Ref HAL: hal-00413372_v1
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We put disks on a sphere between two parallels of this sphere. The disks have the curvature of the sphere and interact via a simplified Hertz law. We analyze the behavior of the total kinetic energy of the whole assembly of disks with Riemanian geometry and contrarily to flat spaces, this kinetic energy increases. This is due to a non radial component of the resulting velocity vector at each interaction between two disks. The study of granular matter in twodimensional curved spaces is therefore not trivial.

Ref HAL: hal-00386806_v1
DOI: 10.1016/j.physb.2009.04.029
WoS: 000268732700037
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We computed a Lennard-Jones frozen liquid with a free surface using classical molecular dynamics. The structure factor curves on the free surface of this sample were calculated for different depths knowing that we have periodic boundary conditions on the other parts of the sample. The resulting structure factor curves show an horizontal shift of their first peak depending on how deep in the sample the curves are computed. We analyze our resulting curves in the light of spatial correlation functions during melting. The conclusion is that the differences between bulk and surface are quite small during melting and that at the end of melting, only the very surface happens to be less dense than the bulk. This result is intrinsic to the shape of the Lennard-Jones potential and does not depend on any other parameter.

Ref HAL: hal-00134775_v4
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We expose first a biological model of memory based on one hand of the mechanical oscillations of axons during action potential and on the other hand on the changes in the extra cellular matrix composition when a mechanical strain is applied on it. Due to these changes, the stiffness of the extra cellular matrix along the most excited neurons will increase close to these neurons due to the growth of astrocytes around them and to the elastoplastic behavior of collagen. This will create preferential paths linked to a memory effect. In a second part, we expose a physical model based on random walk of the action potential on the array composed of dendrites and axons. This last model shows that repetition of the same event leads to long time memory of this event and that paradoxical sleep leads to the linking of different events put into memory.

Commentaires: forthcoming article published online at www.m-hikari.com

Ref HAL: hal-00332085_v1
DOI: 10.1140/epjd/e2008-00209-9
WoS: 000261656400004
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We studied in tight-binding approximation involving spⁱ hybridization (i=2,3), some Si2Cn (n=3 to 42) microclusters. We then investigated, on one hand, fragments of fullerene-like structures (sp2) , and on the other hand, nanodiamonds (sp3) of adamantane-type or a 44-atom nanodiamond (with 2 inner atoms which are assumed to play the role of bulk atoms).We compared the stabilities, i.e. the electronic energies of these clusters, according to the various positions of the 2 Si atoms.Results are very different in the two kinds of hybridization. Besides, they can be analysed according to two different points of view: either the clusters are considered as small particles with limited sizes, or they are assumed to be used as models in order to simulate the Si-atom behaviour in very larger systems. In sp2 hybridization (fullerene-like geometries), the most stable isomer is always encountered when the 2 Si atoms build a Si2 group, and this result holds for both viewpoints quoted above.Conversely, in sp3 hybridization (nanodiamonds), since Si atoms "prefer" sites having the minimum connectivity , they are never found in adjacent sites. We see that with a simple and fast computational method we can explain an experimental fact which is very interesting such as the relative position of two heteroatoms in the cluster. This enhances the generality and the fecondity in the tight binding approximation due essentially to the link between this model and the graph theory, link based on the topology of the clusters.

Ref HAL: hal-00344224_v1
DOI: 10.1142/S0218348X08004071
WoS: 000261381900007
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We compared two models of aggregation which represent the sol gel transition of base-catalyzed colloidal gels. The two models are a Langevin dynamics approach of this transition and the DLCA model (diffusion limited cluster-cluster aggregation). For large numbers of particles, we compared the fractal dimension of the gelling network via the structure factor of the bulk. We observed that the Langevin dynamics approach did give more realistic fractal dimension than the DLCA model. This is due to the fact that Langevin dynamics evolves as a function of a physical time.

Ref HAL: hal-00142508_v5
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By using the FLRW cosmological model, we calculated the relation between the local time and the local curvature in the case of a vacuum dominated universe. We showed that except for special values of the different constants which enter this equation, the time cannot be equal to zero. By using this assumption, we showed also that the demonstration of the uncertainty principle of Heisenberg is only an approximation

Commentaires: version to be published in Advanced Studies in Theoretical Physics

Ref HAL: hal-00387348_v1
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