6,377 research outputs found
Retrograde resonance in the planar three-body problem
We continue the investigation of the dynamics of retrograde resonances
initiated in Morais & Giuppone (2012). After deriving a procedure to deduce the
retrograde resonance terms from the standard expansion of the three-dimensional
disturbing function, we concentrate on the planar problem and construct
surfaces of section that explore phase-space in the vicinity of the main
retrograde resonances (2/-1, 1/-1 and 1/-2). In the case of the 1/-1 resonance
for which the standard expansion is not adequate to describe the dynamics, we
develop a semi-analytic model based on numerical averaging of the unexpanded
disturbing function, and show that the predicted libration modes are in
agreement with the behavior seen in the surfaces of section.Comment: Celestial Mechanics and Dynamical Astronomy, in pres
Asteroids in retrograde resonance with Jupiter and Saturn
We identify a set of asteroids among Centaurs and Damocloids, that orbit
contrary to the common direction of motion in the Solar System and that enter
into resonance with Jupiter and Saturn. Their orbits have inclinations I >= 140
deg and semi-major axes a < 15 AU. Two objects are currently in retrograde
resonance with Jupiter: 2006 BZ8 in the 2/-5 resonance and 2008 SO218 in the
1/-2 resonance. One object, 2009 QY6, is currently in the 2/-3 retrograde
resonance with Saturn. These are the first examples of Solar System objects in
retrograde resonance. The present resonant configurations last for several
thousand years. Brief captures in retrograde resonance with Saturn are also
possible during the 20,000 years integration timespan, particularly in the 1/-1
resonance (2006 BZ8) and the 9/-7 resonance (1999 LE31).Comment: 6 pages, 7 figures, accepted for publication in MNRAS Letter
A new data reduction scheme to obtain the mode II fracture properties of Pinus Pinaster wood
In this work a numerical study of the End Notched Flexure (ENF) specimen was performed
in order to obtain the mode II critical strain energy released rate (GIIc) of a Pinus pinaster wood in the RL crack propagation system. The analysis included interface finite elements and a progressive damage
model based on indirect use of Fracture Mechanics.
The difficulties in monitoring the crack length during an experimental ENF test and the inconvenience of performing separate tests in order to obtain the elastic properties are well known. To avoid these
problems, a new data reduction scheme based on the equivalent crack concept was proposed and validated. This new data reduction scheme, the Compliance-Based Beam Method (CBBM), does not require crack measurements during ENF tests and additional tests to obtain elastic properties.FCT - POCTI/EME/45573/200
Finite element analysis of the ECT test on mode III interlaminar fracture of carbon-epoxy composite laminates
In this work a parametric study of the Edge Crack Torsion (ECT) specimen was performed
in order to maximize the mode III component (GIII) of the strain energy release rate for carbon-epoxy laminates.
A three-dimensional finite element analysis of the ECT test was conducted considering a
[90/0/(+45/-45)2/(-45/+45)2/0/90]S lay-up. The main objective was to define an adequate geometry to obtain an almost pure mode III at crack front. The geometrical parameters studied were specimen dimensions, distance between pins and size of the initial crack.
The numerical results demonstrated that the ratio between the specimen length and the initial crack length had a significant effect on the strain energy release rate distributions. In almost all of the tested
configurations, a mode II component occurred near the edges but it did not interfere significantly with the dominant mode III state.FCT - POCTI/EME/45573/200
Fermi-Bose mixture in mixed dimensions
One of the challenging goals in the studies of many-body physics with
ultracold atoms is the creation of a topological superfluid
for identical fermions in two dimensions (2D). The expectations of reaching the
critical temperature through p-wave Feshbach resonance in spin-polarized
fermionic gases have soon faded away because on approaching the resonance, the
system becomes unstable due to inelastic-collision processes. Here, we consider
an alternative scenario in which a single-component degenerate gas of fermions
in 2D is paired via phonon-mediated interactions provided by a 3D BEC
background. Within the weak-coupling regime, we calculate the critical
temperature for the fermionic pair formation, using Bethe-Salpeter
formalism, and show that it is significantly boosted by higher-order
diagramatic terms, such as phonon dressing and vertex corrections. We describe
in detail an experimental scheme to implement our proposal, and show that the
long-sought p-wave superfluid is at reach with state-of-the-art experiments.Comment: 12 pages, 6 figures, 2 tables and supplementary materia
Spin-glass phase transition and behavior of nonlinear susceptibility in the Sherrington-Kirkpatrick model with random fields
The behavior of the nonlinear susceptibility and its relation to the
spin-glass transition temperature , in the presence of random fields, are
investigated. To accomplish this task, the Sherrington-Kirkpatrick model is
studied through the replica formalism, within a one-step
replica-symmetry-breaking procedure. In addition, the dependence of the
Almeida-Thouless eigenvalue (replicon) on the random fields
is analyzed. Particularly, in absence of random fields, the temperature
can be traced by a divergence in the spin-glass susceptibility ,
which presents a term inversely proportional to the replicon . As a result of a relation between and , the
latter also presents a divergence at , which comes as a direct consequence
of at . However, our results show that, in the
presence of random fields, presents a rounded maximum at a temperature
, which does not coincide with the spin-glass transition temperature
(i.e., for a given applied random field). Thus, the maximum
value of at reflects the effects of the random fields in the
paramagnetic phase, instead of the non-trivial ergodicity breaking associated
with the spin-glass phase transition. It is also shown that still
maintains a dependence on the replicon , although in a more
complicated way, as compared with the case without random fields. These results
are discussed in view of recent observations in the LiHoYF
compound.Comment: accepted for publication in PR
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