High-Temperature Processing of Solids Through Solar Nebular Bow Shocks: 3D Radiation Hydrodynamics Simulations with Particles

A fundamental, unsolved problem in Solar System formation is explaining the melting and crystallization of chondrules found in chondritic meteorites. Theoretical models of chondrule melting in nebular shocks has been shown to be consistent with many aspects of thermal histories inferred for chondrules from laboratory experiments; but, the mechanism driving these shocks is unknown. Planetesimals and planetary embryos on eccentric orbits can produce bow shocks as they move supersonically through the disk gas, and are one possible source of chondrule-melting shocks. We investigate chondrule formation in bow shocks around planetoids through 3D radiation hydrodynamics simulations. A new radiation transport algorithm that combines elements of flux-limited diffusion and Monte Carlo methods is used to capture the complexity of radiative transport around bow shocks. An equation of state that includes the rotational, vibrational, and dissociation modes of H$_2$ is also used. Solids are followed directly in the simulations and their thermal histories are recorded. Adiabatic expansion creates rapid cooling of the gas, and tail shocks behind the embryo can cause secondary heating events. Radiative transport is efficient, and bow shocks around planetoids can have luminosities $\sim$few$\times10^{-8}$ L$_{\odot}$. While barred and radial chondrule textures could be produced in the radiative shocks explored here, porphyritic chondrules may only be possible in the adiabatic limit. We present a series of predicted cooling curves that merit investigation in laboratory experiments to determine whether the solids produced by bow shocks are represented in the meteoritic record by chondrules or other solids.Comment: Accepted for publication in ApJ. Images have been resized to conform to arXiv limits, but are all readable upon adjusting the zoom. Changes from v1: Corrected typos discovered in proofs. Most changes are in the appendi

Chemistry in a gravitationally unstable protoplanetary disc

Until now, axisymmetric, alpha-disc models have been adopted for calculations of the chemical composition of protoplanetary discs. While this approach is reasonable for many discs, it is not appropriate when self-gravity is important. In this case, spiral waves and shocks cause temperature and density variations that affect the chemistry. We have adopted a dynamical model of a solar-mass star surrounded by a massive (0.39 Msun), self-gravitating disc, similar to those that may be found around Class 0 and early Class I protostars, in a study of disc chemistry. We find that for each of a number of species, e.g. H2O, adsorption and desorption dominate the changes in the gas-phase fractional abundance; because the desorption rates are very sensitive to temperature, maps of the emissions from such species should reveal the locations of shocks of varying strengths. The gas-phase fractional abundances of some other species, e.g. CS, are also affected by gas-phase reactions, particularly in warm shocked regions. We conclude that the dynamics of massive discs have a strong impact on how they appear when imaged in the emission lines of various molecular species.Comment: 10 figures and 3 tables, accepted for publication in MNRA

Development of detailed prime mover models and distributed generation for an on-board naval power system trainer

2012 Summer.Includes bibliographical references.A power management platform (PMP) has been developed for an electric generation plant on-board a U.S. naval ship. The control hardware and software interface with a Human Machine Interface (HMI) where the sailor can monitor and control the electric plant state. With the implementation of the PMP, there becomes a need to train the sailors how to effectively use the HMI to manage the power plant. A power system trainer was developed with all the physical parts of the power system modeled in software that communicate to the control software, HMI software, and training software. Previous simulation models of the prime movers created in MATLAB® Simulink® (developed at Woodward, Inc. for control code testing purposes) were inadequate to simulate all the signals the control software receives. Therefore, the goal of this research was to increase the accuracy and detail of the existing prime mover models and add detail to the current electrical grid model for use in a power system trainer while maintaining real-time simulation. This thesis provides an overview encompassing techniques used to model various prime movers, auxiliary systems, and electrical power system grids collected through literary research as well as creative adaptation. For the prime movers, a mean value model (MVM) was developed for the diesel engine as well as a thermodynamic based steam turbine model. A heat transfer model was constructed for an AC synchronous electrical generator with a Totally Enclosed Air to Water Cooled (TEWAC) cooling arrangement. A modular heat exchanger model was implemented and the electrical grid model was expanded to cover all of the electrical elements. Models now dynamically simulate all the hardware signals in software and the training simulation executes in real-time

Sequenceable Sequence-Defined Oligourethanes as a Medium for Information Storage

Physical data storage is an increasingly active field of research. Potential storage media such as DNA or RNA can encode sufficient information to be viable, but they are not stable in the long term. A potential alternative to these heavily studied polymers presented itself in plastics, especially the linear polymers of oligourethanes. These plastics demonstrate both the information density and stability necessary for long-term storage of encoded data, so long as individual units can be decoded and read at a later time. Previous work determined appropriate sequencing conditions for stepwise degradation of the oligourethanes, allowing for the reverse engineering of the sequence-defined polymer. With this proof of concept of information storage, focus was shifted toward solid phase synthesis, labeling, and sequencing of polyurethanes with diverse monomers bearing variable functionalities, to assess stability in the degradation conditions. Interest in the inclusion of Tunable Orthogonal Reversible Covalent (TORC) bonds served as the impetus for the synthesis of a Lysine-based monomer capable of “click” reactions. This monomer was successfully synthesized, integrated into a sequence-defined oligourethane, and modified with a TORC functionality using click chemistry. Moving forward, the project will focus on the sequencing of sequence-defined oligourethanes containing this and other monomers bearing variable functionalities, as well as investigating the capability of TORC-functionalized oligourethanes to form higher-ordered structures akin to DNA.Chemistr

Magnetic Fields Recorded by Chondrules Formed in Nebular Shocks

Recent laboratory efforts (Fu et al., 2014) have constrained the remanent magnetizations of chondrules and the magnetic field strengths at which the chondrules were exposed to as they cooled below their Curie points. An outstanding question is whether the inferred paleofields represent the background magnetic field of the solar nebula or were unique to the chondrule-forming environment. We investigate the amplification of the magnetic field above background values for two proposed chondrule formation mechanisms, large-scale nebular shocks and planetary bow shocks. Behind large-scale shocks, the magnetic field parallel to the shock front is amplified by factors $\sim 10-30$, regardless of the magnetic diffusivity. Therefore, chondrules melted in these shocks probably recorded an amplified magnetic field. Behind planetary bow shocks, the field amplification is sensitive to the magnetic diffusivity. We compute the gas properties behind a bow shock around a 3000 km-radius planetary embryo, with and without atmospheres, using hydrodynamics models. We calculate the ionization state of the hot, shocked gas, including thermionic emission from dust, and thermal ionization of gas-phase potassium atoms, and the magnetic diffusivity due to Ohmic dissipation and ambipolar diffusion. We find that the diffusivity is sufficiently large that magnetic fields have already relaxed to background values in the shock downstream where chondrules acquire magnetizations, and that these locations are sufficiently far from the planetary embryos that chondrules should not have recorded a significant putative dynamo field generated on these bodies. We conclude that, if melted in planetary bow shocks, chondrules probably recorded the background nebular field.Comment: 17 pages, 11 figures, accepted for publication in Ap

Interactions Between Moderate- and Long-Period Giant Planets: Scattering Experiments for Systems in Isolation and with Stellar Flybys

The chance that a planetary system will interact with another member of its host star's nascent cluster would be greatly increased if gas giant planets form in situ on wide orbits. In this paper, we explore the outcomes of planet-planet scattering for a distribution of multiplanet systems that all have one of the planets on an initial orbit of 100 AU. The scattering experiments are run with and without stellar flybys. We convolve the outcomes with distributions for protoplanetary disk and stellar cluster sizes to generalize the results where possible. We find that the frequencies of large mutual inclinations and high eccentricities are sensitive to the number of planets in a system, but not strongly to stellar flybys. However, flybys do play a role in changing the low and moderate portions of the mutual inclination distributions, and erase dynamically cold initial conditions on average. Wide-orbit planets can be mixed throughout the planetary system, and in some cases, can potentially become hot Jupiters, which we demonstrate using scattering experiments that include a tidal damping model. If planets form on wide orbits in situ, then there will be discernible differences in the proper motion distributions of a sample of wide-orbit planets compared with a pure scattering formation mechanism. Stellar flybys can enhance the frequency of ejections in planetary systems, but auto-ionization is likely to remain the dominant source of free-floating planets.Comment: Accepted for publication by Ap

On shocks driven by high-mass planets in radiatively inefficient disks. I. Two-dimensional global disk simulations

Recent observations of gaps and non-axisymmetric features in the dust distributions of transition disks have been interpreted as evidence of embedded massive protoplanets. However, comparing the predictions of planet-disk interaction models to the observed features has shown far from perfect agreement. This may be due to the strong approximations used for the predictions. For example, spiral arm fitting typically uses results that are based on low-mass planets in an isothermal gas. In this work, we describe two-dimensional, global, hydrodynamical simulations of disks with embedded protoplanets, with and without the assumption of local isothermality, for a range of planet-to-star mass ratios 1-10 M_jup for a 1 M_sun star. We use the Pencil Code in polar coordinates for our models. We find that the inner and outer spiral wakes of massive protoplanets (M>5 M_jup) produce significant shock heating that can trigger buoyant instabilities. These drive sustained turbulence throughout the disk when they occur. The strength of this effect depends strongly on the mass of the planet and the thermal relaxation timescale; for a 10 M_jup planet embedded in a thin, purely adiabatic disk, the spirals, gaps, and vortices typically associated with planet-disk interactions are disrupted. We find that the effect is only weakly dependent on the initial radial temperature profile. The spirals that form in disks heated by the effects we have described may fit the spiral structures observed in transition disks better than the spirals predicted by linear isothermal theory.Comment: 10 pages, 8 figures. ApJ, accepte