共查询到20条相似文献,搜索用时 78 毫秒
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空间激光通信凭借其带宽优势,成为未来高速空间通信不可或缺的有效手段,是近年来国际上的研究热点。本文详细介绍了美国、欧洲和日本在空间激光通信技术领域的最新研究进展和未来发展规划,总结了国内外空间激光通信演示计划的主要参数指标。通过对空间激光通信最新研究计划的分析,归纳出空间激光通信高速化、深空化、集成化、网络化、一体化5个发展趋势,以及需要突破的高阶调制、高灵敏度探测、多制式兼容、"一对多"通信等关键技术。为我国激光通信设备及相关研究提供借鉴和参考。 相似文献
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本文首先概述现代保密通信及网络信息安全的主要概念和发展状况 ,对迄今发展的几种现代著名密码算法进行分析比较 ;然后综述国际上已经提出的一些典型的混沌保密通信方案及其应用研究的新发展。从通信角度 ,为了向实用化方向发展 ,我们将混沌通信研究中常用的混沌遮掩、混沌开关、混沌调制三种主要技术方案 ,按照实际应用需要 ,重新把它们分类为三种主要形式 ,即模 模通信、模 数 模通信和数 数通信 ,这样便于实际应用 ,易于借鉴已有知识分析各类通信的性能优劣。在评述性分析了当前国际上三种混沌保密通信方式的典型方案及其进展后 ,最后简要总结混沌保密通信的一些关键技术 ,指出今后值得研究的方向 ,并展望了混沌通信的应用前景。 相似文献
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To develop an apparatus for simultaneous monitoring of heart and respiratory rates using photoplethysmography (PPG) and Fast Fourier Transform algorithm (FFT), the PPG waveform was measured at the radial artery with an original based on diffuse reflectance mode photoplethysmographic device. An FFT algorithm was used to extract heart and respiratory information from the PPG waveform. The results good agree with conventional method. The correlation coefficient of heart rate and respiratory rate obtained using PPG waveform and conventional method is 0.988 and 0.976, respectively. The PPG waveform and FFT algorithm can contribute to quicker and more accurate measurement of human heart rate and respiration rate. A portable watch-like device can be made via this method and be utilized to monitor heart and respiratory rates in hospitals or daily life care. 相似文献
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In this paper we examine the generating function (z) of a renewal sequence arising from the distribution of return times in the turbulent region for a class of piecewise affine interval maps introduced by Gaspard and Wang and studied by several authors. We prove that it admits a meromorphic continuation to the entire complex z-plane with a branch cut along the ray (1, +). Moreover, we compute the asymptotic behavior of the coefficients of its Taylor expansion at z=0. From this, we obtain the exact polynomial asympotics for the rate of mixing when the invariant measure is finite and of the scaling rate when it is infinite. 相似文献
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基于通信速率和误码率在量子保密通信研究中的重要性, 采用1.55 μm上转换单光子探测器, 分析其量子效率随抽运功率的变化关系, 得出1.55 μm上转换单光子探测器较传统的铟镓砷二极管具有较高的量子效率和较低暗计数的优势, 并根据通信距离、上转换单光子探测器的量子效率和暗计数之间建立一种平衡, 得出每种距离上探测器的优化方案; 在考虑个体攻击无量子记忆的条件下, 比较BB84协议, BBM92协议和差分相移协议的量子密钥分配(QKD)系统的安全通信速率和误码率随通信距离的变化关系, 得出了差分相移键控协议的量子密钥分配系统是一个非常实用的, 通信距离大于200 km的很有吸引力的长距离量子密钥分配系统。 相似文献
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Ganesh Prasad Yogesh Prasad G. S. Gusain Manjari Badoni J. M. S. Rana R. C. Ramola 《Indian Journal of Physics》2009,83(6):887-892
Radon was measured in soil-gas and groundwater in the Budhakedar area of Tehri Garhwal, India in summer and winter to obtain
the seasonal variation and its correlation with radon exhalation rate. The environmental surface gamma dose rate was also
measured in the same area. The radon exhalation rate in the soil sample collected from different geological unit of Budhakedar
area was measured using plastic track detector (LR-115 type II) technique. The variation in the radon concentration in soil-gas
was found to vary from 1098 to 31,776 Bq.m−3 with an average of 7456 Bq.m−3 in summer season and 3501 to 42883 Bq.m−3 with an average of 17148 Bq.m−3 in winter season. In groundwater, it was found to vary from 8 to 3047 Bq.l−1 with an average value 510 Bq.l−1 in summer and 26 to 2311 Bq.l−1 with an average value 433 Bq.L−1 in winter. Surface gamma dose rate in the study area varied from 32.4 to 83.6 μR.h−1 with an overall mean of 58.7 μ-R.h−1 in summer and 34.6 to 79.3 μR.h−1 with an average value 58.2 μR.h−1 in winter. Radon exhalation rate from collected soil samples was found to vary from 0.1 × 10−5 to 5.7 × 10−5 Bq.kg−1.h−1 with an average of 1.5 × 10−5 Bq.kg−1.h−1 in summer season and 1.7 × 10−5 to 9.6 × 10−5 Bq.kg−1.h−1 with an average of 5.5 × 10−5 Bq.kg−1.h−1. A weak negative correlation was observed between radon exhalation rate from soil and radon concentration in the soil. Radon
exhalation rate from the soil was also not found to be correlated with the gamma dose rate, while it shows a positive correlation
with radon concentration in water in summer season. Inter-correlations among various parameters are discussed in detail.
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基于X箍缩软X射线辐射点源对单丝及多丝Z箍缩发展过程进行了背光成像研究,实验平台为清华大学电机系研制的脉冲功率装置PPG-Ⅰ(500 kV/400 kA/100 ns)。成像光路安排为:作为X射线源的X箍缩和作为目标物的单丝或多丝(双丝)Z箍缩分别安装在装置的输出主电极阴阳极之间或回流导电杆处,成像胶片采用高分辨力、高灵敏度的X射线胶片。利用自行设计的电流传感器和罗氏线圈对目标物实际流过的电流进行监测。为了测定目标物金属细丝的质量消融率,设计了m级厚度的阶梯光楔。通过大量成像实验,获取了Z箍缩等离子体融合、先驱等离子体形成及不稳定性发展等过程的相关物理图像以及质量消融率、丝芯膨胀率等重要定量参数。 相似文献
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I.F. Huang S.S. Shy C.C. Chang S.C. Li C.M. Huang 《Proceedings of the Combustion Institute》2009,32(2):1755-1762
A 1.5 m long turbulent-wake combustion vessel with a 0.15 m × 0.15 m cross-sectional area is proposed for spatiotemporal measurements of curvature, strain, dilatation and burning rates along a freely downward-propagating premixed flame interacting with a parallel row of staggered vortex pairs having both compression (negative) and extension (positive) strains simultaneously. The wanted wake is generated by rapidly withdrawing an electrically-controlled, horizontally-oriented sliding plate of 5 mm thickness for flame–wake interactions. Both rich and lean CH4/air flames at the equivalence ratios = 1.4 and = 0.7 with nearly the same laminar burning velocity are studied, where flame–wake interactions and their time-dependent velocity fields are obtained by high-speed, high-resolution DPIV and laser-tomography. Correlations among curvature, strain, stretch, and dilatation rates along wrinkled flame fronts at different times are measured and thus their influences on front propagation rates can be analyzed. It is found that strain-related effects have significant influence on front propagation rates of rich CH4/air (diffusionally stable) flames even when the curvature weights more in the total stretch than the strain rate does. The local propagation rates along the wrinkled flame front are more intense at negative strain rates corresponding to positive peak dilatation rates but the global propagation rate averaged along the rich flame front remains constant during all period of flame–wake interaction. For lean CH4/air (diffusionally unstable) flames, the curvature becomes a dominant parameter influencing the structure and propagation of the wrinkled flame front, where both local and global propagation rates increase significantly with time, showing unsteady flame propagation. These experimental results suggest that the theory of laminar flame stretch can be applicable to a more complex flame–wake interaction involving unsteadiness and multitudinous interactions between vortices. 相似文献
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非正交编码协议和诱骗态方法可以有效地抵御光子数分离攻击. 由于相干叠加态中单光子成分高达90%, 常作为单光子量子比特的替代出现, 用于量子信息过程处理和计算. 本文结合非正交编码协议和诱骗态方法提出一种新的量子密钥分发方案, 光源采用相干叠加态, 推导了单光子的密钥生成速率、计数率下限和误码率的上限, 利用Matlab 模拟了无限多诱骗态情况下和有限多诱骗态情况下密钥生成速率和传输距离的关系, 得出该方案可以提升密钥生成速率并且提高安全传输距离, 验证了该方案可以进一步提高量子密钥分发系统的性能. 相似文献
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F. Kreienbring K. Krawielitzki Monika Klein Ruthild Schadereit 《Isotopes in environmental and health studies》2013,49(2-3):89-97
The experiment was carried out with 24 male albino rats (5 weeks old, live weight 79 ± 5.1 g) divided into 2 groups. Gr. 1 (control group) was fed the commercial breeding food Ssniff with 22.4% crude protein ad lib., Gr. 2 (test group) for the first fortnight a mixture of the breeding food/cellulose 60/40 (restriction period) and subsequently for the second fortnight (compensatory period) also the breeding food ad lib. During both of these periods an 8 day N balance trial and a 4 day 15N tracer trial were included for estimation of growth rate and protein synthesis rate. Protein synthesis was ascertained by the endproduct method (oral application, single dose, mixture of 12 15N-labelled amino acids); protein breakdown was calculated as the difference of protein synthesis rate and growth rate. The estimated rates were converted into fractional ones by referring to the body N content of corresponding animals. From the results of this experiment is concluded: The smaller N balance during moderate nutritional restriction can be attributed to a decrease of protein synthesis. The compensatory growth of the animals during the realimentation period is caused by an increase of protein synthesis and the enhanced protein conversion. Protein degradation is nearly unaffected. 相似文献
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掺铒光纤放大器稳态增益和瞬态增益分析 总被引:4,自引:0,他引:4
本文从描述掺铒光纤放大器的速率方程和传播方程出发,得到了稳态增益的解析表达式,并详细分析了基态和受激态离子对信号光变化的响应规律,用以说明瞬态增益的良好线性. 相似文献