Browsing by Subject "numerical"
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Item Photophoresis Boosts Giant Planet Formation(2013-07) Teiser, J.; Dodson-Robinson, S. E.; Dodson-Robinson, S. E.In the core accretion model of giant planet formation, a solid protoplanetary core begins to accrete gas directly from the nebula when its mass reaches similar to 5 M-circle plus. The protoplanet has at most a few million years to reach runaway gas accretion, as young stars lose their gas disks after 10 million years at the latest. Yet gas accretion also brings small dust grains entrained in the gas into the planetary atmosphere. Dust accretion creates an optically thick protoplanetary atmosphere that cannot efficiently radiate away the kinetic energy deposited by incoming planetesimals. A dust-rich atmosphere severely slows down atmospheric cooling, contraction, and inflow of new gas, in contradiction to the observed timescales of planet formation. Here we show that photophoresis is a strong mechanism for pushing dust out of the planetary atmosphere due to the momentum exchange between gas and dust grains. The thermal radiation from the heated inner atmosphere and core is sufficient to levitate dust grains and to push them outward. Photophoresis can significantly accelerate the formation of giant planets.Item Simulating Cosmic Reionization And The Radiation Backgrounds From The Epoch Of Reionization(2012) Shapiro, P. R.; Iliev, I. T.; Mellema, G.; Ahn, K.; Mao, Y.; Friedrich, M.; Datta, K.; Park, H.; Komatsu, E.; Fernandez, E.; Koda, J.; Bovill, M.; Pen, U. L.; Shapiro, Paul R.; Mao, Yi; Park, Hyunbae; Koda, Jun; Bovill, MiaLarge-scale reionization simulations are described which combine the results of cosmological N-body simulations that model the evolving density and velocity fields and identify the galactic halo sources, with ray-tracing radiative transfer calculations which model the nonequilibrium ionization of the intergalactic medium. These simulations have been used to predict some of the signature effects of reionization on cosmic radiation backgrounds, including the CMB, near-IR, and redshifted 21cm backgrounds. We summarize some of our recent progress in this work, and address the question of whether observations of such signature effects can be used to distinguish the relative contributions of galaxies of different masses to reionization.