Piezoelectric shunt damping is a well-known technique to damp mechanical vibrations of a structure, using a piezoelectric transducer to convert mechanical vibration energy into electrical energy, which is dissipated in an electrical resistance. Resonant shunts consisting of a resistance and an inductance connected to a piezoelectric transducer are used to damp structural vibrations in narrow frequency bands, but their performance is very sensitive to variations in structural modal frequencies and transducer capacitance. In order to overcome this drawback, a piezoelectric shunt damping technique with improved performance and robustness is presented in this paper. The design of the adaptive circuit considers the variation of the host structure's natural frequency as a project parameter. This paper describes an adaptive resonant piezoelectric vibration absorber enhanced by a synthetic negative capacitance applied to a shell structure. The resonant shunt circuit autonomously adapts its inductance value by comparing the phase difference of the vibration velocity and the current flowing through the shunt circuit. Moreover, a synthetic negative capacitance is added to the shunt circuit to enhance the vibration attenuation provided by the piezoelectric absorber. The circuitry is implemented using analog components. Validation of the proposed method is done by bonding the piezoelectric absorber on a freeformed metallic shell.

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Background:The Macaw palm (Acrocomia aculeata) is a palm tree native to the Tropical America Forests. This palm has stood out due to its high potential for the production of oil for biofuels, being an excellent source of renewable energy. However, due to the rudimentary way of exploring the Macaw palm, mostly using native people labor, it is not possible to extract the maximum economical potential that this plant can provide. In order to use the Macaw palm in industrial scale, new strategies using highperformance machinery in several segments of the production chain should be employed. Results:For that, its seedlings production must be broadly expanded, using modern techniques for its propagation and production on an industrial scale, since its present low germination rates when the natural way is employed. In this way, the present paper has the objective of establishing a database of the mechanical properties of the endocarp of the Macaw palm when submitted to compression efforts, typically used for removing almonds from the endocarp. The inherent variability of its mechanical properties was quantified, using three different crops sites. Conclusion:Important information about the mechanical properties of the Macaw palm endocarp is presented, serving as guideline for future works to genetic improvement of the Macaw palm, in order to obtain fruits with less variability in the mechanical properties of the endocarp and consequently improve the production on an industrial scale.

In order to reduce the human efforts during manual harvesting and increase the operational capacity and quality, the mechanization of the harvesting operation has been significantly increasing in the last few years for coffee crops. Therefore, for the design of coffee harvesting machines, the physical and mechanical properties of coffee branches are of utmost importance for harvesting machines projects. In this way, using an experimental approach, the present paper analyzes the variability of physical and mechanical properties in the coffee branches, of the Coffea arabica L., cultivar Catuaí-Vermelho (IAC 144). The branches were collected in different positions, along the orthotropic branch: upper, middle and lower parts of the plant. The mass, volume, specific mass, and modulus of elasticity of the collected specimens were determined considering their position in the plant and position along the branches. According to the position in the plant, no significant differences were found between the specific mass averages for the upper, middle, and lower parts of the plant. The research obtained an average of 1.24 GPa with a standard deviation of 0.13 GPa for the elasticity modulus. A significant increase in the elasticity modulus could be noted in the branches from the top to the bottom of the plant in the present research.