19,072 research outputs found
Luminosity of a quark star undergoing torsional oscillations and the problem of gamma ray bursts
We discuss whether the winding-up of the magnetic field by differential
rotation in a new-born quark star can produce a sufficiently-high, energy,
emission rate of sufficiently long duration to explain long gamma-ray bursts.
In the context of magnetohydrodynamics, we study the torsional oscillations
and energy extraction from a new-born, hot, differentially rotating quark star.
The new-born compact star is a rapid rotator that produces a relativistic,
leptonic wind. The star's torsional oscillation modulates this wind emission
considerably when it is odd and of sufficient amplitude, which is relatively
easy to reach. Odd oscillations may occur just after the formation of a quark
star. Other asymmetries can cause similar effects. The buoyancy of wound-up
magnetic fields is inhibited, or its effects are limited, by a variety of
different mechanisms. Direct electromagnetic emission by the torsional
oscillation in either an outside vacuum or the leptonic wind surrounding the
compact object is found to be insignificant. In contrast, the twist given to
the outer magnetic field by an odd torsional oscillation is generally
sufficient to open the star's magnetosphere. The Poynting emission of the star
in its leptonic environment is then radiated from all of its surface and is
enhanced considerably during these open episodes, tapping at the bulk
rotational energy of the star. This results in intense energy shedding in the
first tens of minutes after the collapse of magnetized quark stars with an
initial poloidal field of order of 10**14 Gauss, sufficient to explain long
gamma-ray bursts.Comment: 16 pages, accepted by Astronomy and Astrophysic
Nonlinear Electron Oscillations in a Viscous and Resistive Plasma
New non-linear, spatially periodic, long wavelength electrostatic modes of an
electron fluid oscillating against a motionless ion fluid (Langmuir waves) are
given, with viscous and resistive effects included. The cold plasma
approximation is adopted, which requires the wavelength to be sufficiently
large. The pertinent requirement valid for large amplitude waves is determined.
The general non-linear solution of the continuity and momentum transfer
equations for the electron fluid along with Poisson's equation is obtained in
simple parametric form. It is shown that in all typical hydrogen plasmas, the
influence of plasma resistivity on the modes in question is negligible. Within
the limitations of the solution found, the non-linear time evolution of any
(periodic) initial electron number density profile n_e(x, t=0) can be
determined (examples). For the modes in question, an idealized model of a
strictly cold and collisionless plasma is shown to be applicable to any real
plasma, provided that the wavelength lambda >> lambda_{min}(n_0,T_e), where n_0
= const and T_e are the equilibrium values of the electron number density and
electron temperature. Within this idealized model, the minimum of the initial
electron density n_e(x_{min}, t=0) must be larger than half its equilibrium
value, n_0/2. Otherwise, the corresponding maximum n_e(x_{max},t=tau_p/2),
obtained after half a period of the plasma oscillation blows up. Relaxation of
this restriction on n_e(x, t=0) as one decreases lambda, due to the increase of
the electron viscosity effects, is examined in detail. Strong plasma viscosity
is shown to change considerably the density profile during the time evolution,
e.g., by splitting the largest maximum in two.Comment: 16 one column pages, 11 figures, Abstract and Sec. I, extended, Sec.
VIII modified, Phys. Rev. E in pres
Determination of aerodynamic damping coefficients from wind-tunnel free-flight trajectories of non-axisymmetric bodies
Aerodynamic damping coefficient from wind tunnel free flight trajectories of nonaxisymmetrical bodie
Modeling Longitudinal Oscillations of Bunched Beams in Synchrotrons
Longitudinal oscillations of bunched beams in synchrotrons have been analyzed
by accelerator physicists for decades, and a closed theory is well-known [1].
The first modes of oscillation are the coherent dipole mode, quadrupole mode,
and sextupole mode. Of course, these modes of oscillation are included in the
general theory, but for developing RF control systems, it is useful to work
with simplified models. Therefore, several specific models are analyzed in the
paper at hand. They are useful for the design of closed-loop control systems in
order to reach an optimum performance with respect to damping the different
modes of oscillation. This is shown by the comparison of measurement and
simulation results for a specific closed-loop control system.Comment: 14 pages, 14 figure
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