The main energy source in Poland is still hard coal and lignite. The coal combustion process produces large quantities of by-products, e.g. fly ashes, slag furnace and harmful chemical gases (CO2, NOx, sulfur compounds) which enter the atmosphere. Fly ashes, due to their being fine grained (cement-like), chemical and phase compound and reactivity, have also been widely used in various technological solutions e.g. in the production of ordinary cement, hydro-technical cement and the new generation of cements. The adequate amount of fly ashes additive has a positive effect on fresh and hardened cement slurry properties. What is more, it allows for the pro-ecological and economic production of cement mix The exploitation of natural resources is connected with performance mining excavations at different depths. After a certain period of time, those voids break down which, in turn, leads to the slip of upper layers and the so-called landslides forming on the surface. This situation imposes the necessity of basis and sealing rock mass reinforcement. To minimize the risk connected to geotechnical problems on the mining areas, there is a need to use engineering solutions which could improve soil bearing in a universal, economical and efficient way. This leads to the development of new cement slurry recipes used during geoengineering works, especially in the mining areas. Moreover, economic requirements are forcing engineers to use less expensive technical and technological solutions simultaneously maintaining strength properties. An example of such a solution is to use suitable additives to cement slurry which could reduce the total unit cost of the treatment.

The depletion of stocks of fossil fuels and the environment protection requirements increase the significance of hydrogen as a future energy carrier. The present research is focused on the development of new safe methods of production, transport and storage of hydrogen. The paper presents an analysis of problems related to the assessment of the effects of failure of hydrogen transporting pipelines. Scenarios of hazardous events connected with an uncontrollable leakage of hydrogen are discussed. The sizes of heat radiation and pressure wave hazard zones are determined.

This article tries to give an answer to the question: how much did the development of catechetics as a theological discipline have influence on the presence of the Bible in catechesis? Thus we find here presented a history of the changes that have taken place in catechetics from its beginnings up to today. Changes in catechetics went from seeing it as the methodics of teaching religion to catechetics as a theolo- gical discipline. On each stage of the development of catechetics, the Bible was present in catechetical practice, where in the earlier stages it had a ancillary and auxiliary role. The drawing near of catechetics to theology also was the cause of a very substantial change in the assignment of the place of the Bible, which was acknowledged as the source of catechesis. Even though this situation is directly connected to the kerygmatic movement, the Bible is also the source of catechesis today.

The reflection taken up in this article allows to see the close connection between catechesis and biblical theology. Thus a valid assumption emerges that in the pre- paration of catechists of today it is necessary to be more open to a collaboration with theologians working on the Bible and making attempts to carry over the fruit of their studies to the field of pastoral theology, above all to catechetics.

Ethnic return migration is a widespread strategy for migrants from economically disadvantaged coun-tries. This article is about those ethnic return migrants who might successfully migrate thanks to their ancestors; their decision is based upon economic, pragmatic or rationalistic incentives aside from their diasporic feeling of belonging. Although this phenomenon has already been studied, scholars still mostly refer only to the benefits proposed by immigration policy as a key to understanding it. The impact of policy in the country of emigration on ethnic return migration is understudied. This article fills this gap. I found that when the Soviet Union introduced an attractive policy for Ukrainians/Russians in terms of study or work opportunities and the inhabitants in the Ukrainian Soviet Republic were quick to proclaim themselves as Ukrainians or Russians, the dissolution of the Soviet Union quickly changed this motiva-tion. Ukrainians with Czech ancestors started to aim at obtaining official status as Czech members of the diaspora because of the benefits proposed by the Czech government (mainly permanent residency). However, it is difficult to prove the required link to one’s Czech ancestors due to Soviet-era documents in which the column with the Czech nationality of people’s ancestors is often missing. These observa-tions lead to the conclusion that an attractive immigration policy aimed at the diaspora should not be treated as the only comprehensive explanation for ethnic return migration. Ethnic policy in the country of emigration also shapes this kind of migration and – in this concrete case – could even discourage ethnic return migrants.