Incorporating layer- and local-scale heterogeneities in numerical simulation of unsaturated flow and tracer transport

This study characterizes layer- and local-scale heterogeneities in hydraulic parameters (i.e., matrix permeability and porosity) and investigates the relative effect of layer- and local-scale heterogeneities on the uncertainty assessment of unsaturated flow and tracer transport in the unsaturated zone of Yucca Mountain, USA. The layer-scale heterogeneity is specific to hydrogeologic layers with layerwise properties, while the local-scale heterogeneity refers to the spatial variation of hydraulic properties within a layer. A Monte Carlo method is used to estimate mean, variance, and 5th, and 95th percentiles for the quantities of interest (e.g., matrix saturation and normalized cumulative mass arrival). Model simulations of unsaturated flow are evaluated by comparing the simulated and observed matrix saturations. Local-scale heterogeneity is examined by comparing the results of this study with those of the previous study that only considers layer-scale heterogeneity. We find that local-scale heterogeneity significantly increases predictive uncertainty in the percolation fluxes and tracer plumes, whereas the mean predictions are only slightly affected by the local-scale heterogeneity. The mean travel time of the conservative and reactive tracers to the water table in the early stage increases significantly due to the local-scale heterogeneity, while the influence of local-scale heterogeneity on travel time gradually decreases over time. Layer-scale heterogeneity is more important than local-scale heterogeneity for simulating overall tracer travel time, suggesting that it would be more cost-effective to reduce the layer-scale parameter uncertainty in order to reduce predictive uncertainty in tracer transport.     

Effect of admixture of solid inertant on fire hazard of dust layers oriented at varying degrees of inclination

Unlike metallic dust layers, the layer flammability levels (LFL) of non-metallic dust layers exhibit a wide range from Class 1 (No self-sustained combustion) to Class 6 (explosive combustion). However, determinations of layer flammability have not considered the effect of inclination angle, thereby potentially underestimating fire hazard of combustible dust layers in many industrial situations. In this research, inclined dust layers showed greater fire hazard than did horizontally oriented dust layers. For example, LFL of wood dust jumped from class 3 to class 5 when layers were positioned with an incline. Flame spread rate of PMMA dust layers increased from 1.8 to 3.6 mm/s when the angle of inclination increased from 0 to 40°. Even small amounts of solid inertant significantly decreased surface layer fires. The required amount of inertant to completely inert layer fires was far less than that for smoldering layer fires or dust explosions.     

A fuzzy logic and probabilistic hybrid approach to quantify the uncertainty in layer of protection analysis

Layer of protection analysis (LOPA) is a widely used semi-quantitative risk assessment method. It provides a simplified and less precise method to assess the effectiveness of protection layers and the residual risk of an incident scenario. The outcome failure frequency and consequence of that residual risk are intended to be conservative by prudently selecting input data, given that design specification and component manufacturer's data are often overly optimistic. There are many influencing factors, including design deficiencies, lack of layer independence, availability, human factors, wear by testing and maintenance shortcomings, which are not quantified and are dependent on type of process and location. This makes the risk in LOPA usually overestimated. Therefore, to make decisions for a cost-effective system, different sources and types of uncertainty in the LOPA model need to be identified and quantified. In this study, a fuzzy logic and probabilistic hybrid approach was developed to determine the mean and to quantify the uncertainty of frequency of an initiating event and the probabilities of failure on demand (PFD) of independent protection layers (IPLs). It is based on the available data and expert judgment. The method was applied to a distillation system with a capacity to distill 40 tons of flammable n-hexane. The outcome risk of the new method has been proven to be more precise compared to results from the conventional LOPA approach.     

无性繁殖常用的方式

无性繁殖常用的方式有三种,扦插、压条和嫁接。本文论述了这三种无性繁殖的具体作法。     

Postfire Regeneration in <Emphasis Type="Italic">Pinus pinea</Emphasis> L. and <Emphasis Type="Italic">Pinus pinaster</Emphasis> Aiton in Andalucia (Spain)

The objective of this study was to examine postfire regeneration of tree, shrub, and dwarf shrub species, in relation to levels of damage in four planted pine forests (Pinus pinea, Pinus pinaster) in Andalusia. A prefire vegetation map was used for detailing species composition, vertical structure, and density and another for detailing the extent and intensity of fire damage. Between 3 and 7 years after the fires, an inventory was made of the vegetation in each area, using the step-point method. The information thus obtained was used to determine the amount of cover in the dwarf/shrub and tree layers, the frequency of species in each of the layers, floristic richness, and diversity (Shannon index). The botanical composition of the dwarf and shrub layer was analyzed using TWINSPAN. Variables were poorly correlated with level of fire damage, which suggests that the forests in this study followed the autosuccession model. Because of the artificial origin or seminatural condition, regeneration of the dominant tree species is poor, and it seems unlikely that forests will recover to their prefire state. Therefore action is recommended to restore these ecosystems.     

多层自由旋线分离器的提效增阻作用

文章采用多层旋线布置方式实现了自由旋线分离器分离效率的有效提升,并讨论了多层布置对除尘效率与压力损失的影响规律.在风量2 000 m3/h、液气比0.03 L/m3和粉尘质量浓度1 000 mg/m3的试验条件下,单层旋线和双层旋线的除尘效率均随旋线根数和转速的增加而增加,且双层旋线的除尘效率的增幅高于单层旋线.当旋线...     

环境水样中痕量Fe3+的测定方法研究

在酸性介质中(pH 5.0),Fe3+能与硫氰酸盐生成稳定的配离子[Fe(SCN)6]3-,该配阴离子能与碱性717型阴离子交换树脂定量交换缔合,形成阴离子交换树脂(R+)--金属离子(Mn+)--硫氰酸盐(SCN-)三元配合缔合体系,其最大吸收波长分别为490 μm,与二元水相最大吸收波长相同,通过制作薄层测定了水中Fe3+含量.本法具有较高的灵敏度ε630Fe3+=2.4×105 L·mol-1·cm-1,测定0.6 μgFe3+6次,RSD=2.7%,实测了水样中,Fe3+含量并与AAS法测定结果比较,Fe3+测定的线性范围0～10 μg/25mL,体系检出限为0.12 μmol/L.     

Effect of particle size and dust layer size on ignition characteristics of PMMA dust layer on hot surface

Deposition of combustible dust on a hot surface is a hidden danger of fire. In this work, polymethylmethacrylate (PMMA) dust was selected to analyse the influence of dust layer diameter, dust particle size and dust layer thickness on the ignition characteristics of PMMA dust layer. Critical heating temperatures and ignition time had been measured. The STA-GC/MS-FTIR analysis was used to determine that the main products of PMMA pyrolysis were MMA, CO, CO₂, and C₂H₄, of which CO and C₂H₄ were transported to the ambient to cause gas phase combustion on the surface of the dust layer. For 10 mm thick dust layer, the critical heating temperatures of 5 μm PMMA, 100 nm PMMA, and 30 μm PMMA were 300 °C, 330 °C, and 320 °C. As the thickness of the dust layer increased, the gas transport path became longer, the critical heating temperature and ignition time increased. The characteristic particle size (D [3,2]) was utilized to represent the true particle size, and the ignition time increased with the increase of the characteristic particle size. The increase in the diameter of the dust layer had a slight effect on the temperature history and ignition time of the dust layer.     

铁岭市各类大气污染源浓度贡献分析

利用铁岭市2004年的PM10（可吸入颗粒物）和SO2（二氧化硫）大气环境监测资料、污染源排放清单资料和气象资料,以及AERMOD模型（1）进行了铁岭市大气环境质量区域评价。结果表明：铁岭市低架源对地面浓度的贡献较大,高架源对地面浓度的贡献相对较小。     

Effect of potential HONO sources on peroxyacetyl nitrate (PAN) formation in eastern China in winter

As an important secondary photochemical pollutant, peroxyacetyl nitrate (PAN) has been studied over decades, yet its simulations usually underestimate the corresponding observations, especially in polluted areas. Recent observations in north China found unusually high concentrations of PAN during wintertime heavy haze events, but the current model still cannot reproduce the observations, and researchers speculated that nitrous acid (HONO) played a key role in PAN formation. For the first time we systematically assessed the impact of potential HONO sources on PAN formation mechanisms in eastern China using the Weather Research and Forecasting/Chemistry (WRF-Chem) model in February of 2017. The results showed that the potential HONO sources significantly improved the PAN simulations, remarkably accelerated the RO_x (sum of hydroxyl, hydroperoxyl, and organic peroxy radicals) cycles, and resulted in 80%–150% enhancements of PAN near the ground in the coastal areas of eastern China and 10%–50% enhancements in the areas around 35–40°N within 3 km during a heavy haze period. The direct precursors of PAN were aldehyde and methylglyoxal, and the primary precursors of PAN were alkenes with C > 3, xylenes, propene and toluene. The above results suggest that the potential HONO sources should be considered in regional and global chemical transport models when conducting PAN studies.