Sigma Terms of Light-Quark Hadrons

A calculation of the current-quark mass dependence of hadron masses can help in using observational data to place constraints on the variation of nature's fundamental parameters. A hadron's sigma-term is a measure of this dependence. The connection between a hadron's sigma-term and the Feynman-Hellmann theorem is illustrated with an explicit calculation for the pion using a rainbow-ladder truncation of the Dyson-Schwinger equations: in the vicinity of the chiral limit sigma_pi = m_pi/2. This truncation also provides a decent estimate of sigma_rho because the two dominant self-energy corrections to the rho-meson's mass largely cancel in their contribution to sigma_rho. The truncation is less accurate for the omega, however, because there is little to compete with an omega->rho+pi self-energy contribution that magnifies the value of sigma_omega by ~25%. A Poincare' covariant Faddeev equation, which describes baryons as composites of confined-quarks and -nonpointlike-diquarks, is solved to obtain the current-quark mass dependence of the masses of the nucleon and Delta, and thereby sigma_N and sigma_Delta. This "quark-core" piece is augmented by the "pion cloud" contribution, which is positive. The analysis yields sigma_N~60MeV and sigma_Delta~50MeV.Comment: 22 pages, reference list expande

Shear surface control in blanking by adaptronic systems

Due to the increasing demand of improved geometrical accuracy and reduction of the scattering of mechanical properties in finished products, the need to enhance the active control of dynamic phenomena has become more and more important in the optimization of the blanking processes. The response of the frame to the oscillations arising is strictly dependent on the characteristics of the shock damping systems used and affects the finished shear surface of manufactured parts. In this paper, the application of innovative adaptronic damping systems and the evaluation of their performances are investigated. The developed devices, based on magneto-rheological fluids, allow controllable and reversible changes of damping characteristics during cutting process when an external magnetic field is applied. The experiments, conducted on a hydraulic press using both commercially available hydraulic dampers and magneto-rheological dampers, are presented with particular focus on the excited frequencies and the vibrations to quantify the impact of dynamic phenomena on the quality of final parts. Micro-hardness tests and metallurgical observations were performed to evaluate the quality of shearing surfaces, as well as to correlate the performances of adaptronic devices to the characteristics of the sheared surfaces

Modelling of turbine blades hot forging and cooling

The paper presents the modelling of hot forging and cooling stages in the production of turbine blades. The developed modelling approach utilises both numerical and experimental techniques. 3D numerical models of the forming and cooling stages are developed considering a full coupling between thermal, mechanical and metallurgical events; in order to assure accuracy in their results, these models are suitably calibrated through data obtained from industrial trials and laboratory physical simulation experiments. The possibility of investigating the influence of different cooling paths on the final component geometry through the above mentioned models is then shown and discussed. The approach is applied to two geometries of turbine blades made of two different high- strength steels