A Riemannian manifold optimization strategy is proposed to facilitate the relaxation of the orthonormality constraint in a more natural way in the course of performing independent component analysis (ICA) that employs a mutual information-based source-adaptive contrast function. Despite the extensive development of manifold techniques catering to the orthonormality constraint, only a limited number of works have been dedicated to oblique manifold (OB) algorithms to intrinsically handle the normality constraint, which has been empirically shown to be superior to other Riemannian and Euclidean approaches. Imposing the normality constraint implicitly, in line with the ICA definition, essentially guarantees a substantial improvement in the solution accuracy, by way of increased degrees of freedom while searching for an optimal unmixing ICA matrix, in contrast with the orthonormality constraint. Designs of the steepest descent, conjugate gradient with Hager-Zhang or a hybrid update parameter, quasi-Newton, and cost-effective quasi-Newton methods intended for OB are presented in this paper. Their performance is validated using natural images and systematically compared with the popular state-of-the-art approaches in order to assess the performance effects of the choice of algorithm and the use of a Riemannian rather than Euclidean framework. We surmount the computational challenge associated with the direct estimation of the source densities using the improved fast Gauss transform in the evaluation of the contrast function and its gradient. The proposed OB schemes may find applications in the offline image/signal analysis, wherein, on one hand, the computational overhead can be tolerated, and, on the other, the solution quality holds paramount interest.

A demand responsive transport system (DRTS) is a flexible system in which the stops are fixed and tours are variable. Client takes a reservation about a trip which could be in the same day or in the next. DRTS can be analyzed by two kind of dynamisms. The first is about the way in which requests arrives to the system. In this case DRTS could be static if the algorithm runs after received all the requests, or can be dynamic on line if the algorithm runs while the requests are arriving to the system. The second kind of dynamism is about when the requests are served: on reservation or on service.

To comply with the more and more restrictive international standards and regulations for noise and vibration levels on board passenger ships, a renewed interest on secondary N&V sources, with respect to propeller and machinery sources, has been observed. In particular, the increase of ship performances in terms of velocity has been directed on study the hydrodynamic noise sources and among the others turbulent boundary layer (TBL). The great difficulties encountered in simulating the wall pressure fluctuations (WPF) due to TBL at high Reynolds numbers and for complex configurations typical of a real ship have pushed the research community to develop models for WPF based on theoretical considerations and model scale tests. In particular, scaling laws for pressure spectra have been established at least for simple geometries and flow conditions and models of cross spectral density for their spatial characterization have been obtained. Unfortunately, model scale tests do not allow reaching Reynolds number values comparable with full scale conditions. Therefore, to validate current models an experimental campaign devoted to WPF measurements have been performed on the hull of a Ro-Ro Pax vessel. Numerical simulations of the flow around the ship hull were performed to evaluate mean flow parameters.

We present two possible approaches to calculate the momentum distribution n(p) and the Compton profile within the framework of the ab initio GW approximation on the self-energy. The approaches are based on integration of the Green's function along either the real or the imaginary axes. Examples will be presented on the jellium model and on real bulk sodium. Advantages and drawbacks of both methods are discussed in comparison with accurate quantum Monte Carlo calculations and x-ray Compton scattering experiments. We illustrate the effect of many-body correlations and disentangle them from band-structure and anisotropy effects by a comparison with density functional theory in the local density approximation. Our results suggest the use of G0W0 momentum distributions as reference for future experiments and theory developments.

This paper presents a simple mathematical model describing the bioventing technology for soil remediation. Bacteria biodegrade the pollutant and oxygen is injected in the soil to favorite the biodegradation process. The model is referred to the unsaturated zone and several simplifying hypothesis are used. In particular it is supposed that pure oxygen is injected in the subsoil and it is the unique gas present in the subsoil. From fluid dynamics theory in porous media a system of partial differential equations is obtained.

Marine phytoplankton is known to produce surface-active materials as part of its metabolism. The sea surface tension gradient due to the presence of plankton produced surfactants leads to a surface shear stress, commonly known as Marangoni stress, that can be of non-negligible intensity in areas of converging (or diverging) flows, where surface-active material concentrates (or lacks). A natural set-up where this condition can be observed is the Langmuir circulation that establishes in presence of wind and waves and exhibits periodic and permanent areas of alternating convergence and divergence. In the present work we adopt a simplified Large Eddy Simulation model for describing the Langmuir circulation and, by the use of a numerical model previously published, obtain an estimate of the Marangoni stress. The computed Marangoni stress peaks in the converging flow areas to values that are two orders of magnitude higher than in the case of absence of wind burst, previously studied by the authors. Such stress, usually disregarded within the numerical simulations of sea and other basin waters, is in fact capable to modify sensibly the distribution of the ecosystem biological components and should be considered for inclusion in the mathematical modelling.

Membro dell'International Advisory Board