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 / 26

    • help
    • print

      Print search results

    • export

      Export search results

    Check title to add to marked list
    Conductometer Schott
    Bom, Jesse ; Dijksman, J.A. ; Lageschaar, Luuk ; Galen, Martijn van; Hoogendam, C.W. ; Wegh, R.A.J. - \ 2016
    Wageningen : Wageningen UR
    geleidingsvermogen - instrumenten (meters) - meetinstrumenten - chemie - conductivity - instruments - indicating instruments - chemistry
    Instructievideo over het gebruik van de Schott Conductometer
    Conductometer Knick
    Bom, Jesse ; Dijksman, J.A. ; Lageschaar, Luuk ; Galen, Martijn van; Hoogendam, C.W. ; Wegh, R.A.J. - \ 2016
    Wageningen : Wageningen UR
    geleidingsvermogen - chemie - meetinstrumenten - conductivity - chemistry - indicating instruments
    Instructievideo over het gebruik van de Knick Conductometer
    Photopyroelectric assessment of the thermal effusivity of fresh hen egg and of rehydrated egg powders
    Szafner, G. ; Nemeth, C. ; Bicanic, D.D. ; Doka, O. - \ 2015
    Journal of Thermal Analysis and Calorimetry 120 (2015)1. - ISSN 1388-6150 - p. 363 - 368.
    conductivity - diffusivity - parameters - products - heat - spectroscopy - temperature - milk
    The availability of thermo-physical data of foods and their constituents is of general importance to food industry. The thermal effusivity e is one among the relevant thermodynamical quantities. The latter is normally calculated from the relationship e = (¿¿c)½, where c is specific heat, ¿ is the density, and ¿ is the thermal conductivity. The necessity for performing the time consuming independent measurements of these three quantities is the major reason that the existing database with effusivity of foods is not very wide. This paper describes the application of the inverse photopyroelectric (IPPE) technique that allows the determination of effusivity from a single measurement. This approach was used to directly measure thermal effusivity of fresh egg yolk, egg white, and white/yolk blends. In addition, thermal effusivity of rehydrated egg powders (white, yolk, and the whole egg powder) has been measured and compared to that of the fresh hen egg. In case of the egg white, effusivity of rehydrated egg powders was practically the same as that of the fresh egg. However, the difference in effusivity between fresh egg yolk and rehydrated egg yolk, and between the blend of fresh egg and the rehydrated whole egg power was significant. Finally, thermal effusivity of rehydrated egg yolk, egg white, and the whole egg powder was determined as a function of dilution factor.
    Compensation in Root Water Uptake Models Combined with Three-Dimensional Root Length Density Distribution
    Heinen, M. - \ 2014
    Vadose Zone Journal 13 (2014)2. - ISSN 1539-1663 - 9 p.
    hydraulic architecture - integrated approach - porous-media - absorption - conductivity - systems - soils
    A three-dimensional root length density distribution function is introduced that made it possible to compare two empirical uptake models with a more mechanistic uptake model. Adding a compensation component to the more empirical model resulted in predictions of root water uptake distributions similar to those predicted by the more complex model. Because root water uptake is a considerable component in the soil water balance, a lot of attention has been paid to defining and applying root water uptake models. These models can be grouped into empirical vs. mechanistic root uptake models. Intermodel comparisons are valuable in understanding the different concepts used. Such a comparison is sometimes difficult because the level of information required by the models is different, for example, information on the root length density distribution. Here a three-dimensional root length density distribution function is introduced that makes it possible to compare two empirical uptake models with a more mechanistic uptake model. Adding a compensation component to the more empirical model results in prediction of root water uptake distributions in the root zone similar to those predicted by the more complex model.
    Unsaturated hydraulic properties of xerophilous mosses: towards implementation of moss covered soils in hydrological models
    Voortman, B.R. ; Bartholomeus, R.P. ; Bodegom, P.M. van; Gooren, H.P.A. ; Zee, S.E.A.T.M. van der; Witte, J.P.M. - \ 2014
    Hydrological Processes 28 (2014)26. - ISSN 0885-6087 - p. 6251 - 6264.
    evaporatie - bryophyta - hydraulisch geleidingsvermogen - korstmossen - mossen - hydrologie - waterbalans - bodemwaterretentie - modelleren - evaporation - bryophyta - hydraulic conductivity - lichens - mosses - hydrology - water balance - soil water retention - modeling - sphagnum moss - water - conductivity - bryophytes - desiccation - ecosystems - tolerance
    Evaporation from mosses and lichens can form a major component of the water balance, especially in ecosystems where mosses and lichens often grow abundantly, such as tundra, deserts and bogs. To facilitate moss representation in hydrological models, we parameterized the unsaturated hydraulic properties of mosses and lichens such that the capillary water flow through moss and lichen material during evaporation could be assessed. We derived the Mualem-van Genuchten parameters of the drying retention and the hydraulic conductivity functions of four xerophilous moss species and one lichen species. The shape parameters of the retention functions (2.17¿
    Modeling water potentials and flows in the soil-plant system comparing hydraulic resistances and transpiration reduction fuctions
    Jong, Q. de; Dam, J.C. van; Durigon, A. ; Santos, M.A. dos; Metselaar, K. - \ 2013
    Vadose Zone Journal 12 (2013)3. - ISSN 1539-1663 - 20 p.
    root-water - polymer tensiometers - simulation-model - stress - conductivity - extraction - maize - architecture - transport - movement
    Crop transpiration depends on resistances in the soil–plant–atmosphere system. We present a new deterministic root water uptake model to estimate transpiration and compare it with two other models. We show the sensitivity of actual transpiration to parameters like soil and plant hydraulic properties and root length density distribution with depth. Transpiration reduction functions are often used in hydrological modeling to estimate actual transpiration as a function of soil water status. Empirical reduction functions are most frequently used due to the higher data needs and computational requirements of mechanistic models. Empirical models, however, lack a description of physical mechanisms and their parameters require extensive calibration. We derive a process-based reduction function predicting system potentials, resistances, and water flows. An analytical solution for a special case of Brooks and Corey soils is presented. A numerical version of the reduction function for van Genuchten soils was implemented in the Soil–Water–Atmosphere–Plant (SWAP) hydrological model, allowing predictions for layered soil profiles and root length density variations over depth. The analytical and numerical versions of the model allow an increasingly quantitative insight into the mechanism of root water uptake, such as the existence of a maximum root water uptake rate as a function of soil water status, soil hydraulic properties, root length density, and root radius, in addition to the fact that sensitivity of simulated root water uptake to the radial root conductivity and axial conductance decrease when root length density increases. The approach can be used for the estimation of threshold values for empirical reduction functions.
    Mastitis alert preferences of farmers milking with automatic milking systems
    Mollenhorst, H. ; Rijkaart, L.J. ; Hogeveen, H. - \ 2012
    Journal of Dairy Science 95 (2012)5. - ISSN 0022-0302 - p. 2523 - 2530.
    clinical mastitis - conductivity
    The aim of this study was to assess farmers’ preferences for the performance characteristics of mastitis detection systems. Additionally, we looked at whether certain groups of farmers could be distinguished with specific preferences. Farmers’ opinions concerning mastitis detection systems, as well as general information about the farm and the farmer, were investigated with a standard questionnaire. The second part of the questionnaire was specifically aimed at elucidating preferences. Definitions of time windows and performance parameters, such as sensitivity and specificity, were incorporated into characteristics of a detection system (attributes) that reflect farmers’ daily experience. Based on data from 139 farmers, we concluded that, on average, they prefer a clinical mastitis detection system that produces a low number of false alerts, while alerting in good time and with emphasis on the more severe cases. These 3 attributes were evaluated as more important than the 3 other attributes, representing the costs of the detection system, the number of missed cases, and how long before clinical signs alerts need to be given. Variation in importance per attribute, however, was high, denoting that farmers’ preferences differ considerably. Although some significant relationships were found between farm characteristics and attributes, no clear groups of farmers with specific preferences could be distinguished. Based on these results, we advise making detection systems adaptable for the farmers to satisfy their preferences and to match the circumstances on the farm. Furthermore, these results support that for evaluation of detection algorithms comparisons have to be made at high levels of specificity (e.g., 99%) and time windows have to be kept small (preferably no more than 24 h). Key words: adaptive conjoint analysis, automatic milking system, farmer preference, mastitis detection
    Direct measurement of thermal effusivity of avian eggs and theur constituents: A photopyroelectric study
    Szafner, G. ; Bicanic, D.D. ; Kovacsne, K. ; Doka, O. - \ 2012
    Food Technology and Biotechnology 50 (2012)3. - ISSN 1330-9862 - p. 350 - 354.
    physical-properties - conductivity - parameters - products
    The front configuration photopyroelectric method has been used to determine, in a nondestructive fashion, thermal effusivity of the yolk and the white of eggs of several bird species as well as of the blends of a single egg yolk and egg white (also called liquid eggs) of different avian eggs. Statistically significant differences in thermal effusivity of egg whites were observed in ten out of twenty-one comparisons made. However, in the case of egg yolks, the differences were observed in twenty among twenty-one comparisons carried out. These observations are related to a varying fat content of egg yolk and a large amount of water found in egg white. The effusivity of the blends prepared from yolks and eggs varies because the contents of the yolk and white in avian eggs differ.
    Conductive polymers for carbon dioxide sensing
    Doan, T.C.D. - \ 2012
    Wageningen University. Promotor(en): Cees van Rijn. - S.l. : s.n. - ISBN 9789461734105 - 194
    polymeren - geleidingsvermogen - aftasten - kooldioxide - polymers - conductivity - sensing - carbon dioxide

    Augmented levels of carbon dioxide (CO2) in greenhouses stimulate plant growth through photosynthesis. Wireless sensor networks monitoring CO2 levels in greenhouses covering large areas require preferably low power sensors to minimize energy consumption. Therefore, the main objective of this research is to develop CO2 sensors using conductive polymer/polyelectrolyte blends as low power sensing layers operating at room temperature. The transduction principle is based on a relative change in conductivity of the polymer/blend film with regard to variation in CO2 concentration. Conductive polymers including emeraldine base polyaniline (EB-PANI), sodium salt of sulfonated polyaniline(SPAN-Na) and their blends with poly(vinyl alcohol) (PVA) were investigated for CO2 sensing. Conductivity of EB-PANI did not vary in the required pH range for CO2 sensing (pH4 - pH7), however a sulfonated derivative (SPAN-Na) showed an appropriate conductivity change in this pH range. Frequency-dependent impedance of the polymer films casted on interdigitated platinum electrodes were measured. A significant decrease in impedance of the SPAN-Na:PVA blend films was observed at high CO2 concentrations (above 20,000 ppm) under high humidity. The effect of humidity on intrinsic and ionic conductivity of the polymerswas investigated by electrochemical impedance spectroscopy. In addition, polyethyleneimine (PEI) and its blends with other polyelectrolytes including SPAN-Na, poly(sodium 4-styrenesulfonate) (PSS-Na) and Nafion sodium salt (Nafion-Na) exhibited a better sensitivity over a wide range of CO2 concentrations (from 400 ppm to 10,000 ppm). Both dc resistance and ac impedance increased when the films were exposed to CO2 at high humidity. The relative change in impedance of the PEI films was about 6-12%. The response time was 4-5 min but recovery time was quite long from 20 to 60 min. A novel solution to reduce the recovery time was achieved with PEI blends. The blend of PEI:SPAN-Na exhibited a fast response (1.5-4 min) and a short recovery time (1.5-10 min) but a reduced sensitivity in comparison with pure PEI. Furthermore, blends of PEI with PSS-Na, Nafion-Na gave a good sensitivity (up to 2-3 order improvement) and relatively short recovery time (10-20 min). The interactions between sulfonate groups with amine groups of PEI might explain the higher CO2 sensitivity of this PEI blend. Some perspectives are sketched for polymer sensors to be applied in wireless sensor network for greenhouses and other potential applications.

    Influence of spatial variations of microtopography and infiltration on surface runoff and field scale hydrological connectivity
    Appels, W.M. ; Bogaart, P.W. ; Zee, S.E.A.T.M. van der - \ 2011
    Advances in Water Resources 34 (2011)2. - ISSN 0309-1708 - p. 303 - 313.
    depression-storage capacity - overland-flow generation - tilled soil surfaces - water contamination - roughness - phosphorus - model - approximation - conductivity - variability
    Surface runoff on agricultural fields arises when rainfall exceeds infiltration. Excess water ponding in and flowing through local microtopography increases the hydrological connectivity of fields. In turn, an increased level of hydrological connectivity leads to a higher surface runoff flux at the field boundaries. We investigated the functional hydrological connectivity of synthetical elevation fields with varying statistical properties. For this purpose, we developed an object-oriented ponding and redistribution model to which Philip’s infiltration model was coupled. The connectivity behaviour is determined by the presence of depressions with a large area and spatial organization of microtopography in rills or channels. The presence of microdepressions suppresses the effect of the spatial variation of infiltration properties. Connectivity behaviour of a field with a varying spatial distribution of infiltration properties can be predicted by transforming the unique connectivity function that was defined for a designated microtopography
    Detection of clinical mastitis with sensor data from automatic milking systems is improved by using decision-tree induction
    Kamphuis, C. ; Mollenhorst, H. ; Heesterbeek, J.A.P. ; Hogeveen, H. - \ 2010
    Journal of Dairy Science 93 (2010)8. - ISSN 0022-0302 - p. 3616 - 3627.
    management - conductivity - foremilk
    The objective was to develop and validate a clinical mastitis (CM) detection model by means of decision-tree induction. For farmers milking with an automatic milking system (AMS), it is desirable that the detection model has a high level of sensitivity (Se), especially for more severe cases of CM, at a very high specificity (Sp). In addition, an alert for CM should be generated preferably at the quarter milking (QM) at which the CM infection is visible for the first time. Data were collected from 9 Dutch dairy herds milking automatically during a 2.5-yr period. Data included sensor data (electrical conductivity, color, and yield) at the QM level and visual observations of quarters with CM recorded by the farmers. Visual observations of quarters with CM were combined with sensor data of the most recent automatic milking recorded for that same quarter, within a 24-h time window before the visual assessment time. Sensor data of 3.5 million QM were collected, of which 348 QM were combined with a CM observation. Data were divided into a training set, including two-thirds of all data, and a test set. Cows in the training set were not included in the test set and vice versa. A decision-tree model was trained using only clear examples of healthy (n = 24,717) or diseased (n = 243) QM. The model was tested on 105 QM with CM and a random sample of 50,000 QM without CM. While keeping the Se at a level comparable to that of models currently used by AMS, the decision-tree model was able to decrease the number of false-positive alerts by more than 50%. At an Sp of 99%, 40% of the CM cases were detected. Sixty-four percent of the severe CM cases were detected and only 12.5% of the CM that were scored as watery milk. The Se increased considerably from 40% to 66.7% when the time window increased from less than 24 h before the CM observation, to a time window from 24 h before to 24 h after the CM observation. Even at very wide time windows, however, it was impossible to reach an Se of 100%. This indicates the inability to detect all CM cases based on sensor data alone. Sensitivity levels varied largely when the decision tree was validated per herd. This trend was confirmed when decision trees were trained using data from 8 herds and tested on data from the ninth herd. This indicates that when using the decision tree as a generic CM detection model in practice, some herds will continue having difficulties in detecting CM using mastitis alert lists, whereas others will perform well
    Decoupled leaf and stem economics in rain forest trees
    Baraloto, C. ; Paine, C.E.T. ; Poorter, L. ; Beauchene, J. ; Bonal, D. ; Domenach, A.M. ; Herault, B. ; Patiño, S. ; Roggy, J.C. ; Chave, J. - \ 2010
    Ecology Letters 13 (2010)11. - ISSN 1461-023X - p. 1338 - 1347.
    functional traits - neotropical forests - wood density - strategies - diversity - spectrum - size - phylogenetics - conductivity - architecture
    Cross-species analyses of plant functional traits have shed light on factors contributing to differences in performance and distribution, but to date most studies have focused on either leaves or stems. We extend these tissue-specific analyses of functional strategy towards a whole-plant approach by integrating data on functional traits for 13 448 leaves and wood tissues from 4672 trees representing 668 species of Neotropical trees. Strong correlations amongst traits previously defined as the leaf economics spectrum reflect a tradeoff between investments in productive leaves with rapid turnover vs. costly physical leaf structure with a long revenue stream. A second axis of variation, the ‘stem economics spectrum’, defines a similar tradeoff at the stem level: dense wood vs. high wood water content and thick bark. Most importantly, these two axes are orthogonal, suggesting that tradeoffs operate independently at the leaf and at the stem levels. By simplifying the multivariate ecological strategies of tropical trees into positions along these two spectra, our results provide a basis to improve global vegetation models predicting responses of tropical forests to global chan
    Root Zone Sensors for Irrigation Management in Intensive Agriculture
    Pardossi, A. ; Incrocci, L. ; Incrocci, G. ; Marlorgio, F. ; Battista, P. ; Bacci, L. ; Rapi, B. ; Marzialetti, P. ; Hemming, J. ; Balendonck, J. - \ 2009
    Sensors 9 (2009)4. - ISSN 1424-8220 - p. 2809 - 2835.
    soil-water content - time-domain reflectometry - moisture sensor - tensiometer - conductivity - performance - calibration - texture - network - suction
    Crop irrigation uses more than 70% of the world’s water, and thus, improving irrigation efficiency is decisive to sustain the food demand from a fast-growing world population. This objective may be accomplished by cultivating more water-efficient crop species and/or through the application of efficient irrigation systems, which includes the implementation of a suitable method for precise scheduling. At the farm level, irrigation is generally scheduled based on the grower’s experience or on the determination of soil water balance (weather-based method). An alternative approach entails the measurement of soil water status. Expensive and sophisticated root zone sensors (RZS), such as neutron probes, are available for the use of soil and plant scientists, while cheap and practical devices are needed for irrigation management in commercial crops. The paper illustrates the main features of RZS’ (for both soil moisture and salinity) marketed for the irrigation industry and discusses how such sensors may be integrated in a wireless network for computer-controlled irrigation and used for innovative irrigation strategies, such as deficit or dual-water irrigation. The paper also consider the main results of recent or current research works conducted by the authors in Tuscany (Italy) on the irrigation management of container-grown ornamental plants, which is an important agricultural sector in Italy.
    Critical soil conditions for oxygen stress to plant roots: substituting the Fedds-function by a process-based model
    Bartholomeus, R.P. ; Witte, J.P.M. ; Bodegom, P.M. van; Dam, J.C. van; Aerts, R. - \ 2008
    Journal of Hydrology 360 (2008)1-4. - ISSN 0022-1694 - p. 147 - 165.
    bodemporiënsysteem - bodemlucht - wateropname (planten) - plant-water relaties - transpiratie - waterverzadiging - modellen - oxidatieve stress - bodem-plant relaties - soil pore system - soil air - water uptake - plant water relations - transpiration - waterlogging - models - oxidative stress - soil plant relationships - use systems-analysis - crop growth-models - physical-properties - water-uptake - diffusion - respiration - aeration - compaction - transport - conductivity
    Effects of insufficient soil aeration on the functioning of plants form an important field of research. A well-known and frequently used utility to express oxygen stress experienced by plants is the Feddes-function. This function reduces root water uptake linearly between two constant pressure heads, representing threshold values for minimum and maximum oxygen deficiency. However, the correctness of this expression has never been evaluated and constant critical values for oxygen stress are likely to be inappropriate. In this paper, we propose a fundamentally different approach to assess oxygen stress: we built a plant physiological and soil physical process-based model to calculate the minimum gas filled porosity of the soil at which oxygen stress occurs.
    Effects of insufficient soil aeration on the functioning of plants form an important field of research. A well-known and frequently used utility to express oxygen stress experienced by plants is the Feddes-function. This function reduces root water uptake linearly between two constant pressure heads, representing threshold values for minimum and maximum oxygen deficiency. However, the correctness of this expression has never been evaluated and constant critical values for oxygen stress are likely to be inappropriate. On theoretical grounds it is expected that oxygen stress depends on various abiotic and biotic factors. In this paper, we propose a fundamentally different approach to assess oxygen stress: we built a plant physiological and soil physical process-based model to calculate the minimum gas filled porosity of the soil (phi gas_min) at which oxygen stress occurs. First, we calculated the minimum oxygen concentration in the gas phase of the soil needed to sustain the roots through (micro-scale) diffusion with just enough oxygen to respire. Subsequently, phi gas_min that corresponds to this minimum oxygen concentration was calculated from diffusion from the atmosphere through the soil (macro-scale). We analyzed the validity of constant critical values to represent oxygen stress in terms Of phi gas_min, based on model simulations in which we distinguished different soil types and in which we varied temperature, organic matter content, soil depth and plant characteristics. Furthermore, in order to compare our model results with the Feddes-function, we linked root oxygen stress to root water uptake (through the sink term variable F, which is the ratio of actual and potential uptake). The simulations showed that phi gas-min is especially sensitive to soil temperature, plant characteristics (root dry weight and maintenance respiration coefficient) and soil depth but hardly to soil organic matter content. Moreover, phi gas-min varied considerably between soil types and was larger in sandy soils than in clayey soils. We demonstrated that F of the Feddes-function indeed decreases approximately linearly, but that actual oxygen stress already starts at drier conditions than according to the Feddes-function. How much drier is depended on the factors indicated above. Thus, the Feddes-function might cause large errors in the prediction of transpiration reduction and growth reduction through oxygen stress. We made our method easily accessible to others by implementing it in SWAP, a user-friendly soil water model that is coupled to plant growth. Since constant values for phi gas_min in plant and hydrological modeling appeared to be inappropriate, an integrated approach, including both physiological and physical processes, should be used instead. Therefore, we advocate using our method in all situations where oxygen stress could occur. (C) 2008 Elsevier B.V. All rights reserved.
    Comparing Performance and Parameterization of a One-Dimensional Unsaturated Zone Model across Scales
    Sheikh, V. ; Loon, E.E. van - \ 2007
    Vadose Zone Journal 6 (2007)3. - ISSN 1539-1663 - p. 638 - 650.
    soil hydraulic-properties - water-balance - richards equation - simulation-model - moisture - flow - infiltration - conductivity - evaporation - hillslope
    Received for publication 29 May 2006. The utility of an unsaturated zone soil moisture model is not only its ability to describe the soil moisture dynamics at a given point but also the possibility to generalize the results to larger areas. In this study we investigated the predictive performance of a one-dimensional unsaturated zone soil moisture model when applied at point, field, response unit, and catchment scales, using detailed field observations from a 0.42-km2 catchment in the Netherlands. Our main question was how model parameterization and model performance could be compared across these scales. We considered two different calibration¿validation schemes and three performance statistics. In all cases we applied the same Levenberg¿Marquardt optimization scheme. Differences between calibration¿validation schemes (interpolation vs. extrapolation) were surprisingly small. Using one particular model parameterization across the various aggregation levels, the optimal Mualem¿van Genuchten parameters for a coarser aggregation level can be derived from an underlying level by simple arithmetic averaging. The different performance indices (RMSE, index of agreement, and Nash¿Sutcliffe coefficient) were highly variable between observation locations and for different aggregation levels. Overall, the indices were more favorable at higher aggregation levels, and in correspondence with errors reported in comparable studies. The unsaturated-zone model did not, however, provide satisfactory predictions of independent flux observations, in this case daily catchment discharge. Moreover we did not succeed in deriving a meta-model to scale model performance indices with aggregation level. Our case study therefore supports the view that multiscale calibration studies that use both state and flux observations are required to compare results from unsaturated zone models at different aggregation levels.
    Siloxanes with Pendent Naphtalene Diimides: Synthesis and Fluorescence Quenching
    Ganesan, P. ; Lagen, B. van; Marcelis, A.T.M. ; Sudhölter, E.J.R. ; Zuilhof, H. - \ 2007
    Organic Letters 9 (2007)12. - ISSN 1523-7060 - p. 2297 - 2300.
    fullerene solar-cells - multimetallic compounds - cyclosiloxanes - morphology - oligothiophenes - polythiophene - conductivity - performance - transistors - frameworks
    Cyclic siloxanes with pendent naphthalene diimide groups were synthesized via hydrosilylation to form amorphous electron-accepting compounds. Photophysical measurements and >99.9% fluorescence quenching of well-known p-type polymers by the siloxanes demonstrate that these siloxanes form a new class of highly efficient n-type materials that provide some control over intermolecular interactions.
    Effects of membrane cation transport on pH and microbial fuel cell performance
    Rozendal, R.A. ; Hamelers, H.V.M. ; Buisman, C.J.N. - \ 2006
    Environmental Science and Technology 40 (2006)17. - ISSN 0013-936X - p. 5206 - 5211.
    electricity-generation - ion - nafion(r) - conductivity - electrodes - bacterium - glucose - state - h+
    Due to the excellent proton conductivity of Nation membranes in polymer electrolyte membrane fuel cells (PEMFCs), Nation has been applied also in microbial fuel cells (MFCs). In literature, however, application of Nafion in MFCs has been associated with operational problems. Nafion transports cation species other than protons as well, and in MFCs concentrations of other cation species (Na+, K+, NH4+, Ca 2+, and Mg2+) are typically 105 times higher than the proton concentration. The objective of this study, therefore, was to quantify membrane cation transport in an operating MFC and to evaluate the consequences of this transport for MFC application on wastewaters. We observed that during operation of an MFC mainly cation species other than protons were responsible for the transport of positive charge through the membrane, which resulted in accumulation of these cations and in increased conductivity in the cathode chamber. Furthermore, protons are consumed in the cathode reaction and, consequently, transport of cation species other than protons resulted in an increased pH in the cathode chamber and a decreased MFC performance. Membrane cation transport, therefore, needs to be considered in the development of future MFC systems
    Water productivity analysis of irrigated crops in Sirsa district, India
    Singh, R. ; Dam, J.C. van; Feddes, R.A. - \ 2006
    Agricultural Water Management 82 (2006)3. - ISSN 0378-3774 - p. 253 - 278.
    soil hydraulic-properties - parameter-estimation - flow - performance - evaporation - model - rice - conductivity - management - simulation
    Water productivity (WP) expresses the value or benefit derived from the use of water, and includes essential aspects of water management such as production for arid and semi-arid regions. A profound WP analysis was carried out at five selected farmer fields (two for wheat¿rice and three for wheat¿cotton) in Sirsa district, India during the agricultural year 2001¿02. The ecohydrological soil¿water¿atmosphere¿plant (SWAP) model, including detailed crop simulations in combination with field observations, was used to determine the required hydrological variables such as transpiration, evapotranspiration and percolation, and biophysical variables such as dry matter or grain yields. The use of observed soil moisture and salinity profiles was found successful to determine indirectly the soil hydraulic parameters through inverse modelling. Considerable spatial variation in WP values was observed not only for different crops but also for the same crop. For instance, the WPET, expressed in terms of crop grain (or seed) yield per unit amount of evapotranspiration, varied from 1.22 to 1.56 kg m¿3 for wheat among different farmer fields. The corresponding value for cotton varied from 0.09 to 0.31 kg m¿3. This indicates a considerable variation and scope for improvements in water productivity. The average WPET (kg m¿3) was 1.39 for wheat, 0.94 for rice and 0.23 for cotton, and corresponds to average values for the climatic and growing conditions in Northwest India. Including percolation in the analysis, i.e. crop grain (or seed) yield per unit amount of evapotranspiration plus percolation, resulted in average WPETQ (kg m¿3) values of 1.04 for wheat, 0.84 for rice and 0.21 for cotton. Factors responsible for low WP include the relative high amount of evaporation into evapotranspiration especially for rice, and percolation from field irrigations. Improving agronomic practices such as aerobic rice cultivation and soil mulching will reduce this non-beneficial loss of water through evaporation, and subsequently will improve the WPET at field scale. For wheat, the simulated water and salt limited yields were 20¿60% higher than measured yields, and suggest substantial nutrition, pest, disease and/or weed stresses. Improved crop management in terms of timely sowing, optimum nutrient supply, and better pest, disease and weed control for wheat will multiply its WPET by a factor of 1.5! Moreover, severe water stress was observed on cotton (relative transpiration <0.65) during the kharif (summer) season, which resulted in 1.4¿3.3 times lower water and salt limited yields compared with simulated potential yields. Benefits in terms of increased cotton yields and improved water productivity will be gained by ensuring irrigation supply at cotton fields, especially during the dry years.
    Soil water balance scenario studies using predicted soil hydraulic parameters
    Nemes, A. ; Wösten, J.H.M. ; Bouma, J. ; Várallyay, G. - \ 2006
    Hydrological Processes 20 (2006)5. - ISSN 0885-6087 - p. 1075 - 1094.
    pedo-transfer functions - pedotransfer functions - organic-matter - physical characteristics - conservation tillage - conductivity - retention - accuracy - database - management
    Pedotransfer functions (PTFs) have become a topic drawing increasing interest within the field of soil and environmental research because they can provide important soil physical data at relatively low cost. Few studies, however, explore which contributions PTFs can make to land-use planning, in terms of examining the expected outcome of certain changes in soil and water management practices. This paper describes three scenario studies that show some aspects of how PTFs may help improve decision making about land management practices. We use an exploratory research approach using simulation modelling to explore the potential effect of alternative solutions in land management. We: (i) evaluate benefits and risks when irrigating a field, and the impact of soil heterogeneity; (ii) examine which changes can be expected (in terms of soil water balance and supply) if organic matter content is changed as a result of an alternative management system; (iii) evaluate the risk of leaching to deeper horizons in some soils of Hungary. Using this research approach, quantitative answers are provided to 'what if?' type questions, allowing the distinction of trends and potential problems, which may contribute to the development of sustainable management systems. Copyright (c) 2005 John Wiley & Sons, Ltd.
    Acute phase protein concentrations in serum and milk from healthy cows, cows with clinical mastitis and cows with extramammary inflammatory conditions
    Nielsen, B.H. ; Jacobsen, S. ; Andersen, P.H. ; Niewold, T.A. ; Heegaard, P.M.H. - \ 2004
    Veterinary Record 154 (2004)12. - ISSN 0042-4900 - p. 361 - 365.
    amyloid-a saa - escherichia-coli mastitis - dairy-cows - haptoglobin - infection - cattle - conductivity - expression - secretion - metritis
    The concentrations of the two acute phase proteins, serum amyloid A and haptoglobin, in serum and milk were compared in 10 cows with clinical mastitis, 11 cows with extramammary inflammatory conditions and 10 clinically healthy control cows. The concentrations of both acute phase proteins were higher in the serum and milk of the cows with mastitis than in the cows in the other two groups. Four of the cows with extramammary inflammatory conditions had serum amyloid A concentrations in serum above 100 µg/ml, but negligible concentrations in milk, indicating that a pathogen must be present in the mammary gland for serum amyloid A to accumulate in milk. The acute phase protein concentrations in milk increased significantly with increasing somatic cell count, suggesting that they may be indicators of the severity of an infection.
    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.