1,294 research outputs found
Systematic construction of exact MHD models for astrophysical winds and jets
By a systematic method we construct general classes of exact and
selfconsistent axisymmetric MHD solutions describing flows which originate at
the near environment of a central gravitating astrophysical object. The
unifying scheme contains two large groups of exact MHD outflow models, (I)
meridionally self-similar ones with spherical critical surfaces and (II)
radially self-similar models with conical critical surfaces. The classification
includes known polytropic models, such as the classical Park er model of a
stellar wind and the Blandford and Payne (1982) model of a disk-wind; it also
contains nonpolytropic models, such as those of winds/jets in Sauty and
Tsinganos (1994), Lima et al (1996) and Trussoni et al (1997). Besides the
unification of these known cases under a common scheme, several new classes
emerge and some are briefly analysed; they could be explored for a further
understanding of the physical properties of MHD outflows from various
magnetized and rotating astrophysical objects in stellar or galactic systems.Comment: 13 pages, 11 figure
A statistical physics perspective on criticality in financial markets
Stock markets are complex systems exhibiting collective phenomena and
particular features such as synchronization, fluctuations distributed as
power-laws, non-random structures and similarity to neural networks. Such
specific properties suggest that markets operate at a very special point.
Financial markets are believed to be critical by analogy to physical systems
but few statistically founded evidence have been given. Through a data-based
methodology and comparison to simulations inspired by statistical physics of
complex systems, we show that the Dow Jones and indices sets are not rigorously
critical. However, financial systems are closer to the criticality in the crash
neighborhood.Comment: 23 pages, 19 figure
Symbolic extensions and uniform generators for topological regular flows
Building on the theory of symbolic extensions and uniform generators for
discrete transformations we develop a similar theory for topological regular
flows. In this context a symbolic extension is given by a suspension flow over
a subshift
The distribution of cycles in breakpoint graphs of signed permutations
Breakpoint graphs are ubiquitous structures in the field of genome
rearrangements. Their cycle decomposition has proved useful in computing and
bounding many measures of (dis)similarity between genomes, and studying the
distribution of those cycles is therefore critical to gaining insight on the
distributions of the genomic distances that rely on it. We extend here the work
initiated by Doignon and Labarre, who enumerated unsigned permutations whose
breakpoint graph contains cycles, to signed permutations, and prove
explicit formulas for computing the expected value and the variance of the
corresponding distributions, both in the unsigned case and in the signed case.
We also compare these distributions to those of several well-studied distances,
emphasising the cases where approximations obtained in this way stand out.
Finally, we show how our results can be used to derive simpler proofs of other
previously known results
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