11 research outputs found
Non-linear response of ac conductivity in narrow YBCO film strips at the superconducting transition
Measurements of higher harmonics of the ac voltage response in YBCO thin film
strips under low amplitude and low frequency harmonic excitation, as a function of
temperature, show a non linear response of the conductivity in the superconducting transition
interval. The third and fifth harmonics of the local voltage as a function of T exhibit a peak
near Tc and their amplitudes seem to be closely related to the T-derivative of the first
harmonic. The peaks are linearly dependent on the current amplitude and do not depend on
frequency. The observed data are partially interpreted in terms of ac current induced thermal
modulation of the sample temperature added to strong thermally activated fluctuations in the
transition region. The fit of the model to the data gives information of some sample properties
such as zero temperature critical current, zero onset resistance and thermal boundary
conductance
Why could Electron Spin Resonance be observed in a heavy fermion Kondo lattice?
We develop a theoretical basis for understanding the spin relaxation
processes in Kondo lattice systems with heavy fermions as experimentally
observed by electron spin resonance (ESR). The Kondo effect leads to a common
energy scale that regulates a logarithmic divergence of different spin kinetic
coefficients and supports a collective spin motion of the Kondo ions with
conduction electrons. We find that the relaxation rate of a collective spin
mode is greatly reduced due to a mutual cancelation of all the divergent
contributions even in the case of the strongly anisotropic Kondo interaction.
The contribution to the ESR linewidth caused by the local magnetic field
distribution is subject to motional narrowing supported by ferromagnetic
correlations. The developed theoretical model successfully explains the ESR
data of YbRh2Si2 in terms of their dependence on temperature and magnetic
field.Comment: 5pages, 1 Figur
Paleontology of leaf beetles
`The rate of evolution in any large group is not uniform; there are periods of relatise stability, and periods of comparatively rapid change.' Cockerell and LeVeque, 1931 To Yenli Ych, my beloved wife, a most wonderful person! The fossil record of the Chrysomelidae can be tentatively traced back to the late Paleozoic to early Mesozoic Triassic. Mesozoic records at least 9 subfamilies, 19 genera, and 35 species, are represented by the Sagrinae, the exclusively Mesozoic Proto scelinae, Clytrinae, Cryptocephalinae, Eumolpinae, Chrysomelinae. Galerucinac, Alticinae, and Cassidinae. Cenozoic records at least 12 subfamilies- 63 % of the extant- 12! genera, and 325 species, include the same extant subfamilies as well as the Donaciinae, Zeugophorinae, Criocerinae, and Hispinae and can be frequently identified to genus, especially if preserved in amber. Quaternary records are often identified to extant species. tn total, at least t3! genera about 4 % of total extant, and 357 species < 1 % have been reported. At least, 24 genera <1 % of the extant seem to be extinct. Although reliable biological information associated with the fossil chrysomelids is very scarce, it seems that most of the modern host-plant associations were established, at least, in the late Mesozoic to early Cenozoic. As a whole, stasis seems to be the general rule of the chrysomelid fossil record. Together with other faunal elements, chrysomelids, especially donaciines, have been used as biogeographic and paleoclimatological indicators in the Holocene. I
Non-linear response of ac conductivity in narrow YBCO film strips at the superconducting transition
Measurements of higher harmonics of the ac voltage response in YBCO thin film
strips under low amplitude and low frequency harmonic excitation, as a function of
temperature, show a non linear response of the conductivity in the superconducting transition
interval. The third and fifth harmonics of the local voltage as a function of T exhibit a peak
near Tc and their amplitudes seem to be closely related to the T-derivative of the first
harmonic. The peaks are linearly dependent on the current amplitude and do not depend on
frequency. The observed data are partially interpreted in terms of ac current induced thermal
modulation of the sample temperature added to strong thermally activated fluctuations in the
transition region. The fit of the model to the data gives information of some sample properties
such as zero temperature critical current, zero onset resistance and thermal boundary
conductance
Non-linear response of ac conductivity in narrow YBCO film strips at the superconducting transition
Measurements of higher harmonics of the ac voltage response in YBCO thin film
strips under low amplitude and low frequency harmonic excitation, as a function of
temperature, show a non linear response of the conductivity in the superconducting transition
interval. The third and fifth harmonics of the local voltage as a function of T exhibit a peak
near Tc and their amplitudes seem to be closely related to the T-derivative of the first
harmonic. The peaks are linearly dependent on the current amplitude and do not depend on
frequency. The observed data are partially interpreted in terms of ac current induced thermal
modulation of the sample temperature added to strong thermally activated fluctuations in the
transition region. The fit of the model to the data gives information of some sample properties
such as zero temperature critical current, zero onset resistance and thermal boundary
conductance