In this paper a description is given of the SFXC software correlator, developed and maintained at the Joint Institute for VLBI in Europe (JIVE). The software is designed to run on generic Linux-based computing clusters. The correlation algorithm is explained in detail, as are some of the novel modes that software correlation has enabled, such as wide-field VLBI imaging through the use of multiple phase centres and pulsar gating and binning. This is followed by an overview of the software architecture. Finally, the performance of the correlator as a function of number of CPU cores, telescopes and spectral channels is shown.

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This paper examines the return and volatility spillover effects among S&P 500, crude oil and gold by employing the spillover index of Diebold and Yilmaz (2012). Monthly realized volatility and return series covering the period from January 1986 to August 2018 are used to examine the return and volatility spillovers. Our findings indicate a bi-directional return and volatility spillover among these assets. The full sample empirical evidence is consistent with the structure in which oil plays a central role in the information transmission mechanism. The role of oil and gold as a safe haven has changed over time in financial and non-financial economic turbulence time-span. Commodity market financialization has decreased the effectiveness of adding commodities to portfolios after 2002.

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An improved formulation of drag estimation for thick airfoils is presented. Drag underprediction in XFOIL like viscous-inviscid interaction methods can be quite significant for thick airfoils used in wind turbine applications (up to 30% as seen in the present study). The improved drag formulation predicts the drag accurately for airfoils with reasonably small trailing edge thickness. The derivation of drag correction is based on the difference between the actual momentum loss thickness based on free stream velocity and the one based on the velocity at the edge of the boundary layer. The improved formulation is implemented in the most recent version of XFOIL and RFOIL (an aerodynamic design and analysis method based on XFOIL, developed by a consortium of ECN, NLR and TU Delft after ECN acquired the XFOIL code. After 1996, ECN maintained and improved the tool.) and the results are compared with experimental data, results from commercial CFD methods like ANSYS CFX and other methods like DTU-AED EllipSys2D and CENER WMB. The improved version of RFOIL shows good agreement with experimental data. Nomenclature α Angle of attack ∆θ Error in θ δ Boundary layer thickness δ * Boundary layer displacement thickness ∞ Subscript for incident free stream condition ρ Density of fluid θ Boundary layer momentum thickness ξ, η Streamline space coordinates A, B G − β equilibrium locus coefficients airf oil Subscript for airfoil parameters c Airfoil chord length C τ EQ Equilibrium maximum shear stress coefficient c d Sectional drag coefficient c l Sectional lift coefficient D Drag e Subscript for boundary layer edge condition