Influence of pH and microwave calcination on the morphology of KGd(WO<Subscript>4</Subscript>)<Subscript>2</Subscript> particles derived by Pechini Sol–Gel method

KGd(WO₄)₂ (KGW) particles were synthesized at 3.5, 5.5 and 7.5 pH values by Pechini polymeric complex sol–gel method using potassium nitrate, gadolinium nitrate, ammonium paratungstate, citric acid and ethylene glycol as starting materials. Deionized water was used as solvent. Polymeric precursor gel was formed with citric acid as complexing agent and ethylene glycol as binder. Synthesized gel was analyzed by FT-IR spectroscopy. Prepared precursor gels were further annealed using resistive and microwave processes at 550 and 700 °C, respectively. The properties of heat treated samples were characterized by powder XRD, FT-IR, Raman and SEM analysis to understand the crystallinity, organic liberation, tungstate ribbon formation and surface morphology, respectively. The phase formation and different phases of intermediate oxides in pre-fired samples were investigated by powder XRD. Organic liberation in the samples in relation to temperature, and the carbon content in the pre-fired powder was analyzed using FT-IR spectrum. Raman spectrum reveals the formation of tungsten ribbons as well as the quality of the samples. The morphological changes at different synthesis conditions were observed with SEM micrographs.     

Misting of non-Newtonian liquids in forward roll coating

Misting of liquids in forward roll coating is a problem under certain conditions. The relaxation time is known to influence misting but the fundamental mechanisms are not clear. A new mechanism for misting of dilute non-Newtonian liquids was proposed based on visualizations with a high-speed camera. With these liquids, filaments were created which sometimes transformed into beads-on-string structures and the beads were ejected as mist droplets when the structures broke. Misting was quantified by measuring sizes of the generated droplets, their count and mass concentration. The measurements were related to elasticity of the solutions through their relaxation times. Small levels of elasticity reduce the amount of misting, but higher levels lead to an increase.     

Asymmetric synthesis of (4S,5S)-2-oxo-4-phenyloxazolidine-5-carboxylic acid using a 1,2-addition of PhMgBr to an N-sulfinimine derived from (R)-glyceraldehyde acetonide and (S)-t-BSA

We report an asymmetric synthesis of (4S,5S)-2-oxo-4-phenyloxazolidine-5-carboxylic acid via stereoselective addition of phenylmagnesium bromide (PhMgBr) to an N-sulfinimine derived from (R)-glyceraldehyde acetonide. (S)- and (R)-Glyceraldehyde acetonides, important chiral synthons in synthetic organic chemistry, are prepared from the corresponding epichlorohydrin using an identical synthetic methodology.     

Spectroscopic investigations of 1.06 μm emission in Nd-doped alkali niobium zinc tellurite glasses

Thermal, structural and optical properties of Nd³⁺ ions in tellurite glass (TeO₂-ZnO-Na₂O-Li₂O-Nb₂O₅) have been investigated. Differential thermal analysis revealed reasonably good forming tendency of the glass composition. FTIR spectra were used to analyze the functional groups present in the glass. Judd-Ofelt intensity parameters were derived from the absorption spectrum and used to calculate the radiative lifetime, branching ratio and stimulated emission cross-section of the ⁴F_3/2→⁴I_9/2, _{11/2, 13/2} transitions. The quantum efficiency of the ⁴F_3/2 level is comparable as well as higher than the typical value of the other tellurite based glasses. The decay from the ⁴F_3/2 level is found to be single exponential for different concentrations of Nd³⁺ ions with a shortening of lifetime with increasing concentration. The experimental values of branching ratio and saturation intensity of ⁴F_3/2→⁴I_11/2 transition indicate the favourable lasing action with low threshold power.     

On the parametrization of the toxicity of organic chemicals to Tetrahymena pyriformis. The problem of establishing a uniform activity

In this report we illustrate the importance of making an effort to ensure that all of the dependent variables in a QSAR are associated with one mechanism of action. If this cannot be established, it will not be possible to compare the QSAR with others acting on different biological systems. That is, such information cannot be used to develop a science of chemical-biological interactions. A study of the action of a large set of phenols acting on Tetrahymena pyriformis made by Cronin and Schultz is analyzed to illustrate the problem.     

Highly facile and stereoselective intramolecular [2 +2]photocycloadditions of bis(alkenoyl)ketenedithioacetals

The conformational change induced by the introduction of a ketenedithioacetal moiety at C-4 of 1,7-substituted-1,6-heptadiene-3,5-diones results in favorable spatial relationships between the alkenoyl groups to effect efficient intramolecular cycloadditions: irradiation of bis(alkenoyl)ketenedithioacetals in solution leads to facile and stereospecific intramolecular [2 + 2] photocycloadditions resulting in the formation of substituted bicyclo[3.2.0]heptane-2,4-diones, the observed conformational rigidity of which is attributed to the push-pull character of the ketenedithioacetal group.     

Analysis of finite element methods for second order boundary value problems using mesh dependent norms

This paper presents a new approach to the analysis of finite element methods based onC ⁰-finite elements for the approximate solution of 2nd order boundary value problems in which error estimates are derived directly in terms of two mesh dependent norms that are closely ralated to theL ₂ norm and to the 2nd order Sobolev norm, respectively, and in which there is no assumption of quasi-uniformity on the mesh family. This is in contrast to the usual analysis in which error estimates are first derived in the 1st order Sobolev norm and subsequently are derived in theL ₂ norm and in the 2nd order Sobolev norm — the 2nd order Sobolev norm estimates being obtained under the assumption that the functions in the underlying approximating subspaces lie in the 2nd order Sobolev space and that the mesh family is quasi-uniform.     

The finite element method with Lagrangian multipliers

Summary The Dirichlet problem for second order differential equations is chosen as a model problem to show how the finite element method may be implemented to avoid difficulty in fulfilling essential (stable) boundary conditions. The implementation is based on the application of Lagrangian multiplier. The rate of convergence is proved.This paper was supported by the Atomic Energy Commission under Contract No. AEC AT (40-1) 3443/4.