Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

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Leveraging social networks for agricultural development in Africa
Ross, Martha - \ 2017
University. Promotor(en): Erwin Bulte, co-promotor(en): Maarten Voors. - Wageningen : Wageningen University - ISBN 9789463431910 - 174
social networks - agricultural development - economic development - agricultural production - networks - technology transfer - innovations - innovation adoption - diffusion - interpersonal relations - communication - observation - social learning - social interaction - sociale netwerken - landbouwontwikkeling - economische ontwikkeling - landbouwproductie - netwerken - technologieoverdracht - innovaties - innovatie adoptie - diffusie - intermenselijke relaties - communicatie - observatie - sociaal leren - sociale interactie

This thesis contributes to a growing literature that explores relationships between social networks and innovation diffusion within a developing country context. Given this context, the networks of interest within this thesis are the offline interpersonal relationships between community members. Diffusion channels for new innovation are therefore limited to word-of-mouth communication, observation, and personal experience.

Chapter 2 of this thesis analyses two policy tools in targeting these information gaps. The first is through social learning as part of a farmer extension program. The second combines social learning with experiential learning, reducing the cost to personal experimentation with subsidized improved input packages. Our results indicate that farmers who are exposed to both social learning and learning-by-doing more significantly impacts farmer productivity relative to those receiving no intervention and those exposed only to social learning. I interpret this result as an indication of learning-by-doing combined with social learning being a more effective strategy for facilitating adoption of technologies that have more heterogeneous returns to adoption.

Chapter 3 of this thesis tests the difference in diffusion patterns that result by varying the network contact- point. Specifically, network contact-points are selected as being either the most central or least central individuals within the network. I find evidence that centrality affects the speed of distribution but does not affect the width of diffusion nor which individuals are participating within the diffusion process. Furthermore, large attenuation is observed throughout the diffusion process, which suggests the importance of selecting a sufficiently large set of lead community members for the spread of new technology.

Chapter 4 combines a community-wide polling of network entry-points combined with detailed community network and socio-economic data. First we explore what attributes are prioritized by community members in nominating a resident farmer as an extension contact-point. Second, we use simulations to compare the diffusion spread of top-nominated individuals as network entry-points compared to entry-points that achieve maximal spread within diffusion simulations. We find that community members prioritize network connectedness, pro-social preferences, and socioeconomic indicators of gender, age, formal leadership, and education levels within their nomination decisions. Furthermore, receiving the top three most amount of nominations is found to be significantly correlated with selection as an optimal entry-point within the diffusion simulation. These results suggest that community-wide polling offers a less data-intensive opportunity to realize gains in diffusion warranted through network-based seeding.

Chapter 5 explore whether an individual’s observed social preferences is correlated with an individual’s centrality within the network structure. Our results indicate that individuals with high centrality are more trusting and more trustworthy than individuals with lower centrality. Moreover, individuals with low centrality are treated worse in these interactions—people trust them less initially, and return less money to them. Within a group context, little evidence is found of more central individuals displaying more cooperative behavior. Instead, for group cooperation, when a single monitor can observe contribution decisions, the presence of a direct link and more mutual network connections with a monitor correlates to more cooperative behavior by that individual. Our results suggest that network centrality and pro-social preferences are related but more localized network ties are more strongly correlated with pro-sociality than overall network connectedness.

Nanoparticle diffusometry in hydrogels
Kort, D.W. de - \ 2016
University. Promotor(en): John van Duynhoven, co-promotor(en): Henk van As. - Wageningen University - ISBN 9789462577459 - 178 p.
nanotechnology - particles - gels - diffusion - nuclear magnetic resonance spectroscopy - rheology - nanotechnologie - deeltjes - diffusie - kernmagnetische resonantiespectroscopie - reologie

In order to understand food product functionality such as elastic and flow behavior and mass transport properties, one first has to understand the multi-length-scale structure of the material. The aim of this work is to explore novel methodologies to study and characterize multi-length-scale structures of food hydrogels under static and dynamic conditions. The focus lies on hydrogels comprising polysaccharides, because they show a rich variation in elastic and flow behavior.

The largest part of the thesis focuses on the use of nanoparticles (3–30 nm diameter) that are dissolved into the water phase of hydrogels, and whose mobility is reduced due to the presence of the polymer network. This retardation of nanoparticle self-diffusion in hydrogels relative to self-diffusion in neat water can be used to infer structural information about the microstructure of the polymer network.

In chapter 2, an in-depth review of existing literature on this method, known as “nanoparticle diffusometry”, is provided, with an emphasis on physical models of self-diffusion in polymer gels and applications in food gels. In that chapter, we distinguish between (1) nanoparticle diffusion in (heterogeneous) polymer gels and (2) nanoparticle diffusion in solutions of (semi)flexible polymers. We adhere to this categorization throughout the rest of the thesis.

In chapters 3 and 4 we first describe the design and manufacturing of tailor-made nanoparticles that are functionalized with spectroscopic labels, and the implementation of pulsed-field gradient (PFG) NMR and optical spectroscopy toolboxes for nanoparticle diffusometry. We then use these toolboxes to measure nanoparticle self-diffusion in heterogeneous κ-carrageenan (a polysaccharide) gels. These experiments reveal bimodal nanoparticle self-diffusion (i.e., there are two nanoparticle fractions with different diffusion coefficients) as previously observed in these gels by Lorén et al. The results suggest that the sub-micron structure of these gels is heterogeneous with a wide distribution of pore sizes at the sub-micron scale, leading to “sieving” of nanoparticles resulting in the observation of bimodal self-diffusion.

This hypothesis is further explored in chapter 5, where besides PFG NMR and optical spectroscopy, Overhauser dynamic nuclear polarization (ODNP)-enhanced NMR spectroscopy is employed. This method can determine the local viscosity of water surrounding the two fractions of particles. It turns out that the particle fraction with the lower apparent diffusion coefficient is in fact trapped in small, nanoscopic interstitials within the gel. The ODNP NMR experiments show that the viscosity of water surrounding the trapped particles is significantly lower than the viscosity within the larger interstitials.

Chapter 6 describes a study of nanoparticle diffusion in solutions of poly(ethylene glycol), a flexible polymer with well defined compositions and chain lengths. We use scaling laws to understand the relation between macroviscosity and “microviscosity” as apparent from the nanoparticle diffusivity. We show that the particles probe (near-)macroviscosity only if their size is larger than the size of the PEG polymer coils.

Another topic of this thesis is a study of the behavior of food hydrogels under dynamic conditions. To this end we use rheo-MRI velocimetry, which allows us to study the complex shear flow behavior of hydrogels that (per definition) have a yield stress. In chapter 7, we first employ nanoparticle diffusometry to study the sub-micron structure of dispersions of rigid cellulose microfibrils in the presence of carboxymethyl cellulose. Carboxymethyl cellulose is a charged cellulose derivative that succeeds to disperse the aggregation-prone cellulose microfibrils homogeneously at the sub-micron scale. Rheological characterization shows that the resulting dispersions are thixotropic yield-stress fluids. The flow properties of such fluids are well understood, but rheo-MRI experiments show that shear flow of apparently homogeneous cellulose dispersions does not resemble the flow behavior of typical thixotropic yield-stress fluids. We explain the differences by using a fluidity model to show that persistent micron-scale heterogeneity still dominates the flow behavior.

Cooperativity and segregation in confined flows of soft binary glasses
Laar, T. van de; Schroën, C.G.P.H. ; Sprakel, J.H.B. - \ 2015
Physical Review. E, Statistical nonlinear, and soft matter physics 92 (2015)2. - ISSN 2470-0045 - 8 p.
concentrated suspensions - particle migration - hard - microfiltration - fractionation - transition - diffusion
When a suspension containing particles of different sizes flows through a confined geometry a size gradient can be established, with large particles accumulating in the channel center. Such size separation driven by hydrodynamic interactions is expected to facilitate membrane filtration and may lead to the design of novel and innovative separation techniques. For this, a wide range of particle concentrations has to be investigated, in order to clarify whether shear-induced migration can be utilized at concentrations close to or above the colloidal glass transition, where particle motion is severely hindered and hydrodynamic interactions are screened. We explore this scenario by studying the flow of binary mixtures of soft colloidal microgels, well above their liquid-solid transition, through narrow microchannels. We find that, even though the flow becomes strongly heterogeneous, in both space and time, characterized by a large cooperativity length, size segregation still occurs. This suggests that even above the glass transition shear-induced diffusion could still be used as a fractionation mechanism, which is of great relevance for process intensification purposes.
The development of direct extrusion-injected moulded zein matrices as novel oral controlled drug delivery systems
Bouman, J. ; Belton, P. ; Venema, P. ; Linden, E. van der; Vries, R.J. de; Qi, Sheng - \ 2015
Pharmaceutical Research 32 (2015)8. - ISSN 0724-8741 - p. 2775 - 2786.
solid-state - diffusion - protein - acetaminophen - paracetamol - release - history - ftir
Purpose To evaluate the potential of zein as a sole excipient for controlled release formulations prepared by hot melt extrusion. Methods Physical mixtures of zein, water and crystalline paracetamol were hot melt extruded (HME) at 80 degrees C and injection moulded (IM) into caplet forms. HME-IM Caplets were characterised using differential scanning calorimetry, ATR-FTIR spectroscopy, scanning electron microscopy and powder X-ray diffraction. Hydration and drug release kinetics of the caplets were investigated and fitted to a diffusion model. Results For the formulations with lower drug loadings, the drug was found to be in the non-crystalline state, while for the ones with higher drug loadings paracetamol is mostly crystalline. Release was found to be largely independent of drug loading but strongly dependent upon device dimensions, and predominately governed by a Fickian diffusion mechanism, while the hydration kinetics shows the features of Case II diffusion. Conclusions In this study a prototype controlled release caplet formulation using zein as the sole excipient was successfully prepared using direct HME-IM processing. The results demonstrated the unique advantage of the hot melt extruded zein formulations on the tuneability of drug release rate by alternating the device dimensions.
Comparison of structured adsorbents for the adsorptive isolation of food ingredients from large streams
Rodriguez Illera, M. ; Boon, M.A. ; Boom, R.M. ; Janssen, A.E.M. - \ 2015
Chemical Engineering Research & Design 98 (2015). - ISSN 0263-8762 - p. 240 - 251.
stationary phases - moment equations - monolithic adsorbents - liquid-chromatography - aspect ratio - performance - separation - media - diffusion - dynamics
We present guidelines for the configuration of industrial scale chromatographic separation of small molecules. We compared the performance of different axial packed beds, channeled monoliths and a continuous monolith assuming silica as base material. The calculated mass transfer rates were used to calculate the height of a theoretical plate (HETP). The HETP and pressure drop relations as a function of velocity were used to calculate the resultant velocity and packing length for different conditions (efficiency, pressure drop, affinity constant and throughput). The specific productivity of channeled monoliths can be up to 2.5 orders of magnitude higher than that of a packed bed. This implies that at large scales (in which the pressure drops need to be limited, and the flow rate is high), channeled monoliths are preferred since they may reduce the equipment size up to 100 times and the required resin volume up to 1000 times. Accordingly, we demonstrate the potential of channeled monoliths in chromatographic processes but also draw a window pointing out the feasible configurations to use with the highest productivity for a given set of process requirements.
Environmental potentials of policy instruments to mitigate nutrient emissions in Chinese livestock production
Zheng, C. ; Liu, Y. ; Bluemling, B. ; Mol, A.P.J. ; Chen, J. - \ 2015
Science of the Total Environment 502 (2015). - ISSN 0048-9697 - p. 149 - 156.
spatial models - phosphorus - innovation - implementation - modernization - agriculture - simulation - diffusion
To minimize negative environmental impact of livestock production, policy-makers face a challenge to design and implement more effective policy instruments for livestock farmers at different scales. This research builds an assessment framework on the basis of an agent-based model, named ANEM, to explore nutrient mitigation potentials of five policy instruments, using pig production in Zhongjiang county, southwest China, as the empirical filling. The effects of different policy scenarios are simulated and compared using four indicators and differentiating between small, medium and large scale pig farms. Technology standards, biogas subsidies and information provisioning prove to be the most effective policies, while pollution fees and manure markets fail to environmentally improve manure management in pig livestock farming. Medium-scale farms are the more relevant scale category for a more environmentally sound development of Chinese livestock production. A number of policy recommendations are formulated as conclusion, as well as some limitations and prospects of the simulations are discussed.
Mechanistic modelling of toxicokinetic processess within Mytiophyllum
Heine, S. ; Schmitt, W. ; Schaffer, A. ; Gorlitz, G. ; Buresova, H. ; Arts, G. ; Preuss, T.G. - \ 2015
Chemosphere 120 (2015). - ISSN 0045-6535 - p. 292 - 298.
partition-coefficients - cuticular membranes - risk-assessment - aquatic macrophytes - water permeability - plant cuticles - sensitivity - diffusion - chemicals - linuron
Effects of chemicals are, in most cases, caused by internal concentrations within organisms which rely on uptake and elimination kinetics. These processes might be key components for assessing the effects of time-variable exposure of chemicals which regularly occur in aquatic systems. However, the knowledge of toxicokinetic patterns caused by time-variable exposure is limited, and gaining such information is complex. In this work, a previously developed mechanistic growth model of Myriophyllum spicatum is coupled with a newly developed toxicokinetic part, providing a model that is able to predict uptake and elimination of chemicals, as well as distribution processes between plant compartments (leaves, stems, roots) of M. spicatum. It is shown, that toxicokinetic patterns, at least for most of the investigated chemicals, can be calculated in agreement with experimental observations, by only calibrating two chemical- specific parameters, the cuticular permeability and a plant/water partition coefficient. Through the model-based determination of the cuticular permeabilities of Isoproturon, Iofensulfuron, Fluridone, Imazamox and Penoxsulam, their toxicokinetic pattern can be described with the model approach. For the use of the model for predicting toxicokinetics of other chemicals, where experimental data is not available, equations are presented that are based on the log (Poct/wat) of a chemical and estimate parameters that are necessary to run the model. In general, a method is presented to analyze time-variable exposure of chemicals more in detail without conducting time and labour intensive experiments.
Methane, Carbon Dioxide and Nitrous Oxide Fluxes in Soil Profile under a Winter Wheat-Summer Maize Rotation in the North China Plain
Wang, Y.Y. ; Hu, C.S. ; Ming, H. ; Oenema, O. ; Schaefer, D.A. ; Dong, W.X. ; Zhang, Y.M. ; Li, X.X. - \ 2014
PLoS One 9 (2014)6. - ISSN 1932-6203
forest soils - co2 efflux - gas emissions - n2o fluxes - ch4 - respiration - temperature - mitigation - diffusion - slurry
The production and consumption of the greenhouse gases (GHGs) methane (CH4), carbon dioxide (CO2) and nitrous oxide (N2O) in soil profile are poorly understood. This work sought to quantify the GHG production and consumption at seven depths (0-30, 30-60, 60-90, 90-150, 150-200, 200-250 and 250-300 cm) in a long-term field experiment with a winter wheat-summer maize rotation system, and four N application rates (0; 200; 400 and 600 kg N ha(-1) year(-1)) in the North China Plain. The gas samples were taken twice a week and analyzed by gas chromatography. GHG production and consumption in soil layers were inferred using Fick's law. Results showed nitrogen application significantly increased N2O fluxes in soil down to 90 cm but did not affect CH4 and CO2 fluxes. Soil moisture played an important role in soil profile GHG fluxes; both CH4 consumption and CO2 fluxes in and from soil tended to decrease with increasing soil water filled pore space (WFPS). The top 0-60 cm of soil was a sink of atmospheric CH4, and a source of both CO2 and N2O, more than 90% of the annual cumulative GHG fluxes originated at depths shallower than 90 cm; the subsoil (>90 cm) was not a major source or sink of GHG, rather it acted as a 'reservoir'. This study provides quantitative evidence for the production and consumption of CH4, CO2 and N2O in the soil profile.
Membrane resistance: The effect of salinity gradients over a cation exchange membrane
Galama, A.H. ; Vermaas, D.A. ; Veerman, J. ; Saakes, M. ; Rijnaarts, H. ; Post, J.W. ; Nijmeijer, K. - \ 2014
Journal of Membrane Science 467 (2014). - ISSN 0376-7388 - p. 279 - 291.
electroosmotic water transport - charged membranes - resin membranes - porous membranes - kinetic-theory - power-density - ion transfer - electrodialysis - diffusion - systems
Ion exchange membranes (IEMs) are used for selective transport of ions between two solutions. These solutions are often different in concentration or composition. The membrane resistance (R-M) is an important parameter affecting power consumption or power production in electrodialytic processes. In contrast to real applications, often R-M is determined while using a standard 0.5 M NaCI external solution. It is known that R-M increases with decreasing concentration. However, the detailed effect of a salinity gradient present over an IEM on R-M was not known, and is studied here using alternating and direct current. NaCl solution concentrations varied from 0.01 to 1.1 M. The results show that R-M is mainly determined by the lowest external concentration. R-M can be considered as two resistors in series i.e. a gel phase (concentration independent) and an ionic solution phase (concentration dependent). The membrane conductivity is limited by the conductivity of the ionic solution when the external concentration, c(ext)<0.3 M. The membrane conductivity is limited by the conductivity of the gel phase when c(ext)> 0.3 M, then differences of R-M are small. A good approximation of experimentally determined R-M can be obtained. The internal ion concentration profile is a key factor in modeling Rm. (C) 2014 Elsevier B.V. All rights reserved.
Fractioning electrodialysis: a current induced ion exchange process
Galama, A.H. ; Daubaras, G. ; Burheim, O.S. ; Rijnaarts, H. ; Post, J.W. - \ 2014
Electrochimica Acta 136 (2014). - ISSN 0013-4686 - p. 257 - 265.
divalent ions - seawater desalination - membrane - monovalent - diffusion - transport - charge - nanofiltration - permeability - polarization
In desalination often multi ionic compositions are encountered. A preferential removal of multivalent ions over monovalent ions can be of interest to prevent scaling in the desalination process. Recently, a novel fractionating electrodialysis stack is described by Zhang et al., 2012 (in Sep. purify. Technol. 88). In the present work a small modification to such a stack was made, to create a current induced ion exchange process, in which no longer desalination occurs. This was done by building a membrane stack in which monovalent-selective ion-exchange membranes and standard grade ion-exchange membranes, with similar charge sign (so either anion or cation exchange groups), were placed alternatingly between an anode and a cathode to form a membrane stack. A proof of principle of the fractioning electrodialysis technology is given. Ternary mixtures, with a divalent-monovalent ion ratio similar to seawater, were used as feed water. For a cation and an anion fractioning stack, maximum fractionations of divalent ions were obtained of approximately 90 and 60%. At higher applied current density, ions can be fractionated to a larger extent than at lower applied current density. For both stacks the water recovery was 50%. Coulombic efficiency of both processes decrease rapidly after the start of the experiment. This leads to relatively large volumetric energy consumptions. (C) 2014 Elsevier Ltd. All rights reserved.
Movement behaviour of the carabid beetle Pterostichus melanarius in crops and at a habitat interface explains patterns of population redistribution in the field
Allema, A.B. - \ 2014
habitat interface - population spread - movement - scaling-up - diffusion
Nanoprecipitation of polymers in a bad solvent
Lebouille, J.G.J.L. ; Stepanyan, R. ; Slot, J.J.M. ; Cohen Stuart, M.A. ; Tuinier, R. - \ 2014
Colloids and Surfaces. A: Physicochemical and Engineering Aspects 460 (2014). - ISSN 0927-7757 - p. 225 - 235.
limited coalescence - copolymer micelles - fractal nature - casein gels - nanoparticles - diffusion - kinetics - drug - delivery
Nanoparticles (NPs) composed of polymers are of great interest since they can add a functionality in many applications, ranging from food and pharma to plastics and electronics. A key factor that determines the functionality of NPs is their size. Nanoprecipitation [1] is a commonly used technique to prepare NPs. We have performed a combined experimental and theoretical study on the size of NPs formed by precipitation of polymers into a bad solvent in the presence of a stabilizing surfactant. We propose an extension of the theoretical framework put forward by Lannibois et al. [10] for nanoparticle formation via precipitation. Our theory is based upon a kinetic model for diffusion limited coalescence (DLC) in which the relevant transport and diffusion mechanisms are quantified. We find that the macroscopic mixing time and the diffusivity of the polymer and surfactant are the main parameters determining the final particle size. The theoretical result for the final size can be condensed into a single analytical expression. At given polymer concentration and mixing time, it follows that the smallest particles can be obtained in the excess of surfactant. This situation corresponds well to the experimentally used conditions. The mixing efficiency is predicted to have a profound influence on the final particle diameter: faster mixing results in smaller particles. The final particle size in the slow mixing regime, which is the typical situation in experiments, turns out to be independent of the molar mass of the polymer and scales as a power 1/3 with the initial polymer concentration. An increase of the surfactant molar mass is predicted to lead to larger particles, because of longer mixing time and lower surfactant mobility. We have performed systematic experimental investigations on nanoparticles formation using various systems but focused on polycaprolactone (PCL) polymers in acetone precipitated in aqueous solutions containing polyvinyl alcohol as surfactant. The PCL molar mass and concentration and mixing time were varied. We show that both our experimental results as well as literature data are in good agreement with our theoretical DLC predictions. This work therefore provides a solid framework for tailoring nanoparticles with a desired size.
NMR Nanoparticle Diffusometry in Hydrogels: Enhancing Sensitivity and Selectivity
Kort, D.W. de; Duynhoven, J.P.M. van; Hoeben, F.J.M. ; Janssen, H.M. ; As, H. van - \ 2014
Analytical Chemistry 86 (2014). - ISSN 0003-2700 - p. 9229 - 9235.
fluorescence recovery - laplace inversion - polymer-solutions - field gradient - diffusion - resolution - mobility - gels - spectroscopy - kinetics
From the diffusional behavior of nanoparticles in heterogeneous hydrogels, quantitative information about submicron structural features of the polymer matrix can be derived. Pulsed-gradient spin-echo NMR is often the method of choice because it measures diffusion of the whole ensemble of nanoparticles. However, in 1H diffusion-ordered spectroscopy (DOSY), low-intensity nanoparticle signals have to be separated from a highly protonated background. To circumvent this, we prepared 19F labeled, PEGylated, water-soluble dendritic nanoparticles with a 19F loading of ~7 wt % to enable background free 19F DOSY experiments. 19F nanoparticle diffusometry was benchmarked against 1H diffusion-T2 correlation spectroscopy (DRCOSY), which has a stronger signal separation potential than the commonly used 1H DOSY experiment. We used bootstrap data resampling to estimate confidence intervals and stabilize 2D-Laplace inversion of DRCOSY data with high noise levels and artifacts, allowing quantitative diffusometry even at low magnetic field strengths (30 MHz). The employed methods offer significant advantages in terms of sensitivity and selectivity.
Transport and degradation of propylene glycol in the vadose zone: model development and sensitivity analysis
Schotanus, D. ; Meeussen, J.C.L. ; Lissner, H. ; Ploeg, M.J. van der; Wehrer, M. ; Totsche, K.U. ; Zee, S.E.A.T.M. van der - \ 2014
Environmental Science and Pollution Research 21 (2014)15. - ISSN 0944-1344 - p. 9054 - 9066.
in-situ bioremediation - soil respiration - biodegradation - groundwater - diffusion - water - denitrification - contaminants - simulation - aggregate
Transport and degradation of de-icing chemical (containing propylene glycol, PG) in the vadose zone were studied with a lysimeter experiment and a model, in which transient water flow, kinetic degradation of PG and soil chemistry were combined. The lysimeter experiment indicated that aerobic as well as anaerobic degradation occurs in the vadose zone. Therefore, the model included both types of degradation, which was made possible by assuming advection-controlled (mobile) and diffusion-controlled (immobile) zones. In the mobile zone, oxygen can be transported by diffusion in the gas phase. The immobile zone is always water-saturated, and oxygen only diffuses slowly in the water phase. Therefore, the model is designed in a way that the redox potential can decrease when PG is degraded, and thus, anaerobic degradation can occur. In our model, manganese oxide (MnO2, which is present in the soil) and NO 3 - - 3 (applied to enhance biodegradation) can be used as electron acceptors for anaerobic degradation. The application of NO 3 - - 3 does not result in a lower leaching of PG nor in a slower depletion of MnO2. The thickness of the snowcover influences the leached fraction of PG, as with a high infiltration rate, transport is fast, there is less time for degradation and thus more PG will leach. The model showed that, in this soil, the effect of the water flow dominates over the effect of the degradation parameters on the leaching at a 1-m depth.
The influence of spatiotemporal variability and adaptations to hypoxia on empirical relationships between soil acidity and vegetation
Cirkel, D.G. ; Witte, J.P.M. ; Bodegom, P.M. van; Nijp, J.J. ; Zee, S.E.A.T.M. van der - \ 2014
Ecohydrology 7 (2014)1. - ISSN 1936-0584 - p. 21 - 32.
bodemchemie - bodemaciditeit - vegetatietypen - bodem-plant relaties - soortensamenstelling - plantenfysiologie - rizosfeer - wetlands - heterogeniteit - ecohydrologie - ruimtelijke variatie - soil chemistry - soil acidity - vegetation types - soil plant relationships - species composition - plant physiology - rhizosphere - heterogeneity - ecohydrology - spatial variation - ellenberg indicator values - field-measurements - plant ecology - ph changes - iron - regression - diversity - diffusion - oxidation
Soil acidity is well known to affect the species composition of natural vegetation. The physiological adaptations of plants to soil acidity and related toxicity effects and nutrient deficiencies are, however, complex, manifold and hard to measure. Therefore, generally applicable quantifications of mechanistic plant responses to soil acidity are still not available. An alternative is the semi-quantitative and integrated response variable ‘indicator value for soil acidity’ (Rm). Although relationships between measured soil pH and Rm from various studies are usually strong, they often show systematic bias and still contain high residual variances. On the basis of a well-documented national dataset consisting of 91 vegetation plots and a dataset with detailed, within-plot, pH measurements taken at three periods during the growing season, it is shown that strong spatiotemporal variation of soil pH can be a critical source of systematic errors and statistical noise. The larger part of variation, however, could be explained by the moisture status of plots. For instance, Spearman's rho decreased from 93% for dry plots and 87% for moist plots to 59% for wet plots. The loss of relation between soil pH and Rm in the moderately acid to alkaline range at increasingly wetter plots is probably due to the establishment of aerenchyma-containing species, which are able to control their rhizosphere acidity. Adaptation to one site factor (oxygen deficit) apparently may induce indifference for other environmental factors (Fe2+, soil pH). For predictions of vegetation response to soil acidity, it is thus important to take the wetness of plots into account
Explaining Bacterial Dispersion on Leaf Surfaces with an Individual-Based Model (PHYLLOSIM)
Wal, A. van der; Tecon, R. ; Kreft, J.U. ; Mooij, W.M. ; Leveau, J.H.J. - \ 2013
PLoS One 8 (2013)10. - ISSN 1932-6203
plant-microbe interactions - pseudomonas-syringae - biofilm formation - water availability - growth - detachment - diffusion - motility - colonization - wettability
We developed the individual-based model PHYLLOSIM to explain observed variation in the size of bacterial clusters on plant leaf surfaces (the phyllosphere). Specifically, we tested how different 'waterscapes' impacted the diffusion of nutrients from the leaf interior to the surface and the growth of individual bacteria on these nutrients. In the 'null' model or more complex 'patchy' models, the surface was covered with a continuous water film or with water drops of equal or different volumes, respectively. While these models predicted the growth of individual bacterial immigrants into clusters of variable sizes, they were unable to reproduce experimentally derived, previously published patterns of dispersion which were characterized by a much larger variation in cluster sizes and a disproportionate occurrence of clusters consisting of only one or two bacteria. The fit of model predictions to experimental data was about equally poor (
Linear viscoelasticity of polyelectrolyte complex coacervates
Spruijt, E. ; Cohen Stuart, M.A. ; Gucht, J. van der - \ 2013
Macromolecules 46 (2013)4. - ISSN 0024-9297 - p. 1633 - 1641.
rheological properties - discrete relaxation - dynamic properties - core micelles - time spectra - stability - diffusion - polymers - model - ratio
Two flexible, oppositely charged polymers can form liquid-like complex coacervate phases with rich but poorly understood viscoelastic properties. They serve as an experimental model system for many biological and man-made materials made from oppositely charged macromolecules. We use rheology to systematically study the viscoelastic properties as a function of salt concentration, chain length, chain length matching, and mixing stoichiometry of model complex coacervates of poly(N,N-dimethylaminoethyl methacrylate), PDMAEMA, and poly(acrylic acid), PAA. The dynamics of making and breaking ionic bonds between the oppositely charged chains underlie all linear viscoelastic properties of the complex coacervates. We treat (clusters of) ionic bonds as sticky points and find that there is a remarkable resemblance between the relaxation spectra of these complex coacervates and the classical sticky Rouse model for single polymer systems. Salt affects all relaxation processes in the same way, giving rise to a widely applicable time–salt superposition principle. The viscoelastic properties of the complexes are very different from those of the individual components. In the complexes with a chain length mismatch, the effect of the mismatch on the viscoelastic properties is not trivial: changing the length of the polycation affects the relaxation behavior differently from changing the length of the polyanion
Exploring the Impact of Land Cover and Topography on Rainfall Maxima in the Netherlands
Maat, H.W. ter; Moors, E.J. ; Hutjes, R.W.A. ; Holtslag, A.A.M. ; Dolman, A.J. - \ 2013
Journal of Hydrometeorology 14 (2013)2. - ISSN 1525-755X - p. 524 - 542.
landgebruik - bossen - neerslag - bodemwater - simulatie - modellen - veluwe - land use - forests - precipitation - soil water - simulation - models - climate-change - convective boundary - soil-moisture - surface - model - evaporation - prediction - diffusion - exchange
The relative contribution of topography and land use on precipitation is analyzed in this paper for a forested area in the Netherlands. This area has an average yearly precipitation sum that can be 75–100 mm higher than the rest of the country. To analyze this contribution, different configurations of land use and topography are fed into a mesoscale model. The authors use the Regional Atmospheric Modeling System (RAMS) coupled with a land surface scheme simulating water vapor, heat, and momentum fluxes [Soil–Water–Atmosphere Plant System–Carbon (SWAPS-C)]. The model simulations are executed for two periods that cover varying large-scale synoptic conditions of summer and winter periods. The output of the experiments leads to the conclusion that the precipitation maximum at the Veluwe is forced by topography and land use. The effect of the forested area on the processes that influence precipitation is smaller in summertime conditions when the precipitation has a convective character. In frontal conditions, the forest has a more pronounced effect on local precipitation through the convergence of moisture. The effect of topography on monthly domain-averaged precipitation around the Veluwe is a 17% increase in the winter and a 10% increase in the summer, which is quite remarkable for topography with a maximum elevation of just above 100 m and moderate steepness. From this study, it appears that the version of RAMS using Mellor–Yamada turbulence parameterization simulates precipitation better in wintertime, but the configuration with the medium-range forecast (MRF) turbulence parameterization improves the simulation of precipitation in convective circumstances.
Particle migration leads to deposition-free fractionation
Dinther, A.M.C. van; Schroën, C.G.P.H. ; Boom, R.M. - \ 2013
Journal of Membrane Science 440 (2013). - ISSN 0376-7388 - p. 58 - 66.
cross-flow microfiltration - concentrated suspensions - spherical-particles - membrane filtration - poiseuille flow - couette-flow - spheres - segregation - diffusion - transport
In membrane filtration, theporesizeofthemembranedeterminesthesizeof ‘particles’ that shouldbe rejected,leading to accumulation of particles on the membrane surface and changed particle retention in time.A process without accumulation and thereby constant retention as function of time would be well suited for fractionation of components close in size. In this research ,emulsions consisting of small droplets (~2.0 mm) and large droplets(~5.5 mm), with total concentrations between 10% and 47%, were fractionated.The cross-flowmodul econsisted of a closed channel to allow particle stomigrate, followed by a membrane area with 20 mm poreswhere emulsion fractions could be removed. Under appropriate process conditions, the permeate consisted of only small droplets, at concentrations highe rthan in the original emulsion,leading to very high selectivities. Especially a thigh concentrations known to causes evere fouling in regular membrane filtration, these effects were occurring as a result of shear-induced diffusion of the droplets. If only small particles are targeted, the module can be operate dat fluxes of 40L/(m²/h); iffractionation is targeted the fluxes can be considerably higher. These fluxes are comparable to current operational fluxes, but here cross-flow velocity and trans-membrane pressure are much lower(corresponding to fluxesof1–4 m3/ (m²/h/bar)) with stable retentionand flux as function of time.
Water migration mechanisms in amorphous powder material and related agglomeration
Renzetti, S. ; Voogt, J.A. ; Oliver, L. ; Meinders, M.B.J. - \ 2012
Journal of Food Engineering 110 (2012)2. - ISSN 0260-8774 - p. 160 - 168.
glass-transition - food powders - diffusion - caking - polystyrene - particles - sorption - systems
The agglomeration phenomenon of amorphous particulate material is a major problem in the food industry. Currently, the glass transition temperature (Tg) is used as a fundamental parameter to describe and control agglomeration. Models are available that describe the kinetics of the agglomeration process as a function of the distance of the material from Tg (i.e. T - Tg). In practice these models are often not applied because they assume that the powder material is instantly in equilibrium with the humidity conditions of the environment and that solid mobility only occurs at T > Tg. Insights in the kinetics and mechanisms of water transport in powder material can help to better understand and control powder agglomeration. For this purpose, gravimetric step-change water sorption experiments were performed on maltodextrins as a function of the water activity aw. The maltodextrins vary in dextrose equivalents (DE), particle size and morphology. The experimental results were compared with a Fickian diffusion model in order to understand the dependency of the transport mechanism on water concentration gradient and material relaxation. The water transport kinetics in the maltodextrins with low DE (i.e. 6) were well described by Fickian diffusion for low aw, independently of particle size and morphology, until relaxation phenomena started to occur at an aw corresponding to T - Tg = -20 °C. The importance of the matrix relaxation phenomena on the water transport mechanism increased with increasing DE (i.e. 29 and 32), not showing any relationship with the Tg. The results of this study indicate that the water migration mechanism is controlled by relaxation phenomena when the amorphous material is still far from the glass–rubber transition. The T - Tg at which the relaxation phenomena occur depends on the material. On the contrary, the T - Tg parameter could well describe the onset of agglomeration, independently from the material properties. Therefore, it can be concluded that within the conditions of this study, matrix relaxation occurring far below Tg did not affect the onset of agglomeration.
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