4,421 research outputs found
Raising Bi-O bands above the Fermi energy level of hole-doped BiSrCaCuO and other cuprate superconductors
The Fermi surface (FS) of BiSrCaCuO
(Bi2212) predicted by band theory displays Bi-related pockets around the
point, which have never been observed experimentally. We show that
when the effects of hole doping either by substituting Pb for Bi or by adding
excess O in Bi2212 are included, the Bi-O bands are lifted above the Fermi
energy () and the resulting first-principles FS is in remarkable accord
with measurements. With decreasing hole-doping the Bi-O bands drop below
and the system self-dopes below a critical hole concentration. Computations on
other Bi- as well as Tl- and Hg-based compounds indicate that lifting of the
cation-derived band with hole doping is a general property of the electronic
structures of the cuprates.Comment: 4 pages, 4 figures; PRL (2006, in press
Range Queries on Uncertain Data
Given a set of uncertain points on the real line, each represented by
its one-dimensional probability density function, we consider the problem of
building data structures on to answer range queries of the following three
types for any query interval : (1) top- query: find the point in that
lies in with the highest probability, (2) top- query: given any integer
as part of the query, return the points in that lie in
with the highest probabilities, and (3) threshold query: given any threshold
as part of the query, return all points of that lie in with
probabilities at least . We present data structures for these range
queries with linear or nearly linear space and efficient query time.Comment: 26 pages. A preliminary version of this paper appeared in ISAAC 2014.
In this full version, we also present solutions to the most general case of
the problem (i.e., the histogram bounded case), which were left as open
problems in the preliminary versio
Optimization of material distributions in fast breeder reactors
"MIT-4105-6."Based on a Sc. D. thesis submitted by C.P. Tzanos to the Dept. of Nuclear Engineering, 1971Includes bibliographical references (pages 188-190)AT(30-1)-410
Normal state properties of high angle grain boundaries in (Y,Ca)Ba2Cu3O7-delta
By lithographically fabricating an optimised Wheatstone bridge geometry, we
have been able to make accurate measurements of the resistance of grain
boundaries in Y1-xCaxBa2Cu3O7-d between the superconducting transition
temperature, Tc, and room temperature. Below Tc the normal state properties
were assessed by applying sufficiently high currents. The behaviour of the
grain boundary resistance versus temperature and of the conductance versus
voltage are discussed in the framework charge transport through a tunnel
barrier. The influence of misorientation angle, oxygen content, and calcium
doping on the normal state properties is related to changes of the height and
shape of the grain boundary potential barrier.Comment: 17 pages, 1 table, 5 figures, submitted to PR
European wildcat populations are subdivided into five main biogeographic groups: consequences of Pleistocene climate changes or recent anthropogenic fragmentation?
Extant populations of the European wildcat are fragmented across the continent, the likely consequence of recent extirpations due to habitat loss and over-hunting. However, their underlying phylogeographic history has never been reconstructed. For testing the hypothesis that the European wildcat survived the Ice Age fragmented in Mediterranean refuges, we assayed the genetic variation at 31 microsatellites in 668 presumptive European wildcats sampled in 15 European countries. Moreover, to evaluate the extent of subspecies/population divergence and identify eventual wild × domestic cat hybrids, we genotyped 26 African wildcats from Sardinia and North Africa and 294 random-bred domestic cats. Results of multivariate analyses and Bayesian clustering confirmed that the European wild and the domestic cats (plus the African wildcats) belong to two well-differentiated clusters (average Ф ST = 0.159, r st = 0.392, P > 0.001; Analysis of molecular variance [AMOVA]). We identified from c. 5% to 10% cryptic hybrids in southern and central European populations. In contrast, wild-living cats in Hungary and Scotland showed deep signatures of genetic admixture and introgression with domestic cats. The European wildcats are subdivided into five main genetic clusters (average Ф ST = 0.103, r st = 0.143, P > 0.001; AMOVA) corresponding to five biogeographic groups, respectively, distributed in the Iberian Peninsula, central Europe, central Germany, Italian Peninsula and the island of Sicily, and in north-eastern Italy and northern Balkan regions (Dinaric Alps). Approximate Bayesian Computation simulations supported late Pleistocene-early Holocene population splittings (from c. 60 k to 10 k years ago), contemporary to the last Ice Age climatic changes. These results provide evidences for wildcat Mediterranean refuges in southwestern Europe, but the evolution history of eastern wildcat populations remains to be clarified. Historical genetic subdivisions suggest conservation strategies aimed at enhancing gene flow through the restoration of ecological corridors within each biogeographic units. Concomitantly, the risk of hybridization with free-ranging domestic cats along corridor edges should be carefully monitored
Angular dependent vortex pinning mechanisms in YBCO coated conductors and thin films
We present a comparative study of the angular dependent critical current
density in YBa2Cu3O7 films deposited on IBAD MgO and on single crystal MgO and
SrTiO3 substrates. We identify three angular regimes where pinning is dominated
by different types of correlated and uncorrelated defects. We show that those
regimes are present in all cases, indicating that the pinning mechanisms are
the same, but their extension and characteristics are sample dependent,
reflecting the quantitative differences in texture and defect density. In
particular, the more defective nature of the films on IBAD turns into an
advantage as it results in stronger vortex pinning, demonstrating that the
critical current density of the films on single crystals is not an upper limit
for the performance of the IBAD coated conductors.Comment: 14 pages, 3 figures. Submitted to AP
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Languages and Learning at Key Stage 2: A Longitudinal Study Final Report
In 2006, The Open University, the University of Southampton and Canterbury Christ Church University were commissioned by the then Department for Education and Skills (DfES), now Department for Children, Schools and Families (DCSF) to conduct a three-year longitudinal study of languages learning at Key Stage 2 (KS2). The qualitative study was designed to explore provision, practice and developments over three school years between 2006/07 and 2008/09 in a sample of primary schools and explore children’s achievement in oracy and literacy, as well as the possible broader cross-curricular impact of languages learning
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