Critical Surface Density of the Superfluid Component inHe4Films

ABSTRACT In this work, we investigate the interplay between gravity and turbulence at different spatial scales and in different density regimes. We analyse a sample of 70-μm quiet clumps that are divided into three surface density bins, and we compare the dynamics of each group with the dynamics of their respective filaments. The densest clumps form within the densest filaments, on average, and they have the highest value of the velocity dispersion. The kinetic energy is transferred from the filaments down to the clumps most likely through a turbulent cascade, but we identify a critical value of the surface density, Σ ≃ 0.1 g cm−2, above which the dynamics change from being mostly turbulent-driven to mostly gravity-driven. The scenario we obtain from our data is a continuous interplay between turbulence and gravity, where the former creates structures at all scales and the latter takes the lead when the critical surface density threshold is reached. In the densest filaments, this transition can occur at the parsec, or even larger scales, leading to a global collapse of the whole region and most likely to the formation of the massive objects.

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EXPERIMENTAL STUDIES OF THE DEPENDENCE OF THE CRITICAL SURFACE DENSITY OF HEAT FLUX FROM WIND INFLUENCE

Scientific bulletin Сivil protection and fire safety ◽

10.33269/nvcz.2020.1.107-115 ◽

2020 ◽

Vol 1 (1) ◽

pp. 107-115

Author(s):

А Borysova ◽

V Nignyk ◽

D Sereda

Keyword(s):

Experimental Data ◽

Heat Flux ◽

Surface Heat Flux ◽

Surface Density ◽

Heat Flux Density ◽

Experimental Studies ◽

Surface Heat ◽

Critical Surface ◽

Wind Influence ◽

The Individual

The article presents the results of an experimental study to determine the dependence of the critical surface density of heat flux from wind influence. The convergence of the obtained experimental data in each of the individual experiments was investigated. The dependence of the critical surface heat flux density on wind influence is established and the regression is defined, which describes such dependence with the corresponding coefficients.

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Cosmic rays across the star-forming galaxy sequence – I. Cosmic ray pressures and calorimetry

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab148 ◽

2021 ◽

Vol 502 (1) ◽

pp. 1312-1333

Author(s):

Roland M Crocker ◽

Mark R Krumholz ◽

Todd A Thompson

Keyword(s):

Star Formation ◽

Cosmic Rays ◽

Surface Density ◽

Large Scale ◽

Gamma Ray ◽

Formation Rate ◽

Cosmic Ray ◽

Gas Content ◽

Critical Surface ◽

Pressure Balance

ABSTRACT In the Milky Way (MW), cosmic rays (CRs) are dynamically important in the interstellar medium (ISM), contribute to hydrostatic balance, and may help regulate star formation. However, we know far less about the importance of CRs in galaxies whose gas content or star formation rate (SFR) differ significantly from those of the MW. Here, we construct self-consistent models for hadronic CR transport, losses, and contribution to pressure balance as a function of galaxy properties, covering a broad range of parameters from dwarfs to extreme starbursts. While the CR energy density increases from ∼1 eV cm−3 to ∼1 keV cm−3 over the range from sub-MW dwarfs to bright starbursts, strong hadronic losses render CRs increasingly unimportant dynamically as the SFR surface density increases. In MW-like systems, CR pressure is typically comparable to turbulent gas and magnetic pressure at the galactic mid-plane, but the ratio of CR to gas pressure drops to ∼10−3 in dense starbursts. Galaxies also become increasingly CR calorimetric and gamma-ray bright in this limit. The degree of calorimetry at fixed galaxy properties is sensitive to the assumed model for CR transport, and in particular to the time CRs spend interacting with neutral ISM, where they undergo strong streaming losses. We also find that in some regimes of parameter space hydrostatic equilibrium discs cannot exist, and in Paper II of this series we use this result to derive a critical surface in the plane of star formation surface density and gas surface density beyond which CRs may drive large-scale galactic winds.

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METHOD OF EXPERIMENTAL RESEARCH OF THE DEPENDENCE OF THE CRITICAL SURFACE DENSITY OF THE HEAT FLOW FROM THE WIND INFLUENCE

Municipal economy of cities ◽

10.33042/2522-1809-2020-3-156-200-203 ◽

2020 ◽

Vol 3 (156) ◽

pp. 200-203

Author(s):

A. Borysova ◽

V. Nizhnyk

Keyword(s):

Heat Flux ◽

Flux Density ◽

Experimental Research ◽

Surface Heat Flux ◽

Surface Density ◽

Heat Flux Density ◽

Experimental Studies ◽

Surface Heat ◽

Critical Surface ◽

Wind Influence

According to the results of the analysis of methods for determining the critical value of the surface heat flux density for substances and materials, it is established that there is no single approach to determining the critical surface heat flux density for substances and materials today. The development of the method of experimental research of the dependence of the critical surface density of the heat flow from the wind influence as a basis for substantiation of the regularity of change of density of a heat stream from wind influence is an actual scientific task. The article analyzes the current state of the study of the critical surface heat flux density. A method has been developed and experimental studies of the values of the surface heat flux density from wind exposure for substances and materials have been carried out. At the time of experimental research, the regularities of the change in the heat flux density depending on the influence of the amount of airflow introduced into the study space were determined. The purpose of the study is to identify the pattern of changes in the heat flux density of substances and materials depending on the influence of the amount of airflow introduced into the study space. To achieve this goal it is necessary to justify the type and quantity of required test and measuring equipment, as well as the number, shape, and design of sample fragments, justify the methodology of experimental studies of samples under the influence of airflow of different speeds, justify the range of wind speed. The article briefly presents the procedure for conducting experimental research. The obtained data will be used for further research of the flammability of substances and materials. Keywords: critical surface heat flux density, heat flux, heat transfer, radiation heat transfer

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Motions of neutral hydrogen at high latitudes

Symposium - International Astronomical Union ◽

10.1017/s0074180900101068 ◽

1967 ◽

Vol 31 ◽

pp. 265-278 ◽

Cited By ~ 1

Author(s):

A. Blaauw ◽

I. Fejes ◽

C. R. Tolbert ◽

A. N. M. Hulsbosch ◽

E. Raimond

Keyword(s):

Surface Density ◽

Velocity Dispersion ◽

Neutral Hydrogen ◽

Hydrogen Gas ◽

High Latitudes ◽

Low Velocity

Earlier investigations have shown that there is a preponderance of negative velocities in the hydrogen gas at high latitudes, and that in certain areas very little low-velocity gas occurs. In the region 100° <l< 250°, + 40° <b< + 85°, there appears to be a disturbance, with velocities between - 30 and - 80 km/sec. This ‘streaming’ involves about 3000 (r/100)2solar masses (rin pc). In the same region there is a low surface density at low velocities (|V| < 30 km/sec). About 40% of the gas in the disturbance is in the form of separate concentrations superimposed on a relatively smooth background. The number of these concentrations as a function of velocity remains constant from - 30 to - 60 km/sec but drops rapidly at higher negative velocities. The velocity dispersion in the concentrations varies little about 6·2 km/sec. Concentrations at positive velocities are much less abundant.

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