Coupling of a simplified flow with a phenomenological fire spread modelCouplage d'un écoulement simplifié à un modèle phénoménologique de propagation des feux

Our long-range aim is to propose a forest fire simulator. To this end, we have developed a phenomenological model of fire spread. Then, we have improved it in order to take into account advective transfers thanks to a simplified flow. In this paper, we present in a synthetic way our modelling approach that can also be applied to other phenomenological models. Finally, we compare the model predictions to laboratory experiments. To cite this article: A. Simeoni et al., C. R. Mecanique 330 (2002) 783–790.     

Approximation uniformément valable pour l'écoulement de Falkner–SkanA uniformly valid approximation for a Falkner–Skan flow

In the context of the laminar steady two-dimensional flow of an incompressible Newtonian fluid, we propose a uniformly valid approximation in the whole domain of the flow over a flat plate with incidence. The solution is built from the asymptotic method of matched expansions at order one and has been compared with the classical boundary layer solution and the potential solution. It allows a better approximation of basic flow near the leading edge of the flat plate. The solution has been established at order two for the flow without incidence. These more realistic solutions should be employed when analysing the receptivity and the ensuing destabilisation of boundary layers. To cite this article: S. Saintlos, J. Bretteville, C. R. Mecanique 330 (2002) 673–682.     

On the nature of the boundary layers instabilities in a flow between a rotating and a stationary discSur la nature des instabilités de couche limite dans un écoulement entre un disque fixe et un disque tournant

Both theoretical linear stability analysis and direct numerical simulation are performed to study the transition flow between a stationary and a rotating disc. This paper concerns three-dimensional spiral and annular patterns computed with a high-order (spectral) numerical method and related to Bödewadt layer instabilities. The characteristic parameters of these boundary layer patterns are compared to the theoretical results and interpreted in terms of type I and type II generic instabilities. Moreover, the absolute instability regions are also theoretically identified and the critical Reynolds numbers of the convective/absolute transition in both layers are given. To cite this article: E. Tuliska-Sznitko et al., C. R. Mecanique 330 (2002) 91–99.     

Écoulement cisaillé non visqueux autour d'un cylindre proche d'une paroiInviscid shear flow around a cylinder close to a wall

This Note gives the stream function of a 2D inviscid flow around a circular cylinder close to a wall, induced by the perturbation of an upstream linear shear flow. The derivation of such an explicit solution relies on the image singularity system method and a slight extension of Milne-Thomson's circle theorem. To cite this article: E. Dériat, C. R. Mecanique 330 (2002) 35–38     

Quasi-periodic solutions of a semilinear Liénard equation at resonance

We are concerned with the existence of quasi-periodic solutions for the following equation

Quantum Entanglement of Parallel-Coupled Double Quantum Dots: a Theoretical Study Using the Hierarchical Equations of Motion Approach?

Quantum dots comprise a type of quantum impurity system. The entanglement and coherence of quantum states are significantly influenced by the strong electron-electron interactions among impurities and their dissipative coupling with the surrounding environment. Competition between many-body effects and transfer couplings plays an important role in determining the entanglement among localized impurity spins. In this work, we employ the hierarchical-equations-of-motion approach to explore the entanglement of a strongly correlated double quantum dots system. The relation between the total system entropy and those of subsystems is also investigated.     

G_2型量子群的Gelfand-Kirillov维数

用Gr(o|¨)bner-Shirshov基和PBW代数方法来计算G_2型量子群的Gelfand.Kirillov维数.得到的结论是G_2型量子群的Gelfand-Kirillov维数为14.     

高质量三维光子晶体的制备及其透射谱研究

设计了简易的压强可控自组装实验装置,制备了由直径为260 nm的聚苯乙烯(PS)胶体球组成的面心立方光子晶体.分析了压强的变化对光子禁带(PBG)深度及光子带隙边缘(PBE)坡度的影响,确定了合适的压强生长环境(P=5999.5 Pa).利用该实验装置,还进行了光子晶体的小批量制备,一次性制得了三块光子晶体,并从不同角度对每一块光子晶体的透射谱及不同光子晶体的透射谱进行了测量.同一光子晶体不同位置透射谱的重合、同一批次制备的不同光子晶体透射谱的一致性及光子禁带两侧的Fabry-Pérot振荡等均说明:该装置制备的光子晶体在大区域、大面积上是高度有序、均一和平整的;利用该实验装置进行光子晶体的小批量制备是可行的.     

基于任意系统位置关系的投影云纹形貌测量技术研究

提出了一套完整的基于投影云纹系统的物体表面形貌测量方法,包括理论公式推导、系统线性近似误差分析、全场灵敏度系数标定方法、实际物体的实验测量结果。所提出的方法既不需要特定的系统硬件位置关系设置,也无需人为确定系统的几何参数。该方法在允许测量系统组件任意放置的情况下仍然能够获得很高的分辨率和精度,其有效性及正确性通过真实物体的实验得到证实。     

Period stabilization in the Busse–Heikes model of the Küppers–Lortz instability

The Busse–Heikes dynamical model is described in terms of relaxational and non-relaxational dynamics. Within this dynamical picture a diverging alternating period is calculated in a reduced dynamics given by a time-dependent Hamiltonian with decreasing energy. A mean period is calculated which results from noise stabilization of a mean energy. The consideration of spatial-dependent amplitudes leads to vertex formation. The competition of front motion around the vertices and the Küppers–Lortz instability in determining an alternating period is discussed.