Jožef Stefan Institute

About: Jožef Stefan Institute is a facility organization based out in Ljubljana, Slovenia. It is known for research contribution in the topics: Liquid crystal & Dielectric. The organization has 3828 authors who have published 12614 publications receiving 291025 citations.

Electrocaloric Effect: Theory, Measurements, and Applications

Abstract: The electrocaloric effect (ECE) is a physical phenomenon found in materials with dipolar constituents, that is, with certain dielectric properties. It is manifested in the heating or cooling of an electrocaloric material due to the applied electric field under adiabatic conditions. Electrocaloric effect has been known for many decades; however, the relatively small ECE observed below 2.5 K made it unsuitable for practical applications. Recently, however, materials with large ECE have been predicted and discovered, thus opening the possibility of realizing dielectric refrigeration that has several potential advantages in comparison with other cooling technologies. This chapter provides an extensive introduction to the field, including the basic theory of the electrocaloric phenomenon in ferroelectric, relaxor ferroelectric, and antiferroelectric materials. In addition, a review of various ECE experimental techniques, including indirect and direct experimental techniques, is given together with examples of recent findings obtained in polymeric, perovskite ceramic relaxor, and ferroelectric materials. An overview of various possibilities of the application of the ECE, the comparison with thermoelectric and magnetoelectric materials, and the state of the art of the cooling/heating devices is also presented. Keywords: cooling; dielectric; electrocaloric; materials

Stable self-interacting pais–uhlenbeck oscillator

Abstract: It is shown that the interacting Pais–Uhlenbeck (PU) oscillator necessarily leads to a description with a Hamiltonian that contains positive and negative energies associated with two oscillators. Descriptions with a positive definite Hamiltonians, considered by some authors, can hold only for a free PU oscillator. We demonstrate that the solutions of a self-interacting PU oscillator are stable on islands in the parameter space, as already observed in the literature. If we slightly modify the system, by considering a sine interaction term, and/or by taking unequal masses of the two oscillators, then the system is stable on the continents that extend from zero to infinity in the parameter space. Therefore, the PU oscillator is quite acceptable physical system.