On the advantage of sharing a holdfast: effects of density and occurrence of kin aggregation in the kelp Lessonia berteroana

We investigated the density‐dependent and genetic relatedness that regulate the occurrence of inter‐individual (genet) fusion forming plurigenotypic organisms in the brown alga Lessonia berteroana. Recruitment generally occurs at high densities in the inter‐tidal, allowing contact of neighbouring holdfasts as they grow and expand on the substrate. Algal density, by contrast, is regulated by the effects of herbivory and wave impact, which often lead to low holdfast density. Herein, we investigated whether the occurrence of plurigenotypic organisms and their genotypic composition (number of genotypes per plurigenotypic organism) are density dependent and affected by kin selection in the inter‐tidal kelp L. berteroana. Four microsatellite loci were used to analyse DNA from 260 samples obtained from shared and non‐shared holdfasts, at two sites with high and two site with low holdfast density. Analyses showed that fusions forming plurigenotypic organisms are extremely common. Interestingly, the frequency of fusions was higher in low‐density sites, in which 100% of the plants had at least two genotypes and the average was 3.5. In high‐density sites, 62% of plants were plurigenotypic, with an average of 2.8 genotypes per plant. Additionally, we found that genotypes that shared a holdfast had a significantly higher genetic relatedness than the average in the population, compatible with a kin structure. Density dependence and kin structure suggest that the occurrence of plurigenotypic organisms is linked to environmental quality, and that kin or multilevel selection may be favouring the fusion of genetically related genets.     

Formation of high-grade ignimbrites Part II. A pyroclastic suspension current model with implications also for low-grade ignimbrites

 Analogue experiments in part I led to the conclusion that pyroclastic flows depositing very high-grade ignimbrite move as dilute suspension currents. In the thermo–fluid–dynamical model developed, the degree of cooling of expanded turbulent pyroclastic flows dynamically evolves in response to entrainment of air and mass loss to sedimentation. Initial conditions of the currents are derived from column-collapse modeling for magmas with an initial H₂O content of 1–3 wt.% erupting through circular vents and caldera ring-fissures. The flows spread either longitudinally or radially from source up to a runout distance that increases with higher mass flux but decreases with higher gas content, temperature, bottom slope and coarser initial grain size. Progressive dilution by entrainment and sedimentation causes pyroclastic currents to transform into buoyant ash plumes at the runout distance. The ash plumes reach stratospheric heights and distribute 30–80% of the erupted material as widespread co-ignimbrite ash. Pyroclastic suspension currents with initial mass fluxes of 10⁷-10¹² kg/s can spread for tens of kilometers with only limited cooling, although they move as supercritical, strongly entraining currents for the eruption conditions considered here. With increasing eruption mass flux, cooling during passage through the fountain diminishes while cooling during flow transport increases. The net effect is that eruption temperature exerts the prime control on emplacement temperature. Pyroclastic suspension currents can form welded ignimbrite across their entire extent if eruption temperature is T_o>1.3^.T_mw, the minimum welding temperature. High eruption rates, a large fraction of fine ash, and a ring-fissure vent favor the formation of extensive high-grade ignimbrite. For very hot eruptions producing sticky, partially molten pyroclasts, analysis of particle aggregation systematics shows that factors favoring longer runout also favor more efficient aggregation, which reduces runout. As a result, very high-grade ignimbrites cannot spread more than a few tens of kilometers from their source. In cooler pyroclastic currents, particles do not aggregate, and the sedimentation process may involve re-entrainment of particles, which potentially leads to more extensive cooling and longer runout; such effects, however, are only significant when net erosion of substrate occurs. Model results can be employed to estimate mass flux and duration of ignimbrite eruptions from measured ignimbrite masses and aspect ratios. The model also provides an alternative explanation of the observed decrease in H/Lratios with ignimbrite mass. Received: 10 May 1998 / Accepted: 21 October 1998     

面向分布式服务聚合的“天地图”总体技术架构

介绍了"天地图"面向分布式多节点协同服务的总体架构,以及"天地图"公共地理框架数据体系、在线服务系统、运行支持系统的内容,旨在为同类平台的研究与建设提供参考。     

基于PDF格式开发多媒体电子地图集技术探讨

矢量地理PDF(portable document format)地图具有数据量小、通用性强等特点,是一种具备查询、量算等功能的新型电子地图,其应用需求和前景广阔。单纯利用数字线划图(digital line graphic,DLG)数据,通过符号化和制图编辑等处理制作矢量地理PDF地图的过程持续时间长,工作量大。充分利用已有的地图制图成果来快速制作矢量地理PDF地图,避免影响已有的制图生产工序流程,对提高矢量地理PDF地图生产效率具有重要意义。提出了一种矢量地理PDF地图制作的方法,利用出版原图(publication originals of map,POM)与DLG数据,通过数据预处理、地图坐标系统构建、数据聚合处理与压缩流程,快速生成矢量地理PDF地图。该方法省略了符号化和制图编辑处理流程,经试验验证,制作矢量地理PDF地图的效率高,成果数据量较POM和DLG数据总量显著压缩,适用于DLG和POM数据源条件具备的矢量地理PDF地图大规模快速生产。     

基于多态模糊贝叶斯网络的半潜平台安装风险分析

针对半潜式平台安装作业风险评估中存在的风险多态性和模糊性问题,构建了一种多态模糊贝叶斯网络风险分析模型。根据行业规范推荐标准定义语言性评价模糊集,描述根节点的事故状态发生概率,克服了传统方法中确定性概率难以获取的困难。利用相似性聚合法结合置信度指标融合专家意见,引入改进的去模糊化转换方法,提高了专家知识经验转化为定量数据的合理性和可靠性。基于贝叶斯网络的双向推理和敏感性分析技术,实现了工程作业全过程的风险评估。通过对陵水17-2项目半潜平台整体吊装过程进行风险分析,验证该模型的合理性与有效性,为半潜平台安装作业风险管理与防控策略制定提供指导。     

On the effects of triangulated terrain resolution on distributed hydrologic model response

Distributed hydrologic models based on triangulated irregular networks (TIN) provide a means for computational efficiency in small to large‐scale watershed modelling through an adaptive, multiple resolution representation of complex basin topography. Despite previous research with TIN‐based hydrology models, the effect of triangulated terrain resolution on basin hydrologic response has received surprisingly little attention. Evaluating the impact of adaptive gridding on hydrologic response is important for determining the level of detail required in a terrain model. In this study, we address the spatial sensitivity of the TIN‐based Real‐time Integrated Basin Simulator (tRIBS) in order to assess the variability in the basin‐averaged and distributed hydrologic response (water balance, runoff mechanisms, surface saturation, groundwater dynamics) with respect to changes in topographic resolution. Prior to hydrologic simulations, we describe the generation of TIN models that effectively capture topographic and hydrographic variability from grid digital elevation models. In addition, we discuss the sampling methods and performance metrics utilized in the spatial aggregation of triangulated terrain models. For a 64 km² catchment in northeastern Oklahoma, we conduct a multiple resolution validation experiment by utilizing the tRIBS model over a wide range of spatial aggregation levels. Hydrologic performance is assessed as a function of the terrain resolution, with the variability in basin response attributed to variations in the coupled surface–subsurface dynamics. In particular, resolving the near‐stream, variable source area is found to be a key determinant of model behaviour as it controls the dynamic saturation pattern and its effect on rainfall partitioning. A relationship between the hydrologic sensitivity to resolution and the spatial aggregation of terrain attributes is presented as an effective means for selecting the model resolution. Finally, the study highlights the important effects of terrain resolution on distributed hydrologic model response and provides insight into the multiple resolution calibration and validation of TIN‐based hydrology models. Copyright © 2005 John Wiley & Sons, Ltd.     

Detecting negative spatial autocorrelation in georeferenced random variables

Negative spatial autocorrelation refers to a geographic distribution of values, or a map pattern, in which the neighbors of locations with large values have small values, the neighbors of locations with intermediate values have intermediate values, and the neighbors of locations with small values have large values. Little is known about negative spatial autocorrelation and its consequences in statistical inference in general, and regression-based inference in particular, with spatial researchers to date concentrating mostly on understanding the much more frequently encountered case of positive spatial autocorrelation. What are the spatial contexts within which negative spatial autocorrelation should be readily found? What are its inferential consequences for regression models? This paper presents selected empirical examples of negative spatial autocorrelation, adding to the slowly growing literature about this phenomenon.     

尼日利亚奥贡广东自贸区发展历程与产业聚集研究

利用贸易结合度指数分析中尼双方相互贸易依赖程度,总结中国对尼贸易与投资特征;在回顾尼日利亚奥贡广东自贸区的发展历程基础上,利用EG指数分析园区产业聚集程度,得出了园区多数产业集聚度较高,并符合尼日利亚鼓励先锋行业要求的结果;通过对结果的分析与讨论,总结目前园区在产业、基础设施、东道国政治经济环境等方面面临的挑战;最后从政府与企业两方面提出园区产业优化与发展的建议。