23,311 research outputs found
Coorbital Satellites of Saturn: Congenital Formation
Saturn is the only known planet to have coorbital satellite systems. In the
present work we studied the process of mass accretion as a possible mechanism
for coorbital satellites formation. The system considered is composed of
Saturn, a proto-satellite and a cloud of planetesimals distributed in the
coorbital region around a triangular Lagrangian point. The adopted relative
mass for the proto-satellite was 10^-6 of Saturn's mass and for each
planetesimal of the cloud three cases of relative mass were considered, 10^-14,
10^-13 and 10^-12 masses of Saturn. In the simulations each cloud of
planetesimal was composed of 10^3, 5 x 10^3 or 10^4 planetesimals. The results
of the simulations show the formation of coorbital satellites with relative
masses of the same order of those found in the saturnian system (10^-13 -
10^-9). Most of them present horseshoe type orbits, but a significant part is
in tadpole orbit around L_4 or L_5. Therefore, the results indicate that this
is a plausible mechanism for the formation of coorbital satellites.Comment: 10 pages, 9 figures, 4 table
Cycles of construing in radicalization and deradicalization: a study of Salafist Muslims.
© Taylor & Francis Group, LLC.This article explores radicalization and deradicalization by considering the experiences of six young Tunisian people who had become Salafist Muslims. Their responses to narrative interviews and repertory grid technique are considered from a personal construct perspective, revealing processes of construing and reconstruing, as well as relevant aspects of the structure and content of their construct systems. In two cases, their journeys involved not only radicalization but self-deradicalization, and their experiences are drawn on to consider implications for deradicalization.Peer reviewedFinal Accepted Versio
Stable retrograde orbits around the triple system 2001 SN263
The NEA 2001 SN263 is the target of the ASTER MISSION - First Brazilian Deep
Space Mission. Araujo et al. (2012), characterized the stable regions around
the components of the triple system for the planar and prograde cases. Knowing
that the retrograde orbits are expected to be more stable, here we present a
complementary study. We now considered particles orbiting the components of the
system, in the internal and external regions, with relative inclinations
between , i.e., particles with retrograde
orbits. Our goal is to characterize the stable regions of the system for
retrograde orbits, and then detach a preferred region to place the space probe.
For a space mission, the most interesting regions would be those that are
unstable for the prograde cases, but stable for the retrograde cases. Such
configuration provide a stable region to place the mission probe with a
relative retrograde orbit, and, at the same time, guarantees a region free of
debris since they are expected to have prograde orbits. We found that in fact
the internal and external stable regions significantly increase when compared
to the prograde case. For particles with and , we found
that nearly the whole region around Alpha and Beta remain stable. We then
identified three internal regions and one external region that are very
interesting to place the space probe. We present the stable regions found for
the retrograde case and a discussion on those preferred regions. We also
discuss the effects of resonances of the particles with Beta and Gamma, and the
role of the Kozai mechanism in this scenario. These results help us understand
and characterize the stability of the triple system 2001 SN263 when retrograde
orbits are considered, and provide important parameters to the design of the
ASTER mission.Comment: 11 pages, 8 figures. Accepted for publication in MNRAS - 2015 March
1
Terrestrial Planet Formation in a protoplanetary disk with a local mass depletion: A successful scenario for the formation of Mars
Models of terrestrial planet formation for our solar system have been
successful in producing planets with masses and orbits similar to those of
Venus and Earth. However, these models have generally failed to produce
Mars-sized objects around 1.5 AU. The body that is usually formed around Mars'
semimajor axis is, in general, much more massive than Mars. Only when Jupiter
and Saturn are assumed to have initially very eccentric orbits (e 0.1),
which seems fairly unlikely for the solar system, or alternately, if the
protoplanetary disk is truncated at 1.0 AU, simulations have been able to
produce Mars-like bodies in the correct location. In this paper, we examine an
alternative scenario for the formation of Mars in which a local depletion in
the density of the protosolar nebula results in a non-uniform formation of
planetary embryos and ultimately the formation of Mars-sized planets around 1.5
AU. We have carried out extensive numerical simulations of the formation of
terrestrial planets in such a disk for different scales of the local density
depletion, and for different orbital configurations of the giant planets. Our
simulations point to the possibility of the formation of Mars-sized bodies
around 1.5 AU, specifically when the scale of the disk local mass-depletion is
moderately high (50-75%) and Jupiter and Saturn are initially in their current
orbits. In these systems, Mars-analogs are formed from the protoplanetary
materials that originate in the regions of disk interior or exterior to the
local mass-depletion. Results also indicate that Earth-sized planets can form
around 1 AU with a substantial amount of water accreted via primitive
water-rich planetesimals and planetary embryos. We present the results of our
study and discuss their implications for the formation of terrestrial planets
in our solar system.Comment: Accepted for publication in The Astrophysical Journa
Unusual hyperfine interaction of Dirac electrons and NMR spectroscopy in graphene
Theory of nuclear magnetic resonance (NMR) in graphene is presented. The
canonical form of the electron-nucleus hyperfine interaction is strongly
modified by the linear electronic dispersion. The NMR shift and spin-lattice
relaxation time are calculated as function of temperature, chemical potential,
and magnetic field and three distinct regimes are identified: Fermi-,
Dirac-gas, and extreme quantum limit behaviors. A critical spectrometer
assessment shows that NMR is within reach for fully 13C enriched graphene of
reasonable size.Comment: 5 pages, 3 figure
A Compound model for the origin of Earth's water
One of the most important subjects of debate in the formation of the solar
system is the origin of Earth's water. Comets have long been considered as the
most likely source of the delivery of water to Earth. However, elemental and
isotopic arguments suggest a very small contribution from these objects. Other
sources have also been proposed, among which, local adsorption of water vapor
onto dust grains in the primordial nebula and delivery through planetesimals
and planetary embryos have become more prominent. However, no sole source of
water provides a satisfactory explanation for Earth's water as a whole. In view
of that, using numerical simulations, we have developed a compound model
incorporating both the principal endogenous and exogenous theories, and
investigating their implications for terrestrial planet formation and
water-delivery. Comets are also considered in the final analysis, as it is
likely that at least some of Earth's water has cometary origin. We analyze our
results comparing two different water distribution models, and complement our
study using D/H ratio, finding possible relative contributions from each
source, focusing on planets formed in the habitable zone. We find that the
compound model play an important role by showing more advantage in the amount
and time of water-delivery in Earth-like planets.Comment: Accepted for publication in The Astrophysical Journa
Localization and its consequences for quantum walk algorithms and quantum communication
The exponential speed-up of quantum walks on certain graphs, relative to
classical particles diffusing on the same graph, is a striking observation. It
has suggested the possibility of new fast quantum algorithms. We point out here
that quantum mechanics can also lead, through the phenomenon of localization,
to exponential suppression of motion on these graphs (even in the absence of
decoherence). In fact, for physical embodiments of graphs, this will be the
generic behaviour. It also has implications for proposals for using spin
networks, including spin chains, as quantum communication channels.Comment: 4 pages, 1 eps figure. Updated references and cosmetic changes for v
- …