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.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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Foam properties of proteins, low molecular weight surfactants and their complexes
Lech, F.J. - \ 2016
Wageningen University. Promotor(en): Harry Gruppen; Peter Wierenga; Marcel Meinders. - Wageningen : Wageningen University - ISBN 9789462576247 - 122 p.
surfactants - proteins - bovine serum albumin - beta-lactoglobulin - lysozyme - foams - chemical properties - stability - mixtures - food chemistry - oppervlaktespanningsverlagende stoffen - eiwitten - runderserumalbumine - bèta-lactoglobuline - lysozym - schuim - chemische eigenschappen - stabiliteit - mengsels - voedselchemie

This thesis shows the effects that the addition of low molecular weight surfactants (LWMS) to proteins has on the foam stability of the mixture. For this, the bulk, interfacial, thin liquid films and foam properties are determined for different protein-LWMS mixtures at different molar ratios (MR). It was shown that the MR as well as the charge of the protein and LMWS determine the foam stability of the mixtures. For all mixtures it was found that the proteins have a select number of high affinity binding sites. So, the concentration of free LMWS in the solution is 0 until a critical MR (MRcr), at which all high affinity binding sites are saturated. Above this MRcr, part of the LMWS binds to low affinity binding sites of the proteins. The low affinity binding sites have a binding ratio < 1, which determines the concentration of bound and free LMWS. For similarly charged protein-LMWS mixtures (i.e. b-lactoglobulin (BLG) and sodium dodecyl sulphate (SDS) and bovine serum albumin (BSA) and SDS at pH 7) the foam stability typically decreases from the foam stability of the pure protein solution (MR 0) until MRcr is reached. At MR > MRcr the foam stability is dominated by the amount of free LMWS. For oppositely charged protein-LMWS mixtures, the binding of the LMWS to the proteins can be described in a similar way, although the number of high affinity sites and low affinity binding ratio are different. There is also a regime of MRs in which the protein-LMWS complexes form large aggregates. These aggregates were in some cases found to increase foam stability (lysozyme (LYS) and SDS and BLG-SDS at pH 3), while in another case (BLG and cetyltrimethylammonium bromide (CTAB)) they lead to decreased foam stability. Still, in all cases it was found that above MRD the aggregates dissociate and the foam stability becomes dominated by free surfactants, equivalent to what was observed for similarly charged protein-LMWS mixtures.

A multi-scale model was developed to describe the stability of thin liquid films in terms of rupture time and thickness. Initially, the model was used to predict the stability of surfactant free films of water and electrolyte solutions. Later, it was used to predict the foam stability in LYS-SDS mixtures. For that purpose, the model was combined with a foam drainage model to provide theoretical estimations of foam stability. This model is the basis to understand coalescence of bubbles in foam. Finally, the concept of the critical MRs and the free LMWS was introduced. Using this, the foam properties of protein-LMWS mixtures can partly be predicted by relative charge of the components and the binding to both high and low affinity binding sites.

Shape and stability in liquid threads and jets : a link to droplet formation
Heugten, W.G.N. van - \ 2015
Wageningen University. Promotor(en): Cees van Rijn. - Wageningen : Wageningen University - ISBN 9789462575707 - 172
droplets - controlled droplet application - threads - viscosity - stability - fluid mechanics - druppels - draden - viscositeit - stabiliteit - vloeistofmechanica

This thesis explores relevant fluid dynamic processes for the formation of uniformly sized droplets in microfluidic systems. Growing droplets made from a bulk source have often liquid threads or jets in between to supply liquid to the droplet. Liquid threads and jets are however known to be instable and finding parameters determining their instability/stability will possibly promote a more controlled formation of uniformly sized droplets. Different droplet formation processes in microfluidic devices are explained, such as cross-flow, co-flow and flow focussing.

Dimensionless numbers (introduced in chapter 1) represent the ratio of relevant forces or pressures acting on the fluids and/or their interfaces. These forces and pressures originate from their related fluid dynamic parameters, such as viscosity, interfacial tension, mass density and velocity of the fluid within a specific fluidic confinement with a certain length scale. We show that the dimensionless Reynolds, Weber and Capillary numbers can be associated with the stability of liquid threads and/or jets and provide insight in droplet formation processes.

The phenomenon of spontaneous droplet formation at low flow rates of an inner fluid confined in a microfluidic channel is studied in chapter 2. A short overview of known processes of spontaneous droplet formation with micro-engineered microfluidic devices is presented. We have studied the process of auto breakup with rectangular and round glass capillaries, the latter provided with micro-corrugations and uniform sized droplets were obtained, but only if the outer fluid is able to enter the capillary during droplet formation.

The process of auto breakup is described by a new analytical model described in chapter 3. The model states that the instability of a liquid thread is induced by the decrease of a local liquid thread pressure inside the capillary near the growing droplet. Predicted droplet sizes have been experimentally verified accurately, and also the predicted breakup length inside a micro-corrugated capillary has been verified. The model states that viscous flow stabilises the liquid thread and that auto breakup happens as long as the capillary number is below a critical capillary number of 0.0625. Above 0.0625 droplets grow infinitely large. Auto breakup is however already hampered at Capillary numbers above 0.03, because between 0.03 and 0.0625 no well controlled droplet sizes could be obtained by auto breakup. This is explained by the observed formation of a partially collapsed inner liquid thread that remains open and supplies the growing droplet with inner fluid.

In chapter 4 the formation and stability of a liquid thread in free surface flow feeding a large growing droplet is demonstrated and discussed. The shape of the liquid thread is positively tapering (towards the droplet) and can be described accurately by a Navier-Stokes based ordinary differential equation (ODE) assuming steady state, axisymmetry and an averaged fluid velocity over the cross section of the liquid thread. The axial shape of a viscous liquid thread is concave and its radial dimension has initially a cubic dependence with respect to the axial dimension. A driving force to stabilise the liquid thread was identified, which is a pressure gradient Q = Q0/L – Q1. Q0 is the pressure drop over thread length L, and Q1 is interfacial based dissipation of energy of the outer fluid. The maximum length of the liquid thread is predicted to be reached when Q goes towards 0 as the ratio Q0/Q1.

Shape and stability of emanating liquid jets, which appear after impact of falling droplets from a deep liquid, is presented in chapter 5. During rise and fall of the jet due to gravity, the jet is additionally decelerated towards the liquid surface by a tensile retraction force from the surface tension force exerted on the jet surface by the liquid bath. The retracting force generates an inertial deceleration pressure inside the jet that is balanced by the local Laplace pressure, herewith defining its local curvature and therefore also the shape of the complete jet. A deceleration based Young-Laplace equation is introduced and the predicted shape is experimentally verified for different fluids. Furthermore, the size of droplets forming on the tip of the jet can also be explained by the found pressure balance between the local Laplace pressure and the inertial deceleration of the jet (including the forming droplet).

In general we found that the stability of a liquid thread or jet seems correlated with an applied pressure difference that is distributed between the begin and end of the thread or jet. Studying auto breakup (chapters 2 and 3) of a confined liquid thread it was found that only when the applied pressure is high enough the liquid thread is stable and infinitely large droplets are formed. For the free surface flow liquid thread (chapter 4) it was found that breakup happens when the applied pressure gradient over the length of the thread goes to zero. For the emanating jet (chapter 5) an inertial pressure difference between the base and tip of the jet comes into existence that opposes the squeezing Laplace pressure that wants to break up the liquid jet. Furthermore we found that the last stages of droplet breakup from a liquid thread or jet appeared to follow universal pinch-off, and also that micro-thread formation is observed between droplet and liquid thread or jet.

Microbubble stability and applications in food
Rovers, T.A.M. - \ 2015
Wageningen University. Promotor(en): Erik van der Linden, co-promotor(en): Marcel Meinders; Guido Sala. - Wageningen : Wageningen University - ISBN 9789462574755 - 138
microbubbles - eiwit - stabiliteit - karakterisering - voedsel - voedseladditieven - oppervlaktespanningsverlagende stoffen - zuurbehandeling - reologische eigenschappen - sensorische evaluatie - tribologie - druk - verwarming - koelen - protein - stability - characterization - food - food additives - surfactants - acid treatment - rheological properties - sensory evaluation - tribology - pressure - heating - cooling

Aeration of food is considered to be a good method to create a texture and mouthfeel of food products that is liked by the consumer. However, traditional foams are not stable for a prolonged time. Microbubbles are air bubbles covered with a shell that slows down disproportionation significantly and arrests coalescence. Protein stabilized microbubbles are seen as a promising new food ingredient for encapsulation, to replace fat, to create new textures, and to improve sensorial properties of foods. In order to explore the possible functionalities of microbubbles in food systems, a good understanding is required regarding the formation of protein stabilized microbubbles as well as their stability in environments and at conditions encountered in food products. The aim of this research was to investigate the key parameters for applications of microbubbles in food systems. In Chapter 1 an introduction to this topic is given.

In Chapter 2, the effect of the microbubble preparation parameters on the microbubble characteristics, like the microbubble yield, size and stability, was investigated. The protein Bovine Serum Albumin (BSA) and the method sonication was used to manufacture the microbubbles. The manufactured number and stability of microbubbles was highest when they were prepared at a pH around 5 to 6, just above the isoelectric point, and at an ionic strength of 1.0 M. This can be related to the protein coverage at the air/water interface of air bubbles formed during sonication. At a pH close to the isoelectric point the BSA molecules is in its native configuration. Also the repulsion between the proteins is minimized at these pH values and ionic strength. Both the native configuration and the limited repulsion between the proteins result in an optimal protein coverage during the first part of sonication. Also a high protein concentration contributes to a higher surface coverage. The surface coverage is proportional to the protein concentration up to a concentration of 7.5% after which an increase in protein concentration did not lead to a substantial increase in the number of microbubble . In the second part of sonication the protein layer around the air bubble becomes thicker and stronger by heat induced protein-protein interactions. We found that and at a preheating temperature of 55-60°C, about 5 °C below the BSA denaturation temperature, and a final solution temperature of 60-65°C most microbubbles were obtained, while at higher temperatures mainly protein aggregates and (almost) no microbubbles are formed. This suggests that at temperature of around 60°C to 65°C protein aggregated mostly at the air-water interface creating a multi-layered shell, while at higher temperature, they also aggregated in bulk. These aggregates cannot form microbubbles. We found that optimal preparation parameters strongly depend on the protein batch. We hypothesize that the differences in microbubble formation between the protein batches is due to (small) differences in the protein molecular and denaturation properties that determine the temperature at which the molecules start to interact at the air-water interface. Microbubbles made with different protein concentration and preheating temperatures shrunk in time to a radius between 300 nm and 350 nm, after which the size remained constant during further storage. We argue that the driving force for the shrinkage was the Laplace pressure, resulting in an air flux from the bubbles to the solution. We argue that the constant final size can be explained by a thickening of the microbubble shell as a result of the microbubble shrinkage, thereby withstanding the Laplace pressure.

In Chapter 3 and Chapter 4, microbubble stability at environments and conditions representative for food products were studies. In Chapter 3 we investigated the stability upon addition of surfactants and acid, When surfactants or acid were added, the microbubbles disappeared in three subsequent steps. The release of air from the microbubble can be well described with the two-parameter Weibull process. This suggests two processes are responsible for the release of air: 1) a shell-weakening process and 2) a random fracture of the weakened shell. After the air has been released from the microbubble the third process is identified in the microbubble disintegration: 3) the shell disintegrated completely into nanometer-sized particles. The probability of fracture was exponentially proportional to the concentration of acid and surfactant, meaning that a lower average breaking time and a higher decay rate were observed at higher surfactant or acid concentrations. For different surfactants, different decay rates were found. The disintegration of the shell into monomeric proteins upon addition of acid or surfactants shows that the interactions in the shell are non-covalent and most probably hydrophobic. After surfactant addition, there was a significant time gap between complete microbubble decay (release of air) and complete shell disintegration, while after acid addition the time at which the complete disintegration of the shell was observed coincided with the time of complete microbubble decay.

In Chapter 4 the stability of the microbubbles upon pressure treatment, upon fast cooling after heating and at different storage temperatures was studied. The microbubble stability significantly decreased when microbubbles were pressurized above 1 bar overpressure for 15 seconds or heated above 50°C for 2 minutes. Above those pressures the microbubbles became unstable by buckling. Buckling occurred above a critical pressure. This critical pressure is determined by the shell elastic modulus, the thickness of the shell, and the size of the microbubble. Addition of crosslinkers like glutaraldehyde and tannic acid increased the shell elastic modulus. It was shown that microbubbles were stable against all tested temperatures (up to 120°C) and overpressures (4.7 bar) after they were reinforced by crosslinkers. From the average breaking time at different storage temperatures, we deduced that the activation energy to rupture molecular bonds in the microbubbles shell is 27 kT.

In Chapter 5, we investigated the effect of microbubbles on the rheological, tribological sensorial properties of model food systems and we compared this effect to the effect on food systems with emulsion droplets and without an added colloid. We investigated the effect in three model food systems, namely fluids with and without added thickener and a mixed gelatine-agar gel. In a sensory test panellists were asked whether they could discriminate between samples containing microbubbles, emulsion droplets or no added colloid. Emulsions could be sensorially well distinguished from the other two samples, while the microbubble dispersion could not be discriminated from the protein solution. Thus, we concluded that at a volume fraction of 5% of these BSA covered microbubbles were not comparable to oil-in-water emulsions. The good discrimination of emulsion might be ascribed to the fact that emulsion had a lower friction force (measured at shear rates form 10 mm/s to 80 mm/s) than that microbubbles dispersions and protein solutions. Upon mixing emulsions and microbubble dispersions the friction value approximated that of emulsions. This effect was already noticed at only 1.25% (v/v) oil, indicating that microbubbles had not a significant contributions to the friction of these samples. Also microbubble dispersions with and without protein aggregates were compared. The microbubble dispersions with and without thickener containing protein aggregates had a higher viscosity than the those samples without protein aggregates. Protein aggregates in the gelled microbubble sample yielded a higher Young’s modulus and fracture stress. The differences between the gelled samples could be well perceived by the panellists. We attribute this mainly to the fracture properties of the gel. In general we concluded that microbubbles, given their size of ~ 1 mm and volume fraction of 5%, did not contribute to a specific mouthfeel.

Finally in Chapter 6, the results presented in the previous chapters are discussed and put in perspective of the general knowledge on microbubbles production, stability, and applications in food. We described the main mechanisms leading to microbubble formation and stability. We showed that the production parameters significantly influence the interactions in the microbubble shell, and the those interactions highly determine the stability of the microbubbles under several conditions. We reported about limitations of sonication as a method to produce microbubbles suitable for food applications and we provided some ways to overcome these limitations. The use of microbubbles in food systems has been explored and we clearly see possible applications for microbubbles in food. We reported about directions for possible further research.

In this work we made significant progress in understanding the interactions in the microbubble shell and their relation to microbubble stability. We also advanced in comprehension towards possible applications of microbubbles in food.

Lipid bilayer stability in relation to oxide nanoparticles
Pera, H. - \ 2015
Wageningen University. Promotor(en): Frans Leermakers, co-promotor(en): Mieke Kleijn. - Wageningen : Wageningen University - ISBN 9789462574670 - 144
lipids - membranes - stability - nanotechnology - particles - analytical methods - models - modeling - lipiden - membranen - stabiliteit - nanotechnologie - deeltjes - analytische methoden - modellen - modelleren
Lipid bilayer stability in relation to oxide nanoparticles

All living organisms are composed of cells that are filled with a thick molecular soup. These molecules constitute a complex machinery that brings these cells to life. To contain these molecules, and to protect them from the hostile outer environment, a phospholipid bilayer envelopes the cell. It is essential that this lipid bilayer, also known as the cell membrane, should remain intact and form a perfect barrier at all times. Industrially manufactured nanoparticles are suspect to be able to penetrate this barrier, and thus endanger living organisms in the environment. This thesis deals with some aspects of the structural integrity of lipid bilayers, and especially how this integrity is affected by the interaction with nanoparticles.

Experiments were performed with silica and titanium dioxide nanoparticles, interacting with lipid bilayers, using a variety of experimental techniques. In addition, a theoretical model was applied that is based on the Scheutjens-Fleer Self Consistent Field (SCF) theory. This model delivered detailed structural and thermodynamic information about the lipid bilayer. The modelling work helped us to improve our understanding of lipid bilayer stability, and showed the effect of the interaction with the nanoparticles on the phospholipid bilayer. These latter results could be related directly to our experiments.

Let us first experimentally regard the interaction of lipid bilayers with synthetic oxide nanoparticles. We developed a protocol for high-throughput screening of the nanoparticle-bilayer interaction using a fluorescence technique. Results from this method were combined with reflectometry measurements and atomic force microscopy (AFM). The combination of these methods allowed us to relate lipid bilayer integrity to its interaction with nanoparticles and their adsorption onto the bilayer. In addition, the AFM results yielded detailed structural information at the nano-scale. We found that the interaction strongly depends on both lipid bilayer and nanoparticle charge. However, the specific interaction that depends on the nanoparticle type, starts to play a role when the charges are low. When the total interaction strength is regarded, a regime was found at which interaction is strong enough for the nanoparticles to adsorb onto the bilayer, but too weak to disrupt the bilayer. If, however, the bilayer is disrupted by the nanoparticles, the particle may steal away some lipid molecules from the bilayer, and leave again to disrupt the bilayer elsewhere.

Let us now go into more detail on the SCF modelling. Bilayers are composed of phospholipids, which consist of a hydrophilic head group, and a hydrophobic tail. These bilayers were modelled using a single lipid molecule type, of which the head group structure and lipid tail length could be varied. We thus obtained bilayers that varied in their thickness, and the space that a single lipid takes within the bilayer. Changes in bilayer composition affect the bilayer mechanical properties, such as those constants that describe bilayer stretching or bending. This thesis shows how vesicles, which are bilayers in a globular shape, may become unstable if the bilayer lipid composition is changed. Under certain conditions, a vesicle would prefer to fall apart into many smaller vesicles, which is when highly charged head groups start to repel each other. Or the bilayer may form continuous cubic phases, which might occur if lipids with uncharged head groups but with very long tails are used to form the bilayer. Under very specific and finely tuned conditions, a lipid bilayer may become unstable to form stable pores in the membrane, or to fall apart into tiny lipid discs.

The natural occurrence of chloramphenicol in crops
Berendsen, B.J.A. ; Zuidema, T. ; Jong, J. de - \ 2015
Wageningen : RIKILT Wageningen UR (RIKILT report 2015.009)
chlooramfenicol - antibiotica - stro - halfwaardetijd - stabiliteit - bodemgiftigheid - streptomyces venezuelae - opname van contaminanten - voedselveiligheid - chloramphenicol - antibiotics - straw - half life - stability - soil toxicity - contaminant uptake - food safety
Unexpected findings of the banned antibiotic chloramphenicol in products of animal origin, feed and straw prompted urgent investigation. Therefore a monitoring study in straw was carried out. The monitoring showed that in 37 sample chloramphenicol was detected. In 7 samples a concentration above 0.3 μg kg-1 was found with the highest result at 6.8 μg kg-1. Next the hypothesis was studied that the chloramphenicol is naturally present in soil, through production by soil bacteria, and subsequently can be transferred to crops. First, the stability of chloramphenicol in soil was studied. The fate of chloramphenicol highly depends on soil type and showed a half-life of approximately one day in non-sterile topsoil. It was found to be more stable in sub-soil and sterile soils. Second, the production of chloramphenicol in soil was studied and it was confirmed that Streptomyces venezuelae can produce chloramphenicol at appreciable amounts in non-sterile soil. Third, a transfer study was carried out using wheat and corn grown on three different soils, that were weekly exposed to aqueous chloramphenicol solutions at different levels. Chloramphenicol was taken up by crops as determined by chiral liquid chromatography coupled to tandem mass spectrometric analysis and the levels in crop were found to be bioavailability related. It was concluded that chloramphenicol residues can occur naturally in crops as a result of the production of chloramphenicol by soil bacteria in their natural environment and subsequent uptake by crops.
Analysis and stability of fatty acid esterified xanthophylls from microalgae
Weesepoel, Y.J.A. - \ 2014
Wageningen University. Promotor(en): Harry Gruppen, co-promotor(en): Jean-Paul Vincken. - Wageningen : Wageningen University - ISBN 9789462570450 - 172
xanthofyllen - astaxanthine - stabiliteit - kleurstoffen in voedsel - algen - estervorming - xanthophylls - astaxanthin - stability - food colourants - algae - esterification

Fatty acid esterified xanthophylls (e.g. astaxanthin) produced by microalgae are regarded as a natural alternative for food colourants, but little is known on the stability of these compounds in foods. The aims of this research were (i) to develop protocols to analyze esterified xanthophylls, and their degradation products, from microalgae by UHPLC-PDA-ESI-MS and MALDI-TOF-MS, and (ii) to assess whether esterification influences xanthophyll stability.

Both analytical methods were successfully tested on complex palmitoyl astaxanthin mixtures of Haematococcus pluvialis. MALDI-TOF-MS analysis showed that sodiated [M+Na]+ palmitoyl astaxanthin parents had higher ionization efficiency compared to the radical/protonated parents [M]+•/[M+H]+. Furthermore, TOF/TOF fragmentation of [M+Na]+ parents yielded more diagnostic daughter ions than for [M]+•/[M+H]+ parents.

UHPLC-PDA-ESI-MS was applied to investigate xanthophyll biosynthesis in Chlorella zofingiensis. Upon nitrogen depletion, C. zofingiensis produced, amongst other pigments, ketolutein and its fatty acid ester. Ketolutein production was independent of the production of secondary β,β-carotene derivatives. Furthermore, UHPLC-PDA-ESI-MS was used to assess the oxidation products of palmitoyl astaxanthins and the influence of the fatty acid ester on colour stability. Mild light-accelerated autoxidation led to formation of free apo-astaxanthins and a new class of palmitoyl apo-astaxanthins. Harsh hypochlorite bleaching revealed (palmitoyl) epoxide-apo-9- and 13-astaxanthinones. Similarly, the methine bridges in the tetrapyrrole biliverdin were found to be susceptible to autoxidation.

An increase in palmitate esterification enhanced stability of all-trans-astaxanthin upon light-accelerated autoxidation in hexane. Esterification appeared to modulate the cis-trans equilibrium of astaxanthin, which seems to play a key role in its stability.

Gedrag van verdroogde kades : fase B, C, D: onstaan en gevaar van krimpscheuren in klei- en veenkades
Akker, J.J.H. van den; Hendriks, R.F.A. ; Frissel, J.Y. ; Oostindie, K. ; Wesseling, J.G. - \ 2014
Wageningen : Alterra (Alterra-rapport 2473) - 87
bodemtypen - scheurvorming - dijken - bodemfysica - preferente stroming - bodemwater - stabiliteit - soil types - cracking - dykes - soil physics - preferential flow - soil water - stability
Het beschreven onderzoek in dit rapport is onderdeel van het onderzoeksproject ‘gedrag van verdroogde kades’ van het Hoogheemraadschap Delfland. Het onderzoek van Alterra is een bureau- en modelonderzoek en is gericht op scheuren door krimp, die ontstaan in lange perioden met droogte. Onderzocht zijn veenkaden en kleikaden op veen, met een accent op kleikaden omdat deze in Delfland het meeste voorkomen. Bij kleikaden lijkt het grootste risico preferente stroming via de scheuren te zijn. Bomen kunnen door hun diepe beworteling en grote verdamping een extra risico vormen. Langsscheuren in de kruin kunnen met water gevuld worden en dit kan resulteren in een bezwijkmechanisme. Dit is door Deltares nader onderzocht in een parallel rapport.
Effecten van beregening op het verloop van het freatisch vlak in veenkades
Oostindie, K. ; Wesseling, J.G. ; Kleef, J. van; Ritsema, C.J. - \ 2013
Wageningen : Alterra (Alterra speciaal rapport ) - 37
veengronden - stabiliteit - dijken - bodemfysica - bodemwater - beregening - peat soils - stability - dykes - soil physics - soil water - overhead irrigation
Snelle stijgingen in het verloop van het freatisch vlak onder relatief steile veenkades als gevolg van perioden met veel neerslag kunnen gevolgen hebben voor de mate van stabiliteit van dijklichamen. Door middel van irrigatieproeven zijn op een tweetal kades onderzocht hoe het freatisch vlak reageert op neerslaghoeveelheden die eens in de 100 jaar voorkomen, en die over een periode van 1 tot 9 dagen lengte vallen. Met behulp van het 2 dimensionale model HYDRUS-2D is geprobeerd deze situaties na te bootsen. Hiermee komt dan een instrumentarium beschikbaar waarmee alternatieve scenario’s kunnen worden doorgerekend. Tevens wordt inzichtelijk gemaakt hoe de waterstroming door het dijklichaam plaatsvindt.
Waarom Deltadijken bijdragen aan een robuust systeem
Mens, M. ; Loon-Steensma, J.M. van; Eikelboom, T. - \ 2013
H2O online 2013 (2013)april.
rivierafvoer - hoogwaterbeheersing - dijken - veiligheid - stabiliteit - ontwerp - systeembenadering - stream flow - flood control - dykes - safety - stability - design - systems approach
Klimaatverandering vraagt om een klimaatbestendige gebiedsinrichting. Voor gebieden met een overstromingsrisico betekent dit vaak dat dijken moeten worden versterkt en/of verhoogd. Daarnaast komt er met Meerlaagsveiligheid meer aandacht voor ruimtelijke ordening en rampenbeheersing. Kennis voor Klimaat (KvK) onderzoekt maatregelen die het overstromingsrisico reduceren. Deze maatregelen moeten passen in een strategie voor de lange termijn, die rekening houdt met onzekerheden. De deltadijk is zo’n maatregel. Deltadijken blijken niet alleen het risico van overstromingen te reduceren, maar ook de robuustheid van een gebied voor hoge rivierafvoeren te vergroten.
Deltadijken dragen bij aan ‘robuust’ systeem
Mens, M. ; Loon-Steensma, J.M. van; Eikelboom, T. - \ 2013
H2O : tijdschrift voor watervoorziening en afvalwaterbehandeling 46 (2013)4. - ISSN 0166-8439 - p. 36 - 37.
rivierafvoer - hoogwaterbeheersing - dijken - veiligheid - stabiliteit - ontwerp - systeembenadering - stream flow - flood control - dykes - safety - stability - design - systems approach
Verhoging en versterking van dijken is niet het enige mogelijke antwoord op extreem hoge afvoeren van rivieren. Men kan ook kijken naar de 'robuustheid' van het systeem: is een gebied als geheel - en dus niet alleen de dijk - voorbereid op het vele water? En welke rol kunnen deltadijken daarbij spelen?
Effecten van beheersmaatregelen op vochtgehaltes bij uitdrogende veendijken
Oostindie, K. ; Wesseling, J.G. ; Hendriks, R.F.A. ; Ritsema, C.J. ; Akker, J.J.H. van den - \ 2012
Wageningen : Alterra, Wageningen-UR (Alterra-rapport ) - 25
dijken - bodemprofielen - veengronden - stabiliteit - grondwaterstand - begrazing - graslanden - modellen - dykes - soil profiles - peat soils - stability - groundwater level - grazing - grasslands - models
Beheersmaatregelen op veendijken kunnen invloed hebben op bodem- en gewasverdamping. In deze studie zijn met behulp van het SWAP-model een vijftal maatregelen doorgerekend voor een veendijkprofiel zonder kleidek en een zelfde profiel welk met een kleilaag is afgedekt. De berekeningen zijn uitgevoerd voor 4 worteldiepten en bij drie verschillende grondwaterstanden. Er is gebruik gemaakt van een pseudo meteofile waarbij geen neerslag valt en de potentiele verdamping voor elke dag constant wordt gehouden en van een meteofile met gegevens over het droge jaar van 1976 van het KNMI station De Bilt. In deze studie is de verzadigingsgraad berekend voor de bovenste meter van het bodemprofiel.
On the stability and imaging applications of metal-containing coacervate micelles
Wang Junyou, Junyou - \ 2012
Wageningen University. Promotor(en): Martien Cohen Stuart, co-promotor(en): Jasper van der Gucht; Henk van As. - S.l. : s.n. - ISBN 9789461733993 - 113
micellen - elektrolyten - stabiliteit - micelles - electrolytes - stability
Foaming behaviour of organic and regular milk
Pijnenburg, J. ; Sala, G. ; Valenberg, H.J.F. van; Meinders, M.B.J. - \ 2012
Wageningen : Wageningen UR - 23
melk - biologische voedingsmiddelen - schuimen - stabiliteit - melkproducten - milk - organic foods - foaming - stability - milk products
Organic milk is used more and more by consumers to froth milk that is used e.g. for the preparation of a capuccino. Frequently, organic milk turns out not to foam properly. This report describes a study to find the main couse of this bad foamability of organic milk. The focus of the research was to get insight in the foaming behaviour of a specific brand, indicated as A. The foamability and stability of different milk, both organic and regular, as well as skimmed, semi-skimmed, and full fat, were tested. The foamability of the different milk varieties appeared to be about equal. However, differences were observed for the foam stability. Foams made from A showed the lowest stability of all tested milk varieties. The reason for this is not yet clear, but the bad foam stability of this milk might be probably due to a higher fatty acid content.
Fate of fatty acids during ensiling: relationship with milk fat composition of dairy cows
Khan, N.A. - \ 2011
Wageningen University. Promotor(en): Wouter Hendriks, co-promotor(en): John Cone; V. Fievez. - [S.l.] : S.n. - ISBN 9789085859581 - 158
melkkoeien - melkvet - melksamenstelling - vetzuren - kuilvoerbereiding - graskuilvoer - maïskuilvoer - stabiliteit - voer - ruwvoer (forage) - rundveevoeding - diervoeding - dairy cows - milk fat - milk composition - fatty acids - silage making - grass silage - maize silage - stability - feeds - forage - cattle feeding - animal nutrition

Transition of dairy cows from grazing to silage based rations significantly increases the saturated: unsaturated fatty acids (FA) ratio and decreases the content of beneficial C18:1 cis-9, C18:1 trans-11, C18:2 cis-9,trans-11 and C18:3n-3 in milk fat. This is partly related to a lower polyunsaturated FA (PUFA) supply from ensiled forages. The aim of this thesis was to investigate the scope of increasing the content PUFA in grass and maize silages, and to establish relationships between silage quality on the one hand and the FA content and composition, post-ensiling stability of PUFA, and milk FA composition of dairy cows on the other hand. The first focus of this thesis was to quantify the variation in FA content and composition in grass (n = 101) and maize (n = 96) silages, randomly sampled from commercial dairy farms in the Netherlands, and use multivariate analysis to identify the causes of this variation. The FA content and composition of grass and maize silages were highly variable, and this variation was primarily caused by differences in plant maturity at harvest. Silages made from younger grass and maize have higher contents of C18:3n-3.Most of the variation in FA content in the ensiled forages was caused by differences in plant maturity at harvest. Changes in FA content and composition were investigated in stover (leaves and stem) and ears (cob, shank and husks) in a set of maize genotypes, grown on sandy and clay soils and harvested at 14, 42, 56, 70, and 84 days after flowering (DAF). The contents of C18:3n-3 and total FAs in the stover dry matter (DM) declined at a slow rate up to 56 DAF and then decreased rapidly during 56–84 DAF. On the other hand the content of C18:2n-6 and total FAs in the ears DM increased up to 56 DAF and thereafter remained more or less constant. The maximum amount of PUFA in silage maize can be harvested around 56 DAF. Identifying pre and post-ensiling processes that optimize the stability of PUFA was the next goal. The stability of FA were investigated in untreated and mechanically bruised perennial ryegrass (Lolium perenne L.), wilted under field conditions for 0, 12, 24, 36, and 48 h, or wilted under controlled climate conditions at three temperatures (15, 25 or 35 °C) and two light (dark or light) regimes to DM contents of 425, 525 or 625 g/kg. The oxidation of FAs during wilting of grass was mainly caused by the duration of the wilting, wilting temperature only provoked small differences, whereas mechanical bruising of grass and light intensity did not affect the changes in FA contents. The highly esterified lipids of forages are extensively hydrolysed in the silo. Therefore, the post-ensiling stability of FAs was investigated in grass and maize silages, with a wide range in qualities, exposed to air for 0, 12, and 24 h. Exposure of grass and maize silages to air results in a quantitatively small, but consistent decline in the contents of major unsaturated FAs with a concomitant increase in the proportion of C16:0. The final study evaluated the effects of feeding maize silages, ensiled at different maturities, in combination with a high or low degradable carbohydrate concentrate on nutrient intake, milk production, and composition of milk and milk fatinearly lactating dairy cows. Maize maturity at harvest at a DM content of 300-420 g/kg fresh weight, did not affect the production performance of dairy cows, but resulted in decreased contents of C18:3n-3 and total n-3 and a decreased n-6:n-3 ratio in the milk fat of dairy cows.

Storm, bos, beheer en stabiliteit : een evaluatie na de storm van 2007
Schelhaas, M.J. ; Schulting, R. - \ 2010
Wageningen : Alterra (Alterra-rapport 2008) - 56
bosschade - windschade - stormen - bossen - bosbedrijfsvoering - stabiliteit - nederland - forest damage - wind damage - storms - forests - forest management - stability - netherlands
Na de storm van 18 januari 2007 zijn 18 plots gemeten in bossen waar bomen omgewaaid waren en zijn 21 beheerders geïnterviewd over hun mening ten aanzien van stabiliteit. Met de verkregen informatie is het niet goed mogelijk de huidige blesinstructies af te wijzen of te onderbouwen. Wel zijn er aanwijzingen dat de toekomstbomen bij douglas relatief vaak door de storm waren beschadigd, terwijl dit bij de grove den niet het geval was.
Time dependence in jamming and unjamming
Parker, A. - \ 2009
Wageningen University. Promotor(en): Erik van der Linden. - [S.l. : S.n. - ISBN 9789085853879 - 99
gels - stabiliteit - dynamica - reologie - verouderen - sedimentatie - thixotropie - verarming - uitvlokking - xanthan - gelatine - evenwicht - stability - dynamics - rheology - aging - sedimentation - thixotropy - depletion - flocculation - gelatin - equilibrium
Three different food systems have been studied: emulsion/polymer mixtures, gelatin gels and carrageenan gels. Typically, samples are trapped, or jammed, far from equilibrium. The simple jamming paradigm suggests that, once in the jammed state, these systems are static. This useful approximation is often too simple, since these systems frequently evolve in time. Their evolution has been measured systematically. Where possible, these results have been placed in the context of the physics of out-of-equilibrium systems.
The emulsion/polymer mixtures are a model for salad dressing. The emulsions alone are colloidally stable, but become inhomogeneous, due to the effects of gravity. With sufficient polymer, they can be apparently stable (jammed) for months, but then quite suddenly start to sediment – the system unjams. The kinetics of this delayed sedimentation is measured as a function of the key parameters. A new model is proposed for the mechanism by which polymers stabilize emulsions.
Solutions of gelatin form gels when cooled, due to the formation of portions of helix. A new model relating the amount of helix to the elasticity is described. The gels always evolve slowly. At steady state, the rate of evolution of the elasticity is constant in log(time), so this system conforms to Struick’s physical aging scenario. The effect of temperature changes on the evolution of gels is extremely complex. The results show that there is a deep analogy between this behavior and that of spin glasses, which are exotic magnetic phases.
Gels of iota carrageenan, a seaweed polysaccharide, have unique rheological properties: they regel almost instantly after strong mixing. This property is used in the dairy industry, but has not been studied previously. The kinetics of recovery after shear has been measured for water gels and milk gels.

The relation between geometry, hydrology and stability of complex hillslopes examined using low-dimensional hydrological models
Talebi, A. - \ 2008
Wageningen University. Promotor(en): P.A. Troch; Remko Uijlenhoet. - [S.l.] : S.n. - ISBN 9789085047889 - 120
landdegradatie - bodemdegradatie - heuvels - hellingen - topografie - stabiliteit - hydrologie - meetkunde - wiskundige modellen - land degradation - soil degradation - hill land - slopes - topography - stability - hydrology - geometry - mathematical models
Key words: Hillslope geometry, Hillslope hydrology, Hillslope stability, Complex hillslopes, Modeling shallow landslides, HSB model, HSB-SM model.

The hydrologic response of a hillslope to rainfall involves a complex, transient saturated-unsaturated interaction that usually leads to a water table rise. An increase of saturated groundwater flow can act as the triggering mechanism for slope failure. To account for the three-dimensional hillslope shape in which the groundwater flow and storage processes take place, simple (low-dimensional) but physically realistic models that represent hydrological processes at the hillslope scales are needed for reliable simulation of hillslope stability at the landscape scale. In this thesis the focus is on investigating the relation between hillslope geometry, hillslope hydrology and slope stability in complex hillslopes and hollows.
Several models have been presented in this thesis which examine the stability of nine characteristic hillslope types (landform elements) with three different profile curvatures (concave, straight and convex) and three different plan shapes (convergent, parallel and divergent). In addition to testing our models for nine characteristic hillslope types, a general relationship between plan shape and profile curvature of landform elements and the factor of safety is derived for a predefined hillslope length scale. Our results show that slope stability increases when profile curvature changes from concave to convex. In terms of plan shapes, changing from convergent to divergent, slope stability increases for all length profiles. Our analyses also show that the minimum safety factor occurs when the rate of subsurface flow is maximum. In fact, by increasing the subsurface flow, stability decreases for all hillslope shapes. Moreover, after a certain period of rainfall, the convergent hillslopes with concave and straight profiles become unstable faster than others whilst divergent convex hillslopes remain stable (even after intense rainfall). We also demonstrate that in hillslopes with non-constant soil depth (possible deep landslides), the ones with convex profiles and convergent plan shapes have slip surfaces with the minimum safety factor near the outlet region. Finally, we demonstrate that, in addition to bedrock slope, hillslope shape as represented by plan shape and profile curvature is an important control on hillslope stability.
With respect to the relation between rainfall occurrence and slope instability, a probabilistic model of rainfall-induced shallow landslides in complex hollows is also presented to investigate the relation between return period of rainfall, deposit thickness and landslide occurrence. A long term analysis of shallow landslides by the presented model illustrates that all hollows show a quite different behavior from the stability view point. Finally, we conclude that incorporating a more realistic description of hollow hydrology (the hillslope-storage Boussinesq model instead of the kinematic wave model) in landslide probability models is necessary, especially for hollows with a high convergence degree, which are more susceptible to landsliding. This model helps to theoretically investigate the relationship between return period of rainfall and landslide occurrence related to soil production (deposit thickness) in complex hollows.
In summary this thesis aims to understand theoretically how hydrological processes (subsurface flow and water table dynamics) affect slope stability in complex hillslopes and hollows. The presented models can widely be applied in many investigations of hillslope stability analysis because of their relative simplicity (low-dimensional).
Hydromorphological disturbance : in sandy lowland streams an experimental approach
Dekkers, T.B.M. ; Verdonschot, P.F.M. - \ 2007
klimaatverandering - trichoptera - ecologische verstoring - laboratoriumproeven - substraten - stabiliteit - climatic change - ecological disturbance - laboratory tests - substrates - stability
Hydromorphological conditions in lowland streams will change due to an increase of discharge peaks induced by climate change. Substrate stability, a key parameter at habitat scale for macro invertebrates, will decrease. The effect of substrate disturbance on Trichoptera that represent three stream specialists (Halesus radiatus, Micropterna sequax and Chaetopteryx villosa), and three stream ubiquists (Anabolia nervosa, Limnephilus lunatus and Mystacides longicornis) were tested, using laboratory experiments
Evaluatie Stabiliteitsfonds 2004 en 2005
Frerks, G.E. ; Klem, B. - \ 2007
Amsterdam/Wageningen : BartKlemResearch / Wageningen Universiteit - 92
ontwikkelingshulp - stabiliteit - ontwikkeling - ontwikkelingsbeleid - herstel - preventie - conflict - oorlog - niet-gouvernementele organisaties - ontwikkelingsprogramma's - beoordeling - ontwikkelingslanden - nederland - vrede - reconstructie - development aid - stability - development - development policy - rehabilitation - prevention - war - non-governmental organizations - development programmes - assessment - developing countries - netherlands - peace - reconstruction
Interpretation of results from on-farm experiments: manure-nitrogen recovery on grassland as affected by manure quality and application technique. 1. An agronomic analysis
Groot, J.C.J. ; Ploeg, J.D. van der; Verhoeven, F.P.M. ; Lantinga, E.A. - \ 2007
NJAS Wageningen Journal of Life Sciences 54 (2007)3. - ISSN 1573-5214 - p. 235 - 254.
melkveehouderij - mest - graslandbeheer - stikstofmeststoffen - organisch bodemmateriaal - stabiliteit - agronomische kenmerken - bemesting - dairy farming - manures - grassland management - nitrogen fertilizers - soil organic matter - stability - agronomic characteristics - fertilizer application - cattle slurry - dairy farms - ammonia volatilization - soil - netherlands - management - efficiency - reduction - herbage - performance
In a 5-year field experiment, a comparison was made between the manure application practices of two adjacent dairy farms in the north of the Netherlands. Grassland management systems at Drogeham and Harkema contrasted in manure application technique (surface application versus shallow injection, respectively), quality of applied manure (slurry + MX: slurry with Euromestmix® clay mineral additive versus regular slurry), and some relevant site characteristics (high versus low soil organic matter content and soil moisture supply). Effects of manure types and application techniques, and treatment of the soil with a micro-organism supplement, were tested in a factorial experiment at the two sites, two blocks per site, one with and one without additional application of 157 kg N ha¿1 year¿1 inorganic fertilizer. Apparent N recovery was higher after shallow injection than after surface application. For plots receiving no additional inorganic fertilizer, this difference was largest for slurry + MX applied at site Harkema, since this slurry¿site combination resulted in the highest observed average apparent N recovery following shallow injection (47%) and the lowest N recovery following surface application (20%). For plots receiving additional inorganic fertilizer N the contrasts between treatments were less pronounced. Year effects on N uptake and dry matter production could be related to cumulative temperature and precipitation surplus over the growing season. A simple comparison between the grassland management systems was carried out based on the response curves derived from the experiment. This demonstrated that the grassland system where slurry was applied by shallow injection is not necessarily the lowest in actual amount of N not accounted for (i.e., potentially lost). The efficiency of the Harkema system strongly depended on high N recovery, but showed high potential losses in some years and a high herbage crude protein content in other years, due to the low DM production capacity. On the other hand, the Drogeham system was tuned to high DM production and was characterized by higher system stability, as reflected by more stable relationships between DM production and N not accounted for and herbage crude protein content. These differences between the systems were probably to a large extent caused by differences in water balance and soil organic matter content
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