Staff Publications

Staff Publications

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    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

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    We will mail you new results for this query: keywords==dynamische modellen
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Masterplan for the development of nutrient based dynamic mechanistic response models for pigs and poultry
Jansman, A.J.M. ; Laar, H. van; Veldkamp, A. ; Gerrits, W.J.J. - \ 2014
Wageningen UR Livestock Research (Report / Wageningen UR Livestock Research 765) - 32
modelleren - dynamische modellen - diervoeding - reacties - prestatieniveau - varkens - pluimvee - voedingsstoffenretentie - vleeskuikens - modeling - dynamic models - animal nutrition - responses - performance - pigs - poultry - nutrient retention - broilers
The masterplan describes the development of new nutrient based dynamic mechanistic response models for pigs and poultry predicting the animal’s performance, the retention of nutrients in the body and in “end products”, and the output of non-retained nutrients in the environment. The plan has been developed in the framework of the Public Private Partnership Feed4Foodure (F4F) in the Netherlands.
Quantification of dynamics of soil-borne pathogens and their consequences for yield in crop rotations
Berg, W. van den - \ 2011
University. Promotor(en): Johan Grasman, co-promotor(en): Walter Rossing. - [S.l.] : S.n. - ISBN 9789461730497 - 127
gewassen - rotaties - bodempathogenen - plantenparasitaire nematoden - populatiedynamica - oogstvoorspelling - proefopzet - modellen - dynamische modellen - statistische analyse - crops - rotations - soilborne pathogens - plant parasitic nematodes - population dynamics - yield forecasting - experimental design - models - dynamic models - statistical analysis
Modelling anaerobic digestion of concentrated black water and faecal matter in accumulation system
Elmitwalli, T. ; Zeeman, G. ; Otterpohl, R. - \ 2011
Water Science and Technology 63 (2011)9. - ISSN 0273-1223 - p. 2039 - 2045.
nieuwe sanitatie - afvalwaterbehandeling - anaërobe afbraak - dynamische modellen - feces - urine - huishoudens - biodegradatie - new sanitation - waste water treatment - anaerobic digestion - dynamic models - faeces - households - biodegradation - decentralized sanitation - waste-water - grey water - urban - biodegradability - management - reuse - areas
A dynamic mathematical model based on anaerobic digestion model no. 1 (ADM1) was developed for accumulation (AC) system treating concentrated black water and faecal matter at different temperatures. The AC system was investigated for the treatment of waste(water) produced from the following systems: vacuum toilet for black water (VBW), vacuum toilet for faeces with urine separation (VF), dry toilet (DT), dry toilets for faeces with urine separation (DF), separated faecal matter from conventional black water by filter bag (FB). For evaluation of the AC system treating the proposed waste(water) sources at 20 and 35°C, two options were studied: (1) The filling period of the AC system was constant for all waste(water) sources (either 1, 3 or 6 months) and for each period, the seed sludge volume was varied; (2) The volume of the AC system was constant for all proposed waste(water) sources. The results showed that the filling period of the AC system was the main parameter affecting the system performance, followed by operational temperature, while the increase of the seed sludge volume slightly enhanced the performance of the system. The model results indicated that the filling period of the AC system should be higher than 150 days for obtaining a stable performance. It was found that the hydrolysis of biodegradable particulate chemical oxygen demand (COD) is the rate limiting step, as volatile fatty acid concentration is very low in all experimental conditions (
Adaptive models for operational use in dairy farming : increasing economic results utilising individual variation in response
Andre, G. - \ 2011
University. Promotor(en): Alfons Oude Lansink, co-promotor(en): Paul Berentsen; Bastiaan Engel. - [S.l.] : S.n. - ISBN 9789085858812 - 169
melkveehouderij - melkresultaten - bedrijfsresultaten in de landbouw - melkopbrengst - melkkoeien - dynamische modellen - melkinterval - melkproductie - voeropname - melktempo - nederland - dairy farming - dairy performance - farm results - milk yield - dairy cows - dynamic models - milking interval - milk production - feed intake - milking rate - netherlands
During the last century in the Netherlands milk production per cow has almost tripled. Accordingly, the amount of concentrates yearly fed per cow strongly increased. Furthermore, automation and robotisation has changed dairy management, especially by the introduction of automatic concentrate feeders and milking systems. A new management concept, emerging in the last decades, is Precision Livestock Farming (PLF). The objective of PLF is to optimize livestock production, by on-line monitoring and control of the production process, utilizing the technical possibilities of automation and robotisation. Nowadays, individual settings for daily concentrate supply and milking frequency are based on standards, ignoring individual variation in milk yield response on concentrate intake and milking frequency. This leads to the main hypothesis for this thesis research that profitability of dairy farming can be improved by utilizing information on individual variation in response. The first objective of this research was to quantify the individual variation in milk yield response to concentrate intake and milking interval length, in order to assess the economic prospects of applying individual optimal settings for concentrate supply and milking frequency. The second objective was the development and testing of adaptive models for on-line estimation of the actual individual response in milk yield to concentrate intake and milking interval length. The conclusion is that on-line estimation of the actual individual response in milk yield and milking duration is possible following a Bayesian approach for time series using an adaptive dynamic model. Besides estimation of the actual response the Bayesian approach adequately detects process deteriorations. Therefore, adaptive dynamic models provide a useful tool for control and monitoring of the dairy production process.
FISHRENT; Bio-economic simulation and optimisation model
Salz, P. ; Buisman, F.C. ; Soma, K. ; Frost, H. ; Accadia, P. ; Prellezo, R. - \ 2011
The Hague : LEI, part of Wageningen UR (Report / LEI : Onderzoeksveld Natuurlijke hulpbronnen ) - ISBN 9789086155149 - 74
visserij - economie - biologie - economische modellen - simulatie - dynamische modellen - visbestand - landbouwbeleid - europese unie - fisheries - economics - biology - economic models - simulation - dynamic models - fishery resources - agricultural policy - european union
Key findings: The FISHRENT model is a major step forward in bio-economic model-ling, combining features that have not been fully integrated in earlier models: 1- Incorporation of any number of species (or stock) and/or fleets 2- Integration of simulation and optimisation over a period of 25 years 3- Integration of effort and TAC-driven management policies 4- Three independent relations for stock growth, production and investments. The feedbacks within the model allow for a dynamic simulation. The main application of the model is scenario analysis of policy options. Complementary findings: The model formulates a complete set of mathematical relations, but it also con-tains a number of important assumptions, which remain to be tested empirically. Therefore the model presents a challenging agenda for empirical research, which should lead to further qualitative and quantitative improvements of the in-dividual mathematical equations and parameter values. Method: This model was developed during the EU-funded project 'Remuneration of spawning stock biomass'. Its aim was to generate consistent sets of scenarios for an assessment of potential resource rents in different EU fisheries. The model comprises six modules, each focussing on a different aspect of the functioning of the fisheries system: biology (stocks), economy (costs, earnings and profits), policy (TACs, effort and access fees), behaviour (investments), prices (fish and fuel) and an interface linking the modules together. Input, calculation and output are clearly separated. The model produces a standard set of graphics, which provide a quick insight into the results of any model run. All output of the model runs can be exported to database software for further analysis. The model has been built in Excel, which makes it accessible for most us-ers. It has been used in new applications and even translated to other software. The model is continually further developed.
Econometric analyses of microfinance credit group formation, contractual risks and welfare impacts in Northern Ethiopia
Berhane Tesfay, G. - \ 2009
University. Promotor(en): Arie Oskam, co-promotor(en): Koos Gardebroek; Tassew Woldehanna. - [S.l. : S.n. - ISBN 9789085854258 - 146
krediet - landbouwhuishoudens - financiële instellingen - econometrie - risico - dynamische modellen - groepen - contracten - armoede - plattelandsbevolking - ethiopië - microfinanciering - panelgegevens - credit - agricultural households - financial institutions - econometrics - risk - dynamic models - groups - contracts - poverty - rural population - ethiopia - microfinance - panel data

Key words
Microfinance, joint liability, contractual risk, group formation, risk-matching, impact evaluation, Panel data econometrics, dynamic panel probit, trend models, fixed-effects, composite counterfactuals, propensity score matching, farm households, Ethiopia.

Lack of access to credit is a key obstacle for economic development in poor countries. The underlying problem is related to information asymmetry combined with the poor’s lack of collateral to pledge. New mechanisms in microfinance offer ways to deal with this problem without resorting to collateral requirements. The objective of this thesis is to examine the mechanisms of providing credit through microfinance and assess the long-run borrowing effects on household welfare in Ethiopia. The Ethiopian environment provides a suitable setting to examine these issues. To meet this objective, two unique data sets - a five-wave panel data on 400 and a cross-sectional data on 201 households - from northern Ethiopia are used.
Borrowing decision is first conceptualized using a dynamic stochastic theoretical framework. Two types of risks involved in joint liability lending are incorporated, i.e., risk of partner failure and risk of losing future access to credit. Empirical analysis using recent dynamic panel data probit techniques show that these contractual risks indeed impede participation in borrowing. The impediment is higher for the poorer, and for new than repeat participants. Second, group formation is analyzed within the framework of alternative microeconomic theories of joint liability where the commonly held hypothesis that groups formed are homogeneous in risk profiles is tested. Empirical results reject this hypothesis indicating that the formation of heterogeneous risk profiles is an inherent feature in group formation and repayment. In fact, there is evidence that borrowers take advantage of established informal credit and saving, and other social networks, which also suggests that group formation outcomes vary depending on underlying socioeconomic contexts.
Third, the impact of long-term borrowing on household welfare is assessed from the dimension of intensity and timing of participation in borrowing. Panel data covering relatively long period enabled to account for duration and timing concerns in program evaluation. Recent parametric and semi-parametric panel data techniques are innovatively employed to mitigate participation selection biases. Results from both approaches indicate that borrowing has increased household welfare significantly: the earlier and more frequent the participation the higher the impact partly due to lasting effects of credit. This also suggests that impact studies that are based on a single-shot observation of outcomes and that do not account for the timing and duration of participation may underestimate microfinance credit impacts.

Flexible decision-making in crisis events : discovering real options in the control of foot-and-mouth disease epidemics
Ge, L. - \ 2008
University. Promotor(en): Ruud Huirne, co-promotor(en): A.R. Kristensen; Monique Mourits. - [S.l.] : S.n. - ISBN 9789085049692 - 149
crises - mond- en klauwzeer - epidemieën - besluitvorming - ziektebestrijding - markov-processen - onzekerheid - dynamisch programmeren - bayesiaanse theorie - dynamische modellen - bedrijfseconomie - beslissingsondersteunende systemen - beslissingsmodellen - foot and mouth disease - epidemics - decision making - disease control - markov processes - uncertainty - dynamic programming - bayesian theory - dynamic models - business economics - decision support systems - decision models

Crisis event, foot-and-mouth disease (FMD), epidemic control, real options, decision flexibility, multi-level hierarchic Markov process (MLHMP), uncertainty, decision-support framework, turning moment, dynamic programming, Bayesian forecasting, dynamic models, overreacting, underreacting

This research introduced the real options way of thinking into decision-making in crisis events like animal epidemics, with foot-and-mouth disease (FMD) as a case in point. A unique angle was taken to investigate decision flexibility in choosing optimal control strategies. The main objective was to develop a flexible decision-support framework which corresponds to practice and provides consistent treatment of ongoing uncertainty in controlling animal epidemics. Conceptualisation and operationalisation of decision flexibility were the two main focuses.
A decision analysis revealed the dynamic and sequential nature of decision- making in the control of animal epidemics. The importance of decision flexibility was attributed to the existence of uncertainty and linked decisions in the multi-stage decision process. Timing of control options and the possibility of learning were found to be essential in conceptualising decision flexibility. To operationalise decision flexibility, the main methodological approach was the integration of multi-level hierarchic Markov process (MLHMP) and Bayesian forecasting methods. Based on MLHMP and dynamic generalised linear models (DGLM), a new decision-support framework was developed to investigate the impact of uncertainty and the possibility of learning in choosing the optimal timing of control options over time. The framework paid special attention to the interdependency among strategic, tactical, and operational decisions in managing FMD epidemics. The decision-support framework was shown to be useful in contingency planning for future epidemics.
Addressing the decision flexibility in a dynamic decision process, real options analysis and MLHMP were found to be complementary in developing the flexible decision-support framework. Both required dynamic assessment of future epidemic development and control options. Towards empirical application of the decision-support framework, an integrated epidemic-economic modelling approach was described and illustrated with simulated epidemics. It was shown that, by including decision flexibility in the dynamic decision process of epidemic control, the new modelling approach enabled more realistic estimation of the costs of underreacting or overreacting than the traditional static approaches.

Dynamisch melken en voeren levert geld op
Ouweltjes, W. ; Andre, G. ; Zom, R.L.G. ; Bleumer, E.J.B. - \ 2008
V-focus 5 (2008)april (2). - ISSN 1574-1575 - p. 22 - 23, 25.
melkveehouderij - melken - voedering - krachtvoeding - automatisering - melkstandinrichtingen - robots - lineaire modellen - dynamische modellen - bedrijfsresultaten in de landbouw - dairy farming - milking - feeding - force feeding - automation - milking parlours - linear models - dynamic models - farm results
Op het High-techbedrijf van de Waiboerhoeve is in 2006 een prototype voor een dynamisch lineair adviessysteem voor melken en voeren ontwikkeld en getoetst. De resultaten geven aan dat met deze benadering een aanzienlijk beter saldo behaald kan worden dan met traditionele adviezen
Integrating the production functions of Liebig, Michaelis-Menten, Mitscherlich and Liebscher into one system dynamics model
Nijland, G.O. ; Schouls, J. ; Goudriaan, J. - \ 2008
NJAS Wageningen Journal of Life Sciences 55 (2008)2. - ISSN 1573-5214 - p. 199 - 224.
gewasproductie - voedingsstoffenbalans - stikstofgehalte - fosfor - emissie - dynamische modellen - nutriëntenuitspoeling - dynamisch modelleren - bodem-plant relaties - crop production - nutrient balance - nitrogen content - phosphorus - emission - dynamic models - nutrient leaching - dynamic modeling - soil plant relationships
Any agricultural production process is characterized by input¿output relations. In this paper we show that the production functions of Liebig, Mitscherlich and Liebscher for the relation between nutrient supply and crop production can be regarded as special variants of one 'integrated model'. The model is elaborated for two nutrients, nitrogen and phosphorus, and is based on the Michaelis-Menten hyperbolic equation. This basic equation has two main terms and one multiplicative interaction term. The parameter values determine which one of the aforementioned functions is generated. 'Greenwood's variant of the Michaelis-Menten function' is approached if the main terms dominate. 'De Wit's variant of the Mitscherlich function' is approached if the multiplicative term dominates. Liebig's function emerges from any of these variants if nutrient supply is constrained to such an extent that nutrient uptake continually exhausts the nutrient stock. The 'Liebscher variant' - considered the most appropriate for most empirical situations - is intermediate between those of Liebig, Michaelis-Menten and 'De Wit's Mitscherlich', and can be obtained by parameter calibration. Generally, these functions result in 'decreasing marginal returns' with increasing nutrient supply. However, if interacting nutrients are supplied in precisely the required proportion, the variant with a multiplicative term does show 'increasing marginal returns', but only in conditions of low nutrient supply rates, low nutrient affinities and / or high nutrient losses
Modelling volatile fatty acid dynamics and rumen function in lactating cows
Bannink, A. - \ 2007
University. Promotor(en): Seerp Tamminga; J. France, co-promotor(en): Jan Dijkstra. - [S.l.] : S.n. - ISBN 9789085047858 - 251
koeien - lactatie - vluchtige vetzuren - dynamische modellen - pensfermentatie - absorptie - pensepitheel - voedingsfysiologie - celmetabolisme - cows - lactation - volatile fatty acids - dynamic models - rumen fermentation - absorption - rumen epithelium - nutrition physiology - cell metabolism
Mathematical models are developed to quantity and integrate the various processes involved with rumen fermentation. Three extant mechanistic models of rumen fermentation were studied (Baldwin et al., Danfær and Dijkstra et al.), each with a truly dynamic representation but different conceptual approach. The models were compared on mathematical representation of individual processes and their prediction accuracy was evaluated. Although the models predicted similar rates of substrate degradation and rumen outflow of organic matter, total crude protein and microbial protein, they differed substantially in representation of the underlying microbial mechanisms. The model of Baldwin et al. performed best in prediction of the combination of rumen pool sizes and duodenal flows, whereas the model of Dijkstra et al. was evaluated to deliver the most realistic outflow of rapidly fermentable carbohydrates. Further, it was identified that all models needed improvement with respect to the prediction of amounts and type of volatile fatty acids (VFA) produced. In a subsequent evaluation is was investigated to what extent individual model elements, of a selection of five, could be responsible for inaccurate VFA predictions. The results suggested that inaccuracy of stoichiometric coefficients of VFA yield from fermented substrate (VFA coefficients) and incorrect representations of VFA absorption kinetics are the most likely causes. New values of VFA coefficients were derived by regression of a stoichiometric model of VFA yield against data of VFA molar proportions observed in vivo in rumen fluid of lactating cows. Inputs to the model were observed rates of rumen substrate degradation. Regression against simulated data sets including random error indicated that the accuracy of this method to estimate VFA coefficients is acceptable. Estimates from regressions against in vivo data delivered new sets of VFA coefficients for roughage-rich and concentrate-rich diets. In a follow-up study the representation of stoichiometry was made pH-dependent. With regression of this model against in vivo data a profound effect of rumen pH on the type of VFA formed from rapidly fermentable carbohydrates was established. Besides VFA production, the rumen concentrations and the amount and profile of VFA available for the cow are also affected by absorption and metabolism of VFA by epithelial tissues in the rumen wall. A mechanistic model was constructed that represents the dynamics of these processes, including the effects of changes in VFA concentration differences between different compartments, the effect of competitive inhibition between VFA and the effect of changes in surface area and epithelial mass. Although some essential characteristics of VFA transport and intra-epithelial metabolism could be reproduced by the model, it was concluded that there is a definite need for more experimental data. It is concluded that various levels of functioning need to be included when representing whole rumen function. Besides intrinsic degadation characteristics and passage of ingested substrates, environmental conditions in the rumen and the functionality of the rumen wall need to addressed.
Modelling and dynamic optimisation of quality indicator profiles during drying
Quirijns, E.J. - \ 2006
University. Promotor(en): Gerrit van Straten, co-promotor(en): Wilko van Loon. - [S.l.] : S.n. - ISBN 9085044286 - 254
drogen - droogkwaliteit - kwaliteitsnormen - kwaliteitscontroles - indicatoren - optimalisatie - optimalisatiemethoden - dynamische modellen - drying - drying quality - quality standards - quality controls - indicators - optimization - optimization methods - dynamic models
Dynamic modelling of inter-organisational information management systems and relationships in food chains
Storer, C.E. ; Soutar, G.N. ; Trienekens, J.H. ; Beulens, A.J.M. ; Quaddus, M.A. - \ 2004
In: Dynamics in Chains and Networks. Proceedings of the sixth International Conference on Chain and Network Management in Agribusiness and the Food Industry, Ede, 27-28 May 2004. - Wageningen : Wageningen Academic Publishers - ISBN 907699840X - p. 556 - 565.
information systems - management - dynamic models - agro-industrial chains - informatiesystemen - bedrijfsvoering - dynamische modellen - agro-industriële ketens
Derivation of cation exchange constants for sand, loess, clay and peat soils on the basis of field measurements in the Netherlands
Vries, W. de; Posch, M. - \ 2003
Wageningen : Alterra (Alterra-rapport 701) - 50
bodemtypen - kationenwisseling - verzuring - bodemchemie - dynamische modellen - meting - experimenteel veldonderzoek - nederland - soil types - cation exchange - acidification - soil chemistry - dynamic models - measurement - field experimentation - netherlands
This report presents extensive Tables of cation exchange constants (selectivity coefficients) for sand, loess, clay and peat soils at different depths derived from simultaneous field measure-ments of adsorbed in dissolved concentrations of H, Al, Ca, Mg, K and Na in several hundreds of non-agricultural soils in the Netherlands. Data are provided for the two most widely used cation exchange models (Gaines-Thomas and Gapon) and for all possible combinations of cations, including protons. Results show a wide range in exchange constants, especially when using the Gaines-Thomas exchange description. It appears that Gapon exchange constants are stronger correlated than the corresponding Gaines-Thomas exchange constants, especially for sandy soils. A strong positive correlation means that the ratio between two exchange constants is more characteristic, and less variable, of a certain soil (type) than their absolute numbers, which often vary by several orders of magnitude. In deriving exchange constants, the Al constants were related to free Al3+, the CEC was normalised to a buffered soil pH of 6.5 and the dissolved ion concentrations have all been derived while using a centrifugation method to extract the soil solution. Because of these methodological aspects, they cannot always be used directly in a particular model application. Nevertheless, they provide insight into the numerical ranges of and correlations between exchange constan, and are thus useful for constraining model parameters, e.g. in model calibrations.
Deposition and shaking of dry granular piles
Hasan, M. - \ 2003
University. Promotor(en): Gerard Bot; Johan Grasman, co-promotor(en): Joost van Opheusden. - [S.l.] : S.n. - ISBN 9058088863 - 107
dynamica - dynamische modellen - pijlers - korrels - transportbanden - dynamics - dynamic models - piles - granules - belt conveyors
Design and evaluation of a non-steady state rumen model
Chilibroste, P. ; Dijkstra, J. ; Tamminga, S. - \ 2002
Netherlands Journal of Agricultural Science 49 (2002). - ISSN 0028-2928 - p. 297 - 312.
melkkoeien - pensvertering - simulatiemodellen - dynamische modellen - begrazing - lolium perenne - dairy cows - rumen digestion - simulation models - dynamic models - grazing
A dynamic simulation model of digestion and absorption of nutrients was modified and evaluated under non-steady state conditions. The results of detailed grazing experiments, including allowed grazing times (Exp. 1), combinations of rumen fill and starvation length before grazing (Exp. 2) and contrasting sward masses and sward heights (Exp. 3) as main treatments were used as reference values. The model was modified to run under a discontinuous feed input of ryegrass. Neutral detergent fibre (NDF) and nitrogen rumen pools were predicted with a relatively low root mean square prediction error (MSPE) of the observed means (11€in Exps. 1 and 2, but a higher value (18€was observed in Exp. 3. This significantly higher root MSPE was ascribed to the long period (up to 20.5 hours) of starvation that followed grazing. Prediction was poorer for organic matter rumen pool (root MSPE of 16mthan for NDF and N rumen pools, which requires further validation. Volatile fatty acid (VFA) rumen pool and VFA concentration were predicted with a root MSPE of the observed mean of 32–33°which was close to the random variation observed in the experiments. Ammonia rumen pool was poorly predicted and the way ammonia is represented in the model must be modified to predict ammonia production and absorption under non-steady state conditions. The model can be used to predict ruminal digestion and absorption of nutrients (except ammonia) of grazing lactating dairy cows under discontinuous feeding regimens provided large periods of starvation are avoided
Approaches to analyse interactions of climate change, acidification and ozone
Ierland, E.C. van; Ignaciuk, A. ; Kroeze, C. ; Brink, C. ; Schmieman, E. ; Builtjes, P. ; Roemer, M. ; Mayerhofer, P. - \ 2002
Wageningen [etc.] : Wageningen University [etc.] - ISBN 9789058510860 - 129
luchtverontreiniging - klimaatverandering - verzuring - eutrofiëring - ozon - interacties - wiskundige modellen - dynamische modellen - milieuwetenschappen - ozonlaag - air pollution - climatic change - acidification - eutrophication - ozone - interactions - mathematical models - dynamic models - environmental sciences - ozone layer
The age of innovation. Making business creativity a competence, not a coincidence
Janszen, F. - \ 2000
London [etc.] : Financial Times/Prentice Hall - ISBN 9780273638759 - 230
innovaties - bedrijfsvoering - bedrijven - dynamische modellen - bedrijfseconomie - innovations - management - businesses - dynamic models - business management
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