Polytechnic University of Turin

About: Polytechnic University of Turin is a education organization based out in Turin, Piemonte, Italy. It is known for research contribution in the topics: Finite element method & Computer science. The organization has 11553 authors who have published 41395 publications receiving 789320 citations. The organization is also known as: POLITO & Politecnico di Torino.

Field And Source Equivalence In Source Reconstruction On 3D Surfaces

Abstract: This paper describes in detail difierent formulations of the inverse-source problem, whereby equivalent sources and/or flelds are to be computed on an arbitrary 3-D closed surface from the knowledge of complex vector electric fleld data at a specifled (exterior) surface. The starting point is the analysis of the formulation in terms of the Equivalence Principle, of the possible choices for the internal flelds, and of their practical impact. Love's (zero interior fleld) equivalence is the only equivalence form that yields currents directly related to the flelds on the reconstruction surface; its enforcement results in a pair of coupled integral equations. Formulations resulting in a single integral equation are also analyzed. The flrst is the single-equation, two-current formulation which is most common in current literature, in which no interior fleld condition is enforced. The single-current (electric or magnetic) formulation deriving from continuity enforcement of one fleld is also introduced and analyzed. Single-equation formulations result in a simpler implementation and a lower computational load than the dual-equation formulation, but numerical tests with synthetic data support the beneflts of the latter. The spectrum of the involved (discretized) operators clearly shows a relation with the theoretical Degrees of Freedom (DoF) of the measured fleld for the dual-equation formulation that guarantees extraction of these DoF; this is absent in the single-equation formulation. Examples conflrm that single- equation formulations do not yield Love's currents, as observed both with comparison with reference data and via energetic considerations. The presentation is concluded with a test on measured data which shows the stability and usefulness of the dual-equation formulation in a situation of practical relevance.

Microrheological Modeling of Flow-Induced Crystallization

Abstract: The problem of flow-induced crystallization (FIC) of polymer melts is addressed via a microrheological approach. In particular, the Doi−Edwards model with the so-called independent alignment approximation (DE−IAA) is used to calculate the flow-induced change of free energy. Subsequently, the crystallization induction time, i.e., the nucleation characteristic time, is calculated in isothermal steady shear and uniaxial elongational flows. Asymptotic, analytical expressions for the induction time are also derived in the limit of low and high Deborah number (the product of the deformation rate and the polymer relaxation time). The DE−IAA model is found to give more realistic predictions than those of simpler, dumbbell-like models already proposed in the literature. When compared to existing FIC experimental data in shear flow, good quantitative agreement is found with the polymer relaxation time as the only adjustable parameter of the model.