Thermal conductivity of YBa/sub 2/Cu/sub 3/O/sub 7-//sub delta/ below 1 K: Evidence for normal-carrier transport well below T/sub c

We report measurements of thermal conductivity at temperatures below 1 K on superconducting and insulating (oxygen-deficient) ceramic YBa/sub 2/Cu/sub 3/O/sub 7-//sub delta/. For the superconductor the temperature dependence of the thermal conductivity, kappa, begins to weaken below approx.0.5 K, approaching a T-linear behavior. Below 1 K the insulating material, produced by vacuum-annealing the superconductor, exhibits a kappa proportionalT/sup 3/ dependence characteristic of phonon boundary scattering. Reannealing samples in flowing oxygen restores superconductivity at 90 K and the T-linear behavior of the thermal conductivity at the lowest temperatures. Scanning electron micrographs reveal an identical grain structure before and after successive heat treatments, indicating that the anomaly in kappa for the superconductor is not associated with the specific geometry of the microstructure. The data are consistent with the presence of a small number of normal carriers in the high-T/sub c/ material

MAGNETIC-X-RAY DICHROISM STUDY OF THE NEAREST-NEIGHBOR SPIN-SPIN CORRELATION-FUNCTION AND LONG-RANGE MAGNETIC ORDER-PARAMETER IN ANTIFERROMAGNETIC NIO

A new effect on the X-ray absorption line shape is described which is proportional to the nearest-neighbor spin-spin correlation function. We present theory and demonstrate the use of linear polarized X-ray absorption spectroscopy to study the temperature dependence of the long-range order parameter and the nearest-neighbor spin-spin correlation function in antiferromagnetic NiO

Variable performance of individuals: the role of population density and endogenously formed landscape heterogeneity

1.   Individuals can show positive correlations in performance (e.g. growth and reproduction) through time beyond the effects of size or age. This ‘performance autocorrelation’ has been attributed previously to traits that differ among individuals or to extrinsic generators of environmental heterogeneity. 2.   A model of mobile consumers on a dynamic resource showed that consumer foraging gave rise to resource heterogeneity that in turn generated autocorrelation in growth in consumers. 3.   Resource heterogeneity and growth autocorrelation were most pronounced when consumers were poorer foragers, moving locally and with an imperfect ability to identify the highest resource cells. 4.   The model predicted that lowered population density enhanced resource heterogeneity and the strength of growth autocorrelation. 5.   Consistent with model predictions, an experiment with tidepool limpets demonstrated that autocorrelation in growth changed with population density, with individuals in lower density tidepools showing stronger temporal correlations in growth. 6.   Our model and empirical results contrast with those of previous studies with plants, where dominance and suppression increases with increasing density. 7.   Our results suggest that growth autocorrelation can occur without invoking size-dependent advantages, intrinsic trait differences or extrinsic generators of environmental heterogeneity.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/74301/1/j.1365-2656.2003.00742.x.pd