Synthesis of 4-polyfluoroalkyl-1,3-dithiolanes via [3+2] cycloaddition of thiocarbonyl ylide to polyfluoroalkanethioamides

Chemistry of Heterocyclic Compounds - New 4-polyfluoroalkyl-1,3-dithiolanes were synthesized by reaction of polyfluoroalkanethioamides with thiocarbonyl ylide that was generated in situ by...     

Investigation of surface and thermogravimetric characteristics of carbon-coated iron nanopowder

Demand for high-density press and sinter components is increasing day by day. Of the different ways to improve the sinter density, the addition of nanopowder to the conventional micrometer-sized metal powder is an effective solution. The present investigation is aimed at studying the surface chemistry of iron nanopowder coated with graphitic carbon, which is intended to be mixed with the conventional iron powder. For this purpose, iron nanopowder in the size range of 30 nm to submicron (less than 1 micron) was investigated using thermogravimetry at different temperatures: 400°C, 600°C, 800°C, 1000°C, and 1350°C. The X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and high-resolution scanning electron microscopy (HR-SEM) were used for characterizing the powder as well as samples sintered at different temperatures. The presence of iron, oxygen, carbon, chromium, and zinc were observed on the surface of the nanopowder. Iron was present in oxide state, although a small metallic iron peak at 707 eV was also observed in the XPS spectra obtained from the surface indicating the oxide scale to be maximum of about 5 nm in thickness. For the sample treated at 600°C, presence of manganese was observed on the surface. Thermogravimetry results showed a two-step mass loss with a total mass loss of 4 wt.% when heated to 1350°C where the first step corresponds to the surface oxide reduction.     

QSAR modelling and structural aspects concerning synthetic heterocycles with larvicidal activity against Aedes aegypti

Structural Chemistry - In this paper, we present a quantitative structure–activity relationships modelling for two series of heterocyclic synthetic compounds with larvicidal activity against...     

Everything you wanted to know about phase and reference frequency in one- and two-dimensional NMR spectroscopy

The fundamental concept of phase discussed in this tutorial aimed at providing students with an explanation of the delays and processing parameters they may find in nuclear magnetic resonance (NMR) pulse programs. We consider the phase of radio-frequency pulses, receiver, and magnetization and how all these parameters are related to phases and offsets of signals in spectra. The impact of the off-resonance effect on the phase of the magnetization is discussed before presenting an overview of how adjustment of the time reference of the free induction decay avoids first-order correction of the phase of spectra. The main objective of this tutorial is to show how the relative phase of a pulse and the receiver can be used to change the reference frequency along direct and indirect dimensions of NMR experiments. Unusual of phase incrementation with non-90° angles will be illustrated on one- and two-dimensional NMR spectra.     

Geometro-stochastic locality in quantum spacetime and quantum diffusions

The issue of the intrinsic nonlocality of quantum mechanics raised by J. S. Bell is examined from the point of view of the recently developed method of geometro-stochastic quantization and its applications to general relativistic quantum theory. This analysis reveals that a distinction should be made between the topological concept of locality used in formulating relativistic causality and a type of geometric locality based on the concept of fiber bundle, which can be used in extending the strong equivalence principle to the quantum domain. Both play an essential role in formulating a notion of geometro-stochastic propagation based on quantum diffusions, which throws new light on the EPR paradox, on the origin of the arrow of time, and on other fundamental issues in quantum cosmology and the theory of measurement.     

Geometric Structures on the Complement of a Projective Arrangement

Consider a complex projective space with its Fubini-Study metric. We study certain one parameter deformations of this metric on the complement of an arrangement (= finite union of hyperplanes) whose Levi-Civita connection is of Dunkl type. Interesting examples are obtained from the arrangements defined by finite complex reflection groups. We determine a parameter interval for which the metric is locally of Fubini-Study type, flat, or complex-hyperbolic. We find a finite subset of this interval for which we get a complete orbifold or at least a Zariski open subset thereof, and we analyze these cases in some detail (e.g., we determine their orbifold fundamental group).In this set-up, the principal results of Deligne-Mostow on the Lauricella hypergeometric differential equation and work of Barthel-Hirzebruch-Höfer on arrangements in a projective plane appear as special cases. Along the way we produce in a geometric manner all the pairs of complex reflection groups with isomorphic discriminants, thus providing a uniform approach to work of Orlik-Solomon.     

String Jacobi Matrices with Very Fast Decreasing Weights

In this work we investigate a class of string, compact Jacobi matrices with very rapidly decreasing weights. In particular, we have found Hellinger-Weyls function representation as ratio of two entire functions with known Taylor series representation. The asymptotical estimations of zeroes of this entire functions and of eigenvalues of a corresponding operator are found. The application of this theory to Rogers-Ramanujans functions is considered.Submitted: November 18, 2002 Revised: October 30, 2003     

Homogenization approach for optimal design of perforated layer in acoustic wave propagation

Homogenization provides a reduced model of the acoustic wave propagation through a periodically perforated layer immersed in an inviscid fluid. The shape of the perforation influences some parameters of the non-local transmission condition. We developed and implemented numerically the sensitivity analysis for an optimal design of the perforation. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Solving singular convolution equations using the inverse Fast Fourier Transform

The inverse Fast Fourier Transform is a common procedure to solve a convolution equation provided the transfer function has no zeros on the unit circle. In our paper we generalize this method to the case of a singular convolution equation and prove that if the transfer function is a trigonometric polynomial with simple zeros on the unit circle, then this method can be extended.