The small artificial surface defects in the coarse-grain steel are studied. The size of the used defects is smaller than the most relevant microstructural unit of steel, i.e. the average grain size. The samples of coarse-grain steel are prepared using a welding thermal-cycle simulator and a laboratory furnace. The defects are made by indenting with a Vickers pyramid. One of the final results of the defect making is the existence of local residual stresses. The influence of residual stresses on the crack initiation from those artificial defects is discussed in the article.

The title of the article, formulated by the Editors, requires a few clarifcations of terms. Both phenomena – Christianity and the African culture – are de facto plural and have to be regarded and treated as such. The title also juxtaposes a term that describes a religious reality with a cultural one (this also touches on the understanding of the relation between religion and culture). This can only be done on the assumption that “Christianity” means “a culture permeated by the Gospel message”.

The author argues that Christians have never presented a unifed attitude towards the African culture. As in the Christian antiquity, as in later times (including the present) Christians showed ambivalent attitudes towards the African culture. Some strongly opposed it, some allowed a restricted borrowing, some engaged actively with the African culture. One cannot see these attitudes in terms of development or regress because they have been synchronically present at all times. The attitudes towards African culture also changed at times within the particular strands of Christianity. What was rejected of hardly acceptable at one time becomes the order of the day at other. However, these attitudes have not been synchronized in all christian churches and communities.

After stating the article’s argument and making the terminological reservations, the author substantiate the argument presenting three types of interaction between Christianity and African culture giving examples from different times and regions.

JESSICA initiative as a financial engineering instrument was introduced to enhance and accelerate investments in disadvantaged urban areas. The novel aspect of JESSICA is that this instrument should not only support and promote sustainable urban development but also provide incentives that lower risk capital investments and consequently allow to overcome existing market failures. Thus, the paper aims to identify whether JESSICA projects have contributed to generating positive market effects, as well as to indicate the factors that were most responsible for the occurrence of these phenomena. The results show that 75% out of all projects generated positive market effects in form of new jobs, services or products. The generation of revenues by particular project was the most influential factor determining the capacity of a given project to create positive markets effects.

Ladle plays an important role in the metallurgical industry whose maintenance directly affects the production efficiency of enterprises. In view of the problems such as low maintenance efficiency and untimely maintenance in the current ladle passive maintenance scheme, the life prediction mechanism for ladle composite structures is established which bases on the stress analysis of steel shell and ladle lining in the production process, combining conventional fatigue analysis and extended fracture theory. The mechanism is accurate and effective according to the simulation results. Through which, the useful life of steel shell can be accurately predicted by detecting the crack length of it. Due to the large number of factors affecting the life of the lining of the ladle, it is difficult to accurately predict the life of the ladle lining, so a forecasting mean based on the thermal shock method is proposed to predict the service life of the ladle lining in this paper. The life prediction mechanism can provide data support and theoretical guidance for the active maintenance of the ladle, which is the prerequisite for scientifically formulating ladle initiative maintenance program.

Although the explicit commutativitiy conditions for second-order linear time-varying systems have been appeared in some literature, these are all for initially relaxed systems. This paper presents explicit necessary and sufficient commutativity conditions for commutativity of second-order linear time-varying systems with non-zero initial conditions. It has appeared interesting that the second requirement for the commutativity of non-relaxed systems plays an important role on the commutativity conditions when non-zero initial conditions exist. Another highlight is that the commutativity of switched systems is considered and spoiling of commutativity at the switching instants is illustrated for the first time. The simulation results support the theory developed in the paper.

Time-dependent behavior of rock mass is important for long-term stability analysis in rock engineering. Extensive studies have been carried out on the creep properties and rheological models for variable kinds of rocks, however, the effects of initial damage state on the time-dependent behavior of rock has not yet been taken into consideration. In the present study, the authors proposed a creep test scheme with controlled initial damage to investigate the influence of initial damage on the time-dependent behavior of sandstone. In the test scheme, the initial states of damage were first determined via unloading the specimen from various stresses. Then, the creep test was conducted under different stress levels with specific initial damage. The experimental results show that there is a stress threshold for the initial damage to influence the behavior of the rock in the uniaxial compressive creep tests, which is the stress threshold of dilatancy of rock. When the creep stress is less than the stress threshold, the effect of the initial damage seems to be insignificant. However, if the creep stress is higher than the stress threshold, the initial damage has an important influence on the time-dependent deformation, especially the lateral and volumetric deformation. Moreover, the initial damage also has great influence on the creep failure stress and long-term strength, i.e., higher initial damage leading to lower creep failure stress and long-term strength. The experimental results can provide valuable data for the construction of a creep damage model and long-term stability analysis for rock engineering.

This article discusses the professional careers of foreign scholars in Krakow, one of the leading academic centres in Poland and a regional ‘silicon valley’ (toutes proportions gardées). Central and Eastern Europe is understudied as an immigration region for highly skilled migrants (HSMs). To bridge this gap, we concentrate on three interrelated topics: (a) the perception of Polish science and its infrastruc-ture; (b) careers of international staff employed in Polish academia; and (c) their perception of their achievements in Poland. Foreign scholars come to Poland for various reasons. Two of the most important are the cultural proximity between Poland and their country of origin, and research interests focused directly in Poland. Our findings show that Poland attracts first and foremost scholars with average scientific achievements. We discuss major problems they encounter (e.g., shortage of funds, uncomfortable office space, restricted access to books and papers) and their expectations of life in a semi-periphery country. The paper is mainly based on in-depth interviews with 23 foreign scholars working full time at four universities in Krakow and, as a secondary source, on the analysis of websites of these universities.

Rotation modulation can significantly improve the navigation accuracies of an inertial navigation system (INS) and a strap-down configuration dominating in this type of INS. However, this style of construction is not a good scheme since it has no servo loop to counteract a vehicle manoeuvre. This paper proposes a rotary upgrading method for a rotational INS based on an inertially stabilized platform. The servo control loop is reconstructed on a four-gimbal platform, and it has the functions of providing both a level stability relative to the navigation frame and an azimuth rotation at a speed of 1:2◦/s. With the platform’s rotation, the observability and the convergence speed of the estimation for the initial alignment can be improved, as well as the biases of the gyroscopes and accelerometers be modulated into zero-mean periodic values. An open-loop initial alignment method is designed, and its detailed algorithms are delivered. The experiment result shows that the newly designed rotational INS has reached an accuracy of 0.38 n mile/h (CEP, circular error probable). The feasibility and engineering applicability of the designed scheme have been validated.

The aim of the paper is to formulate physically well founded yield condition for initially anisotropic solids revealing the asymmetry of elastic range. The initial anisotropy occurs in material primarily due to thermo-mechanical pre-processing and plastic deformation during the manufacturing processes. Therefore, materials in the “as-received” state become usually anisotropic. After short account of the known limit criteria for anisotropic solids and discussion of mathematical preliminaries the energy-based criterion for orthotropic materials was formulated and confronted with experimental data and numerical predictions of other theories. Finally, possible simplifications are discussed and certain model of isotropic material with yield condition accounting for a correction of shear strength due to initial anisotropy is presented. The experimental verification is provided and the comparison with existing approach based on the transformed-tensor method is discussed.

The paper considers parametric optimization problems for the steel bar structures formulated as nonlinear programming ones with variable unknown cross-sectional sizes of the structural members, as well as initial prestressing forces introduced into the specified redundant members of the structure. The system of constraints covers load-bearing capacity constraints for all the design sections of the structural members subjected to all the design load combinations at ultimate limit state, as well as displacement constraints for the specified nodes of the bar system, subjected to all design load combinations at serviceability limit state. The method of the objective function gradient projection onto the active constraints surface with simultaneous correction of the constraints violations has been used to solve the parametric optimization problem. A numerical technique to determine the optimal number of the redundant members to introduce the initial prestressing forces has been offered for high-order statically indeterminate bar structures. It reduces the dimension for the design variable vector of unknown initial prestressing forces for considered optimization problems.