The Benjamin Shock Tube Problem in KULL

The goal of the EZturb mix model in KULL is to predict the turbulent mixing process as it evolves from Rayleigh-Taylor, Richtmyer-Meshkov, or Kelvin-Helmholtz instabilities. In this report we focus on a simple example of the Richtmyer-Meshkov instability (which occurs when a shock hits an interface between fluids of different densities) without the complication of reshock. The experiment by Benjamin et al. involving a Mach 1.21 incident shock striking an air / SF6 interface, is a good one to model and understand before moving onto shock tubes that follow the growth of the turbulent mixing zone from first shock through well after reshock

A Tensor Hyperviscosity Model in Kull

A tensor artificial hyper-viscosity model has recently been added to the available list of artificial viscosities that one can chose from when running KULL. This model is based on the theoretical work of A. Cook and B. Cabot, and the numerical results of running the model in the high-order spectral/compact finite difference framework of the Eulerian MIRANDA code. The viscosity model is based on filtering a Laplacian or bi-Laplacian of the strain rate magnitude, and it was desired to investigate whether the formalism that worked so well for the MIRANDA research code could be carried over to an unstructured ALE code like KULL

The Vetter-Sturtevant Shock Tube Problem in KULL

The goal of the EZturb mix model in KULL is to predict the turbulent mixing process as it evolves from Rayleigh-Taylor, Richtmyer-Meshkov, or Kelvin-Helmholtz instabilities. In this report we focus on an example of the Richtmyer-Meshkov instability (which occurs when a shock hits an interface between fluids of different densities) with the additional complication of reshock. The experiment by Vetter & Sturtevant (VS) [1], involving a Mach 1.50 incident shock striking an air/SF{sub 6} interface, is a good one to model, now that we understand how the model performs for the Benjamin shock tube [2] and a prototypical incompressible Rayleigh-Taylor problem [3]. The x-t diagram for the VS shock tube is quite complicated, since the transmitted shock hits the far wall at {approx}2 millisec, reshocks the mixing zone slightly after 3 millisec (which sets up a release wave that hits the wall at {approx}4 millisec), and then the interface is hit with this expansion wave around 5 millisec. Needless to say, this problem is much more difficult to model than the Bejamin shock tube

Combining Equations of State in Kull

For ICF applications, the temperatures are hot enough that materials can transition to an atomic state or plasma. If we are simulating an ICF capsule, then either thru ALE, physical diffusion, transmutation by nuclear reactions, a mix model, or numerical diffusion (if we are running an Eulerian code), we will generate zones that contain multiple materials. It may be desired to treat certain mixtures of materials or mixed zones as atomic mixtures rather than as chunk mixtures. For example, suppose we have a deuterated material that is initially separated from a tritiated material. As these quantities come into contact at the atomic level, high energy neutrons will be generated from the D + T reaction. However, if we had a chunk of deuterium and a chunk of tritium in the same computational zone, then the D + T reaction would not take place. In dealing with atomic mixtures, two topics that immediately come to mind are mixed equations of state and mixed opacities. This report will only focus on the equation of state (EOS) aspect and its implementation in the Kull code. Imagine we have a zone that contains an atomic mixture of plastic and steel. If we know the density, temperature, and isotopics of this mixture, then a natural question is how will we compute the pressure and specific internal energy of the mixture as well as the derivatives of these quantities with respect to density and temperature. Let's consider the case where we have tabular thermodynamic data for plastic and steel (as a function of density and temperature), and our goal is to determine how to use these tables to compute the thermodynamic quantities of interest

Macrostate Data Clustering

We develop an effective nonhierarchical data clustering method using an analogy to the dynamic coarse graining of a stochastic system. Analyzing the eigensystem of an interitem transition matrix identifies fuzzy clusters corresponding to the metastable macroscopic states (macrostates) of a diffusive system. A "minimum uncertainty criterion" determines the linear transformation from eigenvectors to cluster-defining window functions. Eigenspectrum gap and cluster certainty conditions identify the proper number of clusters. The physically motivated fuzzy representation and associated uncertainty analysis distinguishes macrostate clustering from spectral partitioning methods. Macrostate data clustering solves a variety of test cases that challenge other methods.Comment: keywords: cluster analysis, clustering, pattern recognition, spectral graph theory, dynamic eigenvectors, machine learning, macrostates, classificatio

Alternative 3' UTRs direct localization of functionally diverse protein isoforms in neuronal compartments

The proper subcellular localization of RNAs and local translational regulation is crucial in highly compartmentalized cells, such as neurons. RNA localization is mediated by specific cis-regulatory elements usually found in mRNA 3'UTRs. Therefore, processes that generate alternative 3'UTRs-alternative splicing and polyadenylation-have the potential to diversify mRNA localization patterns in neurons. Here, we performed mapping of alternative 3'UTRs in neurites and soma isolated from mESC-derived neurons. Our analysis identified 593 genes with differentially localized 3'UTR isoforms. In particular, we have shown that two isoforms of Cdc42 gene with distinct functions in neuronal polarity are differentially localized between neurites and soma of mESC-derived and mouse primary cortical neurons, at both mRNA and protein level. Using reporter assays and 3'UTR swapping experiments, we have identified the role of alternative 3'UTRs and mRNA transport in differential localization of alternative CDC42 protein isoforms. Moreover, we used SILAC to identify isoform-specific Cdc42 3'UTR-bound proteome with potential role in Cdc42 localization and translation. Our analysis points to usage of alternative 3'UTR isoforms as a novel mechanism to provide for differential localization of functionally diverse alternative protein isoforms

Equation of State Scalings in Kull

In this short report, we consider two types of equation of state (EOS) scalings, which will be referred to as type I (or density scaling) and type II (or Thomas-Fermi scaling). EOS scalings are used to correct for the fact that EOS tables are constructed with a fixed isotopic composition. Even if the isotopics in a computational zone are evolving through chemical or nuclear reactions, the EOS lookups for pressure and energy (and their derivatives with respect to density and temperature) aren't normally cognizant of this fact. The EOS scalings are an attempt to fix this shortcoming. They typically modify the incoming density and/or temperature based on ratios of isotopic quantities (like <A>{sub table}/<A>{sub zone}, <Z>{sub table}/<Z>{sub zone}), and then modify the table lookup values. In this way, the EOS can dynamically respond to the changing isotopics

Ab-initio density functional study of O on the Ag(001) surface

The adsorption of oxygen on the Ag(001) is investigated by means of density functional techniques. Starting from a characterization of the clean silver surfaces oxygen adsorption in several modifications (molecularly, on-surface, sub-surface, Ag$_2$O) for varying coverage was studied. Besides structural parameters and adsorption energies also work-function changes, vibrational frequencies and core level energies were calculated for a better characterization of the adsorption structures and an easier comparison to the rich experimental data.Comment: 26 pages, 8 figures, Surf. Sci. accepte

Intertemporal excess burden, bequest motives, and the budget deficit

The author aims to empirically determine the significant factors that affect the levels of budget deficits of central governments across time and across countries. He empirically tests two prominent theories of budget deficits-the Barro (1979) tax-smoothing approach, and the still-untested theory of negative bequest motives advocated by Cukierman and Meltzer (1989). The author uses econometric techniques including fixed-effects (both country and time) panel regressions spanning 87 countries over the period 1975 to 1992, and the Griliches treatment of missing data. The author finds relatively stronger statistical support for the tax-smoothing approach among developing countries but not in industrial countries. The existence of empirical evidence supporting the theory of negative bequest motives is indeterminate. The author also conducted post-regression analyses to assess the proportion of observed differences in budget deficits the factors were actually able to explain. These reveal that both theories are generally weak in accounting for inter-temporal changes in budget deficit shares for both industrial and developing countries. The theories performed significantly better in accounting for cross-section differences. The author has many contributions to the literature. First, he analyzes the question of what determines the size of central government budget deficits using cross-country time series data leading into the 1990s. Second, he provides empirical tests of the still-untested Cukierman-Meltzer (1989) negative bequest motive theory of budget deficits. By using the panel data, the author attempts to determine the factors that influence not only the inter-temporal differences in budget deficits but also those factors that lead to cross-country differences. Last but not least, he provides some preliminary evidence that poverty reduction is necessary for long-term government budget deficit reduction.Public Sector Economics&Finance,Environmental Economics&Policies,Economic Theory&Research,Banks&Banking Reform,Municipal Financial Management,Public Sector Economics&Finance,Economic Theory&Research,Economic Stabilization,Banks&Banking Reform,National Governance