23,944 research outputs found
Growing perfect cubes
AbstractAn (n,a,b)-perfect double cube is a b×b×b sized n-ary periodic array containing all possible a×a×a sized n-ary array exactly once as subarray. A growing cube is an array whose cj×cj×cj sized prefix is an (nj,a,cj)-perfect double cube for j=1,2,…, where cj=njv/3,v=a3 and n1<n2<⋯. We construct the smallest possible perfect double cube (a 256×256×256 sized 8-ary array) and growing cubes for any a
Space-time segmentation method for study of the vertical structure and evolution of solar supergranulation from data provided by local helioseismology
Solar supergranulation remains a mystery in spite of decades of intensive
studies. Most of the papers about supergranulation deal with its surface
properties. Local helioseismology provides an opportunity to look below the
surface and see the vertical structure of this convective structure. We present
a concept of a (3+1)-D segmentation algorithm capable of recognising individual
supergranules in a sequence of helioseismic 3-D flow maps. As an example, we
applied this method to the state-of-the-art data and derived descriptive
statistical properties of segmented supergranules -- typical size of 20--30 Mm,
characteristic lifetime of 18.7 hours, and estimated depth of 15--20 Mm. We
present preliminary results obtained on the topic of the three-dimensional
structure and evolution of supergranulation. The method has a great potential
in analysing the better data expected from the helioseismic inversions, which
are being developed.Comment: 6 pages, 4 figures, accepted in New Astronom
Measurable circle squaring
Laczkovich proved that if bounded subsets and of have the same
non-zero Lebesgue measure and the box dimension of the boundary of each set is
less than , then there is a partition of into finitely many parts that
can be translated to form a partition of . Here we show that it can be
additionally required that each part is both Baire and Lebesgue measurable. As
special cases, this gives measurable and translation-only versions of Tarski's
circle squaring and Hilbert's third problem.Comment: 40 pages; Lemma 4.4 improved & more details added; accepted by Annals
of Mathematic
Anomalous diffusion and response in branched systems: a simple analysis
We revisit the diffusion properties and the mean drift induced by an external
field of a random walk process in a class of branched structures, as the comb
lattice and the linear chains of plaquettes. A simple treatment based on
scaling arguments is able to predict the correct anomalous regime for different
topologies. In addition, we show that even in the presence of anomalous
diffusion, Einstein's relation still holds, implying a proportionality between
the mean square displacement of the unperturbed systems and the drift induced
by an external forcing.Comment: revtex.4-1, 16 pages, 7 figure
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