scholarly journals The Supershell-Molecular Cloud Connection in the Milky Way and Beyond

2012 ◽  
Vol 8 (S292) ◽  
pp. 83-86
Author(s):  
J. R. Dawson ◽  
N. M. McClure-Griffiths ◽  
Y. Fukui ◽  
J. Dickey ◽  
T. Wong ◽  
...  
Keyword(s):  
Molecular Cloud ◽  
Molecular Clouds ◽  
Large Scale ◽  
Milky Way ◽  
Observational Evidence ◽  
Cloud Formation ◽  
Stellar Feedback ◽  
The Relationship ◽  
Global Contribution

AbstractThe role of large-scale stellar feedback in the formation of molecular clouds has been investigated observationally by examining the relationship between Hi and 12CO(J = 1−0) in supershells. Detailed parsec-resolution case studies of two Milky Way supershells demonstrate an enhanced level of molecularisation over both objects, and hence provide the first quantitative observational evidence of increased molecular cloud production in volumes of space affected by supershell activity. Recent results on supergiant shells in the LMC suggest that while they do indeed help to organise the ISM into over-dense structures, their global contribution to molecular cloud formation is of the order of only ∼ 10%.

scholarly journals Deterministic Self-Propagating Star Formation

1989 ◽  
Vol 120 ◽  
pp. 518-523
Author(s):  
Jan Palouš
Keyword(s):  
Star Formation ◽  
Simple Model ◽  
Molecular Cloud ◽  
Molecular Clouds ◽  
Large Scale ◽  
Galactic Evolution ◽  
Cloud Formation ◽  
Rotating Disks ◽  
Atomic Gas ◽  
High Column

AbstractThe evolution of large scale expanding structures in differentially rotating disks is studied. High column densities in some places may eventually lead to molecular cloud formation and initiate also star-formation. After some time, multi-structured arms evolve, where regions of intensive star-formation are separated from each other by regions of atomic gas or molecular clouds. This is due to the deterministic nature and to the coherence of this process. A simple model of galactic evolution is introduced and the different behaviour of Sa, Sb, and Sc galaxies is shown.

scholarly journals The role of galactic dynamics in shaping the physical properties of giant molecular clouds in Milky Way-like galaxies

2020 ◽  
Vol 498 (1) ◽  
pp. 385-429 ◽  
Author(s):  
Sarah M R Jeffreson ◽  
J M Diederik Kruijssen ◽  
Benjamin W Keller ◽  
Mélanie Chevance ◽  
Simon C O Glover
Keyword(s):  
Molecular Clouds ◽  
Large Scale ◽  
Milky Way ◽  
Gravitational Instability ◽  
Formation Rate ◽  
Tangential Velocity ◽  
Galactic Rotation ◽  
H Ii Regions ◽  
Giant Molecular Clouds

ABSTRACT We examine the role of the large-scale galactic-dynamical environment in setting the properties of giant molecular clouds in Milky Way-like galaxies. We perform three high-resolution simulations of Milky Way-like discs with the moving-mesh hydrodynamics code arepo, yielding a statistical sample of ${\sim}80\, 000$ giant molecular clouds and ${\sim}55\, 000$ H i clouds. We account for the self-gravity of the gas, momentum, and thermal energy injection from supernovae and H ii regions, mass injection from stellar winds, and the non-equilibrium chemistry of hydrogen, carbon, and oxygen. By varying the external gravitational potential, we probe galactic-dynamical environments spanning an order of magnitude in the orbital angular velocity, gravitational stability, mid-plane pressure, and the gradient of the galactic rotation curve. The simulated molecular clouds are highly overdense (∼100×) and overpressured (∼25×) relative to the ambient interstellar medium. Their gravoturbulent and star-forming properties are decoupled from the dynamics of the galactic mid-plane, so that the kpc-scale star formation rate surface density is related only to the number of molecular clouds per unit area of the galactic mid-plane. Despite this, the clouds display clear, statistically significant correlations of their rotational properties with the rates of galactic shearing and gravitational free-fall. We find that galactic rotation and gravitational instability can influence their elongation, angular momenta, and tangential velocity dispersions. The lower pressures and densities of the H i clouds allow for a greater range of significant dynamical correlations, mirroring the rotational properties of the molecular clouds, while also displaying a coupling of their gravitational and turbulent properties to the galactic-dynamical environment.

Pots on mats: mat-impressed salt-extraction pottery at Chalcolithic Provadia-Solnitsata, Bulgaria

Antiquity ◽  
2021 ◽  
pp. 1-16
Author(s):  
Mila Andonova ◽  
Vassil Nikolov
Keyword(s):  
Material Culture ◽  
Large Scale ◽  
Raw Materials ◽  
Salt Production ◽  
Production And Consumption ◽  
Late Chalcolithic ◽  
South Eastern Europe ◽  
Materials Used ◽  
The Relationship

Evidence for both basket weaving and salt production is often elusive in the prehistoric archaeological record. An assemblage of Middle–Late Chalcolithic pottery from Provadia-Solnitsata in Bulgaria provides insight into these two different technologies and the relationship between them. The authors analyse sherds from vessels used in large-scale salt production, the bases of which bear the impression of woven mats. This analysis reveals the possible raw materials used in mat weaving at Provadia-Solnitsata and allows interpretation of the role of these mats in salt production at the site. The results illustrate how it is possible to see the ‘invisible’ material culture of prehistoric south-eastern Europe and its importance for production and consumption.

scholarly journals The atomic hydrogen/molecular cloud association: an unavoidable relationship

1991 ◽  
Vol 147 ◽  
pp. 37-40
Author(s):  
G. Joncas
Keyword(s):  
Atomic Hydrogen ◽  
Molecular Clouds ◽  
Large Scale ◽  
Young Stars ◽  
Physical Processes ◽  
Star Forming ◽  
Dark Clouds ◽  
Star Forming Regions ◽  
The Impact

The presence of HI in the interstellar medium is ubiquitous. HI is the principal actor in the majority of the physical processes at work in our Galaxy. Restricting ourselves to the topics of this symposium, atomic hydrogen is involved with the formation of molecular clouds and is one of the byproducts of their destruction by young stars. HI has different roles during a molecular cloud's life. I will discuss here a case of coexisting HI and H2 at large scale and the origin of HI in star forming regions. For completeness' sake, it should be mentionned that there are at least three other aspects of HI involvement: HI envelopes around molecular clouds, the impact of SNRs (see work on IC 443), and the role of HI in quiescent dark clouds (see van der Werf's work).

scholarly journals COVID-19 and the importance of space in entrepreneurship research and policy

2020 ◽  
Vol 38 (8) ◽  
pp. 697-710 ◽  
Author(s):  
Steffen Korsgaard ◽  
Richard A Hunt ◽  
David M Townsend ◽  
Mads Bruun Ingstrup
Keyword(s):  
Economic System ◽  
Large Scale ◽  
Local Economies ◽  
Spatial Perspective ◽  
Entrepreneurship Research ◽  
Digital Platform ◽  
The Face ◽  
The Relationship ◽  
Research And Policy

Given the COVID-19 crisis, the importance of space in the global economic system has emerged as critical in a hitherto unprecedented way. Even as large-scale, globally operating digital platform enterprises find new ways to thrive in the midst of a crisis, small and medium-sized enterprises (SMEs) nestled in local economies have proven to be fragile to shocks, causing countless local economies to unravel in the face of severe challenges to survival. Here, we discuss the role of entrepreneurship in re-building local economies that are more resilient. Specifically, we take a spatial perspective and highlight how the COVID-19 crisis has uncovered problems in the current tendency for thin contextualisation and promotion of globalisation. Based on this critique, we outline new perspectives for thinking about the relationship between entrepreneurship, resilience and local economies. Here, a particular emphasis is given to resilience building through deeply contextualised policies and research, localised flows of products and labour, and the diversification of local economies.

scholarly journals The atomic hydrogen/molecular cloud association: an unavoidable relationship

1991 ◽  
Vol 147 ◽  
pp. 37-40
Author(s):  
G. Joncas
Keyword(s):  
Atomic Hydrogen ◽  
Molecular Clouds ◽  
Large Scale ◽  
Young Stars ◽  
Physical Processes ◽  
Star Forming ◽  
Dark Clouds ◽  
Star Forming Regions ◽  
The Impact

The presence of HI in the interstellar medium is ubiquitous. HI is the principal actor in the majority of the physical processes at work in our Galaxy. Restricting ourselves to the topics of this symposium, atomic hydrogen is involved with the formation of molecular clouds and is one of the byproducts of their destruction by young stars. HI has different roles during a molecular cloud's life. I will discuss here a case of coexisting HI and H2 at large scale and the origin of HI in star forming regions. For completeness' sake, it should be mentionned that there are at least three other aspects of HI involvement: HI envelopes around molecular clouds, the impact of SNRs (see work on IC 443), and the role of HI in quiescent dark clouds (see van der Werf's work).

scholarly journals A CS survey of massive stars embedded in molecular clouds

1991 ◽  
Vol 147 ◽  
pp. 25-28
Author(s):  
L. Bronfman ◽  
J. May ◽  
L. A. Nyman ◽  
P. Thaddeus
Keyword(s):  
Radial Distribution ◽  
Molecular Cloud ◽  
Molecular Clouds ◽  
Milky Way ◽  
Massive Stars ◽  
Molecular Line ◽  
Stellar Objects ◽  
Thin Line

the CS J=2 →1 molecular line at 98 GHz, a normally optically thin line requiring high densities to be excited, has been detected with SEST (Swedish ESO Submillimeter Telescope) toward 294 IRAS pointlike sources having the characteristic FIR colors of embedded stellar objects and apparently associated with the largest molecular cloud complexes in the southern Milky Way. We present here their Galactocentric radial distribution and a correlation between their FIR and CS luminosities.

scholarly journals Molecular cloud formation by compression of magnetized turbulent gas subjected to radiative cooling

2020 ◽  
Vol 493 (3) ◽  
pp. 3098-3113 ◽  
Author(s):  
Ankush Mandal ◽  
Christoph Federrath ◽  
Bastian Körtgen
Keyword(s):  
Molecular Cloud ◽  
Large Scale ◽  
Turnover Rate ◽  
Radiative Heating ◽  
Cloud Formation ◽  
Neutral Medium ◽  
Contraction Rate ◽  
Mhd Turbulence ◽  
Cloud Properties ◽  
Hydrodynamical Simulations

ABSTRACT Complex turbulent motions of magnetized gas are ubiquitous in the interstellar medium (ISM). The source of this turbulence, however, is still poorly understood. Previous work suggests that compression caused by supernova shockwaves, gravity, or cloud collisions, may drive the turbulence to some extent. In this work, we present three-dimensional (3D) magnetohydrodynamic (MHD) simulations of contraction in turbulent, magnetized clouds from the warm neutral medium of the ISM to the formation of cold dense molecular clouds, including radiative heating and cooling. We study different contraction rates and find that observed molecular cloud properties, such as the temperature, density, Mach number, and magnetic field strength, and their respective scaling relations, are best reproduced when the contraction rate equals the turbulent turnover rate. In contrast, if the contraction rate is significantly larger (smaller) than the turnover rate, the compression drives too much (too little) turbulence, producing unrealistic cloud properties. We find that the density probability distribution function evolves from a double lognormal representing the two-phase ISM, to a skewed, single lognormal in the dense, cold phase. For purely hydrodynamical simulations, we find that the effective driving parameter of contracting cloud turbulence is natural to mildly compressive (b ∼ 0.4–0.5), while for MHD turbulence, we find b ∼ 0.3–0.4, i.e. solenoidal to naturally mixed. Overall, the physical properties of the simulated clouds that contract at a rate equal to the turbulent turnover rate, indicate that large-scale contraction may explain the origin and evolution of turbulence in the ISM.

scholarly journals The role of anatomical connection strength for interareal communication in macaque cortex

2020 ◽  
Author(s):  
Julien Vezoli ◽  
Martin Vinck ◽  
Conrado A. Bosman ◽  
Andre M. Bastos ◽  
Christopher M Lewis ◽  
...  
Keyword(s):  
Large Scale ◽  
Functional Organization ◽  
Brain Regions ◽  
Connection Strength ◽  
Non Invasive ◽  
Large Scale Networks ◽  
Invasive Techniques ◽  
The Relationship ◽  
Anatomical Connection

What is the relationship between anatomical connection strength and rhythmic synchronization? Simultaneous recordings of 15 cortical areas in two macaque monkeys show that interareal networks are functionally organized in spatially distinct modules with specific synchronization frequencies, i.e. frequency-specific functional connectomes. We relate the functional interactions between 91 area pairs to their anatomical connection strength defined in a separate cohort of twenty six subjects. This reveals that anatomical connection strength predicts rhythmic synchronization and vice-versa, in a manner that is specific for frequency bands and for the feedforward versus feedback direction, even if interareal distances are taken into account. These results further our understanding of structure-function relationships in large-scale networks covering different modality-specific brain regions and provide strong constraints on mechanistic models of brain function. Because this approach can be adapted to non-invasive techniques, it promises to open new perspectives on the functional organization of the human brain.

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