Objective: To compare the circulating levels of MMP-2 and TIMP-2 and the MMP-2/TIMP-2 ratio in control, obese, and obese hypertensive children and adolescents and to assess whether hypoadiponectinemia is associated with MMP-2 and TIMP-2 levels and MMP-2/TIMP-2 ratios. Methods: Studies were carried out with 53 control, 73 obese, and 29 obese hypertensive children and adolescents in this cross-sectional study. Adiponectin and TIMP-2 concentrations were measured by ELISA. MMP-2 concentrations were measured by gelatin zymography. Multiple linear regression analysis was carried out to assess the effects of adiponectin on MMP-2 and TIMP-2 levels and MMP-2/TIMP-2 ratios. Results: The obese hypertensive group had the lowest adiponectin levels among groups (P < 0.05) while obese subjects had lower adiponectin levels than control subjects (P < 0.05). Obese hypertensive subjects also had higher circulating MMP-2 concentrations than obese subjects (P < 0.05) and had the highest MMP-2/TIMP-2 ratios among groups (P < 0.05). Moreover, obese/hypertensive subjects had the lowest TIMP-2 levels among groups (P < 0.05). A multiple linear regression analysis showed that MMP-2 levels and MMP-2/TIMP-2 ratios are negatively associated with adiponectin levels (P 5 0.034 and P 5 0.011, respectively) while TIMP-2 levels is positively associated with adiponectin levels (P 5 0.013). Conclusions: Increased activity of MMP-2 (MMP-2/TIMP-2 ratio) and reduced TIMP-2 levels may play an important role in clinical hypertension of childhood obesity. Additionally, hypoadiponectinemia may contribute to increased activity of MMP-2 in obese/hypertensive children and adolescents.

Carbon fibre reinforced carbon composites were turned using uncoated and CVD diamond coated Si 3 N 4 cutting tools. Si 3 N 4 inserts were fabricated by pressureless sintering and some of them were coated with a 2.5µm thick diamond film produced by hot filament chemical vapour deposition. The cutting forces and the tool wear behaviour were investigated as a function of the cutting speed (v = from 2.5 to 10 m•s -1 ). The cutting forces were recorded and the final tool damage was evaluated by optical and scanning electron microscopy observations. The turning tests performed with the uncoated tips show that the cutting forces notably increase with the cutting speed and the cutting length. Severe wear of the tool flank face takes place due to rubbing by the abrasive carbon powder generated during the turning operation, the tool wear increasing with the cutting speed. Conversely, CVD diamond coated Si 3 N 4 tips exhibit low and constant cutting forces at the different cutting parameters, due to the formation of a carbon lubricant layer. The existence of this layer and the outstanding diamond hardness anticipates the use of CVD diamond coated materials for the high speed machining of CFRC composites.

Due to their high hardness and wear resistance Si3N4 based ceramics are one of the most suitable cutting tool materials for machining hardened materials. Therefore, their high degree of brittleness usually leads to inconsistent results and sudden catastrophic failures. Improvement of the functional properties these tools and reduction of the ecological threats may be accomplished by employing the technology of putting down hard coatings on tools in the state-of-the-art PVD processes, mostly by improvement of the tribological contact conditions in the cutting zone and by eliminating the cutting fluids. However in this paper was used a Si3N4 based cutting tool commercial with a layer TiN coating. In this investigation, the performance of TiN coating was assessed on turning used to machine an automotive grade compacted graphite iron. As part of the study were used to characterise the performance of cutting tool, flank wear, temperature and roughness. The results showed that the layer TiN coating failed to dry compacted graphite iron under aggressive machining conditions. However, using the measurement of flank wear technique, the average tool life of was increased by Vc=160 m/min.The latter was also observed using a toolmakers microscope and scanning electron microscopy (SEM).

In this work, an yttrium and rare-earth oxides mixture, CRE2O3, produced at DEMAR-FAENQUIL, was used as sintering additive for silicon nitride (Si3N4) ceramics. Samples were produced by uniaxial hot-pressing, using mixtures of CRE2O3- Al2O3 or CRE2O3-AlN as additives. Four kind of hot-pressed Si3N4 were used as oxidation samples: Si3N4+ 5vol% or 20vol.% of CRE2O3-Al2O3 (forming only β-Si3N4 as crystalline phase), Si3N4+ 5vol.%CRE2O3-AlN (α-SiAlON+β) and Si3N4+ 20vol.%CRE2O3-AlN (only α-SiAlON). The oxidation behavior was evaluated at 13500C, in air up to 160 hours. The oxidation rate of Si3N4 ceramics increased with increasing CRE2O3/Al2O3 content, and oxidation kinetics obeyed the usual parabolic law. Pure α-SiAlONs (Si3N4 +20 vol.% CRE2O3-AlN) were high oxidation resistant with weight gain, after 160 hours, of 0.1 mg.cm-2, while β-Si3N4+20vol.%CRE2O3- Al2O3 showed a weight gain of 1.4 mg.cm-2 after only 10 hours. The oxidation behavior of these ceramics was comparable with ceramics sintered with Y2O3. This result confirms the possibility of the fabrication of high oxidation resistance Si3N4 ceramics using the low cost sintering additive CRE2O3.

There is a substantial increase on carbon-carbon composites use for engineering applications, considering its high temperature properties and low specific mass. However the machining costs are relatively high, and new cutting tools, mainly ceramics, must be developed to overcome such difficulty, aiming cost reductions. In this work, silicon nitride based ceramics has been prepared , by pressureless sintering of silicon nitride powders and appropriate amounts of Al2O3,Ce2O3, Y2O3 and AlN. Cutting tools were prepared from the sintered materials, with geometry according to ISO1832. Selected cutting tools were also diamond coated by a hot filament-assisted Chemical Vapor Deposition (HFCVD) diamond coating process. Carbon Fiber Reinforced Carbon (CFRP) composites machining was performed, to evaluate the diamond coating influence on machining performance. After the tests, the uncoated tools presented severe flank wear and shorter life than the diamond coated ceramic tools. This flank wear is caused by the abrasive carbon powder generated during the facing operation. On CVD diamond coated α-SiAlON ceramic tools, no flank wear was observed, and the cutting edge remained unmodified, even for severe test conditions, such as high cutting length and speed. Carbon particles, originated from the machined composite, do not promotes diamond film rupture, but instead, acts as lubricant film and reduces composite surface initial roughness.