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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    Mapping water-table depths in space and time to assess desiccation of groundwater-dependent ecosystems in the Netherlands
    Hoogland, T. ; Heuvelink, G.B.M. ; Knotters, M. - \ 2010
    Wetlands 30 (2010). - ISSN 0277-5212 - p. 137 - 147.
    models - series - space - fluctuation - vegetation - forest - maps
    During the past decades, groundwater-dependent ecosystems in the Netherlands have been threatened by a decline in the water-table level. However, information on water-table depths and changes in water-table depths is insufficient and outdated. For policy evaluation, spatially explicit and detailed information on water-table depths is required, especially in areas with groundwater-dependent ecosystems including wetlands. Some 35,000 observations of seasonal fluctuation characteristics of water-table depths in nature conservation areas were made since 1980 during soil surveys. These observations were derived from characteristics of the soil profile or from measurements in boreholes. These observations were used in a space-time geostatistical analysis to map the seasonal fluctuation of water-table depths between 1980 and 2007. First, systematic differences between different estimation modes used through the years were corrected. Next, observations were correlated with area-wide available ancillary data using multiple linear regression. Simple kriging was used to interpolate the resulting space-time residuals. Maps of the predicted mean spring water-table depths and the accuracy of these predictions were used to identify areas where the water-table is deeper than favorable. Changes of water-table depths on the national scale over the past 25 years were assessed, and recommendations were made to increase the accuracy of future predictions.
    Testing E-OBS European high-resolution gridded data set of daily precipitation and surface temperature
    Hofstra, N. ; Haylock, M. ; New, M. ; Jones, P. - \ 2009
    Journal of Geophysical Research: Atmospheres 114 (2009). - ISSN 2169-897X - 16 p.
    homogeneity - land - climatology - rainfall - series
    Gridded data sets derived through interpolation of station data have a number of potential inaccuracies and errors. These errors can be introduced either by the propagation of errors in the station data into derived gridded data or by limitations in the ability of the interpolation method to estimate grid values from the underlying station network. Recently, Haylock et al. (2008) reported on the development of a new high-resolution gridded data set of daily climate over Europe (termed E-OBS). E-OBS is based on the largest available pan-European data set, and the interpolation methods used were chosen after careful evaluation of a number of alternatives, yet the data set will inevitably have errors and uncertainties. In this paper we assess the E-OBS data set with respect to: (1) homogeneity of the gridded data; (2) evaluation of inaccuracies arising from available network density, through comparison with existing data sets that have been developed with much denser station networks; and (3) the accuracy of the estimates of interpolation uncertainty that are provided as part of E-OBS. We find many inhomogeneities in the gridded data that are primarily caused by inhomogeneities in the underlying station data. In the comparison of existing data with E-OBS, we find that while correlations overall are high, relative differences in precipitation are large, and usually biased toward lower values in E-OBS. From the analysis of the interpolation uncertainties provided as part of E-OBS, we conclude that the interpolation standard deviation provided with the data significantly underestimates the true interpolation error when cross validated using station data, and therefore will similarly underestimate the interpolation error in the gridded E-OBS data. While E-OBS represents a valuable new resource for climate research in Europe, users of the data need to be aware of the limitations in the data set and use the data appropriately.
    An application of neural networks in microeconomics: input-output mapping in a power generation subsector of the US electricity industry
    Erbas, B.C. ; Stefanou, S.E. - \ 2009
    Expert Systems with Applications 36 (2009)2, part 1. - ISSN 0957-4174 - p. 2317 - 2326.
    efficiency - forecasts - business - models - series
    The use of the artificial neural networks in economics and business goes back to 1950s, while the major bulk of the applications have been developed in more recent years. Reviewing this literature indicates that the field of business benefits from the neural networks in a wide spectrum from prediction to classification, as most of the applications in economics primarily focus on the predictive power of the neural networks. Time series analysis and forecasting, econometrics, macroeconomics constitute the main areas of economics, where there is an increasing interest in application of neural networks. Although their promising contributions to the area of microeconomics, the applications of neural networks in this area are limited in number. This study provides a microeconomic application of an artificial neural network by input-output mapping for 82 US major investor-owned electric utilities using fossil-fuel fired steam electric power generation for the year 1996. We construct a multilayer feed-forward neural network (MFNN) with back-ropagation to represent the relationship between a set of inputs and an electricity production as an output. The network is trained and tested by using approximately 80 percent and 20 percent of the data, respectively. The network is trained with 97% accuracy and performance of the network in testing is 96%. Therefore, this network can be used in calculating electricity output for the given inputs in this subsector of the US electricity market, and these estimations can be employed in policy design and planning
    A European daily high-resolution gridded dataset of surface temperature and precipitation for 1950-2006
    Haylock, M. ; Hofstra, N. ; Klein Tank, A. ; Klok, L. ; Jones, P. ; New, M. - \ 2008
    Journal of Geophysical Research: Atmospheres 113 (2008). - ISSN 2169-897X - 12 p.
    areal rainfall estimation - united-kingdom - satellite data - uncertainties - validation - products - series - sahel - model
    We present a European land-only daily high-resolution gridded data set for precipitation and minimum, maximum, and mean surface temperature for the period 1950–2006. This data set improves on previous products in its spatial resolution and extent, time period, number of contributing stations, and attention to finding the most appropriate method for spatial interpolation of daily climate observations. The gridded data are delivered on four spatial resolutions to match the grids used in previous products as well as many of the rotated pole Regional Climate Models (RCMs) currently in use. Each data set has been designed to provide the best estimate of grid box averages rather than point values to enable direct comparison with RCMs. We employ a three-step process of interpolation, by first interpolating the monthly precipitation totals and monthly mean temperature using three-dimensional thin-plate splines, then interpolating the daily anomalies using indicator and universal kriging for precipitation and kriging with an external drift for temperature, then combining the monthly and daily estimates. Interpolation uncertainty is quantified by the provision of daily standard errors for every grid square. The daily uncertainty averaged across the entire region is shown to be largely dependent on the season and number of contributing observations. We examine the effect that interpolation has on the magnitude of the extremes in the observations by calculating areal reduction factors for daily maximum temperature and precipitation events with return periods up to 10 years
    Displaying remotely sensed vegetation dynamics along natural gradients for ecological studies
    Beck, P.S.A. ; Wang, T.J. ; Skidmore, A.K. ; Liu, X.H. - \ 2008
    International Journal of Remote Sensing 29 (2008)14. - ISSN 0143-1161 - p. 4277 - 4283.
    plant phenology - noaa-avhrr - ndvi - climate - fennoscandia - variability - dataset - series - season - cover
    Normalized difference vegetation index (NDVI) datasets are growing in popularity to represent vegetation dynamics in ecological studies. Because of its multidimensional nature, it is difficult to visualise the spatial and temporal components of NDVI datasets simultaneously. This letter presents a method to display vegetation dynamics as captured by the NDVI along natural gradients and to visualise and test correlations between vegetation phenology and animal movement.
    Dimer Biphenyl Liquid Crystals with Trisiloxane-Containing Spacers
    Achten, R. ; Koudijs, A. ; Giesbers, M. ; Marcelis, A.T.M. ; Sudhölter, E.J.R. - \ 2007
    Molecular Crystals and Liquid Crystals 477 (2007)1. - ISSN 1542-1406 - p. 169 - 176.
    mesogenic fluorinated organosiloxanes - polar order - phase - chirality - systems - series
    Dimeric biphenyl liquid crystals with trisiloxane containing spacers were studied. Both the tail lengths and the spacer lengths to a central hexamethyltrisiloxane group were varied. In most cases a SmC-phase was found with an anticlinic interlayer relation. One of the compounds appears to have a SmA-phase, which could be a de Vries SmA-phase. A few other compounds show liquid crystalline polymorphism. X-ray diffraction experiments show that the smectic layers are strongly interdigitated. The thickness of the layers is mainly dependent on the length of the spacers. The length of the terminal alkyl chains hardly influences the smectic layer thickness.
    Spacer length dependence of TGBC* and SmA phases in cholesteryl and dihydrocholesteryl-containing trimer liquid crystals
    Marcelis, A.T.M. ; Giesbers, M. ; Koudijs, A. - \ 2007
    Liquid Crystals 34 (2007)7. - ISSN 0267-8292 - p. 811 - 817.
    twist grain-boundary - smectic-c-phase - dimesogenic compounds - mesomorphic behavior - optical-properties - mesogenic units - terminal group - dimers - moiety - series
    Two series of trimer liquid crystals were investigated that contain a biphenylyl central group and two cholesteryl or dihydrocholesteryl terminal mesogenic groups. Only compounds with even spacers were investigated. The dihydrocholesteryl-containing trimers show a triply intercalated smectic A (SmA) phase when the spacer lengths are greater than 8, whereas the cholesteryl-containing trimers exhibit this triply intercalated SmA phase when the spacer lengths are more than 6. With shorter spacers, a twist grain boundary C* (TGBC*) phase was found. This is revealed by the formation of a typical dotted square grid pattern upon cooling from the chiral nematic (N*) phase in the planar texture. The dots are spaced by a distance of about 1.5-1.8 µm. Upon cooling from the N* phase in the focal conic texture a striped pattern is observed with the same spacing. X-ray diffraction revealed a repeat distance for the TGBC* phase that corresponds with a monolayer ordering. The results show that the weaker interaction between the dihydrocholesteryl groups compared with cholesteryl groups or longer spacers destabilize the monolayer TGBC* phase.
    Continuous biotransformation of glycopeptide antibiotec A40926 in a cascade of three airlift bioreactors using immobilized Actinoplanes teichomyceticus cells
    Jovetic, S. ; Marinelli, F. ; Tramper, J. - \ 2006
    Enzyme and Microbial Technology 38 (2006)1-2. - ISSN 0141-0229 - p. 34 - 39.
    michaelis-menten kinetics - stirred tank reactors - antibacterial activity - derivatives - deacylation - dalbavancin - mdl-63,246 - a-40926 - design - series
    Immobilized cells of Actinoplanes teichomyceticus ATCC 31121 were used to selectively cleave the acyl group of A40926 yielding the deacylated form of the molecule. The feasibility of this particular biotransformation in a series of three perfectly mixed airlift bioreactors with immobilized cells was examined. A continuously operated airlift cascade was designed using a model for a series of reactors with immobilized biocatalyst beads obeying Michaelis¿Menten kinetics. In independent experimental runs the cascade bioreactor system was operated continuously for 56 days with an overall conversion of 99%. Model estimates for reactor volumes and relative conversions were found to be in a good agreement with the experimental results.
    The Lyapunov exponents of the Van der Pol oscillator
    Grasman, J. ; Verhulst, F. ; Shih, S.D. - \ 2005
    Mathematical Methods in the Applied Sciences 28 (2005)10. - ISSN 0170-4214 - p. 1131 - 1139.
    vanderpol equation - limit-cycle - series
    Lyapunov exponents characterize the dynamics of a system near its attractor. For the Van der Pol oscillator these are quantities for which an approximation should be at hand. Similar to the asymptotic approximation of amplitude and period, expressions are derived for the non-zero Lyapunov exponent for both small and large parameter values
    Drought in groundwater-drought distribution and performance indicators
    Peters, E. ; Lanen, H.A.J. van; Torfs, P.J.J.F. ; Bier, G. - \ 2005
    Journal of Hydrology 306 (2005)1-4. - ISSN 0022-1694 - p. 302 - 317.
    droogte - grondwateraanvulling - tijdreeksen - meteorologie - grondwater - watersystemen - bodemwaterbalans - klimaat - drought - groundwater recharge - time series - meteorology - groundwater - water systems - soil water balance - climate - vulnerability - reliability - precipitation - resilience - simulation - frequency - reservoir - series
    In order to investigate how droughts are changed by the groundwater system and to analyse the performance of groundwater during drought, 10 time series of 1000 years of recharge and groundwater discharge were generated. The 10×1000 years of synthetic daily data were generated using Nearest Neighbour resampling based on 37 years of observed daily meteorological data. The root zone was simulated by a non-linear water balance model and the groundwater system by a linear reservoir model. The size and thus the response time of the reservoir was characterised by a reservoir coefficient. Subsequently, the deficit and duration of the droughts were derived from the time series of recharge and groundwater discharge using the threshold level approach. An analysis of the distribution of these droughts shows that for droughts with small return periods, the deficit in the groundwater discharge is smaller than in the recharge. For droughts with large return periods, the deficit in the groundwater discharge is larger than in the recharge. The performance of groundwater systems with respect to droughts was evaluated using three classical performance indicators (reliability, resilience and vulnerability), a combination of these three indicators (Loucks' sustainability index) and three newly defined overall performance indicators. The newly defined indicators combine the severity and frequency of the droughts, instead of analysing these separately in reliability and vulnerability. The performance is estimated for the groundwater recharge and for the discharge of groundwater systems with three different values of the reservoir coefficient. Of all the performance indicators used, one of the newly introduced overall performance indicators with a strong emphasis on droughts with a high return period appeared to characterise the groundwater droughts best. This indicator shows a more or less constant performance for low and medium high reservoir coefficients and an increasing performance for higher reservoir coefficients
    Cholesterol-containing liquid crystal dimmers with ether linkages between the spacer and mesogenic units
    Marcelis, A.T.M. ; Koudijs, A. ; Karczmarzyk, Z. ; Sudhölter, E.J.R. - \ 2003
    Liquid Crystals 30 (2003)11. - ISSN 0267-8292 - p. 1357 - 1364.
    twist grain-boundary - dimesogenic compounds - optical-properties - mesomorphic behavior - smectic phases - terminal group - oligomers - lengths - moiety - series
    Three series of chiral liquid crystalline dimers were investigated, having a cholesteryl and a cyanobiphenylyl, butoxybiphenylyl or hexyloxybiphenylyl group connected to a variable alkyl spacer through ether linkages. Their properties were compared with those of the corresponding ester derivatives. The phase behaviour of compounds with ether and ester linkages is comparable, showing N* and SmA phases. The melting points of the compounds with ether linkages are in the same range as those of the ester compounds, but the liquid crystal transition temperatures are lower. The smectic layer spacings and smectic ordering properties are also similar. The cyanobiphenylyl compounds have an interdigitated SmA layer structure, which shows a small odd - even effect with spacer parity. The alkoxybiphenylyl compounds have a monolayer SmA phase for short spacers and an intercalated SmA phase for longer spacers. The selective reflection wavelengths of the chiral nematic phase of the ether compounds are lower than those of the corresponding ester compounds. The transition from N* to interdigitated or monolayer SmA is accompanied by a strong increase in the selective reflection wavelength, indicative of an intermediate TGB phase. This is absent for the transition from N* to intercalated SmA.
    Simulation of 6-hourly rainfall and temperature by two resampling schemes
    Wójcik, R. ; Buishand, T.A. - \ 2003
    Journal of Hydrology 273 (2003). - ISSN 0022-1694 - p. 69 - 80.
    neerslag - regen - luchttemperatuur - stochastische modellen - nederland - precipitation - rain - air temperature - stochastic models - netherlands - daily precipitation - rhine basin - model - series
    The joint simulation of time series of 6-hourly precipitation and temperature using nearest-neighbour resampling is studied for Maastricht, the Netherlands. Two resampling schemes are considered: (i) straightforward resampling of 6-hourly values, and (ii) resampling of daily values followed by disaggregation into 6-hourly values using the method of fragments. Second-order statistics of the simulated values are compared with those in the observed data. It appeared that straightforward resampling of 6-hourly values does not adequately preserve the slow decay of the autocorrelation functions of precipitation and temperature. As a result the standard deviations of the monthly precipitation totals and monthly average temperature are strongly underestimated. A negative bias also shows up in the quantiles of the multi-day seasonal maximum precipitation amounts. The autocorrelation coefficients and the standard deviations of the monthly values are much better reproduced if the daily values are generated first. A good correspondence between the historical and simulated distributions of the seasonal maximum precipitation amounts is also achieved with this alternative resampling scheme. (C) 2003 Elsevier Science B.V. All rights reserved.
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