Commensurability oscillations in NdBa2Cu3Oy single crystals

Commensurability between inter-vortex distance and crystal lattice constant is investigated by angular dependent magnetization in very pure twinned and twin-free NdBa₂ Cu₃ O_y single crystals. With increasing temperature the incommensurate states split up and become finally commensurate with half the vortex distance. These new commensurate states are related to a substructure of the intrinsic pinning potential within the unit cell and discussed with respect to temperature, field, anisotropy, and twin structure.     

Determining a 'safe' high-mass limit in matrix-assisted laser desorption/ionisation time-of-flight mass spectra of coal derived materials with reference to instrument noise

Three methods for determining a 'safe' estimate for high-mass limits of MALDI spectra of coal derived liquids were explored, using a sample of coal-tar pitch and its pyridine-insoluble fraction. Co-addition of increasing numbers of single-shot spectra (10, 30, 50 and 100 pulses) showed visually observable reductions in noise levels, consistent with robust and statistically meaningful signals. Three separate types of post-acquisition calculation were used to identify high-mass limits of the spectra. (i) A literature method indicated high-mass limits similar to those observed visually-as a shift from baseline at the highest masses, nearly 350 000 u for the coal tar pitch and about 390 000 u for its pyridine insoluble fraction. (ii) Comparing instrument signal with pre-selected multiples of the standard deviation, upper mass estimates of between 40-60 000 u for the coal-tar pitch and about 95 000 u for its pyridine-insoluble fraction were found. (iii) Calculation of the slope was used to identify 'lift-off' of the spectrum from baseline. The angle between the smoothed spectrum and the baseline was matched to a pre-selected value (e.g. 0.5 degrees and 1 degrees ). However, the arbitrary specification of the key parameter did not establish this last method on a firm basis. The choice of a criterion for estimating high-mass limits of MALDI spectra remains a semi-quantitative procedure; a reasonably conservative high-mass limit may be estimated by comparison of signal with five times the standard deviation. However, evaluation of size exclusion chromatograms of the present samples using polystyrene standards suggests that molecular mass distributions of pitch samples arrived at by MALDI mass spectrometry are, at least partly, determined by the limitations of available instruments. Copyright 1999 John Wiley & Sons, Ltd.     

Perspectives in the development of the theory of spark-source and laser-plasma source mass-spectrometry

The processes of substance evaporation and atom ionization under different conditions of spark discharge or laser radiation are considered. It is shown that the dependence of the relative sensitivity coefficients on the properties of an element can be presented as the product of two exponents with parameters proportional to the atomization energies and first ionization potentials of the element. Differences in matrix composition and conditions influencing a sample in the ion source are considered by means of introducing two fitting parameters-atomization and ionization "temperatures"-into these exponents. Experiments carried out with the help of mass-spectrometers with spark and laser ion sources have corroborated the validity of the suggested quasi-equilibrium model and shown the possibility of its application for the improvement of the accuracy of analysis without use of standards as well as for checking the stability of experimental conditions in the process of analysis with standard samples.     

Differential inclusions with Hukuhara derivative

We introduce two types of differential inclusions with Hukuhara derivative and consider properties of these inclusions. For differential inclusions of the second type, we give different definitions of a solution, prove theorems on the existence of an ordinary solution, and establish the compactness of the set of these solutions. __________ Translated from Neliniini Kolyvannya, Vol. 10, No. 2, pp. 229–246, April–June, 2007.     

Mechanism of Ferromagnetic Ordering of Mn Chains in CaMnGe2O6 Clinopyroxene

JETP Letters - The electronic and magnetic properties of clinopyroxene CaMnGe2O6 were studied using density function calculations within the GGA + U approximation. It is shown that anomalous...     

Syntheses and reactions of some fluorinated dienes,cyclobutenes and furans

There are many reports¹ of the pyrolysis of fluorinated organic compounds, including the defluorination of cyclic fluorocarbons over iron to give aromatic compounds. Extending this technique we have investigated the flow pyrolysis of some readily accessible unsaturated fluorocarbons, such as I, II, and III, and found these to be synthetically

useful routes to fluorinated dienes, cyclobutenes, and furans. Pyrolyses were carried out using a nitrogen flow over platinum, iron or caesium fluoride heated at 430–700°. The various products can all be rationalized in terms of intermediate allylic radicals, and the solid substrate influences which allylic radicals are formed.We are also investigating the chemistry of those now accessible compounds, such as IV, V, and VI, and some of the preliminary results are described.

For example the fluoride ion induced dimerisation of IV gave two major products VII and VIII via a particular interesting mechanism.

     

ChemInform Abstract: The Ground-State Potential Energy Surface of Diazene

has been studied by using a complete active space MCSCF wave function generated by distributing eight electrons among eight orbitals.