4,224 research outputs found
Capturing Trojans and Irregular Satellites - the key required to unlock planetary migration
It is now accepted that the Solar system's youth was a dynamic and chaotic
time. The giant planets migrated significant distances to reach their current
locations, and evidence of that migration's influence on the Solar system
abounds. That migration's pace, and the distance over which it occurred, is
still heavily debated. Some models feature systems in which the giant planets
were initially in an extremely compact configuration, in which Uranus and
Neptune are chaotically scattered into the outer Solar system. Others feature
architectures that were initially more relaxed, and smoother, more sedate
migration. To determine which of these scenarios best represents the formation
of our Solar system, we must turn to the structure of the system's small body
populations, in which the scars of that migration are still clearly visible.
We present the first results of a program investigating the effect of giant
planet migration on the reservoirs of small bodies that existed at that time.
As the planets migrate, they stir these reservoirs, scattering vast numbers of
small bodies onto dynamically unstable orbits in the outer Solar system. The
great majority of those bodies are rapidly removed from the system, through
collisions and ejections, but a small number become captured as planetary
Trojans or irregular satellites. Others are driven by the migration, leading to
a significant sculpting of the asteroid belt and trans-Neptunian region.
The capture and retention efficiencies to these stable reservoirs depend on
the particular migration scenario used. Advocates of chaotic migration from an
initially compact scenario argue that smoother, more sedate migration cannot
explain the observed populations of Trojans and irregular satellites. Our
results draw a strikingly different picture, revealing that such smooth
migration is perfectly capable of reproducing the observed populations.Comment: 13 pages, accepted for publication in the peer-reviewed proceedings
of the 12th annual Australian Space Science Conferenc
Mediation, arbitration and negotiation
We compare three common dispute resolution processes { negotiation, mediation, and arbitration { in the framework of Crawford and Sobel (1982). Under negotiation, the two parties engage in (possibly arbitrarily long) face-to-face cheap talk. Under mediation, the parties communicate with a neutral third party who makes a non-binding recommendation. Under arbitration, the two parties commit
to conform to the third party recommendation. We characterize and compare the optimal mediation and arbitration procedures. Both mediators and arbitrators should optimally filter information, but mediators should also add noise to it. We find that unmediated negotiation performs as well as mediation if and only if the degree of
conflict between the parties is low
Studies of thermionic materials for space power applications informal monthly report, sep. 1 - sep. 30, 1963
Thermionic materials for space power application - uranium carbide-zirconium carbide fuels and tungsten claddin
On collisional capture rates of irregular satellites around the gas-giant planets and the minimum mass of the solar nebula
We investigated the probability that an inelastic collision of planetesimals
within the Hill sphere of the Jovian planets could explain the presence and
orbits of observed irregular satellites. Capture of satellites via this
mechanism is highly dependent on not only the mass of the protoplanetary disk,
but also the shape of the planetesimal size distribution. We performed 2000
simulations for integrated time intervals Myr and found that, given
the currently accepted value for the minimum mass solar nebula and planetesimal
number density based upon the \citet{Nesvorny2003} and \citet{Charnoz2003} size
distribution , the collision rates for the different
Jovian planets range between and \gtrsim 170 \, \Myr^{-1} for
objects with radii, 1 \, \km \le r \le 10 \, \km. Additionally, we found that
the probability that these collisions remove enough orbital energy to yield a
bound orbit was and had very little dependence on the
relative size of the planetesimals. Of these collisions, the collision energy
between two objects was times the gravitational binding energy
for objects with radii km. We find that, capturing irregular
satellites via collisions between unbound objects can only account for of the observed population, hence can this not be the sole method of
producing irregular satellites.Comment: 11 pages 4 figures 1 table; This replaces a prior submission, which
contained some minor contradictions within the text accepted by MNRAS in
pres
Continuous spin reorientation in antiferromagnetic films
We study anisotropic antiferromagnetic one-layer films with dipolar and
nearest-neighbor exchange interactions. We obtain a unified phase diagram as a
function of effective uniaxial D_e and quadrupolar C anisotropy constants. We
study in some detail how spins reorient continuously below a temperature T_s as
T and D_e vary.Comment: 3 LaTeX pages, 3 eps figures. Submitted to JMMM on 25 May 2006.
Accepted on 21 July 200
Nature versus Nurture: The curved spine of the galaxy cluster X-ray luminosity -- temperature relation
The physical processes that define the spine of the galaxy cluster X-ray
luminosity -- temperature (L-T) relation are investigated using a large
hydrodynamical simulation of the Universe. This simulation models the same
volume and phases as the Millennium Simulation and has a linear extent of 500
h^{-1} Mpc. We demonstrate that mergers typically boost a cluster along but
also slightly below the L-T relation. Due to this boost we expect that all of
the very brightest clusters will be near the peak of a merger. Objects from
near the top of the L-T relation tend to have assembled much of their mass
earlier than an average halo of similar final mass. Conversely, objects from
the bottom of the relation are often experiencing an ongoing or recent merger.Comment: 8 pages, 7 figures, submitted to MNRA
Spin-glass model with partially annealed asymmetric bonds
We have considered the two-spin interaction spherical spin-glass model with
asymmetric bonds (coupling constants). Besides the usual interactions between
spins and bonds and between the spins and a thermostat with temperature
there is also an additional factor: the bonds are not assumed
random {\it a priori} but interact with some other thermostat at the
temperature . We show that when the bonds are frozen with respect to the
spins a first order phase transition to a spin-glass phase occurs, and the
temperature of this transition tends to zero if is large. Our analytical
results show that a spin-glass phase can exist in mean-field models with
nonrelaxational dynamics.Comment: 10 pages, late
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