东西传播路径上JJI台站甚低频信号的日出效应研究

甚低频（VLF,Very Low Frequency）波的频率范围为3~30 kHz,因其在地球-电离层波导中传播损耗小、传输距离远而被用于低电离层遥测的相关研究.本文基于武汉大学自主研发的甚低频探测系统在湖北随州（31.57°N,113.32°E）的观测数据,详细研究了中纬度地区来自日本JJI（32.04°N,130.81°E）甚低频台站信号沿东西方向传播的日出效应.在对日出期间接收信号的幅度极小值进行统计分析后发现,幅度极小值出现时间的分布与随州或JJI日出时间的变化趋势基本一致.日出期间JJI信号的幅度响应主要包括type I和type II两种结构,分别对应2个幅度极小值和3个幅度极小值的情况.其中,type I结构主要发生在春夏两季,幅度极小值出现的平均时间落后随州日出时间24 min左右;type II结构主要发生在秋冬两季.基于波模干涉理论对日出期间两种不同模式的JJI甚低频信号进行模拟研究,结果表明,在JJI-随州的东西向传播路径上,若只考虑前两阶模的影响,模拟结果与观测结果差异明显;若考虑前三阶模的影响,那么模拟结果与观测结果基本一致.由此可见,JJI甚低频信号在短路径上传播时高阶模会对信号的传播产生较大的影响,分析此类路径上甚低频台站信号的传播特征时需要考虑前三阶模甚至更高阶模的作用.

     

The Growth and Location of High Order Services in the Canadian Urban System, 1971–1991

In spite of the considerable economic importance of high order (intermediate demand) services, research on the growth and location of these activities has remained at a fairly aggregate level. The behavior of the individual elements of this group has rarely been documented in detail. In this paper, we seek to determine if individual high order service activities are becoming spatially more concentrated or dispersed across the Canadian urban system, and to determine if differential rates of growth may be observed by region and by urban size category. These issues are of considerable importance in the ongoing debate concerning the impact of the tertiarization of the economy on uneven spatial development. We examine the performance and location of 17 individual high order service activities over a set of 152 Canadian urban areas with populations greater than 10,000 inhabitants. Most of these activities are highly concentrated in a small number of very large urban areas, and their level of concentration declined only very slightly over the period 1971–1991. We conclude with an examination of the factors underlying the geographic concentration of high order services at the upper end of the urban hierarchy.     

红十字湖地区锂云母-透锂长石伟晶岩脉中锡锰钽矿的发现

锡锰钽矿(wodginite)理想式为MnSnTa2O8,Z=4,其结构为锡铁钽矿(ixiolite)结构的有序化形式。它是钽的主要工业矿物,是高度分异演化伟晶岩的标志矿物之一。在加拿大红十字湖地区锂云母-透锂长石伟晶岩脉中发现了这一钽矿物。矿物为黑褐色,呈半自形,颗粒达0.2mm,分布于由锂云母钠长石构成的条带中,与之共生的是一套典型的、高演化的花岗伟晶岩矿物组合。锡锰钽矿具有Mn/Fe、Sn/Ti、Ta/Nb比值高,杂质少的特点。矿物平均分子式为:Mn1.00(Sn0.64Ta0.24Ti0.04Mn0.04Zn0.02Fe0.01)0.99(Ta1.69Nb0.31)2.00O8;晶胞参数a=0.9534nm,b=1.1482nm,c=0.5123nm,β=91°07',V=0.5607nm3。依据矿物β>91°、V>0.560nm3、对偶面网221与221具强分裂衍射双峰、I021/I220为0.19和Mn/(Fe+Mn)≈1等特征,在锡锰钽矿与锡铁钽矿所构成的同质多像、有序-部分有序-无序这样一个连续系列中,本区所产锡锰钽矿属有序端员矿物,其阳离子在八面体中分布的有序度约为95%。在钽资源的寻找和开发利用中,应重视含锡锰钽矿的锂云母-透锂长石伟晶岩脉。     

Toroidal oscillations of a transradially isotropic elastic sphere

In order to consider the effect of anisotropy on the periods of the oscillations of the Earth, the problem of toroidal oscillations of a transradially isotropic elastic sphere is considered. At each point, the medium is assumed to be transversely isotropic about the radius through the point. The roots of the frequency equation are obtained for different values of the anisotropy parameter α. It is found that, for large order oscillations, the percentage change in the frequency of the toroidal oscillations on account of the anisotropy is nearly equal to |α-1| × 100.     

划分重力区域异常与局部异常的变阶滑动趋势分析法

本文在分析一般趋势分析缺陷的基础上,提出了变阶滑动趋势分析法,并用正交变换代替趋势分析中的解线性方程组,避免了线性方程组病态而造成的异常失真。最后用理论模型和实际资料处理结果说明了变阶滑动趋势分析的优点。     

Comparative performance of indicator algorithms for modeling conditional probability distribution functions

This paper compares the performance of four algorithms (full indicator cokriging. adjacent cutoffs indicator cokriging, multiple indicator kriging, median indicator kriging) for modeling conditional cumulative distribution functions (ccdf).The latter three algorithms are approximations to the theoretically better full indicator cokriging in the sense that they disregard cross-covariances between some indicator variables or they consider that all covariances are proportional to the same function. Comparative performance is assessed using a reference soil data set that includes 2649 locations at which both topsoil copper and cobalt were measured. For all practical purposes, indicator cokriging does not perform better than the other simpler algorithms which involve less variogram modeling effort and smaller computational cost. Furthermore, the number of order relation deviations is found to be higher for cokriging algorithms, especially when constraints on the kriging weights are applied.     

适用于堆石料的分数阶下加载面模型

堆石料的应力-应变曲线具有应变硬化和软化的特性,并且体积变形会伴随着剪缩和剪胀现象的发生;此外,应力水平、应力路径和密度等因素均会对堆石料的力学特性产生显著的影响。基于临界状态土力学的理论框架,建立了适用于堆石料的分数阶下加载面模型,该模型为典型的双屈服模型。在平均主应力p-剪应力q平面,剪切过程中堆石料当前应力状态点和参考应力点分别位于下加载面和参考屈服面上,两者之间的相对位置与孔隙比之差ρ相关。相比于状态参量Ψ,ρ能够额外考虑应力路径对堆石料剪胀特性的影响。新模型的另一个显著特点在于能够考虑堆石料塑性流动方向与加载方向之间的差异性。在不引入塑性势函数的情况下,新模型对屈服函数进行Caputo微分并得到分数阶塑性流动法则,进而统一描述相关联和非相关联的塑性流动法则。新模型具有形式简单且参数较少等优点,所包含的7个材料参数均具有明确的物理意义,并且可以采用常规的室内试验结果进行标定。通过将模型计算结果与Tacheng堆石料在不同初始孔隙比和围压条件下的三轴压缩排水试验结果进行对比分析,结果表明新模型能够准确地描述堆石料的应力-应变曲线和体积变形特点;同时,新模型也能够合理地描述初始孔隙比对堆石料在e-lnp平面(e为孔隙比)临界状态线的影响。     

对称荷载正多边形孔洞弹性应力解析逼近方法

提出一种简单有效的计算方法,求解对称荷载作用下含正多边形孔洞无限平面体的弹性应力解。将孔洞内边界向两侧延伸至应力可忽略的远处,其外侧构成半无限平面体。相邻两个半无限平面体有一个公共域,其中一个半无限平面体顶边延伸至相邻两个半限平面体体内。孔洞内边界上面力是已知的,延伸至两相邻半无限平面体体内的顶边上面力可先假设,由弹性理论求出半无限平面体体内应力,再计算相邻半无限平面体顶边上面力,根据对称性得到本半无限平面体顶边上面力改进值,迭代求解直至收敛。该方法具有计算过程简单、精度高等优点。算例分析表明,该方法求解的工程尺度下孔洞周边应力场与复变函数方法、有限元方法计算结果吻合,拟合计算的孔边角点处应力奇异性次数与理论解基本一致。     

Experimental Study of Mechanical Behaviour of Rock Joints Under Cyclic Loading

Summary Evaluation of the effects of small repetitive earthquakes on the strength parameters of rock joints in active seismic zones is of interest of the designers of underground constructions. In order to evaluate these effects, it is necessary to study the behaviour of rock joints under dynamic and cyclic loadings. This paper presents the results of a systematic study on the behaviour of artificial rock joints subjected to cyclic shearing. More than 30 identical replicas have been tested using triaxial compression devices under different conditions of monotonic and cyclic loading. At the first stage a few samples have been tested in monotonic loading modes under various confining pressures and rate of displacement. In the second series of tests, small cyclic loads were applied on the samples for increasing number of cycles, frequency levels and stress amplitudes. These were then followed by monotonic loading again. The variations of maximum and residual shear strengths for each test have been studied. The results show increase of shear strength as a result of the increase in confining pressure and they display decrease of shear strength due to the increase of rate of loading, number of cycles, frequency levels and stress amplitudes.