ABSTRACT
Security in communication is vital in modern life. At present, security is realized by an encryption process in cryptography. It is unbelievable if a secure communication is achievable without encryption. In quantum cryptography, there is a unique form of quantum communication, quantum secure direct communication, where secret information is transmitted directly over a quantum channel. Quantum secure direct communication is drastically distinct from our conventional concept of secure communication, because it does not require key distribution, key storage and ciphertext transmission, and eliminates the encryption procedure completely. Hence it avoids in principle all the security loopholes associated with key and ciphertext in traditional secure communications. For practical implementation, defects always exist in real devices and it may downgrade the security. Among the various device imperfections, those with the measurement devices are the most prominent and serious ones. Here we report a measurement-device-independent quantum secure direct communication protocol using Einstein-Podolsky-Rosen pairs. This protocol eradicates the security vulnerabilities associated with the measurement device, and greatly enhances the practical security of quantum secure direct communication. In addition to the security advantage, this protocol has an extended communication distance, and a high communication capacity.
ABSTRACT
Twenty one sub-watersheds in the Jiulong River watershed were chosen for in-situ monitoring water quality of baseflow in flood season, dry season and average season in 2010. Geographical information system and multivariate analysis were coupled to characterize the spatiotemporal variation of water quality and identify its influencing factors. The results show that the water quality in dry season is the worst whereas the water quality in flood season is comparatively good. The first principal component representing sanitary and industrial wastewater pollution, explained 45.58% of the total variance of water quality. The second principal component concerning pollution due to agricultural activities, explained 21.28% of the total variance. NH4(+) -N, SRP, potassium permanganate index, K+, Cl-, Mg2+ and Na had a significantly positive correlation with percentage of built-up and density of population. NO3(-) -N was correlated positively with percentage of cropland. The sub-watersheds with high proportion of build-up area and density of population show high concentration of NH4(+) -N, SRP, potassium permanganate index, K+, Cl-. Comparatively, the sub-watersheds with high percentage of cropland show high level of nitrate concentration. Improvement of the wastewater treatment efficiency and increased recognition of agricultural non-point source pollution were finally highlighted from watershed management perspectives.
