scholarly journals Dust dynamics and vertical settling in gravitoturbulent protoplanetary discs

2020 ◽  
Vol 493 (4) ◽  
pp. 4631-4642 ◽  
Author(s):  
A Riols ◽  
B Roux ◽  
H Latter ◽  
G Lesur
Keyword(s):  
Gravitational Instability ◽  
Scale Height ◽  
Small Scale ◽  
Vertical Diffusion ◽  
Inertial Wave ◽  
Dust Dynamics ◽  
Self Gravity ◽  
Gas Accretion ◽  
Protoplanetary Discs

Abstract Gravitational instability (GI) controls the dynamics of young massive protoplanetary discs. Apart from facilitating gas accretion on to the central protostar, it must also impact on the process of planet formation: directly through fragmentation, and indirectly through the turbulent concentration of small solids. To understand the latter process, it is essential to determine the dust dynamics in gravitoturbulent flow. For that purpose, we conduct a series of 3D shearing box simulations of coupled gas and dust, including the gas’s self-gravity and scanning a range of Stokes numbers, from 10 −3 to ∼0.2. First, we show that the vertical settling of dust in the mid-plane is significantly impeded by gravitoturbulence, with the dust scale height roughly 0.6 times the gas scale height for centimetre grains. This is a result of the strong vertical diffusion issuing from (i) small-scale inertial-wave turbulence feeding off the GI spiral waves and (ii) the larger scale vertical circulations that naturally accompany the spirals. Second, we show that at R  = 50 au concentration events involving submetre particles and yielding order 1 dust-to-gas ratios are rare and last for less than an orbit. Moreover, dust concentration is less efficient in 3D than in 2D simulations. We thus conclude that GI is not especially prone to the turbulent accumulation of dust grains. Finally, the large dust scale height measured in simulations could be, in the future, compared with that of edge-on discs seen by ALMA, thus aiding detection and characterization of GI in real systems.

scholarly journals On the origin of wide-orbit ALMA planets: giant protoplanets disrupted by their cores

2019 ◽  
Vol 489 (4) ◽  
pp. 5187-5201 ◽  
Author(s):  
J Humphries ◽  
S Nayakshin
Keyword(s):  
Gravitational Instability ◽  
Energy Output ◽  
Planetary Satellites ◽  
Multiple Cores ◽  
Dust Dynamics ◽  
Jovian Planets ◽  
Core Accretion ◽  
Collapse Phase ◽  
Partial Destruction ◽  
Protoplanetary Discs

ABSTRACT Recent ALMA observations may indicate a surprising abundance of sub-Jovian planets on very wide orbits in protoplanetary discs that are only a few million years old. These planets are too young and distant to have been formed via the core accretion (CA) scenario, and are much less massive than the gas clumps born in the classical gravitational instability (GI) theory. It was recently suggested that such planets may form by the partial destruction of GI protoplanets: energy output due to the growth of a massive core may unbind all or most of the surrounding pre-collapse protoplanet. Here we present the first 3D global disc simulations that simultaneously resolve grain dynamics in the disc and within the protoplanet. We confirm that massive GI protoplanets may self-destruct at arbitrarily large separations from the host star provided that solid cores of mass ∼10–20 M⊕ are able to grow inside them during their pre-collapse phase. In addition, we find that the heating force recently analysed by Masset & Velasco Romero (2017) perturbs these cores away from the centre of their gaseous protoplanets. This leads to very complicated dust dynamics in the protoplanet centre, potentially resulting in the formation of multiple cores, planetary satellites, and other debris such as planetesimals within the same protoplanet. A unique prediction of this planet formation scenario is the presence of sub-Jovian planets at wide orbits in Class 0/I protoplanetary discs.

Optical and Chemical Characterization of Aerosols Emitted from Coal, Heavy and Light Fuel Oil, and Small-Scale Wood Combustion

2013 ◽  
Vol 48 (1) ◽  
pp. 827-836 ◽  
Author(s):  
Anna K. Frey ◽  
Karri Saarnio ◽  
Heikki Lamberg ◽  
Fanni Mylläri ◽  
Panu Karjalainen ◽  
...  
Keyword(s):  
Chemical Characterization ◽  
Fuel Oil ◽  
Small Scale ◽  
Wood Combustion

scholarly journals Formation of Prestellar Cores via Non-Isothermal Gas Fragmentation

2015 ◽  
Vol 32 ◽  
Author(s):  
S. Anathpindika
Keyword(s):  
Gravitational Instability ◽  
Gas Flows ◽  
Smooth Particle Hydrodynamics ◽  
Three Phase ◽  
Prestellar Cores ◽  
Particle Hydrodynamics ◽  
Unstable Medium ◽  
Stage Process ◽  
Isothermal Gas ◽  
Gas Accretion

AbstractSheet-like clouds are common in turbulent gas and perhaps form via collisions between turbulent gas flows. Having examined the evolution of an isothermal shocked slab in an earlier contribution, in this work we follow the evolution of a sheet-like cloud confined by (thermal) pressure and gas in it is allowed to cool. The extant purpose of this endeavour is to study the early phases of core-formation. The observed evolution of this cloud supports the conjecture that molecular clouds themselves are three-phase media (comprising viz. a stable cold and warm medium, and a third thermally unstable medium), though it appears, clouds may evolve in this manner irrespective of whether they are gravitationally bound. We report, this sheet fragments initially due to the growth of the thermal instability (TI) and some fragments are elongated, filament-like. Subsequently, relatively large fragments become gravitationally unstable and sub-fragment into smaller cores. The formation of cores appears to be a three stage process: first, growth of the TI leads to rapid fragmentation of the slab; second, relatively small fragments acquire mass via gas-accretion and/or merger and third, sufficiently massive fragments become susceptible to the gravitational instability and sub-fragment to form smaller cores. We investigate typical properties of clumps (and smaller cores) resulting from this fragmentation process. Findings of this work support the suggestion that the weak velocity field usually observed in dense clumps and smaller cores is likely seeded by the growth of dynamic instabilities. Simulations were performed using the smooth particle hydrodynamics algorithm.

scholarly journals Characterization of small-scale fisheries in the Camamu-Almada basin, southeast state of Bahia, Brazil

2008 ◽  
Vol 68 (4) ◽  
pp. 711-719 ◽  
Author(s):  
TCM. Souza ◽  
M. Petrere-Jr
Keyword(s):  
Low Income ◽  
Small Scale ◽  
Income Generation ◽  
Target Species ◽  
Market Prices ◽  
Marine Fishery ◽  
Small Scale Fisheries ◽  
Main Factor ◽  
Stock Abundance

In the Camamu-Almada basin, marine fishery is exclusively small-scale, with several structural deficiencies such as boats with low or absent navigational technology, lack of credit and low income. Local fishers complain that shrimp and lobster trawling fishing is the main factor responsible for low stock abundance, but they still persist in these activities as these two species command the highest market prices. So they feel that the target species are already over-fished. We suggest that proper management action, alternative ways of income generation and the payment of job insurance would help to mitigate the problem.

scholarly journals Molecular characterization of Listeria monocytogenes isolates from a small-scale meat processor in Montenegro, 2011–2014

2019 ◽  
Vol 79 ◽  
pp. 116-122 ◽  
Author(s):  
Ivana Zuber ◽  
Brankica Lakicevic ◽  
Ariane Pietzka ◽  
Dubravka Milanov ◽  
Vesna Djordjevic ◽  
...  
Keyword(s):  
Listeria Monocytogenes ◽  
Molecular Characterization ◽  
Small Scale

Experimental Parameters Used to Study Pesticide Degradation in Soil

1996 ◽  
Vol 10 (1) ◽  
pp. 169-173 ◽  
Author(s):  
Michael R. Blumhorst
Keyword(s):  
Small Scale ◽  
Test Substance ◽  
Pesticide Degradation ◽  
Soil System ◽  
Experimental Parameters ◽  
Effective Cost ◽  
Cost Efficient ◽  
Efficient Mechanisms ◽  
Degradation In Soil

Characterization of pesticide degradation in soil is an important component in determining the environmental impact of agriculturally-applied pesticides. Several techniques currently are being used to generate these data, but small-scale laboratory studies remain one of the most effective, cost-efficient mechanisms of evaluating pesticide behavior in soil. With small-scale studies, many different environmental factors can be incorporated into the experimental design, and with the use of14C-labeled material, these studies (often referred to as soil degradation or soil metabolism studies) provide information on test substance persistence, degradation, volatilization, and mineralization. Care must be exercised, however, in selecting the experimental parameters to be used because of the potential adverse or artificial effects on the soil system.

Tribological Characterization of Machining at Very Small Contact Areas

2009 ◽  
Vol 131 (4) ◽  
Author(s):  
Michael R. Lovell ◽  
P. Cohen ◽  
Pradeep L. Menezes ◽  
R. Shankar
Keyword(s):  
High Speed ◽  
Friction Mechanisms ◽  
High Speed Steel ◽  
Small Scale ◽  
Machining Processes ◽  
Macroscopic Theory ◽  
Contact Areas ◽  
Tribological Characterization ◽  
Physical Phenomena

When machining miniaturized components, the contact conditions between the tool and the workpiece exhibit very small contact areas that are on the order of 10−5 mm2. Under these conditions, extremely high contact stresses are generated, and it is not clear whether macroscopic theories for the chip formation, cutting forces, and friction mechanisms are applicable. For this reason, the present investigation has focused on creating a basic understanding of the frictional behavior in very small scale machining processes so that evaluations of standard macroscale models could be performed. Specialized machining experiments were conducted on 70/30 brass materials using high-speed steel tools over a range of speeds, feeds, depths of cut, and tool rake angles. At each operating condition studied, the friction coefficient and the shear factor τk were obtained. Based on the experimental results, it was determined that the standard macroscopic theory for analyzing detailed friction mechanisms was insufficient in very small scale machining processes. An approach that utilized the shear factor, in contrast, was found to be better for decoupling the physical phenomena involved. Utilizing the shear factor as an analysis parameter, the parameters that significantly influence the friction in microscale machining processes were ascertained and discussed.

scholarly journals Gas and multispecies dust dynamics in viscous protoplanetary discs: the importance of the dust back-reaction

2018 ◽  
Vol 479 (3) ◽  
pp. 4187-4206 ◽  
Author(s):  
Giovanni Dipierro ◽  
Guillaume Laibe ◽  
Richard Alexander ◽  
Mark Hutchison
Keyword(s):  
Back Reaction ◽  
Dust Dynamics ◽  
Protoplanetary Discs

scholarly journals Irradiance Variability Quantification and Small-Scale Averaging in Space and Time: A Short Review

Atmosphere ◽  
2018 ◽  
Vol 9 (7) ◽  
pp. 264 ◽  
Author(s):  
Gerald Lohmann
Keyword(s):  
Short Review ◽  
Power Grids ◽  
Small Scale ◽  
Stable Operation ◽  
Data Sets ◽  
Spatial Smoothing ◽  
Spatial And Temporal Scales ◽  
Output Variability ◽  
Temporal Averaging

The ongoing world-wide increase of installed photovoltaic (PV) power attracts notice to weather-induced PV power output variability. Understanding the underlying spatiotemporal volatility of solar radiation is essential to the successful outlining and stable operation of future power grids. This paper concisely reviews recent advances in the characterization of irradiance variability, with an emphasis on small spatial and temporal scales (respectively less than about 10 km and 1 min), for which comprehensive data sets have recently become available. Special attention is given to studies dealing with the quantification of variability using such unique data, the analysis and modeling of spatial smoothing, and the evaluation of temporal averaging.

scholarly journals Topophilia, Placemaking, and Boundary Work

2022 ◽  
Vol 6 (GROUP) ◽  
pp. 1-33
Author(s):  
Janghee Cho ◽  
Samuel Beck ◽  
Stephen Voida
Keyword(s):  
Large Scale ◽  
Methodological Approach ◽  
Work Practice ◽  
Small Scale ◽  
Work From Home ◽  
Humanistic Geography ◽  
Working From Home ◽  
Long Term Impact

The COVID-19 pandemic fundamentally changed the nature of work by shifting most in-person work to a predominantly remote modality as a way to limit the spread of the coronavirus. In the process, the shift to working-from-home rapidly forced the large-scale adoption of groupware technologies. Although prior empirical research examined the experience of working-from-home within small-scale groups and for targeted kinds of work, the pandemic provides HCI and CSCW researchers with an unprecedented opportunity to understand the psycho-social impacts of a universally mandated work-from-home experience rather than an autonomously chosen one. Drawing on boundary theory and a methodological approach grounded in humanistic geography, we conducted a qualitative analysis of Reddit data drawn from two work-from-home-related subreddits between March 2020 and January 2021. In this paper, we present a characterization of the challenges and solutions discussed within these online communities for adapting work to a hybrid or fully remote modality, managing reconfigured work-life boundaries, and reconstructing the home's sense of place to serve multiple, sometimes conflicting roles. We discuss how these findings suggest an emergent interplay among adapted work practice, reimagined physical (and virtual) spaces, and the establishment and continual re-negotiation of boundaries as a means for anticipating the long-term impact of COVID on future conceptualizations of productivity and work.

Sign in / Sign up

Export Citation Format

Share Document