Hyperfine interactions in amorphous and nanocrystalline Fe80Ti7Cu1B12 alloy

⁵⁷Fe Mössbauer spectroscopy is used to elucidate the nature of the hyperfine interactions present in amorphous and nanocrystalline forms of Fe₈₀Ti₇Cu₁B₁₂ alloy. Two mutually independent distributions of hyperfine fields and one sextet of Lorentzian lines are employed to reproduce the broad (atoms in amorphous rest and interface zone) and narrow (ordered) parts of the spectra, respectively. The presented conclusions are derived from three-dimensional mapping of the hyperfine field distributions corresponding to both amorphous and interfacial spectral components. The individual distributions are decomposed into Gaussian components which characterize different types of hyperfine interactions.     

Computer-aided spectral assignment in nuclear magnetic resonance spectroscopy

The proton-carbon correlation spectra, HMBC (heteronuclear multiple bond correlation) and HMQC (heteronuclear multiple quantum correlation), respectively, provide direct and remote connectivity information with high sensitivity. Their combination enables carbon-carbon proximity relationships to be deduced, which are formally identical to those produced by a fictitious INADEQUATE-2D experiment, where correlations would be established exclusively between atoms linked by one or two bonds. The CASA program uses these relationships, as well as DEPT spectra and elementary chemical-shift considerations to assign the ¹³C spectrum of a compound if its structure is known or assumed. If the structure conflicts with the experimental data, no assignment is produced. The CASA program serves as an aid to either spectral assignment or structural elucidation.     

On Small Sumsets in (ℤ/2ℤ)<Superscript><Emphasis Type="Italic">n</Emphasis></Superscript>

It is proved that any subset of (/2)ⁿ, having k elements, such that (with c<4), is contained in a subgroup of order at most u^–1k where u=u(c)>0 is an explicit function of c which does not depend on k nor on n. This improves by a radically different method the corresponding bounds deduced from a more general result of I. Z. Ruzsa.     

Propriété de stabilité de la fonction extrémale relative

Nous donnons une caractérisation des domaines DX pour lesquels la fonction extrémale relative ^*(,E,D) a la propriété de stabilité pour tout ED, i.e. lim _k^*(,E,D _k )=^*(,E,D), ED. Ensuite, nous étudions la relation entre cette propriété et les enveloppes pluripolaires. Nous concluons par quelques remarques sur la propriété de stabilité lim _k^*(,E _k ,D)=^*(,E,D).     

Kinematic regimes of convection at high Prandtl number in a shallow cavityRégimes cinématiques de la convection à haut nombre de Prandtl dans une cavité allongée.

We consider free convection in a horizontal shallow cavity with different end temperatures, filled with a high Prandtl number fluid. From scaling analysis, we find two kinematic regimes resulting from the competition of heat transfer by conduction and by convection. Numerical simulations realized for a large range of Rayleigh number and aspect ratio confirm the phenomenological analysis and provide the threshold between the two regimes. The conductive and convective regimes occur at $\mathit{Ra}{A}^2$ smaller and larger than 443 respectively, where Ra is the Rayleigh number and A is the aspect ratio. In the convective regime, the characteristic velocity is independent of depth of the cavity. To cite this article: J.-M. Flesselles, F. Pigeonneau, C. R. Mecanique 332 (2004).     

Catalytic aziridination of olefins and amidation of thioanisole by a non-heme iron complex

A non-heme iron complex catalyses the aziridination of various olefins and the amidation of thioanisole in good yields at the expense of an aryl iodinane.     

Rheooptical study of the early stages of flow enhanced crystallization in isotactic polypropylene

The effect of a shear flow on the early stages and the kinetics of isothermal crystallization of an isotactic polypropylene has been studied experimentally. In the shear rate region where crystallization proceeds through point-like precursors, the magnitude of the shear rate, the shearing time as well as the instant in time at which the deformation starts have all been varied, in combination with rheooptical measurements. These include depolarized light intensity and birefringence. In agreement with previous work, above a critical shear rate and a critical shearing time, the crystallization kinetics are enhanced. Somewhat surprisingly, below a characteristic time, t_0,max, the kinetics are not affected by the instant in time at which flow is applied or stops. As long as flow takes place before this critical dwell time, only the shearing time and primarily the magnitude of the shear rate seem to matter. When flow is started only after t_0,max, its effect to accelerate crystallization kinetics becomes less efficient. The range over which the different parameters have an effect have been compared to the rheological relaxation times and to the measurements of global chain extension. To investigate the effects of flow on the early stages in more detail, time resolved Small-Angle Light Scattering experiments were used to detect changes in the density and orientation fluctuations. Measurements explicitly compare the effect of temperature and shear flow on the kinetics and the intensity of the density fluctuations.Electronic supplementary material to this paper can be obtained by using the Springer Link server located at