Basis Enrichment and Solid-Fluid Coupling for Model-Reduced Fluid Simulation

We present several enhancements to model-reduced fluid simulation that allow improved simulation bases and twoway solid-fluid coupling. Specifically, we present a basis enrichment scheme that allows us to combine data driven or artistically derived bases with more general analytic bases derived from Laplacian Eigenfunctions. We handle two-way solid-fluid coupling in a time-splitting fashion— we alternately timestep the fluid and rigid body simulators, while taking into account the effects of the fluid on the rigid bodies and vice versa. We employ the vortex panel method to handle solid-fluid coupling and use dynamic pressure to compute the effect of the fluid on rigid bodies

Dust capture and long-lived density enhancements triggered by vortices in 2D protoplanetary disks

We study dust capture by vortices and its long-term consequences in global two-fluid inviscid disk simulations using a new polar grid code RoSSBi. We perform the longest integrations so far, several hundred disk orbits, at the highest resolution attainable in global simulations of disks with dust, namely 2048x4096 grid points. This allows to study the dust evolution well beyond vortex dissipation. We vary a wide range of parameters, most notably the dust-to-gas ratio in the initial setup varies in the range $10^{-3}$ to $0.1$. Irrespective of the initial dust-to-gas ratio we find rapid concentration of the dust inside vortices, reaching dust-to-gas ratios of order unity inside the vortex. We present an analytical model that describes very well the dust capture process inside vortices, finding consistent results for all dust-to-gas ratios. A vortex streaming instability develops which causes invariably vortex destruction. After vortex dissipation large-scale dust-rings encompassing a disk annulus form in most cases, which sustain very high dust concentration, approaching ratios of order unity. The rings are long lived lasting as long as the duration of the simulations. They also develop a streaming instability, which manifests itself in eddies at various scales within which the dust forms compact high density clumps. Such clumps would be unstable to gravitational collapse in absence of strong dissipation by viscous forces. When vortices are particularly long lived, rings do not form but dust clumps inside vortices become then long lived features and would likely undergo collapse by gravitational instability. Rings encompass almost an Earth mass of solid material, while even larger masses of dust do accumulate inside vortices in the earlier stage. We argue that rapid planetesimal formation would occur in the dust clumps inside the vortices as well as in the post-vortex ring.Comment: Preprint version, submitted to the Astrophysical Journal. Due to size constraints on ArXiv, some plots are at low resolution JPEG

Numerical simulation of the effect of pellet injection on ELMs

We report on numerical simulation studies of the dynamical behavior of edge localized modes (ELMs) under the influence of repetitive injection of pellets. In our nonlinear 2-fluid model the ELMs are excited by introducing a particle source in the confinement region and a particle sink in the edge region. The injection of pellets is simulated by periodically raising the edge density in a pulsed manner. We find that when the edge density is raised to twice the normal edge density with a duty cycle (on time:off time) of 1:2, the ELMs are generated on an average at a faster rate and with reduced amplitudes. These changes lead to significant improvements in the plasma beta indicative of an improvement in the energy confinement due to pellet injection. Concurrently, the plasma density and temperature profiles also get significantly modified. A comparative study is made of the nature of ELM dynamics for different magnitudes of edge density enhancements. We also discuss the relative impact on ELMs from resonant magnetic perturbations (RMPs) compared to pellet injection in terms of changes in the plasma temperature, density, location of the ELMs and the nonlinear spectral transfer of energies

Consequences of a Change in the Galactic Environment of the Sun

The interaction of the heliosphere with interstellar clouds has attracted interest since the late 1920's, both with a view to explaining apparent quasi-periodic climate "catastrophes" as well as periodic mass extinctions. Until recently, however, models describing the solar wind - local interstellar medium (LISM) interaction self-consistently had not been developed. Here, we describe the results of a two-dimensional (2D) simulation of the interaction between the heliosphere and an interstellar cloud with the same properties as currently, except that the neutral H density is increased from the present value of n(H) ~ 0.2 cm^-3 to 10 cm^-3. The mutual interaction of interstellar neutral hydrogen and plasma is included. The heliospheric cavity is reduced considerably in size (approximately 10 - 14 AU to the termination shock in the upstream direction) and is highly dynamical. The interplanetary environment at the orbit of the Earth changes markedly, with the density of interstellar H increasing to ~2 cm^-3. The termination shock itself experiences periods where it disappears, reforms and disappears again. Considerable mixing of the shocked solar wind and LISM occurs due to Rayleigh-Taylor-like instabilities at the nose, driven by ion-neutral friction. Implications for two anomalously high concentrations of 10Be found in Antarctic ice cores 33 kya and 60 kya, and the absence of prior similar events, are discussed in terms of density enhancements in the surrounding interstellar cloud. The calculation presented here supports past speculation that the galactic environment of the Sun moderates the interplanetary environment at the orbit of the Earth, and possibly also the terrestrial climate.Comment: 23 pages, 2 color plates (jpg), 3 figures (eps

Numerical modeling tools for chemical vapor deposition

Development of general numerical simulation tools for chemical vapor deposition (CVD) was the objective of this study. Physical models of important CVD phenomena were developed and implemented into the commercial computational fluid dynamics software FLUENT. The resulting software can address general geometries as well as the most important phenomena occurring with CVD reactors: fluid flow patterns, temperature and chemical species distribution, gas phase and surface deposition. The physical models are documented which are available and examples are provided of CVD simulation capabilities

Tidal Disruption of Protoclusters in Giant Molecular Clouds

We study the collapse of protoclusters within a giant molecular cloud (GMC) to determine the conditions under which collapse is significantly disrupted. Motivated by observations of star forming regions which exhibit flattened cloud structures, this study considers collapsing protoclusters with disk geometries. The collapse of a 10^3 Msun protocluster initially a distance of 2-10 pc from a 10^3 - 10^6 Msun point mass is numerically calculated. Simulations with zero initial relative velocity between the two are completed as well as simulations with relative velocities consistent with those observed in GMCs. The results allow us to define the conditions under which it is safe to assume protocluster collapse proceeds as if in isolation. For instance, we find the collapse of a 10^3 Msun protocluster will be significantly disrupted if it is within 2-4 pc of a 10^4 Msun point mass. Thus, the collapse of a 10^3 Msun protocluster can be considered to proceed as if in isolation if it is more than ~ 4 pc away from a 10^4 Msun compact object. In addition, in no portion of the sampled parameter space does the gravitational interaction between the protocluster disk and the massive particle significantly disperse the disk into the background GMC. We discuss the distribution of clusters of young stellar objects within the Perseus and Mon R2 star forming regions, which are consistent with the results of our simulations and the limitations of our results in gas dominated regions such as the Orion cloud.Comment: 12 pages, 6 figures, Accepted for publication in Ap

Adsorption behaviour of molecularly imprinted-beta-cyclodextrin polymers prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization for selective recognition of benzylparaben

Molecularly imprinted polymers (MIPs) are kinds of powerful materials with promising selective molecule recognition abilities. However, the conventional MIPs have relatively low binding capacity. In order to improve this characteristic of MIPs, the modification monomer based on β-cyclodextrin (β-CD) and the essential of reversible addition�fragmentation chain transfer (RAFT) polymerization process were studied to generate potential MIPs. The study focuses on the characterization and adsorption behaviour of MIPs for selective recognition of benzylparaben (BzP) analyte. The potential of β-CD in MIP was investigated by synthesizing a reversible addition-fragmentation chain transfer molecularly imprinted methacrylic acid functionalized β-cyclodextrin polymer; RAFT�MIP(MAA-β-CD) based on methacrylic acid functionalized β-cyclodextrin (MAA-β-CD) monomer, which was then compared to a reversible addition-fragmentation chain transfer molecularly imprinted methacrylic acid polymer; RAFT-MIP(MAA) synthesized without β-CD. Both MIPs were prepared by the RAFT polymerization process in bulk polymerization method. The resulting MIPs were characterized using Fourier Transform Infrared Spectroscopy (FTIR), Field Scanning Electron Microscope (FESEM) and Brunauer-Emmett-Teller (BET) analysis. The batch adsorption study that includes studying of the pH, kinetic, isotherm and thermodynamic was conducted. The essential of RAFT polymerization on MIP was studied by comparing RAFT-MIP(MAA-β-CD) with the molecularly imprinted methacrylic acid functionalized β-cyclodextrin polymer; MIP(MAA-β-CD) was synthesized without RAFT agent, and characterized by using FTIR, elemental analysis, FESEM and BET. The binding experiments demonstrated that the RAFT-MIP(MAA-β-CD) has a higher binding capacity and higher accessibility compared to RAFT-MIP(MAA) and MIP(MAA-β-CD) for selective of BzP, respectively. The β-CD and RAFT polymerization process improved the MIP’s physical properties and iv enhanced its recognition capacity, thus affecting the adsorption behaviour of RAFT�MIP(MAA-β-CD). The effects of RAFT polymerization process were also investigated by a reversible addition-fragmentation transfer molecularly imprinted hydroxylethyl methacrylate functionalized β-cyclodextrin polymer; RAFT-MIP(HEMA-β-CD). The RAFT-MIP(HEMA-β-CD) was synthesized based on the hydroxylethyl-methacrylate functionalized β-cyclodextrin (HEMA-β-CD) monomer and was prepared by the RAFT polymerization process in bulk polymerization method. The molecularly imprinted hydroxylethyl-methacrylate functionalized β-cyclodextrin polymer; MIP(HEMA-β-CD) without a RAFT agent was synthesized as comparison. A similar study to RAFT�MIP(MAA-β-CD) had also been carried out for RAFT-MIP(HEMA-β-CD).The effects of RAFT polymerization on RAFT-MIP(HEMA-β-CD) were contrasted with RAFT�MIP(MAA-β-CD). The compact and non-porous morphology of RAFT-MIP(HEMA-β�CD) reduces its binding capacity performance compared to MIP(HEMA-β-CD). Thus, this directly affected the RAFT-MIP(HEMA-β-CD) adsorption behaviour towards BzP. It was resulted that the RAFT polymerization had not improved the synthesis of RAFT�MIP(HEMA-β-CD). Careful choice of RAFT agent and monomer is essential in realizing good control over the RAFT-MIP polymerization process, and generating potential MIP

Gravitational Collapse in Turbulent Molecular Clouds. I. Gasdynamical Turbulence

Observed molecular clouds often appear to have very low star formation efficiencies and lifetimes an order of magnitude longer than their free-fall times. Their support is attributed to the random supersonic motions observed in them. We study the support of molecular clouds against gravitational collapse by supersonic, gas dynamical turbulence using direct numerical simulation. Computations with two different algorithms are compared: a particle-based, Lagrangian method (SPH), and a grid-based, Eulerian, second-order method (ZEUS). The effects of both algorithm and resolution can be studied with this method. We find that, under typical molecular cloud conditions, global collapse can indeed be prevented, but density enhancements caused by strong shocks nevertheless become gravitationally unstable and collapse into dense cores and, presumably, stars. The occurance and efficiency of local collapse decreases as the driving wave length decreases and the driving strength increases. It appears that local collapse can only be prevented entirely with unrealistically short wave length driving, but observed core formation rates can be reproduced with more realistic driving. At high collapse rates, cores are formed on short time scales in coherent structures with high efficiency, while at low collapse rates they are scattered randomly throughout the region and exhibit considerable age spread. We suggest that this naturally explains the observed distinction between isolated and clustered star formation.Comment: Minor revisions in response to referee, thirteen figures, accepted to Astrophys.