Appearance Of Large-scale Structure Research Articles

Spectral condensation in laboratory two-dimensional turbulence

Due to the inverse energy cascade, when the energy dissipation length scale in two-dimensional turbulence is larger than the domain size, energy is expected to condense into the lowest allowed mode. Thus, the appearance of large-scale structures is often taken as a proxy for spectral condensation, particularly in laboratory realizations of two-dimensional turbulence. We show that large-scale flows alone, however, are not robust indicators of spectral condensation, because small domains may both weaken the inverse cascade and introduce new dissipation mechanisms.

Modeling Gravitational Clustering without Computing Gravitational Force

The large-scale structure in the Universe is believed to arise out of small random density perturbations generated in the very early Universe, that are amplified by gravity. Large and usually intricate N-body simulations are typically employed to model the complex nonlinear dynamics in a self gravitating medium. We suggest a very simple model which predicts, on large scales, the correct density and velocity distributions. The model does not involve an explicit computation of the gravitational force. It is based on a simple transformation of the variables and local conservation laws of mass and {\it generalized} linear momentum. The model demonstrates that the overall appearance of large-scale structure in the Universe is explicitly determined by the initial velocity field and it reveals the most significant large-scale effects of gravity on the formation of structure.

The Transition to Turbulence of Microgravity Gas Jet Diffusion Flames

Abstract This paper discusses results obtained in a study of the transition to turbulence of gas jet diffusion flames in microgravity. The experiments were conducted at the 2.2-second Drop Tower of the NASA Lewis Research Center. Propane flames burning in quiescent air at atmospheric pressure were investigated. Significant differences have been observed between the transition processes of gas jet diffusion flames in microgravity and normal gravity These include the appearance of large scale structures in microgravity which are manifested at the flame base and are convected downstream. These structures appear intermittently at first, and, then, as Reynolds number is increased, a continuous train of structures is observed along the flame front. The experimental observations are explained in terms of flow transition and instability of the shear layer associated with the injection of the jet flow into quiescent surroundings

A study of a 21 centimeter-selected sample of galaxies. I - The survey

view Abstract Citations (35) References (29) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Study of a 21 Centimeter--selected Sample of Galaxies. I. The Survey Henning, P. A. Abstract Known galaxies are rare in the portion of the sky obscured by our Galaxy. This so-called zone of avoidance blocks our view of about one- fifth of the extragalactic sky. A full understanding of the large-scale structure of the universe will eventually require a complete sky mapping, so methods of surveying the zone of avoidance must be found. This paper concerns a pilot survey for galaxies at 21 cm conducted with the NRAO 300 foot (91 m) telescope, which was done to test the feasibility of finding unseen galaxies through the detection of the radiation emitted by neutral hydrogen. This "blind search" method is appropriate in optically obscured regions because the long-wave-length radiation from H I is not blocked by interstellar dust in the Milky Way. As a control experiment, the same style of H I search was conducted in unobscured parts of the sky. The resulting collection of 21 cm-selected galaxies, 37 extragalactic objects, of which 19 were previously known, forms a unique sample. No one has ever investigated the characteristics of objects found in this way before. I have undertaken the study of the 21 cm-selected sample to see if these galaxies differ from optically selected samples. H I mapping of all of the uncataloged galaxies, and a few of the cataloged sources, was done at the VLA to determine accurately the galaxies H I line widths and masses. Although the purpose of this work was not to map large-scale structure, a region of galaxian underdensity, or cosmic void, was evident in the data. It seems that voids are not filled by low surface brightness, dwarf galaxies, but rather are truly lacking in bright and faint galaxies. This paper, the first of two, presents the results of the single-dish and VLA studies and discusses the appearance of large-scale structures in the data. The second paper will detail the analysis of this H I-selected sample, in particular, the comparison with optical- and infrared-selected samples. Publication: The Astrophysical Journal Supplement Series Pub Date: February 1992 DOI: 10.1086/191631 Bibcode: 1992ApJS...78..365H Keywords: Radio Astronomy; Sky Surveys (Astronomy); Astronomical Catalogs; Astronomical Maps; Galactic Structure; Milky Way Galaxy; Universe; Very Large Array (Vla); Astrophysics; GALAXIES: DISTANCES AND REDSHIFTS; RADIO LINES: ATOMIC; SURVEYS full text sources ADS | data products SIMBAD (39) NED (39)