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Number of results: 8961
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Abstract

The paper raises the issue of controlling rural low voltage microgrids in an optimal manner. The impact of different criterion functions, related to the amount of energy exchanged with the distribution system operator network, the level of active power losses, the amount of energy generated by different energy sources and the value of financial performance measures regarding the microgrid operation, on the choice of operating points for devices suggested by the optimization algorithm has been analyzed. Both island and synchronous microgrid operation modes are being considered. We propose two variants of the optimization procedure: the first one is based on the particle swarm optimization algorithm and centralized control logic, and the second one takes advantage of the decentralized approach and Monte Carlo methods. A comparison of the simulation results for two sample rural microgrids, obtained for different objective functions, microgrid operation modes and optimization procedure variants, with the use of prepared algorithm implementations, has been provided. The results show that the proper choice of an objective function can have a crucial impact on the optimization algorithm’s behavior, the choice of operating points and, as a consequence, on microgrid behavior as well. The choice of the proper form of the objective function is the responsibility of the person in charge of both the microgrid itself and its operation. This paper can contribute towards making correct decisions in this area. Generally, slightly better results have been achieved for the centralized control mode of operation. Nevertheless, the results also suggest that in many cases the approach based on distributed logic can return results that are better or sufficiently close to the ones provided by the centralized and more sophisticated approach.
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Abstract

The problems connected to developing inductive power transfer IPT systems in aspects of high efficiency and suppression of electromagnetic field (EMF) emission are discussed. It is shown how important it is to compensate for large leakage impedance of IPT coils (air transformer) to improve efficiency of high power transfer. Such compensation circuits operating with resonant frequencies at soft switching conditions additionally allow for reduction of switching losses in power semiconductor devices of converters. The consideration has been illustrated and verified by experimental results measured on two different test stands (50 kW with planar coils and with two 12 kW receiver coils) built in a laboratory of the Łukasiewicz Research Network – Electrotechnical Institute.
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Abstract

The goal of this paper is to explore and to provide tools for the investigation of the problems of unit-length scheduling of incompatible jobs on uniform machines. We present two new algorithms that are a significant improvement over the known algorithms. The first one is Algorithm 2 which is 2-approximate for the problem Qm|pj  = 1, G = bisubquartic|Cmax. The second one is Algorithm 3 which is 4-approximate for the problem Qm|pj  = 1, G = bisubquartic|ΣCj, where m ∈ {2, 3, 4}. The theory behind the proposed algorithms is based on the properties of 2-coloring with maximal coloring width, and on the properties of ideal machine, an abstract machine that we introduce in this paper.
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Abstract

One of the mathematical tools to measure the generation rate of new patterns along a sequence of symbols is the Lempel-Ziv complexity (LZ). Under additional assumptions, LZ is an estimator of entropy in the Shannon sense. Since entropy is considered as a measure of randomness, this means that LZ can be treated also as a randomness indicator. In this paper, we used LZ concept to the analysis of different flow regimes in cold flow combustor models. Experimental data for two combustor’s configurations motivated by efficient mixing need were considered. Extensive computer analysis was applied to develop a complexity approach to the analysis of velocity fluctuations recorded with hot-wire anemometry and PIV technique. A natural encoding method to address these velocity fluctuations was proposed. It turned out, that with this encoding the complexity values of the sequences are well correlated with the values obtained by means of RMS method (larger/smaller complexity larger/smaller RMS). However, our calculations pointed out the interesting result that most complex, this means most random, behavior does not overlap with the “most turbulent” point determined by the RMS method, but it is located in the point with maximal average velocity. It seems that complexity method can be particularly useful to analyze turbulent and unsteady flow regimes. Moreover, the complexity can also be used to establish other flow characteristics like its ergodicity or mixing.
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Abstract

The article refers to the idea of using the software defined network (SDN) as an effective hardware and software platform enabling the creation and dynamic management of distributed ICT infrastructure supporting the rapid prototyping process. The authors proposed a new layered reference model remote distributed rapid prototyping that allows the development of heterogeneous, open systems of rapid prototyping in a distributed environment. Next, the implementation of this model was presented in which the functioning of the bottom layers of the model is based on the SDN architecture. Laboratory tests were carried out for this implementation which allowed to verify the proposed model in the real environment, as well as determine its potential and possibilities for further development. Thus, the approach described in the paper may contribute to the development and improvement of the efficiency of rapid prototyping processes which individual components are located in remote industrial, research and development units. Thanks to this, it will be possible to better integrate production processes as well as optimize the costs associated with prototyping. The proposed solution is also a response in this regard to the needs of industry 4.0 in the area of creating scalable, controllable and reliable platforms.
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Abstract

This paper presents control method for multiple two-wheeled mobile robots moving in formation. Trajectory tracking algorithm from [7] is extended by collision avoidance, and is applied to the different type of formation task: each robot in the formation mimics motion of the virtual leader with a certain displacement. Each robot avoids collisions with other robots and circular shaped, static obstacles existing in the environment. Artificial potential functions are used to generate repulsive component of the control. Stability analysis of the closed-loop system is based on Lyapunov-like function. Effectiveness of the proposed algorithm is illustrated by simulation results.
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Abstract

This article discusses passages in the works of Greek and Roman writers, from Homer to the Church Fathers and Procopius, in which the seaside is a place of carefree play, those in which looking at the sea seems to have a good influence on the human mind, those in which walking on the shore is an opportunity for a philosophical dispute, and those in which pleasure is derived from being alone near the sea.
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Abstract

This article shows how the Iliad is an object of creative reception by Callimachus in his sixth hymn, the "Hymn to Demeter".
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Abstract

Rufinus, the author of erotic epigrams appearing in book 5 of the Palatine Anthology, remains a mysterious personage since scholars have divergent opinions on the period in which he lived. The article relates those discussions and analyses the contents and style of the poems, ten of which are translated here into Polish.
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Abstract

The Typhonomachia, the episode from Nonnus’ Dionysiaca, in which the poet forcefully depicts the commotion in the universe resulting from the monster’s efforts to subdue Zeus and other gods, is here translated into Polish with a concise introduction and notes.
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Abstract

The article analyses Tacitus’ description of Petronius’ suicide (Ann. XVI 18–19).
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Abstract

This article traces the origin of legends concerning Julian the Apostate’s death and the fate of his body, appearing in such works as The Golden Legend and Boccaccio’s De casibus virorum illustrium.
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Abstract

This paper focuses on the magnum opus of the well-known Greek writer Nikos Kazantzakis (1883–1957), The Odyssey, which even in the author’s country is still astonishingly neglected due to its complexity and obscure language. First published in 1938, in more than 30,000 seventeen-syllable verses, the work describes the subsequent history of Homer’s Odysseus who after killing the suitors, bored with life in Ithaca, sets out on a quest for metaphysical transcendence. Attention is given not only to the reinterpretation of the Homeric hero who becomes the alter ego of the writer, but to a larg extent also to the successive phases of metamorphoses of the epic poem’s protagonist. As it turns out, the latter-day Odysseus, negating everything and yet not ceasing to fight, on his way goes through three stages proposed by the Danish philosopher Søren Kierkegaard (1813–1855): the aesthetic, the ethical, and the religious.
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Abstract

A history of Russian translations of Aristophanes’ comedies, with a deeper analysis of those produced by Adrian Piotrovsky (1898–1937).
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Abstract

Polygonum orientale with beautiful red flowers can be found as one dominant species in the vicinity of most water bodies and wetlands in China. However, its phytoremediation potential has not been sufficiently explored because little is known about its resistance to inorganic or organic pollutants. We investigated P. orientale response to low and moderate levels of phenol stress (≤ 80 mg L-1). Endpoints included phenol tolerance of P. orientale and the removal of the pollutant, antioxidant enzyme activities, damage to the cell membrane, osmotic regulators and photosynthetic pigments. In plant leaves, phenol stress significantly increased the activities of peroxidase (POD) and catalase (CAT), as well as the contents of proline, soluble sugars and carotenoids, whereas superoxide dismutase (SOD), H2O2 and electrolyte leakage (EL) levels remained unaltered. On the other hand, there were significant decreases of soluble protein and chlorophyll contents. We demonstrated that, in combination with phenol tolerance and its removal, P. orientale has efficient protection mechanisms against phenol-induced oxidative damage (≤ 80 mg L-1). We propose that P. orientale could be used as an alternative and interesting material in the phytoremediation of phenol.
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Abstract

The influence of external factors, temperature and flow velocity on the corrosion processes St3 in model solutions petrochemical plant recycled water with high salinity and hardness without open systems and in the presence of the inhibiting composition. It was found that an increase in temperature leads to a linear increase in corrosion rates, and the change in circulating water flow rate leads to the extreme nature of corrosion processes; optimal conditions are determined. Recommended use of cathodic inhibitors or mixed type inhibitor, in particular, the composition "SVOD-BI" (means for controlling the biological corrosion), which can significantly reduce the effect of temperature and flow on the corrosion rate St3, promotes the growth and strengthening of the oxide film in the presence of oxygen, increases the degree of protection of steel and preventing the formation of at its surface carbonate-calcium deposits.
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Abstract

The article presents issues related to the application of a moving horizon estimator for state variables reconstruction in an advanced control structure of a drive system with an elastic joint. Firstly, a short review of the commonly used methods for state estimation in presented. Then, a description of a state controller structure follows. The design methodology based on the poles-placement method is briefly described. Next, the mathematical algorithm of MHE is presented and some crucial features of MHE are analysed. Then, selected simulation and experimental results are shown and described. The investigation shows, among others, the influence of window length on the quality of state variables estimation.
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Abstract

The paper presents the results of research work on the development of a rapidprototyping test stand for testing: servo control algorithms, trajectory generation, algorithms for increasing overall quality of the feed-drive modules within two axis (X-Y) table of the milling machine. Open architecture interface of the prepared control system lets the potential user test functionality of integration of diagnostic tools within the motion controller - directly, without taking into account communication with top-level CNC system.
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Abstract

The paper describes a prototype operator panel, which was designed to operate with the S7-200 family of Programmable Logic Controllers (PLC-s) from Siemens. Most of the functionality of the operator panel was implemented in a computer program, which runs on a PC-class computer. The program communicates with a PLC through its communication port configured in the Freeport mode. Two kinds of interface between the PC, and the PLC are supported: wired, and wireless. For wired connection a standard PC/PPI cable supplied by Siemens is used. For wireless connection two communication modules were designed, which operate in the free 433 MHz band. The operator panel program is intuitive, and easy to use. States of PLC inputs and outputs are presented using graphical objects. It is possible to modify states of the outputs, and monitor and edit any variable in the M and V memory in the PLC. The application supports also alarming. The program can be run on any computer with the MS Windows operating system installed. This makes the solution very cost-effective. Providing both wired and wireless communication radically increases flexibility of the proposed solution. The panel can be quickly mounted in areas, where pulling new cables is inconvenient, difficult or expensive.
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Abstract

A microgrid with parallel structure operating under islanded mode is considered in this paper. Under microgrid islanded operation mode, lines bring adverse effect for power distribution between microsources (MSs). Because traditional droop control ignores this effect, MSs adopting this method can not achieve satisfactory power distribution. A kind of droop control including line compensation applied to this microgrid is proposed. It can eliminate this effect to obtain satisfactory power distribution. The relationship of two kinds of droop control with power distribution is analyzed. The reference voltage generated by droop control is applied to control output voltage of MSs. Comparison of two kinds of droop control through MATLAB/Simulink simulation is made to verify the superiority of droop control including line compensation for power distribution. The relationship between PCC voltage and output power of MSs is also presented.
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Abstract

The purpose of the paper is the investigation of possibility of utilization of a single-phase induction machine, designed and normally operating as a single-phase capacitor induction motor, as a self-excited single-phase induction generator, which can be used to generate electrical energy from non-conventional energy sources. The paper presents dq model of the self-excited single-phase induction generator for dynamic characteristics simulation and steady-state model based on double revolving field theory with two phase symmetrical components – a forward and backward revolving field for performance of the generator under resistive load. Excitation and load characteristics obtained by simulation showed considerable influence of method of capacitor configuration in the load stator winding on terminal voltage, current and output power of the generator under load. An specific construction of the stator windings together with capacitor requirements to obtain nominal output power at desired self-regulating terminal voltage over the operating range will be the aim of further research.
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Abstract

The purpose of this paper is to develop a dynamic thermal model of a permanent magnet excited synchronous motor (PMSM). The model estimates the temperature at specific points of the machine during operation. The model is implemented using thermal network theory, whose parameters are determined by means of analytical approaches. Usually thermal models are initialized and referenced to room temperature. However, this can lead to incorrect results, if the simulations are performed when the electrical machine operates under “warm” conditions. An approach is developed and discussed in this paper, which captures the model in critical states of the machine. The model gives feedback by online measured quantities to estimate the initial temperature. The paper provides an extended dynamic thermal model, which leads to a more accurate and more efficient thermal estimation.
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Abstract

The paper presents abilities and advantages following from the use of the harmonicbalance method for analysis of steady state of a multiphase system with switching devices on example of a matrix converter. Switching elements are modelled as resistances with step-wise variable parameters, what allows to describe the converter by a linear infinite set of equations. The analysis in frequency domain is presented on example of the one-periodic control strategy. External systems were also added using the Thevenin method approach. The numerical calculation results of a linear equations set were verified by the variable structure method in a time domain and the numerical convergence was confirmed. Furthermore, the exemplary complex system was analysed using the cascade method and current waveforms were obtained.
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Abstract

In the paper issues related to the design of a robust adaptive fuzzy estimator for a drive system with a flexible joint is presented. The proposed estimator ensures variable Kalman gain (based on the Mahalanobis distance) as well as the estimation of the system parameters (based on the fuzzy system). The obtained value of the time constant of the load machine is used to change the values in the system state matrix and to retune the parameters of the state controller. The proposed control structure (fuzzy Kalman filter and adaptive state controller) is investigated in simulation and experimental tests.
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