We present a scheme for quantum secure direct communication with quantum encryption. The two authorized users use repeatedly a sequence of the pure entangled pairs (quantum key) shared for encrypting and decrypting the secret message carried by the traveling photons directly. For checking eavesdropping, the two parties perform the single-photon measurements on some decoy particles before each round. This scheme has the advantage that the pure entangled quantum signal source is feasible at present and any eavesdropper cannot steal the message.Keywords: quantum secure direct communication, quantum encryption, quantum key, pure entangled states PACC: 0155, 0367Quantum mechanics provides some novel ways for processing and transmission of quantum information. Quantum key distribution (QKD) is considered to be the safest system for creating a private key between two remote authorized users, say Alice and Bob, and may be the most advanced application of quantum information. The noncloning theorem forbids an eavesdropper, Eve to eavesdrop the quantum communication freely. In 1984, Bennett and Brassard [1] proposed an original QKD protocol with nonorthogonal polarized single photons. As an unknown quantum states cannot be eavesdropped without leaving a trace in the outcomes obtained by the two parties, the BB84 protocol is unconditionally secure [2]. In 1991, Ekert [3] introduced another QKD scheme based on the correlation of an Einstein-Podolsky-Rosen (EPR) pair, the maximally entangled two-particle state, by using Bell inequality for error rate analysis. Subsequently, Bennett, Brassard and Mermin (BBM92) [4] simplified the process for eavesdropping check in this scheme with two nonorthogonal measuring bases. Lo, Chau and Ardehali [5] presented a QKD model with two nonsymmetric bases. Huang et al. [6] and Deng et al. [7] designed two QKD models by using repeatedly a sequence of private classical bits shared initially for improving their efficiency for qubits or reducing the delay time in QKD with some orthogonal states. To date, much attention has been focused on QKD [5,6,7,8,9,10,11].Recently, quantum secure direct communication (QSDC), a novel concept, was proposed and pursued by some groups [12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29]. Different from QKD whose goal is * Published in Chin. Phys. 16, 2149Phys. 16, -2153Phys. 16, (2007 † E-mail addresses: fgdeng@bnu.edu.cn to generate a private key between the two remote parties of communication, QSDC is used to communicate the secret message directly without generating a key in advance and then encrypting the message for its transmission in a classical channel. According to the Deng-Long-Liu criterion [12,13,14], on one hand, the sender Alice should confirm whether the quantum channel is secure before she encodes the message on the quantum states transmitted as the messages cannot be discarded in QSDC [12,13,14]. Moreover, the message should be read out by the receiver Bob directly [12,13,14]. On the other hand, the security of quantum communication is b...
Taking the Beijing-Tianjin-Hebei region as an example, this article puts forward a method of geological hazard risk assessment. By calculating the level of threat of geological hazards and vulnerability of hazard-affected bodies first, we evaluated the geological hazard risk of counties and districts by qualitative comprehensive assessment. Vulnerability of hazard-affected bodies is composed of population vulnerability and property vulnerability, which are represented by the rate of deaths and rate of direct economic loss caused by geological hazards. Combing with the data of geological disaster situation during 2001-2015 from the Ministry of Land and Resources and taking into account the 1950-2000 disaster data, we proposed the classification standards of population vulnerability and property vulnerability. These standards and calculation were applied in the Beijing-Tianjin-Hebei region. The result shows that the overall geological hazard risk is low. Only six areas-Laiyuan, Laishui, Wuan, Qinglong Manchu Autonomous County, Shijingshan, and Yanqing-show medium risk among the total of 204 assessed county and district units. The rest of the counties and districts are in the low risk area, which is in agreement with the reality. The method proposed here is simple and easy to use, and data can be acquired continuously. The spatial difference assessment result can be used to support the disaster prevention and risk reduction efforts and spatial planning and management.
量水平群体, 研究籽粒产量 9000 kg hm -2 群体钾素积累、分配与利用特性。结果表明, 籽粒产量≥9000 kg hm -2 (超高 产)群体钾素吸收高峰期出现在拔节至开花期, 吸收的钾素占一生吸收钾素的 52%~68%; 开花期和成熟期钾素积累 量均极显著高于<9000 kg hm -2 (高产)群体。成熟期叶片、茎鞘、颖壳+穗轴和籽粒钾素积累量与籽粒产量均呈极显著 线性正相关; 花后茎鞘钾素转运量与产量呈极显著线性正相关, 颖壳+穗轴钾素转运量与产量呈极显著线性负相关。 超高产群体开花期和成熟期钾素积累量分别为 430~450 kg hm -2 和 366~408 kg hm -2 ; 成熟期钾素积累量, 茎鞘中最高, 为 244~269 kg hm -2 , 其次是叶片和颖壳+穗轴, 分别为 46~49 kg hm -2 和 40~46 kg hm -2 , 籽粒中仅为 35~46 kg hm -2 ; 花后茎鞘钾素转出量为 46~52 kg hm -2 , 颖壳+穗轴钾素积累量为 9~17 kg hm -2 。超高产群体每 100 kg 籽粒的吸钾量 需达 4.57~4.87 kg, 此时的钾素利用效率为 20.56~22.02 kg kg -1 , 钾收获指数为 0.095~0.112。
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