1,126 research outputs found
Labyrinthine pathways towards supercycle attractors in unimodal maps
We uncover previously unknown properties of the family of periodic
superstable cycles in unimodal maps characterized each by a Lyapunov exponent
that diverges to minus infinity. Amongst the main novel properties are the
following: i) The basins of attraction for the phases of the cycles develop
fractal boundaries of increasing complexity as the period-doubling structure
advances towards the transition to chaos. ii) The fractal boundaries, formed by
the preimages of the repellor, display hierarchical structures organized
according to exponential clusterings that manifest in the dynamics as
sensitivity to the final state and transient chaos. iii) There is a functional
composition renormalization group (RG) fixed-point map associated to the family
of supercycles. iv) This map is given in closed form by the same kind of
-exponential function found for both the pitchfork and tangent bifurcation
attractors. v) There is a final stage ultra-fast dynamics towards the attractor
with a sensitivity to initial conditions that decreases as an exponential of an
exponential of time.Comment: 8 pages, 13 figure
Anchors for the Cosmic Distance Scale: the Cepheids U Sgr, CF Cas and CEab Cas
New and existing X-ray, UBVJHKsW(1-4), and spectroscopic observations were
analyzed to constrain fundamental parameters for M25, NGC 7790, and dust along
their sight-lines. The star clusters are of particular importance given they
host the classical Cepheids U Sgr, CF Cas, and the visual binary Cepheids CEa
and CEb Cas. Precise results from the multiband analysis, in tandem with a
comprehensive determination of the Cepheids' period evolution (dP/dt) from ~140
years of observations, helped resolve concerns raised regarding the clusters
and their key Cepheid constituents. Specifically, distances derived for members
of M25 and NGC 7790 are 630+-25 pc and 3.40+-0.15 kpc, respectively.Comment: To appear in Astronomy and Astrophysic
Asteroseismology of evolved stars to constrain the internal transport of angular momentum. VI. Testing a parametric formulation for the azimuthal magneto-rotational instability
Asteroseismic measurements of the internal rotation rate in evolved stars
pointed out to a lack of angular momentum (AM) transport in stellar evolution
models. Several physical processes in addition to hydrodynamical ones were
proposed as candidates for the missing mechanism. Nonetheless, no current
candidate can satisfy all the constraints provided by asteroseismology. We
revisit the role of a candidate process whose efficiency scales with the
contrast between the rotation rate of the core and the surface which was
proposed to be related to the azimuthal magneto-rotational instability (AMRI)
by Spada et al. We compute stellar evolution models of low- and
intermediate-mass stars with the parametric formulation of AM transport
proposed by Spada et al. until the end of the core-helium burning for low- and
intermediate-mass stars and compare our results to the latest asteroseismic
constraints available in the post main sequence phase. Both hydrogen-shell
burning stars in the red giant branch and core-helium burning stars of low- and
intermediate-mass in the mass range can be simultaneously reproduced by this kind of parametrisation.
Given current constraints from asteroseismology, the core rotation rate of
post-main sequence stars seems to be well explained by a process whose
efficiency is regulated by the internal degree of differential rotation in
radiative zones.Comment: Accepted for publication in Astronomy & Astrophysics. 10 pages, 10
figures, 1 appendi
On Weierstra{\ss} semigroups at one and two points and their corresponding Poincar\'e series
The aim of this paper is to introduce and investigate the Poincar\'e series
associated with the Weierstra{\ss} semigroup of one and two rational points at
a (not necessarily irreducible) non-singular projective algebraic curve defined
over a finite field, as well as to describe their functional equations in the
case of an affine complete intersection.Comment: Beginning of Section 3 and Subsection 3.1 were modifie
Buenas prácticas de gestión de gases de efecto invernadero de R.S.U. en la provincia de Córdoba
Proyecto Integrador (II)--FCEFN-UNC, 2016Elabora un diagnóstico del estado de situación y análisis de alternativas de gestión de residuos para la captación y tratamiento de biogás en toda la provincia de Córdob
Numerical indications of a q-generalised central limit theorem
We provide numerical indications of the -generalised central limit theorem
that has been conjectured (Tsallis 2004) in nonextensive statistical mechanics.
We focus on binary random variables correlated in a {\it scale-invariant}
way. The correlations are introduced by imposing the Leibnitz rule on a
probability set based on the so-called -product with . We show
that, in the large limit (and after appropriate centering, rescaling, and
symmetrisation), the emerging distributions are -Gaussians, i.e., , with , and
with coefficients approaching finite values . The
particular case recovers the celebrated de Moivre-Laplace theorem.Comment: Minor improvements and corrections have been introduced in the new
version. 7 pages including 4 figure
Liquidity and the multiscaling properties of the volume traded on the stock market
We investigate the correlation properties of transaction data from the New
York Stock Exchange. The trading activity f(t) of each stock displays a
crossover from weaker to stronger correlations at time scales 60-390 minutes.
In both regimes, the Hurst exponent H depends logarithmically on the liquidity
of the stock, measured by the mean traded value per minute. All multiscaling
exponents tau(q) display a similar liquidity dependence, which clearly
indicates the lack of a universal form assumed by other studies. The origin of
this behavior is both the long memory in the frequency and the size of
consecutive transactions.Comment: 7 pages, 3 figures, submitted to Europhysics Letter
On the crucial cluster Andrews-Lindsay 1 and a 4% distance solution for its planetary nebula
Andrews-Lindsay 1 is a pertinent open cluster because it may host the planetary nebula (PN) PHR 1315-6555, yet ambiguities linger concerning its fundamental parameters (>50% scatter). New multiband BVJHW1 - 4 photometry for cluster and field stars, in concert with observations of recently discovered classical Cepheids, were used to constrain the reddening and velocity-distance profiles along the sightline. That analysis yielded the following parameters for the cluster: E(J - H) = 0.24 ± 0.03, d = 10.0 ± 0.4 kpc (dJH = 9.9 ± 0.6 kpc, dBV = 10.1 ± 0.5 kpc), and log τ = 8.90 ± 0.15. The steep velocity-distance gradient along ℓ ∼ 305° indicates that two remote objects sharing spatial and kinematic parameters (i.e., PHR 1315-6555 and Andrews-Lindsay 1) are associated, thus confirming claims that the PN is a cluster member. The new distance for PHR 1315-6555 is among the most precise established yet for a Galactic PN (σ/d = 4%).Instituto de Astrofísica de La Plat
Angular momentum transport by magnetic fields in main sequence stars with Gamma Doradus pulsators
Context. Asteroseismic studies showed that cores of post main-sequence stars
rotate slower than theoretically predicted by stellar models with purely
hydrodynamical transport processes. Recent studies on main sequence stars,
particularly Gamma Doradus ( Dor) stars, revealed their internal
rotation rate for hundreds of stars, offering a counterpart on the main
sequence for studies of angular momentum transport. Aims. We investigate
whether such a disagreement between observed and predicted internal rotation
rates is present in main sequence stars by studying angular momentum transport
in Dor stars. Furthermore, we test whether models of rotating stars
with internal magnetic fields can reproduce their rotational properties.
Methods. We compute rotating models with the Geneva stellar evolution code
taking into account meridional circulation and the shear instability. We also
compute models with internal magnetic fields using a general formalism for
transport by the Tayler-Spruit dynamo. We then compare these models to
observational constraints for Dor stars that we compiled from the
literature, combining so the core rotation rates, projected rotational
velocities from spectroscopy, and constraints on their fundamental parameters.
Results. We show that combining the different observational constraints
available for Dor stars enable to clearly distinguish the different
scenarios for internal angular momentum transport. Stellar models with purely
hydrodynamical processes are in disagreement with the data whereas models with
internal magnetic fields can reproduce both core and surface constraints
simultaneously. Conclusions. Similarly to results obtained for subgiant and red
giant stars, angular momentum transport in radiative regions of Dor
stars is highly efficient, in good agreement with predictions of models with
internal magnetic fields.Comment: Accepted for publication in Astronomy & Astrophysics. 16 pages, 17
figures, 1 appendi
Market impact and trading profile of large trading orders in stock markets
We empirically study the market impact of trading orders. We are specifically
interested in large trading orders that are executed incrementally, which we
call hidden orders. These are reconstructed based on information about market
member codes using data from the Spanish Stock Market and the London Stock
Exchange. We find that market impact is strongly concave, approximately
increasing as the square root of order size. Furthermore, as a given order is
executed, the impact grows in time according to a power-law; after the order is
finished, it reverts to a level of about 0.5-0.7 of its value at its peak. We
observe that hidden orders are executed at a rate that more or less matches
trading in the overall market, except for small deviations at the beginning and
end of the order.Comment: 9 pages, 7 figure
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