Surface area, porosity and water adsorption properties of fine volcanic ash particles

Our understanding on how ash particles in volcanic plumes react with coexisting gases and aerosols is still rudimentary, despite the importance of these reactions in influencing the chemistry and dynamics of a plume. In this study, six samples of fine ash (<100 m) from different volcanoes were measured for their specific surface area, a_s, porosity and water adsorption properties with the aim to provide insights into the capacity of silicate ash particles to react with gases, including water vapour. To do so, we performed high-resolution nitrogen and water vapour adsorption/desorption experiments at 77 K and 303 K, respectively. The nitrogen data indicated a_s values in the range 1.1–2.1 m²/g, except in one case where a a_s of 10 m²/g was measured. This high value is attributed to incorporation of hydrothermal phases, such as clay minerals, in the ash surface composition. The data also revealed that the ash samples are essentially non-porous, or have a porosity dominated by macropores with widths >500 Å. All the specimens had similar pore size distributions, with a small peak centered around 50 Å. These findings suggest that fine ash particles have relatively undifferentiated surface textures, irrespective of the chemical composition and eruption type. Adsorption isotherms for water vapour revealed that the capacity of the ash samples for water adsorption is systematically larger than predicted from the nitrogen adsorption a_s values. Enhanced reactivity of the ash surface towards water may result from (i) hydration of bulk ash constituents; (ii) hydration of surface compounds; and/or (iii) hydroxylation of the surface of the ash. The later mechanism may lead to irreversible retention of water. Based on these experiments, we predict that volcanic ash is covered by a complete monolayer of water under ambient atmospheric conditions. In addition, capillary condensation within ash pores should allow for deposition of condensed water on to ash particles before water reaches saturation in the plume. The total mass of water vapour retained by 1 g of fine ash at 0.95 relative water vapour pressure is calculated to be ~10^–2 g. Some volcanic implications of this study are discussed.Editorial responsibility: J. Gilbert     

粉煤灰湿陷变形的三轴试验和计算

采用双压力室三轴仪对粉煤灰试样进行了单线法湿陷试验,研究了在静水压力作用以及在不同应力状态和应力水平下粉煤灰湿陷变形的规律,得出了粉煤灰湿陷变形的经验计算公式.提出了计算粉煤灰地基湿陷变形的"全应变曲线"增量有限元法.基于本文的试验结果,对一个粉煤灰地基的湿陷变形进行了有限元计算.     

模拟区域土地利用变化的多主体模型及其在鄱阳湖区的应用(英文)

在较大区域内,城市用地扩张和农村土地利用发展一般同步进行。为了能够正确理解这类区域内土地利用/土地覆被变化的动力机制,本研究开发了一个基于多主体系统的土地利用模型。模型将鄱阳湖区视为一个典型区域,利用有限扩散聚合算法模拟城市主体的行为,采用基于涌现理论的主体模型模拟农村土地利用。农村子模型包括多种类型的主体和环境影响层,其中最重要的是农户主体,农户主体可以根据自身条件和周围的环境影响参数确定下一步土地利用的决策,政府主体则通过实施不同的政策对土地利用进行宏观控制。我们根据农户总收入和外出务工人员比例将农户主体分为6类,每种类型的农户主体遵循不同的决策规则。结果表明,本模型的模拟结果与鄱阳湖区1985 – 2005年的土地利用/土地覆被变化趋势高度相符。尤其重要的是,模拟结果充分表明农户主体的土地利用决策与国家政策紧密相关。这表明本研究建立的基于多主体的土地利用模型是一种评估政府土地管理政策效果的有效手段。     

Trace elements in world steam coal and their behaviour in Dutch coal-fired power stations: A review

Trace elements associated with the combustion of coal have received more attention recently, as can be seen from the increasing demands laid down in legislation and permits.Knowledge of the trace element content of coal is essential. Coal used in the Netherlands is imported from all over the world. As a consequence, Dutch power stations are designed to burn a wide range of bituminous coals. The largest share nowadays originates from South Africa, Colombia, and Indonesia, with these three countries accounting for more than 85% of the coal fired in the Netherlands in recent years. The coals, as imported in the Netherlands, have been monitored for their (trace) element content. At present the database contains results of own analyses of about 170 coals, originating from 14 different countries. An important uncertainty was the question of how homogeneous the imported lots are. It appears that the lots as imported from overseas are fairly homogeneous.The behaviour and fate of trace elements in coal-fired power stations has been studied in more than 40 mass balance studies since 1977. More than 50 test series have been completed during co-combustion of biomass and waste materials (up to 40% on mass base) since 1993. It has therefore been possible to establish a relationship between (trace) elements in the fuel and the ash, as well as with emissions into the atmosphere.     

Breadth and depth in research on health disparities: commentary on the work of Nancy Krieger

Geocoding and spatial analysis of data describing populations and health events are important methods in health social science now carried out using GIS technology. This commentary considers Nancy Krieger’s work on health disparities in light of the various ways individuals and organizations use geocoded population and health data: analyzing spatial patterns of health and disease including health disparities, aggregating data spatially, assessing health status of individuals based on characteristics of aggregates, modeling neighborhood contextual factors affecting health, designing observation and intervention studies, and delivering health interventions and services. The extent to which her work addresses each of these purposes is considered. The strengths and limitations of the research including choice of spatial analytic units and techniques as reported in the published work are discussed. Krieger’s work, with her colleagues, has used standard methods of spatial analysis to raise the profile of GIS and spatial analysis in the public health community.     

富火山物质烃源岩评价方法——以北疆石炭系为例

正新疆北部石炭系发育一套巨厚的混杂有火山物质的烃源岩。有机质丰度以及类型等指标显示具有作为烃源岩的潜力。笔者综合运用薄片等分析资料将其划分为凝灰岩、沉凝灰岩、凝灰质泥岩、含碳质泥岩,并分类研究了其地球化学特征。针对富火山物质烃源岩成熟度高、有机质丰度低的特点,首次运用生烃模拟实验结合数值模拟开展其有机碳含量恢复,建立了不同火山物质含量烃源岩有机     

武汉东湖淤泥碳化-固化试验研究

引入活性MgO-粉煤灰固化材料,采用碳化-固化联合技术处理武汉东湖疏浚淤泥,通过无侧限抗压强度、扫描电镜和压汞试验,研究加压碳化模式、碳化时间、MgO-粉煤灰配比和固化剂掺量等因素下CO2碳化作用对固化淤泥力学性质和微观结构的影响。结果表明：活性MgO-粉煤灰固化淤泥碳化后抗压强度进一步增长,应力-应变关系曲线压密阶段应变缩小;不同固化剂配比的东湖淤泥试样具有不同的最佳加压模式,而加压模式决定了相同碳化时间下固化淤泥CO2吸入量,从而影响碳化-固化淤泥试样抗压强度;活性MgO掺量低时试样抗压强度整体较低,强度随碳化时间增加先增大后减小;MgO掺量较高时,碳化试样强度随碳化时间快速达到较高值,随后增长缓慢。微观分析表明：水碳镁石、球碳镁石和碳酸镁石等镁碳酸盐是碳化-固化联合技术增强淤泥强度的主要原因,其膨胀性和胶结作用促使土体中团粒内孔隙向颗粒间孔隙转化,土体更密实,抗压强度增加。     

基于时空大数据的城市脉动分析研究

随着新型城镇化建设成为了国家战略,各地政府掀起了智慧城市建设热潮。在智慧城市建设中,公共信息平台建设是不可或缺的重要基础环节。随着平台的深入运行,逐步积累了大量的城市数据。但是,数据资源中蕴含的知识远未得到充分挖掘和应用,致使数据爆炸但知识匮乏。因此,基于数据时空和专题属性,建立科学的城市数据体系是城市管理的迫切需求;同时,基于数据体系,揭示各类数据随时空变化规律,展现城市脉动发展情况是城市决策重要的依据,也是观察和诊治"城市病"的重要技术手段。我们以中新天津生态城所建成的大数据汇聚公共平台为依托,基于数据挖掘技术手段,针对环境、能源、交通脉动进行研究并取得初步成果,科学地揭示了"城市脉动"变化规律,使平台数据发挥最大价值。脉动分析结果以可视化手段表现,反映城市各项指标脉动变化特征。     

The modifiable areal unit problem in hedonic house-price models

When geographically aggregated data are included in hedonic models, the resulting coefficients are biased by the spatial scale and spatial configuration of variable measurement. We explore the effects of this modifiable areal unit problem (MAUP) within the context of hedonic price models with an individual-level dependent variable. Specifically, we developed standard and spatial hedonic regression models in order to examine the effects of the MAUP on model fit and coefficient estimates. Our empirical analysis documents several significant scale and zoning effects in the hedonic modeling framework. First, neighborhood characteristics are clearly important in efforts to improve model fit—and they are more significant contributors in the standard model than in the spatial hedonic model. For aggregation scale, the model fit change of the standard model is relatively large, whereas the change is more modest for spatial models. The patterns of change in model fit for standard and spatial hedonic models clearly diverge from one another, implying the existence of a scale level showing a maximum functional range of the submarket on which scale dependencies are expected to have an impact. Regarding the zoning effect, the model fits for both standard and spatial hedonic models vary according to the submarket systems.