Differential calorimetric enthalpies of adsorption ofp-xylene andm-xylene on y faujasites at 25°C

The differential enthalpies of adsorption ofp-xylene andm-xylene on NaY, KY and BaY zeolites were measured by isothermal calorimetry coupled with isothermal volumetry at 25C. Whatever the zeolite, the enthalpies of adsorption ofp-xylene andm-xylene at low filling were of the same order of magnitude. They did not show significantly the effect of the dipolar moment ofm-xylene. Their absolute values varied in the sequence Q ₀(pX/NaY)<Q ₀(pX/KY) =Q ₀(mX/KY)<Q ₀(pX/BaY)<Q ₀(mX/NaY) =Q ₀(mX/BaY)During the adsorption of the third molecule of xylene per -cage, BaY zeolite exhibited specific behaviour: the differential enthalpies of adsorption decreased with the filling of the -cages in such a way that they became lower than those of the other two zeolites. Some arguments concerning the structures of the zeolite and xylene molecules can explain such behaviour. Whatever the zeolite, the adsorption capacity of the -cages was 3.5 molec.^–1. For relative pressures ranging from 0.2 to 0.5, an additional adsorption of about 0.1 molec.^–1 occurred on the external surface.     

Scaling Limits of Bipartite Planar Maps are Homeomorphic to the 2-Sphere

We prove that scaling limits of random planar maps which are uniformly distributed over the set of all rooted 2k-angulations are a.s. homeomorphic to the two-dimensional sphere. Our methods rely on the study of certain random geodesic laminations of the disk. Received: December 2006, Revision: August 2007, Accepted: October 2007     

Manatee position estimation by passive acoustic localization

Passive sound source localization with sensor arrays is based on the estimation of the time difference of arrival (TDOA), and precise TDOA is required to achieve accurate position estimation. For a majority of practical localization systems (based on TDOA estimation with four sensors in two dimensions), only three time delays are computed to determine the location of interest. This paper presents an approach to determine the position of a manatee by using four hydrophones and all the combinations of the TDOAs available. With four hydrophones, six TDOAs are computed and then combined three by three to get 20 possible points for each position to estimate. Experimental results using the Hilbert envelope peak technique to estimate the TDOAs and the least square method to estimate the position are presented. For the tests conducted it is shown that for a manatee call having a high signal-to-noise ratio, the individual position estimated for each of the 20 combinations of TDOAs lies on a straight line, providing a good estimation of the direction of arrival approximately 85% of the time. However, a good estimation of the position is obtained for a manatee near the hydrophone array approximately 55% of the time.     

Preparation of 5-Hydroxymethyl-pyrimidine Based Nucleosides: A Reinvestigation

5-Hydroxymethyl-pyrimidine-based nucleobases have attracted attention in the last years due to their important role in gene regulation. It prompted the development of efficient routes to the corresponding nucleoside building blocks for further incorporation into oligonucleotides. Several pathways have been employed in recent years to access properly protected 5-hydroxymethyl-pyrimidine based nucleosides, including hydroxymethylation of 2’-deoxyuridine, radical bromination of thymidine followed by bromine substitution, or carbonylative coupling through Stille conditions starting from 5-iodo-2’-deoxyuridine. In this study, we review the different approaches currently used to introduce the 5-hydroxymethyl moiety, we reinvestigate some of them, and finally, we propose an alternative route based on the oxidation of the methyl of thymidine followed by its reduction that allows access to protected 5-hydroxymethyl-2’-deoxyuridine in a simple way with good yields. Finally, we present some examples of application including the synthesis of base J and 5-azidomethyl-2’-deoxyuridine.     

Diophantine approximation for negatively curved manifolds

Let M be a geometrically finite pinched negatively curved Riemannian manifold with at least one cusp. Inspired by the theory of Diophantine approximation of a real (or complex) number by rational ones, we develop a theory of approximation of geodesic lines starting from a given cusp by ones returning to it. We define a new invariant for M, theHurwitz constant of M. It measures how well all geodesic lines starting from the cusp are approximated by ones returning to it. In the case of constant curvature, we express the Hurwitz constant in terms of lengths of closed geodesics and their depths outside the cusp neighborhood. Using the cut locus of the cusp, we define an explicit approximation sequence for a geodesic line starting from the cusp and explore its properties. We prove that the modular once-punctured hyperbolic torus has the minimum Hurwitz constant in its moduli space. Received: 24 October 2000; in final form: 10 November 2001 / Published online: 17 June 2002     

Dynamique sur le rayon modulaire et fractions continues en caracteristique p

Let be the field of formal Laurentseries in X^–1 over the finite field k, and let A be thering of polynomials in X over k. One of the main results ofthe paper is to give a natural coding of the (discrete) geodesicflow on the quotient of the Bruhat–Tits tree of PGL₂() by PGL₂(A), using the continued fractionexpansion of the endpoints of the geodesic lines in (the spaceof ends of identifies with ₁().In particular, the invariance of the Haar measure by the Artintransformation can be deduced from the invariance of the Bowen–Margulismeasure by the geodesic flow.     

Automatic fitting procedures for EPR spectra of disordered systems: matrix diagonalization and perturbation methods applied to fluorocarbon radicals

Two types of automatic fitting procedures for EPR spectra of disordered systems have been developed, one based on matrix diagonalization of a general spin Hamiltonian, the other on 2nd order perturbation theory. The first program is based on a previous Fortran code complemented with a newly written interface in Java to provide user-friendly in and output. The second is intended for the special case of free radicals with several relatively weakly interacting nuclei, in which case the general method becomes slow. A least squares' fitting procedure utilizing analytical or numerical derivatives of the theoretically calculated spectrum with respect to the g- and hyperfine structure (hfs) tensors was used to refine those parameters in both cases. 'Rigid limit' ESR spectra from radicals in organic matrices and in polymers, previously studied experimentally at low temperature, were analyzed by both methods. Fluorocarbon anion radicals could be simulated, quite accurately with the exact method, whereas automatic fitting on, e.g. the c-C(4)F(8)(-) anion radical is only feasible with the 2nd order approximative treatment. Initial values for the (19)F hfs tensors estimated by DFT calculations were quite close to the final. For neutral radicals of the type XCF(2)CF(2)* the refinement of the hfs tensors by the exact method worked better than the approximate. The reasons are discussed. The ability of the fitting procedures to recover the correct magnetic parameters of disordered systems was investigated by fittings to synthetic spectra with known hfs tensors. The exact and the approximate methods are concluded to be complementary, one being general, but limited to relatively small systems, the other being a special treatment, suited for S=1/2 systems with several moderately large hfs.