Analysis of the Surface Integrity in Cryogenic Turning of Ti6Al4 v Produced by Direct Melting Laser Sintering

The Ti6Al4V is widely utilized in the biomedical field thanks to its high biocompatibility, however, due to its low machinability, is classified as a difficult-to-cut material. With the goal of improving the surface quality of biomedical components made of Ti6Al4V produced by the DMLS additive manufacturing technology and later on machined, Liquid Nitrogen was tested as a coolant in semi-finishing turning. The integrity of the machined surfaces is evaluated in terms of surface defects and topography as well as residual stresses. The obtained results showed that the cryogenic machining assured a lower amount of surface defects and higher values of the residual compressive stressed compared to dry cutting, but a general worsening of the surface topography was detected

The simplicity of planar networks

Shortest paths are not always simple. In planar networks, they can be very different from those with the smallest number of turns - the simplest paths. The statistical comparison of the lengths of the shortest and simplest paths provides a non trivial and non local information about the spatial organization of these graphs. We define the simplicity index as the average ratio of these lengths and the simplicity profile characterizes the simplicity at different scales. We measure these metrics on artificial (roads, highways, railways) and natural networks (leaves, slime mould, insect wings) and show that there are fundamental differences in the organization of urban and biological systems, related to their function, navigation or distribution: straight lines are organized hierarchically in biological cases, and have random lengths and locations in urban systems. In the case of time evolving networks, the simplicity is able to reveal important structural changes during their evolution.Comment: 8 pages, 4 figure

Primordial Non-Gaussianity and Primordial Tensor Modes

The discoveries in observational cosmology of the last two decades led to a tremendous progress in cosmology. From a theory with mainly qualitative ideas about the expanding universe originated from a state with high density and temper- ature (Hot Big Bang cosmological model), cosmology rapidly evolved to a quantita- tive science that culminated with the formulation of the so-called ΛCDM model in which the composition and the evolution of the universe are known well enough to make very detailed predictions for a large number of observables on many different scales. Nonetheless, the ΛCDM model lacks in giving a satisfactory explanation of the initial conditions that are necessary to explain the subsequent evolution of the uni- verse. The inflationary paradigm elegantly solves this problem, furthermore it pro- vides a solution for other issues that affect the standard cosmology such as the horizon and the flatness problems. Although the basic framework of inflationary cosmology is now well-established, the microphysical mechanism responsible for the accelerated expansion remains a mystery. In this thesis, we describe how the physics underlying inflation can be probed using the higher-order correlations of primordial density perturbations (non-Gaussianity). In particular, we focus on those correlation functions that involve primordial gravity waves (tensor modes). The importance of primordial tensor modes lies in their theoretical robustness: while scalar perturbations are sensitive to many details, tensor modes are much more model independent. In this thesis we start by stressing this robustness, focussing on tensor non-gaussianity. We show that in single-field models of inflation (i.e. within the framework of the Effective Field Theory of Inflation) the predictions for the correlation functions that involve tensor modes are pretty model independent: tensor bispectra can assume very few shapes. After having discussed the prediction of the simplest models we focus on the squeezed limit of the tensor-scalar-scalar 3-point function. The leading behaviour of this correlator is fixed by the so-called Tensor Consistency Relation in many inflationary theories. This model independent prediction is very robust and can be violated only in theories where there is an additional helicity-2 state besides the graviton or in models that enjoy a symmetry pattern different from the standard one. In the last part of this thesis we explore both these possibilities. First we intro- duce a set of rule that allow us to include light particles with spin in the Effective Field Theory of Inflation, then focussing on the phenomenology that arises from an additional light spin-2 field. Finally, we describe a model of inflation which is very peculiar and cannot be incorporated in the context of the Effective Field Theory of Inflation: Solid Inflation. Here the “stuff” that drives inflation has the same sym- metry as an ordinary solid. We show that even in solids some consistency relations among the non-gaussian correlators can still be derived