208,988 research outputs found
Bicriteria Network Design Problems
We study a general class of bicriteria network design problems. A generic
problem in this class is as follows: Given an undirected graph and two
minimization objectives (under different cost functions), with a budget
specified on the first, find a <subgraph \from a given subgraph-class that
minimizes the second objective subject to the budget on the first. We consider
three different criteria - the total edge cost, the diameter and the maximum
degree of the network. Here, we present the first polynomial-time approximation
algorithms for a large class of bicriteria network design problems for the
above mentioned criteria. The following general types of results are presented.
First, we develop a framework for bicriteria problems and their
approximations. Second, when the two criteria are the same %(note that the cost
functions continue to be different) we present a ``black box'' parametric
search technique. This black box takes in as input an (approximation) algorithm
for the unicriterion situation and generates an approximation algorithm for the
bicriteria case with only a constant factor loss in the performance guarantee.
Third, when the two criteria are the diameter and the total edge costs we use a
cluster-based approach to devise a approximation algorithms --- the solutions
output violate both the criteria by a logarithmic factor. Finally, for the
class of treewidth-bounded graphs, we provide pseudopolynomial-time algorithms
for a number of bicriteria problems using dynamic programming. We show how
these pseudopolynomial-time algorithms can be converted to fully
polynomial-time approximation schemes using a scaling technique.Comment: 24 pages 1 figur
Reliability demonstration for safety-critical systems
This paper suggests a new model for reliability demonstration of safety-critical systems, based on the TRW Software Reliability Theory. The paper describes the model; the test equipment required and test strategies based on the various constraints occurring during software development. The paper also compares a new testing method, Single Risk Sequential Testing (SRST), with the standard Probability Ratio Sequential Testing method (PRST), and concludes that: • SRST provides higher chances of success than PRST • SRST takes less time to complete than PRST • SRST satisfies the consumer risk criterion, whereas PRST provides a much smaller consumer risk than the requirement
Optimal Number, Location, and Size of Distributed Generators in Distribution Systems by Symbiotic Organism Search Based Method
This paper proposes an approach based on
the Symbiotic Organism Search (SOS) for optimal determining
sizing, siting, and number of Distributed
Generations (DG) in distribution systems. The objective
of the problem is to minimize the power loss of the
system subject to the equality and inequality constraints
such as power balance, bus voltage limits, DG capacity
limits, and DG penetration limit. The SOS approach is
defined as the symbiotic relationship observed between
two organisms in an ecosystem, which does not need the
control parameters like other meta-heuristic algorithms
in the literature. For the implementation of the proposed
method to the problem, an integrated approach of
Loss Sensitivity Factor (LSF) is used to determine the
optimal location for installation of DG units, and SOS
is used to find the optimal size of DG units. The proposed
method has been tested on IEEE 33-bus, 69-bus,
and 118-bus radial distribution systems. The obtained
results from the SOS algorithm have been compared to
those of other methods in the literature. The simulated
results have demonstrated that the proposed SOS
method has a very good performance and effectiveness
for the problem of optimal placement of DG units in
distribution systems
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