University of West Bohemia
Recent publications
The optimized protection system is critical in the design of microgrids (MGs) and smart grids (SGs). Different studies have tried to respond to MGs protection challenges, such as the coordination constraint violations due to changes in the system configuration. However, a few references have focused on all N-1 contingency-based configurations, besides the islanded and grid-connected modes. Moreover, in a few available studies considering N-1 contingency, the probability of different configurations has not been concerned. This article aims to fill the discussed research gap by proposing a new coordination optimization problem based on the reliability-oriented probability of various configurations and operation modes. Smart selecting the standard relay curve types (RCTs) to speed up the proposed protection scheme is used in this study. Also, developing a new hybrid optimization algorithm using the genetic algorithm (GA), particle swarm optimization (PSO), and linear programming (LP) is another essential contribution. The distribution network of the IEEE 14-bus test system is selected to examine the proposed protection scheme. It is illustrated that the introduced protection system, using the reliability-oriented probability of the configurations, is around 2.6% faster than the available schemes (with the same weighting coefficients for various configurations) without any selectivity constraint violation.
The smart railway stations (SRSs), as prosumer microgrids, are considered active users in smart grids. By utilizing regenerative braking energy (RBE) and renewable energy resources (RERs) along with energy storage systems (ESSs), these SRSs can participate in the prosumer market. The uncertainties of RERs in SRSs due to meteorological factors have been studied in the literature. However, there is a research gap in developing a stochastic method for optimized operating of SRSs considering the RBE uncertainties besides the RER, load, and number of passengers’ uncertainties. In this paper, a new probabilistic clustering-based framework for the optimal operation of SRSs is presented. By applying Monte Carlo Simulations (MCS), several scenarios are generated and then clustered by the k-means algorithm. The introduced method is applied to an actual SRS in Tehran Urban and Suburban Railway Operation Company. The test results of the MCS, deterministic, and proposed scenario-based approaches are compared to illustrate the proposed method. Test results imply that the related error of the scenario-based method under the real-time pricing can be less than 4.4%, while the computation time significantly decreases. Furthermore, sensitivity analysis is done to determine how the exchanging power constraints and ESS capacity might influence the SRS operation.
Impact-induced anomalies such as travelling waves can be found in many devices or structures. This article provides an experimental method to localize a point of impact in three-dimensional structures using an array of redundant sensors. Concurrent measurement of vibration waveforms in moving measurement points and stationary reference allows determining the times of arrival of the travelling wave and, more importantly, times of arrival relative to the reference. These relative times of arrival allow for employing more measurement points than channels in the data acquisition system. This work proposes a modified method to estimate the times of arrival by combining continuous wavelet transform with optimal interval partitioning. The work also considers that the path between the impact and the measurement point depends on the properties of the structure, causing apparent wave speeds to differ across the measurement points. Therefore, regular triangulation and multilateration methods, which assume equal wave speeds, offer a reduced accuracy. The localization is solved as a constraint optimization problem considering variable apparent speeds.
The colouring defect of a cubic graph, introduced by Steffen in 2015, is the minimum number of edges that are left uncovered by any set of three perfect matchings. Since a cubic graph has defect 0 if and only if it is 3-edge-colourable, this invariant can measure how much a cubic graph differs from a 3-edge-colourable graph. Our aim is to examine the relationship of colouring defect to oddness, an extensively studied measure of uncolourability of cubic graphs, defined as the smallest number of odd circuits in a 2-factor. We show that there exist cyclically 5-edge-connected snarks (cubic graphs with no 3-edge-colouring) of oddness 2 and arbitrarily large colouring defect. This result is achieved by means of a construction of cyclically 5-edge-connected snarks with oddness 2 and arbitrarily large girth. The fact that our graphs are cyclically 5-edge-connected significantly strengthens a similar result of Jin and Steffen (2017), which only guarantees graphs with cyclic connectivity at most 3. At the same time, our result improves Kochol's original construction of snarks with large girth (1996) in that it provides infinitely many nontrivial snarks of any prescribed girth g≥5, not just girth at least g.
One approach to producing hybrid bimetallic parts is to additively manufacture a new material onto a conventionally manufactured base material. This technique can expand the potential applications of additive manufacturing and offer new solutions for the engineering design of hybrid parts. In this work, laser powder bed fusion was used to deposit MS1 maraging steel on a conventionally produced (cast and hot-rolled) 42SiCr martensitic steel base material. Despite the profoundly different chemical compositions and hardening behaviours of these materials, their yield and ultimate tensile strengths in solution-annealed and hardened conditions are quite similar. Various heat treatments were performed to optimise the mechanical properties of the resulting hybrid part. The highest yield strength of 1400 MPa and tensile strength of 1483 MPa was achieved with a post-processing heat treatment which consisted of annealing at 900 °C for 25 min followed by water quenching and subsequent very short tempering at 490 °C. In the tensile tests, all the hybrid parts, regardless of heat treatment parameters, fractured within the base material and neither in the joint nor in the adjacent heat-affected zone. The interface areas and the microstructures of both materials were documented in detail in the as-built state and also after the heat treatment.
Perforation of lithium-ion battery electrodes has recently become an increasing interest in science and industry. Perforated electrodes have shown improved electrochemical properties compared to conventional, nonperforated electrodes. It has been demonstrated that through perforation, the fast-charging capability and the lifetime of these batteries can be significantly improved. The electrodes for lithium-ion batteries consist of a copper foil onto which the electrode material is applied as a porous layer. This layer is mainly composed of active material particles, which are bound together by a binder phase. Here, synthetic graphite was used as an active material. Up to now, it has been shown that an advantageous and precise perforation geometry can be produced by ultrashort laser pulse ablation. Since the ablation volumes during perforation of the porous electrode material with ultrashort laser pulses are unusually high compared to solids, this work investigates the parameter dependency on the ablation mechanisms in detail. For this purpose, in particular, single-pulse ablation was investigated with respect to the ablation thresholds at different pulse durations. The pulse durations were varied over a large range from 400 fs to 20 ps. By varying the number of pulses per perforation up to 50 and the single-pulse energy up to 45 μJ, it could be shown that a homogeneous ablation down to the conductor foil through the 63 μm thick active material layer can be achieved.
The electric train (ET) is a great energy consumer in an electrical network, which regenerates a high amount of energy into the grid at the braking moment. Therefore, in this paper, the optimal operation of the electric railway system is proposed considering renewable sources, hybrid storage systems (battery and ultracapacitor units), switchable capacitor banks, and regenerative braking energy of ET at the same time to attain a favorable economic, environmental and operational condition. Renewable sources reduce operating costs and environmental pollution. The storage system is utilized as a flexible source along with renewable generations. The ultracapacitor stores the ET braking energy, and the capacitor bank regulates the voltage. The scheme minimizes the expected network operating cost, while the AC optimal power flow and other technical limits are considered. This problem is nonlinear, and a linearized approximation formulation is implemented to achieve a unique optimal solution with the best and minimum computation time. The unscented transformation method is used to model uncertainties of load, ETs’ energy consumption, and renewable energies. Finally, by evaluating the numerical results, it is illustrated that the efficiency of the proposed method simultaneously improves the economic, environmental, and operational features of the network.
Next-generation fuels are defined as those produced from non-food resources. A leading member in this group is dimethyl ether− DME (C2H6O), which is a high-energy, non-toxic gas, produced from a wide range of carbon feedstocks and wastes. We explored the oxidation of DME on a highly active catalyst based on Pt3Pd3Sn2 with an atokite structure in comparison to Pt3Sn and Pd3Sn. Following a comprehensive characterization of the new ternary catalyst by electron microscopy, X-ray diffraction, and photoelectron spectroscopy, the DME anodic reaction was analyzed by electrochemical online mass spectrometry of fuel cell gas emission product and supported by density functional theory (DFT) calculations. Pt3Pd3Sn2 catalyst exhibits optimal binding energy (−0.21 eV) and the lowest activation energy for electrochemical oxidation of DME (48.7 kJ mol⁻¹ at 0.80 V). A few preferred oxidation routes were examined at different potentials corroborating with the identified CO2, formic acid, methanol, and methyl-formate by in-operando online mass spectrometry. Fuel-cell constructed using a Pt3Pd3Sn2/C anode catalyst and commercial Pt/C cathode catalyst, delivered an open circuit voltage of 0.9 V, a peak power density of 220 mW cm⁻² at 0.40 V and a gravimetric power density of 135 mW mgpgm⁻¹ at ambient pressure and 80 °C, which exceeded the highest values reported so far for direct DME fuel cells.
The computational complexity of the graph isomorphism problem is considered to be a major open problem in theoretical computer science. It is known that testing isomorphism of chordal graphs is polynomial-time equivalent to the general graph isomorphism problem. Every chordal graph can be represented as the intersection graph of some subtrees of a representing tree, and the leafage of a chordal graph is defined to be the minimum number of leaves in a representing tree for it. We prove that chordal graph isomorphism is fixed parameter tractable with leafage as parameter.
The article reviews and benchmarks machine learning methods for automatic image-based plant species recognition and proposes a novel retrieval-based method for recognition by nearest neighbor classification in a deep embedding space. The image retrieval method relies on a model trained via the Recall@k surrogate loss. State-of-the-art approaches to image classification, based on Convolutional Neural Networks (CNN) and Vision Transformers (ViT), are benchmarked and compared with the proposed image retrieval-based method. The impact of performance-enhancing techniques, e.g., class prior adaptation, image augmentations, learning rate scheduling, and loss functions, is studied. The evaluation is carried out on the PlantCLEF 2017, the ExpertLifeCLEF 2018, and the iNaturalist 2018 Datasets—the largest publicly available datasets for plant recognition. The evaluation of CNN and ViT classifiers shows a gradual improvement in classification accuracy. The current state-of-the-art Vision Transformer model, ViT-Large/16, achieves 91.15% and 83.54% accuracy on the PlantCLEF 2017 and ExpertLifeCLEF 2018 test sets, respectively; the best CNN model (ResNeSt-269e) error rate dropped by 22.91% and 28.34%. Apart from that, additional tricks increased the performance for the ViT-Base/32 by 3.72% on ExpertLifeCLEF 2018 and by 4.67% on PlantCLEF 2017. The retrieval approach achieved superior performance in all measured scenarios with accuracy margins of 0.28%, 4.13%, and 10.25% on ExpertLifeCLEF 2018, PlantCLEF 2017, and iNat2018–Plantae, respectively.
This paper presents the gamma-ray detection performance of the newly developed MAPD-3NM-II type SiPM sensor array (4 ×\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\times$$\end{document} 4) with LaBr3\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\hbox {LaBr}_3$$\end{document}(Ce) scintillator. The gamma-ray spectra of various sources have been measured in the energy range from 26 keV up to 1332 keV. The newly developed array based on MAPD-3NM-II sensors proved ∼\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\sim$$\end{document} 22% enhancement in energy resolution in comparison to the former MAPD-3NM-I based array. The energy resolution of 662 keV gamma-rays measured by MAPD-3NM-II was 3.3% while clearly surpassing 4.25% resolution of MAPD-3NM-I predecessor. The enhancement is related to the high PDE of the new MAPD-3NM-II. Obtained results show that the new MAPD-3NM-II demonstrated good energy resolution and linearity in the studied energy region. The energy resolution of the new detector developed based on MAPD-3NM-II was better than all previous products of MAPD.
Growing number of studies pointed to the importance of the topic of spirituality and religiosity among older people. However, these studies are conducted in countries with high religiosity. The Czech Republic is one of the most secular regions in the world. These facts led us to question the relationship between old age and spirituality in the environment of the Czech Republic. In thirteen semi-structured interviews with seniors from the Czech Republic (age 65+) we focused on the relationship between spirituality and old age. The qualitative analysis procedures formulated by Miles and Huberman for generating meaning were used for the analysis itself. Findings revealed only a limited association between spirituality and old age. Spirituality was used by the elderly for the purpose of expressing gratitude or as a function, which was a response to the particular topic of the old age as control of skills, maintaining relationship or activity.
This chapter deals with Morocco’s pre-colonial history and the form of settlements in this period. The introduction summarizes relations with other countries with an emphasis on the initial penetration of external influences and the reflection of these influences in architecture. Based on a comparison of primary sources (namely travel books) and material heritage, a description is given of the morphology of selected cities and the placement of individual areas or specific buildings with an emphasis on the occurrence of universal elements. Based on an analysis of the layout of settlements, the relationships are defined linked to the placement of buildings and open spaces (such as the structure of marketplaces or the relationship between residential and commercial neighbourhoods). Attention is also given to the function and significance of individual buildings for the local culture and the functioning of society (e.g. public baths), the dichotomy between the public and private, or the strict localization of activities into reserved spaces.
The final chapter of this book takes a comparative perspective on the case studies and analyses provided in the preceding papers that focused on the East African coast, North-West Africa (Morocco) and the Iberian Peninsula from the precolonial to the colonial periods. The contribution of comparative approaches to historical archaeologies is reviewed, while highlighting their relevance for the themes of urbanism and colonialism. The focus remains on the roles of the most important public features identified throughout the book, such as mosques, markets and streets, while offering comparative analyses of their social-spatial character and potential. The semi-public function as a component of specific spaces in otherwise residential or private buildings is analysed in detail. Reflecting on the importance of the courtyard house in Islamic towns, the social role of the courtyard is analysed with the use of space syntax on two contemporary sites at Gede, Kenya and Siyasa, Spain. The theoretical models of colonial urbanism and Islamic urbanism are discussed in reflection on their established characteristics and on the use of these concepts in urban studies and historical archaeology.
This chapter is focused on the colonial period on the coast of East Africa, mainly in what is today Kenya and Tanzania. The period is defined broadly, discussed from its roots in the sixteenth century up to the twentieth century. The types of buildings that characterised the public aspects of urbanism are scrutinised in turn, including their appearance, distribution and configuration in the urban layout. It is demonstrated that a number of public buildings was introduced to the urban space in the colonial era, including markets, seats of business institutions, administration or military buildings. The presented analysis shows that the public sphere of urban life represented in the built environment was significantly altered, as the newly introduced buildings did not have established parallels in the precolonial period. The colonial development accentuated the waterfront, disrupting the preexistent system of urban quarters, and also diverting power away from the networks associated with Swahili houses. It is also assessed how the colonial concepts in the built environment were spatially challenged by the indigenous urban dynamics, and finally that the changes associated with the period paved way for the abandonment of some towns in favour of new sites, and continue to be reflected in the structure of present-day towns.KeywordsColonial architectureSwahiliUrbanismUrban quartersStreet network
This paper deals with the analysis of a suitable compensation topology of a wireless power transmission system for powering the rotating parts of modern automatic machine tools. It summarizes the important properties of the serio-parallel compensation topology suitable for this application and demonstrates a detailed mathematical derivation using the first harmonic approximation. The paper details the industrial implementation of the system in a specific automatic machine tool application and demonstrates the strong technical advantages of the proposed design. Important theoretical conclusions and technical assumptions made when considering the system layout are verified by experimental laboratory measurements and the final deployment of the technology in the professional tool DMU 40 eVo linear.
Dimethyl ether (DME) is an energy‐dense fuel with several advantages over other small organic molecules such as methanol, ethanol, and ammonia for electricity generation using low‐temperature fuel cells. The absence of an active and stable anode catalyst has been hindering the commercialization of direct DME fuel cells. A Vulcan XC72 carbon‐supported Sn‐based ternary metal catalyst (Pt3Pd3Sn2/C) was reported to have yielded the highest specific power density (90 mW mg‐1 PGM) as compared to other catalysts tested for direct DME fuel cells. However, the micropores present in Vulcan XC72 limit fuel utilization by causing Pt agglomeration. Vulcan XC72 composed of non‐graphitized carbon species is also prone to corrosion. Therefore, in this study, carbon supports such as multi‐walled carbon nanotubes (MWCNT), black pearl 2000 (BP2000), and their cold N2 plasma‐treated counterparts were tested to further enhance the activity of the catalyst and systematically describe the comparative advantages over the Vulcan XC‐72 carbon. Electroanalytical tests show that Pt3Pd3Sn2/BP2000 exhibited excellent performance in terms of electrochemical active surface area (ECSA), peak current density (jp), and DME oxidation charge (Qoxi). A beneficial effect of plasma activation on the activity was observed only in the case of MWCNT while having no or negative effect on the other carbons. Laboratory fuel cell test indicated that Pt3Pd3Sn2 nanoparticles supported on optimized binary carbon support containing 75% plasma‐activated MWCNT and 25% BP2000 (Pt3Pd3Sn2/75M25B) provided the highest reported power density of 117 mW mg‐1 PGM at 70 °C fuel cell temperature and ambient pressure. This article is protected by copyright. All rights reserved.
We study the problem of exchange when 1) agents are endowed with heterogeneous indivisible objects, and 2) there is no money. In general, no rule satisfies the three central properties Pareto-efficiency, individual rationality, and strategy-proofness \cite{Sonmez1999}. Recently, it was shown that Top Trading Cycles is $\NP$-hard to manipulate \cite{FujitaEA2015}, a relaxation of strategy-proofness. However, parameterized complexity is a more appropriate framework for this and other economic settings. Certain aspects of the problem - number of objects each agent brings to the table, goods up for auction, candidates in an election \cite{consandlang2007}, legislative figures to influence \cite{christian2007complexity} - may face natural bounds or are fixed as the problem grows. We take a parameterized complexity approach to indivisible goods exchange for the first time. Our results represent good and bad news for TTC. When the size of the endowments $k$ is a fixed constant, we show that the computational task of manipulating TTC can be performed in polynomial time. On the other hand, we show that this parameterized problem is $\W[1]$-hard, and therefore unlikely to be \emph{fixed parameter tractable}.
In this paper, we investigate two research questions related to the phonetic representation of input text in Czech neural speech synthesis: 1) whether we can afford to reduce the phonetic alphabet, and 2) whether we can remove pauses from phonetic transcription and let the speech synthesis model predict the pause positions itself. In our experiments, three different modern speech synthesis models (FastSpeech 2 + Multi-band MelGAN, Glow-TTS + UnivNet, and VITS) were employed. We have found that the reduced phonetic alphabet outperforms the traditionally used full phonetic alphabet. On the other hand, removing pauses does not help. The presence of pauses (predicted by an external pause prediction tool) in phonetic transcription leads to a slightly better quality of synthetic speech.Keywordsneural speech synthesisphonetic representationphonetic reductionspause modelingczech language
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3,326 members
Pavel Mautner
  • Department of Computer Science and Engineering
Otakar Cerba
  • Department of Geomatics
Anna Pankowská
  • Department of Anthropology
Kateřina Ratislavová
  • Department of Nursing and Midwifery
Univerzitní 8, 30614, Pilsen, Czechia