Many smart grid communications are delay sensitive and have very strict timing requirements for message deliveries. For example, trip protection messages must be delivered to the destination within 3 ms according to IEC 61850. Such timecritical communications are vulnerable to flooding attacks which attempt to increase message delivery delay through congesting the network channel and exhausting the computation resources of the communicating nodes. However, there is a lack of understanding on how much flooding attacks affect message delivery delays. In this paper, we conduct experimental studies to investigate how flooding attacks affect message delivery delays for time-critical communications in smart grid. Our experiments are based on both wireless networks in a lab and wired networks in a real, industry-standard electric power facility. Experimental results show that even low-rate flooding attacks can significantly increase the message delivery delays, especially when wireless networks are used.
The earliest steps in bacterial photosynthesis require that an antenna system efficiently capture incident photons and shuttle the excitation energy to the ''special pair'' bacteriochlorophylls within the membrane-bound reaction center where charge separation occurs. Previous work has shown coherent energy transfer -a wavelike transfer process -among peripheral chromophores, bacteriopheophytins and accessory bacteriochlorophylls, at cryogenic temperatures. Whether or not this coherent transfer extends to the special pair, however, has remained elusive at any temperature. Here we report direct evidence that the special pair is coherently coupled to the accessory bacteriochlophylls and that this coherence dephases only upon transfer to the special pair -the maximal amount of coherence physically possible. We employ Gradient Assisted Photon Echo Spectroscopy to simultaneously excite the bacteriopheophytins, accessory bacteriochlorophylls and the special pair in the reaction center from Rhodobacter sphaeroides. These results suggest the bacteria exploits coherent energy transfer at room temperature.
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