Publications Repository - Gdańsk University of Technology

Page settings

polski
Publications Repository
Gdańsk University of Technology

Show publications from the year

Publications from the year 2021

Show all
  • Insights into modification of lignocellulosic fillers with isophorone diisocyanate: structure, thermal stability and volatile organic compounds emission assessment
    • Aleksander Hejna
    • Mariusz Marć
    • Katarzyna Skórczewska
    • Joanna Szulc
    • Jerzy Korol
    • Krzysztof Formela
    2021 Full text European Journal of Wood and Wood Products (HOLZ ALS ROH-UND WERKSTOFF)

    This study presents an analysis of the structure and properties of different types of lignocellulosic fillers modified by isophorone diisocyanate (IPDI) to provide insights into the possibility of their application to the manufacturing of wood polymer composites (WPCs). Moreover, it deals with the environmental aspects of modified fillers, by assessment of volatile organic compounds (VOCs) emitted during modification, as well as from final products. Three types of commercially available lignocellulosic fillers were modified with different content of IPDI (from 1 to 15 wt%) using the internal mixer. The main compounds detected in the air during modifications were terpenes and terpenoids. No IPDI was detected, which is very beneficial considering its toxicity. On the other hand, IPDI was emitted from modified fillers at a slightly elevated temperature of 40 °C, which was associated with a significant rise in its vapor pressure. Successful modification of fillers was confirmed by FTIR spectroscopy and thermogravimetric analysis. Performed modifications of lignocellulosic fillers with IPDI had a relatively small impact on their particle size and color properties. Such an effect can be considered beneficial for the mechanical performance and appearance of WPCs, which could be potentially manufactured using IPDI-modified lignocellulosic fillers.

  • Insights into the Thermo-Mechanical Treatment of Brewers’ Spent Grain as a Potential Filler for Polymer Composites
    • Aleksander Hejna
    • Mariusz Marć
    • Daria Kowalkowska-Zedler
    • Agnieszka Pladzyk
    • Mateusz Barczewski
    2021 Full text Polymers

    This paper investigated the impact of twin-screw extrusion parameters on the properties of brewers’ spent grain. The chemical structure, antioxidant activity, particle size, and color properties, as well as the emission of volatile organic compounds during extrusion, were investigated. The main compounds detected in the air during modifications were terpenes and terpenoids, such as α-pinene, camphene, 3-carene, limonene, or terpinene. They could be considered as a potential threat to human health and the environment. Changes in the chemical structure, antioxidant activity, and color of materials after modification indicated the Maillard reactions during extrusion, which resulted in the generation of melanoidins, especially at higher temperatures. This should be considered an exciting feature of this treatment method because modified brewers’ spent grain may improve the thermooxidative stability of polymer materials. Moreover, the impact of the brewers’ spent grain particle size on color and browning index used to determine the melanoidins content was investigated. The presented results show that proper adjustment of extrusion parameters enables the preparation of brewers’ spent grain with the desired appearance and chemical properties, which could maximize the efficiency of the modification process.

  • Instructor Presence in Video Lectures: Preliminary Findings From an Online Experiment
    • Yen Ying Ng
    • Adam Przybyłek
    2021 Full text IEEE Access

    Motivation. Despite the widespread use of video lectures in online and blended learning environments, there is still debate whether the presence of an instructor in the video helps or hinders learning. According to social agency theory, seeing the instructor makes learners believe that s/he is personally teaching them, which leads to deeper cognitive processing and, in turn, better learning outcomes. Conversely, according to cognitive load theory, adding an image of the instructor may hinder attention engagement with lecture content due to split-attention effect. Not only are theoretical propositions conflicting, but so is the empirical evidence as well. Objective. This study investigates the effects of the presence of the instructor’s face in the corner of an educational video on learning outcomes, perceived cognitive load, and perceived social presence in the context of foreign language vocabulary learning. Method. In an online quasi-controlled experiment with between-subject design, 112 participants were randomly assigned to view a 10-min-long educational video in one of two conditions: instructor-present or instructor-absent. As for the latter condition, the face was shown only at the introduction of the presentation. Afterwards, participants completed a retention test as well as a cognitive load and social presence questionnaire. Results. No significant differences were found for any dependent variable. Conclusion. Individuals differ so much in their language aptitude as well as motivation to perform well that random assignment is probably not enough to ensure balanced groups in this particular study context. Besides, the approach that we used to measure cognitive load as well as social presence is not suited for between-subject design, even though it was previously used in such settings.

  • Integracyjne place zabaw
    • Marek Wysocki
    • Joanna Kowalewska
    2021

    .

  • Integrated membrane bioreactors modelling: A review on new comprehensive modelling framework
    • Jacek Mąkinia
    • Giorgio Mannina
    • Marion Alliet
    • Christoph Brepols
    • Joaquim Comas
    • Jarome Harmand
    • Marc Heran
    • Nesrine Kalboussi
    • Ángel Robles
    • Ferreira Taise Rebouças
    • Bing-Jie Ni
    • Ignasi Rodriguez-Roda
    • María Victoria Ruano
    • Giorgio Bertanza
    • Ilse Smets
    2021 BIORESOURCE TECHNOLOGY

    Integrated Membrane Bioreactor (MBR) models, combination of biological and physical models, have been representing powerful tools for the accomplishment of high environmental sustainability. This paper, produced by the International Water Association (IWA) Task Group on Membrane Modelling and Control, reviews the state-of-the-art, identifying gaps for future researches, and proposes a new integrated MBR modelling framework. In particular, the framework aims to guide researchers and managers in pursuing good performances of MBRs in terms of effluent quality, operating costs (such as membrane fouling, energy consumption due to aeration) and mitigation of greenhouse gas emissions.

  • Integrated plant-wide modelling for evaluation of the energy balance and greenhouse gas footprint in large wastewater treatment plants
    • Ewa Zaborowska
    • Krzysztof Czerwionka
    • Jacek Mąkinia
    2021 Full text APPLIED ENERGY

    Modern wastewater treatment plants (WWTPs) should maintain a balance between three combined sustainability criteria, including effluent quality, energy performance and greenhouse gas (GHG) emissions. All of these criteria were considered in the integrated plant-wide model developed in this study. The proposed model incorporates new features, including: (i) the addition of associated facilities to the overall energy balance and GHG footprint and (ii) the implementation and validation of detailed sub-models of heat and power supply and demand. The aim of the study was to investigate the implications of these new extensions on the energy balance and sustainability assessment of the entire facility. The integrated model was evaluated against full-scale data from a large WWTP performing biological nutrient removal in an activated sludge bioreactor and anaerobic digestion of sewage sludge. Upon applying the investigated operational strategies, the potential decreases in the GHG footprint and effluent total nitrogen concentration were estimated to be 20% and 30%, respectively, in comparison with the current conditions. However, only a slight potential for improving the overall energy balance was found. In contrast, with technological upgrades, energy neutrality and the highest reduction in the GHG footprint (by over 30%) were achieved, but the effluent quality remained unchanged in comparison with the current conditions. It was shown that the heat demand of associated facilities could not be neglected in the overall heat balance and GHG footprint. The detailed models of energy demand and supply improved the assessment of energy performance in the full-scale WWTP.

  • Integrating Digital Twin Technology Into Large Panel System Estates Retrofit Projects
    • Paulina Duch-Żebrowska
    • Katarzyna Zielonko-Jung
    2021 Full text Urban Planning

    As sustainability is now a standard for the proposed developments, the focus ought to be shifted towards the existing buildings and, among them, the worldwide stock of large panel system (LPS) buildings. Major upgrades and retrofits were done to some of the LPS estates in Germany and France, but a leading sustainable way must still be developed for LPS buildings in Eastern European countries, where apartments in those half‐a‐century‐old estates are privately owned. Both sustainability and ownership issues make the demolition option redundant, and therefore the method for deep thermal retrofit and urban intervention is being developed with the use of BIM simulation tools. Digital twin (DT) technology allows for calibration to intertwine with the Internet of Things applications that reward the inhabitants for sustainable behaviour while feeding the relevant data back to the DT. Thanks to this, smart technology can be used to raise the level of social participation in the projects and thus help educate the end‐users, which is paramount in establishing and maintaining good ecological habits, and as such, also for the efficacy and viability of the final endeavour. This article proposes a procedure of creating a 3D model typology repository for facilitating DT technology to provide a good analytical tool for community consultation and enable virtual testing of technical and urban solutions before implementation. It aims to determine the method for virtual technology to give deteriorating estates a new lease of life and improve their perception in the widercommunity while being a conduit for the adaptation of CEE to the digital revolution.

  • Integrating Experience-Based Knowledge Representation and Machine Learning for Efficient Virtual Engineering Object Performance
    • Syed Imran Shafiq
    • Cesar Sanin
    • Edward Szczerbicki
    2021 Full text Procedia Computer Science

    Machine learning and Artificial Intelligence have grown significant attention from industry and academia during the past decade. The key reason behind interest is such technologies capabilities to revolutionize human life since they seamlessly integrate classical networks, networked objects and people to create more efficient environments. In this paper, the Knowledge Representation technique of Set of Experience Knowledge Structure (SOEKS) and Decisional DNA (DDNA) is applied to facilitate Machine Learning. For effective and efficient decision-making in Machine Learning, the environment's own experience is captured, stored and reused using the DDNA technique. The proposed approach is implemented on practical test cases like a Chatbot. Decisional DNA gathers explicit experiential knowledge based on formal decision events and uses this knowledge to support decision-making processes. The experimental test and results of the presented implementation of Decisional DNA Chatbot case studies support it as a technology that can improve and be applied to the technology, enhancing intelligence by predicting capabilities and facilitating knowledge engineering processes.

  • Integrating Statistical and Machine‐Learning Approach for Meta‐Analysis of Bisphenol A‐Exposure Datasets Reveals Effects on Mouse Gene Expression within Pathways of Apoptosis and Cell Survival
    • Nina Lukashina
    • Michael Williams
    • Elena Kartysheva
    • Elizaveta Virko
    • Błażej Kudłak
    • Robert Fredriksson
    • Ola Spjuth
    • Helgi B. Schiöth
    2021 Full text INTERNATIONAL JOURNAL OF MOLECULAR SCIENCES

    Bisphenols are important environmental pollutants that are extensively studied due to different detrimental effects, while the molecular mechanisms behind these effects are less well understood. Like other environmental pollutants, bisphenols are being tested in various experimental models, creating large expression datasets found in open access storage. The meta‐analysis of such datasets is, however, very complicated for various reasons. Here, we developed an integrating statistical and machine‐learning model approach for the meta‐analysis of bisphenol A (BPA) exposure datasets from different mouse tissues. We constructed three joint datasets following three different strategies for dataset integration: in particular, using all common genes from the datasets, uncorrelated, and not co‐expressed genes, respectively.

  • Integration of Fluorescent, NV-Rich Nanodiamond Particles with AFM Cantilevers by Focused Ion Beam for Hybrid Optical and Micromechanical Devices
    • Mateusz Ficek
    • Maciej Głowacki
    • Krzysztof Gajewski
    • Piotr Kunicki
    • Ewelina Gacka
    • Krystian Sycz
    • Mariusz Mrózek
    • Adam M. Wojciechowski
    • Teodor Gotszalk
    • Wojciech Gawlik
    • Robert Bogdanowicz
    2021 Full text Coatings

    In this paper, a novel fabrication technology of atomic force microscopy (AFM) probes integrating cantilever tips with an NV-rich diamond particle is presented. Nanomanipulation techniques combined with the focused electron beam-induced deposition (FEBID) procedure were applied to position the NV-rich diamond particle on an AFM cantilever tip. Ultrasonic treatment of nanodiamond suspension was applied to reduce the size of diamond particles for proper geometry and symmetry. The fabricated AFM probes were tested utilizing measurements of the electrical resistance at highly oriented pyrolytic graphite (HOPG) and compared with a standard AFM cantilever performance. The results showed novel perspectives arising from combining the functionalities of a scanning AFM with optically detected magnetic resonance (ODMR). In particular, it offers enhanced magnetometric sensitivity and the nanometric resolution.

  • Integration of Multi-Source Geospatial Data from GNSS Receivers, Terrestrial Laser Scanners, and Unmanned Aerial Vehicles
    • Paweł Dąbrowski
    • Cezary Specht
    • Mariusz Specht
    • Paweł Burdziakowski
    • Artur Makar
    • Oktawia Lewicka
    2021 Full text CANADIAN JOURNAL OF REMOTE SENSING

    The analysis based on geospatial data from different measurement systems now constitutes a complex numerical and practical enterprise. The dynamic development of modern technologies enables rapid and precise acquisition of such data. Nonetheless, the diversity of reference systems is today one of the main challenges for their correct interpretation. The combined use of the processed measurement results and archival data in paper form constitutes an important direction for the development of this discipline. This issue is visible during the implementation of complex hydrographic and geodetic surveys requiring geospatial integration of results. The publication presents both the theoretical basis and the practical verification of the adopted methodology. The research material comes from the measurement campaign conducted to determine geospatial parameters for the tombolo phenomenon in Sopot. The results of differential GNSS RTK measurements, terrestrial laser scanning, bathymetric survey, photogrammetry, and analog archival bathymetric map were subjected to the integration process. The effectiveness of the presented procedure was confirmed by the obtained error estimators of values not exceeding three centimeters.

  • Inteligentny system decyzyjny jako maszynowa realizacja procesów poznawczych i motywacyjnych
    • Zdzisław Kowalczuk
    • Michał Czubenko
    2021

    W niniejszej książce przedstawiono własny, kompletny i spójny oraz realizowalny model Inteligentnego Systemu Decyzji (ISD), oparty na wiedzy zaczerpniętej z psychologii z elementami motywacyjnymi, w skład którego wchodzi podsystem xEmotion. Wykorzystuje on funkcję i strukturę ludzkich procesów decyzyjnych oraz pewne szczegółowe mechanizmy dedykowane dla obliczeniowych systemów emocji. Model ISD jest w szczególności przeznaczony do realizacji autonomii agenta, zarówno wirtualnego, jak i rzeczywistego, stosowanego w systemach robotycznych. Model Inteligentnego Systemu Decyzyjnego można zatem zaliczać do architektur poznawczych (kognitywnych). Praca przedstawia sformalizowany model procesów poznawczych z uwzględnieniem wybranych humanistycznych teorii motywacji i emocji. Przy czym podstawy psychologiczne dotyczące prezentowanych mechanizmów psychologicznych podano w pracy (M. Czubenko, Z. Kowalczuk: Elementy psychologii w kontekście autonomii robotów, vol. PNT6, PWNT, Gdańsk 2019). Przyjęta struktura pracy w dużej mierze opiera się na podziale procesów poznawczych. Na wstępie przedstawiamy model percepcji agenta (system autonomicznego) wraz z podstawowymi strukturami danych wykorzystywanymi w ścieżce przetwarzania informacji. Następnie wyróżniamy typy pamięci (w kontekście pamięci długotrwałej oraz krótkotrwałej, bądź roboczej). Warto podkreślić, że pamięć sensoryczna ze względu na swoją funkcję buforowania ulokowana jest w systemie percepcji. Po omówieniu struktur pamięciowych, przedstawiamy mechanizmy uwagi, modele motywacyjne z uwzględnieniem wielowymiarowych potrzeb i emocji oraz metody myślenia autonomicznego agenta. Na koniec prezentujemy Czytelnikowi studium badań symulacyjnych, obejmujące częściowe implementacje opracowanego systemu.

  • Interaction Design in Agile IT Projects
    • Marcin Sikorski
    2021 Full text

    In recent years, interactive systems, such as various types of software, online services or mobile applications, have become an integral part of everyday life. Interactive systems and digital services should be easy to use and provide a positive User Experience (UX). For this reason, interaction design has recently emerged as a distinct professional area of information technology (IT). Easy interaction and user experience (UX) are now indispensable elements of IT product quality. Consequently, the User-Centred Design (UCD) approach has been successfully applied to improve IT products' usability and UX. IT projects have undergone radical changes in recent years towards agility. As a result, most of IT solutions nowadays are designed and developed using the agile approach. Regarding to satisfying prospective users’ needs, current IT projects attempt to combine techniques inherited from classical software engineering with novel techniques borrowed from the agile approach. This book presents the impact of the agile approach on User-Centred Design, resulting in gradual adaptation of interaction design methods to agile IT projects. From the perspective of agile project management, the author presents human and social aspects that affect interactive products' quality. Finally, various teamwork management techniques involving prospective users at all stages of an agile IT project are essential for this book.

  • Interactions between polyphenolic antioxidants quercetin and naringenin dictate the distinctive redox-related chemical and biological behaviour of their mixtures
    • Monika Baranowska
    • Zuzanna Koziara
    • Klaudia Suliborska
    • Wojciech Chrzanowski
    • Michael Wormstone
    • Jacek Namieśnik
    • Agnieszka Bartoszek-Pączkowska
    2021 Full text Scientific Reports

    Food synergy concept is suggested to explain observations that isolated antioxidants are less bioactive than real foods containing them. However, mechanisms behind this discrepancy were hardly studied. Here, we demonstrate the profound impact of interactions between two common food flavonoids (individual: aglycones quercetin—Q and naringenin—N− or their glycosides rutin—R and naringin—N+ vs. mixed: QN− and RN+) on their electrochemical properties and redox-related bioactivities. N− and N+ seemed weak antioxidants individually, yet in both chemical and cellular tests (DPPH and CAA, respectively), they increased reducing activity of mixtures synergistically. In-depth measurements (differential pulse voltammetry) pointed to kinetics of oxidation reaction as decisive factor for antioxidant power. In cellular (HT29 cells) tests, the mixtures exhibited properties of a new substance rather than those of components. Pure flavonoids did not influence proliferation; mixtures stimulated cell growth. Individual flavonoids tended to decrease global DNA methylation with growing concentration; this effect was more pronounced for mixtures, but not concentration-dependent. In nutrigenomic studies, expression of gene set affected by QN− differed entirely from common genes modulated by individual components. These results question the current approach of predicting bioactivity of mixtures based on research with isolated antioxidants.

  • Interactions in aqueous solutions of K-peptide and DMSO – spectroscopic and calorimetric studies
    • Julia Godlewska
    • Piotr Bruździak
    2021

    Introduction K-peptide (GILQINSRW) – short 9 amino acid fragment of the hen egg white lysozyme has the ability to form amyloid structures. Dimethyl sulfoxide (DMSO) is an osmolyte which can alter this ability. Our goal was to get an insight into the mechanism of Kpeptide-DMSO interactions in aqueous solutions. Such a knowledge can be helpful to understand processes leading to various neurodegenerative diseases. Methods ATR-FTIR spectroscopy (Thermo Nicolet 8700 equipped with single reflection diamond cell GoldenGate ATR accessory) was used to analyse interactions between solutes in their different proportions: the concentration of DMSO was kept constant in each solution while the peptide concentration varied. In addition, DSC calorimetry (nanoDSC, Thermo) allowed to determine thermal stability of the Kpeptide in aqueous solution with or without the addition of DMSO in the wide temperature range: 10-100 oC. Results The IR spectrum of the K-peptide exhibited a very strong peak usually attributed to beta-sheets. However, its shape was clearly different than in the case of other native or even denatured proteins. We assumed that it was due to the presence of a specific sheets of amyloid structures. The experimental design allowed to observe changes in relatively sharp peaks on ATR-FTIR spectra attributed to chemical bonds of DMSO caused by the presence of the peptide. These changes turned out to be weak, yet DSC calorimetry allowed to conclude that the K-peptide undergoes a few structural changes during the heating process. Depending on the solution composition and protein concentration, the number and exact temperatures of these transitions varied. Acknowledgements This work was funded by the National Science Centre, Poland (grant 2017/26/D/NZ1/00497).

  • Interactions in Ternary Aqueous Solutions of NMA and Osmolytes—PARAFAC Decomposition of FTIR Spectra Series
    • Emilia Kaczkowska
    • Aneta Panuszko
    • Piotr Bruździak
    2021 Full text INTERNATIONAL JOURNAL OF MOLECULAR SCIENCES

    Intermolecular interactions in aqueous solutions are crucial for virtually all processes in living cells. ATR-FTIR spectroscopy is a technique that allows changes caused by many types of such interactions to be registered; however, binary solutions are sometimes difficult to solve in these terms, while ternary solutions are even more difficult. Here, we present a method of data pretreatment that facilitates the use of the Parallel Factor Analysis (PARAFAC) decomposition of ternary solution spectra into parts that are easier to analyze. Systems of the NMA–water–osmolyte-type were used to test the method and to elucidate information on the interactions between N-Methylacetamide (NMA, a simple peptide model) with stabilizing (trimethylamine N-oxide, glycine, glycine betaine) and destabilizing osmolytes (n-butylurea and tetramethylurea). Systems that contain stabilizers change their vibrational structure to a lesser extent than those with denaturants. Changes in the latter are strong and can be related to the formation of direct NMA–destabilizer interactions.

  • Interannual Variability of the GNSS Precipitable Water Vapor in the Global Tropics
    • Zofia Baldysz
    • Grzegorz Nykiel
    • Beata Latos
    • Dariusz Baranowski
    • Mariusz Figurski
    2021 Full text Atmosphere

    This paper addresses the subject of inter-annual variability of the tropical precipitable water vapor (PWV) derived from 18 years of global navigation satellite system (GNSS) observations. Non-linear trends of retrieved GNSS PWV were investigated using the singular spectrum analysis (SSA) along with various climate indices. For most of the analyzed stations (~49%) the GNSS PWV anomaly was related to the El Niño Southern Oscillation (ENSO), although its influence on the PWV variability was not homogeneous. The cross-correlations coefficient values estimated between the Multivariate ENSO Index (MEI) and PWV were up to 0.78. A strong cross-correlation was also found for regional climate pattern expressed through CAR, DMI, HAW, NPGO, TNA and TSA indices. A distinct agreement was also found when instead of climate indices, the local sea surface temperature was examined (average correlation 0.60). The SSA method made it also possible to distinguish small-scale phenomena that affect PWV, such as local droughts or wetter rainy seasons. The overall nature of the investigated changes was also verified through linear trend analysis. In general, not a single station was characterized by a negative trend and its weighted mean value, calculated for all stations was equal to 0.08 ± 0.01 mm/year.

  • Interdisciplinarity in Smart Sustainable City education: exploring educational offerings and competencies worldwide
    • Magdalena Ciesielska
    • Nina Rizun
    • Tomasz Janowski
    2021 Full text

    More and more higher education institutions are offering specialized study programs for current and future managers of Smart Sustainable Cities (SSCs). In the process, they try to reconcile the interdisciplinary nature of such studies, covering at least the technical and social aspects of SSC management, with their own traditionally discipline-based organization. However, there is little guidance on how such interdisciplinarity should be introduced. In order to address this gap, this paper identifies 87 SSC-related study programs from around the world and analyzes their disciplinary and interdisciplinary coverage. The analysis classifies programs and competencies, the former using text mining and clustering algorithms, the latter using Bloom’s taxonomy and correlation analysis.

  • Interspecific and intraspecific variation in organochlorine pesticides and polychlorinated biphenyls using non-destructive samples from Pygoscelis penguins
    • Juliana Silva Souza
    • Aneta Pacyna-Kuchta
    • Larissa Schmauder Teixeira da Cunha
    • Erli Schneider Costa
    • Przemyslaw Niedzielski
    • João Paulo Machado Torres
    2021 Full text ENVIRONMENTAL POLLUTION

    As humans are present in Antarctica only for scientific and tourism-related purposes, it is often described as a pristine region. However, studies have identified measurable levels of Persistent Organic Pollutants (POPs), such as organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs), in the Antarctic region. These are highly toxic anthropogenic compounds with tendency to travel long distances and reach remote environments, where they can bioaccumulate in the biota. Penguins are exposed to POPs mainly through their diet, which they partially eliminate via feathers. Species of the genus Pygoscelis occur around Antarctic continent and its surrounding regions, and can act as indicators of contaminants that reach the continent. Here, we report OCP and PCB levels in feathers of male and female penguins of P. adeliae, P. antarcticus and P. papua from King George Island, South Shetland Islands, Antarctica. Interspecific, sex- and body-size-related differences were investigated in the contamination profiles of PCBs and OCPs. Feather samples were collected from adult penguins (n = 41). Quantification of compounds was performed by gas chromatography-tandem mass spectrometry. The three Pygocelis species presented similar contamination profiles, with higher concentrations of dichlorodiphenyltrichloroethane (ΣDDT; 1.56–3.82 ng g−1 dw), lighter PCB congeners (ΣPCB: 11.81–18.65 ng g−1 dw) and HCB (hexachlorobenzene: 1.65–4.06 ng g−1 dw). Amongst the three penguin species, P. antarcticus had lower and P. papua higher concentrations of most of the compounds identified. We found interspecific differences in POP accumulation as well as sex differences in POP concentrations. Our data indicate a small but significant positive correlation between body size and the concentrations of some compounds. Despite the overall low concentrations found, this study increases knowledge of the occurrence of POPs in Antarctic penguins, thereby reinforcing concerns that Antarctica, although remote and perceived to be protected, is not free from the impact of anthropogenic pollutants.

  • Interval Edge Coloring of Bipartite Graphs with Small Vertex Degrees
    • Anna Małafiejska
    • Michał Małafiejski
    • Krzysztof Ocetkiewicz
    • Krzysztof Pastuszak
    2021

    An edge coloring of a graph G is called interval edge coloring if for each v ∈ V(G) the set of colors on edges incident to v forms an interval of integers. A graph G is interval colorable if there is an interval coloring of G. For an interval colorable graph G, by the interval chromatic index of G, denoted by χ'_i(G), we mean the smallest number k such that G is interval colorable with k colors. A bipartite graph G is called (α,β)-biregular if each vertex in one part has degree α and each vertex in the other part has degree β. A graph G is called (α*,β*)-bipartite if G is a subgraph of an (α,β)-biregular graph and the maximum degree in one part is α and the maximum degree in the other part is β. In the paper we study the problem of interval edge colorings of (k*,2*)-bipartite graphs, for k ∈ {3,4,5}, and of (5*,3*)-bipartite graphs. We prove that every (5*,2*)-bipartite graph admits an interval edge coloring using at most 6 colors, which can be found in O(n^{3/2}) time, and we prove that an interval edge 5-coloring of a (5*,2*)-bipartite graph can be found in O(n^{3/2}) time, if it exists. We show that every (4^*,2^*)-bipartite graph admits an interval edge 4-coloring, which can be found in O(n) time. The two following problems of interval edge coloring are known to be NP-complete: 6-coloring of (6,3)-biregular graphs (Asratian and Casselgren (2006)) and 5-coloring of (5*,5*)-bipartite graphs (Giaro (1997)). In the paper we prove NP-completeness of 5-coloring of (5*,3*)-bipartite graphs.