满足特定平方和指标平衡布尔函数的性质分析

布尔函数是组成序列密码和分组密码算法的重要部件,平方和指标和绝对值指标是衡量布尔函数全局扩散的度量准则。分析了两类达到一定平方和指标的平衡布尔函数的绝对值指标,得到对应绝对值指标的下界,给出满足扩散阶时的绝对值下界。     

Spatiotemporal analysis of vegetation index after typhoons in the mountainous watershed

An extensive land cover change was triggered by a series of typhoons, especially Typhoon Morakot in 2009 in Taiwan. The normalized difference vegetation index (NDVI) series from multiple satellite images were applied to monitor the change processes of land cover. This study applied spatiotemporal analysis tools, including empirical orthogonal functions (EOF), and multiple variograms in analyzing space–time NDVI data, and detected the effects of large chronological disturbances in the characteristics of land cover changes. Spatiotemporal analysis delineated the temporal patterns and spatial variability of NDVI caused by these large typhoons. Results showed that mean of NDVI decreased but spatial variablity of NDVI increased after typhoons in the study area. The EOF can clarify the major component of NDVI variations and identify the core area of the NDVI changes. Various approaches showed consistent results that Typhoon Morakot significantly lowered the NDVI in land cover change process. Furthermore, the spatiotemporal analysis is an effective monitoring tool, which advocates the use of the index for the quantification of land cover change and resilience.     

涉及公共值和公共值集的亚纯函数的正规族

2007年刘晓俊与庞学诚首先研究了亚纯函数及其导函数分担1个具有3个元素的公共值集的正规族问题。2011年刘晓毅与常建明推广了刘晓俊与庞学诚的相应结果。本文将在刘晓毅与常建明的有关结果基础上,进一步研究亚纯函数及其导函数分担公共值集的正规族问题。本文结果进一步推广了刘晓俊与庞学诚以及刘晓毅与常建明的有关结果。     

A creep–rupture model of synthetic fiber ropes for deepwater moorings based on thermodynamics

The synthetic fiber ropes such as polyester, aramid and high modulus polyethylene (HMPE) are increasing applied to deepwater mooring systems for oil and gas exploitation. Due to that mooring ropes generally bear tensions for a long period, synthetic fiber ropes that are composed of the viscoelastic material would present creep behaviors and even the creep rupture, which is the failure mode of greatest concern especially for HMPE ropes and on which still less study can be found. A creep damage analysis of synthetic fiber ropes is of necessity to ensure the safe and economic operation of mooring systems. Therefore further investigation on the creep–rupture behavior is beneficial to fully establishing confidence in the viability of synthetic fiber ropes for deepwater moorings. In the present study, a creep–rupture model is proposed within the framework of thermodynamics to investigate the creep and damage behaviors of synthetic fiber ropes. Methods for identifying the model parameters are also proposed in detail, which apply to any component of fiber ropes such as the fiber, yarn, strand and rope. Experimental data of aramid yarns available from the literature are utilized to validate the constitutive model. Creep and creep–rupture tests of HMPE strands at different loading levels are specially performed to further examine the present model. The present work demonstrates that the proposed model can effectively describe the viscoelastic property and damage evolution of synthetic fiber ropes at different loading levels.     

AN INTEGRATION METHOD WITH FITTING CUBIC SPLINE FUNCTIONS TO A NUMERICAL MODEL OF 2ND-ORDER SPACE-TIME DIFFERENTIAL REMAINDER——FOR AN IDEAL GLOBAL SIMULATION CASE WITH PRIMITIVE ATMOSPHERIC EQUATIONS

In this paper,the forecasting equations of a 2nd-order space-time differential remainder are deduced from the Navier-Stokes primitive equations and Eulerian operator by Taylor-series expansion.Here we introduce a cubic spline numerical model(Spline Model for short),which is with a quasi-Lagrangian time-split integration scheme of fitting cubic spline/bicubic surface to all physical variable fields in the atmospheric equations on spherical discrete latitude-longitude mesh.A new algorithm of"fitting cubic spline—time step integration—fitting cubic spline—……"is developed to determine their first-and2nd-order derivatives and their upstream points for time discrete integral to the governing equations in Spline Model.And the cubic spline function and its mathematical polarities are also discussed to understand the Spline Model’s mathematical foundation of numerical analysis.It is pointed out that the Spline Model has mathematical laws of"convergence"of the cubic spline functions contracting to the original functions as well as its 1st-order and 2nd-order derivatives.The"optimality"of the 2nd-order derivative of the cubic spline functions is optimal approximation to that of the original functions.In addition,a Hermite bicubic patch is equivalent to operate on a grid for a 2nd-order derivative variable field.Besides,the slopes and curvatures of a central difference are identified respectively,with a smoothing coefficient of 1/3,three-point smoothing of that of a cubic spline.Then the slopes and curvatures of a central difference are calculated from the smoothing coefficient 1/3 and three-point smoothing of that of a cubic spline,respectively.Furthermore,a global simulation case of adiabatic,non-frictional and"incompressible"model atmosphere is shown with the quasi-Lagrangian time integration by using a global Spline Model,whose initial condition comes from the NCEP reanalysis data,along with quasi-uniform latitude-longitude grids and the so-called"shallow atmosphere"Navier-Stokes primitive equations in the spherical coordinates.The Spline Model,which adopted the Navier-Stokes primitive equations and quasi-Lagrangian time-split integration scheme,provides an initial ideal case of global atmospheric circulation.In addition,considering the essentially non-linear atmospheric motions,the Spline Model could judge reasonably well simple points of any smoothed variable field according to its fitting spline curvatures that must conform to its physical interpretation.     

Crustal thickness and VP/VS variations in the Grenville orogen (Ontario, Canada) from analysis of teleseismic receiver functions

We have developed a simple semblance-weighted stacking technique to estimate crustal thickness and average V_P/V_S ratio using teleseismic receiver functions. We have applied our method to data from 32 broadband seismograph stations that cover a 700 × 400 km² region of the Grenville orogen, a 1.2–0.98 Ga Himalayan-scale collisional belt in eastern North America. Our seismograph network partly overlaps with Lithoprobe and other crustal refraction surveys. In 8 out of 9 cases where a crustal-refraction profile passes within 30 km of a seismograph station, the two independent crustal thickness estimates agree to within 7%. Our regional crustal-thickness model, constructed using both teleseismic and refraction observations, ranges between 34.0 and 52.4 km. Crustal-thickness trends show a strong correlation with geological belts, but do not correlate with surface topography and are far in excess of relief required to maintain local isostatic equilibrium. The thickest crust (52.4 ± 1.7 km) was found at a station located within the 1.1 Ga mid-continent (failed) rift. The Central Gneiss Belt, which contains rocks exhumed from deep levels of the crust, is characterized by V_P/V_S ranging from 1.78 to 1.85. In other parts of the Grenville orogen, V_P/V_S is found to be generally less than 1.80. The thinnest crust (34.5–37.0 km) occurs northeast of the 0.7 Ga Ottawa–Bonnechere graben and correlates with areas of high intraplate seismicity.     

城市化对平原河网水系结构及功能的影响——以苏州市为例

针对城市化对平原河网水系结构的影响所引起的洪涝灾害频发等一系列水文问题,以我国典型平原河网地区苏州市为例,根据不同城市化程度分为主城区、市辖区、其他市县区,基于1991、2001和2015年三期遥感影像与1960s、1980s和2010s三个时期的水系数据,应用RS/GIS等技术,构建水系结构参数指标,重点探讨了城市化对河网水系结构及功能的影响.结果表明：城镇用地迅速增长,主要以牺牲水田、水域等土地利用方式为代价,到2015年全区城镇用地面积所占比重已达到41.35%,土地利用类型的变化规律与城市化进程的差异性保持一致;水系结构变化主要受城市化影响,且基本与城市化进程呈现同步性.近50年来,全区的水面率、河网密度、支流发育系数、主干河流面积长度比、河网复杂度和河网结构稳定度分别减少了19.63%、6.91%、7.34%、1.06%、5.49%和7.87%,城市化水平与各指数均呈负相关关系;人类活动不仅直接影响河流功能,也间接地通过改变平原河网的水系结构导致其功能发生改变,如河网调蓄能力下降、河流生态功能受损等.该研究为城市化地区河流水系保护及防洪减灾提供参考与理论支撑.     

Improvement to the Evaporation Duct Model by Introducing Nonlinear Similarity Functions in Stable Conditions

Modified refractivity (M) profile is an important parameter to describe the atmospheric refraction environment, as well as a key factor in uniquely evaluating electromagnetic propagation effects. In order to improve the model-derived M profile in stable (especially very stable) conditions, three nonlinear similarity functions, namely BH91, CB05, SHEBA07, are introduced in this paper to improve the original Babin_V25 model, and the performances of these modified models are verified based on the hydrometeorological observations from tower platforms, which are finally compared with the original Babin_V25 model and Local_HYQ92 model. Results show that introducing nonlinear similarity functions can significantly improve the model-derived M profile; especially, the newly developed SHEBA07 functions manage to reduce the predicted root mean square (rms) differences of M and M slope (for both 0–5 m and 5–40 m) by 64.5%, 16.6%, and 60.4%, respectively in stable conditions. Unfortunately, this improved method reacts little on the evaporation duct height; in contrast, Local_HYQ92 model is capable of reducing the predicted rms differences of M, M slope (for both 0–5 m and 5–40 m), and evaporation duct height by 76.7%, 40.2%, 83.7%, and 58.0% respectively. Finally, a new recommendation is made to apply Local_HYQ92 and Babin_SHEBA07 in very stable conditions considering that M slope is more important than evaporation duct height and absolute M value in uniquely determining electromagnetic propagation effects.     

时间序列预报方法的推广

文中讨论了车贝雪夫多项式值计算误差对作者以前提出的一种新的时间序列预报方法的预报结果的影响,并在此基础上对原来的计算方案作了推广,推广后的算法有利于提高预报准确率。     

土-结构动力相互作用对基础隔震的影响

本文研究土-结构动力相互作用对基础隔震的影响。文中根据间接边界元方法，推导了空间域中的格林函数公式，并建立了地基土的动力刚度矩阵；进而在频域内采用子结构法，建立了考虑土-结构动力相互作用的隔震结构的运动方程；通过数值仿真某具有埋置刚性基础的剪切型基础隔震结构的地震反应，分析了地基土的刚度对隔震效果以及结构地震反应的影响，得到了一些有意义的结论。