Russell puts much weight on the concept of relation. In his view relations are real entities that are indispensable in the enterprise of defining mathematical objects, particularly numbers. In the paper I try to extend Russell’s idea beyond the domain of abstract entities. I make an attempt to show that the basic criterion of identity for concrete objects – the criterion of space‑time continuity – can be supplemented, whenever it appears inadequate, by taking into account some relations apart from those that are spatiotemporal. On this occasion I argue for the metaphysical impossibility of time travel and offer some resolutions of the classical paradoxes of identity: amoebas’ reproduction by fission or Theseus’ boat. With respect to relations I argue, against the radical separation of the self from its attributes, that there are essential attributes of the self that constitute its relatively stable individual essence.

Both shrinkage reducing admixtures (SRA) and expansive admixture (EXP) can be used to reduce the risk of cracking in concrete. Synergistic effect of using both of those admixtures simultaneously was a was found, however little information can be found on the effects of using both EXP and SRA on the properties of mortars and concrete other than shrinkage. Therefore in this paper, effect of adding both EXP and SRA on properties of mortars outside of their effect on shrinkage is researched. Mortars with Portland cement CEM I were modified by adding EXP and SRA in amount of full dose recommended by the producer, and half of the recommended dose. Research consisted of tests of properties of fresh mortars (consistency, initial setting time, hydration heat) and hardened mortars (compressive strength and drying shrinkage). It has been found that using both SRA and EXP admixtures leads to maintaining the same setting time which can be prolonged if only SRA is used, decreased compressive strength, possibility of increased consistency. Synergistic effect on shrinkage was also confirmed.

Double-beam model is considered in many investigations both theoretical and typically engineering ones. One can find different studies concerning analysis of such structures behaviour, especially in the cases where the system is subjected to dynamic excitations. This kind of model is successfully considered as a reliable representation of railway track. Inclusion of nonlinear physical and geometrical properties of rail track components has been justified by various computational studies and theoretical analyses. In order to properly describe behaviour of real structures their nonlinear properties cannot be omitted. Therefore a necessity to search appropriate analytical nonlinear models is recognized and highlighted in published literature. This paper presents essential extension of previously carried out double-beam system analysis. Two nonlinear factors are taken into account and parametrical analysis of the semi-analytical solution is undertaken with special emphasis on different range of parameters describing nonlinear stiffness of foundation and layer between beams. This study is extended by preliminary discussion regarding the dynamic effects produced by a series of loads moving along the upper beam. A new solution for the case of several forces acting on the upper beam with different frequencies of their variations in time is presented and briefly discussed.

Increasing numbers of devices of various types are now connected to power lines. Their nonlinear nature harms the operation of the lines, as the line voltage is distorted from a sine wave, which causes disturbances in the operation of other loads. This study proposes a method of active parallel compensation that can be realised using a power supply. The proposed device is a dual-function system: it supplies the load connected to its DC link, and operates as a parallel active filter. This kind of device, with a relatively low value of the rated output power, could be implemented in electrical systems to provide distributed compensation. The second novel aspect of this work is the use of a tunable inductive filter, which is included at the input of the power electronics controlled current source and forms a main part of the power supply. The use of this tunable inductive filter increases the frequency response of the current source, while at the same time, in the quasi-steady state of power supply operation, the pulse modulation component of the input current source remains at a minimum level. This paper discusses the structure of an electrical system with the proposed power supply and the rules of operation for the system, and presents test results based on both a simulation and a laboratory model of the system.