The analysis of tool life and wear mechanisms in spindle speed variation machining

Regenerative chatter vibrations generally limit the achievable material removal rate in machining. The diffusion of spindle speed variation (SSV) as a chatter suppression strategy is mainly restricted to academy and research centers. A lack of knowledge concerning the effects of non-stationary machining is still limiting its use in real shop floors. This research is focused on the effects of spindle speed variation technique on tool duration and on wear mechanisms. No previous researches have been performed on this specific topic. Tool wear tests in turning were carried out following a factorial design: cutting speed and cutting speed modulation were the investigated factors. The carbide life was the observed process response. A statistical approach was used to analyze the effects of the factors on the tool life. Moreover, the analysis was extended to the wear mechanisms involved during both constant speed machining and SSV. The worn-out carbide surfaces were examined under a scanning electron microscope equipped with an energy dispersive X-ray spectrometer. Significant differences were appreciated. It was observed that SSV tends to detach the coatings of the inserts, entailing a mechanism that is quite unusual in wet steel turning and thus fostering the wear of the tool. The performed analysis allowed to deduce that the intensified tool wear (in SSV cutting) is mainly due to thermo-mechanical fatigue

A novel application of cryogenics in dieless sheet metal piercing

In tube punching, if the internal die is necessary to properly pierce the tube avoiding its collapse, it also represents a bottleneck to a rapid change of the punching set. In this research an innovative dieless tube punching approach has been conceived and studied. The use of a cryogenic fluid to force the material ductile-brittle transition is a way to limit the sheet deformation during the piercing process. The analysis of the innovative cryogenic punching was carried out both adopting numerical and experimental methodologies. A finite element FE model of the cryogenic punching was developed and updated in two stages. First, experimental tensile tests, performed at cryogenic temperatures, were used to characterize some material properties. Secondly, some piercing tests in cryogenic conditions were performed at different velocities and temperatures to fine update the model. A validation session was carried out to assess the model and the process feasibility. It was found that the FE model reproduced the experimental results within a maximum estimation error of 10% on both the punching force and tube deflection. Results showed that both the increment of the punching velocity and especially the decrement of the punching temperature could be the only viable solution for making the tube dieless punching industrially feasible

CHARACTERIZATION OF NEMOTIC DENTAL FIBROBLASTS

Oral Communication presented at the ";Forum des Jeunes Chercheurs";, Brest (France) 2011

Electron-phonon interaction in the solid form of the smallest fullerene C20_{20}

The electron-phonon coupling of a theoretically devised carbon phase made by assembling the smallest fullerenes C$_{20}$ is calculated from first principles. The structure consists of C$_{20}$ cages in an {\it fcc} lattice interlinked by two bridging carbon atoms in the interstitial tetrahedral sites ({\it fcc}-C$_{22}$). The crystal is insulating but can be made metallic by doping with interstitial alkali atoms. In the compound NaC$_{22}$ the calculated coupling constant $\lambda/N(0)$ is 0.28 eV, a value much larger than in C$_{60}$, as expected from the larger curvature of C$_{20}$. On the basis of the McMillan's formula, the calculated $\lambda$=1.12 and a $\mu^*$ assumed in the range 0.3-0.1 a superconducting T$_c$ in the range 15-55 K is predicted.Comment: 7 page

EFFECTS OF ZOLEDRONATE ON TWO- AND THREE-DIMENSIONAL OSTEOBLAST CULTURES

Oral Communication presented at the ";;Forum des Jeunes Chercheurs";;, Brest (France) 2011

Fishing activities overlap with bottlenose dolphin core habitats of Ischia and Procida islands

Tursiops truncatus – the common bottlenose dolphin – is a species of conservation interest, listed in Annex II and IV of Habitat Directive (92/43/CEE) that requires strict protection and the creation of specially protected areas for conservation, managed according to the ecological requirements of the species, within the “Nature 2000” network. A local population of bottlenose dolphins has been monitored over fifteen years in the sea waters around Ischia and Procida Islands in the frame of the Ischia Dolphin Project, an ongoing long-term research program on Tyrrhenian cetaceans. The study area lies partially within the boundaries of "Regno di Nettuno" Marine Protected Area (MPA), which is classified by IUCN as an Important Marine Mammal Area (IMMA), where pods of cetacean key species such as common dolphin (Delphinus Delphis), bottlenose dolphin, and fin whale (Balaenoptera physalus) live. Investigating habitat exploitation by bottlenose dolphins is crucial for conserving this protected species. Between 2004 and 2018, 1186 surveys were performed, resulting in 91 encounters with the species. To investigate bottlenose dolphins' habitat exploitation, we combined both behavioral observations and spatial analysis. Kernel Density Estimation and Hotspot analysis allowed to delineate fine-scale areas of higher concentration of critical activities (feeding, socializing/mating, resting) and interactions with fisheries (gillnets and trawlers). Results show a vital region for feeding, resting, social cohesion, and mating, i.e. essential habitat for bottlenose dolphins. Unfortunately, these critical habitats are only partially protected by the zonation of the MPA, because it overlaps with human activities, especially fishing. Although the influence of fisheries on dolphins' behavior and movements needs further investigation, the results thus far collected suggest that effective management measures should take into account the human-animal conflict that can arise in these critical areas

EVALUATION OF THE CYTOTOXICITY OF PULP FLOOR PERFORATION FILLING MATERIALS BY USING IN PARALLEL 2D AND 3D CULTURE MODELS

Oral Communication presented at the ";Forum des Jeunes Chercheurs";, Brest (France) 2011

Vantagens comparativas reveladas e orientação regional das exportações agrícolas brasileiras para a União Européia

The paper analyses the Brazilian agricultural trade with the European Union (EU), in the context of the negotiations for a commercial agreement between Mercosur and the EU. We calculate indexes of revealed comparative advantages (RCA) and regional orientation (RO), for the period from 1991 to 2001. We selected the following products: soybeans, orange juice, tobacco, chicken meat, bovine meat, sugar and coffee. Altogether, these products corresponded to more than 20% of total Brazilian exports in that period. The products that show the highest Brazilian participation in world trade are soybeans, orange juice and coffee. Except for sugar, all the analyzed products had the EU as an important destiny for the exports. The results indicate comparative advantages for the Brazilian products, showing stable or increasing indexes along the decade. Besides, there is a high orientation of Brazilian exports to the EU, except for chicken meat and sugar, but with no increases in the period. Thus, an agreement between the blocs, reducing or eliminating tariff and non-tariff barriers, may result in a trade creation, in favor of Brazilian agricultural exports to the EU.Regional integration, International trade, Comparative advantages, Agriculture, International Relations/Trade,

Influence of diameter on temperature dynamics of hot carriers in photoexcited GaAsP nanowires

Semiconductor nanowires (NWs) often present different structural and opto-electronic properties than their thin film counterparts. The thinner they are, the larger these differences are. Here, we present femtosecond transient absorbance measurements on GaAs0.8P0.2 NWs of two different diameters, 36 and 51 nm. The results show that thinner NWs sustain a higher carrier temperature for longer times than thicker NWs. This observation suggests that, in thinner NWs, the buildup of a hot-phonon bottleneck is easier than in thicker NWs because of the increased phonon scattering at the NW sidewalls, which facilitates the buildup of a large phonon density. Moreover, the important observation that the carrier temperature in thin NWs is higher than in thick NWs already at the beginning of the hot carrier regime suggests that the phonon-mediated scattering processes in the nonthermal regime play a major role at least for the carrier densities investigated here (8 × 1018 to 4 × 1019 cm–3). Our results also suggest that the phonon scattering at crystal defects is negligible compared with the phonon scattering at the NW sidewalls