Effects of glaciations and permafrost upon the development of karst in Canada

Canadian examples suggest that karst landforms may be divided into eight types in terms of their temporal relationships to the record of repeated Quaternary glaciations. Two types are postglacial, two are subglacial, one type occurs where glacial features are adapted to karstic drainage, and three types display sequences of karstic and glacial action. Glacier effects upon karst landforms and their underlying aquifers display the gamut of possibilities. They may destroy, inhibit, preserve, or stimulate karst development. Where continuous permafrost is maintained when covered by glacier ice, postglacial karst is limited to the active layer epikarst. Where permafrost is thawed beneath ice or during deglaciation there are a variety of postglacial karst developments, depending in part upon climate and in part upon local lithologic and relief conditions.     

Environmental impact on the Roman monuments of Tarragona,Spain

The extant remains of the Roman monuments of Tarragona, Spain are made of different types of Miocenic rocks from the quarries surrounding the city, which vary from calcarenite to bioclastic limestones, showing different degrees of dolomitization, depending on their diagenetic evolution. The decay of these monuments is highly dependent on the mineralogy and the fabric of the stone as well as on the environmental conditions to which the monument subjected. As a consequence, different forms of decay are observed on these monuments, namely, granular disintegration, differential erosion between sparitic and micritic areas of the rock, and development of black crust and orange patinas, some of them attributed to a sulfation process. A number of processes have been established as being responsible for the decay forms observed: sulfation on sheltered areas of the building in the urban environment; differential dilatation because of the NaCl of the marine spray that crystallizes inside the porosity; hydric and thermal expansion of the stone, both related to the amount and crystallinity of the clay minerals forming the rock matrix; and biocolonization on the stone surface. An empirical model is proposed to explain the decay forms studied in relation to these factors (rock and environment).     

Existence of the atmosphere attractor

The global asymptotic behavior of solutions for the equations of large scale atmospheric motion with the non-stationary external forcing is studied in the infinite dimensional Hilbert space. Based on the properties of operators of the equations, some energy inequalities and the uniqueness theorem of solutions are obtained. On the assumption that external forces are bounded, the exsitence of the global absorbing set and the atmosphere attractor is proved, and the characteristics of the decay of effect of initial field and the adjustment to the external forcing are revealed. The physical sense of the results is discussed and some ideas about climatic numerical forecast are elucidated Work supported by the State Key Research Project on Dynamics and Predictive Theory of the Climate.     

冻结黄土的拉伸蠕变特性

本以为依据揭示饱水冻结黄土拉伸蠕变过程的若干特点。拉伸蠕变同样具有两类三阶段性质，与压缩蠕变相比，拉伸非衰减蠕变的总变形小，第Ⅲ阶段变形的比例不大，历时短，不论土温高低最终均发生脆性破坏，根据应变速率－时间曲线特征提出拉伸蠕变方程，对第Ⅲ阶段变有较好的表述。     

中国人口流动重力模型回归系数的定量估算及其空间异质性研究

基于中国337个地级及以上行政区划间人口省际流动数据,对人口流动重力模型代理变量的回归系数进行实证推算。结论包括：① 在地级行政单元研究精度下,中国人口流动重力模型代理变量的回归系数呈现出明显的空间异质性,及难以预期的作用效应,因此研究精度的提升将加剧空间交互模型构建的复杂程度,同时假定重力模型回归系数的空间均质性将导致模拟结果空间差异趋势的收敛;② 中国人口省际流动距离衰减系数为1.975,337个地级及以上行政区划距离衰减系数值域为0.434~4.438。研究所展示的各省该系数值域及直辖市、省会城市结果为今后模型应用提供了基础参考数据;③ 地级行政单元下的距离衰减系数存在空间异质性与梯度特征,高值区主要分布在东北沿疆、新疆和珠三角地区,低值区主要位于中国中部和西南地区。结合以往研究成果比较,中国人口省际流动的空间衰减特征与铁路客运网络的可达性格局存在一定程度的一致性。     

The Shape of Mobility: Measuring the Distance Decay Function of Household Mobility

A well-known challenge to studies examining the distance of residential mobility patterns is that the estimates are often constrained to patterns only within a particular metro area or between metro areas. Thus, studies are unable to estimate the entire distance decay functional form. Using a unique data set on the distance of the most recent move for a large sample of households in twenty-three metropolitan areas in the United States over three waves, we flexibly estimate the distance decay function for the entire sample, as well as for a series of subpopulations based on key demographic information.     

Spatial co-location pattern mining of facility points-of-interest improved by network neighborhood and distance decay effects

The aim of mining spatial co-location patterns is to find the corresponding subsets of spatial features that have strong spatial correlation in the real world. This is an important technology for the extraction and comprehension of implicit knowledge in large spatial databases. However, existing methods of co-location mining consider events as taking place in a homogeneous and isotropic context in Euclidean space, whereas the physical movement in an urban space is usually constrained by a road network. Furthermore, previous works do not take the ‘distance decay effect’ of spatial interactions into account, which may reduce the effectiveness of the result. Here we propose an improved spatial co-location pattern mining method, including the network-constrained neighborhood and addition of a distance-decay function, to find the spatial dependence between network phenomena (e.g. urban facilities). The underlying idea is to utilize a model function in the interest measure calculation to weight the contribution of a co-location to the overall interest measure instance inversely proportional to the separation distance. Our approach was evaluated through extensive experiments using facility points-of-interest data sets. The results show that the network-constrained approach is a more effective method than the traditional one in network-structured space. The proposed approach can also be applied to other human activities (e.g. traffic accidents) constrained by a street network.     

Comparative study on the accuracy of solitary wave generations in an ISPH-based numerical wave flume

In the present study, six solitary wave generations by different mathematical approximations are investigated using a piston type wave maker at dimensionless amplitudes ranging from 0.1 to 0.6 and two water depths. Incompressible smoothed particle hydrodynamics is used to simulate solitary wave propagation along the fixed depth channel. The present numerical results are compared with analytical results and experimental data in terms of free surface displacements, fluid particle velocity, phase speed, paddle motion, etc. The present mesh-free numerical results of wave profile variations over time proved that “Rayleigh” has the lowest relative wave height variation. However, its solitary wave has notable phase lead, while “Third order” and “Ninth order” have the least wave lags. Furthermore, the record of present numerical free surface elevation at different distances and the loss of amplitude of the main pulse showed that regarding both of them, “Ninth order” has supremacy over five others. Considering the numerical velocity components of generated solitary wave, “Third order” and “Ninth order” trace analytical results more accurately than other four ones, whereas “Rayleigh” is the most accurate one in predicting the maximum runup. Finally, the paddle motion, its velocity, and displacement, as well as phase speed and outskirts decay coefficient are also compared and discussed intensely.     

波浪在泥床上传播时的波长变化

本文通过长江口航道淤泥的室内波浪试验研究,认为影响波长变化的主要因素有相对泥床厚度、泥床含沙浓度及相对(传播距离)波长等。在本试验范围内,波浪在泥床上传播时的波长变化一般在±5％以内;但在相对泥床厚度、泥床含沙浓度及相对(传播距离)波长均较大时,波浪被急剧衰减,波长也随之迅速减小。     

珠江口咸淡水交汇区水中COD_（Mn）、油类、砷自净规律的试验研究

用采自珠江口咸淡水交汇区河段的水和沉积物进行自净试验。试验池内介质由某一段面的水和相应断面的沉积物组成。试验按加入和未加入污染物、流动状态和静止状态的条件组合进行。从试验获得的数据看，在加入污染物的试验池水中，ＣＯＤＭｎ、油类和砷含量变化有如下规律：以石油含量降解最为迅速，在１—３ｄ内可降至未加入水平；其次是砷，自净速度与盐度有关，其含量降解５０％时在低盐度水试验池中为６ｈ，在盐度较高水中约需２ｄ，水中ＣＯＤＭｎ、油类和砷的自净作用在试验开始后的第一天里进行最快；相同介质的试验池比较，动态条件比静态条件更有利于水中污染物的自净。此外，还应用试验结果对珠江口咸淡水交汇区水中污染物自净效应作了初步的估算。