Invloed van stikstofbemesting en kunstmatige beregening op de landbouwkundige en industriële kwaliteit van verschillende zetmeelaardappelrassen : verslag van de veldproeven KB 9036 en KP 9060 : werkdocument over het derde proefjaar 2000

In 2000 werd in een tweetal veldexperimenten met verschillende stikstof-bemestingstrappen, gecombineerd met al dan niet toepassing van kunstmatige beregening en verschillende zetmeelaardappelrassen, getracht inzicht te verkrijgen in de eigenschappen die bepalend zijn voor de kwaliteit van zetmeelaardappelrassen voor vroege en late oogst en bewaring. Stikstofbemesting had invloed op de kwaliteit van zetmeelaardappelen. Met kunstmatige beregening werd het fosforgehalte in het zetmeel in de fractie kleine knollen van één proef verhoogd. Er waren duidelijke verschillen tussen de zetmeelaardappelrassen (Karakter en Seresta). De rijpheid van de knollen was van invloed op het zetmeelgehalte en het ruw- en winbaar-eiwitgehalte, het aantal en de grootte van de zetmeelkorrels en het fosforgehalte in het zetmeel. Er is bepaald onder welke condities het hoogste uitbetalingsgewicht werd verkregen. Dit rapport beschrijft de resultaten van de aanvullende chemische gewasanalyses en de industriële karakterisering van de knol van de in 2000 uitgevoerde veldexperimenten. In Hoofdstuk 2 worden de opzet van de proeven en de analysebeschrijving beschreven. In Hoofdstuk 3 worden de resultaten gepresenteerd en besproken. Hoofdstuk 4 bevat de conclusies en de aanbevelingen voor de veldexperimenten in 2001

Efficacy of a dynamic collimator for overranging dose reduction in a second- and third-generation dual source CT scanner

Objectives: The purpose of this study was to assess the efficacy of the renewed dynamic collimator in a third-generation dual source CT (DSCT) scanner and to determine the improvements over the second-generation scanner. Methods: Collimator efficacy is defined as the percentage overranging dose in terms of dose–length product (DLP) that is blocked by the dynamic collimator relative to the total overranging dose in case of a static collimator. Efficacy was assessed at various pitch values and different scan lengths. The number of additional rotations due to overranging and effective scan length were calculated on the basis of reported scanning parameters. On the basis of these values, the efficacy of the collimator was calculated. Results: The second-generation scanner showed decreased performance of the dynamic collimator at increasing pitch. Efficacy dropped to 10% at the highest pitch. For the third-generation scanner the efficacy remained above 50% at higher pitch. Noise was for some pitch values slightly higher at the edge of the imaged volume, indicating a reduced scan range to reduce the overranging dose. Conclusions: The improved dynamic collimator in the third-generation scanner blocks the overranging dose for more than 50% and is more capable of shielding radiation dose, especially in high pitch scan modes. Key points: • Overranging dose is to a large extent blocked by the dynamic collimator• Efficacy is strongly improved within the third-generation DSCT scanner• Reducing th

Evolution of surface gravity waves over a submarine canyon

The effects of a submarine canyon on the propagation of ocean surface waves are examined with a three-dimensional coupled-mode model for wave propagation over steep topography. Whereas the classical geometrical optics approximation predicts an abrupt transition from complete transmission at small incidence angles to no transmission at large angles, the full model predicts a more gradual transition with partial reflection/transmission that is sensitive to the canyon geometry and controlled by evanescent modes for small incidence angles and relatively short waves. Model results for large incidence angles are compared with data from directional wave buoys deployed around the rim and over Scripps Canyon, near San Diego, California, during the Nearshore Canyon Experiment (NCEX). Wave heights are observed to decay across the canyon by about a factor 5 over a distance shorter than a wavelength. Yet, a spectral refraction model predicts an even larger reduction by about a factor 10, because low frequency components cannot cross the canyon in the geometrical optics approximation. The coupled-mode model yields accurate results over and behind the canyon. These results show that although most of the wave energy is refractively trapped on the offshore rim of the canyon, a small fraction of the wave energy 'tunnels' across the canyon. Simplifications of the model that reduce it to the standard and modified mild slope equations also yield good results, indicating that evanescent modes and high order bottom slope effects are of minor importance for the energy transformation of waves propagating across depth contours at large oblique angles

Nearshore wave forecasting and hindcasting by dynamical and statistical downscaling

A high-resolution nested WAM/SWAN wave model suite aimed at rapidly establishing nearshore wave forecasts as well as a climatology and return values of the local wave conditions with Rapid Enviromental Assessment (REA) in mind is described. The system is targeted at regions where local wave growth and partial exposure to complex open-ocean wave conditions makes diagnostic wave modelling difficult. SWAN is set up on 500 m resolution and is nested in a 10 km version of WAM. A model integration of more than one year is carried out to map the spatial distribution of the wave field. The model correlates well with wave buoy observations (0.96) but overestimates the wave height somewhat (18%, bias 0.29 m). To estimate wave height return values a much longer time series is required and running SWAN for such a period is unrealistic in a REA setting. Instead we establish a direction-dependent transfer function between an already existing coarse open-ocean hindcast dataset and the high-resolution nested SWAN model. Return values are estimated using ensemble estimates of two different extreme-value distributions based on the full 52 years of statistically downscaled hindcast data. We find good agreement between downscaled wave height and wave buoy observations. The cost of generating the statistically downscaled hindcast time series is negligible and can be redone for arbitrary locations within the SWAN domain, although the sectors must be carefully chosen for each new location. The method is found to be well suited to rapidly providing detailed wave forecasts as well as hindcasts and return values estimates of partly sheltered coastal regions.Comment: 20 pages, 7 figures and 2 tables, MREA07 special issue on Marine rapid environmental assessmen

Proefveldgegevens betreffende de aardappelteelt voor de zetmeelindustrie ten behoeve van modellering : groeicurves van zetmeelaardappelrassen op de proefboerderijen te Rolde en Valthermond (1998-2001)

Gegevens over de groei van aardappelen ten behoeve van de zetmeelindustrie, afkomstig van de zogenaamde groeicurvenproefvelden, worden in deze nota besproken. De veldproeven zijn uitgevoerd op twee noordelijke regionale proefboerderijen, waarbij tijdens het groeiseizoen periodiek de bodembedekking door het gewas en de opbrengst aan biomassa werd bepaald. De gegevens hebben betrekking op de periode 1998-2001. De proefboerderij ‘΄t Kompas’ te Valthermond ligt op veenkoloniale dalgrond en de ‘Kooijenburg’ te Rolde op lemige zandgrond