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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    Ionic liquid pre-treatment of microalgae and extraction of biomolecules
    Desai, Rupali K. - \ 2016
    Wageningen University. Promotor(en): Michel Eppink; Rene Wijffels. - Wageningen : Wageningen University - ISBN 9789462579804 - 126
    salts - liquids - fractionation - extraction - hydrophobicity - algae - biomass production - zouten - vloeistoffen (liquids) - fractionering - extractie - hydrofobiciteit - algen - biomassa productie

    Liquid-liquid extraction (LLE) techniques are widely used in separation primarily due to ease of scale up. Conventional (LLE) systems based on organic solvents are not suitable for extraction of fragile molecules such as proteins as it would result in denaturation. On the other hand aqueous biphasic system though suitable for extraction of proteins they are restricted by limited polarity range. Ionic liquids are salts which are liquid at room temperature. Ionic liquids have gained interest in extraction over the past years due to its non-volatility and tunable property. In this thesis we explored the feasibility of using two ionic liquid based systems for extraction: 1) Ionic liquid based aqueous two phase system for extraction of microalgae proteins and 2) ionic liquid based emulsions for separation of hydrophilic (e.g. proteins) and hydrophobic (e.g. pigments) components from complex biomass such as microalgae. Additionally the influence of IL pre-treatment on microalgae cell walls and subsequent fractionation of its components (e.g. proteins, pigments, lipids) was also investigated.

    Electrically excited liquid water : lessons from floating water bridge
    Wexler, A.D. - \ 2016
    Wageningen University. Promotor(en): Cees Buisman, co-promotor(en): J. Woisetschläger; E.C. Fuchs. - Wageningen : Wageningen University - ISBN 9789462577039 - 223
    water - liquids - electric field - thermodynamics - bridges - equilibrium - disequilibrium - electrodynamics - nuclear magnetic resonance - neutron scattering - infrared spectroscopy - spectroscopy - gas chromatography - electrical conductivity - interferometry - spectral analysis - physics - water - vloeistoffen (liquids) - elektrisch veld - thermodynamica - bruggen - evenwicht - verstoord evenwicht - elektrodynamica - kernmagnetische resonantie - neutronenverstrooiing - infraroodspectroscopie - spectroscopie - gaschromatografie - elektrische geleidbaarheid - interferometrie - spectraalanalyse - fysica

    Water is essential to a healthy and secure world. Developing new technologies which can take full advantage of the unique attributes of water is important for meeting the ever increasing global demand while reducing the production footprint. Water exhibits unexpected departures in more than 70 physical and chemical properties compared to other molecular species of similar chemical composition. The principal cause for this behavior is ascribed to the large number of hydrogen bonds which form between neighboring water molecules. Hydrogen bonds are moderately strong in water and exhibit both electrostatic as well as covalent character. When examining the liquid state these interactions play a significantly role in moderating the interchange between dynamics and structure. In disordered materials such as a liquid there are three length scales of importance: 1) at the microscopic molecular level interactions dominate, 2) the macroscopic level where classical forces act upon the statistically isotropic medium, and 3) the mesoscopic level where heterogeneous interactions dominate through evolving transient structures each with unique dynamical behaviors. The mesoscale is important to most environmental and biological processes and is even more poorly understood than the liquid state in general. The aim of this thesis is to explore the extended molecular behavior of liquid water excited by strong electric field gradients.

    The floating water bridge belongs to a larger class of phenomena called electrohydrodynamic (EHD) liquid bridges. These self-suspending liquid catenaries can occur in a number of polar liquids provided the conductivity is low. They exhibit elevated temperatures and bidirectional flow patterns, as well as sub-Hz diameter oscillations. The flow behavior and dynamics of these bridges is complex but can be addressed by continuum level EHD theory. The polarizing effect of the electric field gradient accelerates the fluid tangentially along the surface resulting in a Taylor pump which supplies the bridge with liquid. The free hanging section is stable against gravity within a band of operational parameters whereby the electric field strength is sufficient confine fluid elements within the bridge. A standardized protocol for operating stable EHD bridges in multiple configurations is developed and presented. This is the primary tool used throughout the thesis and provides a macroscopic object for the experimental examination of how forces which typically only occur over a few nanometers in nature affect the organization of polar liquids, notably water. In order to examine the role that the electric field gradient plays in the observed molecular changes found in EHD bridges a simple point-plane electrode system was also employed.

    There are available a number of tools which provide complimentary information on chemical and physical processes occurring in the liquid state. A brief introduction is given on the interaction between electromagnetic waves and matter with respect to field theory and methods from atomic physics. The basis for interaction over different length scales is established. Electrochemical characterization includes the quantification and identification of the charge carrying species present, the relative proton concentration, and the complex dielectric response. The vibrational and rotational motion of molecules is measured with a combination of infrared emission spectroscopy and imaging and permits the detection of both the thermal bath and non-equilibrium molecular excited states. The local structure of the liquid matter contained in the bridge can be elucidated through the methods discussed here. X-rays provide information on the electron density whereas neutrons reveal nuclear positions. Together with isotope substitution a complete picture of the motionally averaged local structure of the liquid in the bridge can be recovered. QENS is a special case of inelastic scattering which permits the measurement of diffusion, relaxation, and other slow energy or mass transfer modes in materials using a time-of-flight spectrometer. This data compliments the NMR methods used herein specifically to probe the environment of protons in the system; and to provide clues about the strength of both intra- intermolecular coupling in the system. Very small perturbations in the optical properties of a liquid can be detected using interferometry; these ultimately reflect changes in the polarizability of the liquid which can arise from changes in physical properties. Raman scattering is an inelastic method which can probe changes to the polarizability of a liquid that reflect shifts in the local molecular environment and can be used to determine both local and non-local vibrational coupling.

    Magnetic resonance imaging was used to track the flow field present in the bridge without the use of tracer particles; revealing that the bridge has a layered structure, with distinct flow regimes lying one on top of the other. Investigation of the electrochemistry in the water bridge found that protons account for 87% of the charge transport in the bridge. Impedance spectroscopy and pH measurement corroborate the finding that a proton gradient forms across the entire system. The results from elastic neutron and X-ray scattering reveal that the static structure is unchanged within the given accuracy of the employed measurements. However, the systematic analysis of the data using a reverse Monte Carlo computer simulation revealed significant dynamical changes that are reliable above the limited instrument precision. The imposed electric field of an EHD bridge distorts the local Coulombic interactions between molecules altering the dielectric relaxation pathway so that it becomes more favorable for the absorbed energy to become trapped locally for a longer period of time. The electric field in the bridge system is not uniform. Strong field gradients are present which stimulate changes in the molecular polarizability, generating gradients of physical properties, and restricting the allowed rotational-vibrational relaxation transitions. These trends are comparable to those from ultrafast relaxation measurements where the vibrational lifetime of the OH stretch of HDO was found to be significantly shorter in the bridge than in the neat liquid. This absorbed energy, however, remained trapped in a local intermediate state longer in the bridge before being released as a thermal perturbation. The nuclear relaxation dynamics in a glycerol bridge showed similar behavior where the transverse and longitudinal magnetization lifetimes diverged from the expectation values given the systems temperature.

    From the experimental observations several features of electrically excited water appear. At the gross continuum level the operation of a floating water bridge results in the production of a charge imbalance between anolyte and catholyte. This is in part due to the enhanced proton mobility in the bridge. Protons no longer are confined to the hydrogen bond mediated Grotthuss mechanism but can travel even faster through a delocalized state. This means that charge can be pumped faster than it can be neutralized resulting in the observed electrochemical differences. The energy level of protons in the conduction channel is the difference between the ground and excited state levels observed as a non-thermal emission feature in the mid-infrared. The proton channel will be active over relatively short distances and will experience interruptions due to fluctuations in molecular position driven by local force gradients. These channels are localized and discontinuous providing the physical basis for the onset of mesoscale dynamic heterogeneity in the excited liquid. The picture begins to emerge whereby local trapping states and long-range cooperative coupling modes dynamically exchange energy. The energy exchange is far from equilibrium and supports multiple transfer mechanisms. At the mesoscale the excited state exhibits traits of a chaotic dynamical system and provides a varied energetic landscape whereby rotational-vibrational transition dipoles, nuclear spin states, and thermodynamic potentials, such as the configurational entropy, non-adiabatically – that is there is a pumping of heat in response to the induced fluctuating gradient fields. The transfer of perturbations from local to collective modes and vice versa requires that the chemical, thermal, and electromagnetic potentials present in the molecular milieu be linked to the entropy production.

    This early foray into the non-equilibrium dynamics and mesoscale organization of electrically excited liquid water opens an opportunity to develop technologies which better mimic nature. Taking biological systems as the exemplary standard by which to compare it is necessary to develop soft matter based technical systems which take advantage of the link between electric, magnetic, and thermal fields to drive chemical and physical processes with higher efficiency. Water, as well as other polar liquids, can be locally controlled so as to induce spatial variation in the chemical potential whereby one can imagine a reactor where disparate physical or chemical process can occur in close proximity without the need for rigid segregating structures. Furthermore, this level of control is dynamical such that the organization of the partitioning in the liquid can be changed in time so that the total energy requirement of the intended process is optimized. With such an approach it is conceivable that the size, complexity, and energetic costs of performing many industrial and municipal processes can be reduced. Rather than treating liquids as bulk fluids the opportunity presents itself to use the internal structure and dynamics of liquids to build fluid technologies.

    Colloids at liquid interfaces: dynamics and organization
    Ershov, D.S. - \ 2014
    Wageningen University. Promotor(en): Jasper van der Gucht, co-promotor(en): Martien Cohen Stuart. - Wageningen : Wageningen University - ISBN 9789461738943 - 127
    colloïden - oppervlaktechemie - grensvlak - oppervlakteverschijnselen - capillairen - vloeistoffen (liquids) - colloids - surface chemistry - interface - surface phenomena - capillaries - liquids

    This thesis deals with spherical microparticles trapped at liquid interfaces. It focuses on two aspects of their behavior: firstly, the effect of the curvature of a liquid interface on interparticle interactions and their organization; secondly, the mobility of particles at visco-elastic interfaces.

    In Chapter 2of this thesis we showed that it is possible to induce capillary interactions between spherical microparticles with homogeneous surface chemistry by tailoring the curvature of the liquid interface. If the interfacial curvature is anisotropic, the constraint of constant contact angle along the contact line can only be satisfied if the interface is deformed locally. These deformations create excess surface area, which changes when two particles approach each other. This leads to a change in the surface free energy, which manifests itself as a capillary interaction between the particles.

    To study the effect of curvature on the interactions between particles, we created oil-water interfaces of different shape (ellipsoid, dumbbell, torus and squares) and added spherical negatively charged particles that adsorbed at these interfaces. On all these interfaces, we observed quadrupolar capillary interactions that organized the particles into square lattices. The order of this organization increased with increasing curvature anisotropy, indicating that capillary interactions are stronger as well. By contrast, on flat interfaces or on spherical droplets with homogeneous curvature, no attractive interaction was observed and only at very high surface coverage did the particles order in a hexagonal lattice, as a result of repulsive interactions.

    In Chapter 3we studied the interface deformations around particles at curved interfaces and the resulting capillary interactions theoretically. We used the finite element method to solve the Young-Laplace equation for the shape of the interface around a particle and calculated the interaction potential between the particles numerically.

    The main finding of these calculations is that for an anisotropically curved interface, with two different local principal curvatures, the particle deforms the interface in two ways simultaneously: concave deformation along one principal direction and convex – along the other, thus creating a deformation field with quadrupolar symmetry. Two particles with such deformations interact favorably only if the overlapping deformations are similar (concave-concave, convex-convex), which occurs when they approach each other along one of the two principal directions. Since the two local principal directions are always perpendicular, particles interacting along them will tend to arrange into a square pattern.

    As a consequence of the quadrupolar deformation field, two particles approaching each other along a line forming 45 degrees with the principal axes will repel each other (which is confirmed by our observations), because in this case the deformation fields overlap with four different “petals” (2 pairs of concave-convex), and the excessive surface area doesn’t reduce upon approaching, but increases. A system of two particles oriented at an angle with respect to the principal axis is therefore subjected to a torque rotating the axis of the system so that it gets aligned with one of the two principal directions. The torque magnitude reaches its maximum when the system’s axis is at an angle of 45 degrees with respect to the principal direction and decreases to 0 when the axis is aligned with one of the principal directions.

    The family of interaction potentials we obtained allows for calculating the minimum deviatoric curvature needed to initialize capillary interactions strong enough to compete with thermal energy, so that a stable organization can be expected. The calculated value was very close to the deviatoric curvature where ordering was observed experimentally in Chapter 2.

    In Chapter 4we studied the mobility of 3 mm polystyrene particles in a monolayer of 1.5 mm core-shell microparticles deposited at flat air-water interfaces; all the particles present in the system were stabilized by negative charges.

    In this exploratory chapter we made an attempt to characterize the mechanical properties of such monolayers by analyzing the mobility of the larger tracer particles in the monolayer. With increasing particle density of the monolayer, we observed that the mean-square displacement of the tracer particles was reduced, which can be interpreted as an increase of the viscosity of the monolayer. At very high densities the motion of the particles became subdiffusive and confined, pointing at elasticity of the monolayer. We also studied correlated movements between neighboring particles in an attempt to do two-point interfacial microrheology. A comparison between the one-point and two-point methods shows clear indications of heterogeneous dynamics of the tracer particles. Our results therefore call for a further development of two-point microrheology at interfaces.

    In Chapter 5we used tracer particles to study the properties of thin cross-linked actin networks deposited at the surface of oil droplets. These networks are a model system for the intracellular actin cortex. We used the generalized Stokes-Einstein relation to extract the complex frequency-dependent shear modulus of such networks from the movement of the added tracer particles. We studied the effects of the length of actin filaments and the cross-linker concentration on the mechanical properties of these layers.

    The advantage of this system is that actin networks are freely accessible from the water phase, and therefore can be subjected to in-situ addition of cross-linkers, enzymes or other chemicals of interest. Using this, we managed to show strong stiffening after addition of myosin motor proteins and ATP, which we ascribed to contraction of the actin-myosin network.

    Nieuwe techniek zet zwakke zaden aan de kant
    Derkx, R. - \ 2005
    De Boomkwekerij (2005)42. - ISSN 0923-2443 - p. 12 - 14.
    zaadkeuring - zaadkwaliteit - sorteermachines - zaden - technische vooruitgang - stratificatie (zaden) - vloeistoffen (liquids) - seed certification - seed quality - sorters - seeds - technical progress - stratification - liquids
    Een nieuwe manier van uitsorteren van slechte boomzaden is 'vloeistofscheiden'. Een geslaagde vloeistofscheiding bij vijf soorten boomzaden laat zien, door te spelen met de dichtheid van vloeistoffen, dat men goede, minder goede en zwakke zaden apart in handen krijgt. De keuze voor uitzaai is dan snel gemaakt
    Warmtewisselaars met gekromde buizen
    Kelder, J.D.H. ; Klerk, S. de - \ 2004
    Voedingsmiddelentechnologie 37 (2004)13. - ISSN 0042-7934 - p. 14 - 16.
    warmteuitwisseling - voedseltechnologie - uitrusting - automatisering - thermisch rendement - reologie - vloeistoffen (liquids) - stroming - heat exchange - food technology - equipment - automation - thermal efficiency - rheology - liquids - flow
    Ultra High Temperature (UHT) sterilisation is a commonly applied technique to preserve liquid food products. Stork Food & Dairy Systems has marketed coiled tubular UHT-sterilisers. For viscous and especially for gelatinising foods (e.g. custard and pudding) spiral sterilisers bring superior performance. Heat transfer greatly increases and required temperatures are attained faster, thus reducing processing time. Coiled sterilisers are therefore shorter and more compact, minimising the loss of quality factors due to the heat treatment. Finally, gelatinisation occurs rapidly and uniformly, and de reduced thermo-mechanical stresses enable a potentially lower amount of starch needed to obtain a target consistency
    Effects of capillarity and heterogeneity on flow of organic liquid in soil
    Wipfler, E.L. - \ 2003
    Wageningen University. Promotor(en): Sjoerd van der Zee. - Wageningen : Wageningen Universiteit - ISBN 9789058088468 - 147
    bodem - water - oliën - lucht - stroming - waterstroming - luchtstroming - capillaire opstijging - vloeistoffen (fluids) - vloeistoffen (liquids) - modellen - drainage - bodemverontreiniging - soil - water - oils - air - flow - water flow - air flow - capillary rise - fluids - liquids - models - drainage - soil pollution

    Contamination of groundwater by organic liquids, such as gasoline, fuel oils and chlorinated hydrocarbons, forms a serious treat to subsurface water resources. These liquids have a low miscibility with water and move as a discrete liquid phase. A small part of the liquid may dissolve in water and small concentrations can be hazardous for humans. These organic liquids that are also referred to as Non-Aqueous Phase Liquids (NAPLs), may enter the subsurface from a surface spill or a leaking underground pipe or tank. Following a release of sufficient NAPL into the subsurface, NAPL moves through the pores of the soil due to gravitational and capillary forces.

    An enhanced understanding of NAPL flow in the subsurface is needed to identify the critical processes and to determine key parameters in the context of remediation strategies at the field scale. In this thesis we study the behavior of NAPL in soil experimentally and numerically. we focus on the physical aspects of this behavior in the unsaturated part of the soil. This implies that we study the movement, interaction and (re-)distribution in a porous medium (soil) of three fluid phases: water, NAPL and air. The porous medium is water-wet, i.e. water is the wetting fluid, NAPL is the intermediate wetting fluid and air is the non-wetting fluid. This leads to typical three-phase flow behavior. We focus on two problems that are both related to NAPL redistribution into unsaturated soil after a spill: (1) non-drainable residual NAPL and (2) the effect of soil layers on the redistribution of NAPL after a spill. In addition to the introduction, the thesis contains 4 chapters which can be read as self-contained papers.

    Non-drainable residual NAPL is considered to be the NAPL that remains in the capillaries of a porous medium after (gravity) drainage and displacement by air in the presence of residual water in a water-wet soil. Although for remediation strategies it is important to consider this residual NAPL, until now it has not been incorporated into multi phase flow models. In Chapter 2 we develop a constitutive set of saturation-capillary pressure ( Pc-S ) relationships that accounts for non-drainable residual NAPL and that can be used by multi-phase flow models. These relationships are derived from a conceptual pore scale model of which the soil is represented by packed spheres. According to the model, NAPL becomes immobilized (residual) below a certain critical total liquid saturation, S tc. This critical total liquid saturation is porous medium and fluid dependent. Next, the non-drainable residual NAPL saturation increases, when the spreading coefficient of a NAPL decreases. Furthermore, a higher water saturation results in a lower non-drainable residual saturation. Although the model adequately simulated one individual experimental non-drainable residual NAPL data set, this agreement is a shallow basis for assessing whether the model assumptions are valid.

    For this purpose we developed an experiment especially designed to measure three-phase Pc-S relationships and non-drainable residual saturation including independent measurement of the water saturation and pressure. We performed four experiments. We used the fluids water, non-spreading dodecane and air, and sand as the porous medium. The measured non-drainable residual saturation was at most 0.081. From the experimental results no correlation could be observed between the water saturation and the residual NAPL saturation. This might indicate that other mechanisms are involved that are not captured by the constitutive model. In advance of the development of the experimental set up, we searched in the literature for available macroscale experimental data that could provide us with non-drainable residual saturation data that are related to porous medium properties, fluid properties and fluid saturations. After a careful selection we obtained 26 non-drainable residual NAPL data from 9 references. Measured values of non-drainable residual saturation varied between 0.001 and 023. From these data only a relationship between the spreading coefficient Cs , and the residual saturation S or , could be assessed. The value of S or decreases as Cs becomes less negative. It would require a much more comparable description of the different porous media, and a systematic data acquisition for S or as a function of macroscale properties to assess which other factor than the spreading coefficient might be hidden in the data. Changes of porous medium properties such as permeability and porosity across an interface between two soil layers might change the redistribution of NAPL. The mobility may decrease or increase across the interface, which is dependent on the permeability of the layers, the capillarity of the layers and the wetting role that is played by the NAPL with respect to water and air. The effect of these changes have been studied in Chapter 4 and 5.

    In Chapter 4 we focused on the effect of an inclined soil layer with respect to the watertable. Two experiments were performed using a sand filled transparent chamber. The first experiment consisted of Light-NAPL infiltration into a fine sand matrix containing a coarse sand layer and the second experiment consisted of LNAPL infiltration into a coarse sand matrix containing a fine sand layer. The sand was partially saturated with water. We modeled the experiments numerically. The observed LNAPL behavior can be understood by considering that LNAPL might encounter two types of barriers. On the one hand, it may accumulate and spread above a coarse sand layer, that has a low water saturation and, that acts as a capillary barrier for the LNAPL before it may infiltrate into the layer. An on the other hand, it may accumulate and spread above a water saturated fine sand layer that has a high entry pressure for the infiltrating LNAPL. Sensitivity analysis performed with the numerical model shows that the qualitative LNAPL redistribution, in case of inclined layers, is mainly subject to the capillarity contrast between sands.

    In Chapter 5 we considered Dense-NAPL infiltration into a water unsaturated porous medium that consists of two horizontal layers, of which the top layer has a lower intrinsic permeability than the bottom layer. The layer interface forms a barrier to DNAPL flow, which causes the DNAPL to spread out horizontally just above the interface. We have developed an analytical approximation to estimate the DNAPL pressure and saturation and the horizontal extension of the DNAPL plume just above the layer interface at steady state for low water saturations. The analytical approximation shows that the steady state DNAPL infiltration is determined by five dimensionless numbers: the heterogeneity factorg, the Brooks and Corey capillary pressure parameterl, the gravity number Ng , the ratio of the capillary and gravity numbers Nc/Ng , and the critical DNAPL pressure P oc, which indicates the effect of the water saturation on the flow of DNAPL. We compared its predictions with the results of a numerical three-phase flow simulator for a number of parameter combinations. For most of these combinations the analytical approximation predicts the DNAPL pressure and saturation profiles at the interface adequately, although it slightly underestimates the horizontal spreading of the plume at the interface. Using the analytical approximation, we carried out a sensitivity study with respect to the maximum horizontal extension of the plume. The extension of the plumes appears to be highly sensitive to variation of the dimensionless numbers P oc,landg. The extension increases for increasing values oflandgand for decreasing values of P oc.

    Tabaksblad in witte- en rodekool
    Everaarts, A.P. - \ 2000
    PAV-bulletin. Vollegrondsgroenteteelt / Praktijkonderzoek voor de Akkerbouw en de Vollegrondsgroenteteelt 4 (2000)3. - ISSN 1385-5298 - p. 24 - 26.
    koolsoorten - afwijkingen, planten - plantenziektekunde - symptomen - misvormingen - gewasbescherming - cultuurmethoden - brassica oleracea var. capitata - groeitempo - sapstroom - vloeistoffen (liquids) - cabbages - brassica oleracea var. capitata - plant disorders - plant pathology - symptoms - malformations - plant protection - cultural methods - growth rate - sap flow - liquids
    Onderzoek naar tabaksblad in kool toont aan dat deze groeiafwijking ontstaat tijdens de teelt. Factoren die tijdens de teelt van sluitkool het optreden van tabaksblad (inwendig rand) in belangrijke mate beinvloeden zijn de groeisnelheid en de waterhuishouding van het gewas
    Source-sink relations in transgenic tobacco with modified trehalose metabolism : a comparative labelling study with the stable isotopes 13C and 15N of wildtype and five transgenic types
    Visser, A.J.C. de; Leeuwen, P.H. van; Pot, C.S. - \ 1999
    Wageningen : AB-DLO (Note / Agricultural Research Department, Research Institute for Agrobiology and Soil Fertility 179) - 32
    plantengroeiregulatoren - genetische modificatie - nicotiana - trehalose - vloeistoffen (liquids) - sapstroom - distributie - plant growth regulators - genetic engineering - liquids - sap flow - distribution
    Fosfaat moet in dikke fractie bij mestbewerking op varkensbedrijf
    Mandersloot, F. - \ 1999
    Praktijkonderzoek varkenshouderij 13 (1999)3. - ISSN 1382-0346 - p. 12 - 14.
    varkensmest - dierlijke meststoffen - fosfor - scheiding - vloeistoffen (liquids) - mestverwerking - mestoverschotten - pig manure - animal manures - phosphorus - separation - liquids - manure treatment - manure surpluses
    Mestbewerking op bedrijfsniveau blijft financieel gezien een moeilijke zaak. Mechanische scheiding is op bedrijven met vleesvarkens vaak te duur. Bezinken van zeugenmest heeft wel perspectief voor bedrijven die grond beschikbaar hebben om de dunne fractie uit te rijden.
    Dubbele emulsies controleren afgifte of scheiding voedingscomponenten
    Horst, B.M. van der; Langelaan, H.C. - \ 1999
    Voedingsmiddelentechnologie 32 (1999)24. - ISSN 0042-7934 - p. 10 - 16.
    ingrediënten - voedselindustrie - voedseltechnologie - emulsies - dispersie - emulgeermiddelen - scheiding - segregatie - zuiveren - filtratie - technologie - verwerking - vloeistoffen (liquids) - pigmenten - modellen - ingredients - food industry - food technology - emulsions - dispersion - emulsifiers - separation - segregation - purification - filtration - technology - processing - liquids - pigments - models
    Een nieuw concept voor het scheiden van voedingscomponenten, alsmede voor toepassing in de cosmetische en farmaceutische industrie. Het onderzoek op dit gebied door ATO-DLO is gericht op het encapsuleren van (vluchtige) componenten, nieuwe emulgeringsmethoden, bereidingsaspecten, lange termijnstabiliteit, reologische eigenschappen, typen emulgatoren en gecontroleerde afgifte. Tevens werd een modelsysteem ontwikkeld voor het verwijderen van ongewenste componenten uit voedingsmiddelen
    Vochtverbruik en droogtegevoeligheid van voedergewassen : experimenteel onderzoek 1994 - 1996
    Smid, H.G. ; Grashoff, C. ; Aarts, H.F.M. - \ 1998
    Wageningen : AB-DLO (Rapport / Dienst Landbouwkundig Onderzoek, Instituut voor Agrobiologisch en Bodemvruchtbaarheidsonderzoek 91)
    voedergewassen - oogsttoename - oogstverliezen - opbrengsten - groei - gewassen - oogstschade - beschadigingen door droogte - waterbehoefte - vloeistoffen (liquids) - absorptie - emissie - omloop - bodemwatergehalte - fodder crops - yield increases - yield losses - yields - growth - crops - crop damage - drought injury - water requirements - liquids - absorption - emission - circulation - soil water content
    Levering drie Rossum-stuwen Schouwen West
    Boiten, W. - \ 1998
    Wageningen : Landbouwuniversiteit Wageningen (Rapport / Landbouwuniversiteit Wageningen, Afdeling Waterhuishouding 76) - 5
    hydrodynamica - vloeistoffen (liquids) - vloeistoffen (fluids) - stroming - kanalen - kanalen, klein - meting - snelheid - nederland - zeeland - zeeuwse eilanden - hydrodynamics - liquids - fluids - flow - canals - channels - measurement - velocity - netherlands - zeeland - zeeuwse eilanden
    Effecten van het vernevelen van vloeistoffen ter verlaging van de stofconcentratie in pluimveestallen
    Ellen, H.H. ; Drost, H. - \ 1998
    Beekbergen : Praktijkonderzoek Pluimveehouderij (PP uitgave : praktijkonderzoek pluimveehouderij 76) - 33
    pluimveehouderij - pluimveehokken - luchtverontreiniging - stof - stofbestrijding - vernevelen - spuiten - vloeistoffen (liquids) - arbeidsomstandigheden - poultry farming - poultry housing - air pollution - dust - dust control - fogging - spraying - liquids - working conditions
    Het Praktijkonderzoek Pluimveehouderij 'Het Spelderholt' (PP) en het Instituut voor Milieu-en Agritechniek (IMAG-DLO) hebben gezamenlijk onderzoek opgestart naar verlaging van de stofconcentratie in pluimveestallen. Dit heeft geresulteerd in het project 'Effecten van het vernevelen van vloeistoffen ter verlaging van de stofconcentratie in pluimveestallen'. Op basis van een literatuurstudie is binnen dit project gekozen om het terugdringen van de stofconcentratie in pluimveestallen door middel van hetvernevelen van vloeistoffen nader te bekijken.
    Mestscheiding met stro
    Kant, P. ; Blanken, K. - \ 1998
    Praktijkonderzoek Rundvee, Schapen en Paarden. Praktijkonderzoek 11 (1998)1. - ISSN 1386-8470 - p. 20 - 22.
    mest - vloeibare meststoffen - rundveedrijfmest - varkens - scheiding - vloeistoffen (liquids) - klaring - stro - mestoverschotten - mestverwerking - manures - liquid manures - cattle slurry - pigs - separation - liquids - clarification - straw - manure surpluses - manure treatment
    Mestscheiding staat regelmatig in de belangstelling. Er kunnen allerlei redenen zijn waarom het creëren van een dikke en een dunne fractie uit gewone mest interessant kan zijn, zoals mestafzet of een preciezere bemesting. Vaak zijn echter de kosten van het scheiden te hoog. Het PR heeft daarom gekeken naar de technische mogelijkheden van een eenvoudige scheidingstechniek met stro als filtermedium. Het lijkt mogelijk een groot deel van de fosfaat in de dikke fractie te concentreren, waarbij echter weleen deel van de stikstof verloren gaat.
    Modelling water and nutrient uptake of crops grown in protected cultivation
    Willigen, P. de; Heinen, M. - \ 1998
    Acta Horticulturae 456 (1998). - ISSN 0567-7572 - p. 227 - 236.
    bodem - elektrische eigenschappen - elektrische geleiding - magnetische eigenschappen - vloeistoffen (liquids) - absorptie - modellen - onderzoek - computersimulatie - simulatie - simulatiemodellen - glastuinbouw - soil - electrical properties - electrical conductance - magnetic properties - liquids - absorption - models - research - computer simulation - simulation - simulation models - greenhouse horticulture
    This paper presents results of model calculations on uptake of water and nutrients by a lettuce crop grown in a sand bed. Emphasis is on the effect of salt concentration (osmotic head) on water uptake. This effect was studied using a two-dimensional model of water and nutrient transport in and uptake from a rooting medium. The main conclusion is that under normal conditions as found in Dutch horticulture, osmotic effect on water uptake is not important, but that it depends on the distribution of salts with respect to that of the roots.
    De 'beschikbaarheid' van zware metalen voor planten.
    Lexmond, T.M. ; Castilho, P. del - \ 1998
    Bodem 8 (1998). - ISSN 0925-1650 - p. 14 - 16.
    bodem - zware metalen - vloeistoffen (liquids) - absorptie - wortels - soil - heavy metals - liquids - absorption - roots
    The role of macromolecular stability in desiccation tolerance
    Wolkers, W.F. - \ 1998
    Agricultural University. Promotor(en): L.H.W. van der Plas; F.A. Hoekstra. - S.l. : Wolkers - ISBN 9789054858805 - 244
    vloeistoffen (liquids) - absorptie - emissie - omloop - veroudering - abcissie - degeneratie - necrose - verouderen - verwelking - biochemie - metabolisme - polymeren - moleculaire biologie - biofysica - eiwitten - enzymen - nucleïnezuren - celfysiologie - liquids - absorption - emission - circulation - senescence - abscission - degeneration - necrosis - aging - wilting - biochemistry - metabolism - polymers - molecular biology - biophysics - proteins - enzymes - nucleic acids - cell physiology

    The work presented in this thesis concerns a study on the molecular interactions that play a role in the macromolecular stability of desiccation-tolerant higher plant organs. Fourier transform infrared microspectroscopy was used as the main experimental technique to assess macromolecular structures within their native environment.

    Protein secondary structure and membrane phase behavior of Typha latifolia pollen were studied in the course of accelerated aging. The overall protein secondary structure of fresh pollen highly resembled that of aged pollen, which indicates that endogenous proteins in these pollen are very stable, at least with respect to their conformation. In contrast, large changes in membrane phase behavior were detected between fresh and aged pollen. Membranes isolated from fresh pollen occurred mainly in the liquid crystalline phase at room temperature, whereas the membranes of aged pollen were at least partly in the gel phase (Chapter 2).

    The in situ heat stability of the proteins in this pollen was studied as a function of the water content of the pollen. Temperature-induced denaturation of proteins was accompanied by the formation of intermolecular extendedbeta-sheet structures. Below 0.16 g H 2 O g -1dry weight (DW), the temperature at which the proteins began to denature increased rapidly and the extent of protein structural rearrangements due to heating decreased (Chapter 3).

    Inspection of the overall protein secondary structure of thin slices of embryo axes of onion, white cabbage and radish seeds did not show signs of protein aggregation and denaturation after long-term dry storage. It was concluded that, despite the loss of viability and the long postmortem storage period, secondary structure of proteins in desiccation-tolerant dry seed is very stable and conserved during at least several decades of open storage (Chapter 4).

    Adaptations in overall protein secondary structure in association with the acquisition of desiccation tolerance were studied using isolated immature maize embryos. Isolated immature maize ( Zea mays ) embryos acquire tolerance to rapid drying between 22 and 25 days after pollination (DAP) and to slow drying from 18-DAP onwards. In fresh, viable 20- and 25-DAP embryo axes, the overall protein secondary structure was identical, and this was maintained after flash drying. On rapid drying, 20-DAP axes showed signs of protein breakdown and lost viability. Rapidly dried 25-DAP embryos germinated and had a protein profile similar to the fresh control. On slow drying, thealpha-helical contribution in both the 20- and 25-DAP embryo axes increased when compared with that in the fresh controls, and survival of desiccation was high. The protein profile in dry mature axes resembled that after slow drying of the immature axes. Rapid drying resulted in an almost complete loss of membrane integrity in 20-DAP embryo axes and much less so in 25-DAP axes. After slow drying, membrane integrity was retained in both the 20- and 25-DAP axes. It was concluded that slow drying of excised immature embryos leads to an increased proportion ofalpha-helical protein structures in their axes, which coincides with additional tolerance of desiccation stress (Chapter 5).

    A novel FTIR method was used to study glasses of pure carbohydrates and glasses in the cytoplasm of desiccation-tolerant plant organs. The method is based on a temperature study of the position of the OH-stretching vibration band (vOH). The glass transition temperatures ( Tg s) of several dry carbohydrate glasses determined by this FTIR method resembled those of produced by other methods. FTIR analysis gives additional information on the molecular properties of glassy structures. The shift ofvOH with temperature - the wavenumber-temperature coefficient (WTC) - is indicative of the average strength of hydrogen bonding in glasses. The WTC was found to be higher in sugar glasses having higher Tg . This suggests that carbohydrate glasses are more loosely packed when they have higher Tg . For Typha latifolia pollen and dried Craterostigma plantagineum leaves similarvOH vs temperature plots were obtained as for pure carbohydrate glasses, indicating that a glass transition was observed. The data suggested that the carbohydrates that are present in the cytoplasm of these plant organs are the primary components contributing to the glassy state (Chapter 6).

    In order to find a relation between desiccation tolerance and physical stability, the heat stability of proteins and the properties of the glassy matrix in several dry maturation-defective mutant seeds of Arabidopsis thaliana were studied. Proteins in dried wild-type seeds did not denature up to 150°C. In dried desiccation-sensitive lec1-1 , lec1-3 and abi3-5 seeds, protein denaturation occurs at temperatures below 100°C. In desiccation-tolerant abi3-7 and abi3-1 seeds, protein denaturation commenced above 120 and 135°C, respectively. The maximal rate of change ofvH with temperature was much higher in abi3-5 , lec1-1 and lec1-3 mutant seeds than in wild-type, abi3-1 , and abi3-7 seeds. This was interpreted as a higher molecular packing density in dried desiccation-tolerant than in dried desiccation-sensitive seeds, which is associated with a higher, respectively lower protein denaturation temperature. The generally lower physical stability of the desiccation-sensitive mutant seeds coincides with a lack of biochemical adaptations that normally occur in the later stages of seed development (Chapter 7).

    The relation between physical stability and desiccation tolerance was also studied in slowly dried (desiccation-tolerant) and rapidly dried (desiccation-sensitive) carrot somatic embryos. Although protein denaturation temperatures were similar in the embryos after slow or rapid drying, the extent of protein denaturation was higher in the rapidly dried embryos. Slowly dried embryos are in a glassy state at room temperature, whereas no clearly defined glass transition temperature was observed in the rapidly dried embryos. Moreover, the molecular packing density of the cytoplasmic glassy matrix was higher in the slowly dried embryos. While sucrose is the major soluble carbohydrate after rapid drying, on slow drying, the trisaccharide umbelliferose accumulates at the expense of sucrose. Dry umbelliferose and sucrose glasses have almost similar Tg s. Both umbelliferose and sucrose depressed the transition temperature of dry liposomal membranes equally well; prevented leakage from dry liposomes after rehydration, and preserved the secondary structure of dried proteins. The similar protecting properties in model systems and the apparent interchangeability of both sugars in viable dry somatic embryos suggest no special role for umbelliferose in the improved physical stability of the slowly dried somatic embryos. It was suggested that LEA proteins, which are synthesized during slow drying together with the sugars, are responsible for the increased stability of the slowly dried embryos (Chapter 8).

    The dehydration-sensitive polypeptide, poly-L-lysine was used as a model to study dehydration-induced conformational transitions of this polypeptide as influenced by drying rate and carbohydrates. In solution poly-L-lysine adopts a random coil conformation. Upon slow drying of small droplets of the polypeptide solution over a period of several hours, the polypeptide adopts an extendedbeta-sheet conformation. Upon fast air-drying within 2-3 minutes, the aqueous polypeptide structure is preserved. Slow air-drying in the presence of sugars also preserves the aqueous conformation and results in the formation of a glassy state having a higher Tg than that of sugar alone. The importance of direct sugar - polypeptide interaction in stabilization during slow air-drying was studied by drying the polypeptide in the presence of glucose, sucrose or dextran. Compared to dextran (and sucrose to a lesser extent), glucose gives superior protection, while having the lowest Tg and the best interacting properties. It was suggested that during slow drying, a protectant with sufficient interaction is required for preservation of the aqueous protein structure (Chapter 9).

    The structure of a D-7 LEA (late embryogenesis abundant)-like protein protein isolated from Typha latifolia pollen was studied using FTIR. In solution, the protein adopts a random coil conformation. Fast air-drying (5 minutes) leads to the formation ofalpha-helical structure, whereas slow drying (few hours) leads to bothalpha-helical and intermolecular extendedbeta-sheet structures. When dried in the presence of sucrose, the protein adopts predominantlyalpha-helical conformation, irrespective of drying rate. Drying of a mixture of LEA protein and sucrose results in the formation of a glassy state having higher Tg and a higher average strength of hydrogen bonding than a pure sucrose glass. It was suggested that LEA proteins might be involved in the formation of a tight molecular network in the dehydrating cytoplasm of anhydrobiotic organisms, which may contribute to desiccation tolerance (Chapter 10).

    Taken together, in situ FTIR studies can give additional information on the molecular organization in desiccation-tolerant cells. The added value of this approach is that molecular structures and inter-molecular interactions can be studied in intact biological systems (Chapter 11).

    Specifiek brandstofverbruik en vermogensbehoefte van trekkers = Specific fuel consumption and required power of tractors
    Straelen, B.C.P.M. van; Maeyer, E.E.A. de - \ 1997
    Wageningen : IMAG-DLO (Rapport / Dienst Landbouwkundig Onderzoek, Instituut voor Milieu- en Agritechniek 97-10) - ISBN 9789054061588 - 33
    trucks - trekkers - transportvoertuigen - kracht - trekkrachtefficiëncy - prestatieniveau - motoren - technologie - brandstoffen - vloeistoffen (liquids) - mineraaloliën - verbrandingsmotoren - dieselmotoren - aardolie - dieselolie - stookoliën - energie - efficiëntie - energiegebruik - brandstofverbruik - tractors - transporters - power - tractive efficiency - performance - engines - technology - fuels - liquids - mineral oils - internal combustion engines - diesel engines - petroleum - diesel oil - fuel oils - energy - efficiency - energy consumption - fuel consumption
    Zuivering van bloembollenspoelwater met ultrafiltratie
    Heijman, S.G.J. ; Oosterom, H.A. ; Roebroeck, E.J.A. - \ 1997
    Nieuwegein : KIWA [etc.] (Rapport Bloembollenonderzoek nr. 113) - 33
    rioolwater - afvalwater - landbouw - zuiveren - dialyse - oplossen - extractie - ultrafiltratie - diffusie - centrifugeren - vloeistoffen (liquids) - bloembollen - sewage - waste water - agriculture - purification - dialysis - dissolving - extraction - ultrafiltration - diffusion - centrifugation - liquids - ornamental bulbs
    Opname en afvoer van stikstof, fosfaat, kali en magnesium bij spruitkool
    Everaarts, A. - \ 1997
    PAV-bulletin. Vollegrondsgroenteteelt / Praktijkonderzoek voor de Akkerbouw en de Vollegrondsgroenteteelt 1997 (1997)2. - ISSN 1385-5298 - p. 8 - 10.
    brassica oleracea var. gemmifera - spruitjes - vloeistoffen (liquids) - absorptie - emissie - omloop - groei - ontwikkeling - ontogenie - stikstof - fosfor - kalium - magnesium - trofische graden - voedingsstoffen - hydrobiologie - zaaitijd - planttijd - rijenafstanden - plantdichtheid - oogsttoename - oogstverliezen - opbrengsten - brassica oleracea var. gemmifera - brussels sprouts - liquids - absorption - emission - circulation - growth - development - ontogeny - nitrogen - phosphorus - potassium - magnesium - trophic levels - nutrients - hydrobiology - sowing date - planting date - row spacing - plant density - yield increases - yield losses - yields
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