Grammian solutions and pfaffianization of a non-isospectral and variable-coefficient Kadomtsev-Petviashvili equation

In this paper, we first present the Grammian determinant solutions to the non-isospectral and variable-coefficient Kadomtsev-Petviashvili (vcKP) equation. Then, by using the pfaffianization procedure of Hirota and Ohta, a new non-isospectral and variable-coefficient integrable coupled system is generated. Moreover, Gramm-type pfaffian solutions of the pfaffianized system are proposed.     

A fast,new method to enhance the enantiomeric purity of non-racemic mixtures: self-disproportionation of enantiomers in the gas antisolvent fractionation of chlorine-substituted mandelic acid derivatives

Gas antisolvent precipitation is a particle formation technique, when typically pressurized carbon dioxide is added to an organic solution resulting in immediate and high oversaturation and precipitation of fine particles. Provided that a reasonable share of the originally dissolved material remains dissolved in the carbon dioxide – organic mixed solvent, these components can be extracted during the washing phase. This method is called gas antisolvent fractionation. Gas antisolvent fractionation has been applied for the first time to enantiomeric enrichment of non-racemic mixtures, and demonstrated on the example of chlorinated mandelic acid derivatives. Due to self-disproportionation of enantiomers, the precipitated solid and the extracted fractions have different enantiomeric excesses if gas antisolvent fractionation is carried out on a non-racemic mixture. However, there is a limit in the enantiomeric excess (ee) that can be achieved correlating strongly with the atmospheric melting eutectic behavior of the compounds. Thus, if initial enantiomeric mixtures have a higher than eutectic ee, a >99% ee can be reached in the crystalline product. The strong correlation between the high-pressure experiments and the atmospheric melting eutectic behavior suggest that despite the very large oversaturation during the antisolvent precipitation, the composition of the products (i.e., the crystalline and the extracted phases) is thermodynamically determined. Technological advantages such as short operational time, or the possibility of controlling the crystal morphology suggest that the development of an efficient technique of enantiomeric purification is possible based on gas antisolvent fractionation.     

Characterization of a South-Levantine bronze sculpture using position-sensitive prompt gamma activation analysis and neutron imaging

Journal of Radioanalytical and Nuclear Chemistry - Complementary neutron-based elemental analytical and imaging methods, i.e. position sensitive prompt gamma activation analysis and neutron...     

Resolution Enhancement in SEA XLOC for Heteronuclear NMR Long-Range Correlation

It is shown how the resolution in SEA XLOC NMR spectra for distinguishing between heteronuclear two- and three-bond correlations for all ¹³C multiplicities can be improved by a modified experiment delivering absorptive profiles in the indirect dimension. The method is demonstrated with applications to ibuprofen and strychnine.     

Asymmetric cyclopropanation reactions catalyzed by carbohydrate-based crown ethers

Optically active cyclopropane derivatives were prepared by a novel, simple and green approach in high enantioselectivities using monosaccharide-based chiral crown ethers as phase transfer catalysts. The crown ethers having d-glucopyranoside, d-mannopyranoside and d-altropyranoside units proved to be efficient catalyst in a few asymmetric phase transfer cyclopropanation reactions. The Michael-initiated ring closure (MIRC) reactions of diethyl bromomalonate with chalcones took place with complete diastereoselectivity and up to 99% ee. Using benzylidenemalononitrile, 2-arylidenemalononitriles, 2-benzylidene-1,3-indandione, substituted 2-benzylidene-1,3-indandiones, 2-arylidene-1,3-indandiones and 2-benzylidene-1,3-diphenyl-1,3-propanediones enantioselectivities up to 92%, 99%, 54% 93%, 89% and 72%, respectively, were achieved, in the presence of chiral lariat ethers derived from different monosaccharides. The absolute configuration of a cyclopropane diester product was determined by a combined CD spectroscopic and theoretical study.     

An improved method for liquid density measurement using NaI(Tl) detector and low-strength source

In the frame of severe accident topic for pressurized water reactor, the physical-chemistry of Ru fission products were experimentally studied to better understand their behavior inside the reactor coolant system in air or air/steam atmospheres. The tests consisted in vaporizing RuO₂ at 1200 °C and the ruthenium oxides are transported through a controlled thermal gradient tube made of quartz or pre-oxidized stainless steel. Results show that the major part up to 95% is deposited along the tube, the remaining part being transported almost under gaseous form attributed to RuO₄. Impact of carrier gas, temperature profile and nature of the tube are discussed.