Making sense of zebrafish neural development in the Minervois

The meeting 'From sensory perception to motor output: genetic bases of behavior in the zebrafish embryo' was held at Minerve (South of France) on March 16–18, 2007. The meeting site was beautifully situated in the heart of the Minervois wine country, and its remoteness promoted conversations and interaction over the course of the program. The meeting covered neurogenesis and eye development on day 1, ear and lateral line development on day 2, and brain connectivity and behavior on day 3. Underlying all sessions, however, ran the growing importance of live imaging, an approach that takes full advantage of the transparency of fish embryos and early larvae, as illustrated by several movies and links in this report

Control of cell migration in the development of the posterior lateral line: antagonistic interactions between the chemokine receptors CXCR4 and CXCR7/RDC1

BACKGROUND: The formation of the posterior lateral line of teleosts depends on the migration of a primordium that originates near the otic vesicle and moves to the tip of the tail. Groups of cells at the trailing edge of the primordium slow down at regular intervals and eventually settle to differentiate as sense organs. The migration of the primordium is driven by the chemokine SDF1 and by its receptor CXCR4, encoded respectively by the genes sdf1a and cxcr4b. cxcr4b is expressed in the migrating cells and is down-regulated in the trailing cells of the primordium. sdf1a is expressed along the path of migration. There is no evidence for a gradient of sdf1a expression, however, and the origin of the directionality of migration is not known. RESULTS: Here we document the expression of a second chemokine receptor gene, cxcr7, in the migrating primordium. We show that cxcr7 is highly expressed in the trailing cells of the primordium but not at all in the leading cells, a pattern that is complementary to that of cxcr4b. Even though cxcr7 is not expressed in the cells that lead primordium migration, its inactivation results in impaired migration. The phenotypes of cxcr4b, cxcr7 double morphant embryos suggest, however, that CXCR7 does not contribute to the migratory capabilities of primordium cells. We also show that, in the absence of cxcr4b, expression of cxcr7 becomes ubiquitous in the stalled primordium. CONCLUSION: Our observations suggest that CXCR7 is required to provide directionality to the migration. We propose that directionality is imposed on the primordium as soon as it comes in contact with the stripe of SDF1, and is maintained throughout migration by a negative interaction between the two receptors

Integrated species distribution models fitted in INLA are sensitive to mesh parameterisation

The ever-growing popularity of citizen science, as well as recent technological and digital developments, have allowed the collection of data on species' distributions at an extraordinary rate. In order to take advantage of these data, information of varying quantity and quality needs to be integrated. Point process models have been proposed as an elegant way to achieve this for estimates of species distributions. These models can be fitted efficiently using Bayesian methods based on integrated nested Laplace approximations (INLA) with stochastic partial differential equations (SPDEs). This approach uses an efficient way to model spatial autocorrelation using a Gaussian random field and a triangular mesh over the spatial domain. The mesh is constructed by user-defined variables, so effectively represents a free parameter in the model. However, there is a lack of understanding about how to set these mesh parameters, and their effect on model performance. Here, we assess how mesh parameters affect predictions and model fit to estimate the distribution of the serotine bat, Eptesicus serotinus, in Great Britain. A Bayesian INLA model was fitted using five meshes of varying densities to a dataset comprising both structured observations from a national monitoring programme and opportunistic records. We demonstrate that mesh density impacted spatial predictions with a general loss of accuracy with increasing mesh coarseness. However, we also show that the finest mesh was unable to overcome spatial biases in the data. In addition, the magnitude of the covariate effects differed markedly between meshes. This confirms that mesh parameterisation is an important and delicate process with implications for model inference. We discuss how species distribution modellers might adapt their use of INLA in the light of these findings

Robotic Milling: Development of 3D milling forces computation module for tool trajectories adaptation

Usinage Robotisé - Fédération Wallonie Bruxelle

Tri-Dexel Based Cutter-Workpiece Engagement Determination For Robotic Machining Simulator

peer reviewedIn the spirit of digital twins, computer simulations is a crucial aspect for a technology. Within the frame of virtual manufacturing, and more precisely robotic machining simulation, this article aims to present a simulator developed in C++ for test purposes. It computes the machining forces and the update of the workpiece for 5-axis operations. The proposed method is based on the modelling of workpiece using multi-dexels with scalable resolution and a disk modelled tool with triangle-mesh surfaces. Chip thickness computation approaches are based on the interference between the dexel network with the surface swept by cutting edges either modelled as quadratic surfaces or planar swept surfaces coupled with a quadratic interpolation in the tool space, in the view of reducing computation time. Simulation results of both methods are compared with benchmark operations from the literature in terms of machining forces and with each other in terms of computation performances

Coupled Dynamic Simulator with Tri-Dexel Milling Module for Robotic Machining Operations

peer reviewedIn robotic machining, important tool-tip deviations occur resulting from lower stiffness as compared to CNC machines. Hence, this paper aims to present a coupled simulator developed in C++ for offline simulation of machine dynamics while operating, ultimately to estimate tool deviation and machined surface. The dynamic simulator of machine is coupled with a dexel-based machining module computing the forces as well as the updated workpiece geometry. The forces are computed by considering interference between dexel network and triangle-mesh sweep volume with relative closest triangle algorithm. Experimental milling tests are carried out for verification of forces, deviations and hence geometry