13,665 research outputs found
Electronic Transport in Unconventional Superconductors
We investigate the electronic transport coefficients in unconventional
superconductors at low temperatures, where charge and heat transport are
dominated by electron scattering from random lattice defects. We discuss the
features of the pairing symmetry, Fermi surface, and excitation spectrum which
are reflected in the low temperature heat transport. For temperatures k_B T
\la \gamma \ll \Delta_0, where is the bandwidth of impurity induced
Andreev states, certain eigenvalues become {\it universal}, i.e., independent
of the impurity concentration and phase shift. Deep in the superconducting
phase (k_B T \la \gamma) the Wiedemann-Franz law, with Sommerfeld's value of
the Lorenz number, is recovered. We compare our results for theoretical models
of unconventional superconductivity in high-T and heavy fermion
superconductors with experiment. Our findings show that impurities are a
sensitive probe of the low-energy excitation spectrum, and that the
zero-temperature limit of the transport coefficients provides an important test
of the order parameter symmetry.Comment: To appear in the Proceedings of the 1st International Conference on
Quasiclassical Methods in Superconductivity, eds. D. Rainer and J.A. Sauls,
Verditz, Austria (1998
The Debye-Waller factor of stabilized delta-Pu
The Debye-Waller factor has been calculated for stabilized delta-phase
plutonium with 5% aluminum. A quasi-harmonic Born-von Karman force model with
temperature dependent phonon frequencies was used to calculate the mean-square
thermal atomic displacement from absolute zero to 800 K. Implementation of the
observed anomalous softening of the long wavelength phonons with increasing
temperature cannot account for the softening of the measured thermal parameter
at high temperatures nor for its rather high value at low temperatures. The
implications for diffraction measurements on delta-phase stabilized plutonium
alloys are discussed.Comment: Presented at the conference Plutonium Futures - The Science 200
Knight Shift in the FFLO State of a Two-Dimensional D-Wave Superconductor
We report on the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state in
two-dimensional d-wave superconductors with magnetic field parallel to the
superconducting planes. This state occurs at high magnetic field near the
Pauli-Clogston limit and is a consequence of the competition between the pair
condensation and Zeeman energy. We use the quasiclassical theory to
self-consistently compute the spatially nonuniform order parameter. Our
self-consistent calculations show that the FFLO state of a d-wave order
parameter breaks translational symmetry along preferred directions. The
orientation of the nodes in real space is pinned by the nodes of the basis
function in momentum space. Here, we present results for the Knight shift and
discuss the implications for recent nuclear magnetic resonance measurements on
CeCoIn5.Comment: 2 pages, 3 figures: LT-24 Conference, Orlando, Aug. 2005; to appear
in AIP Conference Proceeding
Global crop production forecasting: An analysis of the data system problems and their solutions
Data related problems in the acquisition and use of satellite data necessary for operational forecasting of global crop production are considered for the purpose of establishing a measurable baseline. For data acquisition the world was divided into 37 crop regions in 22 countries. These regions represent approximately 95 percent of the total world production of the selected crops of interest, i.e., wheat, corn, soybeans, and rice. Targets were assigned to each region. Limited time periods during which data could be taken (windows) were assigned to each target. Each target was assigned to a cloud region. The DSDS was used to measure the success of obtaining data for each target during the specified windows for the regional cloud conditions and the specific alternatives being analyzed. The results of this study suggest several approaches for an operational system that will perform satisfactorily with two LANDSAT type satellites
Analysis and optimization of an omnidirectional direction-finding system
System determines the direction of arrival of an electromagnetic wave with the direction information in a readily usable form. It presents a relatively small physical structure and does not require mechanical positioning
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