2021 - Repozytorium publikacji - Politechnika Gdańska

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Classification of Landscape Physiognomies in Rural Poland: The Case of the Municipality of Cekcyn
- Anna Górka
- Kazimierz Niecikowski
2021 Pełny tekst Urban Planning
This article presents a methodology and the results of the classification of the rural landscapes physiognomies conducted on the study area located in the municipality of Cekcyn, Poland. The study aimed to develop a landscape identification method that would combine natural, cultural, and visual criteria with which to implement the provisions of the European Landscape Convention. The realization of the European Landscape Convention in Poland is incomplete due to the lack of practical application of landscape assessment in land management and spatial planning at the commune level. The research was intended at helping to fill this void. The study develops a method using which it will be possible to protect the diversity and beauty of Europe’s rural landscapes more effectively. The goal has so far been of little scientific interest in Poland. The physiognomy of the studied area was analyzed with the use of commonly available spatial data and by means of field studies. Physical‐geographical units and cultural characteristics have been designated based on spatial databases. Landscape patterns were identified by analyzing visual fields with the use of both GIS applications and field studies. This practice made it possible to determine physiognomic units of the landscape which are internally coherent and relatively homogeneous in terms of physical‐geographical, cultural, and visual features. Identifying the landscape physiognomy within the designated landscape physiognomic units serves to harmonize spatial alterations in the area of rural communes in processes of land management and planning.
Classification of submandibular salivary stones based on ultrastructural studies
- Dmitry Tretiakow
- Andrzej Skorek
- Joanna Wysocka
- Kazimierz Darowicki
- Jacek Ryl
2021 ORAL DISEASES
Introduction: Sialolithiasis remains a clinical problem with unclear etiopathogenesis, lack of prevention methods, and only surgical treatment. Materials and methods: An ultrastructure examination of submandibular sialoliths obtained from patients with chronic sialolithiasis was conducted using a scanning electron microscope and X‐ray photoelectron spectroscopy. Results: Based on the results, we divided sialoliths into three types: calcified (CAL), organic/lipid (LIP), and mixed (MIX). The core structure of the CAL and MIX is very similar. The core of the LIP has a prevalence of organic components. The intermediate layers’ structure of the CAL is different from LIP and MIX. In LIP and MIX, the organic component begins to increase in intermediate layers rapidly. The structure of the superficial layers for all types of sialoliths is similar. Conclusions: We introduced a new classification of the submandibular salivary gland stones. Based on the results, it can be said that sialoliths type CAL and LIP have their separate path of origin and development, while MIX is formed as CAL stone, and the further pathway of their growth passes as LIP stones. Organic components were much more than inorganic in all layers of salivary gland stones, which highly prevents their dissolution in the patient's salivary gland duct.
Classifying Emotions in Film Music - A Deep Learning Approach
- Tomasz Ciborowski
- Szymon Reginis
- Adam Kurowski
- Dawid Weber
- Bożena Kostek
2021 Pełny tekst Electronics
The paper presents an application for automatically classifying emotions in film music. A model of emotions is proposed, which is also associated with colors. The model created has nine emotional states, to which colors are assigned according to the color theory in film. Subjective tests are carried out to check the correctness of the assumptions behind the adopted emotion model. For that purpose, a statistical analysis of the subjective test results is performed. The application employs a deep convolutional neural network (CNN), which classifies emotions based on 30 s excerpts of music works presented to the CNN input using mel-spectrograms. Examples of classification results of the selected neural networks used to create the system are shown.
Clays as Inhibitors of Polyurethane Foams’ Flammability
- Aleksander Hejna
2021 Pełny tekst Materials
Polyurethanes are a very important group of polymers with an extensive range of applications in different branches of industry. In the form of foams, they are mainly used in bedding, furniture, building, construction, and automotive sectors. Due to human safety reasons, these applications require an appropriate level of flame retardance, often required by various law regulations. Nevertheless, without the proper modifications, polyurethane foams are easily ignitable, highly flammable, and generate an enormous amount of smoke during combustion. Therefore, proper modifications or additives should be introduced to reduce their flammability. Except for the most popular phosphorus-, halogen-, or nitrogen-containing flame retardants, promising results were noted for the application of clays. Due to their small particle size and flake-like shape, they induce a “labyrinth effect” inside the foam, resulting in the delay of decomposition onset, reduction of smoke generation, and inhibition of heat, gas, and mass transfer. Moreover, clays can be easily modified with different organic compounds or used along with conventional flame retardants. Such an approach may often result in the synergy effect, which provides the exceptional reduction of foams’ flammability. This paper summarizes the literature reports related to the applications of clays in the reduction of polyurethane foams’ flammability, either by their incorporation as a nanofiller or by preparation of coatings.
Cloning, expression in Komagataella phaffii, and biochemical characterization of recombinant sequence variants of Pseudomonas sp. S9 GDSL-esterase
- Monika Wicka-Grochocka
- Hubert Cieśliński
- Marta Wanarska
2021 Pełny tekst Acta Biochimica Polonica
Two recombinant Komagataella phaffii (formerly Pichia pastoris) yeast strains for production of two sequential variants of EstS9 esterase from psychrotolerant bacterium Pseudomonas sp. S9, i.e. αEstS9N (a two-domain enzyme consisting of a catalytic domain and an autotransporter domain) and αEstS9Δ (a single-domain esterase) were constructed. However, only one of recombinant K. phaffii strains, namely Komagataella phaffii X-33/pPICZαestS9Δ, allowed to successfully produce and secrete recombinant αEstS9Δ enzyme outside of the host cell. The purified αEstS9Δ esterase was active towards short-chain p-nitrophenyl esters (C2-C8), with optimal activity for the acetate (C2) ester. The single-domain αEstS9Δ esterase exhibits the highest activity at 60oC and pH 9.5. In addition, the enzyme retains 90% of its activity after 3 hour incubation at 70–90oC. What should be also noted is that αEstS9Δ esterase produced in the K. phaffii expression system has a much higher specific activity (0.069 U/mg of protein) than the recombinant EstS9Δ esterase produced in an E. coli expression system (0.0025 U/mg of protein) (Wicka et al., 2016, Acta Biochim Pol 63: 117–125. https://doi.org/10.18388/ abp.2015_1074).
Closed-Loop Control System Design for Wireless Charging of Low-Voltage EV Batteries with Time-Delay Constraints
- Viktor Shevchenko
- Bohdan Pakhaliuk
- Janis Zakis
- Oleksandr Veligorskyi
- Jarosław Łuszcz
- Oleksandr Husev
- Oleksandr Lytvyn
- Oleksandr Matiushkin
2021 Pełny tekst ENERGIES
This paper presents an inductive power transfer system on the basis of a double single- phase three-level T-type inverter and two split transmitting coils for constant current and constant voltage wireless charging of low-voltage light electric vehicle batteries with closed-loop control, considering time-delay communication constraints. An optimal control structure and a modified control strategy were chosen and implemented to the wireless power transfer system as a result of a review and analysis of existing solutions. The control system analysis and adjustment of the coefficients of the regulator using Laplace transform were performed. Our study addressed the behavior of the control system with different time delays as well as the dynamic response of the system. The detecting algorithm of a secondary coil was proposed, which ensured efficient system operation and increased the functionality, safety and usability of the device. The efficiency of energy transfer of 90% was reached at the transmitted power of 110 W, which is at the level of existing solutions considered in the article and opens the way to the commercialization of the proposed solution. Therefore, the feasibility of using a nonclassical multilevel inverter, together with split transmitting coils for wireless charging was confirmed.
Closer Look at the Uncertainty Estimation in Semantic Segmentation under Distributional Shift
- Sebastian Cygert
- Andrzej Czyżewski
- Bartłomiej Wróblewski
- Radosław Słowiński
- Karol Woźniak
2021 Pełny tekst
While recent computer vision algorithms achieve impressive performance on many benchmarks, they lack robustness - presented with an image from a different distribution, (e.g. weather or lighting conditions not considered during training), they may produce an erroneous prediction. Therefore, it is desired that such a model will be able to reliably predict its confidence measure. In this work, uncertainty estimation for the task of semantic segmentation is evaluated under a varying level of domain shift: in a cross-dataset setting and when adapting a model trained on data from the simulation. It was shown that simple color transformations already provide a strong baseline, comparable to using more sophisticated style-transfer data augmentation. Further, by constructing an ensemble consisting of models using different backbones and/or augmentation methods, it was possible to improve significantly model performance in terms of overall accuracy and uncertainty estimation under the domain shift setting. The Expected Calibration Error (ECE) on challenging GTA to Cityscapes adaptation was reduced from 4.05 to the competitive value of 1.1. Further, an ensemble of models was utilized in the self-training setting to improve the pseudo-labels generation, which resulted in a significant gain in the final model accuracy, compared to the standard fine-tuning (without ensemble).o
Closer look into the structures of tetrabutylammonium bromide–glycerol-based deep eutectic solvents and their mixtures with water
- Patrycja Makoś-Chełstowska
- Renáta Chromá
- Vasil Andruch
2021 Pełny tekst JOURNAL OF MOLECULAR LIQUIDS
In recent years, deep eutectic solvents (DES) and it’s mixture with water have become more and more attention as green solvents used in chemistry. However, there are only a few theoretical studies on the mechanisms of pure DES and DES-water complex formation. Therefore, the structural properties of tetrabutylammonium bromide–glycerol-based deep eutectic solvents and their mixtures with water have been investigated by means of Molecular Dynamics simulations. The obtained results indicate that three types of H-bonds exist in the pure DES structures, and all of these interactions play an important role in DES formation. In addition, between hydrogen bond donors (HBDs) and hydrogen bond acceptor (HBA) weaker non-bonded interactions, i.e. van der Waals exist, which also contribute to the formation of stable DES structures and to lower the melting point of DES compared to pure substances. The small addition of water to DES provides the formation of a stable complex, however, a further increase in water content (higher than 50% v/v) provide to the destruction of the most important hydrogen bonds (O–H···Br) in DES structure.
Coffee Silverskin as a Multifunctional Waste Filler for High-Density Polyethylene Green Composites
- Aleksander Hejna
- Mateusz Barczewski
- Paulina Kosmela
- Olga Mysiukiewicz
- Anton Kuzmin
2021 Pełny tekst Journal of Composites Science
This work aims to describe the coffee silverskin effect as a lignocellulosic waste filler for high-density polyethylene (HDPE) composites development. The main task was to determine various modification effects resulting from the complex chemical composition of coffee silverskin containing compounds with potential antioxidative properties, including caffeine, polyphenols, tannins, or melanoidins. The processing, thermal, physicochemical, and thermomechanical properties of the HDPE-based composites with different filler content (1–20 wt%) were evaluated. Comprehensively realized thermomechanical analysis revealed the filler’s reinforcing effects on the HDPE matrix while defining problems with obtaining adequate adhesion in the interfacial area. At the same time, studies have shown a very beneficial effect of the silverskin addition on the thermal properties of composites, that even the smallest addition allows for a significant increase in the thermooxidative resistance of HDPE composites assessed using the oxidation induction time from 20 min for HDPE up to 140 min for the composites with 20 wt% of the filler. The obtained research results allow classifying the coffee silverskin waste filler, not only as a filler intended for the production of composites with a high degree of filling but also as an additive that significantly changes the properties of polyethylene in the case of using low concentrations. This can have a very beneficial impact on the development of novel wood polymer (WPC) and natural fiber composites (NFC).
Coffee silverskin as a potential bio-based antioxidant for polymer materials: Brief review
- Aleksander Hejna
2021 Pełny tekst Proceedings
Coffee silverskin is one of the by-products generated by the coffee industry. Although it is not the most burdensome one, because it stands only for ~4.2 wt % of coffee, it seems like an auspicious raw material for industrial processes. Coffee silverskin is characterized by a relatively low moisture content of ~5–7%, so it often does not require quite energy-consuming drying processes. The chemical composition of coffee silverskin, as well as other renewable materials, may be significantly affected by its type and origin, in this case, plant Coffea. Nevertheless, due to high fiber content, it could be considered as exciting material for the manufacturing of wood polymer composites. At the same time, it contains noticeable amounts of proteins, which may provide additional features to polymer composites. However, what is most important is the high content of antioxidants, which could noticeably enhance their lifetime by inhibition of the oxidation reactions. In the presented paper, attempts of coffee silverskin incorporation into different polymer matrices were summarized and discussed. Moreover, potential future trends in this area of research were proposed.
Coffee Wastes as Sustainable Flame Retardants for Polymer Materials
- Henri Vahabi
- Maryam Jouyandeh
- Thibault Parpaite
- Mohammad Saeb
- Seeram Ramakrishna
2021 Pełny tekst Coatings
Development of green flame retardants has become a core part of the attention of material scientists and technologists in a paradigm shift from general purpose to specific sustainable products. This work is the first report on the use of coffee biowastes as sustainable flame retardants for epoxy, as a typical highly flammable polymer. We used spent coffee grounds (SCG) as well as SCG chemically modified with phosphorus (P-SCG) to develop a sustainable highly efficient flame retardant. A considerable reduction in the peak of heat release rate (pHRR) by 40% was observed in the pyrolysis combustion flow calorimeter analysis (PCFC), which proved the merit of the used coffee biowastes for being used as sustainable flame retardants for polymers. This work would open new opportunities to investigate the impact of other sorts of coffee wastes rather than SCG from different sectors of the coffee industry on polymers of different family.
Cognitive Systems, Concepts, Processes, and Techniques for the Age of Industry 4.0
- Edward Szczerbicki
- Ngoc-Thanh Nguyen
2021 Pełny tekst CYBERNETICS AND SYSTEMS
The aim of this Guest Edition of Cybernetics and Systems is to present a wide-ranging scale of concepts and processes being currently researched, developed, and evaluated in real life settings in anticipation of incoming Industry 4.0 era. With the fourth industrial revolution expectation, the broad spectrum of cognitive approaches have emerged as an attempt to mimic and augment, in some way, human intelligence. Intelligence, in cognitive systems and computing, can be defined as the ability to learn from experience and use the domain of expert knowledge to adapt and act in contextually new situations. The communicated selection of papers does not postulate ultimate answers to the aspects of Industry 4.0 and cognitive systems that are discussed. Rather, it poses ideas and provokes for additional exploration. It also makes the reader aware of immensely multifaceted and interdisciplinary character of such predicaments.
Collision‐Aware Routing Using Multi‐Objective Seagull Optimization Algorithm for WSN‐Based IoT
- Preetha Jagannathan
- Sasikumar Gurumoorthy
- Andrzej Stateczny
- Parameshachari Bidare Divakarachar
- Jewel Sengupta
2021 Pełny tekst SENSORS
In recent trends, wireless sensor networks (WSNs) have become popular because of their cost, simple structure, reliability, and developments in the communication field. The Internet of Things (IoT) refers to the interconnection of everyday objects and sharing of information through the Internet. Congestion in networks leads to transmission delays and packet loss and causes wastage of time and energy on recovery. The routing protocols are adaptive to the congestion status of the network, which can greatly improve the network performance. In this research, collision‐aware routing using the multi‐objective seagull optimization algorithm (CAR‐MOSOA) is designed to meet the efficiency of a scalable WSN. The proposed protocol exploits the clustering process to choose cluster heads to transfer the data from source to endpoint, thus forming a scalable network, and improves the performance of the CAR‐MOSOA protocol. The proposed CAR‐MOSOA is simulated and examined using the NS‐2.34 simulator due to its modularity and inexpensiveness. The results of the CAR‐MOSOA are comprehensively investigated with existing algorithms such as fully distributed energy‐aware multi‐level (FDEAM) routing, energy‐efficient optimal multi‐path routing protocol (EOMR), tunicate swarm grey wolf optimization (TSGWO), and CoAP simple congestion control/advanced (CoCoA). The simulation results of the proposed CAR‐MOSOA for 400 nodes are as follows: energy consumption, 33 J; endto‐end delay, 29 s; packet delivery ratio, 95%; and network lifetime, 973 s, which are improved compared to the FDEAM, EOMR, TSGWO, and CoCoA.
Colored Tattoo Ink Screening Method with Optical Tissue Phantoms and Raman Spectroscopy
- Filip Sadura
- Maciej Wróbel
- Katarzyna Karpienko
2021 Pełny tekst Materials
Due to the increasing popularity of tattoos among the general population, to ensure their safety and quality, there is a need to develop reliable and rapid methods for the analysis of the composition of tattoo inks, both in the ink itself and in already existing tattoos. This paper presents the possibility of using Raman spectroscopy to examine tattoo inks in biological materials. We have developed optical tissue phantoms mimicking the optical scattering coefficient typical for human dermis as a substitute for an in vivo study. The material employed herein allows for mimicking the tattoo-making procedure. We investigated the effect of the scattering coefficient of the matrix in which the ink is located, as well as its chemical compositions on the spectra. Raman surface line scanning has been carried out for each ink in the skin phantom to establish the spatial gradient of ink concentration distribution. This ensures the ability to detect miniature concentrations for a tattoo margin assessment. An analysis and comparison of the spectra of the inks and the tattooed inks in the phantoms are presented. We recommend the utilization of Raman spectroscopy as a screening method to enforce the tattoo ink safety legislations as well as an early medical diagnostic screening tool.
COMBINATION OF ARCHITECTURAL, ENVIRONMENTAL, AND SOCIAL ASPECTS IN URBAN STORMWATER MANAGEMENT. A CASE STUDY OF THE UNIVERSITY CAMPUS
- Ewa Wojciechowska
- Magdalena Gajewska
- Nicole Nawrot
- Monika Kilanowska
- Hanna Obarska-Pempkowiak
2021 Pełny tekst International Journal of Conservation Science
Increasing a city’s resilience against climate change is one of the major concerns of today. Sustainable stormwater management, using Green Infrastructure units (GI) integrated with an urban area, has proved to be effective in flooding control and to offer extra benefits encompassing groundwater recharge, stormwater treatment, mitigation of air pollution, and an urban micro-climate. Moreover, GI brings cultural benefits for the urban population. However, the “grey” solutions are still popular and widely accepted. This paper presents three conceptions of the revitalisation of a part of campus of the Gdansk University of Technology with different approaches to stormwater management. The first approach (“blue-grey”) is purely based on an architect’s vision, and has some negative aspects from the environmental point of view. The second approach (“blue-grey-green”) is a modification of the previous one, in an attempt to introduce green elements and to obtain more ecosystem services. The third conception (“blue-green”) is fundamentally different, as it relies on GI elements and attempts to respond to the needs reported by the local community of students and university employees accordingly to opinion polls that were conducted. The three solutions are discussed in terms of water sensibility, aesthetics, functionality, usability, and public perception.
Combination of hydrodynamic cavitation and SR-AOPs for simultaneous degradation of BTEX in water
- Kirill Fedorov
- Xun Sun
- Grzegorz Boczkaj
2021 CHEMICAL ENGINEERING JOURNAL
Hydrodynamic cavitation (HC) is an emerging technology gaining interest in water treatment for use in elimination of a wide range of organic pollutants. The energy released during cavitation phenomenon has number of applications and, particularly, it can be utilized for activation of persulfate (PS) and peroxymonosulfate (PMS). In the present study, hybrid techniques: HC combined with persulfates – HC-PS and HC-PMS were tested for the degradation of BTEX in water. Studies on the effect of initial PS and PMS concentration showed that a molar ratio of the oxidant to BTEX equal to 5 is favorable for both cases. Thus, in 240 min HC-PS-5 process allowed to degrade 91.51%, 95.50%, 94.65%, 94.95% of benzene, toluene, ethylbenzene and o-xylene, respectively, while 90.85%, 94.50%, 94.36%, 93.07% of those compounds were degraded by HC-PMS-5. BTEX degradation pathway was proposed for HC-PS-5 and HC-PMS-5 processes relying on the identification of the main reaction intermediates using liquid chromatography coupled with UV diode array detector (HPLC-UV-DAD). Benzyl alcohol, phenol, benzoic acid, benzaldehyde and o-cresol were the main intermediates of BTEX degradation, which multistep pathway involved H-abstraction, OH addition and dealkylation in route to mineralization. At final time of treatment primary and secondary pollutants were effectively degraded. In terms of kinetics, BTEX degradation followed the pseudo-first-order reaction model and the degradation kinetics were faster in HC-PMS-5 system than in HC-PS-5. Surprisingly, the presence of chloride ions (Cl−) in HC-PMS-5 improved the degradation efficiency of alkylated benzene derivatives indicating a synergistic effect of Cl− with SO4•− radicals.
Combined effect of nitrogen-doped functional groups and porosity of porous carbons on electrochemical performance of supercapacitors
- Anna Ilnicka
- Malgorzata Skorupska
- Mariusz Szkoda
- Zuzanna Zarach
- Piotr Kamedulski
- Wojciech Zielinski
- Jerzy P. Lukaszewicz
2021 Pełny tekst Scientific Reports
In this work, nitrogen-doped porous carbons obtained from chitosan, gelatine, and green algae were investigated in their role as supercapacitor electrodes. The effects of three factors on electrochemical performance have been studied— of the specific surface area, functional groups, and a porous structure. Varying nitrogen contents (from 5.46 to 10.08 wt.%) and specific surface areas (from 532 to 1095 m2g−1) were obtained by modifying the carbon precursor and the carbonization temperature. Doping nitrogen into carbon at a level of 5.74–7.09 wt.% appears to be the optimum for obtaining high electrochemical capacitance. The obtained carbons exhibited high capacitance (231 F g− 1 at 0.1 A g−1) and cycle durability in a 0.2 mol L−1 K2SO4 electrolyte. Capacitance retention was equal to 91% at 5 A g−1 after 10,000 chronopotentiometry cycles. An analysis of electrochemical behavior reveals the influence that nitrogen functional groups have on pseudocapacitance. While quaternary-N and pyrrolic-N nitrogen groups have an enhancing effect, due to the presence of a positive charge and thus improved electron transfer at high current loads, the most important functional group affecting energy storage performance is graphite-N/quaternary-N. The study points out that the search for the most favourable organic precursors is as important as the process of converting precursors to carbonbased electrode materials.
Combined environmental testing device for picosatellites
- Adam Dąbrowski
- Róża Pietruszewska
- Szymon Krawczuk
2021 Pełny tekst
As access to space conditions becomes more available, both technically and economically, scientists’ interest in launching finer and more sophisticated experiments grows. To be qualified for launch, such experiments need to be carefully tested prior to the event. The tests should represent actual launch conditions as closely and in a detailed manner. Typical tests for payload include: vibration tests, thermal and vacuum tests, and sometimes shock tests. Acceleration tests with a centrifuge are rarely performed. In traditional static tests the load application tools are usually jacks or weights, in conjunction with a levers system to introduce forces on attachment points or pressure on surface pads. Alternative systems as air-bags are sometimes used. Such approaches are also notorious for their tendency to both over- and under-test at the same time. Furthermore, all these tests are performed separately, which disables study on any crosscorrelation effects, for example changing of stiffness of elements in changing temperature. A solution is suggested in combined environment testing device for picosatellites. A prototype has been successfully tested in the Large Diameter Facility. The aim of the device is to recreate as accurately as possible: dynamic, thermal and vacuum environment of a space rocket. The prototype hosted a 1U CubeSat dummy with sensors to measure various environments. Dynamic environment includes both high frequency but low amplitude vibrations as well as low frequency, quasi-stationary accelerations. This has been achieved by placing a custom designed shaker table inside the centrifuge. By controlling centrifuge, high amplitude, quasi-stationary rocket acceleration can be recreated. By controlling the shaker, high frequency vibrations can be recreated. On the shaker table, a small vacuum chamber is be mounted. Additionally thermal testing is also possible. Many vehicles experience simultaneous acceleration and vibration loads during their missions and are susceptible to nonlinear structural responses that can only be evaluated by combined environments testing. This approach to testing may allow payloads and vehicle subsystems to be tested in a more realistic setting prior to operations in the real world, and may lead to higher performance systems, as well as result in reduced cost. Such device altogether will be able to perform not only tests, but also to recreate conditions of a given rocket launch to enable investigation of failures.
Commitment Ladder in the Relationship between Service Providers and Customers as Added Value in Sustainable Services Development
- Sławomir Ostrowski
2021 Pełny tekst Sustainability
The socioeconomic sphere and the relationships in which commitment occurs are important elements in the development of sustainable services. The study reported in this article identifies the elements that influence the development of the relationship between service providers and their customers and proposes a model that describes the state of the relationship between service providers and customers in terms of symmetrical commitment of both parties. Qualitative research including interviews with experts and case studies was completed, resulting in a ‘ladder of commitment’ model that identifies distinct commitment levels and specific commitment factors functioning at each of those levels. In practice, the proposed model makes it possible to assess the state of customer and provider commitment, identifying commitment deficits on the part of the customer or service provider. This article can provide practical added value for managers who are looking for ways to analyze customer commitment in order to develop sustainable services.
Common Independence in Graphs
- Magdalena Lemańska
- Magda Dettlaff
- Jerzy Topp
2021 Pełny tekst Symmetry-Basel
Abstract: The cardinality of a largest independent set of G, denoted by α(G), is called the independence number of G. The independent domination number i(G) of a graph G is the cardinality of a smallest independent dominating set of G. We introduce the concept of the common independence number of a graph G, denoted by αc(G), as the greatest integer r such that every vertex of G belongs to some independent subset X of VG with |X| ≥ r. The common independence number αc(G) of G is the limit of symmetry in G with respect to the fact that each vertex of G belongs to an independent set of cardinality αc(G) in G, and there are vertices in G that do not belong to any larger independent set in G. For any graph G, the relations between above parameters are given by the chain of inequalities i(G) ≤ αc(G) ≤ α(G). In this paper, we characterize the trees T for which i(T) = αc(T), and the block graphs G for which αc(G) = α(G).