Geometric properties of solutions of the levi-equation

Sunto Data un'ipersuperficie reale M di C² si definisce la curvatura di Levi k di M. Se M è un grafico x₄=u(x₁, x₂, x₃) allora u è soluzione di un'equasione quasi-lineare ellittica degenere L(k; u)=0, l'equazione di Levi. Net presente lavoro si stabiliseono alcune proprietà geometriche delle solusioni dell'equazione L(k; u)=0.

---

---

Supported by M.P.I.     

Diffusion constant of Ga adatom on GaAs (001) surface: Molecular dynamics calculations

A valence force field to reproduce both the phonon dispersion curves of crystalline GaAs and first principle derived interaction energies of Ga adatom on GaAs (001) surface has been optimized. Calculations of diffusion constant of isolated Ga atoms on the GaAs surface have been performed by molecular dynamics classical trajectory simulations.     

A Local Optima Network View of Real Function Fitness Landscapes

The local optima network model has proved useful in the past in connection with combinatorial optimization problems. Here we examine its extension to the real continuous function domain. Through a sampling process, the model builds a weighted directed graph which captures the function’s minima basin structure and its interconnection and which can be easily manipulated with the help of complex networks metrics. We show that the model provides a complementary view of function spaces that is easier to analyze and visualize, especially at higher dimensions. In particular, we show that function hardness as represented by algorithm performance is strongly related to several graph properties of the corresponding local optima network, opening the way for a classification of problem difficulty according to the corresponding graph structure and with possible extensions in the design of better metaheuristic approaches.     

NMR-based metabolomics to evaluate the milk composition from Friesian and autochthonous cows of Northern Italy at different lactation times

It is well established that different factors affect milk composition in cows and that milk composition, in turn, affect both technological and nutritional qualities. In this respect the comprehension of the metabolic variability of milk composition in relation to the lactation time as well as to the genetic background may be of paramount importance for the agri-food industries. In the present study we investigated the variations of the metabolic profiles during lactation in milks obtained from Friesian and autochthonous races from Northern Italy by ¹H NMR metabolomics. Furthermore, the external factors influencing the milk composition were minimized: the cows were breeded in the same farm, were fed with the same diet and were paired for the lactation interval and lactation stage. Our results showed a difference in milk composition between races and in relation to late lactation. The PLS-DA analysis permitted to distinguish the Friesian and autochthonous cow milks at the investigated different lactation times. Interestingly, the metabolites significantly involved into the discrimination between races appeared to be also technological property parameters, highlighting the importance of maintaining the biodiversity of cow breeds. Therefore, NMR-based metabolomics of milk could represent an informative tool to identify metabolites involved in milk quality both from a nutritional and industrial perspective.     

On Some Cohomological Properties of Almost Complex Manifolds

We study a special type of almost complex structures, called pure and full and introduced by T.J. Li and W. Zhang (, 2007), in relation to symplectic structures and Hard Lefschetz condition. We provide sufficient conditions to the existence of the above type of almost complex structures on compact quotients of Lie groups by discrete subgroups. We obtain families of pure and full almost complex structures on compact nilmanifolds and solvmanifolds. Some of these families are parametrized by real 2-forms which are anti-invariant with respect to the almost complex structures.