8,710 research outputs found
On self-protecting singlets in cuprate superconductors
The basal area (Cu-Cu grid) of the cuprate superconductors not only tends to
shrink on hole doping, as expected from single electron quantum chemistry, but
exhibits also an electronically incompressible "hump'' around optimum doping
n_opt = 0.16. The hump collapses near critical doping n_crit = 0.19. We analyze
the origin of the hump in terms of a classical liquid of interacting
incompressible particles in a container with antiferromagnetic walls. Oxygen
holes interacting with the wall form singlets, protect themselves against other
holes by an incompressible "spin fence'', and thus interact also with the
lattice. Occupation of the CuO_2 lattice with holes must therefore follow a
non-double-occupant constraint also for the oxygen cage enclosing the copper
hole. Closest packing of self-protecting singlets is found to occur around
critical doping; closest packing of paired self-protecting singlets around
optimum doping. These singlet-states are bosonic, but are not magnetic
polarons.Comment: reviewed version, 7 pages, 10 figure
Extracellular polymeric bacterial coverages as minimal area surfaces
Surfaces formed by extracellular polymeric substances enclosing individual
and some small communities of {\it Acidithiobacillus ferrooxidans} on plates of
hydrophobic silicon and hydrophilic mica are analyzed by means of atomic force
microscopy imaging. Accurate nanoscale descriptions of such coverage surfaces
are obtained. The good agreement with the predictions of a rather simple but
realistic theoretical model allows us to conclude that they correspond, indeed,
to minimal area surfaces enclosing a given volume associated with the encased
bacteria. This is, to the best of our knowledge, the first shape
characterization of the coverage formed by these biomolecules, with potential
applications to the study of biofilms.Comment: 4 pages, 9 figures. v2: minor changes. v3: Terminology changes and
extra references included. v4: Final versio
Approximation algorithms for multi-facility location
This thesis deals with the development and implementation of efficient algorithms to obtain acceptable solutions for the location of several facilities to serve customer sites. The general version of facility location problem is known to be NP-hard; For locating multiple facilities we use Voronoi diagram of initial facility locations to partition the customer sites into k clusters. On each Voronoi region, solutions for single facility problem is obtained by using both Weizfield\u27s algorithm and Center of Gravity. The customer space is again partitioned by using the newly computed locations. This iteration is continued to obtain a better solution for multi-facility location problem. We call the resulting algorithm: Voronoi driven k-median algorithm ; We report experimental results on several test data that include randomly distributed customers and distinctly clustered customers. The observed results show that the proposed approximation algorithm produces good results
Minimum-Width Double-Strip and Parallelogram Annulus
In this paper, we study the problem of computing a minimum-width double-strip or parallelogram annulus that encloses a given set of n points in the plane. A double-strip is a closed region in the plane whose boundary consists of four parallel lines and a parallelogram annulus is a closed region between two edge-parallel parallelograms. We present several first algorithms for these problems. Among them are O(n^2) and O(n^3 log n)-time algorithms that compute a minimum-width double-strip and parallelogram annulus, respectively, when their orientations can be freely chosen
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Spatially Ordered Treemaps
Existing treemap layout algorithms suffer to some extent from poor or inconsistent mappings between data order and visual ordering in their representation, reducing their cognitive plausibility. While attempts have been made to quantify this mismatch, and algorithms proposed to minimize inconsistency, solutions provided tend to concentrate on one-dimensional ordering. We propose extensions to the existing squarified layout algorithm that exploit the two-dimensional arrangement of treemap nodes more effectively. Our proposed spatial squarified layout algorithm provides a more consistent arrangement of nodes while maintaining low aspect ratios. It is suitable for the arrangement of data with a geographic component and can be used to create tessellated cartograms for geovisualization. Locational consistency is measured and visualized and a number of layout algorithms are compared. CIELab color space and displacement vector overlays are used to assess and emphasize the spatial layout of treemap nodes. A case study involving locations of tagged photographs in the Flickr database is described
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