bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synthesis and characterization of nanosized ZnTiO3doped with reduced graphene oxide (RGO)
Authors: Martinov B L , Staneva A D , Vlakhov T E , Slavov S , Dimitrov D , Marinov Y G , Hadjichristov G B 
Published: February 2021

AbstractComposite materials based on nanosized zinc titanate (ZnTiO3) doped with reduced graphene oxide (RGO) were obtained by means of ultrasonically assisted precipitation. In these composites, the concentration of RGO nanopartiles was varied from 1 wt.% to 20 wt.%. The ZnTiO3ceramic was produced by sol-gel method. RGO was prepared by a modified Hammers method and subsequent chemical reduction with sodium borohydride. Structural and phase characterization of the fabricated composites was performed by XRD, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). It was identified that for all of the studied samples of the RGO/ZnTiO3series, the two phases are uniformly distributed over the observed areas, which proves the formation of homogeneous nanocomposite materials. The electrical properties of the series of RGO/ZnTiO3samples were characterized by complex electrochemical impedance spectroscopy (EIS) in the frequency range from 0.1 Hz to 1 MHz. The results obtained by EIS for the electrical conductance of RGO-doped ZnTiO3as a function of the concentration of RGO nanoparticles were correlated with the data from structural studies.
Influence of the molecular weight and concentration of PVP on the polyol synthesized silver nanoparticles
Authors: Atanasova A , Hristova-Vasileva T , Todorov R 
Published: February 2021

Abstract
In the present work the synthesis of silver nanoparticles by the polyol method is investigated. The self-seeding polyol process was chosen from the number of variations of this method. In this approach AgNO3 was used as a precursor, poly (N-vinylpyrrolidone) (PVP) as capping agent and ethylene glycol as solvent and reducing agent. We investigated the influence of the molecular weight of PVP on the microstructure of the particles considering a polymer with molecular weight Mw = 58 and 360 K by changing the molar ratio of PVP/AgNO3 for both polymers. The molar ratios were varied from 0.5 to 2.5. The as prepared nanoparticles were characterized by microscopic and structural methods. The shape and the size distribution were characterized by Transmission Electron Microscopy. The crystal structure of the nanoparticles was studied by X-ray Diffraction and Selected Area Electron Diffraction. Due to their plasmonic properties, the silver nanoparticles find application for improvement of the efficiently of the solar cells, substrates for surface-enhanced Raman and florescence spectroscopies. All these applications require the frequencies of the localized surface plasmon resonance (LSPR) to appear at an exact position. Therefore we indicated the wavelength of the LSPR of the as prepared nanoparticles trough the absorbance spectra. A variation between 380 and 470 nm was observed.
Magnetic phase transitions in Ba0.5Sr1.5Zn2Fe11.92Al0.08O22 hexaferrites
Authors: Georgieva B , Kolev S , Krezhov K , Ghelev Ch , Kovacheva D , Tran L-M , Babij M , Zaleski A , Vertruyen B , Closset R , Koutzarova T 
Published: February 2021

Abstract
We report studies on the effect of substituting the magnetic Fe3+ cations with nonmagnetic Al3+ cations in Y-type hexaferrite Ba0.5Sr1.5Zn2Fe11.92Al0.08O22 powders on their magnetic properties and especially on the magnetic phase transitions responsible for observing the magnetoelectric effect. In this research, the Y-type hexaferrite powders were synthesized by citric acid sol-gel auto-combustion. After the auto-combustion process, the precursor powders were annealed at 1170 °C in air to obtain the Y-type hexaferrite materials. The effects of Al substitution on the structural, microstructural properties and phase content were investigated in detail using X-ray powder diffraction and scanning electron microscopy. Hysteresis measurements were performed by a physical-property-measurement-system (PPMS) (Quantum Design) at 4.2 K and at room temperature. Dc-magnetic measurements of the temperature dependence of the magnetization at magnetic fields of 50 Oe, 100 Oe and 500 Oe were used to determine the effect of applying a magnetic field on the temperature of magnetic-phase transitions. We demonstrated that the helical spin state can be modified further by varying the magnetic field.
Optimization of AlN films grown by atomic layer deposition
Authors: Beshkova M , Blagoev B S , Mehandzhiev V , Yakimova R , Avramova I , Terziyska P , Kovacheva D , Strijkova V 
Published: February 2021

Abstract
AlN thin films (∼25 nm) have been grown with a Beneq TFS-200 ALD reactor on Si (111) substrates. TMA (trimethylaluminum) and NH3 were used as precursors. The substrate temperatures were 330°C, ALD cycles 550. In order to study the stoichiometry of AlN film the TMA and NH3 doses (pulses) were varied from 60 to 180 ms and from 60 to 90 ms, respectively. X-ray diffraction (XRD) data showed that the AlN films have amorphous structure. Chemical composition and bonding states were investigated by X-ray photoelectron spectroscopy (XPS). High resolution Al 2p and N 1s spectra confirmed the presence of AlN with peaks located at 73.6 and 396.8eV, respectively for all layers. Furthermore, the atomic concentration of constituent elements has been calculated from the high-resolution XPS scan. The results revealed the Al/N ratio is close to the stoichiometric value (1:1) only for AlN film grown at TMA and NH3 doses/pulses of 180 and 90 ms, respectively. AFM analysis showed that RMS roughness value for AlN films grown at TMA: NH3 pulse ratio 2:1 is about 1 nm. The results are promising in view of further studies of AlN films for SAW device application
Properties of ZnSe nanocrystalline thin films prepared by thermal evaporation
Authors: Dzhurkov V , Levi Z , Nesheva D , Hristova-Vasileva T , Terziyska P 
Published: February 2021

Abstract
ZnSe thin films with thickness of 30 nm and 50 nm were prepared on Corning 7059 glass substrates at room temperature by applying periodically interrupted physical vapour deposition of ZnSe and various deposition rates. All as-deposited films were annealed at 200°C and some of them were further annealed at 400°C. Results from spectroscopic ellipsometry have shown that the porosity of the films which is important for the ethanol sensitivity decreases with increasing deposition rate and annealing temperature. The porosity changes caused by annealing of the films at 400°C are accompanied with thickness decrease.
Efficiency study of aeroelastic energy harvester via analytical approach
Authors: Sarbinowski F , Labudzkiand R Talar R 
Published: February 2021

Abstract
In the paper we examined the impact of structure parameters of aeroelastic energy harvester on the efficiency it provides. Study of system was preceded by deriving dimensionless analytical equations describing the power generated by the device. For this purpose, the Harmonic Balance Method method was used while adopting a simplifying assumption about the sinusoidal motion of the device. By analysing the obtained solutions, the characteristic quantities of system has been defined. By further calculations, impact of device parameters on operational flow velocity range was studied.
Chaotic evolutionary algorithms for dynamic instability enhancement
Authors: Sarbinowski F , Labudzki R , Talar R 
Published: February 2021

Abstract
The algorithm principle is presented based on a geometry optimization of aeroelastic energy harvester. Efficiency of this class of devices highly depends on oscillation amplitude caused by dynamic instability of the system, which is related to its geometry. Optimization was performed using a genetic algorithm (GA) that processes data from CFD calculations. This algorithm generated a random population of twenty-arm geometrical figures. Each geometry was subjected to a numerical experiment during which its movement in a fluid-filled channel were simulated and resultant force acting on body was calculated. The calculations were repeated for angular orientation of the object varying from 0 to 180 degrees, at 5 degrees step, in order to obtain a complete characteristic of aerodynamical forces acting on body related to its angular orientation. For each of the obtained functions, satisfaction of Den Hartog’s criterion is examined, which is the basis for geometry evaluation. In order to accelerate the calculations, classical GA has been modified by substituting random crossover process by operation determined by chaotic process — in this case, a logistic map. The numerical calculations was carried by Method of Fundamental Solutions.
The behavior to cavitation erosion-corrosion of the CuZn39Pb3 brass structures, obtained by in-depth heat treatments
Authors: Lazar I , Bordeasu I , Pirvulescu L D , Hluscu M , Mitelea I , Ghera C 
Published: February 2021

Abstract
The paper highlights the behavior at the vibratory cavitation erosion of CuZn39Pb3 brass microstructures, as obtained by in-depth heat treatments. Two heat treatment cycles are analysed (hardening at 800ºC, followed by cooling in water, and hardening at 800ºC, with cooling in water, followed by tempering at 400ºC with cooling in air). The micro-hardness measurements show that the change in the microstructure, relative to the initial status of the material (semi-finished), determines higher values of the micro-hardness. The studies of the cavitation erosion, using the vibrating standard piezoelectric crystal assembly, available in the Cavitation Research Laboratory at the Polytechnic University from Timisoara, presented in the paper, shows significant increases in the surface resistance to the stress determined by the cavitation micro-jets, as compared to the initial state of the material (semi-finished).
Design features of comminution disc and their relation with CO2 emission in disc life cycle
Authors: Kruszelnicka W 
Published: February 2021

Abstract
The structure of the comminution discs has the greatest impact on the comminution process efficiency and energy consumption and on the product fragmentation degree. Manufacturing, use and utilization of machine components carries environmental burdens in the form of emissions and energy consumption. The purpose of the work was to analyze the impact of the design features of the comminution disc (the construction material, the number and diameter of disk holes) on the amount of CO2 emissions in their life cycle. The 3D model of discs was made in SolidWorks and then an analysis of CO2 emission was made in Solid Works on the basis of the LCA and CM method. Sustainability was performed as well. It was found that energy consumption and CO2 emissions were higher for the life cycle of steel discs than those made of HDPE. Emissions of carbon dioxide during the life cycle of the working disk decrease along with an increase in the diameter and the number of holes. Regression equations describing the relationship between the diameter, number of holes in the disc and the amount of CO2 emissions in the life cycle were obtained on the basis of multiple regression analysis.
Free oscillations of a dissipative oscillator with double quadratic nonlinearity
Authors: Ol’shanskii V P , Kharchenko S O , Кovalyshyn S Y , Kharchenko F M , Kovalyshyn O , Tomporowski A , Bałdowska-Witos P 
Published: February 2021

Abstract
Approximate formulas for calculating the amplitudes of free damped oscillations of the oscillator with a quadratic nonlinear elastic characteristic under the action of a resistance force that is proportional to the square of the velocity are derived by the energy balance method. Two variants of this method have been implemented. In the first, an approximate differential equation of the envelope graph of oscillations is composed and its analytical solution is constructed. As a result, for the calculation of amplitudes, iterative relations were obtained using the Lambert W function. The argument of this special function is positive for the hard power characteristic and negative for the soft one. Asymptotic approximations of the Lambert W function, which simplify the practical implementation of analytical solutions, are proposed, and the possibility of using known tables of this special function is indicated. In presenting the second variant of the energy balance method, the recurrent relation between the amplitudes of oscillations related to the analytical solution of the cubic equation is derived. Unlike the first option, it does not require iterations. It has been made a comparison of numerical results, which these methods of calculating the amplitudes lead to, and numerical computer integration of the differential equation of oscillations of the oscillator. Satisfactory consistency of the results obtained in different ways confirmed the suitability of the derived approximate formulas for engineering calculations. The main advantage of this method is that it does not involve the construction and use of an exact solution of the double nonlinear differential equation of motion of the oscillator. In addition to the direct problem, the inverse problem of determining the coefficient of quadratic resistance of the medium based on the results of measuring the amplitudes of free oscillations on the oscillogram is also analytically solved here. The obtained solution of the direct dynamics problem was used to check the accuracy of the coefficient identification.
A slightly different view of complexity
Authors: Malivuk Gak D , Rajilic Z , Stupar N 
Published: February 2021

Abstract
This paper presents a different approach to understanding the concept of complexity and its relation to various phenomena in the field of physics [1-6]. A unique definition of complexity does not yet exist. Complexity Cmp was calculated in three systems simulated in computational experiments. In the first simulation a body in free fall was observed while falling towards body of much greater mass. Second observed system was two bodies with different temperatures, and third system was crystals in crystallization chamber. Complexity increases when the temperatures of two bodies are equalized, when one body falls to another and the crystal grows from the solution. In crystal growth theory, there are also still some concerns about the growth of some types of crystals.
Conformity assessment of metal framing elements
Authors: Bajramovic E , Bajramovic E , Islamovic F 
Published: February 2021

Abstract
Metal framing elements made of thin sheets in combination with gypsum board panels create the system widely used in construction, primarily for partition walls and suspended ceilings. The quality of the metal framing elements depends on the quality and metal sheet thickness from which they are made of, the geometric shape of the profile, the equipment used to produce them, etc. Before being placed on the market, all products used in construction and manufactured in production facilities must meet prescribed technical requirements and specifications. The paper will present the conformity assessment of metal framing elements in accordance with the European harmonized standard EN 14195:2014 and Regulation on Construction Products No. 305/2011. The Regulation defines the conditions for the marketing of construction products on the EU internal market, as well as methods and systems for evaluation to demonstrate the continuity of the characteristics of construction products.
Reduction of pollution by controlled disposal of hazardous pharmaceuticals
Authors: Ardelean E , Ordodi V , Ardelean M , Socalici A , Lemle K L 
Published: February 2021

Abstract
Human activities generate a series of waste increasingly more complex and difficult to manage (through the containment, inertization or destruction). Particular attention must be paid to hazardous waste with a high risk of environmental pollution but especially for infestation to the human generator.
In this context, we considered the possibility of integrated waste management resulted from the pharmaceutical industry, which is frequently mishandled and ends (reach) in the environment. This paper proposes a method for neutralizing some hazardous pharmaceutical waste, using electrochemical methods for inactivation, respectively an electrochemical reactor with asymmetric current densities. The results obtained in the laboratory for four of these substances leads to the generation of viable solutions that can be used in practice.
Impact of silicon carbide reinforcement on characteristics of aluminium metal matrix composite
Authors: Sharma Arun Kumar , Bhandari R , Pinca-Bretotean C 
Published: February 2021

Abstract
The consumption of composites has gradually raised in recent times and is incredibly likely to expand more in the future. Metal Matrix Composites (MMCs) provide an extensive range of benefits when compared with the common materials in certain conditions. Aluminum and its alloy-based composites in the current manufacturing scenario have a significant role to play in the advanced technological fields. Typically Aluminum Metal Matrix Composites (AlMMCs) used for its good strength, less density, excellent stiffness, lightweight, toughness, resistance to corrosion, fatigue, creep and wear relative to non-reinforced alloy. The AlMMCs, since their combination of the above-mentioned properties, are ideal suitable materials for many applications. Enhancement in these properties is accomplished by adequate customizing reinforcements in the base metal matrix. It is commonly used therefore in the aircraft, automobile, marine, leisure, telecommunications industries. In assessing the overall effectiveness of the composites there is a significant factor is reinforcement materials. The decision of a suitable type of reinforcement materials and volume are also important challenges within this paper the impact of different amounts of reinforcement has been studied. The silicon carbide (SiC) used as reinforcement material and Al6061used as Matrix material in AlMMCs are addressed. The effect of SiC on characteristics of AlMMCs explored in brief.
Physico-mechanical and tribological characteristics of composites used for brake pads
Authors: Pinca-Bretotean C , Craciun A L , Preda C , Sharma Arun Kumar 
Published: February 2021

Abstract
Brake pads are a crucial component of the braking system in an automotive vehicle. It is a primary factor in ensuring the normal driving of motor vehicles and the safety of passengers. Therefore, the research and study of the brake pads are extremely important. The materials which used in the manufacturing of brake pads should be environmentally friendly as harmful substances releases during operations by asbestos containing brake pads, which pollute the environment and thus harmful for human so becomes a primary reason of acceleration for research and development of new materials for brake pads. Composite materials have required excellent properties, so it is gaining an important position in this field. In this research, composite materials with coconut fibre are produced in the laboratory which can be used to produce brake pads for braking systems of the medium-performance small car. This research aims primarily towards producing the composite material which consists of the best proportion of organic fibre to have superior physical-mechanical and tribological characteristics. To achieve these goals, the following steps have been taken, the laboratory manufacturing of organic composite materials, technological analysis of the samples, improving the qualitative characteristics of friction materials, determination of the physical-mechanical and tribological characteristics of the materials according to the standards in force. This paper provides a detailed investigation on the characteristics of composite materials made with coconut fibre for brake pads.
A method of detecting the feature of cylindrical pin based on machine vision
Authors: He Y F , Tirian G O 
Published: February 2021

Abstract
As a common mechanic part, cylindrical pin is mainly used for positioning the parts in assembling process. Chamfer angle is an important feature of cylindrical pin, which guides the pin into the pin hole. Manual method is used by cylindrical pin manufacturer to detect the chamfer feature and so as to filter the defective products. But it is found that many problems including inevitable subjective error, high intensity of labor, and low detection efficiency exist during manual operation. A new method based on machine vision is proposed in this paper to detect the chamfer feature and size of cylindrical pin. Contour of cylindrical pin is obtained by camera, chamfer feature and size is then extracted through image analysis. Experiment result proves that the method is feasible.
Characterization of three phase solid state VAR compensation scheme in three phase pulse width modulation voltage source inverter
Authors: Josephine Mbunwe Muncho , Edwin Ezema Ejiofor , Augustine Ngwu Anene , Anghel Drugarin C V , Ajmal Mohammad Rehan , Ayaz Ahmad M 
Published: February 2021

Abstract
The principle of a three phase solid state VAR compensation (SSVC) system that uses a three-phase pulse width-modulated (PWM) Voltage-Source Inverter (VSI) is presented and analyzed. The proposed SSVC system can compensate for leading and lagging displacement power factor and the PWM is used as a means of reducing the size of reactive components. The significant aspect of the presented VAR compensator is the adjustment of the angle difference between the static fundamental circuit output voltage and the utility supply voltage in order to optimize the alternating current (a.c.) power factor to a non-linear load. The SSVC system is analyzed under self-controlled DC bus voltage operating conditions. Other areas of investigation include the design of SSVC reactive components. The dynamic analysis is carried out in a d-q reference frame to verify the performance of the VAR compensator in terms of speed of response and stability. Analysis and stability plots generated confirm a high performance static VAR compensator. Finely, the findings of present research work were found within good agreement with some other workers.
Energy efficiency of wind power plants in various wind condition
Authors: Chioncel C P , Erdodi G , Tirian O G 
Published: February 2021

Abstract
The present paper determines the optimum energy operation area of an electric wind power system, under time varying wind speed conditions. The determinations of the optimal area, from the energy point of view, is done based on experimental values from the Romanian black sea cost, Dobrogea area. The optimum operation area is defined by the optimal mechanical velocity, ωOPTIM. For this, the dependence between the wind speed, v, and ωOPTIM are computed based on the current wind speed and the current mechanical velocity ω. Due to the high inertia of the wind turbine (WT), the generators speed is not able to follow the changes of the wind speed. Knowing the optimum value ωOPTIM, the solution is to determine the load at the permanent magnet synchronous generator (PMSG) in order that the mechanical speed should timely reach his optimum.
The power factor and the upper harmonics
Authors: Spunei E , Piroi I , Protea B , Piroi F 
Published: February 2021

Abstract
Upper harmonics that occur in electrical installations due to the use of semiconductor components increases the angle of phase difference between the voltage and the current of a phase. Following this, the power factor decreases, which necessitate, then, installations to compensate for it - to reduce or cancel the upper harmonics. In this work we present a case study on how upper harmonics influence the power factor. This work has been supported by Project CNFIS-FDI-2018-0282.