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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    Morphological and physiological responses of the potato stem transport tissues to dehydration stress
    Aliche, Ernest B. ; Prusova-Bourke, Alena ; Ruiz-Sanchez, Mariam ; Oortwijn, Marian ; Gerkema, Edo ; As, Henk Van; Visser, Richard G.F. ; Linden, C.G. van der - \ 2020
    Planta 251 (2020)2. - ISSN 0032-0935
    Drought - MRI - Phloem - Potato - Sugar transport - Xylem

    Main conclusion: Adaptation of the xylem under dehydration to smaller sized vessels and the increase in xylem density per stem area facilitate water transport during water-limiting conditions, and this has implications for assimilate transport during drought. Abstract: The potato stem is the communication and transport channel between the assimilate-exporting source leaves and the terminal sink tissues of the plant. During environmental stress conditions like water scarcity, which adversely affect the performance (canopy growth and tuber yield) of the potato plant, the response of stem tissues is essential, however, still understudied. In this study, we investigated the response of the stem tissues of cultivated potato grown in the greenhouse to dehydration using a multidisciplinary approach including physiological, biochemical, morphological, microscopic, and magnetic resonance imaging techniques. We observed the most significant effects of water limitation in the lower stem regions of plants. The light microscopy analysis of the potato stem sections revealed that plants exposed to this particular dehydration stress have higher total xylem density per unit area than control plants. This increase in the total xylem density was accompanied by an increase in the number of narrow-diameter xylem vessels and a decrease in the number of large-diameter xylem vessels. Our MRI approach revealed a diurnal rhythm of xylem flux between day and night, with a reduction in xylem flux that is linked to dehydration sensitivity. We also observed that sink strength was the main driver of assimilate transport through the stem in our data set. These findings may present potential breeding targets for drought tolerance in potato.

    Knowledge transfer in university–industry research partnerships: a review
    Wit-de Vries, Esther de; Dolfsma, Wilfred A. ; Windt, Henny J. van der; Gerkema, M.P. - \ 2019
    Journal of Technology Transfer 44 (2019)4. - ISSN 0892-9912 - p. 1236 - 1255.
    Absorptive capacity - Academic partnerships - Ambiguity - Barriers - Cultural differences - Facilitators - Goals - Knowledge management - Knowledge transfer - Practices - Research collaboration - Trust - University–Business - University–Industry

    This paper identifies practices that can facilitate knowledge transfer in university–industry (U–I) research partnerships by systematically reviewing extant literature. We aim to contribute to the theoretical development in the field of academic engagement and propose that knowledge transfer provides a valuable perspective. We started our review with identifying barriers and facilitators of knowledge transfer. Extant literature identified knowledge differences and differences in goals resulting from different institutional cultures as important barriers to knowledge transfer. They result in ambiguity, problems with knowledge absorption and difficulties with the application of knowledge. Trust, communication, the use of intermediaries and experience are found as facilitators for knowledge transfer that help to resolve the identified barriers. Our analysis offers practical advice for the management of academic engagement. Finally, we identified questions for future research based on inconsistencies in extant research and open questions we encountered during our analysis.

    Magnetic resonance imaging suggests functional role of previous year vessels and fibres in ring-porous sap flow resumption
    Copini, Paul ; Vergeldt, Frank J. ; Fonti, Patrick ; Sass-Klaassen, Ute ; Ouden, Jan Den; Sterck, Frank ; Decuyper, Mathieu ; Gerkema, Edo ; Windt, Carel W. ; As, Henk Van - \ 2019
    Tree Physiology 39 (2019). - ISSN 0829-318X - p. 1009 - 1018.
    Reactivation of axial water flow in ring-porous species is a complex process related to stem water content and developmental stage of both earlywood-vessel and leaf formation. Yet empirical evidence with non-destructive methods on the dynamics of water flow resumption in relation to these mechanisms is lacking. Here we combined in vivo magnetic resonance imaging and wood-anatomical observations to monitor the dynamic changes in stem water content and flow during spring reactivation in 4-year-old pedunculate oaks (Quercus robur L.) saplings. We found that previous year latewood vessels and current year developing earlywood vessels form a functional unit for water flow during growth resumption. During spring reactivation, water flow shifted from latewood towards the new earlywood, paralleling the formation of earlywood vessels and leaves. At leaves' full expansion, volumetric water content of previous rings drastically decreased due to the near-absence of water in fibre tissue. We conclude (i) that in ring-porous oak, latewood vessels play an important hydraulic role for bridging the transition between old and new water-conducting vessels and (ii) that fibre and parenchyma provides a place for water storage.
    Comparing physical and biological impacts on seston renewal in a tidal bay with extensive shellfish culture
    Jiang, Long ; Gerkema, Theo ; Wijsman, Jeroen W.M. ; Soetaert, Karline - \ 2019
    Journal of Marine Systems 194 (2019). - ISSN 0924-7963 - p. 102 - 110.
    Residence time - Seston transport - Suspension feeders - Tidal bay - Tracer experiment - Turnover time

    Shellfish cultures worldwide are often located in sheltered marine bays. The Oosterschelde is such a bay in the southwestern delta of the Netherlands, harboring extensive shellfish cultures, whose yield is partly driven by seston renewal from the North Sea. Tracer experiments performed with a three-dimensional hydrodynamic model were used to study the relative influences of benthic filtration and physical processes on seston replenishment. The model exhibited good skills in reproducing observed water level, temperature, salinity, and current velocity during 2009–2010. Turnover and residence times as indicators of water renewal showed substantial gradients from the mouth to head of the Oosterschelde. Surveyed bivalve biomass and empirical filtration rates were incorporated to estimate the effects of aquaculture on the seston concentration. The filtration created strong bio-deposition suppressing the eastward seston transport and causing <10% of external seston to be delivered to the head of the Oosterschelde. The effect of biological filtration on seston transport was comparable to that of physical forcing. This simple approach combining effects of physics and benthic communities can be applied more generally in food sustainability assessments of tidal bays.

    Beneficial use of dredged sediment to enhance salt marsh development by applying a ‘Mud Motor’
    Baptist, Martin J. ; Gerkema, T. ; Prooijen, B.C. van; Maren, D.S. van; Regteren, M. van; Schulz, K. ; Colosimo, I. ; Vroom, J. ; Kessel, T. van; Grasmeijer, B. ; Willemsen, P. ; Elschot, K. ; Groot, A.V. de; Cleveringa, J. ; Eekelen, E.M.M. van; Schuurman, F. ; Lange, H.J. de; Puijenbroek, M.E.B. van - \ 2019
    Ecological Engineering 127 (2019). - ISSN 0925-8574 - p. 312 - 323.
    Building with Nature - Nature-based solutions - Cohesive sediment - Dredging - Salt marshes - intertidal flats
    We test an innovative approach to beneficially re-use dredged sediment to enhance salt marsh development. A Mud Motor is a dredged sediment disposal in the form of a semi-continuous source of mud in a shallow tidal channel allowing natural processes to disperse the sediment to nearby mudflats and salt marshes. We describe the various steps in the design of a Mud Motor pilot: numerical simulations with a sediment transport model to explore suitable disposal locations, a tracer experiment to measure the transport fate of disposed mud, assessment of the legal requirements, and detailing the planning and technical feasibility. An extensive monitoring and research programme was designed to measure sediment transport rates and the response of intertidal mudflats and salt marshes to an increased sediment load. Measurements include the sediment transport in the tidal channel and on the shallow mudflats, the vertical accretion of intertidal mudflats and salt marsh, and the salt marsh vegetation cover and composition. In the Mud Motor pilot a total of 470,516 m 3
    of fine grained sediment (D50 of ∼10 μm) was disposed over two winter seasons, with an average of 22 sediment disposals per week of operation. Ship-based measurements revealed a periodic vertical salinity stratification that is inverted compared to a classical estuary and that is working against the asymmetric flood-dominated transport direction. Field measurements on the intertidal mudflats showed that the functioning of the Mud Motor, i.e. the successful increased mud transport toward the salt marsh, is significantly dependent on wind and wave forcing. Accretion measurements showed relatively large changes in surface elevation due to deposition and erosion of layers of
    watery mud with a thickness of up to 10 cm on a time scale of days. The measurements indicate notably higher sediment dynamics during periods of Mud Motor disposal. The salt marsh demonstrated significant vertical accretion though this has not yet led to horizontal expansion because there was more hydrodynamic stress than foreseen. In carrying out the pilot we learned that the feasibility of a Mud Motor depends on an assessment of additional travel time for the dredger, the effectiveness on salt marsh growth, reduced dredging volumes in a port, and many other practical issues. Our improved understanding on the transport processes in the channel and on the mudflats and salt marsh yields design lessons and guiding principles for future applications of sediment
    management in salt marsh development that include a Mud Motor approach
    Variation that can be expected when using particle tracking models in connectivity studies
    Hufnagl, Marc ; Payne, Mark ; Lacroix, Geneviève ; Bolle, Loes J. ; Daewel, Ute ; Dickey-Collas, Mark ; Gerkema, Theo ; Huret, Martin ; Janssen, Frank ; Kreus, Markus ; Pätsch, Johannes ; Pohlmann, Thomas ; Ruardij, Piet ; Schrum, Corinna ; Skogen, Morten D. ; Tiessen, Meinard C.H. ; Petitgas, Pierre ; Beek, Jan K.L. van; Veer, Henk W. van der; Callies, Ulrich - \ 2017
    Journal of Sea Research 127 (2017). - ISSN 1385-1101 - p. 133 - 149.
    Ensemble - Lagrangian approach - Marine protected areas - Model intercomparison - Ocean circulation - Renewable energy - Variability - Wind park

    Hydrodynamic Ocean Circulation Models and Lagrangian particle tracking models are valuable tools e.g. in coastal ecology to identify the connectivity between offshore spawning and coastal nursery areas of commercially important fish, for risk assessment and more for defining or evaluating marine protected areas. Most studies are based on only one model and do not provide levels of uncertainty. Here this uncertainty was addressed by applying a suite of 11 North Sea models to test what variability can be expected concerning connectivity. Different notional test cases were calculated related to three important and well-studied North Sea fish species: herring (Clupea harengus), and the flatfishes sole (Solea solea) and plaice (Pleuronectes platessa). For sole and plaice we determined which fraction of particles released in the respective spawning areas would reach a coastal marine protected area. For herring we determined the fraction located in a wind park after a predefined time span. As temperature is more and more a focus especially in biological and global change studies, furthermore inter-model variability in temperatures experienced by the virtual particles was determined. The main focus was on the transport variability originating from the physical models and thus biological behavior was not included. Depending on the scenario, median experienced temperatures differed by 3. °C between years. The range between the different models in one year was comparable to this temperature range observed between modelled years. Connectivity between flatfish spawning areas and the coastal protected area was highly dependent on the release location and spawning time. No particles released in the English Channel in the sole scenario reached the protected area while up to 20% of the particles released in the plaice scenario did. Interannual trends in transport directions and connectivity rates were comparable between models but absolute values displayed high variations. Most models showed systematic biases during all years in comparison to the ensemble median, indicating that in general interannual variation was represented but absolute values varied. In conclusion: variability between models is generally high and management decisions or scientific analysis using absolute values from only one single model might be biased and results or conclusions drawn from such studies need to be treated with caution. We further concluded that more true validation data for particle modelling are required.

    The dynamics of suspended particulate matter (SPM) and chlorophyll-a from intratidal to annual time scales in a coastal turbidity maximum
    Hout, C.M. van der; Witbaard, R. ; Bergman, M.J.N. ; Duineveld, G.C.A. ; Rozemeijer, M.J.C. ; Gerkema, T. - \ 2017
    Journal of Sea Research 127 (2017). - ISSN 1385-1101 - p. 105 - 118.
    Bed shear stress - Chlorophyll-a - In-situ observations - Season - SPM - Wave climate

    The analysis of 1.8. years of data gives an understanding of the response to varying forcing of suspended particulate matter (SPM) and chlorophyll-a (CHL-a) in a coastal turbidity maximum zone (TMZ). Both temporal and vertical concentration variations in the near-bed layer (0-2. m) in the shallow (11. m deep) coastal zone at 1. km off the Dutch coast are shown. Temporal variations in the concentration of both parameters are found on tidal and seasonal scales, and a marked response to episodic events (e.g. storms). The seasonal cycle in the near-bed CHL-a concentration is determined by the spring bloom. The role of the wave climate as the primary forcing in the SPM seasonal cycle is discussed. The tidal current provides a background signal, generated predominantly by local resuspension and settling and a minor role is for advection in the cross-shore and the alongshore direction. We tested the logarithmic Rouse profile to the vertical profiles of both the SPM and the CHL-a data, with respectively 84% and only 2% success. The resulting large percentage of low Rouse numbers for the SPM profiles suggest a mixed suspension is dominant in the TMZ, i.e. surface SPM concentrations are in the same order of magnitude as near-bed concentrations.

    Iron, cobalt, and gadolinium transport in methanogenic granules measured by 3D magnetic resonance imaging
    Bartacek, Jan ; Vergeldt, Frank J. ; Maca, Josef ; Gerkema, Edo ; As, Henk Van ; Lens, Piet N.L. - \ 2016
    Frontiers in Environmental Science 4 (2016)MAR. - ISSN 2296-665X
    Granular biofilm - Magnetic resonance microscopy - Metal diffusion - Metal transport - Methanogenic granular sludge

    Description of processes such as bioaccumulation, bioavailability and biosorption of heavy metals in biofilm matrixes requires the quantification of their transport. This study shows 3D MRI measurements of the penetration of free (Fe 2+ , Co 2+ and Gd 3+ ) and complexed ([FeEDTA] 2- and [GdDTPA] 2- ) metal ions in a single methanogenic granule. Interactions (sorption or precipitation) between free metals and the biofilm matrix result in extreme shortening of the spin-spin relaxation time (T 2 ) and a decrease of the amplitude (A 0 ) of the MRI signal, which hampers the quantification of the metal concentration inside the granular sludge matrix. MRI images clearly showed the presence of distinct regions (dead or living biomass, cracks, and precipitates) in the granular matrix, which influenced the metal transport. For the free metal ions, a reactive barrier was formed that moved through the granule, especially in the case of Gd 2+ . Chelated metals penetrated faster and without reaction front. Diffusion of [GdDTPA] 2- could be quantified, revealing the course of its transport and the uneven (0.2-0.4 mmolL -1 ) distribution of the final [GdDTPA] 2- concentration within the granular biofilm matrix at equilibrium.

    Rhizophoraceae Mangrove Saplings Use Hypocotyl and Leaf Water Storage Capacity to Cope with Soil Water Salinity Changes
    Lechthaler, Silvia ; Robert, Elisabeth M.R. ; Tonné, Nathalie ; Prusova, Alena ; Gerkema, Edo ; As, Henk Van; Koedam, Nico ; Windt, Carel W. - \ 2016
    Frontiers in Plant Science 7 (2016)June2016. - ISSN 1664-462X
    Some of the most striking features of Rhizophoraceae mangrove saplings are their voluminous cylinder-shaped hypocotyls and thickened leaves. The hypocotyls are known to serve as floats during seed dispersal (hydrochory) and store nutrients that allow the seedling to root and settle. In this study we investigate to what degree the hypocotyls and leaves can serve as water reservoirs once seedlings have settled, helping the plant to buffer the rapid water potential changes that are typical for the mangrove environment. We exposed saplings of two Rhizophoraceae species to three levels of salinity (15, 30, and 0–5‰, in that sequence) while non-invasively monitoring changes in hypocotyl and leaf water content by means of mobile NMR sensors. As a proxy for water content, changes in hypocotyl diameter and leaf thickness were monitored by means of dendrometers. Hypocotyl diameter variations were also monitored in the field on a Rhizophora species. The saplings were able to buffer rapid rhizosphere salinity changes using water stored in hypocotyls and leaves, but the largest water storage capacity was found in the leaves. We conclude that in Rhizophora and Bruguiera the hypocotyl offers the bulk of water buffering capacity during the dispersal phase and directly after settlement when only few leaves are present. As saplings develop more leaves, the significance of the leaves as a water storage organ becomes larger than that of the hypocotyl.
    Phloem flow and sugar transport in Ricinus communis L. is inhibited under anoxic conditions of shoot or roots
    Peuke, A.D. ; Gessler, A. ; Trumbore, S. ; Windt, C.W. ; Homan, N. ; Gerkema, E. ; As, H. van - \ 2015
    Plant, Cell & Environment 38 (2015)3. - ISSN 0140-7791 - p. 433 - 447.
    carbon-isotope composition - mushrooms agaricus-bisporus - distance water transport - organic-matter - membrane-permeability - assimilate transport - plants - leaves - starch - stress
    Anoxic conditions should hamper the transport of sugar in the phloem, as this is an active process. The canopy is a carbohydrate source and the roots are carbohydrate sinks.By fumigating the shoot with N2 or flooding the rhizosphere, anoxic conditions in the source or sink, respectively, were induced. Volume flow, velocity, conducting area and stationary water of the phloem were assessed by non-invasive magnetic resonance imaging (MRI) flowmetry. Carbohydrates and d13C in leaves, roots and phloem saps were determined. Following flooding, volume flow and conducting area of the phloem declined and sugar concentrations in leaves and in phloem saps slightly increased. Oligosaccharides appeared in phloem saps and after 3 d, carbon transport was reduced to 77%. Additionally, the xylem flow declined and showed finally no daily rhythm. Anoxia of the shoot resulted within minutes in a reduction of volume flow, conductive area and sucrose in the phloem sap decreased. Sugar transport dropped to below 40% by the end of the N2 treatment. However, volume flow and phloem sap sugar tended to recover during the N2 treatment. Both anoxia treatments hampered sugar transport. The flow velocity remained about constant, although phloem sap sugar concentration changed during treatments. Apparently, stored starch was remobilized under anoxia.
    Temporal niche switching and reduced nest attendance in response to heat dissipation limits in lactating common voles (Microtus arvalis)
    Vinne, V. van der; Simons, M.J.P. ; Reimert, I. ; Gerkema, M.P. - \ 2014
    Physiology and Behavior 128 (2014). - ISSN 0031-9384 - p. 295 - 302.
    According to the heat dissipation limit theory, maximum metabolic turnover is limited by the capacity of the body to dissipate excess heat. Small mammals, including common voles (Microtus arvalis), face a heat dissipation limitation during lactation. Pup growth and milk production are reduced under higher ambient temperatures. Heat dissipation problems might in part be alleviated by modifying behavior, such as reducing nest attendance and being active at energetically optimal times of day. According to the circadian thermo-energetics hypothesis, animals can make use of daily ambient temperature fluctuations to alter their energetic expenditure. In this study we test whether heat challenged (housing at 30 °C compared to 21 °C) lactating common voles allocate their time differently among behaviors and whether their ultradian and circadian behavioral rhythmicity are altered. Behavior was scored every 13 min from automated picture recordings, while general locomotor activity was measured by passive infrared detectors to assess ultradian and circadian organization. The effects of ambient temperature on the ultradian organization of behavior were assessed by determining the ultradian period length and the distribution of activity within the ultradian bout. Changes in circadian organization were assessed by the distribution of activity over the light and dark phase. As a complementary measure nest temperature recordings were used to quantify nest attendance distribution between day and night. Lactating dams at 30 °C reduced the fraction of time spent on the nest while increasing the fraction of time resting without pups away from the nest. The ultradian period of locomotor activity was longer in voles housed at 30 °C during pregnancy and lactation, but not after weaning when the pups were removed. No differences in the distribution of activity within the ultradian bout could be detected. The circadian organization was also modulated by ambient temperature. Lactating voles housed at 30 °C became more day active and a loss of day–night differences in nest temperature suggests a shift of nest attendance towards the night. Reducing the time attending the nest can reduce the risk of hyperthermia, and may be the behavioral component resulting in lower milk production and hence reproductive output. Becoming more day active allows feeding and nursing of the pups during the rest phase to occur during the night at which lower ambient temperatures are expected in the field. In natural situations this strategy will increase heat dissipation and lactation capacity. Whether there are similar benefits associated with a longer ultradian period is currently unknown, but these are likely to result from decreased energy turnover at 30 °C. In conclusion, our study shows that lactating common voles facing heat dissipation problems re-organize their behavior in a way that can maximize heat dissipation capabilities and thereby optimize lactation capacity.
    Visualization of the stem water content of two genera with secondary phloem produced by successive cambia through Magnetic Resonance Imaging (MRI)
    Robert, E.M.R. ; Schmitz, N. ; Copini, P. ; Gerkema, E. ; Vergeldt, F.J. ; Windt, C.W. ; Beeckman, H. ; Koedam, N. ; As, H. van - \ 2014
    The Journal of Plant Hydraulics 1 (2014). - ISSN 2268-4565 - 8 p.
    Shrubs and trees with secondary phloem tissue produced by successive cambia mainly occur in habitats characterized by a periodical or continuous lack of water availability. The amount of this secondary phloem tissue in stems of Avicennia trees rises with increasing soil water salinity and decreasing inundation frequency. Hence, increased water storage in secondary phloem tissue produced by successive cambia was put forward to be advantageous in harsh environmental conditions. It was however never tested whether the secondary phloem cells over the entire stem of woody species showing this wood anatomical feature are indeed water-filled as expected. In this preliminary and pioneering study, we use magnetic resonance imaging (MRI) to visualize the stem water content of three species with successive cambia, the mangroves Avicennia marina and A. officinalis and the non-mangrove Bougainvillea spectabilis. Measurements were conducted in living plants. We tested the hypothesis that not only the outermost phloem tissue has high water content but also the secondary phloem tissues over the entire stem from the bark inward to the pith, herewith serving as water storage sites. We can conclude that all secondary phloem tissue of both Bougainvillea and Avicennia has high water contents. This aligns with the contribution of secondary phloem tissue produced by successive cambia to ecological success in conditions of physiological drought. Further study should however be done to understand the mechanisms through which this secondary phloem tissue contributes to the water household of plants in conditions of water shortage.
    Anomalies in moisture transport during broccoli drying monitored by MRI?
    Jin, X. ; Boxtel, A.J.B. van; Gerkema, E. ; Vergeldt, F.J. ; As, H. van; Straten, G. van; Boom, R.M. ; Sman, R.G.M. van der - \ 2012
    Faraday Discussions 158 (2012). - ISSN 1359-6640 - p. 65 - 75.
    viscoelastic behavior - cooking - model - nmr - simulation - carrot - grain - food - meat
    Magnetic resonance imaging (MRI) offers unique opportunities to monitor moisture transport during drying or heating of food, which can render unexpected insights. Here, we report about MRI observations made during the drying of broccoli stalks indicating anomalous drying behaviour. In fresh broccoli samples the moisture content in the core of the sample increases during drying, which conflicts with Fickian diffusion. We have put the hypothesis that this increase of moisture is due to the stress diffusion induced by the elastic impermeable skin. Pre-treatments that change skin and bulk elastic properties of broccoli show that our hypothesis of stress-diffusion is plausible.
    The impact of metal transport processes on bioavailability of free and complex metal ions in methanogenic granular sludge
    Bartacek, J. ; Fermoso, F.G. ; Vergeldt, F. ; Gerkema, E. ; Maca, J. ; As, H. van; Lens, P.N.L. - \ 2012
    Water Science and Technology 65 (2012)10. - ISSN 0273-1223 - p. 1875 - 1881.
    afvalwaterbehandeling - bioreactoren - anaërobe omstandigheden - korrelslib - biologische beschikbaarheid - metalen - toxiciteit - kernspintomografie - waste water treatment - bioreactors - anaerobic conditions - granular sludge - bioavailability - metals - toxicity - magnetic resonance imaging - magnetic-resonance - dynamics - immobilization - biofilm - nickel
    Bioavailability of metals in anaerobic granular sludge has been extensively studied, because it can have a major effect on metal limitation and metal toxicity to microorganisms present in the sludge. Bioavailability of metals can be manipulated by bonding to complexing molecules such as ethylenediaminetetraacetate (EDTA) or diethylenetriaminepentaacetate (DTPA). It has been shown that although the stimulating effect of the complexed metal species (e.g. [CoEDTA]2-) is very fast, it is not sustainable when applied to metal-limited continuously operated reactors. The present paper describes transport phenomena taking place inside single methanogenic granules when the granules are exposed to various metal species. This was done using magnetic resonance imaging (MRI). The MRI results were subsequently related to technological observations such as changes in methanogenic activity upon cobalt injection into cobalt-limited up-flow anaerobic sludge blanket (UASB) reactors. It was shown that transport of complexed metal species is fast (minutes to tens of minutes) and complexed metal can therefore quickly reach the entire volume of the granule. Free metal species tend to interact with the granular matrix resulting in slower transport (tens of minutes to hours) but higher final metal concentrations.
    Moisture distribution in broccoli: measurements by MRI hot air drying experiments
    Jin, X. ; Sman, R.G.M. van der; Gerkema, E. ; Vergeldt, F.J. ; As, H. van; Boxtel, A.J.B. van - \ 2011
    Procedia Food Science 1 (2011). - ISSN 2211-601X - p. 640 - 646.
    profiles - nmr - diffusivity - model - food - gel
    The internal moisture distribution that arise in food products during drying, is a key factor for the retention of quality attributes. To reveal the course of moisture content in a product, internal moisture profiles in broccoli florets are measured by MRI imaging during drying experiments with controlled air flow and temperature. The 3D images concern a matrix size of 64×64×64 elements. Signal intensity is converted to product moisture content with a linear relationship, while taking a minimum detectable moisture content of 0.3 kg water/ kg dry matter into account. Moisture content as a function of time is presented for a 2D cross sectional area in the middle of a broccoli sample. The average moisture contents for the cross sectional area obtained from the MRI imaging are compared with spatial model simulations for the moisture distribution. In that model the effective diffusion coefficient is based on the Free Volume Theory. This theory has the advantage that the changed mobility of water in the product during drying is taken into account and the theory also predicts the moisture transport in the porous broccoli floret. Key parameters for the Free Volume Theory are estimated by fitting to the experimental MRI results and the effective diffusion coefficient is given as a function of the product water content.
    Moisture Distribution in Broccoli: Measurements by MRI Hot Air Drying Experiments
    Jin, X. ; Sman, R.G.M. van der; Gerkema, E. ; Vergeldt, F.J. ; As, H. van; Boxtel, A.J.B. van - \ 2011
    ABSTRACT The internal moisture distribution that arise in food products during drying, is a key factor for the retention of quality attributes. To reveal the course of moisture content in a product, internal moisture profiles in broccoli florets are measured by MRI imaging during drying experiments with controlled air flow and temperature. The 3D images concern a matrix size of 64×64×64 elements. Signal intensity is converted to product moisture content with a linear relationship, while taking a minimum detectable moisture content of 0.3 kg water/ kg dry matter into account. Moisture content as a function of time is presented for a 2D cross sectional area in the middle of a broccoli sample. The average moisture contents for the cross sectional area obtained from the MRI imaging are compared with spatial model simulations for the moisture distribution. In that model the effective diffusion coefficient is based on the Free Volume Theory. This theory has the advantage that the changed mobility of water in the product during drying is taken into account and the theory also predicts the moisture transport in the porous broccoli floret. Key parameters for the Free Volume Theory are estimated by fitting to the experimental MRI results and the effective diffusion coefficient is given as a function of the product water content. Keywords: diffusion properties; MRI; convective drying; moisture profiles
    Investigation on the influence of pre-treatments on drying behaviour of broccoli by MRI experiments
    Jin, X. ; Sman, R.G.M. van der; Gerkema, E. ; Vergeldt, F.J. ; As, H. van; Straten, G. van; Boom, R.M. ; Boxtel, A.J.B. van - \ 2011
    Abstract: Magnetic Resonance Imaging (MRI) allows the monitoring of internal moisture content of food products during drying non-destructively. In an experimental set-up with continuous and controlled hot air supply, the internal moisture distribution of broccoli with different pre-treatments are measured during drying. Moisture distribution, drying rate and shrinkage are compared and analyzed quantitatively. MRI results indicated that for fresh broccoli stalks the moisture content in the core of the sample increased after some hours of drying. With pre-treatments as peeling, blanching or freezing the moisture transport barrier in the skin of the broccoli sample was reduced. Shrinkage was uniform for most of the pre-treated samples and the moisture increment in the core did not occur. It was also found that with these pre-treatments progress of drying enhanced significantly. Therefore, from an drying efficiency and economic point of view, pre-treatments prior to drying offer important opportunities. Keywords: MRI, hot air drying, broccoli stalk, increased moisture content, pre-treatments
    Characterization of water diffusion in food products for MRI experiments
    Jin, X. ; Sman, R.G.M. van der; Gerkema, E. ; Vergeldt, F.J. ; As, H. van; Boxtel, A.J.B. van - \ 2010
    Characterization of water diffusion in food products from MRI experiments
    Jin, X. ; Sman, R.G.M. van der; Gerkema, E. ; As, H. van; Boxtel, A.J.B. van - \ 2010
    MRI in soils: determination of water concent changes due to root water uptake by means of a multi-slice-multi-echo sequence (MSME)
    Pohlmeier, A. ; Vergeldt, F. ; Gerkema, E. ; As, H. van; Dusschoten, D. van; Vereecken, H. - \ 2010
    The Open Magnetic Resonance Journal 3 (2010). - ISSN 1874-7698 - p. 69 - 74.
    Root water uptake by ricinus communis (castor bean) in fine sand was investigated using MRI with multiecho sampling. Before starting the experiments the plants germinated and grew for 3 weeks in a cylindrical container with a diameter of 9 cm. Immediately before the MRI experiments started, the containers were water-saturated and sealed, so water content changes were only caused by root water uptake. In continuation of a preceding work, where we applied SPRITE we tested a multi-echo multi-slice sequence (MSME). In this approach, the water content was imaged by setting TE = 6.76 ms and nE = 128 with an isotropic resolution of 3.1mm. We calculated the water content maps by biexponential fitting of the multi-slice echo train data and normalisation on reference cuvettes filled with glass beads and 1 mM NiCl2 solution. The water content determination was validated by comparing to mean gravimetric water content measurements. By coregistration with the root architecture, visualised by a 3D fast spin echo sequence (RARE), we conclude that the largest water content changes occurred in the neighbourhood of the roots and in the upper layers of the soil.
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