Papers by Jacques Lauzeral
Cette thèse de doctorat a été numérisée par l'Université libre de Bruxelles. L'auteur qui s'oppos... more Cette thèse de doctorat a été numérisée par l'Université libre de Bruxelles. L'auteur qui s'opposerait à sa mise en ligne dans DI-fusion est invité à prendre contact avec l'Université
Physical Review B, 1997
The mechanical behavior of thin films subjected to laser irradiation is described by a dynamical ... more The mechanical behavior of thin films subjected to laser irradiation is described by a dynamical model that is based on coupled evolution equations for the deformation and vacancy density fields. Lattice vacancies are generated in a thin layer as a result of shallow absorption of electromagnetic laser radiation. The strain field associated with lattice dilatation due to vacancies is shown to couple with bending and stretching mechanical deformation fields. The dynamical model developed here is an extension of the work of Emel'yanov in two respects: ͑1͒ the coupling between the diffusion and mechanical deformation fields is rigorously developed with additional cross-field contributions; ͑2͒ new equations for reduced dynamics are derived from this model, and are used to analyze the physical conditions for the onset of a deformational instability. For a given material, the threshold for this instability is correlated mainly with laser power. We also show that, although the instability threshold and critical wavelengths are given by the linear part of the dynamics, the selection and type of deformation patterns induced by this instability require a nonlinear formulation. Both numerical and analytical analysis are performed here. According to the relative importance of nonlinearities arising from the defect or from the bending dynamics, square or hexagonal planforms are shown to be selected. Furthermore, it appears that one-dimensional gratings are always unstable in isotropic systems. The results for square patterns are consistent with experimental observations, while those for hexagonal and one-dimensional gratings show the importance of anisotropies on their final selection. ͓S0163-1829͑97͒03847-2͔
Nonlinear Phenomena and Complex Systems, 2000
The stationary probability is analytically determined in a suitable approximation for several sys... more The stationary probability is analytically determined in a suitable approximation for several systems presenting a weak noise transition. Numerical simulations are presented which corroborate the analytical results.
Proceedings of the National Academy of Sciences, 1997
Whereas it is relatively easy to account for the formation of concentric (target) waves of cAMP i... more Whereas it is relatively easy to account for the formation of concentric (target) waves of cAMP in the course of Dictyostelium discoideum aggregation after starvation, the origin of spiral waves remains obscure. We investigate a physiologically plausible mechanism for the spontaneous formation of spiral waves of cAMP in D. discoideum . The scenario relies on the developmental path associated with the continuous changes in the activity of enzymes such as adenylate cyclase and phosphodiesterase observed during the hours that follow starvation. These changes bring the cells successively from a nonexcitable state to an excitable state in which they relay suprathreshold cAMP pulses, and then to autonomous oscillations of cAMP, before the system returns to an excitable state. By analyzing a model for cAMP signaling based on receptor desensitization, we show that the desynchronization of cells on this developmental path triggers the formation of fully developed spirals of cAMP. Development...
Physical Review Letters, 1997
The coupling between surface deformation and defect dynamics may be at the origin of deformation ... more The coupling between surface deformation and defect dynamics may be at the origin of deformation patterns in thin films under laser irradiation. We analyze a simple model describing the dynamics of such systems in the case of focused laser irradiation. We show, through linear, nonlinear, and numerical analysis, how rose deformation patterns, with the petal number increasing with laser intensity, naturally arise in this model, in agreement with experimental observations. [S0031-9007(97)04173-2]
Biophysical Chemistry, 1998
We examine the theoretical aspects of temporal and spatiotemporal organization in the cAMP signal... more We examine the theoretical aspects of temporal and spatiotemporal organization in the cAMP signaling system of Dictyostelium discoideum amoebae which aggregate in a wavelike manner after starvation, in response to pulses of cAMP emitted with a periodicity of several minutes by cells behaving as aggregation centers. We first extend the model based on receptor desensitization, previously proposed by Martiel and Goldbeter, by incorporating the role of G proteins in signal transduction. The extended model accounts for observations on the response of the signaling system to successive step increases in extracellular cAMP. In the presence of the positive feedback loop in cAMP synthesis, this model generates sustained oscillations in cAMP and in the fraction of active cAMP receptor, similar to those obtained in the simpler model where the role of the G proteins is not taken into account explicitly. We use the latter model to address the formation of concentric and spiral waves of cAMP in the course of D. discoideum aggregation. Previous analyses of the model showed that a progressive increase in the activity of adenylate cyclase and phosphodiesterase can account for the transitions no relayrelay-oscillations-relay observed in the experiments. We show that the degree of cellular synchronization on such a developmental path in parameter space markedly affects the nature of the spatial patterns generated by the model. These patterns range from concentric waves to a small number of large spirals, and finally to a large number of smaller spirals, as the degree of developmental desynchronization between cells increases.
Europhysics Letters (EPL), 1993
Physico-chemical systems driven away from thermal equilibrium usually undergo various types of in... more Physico-chemical systems driven away from thermal equilibrium usually undergo various types of instabilities leading to the formation of spatio-temporal patterns on macroscopic time and space scales. In two-dimensional geometries, patterns of different symmetries may be simultaneously stable. We study here the phase stability of hexagonal planforms in the framework of amplitude equations and reduced dynamical models close to the instability points.
Uploads
Papers by Jacques Lauzeral