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In recent years, microbial fuel cells (MFCs) have gained much attention due to their potential to generate energy in a sustainable manner from living microorganisms. Research has shown that electrode design is a critical factor for MFCs power enhancement. In this study, we designed and fabricated MFCs energy-harvesting devices with living bacteria, and we investigated the effect of the surface roughness of the electrodes on power generation. In batch experiments of our MFCs, we found that the total power delivered could be enhanced using electrodes having rough surfaces with protruded micro-structures relative to that of electrodes with a flat surface. This was due to the delayed acidification resulting from the changes in bio-film formation between them. [ABSTRACT FROM AUTHOR]

Clamping loss caused by elastic wave radiation to a support is one of the most dominant loss mechanisms in predicting the quality factor of very or ultra high frequency nanocantilever resonators. To consider nanosurface effects and different scales of the resonator and support, we propose a multiscale model combining a scale-bridging model for the resonator and a perfectly matched layer to estimate the loss in the support. The proposed model is used to investigate the surface effect on the nanoresonator and also shows the tradeoff between the resonant frequency and the quality factor with or without the surface effects. [ABSTRACT FROM AUTHOR]

In this work, the structural response of thin-walled composite beams with pretwist angle is investigated by using a mixed beam approach that combines the stiffness and flexibility methods in a unified manner. The Reissner's semi-complimentary energy functional is used to derive the stiffness matrix that approximates the beam in an Euler–Bernoulli level for extension and bending and Vlasov level for torsion. The bending and torsion-related warpings induced by the pretwist effects are derived in a closed form. The developed theory is validated with available literature and detailed finite element structural analysis results using the MSC/NASTRAN. Pretwisted composite beams with rectangular solid and thin-walled box sections are illustrated to validate the current approach. Acceptable correlation has been achieved for cases considered in this study. The effects of pretwist and fiber orientation angles on the static behavior of pretwisted composite beams are also studied. [ABSTRACT FROM AUTHOR]

In this paper, a simple but effective design for implementing a negative wing twist in a beetle-mimicking wing system is presented. The effectiveness of the design in terms of force generation and power consumption is confirmed by both experiment and calculation. An unsteady blade-element-theory model is used to estimate the aerodynamic forces produced by two different wing kinematics of a flapping-wing system. The model was first validated with the measurement data and two three-dimensional computational-fluid-dynamics results from the literature. The difference between the estimated average lift and the measured lift is 5.6%, which proves that the unsteady blade-element-theory model provides reasonable aerodynamic force estimation. The time history of the current estimation is also close to the measured data and is in between the two computational-fluid-dynamics results. The forces generated by the flapping wings with and without wing twist are estimated using the unsteady blade-element theory to investigate effect of the wing twist on the force generation. The result shows that the flapping-wing system with wing twist produces a 9.5 % larger average vertical force or thrust while consuming 37 % less power than the flapping-wing system without wing twist. The measured thrust by the swing test also shows 13.2 % increase for the flapping wing with wing twist. Thus, by the estimation and measurement, it is confirmed that the wing twist improves the thrust generation. [ABSTRACT FROM AUTHOR]