Dan Malaescu, Ioan Grozescu, Paula Sfirloaga, Paulina Vlazan and Catalin N. Marin
Two samples of NaTaO3 perovskite materials were prepared by the standard hydrothermal method at the same reaction temperature (600 °C) but with different sintering times: 6 hours for sample S1 and 12 hours for sample S2.
Using X-ray diffraction (XRD), it shows that samples S1 and S2 are mixtures of Na-Ta oxides (Ta2O5 and the prevailing phase NaTaO3). The scanning electron microscopy analysis (SEM), shows that the grains are connected each other in agglomerated clusters of size about few hundred nanometers.
The frequency (f) dependencies of complex impedance, Z(f) = Z’(f) - i Z’’(f) of the samples, over the frequency range 20 Hz - 2 MHz, at room temperature are presented. The real component Z’ of the complex impedance decreases with increasing frequency and the imaginary component Z’’ has two maximum corresponding to two relaxation processes.
The results obtained from the complex impedance spectroscopy, Z’’(Z’) showed the appearance of two semicircles, corresponding to grain and grain boundary mechanism. Experimental results have been fitted with two parallel RC equivalent circuits connected in series and the parameters R and C have been evaluated.
In this study, time dependent three-dimensional numerical simulations were carried out using the STHAMAS3D software in order to understand the effects of forced convection induced by mechanical stirring of the melt, on the crucible dissolution rate and on the impurities distribution in multicrystalline silicon (mc-Si) melt for different values of the diffusion coefficient.
Numerical simulations were performed on a pilot scale furnace with crucible dimensions of 38x38x40cm3. The computational domain used for the local 3D-simulations consists of melt and crystal.
The dissolution rate was estimated from the total mass of impurities that was found in the silicon melt after a certain period of time. The obtained results show that enhanced convection produced by a mechanical stirrer leads to a significant increase of the dissolution rate and also to a uniform distribution of impurities in the melt.
A laboratory - made nonthermal plasma generator is presented. It has a diameter of 0.020 m and length of 0.155 m and contains two electrodes. The first electrode is a 2% Th-W alloy, 0.002 m in diameter bar, centred inside the generator’s body by means of a four channel teflon piece; the other three channels, 0.003 m in diameter, are used for Ar supply. The second electrode is a nozzle of 0.002 m - 0.008 m diameter and 0.005m length. A ~500 kV/m electric field is generated between the two electrodes by a high frequency source (13.56 MHz ±5%), equipped with a OT-1000 (Tungsram) power triode. For Ar flows ranging from 0.00008 m3/s to 0.00056 m3/s, a plasma jet of length not exceeding 0.015 m and temperature below 315 K is obtained. Anthurium andraeanumis sample , blood matrix, human hair and textile fibers may be introduced in the plasma jet. For time periods of 30 s and 60 s, various effects like, cell detexturization, fast blood coagulation or textile fiber or hair cleaning and smoothing are obtained. These effects are presented and discussed in the paper.
The Schrödinger equation with pseudo-Gaussian potential is investigated. The pseudo-Gaussian potential can be written as an infinite power series. Technically, by an ansatz to the wave-functions, exact solutions can be found by analytic approach . However, to calculate the solutions for each state, a condition that will stop the series has to be introduced. In this way the calculated energy values may suffer modifications by imposing the convergence of series. Our presentation, based on numerical methods, is to compare the results with those obtained in the analytic case and to determine if the results are stable under different stopping conditions.
There are many electromagnetic field (EMF) sources nowadays acting simultaneously, especially in urban areas, making the theoretical estimation of electromagnetic power at ground level very difficult. This paper reports on EMF maps built with measurements collected in Timisoara, at various radiofrequencies. A grid of 15×15 squares was built (approximate resolution 400m x 400m) and measurements of the average and maximum values of the electric field E, magnetic field H and total power density S at 0.9, 1.8 and 2.4 GHz were collected in every node of the grid. Positions of the nodes in terms of latitude and longitude were also collected. Maps were built presenting the spatial distribution of the measured quantities over Timisoara. Potential influences of EMF on public health are discussed.
We consider an application of the tetrad formalism introduced by Cardall et al. [Phys. Rev. D 88 (2013) 023011] to the problem of a rigidly rotating relativistic gas in thermal equilibrium and discuss the possible applications of this formalism to rel- ativistic lattice Boltzmann simulations. We present in detail the transformation to the comoving frame, the choice of tetrad, as well as the explicit calculation and analysis of the components of the equilibrium particle ow four-vector and of the equilibrium stress-energy tensor.
Anca Laura Dumitrescu, Marius Paulescu and Aurel Ercuta
The construction of a solid state device-based pyranometer designated to broadband irradiance measurements is presented in this paper. The device is built on the physical basis that the temperature difference between two bodies of identical shape and external surface area, identically exposed to the incident radiation, but having different absorption and heat transfer coefficients (e.g. one body is painted white and the other is painted black), is proportional to the incident irradiance. This proportionality may be put in evidence if the two bodies consisting of identical arrays of correspondingly painted semiconductor diodes, due to the thermal behaviour of their p-n junction. It is theoretically predicted and experimentally confirmed that the voltage drop across a diode passed through a constant forward current linearly decreases with the temperature of the junction. In other words, a signal proportional to the irradiance of the light source may be obtained via conventional analog electronics. The calibration of the apparatus, as performed by means of a professional device (LP PYRA 03), indicates a good linearity.
In this paper we discuss interplays between the Aharonov-Bohm effect and the transport properties in mesoscopic ring structures based on graphene. The interlayer interaction leads to a change of the electronic structure of bilayer graphene ring such that the electronic energy dispersion law exhibits a gap, either by doping one of the layers or by the application of an external perpendicular electric field. Gap adjustments can be done by varying the external electric field, which provides the possibility of obtaining mesoscopic devices based on the electronic properties of bilayer graphene. This opens the way to controllable manipulations of phase-coherent mesoscopic phenomena, as well as to Aharonov-Bohm oscillations depending on the height of the potential step and on the radius of the ring. For this purpose one resorts to a tight-binding model such as used to the description of conductance.
Mihai Lungu, Raluca Giugiulan, Antoanetta Lungu, Madalin Bunoiu and Adrian Neculae
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.
The paper reports on the presence of various metals in soil in Timis county. A set of 18 samples were collected from different points of interest. The metal content of the samples was investigated using a handheld XRF Niton XLp 300 GOLDD analyzer. Special attention was paid to the metals with harmful potential to humans. Based on the obtained results, a set of conclusions on the environment’s health was drawn.