Matter Transport Processes Research Articles

Quantitative verification of the turbulence barrier effect during heavy haze pollution events

Under calm and steady weather conditions with low wind speeds, turbulent intermittency frequently occurs in the atmospheric boundary layer (ABL), which can significantly weaken the turbulent diffusion of matter and energy between the surface and atmosphere. The turbulence barrier effect is defined as the phenomenon in which turbulence may disappear at certain heights, and during periods of heavy haze, creating what can seem like a barrier layer that hinders vertical transmissions. Although the turbulence barrier effect can explain the physical mechanisms behind the rapid accumulation of PM2.5 (fine particulate matter with diameters smaller than 2.5 μm) and the influence of turbulent diffusion conditions on the vertical distribution of PM2.5, more direct perspectives such as turbulent flux is still required for quantitative verification. Due of challenges in the acquisition of PM2.5 turbulent flux, carbon dioxide (CO2), which has relatively mature flux acquisition technology, was used as a substitute means of verifying and quantifying this phenomenon. The turbulence data collected during heavy haze events, at from five levels of a 255 m meteorological tower located in Tianjin, were analyzed and used to quantitatively verify the influence of the turbulent barrier effect on PM2.5. The results also revealed that the vertical changes in the turbulent barrier effect were consistent with those of the concentrations and flux of CO2. This means that this knowledge about the turbulent barrier effect can be extended to other mass-transfer processes. The analysis also found that the proportion of counter-gradient transport increases when the occurrences of the turbulent barrier effect are frequent. This work validates the presence of the turbulent barrier effect and is an important foundation for its future parameterization, which will help to accurately identify the matter transport processes in the stable boundary layer and under extreme weather conditions, such as intense pollution events.

In-situ multi-sensor characterization of soil cores along an erosion-deposition gradient

Soil landscape research is faced with wide-ranging questions of soil erosion, precision farming, and agricultural risk management. Digital Soil Morphometrics is a powerful tool to provide respective answers or recommendations but requires soil data from the pedon-to-field scale with high horizontal and vertical resolutions, including the subsoil. We present an efficient sampling and measurement method for easily obtainable soil driving cores with low-destructive preparation. Elemental contents and soil organic and mineral matter composition were measured rapidly and in large numbers using a multi-sensor approach, i.e., visible and near-infrared (Vis-NIR), diffuse reflectance infrared Fourier transform (DRIFT), and X-ray fluorescence (XRF) spectroscopy. The suitability of the approach with respect to three-dimensional soil landscape models was tested using soils along a slope representing different stages of erosion and deposition in a hummocky landscape under arable land use (Calcaric Regosols, Calcic Luvisols, Luvic Stagnosols, Gleyic-Colluvic Regosols). The combination of soil core sampling, pedological description, and three spectroscopic techniques enabled rapid determination and interpretation of horizontal and vertical spatial distributions of soil organic carbon (SOC), soil organic and mineral matter composition, as well as CaCO3, Fe, and Mn contents. Depth profiles for SOC, CaCO3, and Fe contents were suitable indicators for site-specific degrees of erosion and matter transport processes at the pedon-to-field scale. Fe and Mn profiles helped identifying zones of reductive and oxic domains in subsoils (gleyzation). Further methodical developments should implement plant-availability of nutrients, characterization of Fe-oxides, and calibration of the spectroscopic techniques to field-moist samples.

Ecology of Contaminant Biotransformation in the Mycosphere: Role of Transport Processes.

Fungi and bacteria often share common microhabitats. Their co-occurrence and coevolution give rise to manifold ecological interactions in the mycosphere, here defined as the microhabitats surrounding and affected by hyphae and mycelia. The extensive structure of mycelia provides ideal "logistic networks" for transport of bacteria and matter in structurally and chemically heterogeneous soil ecosystems. We describe the characteristics of the mycosphere as a unique and highly dynamic bacterial habitat and a hot spot for contaminant biotransformation. In particular, we emphasize the role of the mycosphere for (i) bacterial dispersal and colonization of subsurface interfaces and new habitats, (ii) matter transport processes and contaminant bioaccessibility, and (iii) the functional stability of microbial ecosystems when exposed to environmental fluctuations such as stress or disturbances. Adopting concepts from ecological theory, the chapter disentangles bacterial-fungal impacts on contaminant biotransformation in a systemic approach that interlinks empirical data from microbial ecosystems with simulation data from computational models. This approach provides generic information on key factors, processes, and ecological principles that drive microbial contaminant biotransformation in soil. We highlight that the transport processes create favorable habitat conditions for efficient bacterial contaminant degradation in the mycosphere. In-depth observation, understanding, and prediction of the role of mycosphere transport processes will support the use of bacterial-fungal interactions in nature-based solutions for contaminant biotransformation in natural and man-made ecosystems, respectively.

Mathematical modeling of wave processes and transport of bottom materials in coastal water areas taking into account coastal structures

The necessity of numerical modeling of the mechanisms of formation of the field of suspension and sediment flow determines the urgency of the problem under study. The process of developing shallow coastal zones, with constructive transformation and changes in coastal reliefs, is becoming increasingly important. Assessment of the hydrodynamic impact on shore protection structures and coastal structures installed at the bottom of a shallow water body is an important task at present. With a constructive transformation of the reliefs, one should take into account the dynamics of the formation of the coast investigate the formation of the profile of the bottom in the coastal zone of the reservoir under the influence of wave processes. For determining the dynamics and trend of phenomena occurring in the coastal waters and predicting possible interventions in the ecosystem, the need to build mathematical models of the transport processes of matter in the coastal waters, taking into account the presence of coastal structures, is actualized.

A Review of Dissolved Organic Matter Transport Processes Affecting Soil and Environmental Quality

Dissolved organic matter (DOM) affects several processes in soil and water including nutrient cycling, soil and water pollution and CO2 flux between the soil and atmosphere. The aim of this review is to collate and synthesize the literature on the transport processes of DOM in soil. The DOM normally comprises of only a small fraction of soil organic matter (SOM) and originates mainly from the decomposition and solubilization of SOM, which is accumulated on soil surface or soil profile from plant residues and additions of organic amendments such as animal and poultry manures and other biosolids. The DOM is one of the most reactive and mobile SOM fractions and has a major influence on biogeochemical processes in both terrestrial and aquatic environments. Terrestrially borne DOM is subjected to microbial decomposition, photodegradation and adsorption on soil mineral surfaces. It is sorbed on mineral surfaces and high adsorption capacities of clay minerals and oxides for DOM sorption are demonstrated in laboratory studies. However, these high sorption values are not reproduced in limited field studies. Similarly, a few data available on the transport of DOM through macropores also demonstrate the limited control of sorption on DOM retention in soil profile. Thus, there is a need to further investigate the physical and chemical protection mechanisms, as well as the biodegradability of DOM shown in laboratory studies. There is an increasing need to clearly understand the formation, fate and transport of DOM at field scales. The environmental factors such as precipitation and temperature, land use change, land management, and biological factors have profound and discrete influences on DOM dynamics in soil profile. Future research efforts must focus on the assessment of the influences of these factors by conducting field studies in different climatic zones, soils, and land use and management systems.

Trans-Interfacial Polymerization and Matter Transport Processes in Epoxy-Alumina Nanocomposites Visualized By Scanning Brillouin Microscopy

The structural developments in the vicinity of the interface between the reactants of an epoxy are investigated using time- and space-resolved scanning Brillouin microscopy. The hypersonic profile across the phase boundary evolves with strong spatial asymmetry and exhibits erratic behavior within the resin-rich region, which is attributed to a complex interplay between matter transport, dissolution, polymerization, and molecular unravelling process. The presence of alumina nanoparticles in the resin changes the character of these matter transport and reaction processes significantly. On the one hand, the nanoparticles act as transport barriers, hindering the mixing of the reactive components; on the other hand they seem to have a catalytic influence on the epoxy polymerization under certain circumstances. Their transport against gravity is tentatively attributed to gradients in surface tension.

Influences of seasonal flow regime on the fate and transport of fine particles and a dissolved solute in a New England stream

Fine particles are necessary for biogeochemical cycling but pose a risk to water quality if they are present in excess or carry sorbed contaminants. The objective of this work is to elucidate the effects of flow on the transport and retention of fine particles within a mountain stream and to compare particulate matter transport processes to those of a conservative solute tracer. We measured the migration of bromide (a conservative solute tracer) and micrometer‐sized titanium‐dioxide particles under three seasonal flow regimes in second‐order stream in Connecticut. A one‐dimensional transport model based upon the transient storage model was applied in inverse mode to the measured data to quantify solute and particle transport processes. Rates of particle movement by advection and longitudinal dispersion matched those of bromide. Transient, or temporary, storage influenced conservative solute transport, while particle storage was irreversible on the time scale of our experiments and likely dominated by deposition within the sediments of the hyporheic zone. Both solute transient storage and particle deposition increased with decreasing discharge.

A methodology for improving laser beam induced current images of dye sensitized solar cells

Using the laser beam induced current (LBIC) technique for the study of solar cells and photovoltaic devices, it is possible to obtain images representing the different degrees of quantum efficiency observed on the surface of these elements. Dye sensitized solar cells (DSSCs) or photoelectrochemical solar cells, in contrast to those based on solid-solid interfaces, show a slow response to irradiance variations--up to tens of seconds. This is basically due to both viscous matter transport processes and load transfer. This response is inappreciable when the device is functioning continuously but when a LBIC scan is performed, in which the laser moves quickly from one point to another, the slow response produces a memory effect and the signal generated at one given point depends on the conversion efficiency coefficients of the previously excited positions, resulting in diffuse images and a lack of sharpness. This work presents a methodology to correct high-resolution LBIC mappings of DSSCs using an algorithm based on the kinetics of the discharge process of the irradiated zone. The validity of the proposed method has been evaluated by carrying out experiments where the algorithm has been applied to LBIC mappings.

Optimisation of relief classification for different levels of generalisation

Relief plays an important role in the spatial and temporal distribution of soil water and matter transport processes. Each landscape can be segmented into different landform elements based on a digital elevation model. These landforms contain characteristic properties in terms of energy and material balance. Several algorithms are available to classify landscapes at different scales. However, lack of knowledge exists concerning the applicability of relief parameters for landscape stratification for different generalisation levels of underlying data. The objective of this study was to develop a method for agricultural landscapes to classify landform elements across a series of elevation datasets with different spatial resolutions. A non-linear parameter optimisation algorithm was coupled with a relief classification scheme to optimize four classification parameters with regard to environmentally sensitive landforms: shoulder and footslope. Input datasets were based on a LIDAR scan and topographic maps. The magnitude of the optimized relief parameters decreased with decreasing map scale from 1 : 10,000 to 1 : 100,000 or increasing contour line interval. The main conclusion is that if one set of classification rules for a specific landscape was determined for a high-resolution dataset at a small subset, it could be applied for larger areas even if only coarser digital elevation model information were available.

Seasonal variation of floc characteristics on tidal flats, the Scheldt estuary

The flocculation mechanism dominates the fate of suspended matter in the estuarine environment. By modifying the texture of suspended matter, flocculation is one of the principle factors determining the transport and deposition of suspended matter in estuaries. Surveys of the seasonal variation of dispersed particle and non-dispersed particle characteristics, organic matter content as well as suspended matter deposition in two contrasting intertidal environments, one freshwater and one brackish water, in the Scheldt estuary were undertaken at fortnightly intervals for a year. The study of non-dispersed particle, i.e. floc, is mainly focused on floc size, shape, and microstructure, properties presumed to be significant in the suspended matter transport processes in the estuary. In this study, floc size as well as floc sphericity correlate positively with the change of organic matter content and reveal that floc grows in a three-dimensional way with increasing organic matter. It is observed that relatively condensed, small and elongated flocs appear in winter and spring periods, while loose, large and spherical flocs occur during the summer. The study also reveals that suspended matter transported as dense flocs with size range of ca. 105–250 μm have a greater effect on its short-term deposition than loose flocs with size range of ca. 250–500 μm. As the measured suspended matter deposition is much higher in winter–spring than in summer, it is deduced here that highly compact and relatively dense flocs contribute to deposition during winter and spring periods resulting in a stable layer, while loosely formed flocs likely lead to an easier erodible layer during the summer. This study concludes that floc structure-related density is a more significant parameter than floc size in the suspended matter deposition processes.

Influence of Defect Interactions on Diffusion Processes in UO2+x: a Key Issue for Understanding the Behaviour of Spent Nuclear Fuel.

AbstractThe transformation of UO2 into U3O8 is of technological and academical interest because of the severe consequences on the spent nuclear fuel management. The structural mechanism responsible for the isothermal transformation of UO2 into U3O8 seems still unclear. Several phases (UO2+x, U4O9, β-U3O7, α-U3O7, U3O8 were reported but their true structures, phase boundaries between their existence domains and matter transport processes are still a matter of debate. Gathering accurate information on the behaviour of uranium oxide is a key issue for understanding the behaviour of spent nuclear fuel. The chemical diffusion coefficient ( ~ D) of UO2+x was determined by electrical conductivity experiments. Measurements were performed in transient state for departure from stoichiometry in the range 0<x<0.17 (10-11<P(O2)<10-8 atm.)and for 973<T<1673 K. We have found that ~ D is a decreasing function of the departure from stoichiometry x. This behaviour was attributed to the presence of singly charged (2:2:2) Willis defects as suggested by equilibrium conductivity measurements. The decrease of Dchim can be explained by transport processes occurring via a dynamic exchange between isolated mobile defects and complex defects frozen in clusters or domains. At higher P(O2), near U4O9, the time to reach an equilibrium electrical conductivity value becomes increasingly long. This suggests the presence either of large defect aggregates or of complex defects arranged into domains. Furthermore, the analysis of the transport processes in non equilibrium conditions has allowed us to show that the results of ~ D are consistent with those of the oxygen diffusion coefficient within the P(O2) and temperature range of stability of the [2:2:2] clusters.

Ageing of Solid Oxide Fuel Cells Based on Zirconia or Other Oxide Electrolytes

This work concerns the ageing of solid oxide fuel cells in operative conditions due to matter transport processes, which occur in the electrolyte and oxide electrode material cationic sublattice. The surface stability and kinetic demixing processes in presence of chemical potential gradients through the materials are reviewed. Available experimental results concerning yttria-doped zirconia and iono-covalent oxides are reported. These results are discussed in relation with the microstructure and composition changes near the electrolyte-electrode material interfaces.

Matter transport in meso-scale oceanic fronts of river discharge type

A hybrid model based on the Monte-Carlo method and turbulence model with a third-order closure is developed to forecast transport processes of matter in coastal oceanic fronts of river discharge type. A deterministic part of a particle displacement is modeled with non-linear system of thermodynamic equations. Variations in processes of cooling and heating as well as wind changes are considered as main reasons to govern conditions of the matter transport during a short period of simulation. Distinct diurnal variations of a planar temperature distribution observed by NOAA satellite in the Rhine discharge region are discussed with respect to potentialities of the proposed approach.

Ageing of solid electrolytes and electrode materials in electrochemical devices

The ageing behavior reported in this work concerns the consequences of the matter transport processes on the cationic sublattice which occur in solid electrolytes, mixed ionic conducting compounds and semiconducting oxides subjected to a chemical potential gradient, an applied electrical field or a mechanical stress gradient. The principle of the kinetic demixing under a “generalized” thermodynamic potential gradient is reviewed. Available experimental results concerning yttria-doped zirconia and iono-covalent oxides are reported. The results are discussed in relation with the microstructure and composition evolution of the surfaces and the electrode resistance.

Modeling of Natural Organic Matter Transport Processes in Groundwater

Modeling of Natural Organic Matter Transport Processes in Groundwater

Modeling of natural organic matter transport processes in groundwater.

A forced-gradient tracer test was conducted at the Georgetown site to study the transport of natural organic matter (NOM) in groundwater. In particular, the goal of this experiment was to investigate the interactions between NOM and the aquifer matrix. A detailed three-dimensional characterization of the hydrologic conductivity heterogeneity of the site was obtained using slug tests. The transport of a conservative tracer (chloride) was successfully reproduced using these conductivity data. Despite the good simulation of the flow field, NOM breakthrough curves could not be reproduced using a two-site sorption model with spatially constant parameters. Preliminary results suggest that different mechanisms for the adsorption/desorption processes, as well as their spatial variability, may significantly affect the transport and fate of NOM.

Définition des régimes hydrodynamiques rencontrés au cours de la cristallisation par transport en phase gazeuse

Simulation experiments and observations of traces of sulfur deposits carried out under varying argon pressures allowed us to detect the experimental conditions associated with various matter transport processes: diffusion, convection and mixing of both. In a second part, these experimental data lead under some particular conditions to the evaluation with a reasonable approximation of the transport speed of sulfur or zinc in an inert atmosphere. The thermodynamical conditions are close to those of a CVD process.

Transverse diffusion and heat conduction in a granular layer

The process of non-steady-state transverse diffusion of a passive additive in a granular layer described by a cellular model is investigated. The general results obtained in [1] are applied to an analysis of concrete transport processes of matter and heat in a granular layer. The following four cell models are treated: (1) ideal mixing cells without stagnation zones; (2) ideal mixing cells with stagnation zones; (3) ideal mixing cells with diffusive stagnation zones; (4) ideal mixing cells with diffusive stagnation zones having a finite exchange rate between the free volume and the stagnation zone. The conditions of applicability for each of the above models are found. The time to establish a normal distribution in the transverse diffusion process is determined for all the models. This quantity is then connected with the physical characteristics of transport processes of matter in a layer of nonporous and porous particles, the transport of heat in a granular layer, and the transport of matter in a layer of particles which adsorb an additive.