16,691 research outputs found
Adaptive Mesh Refinement for Supersonic Molecular Cloud Turbulence
We performed a series of three-dimensional numerical simulations of
supersonic homogeneous Euler turbulence with adaptive mesh refinement (AMR) and
effective grid resolution up to 1024^3 zones. Our experiments describe
non-magnetized driven supersonic turbulent flows with an isothermal equation of
state. Mesh refinement on shocks and shear is implemented to cover dynamically
important structures with the highest resolution subgrids and calibrated to
match the turbulence statistics obtained from the equivalent uniform grid
simulations.
We found that at a level of resolution slightly below 512^3, when a
sufficient integral/dissipation scale separation is first achieved, the
fraction of the box volume covered by the AMR subgrids first becomes smaller
than unity. At the higher AMR levels subgrids start covering smaller and
smaller fractions of the whole volume, which scale with the Reynolds number as
Re^{-1/4}. We demonstrate the consistency of this scaling with a hypothesis
that the most dynamically important structures in intermittent supersonic
turbulence are strong shocks with a fractal dimension of two. We show that
turbulence statistics derived from AMR simulations and simulations performed on
uniform grids agree surprisingly well, even though only a fraction of the
volume is covered by AMR subgrids. Based on these results, we discuss the
signature of dissipative structures in the statistical properties of supersonic
turbulence and their role in overall flow dynamics.Comment: 5 pages, 5 figures, revised versio
Qualitative and quantitative analysis of mixtures of compounds containing both hydrogen and deuterium
Method allows qualitative and quantitative analysis of mixtures of partially deuterated compounds. Nuclear magnetic resonance spectroscopy determines location and amount of deuterium in organic compounds but not fully deuterated compounds. Mass spectroscopy can detect fully deuterated species but not the location
Photon Conserving Radiative Transfer around Point Sources in multi-dimensional Numerical Cosmology
Many questions in physical cosmology regarding the thermal and ionization
history of the intergalactic medium are now successfully studied with the help
of cosmological hydrodynamical simulations. Here we present a numerical method
that solves the radiative transfer around point sources within a three
dimensional cartesian grid. The method is energy conserving independently of
resolution: this ensures the correct propagation speeds of ionization fronts.
We describe the details of the algorithm, and compute as first numerical
application the ionized region surrounding a mini-quasar in a cosmological
density field at z=7.Comment: 5 pages, 4 figures, submitted to ApJ
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