Atomic force microscopy studies of twins in yttrium-doped barium titanate

Barium titanate is the main constituent of PTC materials and their electric properties are sensitive to microstructure and defects, in atomic scale, that are significantly affected by processing parameters. The microstructure of barium titanate doped with yttrium was investigated using topographic images obtained by AFM in contact mode. The AFM images of barium titanate doped with yttrium showed the effect of large grains with double twins at different (1 1 1) planes.     

Diffusion constant and surface states of positrons in metals

Positron lifetime spectra and angular correlation curves for seven fine-grained powders of Fe, Co, Ni, and W are analyzed. From the lifetime data, the positron diffusion constant in metals atT=300°K was found to beD ₊=(1.0±0.5)×10^?2 cm² sec^?1. Evidence is presented that positrons are trapped in metal surface states.     

Spiraling spectra of geodesic lines in negatively curved manifolds

Given a negatively curved geodesic metric space M, we study the asymptotic penetration behaviour of geodesic lines of M in small neighbourhoods of closed geodesics and of other compact convex subsets of M. We define a spiraling spectrum which gives precise information on the asymptotic spiraling lengths of geodesic lines around these objects. We prove analogs of the theorems of Dirichlet, Hall and Cusick in this context. As a consequence, we obtain Diophantine approximation results of elements of ${\mathbb{R},\mathbb{C}}$ or the Heisenberg group by quadratic irrational ones.     

Counting Horoballs and Rational Geodesics

Let M be a geometrically finite pinched negatively curved Riemannianmanifold with at least one cusp. The asymptotics of the numberof geodesics in M starting from and returning to a given cusp,and of the number of horoballs at parabolic fixed points inthe universal cover of M, are studied in this paper. The caseof SL(2, Z), and of Bianchi groups, is developed. 2000 MathematicsSubject Classification 53C22, 11J06, 30F40, 11J70.     

Identification of different classes of superoxide dismutase in carnation petals

Isoelectric focusing and nondenaturing two-dimensional electrophoresis, followed by an enzymatic characterization involving use of specific inhibitors were applied to identify the different forms of the superoxide dismutase (SOD) extracted from petals of cut carnation. Electrophoresis was carried out either with the crude extract or with fractions obtained after ion exchange chromatography of the extract. Three forms of the SOD were identified (Cu,Zn-SOD, Fe-SOD and Mn-SOD). They have close pI's (4.7 to 4.9) and most of them are composed of several isoforms.     

The Characterization of Natural and Artificial Calcium Carbonates by Adsorption and Immersion Techniques

Nitrogen adsorption isotherms at 77K and enthalpies of immersion into water at 293K have been measured for a series of artificial and natural calcium carbonates. It appears that the external surface area and the micropore system can be fully characterized if a non-porous sample, present in the series, is used as an internal reference. Data are given for the reference isotherm. Owing to high specific interactions, immersion into water only provides information on the total surface area of the samples.     

Groupes géométriquement finis d’automorphismes d’arbres et approximation diophantienne dans les arbres

We introduce a class of non uniform tree lattices, analogous to the fundamental group of geometrically finite negatively curved manifolds. This class contains all the algebraic examples. Given such a tree lattice, we develop, as in [HP2] in the manifold case, a theory of diophantine approximation of points in the boundary of the tree by the parabolic fixed points. We compute approximation constants for some algebraic examples. All results are expressed intrinsically in terms of a natural geodesic flow for a graph of groups. DMA, UMR 8553 CNRS, École Normale Supérieure, 45 rue dUlm, 75230 Paris Cedex 05, France. e-mail:Frederic.Paulin@ens.fr Mathematics Subject Classification (2000): 20E08, 11J61, 20G25, 11J06     

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.