1,083 research outputs found
Planet Signatures in Collisionally Active Debris Discs: scattered light images
Planet perturbations are often invoked as a potential explanation for many
spatial structures that have been imaged in debris discs. So far this issue has
been mostly investigated with collisionless N-body numerical models. We
numerically investigate how the coupled effect of collisions and radiation
pressure can affect the formation and survival of radial and azimutal
structures in a disc perturbed by a planet. We consider two set-ups: a planet
embedded within an extended disc and a planet exterior to an inner debris ring.
We use the DyCoSS code of Thebault(2012) and derive synthetic images of the
system in scattered light. The planet's mass and orbit, as well as the disc's
collisional activity are explored as free parameters.
We find that collisions always significantly damp planet-induced structures.
For the case of an embedded planet, the planet's signature, mostly a density
gap around its radial position, should remain detectable in head-on images if
M_planet > M_Saturn. If the system is seen edge-on, however, inferring the
presence of the planet is much more difficult, although some planet-induced
signatures might be observable under favourable conditions.
For the inner-ring/external-planet case, planetary perturbations cannot
prevent collision-produced small fragments from populating the regions beyond
the ring: The radial luminosity profile exterior to the ring is close to the
one it should have in the absence of the planet. However, a Jovian planet on a
circular orbit leaves precessing azimutal structures that can be used to
indirectly infer its presence. For a planet on an eccentric orbit, the ring is
elliptic and the pericentre glow effect is visible despite of collisions and
radiation pressure, but detecting such features in real discs is not an
unambiguous indicator of the presence of an outer planet.Comment: Accepted for Publication in A&A (NOTE: Abridged abstract and
(very)LowRes Figures. Better version, with High Res figures and full abstract
can be found at http://lesia.obspm.fr/perso/philippe-thebault/planpapph.pdf
Storage ring measurement of the C IV recombination rate coefficient
The low energy C IV dielectronic recombination (DR) rate coefficient
associated with 2s-2p Delta n=0 excitations of this lithiumlike ion has been
measured with high energy-resolution at the heavy-ion storage-ring TSR of the
Max-Planck-Institut fuer Kernphysik in Heidelberg, Germany. The experimental
procedure and especially the experimental detection probabilities for the high
Rydberg states produced by the recombination of this ion are discussed in
detail. From the experimental data a Maxwellian plasma rate coefficient is
derived with 15% systematic uncertainty and parameterized for ready use in
plasma modeling codes. Our experimental result especially benchmarks the plasma
rate coefficient below 10000 K where DR occurs predominantly via C III (1s2 2p
4l) intermediate states and where existing theories differ by orders of
magnitude. Furthermore, we find that the total dielectronic and radiative C IV
recombination can be represented by the incoherent sum of our DR rate
coefficient and the RR rate coefficient of Pequignot et al. (1991, Astron.
Astrophys., 251, 680).Comment: 9 figures, 2 table
Hindered Coulomb explosion of embedded Na clusters -- stopping, shape dynamics and energy transport
We investigate the dynamical evolution of a Na cluster embedded in Ar
matrices of various sizes from N=30 to 1048. The system is excited by an
intense short laser pulse leading to high ionization stages. We analyze the
subsequent highly non-linear motion of cluster and Ar environment in terms of
trajectories, shapes, and energy flow. The most prominent effects are:
temporary stabilization of high charge states for several ps, sudden stopping
of the Coulomb explosion of the embedded Na clusters associated with an
extremely fast energy transfer to the Ar matrix, fast distribution of energy
throughout the Ar layers by a sound wave. Other ionic-atomic transfer and
relaxation processes proceed at slower scale of few ps. The electron cloud is
almost thermally decoupled from ions and thermalizes far beyond the ps scale.Comment: 12 pages, 10 figures, accepted in Euro. Phys. J.
Classical Monopoles Configuration Of The Su (2) Yang-Mills-Higgs Field Theory.
Teori medan SU(2) Yang-Mills-Higgs telah ditunjukkan bahawa ia mempunyai penyelesaian topologi penting yang mewakili ekakutub magnet dan multiekakutub.
The SU(2) Yang-Mills-Higgs field theory has been shown to possess important topological solutions which represents magnetic monopoles and multimonopole
Integrability and Disorder in Mesoscopic Systems: Application to Orbital Magnetism
We present a semiclassical theory of weak disorder effects in small
structures and apply it to the magnetic response of non-interacting electrons
confined in integrable geometries. We discuss the various averaging procedures
describing different experimental situations in terms of one- and two-particle
Green functions. We demonstrate that the anomalously large zero-field
susceptibility characteristic of clean integrable structures is only weakly
suppressed by disorder. This damping depends on the ratio of the typical size
of the structure with the two characteristic length scales describing the
disorder (elastic mean-free-path and correlation length of the potential) in a
power-law form for the experimentally relevant parameter region. We establish
the comparison with the available experimental data and we extend the study of
the interplay between disorder and integrability to finite magnetic fields.Comment: 38 pages, Latex, 7 Postscript figures, 1 table, to appear in Jour.
Math. Physics 199
Zigzag Filamentary Theory of Broken Symmetry of Neutron and Infrared Vibronic Spectra of YBa2Cu3O(6+x)
Filamentary high-temperature superconductivity (HTSC) theory differs
fundamentally from continuous HTSC theories because it emphasizes
self-organized, discrete dopant networks and does not make the effective medium
approximation (EMA). Analysis of neutron and infrared (especially with c-axis
polarization) vibrational spectra, primarily for YBa2Cu3O(6+x), within the
filamentary framework, shows that the observed vibronic anomalies near 400 cm-1
(50 meV) are associated with curvilinear filamentary paths. these paths pass
through cuprate chains and planes, as well as resonant tunneling centers in the
BaO layers. The analysis and the data confirm earlier filamentary structural
models containing ferroelastic domains of 3-4 nm in the CuO2 planes; it is
these nanodomains that are responsible for the discrete glassy nature of both
electronic and vibronic properties. Chemical trends in vibronic energies and
oscillator strengths, both for neutron and photon scattering, that were
anomalous in continuum models, are readily explained by the filamentary model.Comment: 45 pages, 17 figures, PD
Mechanics of motility initiation and motility arrest in crawling cells
Motility initiation in crawling cells requires transformation of a symmetric
state into a polarized state. In contrast, motility arrest is associated with
re-symmetrization of the internal configuration of a cell. Experiments on
keratocytes suggest that polarization is triggered by the increased
contractility of motor proteins but the conditions of re-symmetrization remain
unknown. In this paper we show that if adhesion with the extra-cellular
substrate is sufficiently low, the progressive intensification of motor-induced
contraction may be responsible for both transitions: from static (symmetric) to
motile (polarized) at a lower contractility threshold and from motile
(polarized) back to static (symmetric) at a higher contractility threshold. Our
model of lamellipodial cell motility is based on a 1D projection of the complex
intra-cellular dynamics on the direction of locomotion. In the interest of
analytical transparency we also neglect active protrusion and view adhesion as
passive. Despite the unavoidable oversimplifications associated with these
assumptions, the model reproduces quantitatively the motility initiation
pattern in fish keratocytes and reveals a crucial role played in cell motility
by the nonlocal feedback between the mechanics and the transport of active
agents. A prediction of the model that a crawling cell can stop and
re-symmetrize when contractility increases sufficiently far beyond the motility
initiation threshold still awaits experimental verification
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