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Dragan Kaluđerović, Eva Koren and Goran Vižintin

Abstract

The analytic element method (AEM) has been successfully used in practice worldwide for many years. This method provides the possibility of fast preliminary quantitative analysis of the hydrogeological systems or boundary conditions of the numerical models, as it is shown in the case study of groundwater source of the city of Vrbas. The AEM is also applicable for the initial analysis of a hydrogeological system, which is of particular importance in case of excess pollution that cannot be predicted where it could happen. One example of the application of the AEM is presented in this article. The analytical model is calibrated based on the measured data from several drilled monitoring wells, and this was the base for the numerical model of the contaminant transport. In this case, the AEM enabled the quick access to information on the hydrogeological system and effective response to excess pollution.

Open access

Izabela Stępińska, Elżbieta Czerwosz, Mirosław Kozłowski, Halina Wronka and Piotr Dłużewski

Abstract

Field emission from materials at high electric fields can be associated with unfavorable or even destructive effect on the surface of the investigated cathode. The impact of high voltage electric power supply causes locally very strong electric fields focusing on the cathode surface. It causes a number of phenomena, which can adversely affect the morphology and the structure of the cathode material. Such a phenomenon is, for example, peeling of an emissive layer from the substrate or its burnout. It results in tearing of the layer and a decrease or loss of its ability to electrons emission. The cold cathodes in a form of CNT films with various CNTs superficial distribution are obtained by physical vapor deposition followed by chemical vapor deposition. CNTs are catalyzed in pyrolytic process with xylene (CVD), by Ni in a form of nanograins (few nm in size) placed in carbonaceous matrix. These films are built of emissive CNTs - carbonaceous film deposited on different substrates. In this work, the morphology and topography of superficial changes resulting from external electric field in such films were investigated.

Open access

Y. Madhava Kumar, K. Bhyagyasree, N.O. Gopal and Ch. Ramu

Abstract

Pure and VO2+ doped methacrylic acid ethylacrylate (MAA:EA) copolymer films were prepared by using a solution casting method. Various techniques including X-ray diffraction, Fourier transform infrared spectroscopy, ultraviolet-visible spectroscopy, scanning electron microscopy and electron paramagnetic resonance were employed for characterization of the samples. XRD patterns showed some degree of crystallinity of the doped polymer films due to interaction of the MAA:EA copolymer with VO2+. FT-IR spectral studies of pure and VO2+ doped MAA:EA copolymer films displayed significant structural changes within the doped copolymer film indicating the complexation. The optical absorbance of the pure and VO2+ doped films were measured in the 200 nm to 800 nm wavelength range. The values of the absorption edge and indirect band gaps were calculated. The optical band gap decreased with the increase of mol% of VO2+. From the EPR spectra, the spin- Hamiltonian parameters (g and A) were evaluated. The values of the spin-Hamiltonian parameters confirmed that the vanadyl ions were present in MAA:EA copolymer films as VO2+ molecular ions in an octahedral site with a tetragonal compression (C4v). The morphology of the copolymer samples was examined by scanning electron microscopy. The enhanced crystalline nature of the doped copolymer was identified from SEM analysis.

Open access

J. Warycha and W. Mielcarek

Abstract

Oxide varistors are made of inhomogeneous material whose properties are determined by active grain boundaries. It is essential that in the microstructure of a varistor only active grain boundaries are present as only such boundaries are involved in the process of conduction. Commercial varistors are characterized by a microstructure with a large amount of electrically inactive areas which include zinc-antimony spinel, bismuth oxide, and pores. Studies on elimination of inactive grain boundaries, which are the intergranular areas rich in reaction products of varistor components and pores, lead to an improvement in the microstructure, thereby improving the electrical properties of the varistor. The results were evaluated using statistical methods, defining the percentage of active grain boundaries in the varistor. Statistical analysis showed that the best results were obtained for a bismuth oxide varistor doped with antimony oxide, containing nearly 100 % conductive grain boundaries in its body.

Open access

Mohamed Afqir, Amina Tachafine, Didier Fasquelle, Mohamed Elaatmani, Jean-Claude Carru, Abdelouahad Zegzouti and Mohamed Daoud

Abstract

The main subject of the presented research is to investigate the dielectric properties of BaBi1.8Ln0.2Nb2O9 (Ln = Ce, Gd) ceramics prepared by conventional solid state reaction route. The materials were examined using XRD and FT-IR methods. Moreover, the AC conductivity, dielectric constant and dielectric loss of the ceramics were determined. X-ray diffraction confirmed that all these compounds crystallize in an orthorhombic structure. Fourier transform infrared spectroscopy study confirmed the presence of two characteristic vibration bands located at around 617 cm-1 and 818 cm-1 for BaBi2Nb2O9. The experimental results show that the substitution of Bi by Ce or Gd causes a decrease in Curie temperature, dielectric constant and dielectric loss.

Open access

Olga Girvica

Abstract

This paper deals with the problem of optimal resource distribution in optimal way among the units of an aviation company. This task could be solved by using the method of dynamic programming. Using Mathcad 14 programming language, there was created a special program that allows to make corresponding calculations. The solution of the real task for an aviation company is observed in this paper as a numerical sample of limited resource distribution between the units of the company in order to get the maximum profit.

Open access

Tanusree Mondal, Sayantani Das, T. P. Sinha and P. M. Sarun

Abstract

This work aims to study the electrical conduction mechanism in the dielectric material BaZr0.1Ti0.9O3 (BZT) ceramics by applying AC signal in the frequency range of 102 Hz to 106 Hz. The phase purity and microstructure of the sample have been studied by X-ray diffraction refinement and field-emission scanning electron microscope (FE-SEM) analysis. The appearance of resonance peaks in the loss tangent at high temperature is due to inherent dielectric relaxation processes of this oxide. The temperature dependent Cole-Cole plot has been studied in details to determine both the grain and grain boundary contribution to the conductivity. Electrical modulus analysis reveals that the hopping of charge carriers is the most probable conduction mechanism in BZT ceramics. The obtained data of AC conductivity obey the universal double power law and have been discussed in terms of microstructural network characteristics. The behavior of frequency exponent n of AC conductivity as a function of temperature verify the applicability of the correlated barrier hopping (CBH) model. The AC conductivity data are used to estimate the minimum hopping length, density of states at Fermi level, thermal conductivity and apparent activation energy. The value of activation energy confirms that the oxygen vacancies play a vital role in the conduction mechanism.

Open access

Agata Felusiak and Paweł Twardowski

Abstract

The present paper presents comparative results of the forecasting of a cutting tool wear with the application of different methods of diagnostic deduction based on the measurement of cutting force components. The research was carried out during the milling of the Duralcan F3S.10S aluminum-ceramic composite. Prediction of the toolwear was based on one variable, two variables regression Multilayer Perceptron(MLP)and Radial Basis Function(RBF)neural networks. Forecasting the condition of the cutting tool on the basis of cutting forces has yielded very satisfactory results.

Open access

Tomasz Trzepiecinski and Magdalena Gromada

Abstract

In this paper, three BaTiO3 powders of various particle size distributions were obtained as a result of mechanical activation in the mixer mill. Green barium titanate pellets and cylindrical specimens were fabricated by both uniaxial and isostatic pressing methods. As a result of the application of different maximal sintering temperatures, the obtained materials were characterized by various average grain sizes: 0.8 μm, 20 μm and 31.0 μm. The basic properties of sintered pellets and cylinders were determined and the influence of materials average grain size on their Young’s modulus and compressive strength were determined through compression tests in a uniaxial testing machine, Zwick/Roell Z100. The elastic properties were similar for tested materials with a different grain size. However, the microstructure of BaTiO3 strongly influenced the compressive strength.

Open access

Magdalena Moczała, Miriam Karpińska, Monika Poznar, Piotr Dobryszycki and Andrzej Sikora

Abstract

This paper presents utilization of argon plasma for gradual etching of calcium carbonate crystals. The plasma treatment has been chosen as it appears to be the technique that enables removal of following material layers, thus, the access to the inside of crystals is possible. Examples of investigations of the morphology and mechanical properties of surfaces of calcium carbonate crystals are presented. The impact of plasma treatment has been verified in terms of roughness and volume changes investigated using atomic force microscopy technique in a multi-step experiment. Therefore, we were able to observe the crystal degradation process, revealing the spatial inhomogeneity of the calcium carbonate crystals resulting from their core-shell structure.