Crystallization and Transformation Mechanism of Calcium Carbonate Polymorphs and the Effect of Magnesium Ion

The crystallization of calcium carbonate was carried out by mixing CaCl(2) and Na(2)CO(3) solutions. The morphology of precursor formed prior to the nucleation of the polymorphous crystals (calcite and vaterite) varies depending on the feed concentration. The faster nucleation rate of polymorphous crystals in 0.2 mol/L than in 0.05 mol/L solution results in the prompt disappearance of the precursor at 0.2 mol/L. In 0.05 mol/L solutions the lifetime of the precursor is relatively long. The crystallization fraction of vaterite increases with the feed concentration and decreases with the addition rate of Na(2)CO(2) solution. Vaterite takes on the various morphologies of the aggregates of the primary flocculation body (spherulite) depending on the crystallization conditions. Vaterite transforms to calcite by a direct solution-mediated mechanism. During crystallization the concentration attains a stationary value, which increases with the feed concentration and decreases with the addition rate of Na(2)CO(2) solution. This may be due to the crystal size decrease expected from the Gibbs-Kelvin equation. Magnesium ion suppresses the transformation of vaterite by inhibiting the growth of the calcite. Magnesium ion is selectively included in calcite and causes the increase of the attained concentration and the remarkable change in the morphology of calcite especially in 0.05 mol/L solution. Copyright 2001 Academic Press.     

Hydrohalogenation of 1- and 2-vinylindazoles

The electronic absorption spectra of 1-vinyl- and 2-vinylindazoles and their protonated forms were analyzed. The spectra were subjected to quantum-chemical calculation within the Pariser-Parr-Pople (PPP) -electron approximation, and the thermodynamic parameters of the reaction of indazoles with phenol (K_as and H) were calculated. It is shown that 1-vinylindazole adds hydrogen halides to the nitrogen atom or the double bond of the vinyl group, depending on the reaction temperature. The formation of hydrohalides is characteristic for 2-vinylindazole.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 952–956, July, 1982.     

Fluorescence spectra,fluorescence quantum yields and fluorescence lifetimes of polymers having trans-1,2-dicarbazolylyclobutane or carbazolyl group

Quantum yields, lifetimes and shapes of fluorescence from polymers containing the trans-1,2-dicarbazolylcyclobutane (DCZB) or carbazolyl structures were studied in N,N-dimethylformamide. No sandwich-type excimer formation was observed for DCZB polymers. The so-called second excimer observed in poly(9-vinylcarbazole) might also be produced in poly(9-ethyl-3-vinylcarbazole).     

Fluorescence spectra and their temperature dependence of amorphous anthracene films doped with naphthacene

Fluorescence spectra and their temperature dependence of amorphous anthracene films doped with naphthacene were observed. An amorphous film was prepared by vacuum evaporation technique on a quartz plate cooled down to 30–40°K. The obtained results were discussed in relation to the structural change in the amorphous film.     

A convenient synthesis of 1-bromoolefins and acetylenes by a chain extension of aldehydes

Aldehydes are easily converted to 1-bromoolefins or terminal acetylenes by the use of Wittig reaction of bromomethylenetriphenylphosphorane which is prepared from bromomethyltriphenylphosphonium bromide with potassium tert-butoxide.     

Unsupervised Image Segmentation Using Hierarchical Clustering

In the analysis of a medical image database aimed at formulating useful knowledge for image diagnosis requires an unsupervised image processing technique without preconceived knowledge. In this paper, we propose a method for unsupervised image segmentation, which is suitable for finding the features contained in an image. A small region around each pixel is considered as a pattern vector, and the set of pattern vectors acquired from the whole image is classified using the hierarchical clustering technique. In hierarchical clustering, the classification of pattern vectors is divided into two clusters at each node according to the statistical criterion based on the entropy in thermodynamics. Results of the test image generated by the Markov random field (MRF) model and real medical images photomicrographs of a colon tumor are shown.     

Density-fluctuation-induced swelling of polymer thin films in carbon dioxide

We report an anomalous swelling of polymer thin films in carbon dioxide (CO(2)) which is associated (in both locus and form) with the density fluctuation ridge that forms along the extension of the coexistence curve of gas and liquid in the P-T phase diagram. Neutron reflectivity results showed that CO(2) could be sorbed to a large extent ( approximately 60%) in thin polymer films even when the bulk miscibility of the polymer with CO(2) is very poor. The anomalous swelling is found to scale with the polymer radius of gyration (R(g)) and extends to a distance approximately 10 R(g).     

Universal function for the brilliance of undulator radiation considering the energy spread effect

Angular and spatial profiles of undulator radiation have been investigated to derive a universal function that evaluates the brilliance of undulator radiation and takes into account the effects of electron beam emittance and energy spread. It has been found that the effects of energy spread on the angular divergence and source size can be expressed by simple analytic expressions, and a universal brilliance function has been derived by convolution with the electron beam distribution functions. Comparisons with numerical results have been carried out to show the validity and applicability of the universal function.