Superacid-Mediated Late-Stage Aromatic Polydeuteration of Pharmaceuticals

The field of medicinal chemistry is currently witnessing a deuterium rush owing to the remarkable properties of this element as bioisoster of hydrogen atom. Aromatic hydrogen isotope exchange (HIE) is one of the most studied strategies nowadays as it promises to access deuterium-modified drugs directly from their non-labeled parents. While most of the recent studies focus on metal-catalyzed C−H activation strategy, the use of superacidic conditions has been largely overlooked. This study shows that the use of TfOD as reaction medium allows the late-stage polydeuteration of a broad library of pharmaceuticals bearing a wide array of functional groups, complementing existing procedures.     

Continuum modeling for the modulated vibration modes of large repetitive structuresModèle continu pour les modes de vibrations modulés des longues structures répétitives

By homogenization theory, one can predict the vibrations of long repetitive structures in the low frequency range. Beyond this range, many modes have a modulated shape. Based on a multiple scale analysis, a continuum model is presented, that is able to account for this class of modes. This model involves a real coefficient that can be computed from the finite element resolution of problems defined on a few basic cells. An application in 2D elasticity is presented. To cite this article: E.M. Daya et al., C. R. Mecanique 330 (2002) 333–338.     

About macroscopic models of instability pattern formation

Various macroscopic models to describe instability pattern formation are discussed in this paper. They are similar to the Ginzburg–Landau envelope equation, but they can remain valid away from the bifurcation and are based on the technique of Fourier series with slowly varying coefficients. We focus on two questions: the need to take phase changes into account and the boundary conditions to be associated with macroscopic models. The analysis is carried out on the basis of numerical simulations for the problem of a compressed beam on a nonlinear foundation that is quite similar to the well known Swift–Hohenberg equation. The first macroscopic model involves a real envelope so that the phase is assumed to be constant. The second model is also macroscopic and it is a sort of Ginzburg–Landau equation with a complex envelope. The third one follows from a multi-scaled approach with a numerical bridging between the full model near the boundary and a macroscopic model in the bulk.     

Suppression of hysteresis in a forced van der Pol–Duffing oscillator

This paper examines the suppression of hysteresis in a forced nonlinear self-sustained oscillator near the fundamental resonance. The suppression is studied by applying a rapid forcing on the oscillator. Analytical treatment based on perturbation analysis is performed to capture the entrainment zone, the quasiperiodic modulation domain and the hysteresis area as well. The analysis leads to a strategy for the suppression of hysteresis occurring between 1:1 frequency-locked motion and quasiperiodic response. This hysteresis suppression causes the disappearance of nonlinear effects leading to a smooth transition between the quasiperiodic and the frequency-locked responses. Specifically, it appears that a rapid forcing introduces additional apparent nonlinear stiffness which can effectively suppress hysteresis in a certain range of the rapid excitation frequency. This work was motivated by the important issue of controlling and eliminating hysteresis often undesirable in mechanical systems, in general, and in application to microscale devices, especially.     

A computational study of hybrid approaches of metaheuristic algorithms for the cell formation problem

In this paper we solve the 0–1 cell formation problem where the number of cells is fixed a priori and where the objective is to maximize the overall efficiency of a production system by grouping together machines providing service to similar parts into a subsystem (denoted cell). Three different methods are introduced and compared numerically. The first local search method is an implementation of simulated annealing (SA) where the definition of the neighbourhood is specific to the application and requires using a diversification and intensification strategies. The second local search method is an adaptive simulated annealing method where the neighbourhood is selected randomly at each iteration. The procedure is adaptive in the sense that the probability of selecting a neighbourhood is updated during the process. The third method is a hybrid method (HM) of a population-based method and a local search method. To improve the solution obtained with HM, we apply a SA method afterward. The best variants are very efficient to solve the 35 benchmark problems commonly used in the literature.     

Hysteresis suppression for primary and subharmonic 3:1 resonances using fast excitation

Nonlinear Dynamics - We analyze the effect of a fast harmonic excitation on hysteresis and on entrainment area in a forced van der Pol–Duffing oscillator near the primary and the 3:1...     

Hyperfine structure in low-lying levels of PtII,AuII and BiII

Far UV lines in the spectra of PtII, AuII and BiII emitted by a hollow-cathode lamp exhibit Fabry-Perot patterns, which are used for determining the hyperfine structure of the low-lying levels of these three spectra and the isotopic shifts in five lines of PtII. The experimental data are compared with those computed through the relativistic Dirac-Fock method. The effect of spin polarisation is discussed. In the case ofd electrons the Hartree-Fock method with spin polarisation is used for explaining the large ratio between the spin polarisation and relativistic effects.     

Total synthesis and conformational analysis of the antifungal agent (-)-PF1163B

[reaction: see text]. (-)-PF1163B, a new macrocyclic antifungal antibiotic isolated from Streptomyces sp., has been prepared in eight steps from (S)-citronellene. The key step is a ring-closing metathesis reaction of an ester and amide derivative obtained from a substituted N-methyl-l-tyrosine.     

Doppler limited laser spectroscopy on hafnium lines. Part II: Hyperfine structure of odd-parity levels

The hyperfine structure of selected odd-parity levels of the configurations 5d6s ^26p and 5d ^26s6p of I was studied in 10 lines lying in the red spectral region. Hyperfine spectra were obtained by the method of laser induced fluorescence in the plasma of a liquid nitrogen cooled hollow cathode discharge. The observed hyperfine structure constants A and B, together with results from earlier studies were analyzed by means of a parametric method. The interpretation has been carried out based on a refined multiconfigurational fine structure calculation including the main Rydberg series configurations mutually interacting. The set of fine structure parameters as well as the leading eigenvector percentages of levels relevant for this paper are given. The following single electron hfs parameters were deduced for : , ,, for the lowest configuration. Received: 16 November 1998 / Received in final form: 5 February 1999     

Predicting Homoclinic Bifurcations in Planar Autonomous Systems

An analytical method to predict the homoclinic bifurcation in a planar autonomous self-excited weakly nonlinear oscillator is presented. The method is mainly based on the collision between the periodic orbit undergoing the homoclinic bifurcation and the saddle fixed point. To illustrate the analytical predictive criteria, two typical examples are investigated. The results obtained in this work are then compared to Melnikov's technique and to a previous criterion based on the vanishing of the frequency. Numerical simulations are also provided.