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11.
Most algorithms in probabilistic sampling-based path planning compute collision-free paths made of straight line segments lying in the configuration space. Due to the randomness of sampling, the paths make detours that need to be optimized. The contribution of this paper is to propose a basic gradient-based algorithm that transforms a polygonal collision-free path into a shorter one. While requiring only collision checking, and not any time-consuming obstacle distance computation nor geometry simplification, we constrain only part of the configuration variables that may cause a collision, and not entire configurations. Thus, parasite motions that are not useful for the problem resolution are reduced without any assumption. Experimental results include navigation and manipulation tasks, eg a manipulator arm-filling boxes and a PR2 robot working in a kitchen environment. Comparisons with a random shortcut optimizer and a partial shortcut have also been studied. 相似文献
12.
Israel Becerra Rafael Murrieta-Cid Raul Monroy Seth Hutchinson Jean-Paul Laumond 《Autonomous Robots》2016,40(2):395-423
In this paper, we address the problem of determining whether a mobile robot, called the pursuer, is able to maintain strong mutual visibility (a visibility notion between regions over a convex partition of the environment) of an antagonist agent, called the evader. We frame the problem as a non cooperative game. We consider the case in which the pursuer and the evader move at bounded speed, traveling in a known polygonal environment with or without holes, and in which there are no restrictions as to the distance that might separate the agents. Unlike our previous efforts (Murrieta-Cid et al. in Int J Robot Res 26:233–253, 2007), we give special attention to the combinatorial problem that arises when searching for a solution through visiting several locations in an environment with obstacles. In this paper we take a step further, namely, we assume an antagonistic evader who moves continuously and unpredictably, but with a constraint over its set of admissible motion policies, as the evader moves in the shortest-path roadmap, also called the reduced visibility graph (RVG). The pursuer does not know which among the possible paths over the RVG the evader will choose, but the pursuer is free to move within all the environment. We provide a constructive method to solve the decision problem of determining whether or not the pursuer is able to maintain strong mutual visibility of the evader. This method is based on an algorithm that computes the safe areas (areas that keep evader surveillance) at all times. We prove decidability of this problem, and provide a complexity measure to this evader surveillance game; both contributions hold for any general polygonal environment that might or not contain holes. All our algorithms have been implemented and we show simulation results. 相似文献
13.
A compressible model able to manage incompressible two-phase flows as well as compressible motions is proposed. After a presentation of the multiphase compressible concept, the new model and related numerical methods are detailed on fixed structured grids. The presented model is a 1-fluid model with a reformulated mass conservation equation which takes into account the effects of compressibility. The coupling between pressure and flow velocity is ensured by introducing mass conservation terms in the momentum and energy equations. The numerical model is then validated with four test cases involving the compression of an air bubble by water, the liquid injection in a closed cavity filled with air, a bubble subjected to an ultrasound field and finally the oscillations of a deformed air bubble in melted steel. The numerical results are compared with analytical results and convergence orders in space are provided. 相似文献
14.
Anne Berry Jean-Paul Bordat Alain Sigayret 《Annals of Mathematics and Artificial Intelligence》2007,49(1-4):117-136
Generating concepts defined by a binary relation between a set of properties and a set of objects is one of the important current problems encountered in Data Mining and Knowledge Discovery in Databases. We present
a new algorithmic process which computes all the concepts, without requiring an exponential-size data structure, and with
a good worst-time complexity analysis, which makes it competitive with the best existing algorithms for this problem. Our
algorithm can be used to compute the edges of the lattice as well at no extra cost.
相似文献
15.
Josef Widder Martin Biely Günther Gridling Bettina Weiss Jean-Paul Blanquart 《Distributed Computing》2012,24(6):299-321
We consider the problem of reaching agreement in distributed systems in which some processes may deviate from their prescribed
behavior before they eventually crash. We call this failure model “mortal Byzantine”. After discussing some application examples
where this model is justified, we provide matching upper and lower bounds on the number of faulty processes, and on the required
number of rounds in synchronous systems. We then continue our study by varying different system parameters. On the one hand,
we consider the failure model under weaker timing assumptions, namely for partially synchronous systems and asynchronous systems
with unreliable failure detectors. On the other hand, we vary the failure model in that we limit the occurrences of faulty
steps that actually lead to a crash in synchronous systems. 相似文献
16.
Céline Druart Evelyne M. Dewulf Patrice D. Cani Audrey M. Neyrinck Jean-Paul Thissen Nathalie M. Delzenne 《Lipids》2014,49(4):397-402
The aim of this human study was to assess the influence of prebiotic-induced gut microbiota modulation on PUFA-derived bacterial metabolites production. Therefore, we analyzed the circulating fatty acid profile including CLA/CLnA in obese women treated during 3 months with inulin-type fructan prebiotics. In these patients, we had already determined gut microbiota composition by phylogenetic microarray and qPCR analysis of 16S rDNA. Some PUFA-derived bacterial metabolites were detected in the serum of obese patients. Despite the prebiotic-induced modulation of gut microbiota, including changes in CLA/CLnA-producing bacteria, the treatment did not impact significantly on the circulating level of these metabolites. However, some PUFA-derived bacterial metabolites were positively correlated with specific fecal bacteria (Bifidobacterium spp., Eubacterium ventriosum and Lactobacillus spp.) and inversely correlated with serum cholesterol (total, LDL, HDL). These correlations suggest a potential beneficial effect of some of these metabolites but this remains to be confirmed by further investigation. 相似文献
17.
Rabeh Slimani Nacer Zazi Jean-Paul Chopart 《Protection of Metals and Physical Chemistry of Surfaces》2016,52(1):111-118
In this work a special regard is given to the morphology of the nickel deposited layers, onto AA1370 aluminum section and central longitudinal surfaces, with and without a weak magnetic field oriented in parallel and perpendicular to the coated surface in modified Watt bath. The obtained results show the formation of honeycomb structure nickel deposits for samples treated with weak parallel oriented field under approximately 0.3 A/cm2, and partial dendritic structure nickel deposit for samples treated with weak perpendicular oriented magnetic field, the perimeter deposits with and without magnetic field is different to the deposits in the remain surface. We attributed the defect of nickel deposits on the surfaces with and without magnetic field to the distribution of the intermetallics particles and we attributed the honeycomb structure to the escapement of hydrogen and oxygen. 相似文献
18.
Taleb Samia Dokhan Nahed Zazi Nacer Chopart Jean-Paul 《Protection of Metals and Physical Chemistry of Surfaces》2019,55(4):781-788
Protection of Metals and Physical Chemistry of Surfaces - In this work the effect of the permanent weak magnetic field on the electrodeposited ZnO nanostructured film on the ITO substrate... 相似文献
19.
Laura Grech Jean-Paul Ebejer Oriana Mazzitelli Kevin Schembri Joseph Borg Elisa Seria 《International journal of molecular sciences》2022,23(1)
Circulating bone marrow mesenchymal progenitors (BMMPs) are known to be potent antigen-presenting cells that migrate to damaged tissue to secrete cytokines and growth factors. An altered or dysregulated inflammatory cascade leads to a poor healing outcome. A skin model developed in our previous study was used to observe the immuno-modulatory properties of circulating BMMP cells in inflammatory chronic wounds in a scenario of low skin perfusion. BMMPs were analysed exclusively and in conjunction with recombinant tumour necrosis factor alpha (TNFα) and recombinant hepatocyte growth factor (HGF) supplementation. We analysed the expression levels of interleukin-8 (IL-8) and ecto-5′-nucleotidase (CD73), together with protein levels for IL-8, stem cell factor (SCF), and fibroblast growth factor 1 (FGF-1). The successfully isolated BMMPs were positive for both hemopoietic and mesenchymal markers and showed the ability to differentiate into adipocytes, chondrocytes, and osteocytes. Significant differences were found in IL-8 and CD73 expressions and IL-8 and SCF concentrations, for all conditions studied over the three time points taken into consideration. Our data suggests that BMMPs may modulate the inflammatory response by regulating IL-8 and CD73 and influencing IL-8 and SCF protein secretions. In conclusion, we suggest that BMMPs play a role in wound repair and that their induced application might be suitable for scenarios with a low skin perfusion. 相似文献
20.
Fouad Al Katrib Gerard Chambat Jean-Paul Joseleau 《Journal of the science of food and agriculture》1988,43(4):309-317
Enzymic saccharification of wheat straw in the absence of any pretreatment was only about 20 %. Acid hydrolysis did not improve the overall cellulose enzymic breakdown, nor did pretreatment by flash autohydrolysis under pressure or sodium chlorite delignification. When wheat straw was treated with N-methyl-morpholine-N-oxide (MMNO) at J20°C for 20–30 min, this treatment and subsequent enzymic hydrolysis produced carbohydrate conversion of 73%. Similar results could be obtained by treating straw with 0·1 M sodium hydroxide. When MMNO treatment was combined with any other pretreatment, the saccharification yield was greatly enhanced. Nearly quantitative conversion was obtained by swelling straw in 0·1 M sodium hydroxide followed by MMNO treatment. The results show that lignin content of plant material does not represent the limiting factor to enzymic saccharification. 相似文献