1,797 research outputs found
Tight Bounds for the Cover Times of Random Walks with Heterogeneous Step Lengths
Search patterns of randomly oriented steps of different lengths have been observed on all scales of the biological world, ranging from the microscopic to the ecological, including in protein motors, bacteria, T-cells, honeybees, marine predators, and more. Through different models, it has been demonstrated that adopting a variety in the magnitude of the step lengths can greatly improve the search efficiency. However, the precise connection between the search efficiency and the number of step lengths in the repertoire of the searcher has not been identified. Motivated by biological examples in one-dimensional terrains, a recent paper studied the best cover time on an n-node cycle that can be achieved by a random walk process that uses k step lengths. By tuning the lengths and corresponding probabilities the authors therein showed that the best cover time is roughly n 1+Θ(1/k). While this bound is useful for large values of k, it is hardly informative for small k values, which are of interest in biology. In this paper, we provide a tight bound for the cover time of such a walk, for every integer k > 1. Specifically, up to lower order polylogarithmic factors, the upper bound on the cover time is a polynomial in n of exponent 1+ 1/(2k−1). For k = 2, 3, 4 and 5 the exponent is thus 4/3 , 6/5 , 8/7 , and 10/9 , respectively. Informally, our result implies that, as long as the number of step lengths k is not too large, incorporating an additional step length to the repertoire of the process enables to improve the cover time by a polynomial factor, but the extent of the improvement gradually decreases with k
Weighted simplicial complex reconstruction from mobile laser scanning using sensor topology
We propose a new method for the reconstruction of simplicial complexes
(combining points, edges and triangles) from 3D point clouds from Mobile Laser
Scanning (MLS). Our method uses the inherent topology of the MLS sensor to
define a spatial adjacency relationship between points. We then investigate
each possible connexion between adjacent points, weighted according to its
distance to the sensor, and filter them by searching collinear structures in
the scene, or structures perpendicular to the laser beams. Next, we create and
filter triangles for each triplet of self-connected edges and according to
their local planarity. We compare our results to an unweighted simplicial
complex reconstruction.Comment: 8 pages, 11 figures, CFPT 2018. arXiv admin note: substantial text
overlap with arXiv:1802.0748
Nonintrusive coupling of 3D and 2D laminated composite models based on finite element 3D recovery
In order to simulate the mechanical behavior of large structures assembled
from thin composite panels, we propose a coupling technique which substitutes
local 3D models for the global plate model in the critical zones where plate
modeling is inadequate. The transition from 3D to 2D is based on stress and
displacement distributions associated with Saint-Venant problems which are
precalculated automatically for a simple 3D cell. The hybrid plate/3D model is
obtained after convergence of a series of iterations between a global plate
model of the structure and localized 3D models of the critical zones. This
technique is nonintrusive because the global calculations can be carried out
using commercial software. Evaluation tests show that convergence is fast and
that the resulting hybrid model is very close to a full 3D model
Alien Registration- Guinard, Frances M. (Portland, Cumberland County)
https://digitalmaine.com/alien_docs/24267/thumbnail.jp
Alien Registration- Guinard, Muriel E. (Brunswick, Cumberland County)
https://digitalmaine.com/alien_docs/31493/thumbnail.jp
Alien Registration- Guinard, Frances M. (Portland, Cumberland County)
https://digitalmaine.com/alien_docs/24267/thumbnail.jp
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