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- ItemA dynamical system with random parameters as a mathematical model of real phenomena(MDPI, 2019-10-30) Diblík, Josef; Dzhalladova, Irada; Růžičková, MiroslavaIn many cases, it is difcult to nd a solution to a system of difference equations with random structure in a closed form. Thus, a random process, which is the solution to such a system, can be described in another way, for example, by its moments. In this paper, we consider systems of linear difference equations whose coefcients depend on a random Markov or semi-Markov chain with jumps. The moment equations are derived for such a system when the random structure is determined by a Markov chain with jumps. As an example, three processes: Threats to security in cyberspace, radiocarbon dating, and stability of the foreign currency exchange market are modelled by systems of difference equations with random parameters that depend on a semi-Markov or Markov process. The moment equations are used to obtain the conditions under which the processes are stable.
- ItemCompatibility of Phase Change Materials and Metals:Experimental Evaluation Based on the Corrosion Rate(MDPI, 2020-06-18) Ostrý, Milan; Bantová, Sylva; Struhala, KarelThe construction and maintenance of building stock is responsible for approximately 36% of all CO(2)emissions in the European Union. One of the possibilities of how to achieve high energy-efficient and decarbonized building stock is the integration of renewable energy sources (RES) in building energy systems that contain efficient energy storage capacity. Phase Change Materials (PCMs) are latent heat storage media with a high potential of integration in building structures and technical systems. Their solid-liquid transition is specifically utilized for thermal energy storage in building applications. The typically quite old example is the use of ice that serves as long-term storage of cold. Large pieces of ice cut in winter were stored in heavily insulated spaces and prepared for cooling of food or beverages in summer. In the contemporary use of the principle, the PCMs for building applications and tested in this study must have a melting range close to the desired temperature in the occupied rooms. As the PCMs need to be encapsulated, several types of metal containers have been developed and tested for their thermal conductivity and resistance to mechanical damage, which enhances the performance of these so-called latent heat thermal energy storage (LHTES) systems. Long-term compatibility of metals with PCMs depends, i.e., on the elimination of an undesirable interaction between the metal and the specific PCM. Heat storage medium must be reliably sealed in a metal container, especially if the LHTES is integrated into systems where PCM leaks can negatively affect human health (e.g., domestic hot water tanks). The aim of this study is to evaluate the interactions between the selected commercially available organic (Linpar 17 and 1820) and inorganic (Rubitherm SP22 and SP25) PCMs and metals widely used for PCM encapsulation (aluminum, brass, carbon steel, and copper). The evaluation is based on the calculation of the corrosion rate (CR), and the gravimetric method is used for the determination of the weight variations of the metal samples. The results show good compatibility for all metals with organic PCMs, which is demonstrated by a mass loss as low as 2.1 mg in case of carbon steel immersed in Linpar 1820 for 12 weeks. The exposure of metals to organic PCMs also did not cause any visual changes on the surface except for darker stains, and tarnishing occurred on the copper samples. More pronounced changes were observed in metal samples immersed in inorganic PCMs. The highest CR values were calculated for carbon steel exposed to inorganic PCM Rubitherm SP25 (up to 13.897 mg center dot cm(-2)center dot year(-1)). The conclusion of the study is that aluminum is the most suitable container material for the tested PCMs as it shows the lowest mass loss and minimal visual changes on the surface after prolonged exposure to the selected PCMs.
- ItemUnder Sleeper Pads in Switches & Crossings(IOP PUBLISHING LTD, DIRAC HOUSE, TEMPLE BACK, BRISTOL BS1 6BE, ENGLAND, 2017-09-21) Plášek, Otto; Hruzíková, MiroslavaUnder sleeper pads (USPs) have been installed in the Czech railway lines since 2007 into two trial sections in switches and crossings and in a trial section with the aim to reduce rail pitch corrugation. The basic motivation for the construction of the trial track sections in turnouts was an evaluation of USPs' influence on improvement of track quality as a consequence of ballast bed protection against extreme stress. The paper comprises experience of USPs installation in the Czech Republic in the two trial sections with switches and crossings built in 2007 and 2014. The paper particularly provides an information about USPs applications focusing on the track settlement received by an evaluation of data from the geodetic surveying by precise levelling. Some positive influence of under sleeper pads on the track quality is observed.
- ItemThere Are No Conformal Einstein Rescalings of Pseudo-Riemannian Einstein Spaces with n Complete Light-Like Geodesics(MDPI, 2019-09-01) Hinterleitner, Irena; Mikeš, Josef; Guseva, NadezdaIn the present paper, we study conformal mappings between a connected n-dimension pseudo-Riemannian Einstein manifolds.
- ItemStabilization of company’s income modeled by a system of discrete stochastic equations(Springer Nature, 2014-11-15) Diblík, Josef; Dzhalladova, Irada; Růžičková, MiroslavaThe paper deals with a system of difference equations where the coefficients depend on Markov chains. The functional equations for a particular density and the moment equations for the system are derived and used in the investigation of mode stability of company-s income. An application of the results is illustrated by two models.