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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    Regional labour force participation across the European Union: a time-space recursive modelling approach with endogenous regressors
    Halleck Vega, Sol Maria ; Elhorst, J.P. - \ 2017
    Spatial Economic Analysis 12 (2017)2-3. - ISSN 1742-1772 - p. 138 - 160.
    labour force participation - European Union regions - dynamic spatial panels - endogenous regressors - panel-data models - spatial econometrics - market participation - unemployment - women - rates - disturbances - restrictions - estimators - dependence
    Regional labour force participation across the European Union: a time–space recursive modelling approach with endogenous regressors. Spatial Economic Analysis. Although there is an abundant regional labour market literature taking a spatial perspective, only a few studies have explored extending the analysis of labour force participation with spatial effects. This paper revisits this important issue, proposing a time–space recursive modelling approach that builds on and appraises Fogli and Veldkamp’s methodology from 2011 and finding for the United States that participation rates vary with past values in nearby regions. Major shortcomings in their study are corrected for, including stationarity and the control for endogenous regressors other than the time and space–time-lagged dependent variable using system generalized method of moments (GMM). The paper also highlights interaction effects among explanatory variables for the first time in this context. Using a panel of 108 regions across the European Union over 1986–2010, the results for total, male and female participation rates throw a new light on the socio-economic relevance of different determinants. Importantly, characteristics in neighbouring regions play a significant role, and neglecting endogeneity is found to have serious consequences, underlining increased attention on the specification and estimation of spatial econometric models with endogenous regressors.
    Plant–soil feedbacks of exotic plant species across life forms: a meta-analysis
    Meisner, A. ; Hol, W.H.G. ; Boer, W. de; Krumins, J.A. ; Wardle, D.A. ; Putten, W.H. van der - \ 2014
    Biological Invasions 16 (2014)12. - ISSN 1387-3547 - p. 2551 - 2561.
    serpentine grassland - invasive plants - native range - biota - communities - pathogens - traits - ecosystems - contribute - dependence
    Invasive exotic plant species effects on soil biota and processes in their new range can promote or counteract invasions via changed plant–soil feedback interactions to themselves or to native plant species. Recent meta-analyses reveale that soil influenced by native and exotic plant species is affecting growth and performance of natives more strongly than exotics. However, the question is how uniform these responses are across contrasting life forms. Here, we test the hypothesis that life form matters for effects on soil and plant–soil feedback. In a meta-analysis we show that exotics enhanced C cycling, numbers of meso-invertebrates and nematodes, while having variable effects on other soil biota and processes. Plant effects on soil biota and processes were not dependent on life form, but patterns in feedback effects of natives and exotics were dependent on life form. Native grasses and forbs caused changes in soil that subsequently negatively affected their biomass, whereas native trees caused changes in soil that subsequently positively affected their biomass. Most exotics had neutral feedback effects, although exotic forbs had positive feedback effects. Effects of exotics on natives differed among plant life forms. Native trees were inhibited in soils conditioned by exotics, whereas native grasses were positively influenced in soil conditioned by exotics. We conclude that plant life form matters when comparing plant–soil feedback effects both within and between natives and exotics. We propose that impact analyses of exotic plant species on the performance of native plant species can be improved by comparing responses within plant life form.
    Improved emulsion stability by succinylation of patatin is caused by partial unfolding rather than charge effects
    Delahaije, R.J.B.M. ; Wierenga, P.A. ; Giuseppin, M.L.F. ; Gruppen, H. - \ 2014
    Journal of Colloid and Interface Science 430 (2014). - ISSN 0021-9797 - p. 69 - 77.
    in-water emulsions - protein-exposed hydrophobicity - beta-lactoglobulin - drop size - adsorption - flocculation - interface - stabilization - ph - dependence
    This study investigates the influence of succinylation on the molecular properties (i.e. charge, structure and hydrophobicity) and the flocculation behavior of patatin-stabilized oil-in-water emulsions. Patatin was succinylated to five degrees (0% (R0) to 57% (R2.5)). Succinylation not only resulted in a change of the protein charge but also in (partial) unfolding of the secondary structure, and consequently in an increased initial adsorption rate of the protein to the oil–water interface. The stability against salt-induced flocculation showed two distinct regimes, instead of a gradual shift in stability as expected by the DLVO theory. While flocculation was observed at ionic strengths > 30 mM for the emulsions stabilized by the variants with the lowest degrees of modification (R0–R1), the other variants (R1.5–R2.5) were stable against flocculation ¿ 200 mM. This was related to the increased initial adsorption rate, and the consequent transition from a protein-poor to a protein-rich regime. This was confirmed by the addition of excess protein to the emulsions stabilized by R0–R1 which resulted in stability against salt-induced flocculation. Therefore, succinylation of patatin indirectly results in stability against salt-induced flocculation, by increasing the initial adsorption rate of the protein to the oil–water interface, leading to a shift to the protein-rich regime.
    Natural Resources and Violent Conflict
    Nillesen, E.E.M. ; Bulte, E.H. - \ 2014
    Annual Review of Resource Economics 6 (2014)1. - ISSN 1941-1340 - p. 69 - 83.
    civil-war - armed conflict - diamonds - curse - dataset - oil - determinants - information - dependence - countries
    We discuss the literature on natural resources and violent conflict. The theoretical literature is rich and ambiguous, and the empirical literature is equally multi-faceted. Theory predicts that resource booms or discoveries may attenuate or accentuate the risk of conflict, depending on various factors. Regression analyses also produce mixed signals, and point to a plethora of mechanisms linking resources to conflict. The empirical literature is gradually evolving from cross-country conflict models to micro-level analyses, explaining variation in local intensity of conflict. This transition has resulted in more credible identification strategies, and an enhanced understanding of the complex relation between resources and conflict.
    Comparison of Soil Respiration in Typical Conventional and New Alternative Cereal Cropping Systems on the North China Plain
    Gao, B. ; Ju, X.T. ; Su, F. ; Gao, F.B. ; Cao, Q.S. ; Oenema, O. ; Christie, P. ; Chen, X.P. ; Zhang, F.S. - \ 2013
    PLoS ONE 8 (2013)11. - ISSN 1932-6203
    carbon-dioxide - water-content - temperature - nitrogen - dependence - ecosystem - tillage - forest - management - moisture
    We monitored soil respiration (Rs), soil temperature (T) and volumetric water content (VWC%) over four years in one typical conventional and four alternative cropping systems to understand Rs in different cropping systems with their respective management practices and environmental conditions. The control was conventional double-cropping system (winter wheat and summer maize in one year - Con. W/M). Four alternative cropping systems were designed with optimum water and N management, i.e. optimized winter wheat and summer maize (Opt. W/M), three harvests every two years (first year, winter wheat and summer maize or soybean; second year, fallow then spring maize - W/M-M and W/S-M), and single spring maize per year (M). Our results show that Rs responded mainly to the seasonal variation in T but was also greatly affected by straw return, root growth and soil moisture changes under different cropping systems. The mean seasonal CO2 emissions in Con. W/M were 16.8 and 15.1 Mg CO2 ha(-1) for summer maize and winter wheat, respectively, without straw return. They increased significantly by 26 and 35% in Opt. W/M, respectively, with straw return. Under the new alternative cropping systems with straw return, W/M-M showed similar Rs to Opt. W/M, but total CO2 emissions of W/S-M decreased sharply relative to Opt. W/M when soybean was planted to replace summer maize. Total CO2 emissions expressed as the complete rotation cycles of W/S-M, Con. W/M and M treatments were not significantly different. Seasonal CO2 emissions were significantly correlated with the sum of carbon inputs of straw return from the previous season and the aboveground biomass in the current season, which explained 60% of seasonal CO2 emissions. T and VWC% explained up to 65% of Rs using the exponential-power and double exponential models, and the impacts of tillage and straw return must therefore be considered for accurate modeling of Rs in this geographical region.
    Cultivation of microalgae on artificial light comes at a cost
    Blanken, W.M. ; Cuaresma Franco, M. ; Wijffels, R.H. ; Janssen, M.G.J. - \ 2013
    Algal Research 2 (2013)4. - ISSN 2211-9264 - p. 333 - 340.
    quantum yield - chlamydomonas-reinhardtii - photosynthetic efficiency - technoeconomic analysis - growth - productivity - irradiance - dependence - biofuels - algae
    Microalgae are potential producers of bulk food and feed compounds, chemicals, and biofuels. To produce these bulk products competitively, it is important to keep costs of raw material low. Light energy can be provided by sun or lamps. Sunlight is free and abundant. Disadvantages of sunlight, however, include day/night cycles, changes in weather conditions, and seasonal changes. These fluctuations in irradiance can be prevented by applying artificial lighting. Artificial lighting will not only increase productivity but will also increase costs associated with microalgae cultivation. This cost increase is recognized, but a detailed quantitative evaluation was still missing. The costs and energy balance related to microalgae cultivation employing artificial light was evaluatedwith a literature study. We calculated that current application of artificial light will increase production costs by 25.3 $ per kilogram of dry-weight biomass. From these calculations, it was determined that 4% to 6% of energy from electric input is fixed as chemical energy in microalgae biomass. Energy loss and increased production cost may be acceptable in the production of high value products, but in general they should be avoided. Microalgae cultivation programs should therefore focus on employing sunlight.
    THC reduces the anticipatory nucleus accumbens response to reward in subjects with a nicotine addiction
    Jansma, J.M. ; Hell, H.H. van; Vanderschuren, L.J.M.J. ; Bossong, M.G. ; Jager, G. ; Kahn, R.S. ; Ramsey, N.F. - \ 2013
    Translational Psychiatry 3 (2013). - ISSN 2158-3188 - 10 p.
    endogenous cannabinoid anandamide - increasing monetary reward - endocannabinoid system - drug-addiction - cb1 receptors - brain - dependence - rats - inhibition - humans
    Recent evidence has implicated the endocannabinoid (eCB) system in nicotine addiction. The eCB system also has an important role in reward mechanisms, and nicotine addiction has been associated with aberrant reward processing. Motivated by this evidence, we tested the hypothesis that eCB modulation of reward processing is altered in subjects with a nicotine addiction (NAD). For this purpose, we compared reward-related activity in NAD with healthy controls (HC) in a pharmacological magnetic resonance imaging (MRI) study using ¿9-tetrahydrocannabinol (THC) administration to challenge the eCB system. Eleven HC and 10 NAD participated in a 3-T functional MRI (fMRI) study with a double-blind, cross-over, placebo-controlled design, using a Monetary Incentive Delay (MID) paradigm with three reward levels. Reward activity in the nucleus accumbens (NAcc) and caudate putamen during anticipation and feedback of reward was compared after THC and placebo. fMRI results indicated a significant reduction of reward anticipation activity in the NAcc in NAD after THC administration, which was not present in HC. This is indicated by a significant group by drug by reward interaction. Our data show that THC significantly reduces the NAcc response to monetary reward anticipation in NAD. These results suggest that nicotine addiction is associated with altered eCB modulation of reward processing in the NAcc. This study adds important human data to existing evidence implicating the eCB system in nicotine addiction.
    Assessment of performance of selected serological tests for diagnosing brucellosis in pigs.
    Munoz, P.M. ; Blasco, J.M. ; Engel, B. ; Miguel, M.J. de; Marín, C.M. ; Dieste, L. ; Mainar-Jaime, R.C. - \ 2012
    Veterinary Immunology and Immunopathology 146 (2012). - ISSN 0165-2427 - p. 150 - 158.
    fluorescence polarization assay - melitensis infection - swine brucellosis - validation - suis - specificity - sensitivity - dependence - antigens - efficacy
    Swine brucellosis due to Brucella suis is considered an emerging zoonotic disease whose control is based on serological testing and the subsequent culling of seropositive animals or the full depopulation of affected flocks. Here we assessed the performance of several serological tests (Rose Bengal Test [RBT], indirect ELISA [i-ELISA], blocking ELISA [b-ELISA], and two competitive ELISAs [c-ELISA]) for diagnosing swine brucellosis caused by B. suis biovar 2. Both frequentistic and Bayesian statistical inference were used. A frequentistic analysis, using sera from known gold standard (GS) populations (i.e., from truly infected or brucellosis free animals), resulted in maximum (100%) diagnostic sensitivity (Se) and specificity (Sp) in the RBT, i-ELISA and b-ELISA tests. However, c-ELISAs resulted in lower diagnostic Se (ranging from 68.5% to 92.6%, according to the different cut-offs selected). A Bayesian analysis of tests yielding the best diagnostic performance with GS sera (RBT, i-ELISA and b-ELISA), but using a large collection of field sera, resulted in similar Se among tests but markedly lower (˜80%) than that resulting from the frequentistic analysis using the GS serum populations. By contrast, the estimated Sp in the Bayesian analysis was only slightly lower than 100%, thus similar to that obtained frequentistically. Our results show that adequate diagnostic tests for brucellosis in swine are available, but also emphasize the need for more extensive validation studies before applying these tests under field conditions.
    Photosynthetic efficiency of Chlamydomonas reinhardtii in attenuated, flashing light
    Vejrazka, C. ; Janssen, M.G.J. ; Streefland, M. ; Wijffels, R.H. - \ 2012
    Biotechnology and Bioengineering 109 (2012)10. - ISSN 0006-3592 - p. 2567 - 2574.
    quantum yield - photobioreactors - cyanobacteria - dependence - microalgae
    As a result of mixing and light attenuation, algae in a photobioreactor (PBR) alternate between light and dark zones and, therefore, experience variations in photon flux density (PFD). These variations in PFD are called light/dark (L/D) cycles. The objective of this study was to determine how these L/D cycles affect biomass yield on light energy in microalgae cultivation. For our work, we used controlled, short light path, laboratory, turbidostat-operated PBRs equipped with a LED light source for square-wave L/D cycles with frequencies from 1 to 100¿Hz. Biomass density was adjusted that the PFD leaving the PBR was equal to the compensation point of photosynthesis. Algae were acclimated to a sub-saturating incident PFD of 220¿µmol¿m(-2) ¿s(-1) for continuous light. Using a duty cycle of 0.5, we observed that L/D cycles of 1 and 10¿Hz resulted on average in a 10% lower biomass yield, but L/D cycles of 100¿Hz resulted on average in a 35% higher biomass yield than the yield obtained in continuous light. Our results show that interaction of L/D cycle frequency, culture density and incident PFD play a role in overall PBR productivity. Hence, appropriate L/D cycle setting by mixing strategy appears as a possible way to reduce the effect that dark zone exposure impinges on biomass yield in microalgae cultivation. The results may find application in optimization of outdoor PBR design to maximize biomass yields.
    Quantifying seed dispersal kernels from truncated seed-tracking data
    Hirsch, B.T. ; Visser, M.D. ; Kays, R. ; Jansen, P.A. - \ 2012
    Methods in Ecology and Evolution 3 (2012)3. - ISSN 2041-210X - p. 595 - 602.
    tropical forests - plant-populations - spatial-patterns - wind dispersal - rain-forest - shadows - consequences - recruitment - dependence - behavior
    1. Seed dispersal is a key biological process that remains poorly documented because dispersing seeds are notoriously hard to track. While long-distance dispersal is thought to be particularly important, seed-tracking studies typically yield incomplete data sets that are biased against long-distance movements. 2. We evaluate an analytical procedure developed by Jansen, Bongers & Hemerik (2004) to infer the tail of a seed dispersal kernel from incomplete frequency distributions of dispersal distances obtained by tracking seeds. This ‘censored tail reconstruction’ (CTR) method treats dispersal distances as waiting times in a survival analysis and censors nonretrieved seeds according to how far they can reliably be tracked. We tested whether CTR can provide unbiased estimates of longdistance movements which typically cannot be tracked with traditional field methods. 3. We used a complete frequency distribution of primary seed dispersal distances of the palm Astrocaryum standleyanum, obtained with telemetric thread tags that allow tracking seeds regardless of the distance moved. We truncated and resampled the data set at various distances, fitted kernel functions on CTR estimates of dispersal distance and determined how well this function approximated the true dispersal kernel. 4. Censored tail reconstruction with truncated data approximated the true dispersal kernel remarkably well but only when the best-fitting function (lognormal) was used. We were able to select the correct function and derive an accurate estimate of the seed dispersal kernel even after censoring 50–60% of the dispersal events. However, CTR results were substantially biased if 5% or more of seeds within the search radius were overlooked by field observers and erroneously censored. Similar results were obtained using additional simulated dispersal kernels. 5. Our study suggests that the CTR method can accurately estimate the dispersal kernel from truncated seed-tracking data if the kernel is a simple decay function. This method will improve our understanding of the spatial patterns of seed movement and should replace the usual practice of omitting nonretrieved seeds fromanalyses in seed-tracking studies
    Photosynthetic efficiency of Chlamydomonas reinhardtii in flashing light
    Vejrazka, C. ; Janssen, M.G.J. ; Streefland, M. ; Wijffels, R.H. - \ 2011
    Biotechnology and Bioengineering 108 (2011)12. - ISSN 0006-3592 - p. 2905 - 2913.
    quantum yield - photobioreactors - microalgae - cyanobacteria - cultivation - dependence - intensity
    Efficient light to biomass conversion in photobioreactors is crucial for economically feasible microalgae production processes. It has been suggested that photosynthesis is enhanced in short light path photobioreactors by mixing-induced flashing light regimes. In this study, photosynthetic efficiency and growth of the green microalga Chlamydomonas reinhardtii were measured using LED light to simulate light/dark cycles ranging from 5 to 100¿Hz at a light-dark ratio of 0.1 and a flash intensity of 1000¿µmol¿m-2¿s-1. Light flashing at 100¿Hz yielded the same photosynthetic efficiency and specific growth rate as cultivation under continuous illumination with the same time-averaged light intensity (i.e., 100¿µmol¿m-2¿s-1). The efficiency and growth rate decreased with decreasing flash frequency. Even at 5¿Hz flashing, the rate of linear electron transport during the flash was still 2.5 times higher than during maximal growth under continuous light, suggesting storage of reducing equivalents during the flash which are available during the dark period. In this way the dark reaction of photosynthesis can continue during the dark time of a light/dark cycle. Understanding photosynthetic growth in dynamic light regimes is crucial for model development to predict microalgal photobioreactor productivities. Biotechnol. Bioeng. 2011;108: 2905–2913. © 2011 Wiley Periodicals, Inc
    Effect of habitat productivity and exploitation on populations with complex life cycles
    Wolfshaar, K.E. van de; Hille Ris Lambers, R. ; Gardmark, A. - \ 2011
    Marine Ecology Progress Series 438 (2011). - ISSN 0171-8630 - p. 175 - 184.
    marine reserves - concentration hypothesis - size - fish - recruitment - dynamics - overcompensation - ecosystems - management - dependence
    In this paper we study the consequences of habitat switching and the corresponding ontogenetic diet shifts between adult and juvenile life stages for harvesting and management of exploited populations using a consumer-resource model with stage-specific mortality. Specifically, we study how differences in stage-specific habitat productivity regulate exploited populations and affect yield. We show that the ratio of adult to juvenile habitat productivity determines whether the population is regulated by processes in the juvenile or adult stage and that population responses to changes in mortality (e.g. fishing) or habitat productivity (e.g. eutrophication or physical destruction) depend critically on the mechanism regulating the population. This result has important consequences for the management of marine fish. For example, in fisheries where the exploited population is regulated by processes in the juvenile stage, management measures aimed at protecting the juvenile habitat may be much more effective than regulating fishing effort on the adults. We find also that intermediate differences in habitat productivity lead to alternative stable states between a population regulated by processes in the juvenile or the adult stage. These alternative stable states may lead to counterintuitive population responses to harvesting
    Genetic analysis of the interaction between Allium species and arbuscular mycorrhizal fungi
    Galvan Vivero, G.A. ; Kuyper, T.W. ; Burger-Meijer, K. ; Keizer, L.C.P. ; Hoekstra, R.F. ; Kik, C. ; Scholten, O.E. - \ 2011
    Theoretical and Applied Genetics 122 (2011)5. - ISSN 0040-5752 - p. 947 - 960.
    quantitative trait loci - modern wheat cultivars - vegetable crops - growth-responses - responsiveness - phosphorus - agriculture - inoculation - fistulosum - dependence
    The response of Allium cepa, A. roylei, A. fistulosum, and the hybrid A. fistulosum × A. roylei to the arbuscular mycorrhizal fungus (AMF) Glomus intraradices was studied. The genetic basis for response to AMF was analyzed in a tri-hybrid A. cepa × (A. roylei × A. fistulosum) population. Plant response to mycorrhizal symbiosis was expressed as relative mycorrhizal responsiveness (R') and absolute responsiveness (R). In addition, the average performance (AP) of genotypes under mycorrhizal and non-mycorrhizal conditions was determined. Experiments were executed in 2 years, and comprised clonally propagated plants of each genotype grown in sterile soil, inoculated with G. intraradices or non-inoculated. Results were significantly correlated between both years. Biomass of non-mycorrhizal and mycorrhizal plants was significantly positively correlated. R' was negatively correlated with biomass of non-mycorrhizal plants and hence unsuitable as a breeding criterion. R and AP were positively correlated with biomass of mycorrhizal and non-mycorrhizal plants. QTLs contributing to mycorrhizal response were located on a linkage map of the A. roylei × A. fistulosum parental genotype. Two QTLs from A. roylei were detected on chromosomes 2 and 3 for R, AP, and biomass of mycorrhizal plants. A QTL from A. fistulosum was detected on linkage group 9 for AP (but not R), biomass of mycorrhizal and non-mycorrhizal plants, and the number of stem-borne roots. Co-segregating QTLs for plant biomass, R and AP indicate that selection for plant biomass also selects for enhanced R and AP. Moreover, our findings suggest that modern onion breeding did not select against the response to AMF, as was suggested before for other cultivated species. Positive correlation between high number of roots, biomass and large response to AMF in close relatives of onion opens prospects to combine these traits for the development of more robust onion cultivars
    Grafted block complex coacervate core micelles and their effect on protein adsorption on silica and polystyrene
    Brzozowska, A.M. ; Keizer, A. de; Norde, W. ; Detrembleur, C. ; Cohen Stuart, M.A. - \ 2010
    Colloid and Polymer Science 288 (2010)10-11. - ISSN 0303-402X - p. 1081 - 1095.
    bovine serum-albumin - beta-lactoglobulin - polymeric micelles - chain stiffness - surfaces - binding - dependence - monolayers - reduction - copolymer
    We have studied the formation and the stability of grafted block complex coacervate core micelles (C3Ms) in solution and the influence of grafted block C3M coatings on the adsorption of the proteins ß-lactoglobulin, bovine serum albumin, and lysozyme. The C3Ms consist of a grafted block copolymer PAA21-b-PAPEO14 (poly(acrylic acid)-b-poly(acrylate methoxy poly(ethylene oxide)), with a negatively charged PAA block and a neutral PAPEO block and a positively charged homopolymer P2MVPI (poly(N-methyl 2-vinyl pyridinium iodide). In solution, these C3Ms partly disintegrate at salt concentrations between 50 and 100 mM NaCl. Adsorption of C3Ms and proteins has been studied with fixed-angle optical reflectometry, at salt concentrations ranging from 1 to 100 mM NaCl. In comparison with the adsorption of PAA21-b-PAPEO14 alone adsorption of C3Ms significantly increases the amount of PAA21-b-PAPEO14 on the surface. This results in a higher surface density of PEO chains. The stability of the C3M coatings and their influence on protein adsorption are determined by the composition and the stability of the C3Ms in solution. A C3M-PAPEO14/P2MVPI43 coating strongly suppresses the adsorption of all proteins on silica and polystyrene. The reduction of protein adsorption is the highest at 100 mM NaCl (>90%). The adsorbed C3M-PAPEO14/P2MVPI43 layer is partly removed from the surface upon exposure to an excess of ß-lactoglobulin solution, due to formation of soluble aggregates consisting of ß-lactoglobulin and P2MVPI43. In contrast, C3M-PAPEO14/P2MVPI228 which has a fivefold longer cationic block enhances adsorption of the negatively charged proteins on both surfaces at salt concentrations above 1 mM NaCl. A single PAA21-b-PAPEO14 layer causes only a moderate reduction of protein adsorption.
    Health monitoring of plants by their emitted volatiles: A model to predict the effect of Botrytis cinerea on the concentration of volatiles in a large-scale greenhouse
    Jansen, R.M.C. ; Hofstee, J.W. ; Wildt, J. ; Vanthoor, B.H.E. ; Verstappen, F.W.A. ; Takayama, K. ; Bouwmeester, H.J. ; Henten, E.J. van - \ 2010
    Biosystems Engineering 106 (2010)1. - ISSN 1537-5110 - p. 37 - 47.
    semivolatile organic-compounds - partition-coefficients - voc emissions - monoterpenes - temperature - dependence - indicator - sorption - stress - system
    This paper describes a model to calculate the concentrations of (Z)-3-hexenol, a-pinene, a-terpinene, ß-caryophyllene, and methyl salicylate in a greenhouse on the basis of their source and sink behaviour. The model was used to determine whether these volatile organic compounds (VOCs) can be used to indicate Botrytis cinerea infection in a large-scale tomato production greenhouse with a volume of 5 × 104 m3 containing 2.2 × 104 plants. Seven experiments were done to parameterise the model for these VOCs. Based on model predictions, the B. cinerea-induced increase in concentration of methyl salicylate is detectable in a large-scale tomato production greenhouse when: (a) windows are fully opened, and (b) the increase continues for at least 1 h, and (c) 5% of the plants are infected. The B. cinerea-induced increase in concentration of methyl salicylate is also detectable when: (a) windows are closed, and (b) the increase continues for at least 6 h, and (c) 5% of the plants are infected. The B. cinerea-induced increase in concentration of (Z)-3-hexenol is detectable under all conditions studied. However, it is expected that besides infected plants, many additional sources of (Z)-3-hexenol exist including plant debris and nearby field crops especially upon harvest or stress. The B. cinerea-induced increases in concentration of a-pinene, a-terpinene and ß-caryophyllene are probably undetectable in a large-scale tomato production greenhouse. Therefore, it is recommended to focus on the detection of methyl salicylate to indicate B. cinerea infections in large-scale tomato production greenhouses.
    Clinical effectiveness of attentional bias modification training in abstinent alcoholic patients
    Schoenmakers, T.M. ; Bruin, M. de; Lux, I.F.M. ; Goertz, A.G. ; Kerkhof, D.H.A.T. van; Wiers, R.W. - \ 2010
    Drug and Alcohol Dependence 109 (2010)1-3. - ISSN 0376-8716 - p. 30 - 36.
    experimental manipulation - heavy drinkers - incentive-sensitization - anxiety disorders - dependence - cues - addiction - smokers - vulnerability - association
    A new training to decrease attentional bias (attentional bias modification training, ABM) was tested in a randomized controlled experimental study with alcohol-dependent patients as an addition to cognitive behavioral therapy. In alcohol dependence, attentional bias has been associated with severity of alcoholism, craving, treatment outcome, and relapse. Forty-three patients with DSM-IV diagnosis of alcohol dependence were randomly assigned to an ABM intervention or control training. The procedure consisted of five sessions in which patients were trained to disengage attention from alcohol-related stimuli (ABM condition) or in which they were trained on an irrelevant reaction-time test (control condition). We measured the effects of ABM on the visual-probe task, with stimuli that were presented in the ABM and with new stimuli. Craving was measured with the Desires for Alcohol Questionnaire. Follow-up data were gathered for overall treatment success, and relapse up to 3 months after the intervention. ABM was effective in increasing the ability to disengage from alcohol-related cues. This effect generalized to untrained, new stimuli. There were no significant effects on subjective craving. For other outcome measures there were indications of clinically relevant effects. Results indicate that ABM among alcohol-dependent patients was effective and that it may affect treatment progression. Large-scale trials are warranted to further investigate this new field
    Adsorption of Pluronic F-127 on Surfaces with Different Hydrophobicities Probed by Quartz Crystal Microbalance with Dissipation
    Nejadnik, M.R. ; Olsson, A.L.J. ; Sharma, P.K. ; Mei, H.C. van der; Norde, W. ; Busscher, H.J. - \ 2009
    Langmuir 25 (2009)11. - ISSN 0743-7463 - p. 6245 - 6249.
    protein adsorption - vesicle adsorption - adhesion - copolymers - brushes - temperature - surfactants - dependence - kinetics - systems
    Triblock copolymers of polyethylene oxide (PEO) and polypropylene oxide (PPO), that is, PEOn-PPOm-PEOn, better known as Pluronic can adsorb to surfaces in either a pancake or a brushlike configuration. The brushlike configuration is advantageous in numerous applications, since it constitutes a surface repellent to proteins and microorganisms. The conformation of the adsorbed Pluronic layer depends on the hydrophobicity of the substratum surface, but the hydrophobicity threshold above which a brushlike conformation is adopted is unknown. Therefore, the aim of this study is to investigate Pluronic F-127 adsorption on surfaces with different hydrophobicities using a quartz crystal microbalance with dissipation. Adsorption in a brushlike conformation occurred on surfaces with a water contact angle above 80 degrees, as inferred from the thickness, viscosity, and elasticity of the adsorbed layer. The concentration of Pluronic F-127 in solution affected only the kinetics of adsorption and not the final layer thickness or conformation of adsorbed Pluronic molecules.
    Influence of the overall charge and local charge density of pectin on the complex formation between pectin and beta-lactoglobulin
    Sperber, B.L.H.M. ; Schols, H.A. ; Cohen Stuart, M.A. ; Norde, W. ; Voragen, A.G.J. - \ 2009
    Food Hydrocolloids 23 (2009)3. - ISSN 0268-005X - p. 765 - 772.
    bovine serum-albumin - whey proteins - aqueous-solution - acid - polyelectrolytes - coacervation - stabilization - conformation - carrageenan - dependence
    The complex formation between ß-lactoglobulin (ß-lg) and pectin is studied using pectins with different physicochemical characteristics. Pectin allows for the control of both the overall charge by degree of methyl-esterification as well as local charge density by the degree of blockiness. Varying local charge density, at equal overall charge is a parameter that is not available for synthetic polymers and is of key importance in the complex formation between oppositely charged (bio)polymers. LMP is a pectin with a high overall charge and high local charge density; HMPB and HMPR are pectins with a low overall charge, but a high and low local charge density, respectively. Dynamic light scattering (DLS) titrations identified pHc, the pH where soluble complexes of ß-lg and pectin are formed and pH, the pH of phase separation, both as a function of ionic strength. pHc decreased with increasing ionic strength for all pectins and was used in a theoretical model that showed local charge density of the pectin to control the onset of complex formation. pH passed through a maximum with increasing ionic strength for LMP because of shielding of repulsive interactions between ß-lg molecules bound to LMP, while attractive interactions were repressed at higher ionic strength. Potentiometric titrations of homo-molecular solutions and mixtures of ß-lg and pectin showed charge regulation in ß-lg¿pectin complexes. Around pH 5.5¿5.0 the pKas of ß-lg ionic groups are increased to induce positive charge on the ß-lg molecule; around pH 4.5¿3.5 the pKa values of the pectin ionic groups are lowered to retain negative charge on the pectin. Since pectins with high local charge density form complexes with ß-lg at higher ionic strength than pectins with low local charge density, pectin with a high local charge density is preferred in food systems where complex formation between protein and pectin is desired.
    Gaining Insight in the Interaction of Zinc and Population Density with a Combined Dynamic Energy Budget and Population Model
    Klok, T.C. - \ 2008
    Environmental Science and Technology 42 (2008)23. - ISSN 0013-936X - p. 8803 - 8808.
    lumbricus-rubellus - growth rate - consequences - soil - reproduction - oligochaeta - dependence
    Laboratory tests are typically conducted under optimal conditions testing the single effect of a toxicant. In the field, due to suboptimal conditions, density dependence can both diminish and enhance effects of toxicants on populations. A review of the literature indicated that general insight on interaction of density and toxicants is lacking, and therefore no predictions on their combined action can be made. In this paper the influence of zinc was tested at different population densities on the demographic rates: growth, reproduction, and survival in the earthworm Lumbricus rubellus. Changes in these rates were extrapolated with a combined Dynamic energy budget (DEB) and a population model to assess consequences at the population level. Inference from the DEB model indicated that density decreased the assimilation of food whereas zinc increased the maintenance costs. The combined effects of density and zinc resulted in a decrease in the intrinsic rate of population increase which suddenly dropped to zero at combinations of zinc and density where development is so strongly retarded that individuals do not mature. This already happened at zinc levels where zinc induced mortality is low and therefore density enhances zinc effects and density dependent compensation is not expected.
    Phase behavior of flowerlike micelles in a SCF cell model
    Sprakel, J.H.B. ; Besseling, N.A.M. ; Cohen Stuart, M.A. - \ 2008
    European Physical Journal E. Soft Matter and Biological Physics 25 (2008)2. - ISSN 1292-8941 - p. 163 - 173.
    capped poly(ethylene oxide) - telechelic associative polymers - modified ethoxylated urethanes - interacting chain molecules - transient network theory - linear viscoelasticity - statistical-theory - adsorption - attraction - dependence
    We study the interactions between flowerlike micelles, self-assembled from telechelic associative polymers, using a molecular self-consistent field (SCF) theory and discuss the corresponding phase behavior. In these calculations we do not impose properties such as aggregation number, micellar structure and number of bridging chains. Adopting a SCF cell model, we calculate the free energy of interaction between a central micelle surrounded by others. Based on these results, we predict the binodal for coexistence of dilute and dense liquid phases, as a function of the length of the hydrophobic and hydrophilic blocks. In the same cell model we compute the number of bridges between micelles, allowing us to predict the network transition. Several quantitative trends obtained from the numerical results can be rationalized in terms of transparent scaling arguments
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