Bylaag: Natuurwet en waarheid*

Die betekenis van natuurwetenskaplike arbeid lê opgesluit in die „natuurwet” en die „waarheid”. Met die natuurwet beheer die natuurwetenskaplike die natuurkragte en verkry hy 'n insig in die natuur wat hom omring. Die waarheid is vir hom die ooreenkoms tussen die natuurgebeure en die verklarende natuurwetenskaplike teorie

Genetic algorithm based two-mode clustering of metabolomics data

Metabolomics and other omics tools are generally characterized by large data sets with many variables obtained under different environmental conditions. Clustering methods and more specifically two-mode clustering methods are excellent tools for analyzing this type of data. Two-mode clustering methods allow for analysis of the behavior of subsets of metabolites under different experimental conditions. In addition, the results are easily visualized. In this paper we introduce a two-mode clustering method based on a genetic algorithm that uses a criterion that searches for homogeneous clusters. Furthermore we introduce a cluster stability criterion to validate the clusters and we provide an extended knee plot to select the optimal number of clusters in both experimental and metabolite modes. The genetic algorithm-based two-mode clustering gave biological relevant results when it was applied to two real life metabolomics data sets. It was, for instance, able to identify a catabolic pathway for growth on several of the carbon sources

Perceived heading during simulated torsional eye movements

AbstractObserver translation through the environment can be accompanied by rotation of the eye about any axis. For rotation about the vertical axis (horizontal rotation) during translation in the horizontal plane, it is known that the absence of depth in the scene and an extra retinal signal leads to a systematic error in the observer’s perceived direction of heading. This heading error is related in magnitude and direction to the shift of the centre of retinal flow (CF) that occurs because of the rotation. Rotation about any axis that deviates from the heading direction results in a CF shift. So far, however, the effect of rotation about the line of sight (torsion) on perceived heading has not been investigated. We simulated observer translation towards a wall or cloud, while simultaneously simulating eye rotation about the vertical axis, the torsional axis or combinations thereof. We find only small systematic effects of torsion on the set of 2D perceived headings, regardless of the simulated horizontal rotation. In proportion to the CF shift, the systematic errors are significantly smaller for pure torsion than for pure horizontal rotation. In contrast to errors caused by horizontal rotation, the torsional errors are hardly reduced by addition of depth to the scene. We suggest the difference in behaviour reflects the difference in symmetry of the field of view relative to the axis of rotation: the higher symmetry in the case of torsion may allow for a more accurate estimation of the rotational flow. Moreover, we report a new phenomenon. Simulated horizontal rotation during simulated wall approach increases the heading-dependency of errors, causing a larger compression of perceived heading in the horizontal direction than in the vertical direction

The art of creating futures. Practical theology and a strategic research sensitivity for the future

This paper explores a futures perspective for practical theology. Although there are some examples of a future orientation, a systematic futures perspective has not been developed. Building on futures studies (including predictive studies on foresight and design and architecture studies), the authors propose a methodological model for future-sensitive practical theology, accounting for the probable, possible, and preferable. The model results in three modes in which practical theology can employ a future orientation: utopian, prognostic-adaptive, and designing-creative

Plant parasitic nematodes associated with crops grown by smallholders in Mozambique

Des enquêtes effectuées sur les cultures du Mozambique de 1992 à 1996 ont révélé la présence et l'importance de nombreux nématodes phytoparasites, #Meloidogyne spp. et #Pratylenchus spp. étant les plus répandus et prédominants. Plusieurs espèces ont été trouvées pour la première fois au Mozambique, tandis que d'autres étaient relevées sur d'autres plantes que celles signalées lors des enquêtes précédentes. #Pratylenchus zeae est fréquent sur le maïs, mais aussi sur le haricot (#Phaseolus vulgaris L.), la canne à sucre et le tournesol. #Meloidogyne spp. sont de sérieux ennemis du haricot commun lorsqu'il est interplanté avec le maïs dans la province de Niassa, et également du niébé dans les champs expérimentaux et les zones irriguées du sud, du tournesol dans la province du Niassa, du tabac dans les provinces de Nampula et Manica, et enfin des plantes maraïchères en de nombreuses localités. Mais au Mozambique ces nématodes ne constituent pas un problème pour le manioc. #Ditylenchus africanus, qui attaque les gousses d'arachide, a été trouvé dans les provinces de Maputo et Gaza et pourrait y avoir été introduit lors de l'importation d'arachides utilisées comme semences ou pour la consommation humaine. (Résumé d'auteur

Variability of parameters for modelling soil moisture conditions : studies on loamy to silty soils on marly bedrock in the Ardeche drainage basin (France)

Field experiments and additional measurements on undisturbed soil samples in the laboratory were done to investigate the variability of the parameters used in modelling soil moisture conditions.The conditions of soil water control the amount of moisture available for the plant cover, crop production, transport of contamination in the unsaturated zone, and are thus of interest for the study of processes of soil erosion and mass movement and for land evaluation.Attention was paid to hydraulic soil characteristics as well as to plant-soil parameters for determining actual evapotranspiration.The research mainly concerned loamy and silty soils in the Ardèche drainage basin.The results demonstrate the need for models in which the variability of the hydraulic characteristics can be reduced to basic parameters. For land evaluation it is important for such parameters to be related to physiographic properties that can be mapped easily.</p

’N narratiewe teologiese verkenning van negatiewe koronêre vatomleidingsoperasieuitkomste: ’n chirurgiese hermeneutiek

Negative outcomes of coronary bypass operations not only have an important impact on the patient and family, but also have an influence on the cardiac surgeon on many levels. Within a specific surgical context and from a tradition of faith, interwoven narratives present the possibility of an interdisciplinary conversation between medical science and theology. By following an auto-ethnographic approach, an invitation is offered to participate in sharing the surgeon’s database as a new hermeneutic text. Fellow cardiac surgeons on a national level are involved by way of a Delphi research model, providing for a collective tracing of God’s involvement in surgical outcomes. In a process of a reinterpretation of negative surgical outcomes, Henri Nouwen’s three poles of a spiritual movement can lead to spiritual transformation. Bearing physiological barriers and lifestyles in mind, as well as God’s involvement, the patient and surgeon can in a new manner reflect on possible negative outcomes following operative procedures

Interimrapportage van het hydrologische proefveld Geestmerambacht; een overzicht van beschikbare gegevens en eerste resultaten

Het rapport is een beschrijving van de proefopzet in een groot hydrologisch proefveld Geestmerambacht ten noorden van Alkmaar. Het proefveld bestaat uit twaalf stroken van ongeveer 10 m x 120 m, waarin vier bodemsubstraten zijn aangebracht en waarin in een matrixstructuur acht boomsoorten groeien sinds 1985. Het grondwaterniveau in elke strook kan worden geregeld via een pomp- en vlottersysteem. Tot 1997 waren er vijf verschillende niveaus, daarna zijn de meeste stroken vernat (hoger grondwater ingesteld); vier natte stroken zijn juist verdroogd. Een belangrijk doel van het rapport is om aan te geven welke gegevens betrouwbaar zijn in de lange meetreeksen, mede in verband met een aantal technische storingen die zijn opgetreden in het proefveld. De aflezingen van de meeste grondwaterbuizen bleken betrouwbaar. Het rapport bevat daarnaast een aantal oriënterende resultaten, onder andere effecten van vernatting op groei van de bomen. De resultaten van het proefveld worden in 2002 gerapporteerd, nadat een volledige statistische analyse is uitgevoerd