A generalization of Kantorovich operators for convex compact subsets

In this paper we introduce and study a new sequence of positive linear operators acting on function spaces defined on a convex compact subset. Their construction depends on a given Markov operator, a positive real number and a sequence of probability Borel measures. By considering special cases of these parameters for particular convex compact subsets we obtain the classical Kantorovich operators defined in the one-dimensional and multidimensional setting together with several of their wide-ranging generalizations scattered in the literature. We investigate the approximation properties of these operators by also providing several estimates of the rate of convergence. Finally, the preservation of Lipschitz-continuity as well as of convexity are discussedComment: Research articl

Drinking wine at home: Hedonic analysis of sicilian wines using quantile regression

Abstract: In recent decades, the Sicilian wine industry has experienced a booming expansion because of the growing preferences of Italian consumers for Sicilian wines, especially in extra-regional markets. These consumers have been paying closer attention to Sicilian premium wines. For this reason, the objective of this study is to inform professional investors and wine managers about the consumer preferences with respect to the most important segment categories of domestically consumed Sicilian wines. Using the quantile regression technique, we analyzed the role of wine attributes and prices as an information tool in order to value for each wine segment the implicit price of the attributes affecting wine consumers\u2019 choices. The results indicate that Protected Designation of Origin (PDO) and Geographical Indication (PGI) certification is the main determinant in the wine price mechanisms and certified wines achieve premium prices that are progressively higher as the price level of the wine increases. Furthermore the effect of the brand on price formation seems to have a significant impact for low-end wines, whereas it has no specific impact on the price mechanism for high-end wines. Keywords: Consumer Scan Dataset, Geographic Origin, Hedonic Price, Robust Regression, Wine Consumptio

Kantorovich-type modifications of certain discrete-type operators on the positive real axis

The paper is concerned with the approximation properties of a modification of Kantorovich-type of a general class of operators of discrete-type. Such a modification was introduced by Agratini in 2015; in particular, we focus on extending its approximation properties in several function spaces, including polynomial weighted spaces of any degree as well as $L^p$-spaces. Some estimates of the rate of convergence are also obtained

Picking out a wine: Consumer motivation behind different quality wines choice

The quality scale of Italian wines is mainly organized in four categories: PDO, PGI, basic and bulk wine. Our analysis explicitly investigates the patterns and determinants of consumption for these four different types of wine by analyzing a representative sample of consumers from a traditional wine-producing country. This study provides for first time insights on quality perceptions of wines and verifies whether Italian consumers perceive significant differences among the different categories of wines. The overall results, obtained through a system of equation estimates, show that consumer motivations and wine consumption determinants change according to each different range of wine quality and thereby support a hierarchical scale of quality wines, as a fact consumers' motivation progressively changes as the quality scales of the wine increase or decrease. In addition, this study highlights for first time any differences in the consumption determinants between the PDO and the PGI wines in a national context and it suggests that the influence of the two different GI labels on the wine choice of consumers is truly different. Important insights were also provided for bulk wine whose consumption seems to be closely related to wine tourism and the desire to buy locally produced wines. Keywords: Basic wines, Bulk wines, Local wines, PDO, PG

A case study for spacegate point-to-point transportation: Evaluation of a reference end-to-end mission operations and assessment of the associated safety aspects

The ALTEC-conducted Spacegate feasibility study addresses the opportunities offered by the sub-orbital flight with special emphasis to future generation transportation. Pursuing the same systemic methodology of the initial Spacegate definition activities, this paper focuses on some specific aspects of suborbital operations and outlines a top level end-to-end operating cycle for a reference suborbital mission spanning from pre-flight, to flight, re-entry and post landing operations and associated Ground Segment. Special focus is given to identification of suitable locations in Italy for suborbital operations, and to liftoff and re-entry phases; the results of specific simulations are also reported, showing some lift off options and the feasibility of the spiral shaped descent maneuver that improves the pilot controllability of the vehicle during the re-entry phase. Further, this paper outlines within the selected reference mission, the main safety aspects considered as driving factors in planning and implementing future generation transportation; areas such as launch/landing range and relevant risk management/mitigation policies, as well as selection of safety driving criteria in the definition of trajectories and space transition corridors, and capabilities to monitor the vehicle ascent and re-entry will be assessed. Safety regulations will also be evaluated to protect launch range, drive spaceport site selection and consequently the ability of the spaceport to accommodate large numbers of passengers and participants, as well as a number of simultaneous operations such as training, vehicle integration tasks, and passenger preparation for flight. For human flight in general, and in particular for commercial point to point activities at this early stage, it is vital to minimize risk since a fatal accident at the very beginning of flights will put the entire business in jeopardy. The regulatory challenges with regards to safety will also be outlined in this paper, related to executing Spacegate activities in Europe and collaborations with the involved Agencies in the USA and Europe (FAA, ENAC, ENAV, SESAR, EASA) will be explored; in particular, some initiatives have already been started, that include active ALTEC participation to the IAASS Space Safety Technical Committee (SSTC) that was created to contribute to the advancement of the Safety in the area of the "Commercial Suborbital Flight"

A fully Eulerian solver for the simulation of multiphase flows with solid bodies: application to surface gravity waves

In this paper a fully Eulerian solver for the study of multiphase flows for simulating the propagation of surface gravity waves over submerged bodies is presented. We solve the incompressible Navier-Stokes equations coupled with the volume of fluid technique for the modeling of the liquid phases with the interface, an immersed body method for the solid bodies and an iterative strong-coupling procedure for the fluid-structure interaction. The flow incompressibility is enforced via the solution of a Poisson equation which, owing to the density jump across the interfaces of the liquid phases, has to resort to the splitting procedure of Dodd & Ferrante [12]. The solver is validated through comparisons against classical test cases for fluid-structure interaction like migration of particles in pressure-driven channel, multiphase flows, water exit of a cylinder and a good agreement is found for all tests. Furthermore, we show the application of the solver to the case of a surface gravity wave propagating over a submerged reversed pendulum and verify that the solver can reproduce the energy exchange between the wave and the pendulum. Finally the three-dimensional spilling breaking of a wave induced by a submerged sphere is considered

Continuous selections of Borel measures, positive operators and degenerate evolution problems

In this paper we continue the study of a sequence of positive linear operators which we have introduced in [9] and which are associated with a continuous selection of Borel measures on the unit interval. We show that the iterates of these operators converge to a Markov semigroup whose generator is a degenerate second-order elliptic differential operator on the unit interval. Some qualitative properties of the semigroup, or equivalently, of the solutions of the corresponding degenerate evolution problems, are also investigated

Beyond Shallow Water: appraisal of a numerical approach to hydraulic jumps based upon the Boundary Layer Theory

International audienceWe study the flow of a thin layer of fluid over a flat surface. Commonly, the 1-D Shallow-water or Saint-Venant set of equations are used to compute the solution of such flows. These simplified equations may be obtained through the integration of the Navier-Stokes equations over the depth of the fluid, but their solution requires the introduction of constitutive relations based on strict hypothesis on the flow régime. Here, we present an approach based on a kind of boundary layer system with hydrostatic pressure. This relaxes the need for closure relations which are instead obtained as solutions of the computation. It is then demonstrated that the corresponding closures are very dependent on the type of flow considered, for example laminar viscous slumps or hydraulic jumps. This has important practical consequences as far as the applicability of standard closures is concerned

Numerical Simulations of Vorticity Banding of Emulsions in Shear Flows

Multiphase shear flows often show banded structures that affect the global behavior of complex fluids e.g. in microdevices. Here we investigate numerically the banding of emulsions, i.e. the formation of regions of high and low volume fraction, alternated in the vorticity direction and aligned with the flow (shear bands). These bands are associated with a decrease of the effective viscosity of the system. To understand the mechanism of banding experimentally observed we have performed interface resolved simulations of the two-fluid system. The experiments were perfomed starting with a random distribution of droplets which, under the applied shear, evolves in time resulting in a phase separation. To numerically reproduce this process, the banded structures are initialized in a narrow channel confined by two walls moving in opposite direction. We find that the initial banded distribution is stable when droplets are free to merge and unstable when coalescence is prevented. In this case, additionally, the effective viscosity of the system increases, resembling the rheological behavior of suspensions of deformable particles. Droplets coalescence, on the other hand, allows emulsions to reduce the total surface of the system and hence the energy dissipation associated to the deformation, which in turn reduces the effective viscosity