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All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Higher-order parabolic approximations for sound propagation in stratified moving media

Asymptotic solutions of order k-n are developed for the equations governing the propagation of sound through a stratified moving medium. Here k is a dimensionless wave number and n is the arbitrary order of the approximation. These approximations are an extension of geometric acoustics theory and provide corrections to that theory in the form of multiplicative functions which satisfy parabolic partial differential equations. These corrections account for the diffraction effects caused by variation of the field normal to the ray path and the interaction of these transverse variations with the variation of the field along the ray. The theory is illustrated by application to simple examples.

Mcaninch, G. L.↗
DOE OSTI2020

Materials Data on K3N by Materials Project

NK3 is Bismuth triodide-like structured and crystallizes in the hexagonal P6_3/mcm space group. The structure is one-dimensional and consists of one NK3 ribbon oriented in the (0, 0, 1) direction. K1+ is bonded in an L-shaped geometry to two equivalent N3- atoms. Both K–N bond lengths are 2.73 Å. N3- is bonded to six equivalent K1+ atoms to form face-sharing NK6 octahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on KN3 by Materials Project

KN3 crystallizes in the tetragonal I4/mcm space group. The structure is three-dimensional. K1+ is bonded in a 8-coordinate geometry to eight equivalent N+0.33- atoms. All K–N bond lengths are 3.03 Å. There are two inequivalent N+0.33- sites. In the first N+0.33- site, N+0.33- is bonded in a linear geometry to two equivalent N+0.33- atoms. Both N–N bond lengths are 1.19 Å. In the second N+0.33- site, N+0.33- is bonded in a 5-coordinate geometry to four equivalent K1+ and one N+0.33- atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on KN3 by Materials Project

KN3 crystallizes in the tetragonal I4/mcm space group. The structure is three-dimensional. K1+ is bonded to six N+0.33- atoms to form corner-sharing KN6 octahedra. The corner-sharing octahedra tilt angles range from 0–75°. There are two shorter (2.69 Å) and four longer (3.08 Å) K–N bond lengths. There are two inequivalent N+0.33- sites. In the first N+0.33- site, N+0.33- is bonded in a trigonal planar geometry to two equivalent K1+ and one N+0.33- atom. The N–N bond length is 1.12 Å. In the second N+0.33- site, N+0.33- is bonded in a linear geometry to two equivalent K1+ atoms.

36 MATERIALS SCIENCE↗