Implementation of a low-mach number modification for high-order finite-volume schemes for arbitrary hybrid unstructured meshes

An implementation of a novel low-mach number treatment for high-order finite-volume schemes using arbitrary hybrid unstructured meshes is presented in this paper. Low-Mach order modifications for Godunov type finite-volume schemes have been implemented successfully for structured and unstructured meshes, however the methods break down for hybrid mesh topologies containing multiple element types. The modification is applied to the UCNS3D finite-volume framework for compressible flow configurations, which have been shown as very capable of handling any type of grid topology. The numerical methods under consideration are the Monotonic Upstream-Centered Scheme for Conservation Laws (MUSCL) and the Weighted Essentially Non-Oscillatory (WENO) schemes for two-dimensional mixed-element type unstructured meshes. In the present study the HLLC Approximate Riemann Solver is used with an explicit TVD Runge-Kutta 3rd-order method due to its excellent scalability. These schemes (up to 5th-order) are applied to well established two-dimensional and three-dimensional test cases. The challenges that occur when applying these methods to low-mach flow configurations is thoroughly analysed and possible improvements and further test cases are suggested

WENO schemes on arbitrary mixed-element unstructured meshes in three space dimensions

The paper extends weighted essentially non-oscillatory (WENO) methods to three dimensional mixed-element unstructured meshes, comprising tetrahedral, hexahedral, prismatic and pyramidal elements. Numerical results illustrate the convergence rates and non-oscillatory properties of the schemes for various smooth and discontinuous solutions test cases and the compressible Euler equations on various types of grids. Schemes of up to fifth order of spatial accuracy are considered

Blind Multiclass Ensemble Classification

The rising interest in pattern recognition and data analytics has spurred the development of innovative machine learning algorithms and tools. However, as each algorithm has its strengths and limitations, one is motivated to judiciously fuse multiple algorithms in order to find the "best" performing one, for a given dataset. Ensemble learning aims at such high-performance meta-algorithm, by combining the outputs from multiple algorithms. The present work introduces a blind scheme for learning from ensembles of classifiers, using a moment matching method that leverages joint tensor and matrix factorization. Blind refers to the combiner who has no knowledge of the ground-truth labels that each classifier has been trained on. A rigorous performance analysis is derived and the proposed scheme is evaluated on synthetic and real datasets.Comment: To appear in IEEE Transactions in Signal Processin

A general BRST approach to string theories with zeta function regularizations

We propose a new general BRST approach to string and string-like theories which have a wider range of applicability than e g the conventional conformal field theory method. The method involves a simple general regularization of all basic commutators which makes all divergent sums to be expressible in terms of zeta functions from which finite values then may be extracted in a rigorous manner. The method is particular useful in order to investigate possible state space representations to a given model. The method is applied to three string models: The ordinary bosonic string, the tensionless string and the conformal tensionless string. We also investigate different state spaces for these models. The tensionless string models are treated in details. Although we mostly rederive known results they appear in a new fashion which deepens our understanding of these models. Furthermore, we believe that our treatment is more rigorous than most of the previous ones. In the case of the conformal tensionless string we find a new solution for d=4.Comment: 21 pages,Latexfile,revised presentation, previous title:"Critical dimensions and zeta regularizations in string theories

Export performance, competitiveness and commodity composition

The study of export performance, especially for countries with serious external imbalances, is essential for economic decision-making. This study attempts to evaluate Greek export performance during the 1996-2006 period, using detailed panel data on bilateral trade by product. Factors explaining Greek export market shares are analysed with the method of Constant Market Shares. In addition, the dynamics of the specialization pattern of Greek exports and the effect of price competitiveness on export market shares are examined. The results show a considerable change in export structure, mainly the geographical structure, with a favourable effect on market shares. Although the pattern of comparative advantages and the technological intensity of Greek exports have improved, exports remain concentrated in low- and medium-technology sectors, while product variety and quality have declined. Finally, the results show heterogeneity among the panels. In the aggregate, export market shares are inelastic with respect to relative and absolute prices, which would call for focus on non-price factors to improve competitiveness in international markets. However, elasticities are greater than one for a considerable proportion of commodities.export performance; market shares; New Trade Theory; comparative advantages; Markov matrix; price and non-price competitiveness.

Adaptive optimal estimation control strategies for systems of simultaneous equations

AbstractThe choice of control strategies to improve estimation of the parameters in a model of a simultaneous equations system with time-varying parameters is considered. Open-loop feedback (OLF) sequential procedures for handling nonlinear restrictions on reduced form parameters implied by the structural form are suggested, and the combination of sequential estimation and design control strategies feature a marked improvement in the behavior of estimates over the nonsequential [open-loop (OL)] formulation. The maximum accuracy control problem considered in this paper can also be treated as an initial phase of a forecasting and/or stochastic control problem. This will avoid solution to a more difficult problem such as the dual control problem