2021 - Publications Repository - Gdańsk University of Technology

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Publications from the year 2021

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The Effect of Conjugation with Octaarginine, a Cell-Penetrating Peptide on Antifungal Activity of Imidazoacridinone Derivative
- Kamila Rząd
- Ewa Paluszkiewicz
- Damian Neubauer
- Mateusz Olszewski
- Katarzyna Kozłowska-Tylingo
- Wojciech Kamysz
- Iwona Gabriel
2021 Full text INTERNATIONAL JOURNAL OF MOLECULAR SCIENCES
Acridine cell-penetrating peptide conjugates are an extremely important family of compounds in antitumor chemotherapy. These conjugates are not so widely analysed in antimicrobial therapy, although bioactive peptides could be used as nanocarriers to smuggle antimicrobial compounds. An octaarginine conjugate of an imidazoacridinone derivative (Compound 1-R8) synthetized by us exhibited high antifungal activity against reference and fluconazole-resistant clinical strains (MICs ≤ 4 μg mL−1). Our results clearly demonstrate the qualitative difference in accumulation of the mother compound and Compound 1-R8 conjugate into fungal cells. Only the latter was transported and accumulated effectively. Microscopic and flow cytometry analysis provide some evidence that the killing activity of Compound 1-R8 may be associated with a change in the permeability of the fungal cell membrane. The conjugate exhibited low cytotoxicity against human embryonic kidney (HEK-293) and human liver (HEPG2) cancer cell lines. Nevertheless, the selectivity index value of the conjugate for human pathogenic strains remained favourable and no hemolytic activity was observed. The inhibitory effect of the analysed compound on yeast topoisomerase II activity suggested its molecular target. In summary, conjugation with R8 effectively increased imidazoacridinone derivative ability to enter the fungal cell and achieve a concentration inside the cell that resulted in a high antifungal effect.
The effect of Fe on chemical stability and oxygen evolution performance of high surface area SrTix-1FexO3-δ mixed ionic-electronic conductors in alkaline media
- Krystian Lankauf
- Aleksander Mroziński
- Patryk Błaszczak
- Karolina Górnicka
- Justyna Ignaczak
- Marcin Łapiński
- Jakub Karczewski
- Grzegorz Cempura
- Piotr Jasiński
- Sebastian Molin
2021 Full text INTERNATIONAL JOURNAL OF HYDROGEN ENERGY
Development of environmentally friendly, high performing oxygen evolution reaction (OER) catalysts is an important research challenge. In this work, iron doped strontium titanates with a general formula SrTi1-xFexO3-δ (x = 0.35, 0.50, 0.70, 0.90, and 1.00) denoted as STFx, were synthesized via a solid state reaction technique and characterized in terms of oxygen evolution reaction electrocatalysis in an alkaline electrolyte (0.1 M KOH). The produced powders were characterized by a high specific surface area (>20 m2 g−1), beneficial for OER. The evaluation of specific activity indicated the following trend of increasing performance: STF35 < STF50 < STF70 < SFO < STF90. The lowest overpotential at 10 mAcm−2 GEO of 410 mV (350 mV at 25 μA cm−2OX) was achieved by STF90 with the corresponding Tafel slope of 60 mV dec−1. The two materials with the highest Fe content (i.e. STF90 and SFO) showed, however, poor chemical stability in alkaline solution demonstrated by the dissolution of Sr. Based on the good electrochemical performance (~460 mV at 10 mA cm−2GEO, ~405 mV at 25 μA cm−2OX) and chemical stability for at least 30 days (no Sr dissolution) of STF50, it can be considered an interesting, working at room temperature OER catalyst based on non-toxic and abundant elements.
The Effect of Increasing the Amount of Indium Alloying Material on the Efficiency of Sacrificial Aluminium Anodes
- Krzysztof Żakowski
- Juliusz Orlikowski
- Kazimierz Darowicki
- Marcin Czekajło
- Piotr Igliński
- Kinga Domańska
2021 Full text Materials
Al-Zn-In alloys having 4.2% zinc content and various indium content in the range of 0.02–0.2% were tested with respect to the most important electrochemical properties of sacrificial anodes in a cathodic protection, i.e., the current capacity and potential of the operating anode. The distribution of In and Zn in the tested alloys was mapped by means of the EDX technique, which demonstrated that these elements dissolve well in the alloy matrix and are evenly distributed within it. The current capacity of such alloys was determined by means of the method of determining the mass loss during the dissolution by a current of known charge. The results obtained demonstrate that the current capacity of Al-Zn-In alloy decreases with the increase in the In content, which results in an increased consumption of anode material and shorter lifetime of anodes. With 0.02% In content, the capacity amounted to approx. 2500 Ah/kg, whereas the alloy with 0.2% In had as much as 30% lower capacity amounting to approx. 1750 Ah/kg. Microscopic examination for the morphology and surface profile of the samples after their exposure demonstrated that a higher indium content in the alloy results in a more uneven general corrosion pattern during the dissolution of such alloy, and the cavities (pits) appearing on the alloy surface are larger and deeper. As the indium content is increased from 0.02% to 0.05%, the Al-Zn-In alloy potential decreases by about 50 mV to −1100 mV vs. Ag/AgCl electrode, which is advantageous in terms of using this alloy as a sacrificial anode. When the indium content is further increased from 0.05% to 0.2%, the potential of the alloy is no longer changed to a more negative one. The results obtained from all these tests demonstrate that alloys containing up to 0.05% of In additive are practically applicable for cathodic protection.
The Effect of Protrusions on the Initiation of Partial Discharges in XLPE High Voltage Cables
- Mohammad AlShaikh Saleh
- S. Shady Refaat
- Marek Olesz
- Haitham Abu-Rub
- Jarosław Guziński
2021 Full text Bulletin of the Polish Academy of Sciences-Technical Sciences
This paper is focusing on 3D Finite Elements Analysis (FEA) based modelling of protrusions as defects or imperfections in the XLPE high voltage cable. This study is aiming to examine the impact protrusions have on the initiation of partial discharges. Spherical and ellipsoidal protrusions with different sizes at the conductor screen of the high voltage cable is an essential content of this paper. In addition, a spherical gas-filled void is placed inside and outside the protrusions, and a water tree produced from protrusions is under consideration. The partial discharge influence taking place at the protrusions and the stress enhancement factor is determined for all the variations mentioned to quantify the rise in the inception of partial discharges due to the protrusions.
The Effect of Surface Treatment with Isocyanate and Aromatic Carbodiimide of Thermally Expanded Vermiculite Used as a Functional Filler for Polylactide-Based Composites
- Mateusz Barczewski
- Olga Mysiukiewicz
- Aleksander Hejna
- Radosław Biskup
- Joanna Szulc
- Sławomir Michałowski
- Adam Piasecki
- Arkadiusz Kloziński
2021 Full text Polymers
In this work, thermally expanded vermiculite (TE-VMT) was surface modified and used as a filler for composites with a polylactide (PLA) matrix. Modification of vermiculite was realized by simultaneous ball milling with the presence of two PLA chain extenders, aromatic carbodiimide (KI), and 4,4’-methylenebis(phenyl isocyanate) (MDI). In addition to analyzing the particle size of the filler subjected to processing, the efficiency of mechanochemical modification was evaluated by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The composites of PLA with three vermiculite types were prepared by melt mixing and subjected to mechanical, thermomechanical, thermal, and structural evaluation. The structure of composites containing a constant amount of the filler (20 wt%) was assessed using FTIR spectroscopy and SEM analysis supplemented by evaluating the final injection-molded samples’ physicochemical properties. Mechanical behavior of the composites was assessed by static tensile test and impact strength hardness measurements. Heat deflection temperature (HDT) test and dynamic thermomechanical analysis (DMTA) were applied to evaluate the influence of the filler addition and its functionalization on thermomechanical properties of PLA-based composites. Thermal properties were assessed by differential scanning calorimetry (DSC), pyrolysis combustion flow calorimetry (PCFC), and thermogravimetric analysis (TGA). The use of filler-reactive chain extenders (CE) made it possible to change the vermiculite structure and obtain an improvement in interfacial adhesion and more favorable filler dispersions in the matrix. This translated into an improvement in impact strength and an increase in thermo-mechanical stability and heat release capacity of composites containing modified vermiculites.
The Effect of the Selection of Three-Dimensional Random Numerical Soil Models on Strip Foundation Settlements
- Kamil Żyliński
- Karol Winkelmann
- Jarosław Górski
2021 Full text Applied Sciences-Basel
This paper delivers a probabilistic attempt to prove that the selection of a random three-dimensional finite element (FE) model of a subsoil affects the computed settlements. Parametricanalysis of a random soil block is conducted, assuming a variable subsoil Young’s modulus inparticular finite elements. The modulus is represented by a random field or different-sized setsof random variables; in both cases, the same truncated Gaussian model is assumed. Mean valuesand standard deviations of random soil settlement are estimated by a Monte Carlo simulationprocedure. With regard to the adopted FE model, the estimated settlement mean values do notvary significantly, but standard deviations do strongly. Similarities also appear in the diagrams ofrandom field correlation length versus settlement standard deviation and the diagrams displayinga total number of model random variables versus settlement standard deviation. Thus, relevantsingle random variable models represent the random field approach well with regard to settlementparameter estimation. This remark is verified upon a settlement analysis of a three-dimensional FEmodel of a hypothetical strip foundation. Following the preliminary model observations, variousprobabilistic geotechnical analyses may be supported, e.g., continuous footing design, slope stabilityanalysis, and foundation reliability assessment.
The Effectiveness of Basic Resuscitation Activities Carried out by Combat Paramedics of the Police, as Exemplified by Polish Counterterrorist Units
- Waldemar Zubrzycki
- Jarosław Przyjemczak
- Beata Świeczko-Żurek
2021 Full text Internal Security
The tasks carried out by Police officers are often accompanied by dangerous situations that threaten the life and health of the people involved, the police themselves, and bystanders. It concerns especially counter-terrorism police units whose activities are aimed at terrorists and particularly dangerous criminals, and their course is violent and aggressive. In conjunction with the inability to bring civilian rescue services into the action zone, this results in the need to expand the assault team by including one more specialisation — combat paramedic, having the appropriate knowledge, skills and qualifications, as well as equipment that allows for independent first aid while the operations are underway. A paramedic’s preparation must be versatile, but the key to effective action is the ability to perform basic activities, including cardiopulmonary resuscitation, after the diagnosis of sudden cardiac arrest. The study aims to present the results of research conducted on a fairly unique research sample regarding the effectiveness of indirect heart massage by combat paramedics of police special units and conclusions resulting from empirical research and their comparison with the results of similar studies, in relation to other professional groups. The knowledge and skills acquired during the training quickly become obsolete, requiring systematic consolidation and improvement. Therefore, cyclical repetition of exercises in the area of rescue activities plays a key role in maintaining the required quality of life support. The collected material may be a premise for further research, indicating their potential directions.
The efficiency of turbomachinery in the zero-and three-dimensional approaches
- Paweł Ziółkowski
- Tomasz Kowalczyk
- Janusz Badur
- Michel Feidt
2021 Entropie
Efficiency of turbomachinery is usually defined using an isentropic process. This approach provides a reliable reference point only when pressure and temperature measurements are available, e.g. at the casing inlet and outlet. In the case of a single stage internal efficiency determination the reference point is difficult. Computational fluid dynamics allows for an exact calculation of values of losses occurring in a turbine stage from turbine blades geometry, clearances, uneven steam distribution and other. Present method is a three-dimensional polytrophic approach based on work comparison of a turbine stage using real and ideal working fluid. The reference state is estimated by iterative simulation of considered geometry using the Eulerian model of compressible fluid. This approach is more convenient and feels natural when using 3D modeling. Moreover, calculations conducted for a control stage indicated differences between results attained using those two approaches less than 0.2%.
The Energy of Finance in Refining of Medical Surge Capacity
- Oleksandr Melnychenko
2021 Full text ENERGIES
The availability of resources and their concentration in the place of greatest need, will not allow us to successfully overcome a medical surge without the energy required to activate these resources and activities, and increase their quantities if necessary, that is why the staff and management of healthcare institutions are forced to making ethical crisis decisions about who wins and who loses. This study highlights the versatility of the concept of ‘energy’ by attributing it to money or financial resources, which are highly essential in dealing with surges as the healthcare system adopts the appropriate capacity level. This study considers the means (space, staff, supplies, and specific resources) at the disposal of healthcare institutions for the control of diseases as economic resources to identify ways for enhancing their capacity, especially during periods of medical surges such as that caused by the coronavirus disease (COVID-19). The medical resources are dependent on ‘energy’, albeit not in the strictest sense of the term. The article, thus, points out that while limited resources are the norm in economic theory, a medical surge provides an opportunity to sufficiently extend the resources within the health system capacity through increased funding.
The equivariant spectral flow and bifurcation of periodic solutions of Hamiltonian systems
- Marek Izydorek
- Joanna Janczewska
- Nils Waterstraat
2021 Full text NONLINEAR ANALYSIS-THEORY METHODS & APPLICATIONS
We define a spectral flow for paths of selfadjoint Fredholm operators that are equivariant under the orthogonal action of a compact Lie group as an element of the representation ring of the latter. This G-equivariant spectral flow shares all common properties of the integer valued classical spectral flow, and it can be non-trivial even if the classical spectral flow vanishes. Our main theorem uses the G-equivariant spectral flow to study bifurcation of periodic solutions for autonomous Hamiltonian systems with symmetries.
The evidence for the impact of policy on physical activity outcomes within the school setting: A systematic review
- Catherine Woods
- Kevin Volf
- Liam Kelly
- Bláthín Casey
- Peter Gelius
- Sven Messing
- Sarah Forberger
- Jeroen Lakerveld
- Joanna Żukowska
- Enrique García Bengoechea
2021 Full text Journal of Sport and Health Science
Purpose Despite the well-established health benefits of physical activity (PA) for young people (aged 4–19 years), most do not meet PA guidelines. Policies that support PA in schools may be promising, but their impact on PA behavior is poorly understood. The aim of this systematic review is to ascertain the level and type of evidence reported in the international scientific literature for policies within the school setting that contribute directly or indirectly to increasing PA. Methods This systematic review is compliant with Preferred Reporting Items for Systematic Review and Meta-Analysis guidelines. Six databases were searched using key concepts of policy, school, evaluation, and PA. Following title and abstract screening of 2323 studies, 25 progressed to data synthesis. Methodological quality was assessed using standardized tools, and the strength of the evidence of policy impact was described based on pre-determined codes: positive, negative, inconclusive, or untested statistically. Results Evidence emerged for 9 policy areas that had a direct or indirect effect on PA within the school setting. These were whole school PA policy, physical education, sport/extracurricular PA, classroom-based PA, active breaks, physical environment, shared use agreements, and active school transport and surveillance. The bulk of the evidence was significantly positive (54%), 27% was inconclusive, 9% was significantly negative, and 11% was untested (due to rounding, some numbers add to 99 or 101). Frequency of evidence was highest in the primary setting (41%), 34% in the secondary setting, and 24% in primary/secondary combined school settings. By policy area, frequency of evidence was highest for sport/extracurricular PA (35%), 17% for physical education PA, and 12% for whole school PA policy, with evidence for shared use agreements between schools and local communities rarely reported (2%). Comparing relative strength of evidence, the evidence for shared use agreements, though sparse, was 100% positive, 60% of the evidence for whole school PA policy was positive, 59% of the evidence for sport/extracurricular PA was positive, 57% of the evidence for physical education was positive, and 50% of the evidence for PA in classroom and for active breaks/recess was positive.
The fate and contamination of trace metals in soils exposed to a railroad used by Diesel Multiple Units: Assessment of the railroad contribution with multi-tool source tracking
- Jacek Szmagliński
- Nicole Nawrot
- Ksenia Pazdro
- Jolanta Walkusz-miotk
- Ewa Wojciechowska
2021 Full text SCIENCE OF THE TOTAL ENVIRONMENT
Soil samples from cut slopes from lightly loaded railway lines used by Diesel Multiple Units for 5 years in Gdansk (Poland) were collected and analyzed for trace metals (TMs): Zn, Pb, Cd, Ni, Cr, Cu, and Fe. The main aim was to assess soil enrichment, contamination status, and distribution of TMs relative to the distance from the railway track. Extensive source tracking analyses were performed using cluster analysis (CA) and the Pb isotope ratios approach (206Pb, 207Pb, and 208Pb). Soil samples were affected by Cr, Cu, Pb, and Zn (max values in mg/kg d.w.: 31.1, 145, 80.5, and 115, respectively). The Enrichment Factor showed moderate (Cr, Zn, Pb) to very severe (Cu) enrichment. CA allowed TMs to be divided into two general groups: a) containing Zn, Pb, Cd with slight interaction with Cu; and b) containing Fe and Niwith slight interactionwith Cr. Correlation analyses indicated Cr as an outlying TM delivered from a separate source associated with the specificity of the construction of railroad 248, where alloys containing Cr were used to counteract increasing wear-and-tear of the rails. Pb isotopic ratios in the ranges of 1.16–1.20 (206Pb/207Pb) and 2.05–2.10 (208Pb/206Pb) corresponded to anthropogenic supplementation (coal combustion, road vehicles, and railroad transport) of Pb and Pb-correlated TMs (Zn, Cd, and partly Cu). Despite the research focus on the impact of the railroad contribution, a comparison with other forms of transport indicated that road transport appeared to have a higher contributing factor to TM pollution at the investigated site. This general conclusion againemphasizes the lower environmental footprint exhibited by railway transport in comparison to road transport.
The Green Approach to the Synthesis of Bio-Based Thermoplastic Polyurethane Elastomers with Partially Bio-Based Hard Blocks
- Ewa Głowińska
- Paulina Kasprzyk
- Janusz Datta
2021 Full text Materials
Bio-based polymeric materials and green routes for their preparation are current issues of many research works. In this work, we used the diisocyanate mixture based on partially bio-based diisocyanate origin and typical petrochemical diisocyanate for the preparation of novel bio-based thermoplastic polyurethane elastomers (bio-TPUs). We studied the influence of the diisocyanate mixture composition on the chemical structure, thermal, thermomechanical, and mechanical properties of obtained bio-TPUs. Diisocyanate mixture and bio-based 1,4-butanediol (as a low molecular chain extender) created bio-based hard blocks (HS). The diisocyanate mixture contained up to 75 wt % of partially bio-based diisocyanate. It is worth mentioning that the structure and amount of HS impact the phase separation, processing, thermal or mechanical properties of polyurethanes. The soft blocks (SS) in the bio-TPU’s materials were built from α,ω-oligo(ethylene-butylene adipate) diol. Hereby, bio-TPUs differed in hard segments content (c.a. 30; 34; 40, and 53%). We found that already increase of bio-based diisocyanate content of the bio-TPU impact the changes in their thermal stability which was measured by TGA. Based on DMTA results we observed changes in the viscoelastic behavior of bio-TPUs. The DSC analysis revealed decreasing in glass transition temperature and melting temperature of hard segments. In general, obtained materials were characterized by good mechanical properties. The results confirmed the validity of undertaken research problem related to obtaining bio-TPUs consist of bio-based hard building blocks. The application of partially bio-based diisocyanate mixtures and bio-based chain extender for bio-TPU synthesis leads to sustainable chemistry. Therefore the total level of “green carbons” increases with the increase of bio-based diisocyanate content in the bio-TPU structure. Obtained results constitute promising data for further works related to the preparation of fully bio-based thermoplastic polyurethane elastomers and development in the field of bio-based polymeric materials
The image of the City on social media: A comparative study using “Big Data” and “Small Data” methods in the Tri-City Region in Poland
- Jianxiang Huang
- Hanna Obracht-Prondzyńska
- Dorota Kamrowska-Załuska
- Yiming Sun
- Lishuai Li
2021 Full text LANDSCAPE AND URBAN PLANNING
“The Image of the City” by Kevin Lynch is a landmark planning theory of lasting influence; its scientific rigor and relevance in the digital age were in dispute. The rise of social media and other digital technologies offers new opportunities to study the perception of urban environments. Questions remain as to whether social media analytics can provide a reliable measure of perceived city images? If yes, what implication does it hold for urban planners? This paper describes a study on the perception of city images using a combination of “big data” and “small data” methods in the Tri-City Region in Poland. The aims were to 1) test the hypothesis whether social media analytics can elicit Lynchian elements of city image in consistency with conventional methods, and 2) develop and evaluate social media-based indicators of Imageability for planning practice. Geo-tagged images and texts were collected from Instagram and Twitter, two popular social media platforms in Poland. Text-Mining, Image Processing, Clustering Analysis, Kernel Density Estimation, and Sentiment Analysis were used. Results were compared with benchmarks constructed from official GIS database, questionnaire responses and sketch maps. “District”, “landmark”, and “path” identified on social media were in good agreements with benchmarks, less so for “edge” and “node”. Two social media-based indicators have influenced the perception of a place: Instagramability, the frequency of a place captured on Instagram, was linked to its perception as an architectural landmark and tourist attraction, while Twitterability, the frequency of a place mentioned on Twitter by name, was linked to its perceived niceness and relevance to everyday life of communities. Methods developed in this study have theoretical and practical implications for urban planners.
The Impact of Covid-19 on the Performance of Exchange Traded Funds on Developed and Emerging Markets
- Krystian Zawadzki
2021 Full text
In this paper an endeavour was made to evaluate the impact of Covid-19 on the achievement of the investment objectives by selected ETFs in developed and emerging markets. For this purpose, the tracking errors calculated for 18 different ETFs operating on the basis of American, Asian and European stock indexes were analyzed. The time range of the research was selected in such a way as to compare the period before the pandemic(pre-Covid) and the period after the pandemic (post-Covid). The research results show that the outbreak of the coronavirus pandemic has not had a negative impact on the degree of implementation of the investment objective, regardless of the degree of market development. For each of the analyzed markets, the calculated tracking errors were not higher in the post-Covid period as compared to the pre-Covid period. In the vast majority of cases, they were even lower. This means that the management of the ETF has run smoothly in the most turbulent period of the 21st century.
The Impact of Decommissioning Cemeteries on the Urban Ecosystem
- Anna Myślińska
- Jakub Szczepański
- Witold Dłubakowski
2021 Full text Sustainability
The decommissioning of cemeteries noticeably transforms the urban fabric. The purpose of this article was to determine what impact the decommissioning of cemeteries has on the urban ecosystem. For this purpose, it was necessary to assess the value of cemeteries within the urban ecosystem. Cemeteries are classified as urban green spaces, and their value as preservers of flora and fauna in local ecosystems has been proven. However, numerous decaying bodies in one place could have adverse effects on the environment. In order to assess the impact of transforming cemetery areas for other uses in the context of sustainable city development, it is necessary to define what these other functions might be. This article presents the main reasons for decommissioning cemeteries and links them with subsequent land use. The history of cemetery locations in five major Polish cities was analyzed to determine the extent to which cemeteries were decommissioned. In the two cities with the highest number of decommissioned cemeteries, further research was carried out in order to establish the typical land use of these former cemeteries, whether this usage is related to the size or type of the former cemetery, and whether change in land use is an advantage or a disadvantage for the urban ecosystem.
The impact of freeze-thaw processes on a cliff recession rate in the face of temperate zone climate change
- Halina Kaczmarek
- Arkadiusz Bartczak
- Sebastian Tyszkowski
- Michał Badocha
- Michał Krzemiński
2021 CATENA
Freeze-thaw action is a common type of geomorphological processes eroding cliff faces in the temperate climate zone. In our previous study, we assessed the geomorphological effects of freeze-thaw fluctuations occurring within the cliff of Jeziorsko Reservoir (central Poland). Based on those findings, we have now determined the number of freeze-thaw cycles to assess their historical impact on the studied cliff. We have also traced the directions and the pace of changes in freeze-thaw processes in Poland. The results reveal a gradually decreasing role of freeze-thaw action in the process of the recession of the cliff of Jeziorsko Reservoir throughout its existence. The same is true nearly across Poland, although with some regional variation. Within 1951–2018, the impact of freeze-thaw action declined most significantly in north-western and central Poland, i.e. the area with the smallest annual number of freeze-thaw cycles. Consequently, this is also where the impact of geomorphological results of freeze-thaw cycles will be the least pronounced. It was only in the north-eastern edges of the country, which are under the dominant influence of continental air masses, where no significant changes in the impact of freeze-thaw processes were identified. The obtained results strongly legitimise the conclusion that global warming in the mid-latitude zone of the temperate climate has reduced the role of freeze-thaw processes in the geomorphological transformation of cliffs developed within river banks and lake or water reservoir shores.
The Impact of Ground Tire Rubber Oxidation with H2O2 and KMnO4 on the Structure and Performance of Flexible Polyurethane/Ground Tire Rubber Composite Foams
- Aleksander Hejna
- Adam Olszewski
- Łukasz Zedler
- Paulina Kosmela
- Krzysztof Formela
2021 Full text Materials
The use of waste tires is a very critical issue, considering their environmental and economic implications. One of the simplest and the least harmful methods is conversion of tires into ground tire rubber (GTR), which can be introduced into different polymer matrices as a filler. However, these applications often require proper modifications to provide compatibility with the polymer matrix. In this study, we examined the impact of GTR oxidation with hydrogen peroxide and potassium permanganate on the processing and properties of flexible polyurethane/GTR composite foams. Applied treatments caused oxidation and introduction of hydroxyl groups onto the surface of rubber particles, expressed by the broad range of their hydroxyl numbers. It resulted in noticeable differences in the processing of the polyurethane system and affected the structure of flexible composite foams. Treatment with H2O2 resulted in a 31% rise of apparent density, while the catalytic activity of potassium ions enhanced foaming of system decreased density by 25% and increased the open cell content. Better mechanical performance was noted for H2O2 modifications (even by 100% higher normalized compressive strength), because of the voids in cell walls and incompletely developed structure during polymerization, accelerated by KMnO4 treatment. This paper shows that modification of ground tire rubber is a very promising approach, and when properly performed may be applied to engineer the structure and performance of polyurethane composite foams.
The Impact of Thermal Stresses on Volume Resistivity: Performance Comparison between TR-XLPE and XLPE Cables
- Jasem Mohammed
- Shady S. Refaat
- Haitham Abu-Rub
- Marek Olesz
- Jarosław Guziński
2021
Most failures in electric power cables are attributed to the development of water trees inside the insulating materials. Thus, the development and utilization of Tree Retardant Cross-Linked Polyethylene (TR-XLPE) based cables have recently been given great attention to overcome the treeing issues. TR-XLPE cables use low-density polyethylene compounds suppressing the formation of water trees while retaining excellent electrical, physical, and processing attributes. This paper investigates and analyzes the impact of thermal stress on a 33kV three-core power cable with TR-XLPE and XLPE insulations in the presence of different types, shapes and sizes of voids. The results have been obtained after 500 hours of the accelerated aging test. The obtained results confirm the superiority of TR-XLPE over XLPE cables in terms of retaining higher volume resistivity. Results obtained from simulations conclude that TR-XLPE insulated cable retains 6% more dielectric strength when compared to XLPE insulated cable.
The Influence of a Photovoltaic Micro-Installation on the Low-Frequency Parameters of Electricity at PCC and Its Impact on the Thermal Characteristics of Selected Devices
- Stanisław Galla
- Mirosław Włas
2021 Full text ENERGIES
This manuscript illustrates the measurement results of parameters describing the quality of energy at the PCC (point of common coupling) of a photovoltaic micro-installation that can significantly affect devices in the same power grid. The analyses reflecting heating of selected devices used in domestic installations, which were performed in an isolated laboratory environment, are also indicated. The conducted study aimed at checking the thermal characteristics of the chosen equipment, i.e., AC/DC power supply, LED and fluorescent light sources, a step-down transformer at synergistically higher voltage harmonics and constant component in the network voltage. The tests were carried out at the disturbance levels recorded at the site of the photovoltaic micro-installation. The conducted tests aimed at indicating the presence of an increased level of synergetic disturbances in the vicinity of micro-photovoltaic installations. Based on the research, recommendations were made for photovoltaic micro-installations.