Search publications of the members of the Royal Belgian institute of natural Sciences
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Les datations radiocarbone à Mitoc-Malu Galben
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Le site du Treurenberg (Bruxelles): resultats d’une etude transdisciplinaire
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Les dates radiocarbone de Maisieres-Canal
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New data on geology, anthracology and palynology from the Scladina cave Pleistocene sequence: preliminary results
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Les abeilles sauvages du parc naturel régional du Vexin français. II. Les Halictes (Hymenoptera: Apoidea: Halictidae: Halictus et Lasioglossum)
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An Updated checklist of Bees of Sri Lanka with new records. MAB (The National Man and the Biosphere). National Science Faundation, Sri Lanka
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The survey of wild bees (Hymenoptera, Apoidea) in Belgium and France
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Une abeille afrotrop!icale spécialisée dans la récolte du pollen de Graminées (Poaceae): Lipotriches notabiolis (Schletterer 1891) (Hymenoptera Apoidea Halictidae)
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Hymenoptera
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Hyménoptères Apocrites nouveaux ou intéressants pour la faune luxembourgeoise
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Classification des Nomiinae africains: le genre Nubenomia Pauly (Hymenoptera, Apoidea, Halictidae)
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La couleur vert pomme chez les Hyménoptères de Madagascar (Vespidae, apidae, Pompilidae, Leucospidae)
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Les Chaleididae de Belgique et du Nord de la France (Hymenoptera: Chalcidoidea).
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Leucospis dorsigera Fabricius, 1775 (Hymenoptera Chalcidoidea Leucospidae) aux Luxembourg et dans le Nord-Est de la France.
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River channel avulsion and the role of human action in causing or preventing flood events.
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Book review: Fischer, P.M. - Tell Abu al-Kharaz in the Jordan Valley. Volume III: the Iron Age
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Multimodal particle size distributions of fine-grained sediments: mathematical modeling and field investigation
- Multimodal particle size distributions (PSDs) of fine-grained cohesive sediments are common in marine and coastal environments. The curve-fitting software in this study decomposed such multimodal PSDs into subordinate log-normal PSDs. Four modal peaks, consisting of four-level ordered structures of primary particles, flocculi, microflocs, and macroflocs, were identified and found to alternately rise and sink in a flow-varying tidal cycle due to shear-dependent flocculation. The four modal PSD could be simplified further into two discrete size groups of flocculi and flocs. This allowed the development of a two-class population balance equation (TCPBE) model with flocculi and flocs to simulate flocculation involving multimodal PSDs. The one-dimensional vertical (1-DV) TCPBE model further incorporated the Navier-Stokes equation with the k-ε turbulence closure and the sediment mass balance equations. Multimodal flocculation as well as turbulent flow and sediment transport in a flow-varying tidal cycle could be simulated well using the proposed model. The 1-DV TCPBE was concluded to be the simplest model that is capable of simulating multimodal flocculation in the turbulent flow field of marine and coastal zones.
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Mine burial in the seabed of high-turbidity area - Findings of a first experiment
- The seabed of the North Sea is covered with ammunition dating back from World Wars I and II. With increasing human interference (e.g. fisheries, aggregate extraction, harbor related activities), it forms a threat to the safety at sea. In this study, test mines were deployed on a sandy seabed for 3 months to investigate mine burial processes as a function of hydrodynamic and meteorological conditions. The mine experiment was conducted in a shallow (9 m), macrotidal environment characterized by highly turbid waters (yearly and depth-averaged suspended particulate matter concentration of 100 mg/l). Results showed some variability of the overall mine burial, which corresponded with scouring processes induced by a (sub-) tidal forcing mechanism. The main burial events however were linked to storm-related scouring processes, and subsequent mine roll into the resulting pit. Two storms affecting the mines during the 3-month experiment resulted in enduring increases in burial volume to 60% and 80%, respectively. More cyclic and ephemeral burial and exposure events appear to be linked to the local hydrodynamic regime. During slack tides, suspended sediment settles on the seabed, increasing the burial volume. In between slack tides, sediment is resuspended, decreasing the burial volume. The temporal pattern of this never reported burial mechanism, as measured optically, mimics the cyclicity of the suspended sediment concentration as recorded by ultrasonic signals at a nearby benthic observatory. Given the similarity in response signals at the two sites, we hypothesize that the formation of high-concentrated mud suspensions (HCMS) is a mechanism causing short-term burial and exposure of mines. This short-term burial and exposure increase the chance that mines are ‘missed’ during tracking surveys. Test mines contribute to our understanding of the settling and erosion of HCMS, and thus shed a light on generic sedimentary processes.
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Hydro-meteorological influences and multimodal suspended particle size distributions in the Belgian nearshore area (southern North Sea)
- Suspended particulate matter (SPM) concentration and particle size distribution (PSD) were assessed in a coastal turbidity maximum area (southern North Sea) during a composite period of 37 days in January–April 2008. PSDs were measured with a LISST 100X and classified using entropy analysis in terms of subtidal alongshore flow. The PSDs during tide-dominated conditions showed distinct multimodal behaviour due to flocculation, revealing that the building blocks of flocs consist of primary particles (<3 μm) and flocculi (15 μm). Flocculi comprise clusters of clay minerals, whereas primary particles have various compositions (calcite, clays). The PSDs during storms with a NE-directed alongshore subtidal current (NE storms) are typically unimodal and characterised by mainly granular material (silt, sand) resuspended from the seabed. During storms with a SW-directed alongshore subtidal current (SW storms), by contrast, mainly flocculated material can be identified in the PSDs. The findings emphasise the importance of wind-induced advection, alongshore subtidal flow and highly concentrated mud suspensions (HCMSs) as regulating mechanisms of SPM concentration, as well as other SPM characteristics (cohesiveness or composition of mixed sediment particles) and size distribution in a high-turbidity area. The direction of subtidal alongshore flow during SW storm events results in an increase in cohesive SPM concentration, HCMS formation, and the armouring of sand; by contrast, there is a decrease in cohesive SPM concentration, no HCMS formation, and an increase in sand and silt in suspension during NE storms.
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Multimodality of a particle size distribution of cohesive suspended 2 particulate matters in a coastal zone
- Particle size distributions (PSDs) of suspended particulate matters in a coastal zone are lognormal and multimodal in general. The multimodal PSD, which is caused by the mixing of multiple particle and aggregate size groups under flocculation and erosion/resuspension, is a record of the particle and aggregate dynamics in a coastal zone. Curve-fitting software was used to decompose the multimodal PSD into subordinate lognormal PSDs of primary particles, flocculi, microflocs, and macroflocs. The curve-fitting analysis for a time series of multimodal PSDs in the Belgian coastal zone showed the dependency of the multimodality on (1) shear-dependent flocculation in a flood and ebb tide, (2) breakage-resistant flocculation in the spring season, and (3) silt-sized particle erosion and advection in a storm surge. Also, for modeling and simulation purposes, the curve-fitting analysis and the settling flux estimation for the multimodal PSDs showed the possibility of using discrete groups of primary particles, flocculi, microflocs, and macroflocs as an approximation of a continuous multimodal PSD.
