Nucleation of superconductivity and vortex matter in superconductor - ferromagnet hybrids

The theoretical and experimental results concerning the thermodynamical and low-frequency transport properties of hybrid structures, consisting of spatially-separated conventional low-temperature superconductor (S) and ferromagnet (F), is reviewed. Since the superconducting and ferromagnetic parts are assumed to be electrically insulated, no proximity effect is present and thus the interaction between both subsystems is through their respective magnetic stray fields. Depending on the temperature range and the value of the external field H_{ext}, different behavior of such S/F hybrids is anticipated. Rather close to the superconducting phase transition line, when the superconducting state is only weakly developed, the magnetization of the ferromagnet is solely determined by the magnetic history of the system and it is not influenced by the field generated by the supercurrents. In contrast to that, the nonuniform magnetic field pattern, induced by the ferromagnet, strongly affect the nucleation of superconductivity leading to an exotic dependence of the critical temperature T_{c} on H_{ext}. Deeper in the superconducting state the effect of the screening currents cannot be neglected anymore. In this region of the phase diagram various aspects of the interaction between vortices and magnetic inhomogeneities are discussed. In the last section we briefly summarize the physics of S/F hybrids when the magnetization of the ferromagnet is no longer fixed but can change under the influence of the superconducting currents. As a consequence, the superconductor and ferromagnet become truly coupled and the equilibrium configuration of this "soft" S/F hybrids requires rearrangements of both, superconducting and ferromagnetic characteristics, as compared with "hard" S/F structures.Comment: Topical review, submitted to Supercond. Sci. Tech., 67 pages, 33 figures, 439 reference

The Effect of Inert Gas in the Mixture with Natural Gas on the Parameters of the Combustion Engine

The article discusses the influence of inert gases (carbon dioxide and nitrogen) in a mixture with natural gas on power and economic parameters of the internal combustion engine LGW 702 designed for micro-cogeneration units. The experimental measurements were made under various engine operating modes and under various compositions of fuel mixtures. The aim of the experiment was to analyze and assess the full impact of the inert components in the gaseous fuel, especially on the particular integral parameters, as well as on the internal combustion engine parameters relating to the course of burning the mixture. Experimental results indicate a decrease in performance parameters and an increase in specific fuel consumption with an increase in the proportion of internal gases in the mixture. Increasing proportion of inert gases leads to decreasing maximum pressure in the cylinder (a decrease approximately by 50% with the mixture CO2NG50 or by 30% with the mixture N2NG50, compared to natural gas) and the position of maximum pressure value is shifted further into the area of expansion stroke