Showing papers in "Acta Physica Polonica A in 2016"
TL;DR: In this paper, the authors synthesize silica nanoparticles using sol-gel method using Tetraethyl orthosilicate as a precursor and use distilled water as catalyst and hydrolyzing agent.
Abstract: Sol-gel method is the simplest method and has the ability to control the particle size and morphology through
systematic monitoring of reaction parameters. The objective of this research is to synthesize silica nanostructures
by sol-gel method and to characterize the synthesized silica nanostructures. Silica nanoparticles were synthesized
via the sol-gel method using Tetraethyl orthosilicate as a precursor. The acetic acid and distilled water were used as
the catalyst and the hydrolyzing agent. Varied parameters of the study were the aging time in the range of 2 to 6 h
and the calcination temperature in the range of 600–700 ◦C. The obtained silica nanopowder was characterized
using FESEM, and Nano-Particle Size Analyzer. The results show that the silica nanospheres were successfully
synthesized by using sol-gel method with the optimum parameters of 700 ◦C of calcination temperature and 2 h of
aging time. The average size of silica nanoparticles was in the range of 79.68 nm to 87.35 nm.
73 citations
TL;DR: In this article, the formation of a tetragonal rutile structure of SnO2 nanostructures was further supported by the Raman spectra, which was estimated from the diffuse reflectance spectra using the Kubelka-Munk function.
Abstract: Nanocrystalline Sn1−xFexO2 (where x = 0, 0.01, 0.02, 0.03 and 0.04) powders have been successfully synthesized by the hydrothermal method followed by sintering at 1000 ◦C for 3 h. The morphology and structure of the samples have been analyzed by field emission scanning electron microscope and X-ray diffraction, respectively. X-ray diffraction results revealed that all diffraction peaks positions agree well with the reflection of a tetragonal rutile structure of SnO2 phase without extra peaks. The formation of a tetragonal rutile structure of SnO2 nanostructures was further supported by the Raman spectra. The band gap of Fe-doped SnO2 nanoparticles was estimated from the diffuse reflectance spectra using the Kubelka–Munk function and it was decreasing slightly with the increase of Fe ion concentration from 3.59 to 3.52 eV. The variation in band gap is attributed predominantly to the lattice strain and particle size. The presence of chemical bonding was confirmed by the Fourier transform infrared spectra.
44 citations
TL;DR: In this paper, a modification of DTO, a commercial activated carbon (AC), to improve CO2 adsorption capacity was investigated, and the results showed that the AC modified with KOH had the highest SBET, Vtot, Vmic values of 2063 m/g, 1.13 cm/g and 0.67 cm /g, respectively.
Abstract: The aim of the investigations was a modification of DTO, a commercial activated carbon (AC), to improve CO2 adsorption capacity. The adsorption of CO2 up to 40 bar at 40 ◦C temperature was investigated. The volumetric method was applied for CO2 adsorption isotherm measurements. The starting material — DTO — was modified using chemical activation (KOH, ZnCl2, K2CO3). The textural parameters of all the ACs were determined by nitrogen adsorption at the liquid nitrogen temperature of –196 ◦C on Quadrasorb SI. Results showed that the AC modified with KOH had the highest SBET, Vtot, Vmic values of 2063 m/g, 1.13 cm/g, and 0.67 cm/g, respectively. ACs with a wider pore size distribution (from micropores to mesopores) were obtained. The maximum CO2 adsorption was equal to 14.44 mmol/g for DTO/KOH — modified carbon whereas 8.07 mmol/g of CO2 was adsorbed at DTO. The CO2 adsorption capacities of the ACs were found to be closely correlated with the BET surface areas of the materials tested. The experimental data was fitted to the Freundlich, Langmuir, Sips and Toth equations to determine the model isotherm. The Sips model was found to be the best for fitting the adsorption of CO2.
39 citations
TL;DR: In this article, the characterization of the microstructure and chemical composition changes after annealing was performed on the Inconel 625 weld overlay deposited on a boiler steel, which was performed for 10 h at temperatures from 600 to 1000 C.
Abstract: The investigation focused on the characterization of the microstructure and chemical composition changes after annealing. The research was conducted on the Inconel 625 weld overlay deposited on a boiler steel. The annealing was performed for 10 h at temperatures from 600 to 1000 ◦C. The microstructure and chemical composition were examined by scanning electron microscope and transmission electron microscope equipped with an energy dispersive X-ray spectrometer. Weld overlays were produced by an innovative method of cold metal transfer.
38 citations
TL;DR: In this article, the Laguerre collocation method was used to approximate high-order nonlinear ordinary differential equations with the initial and boundary conditions, and the results of the proposed method were compared with the existing results in literature.
Abstract: In this study, we consider high-order nonlinear ordinary differential equations with the initial and boundary conditions. These kinds of differential equations are essential tools for modelling problems in physics, biology, neurology, engineering, ecology, economy, astrophysics, physiology and so forth. Each of the mentioned problems are described by one of the following equations with the specific physical conditions: Riccati, Duffing, EmdenFowler, Lane Emden type equations. We seek the approximate solution of these special differential equations by means of a operational matrix technique, called the Laguerre collocation method. The proposed method is based on the Laguerre series expansion and the collocation points. By using the method, the mentioned special differential equations together with conditions are transformed into a matrix form which corresponds to a system of nonlinear algebraic equations with unknown Laguerre coefficients, and thereby the problem is approximately solved in terms of Laguerre polynomials. In addition, some numerical examples are presented to demonstrate the efficiency of the proposed method and the obtained results are compared with the existing results in literature.
38 citations
TL;DR: In this paper, an experimental study has been carried out to investigate tensile, bending, impact and hardness properties of carbon fiber reinforced epoxy composites and four different weight fractions (0, 6, 8, 10%) were added as reinforcement to composites.
Abstract: An experimental study has been carried out to investigate tensile, bending, impact and hardness properties of chopped carbon fiber reinforced epoxy composites. Four different weight fractions (0%, 6%, 8%, 10%) were added as reinforcement to composites. The samples were manufactured by using a special designed mold. Tests were carried out according to the ASTM standards. Results of the tests have shown that hardness increases with the increasing amount of carbon fiber in composites. Tensile, bending and impact performances have increased up to 8% of carbon fiber in the composite and then started to decrease.
36 citations
TL;DR: In this article, polycrystalline silver thin films were deposited on quartz substrates by DC magnetron sputtering method at the same deposition conditions and then, the Ag films were annealed in oxygen atmosphere for 65 min at different annealing temperatures namely 300, 400, 500 and 600 ◦C.
Abstract: Silver nanoparticles have potential applications in fields of nanosicence and technology. In this work, polycrystalline silver (Ag) thin films were deposited on quartz substrates by DC magnetron sputtering method at the same deposition conditions and then, the Ag films were annealed in oxygen atmosphere for 65 min at different annealing temperatures namely 300, 400, 500 and 600 ◦C. The crystal structure of the films was evaluated by X-ray diffraction. The atomic force microscopy and scanning electron microscopy were employed for surface morphological studies of the films. Normal-incidence transmittance over the wavelength range of 200–2500 nm was measured using a spectrophotometer. The results show that the crystallization of the films increases after annealing and that the Ag films without annealing have lowest roughness. Annealing temperature effectively influences the surface morphology of the films. Optical studies reveal that the as-deposited Ag film has metallic behavior with zero transmittance and after annealing, the transmittance increases due to the formation of silver oxide phases in the films.
35 citations
TL;DR: Abdelkawy et al. as discussed by the authors, E.H. Zerrad, A.A. Bhrawy and A.M. Biswas, studied at Al-Imam Mohammad Ibn Saud Islamic University, Riyadh-11566.
Abstract: M.A. Abdelkawy, A.H. Bhrawy, E. Zerrad and A. Biswas Department of Mathematics and Statistics, College of Science, Al-Imam Mohammad Ibn Saud Islamic University, Riyadh-11566, Saudi Arabia Department of Mathematics, Faculty of Science, Beni-Suef University, Beni-Suef, Egypt Department of Physics and Engineering, Delaware State University, Dover, DE 19901-2277, USA Department of Mathematical Sciences, Delaware State University, Dover, DE 19901-2277, USA Department of Mathematics, Faculty of Science, King Abdulaziz University, Jeddah-21589, Saudi Arabia
35 citations
TL;DR: In this paper, TVL and HVL thickness for concretes with different densities were calculated, using a collimated beam of gamma rays from a Cobalt-60 source, and the linear attenuation coefficients μ, were determined from measurements.
Abstract: Half value layer (HVL) is the most frequently used quantitative factor for describing both the penetrating ability of specific radiations and the penetration through specific objects. The half value layers (HVL) and tenth value layers (TVL) are defined as the thickness of a shield or an absorber that reduces the radiation level by a factor of one-half and one tenth of the initial level, respectively. The concepts of HVL and TVL are widely used in shielding design. They are photon energy dependent, like the attenuation coefficient. HVL and TVL values provide useful information about the penetration of a specific radiation in a specific material. In this study, TVL and HVL thickness are calculated for concretes with different densities. For this purpose five types of concrete with different density ranges were selected, with densities between 600–1500 kg/m, called lightweight concrete, 1400–2000 kg/m, called semi lightweight concrete, 2000–2500 kg/m called ordinary concrete, 2500–3000 kg/m, semi heavyweight concrete and 3000–4000 kg/m called heavyweight concrete, respectively. For evaluated TVL and HVL thicknesses, the linear attenuation coefficients μ, were determined from measurements, using a collimated beam of gamma rays from a Cobalt-60 source.
34 citations
TL;DR: Aim of this research is to obtain effective, molasses based activated carbon, which would adsorb big amounts of CO2, by performing CO2 adsorption under high pressure up to 40 atm, at 40 ◦C.
Abstract: Aim of this research is to obtain effective, molasses based activated carbon, which would adsorb big amounts of CO2. Molasses was mixed with KOH. Weight ratio of dry materials was 1:1 (AC1, AC3) and 1:2 (only AC2). Homogeneous mixture was obtained. Material was left for 3 h at 25 ◦C. Drying lasted for 12 h at 200 ◦C, and the material was grounded. The mixture was pyrolysed at 750 ◦C, under constant flow (18 dm/min) of nitrogen. The material was grounded again. Then, powder was washed with water, until filtrate was neutral, which took about 5 dm of water. AC3 was washed with 1 dm of water. After drying, materials were soaked in HCl (0.1 mol/dm) for 19 h, and washed with water, until filtrate was neutral. CO2 adsorption was performed under high pressure up to 40 atm, at 40 ◦C. Specific surface area (according to the Brunauer–Emmett–Teller equation) was calculated for AC1, AC2 and AC3 and it is respectively 1985, 1967, and 2026 m/g, micropore volume — 0.714, 0.707, and 0.728 cm/g and it was between 75% and 89% of total pore volume. The excess uptake at 40 atm pressure was as follows: AC1 — 14.02 mmol/g, AC2 — 12.75 mmol/g, and AC3 — 15.79 mmol/g.
30 citations
TL;DR: In this paper, an energy-dispersive X-ray fluorescence system was used to analyze the set of Polish archaeological artefacts found in an excavation in Masurian Lakes District.
Abstract: The Migration Period on the present Polish territories is considered as a time of depopulation of Oder, Warta, and Vistula basins. The prerequisite for such assumption is lack of the archaeological finds in these regions. In contrast, on the Mrągowo Lake District and in the Lyna basin, one can find wealth of burial crematory equipped with items from the Roman period and made in the Germanic style. The analyses using the physics techniques gives an opportunity to the meeting of history with the contemporary times and the lost things may see the light of present day. The discovered artefacts may constitute a source of knowledge, which, after analysis, will be able to fill the gaps on the map of settlements in the Polish territories. The energy-dispersive X-ray fluorescence system was used to analyze the set of Polish archaeological artefacts found in an excavation in Masurian Lakes District. The compact X-ray tube developed in the National Centre for Nuclear Research (NCBJ) was used as an X-ray source in the system designed for the energy-dispersive X-ray fluorescence studies. The X-ray fluorescence spectra of the artefacts were registered with the Amptek SDD spectrometer and the concentrations of elements were determined. The measurements show that the X-ray system developed in NCBJ with transmission type X-ray tube and the Amptek SDD spectrometer is an effective tool for chemical composition analyses of archaeological objects and can be successfully applied in archaeometry.
TL;DR: In this article, the authors proposed a new energy technology evaluation and planning system for the Korea Institute of Energy Technology Evaluation and Planning (IETE&P) in the country of Ukraine.
Abstract: State Fund for Fun- damental Research; Ministry of Education and Science of Ukraine; New&Renew- able Energy of the Korea Institute of Energy Technology Evaluation and Planning
TL;DR: In this paper, a Monte Carlo code is proposed for determination of mass attenuation coefficients of gamma rays for some polymer and plastic materials, based on simulation of interaction processes of Gamma rays with the energy of 59.5, 80.9, 140.5 keV with matter.
Abstract: A Monte Carlo code is proposed for determination of mass attenuation coefficients of gamma rays for some polymer and plastic materials. It is based on simulation of interaction processes of gamma rays with the energy of 59.5, 80.9, 140.5, 279, 356.5, 511, 661.6, 1173.2, 1332.5 keV with matter. The method was tested by comparison of the simulation results with the literature values (ANSI/ANS-6.4.3 and GRIC toolkit). The compatible behaviour of mass attenuation coefficients versus incident photon energy for the investigated energy range approves the use of this code for the extended energy range and several materials. Also, the values of half-value layer were calculated for assessment of shielding effectiveness of these materials.
TL;DR: In this paper, the radionuclide concentrations in soil samples were determined by gamma-ray spectrometer which contains 3" 3" NaI(Tl) detector connected to multichannel analyser.
Abstract: The level of natural radioactivity may be varied with the increase in dependence of the depth into the earth. In present study, soil samples from dierent depths were collected in Oluz Hoyuk excavation area. The radionuclide concentrations in soil samples were determined by gamma-ray spectrometer which contains 3” 3” NaI(Tl) detector connected to multichannel analyser. The photopeaks at 1460, 1764, and 2615 keV due to 40 K, 226 Ra and 232 Th, respectively, have been used. The obtained activity concentrations of 40 K, 226 Ra and 232 Th ranged from 656.03 to 1791.85 Bq/kg, 62.39 to 180.93 Bq/kg and 48.31 to 125.43 Bq/kg, respectively. To assess the radiological hazard of the natural radionuclides content in the soil samples of these area, the radium equivalent activities (the minimum value was 181.99 Bq/kg and the maximum value was 497.97 Bq/kg), the absorbed dose rate (the minimum value was 86.83 nGy/h and the maximum value was 237.22 nGy/h), annual eective dose rate (the minimum value was 0.11 mSv/y and the maximum value was 0.29 mSv/y) and external hazard index (the minimum value was 0.49 and the maximum value was 1.35) were calculated using measured activities.
TL;DR: In this article, the authors proposed a method to solve the problem of PAS in the context of semiconductor physics, which is similar to the one we consider in this paper.
Abstract: V. Romanyuk, N. Dmitruk, V. Karpyna, G. Lashkarev, V. Popovych, M. Dranchukb,∗, R. Pietruszka, M. Godlewski, G. Dovbeshko, I. Timofeeva, O. Kondratenko, M. Taborska, and A. Ievtushenko Institute of Semiconductor Physics, NASU, prosp. Nauky 45, Kyiv, Ukraine Institute for Problems of Material Science, NASU, Krzhizhanovskogo 3, Kyiv, Ukraine Institute of Physics, PAS, al. Lotników 32/46, 02-668 Warsaw, Poland Institute of Physics, NASU, prosp. Nauky 46, Kyiv, Ukraine
TL;DR: In this paper, the wear behavior of four kinds of thermally sprayed coatings on steel tooth drill bits has been investigated by micro-abrasion wear test and the results showed that the wear mechanisms of the coatings are micro-grooving and micro-rolling.
Abstract: Wear behavior of four kinds of thermally sprayed coatings on steel tooth drill bits have been investigated by micro-abrasion wear test. The fixed ball micro abrasion wear test was applied for bare substrate and for thermal sprayed substrate of each sample. SiC and Al2O3 abrasive powders with grain size of 5 m were used in the abrasion experiments. Ball rotational speed values of 140 rpm and applied loads of 1, 2 and 3 N were used. Experimental results show that the wear mechanisms of the coatings are micro-grooving and micro-rolling. Application of the coatings was found to have an influence on the wear mechanism of the samples. The results also indicate that wear resistance of thermally sprayed coatings can be correlated to porosity, hardness, plasticity, toughness, and cohesion properties of the coatings. In addition, wear resistance of the coated samples had increased in accordance with the increasing coating thickness. DOI: 10.12693/APhysPolA.130.217 PACS/topics: 81.05.Bx, 82.35.Gh, 81.65.Kn
TL;DR: In this article, polymer gel electrolytes were prepared using poly(vinyl alcohol) (PVA) as polymer matrix, and the highest ionic conductivity at room temperature is 8.41 mS/cm.
Abstract: Polymer gel electrolytes were prepared using poly(vinyl alcohol) (PVA) as polymer matrix. 1-methyl-2pyrrolidone (NMP) and γ-butyrolactone (GBL) were preferred as the organic solvents. The alkali metal iodide salt (KI) and iodine (I2) were used as the redox couple. Liquid electrolytes with different concentrations of KI were prepared by dissolving iodide salt/iodine in the binary NMP:GBL (volume ratio 7:3) solvent mixture. PVA was added into the liquid electrolytes and then the resulting mixture was stirred at 110 ◦C for 1 h. Gel form was obtained at room temperature. The highest ionic conductivity at room temperature is 8.41 mS/cm. The temperature dependence of ionic conductivity with respect to the all concentration of KI shows the Arrhenius behaviour. Characterizations of polymer gel electrolytes were performed using the Fourier transform infrared, thermal gravimetric analysis, and differential scanning calorimetry techniques.
TL;DR: In this article, the effects of material non-homogeneity and two-parameter elastic foundation on the fundamental frequency parameters of simply supported beams are examined, taking into account the parabolic variations of Young's modulus and density along the thickness direction of the beam while the value of Poisson's ratio remains constant.
Abstract: In the present study, effects of material non-homogeneity and two-parameter elastic foundation on the fundamental frequency parameters of the simply supported beams are examined. Material non-homogeneity is characterized taking into account the parabolic variations of Young’s modulus and density along the thickness direction of the beam while the value of Poisson’s ratio is assumed to remain constant. The foundation medium is assumed to be linear, homogeneous and isotropic, and it is modeled by the Pasternak model with two parameters for describing the reaction of the elastic foundation on the beam. At first, the equation of the motion including the effects of the material non-homogeneity and two-parameter elastic foundation is provided. Then, the solutions including fundamental frequency parameters versus various non-homogeneity, density and foundation parameters, and length to depth ratio adopting the Timoshenko beam theory as well as the Euler–Bernoulli beam theory are presented. To show the accuracy of the present results, a comparison is carried out and a good agreement is found.
TL;DR: In this paper, two different types of multi-walled carbon nanotubes (I: outer diameter d = 50 ÷ 100 nm, purity ≈84%, synthesized by pyrolysis and II: outeriameter d = 10 ÷ 40 nm, Pristine and functionalized by both acid and alkaline treatment can successfully replace conventional carbon fibers as fillers in polymer composites for sensing application.
Abstract: The subject of this study is chemical functionalization as means of structural modification of multiwalled carbon nanotubes. The main goal of the experiments was to create highest density of carboxyl groups on multiwalled carbon nanotubes surface, necessary for further nanocomposite application. Two different types of multiwalled carbon nanotubes (I: outer diameter d = 50 ÷ 100 nm, purity ≈84%, synthesized by pyrolysis and II: outer diameter d = 10 ÷ 40 nm, purity ≈94%, synthesized by chemical vapor deposition) were treated by concentrated nitric acid (HNO3) and by alkaline mixture (NH4OH+H2O2). The alkaline medium as “milder” and less aggressive than nitric acid, was expected to be less destructive and cause minimal structural damage on multiwalled carbon nanotubes surface. Structural changes due to oxidation were observed by the Raman analysis, while the ratio of the intensities of the D and G peak was used to estimate the concentration of defects. Pristine and functionalized multiwalled carbon nanotubes were characterized by thermogravimetric analysis, scanning electron microscopy, ultraviolet–visible spectroscopy and zeta (ζ) spectroscopy. The results showed that functionalization initiates changes in carbon nanotubes structure as well as in their density of states. It also results in carbon nanotubes shortening and exfoliation and decreases their agglomeration tendency. Carbon nanotubes functionalized by both acid and alkaline treatment can successfully replace conventional carbon fibers as fillers in polymer composites for sensing application.
TL;DR: In this paper, a nanostructured ZnO thin film coatings produced by sol-gel method have been examined and characterized using X-ray diffraction (XRD) and Raman spectroscopy.
Abstract: In this study, nanostructured ZnO thin film coatings produced by sol-gel method have been examined and characterized. ZnO thin film coatings synthesized by the preparation of ZnO sols in the liquid phase from homogeneous solutions with precursor of zinc acetate dihydrate (Zn(CH3COO)2 ·2H2O). Ethanol (C2H5OH) has been used as a solvent material and monoethanolamine (MEA) has been used as a complexing agent. The final solutions have 0.1, 0.3, 0.5, 0.7 and 1 molar concentrations. General morphologies and detailed structural characterizations have been obtained by using scanning electron microscope (SEM). Qualitative analyses of the synthesized coatings were performed using X-ray diffraction (XRD) and Raman spectroscopy. The Raman spectroscopy studies of precursor, solution and final products were carried out to investigate transformation of the chemical compounds from the initial material to the final coating.
TL;DR: In this article, the authors present an exergetic analysis of a combined power and cooling cycle that uses ammonia-water mixture as working fluid, which is an important and economical option for efficient utilization of low temperature heat sources.
Abstract: Ammonia-water power cycles are important for efficient utilization of low temperature heat sources such as geothermal, solar, waste heat sources, etc. For some special conditions ammonia-water power cycle is an important and economical option. This paper presents an exergetic analysis of a combined power and cooling cycle that uses ammonia-water mixture as working fluid. Such cycles, use solar or geothermal energy or waste heat energy from a conventional power cycle. Ammonia-water power cycle can be used as independent cycles to provide power output and cooling. For a range (25–55 Bar) of boiler pressure the performance of the combined power and cooling cycle is investigated. The exergy of the boiler is very low compared to its energy. There is a boiling process and a heat transfer process at low temperature, both of which destruct the energy given to the boiler, so that the energy efficiency is low; however the exergy efficiency is higher than the energy efficiency. Increasing the turbine inlet pressure decreases the energy and exergy efficiencies.
TL;DR: In this article, carbon-fiber-reinforced aluminum honeycomb, aramid and plywood materials were used for armor matrix layers for determining the capability of sequencing the composite layers, ballistic tests for all six combination of sequenced sandwich panels for three different composites were evaluated at a speed of 700 m/s using a 36 caliber one-cored projectile.
Abstract: Impact problems are usually interesting for the military, either for defensive or offensive purposes to develop armor or ammunition. Recently, daily applications request safety of the products, therefore, it is essential to understand the material behavior under intense short duration or impact loadings. Metallic armor is extremely heavy and would not be popular for personal protection. However, reinforced fiber composites have been used for these purposes. In present study, carbon-fiber-reinforced aluminum honeycomb, aramid and plywood materials were used for armor matrix layers. For determining the capability of sequencing the composite layers, ballistic tests for all six combination of sequenced sandwich panels for three different composites were evaluated at a speed of 700 m/s using a 36 caliber one-cored projectile. To obtain cheaper and reliable solutions for further studies of various test conditions, computer aided ballistic simulations were analyzed. To make sufficient correlations, the test results and the computer simulations were compared to each other. Finally, plywood used between the aramid and the carbon-fiber-reinforced aluminum honeycomb sandwich panel has shown the most accurate and the reliable results of the tests and the computer simulations.
TL;DR: In this article, the chemical composition, the crystallographic phase, crystal system, space group, unit cell parameters, the absorption bands, the granulometric analysis and the microscopic observations of quartz in the sand from Mostaganem (Algeria) region have been carried out using X-ray fluorescence, Xray diffraction, infrared spectroscopy, sifting, optical and scanning electron microscopy in order to determine the rate and the nature the crystallinity of its various components and to discover a layer rich in silica, containing a sufficient reserve to feed a unit manufacturing
Abstract: Extracting quartz from sand, as well as extracting silicon from quartz requires knowledge of the physical and chemical properties of quartz found in the sand. In this work the chemical composition, the crystallographic phase, crystal system, space group, unit cell parameters, the absorption bands, the granulometric analysis and the microscopic observations of quartz in the sand from Mostaganem (Algeria) region have been carried out using X-ray fluorescence, X-ray diffraction, infrared spectroscopy, sifting, optical and scanning electron microscopy in order to determine the rate and the nature the crystallinity of its various components and to discover a layer rich in silica, containing a sufficient reserve to feed a unit manufacturing pure silicon starting from silica. The study is driven by current economic importance of the silicon application in the field of photovoltaic solar cells. The X-ray fluorescence indicates that Mostaganem sand has got a very good purity (99.5% silica). The crystallographic parameters of Mostaganem sand have been determined through analysis of X-ray diffraction. The following parameters were found, hexagonal crystal system, space group P3221, unit cell parameters: a = b = 4.9030 A, c = 5.3999 A. The infrared absorption spectrum of studied sand exhibits absorption bands characterizing the SiO2 compound, due to Si-O-Si and Si-O aggregates and others. The granulometric analysis determines the percentage of the various fraction of the grain. The microscopy observation gives the shape of the grain. The results show finally that Mostaganem sand has got good proprieties for the photovoltaic application.
TL;DR: In this paper, the band gap energy and electrical conductivity in MPr2W2O10 Tungstates were investigated and a correlation between the Bandgap Energy and the Electrical Conductivity was established.
Abstract: Correlation between the Band-Gap Energy and the Electrical Conductivity in MPr2W2O10 Tungstates (Where M = Cd, Co, Mn) B. Sawicki, E. Tomaszewicz, M. Piątkowska, T. Grońa,∗, H. Duda and K. Górny University of Silesia, Institute of Physics, Uniwersytecka 4, 40-007 Katowice, Poland West Pomeranian University of Technology, Department of Inorganic and Analytical Chemistry, al. Piastów 42, 71-065 Szczecin, Poland
TL;DR: In this article, an arc-erosion experiment using contactors was performed under inductive loads for up to 40000 switching operations to investigate the effect of different current loads on the arc erosion performance of electrical contacts.
Abstract: In this study, arc-erosion experiments using contactors were performed under inductive loads for up to 40000 switching operations to investigate the effect of different current loads on the arc-erosion performance of electrical contacts. Determination of the mass loss was performed after every 5000 operations. The arc-eroded surfaces were examined using scanning electron microscopy. The chemical composition near the arc was determined by energy dispersive X-ray spectroscopy. The results show that the contact surfaces are greatly affected by arc-erosion, resulting in mass loss due to material migration and/or evaporation. In addition, the arc-affected zones become bigger with the increase in the number of switching operations, especially at 20 A. However, electrical cleaning improves the contact performance by reducing the contact resistance due to breakdown of the non-conducting oxide films formed between 20000 and 25000 switching operations at 20 A. The stationary contacts experience major erosion, whereas the movable contacts suffered less contact erosion under each current load.
TL;DR: In this paper, a study was carried out to determine radioactivity concentrations in surface soil samples of the city of Edirne in connection with the potential radiological hazards due to Chernobyl event.
Abstract: The study was carried out to determine radioactivity concentrations in surface soil samples of the city of Edirne in connection with the potential radiological hazards due to Chernobyl event. The natural radionuclide ((226)Ra, (232)Th and (40)K) contents were determined for nine dierent locations in nine dierent towns of the Edirne city. Radiation levels were measured. Natural beta-ray activity was also determined for the same locations. The average estimated activity values were determined and compared with reported values for other cities in Turkey and also for many countries of the world. The studied areas do not pose radiological risks to the inhabitants due to harmful eects of the ionizing radiation from the natural radioactivity of the soil.
TL;DR: This article aims to identify risk factors that may affect the construction project in Poland in the above-mentioned aspects and to prioritize the significance of those risk factors.
Abstract: The complexity of construction projects increases the likelihood of hazards affecting their successful implementation. There are many risk factors that lead to the failure of the project. These factors should be identified and ordered both because of their degree of importance (significance) and level (volume) of a given factors. This is very important in order to determine their effect on the construction project. Typically, the threats for the construction project include the extension of the project duration, the increase of the project cost and/or the reduce of the quality of the works. This article aims (1) to identify risk factors that may affect the construction project in Poland in the above-mentioned aspects and (2) to prioritize the significance of those risk factors. Due to the uniqueness of individual construction projects, the potential hazards and their effects are usually characterized by different levels of uncertainty. Unfortunately, it is often a non-statistical uncertainty. For this reason, the degree of significance of risk factors is described and modelled using linguistic variables and elements of the theory of fuzzy sets. This method allows to evaluate the risk of construction projects prior to their implementation.
TL;DR: In this paper, the detrending moving average based regression coefficient estimator and the scale-dependent instrumental variable estimator were proposed for a specific case of dependence between stock markets and connected foreign exchange rates.
Abstract: We propose two novel methodological approaches — the detrending moving average based regression coefficient estimator and the scale-dependent instrumental variable estimator — and show their utility on a specific case of dependence between stock markets and connected foreign exchange rates in the Central European region — the Czech Republic, Hungary, and Poland. The methodology has proven useful as we uncovered several interesting findings such as scale dependence of the shock transmission and differences between the Euro and U.S. dollar currency pairs. The Polish currency is also the most sensitive of the three with respect to the stock market shocks. The proposed methodology can be applied to any system with potential endogeneity issues if one is interested in the scale variability of the effect of interest.
TL;DR: Davraz et al. as mentioned in this paper investigated the relationship between Ultrasonic Pulse Velocity and Thermal Conductivity Coefficient in Foam Concretes and found that thermal conductivity coefficient was positively associated with ultrasonic pulse velocity.
Abstract: Investigation of Relationships between Ultrasonic Pulse Velocity and Thermal Conductivity Coefficient in Foam Concretes M. Davraz, Ş. Kilinçarslana,∗, M. Koru and F. Tuzlak Süleyman Demirel University, Natural and Industrial Building Materials Application and Research Center, Isparta, Turkey Süleyman Demirel University, Faculty of Technology, Energy Systems Engineering Department, Isparta, Turkey Süleyman Demirel University, Faculty of Engineering, Civil Engineering Department, Isparta, Turkey
TL;DR: In this article, a (Au/Ti)/Al2O3/n-GaAs structure with thin (30 A) interfacial oxide layer was fabricated to investigate both frequency and applied bias voltage dependences of real and imaginary parts of dielectric constant (e′ and e′′) and electric modulus (M −4 V to +4 V), loss tangent tan δ and ac electrical conductivity σAC in a wide frequency range from 1000 Hz to 1 MHz.
Abstract: An (Au/Ti)/Al2O3/n-GaAs structure with thin (30 A) interfacial oxide layer (Al2O3), formed by atomic layer deposition technique is fabricated to investigate both frequency and applied bias voltage dependences of real and imaginary parts of dielectric constant (e′ and e′′) and electric modulus (M ′ and M ′′), loss tangent tan δ and ac electrical conductivity σAC in a wide frequency range from 1000 Hz to 1 MHz at room temperature. The dielectric properties of the (Au/Ti)/Al2O3/n-GaAs metal-insulator-semiconductor structure are obtained using the forward and reverse bias capacitance-voltage (C-V ) and conductance-voltage (G/ω-V ) measurements in the applied bias voltage range from –4 V to +4 V, at room temperature. Experimental results show that the dielectric parameters were strongly frequency and voltage dependent. For each frequency the (C-V ) plots show a peak and the change in frequency has effect on both the intensity and position of the peak. e′, e′′ and tan δ decrease with increasing frequency, whereas σAC increases with increasing frequency at applied bias voltage. M ′ increases with the increasing frequency and reaches a maximum. M ′′ shows a peak and peak position shifts to higher frequency with increasing applied voltage. It can be concluded that the e′, e′′, tan δ, M ′, M ′′ and σAC values of the (Au/Ti)/Al2O3/ n-GaAs structure are strongly dependent on both the frequency and applied bias voltage especially in the depletion and accumulation region. Also, the results can be deduced to imply that the interfacial polarization is easier at low frequencies, therefore contributing to the deviation of dielectric properties and AC electrical conductivity of (Au/Ti)/Al2O3/n-GaAs structure.