Large deformations during the coalescence of fluid interfaces

Surface forces and shape changes were simultaneously measured during the approach and coalescence of two liquid-liquid and liquid-air interfaces. Large normal and lateral deformations were observed that are nevertheless consistent with a simple theoretical analysis of the long-range effects of short-range attractive van der Waals forces. The results imply that two fluidlike structures such as liquid droplets and soft biological cells can sense each other at much larger separations than previously assumed based on criteria taken from the interactions of hard particles.     

A tetranuclear Cr(III)Ni(II)3 cyano-bridged complex based on M(tacn) derivative building blocks

The reaction of Cr(Bztacn)(CN)3 (Bztacn is 1,4,7-trisbenzyl-1,4,7-triazacyclononane) with Ni(iPrtacn)Cl2 (iPrtacn is 1,4,7-trisisopropyl-1,4,7-triazacyclononane) affords a CrNi3 tetranuclear complex. Variable temperature and magnetization versus field measurements show a S = 9/2 ground state and an appreciable magnetic anisotropy with a negative D(9/2) value equal to -0.54 cm(-1). Magnetization studies on one single crystal using a micro-SQUID show a fast tunneling process at zero field at very low temperature.     

L'électron habillé non relativiste dans un champ magnétique

We consider a nonrelativistic electron interacting with a classical magnetic field pointing along the $x_3$-axis and with a quantized electromagnetic field. Because of the translation invariance along the $x_3$-axis, we consider the reduced Hamiltonian associated with the total momentum along the $x_3$-axis and, after introducing an ultraviolet cutoff and an infrared regularization, we prove that the reduced Hamiltonian has a ground state if the coupling constant and the total momentum along the $x_3$-axis are sufficiently small. Finally, we determine the absolutely continuous spectrum of the reduced Hamiltonian and we prove that the renormalized mass of the electron is greater than its bare one. To cite this article: L. Amour et al., C. R. Acad. Sci. Paris, Ser. I 340 (2005).     

A new method for the absolute measurement of piezoelectric coefficients on thin polymer films

A new quasistatic method to measure piezoelectric coefficients on thin polymer films is presented. This method is based on a combined experimental/analytical approach, where small polymer samples (6 mm x 3 mm x 110 microm) are encapsulated in a soft silicone rubber and an electric field is applied across their thickness (3-direction). Strains are measured optically along three perpendicular directions using a laser Doppler vibrometer, and the experimental measurements are used in a Rayleigh-Ritz energy minimization procedure implemented symbolically in MATHCAD, which yields the absolute piezoelectric coefficients d(3ii). These measured coefficients are material properties of the polymer and do not depend on the specific boundary conditions of the problem. The validity of the method is established using the ATILA finite element code. Experimental values of d(311), d(322), and d(333) obtained for polyvinylidene fluoride (PVDF) at room temperature, in the frequency range 500-2000 Hz, are presented and compared with existing data; excellent agreement is found. The extension of the method to the determination of electrostrictive coefficients on soft polyurethane materials is introduced.     

Acrylnitril-Copolymerisationen. 5. Mitt. Anomale Kinetik und Sekundärreaktionen bei der Copolymerisation mit Vinylchlorid

Ohne Zusammenfassung     

NMR diffusion of hyperpolarised 3He in aerogel: a systematic pressure study.

Diffusion of hyperpolarised 3He in a silica aerogel sample with 98% porosity was measured by NMR, and systematically studied as a function of pressure P in the range 20 mbar -1 bar. Spin-echo amplitudes, recorded with pulsed gradients in the usual CMPG sequence, follow a monoexponential decay, and the decay rate varies quadratically with the gradient intensity: thus the apparent diffusion coefficient of the gas D can be evaluated. Our results show a power-law (1/D proportional to P(0.55)), which could be consistent with a fairly broad mean free path distribution, implying some inhomogeneity in the aerogel structure. We have observed a spatial non-uniformity of D, and some deviation to the quadratic dependence of the decay rate with the gradient intensity, possibly related to sample structure inhomogeneity.     

The oxidized form of nicotin­amide adenine dinucleotide

The crystal structure of the free acid form of NAD⁺ tetrahydrate (nicotin­amide adenine dinucleotide tetrahydrate or 3‐carbamoyl‐1‐β‐d ‐ribo­furan­osyl­pyridinium hydro­xide 5′‐ester with adenosine 5′‐pyrophosphate inner salt tetrahydrate, C₂₁H₂₇N₇O₁₄P₂·4H₂O) has been determined at 100 K. NAD⁺ is the coenzyme of several protein families and plays a dominant role in biological redox processes. In this study, the mol­ecule shows a different conformation from the one usually found in holoenzyme complexes.     

Vinyl Chloride-Vinylidene Chloride Copolymerization in Strong Donor Solvents: A New Interpretation of Structural Defects

Penultimate effects detected on the vinylidene chloride-ended radical in the vinylidene chloride-vinyl chloride copolymers prepared in thtrahydrofuran had previously been interpreted in terms of head-to-head addition. But new ¹H-NMR analysis of the homopolymers and copolymers synthesized in proton-donor and inert solvents suggest these effects, giving abnormal structures, might be due to the proton-transfer reactions, particularly in strong proton-donor solvents. Chain transfer reactions have been found degradative, so the overall polymerization rate is drastically decreased.