This paper presents mathematical modelling and numerical analysis to evaluate entropy generation analysis (EGA) by considering pressure drop and second law efficiency based on thermodynamics for forced convection heat transfer in rectangular duct of a solar air heater with wire as artificial roughness in the form of arc shape geometry on the absorber plate. The investigation includes evaluations of entropy generation, entropy generation number, Bejan number and irreversibilities of roughened as well as smooth absorber plate solar air heaters to compare the relative performances. Furthermore, effects of various roughness parameters and operating parameters on entropy generation have also been investigated. Entropy generation and irreversibilities (exergy destroyed) has its minimum value at relative roughness height of 0.0422 and relative angle of attack of 0.33, which leads to the maximum exergetic efficiency. Entropy generation and exergy based analyses can be adopted for the evaluation of the overall performance of solar air heaters.

The sedimentary environment, sediment characteristics and age−depth models of sediment sequences from Arctic lakes Revvatnet and Svartvatnet, located near the Polish Polar Station in Hornsund, southern Svalbard (77 ° N), were studied with a view to establishing a basis for paleolimnological climate and environmental reconstructions. The results indicate that catchment−to−lake hydroclimatic processes probably affect the transportation, distribution and accumulation of sediments in different parts of lakes Revvatnet and Svartvatnet. Locations with continuous and essentially stable sedimentary environments were found in both lakes between water depths of 9 and 26 m. We used several different dating techniques, including 137 Cs, 210 Pb, AMS 14 C, and paleomagnetic dating, to provide accurate and secured sediment chronologies. A recovered sequence from the northern basin of Revvatnet spans more than one thousand years long with laminated stratigraphy in the upper part of the sediment. Based on AMS 14 C dates, it is possible to suppose that Revvatnet basin was not occupied by a valley glacier during the Little Ice Age. The dates were supported by 137 Cs chronologies, but not confirmed with other independent dating methods that extent beyond the last 50 years. A sedimentary sequence from the northern basin of Svartvatnet provides a potential archive for the study of climate and environmental change for the last ca. 5000 years. Based on the stratigraphy and a Bayesian age−depth model of AMS 14 C and paleosecular variation (PSV) dates, the recovered sediment sections represent a continuous and stable sedimentation for the latter half of the Holocene.

The Covid-19 pandemic is having an unprecedented impact on health systems, on many economic sectors and on the labour market. This critical situation is also accompanied by social destabilisation, which has exacerbated inequalities and severely affected the most disadvantaged population groups, such as migrant workers. This study provides insights into the consequences of the first wave and the lockdown period in Spring 2020 of the Covid-19 pandemic on Romanians living in Italy, using data collected by the International Association Italy-Romania ‘Cuore Romeno’, within a project financed by the Romanian Department for Di-aspora and developed to support actions while strengthening the link with Romanian institutions during the pandemic. Findings show that, during the lockdown, two opposite situations occurred among Romanians. Workers in the ‘key sector’ become indispensable and experienced only small changes, while others lost their job or experienced a worsening of working conditions, with lower wages or an increase in working hours. Most workers chose to stay in Italy, relying on their savings or the support of the Italian government. Job losses, not having new employment, and having limited savings all influenced the decision of a smaller group to return to Romania. In conclusion, the analysis suggests that measures adopted should take into consider-ation that the Covid-19 pandemic might disproportionally hit population groups such as migrants, women, young people and temporary and unprotected workers, particularly those employed in trade, hospitality and agriculture.

The rapid development of the global economy has led to an increasing demand for resources. The disparity between the supply and demand of resources continues to be prominent and shows a situation of short supply. Resource investment projects with large amounts and long construction periods face many risks due to various unpredictable factors. Cultural, legal, economic and other environments vary between different countries. Therefore, comprehensive risk identification, understanding, evaluation, and analysis are important prerequisites for the success of mineral investment. In this paper, the risk of mineral resources investment in host countries is identified. A risk evaluation index system is established to objectively evaluate the risk environment of the host country. The risk evaluation index system includes four first-level indexes: political and legal risk, social and cultural risk, economic and financial risk, and natural risk. The subjective weight was determined by sending questionnaires to experts and scholars in the industry and conducting data processing. The entropy method was used to determine the objective weight. Finally, the subjective weight and the objective weight were combined to obtain a group of scientific and accurate combined weights. The matter-element theory was introduced into the cloud model and a risk assessment model based on the cloud matter-element theory was constructed with comprehensive consideration of the fuzziness and randomness of risks. Eight countries with relatively rich mineral resources were taken as cases to verify the model application. The research results provide a theoretical basis and decision-making methods for mineral enterprise investment.

The two dimensional steady and unsteady flow field at midspan in a low speed axial flow compressor stage has been investigated experimentally, using two systems, based on totally different principles: a 2-sensor fast response straight and 90° triple split fiber probes (TSFP) and two dimensional LOA system with an emphasis on the interaction of the inlet guide vane (IGY) wake with the rotor flow field. To account for the uniformity of the rotor absolute inlet flow field, measurements has been made at eight tangential locations in the absolute frame equally spaced over one IGY pitch. The time resolved investigation, done by TSFP and LOA allows to presenting velocity fields, flow angles and turbulence data at different [GY-rotor positions during one blade passing period. The velocity measurements are decomposed into a time averaged velocity, a periodic velocity component and a unresolved velocity component. Using two measurement systems, one being intrusive and the other non-intrusive, in the same complex flow field, gives the opportunity for a critical comparison of results and opens the view for further improvements. Averaging these results, enabled also comparison with the pneumatic five-hole probe measurement.

This part of the paper presents particular case of Msplit estimation called a squared Msplit estimation whose target function is based on convex squared functions. One can find here theoretical foundations and algorithm of the squared Msplit estimation as well as some numerical examples.

Dealing with risk and addressing risk consequences constitute indispensable and specific elements of every business activity. The aim of this paper has been to assess the level of risk connected with the process of exploitation of hard coal deposits used for the production of coke in Poland, that is why a methodology has been developed which takes into account the impact of significant risk factors resulting from both geological and mining conditions upon unit cost of coal mining. This methodology constitutes a comprehensive approach to sustainable management of hard coal resources. The key source of information pertaining to exploitation risk factors is the digital geological model of hard coal deposit which has been developed. It comprises a structural model as well as a quality model of the basic quality parameters of coal. Structural models and coal quality models have been developed on the basis of litho-stratigraphic profiles from geological exploratory boreholes and underground observations (boreholes drilled from underground workings and their profiling). The structural grid model also contains information on tectonic disturbances (faults) or sedimentation disturbances (intercalations, wash-outs, and the like). The digital model was used as the basis for devising time schedules of development and preparatory works, as well as coal extraction proper. Historical results of mining and economic data from 81 longwalls mined in the years 2016–2022 have been used for the purpose of analysis of the impact of risk factors on unit operating costs. The analysis comprised a total of 23 criteria which influence the costs of mining. From that group, 10 risk factors have been selected by means of statistical analysis using segmented regression, these factors have been utilized to make an assessment of the forecast concerning risk factor level for zones of the deposit meant for mining until the year 2035. The risk factors taken into account were those which are due to natural hazards, geological structure of the deposit (coal seam) and technical limitations. Risk factor (RF) indicator has been developed, for its construction the Fuzzy Analytic Hierarchy Process (FAHP ) has been used. The value of RF, which expresses the aggregated form of variability concerning individual factors pertaining to geology and mining, has been used to determine the adjusted own risk assessment when estimating the economic efficiency of the coking coal deposit for 8 exploitation zones with the use of discounted cash flow method. The assessed average value of RF for the entire deposit amounted to 0.29. The lowest level of RF was noted in case of zone W (RF = 0.17), whereas the highest value of risk occurs in zone PN (RF = 0.64). The values of RF were used to calculate the rate of discount as consolidated measure of own risk, when assessing investment projects in mining. For zone W with the lowest risk of mining the discount rate amounts to 8.34%, whereas in case of zone PN which has the highest risk level, it amounts to 15.02%. Assessing the level of mining risk provides the possibility to optimize the cost of mining, and may be utilized for making decisions concerning the sequence and time of mining from particular zones of the deposit.