80 research outputs found
Hall magnetohydrodynamics of partially ionized plasmas
The Hall effect arises in a plasma when electrons are able to drift with the
magnetic field but ions cannot. In a fully-ionized plasma this occurs for
frequencies between the ion and electron cyclotron frequencies because of the
larger ion inertia. Typically this frequency range lies well above the
frequencies of interest (such as the dynamical frequency of the system under
consideration) and can be ignored. In a weakly-ionized medium, however, the
Hall effect arises through a different mechanism -- neutral collisions
preferentially decouple ions from the magnetic field. This typically occurs at
much lower frequencies and the Hall effect may play an important role in the
dynamics of weakly-ionised systems such as the Earth's ionosphere and
protoplanetary discs.
To clarify the relationship between these mechanisms we develop an
approximate single-fluid description of a partially ionized plasma that becomes
exact in the fully-ionized and weakly-ionized limits. Our treatment includes
the effects of ohmic, ambipolar, and Hall diffusion. We show that the Hall
effect is relevant to the dynamics of a partially ionized medium when the
dynamical frequency exceeds the ratio of ion to bulk mass density times the
ion-cyclotron frequency, i.e. the Hall frequency. The corresponding length
scale is inversely proportional to the ion to bulk mass density ratio as well
as to the ion-Hall beta parameter.Comment: 11 page, 1 figure, typos removed, numbers in tables revised; accepted
for publication in MNRA
Ground State Energy of the One-Component Charged Bose Gas
The model considered here is the `jellium' model in which there is a uniform,
fixed background with charge density in a large volume and in
which particles of electric charge and mass move --- the
whole system being neutral. In 1961 Foldy used Bogolubov's 1947 method to
investigate the ground state energy of this system for bosonic particles in the
large limit. He found that the energy per particle is in this limit, where .
Here we prove that this formula is correct, thereby validating, for the first
time, at least one aspect of Bogolubov's pairing theory of the Bose gasComment: 38 pages latex. Typos corrected.Lemma 6.2 change
Kinetic Theory of Plasmas: Translational Energy
In the present contribution, we derive from kinetic theory a unified fluid
model for multicomponent plasmas by accounting for the electromagnetic field
influence. We deal with a possible thermal nonequilibrium of the translational
energy of the particles, neglecting their internal energy and the reactive
collisions. Given the strong disparity of mass between the electrons and heavy
particles, such as molecules, atoms, and ions, we conduct a dimensional
analysis of the Boltzmann equation. We then generalize the Chapman-Enskog
method, emphasizing the role of a multiscale perturbation parameter on the
collisional operator, the streaming operator, and the collisional invariants of
the Boltzmann equation. The system is examined at successive orders of
approximation, each of which corresponding to a physical time scale. The
multicomponent Navier-Stokes regime is reached for the heavy particles, which
follow a hyperbolic scaling, and is coupled to first order drift-diffusion
equations for the electrons, which follow a parabolic scaling. The transport
coefficients exhibit an anisotropic behavior when the magnetic field is strong
enough. We also give a complete description of the Kolesnikov effect, i.e., the
crossed contributions to the mass and energy transport fluxes coupling the
electrons and heavy particles. Finally, the first and second principles of
thermodynamics are proved to be satisfied by deriving a total energy equation
and an entropy equation. Moreover, the system of equations is shown to be
conservative and the purely convective system hyperbolic, thus leading to a
well-defined structure
Estrogen receptor transcription and transactivation: Basic aspects of estrogen action
Estrogen signaling has turned out to be much more complex and exciting than previously thought; the paradigm shift in our understanding of estrogen action came in 1996, when the presence of a new estrogen receptor (ER), ERÎČ, was reported. An intricate interplay between the classical ERα and the novel ERÎČ is of paramount importance for the final biological effect of estrogen in different target cells
Determination of the degree of cross-linking and nature of the anion of resin-based ion exchangers by pyrolysis gas-chromatography
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