A model of the wave and current boundary‐layer structure

A model of the wave and current boundary‐layer structure was developed using the k–ε turbulent closure model. The finite‐difference method was used to solve the governing equations. Vertical logarithmic grids and equal time steps were adopted. The following modelled simulations were obtained: (1) vertical profiles of wave velocity amplitude, eddy viscosity coefficient and turbulent kinetic energy with waves only; (2) vertical profiles of wave velocity amplitude, mean current velocity, eddy viscosity coefficient and turbulent kinetic energy with waves having a following current. To test the validity and the rationality of the present model, vertical profiles of modelled wave velocity amplitude and mean velocity were compared with corresponding experimental results available in the literature. Copyright © 2006 John Wiley & Sons, Ltd.     

Maximal mass and size of celestial bodies born from superstrings

The generalized Buchdahl inequality in the presence of a positive cosmological constant gives rise to a constraint on the mass density of celestial bodies. We find that such a constraint implies an upper bound on the mass and radius of spherical celestial bodies born from macroscopic superstrings. We obtain a maximal mass of about 10¹⁵ solar masses and a maximal radius of about 80 million light years, not far from the observed mass and size of the largest structures in the universe, viz. the superclusters of galaxies.     

地震层析成像之密度异常驱动地幔对流模型

地震层析成像展现了地球内部横向不均匀性，其描述的地幔结构正是地幔演化热动力学过程的现代表现。然而，如何利用这些最新的观测成果去研究地球特别是地幔的动力学过程是对地球动力学研究的挑战，建立了地幔密度异常（温度异常）直接驱动地幔对流的新方法，并利用现代地震层析成像模型计算了对应的地幔对流的格局，探讨了其和全球构造相关的地幔问题。结果表明，在单层地幔粘滞结构条件下，对流格局仍然以全地幔大尺度对流为主体；所发展的理论和方法可以适用于不同来源的地幔层析成像的数据，可以用于探讨不同边界条件和地幔参数对应的地幔对流模型，也可以用于使用大地水准面异常检验对流模型。     

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????GRACE?????????????????P3M6?????????????350 km?????????????????????????2004?????????Mw9.3????????????????????????????????????????????????仯??4.6 μGal??????????????仯?????-8.3 μGal???y????????λ????????????????????????????н????????????7 a????????????仯????5.6 μGal?????????仯???|?????????????????仯???0.6 μGal????????仯????11%????????????????????????????????????????????????????????????????????????Ч??????????Σ???????????????仯|???????????????????????????????????????????????????????????μ??????仯????С??     

基于混合常应力−光滑应变单元的极限分析方法

极限分析是岩土工程稳定性评价的重要方法之一。传统的有限元极限分析方法,采用低阶三角形单元时需要引入速度间断面并采用特殊网格布局,或者采用高阶三角形单元等措施来克服体积锁定问题和提高数值精度。在光滑有限元法（smoothed finite element method,简称SFEM）的基础上,提出了一种基于新型混合常应力−光滑应变单元的极限分析方法（mixed constant stress-smoothed strain element limit analysis,简称MCSE-LA方法）。在服从关联流动法则和Mohr-Coulomb屈服准则的基础上,MCSE-LA方法最终将数值极限分析转化为以应力和极限荷载乘子为基本未知量的二阶锥规划（second order cone programming,简称SOCP）问题。MCSE-LA方法具有形式简单、优化变量相对较少和无需显式的写出塑性内能耗散函数的优点,并且根据凸锥优化的对偶理论,可以从对偶问题中获得速度场和塑性乘子等信息。此外,还采用基于最大塑性剪应变率的网格自适应加密算法,该算法在塑性区细化网格,显著提高了新数值极限分析方法的计算效率和精度。最后通过边坡稳定分析的结果对比,验证了MCSE-LA方法的计算精度和效率均高于传统的有限元极限分析方法。     

不同边界条件下剪切速率对类岩石节理剪切力学特性的影响

为研究不同边界条件下剪切速率对岩石节理剪切力学特性的影响,采用RDS-200型岩石节理剪切试验系统对人工浇筑的具有相同节理形貌的不规则水泥节理试样进行了常法向应力和常法向刚度2种边界条件下5种剪切速率的直剪试验。结果表明：（1）常法向应力边界条件下,随剪切速率增大,相同法向应力下的类岩石节理峰前剪切刚度减速增大,峰值剪切强度和残余剪切强度呈对数降低;随剪切速率增大,类岩石节理黏聚力减速增大,内摩擦角呈对数降低。（2）常法向刚度边界条件下,随剪切速率增大,相同法向应力的类岩石节理峰前剪切刚度减速增大,峰值剪切强度呈对数降低,较高法向应力下的残余剪切强度先增大后减小;随剪切速率增大,类岩石节理黏聚力呈对数降低,内摩擦角减速增大。（3）与常法向应力边界条件相比,常法向刚度条件下,节理黏聚力平均增加了115.85%,内摩擦角平均降低了8.44%;相同初始法向应力和剪切速率下,峰前剪切刚度、峰值剪切强度和残余剪切强度分别平均增加了11.96%、19.47%和32.32%,峰值法向位移平均降低了40.12%。该研究结论可为不同剪切速率下地表和地下工程岩体节理的剪切失稳评价提供一定参考。     

罗德里格矩阵在资源三号全色影像姿态角常差检校中的应用

在资源三号测绘卫星全色影像立体定位严格几何模型的基础上,提出运用罗德里格矩阵建立姿态角常差检校模型,根据少量地面控制点求出姿态角常差构成的矩阵后,使影像定位精度得到显著提高。同时与利用线性化的姿态角常差改正模型进行了比较,并总结了各自的优缺点。     

Deriving a practical form of IDF formula using transformed rainfall intensities

A general form of formula is presented for the rainfall Intensity–Duration–Frequency (IDF) relationship. This formula is derived from the nearly normal probability distribution function of transformed intensities. In order to transform the raw intensities, a correcting non‐constant spread technique, the Kruskal–Wallis statistic, and the Box–Cox transformation are adopted. These transformations enable to express a simpler model for the IDF formula that agrees well with traditional IDF relationships. Since the proposed method allows the estimation of any percentile value of intensities with a single equation, the intensity percentile at arbitrary duration can be generated easily. The validity of the formula derived by means of the proposed method is assessed using data from major weather stations in Korea. The results show that the percentile intensities produced using the proposed method are in good agreement with those of traditional frequency analysis. Copyright © 2013 John Wiley & Sons, Ltd.     

机载GPS反射信号土壤湿度测量技术

随着全球导航定位系统反射信号(GNSS-R)技术的发展, 近年来提出了利用GPS地表反射信号遥感土壤湿度的新方法, 该方法利用地表反射率与土壤介电常数以及介电常数与土壤湿度之间的关系来建立反演模型。为了可以快速方便的利用DMR实测数据反演得到土壤湿度, 本文根据Wang和Schmugge模型建立了土壤介电常数与湿度之间的分段模型, 实现了从原始反射数据到土壤湿度结果的整个反演流程。为了验证反演的可行性, 利用NASA等机构联合进行的SMEX02试验机载数据反演得到的结果表明, GPS反射信号能够有效地反演