185 research outputs found
Hybrid piezoelectric energy harvesting transducer system
A hybrid piezoelectric energy harvesting transducer system includes: (a) first and second symmetric, pre-curved piezoelectric elements mounted separately on a frame so that their concave major surfaces are positioned opposite to each other; and (b) a linear piezoelectric element mounted separately on the frame and positioned between the pre-curved piezoelectric elements. The pre-curved piezoelectric elements and the linear piezoelectric element are spaced from one another and communicate with energy harvesting circuitry having contact points on the frame. The hybrid piezoelectric energy harvesting transducer system has a higher electromechanical energy conversion efficiency than any known piezoelectric transducer
Gravitational Anomaly and Hawking Radiation of Brane World Black Holes
We apply Wilczek and his collaborators' anomaly cancellation approach to the
3-dimensional Schwarzschild- and BTZ-like brane world black holes induced by
the generalized C metrics in the Randall-Sundrum scenario. Based on the fact
that the horizon of brane world black hole will extend into the bulk spacetime,
we do the calculation from the bulk generalized C metrics side and show that
this approach also reproduces the correct Hawking radiation for these brane
world black holes. Besides, since this approach does not involve the dynamical
equation, it also shows that the Hawking radiation is only a kinematic effect.Comment: 11 pages. v2: minor changes and references adde
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Combining opinions from several experts
This paper addresses the problem of aggregating a number of expert opinions which have been expressed in some numerical form. An important feature of sets of expert opinions is the possibility of stochastic dependence between members of the sets. We develop an approach for combining expert opinions which formally allows for such dependence. This approach is based on an extension of the Dempster-Shafer theory, a well-known calculus for reasoning with uncertainty in artificial intelligence
The Load Capability of Piezoelectric Single Crystal Actuators
Piezoelectric lead magnesium niobate-lead titanate (PMN-PT) single crystal is one of the most promising materials for electromechanical device applications due to its high electrical field induced strain and high electromechanical coupling factor. PMN-PT single crystal-based multilayer stack actuators and multilayer stack-based flextensional actuators have exhibited high stroke and high displacement-voltage ratios. The actuation capabilities of these two actuators were evaluated using a newly developed method based upon a laser vibrometer system under various loading conditions. The measured displacements as a function of mechanical loads at different driving voltages indicate that the displacement response of the actuators is approximately constant under broad ranges of mechanical load. The load capabilities of these PMN-PT single crystal-based actuators and the advantages of the capability for applications will be discussed
Quasi-local energy-momentum and energy flux at null infinity
The null infinity limit of the gravitational energy-momentum and energy flux
determined by the covariant Hamiltonian quasi-local expressions is evaluated
using the NP spin coefficients. The reference contribution is considered by
three different embedding approaches. All of them give the expected Bondi
energy and energy flux.Comment: 14 pages, accepted by Phys.Rev.
Effect of Bending Stiffness of the Electroactive Polymer Element on the Performance of a Hybrid Actuator System (HYBAS)
An electroactive polymer (EAP)-ceramic hybrid actuation system (HYBAS) was developed recently at NASA Langley Research Center. This paper focuses on the effect of the bending stiffness of the EAP component on the performance of a HYBAS, in which the actuation of the EAP element can match the theoretical prediction at various length/thickness ratios for a constant elastic modulus of the EAP component. The effects on the bending stiffness of the elastic modulus and length/thickness ratio of the EAP component were studied. A critical bending stiffness to keep the actuation of the EAP element suitable for a rigid beam theory-based modeling was found for electron irradiated P(VDF-TrFE) copolymer. For example, the agreement of experimental data and theoretical modeling for a HYBAS with the length/thickness ratio of EAP element at 375 times is demonstrated. However, the beam based theoretical modeling becomes invalid (i.e., the profile of the HYBAS movement does not follow the prediction of theoretical modeling) when the bending stiffness is lower than a critical value
Measurement of Elastic Microfence Deflection for Aerodynamic Flow Sensing
Bio-inspired artificial hair sensors have the potential to detect aerodynamic flow features such as stagnation point, flow separation, and flow reattachment that could be beneficial for ight control and performance enhancement of aircraft. In this work, elastic microfence structures were tested on a at-plate setup. The microfences were fabricated from a two-part silicone molded against a template patterned by laser ablation. The response of the microfences to different freestream velocities and to flow reversal at the sensor were recorded via an optical microscope
Shear Stress Sensing with Elastic Microfence Structures
In this work, elastic microfences were generated for the purpose of measuring shear forces acting on a wind tunnel model. The microfences were fabricated in a two part process involving laser ablation patterning to generate a template in a polymer film followed by soft lithography with a two-part silicone. Incorporation of a fluorescent dye was demonstrated as a method to enhance contrast between the sensing elements and the substrate. Sensing elements consisted of multiple microfences prepared at different orientations to enable determination of both shear force and directionality. Microfence arrays were integrated into an optical microscope with sub-micrometer resolution. Initial experiments were conducted on a flat plate wind tunnel model. Both image stabilization algorithms and digital image correlation were utilized to determine the amount of fence deflection as a result of airflow. Initial free jet experiments indicated that the microfences could be readily displaced and this displacement was recorded through the microscope
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