The effects of scale and spatial heterogeneities on diffusion in volcanic breccias and basalts: Amchitka Island, Alaska

Knowledge of the factors that influence the diffusion of contaminants, such as the diffusivity and the connected porosity, is crucial to modeling the long-term fate and transport of contaminants in subsurface systems with small or negligible advective flow, such as in fractured crystalline rock. Fractured rock is naturally heterogeneous, and hence, understanding the diffusivity of a molecule through this material (or the formation factor of the medium) becomes a complex problem, with critical concerns about the scale of laboratory measurements and about the spatial variability of these measurements relative to the scale needed for fate and transport modeling. This study employed both electrical and tracer-based laboratory methods to investigate the effects of scale and pore system connectivity on the diffusivity for volcanic matrix rock derived from the study site, a former underground nuclear test site at Amchitka Island, Alaska. The results of these investigations indicate a relatively well-connected pore system with scale effects generally limited to approximately 6 cm lengths and well-correlated to observed heterogeneous features. An important conclusion resulting from this study, however, is that there is a potential for the estimated diffusivity to be misrepresented by an order of magnitude if multiple samples or longer sample lengths are not used. Given the relatively large number of measurements resulting from these investigations, an analysis of the probability density function (PDF) of the diffusivity was possible. The PDF of the diffusivity was shown to generally follow a normal distribution for individual geologic layers. However, when all of the geologic layers are considered together, the distribution of the subsurface as a whole was shown to follow a lognormal distribution due to the order of magnitude differences amongst the layers. An understanding of these distributions is essential for future stochastic modeling efforts.     

From land cover change to land function dynamics: a major challenge to improve land characterization

Land cover change has always had a central role in land change science. This central role is largely the result of the possibilities to map and characterize land cover based on observations and remote sensing. This paper argues that more attention should be given to land use and land functions and linkages between these. Consideration of land functions that provide a wide range of goods and services makes more integrated assessments of land change possible. The increasing attention to multifunctional land use is another incentive to develop methods to assess changes in land functions. A number of methods to quantify and map the spatial extent of land use and land functions are discussed and the implications for modeling are identified based on recent model approaches in land change science. The mixed use of land cover, land use and land function in maps and models leads to inconsistencies in land change assessments. Explicit attention to the non-linear relations between land cover, land use and land function is essential to consistently address land change. New methods to map and quantify land function dynamics will enhance our ability to understand and model land system change and adequately inform policies and planning.     

Preferred modes of travel among older adults: What factors affect the choice to walk instead of drive?

Introduction

There are many factors that influence older adults' travel choices. This paper explores the associations between mode of travel choice for a short trip and older adults' personal characteristics.

Methods

This study included 406 drivers over the age of 64 who were enrolled in a large integrated health plan in the United States between 1991 and 2001. Bivariate analyses and generalized linear modeling were used to examine associations between choosing to walk or drive and respondents' self-reported general health, physical and functional abilities, and confidence in walking and driving.

Results

Having more confidence in their ability to walk versus drive increased an older adult's likelihood of walking to make a short trip by about 20% (PR = 1.22; 95% CI: 1.06-1.40), and walking for exercise increased the likelihood by about 50% (PR = 1.53; 95% CI = 1.22-1.91). Reporting fair or poor health decreased the likelihood of walking, as did cutting down on the amount of driving due to a physical problem.

Discussion

Factors affecting a person's decision to walk for exercise may not be the same as those that influence their decision to walk as a mode of travel. It is important to understand the barriers to walking for exercise and walking for travel to develop strategies to help older adults meet both their exercise and mobility needs. Impact on Industry: Increasing walking over driving among older adults may require programs that increase confidence in walking and encourage walking for exercise.     

铁碳微电解法在废水处理中的研究进展及应用现状

介绍了铁碳微电解法处理废水的作用机理,概述了近10年来国内外利用铁碳微电解法及其组合工艺对印染、造纸、焦化、炸药、制药等废水处理方面的研究进展及实际的应用状况.提出了铁碳微电解法在运行过程中存在的几个问题,并对今后研究工作的大体方向做了初步的探讨.     

人-机系统事故预防理论研究

分析人-机系统事故发生原因,剖析经典以人失误为主因的事故致因模型存在的不足,在该模型基础上增加"刺激"形成的原因,构建了改进事故致因模型。对两模型进行比较研究,指出人机工程学与防止事故的关系,提出了人机工程学防止事故的方法,并给出人机界面合理性主观评价检查表。研究及论证表明:预防人-机系统事故的本质在于有效防止人失误的发生,除安全管理措施以外,最重要的是人机工程学问题,笔者提出的基于人机工程学的人-机系统事故预防理论,对人-机系统事故的预防起到积极的指导作用。     

矿井通风系统安全性的多层次模糊综合评价

按照事故致因理论,并进行系统安全分析和易发事故分析,建立了矿井通风系统安全性的多层次评价体系;应用层次分析法和Matlab软件,确定矿井通风系统安全性评价体系中各子系统及各指标的权重;结合实际经验,根据安全规范构造各指标隶属度;进而根据评价集构造了梯形分布的隶属函数,并得到各指标对评价集的最终隶属度、模糊关系矩阵和综合评价矩阵;求得矿井通风系统安全状况的综合得分,进而划分安全评价等级,并提出了对应各等级的处理措施。将该评价方法应用到重庆开县桃园联合煤矿,取得了良好的效果。     

学龄儿童肺功能水平影响因素的研究

用逐步回归分析方法对与室内、外空气污染和机体状况等有关的因素对广州市学龄儿童肺功能 (FVC、FEV1 、PEFR和 FEF2 5～ 75 )水平的影响进行研究。结果提示 ,影响肺功能水平的主要因素是内因 ,身高的影响最明显 ,呼吸系统疾病或症状发生与肺功能水平下降有关 ;室外空气污染使肺功能水平下降 ,SO2 、NOx 和 PM2 .5 的影响明显 ,PM2 .5 的影响明显大于 PM1 0 和 TSP;居室或厨房通风不良、家庭烹饪用不洁燃料对儿童肺功能的生长不利 ;被动吸烟对女性儿童肺功能有不利影响。对各种影响因素 ,PEFR和 FEF2 5～ 75 比 FVC和 FEV1 更为敏感     

兰州市空气污染对儿童肺功能影响的前瞻性研究

从不同的角度阐述了室内外空气污染对儿童肺功能 ,特别是小气道功能的影响及其影响程度的前瞻性研究结果。并通过多因素、多指标的综合分析 ,揭示了一些影响儿童肺功能的主要因素。指出了从保护人体健康的角度来说 ,好的环境空气质量和良好的室内空气质量同样重要     

城市生态安全多层次灰色综合评价

从城市生态安全的基本内涵出发,根据压力(pressure)-状态(state)-响应(response)模型,从生态系统压力、生态系统状况、生态系统响应3方面构建一个4层次的城市生态安全评价指标体系,运用灰色系统理论,构建了城市生态安全多层次灰色综合评价模型,并结合实例进行计算。评价结果与实际情况基本相符,表明该模型能有效地利用评价指标的信息,所给出的综合评价值既能用于描述所评价城市的生态安全状况,亦可对不同城市的生态安全状况进行比较,对更加科学合理地评价城市生态安全状况具有参考价值。     

Economies of scale in global iron-making

In this paper, we investigate the presence of economies of scale in the global iron-making industry for integrated steel plants, iron making being the first stage in the steel-making process. Iron making depends on basic commodities, such as iron ore, coke and various forms of energy, required in the operation of the blast furnace, which can be classified as essential inputs and used in fixed proportions to produce iron. A generalized Leontief cost function is estimated using panel data for 69 integrated plants, such a specification being appropriate for technologies with essential inputs that are used in fixed proportions in production. A significant scale effect is observed due to the existence of fixed costs and a linear dependence of the cost function on production. Under a simple linear cost function, a rough estimate of the breakeven scale of plant, where costs equal revenue, is 4.5 Mt per year. Competitiveness, as measured by the ratio of plant average cost per tonne to best practice cost per tonne, can be shown to be positively related to the scale of production as well as the cost of essential inputs. Therefore, low-cost producers are also often producers with low raw material costs and production levels below the estimated breakeven scale of operation. Labor costs, although significant, are comparatively less important as a driver towards low costs.