Sampling Scale Effects in Random Fields and Implications for Environmental Monitoring

The concept of a sampling scale triplet of spacing, extent and support is used to define the spatial dimensions of a monitoring network or a field study. The spacing is the average distance between samples, the extent is the size of the domain sampled and the support is the averaging area of one sample. The aim of this paper is to examine what is the bias and the random error (uncertainty) introduced by the sampling scale triplet into estimates of the mean, the spatial variance and the integral scale of a variable in a landscape. The integral scale is a measure of the average distance over which a variable is correlated in space. A large number of two dimensional random fields are generated from which hypothetical samples, conforming to a certain sampling scale triplet, are drawn which in turn are used to estimate the sample mean, spatial variance and integral scale. The results indicate that the biases can be up to two orders of magnitude. The bias of the integral scale is positively related to the magnitude of any of the components of the scale triplet while the bias of the spatial variance is different for different components of the scale triplet. All sampling scale effects are relative to the underlying correlation length of the variable of interest which is closely related to the integral scale. The integral scale can hence be used for sampling design and data interpretation. Suggestions are given on how to adjust a monitoring network to the scales of the variables of interest and how to interpret sampling scale effects in environmental data.     

聚合氯化铁-腐殖酸(PFC-HA)冷冻干燥絮体的表面与孔分形研究

采用低温急速冷冻-真空干燥技术制备了PFC-HA絮体的粉末样品,研究了这些样品的物理与分形特征.结果表明,PFC-HA絮体具有晶体结构,SEM图象中有方块状形体;絮体主要组成元素为C、O、Fe,所含的特征官能团保留了絮体组成原料的一些特征;絮体的干燥样品的BET比表面积为51～92 m2·g-1,BJH累积吸附孔体积为0.0638～0.108 cm3·g-1,BJH脱附平均孔径为3.53～4.60nm,PSD峰值对应孔径3.9nm(4#样品还有另外一个PSD峰值53.2nm).PFC-HA絮体的干燥样品具有自相似性的粗糙表面,呈现多尺度分形特征;图象法确定的表面分形维数Ds值远低于N2吸附/脱附等温线法确定的结果,分别为2.14～2.22、2.90～2.96;前者的分形尺度大约处于23～390nm之间,主要属于絮体干燥样品的外表面尺度,后者的分形特征尺度区间的下限大约为0.2nm,属于孔表面尺度,因此,PFC-HA絮体干燥样品的表面粗糙度主要集中于孔表面.另外,对同一絮体,N2吸附法和脱附法确定的孔表面分形维数基本相同.通过热力学模型计算出的4#样品的Ds值接近于FHH理论计算出的结果,但分形尺度的区间变小了.     

Assessing alpine plant vulnerability to climate change: a modeling perspective

The potential ecological impact of ongoing climate change has been much discussed. High mountain ecosystems were identified early on as potentially very sensitive areas. Scenarios of upward species movement and vegetation shift are commonly discussed in the literature. Mountains being characteristically conic in shape, impact scenarios usually assume that a smaller surface area will be available as species move up. However, as the frequency distribution of additional physiographic factors (e.g., slope angle) changes with increasing elevation (e.g., with few gentle slopes available at higher elevation), species migrating upslope may encounter increasingly unsuitable conditions. As a result, many species could suffer severe reduction of their habitat surface, which could in turn affect patterns of biodiversity. In this paper, results from static plant distribution modeling are used to derive climate change impact scenarios in a high mountain environment. Models are adjusted with presence/absence of species. Environmental predictors used are: annual mean air temperature, slope, indices of topographic position, geology, rock cover, modeled permafrost and several indices of solar radiation and snow cover duration. Potential Habitat Distribution maps were drawn for 62 higher plant species, from which three separate climate change impact scenarios were derived. These scenarios show a great range of response, depending on the species and the degree of warming. Alpine species would be at greatest risk of local extinction, whereas species with a large elevation range would run the lowest risk. Limitations of the models and scenarios are further discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

省级尺度大气环境监测优化布点研究

以湖北省大气环境质量监测优化布点分析为例 ,对省级尺度的大气环境监测省控测点的选站原则、省控站位及数目的确定进行了研究探讨 ,提出了省级尺度大气环境监测优化布点的综合分析方法     

给水管网中铁释放现象的影响因素研究

在实验室静态试验下,定量分析了给水管网中无机化学水质参数对铁释放现象的影响,包括酸碱条件、氧化还原条件和无机离子等不同类别的水质参数.研究发现,铁释放速率都随着pH值、碱度和氧化剂浓度的升高而降低,随着氯离子浓度的升高而升高.根据管网的一般条件,提出了控制铁释放现象的理论临界释放速率计算公式.根据理论临界铁释放速率,达到控制管网铁释放现象的必要条件时,管网水质条件满足的要求为pH大于7.6,碱度大于150 mg/L,溶解氧浓度大于2 mg/L,氯离子浓度小于150 mg/L.     

颗粒物表面酸碱特性与孔表面分形的研究

通过电位滴定试验,证明了5种颗粒物的表面存在着一定量的OH-受体,其表面位浓度(Hs)在0.1219～0.3134 mmo.·L-1之间,表面位密度(DoH)在0.8586～2.1305个·nm-2之间,且不同采样点的颗粒物,其表面位浓度和表面位密度差别很大.所采集的5种颗粒物的孔结构接近平行板狭缝,孔尺寸分布不是均一的,平均孔径分布范围较宽(1.8～76nm);BET比表面积为9.5669～34.5605 m2·g-1,累积脱附孔体积为0.01729～0.06711 cm3·g-1,BJH脱附平均孔径为5.6768～7.7388nm,处于中孔范围,且平均孔径均大于其PSD峰值对应的孔径.通过分形FHH方程模拟N2吸附和脱附等温线数据计算出这些颗粒物的孔表面分形维数Ds比较接近(2.68～2.82之间),但它们的分形标度区间不同.另外,采用热力学模型和分形FHH理论计算出的表面分形维数的差异主要归因于这些样品孔尺寸分布的不均一性.     

无人机操作主观心理负荷测评与心率数据比较

为探究在无人机实操试验的心理负荷测量中主观量表与心率测评工具的性能,招募14名从未接触过无人机操作的被试者,在参加飞行操作培训后进行4种不同难度的无人机飞行操作情景试验;使用Polar V800监测被试者试验过程中的心率变化,并在试验结束后采用NASA-TLX,MCH,SWAT 3种主观量表进行评分,以比较飞行难度间各...     

Experimental investigation of bubbly flow and turbulence in hydraulic jumps

Many environmental problems are linked to multiphase flows encompassing ecological issues, chemical processes and mixing or diffusion, with applications in different engineering fields. The transition from a supercritical flow to a subcritical motion constitutes a hydraulic jump. This flow regime is characterised by strong interactions between turbulence, free surface and air–water mixing. Although a hydraulic jump contributes to some dissipation of the flow kinetic energy, it is also associated with increases of turbulent shear stresses and the development of turbulent eddies with implications in terms of scour, erosion and sediment transport. Despite a number of experimental, theoretical and numerical studies, there is a lack of knowledge concerning the physical mechanisms involved in the diffusion and air–water mixing processes within hydraulic jumps, as well as on the interaction between the free-surface and turbulence. New experimental investigations were undertaken in hydraulic jumps with Froude numbers up to Fr = 8.3. Two-phase flow measurements were performed with phase-detection conductivity probes. Basic results related to the distributions of void fraction, bubble frequency and mean bubble chord length are presented. New developments are discussed for the interfacial bubble velocities and their fluctuations, characterizing the turbulence level and integral time scales of turbulence representing a “lifetime” of the longitudinal bubbly flow structures. The analyses show good agreement with previous studies in terms of the vertical profiles of void fraction, bubble frequency and mean bubble chord length. The dimensionless distributions of interfacial velocities compared favourably with wall-jet equations. Measurements showed high turbulence levels. Turbulence time scales were found to be dependent on the distance downstream of the toe as well as on the distance to the bottom showing the importance of the lower (channel bed) and upper (free surface) boundary conditions on the turbulence structure.     

Space-time estimation of grid-cell hourly ozone levels for assessment of a deterministic model

We present an approach to estimate hourly grid-cell surface ozone concentrations based on observations from point monitoring sites in space, for comparison with grid-based results from the SARMAP photochemical air-quality model for a region of northern California. Statistical estimation is carried out on a transformed (square root) scale, followed by back-transforming to the original scale of ozone in parts per billion, adjusting for bias and variance. We estimate a spatially-varying diurnal mean structure and a non-separable space-time correlation structure on the transformed scale. Temporal pre-whitening is followed by modelling of a spatially non-stationary, diurnally-varying spatial correlation structure using a spatial deformation approach. Comparisons of SARMAP model results with the estimated grid-cell ozone levels are presented.     

基于污染控制的畜禽养殖场适度规模的理论分析

当前,规模化逐渐成为我国畜禽养殖业发展的主要思路,而现实中大规模养殖在带来经济效益的同时也带来了严重的环境污染。从污染控制的角度看是否存在最优养殖规模成为一个需要研究的问题。基于耕地对氮磷的承载能力、运输成本、排污费等变量构建了数理模型,探讨追求利润最大化的畜禽养殖场的最优规模问题。结果表明：在养殖场自由选择养殖规模时,出售一个养殖单位获得的经济收益越高、耕地对处理剩余物的承载能力越大,则最优养殖规模越大;而一个养殖单位的直接生产成本和粪便处理成本越高、畜禽粪便经处理后的剩余物越多、运输成本越高、排污费越高,则最优规模越小。在养殖规模既定的情况下,提高排污收费时畜禽养殖场将提高其处理剩余物的还田处置比例。最后,指出在畜禽粪便处理技术难以有效去除氮磷、对养殖场是否合理处置最终剩余物难以监管的条件下,对养殖场进行规模控制将是畜禽养殖污染控制的一个政策方向