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  • Author: Antoanetta Lungu x
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The Aharonov-Bohm Effect and Transport Properties in Graphene Nanostructures

Abstract

This paper investigates the possibility to improve the filtering process of flue gas by separation of suspended nanoparticle using dielectrophoresis. The study focuses on the particles having an average radius of about 50-150 nm, that cannot be filtrated by classical techniques but have a harmful effect for environment and human health. The size distribution nanoparticles collected from the flue gas filters of a hazardous waste incinerator plant were evaluated. Based on obtained experimental data and a proposed mathematical model, the concentration distribution of nanoparticle suspended in flue gas inside a microfluidic separation device was analyzed by numerical simulations, using the finite element method. The performances of the device were described in terms of three new specific quantities related to the separation process, namely Recovery, Purity and Separation Efficiency. The simulations could provide the optimal values of control parameters for separation process, and aim to be a useful tool in designing microfluidic devices for separating nanoparticle from combustion gases.

Open access
Complex Impedance of Manganese Ferrite Powders Obtained by Two Different Methods

Abstract

Two samples of manganese ferrite powder were obtained by the calcination method (sample A) and hydrothermal method (sample B). The crystal structure of the samples has been determined using X-ray diffraction analysis (XRD). The results shown that the sample A has three phases (FeMnO3, Mn2O3 and Fe2O3) and the prevailing phase is FeMnO3 with perovskite structure and the sample B has only a single phase (MnFe2O4).

The grain morphology was analyzed by scanning electron microscopy (SEM) and the compositional analysis was done by energy dispersive spectroscopy (EDAX).

Measurements of the frequency (f) and temperature (T) dependent complex impedance, Z(f, T) = Z’(f, T) - i Z’’(f, T) of the samples over the frequency range 20 Hz - 2 MHz, at various temperature values from 300C to 1100C are presented. From these measurements, we have shown that the temperature dependence of the relaxation time is of Arhenius type, which suggests that the conduction process is thermally activated. The values obtained for the activation energy Ea, are: 16meV (sample A) and 147.65meV (sample B).

Applying complex impedance spectroscopy technique, the obtained results shows the shape of a single semicircle at each temperature over the measurement range, meaning that the electrical process obeys to a single relaxation mechanism. The impedance and related parameters of the electrical equivalent circuit depend on the temperature and the microstructure of samples. The resistive and capacitive properties of the investigated samples are dominated with the conduction and relaxation processes associated with the grain boundaries mechanism..

Open access