157 research outputs found
Double loop networks with minimum delay
AbstractDouble loop networks have been widely studied as practical and reliable computer networks. Let N denote the number of stations in a double loop network. The literature has proposed a topology which yields the diameter 2âN. In this paper we give a heuristic method which finds a topology with diameter roughly â3N for large N. We also give several infinite classes of values of N for which topologies are found that achieve the lower bound ââ3Nâ â 2 for the diameter
A new construction of 3Ì-separable matrices via an improved decoding of Maculaâs construction
AbstractMacula proposed a novel construction of pooling designs which can effectively identify positive clones and also proposed a decoding method. However, the probability of an unresolved positive clone is hard to analyze. In this paper we propose an improved decoding method and show that for d=3 an exact probability analysis is possible. Further, we derive necessary and sufficient conditions for a positive clone to be unresolved and gave a modified construction which avoids this necessary condition, thus resulting in a 3Ì-separable matrix
Concurrent Geometric Multicasting
We present MCFR, a multicasting concurrent face routing algorithm that uses
geometric routing to deliver a message from source to multiple targets. We
describe the algorithm's operation, prove it correct, estimate its performance
bounds and evaluate its performance using simulation. Our estimate shows that
MCFR is the first geometric multicast routing algorithm whose message delivery
latency is independent of network size and only proportional to the distance
between the source and the targets. Our simulation indicates that MCFR has
significantly better reliability than existing algorithms
Structural and doping effects in the half-metallic double perovskite CrWO
he structural, transport, magnetic and optical properties of the double
perovskite CrWO with have been studied. By
varying the alkaline earth ion on the site, the influence of steric effects
on the Curie temperature and the saturation magnetization has been
determined. A maximum K was found for SrCrWO having an almost
undistorted perovskite structure with a tolerance factor . For
CaCrWO and BaCrWO structural changes result in a strong
reduction of . Our study strongly suggests that for the double perovskites
in general an optimum is achieved only for , that is, for an
undistorted perovskite structure. Electron doping in SrCrWO by a
partial substitution of Sr by La was found to reduce both
and the saturation magnetization . The reduction of could be
attributed both to band structure effects and the Cr/W antisites induced by
doping. Band structure calculations for SrCrWO predict an energy gap in
the spin-up band, but a finite density of states for the spin-down band. The
predictions of the band structure calculation are consistent with our optical
measurements. Our experimental results support the presence of a kinetic energy
driven mechanism in CrWO, where ferromagnetism is stabilized by a
hybridization of states of the nonmagnetic W-site positioned in between the
high spin Cr-sites.Comment: 14 pages, 10 figure
Identical transitions in the strongly deformed Sr-99 and Sr-100
The decay of the very neutron-rich nucleus Rb-100 has been studied by
gamma-spectroscopy of on-line mass-separated samples. Schemes for beta-decay to
Sr-100 and beta-n-decay to Sr-99 are presented. New sets of transitions in
Sr-99 and Sr-100 with identical energies are observed. All identical bands so
far observed in neutron-rich Sr isotopes obey a simple energy rule valid for
even-even, odd-even and odd-odd bands.Comment: 31 pages, 7 figures, Phys. Rev. C, in prin
Particle swarm optimization for the Steiner tree in graph and delay-constrained multicast routing problems
This paper presents the first investigation on applying a particle swarm optimization (PSO) algorithm to both the Steiner tree problem and the delay constrained multicast routing problem. Steiner tree problems, being the underlining models of many applications, have received significant research attention within the meta-heuristics community. The literature on the application of meta-heuristics to multicast routing problems is less extensive but includes several promising approaches. Many interesting research issues still remain to be investigated, for example, the inclusion of different constraints, such as delay bounds, when finding multicast trees with minimum cost. In this paper, we develop a novel PSO algorithm based on the jumping PSO (JPSO) algorithm recently developed by Moreno-Perez et al. (Proc. of the 7th Metaheuristics International Conference, 2007), and also propose two novel local search heuristics within our JPSO framework. A path replacement operator has been used in particle moves to improve the positions of the particle with regard to the structure of the tree. We test the performance of our JPSO algorithm, and the effect of the integrated local search heuristics by an extensive set of experiments on multicast routing benchmark problems and Steiner tree problems from the OR library. The experimental results show the superior performance of the proposed JPSO algorithm over a number of other state-of-the-art approaches
On Macula's error-correcting pool designs
AbstractWe show that Macula's claim of a Hamming distance 4 between any two candidate sets of positive clones in his pool design is incorrect. However, a previous proof of his on a weaker result (with a condition on design parameters) is correct. We also show that the condition is sharp and the distance 4 result is also sharp for arbitrary parameter values
Enumerating Consecutive and Nested Partitions for Graphs
Consecutive & nested partitions have been extensively studied in the set-partition problem as tools
with which to search efficiently for an optimal partition. We extend the study of consecutive and
nested partitions on a set of integers to the vertex-set of a graph. A subset of vertices is considered
consecutive if the subgraph induced by the subset is connected. In this sense the partition problem on
a set of integers can be treated as a special case when the graph is a line. In this paper we give the
number of consecutive & nested partitions when the graph is a cycle. We also give a partial order
on general graphs with respect to these numbers
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