200,709 research outputs found
A Constant-Factor Approximation for Multi-Covering with Disks
We consider variants of the following multi-covering problem with disks. We
are given two point sets (servers) and (clients) in the plane, a
coverage function , and a constant . Centered at each server is a single disk whose radius we are free to
set. The requirement is that each client be covered by at least
of the server disks. The objective function we wish to minimize is
the sum of the -th powers of the disk radii. We present a polynomial
time algorithm for this problem achieving an approximation
Allocation of control and data channels for Large-Scale Wireless Sensor Networks
Both IEEE 802.15.4 and 802.15.4a standards allow for dynamic channel
allocation and use of multiple channels available at their physical layers but
its MAC protocols are designed only for single channel. Also, sensor's
transceivers such as CC2420 provide multiple channels and as shown in [1], [2]
and [3] channel switch latency of CC2420 transceiver is just about 200s.
In order to enhance both energy efficiency and to shorten end to end delay, we
propose, in this report, a spectrum-efficient frequency allocation schemes that
are able to statically assign control channels and dynamically reuse data
channels for Personal Area Networks (PANs) inside a Large-Scale WSN based on
UWB technology
Improved approximation of arbitrary shapes in dem simulations with multi-spheres
DEM simulations are originally made for spherical particles only. But most of real particles are anything but not spherical. Due to this problem, the multi-sphere method was invented. It provides the possibility to clump several spheres together to create complex shape structures. The proposed algorithm oïŹers a novel method to create multi-sphere clumps for the given arbitrary shapes. Especially the use of modern clustering algorithms, from the ïŹeld of computational intelligence, achieve satisfactory results. The clustering is embedded into an optimisation algorithm which uses a pre-deïŹned criterion. A mostly unaided algorithm with only a few input and hyperparameters is able to approximate arbitrary shapes
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