1,083 research outputs found

    Planet Signatures in Collisionally Active Debris Discs: scattered light images

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    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

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    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

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    We investigate the dynamical evolution of a Na8_8 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 Na8_8 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.

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    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

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    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)

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    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

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    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

    Multiscale modeling and deep learning: reverse-mapping of condensed-phase molecular structures

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