1,372 research outputs found
Satellite downlink scheduling problem: A case study
The synthetic aperture radar (SAR) technology enables satellites to
efficiently acquire high quality images of the Earth surface. This generates
significant communication traffic from the satellite to the ground stations,
and, thus, image downlinking often becomes the bottleneck in the efficiency of
the whole system. In this paper we address the downlink scheduling problem for
Canada's Earth observing SAR satellite, RADARSAT-2. Being an applied problem,
downlink scheduling is characterised with a number of constraints that make it
difficult not only to optimise the schedule but even to produce a feasible
solution. We propose a fast schedule generation procedure that abstracts the
problem specific constraints and provides a simple interface to optimisation
algorithms. By comparing empirically several standard meta-heuristics applied
to the problem, we select the most suitable one and show that it is clearly
superior to the approach currently in use.Comment: 23 page
Parallel local search for solving Constraint Problems on the Cell Broadband Engine (Preliminary Results)
We explore the use of the Cell Broadband Engine (Cell/BE for short) for
combinatorial optimization applications: we present a parallel version of a
constraint-based local search algorithm that has been implemented on a
multiprocessor BladeCenter machine with twin Cell/BE processors (total of 16
SPUs per blade). This algorithm was chosen because it fits very well the
Cell/BE architecture and requires neither shared memory nor communication
between processors, while retaining a compact memory footprint. We study the
performance on several large optimization benchmarks and show that this
achieves mostly linear time speedups, even sometimes super-linear. This is
possible because the parallel implementation might explore simultaneously
different parts of the search space and therefore converge faster towards the
best sub-space and thus towards a solution. Besides getting speedups, the
resulting times exhibit a much smaller variance, which benefits applications
where a timely reply is critical
Effects of spent garnet on the compressive and flexural strengths of concrete
Sand is the non-renewable resource which has been over-exploited from
rivers in sync with the rapid development of construction industries to produce
concrete. This affected the morphology of rivers and interrupted the functionality of
riverine ecosystems by pollution. Meanwhile, the unrecyclable spent garnets were
disposed of on a large scale and led to waste pollution. Therefore, this study aimed to
determine the compressive and flexural strengths of concrete consisting of spent
garnet as sand replacement. The specimens were prepared with consisting of spent
garnet as sand replacement by weight in 0%, 10%, 20%, 30% and 40%. They were
tested under compressive strength test at the age of 7 and 28 days while flexural
strength test was conducted on the 28days. The findings revealed that the workability
of fresh concrete was enhanced by an incremental amount of spent garnet. However,
the compressive and flexural strengths of concrete consisting of spent garnet were
discerned to be lower than control samples at all levels of replacement. Overall, the
replacement with 20% spent garnet showed the optimum compressive and flexural
strengths. It is concluded that the usage of spent garnet is considered as a promising
resource for reducing consumption of sand and thus, improving the environmental
problems
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