Dense Stream Research Articles

Thermal effects in the ultrarelativistic two-stream instability

The dispersion relation for longitudinal waves in a one-dimensional ultrarelativistic plasma is calculated. Analytical and numerical results for the growth rate and frequency of the two-stream instability are presented as a function of the energy spread in the denser stream when the dilute stream is cold. The case of energy spreads in both beams is investigated numerically: it is found that relatively small energy spreads in both streams can lead to suppression of the instability.

A mechanism of generation of Alfv�n waves in the cosmic plasma

The emission of Alfven waves when a contact discontinuity of the solar wind plasma intersects a dense stream of cosmic rays is studied. It is shown that the spectral distribution of the radiation energy density agrees qualitatively and quantitatively with the observational data.

Hydrodynamics of plasma in a dense pinch

Abstract Equilibrium configurations and low-frequency radial oscillations (ionic sound) in dense streams of charged particles are considered in the approximation of hydrodynamics of ideal electron and ion liquids, interacting via the electromagnetic field created by the charges. The macroscopic approach used in this paper is valid without assumptions on the equations of state. Properties of the oscillations, due to a special form of the equation of state of the medium, are expressed by means of a single macroscopic parameter, the sound velocity. In the intermediate region of weak currents the ionic sound oscillations with a wavelength higher than a critical value increase exponentially. This instability is related to a trend towards stratification of the beam into separate jets, if the magnetic field of a current in a separate channel is able to prevent the charges from scattering in the radial direction. In a high current beam the instability to excitation of the radial ionic sound oscillations is suppressed by the current magnetic field.

A Model for Bursting X-Ray Sources

A model given by Henriksen and Chia (1972) for short duty cycle X-ray flare sources has been extended by Henriksen (1976), and applied to the recently discovered X-ray bursters. We use their notation here unless otherwise indicated. The model envisages a rapidly rotating magnetic white dwarf or neutron star located in a dense stream or cloud of gas such as might be found in close binary systems or in dense interstellar clouds. The basic charging mechanism for the flare is the accretion of matter into the hydromagnetic wave zone of the rotator at the ‘Bondi’ or ‘tail-shock’ rate (corresponding to a thermal cloud or a stream,-respectively), AB.

Miniature source of dense streams of neutral particles: V B Yuferov et al, Prib Tekh Eksper, No 1, 1971, 183–185 ( in Russian).

Miniature source of dense streams of neutral particles: V B Yuferov et al, Prib Tekh Eksper, No 1, 1971, 183–185 ( in Russian).

On streams of charged particles in an electromagnetic field

Problems of two kinds arise in the consideration of streams of charged particles in an electromagnetic field. In the first kind of problem (direct problems) the magnetic and electric fields are given, and it is required to study the trajectories which are possible in these fields. This type of problem reduces to the examination of the solutions of the following system of equations with partial derivatives: (v▽)v = e m E + e mc v × H .(1) The electric and magnetic fields in these equations are taken to be known solutions of the Maxwell equations ▽ × H = 4π c ϱτ , ▽ × E = 0, ▽ H = 0, ▽ E = 4 πϱ. (2) For dense streams, the effect of the space charge is taken into account (the effect of the magnetic proper field is not usually considered) and the problem is much more complicated, since equations (1) must be considered together with equations (2) in which the first equation is replaced by ▽( ϱv) = 0. (3) However, in constructing electronic instruments it is often necessary to create a stream of charged particles with given properties. In problems of this kind the stream of charged particles must be considered to be given and the solutions of Maxwell's equations (2) which correspond to such a stream must be examined. This problem is the converse of the previous problem. It has been studied in its application to electron optics in [1] and [2], where in [1] streams close to an arbitrary curve are considered, and in [2] streams close to an arbitrary surface. The problem has been studied in [3] for streans in an electric field, with the restriction that the lines of flow must be coordinate lines of some orthogonal curvilinear coordinate system. An equation is obtained which the Lamb coefficients of this coordinate system must satisfy, and is then solved. The theory of the formation of streams in an arbitrary electromagnetic field is constructed in [4], with similar restrictions. In this work a method is devised to determine the fields from the properties of the stream, given the condition that the considered stream exists. In this paper we consider the following converse problem: we are given a two-parameter family of curves; it is required to find when this family can be the lines of flow of a stream of charged particles in an electromagnetic field.

The Manner and Efficiency of Raptor Depredations on Bats

Large bat colonies such as those in the Carlsbad Caverns, New Mexico, attract many species of predators. The most significant are birds of prey, for they commonly feed on bats and are capable of taking them in flight (Bailey, 1928; Stager, 1941, 1948; Constantine, 1948; Eads, Wiseman and Menzies, 1957; Medway, 1958; Baker, 1961; Downing and Baldwin, 1961). Reptiles and carnivores, that might prey heavily on bats were they not terrestrial, are limited by the virtual inaccessibility of bats in their daytime roosts and by their flight habits. Only in a few congested bat caves are carnivores known to consume large numbers of bats. There are isolated cases of bat depredations by fish (Baker, 1961), amphibians (Kinsey, 1961; Elwell, 1962), birds other than raptores (Clay, 1959; Herreid, 1960; Wilks and Laughlin, 1961) and by rodents (Martin, 1961). Allen (1940) summarizes numerous references to fish, reptiles, birds, and mammals preying on bats and also lists spiders and ants as bat predators. Of all these, avian raptores are likely the most effective predators because when locally abundant, bats can constitute major proportions of raptor diets. Owl pellets from the Carlsbad Caverns are composed almost entirely of bat bones and fur. The number of bats captured, however, is relatively insignificant, and birds of prey are but minor threats to colonies as a whole. The lateness of the hour at which bats emerge almost eliminates them from the diets of diurnal birds, and nocturnal birds are incapable of pursuing and capturing individual bats. Therefore, raptores are a threat only for the relatively short time that bats exit en masse from a cavern entrance in the early evening. During that short time bats are extremely vulnerable. They emerge in dense streams for hours and by hundreds of thousands. In flight, bats are slow, compared to birds, and can be overtaken quickly. Yet, it is surprising that some birds are inefficient at catching bats and the number of captures versus the number of attacks varies greatly among the different species. For example, Red-tailed Hawks (Buteo jamnaicensis) and Great Horned Owls (Bubo virginianus) have difficulty at times in catching bats, and they may miss repeatedly. Accipiters and falcons, however, seldom miss and the reasons lie in the manner of attack and the nature of the bird. At Carlsbad Caverns National Park, park naturalists have had the opportunity for many years to witness bird depredations on the large colonies of Mexican freetail bats (Tadarida brasiliensis mexicana) that exit each evening from the caverns. Through the years, six species of hawks, one falcon, and one owl have been observed. They are: the Cooper Hawk (Accipiter cooperii), Sharp-shinned Hawk (Accipiter striatus), Swainson Hawk (Buteo swainsoni), Red-tailed Hawk, Ferruginous Hawk (Buteo regalis), Marsh Hawk (Circus cyaneus), Sparrow Hawk (Falco sparverius), and Great Horned Owl.

Accelerated self-constricted electron streams in plasma

The mechanism is described of radial oscillations in a neutralized cylindrical electron stream in an accelerating electric field. The analysis is based on the two-fluid model of plasma. Analytical expressions for small amplitude oscillations and numerical solutions for large amplitudes are derived. It is found, when electron-positive ion collisions are taken into account, that for dense streams in low electric fields the radial oscillations (pinch oscillations) can destroy the streaming character of the electron flow and thus prevent its acceleration.

The Orbit of the Leonid Meteor Swarm1

THE great Leonid swarm of meteors consists of ortho-Leonids which pursue nearly the same path round the sun, and clino–Leonids which move in orbits sensibly differing from the ortho–orbit. The present investigation is concerned with the ortho–Leonids. They form a dense stream extended along a portion of an immense orbit round which they travel in 33¼ years. This orbit has its perihelion a little inside the Earth's orbit, and its aphelion a little outside the orbit of Uranus. It intersects the orbits of these two planets, but lies in a plane inclined to the ecliptic, so that the meteors which traverse it pass under the intervening planets on their outward journey and over them on the homeward journey.