Quantifying sample bias in clast fabric measurements

Sampling elongate clasts that protrude from a planar face for clast macro‐fabric analysis introduces a bias into reconstructed fabrics because clasts aligned perpendicular to the sampling face are over‐represented relative to those aligned parallel to the face. This study develops a probability‐based mathematical analysis to quantify sample bias for a variety of clast shapes and population fabrics, including isotropic, clustered and girdled fabric styles. Bias is expressed in terms of sample eigenvalues and eigenvectors relative to those of the parent population. Results indicate that sampling always has the effect of artificially drawing fabrics towards perpendicularity to the sampling face relative to the populations from which they are drawn. This rotation generally has the effect of artificially strengthening population fabrics, by up to 30% in the case of very weakly clustered or girdled populations. However, fabric strengthening is by no means universal and sampling alters different parent populations in different, sometimes complex, ways: the analysis in this paper identifies situations where sampling can strengthen or weaken parent fabrics, where it can rotate parent fabrics (by up to 90° in the case of a very weak population fabric), and where it can even change the style of a population fabric. For example, near‐isotropic population fabrics can appear clustered; weakly clustered and weakly girdled population fabrics can appear isotropic; weakly clustered population fabrics can appear weakly girdled; and girdled population fabrics can appear clustered. Overall, this analysis indicates that weakly orientated population fabrics are most susceptible to bias. Thus, a weakly clustered population fabric aligned parallel to a sample face is particularly susceptible to major sample bias in both fabric strength (artificially overestimated) and orientation (artificially rotated perpendicular to the face). Bias can be reduced either by sampling all the clasts from a cube‐shaped block of sediment excavated from the face, or by sampling equal numbers of clasts from the three orthogonal faces of the same sedimentary unit.     

利用改进的Loheide方法计算地下水的蒸散发量

在干旱—半干旱地区,地下水的蒸散发是最重要的排泄方式之一,提高其计算精度对准确评价地下水资源具有重要意义。目前在已有的利用地下水水位的昼夜波动计算蒸散发的方法中,Loheide方法是计算精度最高并可以计算小时尺度的方法。针对该方法对水位去趋势化的不足,提出了新的潜水位去趋势的方法,即对3~5天的地下水位采用线性或三次多项式去趋势。采用数值模拟方法,对改进效果进行定量评估。结果表明,当相邻两天的水位变化较大时,提出的去趋势化方法使得蒸散发的计算精度有所提高,其中三次多项式去趋势化方法精度最高,比传统方法精度提高了16%,并且相对于Loheide利用1天数据线性去趋势化的方法,3~5天长序列去趋势能够提高去趋势处理的计算效率。     

Quantifying historic skew surges: an example for the Dunkirk Area,France

Natural Hazards - As instrumental records often cover only short time periods, historical information is the main source of data in order to extend natural disaster catalogs. This study...     

Quantifying the effects of environmental change on an oyster population: A modeling study

Three models are combined to investigate the effects of changes in environmental conditions on the population structure of the Eastern oyster,Crassostrea virginica. The first model, a time-dependent model of the oyster population as described in Powell et al. (1992, 1994, 1995a,b, 1996, 1997) and Hofmann et al. (1992, 1994, 1995), tracks the distribution, development, spawning, and mortality of sessile oyster populations. The second model, a time-dependent larval growth model as described in Dekshenieks et al. (1993), simulates larval growth and mortality. The final model, a finite element hydrodynamic model, simulates the circulation in Galveston Bay, Texas. The coupled post-settlement-larval model (the oyster model) runs within the finite element grid at locations that include known oyster reef habitats. The oyster model was first forced with 5 yr of mean environmental conditions to provide a reference simulation for Galveston Bay. Additional simulations considered the effects of long-term increases and decreases in freshwater inflow and temperature, as well as decreases in food concentration and total seston on Galveston Bay oyster populations. In general, the simulations show that salinity is the primary environmental factor controling the spatial extent of oyster distribution within the estuary. Results also indicate a need to consider all environmental factors when attempting to predict the response of oyster populations; it is the superposition of a combination of these factors that determines the state of the population. The results from this study allow predictions to be made concerning the effects of environmental change on the status of oyster populations, both within Galveston Bay and within other estuarine systems supporting oyster populations.     

Research on the urban resilience evaluation with hybrid multiple attribute TOPSIS method: an example in China

Natural Hazards - Cities are important barriers to protect people’s lives and property in the face of natural disasters, economic fluctuations and epidemic diseases. The evaluation of urban...     

衬度返回法在平抑地球化学系统偏倚中应用

在进行1∶10万、1∶25万、1∶50万或更小比例尺地球化学编图时,由于分析单位和工作时间不同,不同的1∶5万、1∶20万图幅间或同图幅不同批次间的化探数据常存在着系统偏倚。因此,编图前必须进行系统偏倚平抑。目前,系统偏倚平抑方法有衬度变换法、平差法、分幅标准化法、分区标准化法、基准单元系数法和边界极限原理法等。笔者在实际工作中,通过反复试验确认＂衬度返回法＂是图幅间或批次间系统偏倚平抑的一种实用且有效的方法。     

Vergence: an evaluation

Fold asymmetry is an independent concept distinct from facing. Fold vergence is a direction relating to the sense of asymmetry of folds. The complementary concept of cleavage vergence is defined allowing asymmetry to be used to locate major fold traces where no minor folds exist. Cleavage vergence is a valuable tool in complex structural terrains. Both concepts can be used singly or in combination to identify refolding. Vergence can define structural way-up where sedimentological or stratigraphic way-up cannot be recognised.     

Use of an aggregated Rhizocarpon'species' in lichenometry: an evaluation

A regular relationship exists between the growth of lichen species within the Section Rhizocarpon and Rhizocarpon alpicola. This can be quantified and used to adjust lichenometric dates to take into account differences in the growth rates of the two groups. R. alpicola colonises deposits later than Section Rhizocarpon species, although subsequent growth by R. alpicola is rapid. If the two groups arc not separated, important dating errors may arise.     

Performance evaluation of disaster monitoring systems

Understanding the performance of disaster monitoring systems is a key to understanding their success; therefore, various qualitative and quantitative measures and metrics can be applied in the characterization and analysis of such systems. Through evaluation studies, problems that impede a disaster monitoring system performance can be identified. The results can be used for system design, control, and capacity planning. Previous studies address technical performance analysis metrics for analyzing monitoring systems leaving out human and organizational dimensions of such systems. Thus, the primary objective of this study is to identify and describe a set of metrics that may be employed to evaluate such systems. This study may be valuable to researchers and practitioners involved in disaster and emergency response studies in planning the transportation of vital first-aid supplies and emergency personnel to disaster-affected areas and in improving chances of survival after a disaster.     

基于生态流量阈值的河流水文健康演变定量归因

环境变化改变了河流水文情势,影响了河流的生态系统健康,亟需开展变化环境下河流水文健康演变定量归因方法研究。选取北方半干旱地区老哈河流域为研究区,依据流域内3个水文站、17个雨量站和6个气象站1964—2016年数据,基于可变下渗容量模型还原河流的天然流量序列;采用概率密度法计算河流生态流量,基于生态流量阈值推求河流水文健康等级;基于"观测-模拟"对比分析法,定量分离气候变化和人类活动对河流水文健康情势的影响。结果表明:人类活动是甸子和太平庄子流域自1980年以来河流水文健康情势退化的主要原因,其贡献率分别为86.9%和87.9%;大面积农业灌溉用水引起地表径流下降以及水利工程改变天然水文情势,影响了河流水文健康情势;90年代降水量较为充沛,研究流域受人类活动影响程度较小,河流水文健康等级维持在较高的水平。综合生态流量阈值和"观测-模拟"对比分析方法可定量识别河流水文健康情势演变原因,为适应环境变化的河流健康管理提供科学依据。     

Quantifying the uncertainty in the spatial layout of rock type domains in an iron ore deposit

This work addresses the problem of delineating the spatial layout of ten rock type domains in an iron ore body and of assessing the uncertainty in the domain boundaries. A stochastic approach is proposed to this end, based on truncated Gaussian simulation, which consists in defining successive partitions of the space that comply with the desired spatial continuity and contact relationships between rock type domains. The sequencing of these domains is driven by their position (surficial vs. underlying rocks), granulometry (compact vs. friable rocks), and grades (rich vs. poor) of iron, alumina, manganese and loss on ignition. A total of 100 realizations are produced, conditioned to available drill hole data, and used to quantify the uncertainty in the occurrence of each rock type domain, at both global and local scales.     

岩溶塌陷灾害监测预报技术与方法初步研究--以桂林市柘木村岩溶塌陷监测为例

我国可溶岩分布面积达365万km2,占国土面积的1/3以上,是世界上岩溶最发育的国家之一.近年来,随着岩溶区城市化建设的飞速发展,岩溶区土地资源、水资源和矿产资源开发的不断增强,由此而引发的岩溶塌陷问题日益突出,已成为岩溶区城市主要地质灾害,严重妨碍城市经济建设与发展.由于岩溶塌陷的产生在时间上具突发性,在空间上具隐蔽性,在机制上具复杂性.因此,被普遍认为难以采取地面常规监测手段,对塌陷进行监测预报.另一方面,试验研究表明,岩溶水气压力变化对塌陷具有触发作用,可以以此作为衡量塌陷发育的临界条件.这就意味着通过对岩溶管道系统的水(气)压力的动态变化进行观测,可以达到对塌陷进行预报的目的.论文以位于广西桂林柘木村的岩溶塌陷监测站为例,详细讨论这一技术方法.     

Quantifying the Effects of Commercial Clam Aquaculture on C and N Cycling: an Integrated Ecosystem Approach

Increased interest in using bivalve cultivation to mitigate eutrophication requires a comprehensive understanding of the net carbon (C) and nitrogen (N) budgets associated with cultivation on an ecosystem scale. This study quantified C and N processes related to clam (Mercenaria mercenaria) aquaculture in a shallow coastal environment (Cherrystone Inlet, VA) where the industry has rapidly increased. Clam physiological rates were compared with basin-wide ecosystem fluxes including primary production, benthic nutrient regeneration, and respiration. Although clam beds occupy only 3 % of the ecosystem’s surface area, clams filtered 7–44 % of the system’s volume daily, consumed an annual average of 103 % of the phytoplankton production, creating a large flux of particulate C and N to the sediments. Annually, N regenerated and C respired by clam and microbial metabolism in clam beds were ～3- and ～1.5-fold higher, respectively, than N and C removed through harvest. Due to the short water residence time, the low watershed load, and the close vicinity of clam beds to the mouth of Cherrystone Inlet, cultivated clams are likely subsidized by phytoplankton from the Chesapeake Bay. Consequently, much of the N released by mineralization associated with clam cultivation is “new” N as it would not be present in the system without bivalve facilitation. Macroalgae that are fueled by the enhanced N regeneration from clams represents a eutrophying process resulting from aquaculture. This synthesis demonstrates the importance of considering impacts of bivalve aquaculture in an ecosystem context especially relative to the potential of bivalves to remove nutrients and enhance C sinks.     

改进三峰谷雨流计数法在爆破震动损伤评价中的应用

构筑物在爆破地震载荷作用下发生破坏是一个非常复杂的损伤累积过程。在进行爆破地震效应研究时,不仅要考虑几何距离、爆破条件以及地质条件对爆破振动强度的影响,也要关注结构本身的劣化过程。据此提出应用疲劳理论进行爆破地震效应分析的思路。首先,阐述了爆破震动应力谱测量的基本方法。其次,针对于三峰谷雨流计数模型的不足,提出了改进方案。改进后的计数模型融等值点压缩、峰谷值检测以及循环计数为一体,简化了计数过程,运用改进的计数模型分析了震动应力谱,得出了各种循环的频数分布规律。统计结果表明,单次爆破中绝大部分为小幅疲劳循环,而且拉压循环所占的比例比较大。     

三角形量测法在隧道变形监测中的应用研究

通过对隧道变形监测中三角形量测法原理、计算公式的分析,认为公式中的三角形三边长度并不是收敛计的读数,两者相差一个收敛计本身的附加长度,这是使监测数据产生误差的原因之一。同时探讨了忽略收敛计附加长度引起的误差对监测结果的影响,并结合工程实例介绍了在实测过程中应注意的问题及误差原因。     

Quantifying solute distributions in the bioturbated zone of marine sediments by defining an average microenvironment

The bioturbated zone of marine sediments is a region having a complex, time-dependent geometry of diffusion and chemical reactions. It is possible to simplify this geometry by postulating an average sediment microenvironment and modelling it as representative of the sediment body as a whole. The microenvironment is assumed to correspond to a single, tube-dwelling animal together with its surrounding sediment and can be represented by a finite hollow cylinder. A transport-reaction model derived from this postulate produces good agreement between observed and predicted pore water profiles using realistic physical constants. The average vertical distributions of pore water solutes and their sediment-water fluxes are influenced by the presence of irrigated burrows to varying degrees depending on the kind of reactions governing their behavior. Pore water profiles of solutes, such as NH⁺₄, subject to zero order reaction rates are highly sensitive to the abundance and sizes of burrows while the net flux of the constituent across the sediment-water interface is not. In contrast, profiles of solutes such as Si that are subject to first order reaction rates are less sensitive to the presence of irrigated burrows but net fluxes are greatly affected. Average pore water concentrations, fluxes of solutes like Si and the apparent one-dimensional diffusion coefficients required to match vertical gradients with measured solute fluxes, are influenced by both the size and spacing of burrows. Because of the range of solute concentrations within the microenvironment at any given depth it is not strictly valid to make detailed solubility calculations on the basis of average pore water concentrations within the bioturbated zone.     

Safety evaluation of an ancient masonry seawall structure with modified DDA method

The ancient masonry seawall along China’s Qiantang River is an important structure for defending the prosperous estuarine area, including Hangzhou, Jiaxing, and part of Shanghai, against violent floods, tides and waves. Modified discontinuous deformation analysis (DDA) is used here to analyze the failure mechanisms and stability of the blocky seawall structure. The backfilling soil is properly integrated into the DDA model, by means of the proposed soil discretization approach, and with an accurate interface shear strength model that the authors presented. According to the simulation results by the modified DDA, the existing seawall is generally in good state. Nevertheless, routine inspection and early restoration are recommended to avoid progressive failures of the seawall.