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  • Author: A. H. H. Wong x
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Abstract

A 7514-Da chymotrypsin inhibitor was isolated from the seed extract of Momordica cochinchinensis (Family Cucurbitaceae) by chromatography on chymotrypsin Sepharose 4B and subsequently by C18 reversed-phase HPLC. This inhibitor, named MCoCI, possessed remarkable thermostability and was stable from pH 2 to 12. MCoCI also inhibited subtilisin, but had at least 50-fold lower inhibitory activity towards trypsin and elastase. Amino acid sequencing of a peptide fragment of MCoCI revealed a sequence of 23 amino acids. Comparison of this sequence and the molecular mass with those of other protease inhibitors suggests that MCoCI belongs to the potato I inhibitor family.

Abstract

The performance of single photon pulsed polarization based BB84 and B92 platforms against individual attacks for free space quantum optical communication links between a ground station and a satellite in the low earth orbit is compared. The comparison is attained by evaluating the quantum bit error rate and secure communication bit rate on secure optical link loss and the sensitivity of different parameters. Precisely, realistic experimental parameters are used and the obtained results are compared with those of other papers. Quantum bit error rates as low as 3.5% have been regularly obtained. Moreover, with repetition rate of 10MHz at the low earth orbit standard orbital altitude of 100 km and at zenith angle of 60 degrees, secure communication bit rates of ~ 280 kHz and ~ 70 kHz were received for the BB84 and B92, respectively. The obtained results show that the BB84 protocol exhibits better performance than B92 in the distribution of the secure communication key over long distance. Overall, these results reveal that it is possible to obtain secure key exchange in the low earth orbit, an idea which can be extended to other long distance laser links such as geostationary orbit.

Two classes of rotaxanes are described in which photoinduced processes modulate a large-amplitude motion. In the first type, E–Z-isomerization of a fumaric diamide unit to a maleic diamide leads to a substantial weakening of the hydrogen bonds between the diamide and the macrocyclic ring that surrounds it. As a result, the rate of the pirouetting motion is increased approximately by six orders of magnitude. In the second type, intermolecular photoinduced electron transfer is used to induce a reversible shuttling motion on a time scale of microseconds. Medium effects on the rate of shuttling are presented.