Intra-annual to multi-decadal xylem traits in a tropical moist semi-deciduous forest of Central Africa

A witness of a tree’s past conditions is the wood itself. The main research question of this dissertation is how to assess and reveal the driving forces of the patterns of wood traits on pith-to-bark cross-sections in tropical trees. Cambial and leaf phenology was monitored in the Luki Reserve (Mayombe forest, D.R. Congo). Furthermore, X-ray CT densitometry was explored to assess traits in a reliable way, for multiple species. Variability in phenology is observed for T. superba, which requires traits of individual trees to be fixed on a time axis. Furthermore, X-ray CT is a suitable method for assessing traits in a fast way. Cambial activity of understory trees has shown to be species-specific, whilst many trees show zero xylem growth. Finally, 66 years of tree growth was analysed, while trait analysis revealed a median ring count of only 32, thus implying many non-periodical rings. This work presents methodological improvements to measure traits as continuous variables from pith to bark, but also acknowledges that phenology still remains a key aspect in order to fix traits on a time axis. Key words: leaf phenology, wood anatomy, stable isotopes, Mayombe, dendrochronology, X-ray CT densitometr

PluralisMAC: a generic multi-MAC framework for heterogeneous, multiservice wireless networks, applied to smart containers

Developing energy-efficient MAC protocols for lightweight wireless systems has been a challenging task for decades because of the specific requirements of various applications and the varying environments in which wireless systems are deployed. Many MAC protocols for wireless networks have been proposed, often custom-made for a specific application. It is clear that one MAC does not fit all the requirements. So, how should a MAC layer deal with an application that has several modes (each with different requirements) or with the deployment of another application during the lifetime of the system? Especially in a mobile wireless system, like Smart Monitoring of Containers, we cannot know in advance the application state (empty container versus stuffed container). Dynamic switching between different energy-efficient MAC strategies is needed. Our architecture, called PluralisMAC, contains a generic multi-MAC framework and a generic neighbour monitoring and filtering framework. To validate the real-world feasibility of our architecture, we have implemented it in TinyOS and have done experiments on the TMote Sky nodes in the w-iLab.t testbed. Experimental results show that dynamic switching between MAC strategies is possible with minimal receive chain overhead, while meeting the various application requirements (reliability and low-energy consumption)

Characterization of 27 mycotoxin detoxifiers and the relation with in vitro zearalenone binding

Addition of mycotoxin detoxifiers to feed is a common practice to counteract the deleterious effects of mycotoxins on animal health. Although a variety of this kind of feed additives is available on the market, little is known about their detailed composition and physico-chemical properties. This lack of knowledge might pose some difficulties for researchers and users to compare and evaluate the efficacy and safety of these additives. The present study describes the characterization of 27 commercially available mycotoxin detoxifiers collected from various sources in Flanders and The Netherlands. Characterization comprised XRD-profiling of the mineral content, determination of the cation exchange capacity and exchangeable cations, acidity, mineral fraction, humidity and swelling volume. The XRD- and mineral fraction data were analysed with principal component analysis and explorative cluster analysis which enabled the identification of three distinct groups: smectite based (n=19), non-smectite based (n=5) and organic based detoxifiers (n=4). In a second experiment, an in vitro zearalenone binding test was conducted using phosphate buffered saline at pH 2.5, 6.5 and 8.0. The zearalenone binding of the smectite based group was related to the physico-chemical properties using a multivariate linear regression model. The binding in the non-smectite based and organic based groups was analysed using a one-way ANOVA. A large variability in binding properties was present, especially in the smectite containing group. Additives with smectite-containing mixed-layered minerals and additives containing humic acids expressed the highest binding which amounted to over 90%. The retained multivariate linear model included exchangeable potassium (p≤0.05), moist content (p≤0.05) and mineral fraction (0.05≤p≤0.1), indicating a statistical relation of these parameters with the in vitro zearalenone binding