Propagation of transverse acoustic waves in a spin-density-wave metal.
Attenuation and velocity of shear acoustic waves propagating parallel to magnetic field for spin density wave metal
WAVE ATTENUATION↗
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Nonlinear density waves in planetary rings
The steady-state structure of planetary rings in the presence of density waves at the Lindblad resonances of a satellite is indicated. The study is based on the dispersion relation and damping rate for nonlinear density waves, derived by Shu et al. (1985) and by Borderies, Goldreich, and Tremaine (1985). It is shown that strong density waves lead to an enhancement of the background surface density in the wave zone.
Borderies, Nicole↗
Density wave theory
The prospect that density waves and galactic shock waves are present on the large-scale in disk-shaped galaxies has received support in recent years from both theoretical and observational studies. Large-scale galactic shock waves in the interstellar gas are suggested to play an important, governing role in star formation, molecule formation, and the degree of development of spiral structure. Through the dynamics of the interstellar gas and the galactic shock wave phenomenon, a new insight into the physical basis underlying the morphological classification system of galaxies is suggested.
Roberts, W. W., Jr.↗
Density wave theory
The prospect that density waves and galactic shock waves are present on the large scale in disk shaped galaxies has received support in recent years from both theoretical and observational studies. Large-scale galactic shock waves in the interstellar gas are suggested to play an important governing role in star formation, molecule formation, and the degree of development of spiral structure. Through the dynamics of the interstellar gas and the galactic shock-wave phenomenon, a new insight into the physical basis underlying the morphological classification system of galaxies is suggested.
Roberts, W. W., Jr.↗
Resonance excitation of spiral density waves in a gaseous disk. II - A nonlinear theory and application to the 3 kiloparsec arm
The present nonlinear theory of spiral density waves in a thin, viscous, self-gravitating gaseous disk views the waves as generated near the Lindblad resonance by periodic disturbances through an excitation mechanism. The suggestion of Yuan (1984), that either a minor oval distortion or an uneven distribution of mass in the center can excite a spiral density wave whose radial velocity and mass concentration are in excellent agreement with observations of the 3 kpc arm of the Galaxy, is confirmed. Reliable results are obtained for nonlinear density waves either in a gaseous disk or in the gas components of a galactic disk.
Yuan, Chi↗
Comparison of density waves in the rings of Saturn and Uranus
The similarity of density waves in the rings of Saturn and Uranus are addressed. It is found that all ring systems are grossly similar in that they all encircle the primary in its equatorial plane and exhibit responses to resonant satellite perturbations. The dominant response of Saturn's rings is the clearing of gaps and generation of density and bending waves. The Uranian rings appear to be confined by the presence of shepherd satellites. Three possible density waves have been identified, two in the epsilon ring and one in the delta ring.
Yanamandra-Fisher, Padmavati A.↗
''density-wave'' oscillations in boiling Freon-11 flow.
Density wave type flow oscillations in boiling Freon 11 examined, noting effects of partial evaporation superheat and liquid inlet temperature on stability
DENSITY MEASUREMENT↗
Physical properties of Uranian delta ring from a possible density wave
On the basis of wavelength and amplitude behavior, as well as observed feature morphology, that are indicative of a density wave, the presently studied Voyager PPS stellar occultation observations of the Uranus delta ring are held to indicate the presence of a moonlet interior to the delta ring. Lindblad resonances are calculated for all 65 discrete possible locations for this moonlet; the locations are labeled by azimuth number of the resonance associated with each location that would excite the observed density wave in the delta ring.
Horn, L. J.↗
Nonlinear spiral density waves - Viscous damping
The formalism of Borderies, Goldreich, and Tremaine (1984), as simplified by Shu and Stewart (1985), is used to develop a theory for the viscous damping of nonlinear density waves in particulate disks of moderate collision frequency. The specific application is to Saturn's rings, but the development is general enough to allow application to a wider context (e.g., to gas clouds in a spiral galaxy). A Krook formulation is used rather than a Boltzmann formulation to treat the statistical effects of inelastic collisions. Issues that have arisen as a result of the study include a self-induced Q barrier in the first wavelength or two of the Mimas 5:3 density wave train and the surprising discovery that Saturn's B ring may behave almost as a superfluid, with hardly any viscous losses.
Shu, F. H.↗
Protostellar angular momentum transport by spiral density waves
The application of rotational stability criteria to a specific model of star formation leads to the conclusion that the growth of stellar angular momentum is limited by its transfer to the disk. Excess accreted angular momentum can be transferred by torques connected with spiral density waves induced by even a slight protostellar triaxiality. In addition, viscous damping of the density waves is likely to cause the excess angular momentum to be deposited within a small region close to the protostar. Thus, it would be appropriate to treat that part of the growing protostellar disk beyond the outer Lindblad resonance as an accretion disk with a torque applied to its inner edge. It is noted that this situation is directly relevant to certain models of the evolution of the protosun and solar nebula.
Yuan, C.↗
Theory of kilometer-size density waves in the nightside Venus ionosphere
Quasi-sinusoidal density waves were frequently observed during the end of the Pioneer Venus Orbiter (PVO) mission when the orbiter was at low periapsis. These waves occur at altitudes approx. 145 - 155 km and have wavelengths approx. 1 km. It is suggested that a radial, ambipolar electric field E(sub 0), directed downward, is established in the Venus ionosphere during electron pressure enhancements above approx. 160 km. This field generates an electron E x B drift V(sub E); the ions move radially and do not E x B drift because they are unmagnetized (i.e, nu(sub in) much greater than Omega(sub i)). This drift is shown to drive a collisional drift wave instability for sufficiently large values of V(sub E), nominally, V(sub E) greater than nu(sub i) where nu(sub i) is the ion thermal velocity. For parameters typical of the nightside Venus ionosphere, this instability generates plasma fluctuations with wavelengths approx. 1 km, consistent with observations.
Huba, J. D.↗
Theory of Kilometer-Size Density Waves in the Nightside Venus Ionosphere
Quasi-sinusoidal density waves were frequently observed during the end of the Pioneer Venus Orbiter (PVO) mission when the orbiter was at low periapsis. These waves occur at altitudes approx. 145 - 155 km and have wavelengths approx. 1 km. It is suggested that a radial, ambipolar electric field E(sub O), directed downward, is established in the Venus ionosphere during electron pressure enhancements above approx. 160 km. This field generates an electron E X B drift V(sub E); the ions move radially and do not E X B drift because they are unmagnetized (i.e., V(sub in) much greater than Omega(sub i)). This drift is shown to drive a collisional drift wave instability for sufficiently large values of V(sub E), nominally, V(sub E) greater than upsilon(sub i) where upsilon(sub i) is the ion thermal velocity. For parameters typical of the nightside Venus ionosphere, this instability generates plasma fluctuations with wavelengths approx. 1 km, consistent with observations.
Huba, J. D.↗
Density wave triggered star formation in grand design spirals
In normal spiral galaxies the arms are the main sites for star formation. This is the cause of their optical contrast compared with the rest of the disc. The spiral structure can be observed as a higher concentration of H2 regions, neutral gas (both atomic and molecular via CO), dust and stars than in the interarm disc. It seens generally accepted that, at least in grand design spirals, there are density waves in the discs. However, several questions are not clear yet and still under discussion. An important question could be termed the triggering dilemma (by analogy with the 'winding dilemma' raised in the forties): Is the enhanced star formation in the spiral arms triggered by the passage of a system of density waves or is it simply due to the presence of a higher column density of gas there? In the present work, we use triggering in the same sense as the moderate to strong triggering defined by Elmegreen (1992), that is to say that star formation in the arms occurs at a rate faster than that in the interarm zone, relative to the available placental gas. Our group has designed several tests to elucidate whether or not star formation is triggered in the arms with respect to the interarm region and we summarize one of them, that of the ratio of the star formation efficiency in the arms divided by that of the interarm zone at the same galactocentric distance which we may call the relative massive star formation efficiency, where the efficiency is defined using the ratio of the mass of stars (evaluated via the H alpha flux) to the mass of neutral gas, atomic plus molecular (which must be measured with the adequate angular resolution). If the relative efficiency is of order unity, the star formation is proportional to the mass of gas, if some kind of induced star formation is present, the relative efficiency should be considerably larger than unity.
Cepa, J.↗
Excitation of turbulence by density waves
A nonlinear system describes the microdynamical state of turbulence that is excited by density waves. It consists of an equation of propagation and a master equation. A group-scaling generates the scaled equations of many interacting groups of distribution functions. The two leading groups govern the transport processes of evolution and eddy diffusivity. The remaining sub-groups represent the relaxation for the approach of diffusivity to equilibrium. In strong turbulence, the sub-groups disperse themselves and the ensemble acts like a medium that offers an effective damping to close the hierarchy. The kinetic equation of turbulence is derived. It calculates the eddy viscosity and identifies the effective damping of the assumed medium self-consistently. It formulates the coupling mechanism for the intensification of the turbulent energy at the expense of the wave energy, and the transfer mechanism for the cascade. The spectra of velocity and density fluctuations find the power law k sup-2 and k sup-4, respectively.
Tichen, C. M.↗
Application of the density-wave theory to the spiral structure of the Milky Way system. II
Density wave theory and spiral gravitational field effects in migrating stars orbits and origins in Milky Way spiral arm, using Schmidt model
Yuan, C.↗
Nonlinear spiral density waves - An inviscid theory
It is pointed out that the theory of spiral density waves, invented to explain the spiral structure of disk galaxies, has also been found useful for the study of planetary rings. The linear theory is by now well developed, while the nonlinear theory is less complete. Analytical calculations which include self-gravitation have, so far, obtained results only in the slightly nonlinear regime, or have concentrated on partial effects which are not of primary importance to the physical problem at hand. In the present paper, it is attempted to remedy these shortcomings. The simplest asymptotic ordering which can still yield useful results is adopted. Attention is given to the reduction to a nonlinear integral equation in a single variable, the use of the Wentzel-Kramers-Brillouin-Jeffreys theory, and the replacement of an equation by another which is easier to handle numerically.
Shu, F. H.↗
Density waves in Saturn's rings
Certain radial brightness variations in the outer Cassini division of Saturn's rings may be spiral density waves driven by Saturn's large moon Iapetus, in which case a value of approximately 16 g/sq cm for the surface density is calculated in the region where the waves are seen. The kinematic viscosity in the same region is approximately 170 sq cm/s and the vertical scale height of the ring is estimated to be a maximum of approximately 40 m.
Cuzzi, J. N.↗
Star-gas density waves in spiral galaxies
The steady state dynamics of spiral galaxies is analyzed as a two-component system consisting of stars and gas within the framework of the WKB density wave theory. The gravitational influence of the gas is included for the first time in a steady state calculation. The full set of equations for a star-gas galaxy is presented, and the equations are analyzed for small-amplitude forcing. Wave properties near the solar circle are examined, and it is found that the large-scale gas shock disappears for gas content above 8 percent. Instead, gas density profiles change to highly symmetric shapes as a result of the action of the gas self-gravity. The stellar wave is damped by the torque exerted by the gas.
Lubow, Stephen H.↗