Papers by Huib C. de Vriend
Futures, 2014
ABSTRACT This paper assesses the possible roles of biosolar energy systems in the Netherlands in ... more ABSTRACT This paper assesses the possible roles of biosolar energy systems in the Netherlands in the coming years. The appraisal is made in the light of EU Directives on renewable energy and reduction of CO2 emissions, and the new Dutch Energy Agreement for Sustainable Growth. The assessment is made within the Dutch BioSolar Cells (BSC) research programme on photosynthesis and its application in fuel production. Part of the programme is committed to societal debate by considering different options and uses of biosolar technology. To provide building blocks for these discussions, we conducted a comprehensive desk study supplemented with key expert interviews, and we identified and articulated the main drivers for the Dutch transition towards more sustainable energy supply. Next, these drivers were used to develop two futures: Energy Port and Energy Farm, representing institutional settings in which BSC technology could be implemented. Both represent fundamentally different types of innovation and are useful in assessing the effect of policies on future energy systems. Both scenarios were used in workshops with BSC researchers and policymakers. Their possible implications for the BSC programme itself, as well as the broader policy significance of the use of biosolar technologies in the Netherlands, are indicated.
Euphytica, 2010
Plant geneticists consider molecular marker assisted selection a useful additional tool in plant ... more Plant geneticists consider molecular marker assisted selection a useful additional tool in plant breeding programs to make selection more efficient. Standards for organic agriculture do not exclude the use of molecular markers as such, however for the organic sector the appropriateness of molecular markers is not self-evident and is often debated. Organic and low-input farming conditions require breeding for robust and flexible varieties, which may be hampered by too much focus on the molecular level. Pros and contras for application of molecular markers in breeding for organic agriculture was the topic of a recent European plant breeding workshop. The participants evaluated strengths, weaknesses, opportunities, and threats of the use of molecular markers and we formalized their inputs into breeder's perspectives and perspectives seen from the organic sector's standpoint. Clear strengths were identified, e.g. better knowledge about gene pool of breeding material, more efficient introgression of new resistance genes from wild relatives and testing pyramided genes. There were also common concerns among breeders aiming at breeding for organic and/ or conventional agriculture, such as the increasing competition and cost investments to get access to marker technology, and the need for bridging the gap between phenotyping and genotyping especially with complex and quantitative inherited traits such as nutrient-efficiency. A major conclusion of the authors is that more interaction and mutual understanding between organic and molecular oriented breeders is necessary and can benefit both research communities.
Euphytica, 2010
Plant geneticists consider molecular marker assisted selection a useful additional tool in plant ... more Plant geneticists consider molecular marker assisted selection a useful additional tool in plant breeding programs to make selection more efficient. Standards for organic agriculture do not exclude the use of molecular markers as such, however for the organic sector the appropriateness of molecular markers is not self-evident and is often debated. Organic and low-input farming conditions require breeding for robust and flexible varieties, which may be hampered by too much focus on the molecular level. Pros and contras for application of molecular markers in breeding for organic agriculture was the topic of a recent European plant breeding workshop. The participants evaluated strengths, weaknesses, opportunities, and threats of the use of molecular markers and we formalized their inputs into breeder's perspectives and perspectives seen from the organic sector's standpoint. Clear strengths were identified, e.g. better knowledge about gene pool of breeding material, more efficient introgression of new resistance genes from wild relatives and testing pyramided genes. There were also common concerns among breeders aiming at breeding for organic and/ or conventional agriculture, such as the increasing competition and cost investments to get access to marker technology, and the need for bridging the gap between phenotyping and genotyping especially with complex and quantitative inherited traits such as nutrient-efficiency. A major conclusion of the authors is that more interaction and mutual understanding between organic and molecular oriented breeders is necessary and can benefit both research communities.
Nature Biotechnology, 2006
Phys Fluids, 2005
In spite of its importance, little is known about the turbulence characteristics in open-channel ... more In spite of its importance, little is known about the turbulence characteristics in open-channel bends. This paper reports on an experimental investigation of turbulence in one cross section of an open-channel bend. Typical flow features are a bicellular pattern of cross-stream circulation (secondary flow) and a turbulence activity in the outer bend that is significantly less than in the equivalent straight uniform shear flow. Measured distributions are given of the turbulent kinetic energy, its production, the mixing coefficients, some parameters characterizing the turbulence structure, and the fourth-order correlations of the turbulent velocity fluctuations. The transport equation for the turbulent kinetic energy is evaluated term by term, on the basis of the measured data. The results show that the turbulence structure is different from straight uniform flow, in that the Reynolds stress tensor is more diagonally dominant. This is shown to be the main cause of the observed reduction of turbulence activity in the outer bend. The usual two-equation turbulence closure models include a transport equation for the turbulent kinetic energy, but they do not account for this modified turbulence structure. The departures of the measured turbulence structure from its equivalent in straight uniform shear flow are related to a curvature-flux-Richardson number Rf which includes the streamline curvature. Such a relation may be useful to improve simple turbulence closure models for curved open-channel flow.
Water Science and Technology, Feb 1, 2009
Many scientists feel that scientific outcomes are not sufficiently taken into account in policy-m... more Many scientists feel that scientific outcomes are not sufficiently taken into account in policy-making. The research reported in this paper shows what happens with scientific information during such a process. In 2001 the Dutch Ministry of Transport, Public Works and Water Management commissioned their regional office in Limburg to assess how flood management objectives can be achieved in future in the Dutch Meuse valley, assuming climate change will increase peak discharges. To ensure political support, regional discussion rounds were to help assess the measures previously identified. This paper discusses the ways in which hydrological and hydraulic expertise was input, understood and used in this assessment process. Project participants as a group had no trouble contesting assumptions and outcomes. Nevertheless, water expertise was generally accepted as providing facts, once basic choices such as starting situation had been discussed and agreed. The technical constraints determined that politically unacceptable measures would have to be selected to achieve the legally binding flood management objective. As a result, no additional space will be set aside for future flood management beyond the already reserved floodplain. In this case, political arguments clearly prevail over policy objectives, with hydraulic expertise providing decisive arbitration between the two.
Coastal Engineering 1992, 1993
Continental Shelf Research, Dec 31, 2002
Sand waves form a prominent regular pattern in the offshore seabed of sandy shallow seas. The pos... more Sand waves form a prominent regular pattern in the offshore seabed of sandy shallow seas. The positions of sand-wave crests and troughs slowly change in time. Sand waves are usually assumed to migrate in the direction of the residual current. This paper considers the physical mechanisms that may cause sand waves to migrate and methods to quantify the associated migration rates. We carried out a theoretical study based on the assumption that sand waves evolve as free instabilities of the system. A linear stability analysis was then performed on a 2DV morphological model describing the interaction between the vertically varying water motion and an erodible bed in a shallow sea. Here, we disrupted the basic tidal symmetry by choosing a combination of a steady current ( M0) and a sinusoidal tidal motion ( M2) as the basic flow. We allowed for two different physical mechanisms to generate the steady current: a sea surface wind stress and a pressure gradient. The results show that similar sand waves develop for both flow conditions and that these sand waves migrate slowly in the direction of the residual flow. The rates of migration and wavelengths found in this work agree with theoretical and empirical values reported in the literature.
Journal of Hydraulic Research, Apr 1, 2001
Alternate bars are large wave patterns in sandy beds of rivers and channels. The crests and troug... more Alternate bars are large wave patterns in sandy beds of rivers and channels. The crests and troughs alternate between the banks of the channel. These bars, which move downstream several meters per day, reduce the navigability of the river. Recent modelling of alternate bars has focused on stability analysis techniques. We think, that the resulting models can predict large rhythmic patterns in sandy beds, especially if the models can be combined with data-assimilation techniques. The results presented in this paper confirm this thought. We compared the wavelength and height of alternate bars as predicted by the model of Schielen et al. [14], with the values measured in several flume experiments. Given realistic hydraulic conditions > 2*10³, (R the width-to-depth ratio and R e the Reynolds number), the predictions are in good R Re agreement with the measurements. In addition, the model predicts the bars measured in experiments with graded sediment. If < 2*10³, the agree-R Re ment between model results and measurements is lost. The wave height is clearly underestimated, and the standard deviation of the differences between predictions and measurements increases. This questions the usefulness of small flume experiments for morphodynamic problems.
Coastal Engineering 1990, 1991
Nature and Culture, 2007
... Paul Simon, from The Boxer Anna Wesselink was trained as a tropical land and water developm... more ... Paul Simon, from The Boxer Anna Wesselink was trained as a tropical land and water development engineer, then moved into water resources research and management. This has taken her to the UK, the Central African Republic, and Madagascar. ...
Journal of Hydraulic Engineering, Sep 1, 2010
Experiments have been carried out in a mobile-bed laboratory flume in order to study the sediment... more Experiments have been carried out in a mobile-bed laboratory flume in order to study the sediment exchange process between the main channel and the groyne fields. The flume represented half the width of a schematized river reach with a series of groynes. The experiment was designed to represent typical dimensions of the Dutch River Waal at a geometrical scale of 1:100. The conditions were set to guarantee bed load as well as suspended load sediment transport. Conditions with submerged and emerged groynes were investigated. In addition to traditional measurements, viz., bed-level changes, suspended sediment concentrations, and flow velocities, bed-form propagation was measured in two dimensions using a the particle image velocimetry technique. The results were analyzed with focus on sediment exchange mechanisms and sediment transport patterns. The results demonstrate that under all flow conditions there is a net import of sediment into the groyne fields. The prevailing transport mechanisms vary with the flow stage: if the groynes are emerged it is mainly advection by the primary circulation cell, whereas if the groynes are submerged it is rather residual advection by large-scale coherent flow structures ͑in a straight reach͒. Additional entrainment of sediment by enhanced turbulence complicates the erosion/ deposition patterns.
Coastal Engineering 1988, 1989
ABSTRACT
Journal of Artificial Societies and Social Simulation the, 2001
... Recent publications are (Arthur 1994, Axelrod 1997, Gilbert 1996, Gilbert and Troitzsch 1999,... more ... Recent publications are (Arthur 1994, Axelrod 1997, Gilbert 1996, Gilbert and Troitzsch 1999, Conte, Hegselmann and Terna 1997, Tesfatsion 1998 ... of the employment opportunities of agents is important, since it affects the travel time to work (Evers and Van der Veen, 1986, Van ...
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Papers by Huib C. de Vriend