In the paper experimental investigation results of three elements are presented. Two of them were made of reinforced concrete. The strengthened bracket had the steel accessory mounted to cracked loaded corbel (while it was loaded to half ultimate force of the reference element), the reference one was tested without any accessory. The third corbel was the steel accessory mounted to the concrete column. Full scale corbels were 450 mm deep and 250 mm wide, steel accessory was 320 mm high. The aim of the research was to verify the following thesis: short corbels (shear slenderness ac /h ≈ 0,3) can be strengthened by a steel accessory. Load carrying capacity of strengthened member increased by 40 %. The ultimate force obtained for the steel accessories mounted to concrete column was 66 % of reference value. While testing some observations and measurements (strain of reinforcement and concrete, development of cracking) were made which allowed to describe corbel behaviour under increasing load.
The paper investigates the mechanisms behind the formation and maintenance of those migrants’ social ties which translate into a particular composition of the network and become a source of social capital. Based on a number of in-depth interviews with Ukrainian migrants in Warsaw, we find that Ukrainian migrants’ networks are based primarily on ties homogenous in regard to nationality, level of education and character of work. The institutional context of social interaction determines with whom migrants form relations and whether these ties become a source of social advancement. The studied migrants do form bridging ties with more experienced, as well as socially and legally embedded persons, mainly other migrants, receiving both instrumental and emotional support.
Current networks are designed for peak loads leading to low utilization of power resources. In order to solve this problem, a heuristic energy-saving virtual network embedding algorithm based on the Katz centrality (Katz-VNE) is proposed. For solving an energy-saving virtual network embedding problem, we introduce the Katz centrality to represent the node influence. In order to minimize the energy consumption of the substrate network, the energy-saving virtual network embedding problem is formulated as an integer linear program, and the Katz-VNE is used to solve this problem. The Katz-VNE tries to embed the virtual nodes onto the substrate nodes with high Katz centrality, which is effective, and uses the shortest paths offering the best factor of bandwidths to avoid the hot nodes. The simulation results demonstrate that the long-term average energy consumption of the substrate network is reduced significantly, and the long-term revenue/cost ratio, the acceptance rate of virtual network requests, and the hibernation rate of substrate nodes as well as links are improved significantly.
The problem of effective gas extraction from Polish shale rocks is an interesting research subject for scientists. A properly selected proppant, which protects cracks from closing during the fracturing process, inestimably contributes to an increase of extraction. Grains of proppant are transported along with a fracturing medium to reach the deepest regions of the crack. The proper support of the crack provides an easy flow of gas, therefore it is important in terms of extraction efficiency. This paper shows the interactions of a proppant grain with the crack surface in shale rock. FEM analysis was conducted to observe the stress region, which is generated as a result of pressing the grain into the crack surface. A model of a sphere which was pressed into the rock model with constant velocity was applied. The received results of stress depend on material properties and a range of proppant grain pressing.
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