2,199 research outputs found
Dynamics of Enceladus and Dione inside the 2:1 Mean-Motion Resonance under Tidal Dissipation
In a previous work (Callegari and Yokoyama 2007, Celest. Mech. Dyn. Astr.
vol. 98), the main features of the motion of the pair Enceladus-Dione were
analyzed in the frozen regime, i.e., without considering the tidal evolution.
Here, the results of a great deal of numerical simulations of a pair of
satellites similar to Enceladus and Dione crossing the 2:1 mean-motion
resonance are shown. The resonance crossing is modeled with a linear tidal
theory, considering a two-degrees-of-freedom model written in the framework of
the general three-body planar problem. The main regimes of motion of the system
during the passage through resonance are studied in detail. We discuss our
results comparing them with classical scenarios of tidal evolution of the
system. We show new scenarios of evolution of the Enceladus-Dione system
through resonance not shown in previous approaches of the problem.Comment: 36 pages, 12 figures. Accepted in Celestial Mechanics and Dynamical
Astronom
Multiple plasmon resonances in naturally-occurring multiwall nanotubes: infrared spectra of chrysotile asbestos
Chrysotile asbestos is formed by densely packed bundles of multiwall hollow
nanotubes. Each wall in the nanotubes is a cylindrically wrapped layer of . We show by experiment and theory that the infrared spectrum
of chrysotile presents multiple plasmon resonances in the Si-O stretching
bands. These collective charge excitations are universal features of the
nanotubes that are obtained by cylindrically wrapping an anisotropic material.
The multiple plasmons can be observed if the width of the resonances is
sufficiently small as in chrysotile.Comment: 4 pages, 5 figures. Revtex4 compuscript. Misprint in Eq.(6) correcte
Low frequency Raman studies of multi-wall carbon nanotubes: experiments and theory
In this paper, we investigate the low frequency Raman spectra of multi-wall
carbon nanotubes (MWNT) prepared by the electric arc method. Low frequency
Raman modes are unambiguously identified on purified samples thanks to the
small internal diameter of the MWNT. We propose a model to describe these
modes. They originate from the radial breathing vibrations of the individual
walls coupled through the Van der Waals interaction between adjacent concentric
walls. The intensity of the modes is described in the framework of bond
polarization theory. Using this model and the structural characteristics of the
nanotubes obtained from transmission electron microscopy allows to simulate the
experimental low frequency Raman spectra with an excellent agreement. It
suggests that Raman spectroscopy can be as useful regarding the
characterization of MWNT as it is in the case of single-wall nanotubes.Comment: 4 pages, 2 eps fig., 2 jpeg fig., RevTex, submitted to Phys. Rev.
Mass corrections in decay and the role of distribution amplitudes
We consider mass correction effects on the polar angular distribution of a
baryon--antibaryon pair created in the chain decay process , generalizing a previous analysis of Carimalo. We show the
relevance of the features of the baryon distribution amplitudes and estimate
the electromagnetic corrections to the QCD results.Comment: 26 pages + 3 figures, REVTEX 3.0, figures appended as uuencoded,
tar-compressed postscript fil
The possible - mixing in QCD sum rules
We calculate the on-shell - mixing parameter with
the method of QCD sum rule. Our result is MeV. The electromagnetic interaction is not included
Ghost-busting: Patch occupancy and habitat preferences of Ocyale ghost (Araneae: Lycosidae), a single site endemic in north-western Madagascar
Microendemic species are of great conservation concern due to their vulnerability to stochastic events and environmental change. Therefore, understanding the basic ecology of such organisms is integral to future efforts to conserve them. Here, we present the first ecological study of the only known population of Ocyale ghost (Lycosidae) – the single species within this genus in Madagascar – located at a small lake shore in the north-west of the island. We aimed to reveal spatial patterns of microhabitat selection and patch occupancy in relation to substrate patch covariates, including distance to lake edge, topography, and sand coverage. We found microhabitat selection to be strong in our occupancy models, with plots closer to the lake edge and with a higher proportion of sand showing the highest estimated occupancy. We suggest decreases in prey availability and changes in the physical characteristics of the substrate in relation to the distance from lake shore and sand availability (important for burrowing and temperature regulation), respectively, as potential factors behind occupancy. We discuss our findings in the context of the proportional underrepresentation of invertebrates in conservation research, which threatens the persistence of endemic and microendemic invertebrates in the face of significant global and local environmental change
The role of chaotic resonances in the solar system
Our understanding of the Solar System has been revolutionized over the past
decade by the finding that the orbits of the planets are inherently chaotic. In
extreme cases, chaotic motions can change the relative positions of the planets
around stars, and even eject a planet from a system. Moreover, the spin axis of
a planet-Earth's spin axis regulates our seasons-may evolve chaotically, with
adverse effects on the climates of otherwise biologically interesting planets.
Some of the recently discovered extrasolar planetary systems contain multiple
planets, and it is likely that some of these are chaotic as well.Comment: 28 pages, 9 figure
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