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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    Fourier transform assisted deconvolution of skewed peaks in complex multi-dimensional chromatograms
    Hanke, A.T. ; Verhaert, P.D.E.M. ; Wielen, L.A.M. van der; Eppink, M.H.M. ; Sandt, E.J.A.X. ; Ottens, M. - \ 2015
    Journal of Chromatography. A, Including electrophoresis and other separation methods 1394 (2015). - ISSN 0021-9673 - p. 54 - 61.
    multivariate curve resolution - purification process-development - ion-exchange chromatography - multicomponent chromatograms - liquid-chromatography - automatic program - parameters - optimization - algorithms - equations
    Lower order peak moments of individual peaks in heavily fused peak clusters can be determined by fitting peak models to the experimental data. The success of such an approach depends on two main aspects: the generation of meaningful initial estimates on the number and position of the peaks, and the choice of a suitable peak model. For the detection of meaningful peaks in multi-dimensional chromatograms, a fast data scanning algorithm was combined with prior resolution enhancement through the reduction of column and system broadening effects with the help of two-dimensional fast Fourier transforms. To capture the shape of skewed peaks in multi-dimensional chromatograms a formalism for the accurate calculation of exponentially modified Gaussian peaks, one of the most popular models for skewed peaks, was extended for direct fitting of two-dimensional data. The method is demonstrated to successfully identify and deconvolute peaks hidden in strongly fused peak clusters. Incorporation of automatic analysis and reporting of the statistics of the fitted peak parameters and calculated properties allows to easily identify in which regions of the chromatograms additional resolution is required for robust quantification.
    Nondestructive estimates of above-ground biomass using terrestrial laser scanning
    Calders, K. ; Newnham, G. ; Burt, A. ; Murphy, S. ; Raumonen, P. ; Herold, M. ; Culvenor, D. ; Avitabile, V. ; Disney, M. ; Armston, J. ; Kaasalainen, M. - \ 2015
    Methods in Ecology and Evolution 6 (2015)2. - ISSN 2041-210X - p. 198 - 208.
    carbon-density - tree - lidar - models - equations - systems - volume - stocks
    Allometric equations are currently used to estimate above-ground biomass (AGB) based on the indirect relationship with tree parameters. Terrestrial laser scanning (TLS) can measure the canopy structure in 3D with high detail. In this study, we develop an approach to estimate AGB from TLS data, which does not need any prior information about allometry. We compare these estimates against destructively harvested AGB estimates and AGB derived from allometric equations. We also evaluate tree parameters, diameter at breast height (DBH) and tree height, estimated from traditional field inventory and TLS data. Tree height, DBH and AGB data are collected through traditional forest inventory, TLS and destructive sampling of 65 trees in a native Eucalypt Open Forest in Victoria, Australia. Single trees are extracted from the TLS data and quantitative structure models are used to estimate the tree volume directly from the point cloud data. AGB is inferred from these volumes and basic density information and is then compared with the estimates derived from allometric equations and destructive sampling. AGB estimates derived from TLS show a high agreement with the reference values from destructive sampling, with a concordance correlation coefficient (CCC) of 0·98. The agreement between AGB estimates from allometric equations and the reference is lower (CCC = 0·68–0·78). Our TLS approach shows a total AGB overestimation of 9·68% compared to an underestimation of 36·57–29·85% for the allometric equations. The error for AGB estimates using allometric equations increases exponentially with increasing DBH, whereas the error for AGB estimates from TLS is not dependent on DBH. The TLS method does not rely on indirect relationships with tree parameters or calibration data and shows better agreement with the reference data compared to estimates from allometric equations. Using 3D data also enables us to look at the height distributions of AGB, and we demonstrate that 80% of the AGB at plot level is located in the lower 60% of the trees for a Eucalypt Open Forest. This method can be applied in many forest types and can assist in the calibration and validation of broad-scale biomass maps.
    Grass allometry and estimation of above-ground biomass in tropical alpine tussock grasslands
    Oliveras Menor, I. ; Eynden, M. van der; Malhi, Y. ; Cahuana, N. ; Menor, C. ; Zamora, F. ; Haugaasen, T. - \ 2014
    Austral Ecology: a journal of ecology in the Southern Hemisphere 39 (2014)4. - ISSN 1442-9985 - p. 408 - 415.
    net primary productivity - carbon stocks - forests - transformation - vegetation - equations - dynamics - ecuador - balance - paramo
    The puna/páramo grasslands span across the highest altitudes of the tropical Andes, and their ecosystem dynamics are still poorly understood. In this study we examined the above-ground biomass and developed species specific and multispecies power-law allometric equations for four tussock grass species in Peruvian high altitude grasslands, considering maximum height (hmax), elliptical crown area and elliptical basal area. Although these predictors are commonly used among allometric literature, they have not previously been used for estimating puna grassland biomass. Total above-ground biomass was estimated to be of 6.7¿±¿0.2 Mg ha-1 (3.35¿±¿0.1 Mg C ha-1). All allometric relationships fitted to similar power-law models, with basal area and crown area as the most influential predictors, although the fit improved when tussock maximum height was included in the model. Multispecies allometries gave better fits than the other species-specific equations, but the best equation should be used depending on the species composition of the target grassland. These allometric equations provide an useful approach for measuring above-ground biomass and productivity in high-altitude Andean grasslands, where destructive sampling can be challenging and difficult because of the remoteness of the area. These equations can be also applicable for establishing above-ground reference levels before the adoption of carbon compensation mechanisms or grassland management policies, as well as for measuring the impact of land use changes in Andean ecosystems.
    Nonequilibrium thermodynamics of nucleation
    Schweizer, M. ; Sagis, L.M.C. - \ 2014
    Journal of Chemical Physics 141 (2014). - ISSN 0021-9606 - 13 p.
    homogeneous nucleation - inhomogeneous-media - general formalism - complex fluids - systems - clusters - dynamics - temperature - interface - equations
    We present a novel approach to nucleation processes based on the GENERIC framework (general equation for the nonequilibrium reversible-irreversible coupling). Solely based on the GENERIC structure of time-evolution equations and thermodynamic consistency arguments of exchange processes between a metastable phase and a nucleating phase, we derive the fundamental dynamics for this phenomenon, based on continuous Fokker-Planck equations. We are readily able to treat non-isothermal nucleation even when the nucleating cores cannot be attributed intensive thermodynamic properties. In addition, we capture the dynamics of the time-dependent metastable phase being continuously expelled from the nucleating phase, and keep rigorous track of the volume corrections to the dynamics. Within our framework the definition of a thermodynamic nuclei temperature is manifest. For the special case of nucleation of a gas phase towards its vapor-liquid coexistence, we illustrate that our approach is capable of reproducing recent literature results obtained by more microscopic considerations for the suppression of the nucleation rate due to nonisothermal effects.
    A unit stream power based sediment transport function for overland flow
    Ali, M. ; Seeger, K.M. ; Sterk, G. ; Moore, D. - \ 2013
    Catena 101 (2013). - ISSN 0341-8162 - p. 197 - 204.
    soil-erosion model - capacity - catchment - equations - detachment - eurosem - beds - load
    Soil erosion is a serious global problem requiring effective modeling for accurate assessment of sensitive areas and related erosion rates. The outcome of soil erosion models depends strongly on the estimation of sediment transport capacity. In most of the existing spatially distributed soil erosion models sediment transport capacity of overland flow is often estimated using stream flow transport capacity functions. The applicability of stream flow functions to overland flow conditions is questionable because hydraulic conditions like flow depth, slope steepness and surface roughness under overland flow are substantially different from stream flow conditions. Hence, the main objectives of this study were i) to check the suitability of five existing well known and widely used transport capacity functions (Yalin 1963; Low, 1989; Govers, 1990; modified Engelund and Hansen (Smith et al., 1995); and Abrahams et al., 2001) for use under overland flow conditions, and ii) to derive a new function based on unit stream power by dimensional analysis to quantify transport capacity for overland flow. To accomplish the objectives, experiments in a 3.0 m long and 0.5 m wide flume were carried out using four different sands (0.230, 0.536, 0.719, and 1.022 mm). The unit discharges used for experimentation ranged from 0.07 to 2.07 x 10(-3) m(2) s(-1) and slopes ranged from 5.2 to 17.6%. In this study, none of the predictions with the existing functions was in good agreement with measured results over the whole range of experimental conditions, especially at low flow intensities. The percentages of observations in which the discrepancy ratio ranged between 0.5 and 2.0 were: 65% (Yalin 1963), 74% (Low, 1989), 57% (Govers, 1990), 54% (modified Engelund and Hansen (Smith et al., 1995)), and 25% (Abrahams et al., 2001). The results showed that the selected functions reasonably estimate transport capacities only under those ranges of conditions for which they were formulated. Although the excess.shear stress concept based function (i.e. Low's function) produced excellent results, the degree of accuracy of the results varied substantially with grain size (P.O.(0.5-2.0): 53-100%). In contrast, the performance of the Govers' function, which is based on the unit stream power concept, was quite similar for all the selected sands (P.O.(0.5-2.0): 50-63%). Based on the unit stream power concept, a new function for low flow intensities was derived by dimensional analysis using the data gained from the flume experiments. (c) 2012 Elsevier B.V. All rights reserved.
    Development of a model for the prediction of feed intake by dairy cows. 2. Evaluation of prediction accuracy
    Zom, R.L.G. ; André, G. ; Vuuren, A.M. van - \ 2012
    Livestock Science 143 (2012)1. - ISSN 1871-1413 - p. 58 - 69.
    voluntary intake - holstein cows - grass silages - food-intake - equations - systems - cattle
    In a previous paper we have proposed a new concept of a model for the prediction of feed intake by Holstein Friesian dairy cows (Zom et al., 2011). This model predicts feed intake from feed composition and digestibility and the cow's lactation number, stage of lactation and pregnancy. Contrary to many other often used models, this does not include animal performance (milk yield, bodyweight) to predict feed intake. However, BW and MY are highly correlated with DMI. Therefore, the objective of present study was to evaluate the accuracy and robustness of the novel feed intake model and to compare its accuracy and robustness with four other commonly used models for the prediction of feed intake. An evaluation was performed using an independent dataset containing 8974 weekly means of DMI from 348 individual cows observed in 6 feeding experiments including a wide range of diets and management practices was used in this study. Sub-datasets were formed by combining the DMI data by experiment, lactation number, lactation week, and maize silage to grass silage ratios in order to compare the accuracy of the intake models for different feeding practices and groups of cows using mean square prediction error (MSPE) and relative prediction error (RPE) as criteria. The novel model was most accurate as indicated by the MSPEs and RPEs for the whole dataset and the most of the sub-datasets. The results prove that the model of Zom et al. (2011) is able to predict DMI without the use of milk yield or body weight as inputs. It was concluded that novel model was robust and can be applied to various diets and feeding management situations in lactating HF cows.
    Estimating carbon stock in secondary forests: decisions and uncertainties associated with allometric biomass models.
    Breugel, M. van; Ransijn, J. ; Craven, D. ; Bongers, F. ; Hall, J. - \ 2011
    Forest Ecology and Management 262 (2011)8. - ISSN 0378-1127 - p. 1648 - 1657.
    aboveground tree biomass - tropical rain-forest - wood density - climate-change - functional-groups - brazilian amazon - landscape-scale - land-use - deforestation - equations
    Secondary forests are a major terrestrial carbon sink and reliable estimates of their carbon stocks are pivotal for understanding the global carbon balance and initiatives to mitigate CO2 emissions through forest management and reforestation. A common method to quantify carbon stocks in forests is the use of allometric regression models to convert forest inventory data to estimates of aboveground biomass (AGB). The use of allometric models implies decisions on the selection of extant models or the development of a local model, the predictor variables included in the selected model, and the number of trees and species for destructive biomass measurements. We assess uncertainties associated with these decisions using data from 94 secondary forest plots in central Panama and 244 harvested trees belonging to 26 locally abundant species. AGB estimates from species-specific models were used to assess relative errors of estimates from multispecies models. To reduce uncertainty in the estimation of plot AGB, including wood specific gravity (WSG) in the model was more important than the number of trees used for model fitting. However, decreasing the number of trees increased uncertainty of landscape-level AGB estimates substantially, while including WSG had limited effects on the accuracy of the landscape-level estimates. Predictions of stand and landscape AGB varied strongly among models, making model choice an important source of uncertainty. Local models provided more accurate AGB estimates than foreign models, but high variability in carbon stocks across the landscape implies that developing local models is only justified when landscape sampling is sufficiently intensive. --------------------------------------------------------------------------------
    Wiskunde in Werking: van A naar B
    Gee, M. de - \ 2011
    Utrecht : Epsilon Uitgaven (Epsilon uitgaven 70) - ISBN 9789050411271 - 480
    wiskunde - vergelijkingen (wiskundig) - intergraalvergelijkingen - differentiaalvergelijkingen - studieboeken - mathematics - equations - integral equations - differential equations - textbooks
    Modeling of desorption of Alfalfa (Medicago sativa) stems and leaves.
    ArabHosseini, A. ; Huisman, W. ; Müller, J. - \ 2011
    Industrial Crops and Products 34 (2011)3. - ISSN 0926-6690 - p. 1550 - 1555.
    moisture sorption isotherms - temperature - equations - dryer
    The equilibrium moisture content of agricultural products is necessary to optimize drying process and helps to keep the quality of the product during the period of storage. The main aim of this research was to find the best model which could define well, the exchange of moisture between alfalfa (Medicago sativa) and the surrounding air. The desorption isotherms of alfalfa (stem and leaf) were determined separately by using the saturated salt solutions method at three temperatures (25, 50 and 70 °C) within a range of 5–90% relative humidity. Experimental curves of desorption isotherms were fitted to modified equations of Henderson, Halsey, Oswin and Chung-Pfost as well as the GAB model and then evaluated visually by using residual plots and also by some statistical error parameters. The modified Halsey model was found to be the most suitable for describing the relationship between equilibrium moisture content, relative humidity and temperature.
    Two-fluid model for the simultaneous flow of colloids and fluids in porous media
    Biesheuvel, P.M. - \ 2011
    Journal of Colloid and Interface Science 355 (2011)2. - ISSN 0021-9797 - p. 389 - 395.
    irreversible thermodynamics - membrane-transport - nanofiltration membranes - reverse electrodialysis - neutral solute - osmosis - water - salt - equations - sedimentation
    To describe the velocities of particles such as ions, protein molecules and colloids dispersed or dissolved in a fluid, it is important to also describe the forces acting on the fluid, including pressure gradients and friction of the fluid with the particles and with the porous media through which the fluid flows. To account for this problem, the use of a two-fluid model is described, familiar in the field of fluid mechanics, extended to include osmotic effects. We show how familiar relationships follow in various situations and give examples of combined fluid/particle transport in neutral and charged membranes driven by a combination of electrostatic, diffusional and pressure forces. The analysis shows how the same modeling framework can be generally used both for multidimensional electrokinetic flow through macroscopic channels and around macroscopic objects, as well as for mean-field modeling of transport through porous media such as gels and membranes.
    Modeling of the equilibrium moisture content (EMC) of Miscanthus (Miscanthus x giganteus)
    ArabHosseini, A. ; Huisman, W. ; Muller, J. - \ 2010
    Biomass and Bioenergy 34 (2010)4. - ISSN 0961-9534 - p. 411 - 416.
    sorption isotherms - equations - crop
    The desorption isotherms of miscanthus, Miscanthus x giganteus (stems and leaves) were determined separately by using the saturated salt solutions method at three temperatures (25, 50 and 70 degrees C) within a range from 5 to 90% relative humidity. Experimental curves of desorption isotherms were fitted to Modified Henderson, Modified Halsey, Modified Oswin and Modified Chung-Pfost models and evaluated by Residual Sum of Squares (RSS), Standard Error Estimation (SEE) and Mean Relative Deviation (MAD) methods. The Modified Oswin model was found to be the most suitable for describing the correlation between equilibrium moisture content, relative humidity and temperature.
    Balanced dynamics in the Tropics
    Verkley, W.T.M. ; Velde, I.R. van der - \ 2010
    Quarterly Journal of the Royal Meteorological Society 136 (2010)646. - ISSN 0035-9009 - p. 41 - 49.
    sphere - approximation - equations
    For the shallow-water equations on an equatorial beta plane, the properties of low-frequency Rossby waves and (mixed) Rossby-gravity waves are investigated. It is shown that in the low-frequency limit the horizontal divergence of these solutions is zero and their geopotential satisfies = f, where f = y is the Coriolis parameter and is the stream function of the non-divergent velocity field. This type of balance is rather different from the geostrophic balance satisfied by Kelvin waves. It can be used to formulate a balanced potential vorticity equation in the single variable that, while filtering out Kelvin waves and inertia-gravity waves, exactly reproduces Rossby waves and Rossby-gravity waves in the low-frequency limit.
    Weakly nonlinear thermoacoustics for stacks with slowly varying pore cross-sections
    Panhuis, P.H.M.W. in 't; Rienstra, S.W. ; Molenaar, J. ; Slot, J.J.M. - \ 2009
    Journal of Fluid Mechanics 618 (2009). - ISSN 0022-1120 - p. 41 - 70.
    driven acoustic-oscillations - porous-media - performance - equations - engine - tubes - flow
    A general theory of thermoacoustics is derived for arbitrary stack pores. Previous theoretical treatments of porous media are extended by considering arbitrarily shaped pores with the only restriction that the pore cross-sections vary slowly in the longitudinal direction. No boundary-layer approximation is necessary. Furthermore, the model allows temperature variations in the pore wall. By means of a systematic approach based on dimensional analysis and small parameter asymptotics, we derive a set of ordinary differential equations for the mean temperature and the acoustic pressure and velocity, where the equation for the mean temperature follows as a consistency condition of the assumed asymptotic expansion. The problem of determining the transverse variation is reduced to finding a Green's function for a modified Helmholtz equation and solving two additional integral equations. Similarly the derivation of streaming is reduced to finding a single Green's function for the Poisson equation on the desired geometry
    Use of bioelectrical impedance analysis to assess body composition in rural Gambian children
    Prins, M. ; Hawkesworth, S. ; Wright, A. ; Fulford, A.J.C. ; Jarjou, L.M.A. ; Prentice, A.M. ; Moore, S.E. - \ 2008
    European Journal of Clinical Nutrition 62 (2008)9. - ISSN 0954-3007 - p. 1065 - 1074.
    fat-free mass - bioimpedance analysis - deuterium dilution - african-american - white-children - birth-weight - women - equations - density - anthropometry
    Objective: To validate the Tanita BC-418MA Segmental Body Composition Analyser and four-site skinfold measurements for the prediction of total body water (TBW), percentage fat-free mass (% FFM) and percentage body fat (%BF) in a population of rural Gambian children. Subjects/Methods: One hundred and thirty-three healthy Gambian children (65 males and 68 females). FFM estimated by the inbuilt equations supplied with the Tanita system was assessed by comparison with deuterium oxide dilution and novel prediction equations were produced. Deuterium oxide dilution was also used to develop equations for %BF based on four-site skinfolds (biceps, triceps, subscapular and suprailiac). Results: The inbuilt equations underestimated FFM compared to deuterium oxide dilution in all the sex and age categories (P <0.003), with greater accuracy in younger children and in males. The best prediction of % FFM was obtained from the variables height, weight, sex, impedance, age and four skinfold thickness measurements (adjusted R-2 = 0.84, root mean square error (MSE) = 2.07%). Conclusions: These data suggest that the Tanita instrument may be a reliable field assessment technique in African children, when using population and gender-specific equations to convert impedance measurements into estimates of FFM.
    Diagnostic equations for the stable boundary-layer height: evaluation and dismensional analysis
    Steeneveld, G.J. ; Wiel, B.J.H. van de; Holtslag, A.A.M. - \ 2007
    Journal of Applied Meteorology and Climatology 46 (2007). - ISSN 1558-8424 - p. 212 - 225.
    grenslaag - vergelijkingen (wiskundig) - prestatieniveau - meteorologische waarnemingen - grenslaagmeteorologie - boundary layer - equations - performance - meteorological observations - boundary-layer meteorology - nocturnal surface inversion - large-eddy simulations - mixing height - equilibrium depth - model - turbulence - formulations - variability - sensitivity - parameters
    The performance of diagnostic equations for the stable boundary layer height h is evaluated with four observational datasets that represent a broad range of latitudes, land use, and surface roughness. In addition, large-eddy simulation results are used. Special care is given to data-quality selection.
    The performance of diagnostic equations for the stable boundary layer height h is evaluated with four observational datasets that represent a broad range of latitudes, land use, and surface roughness. In addition, large-eddy simulation results are used. Special care is given to data-quality selection. The diagnostic equations evaluated are so-called multilimit equations as derived by Zilitinkevich and coworkers in a number of papers. It appears that these equations show a serious negative bias, especially for It <100 m, and it was found that the parameters involved could not be determined uniquely with calibration. As an alternative, dimensional analysis is used here to derive a formulation for h that is more robust. The formulation depends on the surface friction velocity u(*), surface buoyancy flux B-s, Coriolis parameter, and the free-flow stability N. The relevance of the Coriolis parameter for the boundary layer height estimation in practice is also discussed. If the Coriolis parameter is ignored, two major regimes are found: h similar to u(*)/N for weakly stable conditions and h similar to (vertical bar B-N vertical bar/N-3)(1/2) for moderate to very stable conditions.
    Multidimensional Scaling with Regional Restrictions for Facet Theory: an Application to Levi's Political Protest Data
    Groenen, P.J.F. ; Lans, I.A. van der - \ 2006
    Rotterdam : RSM Erasmus Univ., Erasmus Research Inst. Management (ERIM) (ERIM report series research in management ERS-2006-057-MKT) - 20
    schaalverandering - dimensie-analyse - wiskundige modellen - algoritmen - vergelijkingen (wiskundig) - correlatieanalyse - classificatie - scaling - dimensional analysis - mathematical models - algorithms - equations - correlation analysis - classification
    Multidimensional scaling (MDS) is often used for the analysis of correlation matrices of items generated by a facet theory design. The emphasis of the analysis is on regional hypotheses on the location of the items in the MDS solution. An important regional hypothesis is the axial constraint where the items from different levels of a facet are assumed to be located in different parallel slices. The simplest approach is to do an MDS and draw the parallel lines separating the slices as good as possible by hand. Alternatively, Borg and Shye (1995) propose to automate the second step. Borg and Groenen (1997, 2005) proposed a simultaneous approach for ordered facets when the number of MDS dimensions equals the number of facets. In this paper, we propose a new algorithm that estimates an MDS solution subject to axial constraints without the restriction that the number of facets equals the number of dimensions. The algorithm is based on constrained iterative majorization of De Leeuw and Heise...
    Parameterization of entrainment in a sheared convective boundary layer using a first-order jump model
    Kim, S.W. ; Park, S.U. ; Pino, D. ; Vilà-Guerau de Arellano, J. - \ 2006
    Boundary-Layer Meteorology 120 (2006)3. - ISSN 0006-8314 - p. 455 - 475.
    large-eddy-simulation - capping inversion structure - mixed-layer - wind shear - dynamics - growth - flows - turbulence - equations - energy
    Basic entrainment equations applicable to the sheared convective boundary layer (CBL) are derived by assuming an inversion layer with a finite depth, i.e., the first-order jump model. Large-eddy simulation data are used to determine the constants involved in the parameterizations of the entrainment equations. Based on the integrated turbulent kinetic energy budget from surface to the top of the CBL, the resulting entrainment heat flux normalized by surface heat flux is a function of the inversion layer depth, the velocity jumps across the inversion layer, the friction velocity, and the convection velocity. The developed first-order jump model is tested against large-eddy simulation data of two independent cases with different inversion strengths. In both cases, the model reproduces quite reasonably the evolution of the CBL height, virtual potential temperature, and velocity components in the mixed layer and in the inversion layer
    An improved experimental and regression methodology for sorption isotherms
    Quirijns, E.J. ; Boxtel, A.J.B. van; Loon, W.K.P. van; Straten, G. van - \ 2005
    Journal of the Science of Food and Agriculture 85 (2005)2. - ISSN 0022-5142 - p. 175 - 185.
    equilibrium moisture-content - water activity - 3 temperatures - desorption - equations - products - fruit - foods - seeds - fufu
    Sorption isotherms of corn and starch cylinders with immobilised catalase are experimentally determined at different temperatures for use in drying models in optimal control studies. This application of the sorption isotherm requires an accurate prediction of the sorption data at different temperatures for the low water activity range. The GAB equation is used for the prediction of the sorption isotherms. Two major problems are encountered by employing standard procedures, ie prediction of sorption at aw <0.11 and sensitivity of the GAB parameters to the applied data range. An improved methodology is developed, consisting of extending the standard experimental procedure with additional data points in the low water activity range and changing the criterion in the regression procedure in the sum of squares, which is weighed by the variance of the experimental data. The new methodology leads to accurate, consistent and physically relevant parameters of the GAB equation, which are independent of the applied data range in the regression analysis and which result in accurate predictions of the sorption behaviour at low water activity. The sorption data at different temperatures at low water activity can be predicted in the best way with parameters obtained after direct regression based on weighed SSQ.
    Capital adjustment patterns on Dutch pig farms
    Gardebroek, C. - \ 2004
    European Review of Agricultural Economics 31 (2004)1. - ISSN 0165-1587 - p. 39 - 59.
    asymmetric adjustment - dynamic adjustment - investment - uncertainty - cost - specification - expectations - equations - industry - models
    This paper develops a generalised adjustment cost framework that explicitly accounts for zero investments on Dutch pig farms. A farm-specific flexible adjustment cost function is used to account for differences in adjustment costs between farms. Using the Generalised Method of Moments the Euler equations for investment in buildings and machinery are estimated on a panel of specialised Dutch pig farms. It is found that adjustment costs are an important determinant in investment for buildings but not for machinery.
    Distancia entre drenes parolelos
    Lenselink, K.J. - \ 1997
    Wageningen etc. : ILRI [etc.] - 21
    drainage - drainagekanalen - drainagesystemen - waterbouwkunde - hydraulische systemen - waterstroming - vergelijkingen (wiskundig) - drainage channels - drainage systems - hydraulic engineering - hydraulic structures - water flow - equations
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