109 research outputs found
Conservation implications of <i>Sabellaria spinulosa</i> reef patches in a dynamic sandy-bottom environment
No full textBiogenic reefs form biodiversity hotspots and are key components of marine ecosystems, making them priority habitats for nature conservation. However, the conservation status of biogenic reefs generally depends on their size and stability. Dynamic, patchy reefs may therefore be excluded from protection. Here, we studied epibenthos and epifauna density, richness, and community composition of patchy, dynamic Sabellaria spinulosa (ross worm) reefs in the North Sea. This study was conducted by comparing boxcore (endobenthos) and video transect (epifauna) data from two research campaigns in 2017 and 2019 to the Brown Bank area on the Dutch Continental Shelf, where S. spinulosa reefs were first discovered in 2017. The Brown Bank area is characterized by dynamic, migratory bedforms at multiple scales which potentially affect biogenic reef stability. We showed that S. spinulosa habitats had a patchy distribution and alternated with habitats comprised of plain sand. Average S. spinulosa habitat patch size was 5.57 ± 0.99 m and 3.94 ± 0.22 m in 2017 and 2019 respectively (mean ± SE), which especially in 2019 closely resembled the small-scale megaripple bedforms. Contrary to the endobenthos communities that were unaffected by S. spinulosa, epifauna density and species richness were at least two times higher in S. spinulosa habitats compared to sandy habitats, resulting in different community compositions between the two habitat types. We showed that S. spinulosa persisted in the area for almost 2 years. Although the stability of individual patches remained unclear, we demonstrated that even patchy biogenic reefs may promote density and local biodiversity of mobile, epibenthic species, very likely as a result of increased habitat heterogeneity provided by reef habitat patches. This indicates that patchy biogenic reefs that occur in dynamic environments may also have high ecological value and their conservation status should be (re)considered to ensure their protection
Measuring centimeter-scale sand ripples using multibeam echosounder backscatter data from the Brown Bank area of the Dutch continental shelf
No full textBackscatter data from multibeam echosounders are commonly used to classify seafloor sediment composition. Previously, it was found that the survey azimuth affects backscatter when small organized seafloor structures, such as sand ripples, are present. These sand ripples are too small to be detected in the multibeam bathymetry. Here, we show that such azimuth effects are time dependent and are useful to examine the orientation of sand ripples in relation to the flow direction of the tide. To this end, multibeam echosounder data at four different frequencies were gathered from the area of the Brown Bank in the North Sea. The acoustic results were compared to video and tide-flow data for validation. The sand ripples affected the backscatter at all frequencies, but for the lowest frequencies the effect was spread over more beam angles. Using the acoustic data made it possible to deduce the orientations of the sand ripples over areas of multiple square kilometers. We found that the top centimeter(s) of the seafloor undergoes a complete transformation every six hours, as the orientation of the sand ripples changes with the changing tide. Our methodology allows for morphology change detection at larger scales and higher resolutions than previously achieved
The Existence and Origin of Multiple Equilibria in Sand-Mud Sediment Beds
No full textThe sediment composition of the seabed governs its mobility, hence determining sediment transport and morphological evolution of estuaries and tidal basins. Bed sediments often consist of mixtures of sand and mud, with spatial gradients in the sand/mud content. This study aims at increasing the understanding of processes driving the sediment composition in tidal basins, focusing on depositional processes. We show that bed sediments in the Wadden Sea tend to be either mud-dominated or sand-dominated, resulting in a bimodal distribution of the mud content where the two modes represent equilibrium conditions. The equilibria depend primarily on the sediment deposition fluxes, with bimodality originating from the dependence of suspended sand/mud concentrations on the local bed composition. Our analysis shows that bimodality is a phenomenon that is not only specific for the Wadden Sea; it can be expected for a wide range of suspended sediment concentrations and thus also in other systems worldwide.Coastal EngineeringEnvironmental Fluid Mechanic
Cellular regulation of glucose uptake by glucose transporter GLUT4.
No full textInternational audienceGLUT4 is regulated by its intracellular localization. In the absence of insulin, GLUT4 is efficiently retained intracellularly within storage compartments in muscle and fat cells. Upon insulin stimulation (and contraction in muscle), GLUT4 translocates from these compartments to the cell surface where it transports glucose from the extracellular milieu into the cell. Its implication in insulin-regulated glucose uptake makes GLUT4 not only a key player in normal glucose homeostasis but also an important element in insulin resistance and type 2 diabetes. Nevertheless, how GLUT4 is retained intracellularly and how insulin acts on this retention mechanism is largely unclear. In this review, the current knowledge regarding the various molecular processes that govern GLUT4 physiology is discussed as well as the questions that remain
Beyond connecting the dots: A multi-scale, multi-resolution approach to marine habitat mapping
No full textConflicts of interests between economic and nature conservation stakeholders are increasingly common in coastal seas, inducing a growing need for evidence-based marine spatial planning. This requires accurate, high-resolution habitat maps showing the spatial distribution of benthic assemblages and enabling intersections of habitats and anthropogenic activities. However, such detailed maps are often not available because relevant biological data are scarce or poorly integrated. Instead, physiotope maps, solely based on abiotic variables, are now often used in marine spatial planning. Here, we investigated how pointwise, relatively sparse biological data can be integrated with gridded, high-resolution environmental data into informative habitat maps, using the intensively used southern North Sea as a case-study. We first conducted hierarchical clustering to identify discrete biological assemblages for three faunal groups: demersal fish, epifauna, and endobenthos. Using Random Forest models with high-resolution abiotic predictors, we then interpolated the distribution of these assemblages to high resolution grids. Finally, we quantified different anthropogenic pressures for each habitat. Habitat maps comprised a different number of habitats between faunal groups (6, 13, and 10 for demersal fish, epifauna, and endobenthos respectively) but showed similar spatial patterns for each group. Several of these ‘fauna-inclusive’ habitats resembled physiotopes, but substantial differences were also observed, especially when few (6; demersal fish) or most (13; epifauna) physiotopes were delineated. Demersal fishing and offshore wind farms (OWFs) were clearly associated with specific habitats, resulting in unequal anthropogenic pressure between different habitats. Natura-2000 areas were not specifically associated with demersal fishing, but OWFs were situated mostly inside these protected areas. We thus conclude that habitat maps derived from biological datasets that cover relevant faunal groups should be included more in ecology-inclusive marine spatial planning, instead of only using physiotope maps based on abiotic variables. This allows better balancing of nature conservation and socio-economic interests in continental shelf seas.</p
Seafloor classification in a sand wave environment on the Dutch continental shelf using multibeam echosounder backscatter data
No full textHigh resolution maps of sandy seafloors are valuable to understand seafloor dynamics, plan engineering projects, and create detailed benthic habitat maps. This paper presents multibeam echosounder backscatter classification results of the Brown Bank area of the North Sea. We apply the Bayesian classification method in a megaripple and sand wave area with significant slopes. Prior to the classification, corrections are implemented to account for the slopes. This includes corrections on the backscatter value and its corresponding incident angle. A trade-off in classification resolutions is found. A higher geo-acoustic resolution is obtained at the price of losing spatial resolution, however, the Bayesian classification method remains robust with respect to these trade-off decisions. The classification results are compared to grab sample particle size analysis and classified video footage. In non-distinctive sedimentary environments, the acoustic classes are not attributed to only the mean grain size of the grab samples but to the full spectrum of the grain sizes. Finally, we show the Bayesian classification results can be used to characterize the sedimentary composition of megaripples. Coarser sediments were found in the troughs and on the crests, finer sediments on the stoss slopes and a mixture of sediments on the lee slopes
Privacy-preserving Model Predictive Control: Using Homomorphic Encryption
No full textThis thesis is focused on protecting sensitive data in optimization-based control methods. We propose a novel Privacy-preserving Model Predictive Controller (PMPC) where multiple agents are controlled by an untrusted external coordinator. By using the Paillier additively Homomorphic Encryption (HE) scheme, our PMPC allows the coordinator to solve a Quadratic Programming (QP) problem over encrypted data. The PMPC is based on a Projected Gradient Scheme (PGS) on the Lagrange-dual, which enables the use of quadraticcost functions with complicated constraints (e.g., constraints on linear combinations of states and inputs). Compared to the state-of-the-art, the proposed controller protects not only the states and inputs of the agents, but also the system models, cost function and constraints. Optimization problems with quadratic cost functions and linear constraints, form the basis of a wide class of Model Predictive Control (MPC) problems. Examples of applications are smart-grids, large industrial plants and robotics. To test our PMPC, we focus on the application in self-driving vehicles. Motivated by the AUTOTRAC 2020 competition, we formulate a controller for multiple vehicles in a platoon. An external coordinator controls the longitudinal velocities of up to ten vehicles, while complicated constraints on the positions prevent collisions. By using our PMPC, the external coordinator does not gain access to the private data of the vehicles, protecting their privacy. Because of the wide application domain of MPC, we would like to extend this research in the future by testing the MPC on other applications as well.Mechanical Engineering | Systems and Contro
Virtual Tourism Destination Image: Glocal identities constructed, perceived and experienced
No full textHet opdoemend netwerk van mondiale hubs en stromen van geld, media, technologie en migratie, hebben geleid tot een algemene bewustwording rond oplopende spanningen tussen mondiale en locale identiteiten en imago’s. Dubai, het onderzoeksdecor van dit proefschrift, is een goed voorbeeld. Met internet en mobiele technologie bestaat het creëren van bestemmingsimago’s niet langer uit een eenzijdig pushproces van massacommunicatie. Steeds belangrijker worden dynamische interactieve processen van reflecteren, selecteren, debatteren en ervaren. Dit proefschrift construeert daarom een dynamisch toeristisch bestemmingsimago-ontwikkelingsmodel waarbij de driehoeksverhouding tussen plaatsidentiteit, geprojecteerd imago en gepercipieerd imago leidt tot een spanningsveld, welke wordt kortgesloten tijdens de reisbeleving, wanneer host (aanbod) en gast (vraag) elkaar ontmoeten. Op dat moment kunnen drie kloven in het model een negatief effect hebben op de klanttevredenheid, hetgeen in dit proefschrift empirisch wordt onderzocht door het meten van geprojecteerd en gepercipieerd imago. Dit wordt bewerkstelligd door een innovatieve methodologie gebaseerd op geautomatiseerde inhoudsanalyse. Het geprojecteerd imago is vestgesteld door middel van inhoudsanalyse op 20 in Dubai gevestigde toeristische websites, terwijl gepercipieerd imago is gemeten door middel van inhoudsanalyse op 1.100 online reacties op een kwalitatief imago-onderzoek. De resultaten tonen aan dat men in Dubai de drie kloven dient te overbruggen, aangezien de snelle ontwikkeling van Dubai als een mondiale hub soms voorbij gaat aan de verankering in de sterke lokale identiteit en het gevestigd imago. Een theoretische oplossing voor het overbruggen van de kloven wordt besproken en conceptueel toegepast in het concluderend hoofdstuk. Het is gebaseerd op de literatuur rond stedelijke of regionale merkontwikkeling en staaft de algemene bruikbaarheid van het model en de onderzoeksmethodologie zoals die in dit proefschrift ontwikkeld werden.Robert Govers, who was born on May 16, 1968 in The Hague, The Netherlands, is currently serving as research coordinator at the Flemish Center for Tourism Policy Studies of the University of Leuven, Belgium. Prior to this he worked in Dubai as a senior lecturer in tourism and marketing for four years, including two years at the Emirates Academy of
Hospitality Management. Robert graduated with a Master’ s degree in Marketing from the Rotterdam School of Management, but also holds a Bachelor’ s degree in Information Management. Robert started his teaching career as a visiting lecturer at the Witwatersrand Technikon Johannesburg (RSA). After that he was a Research Associate for the Centre for Tourism Management at the Rotterdam School of Management. With Prof. dr. Frank M.
Go, Robert is the author of Entrepreneurship in Tourism, a paperback published in Dutch.
He also co-authored several journal articles and conference papers in the field of tourism,
hospitality and quality management, e-commerce in tourism and tourism research and
marketing. As a project manager, Robert has been involved in many consultancy projects for reputable organisations such as IATA, the European Commission, the Flemish
Government and various Dutch ministries and tourism promotion boards.The emerging network of global hubs and flows of finance, media, technology and migration has raised awareness regarding the tensions between global and local identities and images. Dubai, as the central research background for this dissertation, is a good case in point. With internet and mobile technology, creating destination image is no longer a one-way ‘push’ process of mass communication, but rather a dynamic one of selecting, reflecting, sharing, and experiencing. This dissertation therefore constructs a dynamic tourism destination image formation model, which identifies a triadic tension between place identity, its projection and the perceived image. This tension is short circuited during the travel experience, when host (supply) meets guest (demand). At this instance, three potential gaps could negatively affect the level of satisfaction experienced in the host – guest encounter. The empirical research focuses on measuring projected and perceived images in order to test the way in which the gaps can be assessed. This is accomplished through an innovative methodology based on computerised content analysis. The projected image is measured through a content analysis of 20 Dubai based websites while the perceived images are gauged by content analysing 1.100 online responses to a qualitative image survey. The results indicate that for Dubai, the three gaps need bridging as there is a clear tension between its rapid development as a global hub and its strong local identity and image. A theoretical solution for bridging the gaps is discussed and conceptually applied in the concluding chapter. It is based on the destination branding literature and establishes the general usefulness of the model and its research methodology
A possible role for glucose transporter inhibition in the genistein-induced amelioration of a high glucose C. elegans Alzheimer disease model.
No full textInternational audienceWang and colleagues (Wang, et al, Free Rad Biol Med, 242 (2026) 167-187) have found in in silico and in vitro experiments, that multifaceted molecule genistein inhibits many of the detrimental effects of high glucose in a C. elegans-based Alzheimer disease model that expresses β-amyloid in a temperature-dependent fashion. Genistein inhibits, amongst many other pathophysiogical parameters, the glucose-induced aggregation of β-amyloid. While these findings are of interest, a few possible explanations are missing. Here, we hypothesize that genistein may inhibit some of the high glucose effects through its previously described inhibitory interaction with glucose transporters
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