On the relation between electronic and nuclear vibrations via the response matrix derived from semiempirical density functional-based sensitivity analysis

Energetic and physical aspects of the intuitive (mapping) relations between independent (normal) charge polarization patterns and nuclear vibration modes are derived within the atoms-in-molecules (AIM ) electronegativity equalization method (EEM ) formulation of the charge sensitivity analysis (CSA ). The concepts are demonstrated with calculations on homologous series of small organic molecules. © 1995 John Wiley & Sons, Inc.     

Synthesis and optical characterizations of undoped and rare-earth-doped CaF2 nanoparticles

The synthesis of undoped as well as Yb or Er-doped CaF₂ nanocrystals using a reverse micelle method is reported. X-ray powder diffraction and transmission electron microscopy analysis showed that the products were single phased and rather monodispersed with an average particles size around 20 nm. The emission spectra and fluorescence decay times of both Yb³⁺ and Er³⁺ rare earths (RE) ions in CaF₂ nanoparticles are presented. The particles size is increased by heating the as-obtained nanoparticles at different temperatures. The effect of annealing on the optical properties of the two RE ions in CaF₂ is also investigated.     

Toward a better understanding on the mechanism of ortholithiation. Tuning of selectivities in the metalation of meta-anisic acid by an appropriate choice of base

[reaction: see text] If employed in THF at 0 degrees C, LTMP metalates meta-anisic acid at the doubly activated position. In contrast, n-BuLi/t-BuOK deprotonates position C-4 preferentially at low temperature. Functionalization at C-6 requires protection of the C-2 site beforehand. As a result of these findings, a new mechanism is proposed for the heteroatom-directed ortholithiation of aromatic compounds.     

Determination of boron in magnesium oxide by charged particle activation analysis

The determination of boron in magnesium oxide using the¹⁰B/p, /⁷Be,¹⁰B/d, n/⁷Be, and¹⁰B/d, n/¹¹C reactions is described. Lithium interferes the nuclear reactions leading to beryllium-7. Combination of a proton and deuteron irradiation, each followed by measurement of the induced beryllium-7 activity, allows a simultaneous determination of boron and lithium. The¹⁰B/d, n/¹¹C reaction is free from nuclear interferences. The boron concentration ranges from 1.5 to 850 g g^–1. The results obtained by the two methods are in good agreement.Senior Research Associate of the Belgian National Fund for Scientific Research.     

Relating pore structure to activity at the subcrystal level for ZSM-5: an electron backscattering diffraction and fluorescence microscopy study

The catalytic performance of microporous materials such as zeolites is determined not only by the active sites' molecular architecture, but also by the organization of the surrounding pores with varying diameter, shape, and directionality. These pores control transport of reagents and products and induce shape selectivity. Rather than being ideal single crystals, zeolites often have complex 3-dimensional morphologies, comprising intergrowths and various defect types. Here, the underlying pore architecture of the hexagonal facet of an individual zeolite ZSM-5 crystal is successfully determined by electron beam scattering diffraction and is correlated with the initial reactivity toward the acid-catalyzed oligomerization of furfuryl alcohol using polarized fluorescence microscopy.     

An evaluation of the Larson-Doi model for liquid crystalline polymers using recoil

The mesoscopic models for the rheological properties of liquid crystalline polymers proposed by Larson and Doi in 1991 and Kawaguchi and Denn in 1999 are based on phenomenological expressions that describe the evolution of the defect density and the contribution of the “texture” to the stress. In the present work, we attempt to assess some of these assumptions by monitoring how the energy stored in the texture of liquid crystalline materials evolves during shear flows. For that purpose, strain recovery is measured as a function of the applied strain for flow reversal and intermittent flow. Solutions of poly-benzylglutamate in m-cresol, hydroxypropylcellulose in water and a nematic surfactant solution are used as model systems. Although the behaviour is described qualitatively by the model, discrepancies between the predictions and the experiments are observed, especially when the shear history includes rest periods. Received: 14 July 1999 /Accepted: 30 August 1999