Intensive electrocaloric effect in the multilayer capacitor under equilibrium and nonequilibrium thermal conditions

Precise direct measurements of the intensive electrocaloric effect (ECE) in commercial multilayer capacitor based on doped BaTiO3 were performed using an adiabatic calorimeter. High reversibility of ECE studied under equilibrium thermal conditions was observed. The nonequilibrium thermal conditions caused by fixing the temperature of one of the ends of the linear EC element lead to the predominance of ECE when the electric field is turned off. The heat flow through the EC element appearing under the influence of a periodic electric field and depending on its frequency makes it possible to create a cooling cycle without thermal keys

Influence of thermal conditions on the electrocaloric effect in a multilayer capacitor based on doped BaTiO3

We present the results of studies of thermal expansion, heat capacity, permittivity, polarization and the influence of different thermal conditions on the intensive electrocaloric effect (ECE), ΔTAD, in a commercial multilayer capacitor based on doped BaTiO3. Investigations in a wide temperature range revealed one anomaly in the behavior of the physical properties at about 290K characteristic for the relaxors. Direct measurements showed a high reversibility of ECE under equilibrium thermal conditions. Good agreement was found between the values of ΔTAD determined by direct and indirect measurements at the electric field up to 15.4kV/cm. Quasi-isothermal conditions lead, firstly, to decrease of large ΔTAD≈0.94K obtained in adiabatic conditions under E=308kV/cm to 0.87K, and, secondly, the appearance of a difference between the values of ΔTON and ΔTOFF determined when the electric field is applied and removed. Using this phenomenon and changing the frequency of the periodic electric field, E=15.4kV/cm, the effect of cooling was obtained equal to [(ΔTON+ΔTOFF)∕2]max=−0.032K. The results obtained are useful for further development of the electrocaloric refrigeration technique without thermal switches

Influence of thermal conditions on the electrocaloric effect in a multilayer capacitor based on doped BaTiO3

We present the results of studies of thermal expansion, heat capacity, permittivity, polarization and the influence of different thermal conditions on the intensive electrocaloric effect (ECE), TAD, in a commercial multilayer capacitor based on doped BaTiO3. Investigations in a wide temperature range revealed one anomaly in the behavior of the physical properties at about 290 K characteristic for the relaxors. Direct measurements showed a high reversibility of ECE under equilibrium thermal conditions. Good agreement was found between the values of TAD determined by direct and indirect measurements at the electric field up to 15.4 kV/cm. Quasi-isothermal conditions lead, firstly, to decrease of large TAD 0.94 K obtained in adiabatic conditions under E ¼ 308 kV/cm to 0.87 K, and, secondly, the appearance of a difference between the values of T ON and T OFF determined when the electric field is applied and removed. Using this phenomenon and changing the frequency of the periodic electric field, E ¼ 15:4 kV/cm, the effect of cooling was obtained equal to ½ð T ON þ T OFFÞ=2max ¼ 0:032 K. The results obtained are useful for further development of the electrocaloric refrigeration technique without thermal switches

Urupocidin A: A New, Inducing iNOS Expression Bicyclic Guanidine Alkaloid from the Marine Sponge <i>Monanchora pulchra</i>

Urupocidins A and B (<b>1</b> and <b>2</b>), bisguanidine alkaloids with an unprecedented skeleton system, derived from polyketide precursors and containing an unusual <i>N</i>-alkyl-<i>N</i>-hydroxyguanidine moiety, have been isolated from the sponge <i>Monanhora pulchra</i>. The structures of <b>1</b> and <b>2</b>, including absolute configuration, were established using the detailed analysis of 1D and 2D NMR, CD, and mass spectra as well as chemical transformations. Compound <b>1</b> increases nitric oxide production in murine macrophages via inducing iNOS expression