The biofiltration process in the biologically activated carbon filters (BAC) is one of advanced methods of water treatment. It enables efficient elimination of dissolved organic matter and some inorganic pollutants. The production of high-quality drinking water requires an appropriate method of filter work control based on biofilm growth assessment. The first aim of the study was to assess the microbial development in beds of two BAC filters with the use of various methods. The second aim was to compare the obtained results and indicate the method which could support filter operators during routine control of biofiltration process. The study was carried out in a pilot scale on models of BAC filters during two filter runs. The analysis of Microorganisms was performed in water samples collected from different depths of the filter beds with the use of culture method (HPC), metabolica ctivity assay (with the FDA), epifluorescence microscopy – total cell count method (TCC) and biochemical method (system Vitek 2 Compact). No statistical correlation between HPC and metabolic activity assay was noted. Total bacteria number determined with the use of TCC was approx. 100–900 times higher than in the HPC method. The biochemical tests revealed the presence of several Gram-negative species. The comparison of the applied methods shows that microbial activity assay is the most useful, fast and low-cost method which may be applied additionally to the HPC method at standard water treatment plant laboratory.

In the future, medical students will be rewarded for knowing how to access information in real time and find the solution to the problem confronting them. The key role of medical school faculty will be to teach them how to do so - says Darrell G. Kirch.

The following paper presents the process of decarbonization of the energy sector in Greece and points out to different methods the Greek authorities are adopting in order to reduce the emission of greenhouse gases generated by electricity production. Greece is a country which is modernizing its energy sector gradually, yet dynamically. One of the prime aims is to reduce the level of energy produced in coal-fired power plants by focusing on the renewable energy and the gas sector. In 2010 still more than half of the electrical energy was generated by lignite-fired power plants. Almost ten years later the ratio has dropped to only slightly more than 30%. A significant reduction in coal consumption was possible thanks to investments in renewable energy sources, especially in the wind and solar energy sectors. Both sectors have seen a large increase in production, making renewable energy sources already accounting for over 20% of Greek electricity production. Capital-intensive investments were also made in the country’s gas supply through the expansion of gas-fired power plants and gas transmission networks. As a result, natural gas remains the main source of energy for Greece next to coal. Unfortunately, a big challenge in terms of decarbonization is the need for increased imports of electricity from abroad, due to the insufficient capacity of the Greek energy sector. Therefore, the main purpose of this paper is to define a Greek model of decarbonization and to point out to its benefits and dangers. Greek strategy might serve as an example of how to successfully solve the energy issues in the countries with similar energy profile.

The authors draw on their experience and past mountain landscape studies to describe an emerging collaborative research project designed to conduct advanced field studies and generate (and test) archaeological landscape models of past hunter-gatherer populations as well as pastoralist and early farming community seasonal transhumance migrations between lowland river valleys of Poland’s Podhale Basin and high altitude forests and meadows its adjacent High Tatra Mountains.

At present, electromobility is a very dynamically developing segment and at the same time has many unknowns that enterprises that want to develop this area in their structures have to face. This article aims is to show the difficulties of electromobility development from the perspective of Polish energy groups which are closely related to this area, especially considering the obligations imposed on energy companies by the legislator. The electrification of transport has become a reality and in order to use its potential to develop new services or implement innovations and new technologies, it is necessary to identify development barriers and prepare a response plan. The authors of the article decided to show the formal and legal implications for the development of electromobility in Poland in first order, and then examine the development strategies of Polish energy groups in terms of electromobility and indicate explored areas related to it. The next section focuses on identifying the main barriers to the implementation of business models, classifying them according to the following factors: economic, operational, technical, social and legal. This presentation of the problem allows for an in-depth recognition of the issue and realizing that in order to achieve the goals set by the Legislator, close cooperation of all stakeholders is necessary both at the national and local level, while engaging energy groups, financial companies, electric vehicle manufacturers, and above all local government units in these activities.

This paper summarizes the arguments and counterarguments within the scientific discussion

on developing the free-carbon economy in Ukraine. The main purpose of the paper is elaborating

the energy efficiency profile of Ukraine to assure the development of the free-carbon economy. To

achieve this purpose, the authors carried out an investigation in the following logical sequence.

Firstly, the bibliometric analysis of 4674 of the most cited articles indexed by the Scopus database

was conducted. The obtained findings indicated that the green economy transformation depended

on the main factors such as economic performance, corruption, macroeconomic stability, social

welfare, shadow economy etc. As a result, the forecast of the final energy consumption to 2030

was performed. The methodological tool of this research is based on the Autoregressive Integrated

Moving Average (ARIMA) model. This study involved data of the Visegrad countries (Poland, the

Czech Republic, the Slovak Republic and Hungary) and Ukraine from 2000 to 2018. The base of

data is Eurostat, the EU statistical service. Based on the obtained results of analyzing the green

economic transformation in the Visegrad countries and Ukraine, the authors intimated the existence

of the significant energy-efficient gap in Ukraine compared to the analyzed countries. In reliance on

the experience of the Visegrad countries and the forecast results, the authors provided the main recommendations

for providing the green transforming in Ukraine. The authors highlighted that the obtained

results of this paper were considered to be the base for future investigations considering the influence

of endogenous and exogenous factors on developing the free-carbon economy in Ukraine.

In Poland, there is a growing awareness of the need to change the sources of electricity and heat. An expression of this is the adoption of the document entitled Poland’s Energy Policy until 2040 (PEP 2040) in February 2020 by the Council of Ministers. The goal of the Polish Energy Policy until 2040 is “energy security – ensuring the competitiveness of the economy, energy efficiency and reducing the environmental impact of the energy sector – taking into account the optimal use of own energy resources”. In PEP 2040, the previous assumptions of the state’s long-term energy policy were amended and an increase in the use of low- or non-emission sources was declared. In addition, the energy policy guidelines contain forecasts for the production of steam coal and the demand for this raw material. Based on the provisions of the document, as well as forecasts of the coal-production volume prepared by the authors and the assessments of experts in the fields related to energy and mining, the article contains considerations on the validity of the developed forecasts together with the determination of the production capacity of domestic mining enterprises in terms of covering the demand for steam coal used for the production of electricity and heat. It is planned, inter alia, that blocks of coal-fired power plants will be decommissioned and, in their place, there is to be the expansion of solar and wind energy and the commissioning of the first blocks of a nuclear power plant. Such activities, which cause a decrease in the demand for coal, are also related to the plans of changes in the functioning of mining enterprises – there will be successive closures of individual mines and mining plants.

The 2030 Agenda for Sustainable Development was adopted in 2015. The United Nations framework does not directly include raw materials in Sustainable Development Goals (SDGs). The mining industry has a great impact not only for the environment but also for its stakeholders, both from the nearest and the most remote surrounding. As such, the mining industry has the opportunity and potential to both positively and negatively impact on all seventeen SDGs. The introduction of the EU directive on the disclosure of non-financial data has a great impact on the reporting of sustainable development reporting. Additionally, in March 2020, the European Commission published the EU Taxonomy. With regard to the current geopolitical situation, some European Union members, such as Germany, France and the Netherlands, have taken the decision to open or re-open of their coal-fired plants. Admittedly, these countries underline that the inclusion of coal in their power industry is only temporary and limited to a well-defined period of time. The implementation of the SDGs should be partially important in the case of mining, the activities of which involve the extraction of various types of mineral resources, especially non-renewable resources. This raises two fundamental research questions; what is the actual level of the reporting of SDGs in the polish mining industry, and if the EU Taxonomy Regulations will increase the reporting of SDGs in Polish mining?

Natural resources and the extractive industries play a central role in the economy of developing countries and the lives of nearly half of the world’s population. The increasing demand for oil, gas, and mineral resources has led some countries to prioritize the extractive industries; yet, there is growing empirical evidence that in some cases governments have neglected other sectors of the economy, making them highly dependent and vulnerable to volatile commodity prices. Latin American countries face the challenge of changing their model of primary-export specialization and move away from their dependence on natural resource-intensive exports in order to avoid being vulnerable to commodity cycles. In this context, given the limited literature available on measuring the dependence on the extraction of oil, gas and minerals of the Ecuadorian economy, the objective of this article is to twofold. First, to provide a snapshot of the historical and current situation of Ecuador’s natural resource dependence. Second, to estimate the Extractives Dependence Index (EDI) scores for Ecuador for the years 2003 to 2017. The EDI is a generally accepted method for measuring a country’s aggregate dependence on natural and mineral resources. Based on the EDI scores obtained, we analyze the variation of this indicator and investigate the effect of extractives dependence on the Ecuadorian economy. Results show that despite the government’s significant efforts to diversify Ecuador’s economy, the country has a persistent dependence on the extractive sector.

Generation of coal-based electricity is always associated with the origination of large amount of combustion waste. The presented article is a review concerning the possibilities of innovative directions of management for one of the by-products of coal combustion: fly ash. The storage of these waste products is associated with their negative impact on the environment. This is why research has been undertaken worldwide on the implementation of the concept of a circular economy. This article includes the examination of basic physical, chemical, and mineralogical properties of the most valuable components of fly ash (microspheres, magnetic fraction, and glass). It contains the examination of methods of separating these components and indicates the prospective directions of their use, e.g. as light fillers for polymers, sorbents, catalysts, composite materials, light ceramics, lightweight concretes, thermal insulation materials, biomaterials, raw material for the synthesis of zeolites or geopolymers. The paper also presents the components of fly ash, which can be treated as an alternative source of valuable elements, including critical elements. Moreover, it points to the necessity of capturing flammable substances from combustion by-products in order to obtain raw material characterised by a high degree of purity. It has been demonstrated that this way of ash management can lead to high recycling rates and bring valuable materials back to the economy. Such actions fit perfectly into global efforts for sustainable development and the circular economy.

The paper presents multi-criteria optimization method allowing for selection of the best production scenarios in underground coal mines. We discuss here the dilemma between strategies maximizing economic targets and rational resources depletion. Elaborated method combines different geological and mining parameters, structure of the deposit, mine’s infrastructure constrains with economic criteria such as the net present value (NP V), earnings before deducting interest and taxes (EBIT ) and the free cash flows to firm (FCFF). It refers to strategic production planning. Due to implementation of advanced IT software in underground coal mines (digital model, automated production scheduling) we were able to identify millions of scenarios finally reduced to a few – the best ones. The method was developed and tested using data from mine operation “X” (a real project – an example of a coking coal mine located in Poland). The reliability of the method was approved; we were able to identify multiple production scenarios better than the one chosen for implementation in the “X” mine. The final product of the method were rankings of scenarios grouped according to economic decision criteria. The best scenarios reached NP V nearly 50% higher than the Base Case, which held only 52. position out of 60. According to EBIT and FCFF criteria, 10 scenarios achieved results higher than the Base Case, but the percentage differences were very small, below 2 and 4%, respectively. The developed method is of practical importance and can be successfully applied to many other coal projects.

Modelowanie obiektów rzeczywistości geograficznej, stanowiących geokomonenty, zasadza się na wyróżnieniu trzech składowych tych obiektów: geometrii, atrybutów i ich wartości. Uporządkowany zbiór elementarnych obiektów, zwanych tu topograficznymi, zawiera baza danych topograficznych, jako podstawowy komponent fizyczny systemu informacji topograficznej. Wizualizacja kartograficzna danych może odbywać się na trzech poziomach, związanych ze stopniem przetworzenia graficznego obrazu - od prezentacji danych nieprzetworzonych (szkieletowa), poprzez prezentację uproszczoną, do prezentacji pełnej, ukierunkowanej na spelniene wymogów percepcji wzrokowej. Przedmiotem zainteresowania jest tu poziom trzeci - prezentacja pełna, będąca najdalej przetworzonym obrazem mapy, powstającej wewnątrz systemu informacji topograficznej, jako modelu rzeczywistości. Przyjęto model znaku kartograficznego skonstruowany jako triada: nośnik, znaczenia, przdmiot, interpretant. Wskazano na rolę znaczenia, pozwalającego na poprawne odczytanie relacji semantycznych, pomiędzy nośnikiem znaczenia a obiektem rzeczywistości geograficznej. Znak kartograficzny składa się z dwóch zasadniczych typów elementów: konturów i wypełnień figur geometrycznych. W konstruowaniu znaku różnicowaniu podlegają atrybuty tych elementów, które określono jako komponenty graficzne znaku. Atrybuty te, zwane zmiennymi graficznymi, uporządkowano i scharakteryzowano na podstawie wyróżnień MacEachrena. Rozłączność nośników znaczenia warunkuje jednoznaczność odbioru treści mapy. Elementarnym warunkiem poprawnej prezentacji jest więc nie nakładanie się zakresów pojęciowych wizualizowanych obiektów. Na etapie klasyfikacji treści bazy danych dokonuje się wyróżnienia atrybutów obiektów topograficznych. Następnie należy wskazać relacje, które tym cechom odpowiadają i ujawnić odpowiedni poziom pomiarowy wartości cech. Każdej z tych relacji (w sensie ontologicznym) przyporządkowuje się zmienną graficzną i stosuje się ją w odniesieniu do komponentów graficznych konkretnego znaku. Obiekty zapisane w bazie danych jako obszary (platy płaszczyzny) mogą być prezentowane przez znaki powierzchniowe bądź punktowe. Redukcja wymiarów (również dla obiektów liniowych) może nastąpić na drodze uogólnienia strukturalnego lub w końcowym etapie prezentacji kartograficznej. Zestawiono własności nośników znaczenia, dzięki którym zagwarantowane będzie zachowanie tzw. szkieletu strukturalnego w prezentacjach graficznych. Pewien stopień uporządkowania odbioru grafiki mapy wprowadza pojęcie barwy nadrzędnej, przyporządkowanej kategoriom tematycznym poszczególnych geokomponentów. W artykule zawarto propozycję tych barw, wskazując jako najważniejsze odejście od prezentacji tzw. sytuacji w barwie czarnej. W zapewnieniu prawidłowej interpretacji znaku pomagać też powinna jego poglądowość, która jest pochodną izomorfizmu postaci. Przejawia się ona poprzez nawiązanie zmiennych graficznych komponentów znaku do fizjonomicznych cech obiektu, a także, zwłaszcza w odniesieniu do obiektów roślinnych, do rzeczywistego wyglądu tych obiektów na zdjęciach lotniczych. Sformułowano też wskazówki zapewniające taki dobór zmiennych graficznych, który zagwarantuje równowagę wizualną pomiędzy szczegółami prezentowanymi na mapie. Podreślając trwałość zapisu obrazu graficznego, a jednocześnie łatwość jego modyfikcji wskazano kierunki automatyzacji redakcji map topograficznych. Zaznaczono, iż mapa topograficzna, poprzez poprawnie skomponowany system znaków kartograficznych, ma poprawnie informować ale też ujawniać swoją estetykę.

The study presents results of the internal reliability analysis of structural modules used for the determination of horizontal displacement in incomplete trigonometric network. The influence of such elements as: number of control points, sight line length and arrangement of control points around the instrument station on reliability was analysed. Furthermore the analysis of the influence of diversification of reliability indices calculated for individual observations on the detection efficiency of non-dislocated control points was performed. The presented numerical example illustrates the possibility of incorrect valuation of control point stability because of a large diversification of reliability indices. The summary contains recommendations from the point of view of internal reliability for optimal designing of structural modules in incomplete trigonometric networks.

In the present study, we analyse the influence of goal maintenance and goal change on the efficiency of executive control. Although there is empirical evidence on the impact of goal maintenance and task-switching on executive control, little is known about the consequences of changing between processing goals (e.g., speed or accuracy goals). We assessed the influence of changing between speed and accuracy goals while performing a task-switching procedure that requires social categorization. Experiment 1 included frequent goal changes, whereas Experiment 2 included one goal change across the experimental session. The results showed that both goals influence general performance and flexibility. A comparison between experiments suggested that frequent goal change (Experiment 1) resulted in worse performance and lower flexibility overall, compared to sequential goal change (Experiment 2). Frequent goal change was also associated with increased difficulties in pursuing the accuracy goal. The implications regarding the role of goal maintenance and goal change on executive control are discussed, as well as new research possibilities.

Virtual reality (VR) technology now provides players with immersive and realistic experiences as never before. Spatial presence plays a crucial role in the introduction of immersive experience in a VR environment. Spatial presence is a special feeling of personal and physical presence in the displayed environment. In this study, we found that the first-person perspective (1PP) was more effective in raising the sense of spatial presence that induces immersive experience compared to the third-person perspective (3PP) in a VR shooting game. Moreover, eye blink rate was significantly higher in the 1PP compared with the 3PP. The 1PP game setting was more realistic than the 3PP setting, and may have raised participants’ sense of immersion and facilitated eye blink. These results indicate that eye blink rate is increased by the sense of spatial presence, and can be a good measure of subjective immersive experience in a VR environment. Neuroscientific evidences suggest that dopaminergic system is involved in such emotional experiences and physiological responses.

The issue of the educational system remains one of the crucial areas for the discussions pertaining to migrants’ integration and contemporary multicultural societies. Ever since the inception of compulsory schooling, children and youth have partaken in largely state-governed socialisation in schools, which provide not only knowledge and qualifications, but are also responsible for transferring the culture and values of a given society. Under this premise, the schooling system largely determines opportunities available to migrant children. This paper seeks to address the questions about the pathways to youth Polish migrant integration, belonging and achievement (or a lack thereof) visible in the context of the Norwegian school system. The paper draws on 30 interviews conducted in 2014 with Polish parents raising children abroad, and concentrates on the features of Norwegian school as seen through the eyes of Polish parents. Our findings show that the educational contexts of both sending and receiving socie-ties are of paramount importance for the understanding of family and parenting practices related to children’s schooling. In addition, we showcase the significance of Norwegian schools for children’s integration, illuminate the tensions in parental narratives and put the debates in the context of a more detailed analysis of the relations between school and home environments of migrant children. The paper relies on parental narratives in an attempt to trace and reflect the broader meanings of children’s education among Poles living abroad.

Ireland has become one of the main destination countries for Polish migrants after Poland’s EU accession in 2004. While much of the literature on Polish migration to Ireland post-2004 focuses on its labour-market element, in this paper we analyse the political participation of Polish migrants. We utilise data from a survey conducted by the Centre of Migration Research (University of Warsaw) with Polish migrants in Ireland which documents low levels of political engagement as measured by voting turnout in Polish presidential and parliamentary elections as well as the Irish local elections and elections to the European Parliament. A lack of knowledge about political participation rights or how to engage in voting is one explanation for the low levels of voting, especially in Irish local and European parliamentiary elections. Another explanation may be the attitude that migrants have towards the political system and how they can influence it. Polish migrants predominantly report that they have no or little influence on politics in Poland and have relatively less trust in the authorities and politicians there (compared to Ireland). The key individual-level characteristic affecting Polish migrant respondents’ electoral participation in Ireland is their (lack of) voting habit formed before migration.

This paper examines the Albanian state–nation constellation in the Balkans in the light of the European Union (EU) integration process with a focus on citizenship configurations in Kosovo and Albania. It addresses an important puzzle: why legal norms of citizenship do not follow the emerging practice of stronger trans-border co-operation in the Albanian ethnic and cultural space. The study shows that the process of EU integration is the key to understanding and explaining this puzzle, for it provides an opportunity for ‘constructive ambiguity’ around which both ethnic and statist brands of Albanian na-tionalism, as well as various elite fractions, can coalesce and coexist. In a wider context, Albanian citizenship configurations are shaped by the ever-evolving complex relationship between nation, state and Europe.

This article examines the changing migration projects of Central and Eastern European migrants in Northern Ireland. It sets out the context for settlement scheme applications, linking it to broader hostile environment pol-icies in the UK. It explores the dynamic nature of people’s migration projects and how these have been chal-lenged in the context of Brexit and the EU Settlement Scheme. The paper discusses the ruptures in migrants’ narratives in relation to how they envision their future in Northern Ireland and their countries of origin, with some moving towards indeterminacy and some searching for fixity/stability in their migration projects. It exam-ines how the Northern Irish context – and the question of the Irish border specifically – adds an additional layer of complexity to the migrants’ shifting future imaginaries. The paper draws on my covert research and in-depth interviews with CEE migrants, where consent was given retrospectively. It discusses the role of the researcher in cutting the covert/overt continuum and ethical dilemmas in the field.

Consumption of energy is one of the important indicators in developing countries, but a lot of companies from the energy sector have to cope with three key challenges, namely how to reduce their impact on the environment, how to ensure the low cost of the energy production and how to improve the system overall performance? For Polish energy market, the number of challenges is greater. The growing demand for electricity and contemporary development of nuclear power technology allow today’s design, implement new solutions for high energy conversion system low unit cost for energy and fuel production. In the present paper, numerical analysis of modular high-temperature nuclear reactor coupled with the steam cycle for electricity production has been presented. The analysed system consists of three independent cycles. The first two are high-temperature nuclear reactor cycles which are equipped with two high-temperature nuclear reactors, heat exchangers, blowers, steam generators. The third cycle is a Rankine cycle which is equipped with up to four steam turbines, that operate in the heat recovery system. The analysis of such a system shows that is possible to achieve significantly greater efficiency than offered by traditional nuclear reactor technology.

Solar photovoltaic power is widely utilized in the energy industry. The performance of solar panels is influenced by different variables, including solar radiation, temperature, wind speed, relative humidity and the presence of haze or dirt. Outdoor solar panels are particularly susceptible to a decrease in energy efficiency due to the accumulation of dust particles in the air, which occurs as a result of natural weather conditions. The extent of dust deposition is primarily determined by factors such as the tilt angle of the panel, wind direction, cleaning frequency as well as local meteorological and geographical conditions. The dust on the solar cell glazing reduces the optical transmittance of the light beam, causing shadowing and diminishing the energy conversion productivity of the panels. Sand storms, pollution levels and snow accumulations all significantly impact the photovoltaic panel performance. These circumstances reduce the efficiency of solar panels. The experiment was carried out on two identical dust-accumulated and dust-free panels. The evaluation was carried out in two different situations on the offgrid stand-alone system: in a simulated atmosphere and in an open space during the day. The current-voltage curves have been developed for both panels at various tilt degrees. The features provide sufficient information to analyse the performance of the panels under consideration. The measurements demonstrate that as dust collects on the panel’s surface, the average output power and short circuit current decrease dramatically. The installation tilt angle affected the ratio of efficiency and average power outputs of dusty and clean panels.

The presence of more than one solute diffused in fluid mixtures is very often requested for discussing the natural phenomena such as transportation of contaminants, underground water, acid rain and so on. In the paper, the effect of nonlinear thermal radiation on triple diffusive convective boundary layer flow of Casson nanofluid along a horizontal plate is theoretically investigated. Similarity transformations are utilized to reduce the governing partial differential equations into a set of nonlinear ordinary differential equations. The reduced equations are numerically solved using Runge-Kutta-Fehlberg fourth-fifth order method along with shooting technique. The impact of several existing physical parameters on velocity, temperature, solutal and nanofluid concentration profiles are analyzed through graphs and tables in detail. It is found that, modified Dufour parameter and Dufour solutal Lewis number enhances the temperature and solutal concentration profiles respectively.

The main source of spatial information on concentration and deposition of air pollutants in Poland is the continental scale EMEP model with 50 km x 50 km grid. The coarse resolution of the EMEP model may be insufficient for regional scale studies. A new proposal is the application of the national scale atmospheric transport model FRAME (Fine Resolution Atmospheric Multi-pollutant Exchange), originally developed for the United Kingdom. The model works with 5 km x 5 km spatial resolution and the air column is divided into 33 layers. FRAME was used here to assess the spatial patterns of yearly averaged air concentrations, and wet and dry deposition of sulphur and nitrogen compounds for the area of Poland. This study presents preliminary results of the modeling of the yearly average concentrations as well as dry and wet depositions of SO,, NO, and NH, for Poland. FRAME results were compared with available measurements from the monitoring sites and national deposition budget with the EMEP and IMGW estimates. The results show close agreement with the measured concentrations expressed by determination coefficient close to O. 7 for both SO, and NO . The dry and wet deposition budgets for FRAME are also in close agreement with the EMEP and GIOŚ estimates. The FRAME model, despite its relatively simple meteorological parameterizations, is well suited to calculate the spatial pattern of annual average concentration and yearly deposition of atmospheric pollutants which was earlier presented for the UK and was shown in this paper for Poland. The model can also be used to analyze the impact of individual point sources or different emission sectors on spatial pattern of air concentration and deposition as well as testing the changes in deposition resulting from future emissions reduction scenarios.

Noise reduction inside waveguide systems has gained momentum owing to a great interest in it. To attenuate the sound in a broad frequency range, this study aims to compare the effects of two acoustic liners, a perforated plate backed by an air cavity (PP-Air cavity), or by a porous material (PP-PM), on the acoustic behaviour of lined ducts using a numerical model to compute the multimodal scattering matrix. From this matrix, the reflection and the transmission coefficients are computed and therefore the acoustic power attenuation is deduced. Moreover, the effects of geometry of ducts with and without changes in the section are investigated. The numerical results are obtained for five configurations, including cases of narrowing and widening of a duct portion with sudden or progressive discontinuities. Accordingly, numerical coefficients of reflection and transmission as well as the acoustic power attenuation show the relative influence of acoustic liners in each type of configuration.