1,888 research outputs found
Chains of rotational tori and filamentary structures close to high multiplicity periodic orbits in a 3D galactic potential
This paper discusses phase space structures encountered in the neighborhood
of periodic orbits with high order multiplicity in a 3D autonomous Hamiltonian
system with a potential of galactic type. We consider 4D spaces of section and
we use the method of color and rotation [Patsis and Zachilas 1994] in order to
visualize them. As examples we use the case of two orbits, one 2-periodic and
one 7-periodic. We investigate the structure of multiple tori around them in
the 4D surface of section and in addition we study the orbital behavior in the
neighborhood of the corresponding simple unstable periodic orbits. By
considering initially a few consequents in the neighborhood of the orbits in
both cases we find a structure in the space of section, which is in direct
correspondence with what is observed in a resonance zone of a 2D autonomous
Hamiltonian system. However, in our 3D case we have instead of stability
islands rotational tori, while the chaotic zone connecting the points of the
unstable periodic orbit is replaced by filaments extending in 4D following a
smooth color variation. For more intersections, the consequents of the orbit
which started in the neighborhood of the unstable periodic orbit, diffuse in
phase space and form a cloud that occupies a large volume surrounding the
region containing the rotational tori. In this cloud the colors of the points
are mixed. The same structures have been observed in the neighborhood of all
m-periodic orbits we have examined in the system. This indicates a generic
behavior.Comment: 12 pages,22 figures, Accepted for publication in the International
Journal of Bifurcation and Chao
Chaotic and regular motion around generalized Kalnajs discs
The motion of test particles in the gravitational fields generated by the
first four members of the infinite family of generalized Kalnajs discs, is
studied. In first instance, we analyze the stability of circular orbits under
radial and vertical perturbations and describe the behavior of general
equatorial orbits and so we find that radial stability and vertical instability
dominate such disc models. Then we study bounded axially symmetric orbits by
using the Poincare surfaces of section and Lyapunov characteristic numbers and
find chaos in the case of disc-crossing orbits and completely regular motion in
other cases
Instabilities and stickiness in a 3D rotating galactic potential
We study the dynamics in the neighborhood of simple and double unstable
periodic orbits in a rotating 3D autonomous Hamiltonian system of galactic
type. In order to visualize the four dimensional spaces of section we use the
method of color and rotation. We investigate the structure of the invariant
manifolds that we found in the neighborhood of simple and double unstable
periodic orbits in the 4D spaces of section. We consider orbits in the
neighborhood of the families x1v2, belonging to the x1 tree, and the z-axis
(the rotational axis of our system). Close to the transition points from
stability to simple instability, in the neighborhood of the bifurcated simple
unstable x1v2 periodic orbits we encounter the phenomenon of stickiness as the
asymptotic curves of the unstable manifold surround regions of the phase space
occupied by rotational tori existing in the region. For larger energies, away
from the bifurcating point, the consequents of the chaotic orbits form clouds
of points with mixing of color in their 4D representations. In the case of
double instability, close to x1v2 orbits, we find clouds of points in the four
dimensional spaces of section. However, in some cases of double unstable
periodic orbits belonging to the z-axis family we can visualize the associated
unstable eigensurface. Chaotic orbits close to the periodic orbit remain sticky
to this surface for long times (of the order of a Hubble time or more). Among
the orbits we studied we found those close to the double unstable orbits of the
x1v2 family having the largest diffusion speed.Comment: 29pages, 25 figures, accepted for publication in the International
Journal of Bifurcation and Chao
Density hardening plasticity and mechanical aging of silica glass under pressure: A Raman spectroscopic study
In addition of a flow, plastic deformation of structural glasses (in
particular amorphous silica) is characterized by a permanent densification.
Raman spectroscopic estimators are shown to give a full account of the plastic
behavior of silica under pressure. While the permanent densification of silica
has been widely discussed in terms of amorphous-amorphous transition, from a
plasticity point of view, the evolution of the residual densification with the
maximum pressure of a pressure cycle can be discussed as a density hardening
phenomenon. In the framework of such a mechanical aging effect, we propose that
the glass structure could be labelled by the maximum pressure experienced by
the glass and that the saturation of densification could be associated with the
densest packing of tetrahedra only linked by their vertices
The intermediate neutron capture process: IV. Impact of nuclear model and parameter uncertainties
We investigate both the systematic and statistical uncertainties associated
with theoretical nuclear reaction rates of relevance during the i-process and
explore their impact on the i-process elemental production, and subsequently on
the surface enrichment, for a low-mass low-metallicity star during the early
AGB phase. We use the TALYS reaction code (Koning et al. 2023) to estimate both
the model and parameter uncertainties affecting the photon strength function
and the nuclear level densities, hence the radiative neutron capture rates. The
STAREVOL code (Siess et al. 2006) is used to determine the impact of nuclear
uncertainties on the i-process nucleosynthesis in a 1 [Fe/H] = -
2.5 model star during the proton ingestion event in the early AGB phase. A
large nuclear network of 1160 species coherently coupled to the transport
processes is solved to follow the i-process nucleosynthesis. We find that the
non-correlated parameter uncertainties lead the surface abundances
uncertainties of element with to range between 0.5 and 1.0 dex, with
odd- elements displaying higher uncertainties. The correlated model
uncertainties are of the same order of magnitude, and both model and parameter
uncertainties have an important impact on potential observable tracers such as
Eu and La. Both the correlated model and uncorrelated parameter uncertainties
need to be estimated coherently before being propagated to astrophysical
observables through multi-zone stellar evolution models. Many reactions are
found to affect the i-process predictions and will require improved nuclear
models guided by experimental constraints. Priority should be given to the
reactions influencing the observable tracers.Comment: Accepted: October 11, 2023 \\ 14 Pages, 14 Figures, 2 Table
Natural cement and monumental restoration
Natural cement, called "Roman” cement, was invented at the end of the 19th century and played an important role in the development of civil engineering works until the 1860s. More surprisingly, it was also used to restore historic buildings, such as gothic cathedrals. This paper deals with the mineralogy and the durability of natural cement in the particular case of the Bourges Cathedral in France. This study illustrates the interest of this material particularly adapted in stone repair or substitution. Contrary to traditional mortars, the present samples are made of neat cement paste, revealed by the absence of mineral additions as quartz or carbonate sand. Several combined techniques (SEM-EDS, TGA, XRD) were carried out to determine the composition of the hydraulic binder rich in calcium aluminate hydrates. The raw marl at the origin of the cement production contains oxidized pyrites which consist in a potential source of sulphate pollution of the surrounding limestone. The exposition of the cement in urban environment leads to some weathering features as atmospheric sulfation. Finally a petrophysical approach, based on water porosity, capillary sorption and compressive strength, has been performed to demonstrate the durability and the compatibility of natural cement applied as an historical building restoration morta
Characterization at cryogenic temperatures of piezostacks dedicated to fast tuners for SRF cavities
Stellar kinematics in double-barred galaxies: the sigma-hollows
We present SAURON integral-field stellar velocity and velocity dispersion
maps for four double-barred early-type galaxies: NGC2859, NGC3941, NGC4725 and
NGC5850. The presence of the inner bar does not produce major changes in the
line-of-sight velocity, but it appears to have an important effect in the
stellar velocity dispersion maps: we find two sigma-hollows of amplitudes
between 10 and 40 km/s on either side of the center, at the ends of the inner
bars. We have performed numerical simulations to explain these features. Ruling
out other possibilities, we conclude that the sigma-hollows are an effect of
the contrast between two kinematically different components: the high velocity
dispersion of the bulge and the more ordered motion (low velocity dispersion)
of the inner bar.Comment: 5 pages, 2 figures. Accepted for publication in ApJ Letter
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