Results 1 - 10 of 54126
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[en] Starting with basic data, a dynamical model is derived for the velocity dispersion in the bulge of M31. There is good agreement between the r.m.s. components and the experimental range. (C.F.)
[en] Transverse magnetic (TM) modes with phase velocities at or just below the speed of light, c, are intended to accelerate relativistic particles in hollow-core, photonic band gap (PBG) fibers. These are so-called 'surface defect modes', being lattice modes perturbed by the defect to have their frequencies shifted into the band gap, and they can have any phase velocity. PBG fibers also support so-called 'core defect modes' which are characterized as having phase velocities always greater than c and never cross the light line. In this paper we explore the nature of these two classes of accelerating modes and compare their properties.
[en] The effect of flowing metal walls on the resistive wall instabilities is analyzed for a general cylindrically symmetric diffusive pinch configuration. Two types of liquid metal flow are analyzed: a uniform flow which is poloidally symmetric, and a two-stream flow consisting of two opposite streams splitting at the top and merging at the bottom. It is found in both configurations that when the liquid wall flow velocity exceeds a critical value, the resistive wall mode is stabilized. However, for the two-stream flow the critical velocity is several times smaller than that for the uniform flow. Still in a realistic experiment one needs a flow velocity of a few tens m/s to stabilize the resistive wall mode
[en] On the basis of a two-component (two-fluid) hydrodynamic model, it is shown that the probable phenomenon of solar core rotation with a velocity higher than the average velocity of global rotation of the Sun, discovered by the SOHO mission, can be related to fast solid-body rotation of the light hydrogen component of the solar plasma, which is caused by thermonuclear fusion of hydrogen into helium inside the hot dense solar core. Thermonuclear fusion of four protons into a helium nucleus (α-particle) creates a large free specific volume per unit particle due to the large difference between the densities of the solar plasma and nuclear matter. As a result, an efficient volumetric sink of one of the components of the solar substance—hydrogen—forms inside the solar core. Therefore, a steady-state radial proton flux converging to the center should exist inside the Sun, which maintains a constant concentration of hydrogen as it burns out in the solar core. It is demonstrated that such a converging flux of hydrogen plasma with the radial velocity vr(r) = −βr creates a convective, vr∂vφ/∂r, and a local Coriolis, vrvφ/r,φ nonlinear hydrodynamic forces in the solar plasma, rotating with the azimuthal velocity vφ. In the absence of dissipation, these forces should cause an exponential growth of the solid-body rotation velocity of the hydrogen component inside the solar core. However, friction between the hydrogen and helium components of the solar plasma due to Coulomb collisions of protons with α-particles results in a steady-state regime of rotation of the hydrogen component in the solar core with an angular velocity substantially exceeding the global rotational velocity of the Sun. It is suggested that the observed differential (liquid-like) rotation of the visible surface of the Sun (photosphere) with the maximum angular velocity at the equator is caused by sold-body rotation of the solar plasma in the radiation zone and strong turbulence in the tachocline layer, where the turbulent viscosity reaches its maximum value at the equator. There, the tachocline layer exerts the most efficient drag on the less dense outer layers of the solar plasma, which are slowed down due to the interaction with the ambient space plasma (solar wind).
[en] Radial velocities of members of the globular cluster M3 by Gunn and Griffin (1979) were used for determining the rotation of the cluster at different distances from its center. The projection of angular velocity on the plane of the sky and its position angle are found to be the functions of the distance from the center. The angular velocity is about 2x10-6 yr-1 in the central region at r <=0.5 and smaller by an order of magnitude at r >=2.5. The rotational parameters correlate with the parameters derived from equidensity curves
[en] When considering relativistic motion within the special theory of relativity the question of the gravity free fall result for relativistic radial velocities is an interesting and surprisingly difficult one. Can Newton's force law for gravity be generalized and a Lorentz covariant equation of gravitational free fall be obtained. Einstein found that gravitation does not easily fit within the structure of Lorentz covaraince and was thus led to generalize the theory. Gravity, he suggested, causes a fundamental change in relativistic physics. Space-time itself becomes distorted (curved). It is considered by the author that the nice discussion of the general orbital motion in curved space given by Markley (Am. J. Phys.; 41:45 (1972)) is generally beyond the scope of introductory physics classes and a simplified answer is here given for the relativistic correction for which it is only necessary to impose the restriction of small distance free fall at relativistic speeds. (U.K.)