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Number of results: 25
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Abstract

The article presents the consequences of the introduction of EU regulation 2016/631 for power park modules (PPMs), of which wind farms are a typical example. Analysing the yearlong course of changes in the generated power, the possibility of a typical wind farm meeting the requirements for the production and absorption of reactive power was checked. It was shown that in the selected cases it was necessary to introduce additional sources of reactive power on the side of the farm’s MV.
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Abstract

The aim of this study was to measure serum neopterin and C-reactive protein (CRP) concen- trations in female dogs with mammary tumours and evaluate the association between the values of these indicators and some clinical characteristics of the tumour. Fifty three female dogs were used for this study, including 43 dogs with mammary gland tumours (10 benign and 33 malignant) and 10 healthy controls. The concentrations of neopterin and CRP were determined using the ELISA technique and commercial ELISA kits. The mean serum neopterin concentration in fe- male dogs with mammary tumours was lower than in healthy dogs, but significant difference was not found. Similarly, there were no significant differences in neopterin concentrations in female dogs based on tumour size, tumour ulceration and metastasis. The mean CRP concentration was significantly higher (p<0.05) in dogs with malignant tumours compared to dogs with benign tu- mours and control. Furthermore, serum CRP concentration was significantly higher (p<0.05) in dogs with metastatic malignant tumours compared to dogs with non-metastatic mammary tu- mours. The CRP concentration was significantly lower (p<0.05) in dogs with tumours less than 3 cm compared to those with larger tumours, and significantly higher in dogs with ulcerated tu- mours compared to those without ulceration. Our findings suggest that the neoplastic process in the mammary gland does not cause significant changes in serum neopterin concentrations in dogs. Higher concentrations of serum CRP in dogs with advanced stages of malignant tumours may suggest that CRP could be a potential prognostic marker in canine malignant mammary tu- mours, but this hypothesis needs further study.
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Abstract

In order to investigate the mechanism of adsorption of reactive dyes from the textile industry on ash from heating plant produced by brown coal combustion, some characteristic sorption constants are determined using Langergren adsorption equations for pseudo-fi rst and pseudo-second order. Combined kinetic models of pseudo-first order and pseudo-second order can provide a simple but satisfactory explanation of the adsorption process for a reactive dye. According to the characteristic diagrams and results of adsorption kinetic parameters of reactive dyes on ashes, for the applied amounts of the adsorbents and different initial dye concentrations, it can be concluded that the rate of sorption is fully functionally described by second order adsorption model. According to the results, the rate constant of pseudo-second order decreases with increasing initial dye concentration and increases with increasing amount of adsorbent – ash.
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Abstract

This paper presents the resolution of the optimal reactive power dispatch (ORPD) problem and the control of voltages in an electrical energy system by using a hybrid algorithm based on the particle swarmoptimization (PSO) method and interior point method (IPM). The IPM is based on the logarithmic barrier (LB-IPM) technique while respecting the non-linear equality and inequality constraints. The particle swarmoptimization-logarithmic barrier-interior point method (PSO-LB-IPM) is used to adjust the control variables, namely the reactive powers, the generator voltages and the load controllers of the transformers, in order to ensure convergence towards a better solution with the probability of reaching the global optimum. The proposed method was first tested and validated on a two-variable mathematical function using MATLAB as a calculation and execution tool, and then it is applied to the ORPD problem to minimize the total active losses in an electrical energy network. To validate the method a testwas carried out on the IEEE electrical energy network of 57 buses.
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Abstract

The levitation melting has a potentially wide range of applications, especially in the processing of reactive metals whose contact with the crucible material causes their contamination and damage to the crucible itself. Despite its advantages, levitation melting, already proposed in the 1920s, has not yet found significant use in industrial conditions. This is due to the nature of the electromagnetic field used in previously developed devices. The disappearance of this field in the system axis causes overcoming, in the case of larger charges, surface tension forces and metal leakage from the device. The article contains a comparative analysis of a conventional solution and a newly developed levitation melting device, whose completely different design eliminates the previous weight limit of the charge.
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Abstract

Single-branch filters are still popular and are commonly used for power quality improvement purposes. Analysis of a single-branch filter is a relatively simple task. Although individual filters tuned to specific harmonics can be easily designed, after connecting them into a group it turns out that the capacitance and inductance mutually influence each other, distorting the resulting frequency characteristics. This article presents a matrix method for design a group of single-branch filters, so that the resultant frequency characteristic satisfies the design requirements including the requirements for location of the frequency characteristic maxima. Designer indicates the frequencies of the parallel resonances.
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Abstract

In the present study the adsorption of Reactive Blue 19 dye on the hydroxyapatite (HAp) nanopowders was investigated. The batch adsorption experiments were performed by monitoring the adsorbent dosage, contact time, dye solution concentration, pH and temperature. At pH 3 and 20°C, high dye removal rates of about 95.58% and 86.95% for the uncalcined and calcined nanohydroxyapatites, respectively, were obtained. The kinetic studies indicated the dye adsorption onto nanohydroxyapatite samples to follow a pseudo-second order model. The Langmuir isotherm was found to be the best to represent the equilibrium with experimental data. The maximum adsorption capacity of uncalcined and calcined nanohydroxyapatite samples has been found to be 90.09 mg/g and 74.97 mg/g, respectively.
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Abstract

This paper proposes a fair calculation approach for the cost and emission of generators. Generators also have reactive power requirements along with the active power demand to meet up the total power demand. In this paper, firstly the reactive power is calculated considering the random active power operating points on the capability curve of a generator then the cost for reactive power generation as well as emission are calculated. In order to develop the mathematical function for the reactive power cost and reactive power emission, a curve-fitting technique is applied, which gives the generalised reactive power cost and reactive power emission functions. At the end, the problem is formulated as a multiobjective problem, considering conflicting objectives such as combined active- reactive economic dispatch and combined active-reactive emission dispatch. The problem is converted from the multiobjective load dispatch problem (MOLDP) into a scalar problem, using the weighting method and the best compromised solution has been calculated using the particle swarmoptimization (PSO) technique.Afuzzy cardinal method has been applied to choose the best solution. In order to demonstrate the efficiency of developed functions the proposed method is applied on a 3 generator unit system and a 10 generator unit system, the results obtained show its validity and effectiveness.
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Abstract

The presented paper concerns the issues of communication networks applied to monitoring and control of reactive power compensator for small hydroelectric plants installed in areas distant from urban agglomerations. Ethernet, CAN, Modbus and GPRS transmission protocols has been used. Industrial programmable controller as a data collector has been used also.
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Abstract

Recently, there has been research on high frequency dissipative mufflers. However, research on shape optimization of hybrid mufflers that reduce broadband noise within a constrained space is sparse. In this paper, a hybrid muffler composed of a dissipative muffler and a reactive muffler within a constrained space is assessed. Using the eigenvalues and eigenfunctions, a coupling wave equation for the perforated dissipative chamber is simplified into a four-pole matrix form. To efficiently find the optimal shape within a constrained space, a four-pole matrix system used to evaluate the acoustical performance of the sound transmission loss (STL) is evaluated using a genetic algorithm (GA). A numerical case for eliminating a broadband venting noise is also introduced. To verify the reliability of a GA optimization, optimal noise abatements for two pure tones (500 Hz and 800 Hz) are exemplified. Before the GA operation can be carried out, the accuracy of the mathematical models has been checked using experimental data. Results indicate that the maximal STL is precisely located at the desired target tone. The optimal result of case studies for eliminating broadband noise also reveals that the overall sound power level (SWL) of the hybrid muffler can be reduced from 138.9 dB(A) to 84.5 dB(A), which is superior to other mufflers (a one-chamber dissipative and a one-chamber reactive muffler). Consequently, a successful approach used for the optimal design of the hybrid mufflers within a constrained space has been demonstrated.
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Abstract

With the increasing penetration rate of grid-connected renewable energy generation, the problem of grid voltage excursion becomes an important issue that needs to be solved urgently. As a new type of voltage regulation control method, electric spring (ES) can alleviate the fluctuations of renewable energy output effectively. In this paper, the background and basic principle of the electric spring are introduced firstly. Then, considering the influence of an electric spring on noncritical load voltage, noncritical loads are classified reasonably, and based on the electric spring phasor diagram, the control method to meet the noncritical load voltage constraint is proposed. This control method can meet the requirements of voltage excursions of different kinds of noncritical load, increase the connection capacity of the noncritical load and improve the voltage stabilization capacity of the electric spring. Finally, through the simulation case, the feasibility and validity of electric spring theory and the proposed control method are verified.
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Abstract

Asynchronized (doubly-fed) machines with two (three) excitating winding and reversing excitation system allow to control vector of magnetomotive force. This solution allows separating regulation of the electromagnetic torque (active power) and voltage (reactive power). This paper describes the experience in the development and operation of asynchronized turbogenerators and condensers.
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Abstract

Silver nanoparticles (AgNPs) are widely used in numerous industries and areas of daily life, mainly as antimicrobial agents. The particles size is very important, but still not suffi ciently recognized parameter infl uencing the toxicity of nanosilver. The aim of this study was to investigate the cytotoxic effects of AgNPs with different particle size (~ 10, 40 and 100 nm). The study was conducted on both reproductive and pulmonary cells (CHO-9, 15P-1 and RAW264.7). We tested the effects of AgNPs on cell viability, cell membrane integrity, mitochondrial metabolic activity, lipid peroxidation, total oxidative and antioxidative status of cells and oxidative DNA damage. All kinds of AgNPs showed strong cytotoxic activity at low concentrations (2÷13 μg/ml), and caused an overproduction of reactive oxygen species (ROS) at concentrations lower than cytotoxic ones. The ROS being formed in the cells induced oxidative damage of DNA in alkaline comet assay. The most toxic was AgNPs<10 nm. The results indicate that the silver nanoparticles, especially less than 10 nm, may be harmful to the organisms. Therefore, risk should be considered when using nanosilver preparations and provide appropriate protective measures when they are applied.
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Abstract

The paper presents a concept of a control system for a high-frequency three-phase PWM grid-tied converter (3x400 V / 50 Hz) that performs functions of a 10-kW DC power supply with voltage range of 600÷800 V and of a reactive power compensator. Simulation tests (in PLECS) allowed proper selection of semiconductor switches between fast IGBTs and silicon carbide MOSFETs. As the main criterion minimum amount of power losses in semiconductor devices was adopted. Switching frequency of at least 40 kHz was used with the aim of minimizing size of passive filters (chokes, capacitors) both on the AC side and on the DC side. Simulation results have been confirmed in experimental studies of the PWM converter, the power factor of which (inductive and capacitive) could be regulated in range from 0.7 to 1.0 with THDi of line currents below 5% and energy efficiency of approximately 98.5%. The control system was implemented in Texas Instruments TMS320F28377S microcontroller.
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Abstract

In this review, research carried out on sorption-enhanced steam methane reforming (SESMR) process is presented and discussed. The reactor types employed to carry out this process, fixed packed bed and fluidized bed reactors, are characterized as well as their main operating conditions indicated. Also the concepts developed and investigations performed by the main research groups involved in the subject are summarized. Next the catalysts and CO2 sorbents developed to carry out SE-SMR are characterized and the relationships describing the reaction and sorption kinetics are collected. A general approach to model the process is presented as well as results obtained for a calculation example, which demonstrate the main properties of SE-SMR.
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Abstract

Analysis of power consumption presents a very important issue for power distribution system operators. Some power system processes such as planning, demand forecasting, development, etc.., require a complete understanding of behaviour of power consumption for observed area, which requires appropriate techniques for analysis of available data. In this paper, two different time-frequency techniques are applied for analysis of hourly values of active and reactive power consumption from one real power distribution transformer substation in urban part of Sarajevo city. Using the continuous wavelet transform (CWT) with wavelet power spectrum and global wavelet spectrum some properties of analysed time series are determined. Then, empirical mode decomposition (EMD) and Hilbert-Huang Transform (HHT) are applied for the analyses of the same time series and the results showed that both applied approaches can provide very useful information about the behaviour of power consumption for observed time interval and different period (frequency) bands. Also it can be noticed that the results obtained by global wavelet spectrum and marginal Hilbert spectrum are very similar, thus confirming that both approaches could be used for identification of main properties of active and reactive power consumption time series.
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Abstract

In this work, the effect of heat transfer during explosive welding (EXW) and post-processing annealing on the microstructural and chemical composition changes have been thoroughly analysed using scanning and transmission electron microscopies and X-ray synchrotron radiation. Several combination of explosively welded metal compositions were studied: Ti with Al, Cu with Al, Ta or stainless steel, stainless steel with Zr or Ta and Ti with carbon steel. It was found that the melted metals exhibit a strong tendency to form brittle crystalline, nano-grained or even amorphous phases during the solidification. For all analysed metal combinations most of the phases formed in the zones of solidified melt do not appear in the equilibrium phase diagrams. Concurrently, the interfacial layers undergo severe plastic deformation forming nano-grained structures. It has been established that these heavily deformed areas can undergo dynamic recovery and recrystallization already during clad processing. This leads to the formation of new stress-free grains near the interface. In the case of low temperature and short time post processing annealing only the melted zones and severely deformed layers undergo recovery and recrystallization. However, drastic changes in the microstructure occurs at higher temperature and for longer annealing times. Applying such conditions leads to diffusion dominant processes across the interface. As a consequence continuous layers of intermetallic phases of equilibrium composition are obtained.
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Abstract

In this research reactive powder concrete (RPC) was prepared using sand from North Sinai. The mechanical properties of locally cast RPC were investigated and evaluated by studying the effects of using different cement and silica fume contents and new steel fi bers’ aspect ratios as reinforce-ment for RPC. Specimens’ preparation, curing regimes and testing procedures to evaluate the com-pressive strength, the modulus of elasticity, the indirect tensile strength and the fl exural strength were discussed. A compressive strength of 154.5 MPa, indirect tensile strength of 11.98 MPa, mod-ulus of elasticity of 45.1 GPa and fl exural strength of 30.26 MPa have been achieved for reinforced RPC contains 800 kg/m³ cement content and silica fume content 30% of cement weight. The test results showed some improvements by increasing cement and silica fume contentsas well as adding steel fi bers on the compressive strength, modulus of elasticity and indirect tensile strength.
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Abstract

In this paper a novel non-linear optimization problem is formulated to maximize the social welfare in restructured environment with generalized unified power flow controller (GUPFC). This paper presents a methodology to optimally allocate the reactive power by minimizing voltage deviation at load buses and total transmission power losses so as to maximize the social welfare. The conventional active power generation cost function is modified by combining costs of reactive power generated by the generators, shunt capacitors and total power losses to it. The formulated objectives are optimized individually and simultaneously as multi-objective optimization problem, while satisfying equality, in-equality, practical and device operational constraints. A new optimization method, based on two stage initialization and random distribution processes is proposed to test the effectiveness of the proposed approach on IEEE-30 bus system, and the detailed analysis is carried out.
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Abstract

This paper presents a novel approach for reactive power planning of a connected power network. Reactive power planning is nothing but the optimal usage of all reactive power sources i.e., transformer tap setting arrangements, reactive generations of generators and shunt VAR compensators installed at weak nodes. Shunt VAR compensator placement positions are determined by a FVSI (Fast Voltage Stability Index) method. Optimal setting of all reactive power reserves are determined by a GA (genetic algorithm) based optimization method. The effectiveness of the detection of the weak nodes by the FVSI method is validated by comparing the result with two other wellknown methods of weak node detection like Modal analysis and the L-index method. Finally, FVSI based allocation of VAR sources emerges as the most suitable method for reactive power planning.
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Abstract

This paper presents a novel speed estimator using Reactive Power based Model Reference Neural Learning Adaptive System (RP-MRNLAS) for sensorless indirect vector controlled induction motor drives. The Model Reference Adaptive System (MRAS) based speed estimator using simplified reactive power equations is one of the speed estimation method used for sensor-less indirect vector controlled induction motor drives. The conventional MRAS speed estimator uses PI controller for adaptation mechanism. The nonlinear mapping capability of Neural Network (NN) and the powerful learning algorithms have increased the applications of NN in power electronics and drives. This paper proposes the use of neural learning algorithm for adaptation in a reactive power technique based MRAS for speed estimation. The proposed scheme combines the advantages of simplified reactive power technique and the capability of neural learning algorithm to form a scheme named “Reactive Power based Model Reference Neural Learning Adaptive System” (RP-MRNLAS) for speed estimator in Sensorless Indirect Vector Controlled Induction Motor Drives. The proposed RP-MRNLAS is compared in terms of accuracy, integrator drift problems and stator resistance versions with the commonly used Rotor Flux based MRNLAS (RF-MRNLAS) for the same system and validated through Matlab/Simulink. The superiority of the RP-MRNLAS technique is demonstrated.
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Abstract

The paper deals with the properties and microstructure of Reactive Powder Concrete (RPC), which was developed at Cracow University of Technology. The influence of three different curing conditions: water (W), steam (S) and autoclave (A) and also steel fibres content on selected properties of RPC was analyzed. The composite characterized by w/s ratio equal to 0.20 and silica fume to cement ratio 20%, depending on curing conditions and fibres content, obtained compressive strength was in the range from 200 to 315 MPa, while modulus of elasticity determined during compression was about 50 GPa. During three-point bending test load-deflection curves were registered. Base on aforementioned measurements following parameters were calculated: flexural strength, stress at limit of proportionality (LOP), stress at modulus of rapture (MOR), work of fracture (WF), and toughness indices I₅, I₁₀ and I₂₀. Both amount of steel fibres and curing conditions influence the deflection of RPC during bending.
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Abstract

Transmission line loss minimization in a power system is an important research issue and it can be achieved by means of reactive power compensation. The unscheduled increment of load in a power system has driven the system to experience stressed conditions. This phenomenon has also led to voltage profile depreciation below the acceptable secure limit. The significance and use of Flexible AC Transmission System (FACTS) devices and capacitor placement is in order to alleviate the voltage profile decay problem. The optimal value of compensating devices equires proper optimization technique, able to search the optimal solution with less computational burden. This paper presents a technique to provide simultaneous or individual controls of basic system parameter like transmission voltage, impedance and phase angle, thereby controlling the transmitted power using Unified Power Flow Controller (UPFC) based on Bacterial Foraging (BF) algorithm. Voltage stability level of the system is defined on the Fast Voltage Stability Index (FVSI) of the lines. The IEEE 14-bus system is used as the test system to demonstrate the applicability and efficiency of the proposed system. The test result showed that the ocation of UPFC improves the voltage profile and also minimize the real power loss.
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Abstract

In the present study on Bubalus bubalis of the Campania Region (Italy) the serum levels of derivatives of reactive oxygen metabolites (d-ROMs), anti-ROM and oxidative stress index (Osi) were evaluated. These data were then related to the seropositive status of the animals against alpha-herpesviruses, precisely Bubaline herpesvirus 1 (BuHV-1) and Bovine herpesvirus 1 (BoHV-1). Clinically healthy Mediterranean buffaloes were selected for this study. The serum samples of these animals were taken, and d-ROMs, anti-ROM and Osi were measured using commercially available tests. The preliminary data demonstrated that animals seropositive to both BuHV-1 and BoHV-1 present more oxidative stress than seronegative animals, as revealed by a significant increase in d-ROMs. Our results provide, for the first time, insight into the reac- tive oxygen species (ROS) modulation induced by the herpesvirus in Bubalus bubalis.
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Abstract

The genesis of both coherent structures and reactive flow control strategies is explored. Futuristic control systems that utilize mi-crosensors and microactuators together with artificial intelligence to target specific coherent structures in a transitional or turbulent flow are considered. Of possible interest to the readers of this journal is the concept of smart wings, to be briefly discussed early in the article.
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