Edge-carboxylated graphite (ECG) was produced by grinding pristine graphite in a planetary ball-mill machine. Transmission electron microscope was used to confirm the layers of graphene in ECG. The elemental analyses showed that the oxygen contents are different between ECG samples. The vibrational analysis of single-and five-layered graphene was conducted using finite element method within ANSYS. The vibrational behaviors of cantilevered and fixed graphene with one or five layers were modeled using three-dimensional elastic beams of carbon bonds and point masses. The dynamic analysis was conducted using nonlinear elastic elements within LS-DYNA. The natural frequencies, strain and kinetic energy of the beam elements were calculated considering the van der Waals forces between the carbon atoms in the hexagonal lattice. The natural frequencies, strain and kinetic energy of the graphene sheets were estimated based on the geometrical type and the layered sheets with boundary conditions. In the dynamic analysis, the change in displacement over time appears larger along the x-and y-axes than along the z-axis, and the value of the displacement vector sum appears larger in the five-layer graphene than in the single-layer graphene.
Our objective in this study was to investigate a sensor for volatile organic compounds based on a graphite (G)/polypropylene glycol (PPG) hybrid composite (HC) for sensing hybrid elements. The G/PPG HC sensor films for organic-matter detection were successfully fabricated on polyethylene terephthalate (PET) film with a simple blade-coating method. The sensing paste based on G/PPG (1:2) HC showed good dispersibility and stability. In addition, G/PPG HC sensor films with organic compounds showed different thickness changes as a function of the G/PPG ratio because of the swelling effect of the polymer. The observed differences in resistance of the G/PPG HC films corresponded to those of common organic compounds, suggesting that the disconnection of graphite caused by the swollen PPG matrix caused explosive resistance change. Moreover, we evaluated the sensitivity of typical hydrocarbon materials, such as benzene and toluene, in the sensor film as well as petroleum materials without moisture-induced malfunctions. This study could provoke knowledge about superior sensing with cost-effective and easily scalable materials using polymer/graphite composite-based sensors to improve the sensitivity, selectivity, and stability of chemical sensor applications.
In this paper, the robustness in practical control problems is studied and verified. For such study and verification, the position control of a twin rotor MIMO system is considered in terms of both the simulation and the experiment. With the coupled model of the twin rotor MIMO system, the conventional input-output feedback linearization based nonlinear controller is designed first without the consideration of model uncertainties and its performance is analyzed through both the simulation and the experiment. Based on the analysis results, a robust controller, the sliding mode controller for the twin rotor MIMO system is designed. Accordingly, it is concluded that the importance of the robustness consideration in practice and practical issue for designing a robust controller are verified.
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