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Register a new userDiscrete tomography: Magic numbers for $N$-fold symmetry
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We consider the problem of distinguishing convex subsets of $n$-cyclotomic model sets $varLambda$ by (discrete parallel) X-rays in prescribed $varLambda$-directions. In this context, a `magic number $m_{varLambda}$ has the property that any two convex subsets of $varLambda$ can be distinguished by their X-rays in any set of $m_{varLambda}$ prescribed $varLambda$-directions. Recent calculations suggest that (with one exception in the case $n=4$) the least possible magic number for $n$-cyclotomic model sets might just be $N+1$, where $N=operatorname{lcm}(n,2)$.
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The coincidence problem for planar patterns with $N$-fold symmetry is considered. For the N-fold symmetric module with $N<46$, all isometries of the plane are classified that result in coincidences of finite index. This is done by reformulating the problem in terms of algebraic number fields and using prime factorization. The more complicated case $N ge 46$ is briefly discussed and N=46 is described explicitly. The results of the coincidence problem also solve the problem of colour lattices in two dimensions and its natural generalization to colour modules.
Discrete tomography is a well-established method to investigate finite point sets, in particular finite subsets of periodic systems. Here, we start to develop an efficient approach for the treatment of finite subsets of mathematical quasicrystals. To this end, the class of cyclotomic model sets is introduced, and the corresponding consistency, reconstruction and uniqueness problems of the discrete tomography of these sets are discussed.
This paper has been withdrawn by Wenji Deng (e-mail: [email protected]) for further modification at Oct. 12, 1998. {PACS: 03.75.Fi, 05.30.Jp.64.60.-i, 32.80.Pj}
The nuclear shell model is a benchmark for the description of the structure of atomic nuclei. The magic numbers associated with closed shells have long been assumed to be valid across the whole nuclear chart. Investigations in recent years of nuclei far away from nuclear stability at facilities for radioactive ion beams have revealed that the magic numbers may change locally in those exotic nuclei leading to the disappearance of classic shell gaps and the appearance of new magic numbers. These changes in shell structure also have important implications for the synthesis of heavy elements in stars and stellar explosions. In this review a brief overview of the basics of the nuclear shell model will be given together with a summary of recent theoretical and experimental activities investigating these changes in the nuclear shell structure.
The discrete Laplace operator on a triangulated polyhedral surface is related to geometric properties of the surface. This paper studies extremum problems for eigenvalues of the discrete Laplace operators. Among all triangles, an equilateral triangle has the maximal first positive eigenvalue. Among all cyclic quadrilateral, a square has the maximal first positive eigenvalue. Among all cyclic $n$-gons, a regular one has the minimal value of the sum of all nontrivial eigenvalues and the minimal value of the product of all nontrivial eigenvalues.
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