particles(Mg–Al/Mg–Zn) on the risk of wet dust collector under different environmental conditions, and a two-stage hydrogen evolution model was constructed. Secondly, from a technical point of view, a method of using environmentally-friendly, cost-effective sodium phosphate to inhibit the hydrogen evolution reaction of Mg alloys is also proposed. The morphologies of Mg alloy dust particles before and after reaction were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and chemical dynamics modeling before the related reaction mechanisms were identified. The research outcome of the present study could provide effective technical guidance for preventing hydrogen explosion accidents at Mg alloy fabrication facilities.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
6.
A Highly Settled Disk around Oph163131 Villenave, M.; Stapelfeldt, K. R.; Duchêne, G. ...
Astrophysical journal/The Astrophysical journal,
05/2022, Volume:
930, Issue:
1
Journal Article
Peer reviewed
Open access
Abstract
High dust density in the midplane of protoplanetary disks is favorable for efficient grain growth and can allow fast formation of planetesimals and planets, before disks dissipate. Vertical ...settling and dust trapping in pressure maxima are two mechanisms allowing dust to concentrate in geometrically thin and high-density regions. In this work, we aim to study these mechanisms in the highly inclined protoplanetary disk SSTC2D J163131.2-242627 (Oph 163131,
i
∼ 84°). We present new high-angular-resolution continuum and
12
CO ALMA observations of Oph 163131. The gas emission appears significantly more extended in the vertical and radial direction compared to the dust emission, consistent with vertical settling and possibly radial drift. In addition, the new continuum observations reveal two clear rings. The outer ring, located at ∼100 au, is well-resolved in the observations, allowing us to put stringent constraints on the vertical extent of millimeter dust particles. We model the disk using radiative transfer and find that the scale height of millimeter-sized grains is 0.5 au or less at 100 au from the central star. This value is about one order of magnitude smaller than the scale height of smaller micron-sized dust grains constrained by previous modeling, which implies that efficient settling of the large grains is occurring in the disk. When adopting a parametric dust settling prescription, we find that the observations are consistent with a turbulent viscosity coefficient of about
α
≲ 10
−5
at 100 au. Finally, we find that the thin dust scale height measured in Oph 163131 is favorable for planetary growth by pebble accretion: a 10
M
E
planet may grow within less than 10 Myr, even in orbits exceeding 50 au.
Understanding planet formation requires one to discern how dust grows in protoplanetary disks. An important parameter to measure in disks is the maximum dust grain size present. This is usually ...estimated through measurements of the dust opacity at different millimeter wavelengths assuming optically thin emission and dust opacity dominated by absorption. However, Atacama Large Millimeter/submillimeter Array (ALMA) observations have shown that these assumptions might not be correct in the case of protoplanetary disks, leading to overestimation of particle sizes and to underestimation of the disk's mass. Here, we present an analysis of high-quality ALMA and Very Large Array images of the HL Tau protoplanetary disk, covering a wide range of wavelengths, from 0.8 mm to 1 cm, and with a physical resolution of ∼7.35 au. We describe a procedure to analyze a set of millimeter images without any assumption about the optical depth of the emission, and including the effects of absorption and scattering in the dust opacity. This procedure allows us to obtain the dust temperature, the dust surface density, and the maximum particle size at each radius. In the HL Tau disk, we found that particles have already grown to a few millimeters in size. We detect differences in the dust properties between dark and bright rings, with dark rings containing low dust density and small dust particles. Different features in the HL Tau disk seem to have different origins. Planet-disk interactions can explain substructure in the external half of the disk, but the internal rings seem to be associated with the presence of snow lines of several molecules.
The concept of a hybrid nanofluid has piqued the interest of numerous researchers due to its potential for increased thermal properties, which results in high transfer rates. Hybrid nanofluids are ...used in heat transport systems such as electronic cooling, and applications in biomedical and pharmaceutical relief. Thus, the present paper inspects the impact of Lorentz forces on the Casson fluid flow of water-based Fe
3
O
4
-MWCNT hybrid nanofluid induced by dust particles from a stretching sheet. The leading PDEs are changed into ODEs by employing similarity variables and then achieving an exact solution for these transformed ODEs. The impacts of distinct physical constraints including fluid interaction particle parameter, Casson parameter, and magnetic parameter on the dust velocity and fluid velocity for normal nanofluid (Fe
3
O
4
/H
2
O) and hybrid nanofluid (Fe
3
O
4
-MWCNT/ H
2
O) are addressed in detail. The present analytic solution shows a strong correlation with earlier published numerical studies in limited cases.
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•The basic principle of the GBF and its filtration mechanism are reviewed.•The recent researches about filtration performance of GBF are introduced.•The development of performance optimization method ...of the GBF are presented.•The microscale mechanism of agglomeration and growth of particles are introduced.
The dust particles contained in the industrial flue gas are discharged from many industrial factories, which have seriously polluted the air and endangered the health of not only human beings but also the animals living on the earth, so they are gaining much attention all over the world. In order to provide possible solutions to the above problems, many filtration technologies have been proposed and developed. As a promising filtration method, the granular bed filter (GBF) based filtration technology has been widely used in the filtration of high temperature flue gas with complex components in recent years owing to its advantages of high efficiency, low cost, simplicity, and resistance to high temperature and high pressure. Inspired by the development of numerical simulation method and experimental technology, the performance of GBF has been optimized and improved, much deeper insight of the formation and growth of dust particles has been obtained. This review focus on the basic principle of the GBF and its performance investigated by numerical and experimental methods. The reviews and outlooks of investigations on the influence factors of GBF filtration performance and the development of performance optimization method of the GBF were also presented. In addition, the microscale mechanism of the agglomeration and growth of dust particles contained in the industrial flue gas during the filtration in the GBF by means of molecular dynamics simulation were introduced, the numerical and experimental method of dust particles filtration in GBF were also discussed. Finally, available recommendations for future research of GBF are proposed, which is expected to be helpful for actual industrial engineering applications.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The Sample Analysis at Mars (SAM) instrument on board the Mars Science Laboratory Curiosity rover is designed to conduct inorganic and organic chemical analyses of the atmosphere and the surface ...regolith and rocks to help evaluate the past and present habitability potential of Mars at Gale Crater. Central to this task is the development of an inventory of any organic molecules present to elucidate processes associated with their origin, diagenesis, concentration, and long‐term preservation. This will guide the future search for biosignatures. Here we report the definitive identification of chlorobenzene (150–300 parts per billion by weight (ppbw)) and C2 to C4 dichloroalkanes (up to 70 ppbw) with the SAM gas chromatograph mass spectrometer (GCMS) and detection of chlorobenzene in the direct evolved gas analysis (EGA) mode, in multiple portions of the fines from the Cumberland drill hole in the Sheepbed mudstone at Yellowknife Bay. When combined with GCMS and EGA data from multiple scooped and drilled samples, blank runs, and supporting laboratory analog studies, the elevated levels of chlorobenzene and the dichloroalkanes cannot be solely explained by instrument background sources known to be present in SAM. We conclude that these chlorinated hydrocarbons are the reaction products of Martian chlorine and organic carbon derived from Martian sources (e.g., igneous, hydrothermal, atmospheric, or biological) or exogenous sources such as meteorites, comets, or interplanetary dust particles.
Key Points
First in situ evidence of nonterrestrial organics in Martian surface sediments
Chlorinated hydrocarbons identified in the Sheepbed mudstone by SAM
Organics preserved in sample exposed to ionizing radiation and oxidative condition
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