2021 - Repozytorium publikacji - Politechnika Gdańska

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Structural analysis as a supporting method for the research of the medieval brick architecture
- Piotr Samól
- Piotr Iwicki
- Jarosław Przewłócki
2021
Chronology of brick historical buildings might be established much more precisely than the chronology of stone ones due to the architectural and metrical analysis of bricks, mortars and brickworks. Comparison of historical sources allows to reconstruct the previous stages of constructing monuments. Causations between transformations and developments of monuments are usually interpreted as the results of artistic or ideological influence rather than pragmatic decisions. Such explanations neglect, however, the impact of structural disasters and imperfections. Experience, delivered by the previous erroneous solutions or failures, undoubtedly influenced the further development of architecture. In this paper the authors present how numerical modelling and structural analysis of complex historical brick buildings and different stages of their alterations might be used as a supporting method for the research of their history. Consequently, modern numerical tools for structural analysis can also be useful in investigating of the process of creating architectural solutions [1]. Because more accurate historical analyses belong to the qualitative research, it is not possible to examine very wide group of different monuments. Therefore the authors chose for that purpose the homogeneous group of the mendicant orders’ medieval churches in the former State of Teutonic Order in Prussia, which have been the subject of authors’ in situ research since 2009 [2]. This group is thought to be representative for the medieval techniques of the brick architecture in northern Europe and Baltic Sea Region. The aim of this research is to find out whether structural analysis might be carried out in a historical building in which consecutive transformations partially erased its original form (reconstructed on the base of the architectural and archaeological research)? A positive answer to that question allows to put another one – about whether the numerical modelling of the structure of monument might give some additional information on its history? The results of described research might give a new tool for conservators, architects, archaeologists and engineers in their research and other conducting works.
Structural and Material Determinants Influencing the Behavior of Porous Ti and Its Alloys Made by Additive Manufacturing Techniques for Biomedical Applications
- Magda Dziaduszewska
- Andrzej Zieliński
2021 Pełny tekst Materials
One of the biggest challenges in tissue engineering is the manufacturing of porous structures that are customized in size and shape and that mimic natural bone structure. Additive manufacturing is known as a sufficient method to produce 3D porous structures used as bone substitutes in large segmental bone defects. The literature indicates that the mechanical and biological properties of scaffolds highly depend on geometrical features of structure (pore size, pore shape, porosity), surface morphology, and chemistry. The objective of this review is to present the latest advances and trends in the development of titanium scaffolds concerning the relationships between applied materials, manufacturing methods, and interior architecture determined by porosity, pore shape, and size, and the mechanical, biological, chemical, and physical properties. Such a review is assumed to show the real achievements and, on the other side, shortages in so far research.
Structural Changes and Their Implications in Foamed Flexible Polyurethane Composites Filled with Rapeseed Oil-Treated Ground Tire Rubber
- Paulina Kosmela
- Adam Olszewski
- Łukasz Zedler
- Paulina Burger
- Krzysztof Formela
- Aleksander Hejna
2021 Pełny tekst Journal of Composites Science
The utilization of post-consumer car tires is an essential issue from an ecological andeconomic point of view. One of the simplest and the least harmful methods is their material recyclingresulting in ground tire rubber (GTR), which can be further applied as fillers for polymer-basedcomposites. Nevertheless, insufficient interfacial interactions implicate the necessity of GTR modi-fication before introduction into polymer matrices. In this study, we investigated the influence ofrapeseed oil-assisted thermo-mechanical treatment of GTR using a reactive extrusion process on theprocessing, structure, and performance of flexible polyurethane/GTR composite foams. Appliedmodifications affected the processing of polyurethane systems. They caused a noticeable reductionin the average cell size of foams, which was attributed to the potential nucleating activity of solidparticles and changes in surface tension caused by the presence of oil. Such an effect was especiallypronounced for the waste rapeseed oil, which resulted in the highest content of closed cells. Structuralchanges caused by GTR modification implicated the enhancement of foams’ strength. Mechanicalperformance was significantly affected by the applied modifications due to the changes in glasstransition temperature. Moreover, the incorporation of waste GTR particles into the polyurethanematrix noticeably improved its thermal stability.
Structural changes of bacterial cellulose due to incubation in conditions simulating human plasma in the presence of selected pathogens
- Paulina Dederko-Kantowicz
- Agata Sommer
- Hanna Staroszczyk
2021 Pełny tekst CARBOHYDRATE POLYMERS
Bacterial nanocellulose (BNC) is a natural biomaterial with a wide range of medical applications. However, it cannot be used as a biological implant of the circulatory system without checking whether it is biodegradable under human plasma conditions. This work aimed to investigate the BNC biodegradation by selected pathogens under conditions simulating human plasma. The BNC was incubated in simulated biological fluids with or without Staphylococcus aureus, Candida albicans and Aspergillus fumigatus, and its physicochemical properties were studied. The results showed that the incubation of BNC in simulated body fluid with A. fumigatus con-tributes more to its degradation than that under other conditions tested. The rearrangement of the hydrogen- bond network in this case resulted in a more compact structure, with an increased crystallinity index, reduced thermal stability and looser cross-linking. Therefore, although BNC shows great potential as a cardiovascular implant material, before use for this purpose its biodegradability should be limited.
Structural, electrical, and magnetic study of La-, Eu-, and Er- doped bismuth ferrite nanomaterials obtained by solution combustion synthesis
- Angelika Wrzesińska
- Alexander Khort
- Marcin Witkowski
- Jacek Szczytko
- Jacek Ryl
- Jacek Gurgul
- Dmitry Kharitonov
- Kazimierz Łątka
- Tadeusz Szumiata
- Aleksandra Wypych-puszkarz
2021 Pełny tekst Scientific Reports
In this work, the multiferroic bismuth ferrite materials Bi0.9RE0.1FeO3 doped by rare-earth (RE = La, Eu, and Er) elements were obtained by the solution combustion synthesis. Structure, electrical, and magnetic properties of prepared samples were investigated by X-ray photoelectron spectroscopy, Mössbauer spectroscopy, electrical hysteresis measurement, broadband dielectric spectroscopy, and SQUID magnetometry. All obtained nanomaterials are characterized by spontaneous electrical polarization, which confirmed their ferroelectric properties. Investigation of magnetic properties at 300.0 K and 2.0 K showed that all investigated Bi0.9RE0.1FeO3 ferrites possess significantly higher magnetization in comparison to bismuth ferrites obtained by different methods. The highest saturation magnetisation of 5.161 emu/g at 300.0 K was observed for the BLaFO sample, while at 2.0 K it was 12.07 emu/g for the BErFO sample. Several possible reasons for these phenomena were proposed and discussed.
Structural evaluation of percolating, self-healing polyurethane–polycaprolactone blends doped with metallic, ferromagnetic, and modified graphene fillers
- Damian Włodarczyk
- Iwona Żmuda-Trzebiatowska
- J. Karczewski
- Martyna Lubinska-Szczygeł
- Magdalena Urban
- Antoni Marciniak
- Anna Kamińska
- Patrycja Sikorska
- Magda Graczyk
- Michał Strankowski
2021 POLYMERS & POLYMER COMPOSITES
Composites with differently shaped micro- and nanofillers show various, unique thermal, and physicochemical properties when mixed with carefully chosen polymer matrix. Selected composition holds strategic value in achieving desired properties that is biodegradability, thermoelectric conductivity, and shape memory for organic coating. The main aim of this work is to briefly examine structural changes after reaching percolation threshold and activating healing abilities within exploited (8–2 wt ratio) polyurethane–polycaprolactone thin films mixed up with different types of metallic and ferromagnetic microfillers. They, with applicable dosages of reduced graphene oxide nanoparticles, should enhance materials’ mechanical and conductive properties. Microscopic and spectroscopic techniques accompanied by extensive thermal analysis have been chosen to provide useful information about local changes in surface structure and morphology. Moreover, pristine, percolating surface with inner-formed, metallic structures shows moderate conducting properties within exploited materials which unfortunately diminish after thermal healing stimulus is being applied. This statement is supported by observing the coverage of regional defects and nearby pores with a concise, uniform layer of blend having different PU:PCL ratio. Including the additional fact that apparent filler migration is changing local dopant composition brings up an assumption that both phenomena have negative synergy effect on each other.
Structure and magnetic properties of BeO-Fe2O3-Al2O3-TeO2 glass-ceramic composites
- Natalia Wójcik
- N Tagiara
- Sharafat Ali
- Karolina Górnicka
- H Segawa
- Tomasz Klimczuk
- B Jonson
- Doris Möncke
- Efstratios Kamitsos
2021 Pełny tekst JOURNAL OF THE EUROPEAN CERAMIC SOCIETY
In this work, glass-ceramics in the xBeO–20Fe2O3–(80-x)TeO2 system with x = 0–25 mol% were synthesized by the traditional melt quenching route and studied by inductively coupled plasma optical emission spectroscopy, X-ray diffraction, confocal microscopy, infrared and Raman spectroscopy. BeO addition was found to support the crystallization process of Fe2O3 during melting, and an increased BeO content was associated with an increased fraction of the crystalline Fe2O3 phase and an increased size of these crystallites. Furthermore, samples doped with BeO exhibit an increasing polymerization of the residual tellurite glass network compared to the undoped sample. The magnetic properties and specific heat of all synthesized materials were measured, and the results show that all studied samples behave as spin-glasses. Also, the Morin transition of hematite was observed at 260 K with intensity depending on the material content in Fe2O3 crystalline phase, the formation of which correlates with the amount of added BeO.
Structure and properties comparison of poly(ether-urethane)s based on nonpetrochemical and petrochemical polyols obtained by solvent free two-step method
- Paulina Kasprzyk
- Ewa Głowińska
- Janusz Datta
2021 Pełny tekst EUROPEAN POLYMER JOURNAL
The application of thermoplastic polyurethanes (TPU) is becoming more and more extensive, and the decreasing of used petrochemical monomers and reduction of energy for the polymerization and processing processes is getting increasingly important. In this paper, we confirmed the positive influence of high bio-based monomers contents (by replacing petrochemical polyol and glycol by bio-based counterparts) on processing and properties of obtained materials. A series of partially bio-based thermoplastic poly(ether-urethane)s (bio-based TPU) were obtained from bio- and petrochemical-based polyols, bio-based 1,4-butanediol, and 4,4′-diphenylmethane diisocyanate by the two-step method without using any solvents. Both the monomers’ origin and polyurethane prepolymer processing parameters were taken into account in characterization of the obtained materials. The TPUs' chemical structure was analyzed by FTIR spectroscopy and 1H NMR and the number average molecular weight was examined by 1H NMR and GPC. The measurements of dynamic mechanical thermal analysis, tensile test, hardness, density method, and rheological behavior provided useful information about the properties of prepolymers and TPUs. The processing properties and an activation energy of prepared materials was examined using the melt-flow index. It has been confirmed that despite the origin of polyols obtained thermoplastic poly(ether-urethanes) exhibited comparably good mechanical and thermo-mechanical properties, and an appropriate melt flow index facilitates their processing. Nevertheless, the use of high amount of bio-based monomers resulted in obtaining more eco-friendly materials.
Structure and Randomness in Planning and Reinforcement Learning
- Konrad Czechowski
- Piotr Januszewski
- Piotr Kozakowski
- Łukasz Kuciński
- Piotr Miłoś
2021
Planning in large state spaces inevitably needs to balance the depth and breadth of the search. It has a crucial impact on the performance of a planner and most manage this interplay implicitly. We present a novel method \textit{Shoot Tree Search (STS)}, which makes it possible to control this trade-off more explicitly. Our algorithm can be understood as an interpolation between two celebrated search mechanisms: MCTS and random shooting. It also lets the user control the bias-variance trade-off, akin to TD(n), but in the tree search context. In experiments on challenging domains, we show that STS can get the best of both worlds consistently achieving higher scores.
Structure and thermoelectric properties of nickel-doped copper selenide synthesised in a hydrogen atmosphere
- Agata Ducka
- Bartosz Trawiński
- Beata Bochentyn
- A. Dubiel
- Bogusław Kusz
2021 Pełny tekst MATERIALS RESEARCH BULLETIN
Nickel-doped copper selenide—Cu2-xNixSe (x = 0; 0.01; 0.02; 0.03)—materials with high thermoelectric properties were synthesised through reduction of reagents in hydrogen. The impact of the nickel content on both the microstructure and thermoelectric properties was examined. The nickel-doped samples’ microstructure differed significantly from pristine copper selenide. Besides Cu2Se, copper precipitations were present in the materials. The presence of the metallic nanoparticles in the nickel-doped materials enhanced the electrical conductivity without significantly changing the Seebeck coefficient. Above 500 K, the structure of the doped samples also resulted in decreased thermal conductivity. Also, the impact of the Cu2Se phase transition on thermoelectric properties is visible. The highest ZT value, equal to 0.8 at 650 K, was reached for the Cu1.98Ni0.02Se sample.
Structure and transport properties of donor-doped barium strontium cobaltites
- Tadeusz Miruszewski
- Wojciech Skubida
- Arkadiusz Dawczak
- Kacper Dzierzgowski
- Sebastian Wachowski
- Aleksandra Mielewczyk-Gryń
- Maria Gazda
2021 JOURNAL OF THE EUROPEAN CERAMIC SOCIETY
In this work, Nb-substituted barium strontium cobaltites Ba0.5Sr0.5Co1-xNbxO3-δ (x = 0 – 0.4) have been fabricated and studied. The structural analysis showed that the Nb content influences the lattice constant as well as the distance between the (Co, Nb) and oxygen atoms. The study of morphology of samples showed that the Nb content does not change the porosity, grain size and morphology of the ceramics. The total electrical conductivity was studied as a function of temperature and pO2/pH2O. It was shown, that total conductivity is influenced by the cobalt to niobium ratio while the conduction mechanism was similar in all analyzed samples. Transport properties and the presence of protonic conductivity were studied in a dry and humidified atmosphere. A non-negligible difference between total conductivities in dry and wet atmospheres below 500 °C was observed what indicates the presence of protonic defects in these structures. Hydrogenation as a predominant protons formation mechanism was proposed.
Structure and transport properties of triple-conducting BaxSr1−xTi1−yFeyO3−δ oxides
- Tadeusz Miruszewski
- Kacper Dzierzgowski
- Piotr Winiarz
- Daniel Jaworski
- Katarzyna Wiciak-Pawłowska
- Wojciech Skubida
- Sebastian Wachowski
- Aleksandra Mielewczyk-Gryń
- Maria Gazda
2021 Pełny tekst RSC Advances
In this work, BaxSr1−xTi1−yFeyO3−δ perovskite-based mixed conducting ceramics (for x = 0, 0.2, 0.5 and y = 0.1, 0.8) were synthesized and studied. The structural analysis based on the X-ray diffraction results showed significant changes in the unit cell volume and Fe(Ti)–O distance as a function of Ba content. The morphology of the synthesized samples studied by means of scanning electron microscopy has shown different microstructures for different contents of barium and iron. Electrochemical impedance spectroscopy studies of transport properties in a wide temperature range in the dry- and wet air confirmed the influence of barium cations on charge transport in the studied samples. The total conductivity values were in the range of 10−3 to 100 S cm−1 at 600 °C. Depending on the barium and iron content, the observed change of conductivity either increases or decreases in humidified air. Thermogravimetric measurements have shown the existence of proton defects in some of the analysed materials. The highest observed molar proton concentration, equal to 5.0 × 10−2 mol mol−1 at 300 °C, was obtained for Ba0.2Sr0.8Ti0.9Fe0.1O2.95. The relations between the structure, morphology and electrical conductivity were discussed.
Studies on Aminoanthraquinone-Modified Glassy Carbon Electrode: Synthesis and Electrochemical Performance toward Oxygen Reduction
- Łukasz Macewicz
- Grzegorz Skowierzak
- Paweł Niedziałkowski
- Jacek Ryl
- Tadeusz Ossowski
- Robert Bogdanowicz
2021 RUSSIAN JOURNAL OF ELECTROCHEMISTRY
In this paper, 9,10-anthraquinone (AQ) derivative-modified glassy carbon (GC) electrodes were studied towards the electrochemical reduction of oxygen in aqueous and non-aqueous solutions. The reaction of 1-chloro-9,10-anthraquinone with aliphatic diamines was applied for the synthesis of amino-9,10-anthraquinone derivatives. The obtained AQ derivatives were grafted onto the surface of glassy carbon electrodes by electropolymerisation using diazonium salts. The modified GC electrodes are sensitive to oxygen, determined by cyclic voltammetry. Changes in the oxygen determination efficiency depend mostly on the length of the side chain AQ derivative which is grafted to the GC electrode and is nearly double in comparison to a bare GC electrode modified by 1-((2-((2-aminoethyl)amino)ethyl)amino)-9,10-anthraquinone.
Studium wprowadzenia elektrycznych zespołów trakcyjnych z zasobnikami energii na częściowo zelektryfikowanej trasie Orunia Górna - Port Oksywie
- Natalia Karkosińska-Brzozowska
- Dominika Macedońska
- Dariusz Karkosiński
2021 Automatyka Elektryka Zakłócenia
W artykule rozważono innowacyjny układ przewozów pasażerskich Metropolii Trójmiejskiej. Dla układu z naprzemiennie występującymi odcinkami zelektryfikowanymi i niezelektryfikowanymi wyznaczono zapotrzebowanie energetyczne i dobrano hipotetyczny zasobnik, składający się z baterii akumulatorów oraz superkondesarorów. W wyniku przeprowadzonej analizy wykazano, że zastosowanie elektrycznych zespołów zasobnikowych w stosunku do zespołów z napędem spalinowym oraz budowy sieci trakcyjnej może być ekonomicznie i środowiskowo korzystme
Study of a Multicriterion Decision-Making Approach to the MQL Turning of AISI 304 Steel Using Hybrid Nanocutting Fluid
- Dubey Vineet
- Kumar Anuj Sharma
- Prameet Vats
- Danil Yurievich Pimenov
- Khaled Giasin
- Daniel Chuchała
2021 Pełny tekst Materials
The enormous use of cutting fluid in machining leads to an increase in machining costs, along with different health hazards. Cutting fluid can be used efficiently using the MQL (minimum quantity lubrication) method, which aids in improving the machining performance. This paper contains multiple responses, namely, force, surface roughness, and temperature, so there arises a need for a multicriteria optimization technique. Therefore, in this paper, multiobjective optimization based on ratio analysis (MOORA), VIseKriterijumska Optimizacija I Kompromisno Resenje (VIKOR), and technique for order of preference by similarity to ideal solution (TOPSIS) are used to solve different multiobjective problems, and response surface methodology is also used for optimization and to validate the results obtained by multicriterion decision-making technique (MCDM) techniques. The design of the experiment is based on the Box–Behnken technique, which used four input parameters: feed rate, depth of cut, cutting speed, and nanofluid concentration, respectively. The experiments were performed on AISI 304 steel in turning with minimum quantity lubrication (MQL) and found that the use of hybrid nanofluid (Alumina–Graphene) reduces response parameters by approximately 13% in forces, 31% in surface roughness, and 14% in temperature, as compared to Alumina nanofluid. The response parameters are analyzed using analysis of variance (ANOVA), where the depth of cut and feed rate showed a major impact on response parameters. After using all three MCDM techniques, it was found that, at fixed weight factor with each MCDM technique, a similar process parameter was achieved (velocity of 90 m/min, feed of 0.08 mm/min, depth of cut of 0.6 mm, and nanoparticle concentration of 1.5%, respectively) for optimum response. The above stated multicriterion techniques employed in this work aid decision makers in selecting optimum parameters depending upon the desired targets. Thus, this work is a novel approach to studying the effectiveness of hybrid nanofluids in the machining of AISI 304 steel using MCDM techniques.
STUDY OF ARRAY OF MEMS INERTIAL MEASUREMENT UNITS UNDER QUASI-STATIONARY AND DYNAMIC CONDITIONS
- Jerzy Demkowicz
- Krzysztof Bikonis
2021 Pełny tekst Polish Maritime Research
A measurement system includes all components in a chain of hardware and software that leads from a measured variable to processed data. In that context, the type and quality of the sensors or measuring devices are critical to any measurement system. MEMS/IMU sensors lag behind leading technologies in this respect, but the MEMS/IMU performance rapidly changes while is relatively inexpensive. For this reason, the paper proposes some investigations of currently available MEMS/IMUs, but in an array configuration. The article presents the results of research undertaken on this type of IMU sensor configuration under quasi-stationary and dynamic conditions and answers the question of whether the precision of current MEMS technologies for acceleration and angular velocity sensors is still improved using this kind of approach.
Study of Integer Spin S = 1 in the Polar Magnet β-Ni(IO3)2
- Ebube E. Oyeka
- Michał Winiarski
- Thao Tran
2021 Pełny tekst MOLECULES
Polar magnetic materials exhibiting appreciable asymmetric exchange interactions can potentially host new topological states of matter such as vortex-like spin textures; however, realizations have been mostly limited to half-integer spins due to rare numbers of integer spin systems with broken spatial inversion lattice symmetries. Here, we studied the structure and magnetic properties of the S = 1 integer spin polar magnet β-Ni(IO3)2 (Ni2+, d8, 3F). We synthesized single crystals and bulk polycrystalline samples of β-Ni(IO3)2 by combining low-temperature chemistry techniques and thermal analysis and characterized its crystal structure and physical properties. Single crystal X-ray and powder X-ray diffraction measurements demonstrated that β-Ni(IO3)2 crystallizes in the noncentrosymmetric polar monoclinic structure with space group P21. The combination of the macroscopic electric polarization driven by the coalignment of the (IO3)− trigonal pyramids along the b axis and the S = 1 state of the Ni2+ cation was chosen to investigate integer spin and lattice dynamics in magnetism. The effective magnetic moment of Ni2+ was extracted from magnetization measurements to be 3.2(1) µB, confirming the S = 1 integer spin state of Ni2+ with some orbital contribution. β-Ni(IO3)2 undergoes a magnetic ordering at T = 3 K at a low magnetic field, μ0H = 0.1 T; the phase transition, nevertheless, is suppressed at a higher field, μ0H = 3 T. An anomaly resembling a phase transition is observed at T ≈ 2.7 K in the Cp/T vs. T plot, which is the approximate temperature of the magnetic phase transition of the material, indicating that the transition is magnetically driven. This work offers a useful route for exploring integer spin noncentrosymmetric materials, broadening the phase space of polar magnet candidates, which can harbor new topological spin physics.
Study of Multi-Class Classification Algorithms’ Performance on Highly Imbalanced Network Intrusion Datasets
- Viktoras Bulavas
- Virginijus Marcinkevičius
- Jacek Rumiński
2021 Pełny tekst Informatica
This paper is devoted to the problem of class imbalance in machine learning, focusing on the intrusion detection of rare classes in computer networks. The problem of class imbalance occurs when one class heavily outnumbers examples from the other classes. In this paper, we are particularly interested in classifiers, as pattern recognition and anomaly detection could be solved as a classification problem. As still a major part of data network traffic of any organization network is benign, and malignant traffic is rare, researchers therefore have to deal with a class imbalance problem. Substantial research has been undertaken in order to identify these methods or data features that allow to accurately identify these attacks. But the usual tactic to deal with the imbalance class problem is to label all malignant traffic as one class and then solve the binary classification problem. In this paper, however, we choose not to group or to drop rare classes but instead investigate what could be done in order to achieve good multi-class classification efficiency. Rare class records were up-sampled using SMOTE method (Chawla et al., 2002) to a preset ratio targets. Experiments with the 3 network traffic datasets, namely CIC-IDS2017, CSE-CIC-IDS2018 (Sharafaldin et al., 2018) and LITNET-2020 (Damasevicius et al., 2020) were performed aiming to achieve reliable recognition of rare malignant classes available in these datasets. Popular machine learning algorithms were chosen for comparison of their readiness to support rare class detection. Related algorithm hyper parameters were tuned within a wide range of values, different data feature selection methods were used and tests were executed with and without over-sampling to test the multiple class problem classification performance of rare classes. Machine learning algorithms ranking based on Precision, Balanced Accuracy Score, G¯ , and prediction error Bias and Variance decomposition, show that decision tree ensembles (Adaboost, Random Forest Trees and Gradient Boosting Classifier) performed best on the network intrusion datasets used in this research.
Study of Non-Newtonian biomagnetic blood flow in a stenosed bifurcated artery having elastic walls
- Hasan Shahzad
- Xinhua Wang
- Ioannis Sarris
- Kaleem Iqbal
- Muhammad Bilal Hafeez
- Marek Krawczuk
2021 Pełny tekst Scientific Reports
Fluid structure interaction (FSI) gained attention of researchers and scientist due to its applications in science felds like biomedical engineering, mechanical engineering etc. One of the major application in FSI is to study elastic wall behavior of stenotic arteries. In this paper we discussed an incompressible Non-Newtonian blood fow analysis in an elastic bifurcated artery. A magnetic feld is applied along x direction. For coupling of the problem an Arbitrary Lagrangian–Eulerian formulation is used by twoway fuid structure interaction. To discretize the problem, we employed P2P1 fnite element technique to approximate the velocity, displacement and pressure and then linearized system of equations is solved using Newton iteration method. Analysis is carried out for power law index, Reynolds number and Hartmann number. Hemodynamic efects on elastic walls, stenotic artery and bifurcated region are evaluated by using velocity profle, pressure and loads on the walls. Study shows there is signifcant increase in wall shear stresses with an increase in Power law index and Hartmann number. While as expected increase in Reynolds number decreases the wall shear stresses. Also load on the upper wall is calculated against Hartmann number for diferent values of power law index. Results show load increases as the Hartmann number and power law index increases. From hemodynamic point of view, the load on the walls is minimum for shear thinning case but when power law index increased i.e. for shear thickening case load on the walls increased.
Study of probe signal bandwidth influence on estimation of coherence bandwidth for underwater acoustic communication channel
- Iwona Kochańska
- Jan Schmidt
- Aleksander Schmidt
2021 Pełny tekst APPLIED ACOUSTICS
A signal transmitted in a shallow Underwater Acoustic Communication (UAC) channel suffers from time dispersion due to the multipath propagation and the refraction phenomena. This causes intersymbol interference of the received signal and frequency-selective fading observed in its spectrum. Coherence bandwidth is one of the key transmission parameters used for designing the physical layer of a data transmission system to minimise the influence of time dispersion on the received signal. It can be calculated on the basis of the channel impulse response, measured with the use of the correlation method and frequency modulated signals or pseudorandom binary sequences. Such signals have a narrow, impulselike autocorrelation function if considered in baseband. However, in the case of bandpass measurements, the influence of the probe signal on the estimate of the impulse response, and thus on the estimate of transmission parameters, is no longer negligible. The paper presents the results of an experimental study on probe signal bandwidth influence on estimation of coherence bandwidth. Simulations were carried out using UAC channel impulse responses measured in an inland reservoir.