637 research outputs found
A certification method for the milling process of free-form surfaces using a test part
International audienceIt is generally admitted that the manufacturing of free-form surfaces requires the use of a CAD-CAM system. The toolpath accuracy and the dimensional quality of the final shape have to be in accordance with the geometrical specifications. But most of the time, the final parts present deviations from the expected shape. These deviations may be due to either the toolpath calculation (CAM system) or the cutting process itself. In the paper, we propose an analysis of the whole milling process to point out the possible sources of errors. These errors generally lead to geometrical deviations and the final part does not meet the required specifications. As the errors can be linked to geometrical particularities of the shape, we propose a test part associated with check means to bring out problems. The milling of this part using two different techniques of toolpath generation shows that obviously both toolpaths are not error-free and that errors result from different geometrical particularities of the part surfaces
A Novel Approach for 3D Part Inspection Using Laser-plane Sensors
AbstractThe paper deals with the relevance of using laser-plane sensors in 3D part inspection. First, based on the evaluation of the measuring system capacities, a digitizing strategy permits to obtain a set of points with a sufficient quality as regards geometrical specifications. Despite the optimized strategy, the digitizing noise associated to the sensor alters data quality, and may affect the estimation of the surface defects (form deviation for instance is strongly affected by digitizing noise). An original filtering method is proposed to remove digitizing noise before the evaluation of the specifications
Surface decoration of catanionic vesicles with superparamagnetic iron oxide nanoparticles: a model system for triggered release under moderate temperature conditions
International audienceWe report the design of new catanionic vesicles decorated with iron oxide nanoparticles, which could be used as a model system to illustrate controlled delivery of small solutes under mild hyperthermia. Efficient release of fluorescent dye rhodamine 6G was observed when samples were exposed to an oscillating magnetic field. Our system provides direct evidence for reversible permeability upon magnetic stimulation
Tests of mode coupling theory in a simple model for two-component miscible polymer blends
We present molecular dynamics simulations on the structural relaxation of a
simple bead-spring model for polymer blends. The introduction of a different
monomer size induces a large time scale separation for the dynamics of the two
components. Simulation results for a large set of observables probing density
correlations, Rouse modes, and orientations of bond and chain end-to-end
vectors, are analyzed within the framework of the Mode Coupling Theory (MCT).
An unusually large value of the exponent parameter is obtained. This feature
suggests the possibility of an underlying higher-order MCT scenario for dynamic
arrest.Comment: Revised version. Additional figures and citation
Model for performance prediction in multi-axis machining
This paper deals with a predictive model of kinematical performance in 5-axis
milling within the context of High Speed Machining. Indeed, 5-axis high speed
milling makes it possible to improve quality and productivity thanks to the
degrees of freedom brought by the tool axis orientation. The tool axis
orientation can be set efficiently in terms of productivity by considering
kinematical constraints resulting from the set machine-tool/NC unit. Capacities
of each axis as well as some NC unit functions can be expressed as limiting
constraints. The proposed model relies on each axis displacement in the joint
space of the machine-tool and predicts the most limiting axis for each
trajectory segment. Thus, the calculation of the tool feedrate can be performed
highlighting zones for which the programmed feedrate is not reached. This
constitutes an indicator for trajectory optimization. The efficiency of the
model is illustrated through examples. Finally, the model could be used for
optimizing process planning
The Sigma 13 (10-14) twin in alpha-Al2O3: A model for a general grain boundary
The atomistic structure and energetics of the Sigma 13 (10-14)[1-210]
symmetrical tilt grain boundary in alpha-Al2O3 are studied by first-principles
calculations based on the local-density-functional theory with a mixed-basis
pseudopotential method. Three configurations, stable with respect to
intergranular cleavage, are identified: one Al-terminated glide-mirror twin
boundary, and two O-terminated twin boundaries, with glide-mirror and two-fold
screw-rotation symmetries, respectively. Their relative energetics as a
function of axial grain separation are described, and the local electronic
structure and bonding are analysed. The Al-terminated variant is predicted to
be the most stable one, confirming previous empirical calculations, but in
contrast with high-resolution transmission electron microscopy observations on
high-purity diffusion-bonded bicrystals, which resulted in an O-terminated
structure.
An explanation of this discrepancy is proposed, based on the different
relative energetics of the internal interfaces with respect to the free
surfaces
Leptin Resistance in Vagal Afferent Neurons Inhibits Cholecystokinin Signaling and Satiation in Diet Induced Obese Rats
Background and Aims: The gastrointestinal hormone cholecystokinin (CCK) plays an important role in regulating meal size and duration by activating CCK1 receptors on vagal afferent neurons (VAN). Leptin enhances CCK signaling in VAN via an early growth response 1 (EGR1) dependent pathway thereby increasing their sensitivity to CCK. In response to a chronic ingestion of a high fat diet, VAN develop leptin resistance and the satiating effects of CCK are reduced. We tested the hypothesis that leptin resistance in VAN is responsible for reducing CCK signaling and satiation. Results: Lean Zucker rats sensitive to leptin signaling, significantly reduced their food intake following administration of CCK8S (0.22 nmol/kg, i.p.), while obese Zucker rats, insensitive to leptin, did not. CCK signaling in VAN of obese Zucker rats was reduced, preventing CCK-induced up-regulation of Y2 receptor and down-regulation of melanin concentrating hormone 1 receptor (MCH1R) and cannabinoid receptor (CB1). In VAN from diet-induced obese (DIO) Sprague Dawley rats, previously shown to become leptin resistant, we demonstrated that the reduction in EGR1 expression resulted in decreased sensitivity of VAN to CCK and reduced CCK-induced inhibition of food intake. The lowered sensitivity of VAN to CCK in DIO rats resulted in a decrease in Y2 expression and increased CB1 and MCH1R expression. These effects coincided with the onset of hyperphagia in DIO rats. Conclusions: Leptin signaling in VAN is required for appropriate CCK signaling and satiation. In response to high fat feeding
Constructing large DNA segments by iterative clone recombination
Methods for constructing large contiguous segments of DNA will be enabling for Synthetic Biology, where the assembly of genes encoding circuits, biosynthetic pathways or even whole microbial organisms is of interest. Currently, in vitro approaches to DNA synthesis are adequate for generating DNAs that are up to 10s of kbp in length, and in vivo recombination strategies are more suitable for building DNA constructs that are 100 kbp or larger. We have developed a vector system for efficient assembly of large DNA molecules by iterative in vivo recombination of fosmid clones. Two custom fosmid vectors have been built, pFOSAMP and pFOSKAN, that support antibiotic switching. Using this technique we rebuilt two non-contiguous regions of the Haemophilus influenzae genome as episomes in recombinogenic Escherichia coli host cells. These regions together comprise190 kbp, or 10.4% of the H. influenze genome
Computer Aided Inspection: design of customer oriented benchmark for non contact 3D scanners evaluation
- …