Effects of a locally injected signal on phase synchronization in a network of self-excited cells

We consider in this paper the problem of phase synchronization in a network of coupled self-excited cells with free-end boundary conditions. The eigenvalues properties are used to perform the stability boundaries of the synchronization process for pure sinusoidal and quasi-sinusoidal oscillatory states. In the case where the cells’ oscillatory states are quasi-periodic, more energy and time are required for the network to become fully synchronized, compared to the case where each cell exhibits a periodic oscillation. The influence on the stability boundaries of a periodic external excitation locally injected in the network is tackled. For both cases (with and without local injection), numerical simulations are used to check the accuracy and to complement the results derived from the analytical treatment. In this configuration, the local injection helps to drastically increase the range of the coupling parameter for which all cells become synchronized.     

Stereoselective synthesis of enantiopure N-protected-3-arylpiperazines from keto-esters

An efficient method for a stereoselective synthesis of optically pure N-Boc-3-arylpiperazines has been developed. After optimization of the protecting group strategy and experimental conditions, compounds were obtained via a highly stereoselective synthesis in up to 45% overall yield. This is a practical route to optically pure piperazines for medicinal chemistry.     

Resonance Paramagnetique Electronique: Etude au Moyen d'une Sonde Radicalaire Nitroxyde Deuteree,de l'Orientation Macroscopique et Microscopique des Phases Isotrope et Nematique de l'E.B.B.A.

Abstract

Les spectres de R.P.E. d'une sonde nitroxyde deutérée, de forme allongée, ont été analysés dans les phases isotrope et nématique de l'E.B.B.A.

Les résultats expérimentaux concernant la mesure des paramètres d'ordre et la réorientation moléculaire sont en bon accord avec l'utilisation d'un potentiel décrivant l'orientation moléculaire, de la forme U=u ₂ (P ₂P₂ + λP ₄P₄).

La détermination des temps caractéristiques de la réorientation moléculaire τ₂₀ et τ₂₂ montre qu'ils ne subissent pas de variations notables lorsque I'on passe de la phase isotrope é la phase nématique. L'ordre local à l'échelle microscopique du cristal liquide ne subit donc pas de profondes modifications de part et d'autre de la transition. D'autre part, sauf au voisingage du point de clarification les temps de corrélation pour la réorientation du grand axe moléculaire de la sonde obéissant à la loi usuelle: τ₂₀=(τ₂₀) _oe -^?E/kT avec E=8.5 kcal/mole dans la phase isotrope et E=9 kcal/mole dans la phase nématique.

The E.S.R. spectra of a long shaped deuterated nitroxide probe dissolved in the isotropic and the nematic phases of E.B.B.A. have been studied.

Experimental and theoretical results for anisotropic ordering and molecular motions are able to achieve good fits by means of an orientational potential like this described by Humphries et al.: U=z ₂(P ₂ + λP ₄,P₄).

The determination of the rotational correlation times τ₂₀ and τ₂₂ of the probe shows that no important discontinuity occurs for the local ordering structure of the liquid crystal when one goes through the isotropic-nematic transition. Relatively far of this transition the correlation time τ₂₀ obeys the classic temperature dependence: τ₂₀=(τ₂₀)oe ^?E/kT with E=8.5 k cal/mole in the isotropic phase and E=9 kcal/mole in the nematic phase.     

Wave Trains Generation in a Delayed Nonlinear Response of Bose-Einstein Condensates with Three-Body Interactions

We investigate the modulational instability of matter-wave condensates in a modified Gross-Pitaevskii equation which takes into account effects of the three-body interaction. This three-body interaction consists of a quintic term and an additional one representing the delayed nonlinear response of condensates which are trapped both in an attractive and a repulsive harmonic potentials. Our theoretical study uses a modified lens-type transformation and we obtain a modulational instability criterion, and an explicit growth rate. We show that the presence of the three-body interaction destabilizes the condensate, and enhances the appearance of instability in the condensate. Numerical experiments agree well with analytical predictions. Furthermore, our numerical simulations show that the three-body interaction modifies the symmetry of the trail of soliton chains created. The expulsive potential enhances the instability, while the attractive potential appears to soften the instability.     

On two different inverse form finding methods for hyperelastic and elastoplastic materials

This contribution focuses on two different developments of mechanical-computational methods for the optimal determination of the initial shape of formed functional components knowing the deformed configuration, the applied loads and the boundary conditions. The first method uses an inverse mechanical formulation and can be applied to materials with hyperelastic behaviors. For materials with elastoplastic properties this method is not advocated, without knowing the final plastic strains, due to the non uniqueness of the solution. The second method uses a shape optimization formulation in the sense of an inverse problem via successive iterations of the direct problem. For hyperelastic materials the inverse mechanical formulation is preferred for its velocity and the non exhibition of possible mesh distortions. In the shape optimization formulation mesh distortions can be avoided by an update of the reference configuration of the functional part. Both methods are using a formulation in the logarithmic strain space. A numerical example for materials with isotropic elastoplastic behaviors illustrates the shape optimization formulation. (© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

NMR Microscopy of an “Anisotropic” Polymer

Two different samples of high-density polyethylene (HDPE) have been studied. One (isotropic) is extracted from the material core whereas the other (anisotropic) involves two sides which have been in contact with the injection mold. It is observed by NMR microscopy (using radiofrequency field gradients) that these two sides favor toluene penetration into the material. The distribution of toluene nuclear spin relaxation times (extracted from proton T₁ and T₂ images) exhibits likewise important differences between the two samples. These differences can be accounted for by partial molecular ordering at the vicinity of the “mold sides”. Finally, in investigating the anisotropic sample (without solvent), three different phases (two amorphous and one crystalline) are revealed by ¹³C chemical shift imaging experiments (performed with radiofrequency field gradients under CP/MAS conditions). Each amorphous component is preferentially present at one of the two “mold sides”.     

Mutagenic heterocyclic nitrogen compounds related to protein pyrolysates. V. Electron impact fragmentation of L-glutamic acid and related dipyrido[1,2-a:3′,2′-d]imidazoles

Six dipyrido[1,2-a:3′,2′d]imidazole derivatives related to glutamic acid pyrolysates have been studied by mass spectrometry. The data indicate that there are certain ions which are characteristic of the fragmentation of this family of compounds under electron impact. These compounds should thus be amenable to analysis if they were produced during the combustion of foods. In addition, electronolysis of L-glutamic acid was also studied: the fragmentation pattern of the latter has shown the formation of some known dipyridoimidazoles for temperatures higher than 100°. Similarities between pyrolysis and electronolysis of this acid are discussed.     

Functional Concepts in Continuum Mechanics

This paper is an attempt to give a concise presentation of the main concepts of continuum mechanics and to show their articulation. Functional definitions have been favoured.The first section is devoted to a review of continuum mechanics.The second section deals with the mechanics of materials.Constitutive equations of the material are given first by equations of state and then by complementary equations written in order to fulfil the fundamental inequality concerning the production of entropy and the physical properties of the material (viscosity, plasticity, damage etc.).Section 3 gives the Lagrangian and the Hamiltonian formulations for a moving body. Section 4 is devoted to the motion of surfaces through which discontinuities appear, to show briefly two examples of application of the previous concepts. One can easily define the source of intrinsic inhomogeneity, of heat, of irreversible entropy on a surface of phase transition and also for a shockwave.SommarioIn questo lavoro si cerca di dare una presentazione concisa dei concetti fondamentali della meccanica dei continui e di mostrare le loro articolazioni,con particolare rilievo alle definizioni funzionali. La prima sezione è dedicata ad un esame generale introduttivo. La seconda alla meccanica dei materiali, le cui equazioni costitutive sono date come equazioni di stato e come equazioni complementari scritte al fine di soddisfare le diseguaglianze concernenti la produzionedi entropia e le proprietà fisiche dei materiali (qualiviscosità, plasticità, guasti...).La terza sezione dà le formulazioni Lagrangiana ed Hamiltoniana per il moto di un corpo.La quarta sezione è dedicata al moto di superfici di discontinuità per mostrare brevemente due esempi di applicazione dei concetti precedenti.Viene quindi definita la sorgente di disomogeneità intrinseca, di calore, di entropia irreversibile su di una superficie, di transizione di fase ed anche di un' onda d'urto.     

Role of the hydrogen in the light-induced defects in undoped hydrogenated amorphous silicon

We have investigated the effect of the deposition temperature (i.e. the hydrogen content) on the light-induced effects in undoped hydrogenated amorphous silicon (a-Si:H). Combined junction capacitance-temperature (C-T), ESR and IR absorption measurements are carried out in both the dark annealed state (A) and the saturated light-soaked state (B), as well as after partial annealing of the samples, starting from state B. The experimental results indicate that the films deposited at the highest substrate temperature (i.e. the lowest H content) exhibit a completely different behaviour from those deposited at lower substrate temperature (i.e. with higher H concentration), when the samples are left for long times at room temperature in the dark after partial annealing. These results are discussed in detail in relation to the different models proposed to explain the light-induced effects in a-Si:H.