67,289 research outputs found
The Dynamo Effects in Laboratory Plasmas
A concise review of observations of the dynamo effect in laboratory
plasmas is given. Unlike many astrophysical systems, the laboratory pinch
plasmas are driven magnetically. When the system is overdriven, the resultant
instabilities cause magnetic and flow fields to fluctuate, and their
correlation induces electromotive forces along the mean magnetic field. This
-effect drives mean parallel electric current, which, in turn, modifies
the initial background mean magnetic structure towards the stable regime. This
drive-and-relax cycle, or the so-called self-organization process, happens in
magnetized plasmas in a time scale much shorter than resistive diffusion time,
thus it is a fast and unquenched dynamo process. The observed -effect
redistributes magnetic helicity (a measure of twistedness and knottedness of
magnetic field lines) but conserves its total value. It can be shown that fast
and unquenched dynamos are natural consequences of a driven system where
fluctuations are statistically either not stationary in time or not homogeneous
in space, or both. Implications to astrophysical phenomena will be discussed.Comment: 21 pages, 15 figures, submitted to Magnetohydrodynamic
Conformal Symmetry and Pion Form Factor: Soft and Hard Contributions
We discuss a constraint of conformal symmetry in the analysis of the pion
form factor. The usual power-law behavior of the form factor obtained in the
perturbative QCD analysis can also be attained by taking negligible quark
masses in the nonperturbative quark model analysis, confirming the recent
AdS/CFT correspondence. We analyze the transition from soft to hard
contributions in the pion form factor considering a momentum-dependent
dynamical quark mass from a nonnegligible constituent quark mass at low
momentum region to a negligible current quark mass at high momentum region. We
find a correlation between the shape of nonperturbative quark distribution
amplitude and the amount of soft and hard contributions to the pion form
factor.Comment: 7 pages, 6 figures, extensively revised, to appear in Phys. Rev.
Relatively hyperbolic groups, rapid decay algebras, and a generalization of the Bass conjecture
By deploying dense subalgebras of we generalize the Bass
conjecture in terms of Connes' cyclic homology theory. In particular, we
propose a stronger version of the -Bass Conjecture. We prove that
hyperbolic groups relative to finitely many subgroups, each of which posses the
polynomial conjugacy-bound property and nilpotent periodicity property, satisfy
the -Stronger-Bass Conjecture. Moreover, we determine the
conjugacy-bound for relatively hyperbolic groups and compute the cyclic
cohomology of the -algebra of any discrete group.Comment: 32 pages, 2 figures; added an appendix also by C. Ogl
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