This archive contains features computed from satellites images in Kordofan State in Sudan. SPOT (Systeme Probatoire d’Observation de la Terre) images with a 10-m ground resolution and preprocessing level 2A were divided into non-overlapping square windows of 410 by 410 m. We calculated for each of these windows: skewness of the grayscale distribution of each window index of vegetation pattern anisotropy azimuthal angle in the first PCA plane, which directly correlates with the dominant frequency in the windows distance from PCA origin, which expresses the degree of scale dominance mean annual rainfall computed from gridded monthly estimates from the Tropical Rainfall Measuring Mission (TRMM, NASA/JAXA) 3B43 V6 product acquired from 1 January 1998 to 31 December 2007 and resampled to 410 by 410 m. slope computed from the Shuttle Radar Topography Mission (SRTM) digital elevation model with three arc secondshorizontal (ca 92 m in this area) spatial resolution. The resulting pattern classification: 1, spots 2, labyrinthine 3, gaps 4, bands 5, non-periodic Nodata, area not covered by SPOT images Data is provided as rasters in Arc/Info ASCII grid format (also known as Esri grid). The projection and datum for all datasets are UTM zone 35 N, WGS 1984. Details on the methods are availble in the following publication: Deblauwe, V., Couteron, P., Lejeune, O., Bogaert, J. & Barbier, N. (2011) Environmental modulation of self-organized periodic vegetation patterns in Sudan. Ecography, 34, 990-1001. https://doi.org/10.1111/j.1600-0587.2010.06694.x

Understanding the mechanisms involved in long-term persistence of humoral immunity after natural infection or vaccination is challenging and crucial for further research in immunology, vaccine development as well as health policy. Long-lived plasma cells, which have recently been shown to reside in survival niches in the bone marrow, are instrumental in the process of immunity induction and persistence. We developed a mathematical model, assuming two antibody-secreting cell subpopulations (short- and long-lived plasma cells), to analyze the antibody kinetics after HAV-vaccination using data from two long-term follow-up studies. Model parameters were estimated through a hierarchical nonlinear mixed-effects model analysis. Long-term individual predictions were derived from the individual empirical parameters and were used to estimate the mean time to immunity waning. We show that three life spans are essential to explain the observed antibody kinetics: that of the antibodies (around one month), the short-lived plasma cells (several months) and the long-lived plasma cells (decades). Although our model is a simplified representation of the actual mechanisms that govern individual immune responses, the level of agreement between long-term individual predictions and observed kinetics is reassuringly close. The quantitative assessment of the time scales over which plasma cells and antibodies live and interact provides a basis for further quantitative research on immunology, with direct consequences for understanding the epidemiology of infectious diseases, and for timing serum sampling in clinical trials of vaccines.

Spatially periodic vegetation patterns in arid to semi-arid regions have inspired numerous mechanistic models in the last decade. All embody a common principle of self-organization and make concordant, hence robust, predictions on how environmental factors may modulate the morphological properties of these patterns. Such an array of predictions still needs to be corroborated by synchronic and diachronic field observations on a large scale. Using Fourier-based texture analysis of satellite imagery, we objectively categorized the typical morphologies of periodic patterns and their characteristic scales (wavelength) over extensive areas in Sudan. We then analyzed the environmental domain and the modulation of patterns morphologies at different dates to test the theoretical predictions within a single synthetic and quantitative study. Our results show that, below a critical slope gradient which depends on the aridity level, pattern morphologies vary in space in relation to the decrease of mean annual rainfall in a sequence consistent with the predictions of self-organization models: gaps, labyrinths and spots with increasing wavelengths. Moreover, the same dynamical sequence was observed over time during the Sahelian droughts of the 1970s and 1980s. For a given morphology, the effect of aridity is to increase the pattern wavelength. Above the critical slope gradient, we observed a pattern of parallel bands oriented along the contour lines (the so called tiger-bush). The wavelength of these bands displayed a loose inverse correlation with the slope. These results highlight the pertinence of self-organization theory to explain and possibly predict the dynamics of these threatened ecosystems.

Quels seraient les coûts et les bénéfices associés à des programmes de vaccination contre la varicelle chez les enfants et contre le zona chez les adultes ? Le Centre d’évaluation économique et de modélisation des maladies infectieuses de l’Université d’Anvers (CHERMID) a examiné ces questions pour le compte du Centre fédéral d’expertise des soins de santé (KCE). L’étude révèle qu’un programme de vaccination contre la varicelle n’est souhaitable que si l’on est certain qu’il n’engendrera pas d’augmentation trop importante du nombre de zonas. Les résultats, non encore disponibles, d’autres pays où la vaccination a déjà lieu devraient nous permettre d’en savoir plus. Les avantages de la vaccination des personnes âgées contre le zona ne sont pas clairs non plus à cause du manque actuel de données fiables.

Een vaccinatieprogramma van kinderen tegen windpokken, en van ouderen tegen zona, wat zouden de kosten en baten hiervan zijn? Deze vraag onderzocht het Centrum voor Gezondheidseconomie en Modellering van Infectieziekten (Universiteit Antwerpen) in opdracht van het Federaal Kenniscentrum voor de Gezondheidszorg (KCE). Een vaccinatieprogramma tegen windpokken kan best pas opgestart worden als men zeker is dat daardoor het aantal gevallen van zona niet tegelijkertijd te sterk toeneemt. Daarvoor moeten de resultaten in een aantal landen, die reeds met vaccinatie zijn gestart, worden afgewacht. Voor vaccinatie tegen zona van zestig plussers zijn er te weinig betrouwbare gegevens beschikbaar om de baten eenduidig in te schatten.

A la demande du Centre fédéral d’expertise des soins de santé (KCE), le Centre pour l’évaluation des vaccinations (CEV) de l’Université d’Anvers a étudié l’intérêt et le rapport coût efficacité d’une vaccination universelle et ciblée vis-à-vis de l’hépatite A. Les résultats de l’étude conduisent le KCE à recommander le financement de cette vaccination pour tous les enfants de 1 à 12 ans qui se rendent dans des régions où la maladie survient encore fréquemment. Une vaccination universelle des nourrissons et des adultes n’est pas efficiente et donc pas recommandée par le KCE.

The dynamics of vegetation is formulated in terms of the allometric and structural properties of plants. Within the framework of a general and yet parsimonious approach, we focus on the relationship between the morphology of individual plants and the spatial organization of vegetation populations. So far, in theoretical as well as in field studies, this relationship has received only scant attention. The results reported remedy to this shortcoming. They highlight the importance of the crown/root ratio and demonstrate that the allometric relationship between this ratio and plant development plays an essential part in all matters regarding ecosystems stability under conditions of limited soil (water) resources. This allometry determines the coordinates in parameter space of a critical point that controls the conditions in which the emergence of self-organized biomass distributions is possible. We have quantified this relationship in terms of parameters that are accessible by measurement of individual plant characteristics. It is further demonstrated that, close to criticality, the dynamics of plant populations is given by a variational Swift–Hohenberg equation. The evolution of vegetation in response to increasing aridity, the conditions of gapped pattern formation and the conditions under which desertification takes place are investigated more specifically. It is shown that desertification may occur either as a local desertification process that does not affect pattern morphology in the course of its unfolding or as a gap coarsening process after the emergence of a transitory, deeply gapped pattern regime. Our results amend the commonly held interpretation associating vegetation patterns with a Turing instability. They provide a more unified understanding of vegetation self-organization within the broad context of matter order–disorder transitions.

In opdracht van het Federaal Kenniscentrum voor de Gezondheidszorg (KCE) onderzocht het Centrum voor de Evaluatie van Vaccinaties (CEV) van de Universiteit Antwerpen het nut en de kosteneffectiviteit van een algemene en een doelgroepgerichte vaccinatie tegen hepatitis A. Op basis van de onderzoeksresultaten pleit het KCE voor de financiering van deze vaccinatie voor alle kinderen (1 tot 12 jaar) die naar gebieden reizen waar de ziekte nog vaak voorkomt. Een algemene vaccinatie van volwassenen en zuigelingen is niet kosteneffectief en de financiering hiervan wordt daarom door het KCE niet aanbevolen.

Spatially periodic vegetation patterns, forming gaps, bands, labyrinths, or spots, are characteristic of arid and semiarid landscapes. Self-organization models can explain this variety of structures within a unified conceptual framework. All these models are based on the interplay of positive and negative effects of plants on soil water, but they can be divided according to whether they assume the interactions to be mediated by water redistribution through runoff/diffusion or by plants' organs. We carried out a multi-proxy approach of the processes operating in a gapped pattern in southwest Niger dominated by a shrub species. Soil moisture within the root layer was monitored in time and space over one month of the rainy season. Soil water recharge displayed no spatial variation with respect to vegetation cover, but the stock half-life under cover was twice that of bare areas. A kernel of facilitation by the aboveground parts of shrubs was parameterized, and soil water half-life was significantly correlated to the cumulated facilitative effects of shrubs. The kernel range was found to be smaller than the canopy radius (81%). This effect of plants on soil water dynamics, probably through a reduction of evaporation by shading, is shown to be a better explanatory variable than potentially relevant soil and topography parameters. The root systems of five individuals of Combretum micranthum G. Don were excavated. Root density data were used as a proxy to parameterize a kernel function of interplant competition. The range of this kernel was larger than the canopy radius (125%). The facilitation-to-competition range ratio, reflecting the above-to-belowground ratio of plant lateral extent, was smaller than 1 (0.64), a result supporting models assuming that patterning may emerge from an adaptation of plant morphology to aridity and shallow soils by means of an extended lateral root system. Moreover, observed soil water gradients had directions opposite to those assumed by alternative mathematical models based on underground water diffusion. This study contributes to the growing awareness that combined facilitative and competitive plant interactions can induce landscape-scale patterns and shape the two-way feedback loops between environment and vegetation.

Hepatitis A is het mogelijke gevolg van feco-orale overdracht en infectie met het hepatitis A virus. De infectie komt meer voor bij kinderen dan bij volwassenen. De meeste kinderen zullen relatief weinig last ondervinden. Uitzonderlijk kan de ziekte, vooral dan bij volwassenen, erge gevolgen hebben voor de lever. Vooral een verbeterde hygiene heeft ertoe geleid dat deze infectie nu minder voorkomt bij ons, en een groot deel van de volwassenen zijn opgegroeid zonder de infectie door te maken. Ze zijn dus ook niet beschermd tegen het virus. Af en toe worden nog clusters van hepatitis A gerapporteerd, soms grootschalig na een voedselinfectie, meestal op kleine schaal in creches en scholen. De meeste gevallen worden waarschijnlijk niet gerapporteerd, ook al bestaat een verplichting. Sinds 1992 bestaat een vaccin tegen hepatitis A, dat goed verdragen wordt. In een groot deel van de wereld is hepatitis A nog hoog-endemisch en worden reizigers naar die streken aangeraden zich te laten vaccineren. De veranderende epidemiologische toestand roept vragen op naar de huidige ziektelast door hepatitis A in Belgie en het te volgen vaccinatie beleid. De gegevens nodig om dit grondig te bestuderen waren niet steeds beschikbaar. We danken hierbij speciaal het “Team Infectieziektes” van het “Toezicht Volksgezondheid” van de Vlaamse Gemeenschap voor het verzamelen van de gegevens en de equipe van de Universiteit Antwerpen voor de kritische analyse en verwerking met een wiskundig model. Overstappen van een wiskundig model naar praktische beleidsaanbevelingen is niet steeds eenvoudig. We hopen dat de aanbevelingen voortvloeiend uit de studie van nut zullen zijn. (REPORT IN ENGLISH WITH ABSTRACT IN DUTCH)

Aim Vegetation exhibiting landscape-scale regular spatial patterns has been reported for arid and semi-arid areas world-wide. Recent theories state that such structures are bound to low-productivity environments and result from a self-organization process. Our objective was to test this relationship between periodic pattern occurrence and environmental factors at a global scale and to parametrize a predictive distribution model.Location Arid and semi-arid areas world-wide.Methods We trained an empirical predictive model (Maxent) for the occurrence of periodic vegetation patterns, based on environmental predictors and known occurrences verified on Landsat satellite images.Results This model allowed us to discover previously unreported pattern locations, and to report the first ever examples of spotted patterns in natural systems. Relationships to the main environmental drivers are discussed.Main conclusions These results confirm that periodic patterned vegetations are ubiquitous at the interface between arid and semi-arid regions. Self-organized patterning appears therefore to be a biome-scale response to environmental conditions, including soil and topography. The set of correlations between vegetation patterns and their environmental conditions presented in this study will need to be reproduced in future modelling attempts.