28,829 research outputs found
Flux emergence in a magnetized convection zone
We study the influence of a dynamo magnetic field on the buoyant rise and
emergence of twisted magnetic flux-ropes, and their influence on the global
external magnetic field. We ran 3D MHD numerical simulations using the ASH code
and analysed the dynamical evolution of such buoyant flux-ropes from the bottom
of the convection zone until the post-emergence phases. The global nature of
this model represents very crudely and inaccurately the local dynamics of the
buoyant rise, but allows to study the influence of global effects such as
self-consistently generated differential rotation, meridional circulation and
Coriolis forces. Although motivated by the solar context, this model cannot be
thought of as a realistic model of the rise of magnetic structures and their
emergence in the Sun where the local dynamics are completely different. The
properties of initial phases of the buoyant rise in good agreement with
previous studies. However, the effects of the interaction of the background
dynamo field become increase as the flux-ropes evolve. During the buoyant rise
across the CZ, the flux-rope's magnetic field strength and scales as ,
with . An increase of velocity, density and current precedes flux
emergence at all longitudes. The geometry, latitude and relative orientation of
the flux-ropes with respect to the background magnetic field influences the
rise speeds, zonal flow amplitudes (which develop within the flux-ropes) and
the corresponding surface signatures. This influences the morphology, duration
and amplitude of the associated surface shearing and Poynting flux. The emerged
flux influences the system's global polarity, leading in some cases to a
polarity reversal while inhibiting background dynamo from doing so in some
others. The emerged magnetic flux is slowly advected poleward, while being
diffused and assimilated by the background dynamo field.Comment: Accepted for publication in Ap
Spectra of primordial fluctuations in two-perfect-fluid regular bounces
We introduce analytic solutions for a class of two components bouncing
models, where the bounce is triggered by a negative energy density perfect
fluid. The equation of state of the two components are constant in time, but
otherwise unrelated. By numerically integrating regular equations for scalar
cosmological perturbations, we find that the (would be) growing mode of the
Newtonian potential before the bounce never matches with the the growing mode
in the expanding stage. For the particular case of a negative energy density
component with a stiff equation of state we give a detailed analytic study,
which is in complete agreement with the numerical results. We also perform
analytic and numerical calculations for long wavelength tensor perturbations,
obtaining that, in most cases of interest, the tensor spectral index is
independent of the negative energy fluid and given by the spectral index of the
growing mode in the contracting stage. We compare our results with previous
investigations in the literature.Comment: 11 pages, 5 figure
Explosion of smoothness for conjugacies between multimodal maps
Let and be smooth multimodal maps with no periodic attractors and no
neutral points. If a topological conjugacy between and is
at a point in the nearby expanding set of , then is a smooth
diffeomorphism in the basin of attraction of a renormalization interval of .
In particular, if and are unimodal maps and
is at a boundary of then is in .Comment: 22 page
Multi-Step Knowledge-Aided Iterative ESPRIT for Direction Finding
In this work, we propose a subspace-based algorithm for DOA estimation which
iteratively reduces the disturbance factors of the estimated data covariance
matrix and incorporates prior knowledge which is gradually obtained on line. An
analysis of the MSE of the reshaped data covariance matrix is carried out along
with comparisons between computational complexities of the proposed and
existing algorithms. Simulations focusing on closely-spaced sources, where they
are uncorrelated and correlated, illustrate the improvements achieved.Comment: 7 figures. arXiv admin note: text overlap with arXiv:1703.1052
Relativistic deuteron structure function at large Q^2
The deuteron deep inelastic unpolarized structure function F_2^D is
calculated using the Wilson operator product expansion method. The long
distance behaviour, related to the deuteron bound state properties, is
evaluated using the Bethe-Salpeter equation with one particle on mass shell.
The calculation of the ratio F_2^D/F_2^N is compared with other convolution
models showing important deviations in the region of large x. The implications
in the evaluation of the neutron structure function from combined data on
deuterons and protons are discussed.Comment: 7 pages, 1 ps figure, RevTeX source, 1 tar.gz file. Submited to
Physical Letter
Symmetry Aspects in Nonrelativistic Multi-Scalar Field Models and Application to a Coupled Two-Species Dilute Bose Gas
We discuss unusual aspects of symmetry that can happen due to entropic
effects in the context of multi-scalar field theories at finite temperature. We
present their consequences, in special, for the case of nonrelativistic models
of hard core spheres. We show that for nonrelativistic models phenomena like
inverse symmetry breaking and symmetry non-restoration cannot take place, but a
reentrant phase at high temperatures is shown to be possible for some region of
parameters. We then develop a model of interest in studies of Bose-Einstein
condensation in dilute atomic gases and discuss about its phase transition
patterns. In this application to a Bose-Einstein condensation model, however,
no reentrant phases are found.Comment: 8 pages, 1 eps figure, IOP style. Based on a talk given by R. O.
Ramos at the QFEXT05 workshop, Barcelona, Spain, September 5-9, 2005. One
reference was update
Effective action in DSR1 quantum field theory
We present the one-loop effective action of a quantum scalar field with DSR1
space-time symmetry as a sum over field modes. The effective action has real
and imaginary parts and manifest charge conjugation asymmetry, which provides
an alternative theoretical setting to the study of the particle-antiparticle
asymmetry in nature.Comment: 8 page
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