Slovak University of Technology in Bratislava
  • Bratislava, Slovakia, Slovakia
Recent publications
Sugeno-like operators are binary operations based generalization of Sugeno integral and are still defined on real valued fuzzy measures. This work discusses the aggregation methods in the situation where both inputs and fuzzy measures are attached with numerical uncertainties. That is, when an input vector and a fuzzy measure are given, each of the entries of the vector and the measure value on each subset can be attached with numerical uncertainty degrees. To fulfill this meaningful aim of performing Sugeno-like aggregation with numerical uncertainties, it needs two parts of work. We firstly formally define basic uncertain vector and basic uncertain fuzzy measure. Then we discuss the methods to construct or adjust basic uncertain vector and basic uncertain fuzzy measure in two situations, the general fuzzy measure situation and the probability measure only situation, respectively. With uncertain input and uncertain fuzzy measure, we then accordingly propose the corresponding restricted Sugeno-like operator, for which some different logic restrictions are analyzed. All the proposals also have full consistency for they can immediately degenerates into Sugeno-like operator when the attached uncertainties disappear.
This study defines interval type basic uncertain information and BUI type basic uncertain information, which are two extensions of basic uncertain information and can model more types of uncertainties and uncertainty involved evaluation problems. Under rules based and linguistic decision making environments, we analyze and provide some classification rules with real values, interval values, BUI granules, interval type basic uncertain information and BUI type basic uncertain information. Using the proposed new concepts and decision making methods, an illustrative example in preference and uncertainty involved multi-source evaluation is presented.
Basic uncertain information is a newly proposed normative formulation to express and model uncertain information. This study further generalizes this concept by introducing the concept of refined interval of discourse in which the true value is known to be included. Hence, we define some new definitions of relative basic uncertain information, relative certainty/uncertainty degree and comprehensive certainty/uncertainty with some related measurements and analysis. With the introduced uncertain data type, we define two corresponding aggregation operators, namely, the relative basic uncertain information valued weighted arithmetic mean operator and the interval induced relative basic uncertain information valued ordered weight averaging operator. An application of the proposed concepts and methods in multi-agents evaluation is provided.
Rao algorithms that include three algorithms are very simple and parameter-less algorithms with effective and desirable performance. This paper modifies these three algorithms, merges them, and establishes a powerful group algorithm. In the first optimization step, the suggested algorithm is tested on 30 standard CEC2014 functions with 50 dimensions to compare it with main algorithms, several well-known algorithms, and modified versions of RAO algorithm. It becomes evident in the first test that the suggested optimizer is effective, and reliable for optimization of real-parameter functions, and it has shown its superiority to original RAO algorithm and several modern and modified versions of RAO algorithms for most of the test functions and achieved more acceptable results than them. Moreover, the suggested algorithm benefits a faster convergence characteristic than original RAO algorithms. The proposed Colonial Competitive RAO (CCRAO) has been applied on five popular engineering problems and its results have been compared with those of recent papers. According to the results, CCRAO is an effective, robust, and reliable optimizer for engineering design problems and can contain all useful features of RAO algorithms altogether. CCRAO has succeeded to converge to the best solution for these engineering problems and surpasses most of the other algorithms.
When exposed to fluid flow, elastically supported multiple square cylinders may experience either one or a combination of vortex-induced vibration, galloping, and wake-induced vibration phenomena. Due to these high-amplitude instabilities, it is necessary to utilize vibration control devices. The present paper studies the suppression of flow-induced vibration (FIV) of tandem-arranged square-section cylinders, which can oscillate independently in the streamwise and transverse directions at low Reynolds numbers. The vibration reduction is achieved by directly applying opposing forces using an active FIV control system based on the intelligent proportional-integral-derivative controller. In the present study, the fluid flow equations are calculated through the finite volume technique, by which the aerodynamic forces are attained. Next, based on the computed excitation forces, the motion equations of cylinders are solved within a user-defined function code. The numerical results show that the controller successfully suppresses the vibrations of the front and rear cylinders by a maximum of 94% and 92% at Re = 80 and by 98% and 97% at Re = 100. At Re = 230 and 250, the controller successfully diminishes the oscillation of the front cylinder by a maximum of 79% and 80%, respectively. The significant intensity of the front cylinder's wake makes the active control system unable to capably affect the vibrations of the downstream cylinder at Re = 230 and 250.
This work presents the direct crude glycerol use by high cell-density fermentation of Escherichia coli expressing recombinant glycoside hydrolase that cleaves steryl glucosides, one of the main biodiesel contaminants. Optimized fermentation with crude glycerol reached the biomass concentration of 30 g/l with the 0.285 U/mgDCW specific activity, which is comparable with the pure glycerol production. The expression of the inclusion bodies was eliminated by the increase of the induction temperature to 40 °C. The produced enzyme was able to hydrolyze 300 ppm of steryl glucosides, the major biodiesel contaminants, and reached 100 % conversion. This model approach of waste carbon recycling (crude glycerol) for biorefinery-beneficial recombinant enzyme production is in line with the sustainable circular bioeconomy concept.
At the DREAMS (DREsden AMS) facility we are implementing a so-called Super-SIMS (SIMS = Secondary Ion Mass Spectrometry) device, which combines the micron-scale spatial resolution of a commercial SIMS (CAMECA IMS 7f-auto) with the very high selectivity through molecule suppression by AMS. We have demonstrated high transmission for major element ions including silicon, fluorine and iodine, however the lack of well characterized calibration materials makes a true quantification of trace and ultra-trace elements contents difficult. Measurements of P in Si show the linearity of the instrument’s relative sensitivity factor over more than three orders of magnitude, and measurements of the isotopic ratio of bromine in ZnS document the reliability of our approach. The goal of the DREAMS Super-SIMS project is to provide quantitative concentration data of ultra-trace elements in geological samples in the context of resource technology.
Photovoltaic solar-based façade concepts are considered one of the promising representatives in the overall energy-saving campaign. The presented study aims at the simulation approach and its validation relative to experimental measurements of a double-skin building-integrated photovoltaic (BiPV) concept coupled with phase change material (PCM) in climate-responsive façade design. A comparative study of the thermo-responsive reactions and electricity production of two BiPV façades (with and without PCM layer) was conducted using the building energy simulation (BES) method to reveal the complexity of building performance predictions. An empirical validation of the BES tool working under the EnergyPlus computational engine is conducted in this connection. The consistency between the simulation results and the experimental data obtained via calorimetry and dynamic outdoor tests is comprehensively investigated. The current zonal modelling approach of the BES method is suitable when predicting the thermo-responsive capabilities of a PCM-based BiPV façade. Accordingly, the best agreement is found in the PCM data based on Triple-layer calorimetry (3LC). Using PCM in a BiPV system can increase the maximum peak electricity production from 4.3 to 4.8 % obtained experimentally with a 10–14 K decrease in PV panel operating temperature. In contrast, a difference, from 3.8 to 5.4 %, is observed with the equivalent one-diode model between the simulation results for solar panels based on copper‑indium‑gallium-selenide (CIGS) technology. Hence, the performance prediction of PV electrical conversion efficiency is calibrated using a semiconductor band gap at a value of 1.4 eV.
Accurate estimation of the longitudinal dispersion coefficient (LDC) is essential for modeling the pollution status in rivers. This research investigates the capabilities of machine-learning methods such as multi-layer perceptron (MLP), multi-layer perceptron trained with particle swarm optimization (MLP-PSO), multi-layer perceptron trained with Stochastic gradient descent deep learning (MLP-SGD) and different regressions including linear and non-linear regressions (LR and NLR) methods for determining the LDC of pollution in natural rivers and evaluates the accuracy of these methods in comparison with real measured data. Furthermore, the correlation coefficient (CC), root mean squared error (RMSE) and Willmott’s Index (WI) were implemented to evaluate the accuracies of the mentioned methods. Comparison of the results showed the superiority of the MLP-SGD model with CC of 0.923, RMSE of 281.4 and WI of 0.954, which indicates the undeniable accuracy and quality of the deep-learning model that can be used as a powerful model for LDC simulation. Also due to the acceptable performance of the PSO algorithm in the hybridization of the MLP model, the use of PSO algorithms is recommended to train machine-learning techniques for LDC estimation.
With the increasing number of devices connected to the Internet of Things, expectations from its technologies are getting higher. One of the most promising technologies for IoT networks is LoRa. It enables transmission over long distances with minimum power consumption. However, the current solution for network optimization, adaptive data rate, is only able to set the configuration for the stationary environment, where the conditions in the network do not change very often. Adaptive data rate is also not able to deal with mobile nodes. This results in a high number of collisions in a harsh environment, which leads to higher power consumption. Some of the devices have only a very limited power supply and need to prolong the battery lifetime. The latest research has shown that using reinforcement learning techniques, especially algorithms for a multi-armed bandit problem, leads to a better power efficiency and higher packet delivery ratio. In this paper, we briefly introduce energy-wise LoRa@FIIT protocol. We list and briefly describe different algorithms for communication parameters selection and propose a network testbed for simulations. Furthermore, we present results from performed simulations and compare results of two popular multi-armed bandit algorithms, Thompson sampling and upper confidence bound. The results show that the first one provides about 20% higher packet delivery ratio, while the second one provides a slightly lower power consumption.
Research infrastructures play a key role in technological development supporting science, technology and innovation. For the scientific community, but also for the creation of state science policy, it is necessary to have an overview of the research infrastructures that are available. Information is required on what infrastructures are available, who manages them and what services they provide. The evidence of research infrastructures is an integral part of the R&D information system. Its development at national level follows from EU activities in this area. The software module for research infrastructure should meet the requirements of CRIS system. It should contain well-defined workflow and user interface. The second requirement for created data model has been to achieve the maximal level of CERIF compatibility, including linking with main CRIS entities. The article presents brief situation overview in Slovakia and the experience with the implementation of the Map of research infrastructure, and with its integration to the information system SK CRIS.
A divergent strategy for natural polyketides synthesis has been designed. This synthetic route allowed chemical alterations leading to all stereoisomers of the natural agropyrenol 1, sordarial 2, and heterocornol B 4. Key steps involve desymmetrization of divinylcarbinol using asymmetric Sharpless epoxidation and Heck coupling of an easily available aromatic partner and prepared chiral alkene. The versatility of the synthetic method was demonstrated on the preparation of heterocornol A 3 and sordariol 5. The absolute and relative configurations of prepared natural compounds 2·1/3C6H12 and 4 were confirmed and assigned by single-crystal X-ray analysis.
Magnetically Soft Materials The cover image shows a supersilent grid transformer (inaudible to a human ear) with the core produced from a zero‐magnetostriction, magnetically soft AlCoNiFeCu2 ferromagnetic high‐entropy alloy, as described in article number 2201535 by Jože Luzar, Janez Dolinšek, and colleagues. Supersilence is a consequence of the material's decomposition into three phases, which creates a specific nanostructure that averages the magnetic anisotropy and the magnetostriction to zero.
The present study has been undertaken to study the microstructure and microhardness of the multi-component B–C–N diffusion coatings developed on AISI M2 high-speed steel substrate at 560 and 650 oC for 1 and 4 h for each temperature respectively. The investigation of the coatings was fulfilled using scanning electron microscopy, energy dispersion spectroscopy and X-ray diffraction analysis. Additionally, Vickers microhardness measurements were performed. The results showed that varying conditions of the thermochemical treatment led to a variety of coatings in the sense of their microstructure and phase composition.
Chalcogenide perovskites (CPs), with the general composition ABX3, where A and B are metals and X = S and Se, have recently emerged as promising materials for application in photovoltaics. However, the development of CPs and their applications has been hindered by the limitations of available preparation methods. Here we present a new approach for the synthesis of CPs, based on the sulfurization of ternary and binary oxides or carbonates with in situ formed boron sulfides. In contrast to the previously described approaches, the method presented here uses chemically stable starting materials and yields pure-phase crystalline CPs within several hours, under low hazard conditions. CP yields over 95% are obtained at temperatures as low as 600 °C. The generality of the approach is demonstrated by the preparation of CPs with compositions BaZrS3, β-SrZrS3, BaHfS3, SrHfS3, and EuHfS3. Mechanistic insights about the formation of CPs are discussed.
The die drawing process is used as a final drawing operation, especially in the production of precise tubes of smaller diameter, while the advantage of the mentioned technology is a reduction of the drawing force and thereby also the decrease of the risk of possible tube rupture during the drawing process. The paper is focused on the research of the influence of the strain size and the method drawing process on the final thickness of the wall and the outer diameter of the tube during die drawing. The sinking drawing experiment was performed by single-pass and two-pass drawing technology to the final tube diameter Ø12 mm without inter-operational annealing. The output of the paper are bar graphs that allows to compare the influence of the strain size and the method of tube drawing technology (single-pass and two-pass) on the dimensional accuracy of the final Ø12 mm tubes made of E235 and E355 steel. The advantage of the single-pass drawing technology when achieving the required wall thickness within the prescribed tolerance (±10 %) would be a reduction of the number of draws.It was found that only in one case of the two-pass drawing technology of E355 steel tube production, the permitted positive tolerance of the tube wall thickness was slightly exceeded, in the case of increasing the reduction (size strain R) from 24 % to 32 %.
NANOMET-type soft magnetic alloys of Fe82Si4B10P3Cu1 and Fe78Si8B10P3Cu1 were studied. Nanocrystalline alloys were prepared by annealing the amorphous precursors at a temperature of 420 °C for 20 and 60 min in vacuum and in Ar atmosphere. The effect of the annealing atmosphere and time of annealing on the alloy structural and magnetic properties were investigated by X-ray diffraction (XRD), Mössbauer spectroscopy (MS), magnetic measurements and atomic force microscopy (AFM). XRD unveiled partial crystallization of the Fe82Si4B10P3Cu1 alloy and confirmed amorphous structure of the Fe78Si8B10P3Cu1 alloy. The technique also indicated larger grain size after annealing in vacuum as compared to that in argon. MS disclosed the effect of the silicon content on the annealed alloys microstructure, namely the lower relative volumetric fraction of the A8 crystalline phase component for the alloy with 8 at. % Si as compared to the alloy with 4 at. % Si. Variations of the parameters reflecting the magnetic microstructure were also observed and are discussed with relation to different annealing times and atmospheres. Magnetic measurements showed better soft magnetic properties for sample with 8 at. % Si whose coercivity was lower as well as the determined magnetization work. They also indicated lower coercivity for argon annealed samples and showed that longer annealing times are reflected in the increased resultant coercivity. For both studied compositions, the AFM measurements inspecting the morphology of the sample surfaces manifested the presence of lower protrusions on the surfaces of the vacuum annealed samples as compared to the argon annealed ones, where also larger agglomerates were disclosed.
This paper presents an experimental investigation of irradiation-induced evolutions in three different oxide dispersion strengthening (ODS) alloys. High-dose, dual beam Ni–He ion irradiations are carried out up to 700 °C. The significant dose-dependent changes in the ODS particle size and number density are documented and interpreted in terms of specific point defect transport mechanisms, from small angle neutron scattering, TEM, and pulsed low-energy positron system measurements combined. The corresponding micro-mechanical changes in the alloys are evaluated based on the indentation response, which is, in turn, interpreted in terms of related, sub-grain plasticity mechanisms. The room temperature tests (without dwell time) reveal that the microscale work-hardening rate increases with decreasing the particle number density and pronounced strain localization effect. The elevated temperature tests (up to 600 °C, with dwell time) show that the indentation creep compliance is mostly temperature-independent after irradiation up to 25 dpa at T irr = 500 °C and markedly temperature-dependent, after irradiation beyond 40 dpa at T irr = 600 °C. This effect is ascribed to particular creep mechanisms associated with indent-induced plasticity, i.e., high stress and high dislocation density conditions.
The process parameters of the Laser Metal Deposition technology in the production of simple components made of NiCuBSi type metal powder were verified in this paper. A laser head with a coaxial powder supply and argon gas was used in the production. The powder was welded to a S235J2G3 steel plate. The used parameters (heat input 0.25 ⁻¹ ) enabled the production of samples with a minimum porosity (1.2 %) and without the defects (cold joints, pores) between the weld layers.
The structure of steering gear’s HATLAPA mechanism is analyzed. It is shown that presence of redundant constraints in it increases laboriousness of gear montage and respectively worsen maintainability. On the basis of provided analysis developed mechanism with reduced more than twice redundant constrainsts number.
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Martin Weis
  • Institute of Electronics and Photonics
Mikulas Huba
  • Institute of Automotive Mechatronics
Vazovova 5, 812 43, Bratislava, Slovakia, Slovakia
Head of institution
prof. Ing. Miroslav Fikar, DrSc.
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