59,844 research outputs found
Multifractal analysis of nonhyperbolic coupled map lattices: Application to genomic sequences
Symbolic sequences generated by coupled map lattices (CMLs) can be used to
model the chaotic-like structure of genomic sequences. In this study it is
shown that diffusively coupled Chebyshev maps of order 4 (corresponding to a
shift of 4 symbols) very closely reproduce the multifractal spectrum of
human genomic sequences for coupling constant if .
The presence of rare configurations causes deviations for , which
disappear if the rare event statistics of the CML is modified. Such rare
configurations are known to play specific functional roles in genomic sequences
serving as promoters or regulatory elements.Comment: 7 pages, 6 picture
An uncombed inversion of multi-wavelength observations reproducing the Net Circular Polarization in a sunspots' penumbra
I derived a geometrical model of the penumbral magnetic field topology from
an uncombed inversion setup that aimed at reproducing the NCP of simultaneous
spectra in near-IR (1.56 mu) and VIS (630 nm) spectral lines. I inverted the
spectra of five photospheric lines with a model that mimicked vertically
interlaced magnetic fields with two components, labeled background field and
flow channels. The flow channels were modeled as a perturbation of the
background field with a Gaussian shape using the SIRGAUS code. The location and
extension of the Gaussian perturbation in the optical depth scale was then
converted to a geometrical height scale. I investigated the relative amount of
magnetic flux in the flow channels and the background field atmosphere. The
uncombed model is able to reproduce the NCP well on the limb side of the spot
and worse on the center side; the VIS lines are better reproduced than the
near-IR lines. The Evershed flow happens along nearly horizontal field lines
close to the solar surface. The magnetic flux that is related to the flow
channels makes up about 20-50% of the total magnetic flux in the penumbra. The
gradients obtainable by a Gaussian perturbation are too small for a perfect
reproduction of the NCP in the IR lines with their small formation height
range. Two peculiarities of the observed NCP, a sign change of the NCP of the
VIS lines on the center side and a ring structure around the umbra in the Ti
line at 630.37nm and the FeI line at 1565.2nm deserve closer attention. The
large fraction of magnetic flux related to the flow channel component could
allow to replenish the penumbral radiative losses in the flux tube picture.Comment: 12 pages, 14 figures + 4 pages Appendix, 5 figures, accepted by
Astronomy & Astrophysic
Molecular resonance phenomena and alpha-clustering: recent progress and perspectives
The connection between molecular resonance phenomena in light heavy-ion
collisions, alpha-clustering and extremely deformed states in light
-like nuclei is discussed. For example, the superdeformed bands
recently discovered in light N=Z nuclei such as Ar, Ca,
Cr, and Ni by -ray spectroscopy may have a special link
with resonant states in collisions with -like nuclei. The resonant
reactions involving identical bosons such as C+C,
O+O Mg+Mg and Si+Si are of interest.
For instance, a butterfly mode of vibration of the J = 38
resonance of Si+Si has been discovered in recent particle
-ray angular correlations measurements. The search for signatures of
strongly deformed shapes and clustering in light N=Z nuclei is also the domain
of charged particle spectroscopy. The investigation of -decays in
Mg has been undertaken for excitation energies where previously nuclear
molecular resonances were found in C+C collisions. In this case
the C-C scattering states can be related to the breakup resonance
and, tentatively, to the resonant radiative capture C+C reaction.Comment: 7 pages, 3 figures included. Invited Talk 8th Int. Conf. on
Clustering Aspects of Nuclear Structure and Dynamics, Nara, Japan, Nov.
24-29, 2003; To be published in Nucl. Phys.
Molecular structures and clustering effects in reactions induced by light nuclei
-clustering study since the pioneering discovery of C+C
molecular resonances half a century ago. Our knowledge on physics of nuclear
molecules has increased considerably and nuclear clustering remains one of the
most fruitful domains of nuclear physics, facing some of the greatest
challenges and opportunities in the years ahead. The occurrence of "exotic"
shapes in light = -like nuclei is investigated. Various
approaches of the superdeformed and hyperdeformed bands associated with
quasimolecular resonant structures are presented. Evolution of clustering from
stability to the drip-lines is examined: clustering aspects are, in particular,
discussed for light exotic nuclei with large neutron excess such as
neutron-rich Oxygen isotopes with their complete spectrocopy.Comment: 16 pages, 7 figures, Invited Talk presented at the First
International African Symposium on Exotic Nuclei IASEN2013 Ithemba LABS Cape
Town, South Africa, December 2-6, 2013; Proceedings to be published by World
Scientifi
Competition between quasi-molecular resonances and fusion-fission in light dinuclear systems
The results presented in this paper clearly suggest that a coherent framework
may exist which connects the topics of heavy-ion molecular resonances,
hyperdeformation effects, and fission shape isomerism. New data on
particle-particle- triple coincidences of the Si+Si
reaction at a beam energy corresponding to the population of a conjectured
J = 38 resonance in Ni are presented. The absence of
alignment of the spins of the outgoing fragments with respect to the orbital
angular momentum is found to be in contrast with the alignment as measured for
the Mg+Mg resonances. A molecular-model picture is presented to
suggest a "butterfly" motion of two oblate Si nuclei interacting in a
equator-to-equator molecular configuration.Comment: 10 pages standard REVTeX file, 7 ps and eps Figures included -- Talk
given at the International Conference ``Nuclear Physics close to the
Barrier", Warsaw, Poland, June 30- July 4, 1998 (Proceedings to be published
in Acta Physica Polonica A, fall 1998) -
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