Seismic structure of Iceland from Rayleigh wave inversions and geodynamic implications

Author Posting. © The Authors, 2005. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Earth and Planetary Science Letters 241 (2006): 901-912, doi:10.1016/j.epsl.2005.10.031.We have constrained the shear-wave structure of crust and upper mantle beneath Iceland by analyzing fundamental mode Rayleigh waves recorded at the ICEMELT and HOTSPOT seismic stations in Iceland. The crust varies in thickness from 20 to 28 km in western and northern Iceland and from 26 to 34 km in eastern Iceland. The thickest crust of 34-40 km lies in central Iceland, roughly 100 km west to the current location of the Iceland hotspot. The crust at the hotspot is ~32 km thick and is underlain by low shearwave velocities of 4.0-4.1 km/s in the uppermost mantle, indicating that the Moho at the hotspot is probably a weak discontinuity. This low velocity anomaly beneath the hotspot could be associated with partial melting and hot temperature. The lithosphere in Iceland is confined above 60 km and a low velocity zone (LVZ) is imaged at depths of 60 to 120 km. Shear wave velocity in the LVZ is up to 10% lower than a global reference model, indicating the influence of the Mid-Atlantic Ridge and the hotspot in Iceland. The lowest velocities in the LVZ are found beneath the rift zones, suggesting that plume material is channeled along the Mid-Atlantic Ridge. At depths of 100 to 200 km, low velocity anomalies appear at the Tjornes fracture zone to the north of Iceland and beneath the western volcanic zone in southwestern Iceland. Interestingly, a relatively fast anomaly is imaged beneath the hotspot with its center at ~135 km depth, which could be due to radial anisotropy associated with the strong upwelling within the plume stem or an Mgenriched mantle residual caused by the extensive extraction of melts.This work is supported by University of Houston, Woods Hole Oceanographic Institution, and NSF grant OCE-0117938

Compare Pilot-Scale And Industry-Scale Models Of Pulverized Coal Combustion In An Ironmaking Blast Furnace

In order to understand the complex phenomena of pulverized coal injection (PCI) process in blast furnace (BF), mathematical models have been developed at different scales: pilot-scale model of coal combustion and industry-scale model (in-furnace model) of coal/coke combustion in a real BF respectively. This paper compares these PCI models in aspects of model developments and model capability. The model development is discussed in terms of model formulation, their new features and geometry/regions considered. The model capability is then discussed in terms of main findings followed by the model evaluation on their advantages and limitations. It is indicated that these PCI models are all able to describe PCI operation qualitatively. The in-furnace model is more reliable for simulating in-furnace phenomena of PCI operation qualitatively and quantitatively. These models are useful for understanding the flow-thermo-chemical behaviors and then optimizing the PCI operation in practice. 2013 AIP Publishing LLC

Ab Initio Study of Phase Stability in Doped TiO2

Ab-initio density functional theory (DFT) calculations of the relative stability of anatase and rutile polymorphs of TiO2 were carried using all-electron atomic orbitals methods with local density approximation (LDA). The rutile phase exhibited a moderate margin of stability of ~ 3 meV relative to the anatase phase in pristine material. From computational analysis of the formation energies of Si, Al, Fe and F dopants of various charge states across different Fermi level energies in anatase and in rutile, it was found that the cationic dopants are most stable in Ti substitutional lattice positions while formation energy is minimised for F- doping in interstitial positions. All dopants were found to considerably stabilise anatase relative to the rutile phase, suggesting the anatase to rutile phase transformation is inhibited in such systems with the dopants ranked F>Si>Fe>Al in order of anatase stabilisation strength. Al and Fe dopants were found to act as shallow acceptors with charge compensation achieved through the formation of mobile carriers rather than the formation of anion vacancies

Microdynamic analysis of ellipsoidal particle flow in a shear cell

This paper studies rheological properties of ellipsoidal particles in a model annular shear cell and compares them with the relevant parameters obtained for spherical particles under similar conditions using the discrete element method (DEM). Some important microdynamic variables such as velocity, coordination number, volume fraction and stress were considered. It was found that there are some differences between the spherical and ellipsoidal particles in terms of these properties. The feature was explained by the microscopic structures at particle scale such as those related to particle alignment and interparticle force

Discrete Particle Simulation of the Gas-Solid Flow in a Circulating Fluidized Bed

This paper presents a numerical study of the gas-solid flow in a three-dimensional Circulating Fluidized Bed (CFB) by means of Combined Continuum and Discrete Method (CCDM) in which the motion of discrete particles is described by Discrete Particle Method (DPM) on the basis of Newton’s laws of motion applied to individual particles and the flow of continuum fluid by the traditional Computational Fluid Dynamics (CFD) based on the local averaged Navier-Stokes equations. The simulation is achieved by incorporating DPM codes into the commercial CFD software package Fluent. It is shown that the discrete particle simulation can capture the key flow features in CFB such as core-annulus structure, axial solid segregation and S-shaped axial solid concentration. The numerical results also show the effect of the pulsation arising from the expansion of the fluidized bed on the performance of the cyclone separator. The gas-solid, particle-wall and particle-particle interactions are analysed to understand the underlying mechanisms of CFB systems

Contact force models for non-spherical particles with different surface properties : a review

This paper reviews the state-of-the-art contact force models for non-spherical particles, which describe the relationship between the contact force and the geometrical, material, and mechanical properties of the contacting particles. The review aims to select better contact force models to improve the current simplified contact force models used in discrete element method (DEM) simulations. First, the contact force models based on the extension of the classical Hertz theory are reviewed, in which a recent accurate geometrical contact force model is highlighted. Secondly, the research on the effects of different variables such as elastoplasticity, viscoelasticity, adhesion and surface roughness on contact force are reviewed respectively and then incorporated into the accurate geometrical contact force model. Thirdly, tangential force models for non-spherical particles in contact under various loading regimes are reviewed as well. Based on the review, a full set of improved contact force models for DEM is recommended. These contact force models can more accurately predict the contact force and contact area for non-spherical particles, which can be beneficial to the DEM simulation in emerging areas, such as nanoparticles and additive manufacturing

Adaptive Treatment of van der Waals Interactions in Empirical Bond-Order Potentials with Application to Junction Formation in Carbon Nanotubes

Molecular dynamics (MD) simulation of reactive condensed-phase hydrocarbon systems is a challenging research area. The AIREBO potential is particularly useful in this area because it can simulate bond breaking and bond forming during chemical reactions. It also includes non-bonded interactions for systems with significant intermolecular interactions. The first part of this dissertation describes a method to adaptively incorporate van der Waals interaction of carbon atoms into the AIREBO force field. In bond-order potentials, the covalent bonding interactions adapt to the local chemical environment, allowing bonded interactions to change in response to local chemical changes. Non-bonded interactions should adjust to their chemical environment as well, although this adaptivity has been somewhat limited in previous implementations. Here the AIREBO potential is extended to include an adaptive Lennard-Jones potential, allowing the van der Waals radius and well depth to vary adaptively in response to chemical reactions. The resulting potential energy surface and its gradient remain continuous, allowing it to be used for dynamics simulations. This new potential is parameterized for hydrocarbons, and is fit to the energetics and densities of a variety of condensed phase molecular hydrocarbons. The resulting model is more accurate for modeling aromatic and other unsaturated hydrocarbon species, for which the original AIREBO potential had some deficiencies. Testing on compounds not used in the fitting procedure shows that the new model performs substantially better in predicting heats of vaporization and pressures (or densities) of condensed-phase molecular hydrocarbons. The second part of this dissertation describes the investigation of nanotube welding by ion bombardment. Nanotube technology has found many applications in recent years. Junctions between heterostructured nanotubes are of particular interest because of their possible application in nanoscale devices. Simulation is performed on the formation of junctions by Ar ion irradiation of nanotubes using the AIREBO force field. Two groups of nanotubes are used in this research. One includes larger nanotubes of diameter 13 \AA, another includes smaller nanotubes of diameter about 7-8 \AA. Nanotube junction formation under different bombardment ion energies is explored. In both large and small nanotubes, junctions can be formed by ion irradiation. It is found that for large nanotubes, high energy impacts are needed in order to form junctions. Smaller nanotubes are badly damaged by high energy ions. The different types of defects created by ion impact are also investigated. Cross-links in the nanotube intersection are used as a primary index of junction formation. A comparison of longer relaxation and cooling times is also performed. The evaluation of conductivity of nanotube junctions during simulation is explored. For (10,0) nanotubes, conductance across the junction becomes non-zero after the first impact for 330 eV energy impact