Base-mediated intermolecular sp2 C-H bond arylation via benzyne intermediates

A transition-metal-free method for arylation of heterocycle and arene carbon-hydrogen bonds by aryl chlorides and fluorides has been developed. The reactions proceed via aryne intermediates and are highly regioselective with respect to the C-H bond coupling component.     

Unirationality of Ueno-Campana’s threefold

We shall prove that the threefold studied in the paper “ Remarks on an Example of K. Ueno” by F. Campana is unirational. This gives an affirmative answer to a question posed in the paper above and also in the book by K. Ueno, “Classification theory of algebraic varieties and compact complex spaces”.     

On a generalized X-ray transform and a new method for defect detection using the medium electronic density

We consider a generalization of the X-ray transform which maps a function $\text{f(}\text{V}\text{)}$ defined in $\text{R}{}^3$ onto its integrals over a pair of parallel straight lines and not over a single straight line as in a conventional X-ray transform. This new transformation arises from the image formation by double Compton-scattered radiation in transmission imaging. The problem of reconstructing $\text{f(}\text{V}\text{)}$ from its line pair integrals is formulated as an inverse problem for this generalized X-ray transform. Exploiting the line duality in the new transformation, we derive an equivalent nonlinear integral equation for $\text{f(}\text{V}\text{)}$. Special classes of solutions can be constructed. They may serve as basis for a new method of defect detection, using the medium electronic density, in non-destructive inspection. To cite this article: M.K. Nguyen, T.T. Truong, C. R. Acad. Sci. Paris, Ser. I 336 (2003).     

Acoustic wave origin in excimer lasers

Received: 2 May 1996/Revised version: 9 October 1996     

Some remarks on Yang-Baxter algebras

We point out the existence of an alternative algebraic structure in Yang-Baxter algebra with trigonometric R-matrix, which appears to be the generalization of the Yangian in Yang-Baxter algebras with rational R-matrix and which is described most naturally by q-commutators. Some properties are presented, in particular in the case of the well-known symmetric six-vertex model. Received: 13 February 1998 / Revised: 16 March 1998 / Accepted: 17 April 1998     

Random walks generated by area preserving maps with zero Lyapounov exponents

We study the asymptotic limit distributions of Birkhoff sums S_n of a sequence of random variables of dynamical systems with zero entropy and Lebesgue spectrum type. A dynamical system of this family is a skew product over a translation by an angle α. The sequence has long memory effects. It comes that when α/π is irrational the asymptotic behavior of the moments of the normalized sums S_n/f_n depends on the properties of the continuous fraction expansion of α. In particular, the moments of order k, , are finite and bounded with respect to n when α/π has bounded continuous fraction expansion. The consequences of these properties on the validity or not of the central limit theorem are discussed.     

Fluorescence evidence for cholesterol regular distribution in phosphatidylcholine and in sphingomyelin lipid bilayers

Our previous studies indicated that sterols (including cholesterol and dehydroergosterol) can be regularly distributed into hexagonal superlattices in the plane of liquid-crystalline phosphatidylcholine bilayers. It was suggested that regular and irregular regions coexist in the membrane. In the present study, we report supporting evidence for our sterol regular distribution model. We have examined the fractional concentration dependencies of dehydroergosterol (a naturally occurring cholesterol analogue) fluorescence intensity and lifetime in various phosphatidylcholine and sphingomyelin bilayers. Fluorescence intensity and lifetime dips have been observed at specific sterol mole fractions. At those mole fractions, the acrylamide quenching rate constant of dehydroergosterol fluorescence reaches a local maximum. Those mole fractions match the critical sterol mole fractions at which sterol molecules are expected to be regularly distributed into hexagonal superlattices. The results support the idea that the sterols in the regular region are embedded in the bilayer less deep than those in the irregular regions. We have also examined the fractional cholesterol concentration dependencies of diphenylhexatriene (DPH) fluorescence intensity, lifetime, and polarization in DMPC vesicles. DPH fluorescence intensity and polarization also exhibit distinct dips and peaks, respectively, at critical sterol mole fractions for hexagonal superlattices. However, DPH lifetime changes little with sterol mole fraction. As a comparison, the fluorescence properties of DHE and DPH behave differently in response to the formation of sterol regular distribution. Furthermore, finding evidence for sterol regular distribution in both phosphatidylcholine and sphingomyelin membranes raises the possibility that sterol regular distribution may occur within phospholipid/cholesterol enriched domains of real biological membranes.     

Numerical prediction of the thermal conductivity of fibers

The need to determine the thermal conductivity of fibers for design purposes of new composite materials and the inherent difficulties in the direct measurement of the thermal conductivity of fibers motivated the present work due to its importance for energy conservation purposes. In this work, a correlation formula is developed to predict the thermal conductivities of fiber as function of the effective thermal conductivity of a fiber-reinforced composite laminates and their constituents which are easy to measure. The parallel and series thermal models of composite walls have been utilized in developing this correlation equation. The coefficients of this formula can be given as functions of the voids volume fraction for each fiber to resin volume ratio considered. The validity of the models is verified through finite element analysis. This model also shows excellent agreement with the available experimental values.