Sharif Digital Repository

Purpose - The purpose of this paper is to investigate the effect of power on pulsed plasma thruster (PPT) discharge current with respect to its peak, duration, and behavior while the power elevates in a low power range. Design/methodology/approach - A rectangular parallel-plate breech-fed PPT has been developed with a self-inductor coupling element connecting the PPT cathode to the ignitor plug cathode. The PPT has been operated in vacuum chamber at 10-6mbar and its discharge current has been recorded using a Rogowski coil while input power has been changed by means of varying the capacitor voltage at given capacitance and frequency. Findings - The analysis leads to elucidate the effects of... 

The preparation of composite manganese dioxide (MnO2) nanoparticles in an ordered mesoporous carbon (CMK-3) matrix and its use for constructing a new wide-potential-window supercapacitor is reported. CMK-3 is prepared using mesoporous silica as a hard template and sucrose as carbon source. The different ratios of MnO2/CMK-3 composite is synthesized by impregnating CMK-3 with a Mn(NO3)2·4H 2O solution followed by annealing in nitrogen. Physical properties, morphology, and specific surface area were characterized by X-ray diffraction, transmission electron microscopy, and nitrogen sorption measurements, respectively. The electrochemical properties of the composite were studied by cyclic... 

Partial Discharge (PD) measurements in Ultra High Frequency (UHF) band requires modern techniques for monitoring of power transformer. This is a topic of interest investigated in this field, especially in recent years. Different experimental models, such as: defect models, and winding models are used in PD studies of power transformer. The purpose in application of these models is to represent and simulate the real transformer performance using a simple model. The proposed model needs to be a simplified one which can be implemented of them. However, the applied simplifications may result in some changes (inaccuracy) into the recorded PD current signals captured by UHF sensors. These changes... 

We fabricated gas sensors based on field ionization from multiwalled carbon nanotube (MWCNT) arrays grown on porous silicon templates. MWCNTs were grown through thermal chemical vapor deposition. We measured breakdown voltages, discharge and pre-discharge currents of the device for various gases in different concentrations. Our gas ionization sensors (GIS) presented good sensitivity, selectivity and short response time. The GISs based on porous substrates showed higher discharge current and good mechanical stability in comparison to those which were fabricated on polished silicon substrates. Additionally, we applied a high electric field to align CNTs. This increased the pre-breakdown... 

We fabricated a high rate capability supercapacitor based on fluorine-doped graphene-carbon nanotubes aerogel network (G-CNT-F). Based on the electrochemical impedance spectroscopy data, the fluorination decreases the charge transfer resistance of graphene sheets, while CNTs act as spacer in the 3D structure. Therefore, both treatments improved the electrochemical properties of the resulted aerogel. Based on the Fourier transform infrared spectroscopy and XPS results, these excellent performances are attributed to semi-ionic bonds between fluorine and carbon. The specific capacitance of the graphene aerogel showed 78% decrease, when discharge current increases from 2 to 40 mA, while the... 

A mathematical model was developed to describe the performance of nanoparticulate mixed oxide pseudocapacitors based on RuO 2-MO 2 (M being another suitable transition metal) under galvanostatic charge/discharge regime. Both double layer and faradaic processes were taken into account. The effects of the active material's particle size and composition were examined. Furthermore, the influence of discharge current on the extents of double layer and faradaic contributions was analyzed. The model analysis showed that the energy density declined upon increasing the volume fraction of larger particles. © 2008 Springer-Verlag