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211.
Yehuda Ben-Shimol Boaz Ben-Moshe Yoav Ben-Yehezkel Amit Dvir Michael Segal 《Journal of Heuristics》2007,13(3):243-263
This article addresses a real-life problem - obtaining communication links between multiple base station sites, by positioning
a minimal set of fixed-access relay antenna sites on a given terrain. Reducing the number of relay antenna sites is considered
critical due to substantial installation and maintenance costs. Despite the significant cost saved by eliminating even a single
antenna site, an inefficient manual approach is employed due to the computational complexity of the problem. From the theoretical
point of view we show that this problem is not only NP hard, but also does not have a constant approximation. In this paper
we suggest several alternative automated heuristics, relying on terrain preprocessing to find educated potential points for
positioning relay stations. A large-scale computer-based experiment consisting of approximately 7,000 different scenarios
was conducted. The quality of alternative solutions was compared by isolating and displaying factors that were found to affect
the standard deviation of the solutions supplied by the tested heuristics. The results of the simulation based experiments
show that the saving potential increases when more base stations are needed to be interconnected. The designs of a human expert
were compared to the automatically generated solutions for a small subset of the experiment scenarios. Our studies indicate
that for small networks (e.g., connecting up to ten base stations), the results obtained by human experts are adequate although
they rarely exceed the quality of automated alternatives. However, the process of obtaining these results in comparison to
automated heuristics is longer. In addition, when more base station sites need to be interconnected, the human approach is
easily outperformed by our heuristics, both in terms of better results (fewer antennas) and in significant shorter calculation
times. 相似文献
212.
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215.
W. H. Eugen Schwarz 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》1989,101(7):958-958
216.
217.
A simple procedure to obtain the derivative of the temperature integral with respect to the activation energy is presented. 相似文献
218.
The complexes AgL (L = theobromine, 1,3,8-trimethylxanthine and 3,8-dimethylxanthine) Hg2L·NO3 (L = 3,8-dimethylxanthine and 1,3,8-trimethylxanthine) and Hg2C2(NO3)2 (C = caffeine), were prepared in aqueous and HNO3 medium. These complexes were characterized by IR, 1H-NMR, TG, DTG and DSC techniques. 相似文献
219.
The authors present their results concerning the changes of activation energy determined under non-isothermal conditions with the conversion degree. An interpretation of this effect is suggested. 相似文献
220.