106,746 research outputs found
Tangled Magnetic Fields in Solar Prominences
Solar prominences are an important tool for studying the structure and
evolution of the coronal magnetic field. Here we consider so-called "hedgerow"
prominences, which consist of thin vertical threads. We explore the possibility
that such prominences are supported by tangled magnetic fields. A variety of
different approaches are used. First, the dynamics of plasma within a tangled
field is considered. We find that the contorted shape of the flux tubes
significantly reduces the flow velocity compared to the supersonic free fall
that would occur in a straight vertical tube. Second, linear force-free models
of tangled fields are developed, and the elastic response of such fields to
gravitational forces is considered. We demonstrate that the prominence plasma
can be supported by the magnetic pressure of a tangled field that pervades not
only the observed dense threads but also their local surroundings. Tangled
fields with field strengths of about 10 G are able to support prominence
threads with observed hydrogen density of the order of 10^(11) cm^(-3).
Finally, we suggest that the observed vertical threads are the result of
Rayleigh-Taylor instability. Simulations of the density distribution within a
prominence thread indicate that the peak density is much larger than the
average density. We conclude that tangled fields provide a viable mechanism for
magnetic support of hedgerow prominences.Comment: 14 pages (emulateapj style), 10 figures, ApJ, in pres
Tangled Circuits
The theme of the paper is the use of commutative Frobenius algebras in
braided strict monoidal categories in the study of varieties of circuits and
communicating systems which occur in Computer Science, including circuits in
which the wires are tangled. We indicate also some possible novel geometric
interest in such algebras
On the thermal conduction in tangled magnetic fields in clusters of galaxies
Thermal conduction in tangled magnetic fields is reduced because heat
conducting electrons must travel along the field lines longer distances between
hot and cold regions of space than if there were no fields. We consider the
case when the tangled magnetic field has a weak homogeneous component. We
examine two simple models for temperature in clusters of galaxies: a
time-independent model and a time-dependent one. We find that the actual value
of the effective thermal conductivity in tangled magnetic fields depends on how
it is defined for a particular astrophysical problem. Our final conclusion is
that the heat conduction never totally suppressed but is usually important in
the central regions of galaxy clusters, and therefore, it should not be
neglected.Comment: 16 pages, 4 figure
Small-scale microwave background anisotropies due to tangled primordial magnetic fields
An inhomogeneous cosmological magnetic field creates vortical perturbations
that survive Silk damping on much smaller scales than compressional modes. This
ensures that there is no sharp cut-off in anisotropy on arc-minute scales. As
we had pointed out earlier, tangled magnetic fields, if they exist, will then
be a potentially important contributor to small-angular scale CMBR
anisotropies. Several ongoing and new experiments, are expected to probe the
very small angular scales, corresponding to multipoles with l>1000. In view of
this observational focus, we revisit the predicted signals due to primordial
tangled magnetic fields, for different spectra and different cosmological
parameters. We also identify a new regime, where the photon mean-free path
exceeds the scale of the perturbation, which dominates the predicted signal at
very high l. A scale-invariant spectrum of tangled fields which redshifts to a
present value B_{0}=3\times 10^{-9} Gauss, produces temperature anisotropies at
the 10 micro Kelvin level between l ~ 1000-3000. Larger signals result if the
univese is lambda dominated, if the baryon density is larger, or if the
spectral index of magnetic tangles is steeper, n > -3. The signal will also
have non-Gaussian statistics. We predict the distinctive form of the increased
power expected in the microwave background at high l in the presence of
significant tangled magnetic fields. We may be on the verge of detecting or
ruling out the presence of tangled magnetic fields which are strong enough to
influence the formation of large-scale structure in the Universe.Comment: 5 pages, 2 figures, submitted to MNRAS Letter
Tangled Roots, Bittersweet Exposure
Accompanied by tree portraits, this personal narrative reflects upon the intersecting histories between the indigenous peoples of Marin County (north of San Francisco, CA) and the author, who is Euro-American, while contemplating the changing relationship to their shared woodland, the effects of colonization, and possibilities for healing
- …