Brno University of Technology
Recent publications
Although the general concept of nanotechnology relies on exploitation of size-dependent properties of nanoscaled materials, the relation between the size/morphology of nanoparticles with their biological activity remains not well understood. Therefore, we aimed at investigating the biological activity of Se nanoparticles, one of the most promising candidates of nanomaterials for biomedicine, possessing the same crystal structure, but differing in morphology (nanorods vs. spherical particles) and aspect ratios (AR, 11.5 vs. 22.3 vs. 1.0) in human cells and BALB/c mice. Herein, we report that in case of nanorod-shaped Se nanomaterials, AR is a critical factor describing their cytotoxicity and biocompatibility. However, spherical nanoparticles (AR 1.0) do not fit this statement and exhibit markedly higher cytotoxicity than lower-AR Se nanorods. Beside of cytotoxicity, we also show that morphology and size substantially affect the uptake and intracellular fate of Se nanomaterials. In line with in vitro data, in vivo i.v. administration of Se nanomaterials revealed the highest toxicity for higher-AR nanorods followed by spherical nanoparticles and lower-AR nanorods. Moreover, we revealed that Se nanomaterials are able to alter intracellular redox homeostasis, and affect the acidic intracellular vesicles and cytoskeletal architecture in a size- and morphology-dependent manner. Although the tested nanoparticles were produced from the similar sources, their behavior differs markedly, since each type is promising for several various application scenarios, and the presented testing protocol could serve as a concept standardizing the biological relevance of the size and morphology of the various types of nanomaterials and nanoparticles.
The paper presents research focused on behaviour of cement-bonded particleboards with modified composition during sudden changes of temperature and humidity. Four types of boards were made—one control and three modified ones. Finely ground limestone was used as a modifying component in binder. Secondary wood particles made from crushing cuttings of cement-bonded particleboards were used as chips substituent. Two sets of test specimens (1 set = 6 test specimens) were manufactured. The first set was stored in laboratory conditions. The second set was subjected to 10 cycles of sudden changes of temperature (− 20 °C to + 70 °C) and humidity in accordance with EN 321 (further in the paper referred to as “wet–frost–dry cycle”.) After each cycle, dimensions and mass of the test specimens as well as ultrasonic pulse velocity were determined. A detailed analysis of structural changes in boards during cycling was carried out by an optical microscope. After 10 wet–frost–dry cycles were completed, bending strength and modulus of elasticity in bending were determined. The analysis of test results implies a very good relation between change of ultrasonic pulse velocity and width of cracks in the area of interfacial zone between cement matrix and wood particles. This finding also corresponds with dimensional and volumetric changes of the boards. Dependence of bending strength and modulus of elasticity in bending on composition of boards is apparent. Positive influence of secondary spruce chips on dimensional changes of cement-bonded particleboards caused by sudden changes of temperature and humidity was proved. Finely ground limestone contributes to more resistant structure of boards which leads to improved bending properties. Adverse conditions had more considerable influence on bending strength (decrease by 21% to 26%) than on modulus of elasticity in bending (decrease by 12% to 19%).
In this work, the preparation of homogenous TiO2 nanotube (TNT) layers with different thicknesses via anodization on Ti substrates with a large geometrical area of two times 5 cm x 10 cm (i.e. both sides of the Ti substrate) is shown for the first time. TNT layers with four different thicknesses of ∼0.65 µm, ∼1 µm, ∼7 µm, and ∼14 µm were prepared with excellent conformality and homogeneity over the anodized area. These TNT layers were successfully employed as photocatalysts for the degradation of hexane and benzene as model compounds in the gas phase under ISO standards, showing an increase of the conversion for both model compounds with the TNT layer thickness. While a stable hexane conversion was observed for all TNT layers during the measuring time of three hours, in case of benzene degradation an initial conversion decrease was monitored before the conversion stabilized. Despite this trend, SEM and XPS analyses did not reveal any significant amount of reaction products on the TNT layer surface.
The effect of top of rail lubricant composition on adhesion has been investigated using a laboratory ball-on-disc tribometer. Rheological properties were analysed using viscosimeter and high pressure torsion device. As a base medium, a biodegradable ester oil with bentonite thickener was selected. Added particles for friction modification were aluminium oxide, zinc oxide, copper sulfide and solid lubricants molybdenum disulfide and graphite. The effect of these components in the base medium on adhesion was evaluated. It was found that the most dominant component was the solid particles for friction modification. Based on the results, top of rail lubricant substances were prepared and tested. The best performing substances provided the optimal level of adhesion. These substances also showed resilience to overdosing, which caused commercial products to provide very low adhesion conditions. The rheological investigation confirmed the very low adhesion is controlled by elastohydrodynamic regime while the stable values are a result of transition to boundary lubrication.
As one promising high-efficiency equipment, flat-plate heat pipes show an important influence on the thermal management of energy systems. This research experimentally investigates the effects of working fluids (acetone, ethanol, and 1.0 wt% Al2O3 water-based nanofluid), liquid filling ratios (30%, 45%, 60%, and 80%), and inclination angles (0°, 30°, 60°, and 90°) on thermal resistance and equivalent heat transfer coefficient of flat-plate heat pipes under input powers of 15 W, 30 W, 45 W, and 60 W. Results indicate that the flat-plate heat pipe with filling ratio of 60% has the minimum thermal resistance of 2.50 °C/W. Compared with filling ratios of 30%, 45%, and 80%, thermal resistance for 60% filling ratio decreases by 42.8%, 27.8%, and 50.7%. The thermal resistances for inclination angles of 0°, 30°, and 90° increase by 88.9%, 2.97%, and 11.8% compared to that with an inclination angle of 60°. The equivalent heat transfer coefficient of the flat-plate heat pipe increases by 90.8% when the inclination angle increases from 0° to 60° due to an effect of gravity. The heat transfer coefficient of the flat-plate heat pipe decreases by 7.2% when the inclination angle increases from 60° to 90°. The thermal resistance of the flat-plate heat pipe using Al2O3 nanofluid as the working medium decreases by 15.2% and 58.7% compared to those with acetone and ethanol. It is observed that partial dryout occurs when the input power is above 30 W. The evaporator with 5 cm length shows the best heat transfer performance of the flat-plate heat pipe.
There is a shared belief across latest literature that hydrogen and algae biodiesel are promising substitutes for fossil fuels. However, hydrogen infrastructure for everyday mobility is still in its early stage from a global perspective and there is no algae biodiesel refinery in operation. Despite all this, recent geopolitical developments have caused a tipping point to be reached in the EU and hydrogen mobility has become cheaper (7 €/100 km) than conventional fossil fuels (15.6 €/100 km) for the first time. In many other countries the breaking point is also approaching and recent methods in waste refining could make hydrogen production even cheaper (5.4 €/100 km). Switching to algae biodiesel is less technically challenging for the industry. Nevertheless, technological barriers in scaling up commercial-scale algae production make the hypothetical price of algae biodiesel far from price-competitive (292 €/100 km). At the present state of knowledge it is recommended to refine algae for non-energy purposes.
The Internet of Medical Things (IoMT) has played an unrivaled role in rendering the ever-growing advancements in remote healthcare and sensor informatics. The body-sensor devices employed in remote healthcare applications are not only resource-constrained but are also vulnerable to various security attacks. Hence, to pact with the energy limitations and security vulnerability of these body-sensor devices, in this paper, we suggest ESRO: An Energy-efficient and Secured Communication framework using recently proposed meta-heuristic approach, i.e., Remora Optimization Algorithm (ROA). We employ a distributed cluster-based routing mechanism with the novel secured selection of Cluster Head (CH) using ROA. We ensure secured transmission using risky mode and γ risky mode. Extensive simulation of the ESRO demonstrates the supremacy of the proposed work over the existing techniques when evaluated on a benchmark of different performance metrics. ESRO not only preserves the energy but also ensures secured communication for IoMT.
As the renewable energy sources (RES) continues to grow in power system due to emissions decarbonisation and sustainability policies, a fast and reliable connection between RES components and equipment is crucial to ensure quality power delivery. This review provides a detailed insight into the full potential in 6G for the acceleration of RES with the faster and stable data bandwidth. The potential applications of 6G wireless networks for faster data processing in RES include P2P energy trade market, vehicular network, wireless energy transfer, energy management system, smart grid, self-healing, smart batteries and AI-based weather forecasting. This paper also lists the advantages and challenges of 6G in RES sectors, the practical implementations and the potential applications. It was found out that although the 6G is a visionary application in the RES sector to improve the security, connectivity, integration and sensory data processing of RES, 6G still possesses various technical limitations, including incompatibility issues of older devices, higher power consumption and higher operating cost. Future research should focus on the improvements of 6G in RES in terms of cost-effectiveness, compatibility issues and power consumption to balance between the advancement and limitations. This review serves as a visionary for 6G wireless communication to be applied in the RES sector in the near future. 6G in the RES sector encountered several critical limitations needing an intensive development, including still the issues of security and privacy, prone to hacking or data bleaching, required advanced hardware support and requirements for ultra-fast communications with low latency.
Flashpoint of organic materials is a crucial physical property in industrial applications and laboratory experiments, which provides information on safety standards and needed precautions in handling various organic materials. Proposed methods to determine the flashpoint of an organic material suffer from dependency on other physical properties of the chemical or demand complicated calculations which are time-consuming. In this work, a direct system model is proposed to anticipate the flashpoints of organic materials for a wide range of chemical compounds. The following models of genetic algorithm-adaptive neuro-fuzzy inference system, the least-squares version of the support vector machine, particle swarm optimisation-adaptive neuro-fuzzy inference system, and artificial neural network were applied to develop the model. This system model can speed up the flashpoint determination process and its accuracy. It can also anticipate the flashpoints of new organic materials. 79 functional groups were gathered to form a group contribution method to estimate the flashpoints of various chemical compounds. The functional groups were correlated with the model, known as the committee machine intelligent system, which performs accurately to prognosticate the flashpoint for every compound. 1,378 chemical compounds of different chemical categories were used to develop the model, making it suitable to estimate the flashpoints. This system model can determine or anticipate the flashpoints of organic materials with high accuracy and provide useful information for safety considerations in laboratory and industrial applications.
Currently, increasing energy demand due to overpopulation has provoked an urge for renewable energy sources like biodiesel. Biodiesel production from non-edible seed oils provides striking solution to the problems associated with the energy crisis. In this study, the potential of Citrus medica as a novel and non-edible seed oil (33% w/w) producing feedstock was investigated for biodiesel production using green and recyclable nanoparticles (NPs) of copper oxide synthesized with aqueous leaf extract of Portulaca oleracea. Green NPs of copper oxide were characterized by advanced techniques like X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Energy Diffraction X-Ray (EDX). A maximum yield of 93% of methyl ester was achieved at the optimum reaction condition of methanol to oil ratio 8:1, catalyst loading 0.18 wt%, reaction time 120 min and temperature 85 ◦C. Both Fourier-transform infrared spectroscopy (FTIR) and nuclear magnetic resonance of biodiesel confirmed the presence of methyl ester in the synthesized biodiesel sample. Five distinct peaks of methyl esters were identified in biodiesel by gas chromatography-mass spectrometry (GC–MS) analysis. Fuel properties of methyl esters were investigated and found analogous to the international standards. The results indicated that Citrus medica is a potential, environmentally friendly biomass feedstock for renewable production of biodiesel using green NPs of copper oxide as catalyst.
The worldwide plastic waste accumulation has posed probably irreversible harm to the environment, and the main dilemma for this global issue is: How to define the waste quality grading system to maximise plastic recyclability? This work reports a machine learning approach to evaluating the recyclability of plastic waste by categorising the quality trends of the contained polymers with auxiliary materials. The result reveals the hierarchical resource quality grades predictors that restrict the mapping of the waste sources to the demands. The Pinch Analysis framework is then applied using the quality clusters to maximise plastic recyclability. The method identifies a Pinch Point – the ideal waste quality level that limits the plastic recycling rate in the system. The novel concept is applied to a problem with different polymer types and properties. The results show the maximum recycling rate for the case study to be 38 % for PET, 100 % for PE and 92 % for PP based on the optimal number of clusters identified. Trends of environmental impacts with different plastic recyclability and footprints of recycled plastic are also compared.
Process safety in the storage and processing of agricultural products is an important aspect related not only to reducing the risk of damage to the human health or property, but is also strategical to national food safety. A special emphasis must therefore be placed on risk assessment of the operation of these facilities. One of the cornerstones of the risk assessment process is the use of knowledge of past accidents. As the agricultural industry is rather marginal in the field of safety engineering compared to other sectors of the economy, available publications dealing with this topic are rather an exception. The aim of this paper is to conduct research on the available information on accidents that have occurred in agricultural processing and storage facilities in the past. The purpose is to provide professionals and operators with a comprehensive source of information useful for activities related to the prevention of these accidents. The output of the work is then a previously unrealised representative database of systematically sorted information on accidents that have occurred in the process of treatment or storage of agricultural products. This information was subsequently analysed and evaluated. The created database consists of 195 records of accidents that occurred between 1989 and 2018. To create a unique representative database, mainly publicly available databases of industrial accidents or professional publications were used. The author's database contains information on accident locations, accident causes and accident prevention measures. A total of 21 persons died and 32 persons were injured during the accidents. The analysis shows that fires are the most frequent manifestation of accidents (86%) and accidents in material handling facilities are the most frequent (33%). According to the information available in the database, organisational factors were identified as the most frequent causative factors of accidents (47%). For a better understanding of the accident process, a description of selected accident scenarios was also provided in the work. A linear model was used for this purpose. Due to the strategic importance of the evaluated facilities for processing and storage of agricultural products, efforts are made to prevent accidents from recurring or to reduce their impact on the surrounding area. Therefore, an integral part of the work is the description of possible measures against the recurrence of similar accidents.
This paper introduces the recent developments in Renewable Energy Systems for building heating, cooling and electricity production with thermal energy storage. Due to the needed Clean Energy Transition in the many countries and regions and the goal of closing Net Zero Energy Buildings, it is crucial to provide efficient Renewable Energy Based heating/cooling systems for buildings. The buildings contribute about 40% of total energy consumption, with significant potential for primary energy savings. The application of various Renewable Energy based systems is discussed including: the presentation of Hybrid Renewable Energy bases systems, methodology for their design and methods for the optimisation of Buildings RES. At present, mostly the systems based on heat pumps and photovoltaics are applied in buildings. However, the sources of those energy systems are unstable, and they are influenced by the climate environment. It makes it necessary to combine thermal and electrical energy storage, to achieve high efficiency. The recently developing electrical energy and chemical storage are Battery Energy Storage Systems and Hydrogen Energy Systems, through it is urgently necessary to overcome the difficulties of high cost, relatively low efficiency and demanding storage environment and so on. For the thermal energy storage, Phase Change Materials (PCMs) show great potential for application – with their use the thermal energy can be accumulated at the time of low energy demand or availability and recovered during a high consumption period. This review also presents the recent developments in PCMs for their application in buildings, both for heating and cooling. Finally, it sorts out some challenging issues of the RES today and guides future development.
The heat exchanger is an essential component of the supercritical CO2 Brayton cycle. To attenuate the temperature fluctuations in the cycle, this study proposes a new structure with phase change materials embedded in the printed circuit heat exchanger. This structure package can contain a variety of phase change materials in a stepwise arrangement and a composite phase change material with expanded graphene. The effects of different flow directions, the number of layers in the phase change material ladder, whether the phase change material is compounded with expanded graphene or not, and the thickness of the phase change material were numerically compared. The results show that the PCM layer with 0.45 mm thickness has a smaller amplitude of both temperature fluctuations and liquid fraction fluctuations than that of 0.25 mm. Relative to the case without PCM, the outlet of hot side’ temperature fluctuation amplitude of PCM/EG-3 and PCM/EG-5 with 0.45 mm thickness decreased by 17.11% and 22.37%, and the outlet of cold side’ temperature fluctuation amplitude decreased by 36.84% and 38.16%, while the heat exchange decreased by only 2.28% and 1.78%, respectively.
Biodiesel is known as one of the best alternative fuels for diesel engines. Low-cost Jatropha oil is considered a potential non-edible feedstock for biodiesel production in India and many other parts of the world. Jatropha oil contains a large amount of free fatty acids (FFA), and soap formation occurs during the alkali catalysed trans-esterification process, hence decreasing the biodiesel yield. The acid catalyst is less sensitive to FFA, but the reaction rate is extremely slow if the transesterification reaction occurs by conventional heating. In the present investigation, microwave heating was used for biodiesel production by the single-step transesterification reaction of Jatropha oil in the presence of an acidic catalyst (sulphuric acid). The central composite rotatable design (CCRD) matrix of response surface methodology (RSM) was employed to determine the optimum design conditions for the transesterification reaction under microwave irradiation. The effects of three selected variables, namely reaction time, catalyst concentration, and methanol, on the oil molar ratio, were assessed. The maximum yield of biodiesel produced in the selected design space by microwave heating was found to be 61.10% under the 11:7 M ratio of the methanol to oil, 2 wt% catalyst concentration, and 90 min reaction time, which was much higher than the biodiesel yield by conventional heating method (3.8%) for the same reaction time. The modified polynomial model for the microwave heating method was developed with the help of ANOVA, main effect plots, interaction plots, and surface plots. The experimental and predicted yield values for fatty acid methyl ester (FAME) showed a linear relationship. The validation of experiments confirmed the accuracy of the suggested model. The produced biodiesel was of good quality, as all the properties were within the prescribed limits of the ASTM D6751 standard. The results of this study showed that the microwave heating method can be used efficiently to obtain a high biodiesel yield from low-cost, high-FFA feedstock such as Jatropha oil in a sulphuric acid-catalysed single-step transesterification reaction.
Background Elemental sulfur (S ⁰ ) is a cost-efficient fertilizer and the least rapidly utilizable source of S for soil microorganisms and plants. Its bacterial-mediated oxidation to sulfates is dependent on particle size. Finely formulated (micronized, nanosized) S ⁰ exerts enhanced oxidation rate and benefit due to nutrient availability and crop nutrition efficiency. Graphene oxide (GO) affects soil properties both negatively and positively. A pot experiment was carried out with lettuce using soil supplemented with S ⁰ in different composition, applied alone or in combination with GO. The following variants were tested: control, GO, micro-S ⁰ , micro-S ⁰ + GO, nano-S ⁰ , nano-S ⁰ + GO. Results Nanosized S ⁰ improved most of enzyme activities (dehydrogenase, arylsulfatase, N -acetyl-β- d -glucosaminidase, β-glucosidase, phosphatase). However, respirations induced by d -glucose, protocatechuic acid, l -arginine were decreased. GO mitigated negative to neutral effect of micro-S ⁰ in the soil pH, dehydrogenase and urease activity. Furthermore, micro-S ⁰ positively affected basal respiration and respirations induced by d -trehalose and N -acetyl-β- d -glucosamine. Nano-S ⁰ + GO improved plant biomass yield and enzyme activities. However, nano-S ⁰ + GO significantly decreased all substate-induced respirations. Conclusions The benefit of soil treatment with nano-/micro-sized S ⁰ and its combination with GO on soil biological parameters was partially demonstrated. Graphical Abstract
This study compares two types of bioresorptive cellulose, i.e., calcium-sodium salt of oxidized cellulose (OC) and sodium salt of carboxymethylcellulose (CMC). It investigates which type would be preferable as an implant material in terms of biocompatibility, biomechanical and biological properties, and also in terms of its behavior in combination with collagen fibrils (Col) in composite Col/OC or Col/CMC scaffolds. OC significantly supported the stiffness and elasticity of Col fibrils, whereas CMC significantly reduced these properties. OC also enabled a strong interaction with Col fibrils even in a moist environment, accompanied by a significant drop in elastic modulus. The addition of cellulose did not significantly influence scaffold porosity; however, changes in surface morphology and the lower swelling capacity of OC, with a degree of oxidation of its chains between 16 and 24%, supported the idea of improved cell-material interaction. The elasticity and the stiffness of Col/OC guided human adipose-derived stem cells (hADSCs) to significantly higher adhesion, proliferation, and metabolic activity. On the contrary, the Col/CMC provided only limited mechanical support for the cells and inhibited their attachment and proliferation, although without any signs of cytotoxicity. This phenomenon could be used for future control of the differentiation of hADSCs towards a desired phenotype to generate advanced tissue replacements using modern methods of tissue engineering. The oxidation of cellulose resulted in a firmer scaffolding material, as required in vascular or skin tissue engineering. CMC is suitable for moist wound healing, e.g. as a mucoadhesive gel, where cell adhesion is not desirable. Graphical abstract
An n-th order delayed differential equation y(n)(t)=f(t,yt,yt′,…,yt(n−1)) is considered, where yt(θ)=y(t+θ), θ∈[−τ,0], τ>0, if t→∞. A criterion is formulated guaranteeing the existence of a solution y=y(t) in a cone 0<(−1)i−1y(i−1)(t)<(−1)i−1φ(i−1)(t), i=1,…,n where φ is an n-times continuously differentiable function such that 0<(−1)iφ(i)(t), i=0,…,n. The proof is based on a similar result proved first for a system of delayed differential equations equivalent in a sense. Particular linear cases are considered and an open problem is formulated as well.
This paper discusses the pitfalls of using response surface methods when solving inverse problems and presents an adaptive artificial neural network-based inverse response surface method. The procedure is based on a coupling of the adaptive response surface method and artificial neural network-based inverse reliability analysis. The validity and accuracy of the method are tested on several examples. The first is a problem with a theoretical explicit nonlinear limit state function and one design parameter. Here, the accuracy of surrogate models for design parameter identification was tested for cases with the target values of the identified parameter both inside and outside of the initial range of values. The absolute percentage errors were 11.79 % and 0.19 % after the first and the last iteration of the identification process, respectively. The other two examples represent practical applications of the reliability design of structures with multiple design parameters and multiple reliability constraints. In the former, the limit state functions are defined explicitly, while in the latter, they are defined implicitly in the form of a structural analysis using the nonlinear finite element method. When assessing the reliability index values, very low absolute percentage error values were obtained in both examples. For the explicit form of the limit state function, the values were up to 0.50 % in all iterations. In the case of the implicitly defined limit state function, the absolute percentage error was equal to 6.45 % after the fist iteration and 0.79 % after the second iteration.
Distribution of energy from a Total Site Trigeneration Energy System (TSTES) to fulfil process energy demands can result in transmission losses due to frictions in pipelines and the electrical grid. Sensitivity analysis can be used to design the required backup system to address such risk. Previously, the Trigeneration System Cascade Analysis (TriGenSCA) method that was used to design a TSTES has assumed no transmission losses and ignored the need for a backup utility system. This paper proposes an extension of the TriGenSCA to consider transmission and storage energy losses and sensitivity analysis to enable a trigeneration system involving batch processes to produce realistic energy targets and to design a backup utility system of appropriate capacity. The methodology was applied on a case study involving a Pressurised Water Reactor (PWR) integrated with a trigeneration system within an industrial Total Site comprising four process plants. This study shows an increase of up to 15% in total annual cost for a trigeneration system with transmission losses as compared to the one without transmission losses, and it shows that Plant B shutdown, which requires additional 3.1 MW low-pressure steam and 3.25 MW of hot water represents the worst-case scenario of a single plant shutdown.
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6,680 members
Ivan Saldan
  • Central European Institute of Technology "CEITEC"
Sudeep Roy
  • Department of Bio-medical Engineering
Lubomir Brancik
  • Department of Radio Electronics
Jiri Kucerik
  • Institute of Chemistry and Technology of Environmental Protection "ICTEP"
Information
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Antonínská 548/1, 601 90, Brno, Czechia
Head of institution
prof. RNDr. Ing. Petr Štěpánek, CSc.
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http://www.vutbr.cz/en/
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+420 541 141 111