20,743 research outputs found
Observation of inhomogeneous domain nucleation in epitaxial Pb(Zr,Ti)O3 capacitors
We investigated domain nucleation process in epitaxial Pb(Zr,Ti)O3 capacitors
under a modified piezoresponse force microscope. We obtained domain evolution
images during polarization switching process and observed that domain
nucleation occurs at particular sites. This inhomogeneous nucleation process
should play an important role in an early stage of switching and under a high
electric field. We found that the number of nuclei is linearly proportional to
log(switching time), suggesting a broad distribution of activation energies for
nucleation. The nucleation sites for a positive bias differ from those for a
negative bias, indicating that most nucleation sites are located at
ferroelectric/electrode interfaces
Polarization Switching Dynamics Governed by Thermodynamic Nucleation Process in Ultrathin Ferroelectric Films
A long standing problem of domain switching process - how domains nucleate -
is examined in ultrathin ferroelectric films. We demonstrate that the large
depolarization fields in ultrathin films could significantly lower the
nucleation energy barrier (U*) to a level comparable to thermal energy (kBT),
resulting in power-law like polarization decay behaviors. The "Landauer's
paradox": U* is thermally insurmountable is not a critical issue in the
polarization switching of ultrathin ferroelectric films. We empirically find a
universal relation between the polarization decay behavior and U*/kBT.Comment: 5 pages, 4 figure
Spontaneous separation of two-component Fermi gases in a double-well trap
The two-component Fermi gas in a double-well trap is studied using the
density functional theory and the density profile of each component is
calculated within the Thomas-Fermi approximation. We show that the two
components are spatially separate in the two wells once the repulsive
interaction exceeds the Stoner point, signaling the occurrence of the
ferromagnetic transition. Therefore, the double-well trap helps to explore
itinerant ferromagnetism in atomic Fermi gases, since the spontaneous
separation can be examined by measuring component populations in one well.Comment: 6 pages, 6 figures, to appear in ep
Phase Sensitive Recombination of Two Bose-Einstein Condensates on an Atom Chip
The recombination of two split Bose-Einstein condensates on an atom chip is
shown to result in heating which depends on the relative phase of the two
condensates. This heating reduces the number of condensate atoms between 10 and
40% and provides a robust way to read out the phase of an atom interferometer
without the need for ballistic expansion. The heating may be caused by the
dissipation of dark solitons created during the merging of the condensates.Comment: 5 pages, 4 figure
The Knowledge Base for Geography Teaching (GeoKBT): A Preliminary Model
Funded by the National Center for Research in Geography Education, this study investigated the nature of the knowledge needed for geography teaching. Informed by existing research about science and mathematics teachers’ pedagogical content knowledge (PCK), the research group developed a conceptual model of the knowledge base for geography teaching, identifying six key components: (a) orientations toward teaching geography, (b) knowledge of geography curricula, (c) knowledge of students’ understanding of geography and responses to geography learning, (d) knowledge of instructional strategies appropriate to learning geography, (e) knowledge of assessment of geography learning, and (f) knowledge of educational contexts. The conceptual model was refined and revised according to the results of case studies of four expert geography teachers. Data analyzed included classroom observations, teacher interviews, geography lesson video-recordings, teachers’ lesson plans and reflections, and student work samples. The resulting preliminary model (GeoKBT) is offered to the geography education community to inform both geography teacher education and further research on geography-related pedagogical knowledge
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