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 $\sim 2$ 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 $dN \sim D^{-3.5} dD$, the collision rates for the different Jovian planets range between $\sim 0.6$ 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 $\lesssim 10^{-5}$ and had very little dependence on the relative size of the planetesimals. Of these collisions, the collision energy between two objects was $\gtrsim 10^3$ times the gravitational binding energy for objects with radii $\sim 100$ km. We find that, capturing irregular satellites via collisions between unbound objects can only account for $\sim 0.1$ 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 $T_{\sigma}$ there is also an additional factor: the bonds are not assumed random {\it a priori} but interact with some other thermostat at the temperature $T_{J}$. 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 $T_J$ is large. Our analytical results show that a spin-glass phase can exist in mean-field models with nonrelaxational dynamics.Comment: 10 pages, late