5,358 research outputs found
Rate of lineage origin explains the diversity anomaly in the World’s mangrove vegetation
The contribution of nonecological factors to global patterns in diversity is evident when species richness differs between regions with similar habitats and geographic area. Mangrove environments in the Eastern Hemisphere harbor six times as many species of trees and shrubs as similar environments in the New World. Genetic divergence of mangrove lineages from terrestrial relatives, in combination with fossil evidence, suggests that mangrove diversity is limited by evolutionary transition into the stressful marine environment, the number of mangrove lineages has increased steadily over the Tertiary with little global extinction, and the diversity anomaly in mangrove vegetation reflects regional differences in the rate of origin of new mangrove lineages
An information-theoretic security proof for QKD protocols
We present a new technique for proving the security of quantum key
distribution (QKD) protocols. It is based on direct information-theoretic
arguments and thus also applies if no equivalent entanglement purification
scheme can be found. Using this technique, we investigate a general class of
QKD protocols with one-way classical post-processing. We show that, in order to
analyze the full security of these protocols, it suffices to consider
collective attacks. Indeed, we give new lower and upper bounds on the
secret-key rate which only involve entropies of two-qubit density operators and
which are thus easy to compute. As an illustration of our results, we analyze
the BB84, the six-state, and the B92 protocol with one-way error correction and
privacy amplification. Surprisingly, the performance of these protocols is
increased if one of the parties adds noise to the measurement data before the
error correction. In particular, this additional noise makes the protocols more
robust against noise in the quantum channel.Comment: 18 pages, 3 figure
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