Staff Publications

Staff Publications

  • external user (warningwarning)
  • Log in as
  • language uk
  • About

    '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.

    We have a manual that explains all the features 

    Current refinement(s):

    Records 1 - 20 / 387

    • help
    • print

      Print search results

    • export
      A maximum of 250 titles can be exported. Please, refine your queryYou can also select and export up to 30 titles via your marked list.
    Check title to add to marked list
    Reducing inbreeding rates with a breeding circle : Theory and practice in Veluws Heideschaap
    Windig, Jack J. ; Verweij, Marjolein J.W. ; Oldenbroek, J.K. - \ 2019
    Journal of Animal Breeding and Genetics 136 (2019)1. - ISSN 0931-2668 - p. 51 - 62.
    computer simulation - DNA analysis - genetic conservation - local breeds - sheep

    Breeding circles allow genetic management in closed populations without pedigrees. In a breeding circle, breeding is split over sub-populations. Each sub-population receives breeding males from a single sub-population and supplies breeding males to one other sub-population. Donor-recipient combinations of sub-populations remain the same over time. Here, we derive inbreeding levels both mathematically and by computer simulation and compare them to actual inbreeding rates derived from DNA information in a real sheep population. In Veluws Heideschaap, a breeding circle has been in operation for over 30 years. Mathematically, starting with inbreeding levels and kinships set to zero, inbreeding rates per generation (ΔF) initially were 0.29%–0.47% within flocks but later converged to 0.18% in all flocks. When, more realistically, inbreeding levels at the start were high and kinship between flocks low, inbreeding levels immediately dropped to the kinship levels between flocks and rates more gradually converged to 0.18%. In computer simulations with overlapping generations, inbreeding levels and rates followed the same pattern, but converged to a lower ΔF of 0.12%. ΔF was determined in the real population with a 12 K SNP chip in recent generations. ΔF in the real population was 0.29%, based on markers to 0.41% per generation based on heterozygosity levels. This is two to three times the theoretically derived values. These increased rates in the real population are probably due to selection and/or the presence of dominant rams siring a disproportionate number of offspring. When these were simulated, ΔF agreed better: 0.35% for selection, 0.38% for dominant rams and 0.67% for both together. The realized inbreeding rates are a warning that in a real population inbreeding rates in a breeding circle can be higher than theoretically expected due to selection and dominant rams. Without a breeding circle, however, inbreeding rates would have been even higher.

    PermVeg: a generic tool to design and assess crop rotations for permanent vegetable production systems; User manual
    Wassink, B. ; Berg, W. van den; Putter, H. de; Hengsdijk, H. - \ 2015
    Wageningen : Wageningen UR (vegIMPACT report 9) - 10
    rotatie - groenteteelt - computersimulatie - simulatiemodellen - handbediening - vietnam - indonesië - rentabiliteit - arbeidskosten - pesticiden - handleidingen - rotation - vegetable growing - computer simulation - simulation models - manual operation - vietnam - indonesia - profitability - labour costs - pesticides - guide books
    This manual describes a generic tool to design and assess alternative vegetable rotations. The model combines vegetable crops to generate all possible crop rotations for a given period, based on a number of explicit criteria (objectives and restrictions) controlled by the user. The criteria eliminate in early stages those crop rotations that are undesirable. The criteria relate among others to the most important socio-economic and environmental factors in vegetable production, i.e. profitability, labor requirements and costs of pesticide use.
    Gaming and simulation to explore resilience of contested agricultural landscapes
    Speelman, E.N. - \ 2014
    Wageningen University. Promotor(en): Pablo Tittonell, co-promotor(en): Jeroen Groot; L.E. Garcia-Barrios. - Wageningen : Wageningen University - ISBN 9789461739049 - 221
    bedrijfssystemen - spelsimulatie - computersimulatie - landgebruik - landschap - farming systems - gaming simulation - computer simulation - land use - landscape

    Keywords:

    Complex systems, resilience thinking theory, communal decision-making, agent-based modeling, serious games

    Over the past decades, smallholder farming communities have become increasingly affected by an ever larger number of (unexpected) non-local economic and institutional drivers. At the same time, also environmental consequences of past and current agricultural activities have become more apparent. Consequently, farmer’s decision-making is now part of a complex social-ecological system in which stakeholders from various scales and levels exert power to influence smallholders’ decision-making. The capacity of rural communities to adapt to this fast-changing environment is key in securing the continuation of livelihoods in rural parts of the world. Improving the adaptive capacity of rural communities has been proposed as the largest challenge of the century, especially in contested areas were the interests of non-local stakeholders often strongly conflict with those of local communities. Although the attributes that underpin adaptive capacity are widely agreed upon in literature, (i) empirical evidence on how rural communities can construct trajectories of change based on adaptation, and (ii) tools that can facilitate the development of adaptive capacity are still lacking. This PhD thesis addressed both these issues. This research was based on extensive fieldwork in a usufruct community in the buffer zone of a Biosphere Reserve in Chiapas, Mexico, where objectives to conserve nature and produce food make completing claims on land and on a series of gaming and simulation workshops including a variety of stakeholders. Data showed that communities can strengthen their resilience to the sometimes strong negative effects of changes in legislation and markets. Improved local organization, diversification of land use and cooperation among farmers proved essential in this process. Four gaming and simulation tools were developed and applied with various stakeholders within this thesis. Results showed that the understanding of difficult concepts and processes among participants improved as a result of the gaming and simulation tools and that the workshops provided an opportunity to share ideas.

    Nu ook droge biologen in Wageningen
    Molenaar, J. - \ 2012
    Kennis Online 9 (2012)december. - p. 12 - 13.
    systeembiologie - modellen - computersimulatie - insect-plant relaties - gewasgroeimodellen - gewasbescherming - akkerbouw - systems biology - models - computer simulation - insect plant relations - crop growth models - plant protection - arable farming
    De systeembiologie, de wetenschapstak die computermodellen combineert met biologische waarnemingen, groeit wereldwijd onstuimig. Wageningen liep achter, maar speelt nu mee, zegt wiskundige Jaap Molenaar van Wageningen University, onderdeel van Wageningen UR.
    Morfologische en ecologische aspecten van hermeanderen
    Hoitink, Ton - \ 2012
    streams - brook valleys - ecological engineering - geomorphology - computer simulation
    Teelt optimaliseren met simulatie in virtuele kas (interview met Pieter de Visser)
    Visser, P. ; Visser, P.H.B. de - \ 2012
    Groenten en Fruit Actueel 2012 (2012)25. - ISSN 0925-9694 - p. 11 - 11.
    computersimulatie - 3d visualisatie - gewasgroeimodellen - glastuinbouw - belichting - computer simulation - 3d visualization - crop growth models - greenhouse horticulture - illumination
    Een 3D-model dat belichtingssituaties in de kas nabootst biedt uitgebreide mogelijkheden om allerlei variaties door te rekenen op effectiviteit en zo de teelt te optimaliseren. Of om praktijkonderzoek gericht te ondersteunen. Binnen het programma Kas als Energiebron heeft Wageningen UR Glastuinbouw, in een door PT en EL&I gefinancierd project, onderzocht welke mogelijkheden een driedimensionaal model van gewassen kan bieden bij tomaat en roos.
    From field to globe: upscaling of crop growth modelling
    Bussel, L.G.J. van - \ 2011
    Wageningen University. Promotor(en): Herman van Keulen; Martin van Ittersum, co-promotor(en): F. Ewert; Peter Leffelaar. - [S.l.] : S.n. - ISBN 9789461730152 - 212
    gewassen - gewasgroeimodellen - modelleren - computersimulatie - tarwe - maïs - klimaat - crops - crop growth models - modeling - computer simulation - wheat - maize - climate

    Recently, the scale of interest for application of crop growth models has extended to the region or even globe with time frames of 50-100 years. The application at larger scales of a crop growth model originally developed for a small scale without any adaptation might lead to errors and inaccuracies. Moreover, application of crop growth models at large scales usually gives problems with respect to missing data.

    Knowledge about the required level of modelling detail to accurately represent crop growth processes in crop growth models to be applied at large scales is scarce. In this thesis we analysed simulated potential yields, which resulted from models which apply different levels of detail to represent important crop growth processes. Our results indicated that, after location-specific calibration, models in which the same processes were represented with different levels of detail may perform similarly. Model performance was in general best for models which represented leaf area dynamics with the lowest level of detail. Additionally, the results indicated that the use of a different description of light interception significantly changes model outcomes. Especially the representation of leaf senescence was found to be critical for model performance.

    Global crop growth models are often used with monthly weather data, while crop growth models were originally developed for daily weather data. We examined the effects of replacing daily weather data with monthly data. Results showed that using monthly weather data may result in higher simulated amounts of biomass. In addition, we found increasing detail in a modelling approach to give higher sensitivity to aggregation of input data.

    Next, we investigated the impact of the use of spatially aggregated sowing dates and temperatures on the simulated phenology of winter wheat in Germany. We found simulated winter wheat phenology in Germany to be rather similar using either non-aggregated input data or aggregated input data with a 100 km × 100 km resolution.

    Generation or simulation of input data for crop growth models is often neces­sary if the model is applied at large scales. We simulated sowing dates of several rainfed crops by assuming farmers to sow either when temperature exceeds a crop-specific threshold or at the onset of the wet season. For a large part of the globe our methodology is capable of simulating reasonable sowing dates. To simulate the end of the cropping period (i.e. harvesting dates) we developed simple algorithms to generate unknown crop- and location-specific phenological parameters. In the main cropping regions of wheat the simulated lengths corresponded well with the observations; our methodology worked less well for maize (over- and underestimations of 0.5 to 1.5 month). Importantly, our evaluation of possible consequences for simulated yields related to uncertainties in simulated sowing and harvesting dates showed that simulated yields are rather similar using either simulated or observed sowing and harvesting dates (a maximum difference of 20%), indicating the applicability of our methodology in crop productivity assessments.

    The thesis concludes with a discussion on a proposed structure of a global crop growth model which is expected to simulate reasonable potential yields at the global scale if only monthly aggregates of climate data at a 0.5° × 0.5° grid are available. The proposed model consists of a forcing function, defined in terms of sigmoidal and quadratic functions to represent light interception, combined with the radiation use efficiency approach, and phenology determining the allocation of biomass to the organs of the crop. Within the model sowing dates and pheno­logical cultivar characteristics are simulated. Based on the proposed model the thesis finally derives directions for future research to further enhance global crop growth modelling.

    Handleiding MEBOT onderwijs 2.03 : MEBOT onderwijs 2.0 : milieutechnisch, economisch bedrijfsmodel open teelten
    Hendriks, V.J.C. ; Reeuwijk, P. van - \ 2010
    Praktijkonderzoek Plant & Omgeving B.V. - 33
    handleidingen - economische modellen - scenario-analyse - gewasbescherming - bemesting - agrarisch onderwijs - computersimulatie - computer software - akkerbouw - vollegrondsteelt - guide books - economic models - scenario analysis - plant protection - fertilizer application - agricultural education - computer simulation - computer software - arable farming - outdoor cropping
    In deze handleiding staat informatie over het installeren van MEBOT en een algemene uitleg van het programma. Daarnaast staat hierin informatie over het invoeren van gegevens in MEBOT en hoe rapportages gemaakt kunnen worden. Het Milieutechnisch, Economie Bedrijfsmodel Open Teelten (MEBOT) is ontwikkeld als onderzoeksinstrument voor de economische evaluatie van zowel het mineralen als het gewasbeschermingsbeleid. Het model biedt de mogelijkheid om voor uiteenlopende bedrijfssituaties de effecten van verschillende (beleids)scenario’s in kaart te brengen. In overleg met COP plant (Landelijke expertisegroep van docenten in het agrarisch onderwijs die sturing geven aan het plantaardig onderwijs) is er een pilot gestart waarbij MEBOT in het schooljaar 2009/2010 wordt ingezet voor het Groen Onderwijs. Speciaal voor het onderwijs is een onderwijsversie gemaakt. In deze versie zijn alleen onderdelen beschikbaar die voor het onderwijs van belang zijn.
    Handleiding MEBOT gewasbeschermings module : MEBOT onderwijs 2.0 : milieutechnisch, economisch bedrijfsmodel open teelten
    Hendriks, V.J.C. ; Spruijt, J. - \ 2010
    Wageningen : Praktijkonderzoek Plant & Omgeving B.V. - 12
    gewasbescherming - kosten - agrarische bedrijfsvoering - handleidingen - agrarisch onderwijs - computer software - computersimulatie - economische modellen - vollegrondsteelt - akkerbouw - plant protection - costs - farm management - guide books - agricultural education - computer software - computer simulation - economic models - outdoor cropping - arable farming
    In deze handleiding staat een korte toelichting over de milieu indicatoren die MEBOT berekend en de rekenregels die MEBOT hanteert. Daarnaast is er een uitleg over het invoeren in de deelmodule en het maken van rapportages. Het Milieutechnisch, Economisch Bedrijfsmodel Open Teelten (MEBOT) is ontwikkeld als onderzoeksinstrument voor de economische evaluatie van zowel het mineralen- als het gewasbeschermingsbeleid. Speciaal voor beleidsstudies is er in MEBOT een aparte deelmodule gewasbescherming gemaakt. Deze deelmodule maakt het mogelijk om met een beperkt aantal vragen de milieubelasting door gebruik van gewasbeschermingsmiddelen te berekenen. Vanuit het onderwijs is de wens uitgesproken om een dergelijke deelmodule in te zetten voor het onderwijs. In samenwerking met het onderwijs is er een aparte onderwijsversie gemaakt van de deelmodule. Door het gebruik van de MEBOT gewasbeschermingsmodule verkrijgt de cursist inzicht in de kosten en de milieubelasting van zijn of haar gewasbeschermingsstrategie.
    Estimating genetic diversity across the neutral genome with the use of dense marker maps
    Engelsma, K.A. ; Calus, M.P.L. ; Bijma, P. ; Windig, J.J. - \ 2010
    Genetics, Selection, Evolution 42 (2010). - ISSN 0999-193X - 10
    populatiegenetica - computersimulatie - genetische diversiteit - merkergenen - population genetics - computer simulation - genetic diversity - marker genes - linkage disequilibrium - prediction - selection - conservation - populations - haplotypes
    Background With the advent of high throughput DNA typing, dense marker maps have become available to investigate genetic diversity on specific regions of the genome. The aim of this paper was to compare two marker based estimates of the genetic diversity in specific genomic regions lying in between markers: IBD-based genetic diversity and heterozygosity. Methods A computer simulated population was set up with individuals containing a single 1-Morgan chromosome and 1665 SNP markers and from this one, an additional population was produced with a lower marker density i.e. 166 SNP markers. For each marker interval based on adjacent markers, the genetic diversity was estimated either by IBD probabilities or heterozygosity. Estimates were compared to each other and to the true genetic diversity. The latter was calculated for a marker in the middle of each marker interval that was not used to estimate genetic diversity. Results The simulated population had an average minor allele frequency of 0.28 and an LD (r2) of 0.26, comparable to those of real livestock populations. Genetic diversities estimated by IBD probabilities and by heterozygosity were positively correlated, and correlations with the true genetic diversity were quite similar for the simulated population with a high marker density, both for specific regions (r = 0.19-0.20) and large regions (r = 0.61-0.64) over the genome. For the population with a lower marker density, the correlation with the true genetic diversity turned out to be higher for the IBD-based genetic diversity. Conclusions Genetic diversities of ungenotyped regions of the genome (i.e. between markers) estimated by IBD-based methods and heterozygosity give similar results for the simulated population with a high marker density. However, for a population with a lower marker density, the IBD-based method gives a better prediction, since variation and recombination between markers are missed with heterozygosity.
    A framework to introduce flexibility in crop modelling: from conceptual modelling to software engineering and back
    Adam, M.Y.O. - \ 2010
    Wageningen University. Promotor(en): Herman van Keulen; J. Wery, co-promotor(en): F.A. Ewert; Peter Leffelaar. - [S.l. : S.n. - ISBN 9789085857648 - 190
    systeemanalyse - computersimulatie - wiskundige modellen - computer software - engineering - gewasproductie - gewasopbrengst - systems analysis - computer simulation - mathematical models - computer software - engineering - crop production - crop yield

    Keywords: model structure, uncertainty, modularity, software design patterns, good modelling practices, crop growth and development.

    This thesis is an account of the development and use of a framework to introduce flexibility in crop modelling. The construction of such a framework is supported by two main beams: the implementation and the modelling beam. Since the beginning of the 1990s, the implementation beam has gained increasing attention in the crop modelling field, notably with the development of APSIM (Agricultural Production Systems sIMulator) in Australia, OMS (Object Modelling System) in the United States, and APES (Agricultural Production and Externalities Simulator) in Europe. The main focus of this thesis is on the modelling beam and how to combine it with the implementation beam. I first explain how flexibility is adopted in crop modelling and what is required for the implementation beam of the framework, namely libraries of modules representing the basic crop growth and development processes and of crop models (i.e. modelling solutions). Then, I define how to deal with this flexibility (i.e. modelling beam) and more specifically I describe systematic approaches to facilitate the selection of the appropriate model structure (i.e. a combination of modules) for a specific simulation objective. While developing the framework, I stress the need for better documentation of the underlying assumptions of the modules and of the criteria applied in the selection of these modules for a particular simulation objective. Such documentation should help to point out the sources of uncertainties associated with the development of crop models and to reinforce the role of the crop modeller as an intermediary between the software engineer, coding the modules, and the end users, using the model for a specific objective. Finally, I draw conclusions for the prospects of such a framework in the crop modelling field. I see its main contribution to (i) a better understanding in crop physiology through easier testing of alternatives hypotheses, and (ii) integrated studies by facilitating model reuse.



    Tool to determine the coefficient of variation of DegT50 of plant protection products in water-sediment systems for different values of the sorption coefficient
    Horst, M.M.S. ter; Groenwold, J.G. - \ 2009
    Wageningen : Wettelijke Onderzoekstaken Natuur & Milieu (WOt-werkdocument 171) - 68
    pesticiden - waterverontreiniging - sedimenttest - grensvlak tussen sediment en water - halfwaardetijd - simulatiemodellen - computersimulatie - computer software - toelating van bestrijdingsmiddelen - verontreinigde sedimenten - waterbodems - pesticides - water pollution - sediment test - sediment water interface - half life - simulation models - computer simulation - computer software - authorisation of pesticides - contaminated sediments - water bottoms
    In the present Dutch registration procedure and the EU procedure for inclusion of pesticides in a positive Community list of pesticide substances ( Annex1 ; Directive 91/414) inverse modeling of water-sediment experiments is used to estimate degradation rates in both the water layer and the sediment. However the original aim of a water-sediment experiment was to get a picture of the products formed for the pesticide and their persistence in water-sediment systems. Till now it is still unclear whether water-sediment experiments are suitable for estimating of the degradation half lives in the water layer and the sediment separately. This question was tested using simulations with a model describing pesticide behaviour in a water layer and its underlying sediment, in order to exclude experimental errors and peculiarities.
    Using a groundwater quality negotiation support system to change land-use management near a drinking-water abstraction in the Netherlands
    Brink, C. van den; Zaadnoordijk, W.J. ; Grift, B. van der; Ruiter, P.C. de; Griffioen, J. - \ 2008
    Journal of Hydrology 350 (2008)3-4. - ISSN 0022-1694 - p. 339 - 356.
    grondwater - hulpbronnenbeheer - watervoorraden - besluitvorming - nitraten - drinkwater - landgebruiksplanning - grondwaterwinning - waterbeheer - computersimulatie - infiltratie - landgebruik - duurzaamheid (sustainability) - waterkwaliteit - nederland - grondwaterkwaliteit - beslissingsondersteunende systemen - groundwater - resource management - water resources - decision making - nitrates - drinking water - land use planning - groundwater extraction - water management - computer simulation - infiltration - land use - sustainability - water quality - netherlands - groundwater quality - decision support systems - nitrate pollution - catchment scale - model - transport - aquifer - vulnerability - uncertainties - simulation - impact - fate
    A negotiation support system (NSS) was developed to solve groundwater conflicts that arose during land-use management. It was set up in cooperation with the stakeholders involved to provide information on the impact of land use, e.g., agriculture, nature (forested areas), recreation, and urban areas, on the quality of both infiltrating and abstracted groundwater. This NSS combined simulation programs that calculate (1) the concentrations of nitrate in shallow groundwater for each land-use area and (2) the transport of nitrate in the groundwater-saturated zone. The user interface of the NSS enabled scenario analyses. The NSS was validated at a drinking-water abstraction near Holten (the Netherlands) using a spatial planning process aimed at sustainable land-use and groundwater-resource management. Two land-use scenarios were considered: a base scenario reflecting the autonomous development and an adapted land-use scenario. The calculated results for shallow groundwater provided an explicit spatial overview of the impact of historical land use and N application on the quality of abstracted groundwater as well as insight into the impact of changes in land use and N application. Visualization of the conflicting interests of agriculture and the drinking-water abstraction helped all stakeholders accept the necessary changes in land use identified by the adapted land-use scenario of the NSS. These changes were included in the preferred land-use management option in the regional planning process, which has since been formalized. The NSS provided system insight, scoping analyses, and education, in addition to generating quantitative information on the impact of land-use functions on groundwater quality.
    Stoeien met de gebruiksnormen computerapplicatie MEBOT helpt u op weg!
    Schreuder, R. ; Dijk, W. van; Wolf, M. de - \ 2008
    simulatiemodellen - agrarische bedrijfsvoering - akkerbouw - bollen - besluitvorming - computersimulatie - computer software - beslissingsondersteunende systemen - vollegrondsgroenten - simulation models - farm management - arable farming - bulbs - decision making - computer simulation - computer software - decision support systems - field vegetables
    Global drought in the 20th and 21st centuries : analysis of retrospective simulations and future projections of soil moisture
    Sheffield, J. - \ 2008
    Wageningen University. Promotor(en): P.A. Troch, co-promotor(en): E.F. Wood. - [S.l.] : S.n. - ISBN 9789085048060 - 206
    droogte - bodemwater - computersimulatie - simulatiemodellen - historische verslagen - projecties - toekomst - drought - soil water - computer simulation - simulation models - historical records - projections - future
    We describe the analysis of global and regional drought over the second half of the 20th century from a retrospective model simulation of the terrestrial water cycle, and projected 21st century changes using multi-scenario data from multiple climate models. A global meteorological forcing dataset is developed for 1948-2000 to drive the retrospective simulation by combining observations with reanalysis. Biases in the reanalysis precipitation, temperature and radiation are corrected for systematic bias and spurious trends, which exert erroneous effects on the land water budgets. A monthly soil moisture based drought index is developed from the simulation and is used to investigate the occurrence, variability and trends in drought for 1950-2000. The frequencies of short-term droughts (6 months and less) are highest in humid regions. Medium term droughts (6-12 months) are more prevalent in mid- to high-latitudes, driven by persistent frozen soil moisture anomalies. Over the Sahel and parts of high northern latitudes, the frequency of long-term droughts is at a maximum. Severe drought events are systematically identified in terms of spatial coverage, including the 1988 USA, 1982/83 Australian, 1983/4 Sahel and 1965/66 Indian droughts. There is an overall increasing trend in global soil moisture, driven by precipitation, reflected especially in North America. Regional variation is nevertheless apparent and significant drying over West Africa, stands out. Trends in drought characteristics are mostly decreasing but statistically significant changes are limited in areal extent and generally less than 10% of continental areas. Concurrent decreases in global drought spatial extent are 0.04% yr−1. Within the long-term trends we find interannual and decadal variations in soil moisture and drought characteristics driven mainly by ENSO variability, although the AMO plays an important role in many regions. Drought is driven primarily by variability in precipitation, but temperature has an effect that appears to be exaggerated in the late 20th century, especially in high northern latitudes. At global scales the soil moisture index and the PDSI are reasonably well correlated but this breaks down in cooler regions and seasons, and notably for recent years when the PDSI shows a larger drying trend, possibly due to its temperature-based evaporation estimate. To investigate future projected changes in drought, soil moisture data is analyzed for three future IPCC AR4 climate scenarios (B1, A1B, A2) from eight GCMs. A decrease in 21st century global soil moisture is accompanied by a doubling of the spatial extent and frequency of short-term droughts. Long-term droughts become three v times more common. Regionally, the Mediterranean, West African, Central Asian and Central American regions show large increases, as does mid-latitude North America but with larger inter-scenario variation. Changes under the B1 scenario are the least and the A1B and A2 results are similar. Although the changes are generally monotonic increasing, they are not statistically different from natural variability for multiple decades, in contrast to air temperature, and this depends on the drought variable, magnitude of change, natural variability and statistical confidence. In contrast, changes in the means of hydrologic variables, including soil moisture, are essentially undetectable within the 21st century, implying that changes in extremes may be more detectable than changes in mean quantities.
    Reconstructie van de historische hydrologie
    Gaast, J.W.J. van der; Massop, H.T.L. - \ 2007
    H2O : tijdschrift voor watervoorziening en afvalwaterbehandeling (2007)7. - ISSN 0166-8439 - p. 36 - 40.
    waterbalans - hydrologie - afvoer - evapotranspiratie - bodemwatergehalte - bodemwaterbalans - computersimulatie - klimaatverandering - grondwaterstand - neerslag - hydrologie van stroomgebieden - geschiedenis - kwel - geohydrologie - water balance - hydrology - discharge - evapotranspiration - soil water content - soil water balance - computer simulation - climatic change - groundwater level - precipitation - catchment hydrology - history - seepage - geohydrology
    De WB21-studie heeft geleid tot wateropgaven waarbij de trits vasthouden-bergen-afvoeren de voorkeursvolgorde geeft voor het reduceren van piekafvoeren. In het verleden is het watersysteem echter ook aangepast, wat invloed heeft gehad op de werking van het watersysteem. Om te kunnen leren uit het verleden is bij Alterra een onderzoek uitgevoerd waarbij de historische hydrologische situatie voor een stroomgebied in het zandgebied van Nederland modelmatig is gereconstrueerd. Uit de vergelijking tussen de historische en de huidige situatie blijkt dat bij extreme neerslag, die gemiddeld vaker dan éénmaal per jaar voorkomt, de afvoer vroeger duidelijk minder was, omdat veel meer water tijdelijk op het maaiveld werd geborgen. Het is echter de vraag in hoeverre we nog terug kunnen naar die omstandigheden
    Negociatrix policy game: building capacities in trade policy analysis
    Balie, J. ; Hofwegen, G. van; Jongeneel, R. ; Koning, N.B.J. - \ 2007
    Rome : FAO - Wageningen UR - 28
    internationale handel - handelspolitiek - computersimulatie - computer software - spellen - handelsonderhandelingen - handelsrelaties - voedsel- en landbouworganisatie - agrarische handel - besluitvorming - analyse van besluiten - handelsakkoorden - international trade - trade policy - computer simulation - computer software - games - trade negotiations - trade relations - food and agriculture organization - agricultural trade - decision making - decision analysis - trade agreements
    The Negociatrix Policy Game is a tool for training in multilateral negotiation, which has been developed through a partnership between FAO and the University of Wageningen in the Netherlands. This tool is a software based on a quantitative model and a simulation that consents to underline the importance of analytical capacities in negotiations and to demonstrate the importance of consistency of the strategies of negotiation. This software is applied to the multilateral trade negotiations for agriculture. It is inspired by the simulation called Negociatrix (www.fao.org/tc/tca/negotiation) that FAO developed at an earlier stage (2005) and that has been presented at the Harvard PON/IRENE conference in November 2005 in Paris. The software allows simulating several successive rounds of negotiation and notably revealing after each round the impact of the agreement concluded to the previous round. In that sense, the strategy of negotiation adopted can be more directly evaluated. The software is conceived like a tool to support the preparation of decisions and negotiations. This article presents the structure of the software, explains how it works, comments the first application modalities and proposes the conditions of use.
    Macroscopic modelling of solid-state fermentation
    Hoogschagen, M.J. - \ 2007
    Wageningen University. Promotor(en): Hans Tramper, co-promotor(en): Arjen Rinzema. - [S.l.] : S.n. - ISBN 9789085045786 - 120
    fysische modellen - groeimodellen - computersimulatie - aspergillus - tarwe - vast-substraatfermentatie - physical models - growth models - computer simulation - aspergillus - wheat - solid-state fermentation

    Solid-state fermentation is different from the more well known process of liquid fermentation because no free flowing water is present. The technique is primarily used in Asia. Well-known products are the foods tempe, soy sauce and saké. In industrial solid-state fermentation, the substrate usually consists of loose substrate particles, although in research situations agar like substrates are also common. Solid-state fermentations cannot be mixed as easily as liquid fermentations. Because of this, it is difficult to maintain the temperature in the fermentation at an acceptable level and to prevent differences in substrate availability throughout the solid material. An advantage of solid-state fermentation is that the process is cheap, and that products are in some cases easier to separate from the substrate than in liquid. Because of this, the technique is economically interesting. The process has not been studied as extensively as liquid fermentation. This thesis extends the available knowledge by providing several mathematical models for both biological and physical processes that occur in aerated packed beds.

    In aerated packed beds, the metabolic heat that is released in the microbial process is removed by blowing air through the packed material. The effectiveness of the aeration is the result of both the heat uptake capacity of the air itself and of the evaporation of moisture to the air. In fact, the evaporation contributes more to the heat removal than the air itself. A side effect of the evaporation is that the decreasing moisture level in the substrate can become limiting for the microbial process.

    In this thesis, the growth of Aspergillus oryzae and Aspergillus sojae, two related species of fungi, in an aerated packed bed of moist wheat kernels is studied. The study deals with both the microbial and physical aspects of the system.

    Many different types of substrate have been used in studies on solid-state fermentation. Prior to starting the work on the mathematical models, we checked if the fermentation results of A. oryzae on several types of wheat matched, The check was done by matching respiration profiles for several types of wheat and two pretreatment methods. It turned out that considerable differences between the pretreatment methods can exist, which indicated the importance of using the exact same type of substrate and pretreatment in experiments that are to be compared.

    No accurate model description of the microbial aspects of SSF is available yet. Because the focus of the major part of the thesis is on deriving model descriptions for the physical aspects of cooling and drying-out in aerated packed beds, it was decided that using a temperature-response model for the description of heat development would incorporate too many uncertainties in the overall packed-bed model. The heat development in the further studies presented was therefore based on fitted oxygen consumption profiles instead of on modelled microbial growth.

    For the validation of the physical models in this thesis, experiments were carried out in a packed bed of approximately 50 cm height. This packed bed was insulated thermally, and offered the possibility of taking online temperature measurements and sampling the moisture content. The models that were derived to describe the changes in growth conditions in the packed bed in time and space were based on well-known physical relations. All physical models are composed of heat- and mass balances. As described above, the temperature dependence of the fungus was neglected, and the metabolic heat development was incorporated in the balances by means of fitted respiration profiles. This way, inaccuracies in the heat production in the physical model were prevented, allowing the focus on the correct description of heat and mass transfer.

    The first model presented was based on an existing model, which overestimated the drying out of the solid material. This overestimation was due to the assumption of constant saturation of the gas phase with water vapour. The overestimation of the drying out meant that the assumption of vapour saturation needed to be adjusted. Heat and mass transfer coefficients were determined for the substrate involved, and besides this water activity was introduced as a factor that limited the evaporation of water from the substrate. The addition of water activity was of great influence on the model results.

    The insight in the effect of local water activity on the fermentation was the onset for a study on the response of fungi to changing water activity. A system was designed that allowed the dynamic response of the fungus on decreasing water activity to be measured. The experimental set-up was based on isothermal experiments that were slowly dried out by blowing dry air through them, with simultaneous experiments carried out at aw ~ 1 for comparison with the response to the drying out. Considering the fact that all studies on water activity that preceded this approach were based on static and artificial conditions, this set-up is more similar to the actual conditions in a packed-bed fermentation.

    Contrary to the expectations, the system that was dried out showed a decreased fungal growth rate when the water activity in the substrate was still the same as it was in the reference experiment. We checked two possible causes for this phenomenon. Moisture gradients in the particle were ruled out, because these were too small to be able to cause the difference in growth rate. We found that there is most likely a region of very cold substrate material due to wet-bulb cooling. Wet-bulb cooling is a phenomenon in which the evaporation of water from a system to a passing airflow allows the system to cool to temperatures below the temperature of the air. Because we used dry air in our experiment, the effect was too large to be compensated through conduction. An estimated 5% of the bed could not be fermented because of the low temperature. For a successful series of experiments, we need to obtain drying with a 100% constant bed temperature. For such a series, a good comparison of the effect of drying on fungal behaviour will be possible.

    During the experiments in the packed-bed involving Aspergillus oryzae strong shrinkage of the packed-bed occurred because the fungus tied the substrate particles together. Because of the shrinkage, the aeration lost effectivity and the fermentation results were suboptimal. A model was designed to describe the amount of shrinkage, based on the decrease in water content in the bed. The validation of this model could not be performed with A. oryzae, because it was impossible to carry out controlled fermentations with this fungus. Therefore, A. sojae was used, which has the same growth characteristics as A. oryzae, except for the formation of substrate ties. The model on shrinkage offers a good prediction of the shrinkage that is expected with the combined effect of fungal growth and dehydration. 1f in industrial fermentations a different shrinkage pattern is observed, this is an indication that there is channel formation somewhere in the bed. This observation can be than followed by for instance a mixing event, improving the overall performance of the fermentation.

    In the final chapter of this thesis, an overview of the work that could possibly offer further improvements to the present models is given. It was concluded that the modelling of the microbial aspects offer the biggest chances for success in this respect, since this aspect has of yet been modelled less accurately than the physical part.

    'Belichten in winter is energetisch gunstiger dan in zomer' : belichtingsstrategie achter de computer bepalen
    Jongschaap, R.E.E. ; Dueck, T.A. ; Arkesteijn, M. - \ 2006
    Onder Glas 3 (2006)4. - p. 11 - 13.
    teelt onder bescherming - rozen - belichting - economische haalbaarheid - winter - teeltsystemen - computersimulatie - energiegebruik - glastuinbouw - snijbloemen - protected cultivation - roses - illumination - economic viability - winter - cropping systems - computer simulation - energy consumption - greenhouse horticulture - cut flowers
    Raymond Jongschaap van PRI heeft berekend wat extra belichten bij roos kost en oplevert. 's Winters levert belichting energetisch gezien meer op dan in de zomer. Wel is er een optimum. Daarboven levert het relatief gezien minder op, maar het blijft aantrekkelijk. Zeker als dit gekoppeld wordt aan de opbrengstprijzen voor rozen, die 's winters hoger liggen. Als de energieprijzen stijgen, is het in eerste instantie in de zomermaanden minder aantrekkelijk om te belichten
    Design of membrane systems for fractionation of particle suspensions
    Brans, G.B.P.W. - \ 2006
    Wageningen University. Promotor(en): Remko Boom, co-promotor(en): Karin Schroen; Ruud van der Sman. - Wageningen : s.n. - ISBN 9789085043799 - 60
    deeltjes - fractionering - membranen - computersimulatie - deeltjesgrootteverdeling - particles - fractionation - membranes - computer simulation - particle size distribution
    The aim of this research was to obtain more insight in membrane processes for the fractionation of micro sized particles (0.1 - 10 μm) with small size differences, and with special attention for microsieve technology as an alternative for conventional membranes.
    Check title to add to marked list
    << previous | next >>

    Show 20 50 100 records per page

     
    Please log in to use this service. Login as Wageningen University & Research user or guest user in upper right hand corner of this page.