Afivo: a framework for quadtree/octree AMR with shared-memory parallelization and geometric multigrid methods

Afivo is a framework for simulations with adaptive mesh refinement (AMR) on quadtree (2D) and octree (3D) grids. The framework comes with a geometric multigrid solver, shared-memory (OpenMP) parallelism and it supports output in Silo and VTK file formats. Afivo can be used to efficiently simulate AMR problems with up to about $10^{8}$ unknowns on desktops, workstations or single compute nodes. For larger problems, existing distributed-memory frameworks are better suited. The framework has no built-in functionality for specific physics applications, so users have to implement their own numerical methods. The included multigrid solver can be used to efficiently solve elliptic partial differential equations such as Poisson's equation. Afivo's design was kept simple, which in combination with the shared-memory parallelism facilitates modification and experimentation with AMR algorithms. The framework was already used to perform 3D simulations of streamer discharges, which required tens of millions of cells

Parametric study of space power systems. Volume 1 - Summary Final report

Summary of methodology and results of study of space power system

Zero-gravity venting of three refrigerants

An experimental investigation of venting cylindrical containers partially filled with initially saturated liquids under zero-gravity conditions was conducted in the NASA Lewis Research Center 5-second zero-gravity facility. The effect of interfacial mass transfer on the ullage pressure response during venting was analytically determined, based on a conduction analysis applied to an infinitely planer (flat) liquid-vapor interface. This pressure response was compared with both the experimental results and an adiabatic decompression computation

Exact Diagonalization Dynamical Mean Field Theory for Multi-Band Materials: Effect of Coulomb correlations on the Fermi surface of Na_0.3CoO_2

Dynamical mean field theory combined with finite-temperature exact diagonalization is shown to be a suitable method to study local Coulomb correlations in realistic multi-band materials. By making use of the sparseness of the impurity Hamiltonian, exact eigenstates can be evaluated for significantly larger clusters than in schemes based on full diagonalization. Since finite-size effects are greatly reduced this approach allows the study of three-band systems down to very low temperatures, for strong local Coulomb interactions and full Hund exchange. It is also shown that exact diagonalization yields smooth subband quasi-particle spectra and self-energies at real frequencies. As a first application the correlation induced charge transfer between t2g bands in Na_0.3CoO_2 is investigated. For both Hund and Ising exchange the small eg' Fermi surface hole pockets are found to be slightly enlarged compared to the non-interacting limit, in agreement with previous Quantum Monte Carlo dynamical mean field calculations for Ising exchange, but in conflict with photoemission data.Comment: 9 pages, 7 figure

P/2010 A2 LINEAR II: dynamical dust modelling

P/2010 A2 is an object on an asteroidal orbit that was observed to have an extended tail or debris trail in January 2010. In this work, we fit the outburst of P/2010 A2 with a conical burst model, and verify previous suspicions that this was a one--time collisional event rather than an sustained cometary outburst, implying that P/2010 A2 is not a new Main Belt Comet driven by ice sublimation. We find that the best--fit cone opening angle is about 40 to 50 degrees, in agreement with numerical and laboratory simulations of cratering events. Mapping debris orbits to sky positions suggests that the distinctive arc features in the debris correspond to the same debris cone inferred from the extended dust. From the velocity of the debris, and from the presence of a velocity maximum at around 15 cm/s, we infer that the surface of A2 probably has a very low strength (<1 kPa), comparable to lunar regolith.Comment: 14 pages, 25 figures; accepted by Astronomy and Astrophysic

Prediction and control of organic xerogel microstructure, experiments and modelling

Resorcinol-formaldehyde (RF) gels are a fairly new addition to the variety of porous materials used by current industry. However, a better understanding of their formation processes is crucial for efficient structure tailoring, leading to high-performance materials for a range of applications. The usual RF gel manufacture process involves gelation of an RF sol at elevated temperatures, followed by exchanging water within the structure for another liquid, in order to limit shrinkage during the final drying step. Yet, despite significant research efforts, the RF growth processes are still not fully understood and there is no accepted model describing these processes. Therefore, this study combines experimental and simulation approaches to better understand the gel growth process, and how the resulting structure depends on the growth conditions. The experimentally investigated areas include the influence of sodium carbonate catalyst concentration, processing temperature, solvent exchange and drying methods, as well as the presence of different anions within the reaction solution. Discussion on optimal processing parametersis included, in order to preserve the majority of the porous structure of RF xerogel materials, taking process economics into account, and the diversity of textural properties for obtained materials is examined. In order to model the growth processes in RF gels, and investigate how they impact the structural properties of final materials, a two-dimensional lattice-based computational model, using kinetic Monte Carlo, was developed in this work. The presented model is developed to capture growth from monomeric species present in the initial stages of the gelation composition. Experimentally, gel growth is primarily controlled through catalyst concentration, which determines the density of species that are activated for rapid growth, and solids concentration; the model captures both of these dependencies.;Generated cluster structures were analysed for textural properties, such as accessible porosity and accessible surface area, as well as fractal properties, in the form of the correlation dimension and the Hurst exponent. Increasing both solids content and percentage of activated monomers led to an observed increase in complexity of cluster arrangement and tortuosity of pore structure, both reflected in the values of evaluated fractal properties. In order to allow comparison of generated cluster structures with trends observed for experimental samples, gas sorption was modelled here using a lattice gas in a mean field approximation. The observations for model pores with varying dimensions agree with the background theory and the trends observed for the cluster structures were in line with those obtained experimentally. This helps to close the loop from growth processes to textural properties, providing the possibility to tailor materials for specific application.Resorcinol-formaldehyde (RF) gels are a fairly new addition to the variety of porous materials used by current industry. However, a better understanding of their formation processes is crucial for efficient structure tailoring, leading to high-performance materials for a range of applications. The usual RF gel manufacture process involves gelation of an RF sol at elevated temperatures, followed by exchanging water within the structure for another liquid, in order to limit shrinkage during the final drying step. Yet, despite significant research efforts, the RF growth processes are still not fully understood and there is no accepted model describing these processes. Therefore, this study combines experimental and simulation approaches to better understand the gel growth process, and how the resulting structure depends on the growth conditions. The experimentally investigated areas include the influence of sodium carbonate catalyst concentration, processing temperature, solvent exchange and drying methods, as well as the presence of different anions within the reaction solution. Discussion on optimal processing parametersis included, in order to preserve the majority of the porous structure of RF xerogel materials, taking process economics into account, and the diversity of textural properties for obtained materials is examined. In order to model the growth processes in RF gels, and investigate how they impact the structural properties of final materials, a two-dimensional lattice-based computational model, using kinetic Monte Carlo, was developed in this work. The presented model is developed to capture growth from monomeric species present in the initial stages of the gelation composition. Experimentally, gel growth is primarily controlled through catalyst concentration, which determines the density of species that are activated for rapid growth, and solids concentration; the model captures both of these dependencies.;Generated cluster structures were analysed for textural properties, such as accessible porosity and accessible surface area, as well as fractal properties, in the form of the correlation dimension and the Hurst exponent. Increasing both solids content and percentage of activated monomers led to an observed increase in complexity of cluster arrangement and tortuosity of pore structure, both reflected in the values of evaluated fractal properties. In order to allow comparison of generated cluster structures with trends observed for experimental samples, gas sorption was modelled here using a lattice gas in a mean field approximation. The observations for model pores with varying dimensions agree with the background theory and the trends observed for the cluster structures were in line with those obtained experimentally. This helps to close the loop from growth processes to textural properties, providing the possibility to tailor materials for specific application

Markovian Monte Carlo program EvolFMC v.2 for solving QCD evolution equations

We present the program EvolFMC v.2 that solves the evolution equations in QCD for the parton momentum distributions by means of the Monte Carlo technique based on the Markovian process. The program solves the DGLAP-type evolution as well as modified-DGLAP ones. In both cases the evolution can be performed in the LO or NLO approximation. The quarks are treated as massless. The overall technical precision of the code has been established at 0.05% precision level. This way, for the first time ever, we demonstrate that with the Monte Carlo method one can solve the evolution equations with precision comparable to the other numerical methods.Comment: 38 pages, 9 Postscript figure

The development of an elastic reverse gradient garment to be used as a countermeasure for cardiovascular deconditioning

Using a new Nomex-Lycra elastic fabric and individualized garment engineering techniques, reverse gradient garments (RGG's) were designed, constructed, and tested for effectiveness as a countermeasure against cardiovascular deconditioning. By combining torso-compensated positive pressure breathing with a distally diminishing gradient of counterpressure supplied by the elastic fabric on the limbs, the RGG acts to pool blood in the extremities of recumbent persons much as though they were standing erect in 1 g. It was theorized that through the use of a dynamic pressurization scheme, the RGG would stress the vasculature in a fashion similar to that experienced by the noramlly active man, hence preventing or limiting the development of post-weightlessness orthostatic intolerance and related conditions. Four male, college-age subjects received daily treatments with the RGG during a 15-day bedrest study. Four additional subjects also underwent the bedrest, but received no treatments; they served as controls. The design and construction of the garments are described, and results of the treatment related measurements are given

An interactive interface for NCAR Graphics

The NCAR Graphics package has been a valuable research tool for over 20 years. As a low level Fortran library, however, it was difficult to use for nonprogramming researchers. With this grant and NSF support, an interactive interface has been created which greatly facilitates use of the package by researchers of diverse computer skill levels