We give an on-line deterministic algorithm for the weighted bipartite matching problem that achieves a competitive ratio of (2n − 1) in any metric space (where n is the number of vertices). This algorithm is optimal-there is no on-line deterministic algorithm that achieves a competitive ratio better than (2n − 1) in all metric spaces. We also study the stable marriage problem, where we are interested in the number of unstable pairs produced. We show that the simple "first come, first served" deterministic algorithm yields on the average O(n log n) unstable pairs, but in the worst case no deterministic or randomized on-line algorithm can do better than Ω(n 2) unstable pairs. This appears to be the first on-line problem for which provably one cannot do better with randomization; for most on-line problems studied in the past, randomization has helped in improving the performance.
Condition monitoring of an operating apparatus is essential for lifespan assessment and maintenance planning in a power system. Electrical insulation is a critical aspect to be monitored, since it is susceptible to failure under high electrical stress. To avoid unexpected breakdowns, the level of partial discharge (PD) activity should be continuously monitored because PD occurrence can accelerate the aging process of insulation in high voltage equipment and result in catastrophic failure if the associated defects are not treated at an early stage. For on-site PD detection, the ultra-high frequency (UHF) method was employed in the field and showed its effectiveness as a detection technique. The main advantage of the UHF method is its immunity to external electromagnetic interference with a high signal-to-noise ratio, which is necessary for on-site monitoring. Considering the detection process, sensors play a critical role in capturing signals from PD sources and transmitting them onto the measurement system. In this paper, UHF sensors applied in PD detection were comprehensively reviewed. In particular, for power transformers, the effects of the physical structure on UHF signals and practical applications of UHF sensors including PD localization techniques were discussed. The aim of this review was to present state-of-the-art UHF sensors in PD detection and facilitate future improvements in the UHF method.
We give an on-line deterministic algorithm for the weighted bipartite matching problem that achieves a competitive ratio of (2n − 1) in any metric space (where n is the number of vertices). This algorithm is optimal -there is no on-line deterministic algorithm that achieves a competitive ratio better than (2n − 1) in all metric spaces.We also study the stable marriage problem, where we are interested in the number of unstable pairs produced. We show that the simple "first come, first served" deterministic algorithm yields on the average O(n log n) unstable pairs, but in the worst case no deterministic or randomized on-line algorithm can do better than Ω(n 2 ) unstable pairs. This appears to be the first on-line problem for which provably one cannot do better with randomization; for most on-line problems studied in the past, randomization has helped in improving the performance.
For over a decade the Cornell Bioacoustics Research Program has been using passive sparse acoustic arrays to locate calling marine mammals in the near field in shallow water, as well as birds and other animals in air. The techniques used have been cross correlation followed by all-pairs hyperbolic geometric positioning, using the simplest propagation model, and iterative nonlinear least-squares error minimization. This talk describes some of our experiences with this process, including the results of calibrated field tests. Applications to whale population censusing and research into the countersinging behavior of song sparrows will be discussed. Many bioacoustic passive array experiments depend on accurate locations at the extremes of the near field, where range is difficult to determine. Analysis techniques for passive near-field arrays have appeared in the literature over the past 50 years. Recently there has been much work devoted to using detailed propagation modeling to improve the accuracy of undersea localization of marine vessels. It is argued that, in the case of animal calls, there are also accuracy improvements to be had from improved signal modeling.
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