Particle swarm optimization for cooperative multi-robot task allocation: a multi-objective approach

This paper presents a new Multi-Objective Particle Swarm Optimization (MOPSO) approach to a Cooperative Multi Robot Task Allocation (CMRTA) problem, where the robots have to minimize the total team cost and, additionally, balance their workloads. We formulate the CMRTA problem as a more complex variant of multiple Travelling Salesman Problems (mTSP) and, in particular, address how to minimize the total travel distance of the entire robot team, as well as how to minimize the highest travel distance of an individual robot. The proposed approach extends the standard single-objective Particle Swarm Optimization (PSO) to cope with the multiple objectives, and its novel feature lies in a Pareto front refinement strategy and a probability-based leader selection strategy. To validate the proposed approach, we first use three benchmark functions to evaluate the performance of finding the true Pareto fronts in comparison with four existing well-known algorithms in continuous spaces. Afterwards, we use six datasets to investigate the task allocation mechanisms in dealing with the CMRTA problem in discrete spaces.benchmark functions to evaluate the performance of findingthe true Pareto fronts in comparison with four existing wellknownalgorithms in continuous spaces. Afterwards, we use sixdatasets to investigate the task allocation mechanisms in dealingwith the CMRTA problem in discrete spaces

The First Data Release of the Beijing-Arizona Sky Survey

The Beijing-Arizona Sky Survey (BASS) is a new wide-field legacy imaging survey in the northern Galactic cap using the 2.3m Bok telescope. The survey will cover about 5400 deg$^2$ in the $g$ and $r$ bands, and the expected 5$\sigma$ depths (corrected for the Galactic extinction) in the two bands are 24.0 and 23.4 mag, respectively. BASS started observations in January 2015, and has completed about 41% of the whole area as of July 2016. The first data release contains both calibrated images and photometric catalogs obtained in 2015 and 2016. The depths of single-epoch images in the two bands are 23.4 and 22.9 mag, and the full depths of three epochs are about 24.1 and 23.5 mag, respectively.Comment: 16 pages, published by A

Finite element modeling of the human mitral valve: Implications of morphologies and dynamics of the annulus and the chordae tendineae

Objectives: To investigate the influences caused by special morphologies and dynamics of the substructures of mitral valve by the explicit finite element program LS-DYNA. Methods: A new finite element model for the mitral apparatus characterized by layered structure of leaflets tissue, saddle shape and contraction of annulus, an approximately accurate morphology of chordae tendineae was developed. The coaptation length, leaflets stress and strain of the present model were compared with those of two auxiliary models, one with planar annulus and the other with fixed annulus. The tensile function and force distribution of chordae tendineae were analyzed in the models with and without chordae tendineae. Results: The stretch ratios computed by the present model were most closely to the experimental data. The leaflets instantly turned over to the atrial side and larger load was observed in the model without chordae tendineae. Besides, tensile force was highly correlated with average diameter of chordae tendineae (r = 0.965). Conclusion: The saddle shape of annulus benefits valve coaptation and the contraction of annulus could help decrease loads on leaflets and prevent stress concentrating excessively. Chordae tendineae could bear partial loads on the leaflets, and prevent the leaflets to turn over to the side of the atrium and help the valve close successfully. ? 2014 World Scientific Publishing Company

Relationships between Cortical Bone Quality Biomarkers: Stiffness, Toughness, Microstructure, Mineralization, Cross-Links and Collagen

Ultrasonics Symposium (IUS), 2017 IEEE International, WASHINGTON, ETATS-UNIS, 06-/09/2017 - 09/09/2017Bone quality encompasses bone properties that contribute to fracture risk, such as bone stiffness, microstructure, matrix constituents or tissue material properties. These aspects cannot be quantified in-vivo except for stiffness, a surrogate biomarker of strength, which can be assessed using quantitative ultrasound techniques. To better predict bone fracturerisk, investigating the relationships between stiffness and other bone quality factors is important. Toward this goal, our group adapted resonant ultrasound spectroscopy (RUS) to precisely measure the whole set of stiffness coefficients of cortical bone by improving the signal processing and automatizing the inversion procedure based on a Bayesian framework. In this work, we present the relationships between bone quality biomarkers including stiffness, fracture toughness, microstructure, mineralization, cross-links and collagen.Statement of Contribution/MethodsFrom the mid-diaphysis of the femoral cortex of 27 human donors, 54 cuboid specimens (3x4x5 mm3, axis 1=radial; axis 2=circumferential; axis 3=axial) were prepared. The mesoscale transverse isotropic stiffness tensor Cij of the specimens was measured by RUS. The microstructure (i.e., vascular porosity) and degree of mineralization of bone (DMB)were estimated from synchrotron radiation micro-computed tomography (voxel size 6.5 ?m). Another set of 54 samples (3x4x25 mm3) which were adjacent to the previous ones, was harvested for mechanical testing. Each of them were divided into two samples (1x2x25 mm3) then notched (1 mm length) in their middle in the transverse direction. Three-pointbending tests were conducted at two strain rates 10-4 s-1 and 10-1 s-1 to measure the fracture toughness (quasi-static KJcStat and dynamic KjcDyn). Biochemical tests were conducted on small adjacent bone fragments to assess collagen quantity and cross-links.Results/DiscussionWhile all the stiffness coefficients significantly correlate with toughness (-0.35 < r < -0.53, p < 0.05) except for C33, different biomarkers seem to differently affect toughness and stiffness. Indeed, markers that showed an effect on toughness did not on stiffness (Table 1). This work demonstrates the correlations between cortical bone quality biomarkers and givesinsights for a better assessment of bone fracture risk using stiffness measured in-vivo

On the cortical bone elasticity, toughness and bone quality

21st International Bone Densitometry Workshop & 7th European Symposium on Ultrasonic Characterization of Bone, KLOSTER BANZ, ALLEMAGNE, 26-/06/2017 - 30/06/2017This study aims at investigating the relationship between different aspects of bone quality and understanding how bone quality may affect stiffness at the mm-scale and toughness. The transverse isotropic effective stiffness tensor was measured by resonant ultrasound spectroscopy (RUS) and the vascular porosity was estimated from synchrotron radiation micro-computed tomography (SR-¼CT) images. A cross-section at the mid-diaphysis was sectioned from the left femur of 27 human cadavers. Then, a set of 54 parallelepiped-shape samples (size 3x4x5 mm3) was prepared for RUS measurements and SR-¼CT imaging at ERSF (voxel size 6.5 µm). Another set of adjacent 54 samples (size 3x4x25 mm3) was harvested for mechanical testing and the remaining material was used for cross-links and collagen quantification. These last samples were divided into two samples (1x2x25 mm3) then notched (1 mm length) in their middle, in the transverse direction. Three-point bending tests were conducted at two strain rates 10-4 s-1 and 10-1 s-1 to measure toughness (quasi-static KJcStat and dynamic KJcDyn). Specimen dimensions are defined by the anatomical shape of femoral diaphysis: radial (axis 1), circumferential (axis 2) and axial direction (axis 3). Immature and mature collagen crosslinks were separated by reversed-phase HPLC method and quantified using fluorescence and mass spectrometry detection. Relationships between variables were investigated with Spearman's rank correlation coefficients. The bone-quality markers analysed here seem to differently affect toughness and stiffness. Indeed, markers that showed an effect in toughness did not in stiffness. Vascular porosity was significantly correlated with all stiffness coefficients but not with toughness. Enzymatic immature cross-links significantly correlated with stiffness coefficients, while only the non-enzymatic cross link pentosidine significantly affected toughness. Finally, the existing correlations between elastic parameters and toughness are shown in Table 1. Knowing the effects of these markers in the mechanical properties of bone may provide a more precise estimate for the fracture risk

On the cortical bone elasticity, toughness and bone quality

21st International Bone Densitometry Workshop & 7th European Symposium on Ultrasonic Characterization of Bone, KLOSTER BANZ, ALLEMAGNE, 26-/06/2017 - 30/06/2017This study aims at investigating the relationship between different aspects of bone quality and understanding how bone quality may affect stiffness at the mm-scale and toughness. The transverse isotropic effective stiffness tensor was measured by resonant ultrasound spectroscopy (RUS) and the vascular porosity was estimated from synchrotron radiation micro-computed tomography (SR-¼CT) images. A cross-section at the mid-diaphysis was sectioned from the left femur of 27 human cadavers. Then, a set of 54 parallelepiped-shape samples (size 3x4x5 mm3) was prepared for RUS measurements and SR-¼CT imaging at ERSF (voxel size 6.5 µm). Another set of adjacent 54 samples (size 3x4x25 mm3) was harvested for mechanical testing and the remaining material was used for cross-links and collagen quantification. These last samples were divided into two samples (1x2x25 mm3) then notched (1 mm length) in their middle, in the transverse direction. Three-point bending tests were conducted at two strain rates 10-4 s-1 and 10-1 s-1 to measure toughness (quasi-static KJcStat and dynamic KJcDyn). Specimen dimensions are defined by the anatomical shape of femoral diaphysis: radial (axis 1), circumferential (axis 2) and axial direction (axis 3). Immature and mature collagen crosslinks were separated by reversed-phase HPLC method and quantified using fluorescence and mass spectrometry detection. Relationships between variables were investigated with Spearman's rank correlation coefficients. The bone-quality markers analysed here seem to differently affect toughness and stiffness. Indeed, markers that showed an effect in toughness did not in stiffness. Vascular porosity was significantly correlated with all stiffness coefficients but not with toughness. Enzymatic immature cross-links significantly correlated with stiffness coefficients, while only the non-enzymatic cross link pentosidine significantly affected toughness. Finally, the existing correlations between elastic parameters and toughness are shown in Table 1. Knowing the effects of these markers in the mechanical properties of bone may provide a more precise estimate for the fracture risk

Anisotropic elastic properties of human femoral cortical bone and relationships with composition and microstructure in elderly

The strong dependence between cortical bone elasticity at the millimetre-scale (mesoscale) and cortical porosity has been evidenced by previous studies. However, bone is an anisotropic composite material made by mineral, proteins and water assembled in a hierarchical structure. Whether the variations of structural and compositional properties of bone affect the different elastic coefficients at the mesoscale is not clear. Aiming to understand the relationships between bone elastic properties and compositions and microstructure, we applied state-of-the-art experimental modalities to assess these aspects of bone characteristics. All elastic coefficients (stiffness tensor of the transverse isotropic bone material), structure of the vascular pore network, collagen and mineral properties were measured in 52 specimens from the femoral diaphysis of 26 elderly donors. Statistical analyses and micromechanical modeling showed that vascular pore volume fraction and the degree of mineralization of bone are the most important determinants of cortical bone anisotropic mesoscopic elasticity. Though significant correlations were observed between collagen properties and elasticity, their effects in bone mesoscopic elasticity were minor in our data. This work also provides a unique set of data exhibiting a range of variations of compositional and microstructural cortical bone properties in the elderly and gives strong experimental evidence and basis for further development of biomechanical models for human cortical bone. STATEMENT OF SIGNIFICANCE: This study reports the relationships between microstructure, composition and the mesoscale anisotropic elastic properties of human femoral cortical bone in elderly. For the first time, we provide data covering the complete anisotropic elastic tensor, the microstructure of cortical vascular porosity, mineral and collagen characteristics obtained from the same or adjacent samples in each donor. The results revealed that cortical vascular porosity and degree of mineralization of bone are the most important determinants of bone anisotropic stiffness at the mesoscale. The presented data gives strong experimental evidence and basis for further development of biomechanical models for human cortical bone