1,011 research outputs found
New analysis method of the halo phenomenon in finite many-fermion systems. First applications to medium-mass atomic nuclei
A new analysis method to investigate halos in finite many-fermion systems is
designed, as existing characterization methods are proven to be
incomplete/inaccurate. A decomposition of the internal wave-function of the
{-body} system in terms of overlap functions allows a model-independent
analysis of medium-range and asymptotic properties of the internal one-body
density. The existence of a spatially decorrelated region in the density
profile is related to the existence of three typical energy scales in the
excitation spectrum of the {-body} system. A series of model-independent
measures, taking the internal density as the only input, are introduced. The
new measures allow a quantification of the potential halo in terms of the
average number of fermions participating to it and of its impact on the system
extension. Those new "halo factors" are validated through simulations and
applied to results obtained through energy density functional calculations of
medium-mass nuclei. Performing spherical Hartree-Fock-Bogoliubov calculations
with state-of-the-art Skyrme plus pairing functionals, a collective halo is
predicted in drip-line Cr isotopes, whereas no such effect is seen in Sn
isotopes.Comment: 27 Pages, 29 Figures. Accepted for publication in Phys. Rev. C
back-to-back with second part (arXiv:0711.1275
Halo phenomenon in finite many-fermion systems. Atom-positron complexes and large-scale study of atomic nuclei
The analysis method proposed in Ref. \cite{rotival07a} is applied to
characterize halo properties in finite many-fermion systems. First, the
versatility of the method is highlighted by applying it to light and
medium-mass nuclei as well as to atom-positron and ion-positronium complexes.
Second, the dependence of nuclear halo properties on the characteristics of the
energy density functional used in self-consistent Hartree-Fock-Bogoliubov
calculations is studied. It is found that (a) the low-density behavior of the
pairing functional and the regularization/renormalization scheme must be chosen
coherently and with care to provide meaningful predictions, (b) the impact of
pairing correlations on halo properties is significant and is the result of two
competing effects, (c) the detailed characteristics of the pairing functional
has however only little importance, (d) halo properties depend significantly on
any ingredient of the energy density functional that influences the location of
single-particle levels; i.e. the effective mass, the tensor terms and the
saturation density of nuclear matter. The latter dependencies give insights to
how experimental data on medium-mass drip-line nuclei can be used in the
distant future to constrain some characteristics of the nuclear energy density
functional. Last but not least, large scale predictions of halos among all
spherical even-even nuclei are performed using specific sets of particle-hole
and particle-particle energy functionals. It is shown that halos in the ground
state of medium-mass nuclei will only be found at the very limit of neutron
stability and for a limited number of elements.Comment: 24 Pages, 32 Figures. Accepted for publication in Phys. Rev. C
back-to back with first part (nucl-th/0702050
Domain wall interacting with a black hole: A new example of critical phenomena
We study a simple system that comprises all main features of critical
gravitational collapse, originally discovered by Choptuik and discussed in many
subsequent publications. These features include universality of phenomena,
mass-scaling relations, self-similarity, symmetry between super-critical and
sub-critical solutions, etc.
The system we consider is a stationary membrane (representing a domain wall)
in a static gravitational field of a black hole. For a membrane that spreads to
infinity, the induced 2+1 geometry is asymptotically flat. Besides solutions
with Minkowski topology there exists also solutions with the induced metric and
topology of a 2+1 dimensional black hole. By changing boundary conditions at
infinity, one finds that there is a transition between these two families. This
transition is critical and it possesses all the above-mentioned properties of
critical gravitational collapse. It is remarkable that characteristics of this
transition can be obtained analytically. In particular, we find exact
analytical expressions for scaling exponents and wiggle-periods.
Our results imply that black hole formation as a critical phenomenon is far
more general than one might expect.Comment: 23 pages, 5 postscript figures include
The geological setting of Carboniferous magmatism in the proto-Andean margin of Gondwana, Sierra Pampeanas, Argentina
Fil: Dahlquist, J. A. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; Argentina.Fil: Dahlquist, J. A. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro de Investigaciones en Ciencias de la Tierra; Argentina.Fil: Basei, M. Universida de de Sao Paulo. Instituto de Geociencias; Brasil.Fil: Alasino, P. H. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; Argentina.Fil: Alasino, P. H. Universidad Nacional de la Rioja. INGeReN-CENIIT; Argentina.Fil: Alasino, P. H. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja; Argentina.Fil: Campos, M. Universidade de Sao Paulo. Instituto de Geociencias; Brasil.Fil: Casquet, C. Universidad Complutense. Departamento de Petrología y Geoquímica; España.Our petrogenetic understanding of the Carboniferous granites of the Sierras Pampeanas has
improved in recent years, but their geodynamic setting is still not well constrained. Domeier and
Torsvik (2014) affirm that there is no documented and unambiguous evidence of an active margin
in the proto-Andean margin of Gondwana before the late Carboniferous (~ 320 Ma).Fil: Dahlquist, J. A. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; Argentina.Fil: Dahlquist, J. A. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro de Investigaciones en Ciencias de la Tierra; Argentina.Fil: Basei, M. Universida de de Sao Paulo. Instituto de Geociencias; Brasil.Fil: Alasino, P. H. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; Argentina.Fil: Alasino, P. H. Universidad Nacional de la Rioja. INGeReN-CENIIT; Argentina.Fil: Alasino, P. H. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja; Argentina.Fil: Campos, M. Universidade de Sao Paulo. Instituto de Geociencias; Brasil.Fil: Casquet, C. Universidad Complutense. Departamento de Petrología y Geoquímica; España.Geoquímica y Geofísic
Directional persistence & the optimality of run-and-tumble chemotaxis
E. coli does chemotaxis by performing a biased random walk composed of alternating periods of swimming (runs) and reorientations (tumbles). Tumbles are typically modelled as complete directional randomisations but it is known that in wild type E. coli, successive run directions are actually weakly correlated, with a mean directional difference of not, vert, similar63°. We recently presented a model of the evolution of chemotactic swimming strategies in bacteria which is able to quantitatively reproduce the emergence of this correlation. The agreement between model and experiments suggests that directional persistence may serve some function, a hypothesis supported by the results of an earlier model. Here we investigate the effect of persistence on chemotactic efficiency, using a spatial Monte Carlo model of bacterial swimming in a gradient, combined with simulations of natural selection based on chemotactic efficiency. A direct search of the parameter space reveals two attractant gradient regimes, (a) a low-gradient regime, in which efficiency is unaffected by directional persistence and (b) a high-gradient regime, in which persistence can improve chemotactic efficiency. The value of the persistence parameter that maximises this effect corresponds very closely with the value observed experimentally. This result is matched by independent simulations of the evolution of directional memory in a population of model bacteria, which also predict the emergence of persistence in high-gradient conditions. The relationship between optimality and persistence in different environments may reflect a universal property of random-walk foraging algorithms, which must strike a compromise between two competing aims: exploration and exploitation. We also present a new graphical way to generally illustrate the evolution of a particular trait in a population, in terms of variations in an evolvable parameter
Peraluminous granitoids and their relationship with the source rocks
Comparative compositional studies between two peraluminous unit with magmatic andalucite and cordierite
indicate that they were produced by partial melting of two differents metasedimentary source rocks. We
conclude that geochemical studies from peraluminous unit contributes to define the source rocks and to
constrain the pre-orogenic geotectonic environmen
Scars of Invariant Manifolds in Interacting Chaotic Few-Body Systems
We present a novel extension of the concept of scars for the wave functions
of classically chaotic few-body systems of identical particles with rotation
and permutation symmetry. Generically there exist manifolds in classical phase
space which are invariant under the action of a common subgroup of these two
symmetries. Such manifolds are associated with highly symmetric configurations.
If sufficiently stable, the quantum motion on such manifolds displays a notable
enhancement of the revival in the autocorrelation function which is not
directly associated with individual periodic orbits. Rather, it indicates some
degree of localization around an invariant manifold which has collective
characteristics that should be experimentally observable.Comment: 4 pages, RevTeX, 4 PS/EPS-figures, uses psfig.sty, quantum
computation changed, to be published in Physical Review Letter
On Fourier integral transforms for -Fibonacci and -Lucas polynomials
We study in detail two families of -Fibonacci polynomials and -Lucas
polynomials, which are defined by non-conventional three-term recurrences. They
were recently introduced by Cigler and have been then employed by Cigler and
Zeng to construct novel -extensions of classical Hermite polynomials. We
show that both of these -polynomial families exhibit simple transformation
properties with respect to the classical Fourier integral transform
Lagrangian Reachabililty
We introduce LRT, a new Lagrangian-based ReachTube computation algorithm that
conservatively approximates the set of reachable states of a nonlinear
dynamical system. LRT makes use of the Cauchy-Green stretching factor (SF),
which is derived from an over-approximation of the gradient of the solution
flows. The SF measures the discrepancy between two states propagated by the
system solution from two initial states lying in a well-defined region, thereby
allowing LRT to compute a reachtube with a ball-overestimate in a metric where
the computed enclosure is as tight as possible. To evaluate its performance, we
implemented a prototype of LRT in C++/Matlab, and ran it on a set of
well-established benchmarks. Our results show that LRT compares very favorably
with respect to the CAPD and Flow* tools.Comment: Accepted to CAV 201
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