共查询到19条相似文献，搜索用时 140 毫秒
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在数字电视条件接收系统中,单向密码体系存在服务器端无法获取用户端的信息出现伪造用户智能卡等现象。针对这些问题,在原有单向密码体系的基础上,提出了使用基于椭圆曲线的多对一加密认证方案实现客户端向服务器端传送认证信息,构成了数字电视条件接收系统双向加密体系结构。多对一加密认证方案的发送者使用的密钥与身份和解密密钥有关,解密者仅使用唯一的解密密钥就可以解密任何合法的密文,并可以认证发送者的身份。将多对一加密认证方案用于数字电视条件接收系统能够有效的抵制非授权用户窃取、伪造信息等安全问题。 相似文献
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重力异常垂向一阶导数的一种简便算法 总被引：1，自引：0，他引：1
利用拉格朗日插值导出了重力异常垂向一阶导数的计算公式，给出了地面以及地面之上不同高度的求导系数。该公式可以计算地面上的重力垂向一阶导数，还可以直接计算地面之上任意高度上的垂向一阶导数。鉴于该公式除系数不同外，与上延公式完全相同，因此，程序设计尤为简单。使用本公式对模型数据和实际资料进行了处理，证明了本算法的实用性。 相似文献
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根据一种三维潮致拉格朗日余流的弱非线性理论,考虑单一频率潮波系统,在零阶天文潮和一阶拉格朗日余流数值计算的基础上,计算了二阶拉格朗日余流,然后对8个具有代表性的标识质点运动轨迹进行了数值跟踪。对水平及垂直运动性质进行了分析,并用卫片资料对结果进行了验证。提出一些有启发性的初步结果。 相似文献
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LOESS四维客观分析在中国近海的应用 总被引：2，自引：0，他引：2
利用全国海洋综合调查资料和世界大洋数据库(WOD)资料,运用局部加权回归法(LOESS)四维客观分析方案对中国近海的温度场进行了客观分析,将散布在空间中的温度资料点插值到均一的网格中。在分析中充分考虑了中国海曲折复杂的海岸特点,将底深调整系统(TAR)和障碍调整系统(BAR)整合到四维插值系统中,使得资料点空间权重的计算更为合理。计算结果显示,LOESS客观分析方案充分考虑了空间因素(经度、纬度、深度)和时间因素,能客观反映出中国近海一年四季的温度时间-空间结构。通过与Kriging插值方法的对比,发现LOESS方法能更精确地把中国近海温度结构反映出来。 相似文献
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吴举林 《中国海洋大学学报(自然科学版)》1991,(1)
证明了弦图的团二分图是子树二分图,从而把弦图上一般形式的团复盖问题化为弦图上的对点团复盖,可以在多项式时间内求解。对强弦图上的邻域复盖问题,本文提出两条求解途径:一是化为弦图上的团复盖问题,一是化为可用组合方法求解的线性规划问题。 相似文献
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水下采油树井口连接器是连接采油树和井口的关键设备,对深海水下勘探开发及采油树的安装连接具有不可或缺的重要意义。以一种锁块式水下连接器为例,介绍其结构组成和工作原理,通过有限元建立连接器的三维模型,分析连接器在下放安装工况、连接锁紧工况、正常生产工况和钻完井工况下的连接性能,得出井口与采油树本体接触面作用力、VX钢圈接触应力和锁块受力情况随外部载荷的相互关系。结果表明,VX钢圈在整个过程中都能够保持良好密封,井口与采油树本体接触面未发生分离,弯矩对连接器连接性能影响很大,在额定弯矩作用时连接器部分锁块已发生弹塑性失效。 相似文献
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海上溢油粒子追踪预测模型中的两种数值方法比较 总被引：2，自引：0，他引：2
在海上溢油粒子追踪预测模型中,关键的是对拉格朗日微分方程的求解。本文首先通过数值实验比较了欧拉法和龙格-库塔法求解拉格朗日溢油轨迹微分方程的优劣,然后将其应用到2005年4月3日发生在大连附近的“ARTEAGA”油轮溢油事故的油膜粒子追踪模型中。数值实验和应用结果表明,在近岸不均匀流场下,用龙格-库塔方法解拉格朗日油粒子微分方程比用欧拉法求解精度高,用龙格-库塔方法模拟“ARTEAGA”油轮轨迹及其扩散范围与实际观测更为接近,而用欧拉法模拟溢油扩散的面积偏大。 相似文献
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对以杏、李、樱桃和石榴为主的果树载培在青岛沿海地区园林绿化中的应用情况进行了分析。对每种果树的形态特征、开花结果日期、分布、生长环境、生物学特性及用途作了详细介绍 相似文献
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When quantifying the uncertainty of the response of a computationally costly oceanographic or meteorological model stemming from the uncertainty of its inputs, practicality demands getting the most information using the fewest simulations. It is widely recognized that, by interpolating the results of a small number of simulations, results of additional simulations can be inexpensively approximated to provide a useful estimate of the variability of the response. Even so, as computing the simulations to be interpolated remains the biggest expense, the choice of these simulations deserves attention. When making this choice, two requirement should be considered: (i) the nature of the interpolation and (ii) the available information about input uncertainty. Examples comparing polynomial interpolation and Gaussian process interpolation are presented for three different views of input uncertainty. 相似文献
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从树轮纤维素中氧的来源、植物体内氧的分馏、最近的研究成果等三个方面评述树轮纤维素氧同位素组成的温度计意义。结果表明，树轮纤维素氧同位素组成的变化是温度变化的良好载体，但在定量恢复古温度变化时遇到了不少限制，有待于进一步完善分馏模型。 相似文献
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Mohammad Najafzadeh Jalal Shiri Mohammad Rezaie-Balf 《Marine Georesources & Geotechnology》2018,36(2):227-235
Scouring in the channel contractions occurs due to the flow concentration within them inducing excessive bed shear stress. This is a complex process, so it is difficult to describe it through a general empirical model, the present research work describes contemporary conceptual relationships to estimate the local scour depth under equilibrium and clear water conditions in rectangular channels. Incidentally, gene-expression programming (GEP), evolutionary polynomial regression (EPR), and model tree (MT)-based formulations were utilized to predict the scour depth at long contractions. The input variables comprising average flow velocity, critical threshold velocity of sediment movement, flow depth, median particle diameter, geometric standard deviation, and uncontracted and contracted channel widths were used to feed the applied models. The performances of the developed approach were compared with those calculated using existing scour prediction equations. The results showed that the developed MT approach in terms of linear relationships could predict the scour depth more precisely than GEP, EPR, and the traditional equations. What is more, dimensionless parameter of h1/b1 (ratio of upstream flow depth to uncontracted channel width) was determined as the most influential variable in predicting the scour depth in long contractions. 相似文献
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Bottom-penetrating sonar can be used to visualize large areas, for example by normal logging and printing of collected pings. In many applications, it is necessary to obtain an impression of three-dimensional (3-D) structures, but this is not easy because of the irregular spatial sampling due to coarse ship trajectories. Normally, the ping map and the ping data, cover only a very small part of a region of interest. In this paper, we describe a new method for interpolating irregularly spaced sonar data. The basic idea is to use a two-dimensional quadtree of the ping map in order to guide the 3-D interpolation process: since gaps between pings become smaller at higher tree levels, the volume can be filled by marking neighborhood relations in the quadtree and interpolating available pings when they become neighbors. Different marking schemes and their central processing unit times are compared. In the interpolation process, we apply cross correlations of ping data in order to construct continuity of sloping reflections. Our results show that excellent results can be obtained on real sonar data sets, even for volumes filled for less than 7%, for which processing times are reasonable even for large areas, and that the interpolated data can be used for volumetric interactive visualization. 相似文献