Capillary surface discontinuities above reentrant corners

A particular configuration of a vertical capillary tube for which S is the equilibrium interface between two fluids in the presence of a downward pointing gravitational field was investigated. S is the graph a function u whose domain is the (horizontal) cross section gamma of the tube. The mean curvature of S is proportional to its height above a fixed reference plane and lambda is a prescribed constant and may be taken between zero and pi/2. Domains gamma for which us is a bounded function but does not extend continuously to d gamma are sought. Simple domains are found and the behavior of u in those domains is studied. An important comparison principle that has been used in the literature to derive many of the results in capillarity is reviewed. It allows one to deduce the approximate shape of a capillary surface by constructing comparison surfaces with mean curvature and contact angle close to those of the (unknown) solution surface. In the context of nonparametric problems the comparison principle leads to height estimates above and below for the function u. An example from the literature where these height estimates have been used successfully is described. The promised domains for which the bounded u does not extend continuously to the boundary are constructed. The point on the boundary at which u has a jump discontinuity will be the vertext of a re-entrant corner having any interior angle theta pi. Using the comparison principle the behavior of u near this point is studied

The Changing role of agriculture in Dutch society

Dutch agriculture has undergone significant changes in the past century, similar to many countries in the European Union. Due to economies of scale and in order to remain economically profitable, it became necessary for farmers to increase farm size, efficiency and external inputs, while minimizing labour use per hectare. The latter has resulted in fewer people working in the agricultural sector. Consequently, Dutch society gradually lost its connection to agricultural production. This divergence resulted in a poor image for the agricultural sector, because of environmental pollution, homogenization of the landscape, outbreaks of contagious animal diseases and reduced animal welfare. Although the general attitude towards agriculture seems to have improved slightly in recent years, there is still a long way to go in regaining this trust. In order to keep the Dutch countryside viable, farmers are considered indispensable. However, their methods of production should match the demands of society in terms of sustainability. This applies both to farming systems that are used in a monofunctional way (production only) and to multifunctional farming systems. For researchers involved in development of these farming systems, this requires new capabilities; contrary to the situation in the past, citizens and stakeholder groups now demand involvement in the design of farming systems. In the current paper, it is suggested that, besides traditional mainstream agriculture, other alternative farming systems should be developed and implemented. Hence, Dutch agricultural research should remain focused on the cutting edge of economy and society. Despite all efforts, not all of these newly developed systems will acquire a position within the agricultural spectrum. However, some of the successful ones may prove extremely valuable

Klimaat en landbouw; risico's en kansen

Klimaatverandering zal gevolgen hebben voor alle sectoren van de samenleving. Ook de landbouw ontkomt er niet aan om maatregelen te nemen. Maatregelen om de eigen bedrijfsvoering klimaatbestendiger te maken, maar de landbouw kan ook helpen om de negatieve gevolgen van klimaatverandering voor de omgeving te verminderen. Wat zijn de risico’s van klimaatverandering? Welke maatregelen kunnen bedrijven nemen? En biedt het ook kansen voor ondernemers

Produktie en voederwaarde van gras bij gebruiks- en bemestingsbeperkingen voor natuurbeheer

The effects of restrictions in grassland management on behalf of nature conservation were studied. In this thesis it was investigated to which extent soil fertility, botanical composition, growth curves, dry matter production, chemical composition, digestibility and nutritive value were affected by a delay of first cutting date and restricted amounts of N-, P- and K-fertilizers. The average number for growing days to reach certain amounts of dry matter during growing season and the consequences for chemical composition and nutritive values are presentedOn the studied humous soils with a sufficient phosphate (P) and potassium (K) fertilization but without nitrogen (N) application the dry matter production was c. 8 ton.ha -1.year -1. Without P- and K-fertilization the production decreased sharply within 2 to 4 years. The digestibility of the grass was strongly affected by growing stage as well as by botanical composition of the sward. The differences in digestibility between (indigenous) grass species were considerable. At any time Lolium perenne had the highest digestibility at a certain crude fibre content.</p

Dissimilar response of plant and soil biota communities to long-term nutrient adition in grasslands

The long-term effect of fertilizers on plant diversity and productivity is well known, but long-term effects on soil biota communities have received relatively little attention. Here, we used an exceptional long-lasting (>40 years) grassland fertilization experiment to investigate the long-term effect of Ca, N, PK, and NPK addition on the productivity and diversity of both vegetation and soil biota. Whereas plant diversity increased by liming and decreased by N and NPK, the diversity of nematodes, collembolans, mites, and enchytraeids increased by N, PK, or NPK. Fertilization with NPK and PK increased plant biomass and biomass of enchytraeids and collembolans. Biomass of nematodes and earthworms increased by liming. Our results suggest that soil diversity might be driven by plant productivity rather than by plant diversity. This may imply that the selection of measures for restoring or conserving plant diversity may decrease soil biota diversity. This needs to be tested in future experiment