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Gdańsk University of Technology

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Publications from the year 2022

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  • A Comprehensive Survey on Antennas On-Chip Based on Metamaterial, Metasurface, and Substrate Integrated Waveguide Principles for Millimeter-Waves and Terahertz Integrated Circuits and Systems
    • Mohammad Alibakhshikenari
    • Esraa Mousra Ali
    • Mohammad Soruri
    • Mariana Dalarsson
    • Mohammad Naser-moghadasi
    • Bal S. Virdee
    • Caslav Stefanovic
    • Anna Pietrenko-Dąbrowska
    • Sławomir Kozieł
    • Stanisław Szczepański
    • Ernesto Limiti
    2022 Full text IEEE Access

    Antennas on-chip are a particular type of radiating elements valued for their small footprint. They are most commonly integrated in circuit boards to electromagnetically interface free space, which is necessary for wireless communications. Antennas on-chip radiate and receive electromagnetic (EM) energy as any conventional antennas, but what distinguishes them is their miniaturized size. This means they can be integrated inside electronic devices. Although on-chip antennas have a limited range, they are suitable for cell phones, tablet computers, headsets, global positioning system (GPS) devices, and WiFi and WLAN routers. Typically, on-chip antennas are handicapped by narrow bandwidth (less than 10%) and low radiation efficiency. This survey provides an overview of recent techniques and technologies investigated in the literature, to implement high performance on-chip antennas for millimeter-waves (mmWave) and terahertz (THz) integrated-circuit (IC) applications. The technologies discussed here include metamaterial (MTM), metasurface (MTS), and substrate integrated waveguides (SIW). The antenna designs described here are implemented on various substrate layers such as Silicon, Graphene, Polyimide, and GaAs to facilitate integration on ICs. Some of the antennas described here employ innovative excitation mechanisms, for example comprising open-circuited microstrip-line that is electromagnetically coupled to radiating elements through narrow dielectric slots. This excitation mechanism is shown to suppress surface wave propagation and reduce substrate loss. Other techniques described like SIW are shown to significantly attenuate surface waves and minimise loss. Radiation elements based on the MTM and MTS inspired technologies are shown to extend the effective aperture of the antenna without compromising the antenna’s form factor. Moreover, the on-chip antennas designed using the above technologies exhibit significantly improved impedance match, bandwidth, gain and radiation efficiency compared to previously used technologies. These features make such antennas a prime candidate for mmWave and THz on-chip integration. This review provides a thorough reference source for specialist antenna designers.

  • A conceptual framework for digital tax administration - A systematic review
    • Edidiong Bassey
    • Emer Mulligan
    • Adegboyega Ojo
    2022 Full text GOVERNMENT INFORMATION QUARTERLY

    Tax administrations worldwide have become highly digitised with a diverse and sophisticated array of e-services to enhance the taxpayer experience. Nevertheless, given the high rates of failure of e-government services, it is critical to understand the factors that are essential to the success of a digital tax system. Drawing on a systematic review of ninety-six publications across the digital taxation, taxation, and information systems (IS) literature, a comprehensive conceptual framework is developed to improve our success of digital services in tax administration. The conceptual framework identifies fifteen themes for consideration by policymakers when designing digital services in tax administrations clustered around four categories – Context, Stakeholders, Technology and Demonstrated Results. The framework should also serve as a reference point in successfully developing strategies and measures to embed digital services in tax administrations. Future research directions are also proposed based on the conceptual framework that will help advance our understanding of digital services in tax administration beyond technology acceptance models.

  • A Control Theoretical Approach to Spectral Factorization is Unstable
    • Michał Meller
    • Adam Lasota
    2022 Full text CIRCUITS SYSTEMS AND SIGNAL PROCESSING

    Local stability analysis of a recently proposed recursive feedback-based approach to spectral factorization is performed. The method is found not to give stability guarantees. Interestingly enough, its global behavior often allows one to obtain reasonable approximations of spectral factorizations if a suitable stopping criterion is employed.

  • A convergence result for mountain pass periodic solutions of perturbed Hamiltonian systems
    • Marek Izydorek
    • Joanna Janczewska
    • Pedro Soares
    2022 Full text COMMUNICATIONS IN CONTEMPORARY MATHEMATICS

    In this work, we study second-order Hamiltonian systems under small perturbations. We assume that the main term of the system has a mountain pass structure, but do not suppose any condition on the perturbation. We prove the existence of a periodic solution. Moreover, we show that periodic solutions of perturbed systems converge to periodic solutions of the unperturbed systems if the perturbation tends to zero. The assumption on the potential that guarantees the mountain pass geometry of the corresponding action functional is of independent interest as it is more general than those by Rabinowitz [Homoclinic orbits for a class of Hamiltonian systems, Proc. R. Soc. Edinburgh A 114 (1990) 33–38] and the authors [M. Izydorek and J. Janczewska, Homoclinic solutions for a class of the second-order Hamiltonian systems, J. Differ. Equ. 219 (2005) 375–389].

  • A Cost-Effective Method for Reconstructing City-Building 3D Models from Sparse Lidar Point Clouds
    • Marek Kulawiak
    2022 Full text Remote Sensing

    The recent popularization of airborne lidar scanners has provided a steady source of point cloud datasets containing the altitudes of bare earth surface and vegetation features as well as man-made structures. In contrast to terrestrial lidar, which produces dense point clouds of small areas, airborne laser sensors usually deliver sparse datasets that cover large municipalities. The latter are very useful in constructing digital representations of cities; however, reconstructing 3D building shapes from a sparse point cloud is a time-consuming process because automatic shape reconstruction methods work best with dense point clouds and usually cannot be applied for this purpose. Moreover, existing methods dedicated to reconstructing simplified 3D buildings from sparse point clouds are optimized for detecting simple building shapes, and they exhibit problems when dealing with more complex structures such as towers, spires, and large ornamental features, which are commonly found e.g., in buildings from the renaissance era. In the above context, this paper proposes a novel method of reconstructing 3D building shapes from sparse point clouds. The proposed algorithm has been optimized to work with incomplete point cloud data in order to provide a cost-effective way of generating representative 3D city models. The algorithm has been tested on lidar point clouds representing buildings in the city of Gdansk, Poland.

  • A Cross-Polarisation Discrimination Analysis of Off-Body Channels in Passenger Ferryboat Environments
    • Sławomir Ambroziak
    • Krzysztof Cwalina
    • Piotr Rajchowski
    • Filipe D. Cardoso
    • Manuel M. Ferreira
    • Luis M. Correia
    2022 Full text IEEE Access

    There is a need for investigating radio channels for Body Area Networks considering the depolarisation phenomenon and new types of environments, since these aspects are becoming very important for systems design and deployment. This paper presents an analysis of cross-polarisation discrimination for off-body channels based on a measurement campaign performed in a passenger ferryboat, i.e., where all walls, floors and ceilings are made of metal. Firstly, the measurement campaign, including test-bench and scenarios, as well as the analysis approach, including classification of mutual antennas’ orientation and definition of parameters are described. The analysis of results includes distance, on-body antennas location and several scenarios, addressing statistical parameters. Mean values for the cross-polarisation discrimination are in the range of [3.7, 6.8] dB while the standard deviation is around 10.0 dB. There is no dependence of the cross-polarisation discrimination on distance, within the measured range (up to 16 m). It is found that there is no correlation between radio signals received by vertically and horizontally polarised receiving antennas, hence, enabling the application of polarisation diversity in Body Area Networks. The Normal Distribution is the best fit for describing cross-polarisation discrimination, as shown by the analysis of goodness of fit parameters, since it passes many of the tests.

  • A Direct Modulation for Matrix Converters based on the Onecycle Atomic operation developed in Verilog HDL.
    • Paweł Szczepankowski
    • Wojciech Śleszyński
    • Tomasz Bajdecki
    2022 Full text IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS

    This paper presents a fast direct Pulse Width Modulation (PWM) algorithm for the Conventional Matrix Converters (CMC) developed in Verilog Hardware Description language (HDL). All PWM duty cycle calculations are performed in one cycle by an atomic operation designed as a digital module using FPGA basic blocks. The algorithm can be extended to any number of output phase. The improved version of the discontinuous Direct Analytic Voltage PWM (DAV–PWM) method is proposed, in which the use of trigonometry, angles and program loops has been eliminated. The proposed DAV-PWM is equivalent to the Space Vector Modulation (SVM), it can be applied during input asymmetry and also allows for the control of the displacement input angle. The proposal has been verified using the circuit simulation in PSIM, digital structure modelling in ModelSim, and finally through an experiment.

  • A dual-control strategy based on electrode material and electrolyte optimization to construct an asymmetric supercapacitor with high energy density
    • Xianyu Chu
    • Fanling Meng
    • Wei Zhang
    • He Yang
    • Xu Zou
    • Sebastian Molin
    • Piotr Jasiński
    • Xiangcheng Sun
    • Weitao Zheng
    2022 NANOTECHNOLOGY

    Metal-organic frames (MOFs) are regarded as excellent candidates for supercapacitors that have attracted much attention because of their diversity, adjustability and porosity. However, both poor structural stability in aqueous alkaline electrolytes and the low electrical conductivity of MOF materials constrain their practical implementation in supercapacitors. In this study, bimetallic CoNi-MOF were synthesized to enhance the electrical conductivity and electrochemical activity of nickel-based MOF, as well as the electrochemical performance of the CoNi-MOF in multiple alkaline electrolytes was investigated. The CoNi-MOF/active carbon device, as-fabricated with a 1 M KOH electrolyte, possesses a high energy density of 35 W h kg−1 with a power density of 1450 W kg−1, exhibiting outstanding cycling stability of 95% over 10,000 cycles. The design of MOF-based electrode materials and the optimization selection of electrolytes pave the way for constructing high-performance supercapacitors.

  • A Dual-Polarized 39 GHz 4x4 Microstrip Antenna Array for 5G MU-MIMO Airflight Cabin Connectivity
    • Kamil Trzebiatowski
    • Jan Fromme
    • Damian Duraj
    • Łukasz Kulas
    • Krzysztof Nyka
    2022 Full text

    This paper presents the design, fabrication, and experimental validation of a 39 GHz dual-polarized 4x4 microstrip antenna array. The array consists of 16 slot coupled circular microstrip patches, fed through SMPS connectors. The procedure requiring a reduced number of cables for measurement of the uniformly excited antenna array is also presented. The array exhibits 18 dBi peak gain and 2.9 GHz reflection bandwidth and is intended for use in a 5G base station inside an airplane. The presented antenna is characterized by a simple feeding system which results in a reduced number of via-holes and dielectric layers.

  • A facile approach to fabricate load-bearing porous polymer scaffolds for bone tissue engineering
    • Tairong Kuang
    • Shaowei Chen
    • Zhipeng Gu
    • Zhisen Shen
    • Aleksander Hejna
    • Mohammad Saeb
    • Feng Chen
    • Mingqiang Zhong
    • Tong Liu
    2022 Advanced Composites and Hybrid Materials

    Biodegradable porous scaffolds with oriented interconnected pores and high mechanical are load-bearing biomaterials for bone tissue engineering. Herein, we report a simple, non-toxic, and cost-effective method to fabricate high-strength porous biodegradable scaffolds, composed of a polymer matrix of polycaprolactone (PCL) and water-soluble poly (ethylene oxide) (PEO) as a sacrificial material by integrating annealing treatment, pressure-induced flow (PIF) processing and particulate leaching techniques. The microstructure, crystal orientation, and crystallization behavior were studied by scanning electron microscope (SEM), 2D X-ray techniques, and differential scanning calorimetry (DSC). Through the analysis of SEM and 2D X-ray results, the proposed hybrid strategy aided formation of porous PCL scaffolds with highly oriented pore structures as well as suitable pore size and pore connectivity. Owing to the improvement of crystal orientation and crystallinity after PIF processing, the obtained scaffolds exhibited higher tensile strength (14.1 MPa), compressive strength (6.6 MPa), bending strength (5.9 MPa), and elongation at break (above 150%) compared with the non-oriented porous scaffolds. In addition, NIH-3T3 fibroblast cell culture unveiled in vitro biocompatibility of the scaffolds. Overall, the obtained oriented porous PCL scaffolds exhibited good biocompatibility, elongated cell morphology, and highly strengthened oriented structure for load-bearing bone tissue applications.

  • A facile method for Tauc exponent and corresponding electronic transitions determination in semiconductors directly from UV–Vis spectroscopy data
    • Łukasz Haryński
    • Adrian Olejnik
    • Katarzyna Grochowska
    • Katarzyna Siuzdak
    2022 OPTICAL MATERIALS

    In this work, a facile method allowing for estimation of the exponent in the Tauc equation directly from the UV–vis spectra is presented. It is based on the Taylor expansion of the logarithmic version of the Tauc equation. The Tauc exponent is calculated from the tangent slope of the absorption data. Knowledge of this coefficient provides information about the optical transition types and is used as an input for the calculations of the band gap. As an exemplar material, TiO2 in form of thin film and nanotubes as well as their nanocomposites with other metal oxides are chosen. For the transparent thin 15 nm film of TiO2, two linear ranges with n = 2.0 and 1.2 are found. The first is assigned to the well-established indirect (allowed) transition. In the case of the second one, the n does not correspond to typically used values. Therefore, it is speculated that more than one transition is probable. This consideration is supported with ab-initio DFT calculations of the band structure of TiO2 with Hubbard U correction. Similar results are found for TiO2 nanotubes using diffuse reflectance spectroscopy indicating that the presented method applies both to transmission and reflection.

  • A facile structural manipulation strategy to prepare ultra-strong, super-tough, and thermally stable polylactide/nucleating agent composites
    • Tairong Kuang
    • Jiajun Ju
    • Tong Liu
    • Aleksander Hejna
    • Mohammad Saeb
    • Shuidong Zhang
    • Xiangfang Peng
    2022 Advanced Composites and Hybrid Materials

    Polylactide (PLA) is a biodegradable thermoplastic widely used in diferent felds, but it should be adequately modifed considering high-performance applications. However, the current processes for developing PLA materials achieve high strength at the expense of toughness or ductility of the materials. Therefore, there is need to develop new strategies for generation of PLA materials with high strength, great toughness, good ductility, and high heat resistance. The present study reported a facile and cost-efective structural manipulation strategy for fabricating high-performance PLA composites that involved addition of 0.5 wt% self-assembled nucleation agent (TMC-306). During the structural manipulation process, the nucleation agent (TMC-306 shish) initially induced the PLA materials to develop a random shish-kebab crystal structure. A chain-like interlocking shish-kebab crystal structure with gradients in both length and thickness was then achieved through semi-solid high-pressure molding. The resulting super-PLA product showed excellent tensile strength (98.7 MPa), superb toughness (82.7 kJ/m2 ), and high elongation at break (117.5%). The reported qualities of the super-PLA materials were superior to that of most commercially available commodity polymers and were comparable to engineering plastics. In addition, PLA composites exhibited a lower thermal deformation variable and a higher Vicat softening temperature (112.4 °C) than neat PLA (62.1 °C). The facile strategy reported in the present study allows development of strong, tough, ductile, and thermally stable PLA, making it a potential alternative plastic material to commodity and engineering plastics used in many technical felds.

  • A finite element analysis of thermal energy inclination based on ternary hybrid nanoparticles influenced by induced magnetic field
    • Muhammad Bilal Hafeez
    • Marek Krawczuk
    • Sooppy Nisar Kottakkaran
    • Wasim Jamshed
    • Amjad Ali Pasha
    2022 Full text INTERNATIONAL COMMUNICATIONS IN HEAT AND MASS TRANSFER

    The use of hybrid nanoparticles to improve thermal processes is a key method that has implications for a variety of interventions utilized in many sectors. This paper aimed to look into the impacts of ternary nanoparticles on hyperbolic tangent materials to establish their thermal characteristics. Flow describing equations have been explored in the presence of heat production, non-Fourier heat flux, and an induced magnetic field. Boundary layer analysis, which generates partial differential equations, was used to model the physical situation under several major physical properties (PDEs). The flow rheology is expanded and calculated in a rotating frame by supposing that the flow is created by a spinning disk. The solution of complicated generated PDEs was calculated using the Galerkin finite element technique (G-FEM) after translating them into corresponding ODEs. Several major bodily repercussions have been seen and documented because of increasing the implicated influencing factors.

  • A framework for onboard assessment and monitoring of flooding risk due to open watertight doors for passenger ships
    • Pekka Ruponen
    • Jakub Montewka
    • Markus Tompuri
    • Teemu Manderbacka
    • Spyros Hirdaris
    2022 Full text RELIABILITY ENGINEERING & SYSTEM SAFETY

    Post-accident safety of ships is governed by damage stability, affected by watertight subdivisions which limit accidental flooding. This is important for passenger ships with watertight doors (WTDs) often fitted in the bulkheads. Awareness of the ship flooding risk due to open WTDs and the conditions under which the associated risk level changes are prerequisites for proactive risk mitigation. Accident risk is often expressed as a combination of accident likelihood and its consequences. Current solu-tions for flooding risk mitigation often treat these elements separately, or the adopted metrics are based on quantities not allowing proper active control of risk. In this paper an attempt is made to fill this gap by introducing a novel concept for rapidly assessing the flooding risk onboard passenger ships, accounting for the two dimensions of flooding accidents. The likelihood part is based on the complexity of surrounding traffic, operational conditions, and human reliability assessment. The consequences are based on precalculated probabilistic damage stability results of ship survivability. The presented case studies indicate that active monitoring of flooding risk can increase the crew’s situational awareness of the effect of open WTDs on the flooding risk, thus positively influencing the safety culture onboard the ship.

  • A general isogeometric finite element formulation for rotation‐free shells with in‐plane bending of embedded fibers
    • Thang X. Duong
    • Mikhail Itskov
    • Roger Sauer
    2022 Full text INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING

    This article presents a general, nonlinear isogeometric finite element formulation for rotation-free shells with embedded fibers that captures anisotropy in stretching, shearing, twisting, and bending - both in-plane and out-of-plane. These capabilities allow for the simulation of large sheets of heterogeneous and fibrous materials either with or without matrix, such as textiles, composites, and pantographic structures. The work is a computational extension of our earlier theoretical work that extends existing Kirchhoff-Love shell theory to incorporate the in-plane bending resistance of initially straight or curved fibers. The formulation requires only displacement degrees-of-freedom to capture all mentioned modes of deformation. To this end, isogeometric shape functions are used in order to satisfy the required C1-continuity for bending across element boundaries. The proposed formulation can admit a wide range of material models, such as surface hyperelasticity that does not require any explicit thickness integration. To deal with possible material instability due to fiber compression, a stabilization scheme is added. Several benchmark examples are used to demonstrate the robustness and accuracy of the proposed computational formulation.

  • A general theory for anisotropic Kirchhoff–Love shells with in-plane bending of embedded fibers
    • Thang X. Duong
    • Vu N Khiêm
    • Mikhail Itskov
    • Roger Sauer
    2022 Full text MATHEMATICS AND MECHANICS OF SOLIDS

    This work presents a generalized Kirchhoff–Love shell theory that can explicitly capture fiber-induced anisotropy not only in stretching and out-of-plane bending, but also in in-plane bending. This setup is particularly suitable for heterogeneous and fibrous materials such as textiles, biomaterials, composites and pantographic structures. The presented theory is a direct extension of classical Kirchhoff–Love shell theory to incorporate the in-plane bending resistance of fibers. It also extends existing second-gradient Kirchhoff–Love shell theory for initially straight fibers to initially curved fibers. To describe the additional kinematics of multiple fiber families, a so-called in-plane curvature tensor—which is symmetric and of second order—is proposed. The effective stress tensor and the in-plane and out-of-plane moment tensors are then identified from the mechanical power balance. These tensors are all second order and symmetric in general. Constitutive equations for hyperelastic materials are derived from different expressions of the mechanical power balance. The weak form is also presented as it is required for computational shell formulations based on rotation-free finite element discretizations. The proposed theory is illustrated by several analytical examples.

  • A hierarchical porous composite magnetic sorbent of reduced graphene oxide embedded in polyvinyl alcohol cryogel for solvent‐assisted‐solid phase extraction of polycyclic aromatic hydrocarbons
    • Natnaree Rattanakunsong
    • Sirintorn Jullakan
    • Justyna Płotka-Wasylka
    • Opas Bunkoed
    2022 Full text JOURNAL OF SEPARATION SCIENCE

    A hierarchical porouscomposite magnetic sorbent was fabricated and applied tothe dispersive solvent-assisted solid-phase extraction of five polycyclic aromatichydrocarbons. A sorbent was first prepared by incorporating graphene oxide,calcium carbonate, and magnetite nanoparticles into a polyvinyl alcohol cryo-gel. The graphene oxide was converted to reduced graphene oxide using ascorbicacid and a hierarchical porous structure was produced by reacting hydrochlo-ric acid with incorporated calcium carbonate to generate carbon dioxide bubbleswhichcreatedasecondnetwork.Beforeextractingthetargetanalytes,theextrac-tion solvent was introduced into the hierarchical pore network of the sorbent.The extraction was based on the partition between the analytes and introducedextraction solvent and the adsorption of analytes on reduced graphene oxide.Theextraction efficiency was enhanced through π-π and hydrophobic interactionsbetween polycyclic aromatic hydrocarbons and reduced graphene oxide andextraction solvent. The extracted polycyclic aromatic hydrocarbons were deter-mined by using high-performance liquid chromatography coupled with a fluo-rescence detector. The developed method was applied to extract polycyclic aro-matic hydrocarbons in disposable diaper, coffee, and tea samples and recoveriesfrom 84.5 to 99.4% were achieved with relative standard deviations below 7%.The developed sorbent exhibited good reproducibility and could be reused for 10cycles.The developed sorbent exhibited good reproducibility and could be reusedfor 10 cycles.The developed sorbent exhibited good reproducibility and could bereused for 10 cycles.

  • A method for a comprehensive lipidomic analysis of flaxseed (Linum usitatissimum) with the use of LC–Q-TOF-MS and dispersive micro-solid-phase (μDSPE) extraction
    • Inal Bakhytkyzy
    • Weronika Hewelt-Belka
    • Agata Kot-Wasik
    2022 FOOD CHEMISTRY

    Flaxseed (FS) is one of the richest sources of α-linolenic acid oil and lignans, and it is suggested that the consumption of flaxseed may contribute to the prevention of certain chronic diseases such as many types of cancer, diabetes, cardiovascular diseases and cerebrovascular stroke. Here, we demonstrate a new method for comprehensive FS lipidome profiling with the use of LC–Q-TOF-MS and dispersive micro-solid-phase extraction. The effects of stationary phase amount, flaxseed amount and different organic solvents for non-polar lipid elution on the FS lipidome coverage were investigated. The developed and validated protocol allowed for improved monitoring of both polar and non-polar lipids simultaneously, overcoming the challenge of low- and high-abundance lipid species. Furthermore, the method was applied to characterize a set of brown flaxseed and yellow flaxseed samples, as well as flaxseed meal.

  • A method for the analysis of methylmercury and total Hg in fungal matrices
    • Małgorzata Rutkowska
    • Jerzy Falandysz
    • Martyna Saba
    • Piotr Szefer
    • Małgorzata Misztal-Szkudlińska
    • Piotr Konieczka
    2022 Full text APPLIED MICROBIOLOGY AND BIOTECHNOLOGY

    The aim of the study was to develop an efficient method for the determination of monomethyl-mercury (MeHg) and total mercury (THg) content in materials such as fungal sporocarps and sclerotia. Certified Reference Materials (CRMs) with the assigned values of MeHg and THg as well as the control materials (dried mushrooms) with known content of THg were evaluated for method validation. Recovery of MeHg from reference materials was at the following levels: from tuna fish at 87.0 ± 2.3% (THg at 101.9 ± 1.2%), from fish protein at 99.4 ± 1.3% (THg at 92.70 ± 0.41%), and from dogfish liver at 96.45 ± 0.73%. Recovery of THg from the fungal control material CS-M-5 was at 104.01 ± 0.60% (contribution of MeHg in THg content was at 6.2%), from CS-M-4 at 101.1 ± 2.0% (contribution at 3.2%), from CS-M-3 at 100.55 ± 0.67% (contribution at 0.6%), and from CS-M-2 at 101.5 ± 2.7% (contribution at 3.7%). The content of MeHg in randomly selected wild fungi and their morphological parts was in the range from 0.006 to 0.173 mg kg−1 dry weight (dw). In the case of THg, the concentration values were in the range from 0.0108 to 10.27 mg kg−1 dw. The MeHg content in the control materials with the assigned THg values was determined. Since the control materials play an important role in all elements of the quality assurance system of measurement results, they can be used to analyse MeHg as the first control material for fungi.

  • A model of damaged media used for describing the process of non-stationary creep and long-term strength of polycrystalline structural alloys
    • Leonid A. Igumnov
    • Ivan Volkov
    • Evgeny Boev
    • Victor Eremeev
    2022 Full text CONTINUUM MECHANICS AND THERMODYNAMICS

    The main laws of the processes of creep and long-term strength of polycrystalline structural alloys are considered. From the viewpoint of continuum damaged media (CDM), a mathematical model is developed that describes the processes of viscoplastic deformation and damage accumulation under creep. The problem of determining material parameters and scalar functions of the developed constitutive relations based on the results of specially set basic experiments is discussed. An experimental–theoretical methodology for determining material parameters of the derived constitutive relations of CDM is developed based on analyzing the viscoplastic deformation and failure processes of laboratory specimens in the conditions of soft loading (stress controlled). Experimental results of short-term creep of the VZh-159 heat-resistant alloy are presented. The obtained numerical results are compared with the test data using the numerical modeling method of experimental processes. Qualitative and quantitative agreement between numerical results and experimental data is shown. It is concluded that the developed constitutive relations are reliable, and that the proposed methodology accurately determines the material parameters of the model under degradation of initial strength properties of structural materials according to the long-term strength mechanism.