A new topological aspect of the arbitrary dimensional topological defects

We present a new generalized topological current in terms of the order parameter field $\vec \phi$ to describe the arbitrary dimensional topological defects. By virtue of the $$-mapping method, we show that the topological defects are generated from the zero points of the order parameter field $\vec \phi$, and the topological charges of these topological defects are topological quantized in terms of the Hopf indices and Brouwer degrees of $\phi$-mapping under the condition that the Jacobian $$. When $J(\frac \phi v)=0$, it is shown that there exist the crucial case of branch process. Based on the implicit function theorem and the Taylor expansion, we detail the bifurcation of generalized topological current and find different directions of the bifurcation. The arbitrary dimensional topological defects are found splitting or merging at the degenerate point of field function $\vec \phi$ but the total charge of the topological defects is still unchanged.Comment: 24 pages, 10 figures, Revte

The short coiled-coil domain-containing protein UNC-69 cooperates with UNC-76 to regulate axonal outgrowth and normal presynaptic organization in Caenorhabditis elegans

BACKGROUND: The nematode Caenorhabditis elegans has been used extensively to identify the genetic requirements for proper nervous system development and function. Key to this process is the direction of vesicles to the growing axons and dendrites, which is required for growth-cone extension and synapse formation in the developing neurons. The contribution and mechanism of membrane traffic in neuronal development are not fully understood, however. RESULTS: We show that the C. elegans gene unc-69 is required for axon outgrowth, guidance, fasciculation and normal presynaptic organization. We identify UNC-69 as an evolutionarily conserved 108-amino-acid protein with a short coiled-coil domain. UNC-69 interacts physically with UNC-76, mutations in which produce similar defects to loss of unc-69 function. In addition, a weak reduction-of-function allele, unc-69(ju69), preferentially causes mislocalization of the synaptic vesicle marker synaptobrevin. UNC-69 and UNC-76 colocalize as puncta in neuronal processes and cooperate to regulate axon extension and synapse formation. The chicken UNC-69 homolog is highly expressed in the developing central nervous system, and its inactivation by RNA interference leads to axon guidance defects. CONCLUSION: We have identified a novel protein complex, composed of UNC-69 and UNC-76, which promotes axonal growth and normal presynaptic organization in C. elegans. As both proteins are conserved through evolution, we suggest that the mammalian homologs of UNC-69 and UNC-76 (SCOCO and FEZ, respectively) may function similarly

An analytical stress-strain model for open-cell metal foam

International audienceThe main objective of the present investigation is to develop an analytical stress-strain model to quantitatively describe the stress-strain behavior of open-cell metal foam. Based on solid mechanics, an analytical stress-strain model is developed. This new stress-strain model involves two main parameters: relative density and plastic Poisson's ratio. As a key characteristic of metal foam, relative density directly takes effect on the uniaxial stress-strain behavior of metal foam and the uniaxial stress of metal foam increases with increasing relative density. Plastic Poisson's ratio is measured as a function of uniaxial compressive plastic strain and its value is neither 0 nor 0.5. Corresponding uniaxial compression tests of metal foams were conducted and numerical simulations were also carried out. The results indicate that this analytical stress-strain model of metal foam is in good agreement with both the experimental validations and the numerical simulations. This work provides useful information for understanding the deformation mechanism of open-cell metal foam

Mechanical properties of open-cell metal foams under low-velocity impact loading

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Study of compressive properties of metal porous polymer composites under different temperature conditions

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Modélisation analytique et numérique de structure des mousses métalliques MPPCs et du comportement mécanique

L objectif principal de ce travail est la modélisation analytique et numérique du comportement statique, dynamique et thermique des matériaux innovants (mousses métalliques et composites MPPCs). Dans un premier temps, la technique d infiltration à pression négative est utilisée pour la fabrication des mousses d aluminium à cellules ouvertes et des composites MPPCs. Compte tenu des arrangements des cellules ouvertes, trois modèles analytiques sont proposés à l échelle microscopique pour prédire et optimiser la porosité du matériau. Les microstructures sont analysées expérimentalement afin d étudier le comportement mécanique des composites MPPCs. Dans la seconde étape, nous avons proposé un modèle constitutif de contrainte-déformation dans le cas de la compression uni axiale statique sur la mousse d aluminium. Ce modèle est utilisé pour simuler numériquement par éléments finis le comportement en compression. Le modèle est ensuite utilisé dans le cas dynamique en choc. Les modèles sont validés par des essais expérimentaux. La dernière partie concerne l étude du comportement thermomécanique des composites MPPCs avec les microstructures des cellules sphériques et de Kelvin. Des simulations numériques en thermomécaniques sont réalisées sur ABAQUSThe main objective of this work is analytical and numerical modeling of the static, dynamic and thermal mechanical properties of the innovative materials (metal foam and composites MPPCs). Initially, the negative pressure infiltration technique is applied to manufacture the open-cell aluminum foams and the composites MPPCs. Considering the open-cell arrangements, three analytical models are proposed at the microscopic level to predict and optimize the porosity of the materials. The microstructures are experimentally analyzed to study the mechanical behavior of the composites MPPC. Secondly, we proposed a constitutive model of stress-strain in the case of uniaxial static compression of metal foam. This model is utilized with the finite element to numerically simulate the compressive behavior. Afterwards, the model is once again used in the case of dynamic low-velocity impact of metal foam. These models are verified by the experimental tests. Finally, we study the thermomechanical behavior of the composites MPPCs with the micro-structures of spherical and Kelvin cells. The numerical simulations of thermomechanical properties are carried out with the program ABAQUSTROYES-SCD-UTT (103872102) / SudocSudocFranceF

Influence du taux de remplissage de polymère sur les propriétés en compression des métaux poreux polymères composites (MPPC)

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Study of dynamic drop impact response of open-cell metal foam

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Porosity predication with microstructural method for open-cell aluminum foam

International audienceThe mechanical property of open-cell aluminum foam directly depends on the foam porosity. This paper proposes three representative microstructural models of pores: 6-interface, 8-interface, and 12-interface microstructural models for open-cell aluminum foams, which are manufactured by the infiltration technique. It seems that the foam porosity is independent of the average sizes of particles; in contrast, it's strongly dependent on the arrangements of particles in the pre-forms. The predicted foam porosity, which changes from 0.52 to 0.71, is in accordance with the experimental results. In addition, the 12-interface microstructural model is recommended for the structure of the open-cell aluminum foam; on the contrary, the 6-interface microstructural model hardly appears in the structure of the open-cell aluminum foam. This analysis makes a good base to further the numerical modeling of the mechanical property for open-cell aluminum foam. It also provides a useful study of the mechanism of the foam porosity forming, variation, and some other effects in the manufacturing process