1,469 research outputs found
Numeriek model voor de bepaling van het zandtransport onder invloed van golven
No full textEr zijn door o.a. Vetlinga en Schepers proeven gedaan in een laboratoriumgoot ter bepaling van zandtransport in de voortplantingsrichting van golven onder invloed van die golven. Doel van deze proeven is om neer inzicht te krijgen in de opwoeling van het bcdemmateriaal aan de bcdem en op die manier in het zandtransportmechanisme . In al die proeven is als bcdemmateriaal zand van verschillende dianeter gebruikt. Aangezien het verschijnsel aan de bcdem zeer gecompliceerd is, is uitgegaan van een benadering via een rechtstreekse bepaling van het zandtransport. Bij de proeven van Schepers, die tevens een aantal proeven deed met fijn zand, D50 = 125 um, bleek dat dit zand anders reageerde op de golfbeweging dan het wat grovere zand door Vellinga en Schepers gebruikt. Omdat daar in eerste instantie geen sluitende verklaring voor was te vinden is een aanzet gemaakt tot een cornputerberekening. Aan de hand van een geschematiseerde aanpak van het opwoelingsmechanisme en het neerslaan van dit zand is het effect van de valsnelheid te onderzoeken. In eerste instantie is, het probleem simpel gehouden om duidelijk te herkennen wat een variatie in de valsnelheid voor gevolgen heeft. Omdat ook het faseverschil tussen de top van de lste harmonische en de top van de resulterende 2de hanronische een rol speelt, is dit aan de hand van berekeningen nagegaan. Bij enkele berekeningen is een eenparige stroom toegevoegd. Hoewel dUidelijk was dat het effect hiervan niet zou overeenkomen met de proeven van Schepers op dit gebied, was het als indicatie voor proeven met wat grotere eenparige stroming waardevol.Hydraulic EngineeringCivil Engineering and Geoscience
Umwelt als Nebensache? - Umweltkommunikation für Jugendliche im Hörfunk
No full textSchepers G, Pyhel T. Umwelt als Nebensache? - Umweltkommunikation für Jugendliche im Hörfunk. 21 - Das Magazin für zukunftsfähige Bildung. 2003;1:47-49
Epidemiology and integrated control of Potato Late Blight in Europe
No full textPhytophthora infestans, the causal agent of late blight, is a major threat to potato production in northwestern Europe. Before 1980, the worldwide population of P. infestans outside Mexico appeared to be asexual and to consist of a single clonal lineage of A1 mating type characterized by a single genotype. It is widely believed that new strains migrated into Europe in 1976 and that this led to subsequent population changes including the introduction of the A2 mating type. The population characteristics of recently collected isolates in NW Europe show a diverse population including both mating types, sexual reproduction and oospores, although differences are observed between regions. Although it is difficult to find direct evidence that new strains are more aggressive, there are several indications from experiments and field epidemics that the aggressiveness of P. infestans has increased in the past 20 years. The relative importance of the different primary inoculum sources and specific measures for reducing their role, such as covering dumps with plastic and preventing seed tubers from becoming infected, is described for the different regions. In NW Europe, varieties with greater resistance tend not to be grown on a large scale. From the grower’s perspective, the savings in fungicide input that can be achieved with these varieties are not compensated by the higher (perceived) risk of blight. Fungicides play a crucial role in the integrated control of late blight. The spray strategies in NW Europe and a table of the specific attributes of the most important fungicides in Europe are presented. The development and use of decision support systems (DSSs) in NW Europe are described. In The Netherlands, it is estimated that almost 40% of potato growers use recommendations based on commercially available DSS. In the Nordic countries, a new DSS concept with a fixed 7-day spray interval and a variable dose rate is being tested. In the UK, commercially available DSSs are used for c. 8% of the area. The validity of Smith Periods for the new population of P. infestans in the UK is currently being evaluated
Appreciating Johann Schepers.
No full textAs an expert leader in psychometrics, eminent scholar, gatekeeper, study leader and mentor, Johann M. Schepers has had a profound effect on the development of Psychology and Industrial Psychology in South Africa. By means of an appreciative inquiry the outstanding ability of this man has been highlighted in stories which resulted in a rich profile and a legacy that needs to be protected and nurtured
Eine Utopie: Ökotourismus in Tadschikistan
No full textSchepers G. Eine Utopie: Ökotourismus in Tadschikistan. In: Wennemann M, ed. Pamir Expedition 2002. Bielefeld - Bonn - Dushanbe 27.07.-24.08.2002. Bielefeld: Universität Bielefeld, Fakultät für Biologie, Abt. Ökologie; Draft: 100-105
Naturethik in der Architekturwissenschaft
No full textSchepers G. Naturethik in der Architekturwissenschaft. In: Dangl M, Franz JH, eds. Natur, Kultur und Technik. Philosophie, Naturwissenschaft und Technik. Berlin: Frank & Timme GmbH; 2024: 153-165
Experimental control strategies reducing the fungicide input at a practical scale
No full textPhytophthora infestans is the most devastating disease in potato cultivation. Chemical control is necessary to ensure a healthy crop. At the same time Dutch governmental policy asks for a reduction of the environmental impact of potato late blight control by 75% in 2012 as compared to 1996-1998. The aim of the experiments was to compare Decision Support Systems with different approaches to blight risk management for their ability to reduce the fungicide input without compromising control efficacy. Considerable savings, up to 81% when compared to weekly, full dose rate, spray schedules, can be achieved by using information on cultivar resistance, length of the critical period and disease pressure to decide whether or not to spray. The subroutine calculating the potential for viable transport of spores is only effective on resistant varieties as the threshold was exceeded with every critical period on less resistant cultivars. Implications of the experimental control strategies for agricultural practise are discusse
Pragmatic Models: BEM with Engineering Add-Ons
No full textThis chapter discusses several aspects related to engineering methods in wind turbine design codes. Current engineering models for rotor aerodynamics topic are built around the Blade Element Momentum (BEM) theory. The Blade Element Momentum theory in itself is very basic, e.g., it is derived for two-dimensional, stationary, homogenous, and non-yawed conditions. For this reason, several engineering models have been developed which overcome these simplifications and which act as add-ons to the basic BEM theory. This chapter describes the BEM theory, the most important engineering add-ons, and an assessment of BEM with engineering add-ons with results from higher fidelity models and measurements
TS2PACK: A Two-Level Tabu Search for the Three-dimensional Bin Packing Problem
No full textThree-dimensional orthogonal bin packing is a problem NP-hard in the strong sense where a set of boxes must be orthogonally packed into the minimum number of three-dimensional bins. We present a two-level tabu search for this problem. The first-level aims to reduce the number of bins. The second optimizes the packing of the bins. This latter procedure is based on the Interval Graph representation of the packing, proposed by Fekete and Schepers, which reduces the size of the search space. We also introduce a general method to increase the size of the associated neighborhoods, and thus the quality of the search, without increasing the overall complexity of the algorithm. Extensive computational results on benchmark problem instances show the effectiveness of the proposed approach, obtaining better results compared to the existing one
Precision phrase linking and pulling – ispantu
No full textPrecision semantic linking and pulling:
The semantic web can be interpreted as a web of sem
antic units – or ideas. An idea
can occasionally be found succinctly expressed in a
phrase on a remote web-page. To
make sense of the semantic web we ought to be able
to link precisely to such a text-
phrase, plucking it from its surroundings and re-pr
esenting it, while intrinsically
attributing its derivation: its semantic context.
A new page could be built from a
mosaic of such verbatim citations pulled
in situ
from over the web. For this to be of
enduring value the integrity of phrases once cited
should be verifiable later. All this
becomes less of an academic exercise when one consi
ders the multilingual field –
where, for challenging translations, re-tracing the
precise source-language context
often assists a broader comprehension
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