Publications Repository - Gdańsk University of Technology

Page settings

polski
Publications Repository
Gdańsk University of Technology

Show publications from the year

Publications from the year 2022

Show all
  • Design of Microstrip UWB Balun Using Quasi-TEM Approach Aided by the Artificial Neural Network
    • Włodzimierz Zieniutycz
    • Łukasz Sorokosz
    2022 Progress in Electromagnetics Research Letters

    The design procedure for UWB balun realized in the microstrip technology is proposed in the paper. The procedure applies Artificial Neural Network which corrects the dimensions of the approximate design found by appropriate scaling of the dimensions of the prototype. The scale coefficients for longitudinal and transverse dimensions of microstrip lines are determined from electromagnetic modeling based on transmission line equations. The scaling procedure of radial stubs is also proposed. The design procedure was verified experimentally for exemplary balun with radial stub.

  • Design of residential buildings in architecture education
    • Antoni Taraszkiewicz
    • Karolina Taraszkiewicz
    2022 Full text World Transactions on Engineering and Technology Education

    This article is based on an analysis of residential building designs made by students of the Faculty of Architecture at Gdańsk University of Technology (FA-GUT), Poland, and on the results of a survey conducted among these students. The purpose of the survey was to verify the broad, interdisciplinary knowledge of the students required in preparation for taking up design issues, as well as their ability to use this knowledge in the design of residential buildings. When examining these issues, particular emphasis was placed on the possibility of creating methods of architectural education that would allow today’s students and future engineers to be appropriately trained, and thus become aware of the need to understand construction requirements, functional systems and their flexibility, principles of universal design and proxemics, economics of construction and use, energy efficiency and environmental protection, as well as psychological and spiritual needs of potential residents and other users. Respect for the context of the place also needs to be developed, and creative thinking and searching for architectural beauty encouraged and facilitated.

  • Design of three control algorithms for an averaging tank with variable filing
    • Michał Kolankowski
    • Robert Piotrowski
    2022 Full text Acta Mechanica et Automatica

    An averaging tank with variable filling is a nonlinear multidimensional system and can thus be considered a complex control sys-tem. General control objectives of such object include ensuring stability, zero steady state error and achieving simultaneously shortest possible settling time and minimal overshoot. The main purpose of this research work was the modelling and synthesis of three control systems for an averaging tank. In order to achieve the intended purpose, in the first step a mathematical model of the control system was derived. The model was adapted to the form required to design two out of three planned control systems by linearization and reduction of its dimensions, resulting in two system variants. A multivariable PID control system for the averaging tank was developed using optimization for tuning PID controllers. A state feedback and output feedback with integral action control (IC) system was designed using a linear-quadratic regulator (LQR) and optimization of weights. A fuzzy control system was de-signed using Mamdani inference system. The developed control systems were tested using Matlab environment. Finally, the simu-lation results for each control algorithm (and their variants) were compared and their performance was assessed, as well as the ef-fects of optimization in the case of PID and IC systems.

  • Design specification management with automated decision-making for reliable optimization of miniaturized microwave components
    • Sławomir Kozieł
    • Anna Pietrenko-Dąbrowska
    • Piotr Płotka
    2022 Full text Scientific Reports

    The employment of numerical optimization techniques for parameter tuning of microwave components has nowadays become a commonplace. In pursuit of reliability, it is most often carried out at the level of full-wave electromagnetic (EM) simulation models, incurring considerable computational expenses. In the case of miniaturized microstrip circuits, densely arranged layouts with strong cross-coupling effects make EM-driven tuning imperative to achieve the optimum performance. The process is even more challenging due to a typically large number of geometry parameters, and the lack of reasonable initial designs. The latter often encourages the use of global search procedures, which may be prohibitively expensive. In this paper, a novel automated framework for reliable optimization of miniaturized microwave components is proposed. Our methodology is based on design specification management, where the performance requirements imposed on the system are temporarily relaxed if the current design is unlikely to be improved (e.g., due to being away from the target operating frequency). The specifications are re-adjusted at each iteration of the algorithm, and eventually converge to their original values. Using two examples of compact microstrip couplers and a power divider, the presented technique is demonstrated to significantly improve the efficacy of local search routines under challenging design scenarios.

  • Design, synthesis and biological evaluation of novel N-phosphorylated and O-phosphorylated tacrine derivatives as potential drugs against Alzheimer’s disease
    • Maja Przybyłowska
    • Krystyna Dzierzbicka
    • Kowalski Szymon
    • Sebastian Demkowicz
    • Mateusz Daśko
    • Iwona Inkielewicz-Stępniak
    2022 Full text JOURNAL OF ENZYME INHIBITION AND MEDICINAL CHEMISTRY

    In this work, we designed, synthesised and biologically investigated a novel series of 14N- and O-phosphorylated tacrine derivatives as potential anti-Alzheimer’s disease agents. In the reaction of 9-chlorotacrine and corresponding diamines/aminoalkylalcohol we obtained diamino and aminoalkylhydroxy tacrine derivatives. Next, the compounds were acid to give final products 6–13 and 16–21 that were characterised by 1H, 13 C, 31P NMR and MS. The results of the docking studies revealed that the designed phosphorus hybrids, in theory can bind to AChE and BChE. All compounds exhibited significantly lower AutoDock Vina scores compared to tacrine. The inhibitory potency evaluation was performed using the Ellman’s method. The most inhibitory activity against AChE exhibited compound 8 with an IC50 value of 6.11nM and against BChE 13 with an IC50 value of 1.97 nM and they were 6- and 12-fold potent than tacrine. Compound 19 showed the lack of hepatocytotoxicity in MTT assay.

  • Design, synthesis, and biological evaluation of tetrahydroquinolinones and tetrahydroquinolines with anticancer activity
    • Małgorzata Ryczkowska
    • Natalia Maciejewska
    • Mateusz Olszewski
    • Milena Witkowska
    • Sławomir Makowiec
    2022 Full text Scientific Reports

    Colorectal cancer (CRC) is the most commonly diagnosed cancer in Europe and the United States and the second leading cause of cancer related mortality. A therapeutic strategy used for the treatment of CRC involves targeting the intracellular levels of reactive oxygen species (ROS). In this study, we synthesized a series of novel tetrahydroquinolinones and assessed their ability to inhibit CRC growth and proliferation by evoking cellular stress through ROS. Our results revealed that (2-oxo-4-phenyl- 5,6,7,8-tetrahydroquinolin-8-yl) N-(3-fluorophenyl)carbamate (20d) exhibited in vitro antiproliferative activity at micromolar concentrations. The compound also suppressed colony formation and the migration of HCT-116 cells, as well as deregulated the expression of several proteins involved in cell proliferation and metastasis. Furthermore, 20d induced massive oxidative stress by disrupting the balance of cells survival resulting in autophagy via the PI3K/AKT/mTOR signaling pathway. These findings suggest that this tetrahydroquinolinone can be an ideal lead compound for drug discovery based on quinone derivatives.

  • Desulfurization of raw naphtha cuts using hybrid systems based on acoustic cavitation and advanced oxidation processes (AOPs)
    • Elvana Cako
    • Reza Darvishi
    • Xun Sun
    • Grzegorz Boczkaj
    2022 Full text CHEMICAL ENGINEERING JOURNAL

    A combination of dual-frequency acoustic cavitation (acoustic cavitation) and UV assisted advanced oxidation processes (AOPs) reaction system was developed for desulfurization of raw naphtha used to produce aviation fuels. Various types of oxidants in hybrid systems including hydrogen peroxide, acetic acid, acetone, air and ozone were compared. At optimum oxidant to sulfur compounds molar ratio (rox) of 5.0, the hybrid process of acoustic cavitation /acetic acid/hydrogen peroxide (acoustic cavitation/peracetic acid) was the most effective treatment process with synergistic index of 7.55 and desulfurization efficiency of 100% (highest reaction rate constant of 0.1337 min-1) for all sulfur compounds present in naphtha within the short reaction time of 30 min. At rox of 0.5 and 1.0, the synergy coefficients of 3.77 and 5.41 corresponding to the desulfurization efficiencies of 93.07 and 95.10% were obtained in 180 min, respectively. Comparatively, at the rox of 5.0, the efficiency of acoustic cavitation combined with hydrogen peroxide alone and acetic acid alone was 63.68 and 47.36%, respectively. Alternative treatment process of acoustic cavitation /UV/acetone/water can be used for the complete desulfurization (100%) of specific sulphur compounds including dibutyl sulfide, di-tert butyl disulfide, 1,4-butanedithiol and benzyl thiol considering the optimum acetone to water ratio of 2:1. All acoustic cavitation-based treatment systems followed the pseudo first order kinetic model. The most expensive process was ozone-aided acoustic cavitation with treatment costs exceeding 100 USD m-3. The peracetic acid-based system was the most economic process with a treatment cost of 15 USD/m3 with electric energy consumption of 100.17 kWh/m3.

  • Detection and removal of priority substances and emerging pollutants from stormwater: case study of the Kołobrzeska collector, Gdańsk, Poland
    • Jakubowicz Paweł
    • Karolina Fitobór
    • Magdalena Gajewska
    • Małgorzata Drewnowska
    2022 Full text Sustainability

    Progressive urban development affects environmental balance and disrupts the hydrologic cycle, in which rainfall plays a significant role. Since rainwater is considered a valuable resource of the environment, many technical solutions are implemented that enable effective rainwater management. On the other hand, stormwater runoff from urban areas contains numerous (also toxic) substances, and therefore should be properly treated. In this study, a multistage constructed wetland (MCW) pilot installation was used to remove selected groups of priority substances and emerging pollutants from rainwater discharged from the urbanized catchment of the Kołobrzeska stormwater collector in Gdańsk, Poland. The obtained results show that rainwater runoff was characterized by a variable concentrations of heavy metals (Zn, Cd, Cu, Ni, Pb, Hg), polycyclic aromatic hydrocarbons (benzo(a)pyrene, benzo(b)fluoranthene, phenanthrene, fluoranthene and pyrene) and microplastics. Depending on the hydraulic load of the bed, the reduction efficiency for heavy metals ranged from 26.19 to 100%, and for microplastics from 77.16 to 100%, whereas for polycyclic aromatic hydrocarbons it was consistently high, and equaled 100%.

  • Detection of anomalies in bee colony using transitioning state and contrastive autoencoders
    • Tymoteusz Cejrowski
    • Julian Szymański
    2022 Full text COMPUTERS AND ELECTRONICS IN AGRICULTURE

    Honeybees plays vital role for the environmental sustainability and overall agricultural economy. Assisting bee colonies within their proper functioning brings the attention of researchers around the world. Electronics systems and machine learning algorithms are being developed for classifying specific undesirable bee behaviors in order to alert about upcoming substantial losses. However, classifiers could be impaired when used for general honeybee colony state inference. Application of the classifier models for the hazardous situations detection without focusing on the model’s genericity could result with systems that are not applicable in the real environment. Furthermore, the detection of a specific phenomenon does not provide researchers with any new conclusions about the honeybee colony life but only with the binary information about hazardous situation presence. In our research we propose a method for inferring the bee colony state using a sensitive contrastive autoencoder and an anomaly detection model. With presented approach, hive’s internal state is modeled with the use of an autoencoder’s latent vector extended with in-hive temperature dynamics. We test our methodology with a bee feeding experiment where the glucose syrup application was detected and the length of food intake was estimated. As our methodology has been applied successfully, we argue that contrastive autoencoders can be used for precise inference about the behavior of honeybees.

  • Detection of Anomalies in the Operation of a Road Lighting System Based on Data from Smart Electricity Meters
    • Tomasz Śmiałkowski
    • Andrzej Czyżewski
    2022 Full text ENERGIES

    Smart meters in road lighting systems create new opportunities for automatic diagnostics of undesirable phenomena such as lamp failures, schedule deviations, or energy theft from the power grid. Such a solution fits into the smart cities concept, where an adaptive lighting system creates new challenges with respect to the monitoring function. This article presents research results indicating the practical feasibility of real‐time detection of anomalies in a road lighting system based on analysis of data from smart energy meters. Short‐term time series forecasting was used first. In addition, two machine learning methods were used: one based on an autoregressive integrating moving average periodic model (SARIMA) and the other based on a recurrent network (RNN) using long short‐term memory (LSTM). The algorithms were tested on real data from an extensive lighting system installation. Both approaches enable the creation of self‐learning, real‐time anomaly detection algorithms. Therefore, it is possible to implement them on edge computing layer devices. A comparison of the algorithms indicated the advantage of the method based on the SARIMA model.

  • Determinants and effects of Poland’s road accidents in the context of the 2030 agenda for sustainable development – poviat level analysis for the years 2010-2019
    • Aleksandra Romanowska
    • Sylwia Pangsy-Kania
    • Marcin Budzyński
    • Katarzyna Wierzbicka
    • Joanna Prystrom
    2022 Full text Ekonomia i Środowisko

    The objective of the research was to assess how selected factors influence road safety in Poland’s poviats. To that end, an analysis was conducted of road accident determinants and effects in the poviats in the years 2010-2019. The time horizon fits in with Goal 3.6. of Agenda 2030, which is to halve the number of global deaths and injuries from road traffic accidents by 2020. The article pres-ents the analysis results for the following determinants: the rate of car ownership by poviat, poviat spending on transport and length of the road network, and quality of road infrastructure. The research problem was to establish which of the poviats are closest to achieving Goal 3.6. of Agenda 2030 and how likely it is, and, as a consequence, which of the poviats should step up their road safety policies to align them to the targets set out in the Agenda. To identify groups of poviats sharing similar character-istics, they were grouped using the k-means method. Five groups of poviats were identified and analysed for how their road safety indicators changed between 2010 and 2019. The results of the analysis show that the highest fatality reduction (-40%) was achieved by urban poviats with the highest per capita spending on transport. The same poviats, however, have the highest increases in serious inju-ries (+30%). The analyses show that Polish poviats are still far from achieving Goal 3.6 of Agenda 2030. The research results presented in the article are original for the poviat level

  • Determinants of Directionality and Efficiency of the ATP Synthase Fo Motor at Atomic Resolution
    • Antoni Marciniak
    • Paweł Chodnicki
    • Kazi Hossain
    • Joanna Słabońska
    • Jacek Czub
    2022 Full text Journal of Physical Chemistry Letters

    Fo subcomplex of ATP synthase is a membrane-embedded rotary motor that converts proton motive force into mechanical energy. Despite a rapid increase in the number of high-resolution structures, the mechanism of tight coupling between proton transport and motion of the rotary c-ring remains elusive. Here, using extensive all-atom free energy simulations, we show how the motor’s directionality naturally arises from the interplay between intraprotein interactions and energetics of protonation of the c-ring. Notably, our calculations reveal that the strictly conserved arginine in the a-subunit (R176) serves as a jack-of-all-trades: it dictates the direction of rotation, controls the protonation state of the proton-release site, and separates the two proton-access half-channels. Therefore, arginine is necessary to avoid slippage between the proton flux and the mechanical output and guarantees highly efficient energy conversion. We also provide mechanistic explanations for the reported defective mutations of R176, reconciling the structural information on the Fo motor with previous functional and single-molecule data.

  • Determinants of judges’ career choices and productivity: a Polish case study
    • Przemysław Banasik
    • Katarzyna Metelska-Szaniawska
    • Małgorzata Godlewska
    • Sylwia Morawska
    2022 Full text European Journal of Law and Economics

    The goal of this paper is to identify factors which affect judges’ productivity and career choice motives with the view of increasing judicial efficiency. Specifically, the investigation focuses on such aspects as judges’ remuneration, promotion, threat of judgment revocation, service/mission, periodic assessment, the threat of a complaint about protracted proceedings or of disciplinary proceedings, the threat of destabilization of the employment relationship, status/prestige of the profession, power/authority, social recognition, leisure, as well as administrative supervision and self-monitoring. To this end, a survey was conducted among judges of three of the largest Polish regional courts and subordinate district courts. The descriptive and statistical analyses show that judges’ care for the number of cases resolved, proxying for their productivity, is significantly correlated with self-monitoring of their adjudication activity. The stability of employment, the status/prestige of the profession and a relatively high remuneration are the most important factors in terms of judges’ career choices. In their care for the number of cases resolved remuneration is, albeit, no longer a relevant factor. Judges monitor their productivity due to reasons other than remuneration, possibly the sense of service/mission and the threat of various adverse consequences, the evidence for which is, however, also rather weak.

  • DETERMINANTY (NIE)PRZEJRZYSTOŚCI FINANSÓW SAMORZĄDOWYCH
    • Maria Jastrzębska
    2022 Full text Optimum. Studia Ekonomiczne

    Cel – Celem artykułu jest identyfikacja determinant przejrzystości finansów samorządowych oraz wskazanie, które z nich pozytywnie i negatywnie oddziałują na jej poziom, ze szczególnym uwzględnieniem sytuacji w Polsce. Metody – Artykuł ma charakter teoretyczny, jest oparty na przeglądzie literatury przedmiotu z zakresu ekonomii i finansów, organizacji i zarządzania oraz socjologii. Wykorzystano metodę analizy deskryptywnej oraz komparatywnej. Wyniki – Rola sprawozdawczości jednostki samorządu terytorialnego jako źródła użytecznej informacji oraz przepływ informacji o stanie finansów samorządowych i stanie majątku komunalnego między władzą samorządową a mieszkańcami są ograniczone. Częste zmiany regulacji prawa finansów samorządowych zwiększają ich nieprzejrzystość. Centralizacja finansów publicznych zmniejsza samodzielność finansową samorządu terytorialnego i negatywnie wpływa na przejrzystość jego finansów. Oryginalność/wartość/implikacje/rekomendacje – Badania w zakresie oceny przejrzystości finansów samorządowych w Polsce są podejmowane rzadko. W niniejszym artykule zwrócono uwagę na podejście podażowe i popytowe do przejrzystości finansów samorządowych. Zidentyfikowano determinanty przejrzystości finansów jednostek samorządu terytorialnego w ich otoczeniu dalszym (makrootoczeniu): społeczno-kulturowe, polityczno-prawne, ekonomiczne oraz w otoczeniu bliższym (mikrootoczeniu): instytucjonalne.

  • Determination of Changes in Viscosity of Hydrogel Depending on Shear Rates
    • Szymon Mania
    • Robert Tylingo
    • Katarzyna Kozłowska-Tylingo
    2022 Full text

    The datasets entitled Determination of changes in viscosity of hydrogel depending on shear rate contain the results of viscosity measurements using a Brookfield viscometer, with different kinds of spindles and shear rates. The data allowed the used hydrogel preparations to be characterised and their functional parameters, as substances modifying the rheology of thickeners and determining the effect of shear rate on the viscosity of hydrogels, to be assessed.

  • Determination of Heavy Metals Concentration in Water and Soil at Various Locations in Lahore and their Harmful Impacts on Human and Plants life
    • Ayesha Noreen
    • Sajid Hussain
    • Umar Farooq
    • Younas Tasaddaq
    • Rahid Khan
    • Gamal Mohamed
    2022 Full text Pakistan Journal of Medical & Health Sciences

    Heavy metals poisoning of soil and water has resulted from industrial expansion in Lahore, Pakistan, creating a significant environmental hazard. As a result, monitoring the contamination of soil and water around industrial sites is critical. The fact that higher concentrations of heavy metals have a negative influence on both plants and human life and this cannot be ignored. Higher heavy metal concentrations have a direct impact on human health due to their presence in drinking water. Consumable plants and vegetables cultivated in these polluted areas may collect higher concentrations of heavy metals from soil and water via the phytoremediation process. Its worth mentioning that the accumulation of toxic metals in edible plants and vegetables also has a direct negative impact on human and animal health. The purpose of this study is to find the heavy metals concentration in the soil and ground water in the Lahore area. Five industrial zones were evaluated for water and soil throughout the research period of December 2021 to January 2022 (pre-monsoon). pH and heavy metals content measurements were performed on the collected soil and water samples. We discovered that the water had a higher pH and that the soil was heavily contaminated with significantly higher concentrations of toxic heavy metals. According to the research, there is a gangrenous influence of pollution caused by industrial waste and the surrounding environment on soil and water resources, which affects living creatures.

  • Determination of Odor Air Quality Index (OAQII) Using Gas Sensor Matrix
    • Dominik Dobrzyniewski
    • Bartosz Szulczyński
    • Jacek Gębicki
    2022 Full text MOLECULES

    This article presents a new way to determine odor nuisance based on the proposed odor air quality index (OAQII), using an instrumental method. This indicator relates the most important odor features, such as intensity, hedonic tone and odor concentration. The research was conducted at the compost screening yard of the municipal treatment plant in Central Poland, on which a self-constructed gas sensor array was placed. It consisted of five commercially available gas sensors: three metal oxide semiconductor (MOS) chemical sensors and two electrochemical ones. To calibrate and validate the matrix, odor concentrations were determined within the composting yard using the field olfactometry technique. Five mathematical models (e.g., multiple linear regression and principal component regression) were used as calibration methods. Two methods were used to extract signals from the matrix: maximum signal values from individual sensors and the logarithm of the ratio of the maximum signal to the sensor baseline. The developed models were used to determine the predicted odor concentrations. The selection of the optimal model was based on the compatibility with olfactometric measurements, taking the mean square error as a criterion and their accordance with the proposed OAQII. For the first method of extracting signals from the matrix, the best model was characterized by RMSE equal to 8.092 and consistency in indices at the level of 0.85. In the case of the logarithmic approach, these values were 4.220 and 0.98, respectively. The obtained results allow to conclude that gas sensor arrays can be successfully used for air quality monitoring; however, the key issues are data processing and the selection of an appropriate mathematical model.

  • Determination of phenylbutazone, sulfamethazine, carbendazim and linuron using a novel pine bark biosorbent for solid-phase extraction (SPE) with high-performance liquid chromatography (HPLC)
    • Hassen Khazri
    • Grzegorz Boczkaj
    • Ibtissem Ghorbel-Abid
    • Malika Trabelsi-Ayadi
    2022 INSTRUMENTATION SCIENCE & TECHNOLOGY

    The paper presents a novel pine bark based biosorbent for solid-phase extraction (SPE). The morphology and composition of the pine bark were characterized using Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The biosorbent was used for the preparation of wastewater for the determination of phenylbutazone, sulfamethazine, carbendazim, and linuron by high performance liquid chromatography with ultraviolet detection (HPLC-UV). The SPE conditions were optimized with respect to elution solvent, sample volume, and extraction pH. The results showed that developed sorbent provides good repeatability. The relative standard deviation (n = 3), was between 0.3 and 2.2%. The limits of detection (LOD) were between 0.11 and 0.4 µg.L−1. The developed method was used for determination of the analytes in effluent from a wastewater treatment plant.

  • Determination of stepped plate thickness distribution using guided waves and compressed sensing approach
    • Beata Zima
    2022 Full text MEASUREMENT

    Guided waves recently have attracted significant interest as a very promising research area. The signals registered by a specially designed sensor network are processed to assess the state of the tested structure. Despite the constant development of novel damage detection algorithms employing guided waves, the phenomenon of wave propagation still needs detailed recognizing and understanding for the further progress of non-destructive wave-based methods. Special attention is paid to guided waves in plate-like structures, but the majority of considered cases concern plates with constant thickness. However, in the real world, we often deal with specimens with variable thickness. The thickness variability of the specimen is often forced to fulfill the construction requirements and optimize stress distribution or is the result of degradation i.e. corrosion. Thus, the development of NDT methods forces the need of considering specimens with complex geometry and the problem of wave propagation in waveguides with variable thickness is crucial for improving novel as well as so far proposed algorithms. The article presents the results of the analytical, numerical and experimental analysis of wave propagation in plates with variable thickness. The analysis concerns the influence of thickness distribution of plate structure on wave velocity, the time course wave packet and amplitude. Moreover, the novel approach based on constrained convex optimization for determining the plate thickness distribution has been proposed and verified during numerical and experimental campaigns.

  • Determination of vertical displacements by using the hydrostatic levelling systems with the variable location of the reference sensor,
    • Waldemar Kamiński
    2022 Full text Archives of Civil Engineering

    Abstract: In this paper, the author proposed a new method for determination of vertical displacements with the use of hydrostatic levelling systems. The traditional method of hydrostatic levelling uses a rule in which a position of reference sensor is stable. This assumption was not adapted in the proposed method. Regarding the issue mentioned above, the reference sensor is treated in the same way as the others sensors that measure the liquid level. As a consequence of this approach there is a possibility of vertical displacement determination of both the reference sensor as well as the remaining controlled sensors. A theoretical considerations were supplemented with the practical examples. The possibility of calculating the vertical displacement of reference sensor is an undoubted advantage of the submitted proposal. This information enables more detailed interpretation of the vertical displacements results obtained from hydrostatic levelling systems. Thus, wider knowledge about maintenance of the entire examined object treated as the rigid body is obtained. The tests that were carried out confirm the theoretical assumptions and encourage to perform further, more precise empirical analyses.