Suchergebnisse

The results are described of the study of temperature deformation of different types of frozen soil in the cycles of cooling-heating at sudden change in temperature. The differences in the nature of the temperature deformation at step and one stage temperature change are shown. The dependences are investigated of the temperature deformation of frozen soils on soil type, moisture and total number of cycles of cooling-heating.

Reprinted from Journal of Atmospheric Sciences, Vol. 23, No. 6, pp. 678-681, November 1966. ; Research supported by the Air Force Cambridge Research Laboratories, Office of Aerospace Research, United States Air Force, L.G. Hanscom Field, Bedford, Massachusetts. ; Meteorology Laboratory Project 7655. ; "February 1967." ; Includes bibliographical references. ; Mode of access: Internet.

"Near room-temperature magnetic and magnetocaloric properties of the compounds Pr0.63-xHoxSr0.37MnO3 (x=0, 0.05) were investigated. The parent compound Pr0.63Sr0.37MnO3 has a large magnetocaloric effect around its Curie temperatures of about 300 K. Partially replacing of Pr3+ ions with Ho3+ ions in Pr0.63Sr0.37MnO3 gives rise to disorder which leads to the decrease of the Curie temperature without a significant reduction of the magnetocaloric effect. The samples were prepared by solid state reaction and were found to be single phase by x-ray diffraction. The magnetic measurements reveal paramagnetic to ferromagnetic second order phase transitions. For the sample with x = 0, the magnetic entropy change |ΔSM| was in the range from 1.91 J/kg٠K (RCP = 42 J/kg) forμ0 ΔH = 1 T to 4.86 J/kg٠K (RCP = 184 J/kg) for μ0 ΔH = 4 T. For the sample with x = 0.05, the magnetic entropy change |ΔSM| was in the range from 1.61 J/kg٠K (RCP = 57.9 J/kg) forμ0 ΔH = 1 T to 4.38 J/kg٠K (RCP = 236 J/kg) for μ0 ΔH = 4 T and Tc = 216 K. These values recommend these materials to be potential candidates to be used in near room-temperature refrigeration applications. Keywords: Perovskite manganites, phase transition, magnetocaloric effect. "