Detection of multicomponent signals: effect of difference in level between components

The detection of multicomponent signals for which the components are not equidetectable is precisely investigated as a function of the level difference ΔL(i∕j) between components. The detection thresholds are determined for a seven-tone complex signal with random starting phases masked by white noise. Level differences between the components are examined. A model for non-equidetectable conditions based on the statistical summation model is described. The improvement in detection is calculated from the level difference between components that is related to the thresholds for single components. The model predictions are in accordance with the experimental results.     

Multiple resonance heteronuclear decoupling under MAS: dramatic increase of spectral resolution at moderate magnetic field and MAS frequencies

The effects of multiple-resonance heteronuclear decoupling under magic angle spinning (MAS) on the resolution of one-dimensional ¹⁹F and ³¹P and various two-dimensional MAS NMR spectra and on the residual non-refocusable coherence lifetimes in fluorinated aluminophosphate AlPO₄-CJ2, i.e. a compound that contains numerous highly abundant nuclei but no homonuclear spin bath, has been investigated. The design of the four-channel (¹H, ¹⁹F, ²⁷Al, ³¹P) MAS probe used for this study is first described. ¹H and ¹H–²⁷Al double-resonance decouplings allows lengthening the optimized transverse relaxation and increasing the resolution in the ¹⁹F and ³¹P dimensions. Under the application of multi-nuclear decoupling, a two-dimensional ¹⁹F–³¹P CP-HETCOR correlation spectrum for AlPO₄-CJ2 is recorded with unprecedented high-resolution in the two dimensions. Moreover, because ¹H-decoupling increases the ¹⁹F , it has been applied during the entire duration of the 2D NMR experiments, allowing the direct use of residual small interactions to generate ¹⁹F–¹⁹F and ¹⁹F–²⁷Al 2D NMR correlation spectra in AlPO₄-CJ2.     

On the “viscous incompressible fluid + rigid body” system with Navier conditions

In this paper we consider the motion of a rigid body in a viscous incompressible fluid when some Navier slip conditions are prescribed on the body's boundary. The whole system “viscous incompressible fluid + rigid body” is assumed to occupy the full space R³${\mathbb{R}}^3$. We start by proving the existence of global weak solutions to the Cauchy problem. Then, we exhibit several properties of these solutions. First, we show that the added-mass effect can be computed which yields better-than-expected regularity (in time) of the solid velocity-field. More precisely we prove that the solid translation and rotation velocities are in the Sobolev space H¹$H^1$. Second, we show that the case with the body fixed can be thought as the limit of infinite inertia of this system, that is when the solid density is multiplied by a factor converging to +∞. Finally we prove the convergence in the energy space of weak solutions “à la Leray” to smooth solutions of the system “inviscid incompressible fluid + rigid body” as the viscosity goes to zero, till the lifetime T   of the smooth solution of the inviscid system. Moreover we show that the rate of convergence is optimal with respect to the viscosity and that the solid translation and rotation velocities converge in H¹(0,T)$H^1(0,T)$.     

Application of a multi-component Eulerian approach to capture interface evolution and vorticity generation in compressible multiphase flow

The hyperbolic Eularian model is used as a mathematical framework for compressible multiphase flows. The formulation was obtained after an averaging process of the single phase Navier-Stokes equations. The closure of multi-component system leads to the volume fraction equation containing a non-conservative term and a pressure equilibrium condition. As a result the model equations cannot be written in a conservative form. To solve the equations a finite volume Godunov type computational approach is developed which uses an approximate Riemann solver combined with a numerical scheme to tackle the non-conservative terms. The approach accounts for pressure non-equilibrium. It enables resolving interfaces separating compressible fluids and captures the baroclinic source of vorticity generation. The computations are performed for various initial conditions and compared with theoretical and experimental data for a shock-bubble interaction problem. The investigated cases include acoustic wave transmission through isolated bubbles of helium and krypton. The numerical results illustrate the characteristic features of the evolving interfaces. The impulsively generated flow perturbations are dominated by the reflection and refraction of the shock and by the vorticity generation within the media. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Allenylzincs and tert-butylsulfinylimines: a fruitful marriage for synthesis

The stereoselective synthesis of alkynyl 1,2-amino alcohols by the addition of 3-chloro- and 3-methoxymethoxy- allenylzincs to chiral tert-butylsulfinylimines is described. The methodology is applicable to the preparation of alkynyl 2-amino-1,3-diols (O,N,O stereotriads) using α-alkoxy tert-butylsulfinylimines as chiral starting materials. The scope and limitations of the methodology along with recent applications to the efficient asymmetric syntheses of natural and/or bioactive alkaloids and polyhydroxylated alkaloids are presented.     

PHOTOOXIDATION PRODUCTS OF MEROCYANINE 540 FORMED UNDER PREACTIVATION CONDITIONS FOR TUMOR THERAPY

In order to gain insight into the preactivation of merocyanine 540 (MC540) 1 for the photodynamic therapy (Gulliya et al., 1990a, Photochem. Photobiol. 52, 831-838) its photo-oxidation was investigated. After irradiation of MC540 1 on a preparative scale three main photodegradation products were isolated with 16-20% yields. They turned out to be derivatives of benzoxazole, thiouracil and thiohydantoin with the structures 4, 5 and 6, respectively. It may be possible that they contribute to the cytostatic and antiviral activity of preactivated MC540 1.     

Stress-based upper-bound method and convex optimization: case of the Gurson materialMéthode cinématique par les contraintes et optimisation convexe : cas du matériau de Gurson

A nonlinear interior point method associated with the kinematic theorem of limit analysis is proposed. Associating these two tools enables one to determine an upper bound of the limit loading of a Gurson material structure from the knowledge of the sole yield criterion. We present the main features of the interior point algorithm and an original method providing a rigorous kinematic bound from a stress formulation of the problem. This method is tested by solving in plane strain the problem of a Gurson infinite bar compressed between rough rigid plates. To cite this article: F. Pastor et al., C. R. Mecanique 334 (2006).