3,873 research outputs found
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
Strong Pinning Enhancement in MgB2 Using Very Small Dy2O3 Additions
0.5 to 5.0 wt.% Dy2O3 was in-situ reacted with Mg + B to form pinned MgB2.
While Tc remained largely unchanged, Jc was strongly enhanced. The best sample
(only 0.5 wt.% Dy2O3) had a Jc of 6.5 x 10^5 A/cm^2 at 6K, 1T and 3.5 x 10^5
A/cm^2 at 20K, 1T, around a factor of 4 higher compared to the pure sample, and
equivalent to hot-pressed or nano-Si added MgB2 at below 1T. Even distributions
of nano-scale precipitates of DyB4 and MgO were observed within the grains. The
room temperature resistivity decreased with Dy2O3 indicative of improved grain
connectivity.Comment: 13 pages, 4 figures and 1 tabl
Improved Current Densities in MgB2 By Liquid-Assisted Sintering
Polycrystalline MgB2 samples with GaN additions were prepared by reaction of
Mg, B, and GaN powders. The presence of Ga leads to a low melting eutectic
phase which allowed liquid phase sintering and produces plate-like grains. For
low-level GaN additions (5% at. % or less), the critical transition
temperature, Tc, remained unchanged and in 1T magnetic field, the critical
current density, Jc was enhanced by a factor of 2 and 10, for temperatures of
\~5K and 20K, respectively. The values obtained are approaching those of hot
isostatically pressed samples.Comment: 12 pages, 1 table, 4 figures, accepted in Applied Physics Letter
Recommended from our members
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
Student Performance In Upper-Division Business Core Courses: Using Control Variables To Determine The Effect Of Class Size
Although the effect of class size upon student performance has been the focus of numerous studies, the results have been extremely mixed, including positive effects, no effects, and negative effects. The authors of this study believe that this lack of consensus could be due, at least in part, to the shortage of control variables employed in previous studies. The purpose of this study was to determine whether the addition of four control variables (course being taught, length of class period, instructor, and student ability level) to the analysis would be helpful in isolating the effect, if any, of class size upon student performance. To more fully explore the effects of including control variables upon the results, the control variables would be added sequentially, one at a time. The analysis would thus consist of a series of five regression sets. The first set would be a single, simple regression of student performance on class size. The second and subsequent sets would each consist of a group of simple regressions that controlled for one, two, three, and then finally all four of the control variables. The data to be used would be 113,468 course grade records (for the years 1990-2002) for 10 upper-division business core courses. Student performance would be defined as course grade; class size would be defined as either large (75 or more students) or small (60 or fewer students). The results showed that an initial slightly positive effect (.06 grade points) of class size on student performance (found in the Regression Set 1 before the addition of any control variables) changed substantially to 4 positive effects, 57 no effects, and 21 negative effects (after the addition of all four control variables in Regression Set 5). The Adjusted R-Squares also increased (from a rounded value of .000 in Regression Set 1 to a high of .428 in Regression Set 5) as did the grade point differences in performance between small and large classes (from .06 grade points in Regression Set 1 to a range of from .68 to -1.24 grade points in Regression Set 5). Although more research is certainly needed in this area before definitive conclusions can be reached about the effect of class size upon student performance, it appears that the control variable approach used in this study does shed some light on the seemingly inconsistent results of previous studies. Specifically, our results show that: (1) it quite likely (57/82 or 70%) that there will be no significant effect of class size upon student performance, (2) if there is an effect, it will most likely (21/25 or 84%) be a negative one, and (3) the effect, if any, is highly dependent upon the specific combination of course, class length, instructor, and student ability level involved
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
Focusing on size and energy dependence of electron microbursts from the Van Allen radiation belts
- …