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See detailHow does the visuo-spatial deficit impact basic numerical processing in Williams syndrome? The question of domain specificity.
Rousselle, Laurence ULg; Noel, Marie-Pascale

Conference (2014, October 02)

It has been suggested that mathematics learning disabilities, including those of genetic origin, result from a basic impairment of quantitative representations. In Williams syndrome (WS) in particular ... [more ▼]

It has been suggested that mathematics learning disabilities, including those of genetic origin, result from a basic impairment of quantitative representations. In Williams syndrome (WS) in particular, latest studies report a specific deficit in tasks requiring symbolic and non-symbolic numerical magnitude processing (Krajcsi et al., 2009 ; O’Hearn & Landau, 2007; Paterson et al., 2006). However, non-numerical quantitative processing has never been investigated and contradictory evidence has been reported about their ability to subitize small collections(Ansari et al., 2007; O’Hearn et al., 2005, 2011). Moreover, as patients with WS were always tested in the visual modality, it remains unclear whether their deficit is specific to the processing of numerical magnitude or result from their basic visuo-spatial impairment, which is a main characteristic of the WS cognitive phenotype. Therefore, numerical and non-numerical acuity were assessed in a group of patients with WS using quantitative comparison tasks with different visuo-spatial processing requirements. Participants were asked to compare: (1) the length of two sticks (spatial dimension) vs. the duration of two sounds (temporal dimension) to assess non numerical quantitative processing, (2) the numerosity of two visual arrays (spatial arrangement) versus two sequences of flashs (no spatial processing) to assess non-symbolic numerical processing, and (3) two Arabic numbers vs two Spoken verbal numerals to examine the access to symbolic number meaning. They also had to enumerate sets of 1 to 7 dots shown for 250 ms to explore their subitizing abilities. Results indicate that participants with WS are impaired in quantitative tasks requiring the processing of visuo-spatial dimension(s) (i.e. comparison of lengths or collections) but not in a visual task requiring processing numerosities with no spatial processing component (i.e. numerical comparison of sequences of flashs). They also present difficulties in accessing the meaning of numerical symbols whatever the format and present smaller subitizing range. [less ▲]

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See detailHow does the visuo-spatial deficit impact basic numerical processing in Williams syndrome? The question of domain specificity.
Rousselle, Laurence ULg; Noel, Marie-Pascale

Poster (2014, April 17)

It has been suggested that mathematics learning disabilities, including those of genetic origin, result from a basic impairment of quantitative representations. In Williams syndrome (WS) in particular ... [more ▼]

It has been suggested that mathematics learning disabilities, including those of genetic origin, result from a basic impairment of quantitative representations. In Williams syndrome (WS) in particular, latest studies report a specific deficit in tasks requiring symbolic and non-symbolic numerical magnitude processing (Krajcsi et al., 2009 ; O’Hearn & Landau, 2007; Paterson et al., 2006). However, non-numerical quantitative processing has never been investigated. Moreover, as patients with WS were always tested in the visual modality, it remains unclear whether their deficit is specific to the processing of numerical magnitude or result from their basic visuo-spatial impairment, which is a main characteristic of the WS cognitive phenotype. Therefore, numerical and non-numerical acuity were assessed in a group of 20 patients with WS using quantitative comparison tasks with different visuo-spatial processing requirements. They were compared to 40 typically developing children, half of them matched on verbal mental age and the other half matched on nonverbal mental age. Participants were asked to compare: (1) the length of two sticks (spatial dimension) vs. the duration of two sounds (temporal dimension) to assess non numerical quantitative processing, (2) the numerosity of two visual arrays (spatial arrangement) versus two sequences of flashs (no spatial processing) to assess non-symbolic numerical processing, and (3) two Arabic numbers vs two Spoken verbal numerals to examine the access to symbolic number meaning. Compared to verbal matched participants, participants with WS are impaired in quantitative tasks requiring the processing of visuo-spatial dimension(s) (i.e. comparison of lengths or collections) but not in a visual task requiring processing numerosities with no spatial processing component (i.e. numerical comparison of sequences of flashs). They also present difficulties in accessing the meaning of numerical symbols whatever the format. Their performance corresponds to those of the non verbal typically developing children. [less ▲]

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See detailHow does thymus infection by coxsackievirus contribute to the pathogenesis of type 1 diabetes?
Michaux, Hélène ULg; Martens, Henri ULg; Jaïdane, Hela et al

in Frontiers in Immunology (2015), 6(Article 338), 1-6

Through synthesis and presentation of neuroendocrine self-antigens by major histocom- patibility complex proteins, thymic epithelial cells (TECs) play a crucial role in programing central immune self ... [more ▼]

Through synthesis and presentation of neuroendocrine self-antigens by major histocom- patibility complex proteins, thymic epithelial cells (TECs) play a crucial role in programing central immune self-tolerance to neuroendocrine functions. Insulin-like growth factor- 2 (IGF-2) is the dominant gene/polypeptide of the insulin family that is expressed in TECs from different animal species and humans. Igf2 transcription is defective in the thymus of diabetes-prone bio-breeding rats, and tolerance to insulin is severely decreased in Igf2−/− mice. For more than 15 years now, our group is investigating the hypothesis that, besides a pancreotropic action, infection by coxsackievirus B4 (CV- B4) could implicate the thymus as well, and interfere with the intrathymic programing of central tolerance to the insulin family and secondarily to insulin-secreting islet β cells. In this perspective, we have demonstrated that a productive infection of the thymus occurs after oral CV-B4 inoculation of mice. Moreover, our most recent data have demonstrated that CV-B4 infection of a murine medullary (m) TEC line induces a significant decrease in Igf2 expression and IGF-2 production. In these conditions, Igf1 expression was much less affected by CV-B4 infection, while Ins2 transcription was not detected in this cell line. Through the inhibition of Igf2 expression in TECs, CV-B4 infection could lead to a breakdown of central immune tolerance to the insulin family and promote an autoimmune response against insulin-secreting islet β cells. Our major research objective now is to understand the molecular mechanisms by which CV-B4 infection of TECs leads to a major decrease in Igf2 expression in these cells. [less ▲]

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See detailHow Does Your Formulation of Lesion-Induced States of Diminished Consciousness Fit with AIM? Do You Suppose That Brain Stem Damage Affects Activation (A) and Modulation (M)?
Charland-Verville, Vanessa ULg; Laureys, Steven ULg

in J. Allan Hobson, Nicholas Tranquillo (Ed.) Dream Consciousness: A New Approach to the Brain and Its Mind (2014)

Allan Hobson’s AIM model (Hobson, 1998) is build according to three main dimensions. The first component, Activation, describes brain’s activation processes and is closely linked to the level of ... [more ▼]

Allan Hobson’s AIM model (Hobson, 1998) is build according to three main dimensions. The first component, Activation, describes brain’s activation processes and is closely linked to the level of consciousness. According to the model, the brain is highly active in wakefulness and REM sleep but will show much less activity during NREM sleep. The second component, Input/output gateway, controls the inhibition of external stimuli. When slowly falling asleep, the gateway shuts down and inhibits the external stimuli; the brain is no longer involved in processing external perceptions. Then the brain starts its oniric phase and the focus switches to internal inputs. Finally, the third dimension, Modulation, refers to the different ways of cognitive processing (executive functions), judgment, volition and memory. According to the model, those cognitive processes are lacking in REM sleep (i.e., the brain cannot keep a record of its conscious experience during dreaming as opposed to waking state) because of the changes between the aminergic system (norepinephrine and serotonin; dominant in waking but ineffective in REM sleep) and the cholinergic system (acetylcholine; unfettered in REM sleep). These three dimensions maintain a dynamic and reciprocal interaction over the sleep-wake cycle’s variations (wakefulness, NREM and REM sleep) and each of them can be expressed with lower or higher intensities depending on the level of consciousness. [less ▲]

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See detailHow dynamical clustering triggers Maxwell's demon in microgravity
Opsomer, Eric ULg; Noirhomme, Martial ULg; Vandewalle, Nicolas ULg et al

in Physical Review. E : Statistical, Nonlinear, and Soft Matter Physics (2013), 88

In microgravity, the gathering of granular material can be achieved by a dynamical clustering whose existence depends on the geometry of the cell that contains the particles and the energy that is ... [more ▼]

In microgravity, the gathering of granular material can be achieved by a dynamical clustering whose existence depends on the geometry of the cell that contains the particles and the energy that is injected into the system. By compartmentalizing the cell in several subcells of smaller volume, local clustering is triggered and the so formed dense regions act as stable traps. In this paper, molecular dynamics simulations were performed in order to reproduce the phenomenon and to analyze the formation and the stability of such traps. Depending on the total number N of particles present in the whole system, several clustering modes are encountered and a corresponding bifurcation diagram is presented. Moreover, an iterative model based on the measured particle flux F as well as a theoretical model giving the asymptotical steady states are used to validate our results. The obtained results are promising and can provide ways to manipulate grains in microgravity. [less ▲]

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See detailHow education adapts to meet the requirements?
Billen, Roland ULg

Scientific conference (2015, September 17)

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See detailHow effective are soil conservation techniques in reducing plot runoff and soil loss in Europe and the Mediterranean?
Maetens, W.; Poesen, J.; Vanmaercke, Matthias ULg

in Earth-Science Reviews (2012), 115(1-2), 21-36

The effects of soil and water conservation techniques (SWCTs) on annual runoff (R a), runoff coefficients (RC a) and annual soil loss (SL a) at the plot scale have been extensively tested on field runoff ... [more ▼]

The effects of soil and water conservation techniques (SWCTs) on annual runoff (R a), runoff coefficients (RC a) and annual soil loss (SL a) at the plot scale have been extensively tested on field runoff plots in Europe and the Mediterranean. Nevertheless, a comprehensive overview of these effects and the factors controlling the effectiveness of SWCTs is lacking. Especially the effectiveness of SWCT in reducing R a is poorly understood. Therefore, an extensive literature review is presented that compiles the results of 101 earlier studies. In each of these studies, R a and SL a was measured on field runoff plots where various SWCTs were tested. In total, 353 runoff plots (corresponding to 2093 plot-years of data) for 103 plot-measuring stations throughout Europe and the Mediterranean were considered. SWCTs include (1) crop and vegetation management (i.e. cover crops, mulching, grass buffer strips, strip cropping and exclosure), (2) soil management (i.e. no-tillage, reduced tillage, contour tillage, deep tillage, drainage and soil amendment) and (3) mechanical methods (i.e. terraces, contour bunds and geotextiles). Comparison of the frequency distributions of SL a rates on cropland without and with the application of SWCTs shows that the exceedance probability of tolerable SL a rates is ca. 20% lower when SWCT are applied. However, no notable effect of SWCTs on the frequency distribution of RC a is observed. For 224 runoff plots (corresponding to 1567 plot-year data), SWCT effectiveness in reducing R a and/or SL a could be directly calculated by comparing measured R a and/or SL a with values measured on a reference plot with conventional management. Crop and vegetation management techniques (i.e. buffer strips, mulching and cover crops) and mechanical techniques (i.e. geotextiles, contour bunds and terraces) are generally more effective than soil management techniques (i.e. no-tillage, reduced tillage and contour tillage). Despite being generally less effective, no-tillage, reduced tillage and contour tillage have received substantially more attention in the literature than the other SWCTs. Soil and water conservation techniques are generally less effective in reducing R a than in reducing SL a, which is an important consideration in areas where water is a key resource and in regions susceptible to flooding. Furthermore, all SWCTs show a more consistent and effective reduction of both R a and SL a with increasing R a and SL a magnitude, which is attributed to the reduced influence of measurement uncertainties. Although some significantly negative correlations between SWCT effectiveness and plot slope length, slope gradient or annual precipitation were found, the importance of these factors in explaining the observed variability in effectiveness seems limited. Time-series analyses of R a during multiple years of SWCT application strongly indicate that no-tillage and conservation tillage become less effective in reducing R a over time. Such an effect is not observed for SL a. © 2012 Elsevier B.V. [less ▲]

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See detailHow efficiency and automated can be serology and stool testing?
HUYNEN, Pascale ULg

in Clinical Chemistry & Laboratory Medicine (2015), 53(S1), 161

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See detailHow efficient and automated can be Serology and Stool Testing?
HUYNEN, Pascale ULg

in Year (2015), 13(9), 2-4

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See detailHow electroencephalography serves the anesthesiologist.
Marchant, Nicolas ULg; Sanders, Robert; Sleigh, Jamie et al

in Clinical EEG and neuroscience (2014), 45(1), 22-32

Major clinical endpoints of general anesthesia, such as the alteration of consciousness, are achieved through effects of anesthetic agents on the central nervous system, and, more precisely, on the brain ... [more ▼]

Major clinical endpoints of general anesthesia, such as the alteration of consciousness, are achieved through effects of anesthetic agents on the central nervous system, and, more precisely, on the brain. Historically, clinicians and researchers have always been interested in quantifying and characterizing those effects through recordings of surface brain electrical activity, namely electroencephalography (EEG). Over decades of research, the complex signal has been dissected to extract its core substance, with significant advances in the interpretation of the information it may contain. Methodological, engineering, statistical, mathematical, and computer progress now furnishes advanced tools that not only allow quantification of the effects of anesthesia, but also shed light on some aspects of anesthetic mechanisms. In this article, we will review how advanced EEG serves the anesthesiologist in that respect, but will not review other intraoperative utilities that have no direct relationship with consciousness, such as monitoring of brain and spinal cord integrity. We will start with a reminder of anesthestic effects on raw EEG and its time and frequency domain components, as well as a summary of the EEG analysis techniques of use for the anesthesiologist. This will introduce the description of the use of EEG to assess the depth of the hypnotic and anti-nociceptive components of anesthesia, and its clinical utility. The last part will describe the use of EEG for the understanding of mechanisms of anesthesia-induced alteration of consciousness. We will see how, eventually in association with transcranial magnetic stimulation, it allows exploring functional cerebral networks during anesthesia. We will also see how EEG recordings during anesthesia, and their sophisticated analysis, may help corroborate current theories of mental content generation. [less ▲]

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See detailHow elites talk about their political career: Metaphors in spontaneous and informal political discourse
Heyvaert, Pauline ULg

Conference (2016, July 02)

It has often been acknowledged that political discourse is a genre that naturally allows for metaphor use. Moreover, recent research has demonstrated the importance of analysing the political impact of ... [more ▼]

It has often been acknowledged that political discourse is a genre that naturally allows for metaphor use. Moreover, recent research has demonstrated the importance of analysing the political impact of these metaphors: “Examining metaphors that appear in political discourse provides insights into the way speakers understand their situation, and how they seek to accomplish their ends” (Ritchie, 2013). Previous research (Perrez&Reuchamps, 2014) has demonstrated the usefulness of applying Steen’s three-dimensional model of metaphor analysis in communication to a corpus of political discourse. I therefore propose to apply this model to a particular type of elite discourse. The corpus used for this research consists of biographical interviews conducted with Walloon politicians, each describing at length their personal political career within the political dynamics of their country. This corpus offers an interesting ground of investigation because of its spontaneous and informal character. Moreover, most studies on the use of metaphors in political discourse tend to focus on elite discourse with the underlying assumption that elites might knowingly use metaphors to convince the audience. What is interesting with our corpus, is that the interviews do not have a clear addressee or audience. Analysing the form, and particularly the metaphor use of these interviews comes with a number of questions: (i) do politicians use metaphors in spontaneous discourse; (ii) if so, when and (iii) why do they use these metaphors, i.e. do they use them with a specific purpose, as for example explaining a complex political issue, or not? To assess the extent to which politicians use metaphors in spontaneous discourse, we conducted a corpus analysis by applying the MIPVU procedure (Steen et al., 2010) in order to identify potential metaphorical contexts. In line with Steen’s three-dimensional model, we subsequently analysed the identified metaphors by making a distinction between three different layers of metaphor, respectively at the linguistic, conceptual and communicative level. [less ▲]

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See detailHow ergodic is the Fragmentation of the Pyridine Cation ? A Maximum Entropy Ananlysis
Gridelet, E.; Locht, Robert ULg; Lorquet, Andrée ULg et al

in Anton, J.; Cederquist, H.; Larsson, M. (Eds.) et al 23rd International Conference on the Photonic, Electronic and Atomic Collisions: Book of Abstracts. (2003)

The experimental KER and the statistical distributions are compared by the Maximum Entropy Method. An Ergodicity Index F(E) is defined to measure the phase space sampling efficiency. This is applied to ... [more ▼]

The experimental KER and the statistical distributions are compared by the Maximum Entropy Method. An Ergodicity Index F(E) is defined to measure the phase space sampling efficiency. This is applied to the KERD of C4H4+ cation produced by the C5H5N+ -> HCN+C4H4+ fragmentation path. In this particular case the F(E) is found to decrease steadily with increasing internal energy. [less ▲]

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See detailHow ergodic is the fragmentation of the pyridine cation? A maximum entropy analysis
Gridelet, E.; Locht, Robert ULg; Lorquet, Andrée ULg et al

in International Journal of Mass Spectrometry (2003), 228(2-3), 389-402

The kinetic energy released to the C4H4+ and HCN fragments produced by the dissociation of the pyridine ion has been determined by a retarding field technique up to an internal energy of 4eV above the ... [more ▼]

The kinetic energy released to the C4H4+ and HCN fragments produced by the dissociation of the pyridine ion has been determined by a retarding field technique up to an internal energy of 4eV above the reaction threshold. This extends our previous study limited to the metastable domain [Int. J. Mass Spectrom. Ion Process. 185/186/187 (1999) 155]. Retarding potential curves resulting from dissociative photoionization using the He(I), Ne(I), and Ar(II) resonance lines have been analyzed by the maximum entropy method. The comparison between the experimentally measured curves and those calculated for the prior (i.e., most statistical) situation reveals the existence of dynamical constraints that prevent phase space from being fully explored. The "ergodicity index" F(E) that measures the efficiency of phase space sampling as a function of the internal energy E of the molecular ion is found to decrease steadily as a function of E and to level off at a value of about 50% when E greater than or equal to 2.5 eV At these high internal energies where phase space exploration no longer decreases, spontaneous intramolecular vibrational energy redistribution (i.e., resulting from the anharmonicity of the molecular vibrations) is thought to contribute to internal energy randomization to a limited extent only. When the lifetime is short, phase space exploration is believed to result instead from the relaxation of the electronic energy via a cascade of non-radiative transitions, which leads to a great diversity of initial conditions, and thus, contributes to statisticity. (C) 2003 Elsevier Science B.V. All rights reserved. [less ▲]

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See detailHow errors on meteorological variables impact simulated ecosystem fluxes: A case study for six French sites
Zhao, Yuchen ULg; Ciais, P.; Peylin, P. et al

in Biogeosciences (2012), 9(7), 2537-2564

We analyze how biases of meteorological drivers impact the calculation of ecosystem CO2, water and energy fluxes by models. To do so, we drive the same ecosystem model by meteorology from gridded products ... [more ▼]

We analyze how biases of meteorological drivers impact the calculation of ecosystem CO2, water and energy fluxes by models. To do so, we drive the same ecosystem model by meteorology from gridded products and by meteorology from local observation at eddy-covariance flux sites. The study is focused on six flux tower sites in France spanning across a climate gradient of 7-14 °C annual mean surface air temperature and 600-1040 mm mean annual rainfall, with forest, grassland and cropland ecosystems. We evaluate the results of the ORCHIDEE process-based model driven by meteorology from four different analysis data sets against the same model driven by site-observed meteorology. The evaluation is decomposed into characteristic time scales. The main result is that there are significant differences in meteorology between analysis data sets and local observation. The phase of seasonal cycle of air temperature, humidity and shortwave downward radiation is reproduced correctly by all meteorological models (average <i>R</i>2 Combining double low line 0.90). At sites located in altitude, the misfit of meteorological drivers from analysis data sets and tower meteorology is the largest. We show that day-to-day variations in weather are not completely well reproduced by meteorological models, with <i>R</i>2 between analysis data sets and measured local meteorology going from 0.35 to 0.70. The bias of meteorological driver impacts the flux simulation by ORCHIDEE, and thus would have an effect on regional and global budgets. The forcing error, defined by the simulated flux difference resulting from prescribing modeled instead of observed local meteorology drivers to ORCHIDEE, is quantified for the six studied sites at different time scales. The magnitude of this forcing error is compared to that of the model error defined as the modeled-minus-observed flux, thus containing uncertain parameterizations, parameter values, and initialization. The forcing error is on average smaller than but still comparable to model error, with the ratio of forcing error to model error being the largest on daily time scale (86%) and annual time scales (80%). The forcing error incurred from using a gridded meteorological data set to drive vegetation models is therefore an important component of the uncertainty budget of regional CO2, water and energy fluxes simulations, and should be taken into consideration in up-scaling studies. [less ▲]

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See detailHow eye movements and expertise can explain memory of visual items of central or marginal interest
Blavier, Adelaïde ULg; Nyssen, Anne-Sophie ULg

in Journal of Vision (2009)

In complex scene, memory for central interest items is better than memory for marginal interest items and this difference remains stable independently of the scene presentation duration (Melcher, 2006 ... [more ▼]

In complex scene, memory for central interest items is better than memory for marginal interest items and this difference remains stable independently of the scene presentation duration (Melcher, 2006). However, without eye movement recording, it is not possible to know whether central interest items are better remembered because they are more fixated or because they are more meaningful. In order to answer this question, we analysed the memory of complex scenes (paintings) according to the eye movements and subjects’ expertise. 15 novice subjects and 15 art historians (experts) were asked to look at 6 paintings that were separately and randomly presented for 10 seconds. After each painting presentation, subjects were asked questions about painting knowledge (author’s name, painting’s name) in order to evaluate their painting knowledge and about pictorial details of 3 categories: details of central or marginal interest and background information. If the expert and novice groups significantly differed concerning the knowledge they had about all paintings, the accuracy of answers about the painting details did not differ between both groups. Moreover, we showed novice’s answers were more accurate when they looked longer at the asked detail and when this detail was watched early on in the presentation while in the expert group, the accuracy of the answer was not influenced by the duration and moment they watched the asked detail. These findings suggest experts have some wrong representations which are not influenced by eye movements contrary to novices whom memory accuracy is influenced by their eye movements. [less ▲]

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See detailHow far and how fast do bryophytes travel at the landscape scale?
Hutsemekers, Virginie ULg; Dopagne, Claude ULg; Vanderpoorten, Alain ULg

in Diversity & Distributions (2008), 14(3), 483-492

Dispersal ability is a factor of prime importance to explain biotic distributions. Yet, it is extremely difficult to measure directly. In this study, we take advantage of the natural experimental design ... [more ▼]

Dispersal ability is a factor of prime importance to explain biotic distributions. Yet, it is extremely difficult to measure directly. In this study, we take advantage of the natural experimental design of slag heap colonization in Belgium to document the timing and range of dispersal of bryophytes at the landscape scale. On the basis of a species atlas with a 4 × 4 km grid, the minimum distance separating species found on 52 slag heaps from potential source populations was determined. Minimum dispersal rates were inferred by coupling the information on minimum distance between slag heap and source populations with time since colonization. The number of species per slag heap is significantly correlated with time since colonization and area size. The frequency distribution of the longest dispersal events is highly skewed, with 44% of the species recruited within the nearest 6 km. In the remaining 56% of the species, recruitments from source populations located within a range of at least 6–86 km occurred within a period of less than 50 years. The majority of the species that are not recruited within the nearest vicinity of the slag heaps, including rare species at the regional scale, occur on slag heaps that have been colonized for 25–50 years. Most recently colonized slag heaps are indeed characterized by 'fugitive', weedy species, whereas slag heaps that have been colonized for > 50 years tend to accumulate perennial species with a 'stayer' life strategy. These observations suggest that rare species may display the dispersal ability to travel across the landscape, but are subsequently limited by their ability to establish a viable community because of more competitive neighbours. Rare species therefore tend to accumulate at intermediate colonization stages, which represent a trade-off between an increasing probability of colonization with time and a decreasing probability of establishment due to competition. [less ▲]

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See detailHow far are we in the chase after the lowest detectable level for Dioxins?
Focant, Jean-François ULg; L'Homme, B; Calaprice, Chiara ULg et al

Scientific conference (2015, April)

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See detailHow fast do gully headcuts retreat?
Vanmaercke, Matthias ULg; Poesen, J.; Van Mele, B. et al

in Earth-Science Reviews (2016), 154

Gully erosion has important on and off site effects. Therefore, several studies have been conducted over the past decades to quantify gully headcut retreat (GHR) in different environments. Although these ... [more ▼]

Gully erosion has important on and off site effects. Therefore, several studies have been conducted over the past decades to quantify gully headcut retreat (GHR) in different environments. Although these led to important site-specific and regional insights, the overall importance of this erosion process or the factors that control it at a global scale remain poorly understood. This study aims to bridge this gap by reviewing research on GHR and conducting a meta-analysis of measured GHR rates worldwide. Through an extensive literature review, GHR rates for 933 individual and actively retreating gullies have been compiled from more than 70 study areas worldwide (comprising a total measuring period of >19 600 years). Each GHR rate was measured through repeated field surveys and/or analyses of aerial photographs over a period of at least one year (maximum: 97 years, median: 17 years). The data show a very large variability, both in terms of gully dimensions (cross-sectional areas ranging between 0.11 and 816 m2 with a median of 4 m2) and volumetric GHR rates (ranging between 0.002 and 47 430 m3 year- 1 with a median of 2.2 m3 year- 1). Linear GHR rates vary between 0.01 and 135 m year- 1 (median: 0.89 m year- 1), while areal GHR rates vary between 0.01 and 3628 m2 year- 1 (median: 3.12 m2 year- 1). An empirical relationship allows estimating volumetric retreat rates from areal retreat rates with acceptable uncertainties. By means of statistical analyses for a subset of 724 gullies with a known contributing area, we explored the factors most relevant in explaining the observed 7 orders of magnitudes of variation in volumetric GHR rates. Results show that measured GHR rates are significantly correlated to the runoff contributing area of the gully (r2 = 0.15) and the rainy day normal (RDN; i.e. the long-term average annual rainfall depth divided by the average number of rainy days; r2 = 0.47). Other factors (e.g. land use or soil type) showed no significant correlation with the observed GHR rates. This may be attributed to the uncertainties associated with accurately quantifying these factors. In addition, available time series data demonstrate that GHR rates are subject to very large year-to-year variations. As a result, average GHR rates measured over short (<5 year) measuring periods may be subject to very large (>100%) uncertainties. We integrated our findings into a weighted regression model that simulates the volumetric retreat rate of a gully headcut as a function of upstream drainage area and RDN. When weighing each GHR observation proportional to its measuring period, this model explains 68% of the observed variance in GHR rates at a global scale. For 76% of the monitored gullies, the simulated GHR values deviate less than one order of magnitude from their corresponding observed value. Our model clearly indicates that GHR rates are very sensitive to rainfall intensity. Since these intensities are expected to increase in most areas as a result of climate change, our results suggest that gully erosion worldwide will become more intense and widespread in the following decades. Finally, we discuss research topics that will help to address these challenges. © 2016 Elsevier B.V. [less ▲]

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See detailHow fertilizer and soil nitrogen are distributed into winter wheat plant
Boulelouah, Nadia; Destain, Jean-Pierre ULg; Bodson, Bernard ULg et al

(2007, September 16)

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See detailHow general pedagogical knowledge and teacher’s self-efficacy at the onset of teacher education depend on teaching experience and prior education ?
Vaudroz, Cynthia; Berger, Jean-Louis; Girardet, Céline et al

Conference (2014)

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