Resolvable decomposition of Kn1

In this paper, we prove that $\text{K}{}_{\mathrm{n}}{}^1$ admits a resolvable decomposition into TT₃ or C₃ if and only if n ≡ 0 (mod. 3), n ≠ 6.     

Rapid determination of polycyclic aromatic hydrocarbons in sewage sludges using microwave-assisted solvent extraction. Comparison with other extraction methods

The presence of toxic organic micropollutants in municipal sewage sludges is a major problem on account of risks associated with the agricultural use of the sludges and therefore maximum tolerance limits are imposed. The aim of our study was to develop a reliable and fast analytical procedure for the determination of polycyclic aromatic hydrocarbons in sewage sludges, using focused microwave-assisted extraction. Optimization of the extraction conditions was performed on real matrices. The results of a 2(3) factorial design showed that extraction time was the only influential factor. The selected conditions (30 W, 10 min, 30 ml solvent) were used for real sludges and a certified marine sediment, leading to recoveries of between 56 and 75%. Results of an interlaboratory test confirmed these values. Finally, the technique was compared to traditional techniques (Soxhlet, sonication), and the more recent pressurized liquid extraction technique. Focused microwave-assisted extraction remains an attractive alternative technique due to its rapidity, the low solvent volume required and its moderate investment cost.     

H-transfer rates in ion-neutral complexes versus those in intact aliphatic ions

The relative rates of H-transfer between partners in ion-neutral complexes were compared with those in intramolecular rearrangements using results of first differential photoionization mass spectrometry measurements. Complex-mediated H-transfers are inferred to have rates of the same order as those for intramolecular hydrogen rearrangements, suggesting a similar range of motion of the reactive sites in both types of reactions. It is also concluded that at their fastest H-transfers take place between the partners in ion-neutral complexes within at most the time of several rotations of the partners in the complexes. Copyright 1999 John Wiley & Sons, Ltd.     

Shortest coverings of graphs with cycles

It is shown that the edges of a bridgeless graph G can be covered with cycles such that the sum of the lengths of the cycle is at most $\text{|E(G) +}\text{min}\text{{}\text{2}\text{3}\text{|E(G)|,}\text{7}\text{3}\text{(|V(G)| ? 1)}}$.     

Decomposition of the complete directed graph into k-circuits

We study the decomposition of $\text{K}{}_{\mathrm{n}}{}^1$ (the complete directed graph with n vertices) into arc-disjoint elementary k-circuits, primarily for the case k even. We solve the problem for many values of (n, k) and in particular for all n in the cases k = 4, 6, 8, and 16.     

Numerical data and experimental proof of the unified theory of electron emission (Christov)

In order to check the unified theory of electron emission (Christov), the temperature dependence of the electron emission from the (013), (001) and (112) single crystal faces of tungsten is measured between 300 °K and 1500 °K at relatively low fields yielding low current densities (10^?1 to 10^?7 A/cm²). Experiments are performed in a field electron microscope using a probe hole technique with an electron multiplier. The experimental results are in a fairly good agreement with Christov's theory. Tables of numerical data of Christov's formulae are presented. Using these tables, typical results of the theory are described.     

Application of a Sequential Extraction Procedure to Calcareous Soil Samples: Preliminary Studies

Abstract

The localization of trace metals in soils is usually performed by sequential extraction procedures. Our purpose was to study the fractioning of copper in calcareous soils, in order to predict its mobility, using the extraction procedure proposed by Tessier et al. This preliminary study is devoted to the improvements of this method applied to calcareous soil samples.

First, it was necessary to assess the experimental conditions allowing the complete solubilisation of the different compartments involved in the extraction procedure with their appropriate reagent (acetic acid-sodium acetate and carbonates, iron hydroxide and hydroxylamine, organic matter and hydrogen peroxide, fluorhydric-perchloric acid and residual fraction). The complete solubilisation of each compartment was tested by measuring the residual phase.

Secondly, it was necessary to study the analytical protocol for the determination of copper with electrothermal atomic absorption; an improvement of this determination was particularly necessary for the reagent used for the exchangeable fraction (sodium acetate at pH = 8.5).

According to the experimental results, the quality (repeatability, concordance of the sum of fractions with the total content of copper determined with independent measurement) of the proposed protocol seems to be quite good.

Some results of the fractioning of copper in calcareous soil samples are given; these samples are characterised by a high value of copper in the residual fraction corresponding to a poor availability of this element.     

Disentangling the effects of phonation and articulation: Hemispheric asymmetries in the auditory N1m response of the human brain

Background  

The cortical activity underlying the perception of vowel identity has typically been addressed by manipulating the first and second formant frequency (F1 & F2) of the speech stimuli. These two values, originating from articulation, are already sufficient for the phonetic characterization of vowel category. In the present study, we investigated how the spectral cues caused by articulation are reflected in cortical speech processing when combined with phonation, the other major part of speech production manifested as the fundamental frequency (F0) and its harmonic integer multiples. To study the combined effects of articulation and phonation we presented vowels with either high (/a/) or low (/u/) formant frequencies which were driven by three different types of excitation: a natural periodic pulseform reflecting the vibration of the vocal folds, an aperiodic noise excitation, or a tonal waveform. The auditory N1m response was recorded with whole-head magnetoencephalography (MEG) from ten human subjects in order to resolve whether brain events reflecting articulation and phonation are specific to the left or right hemisphere of the human brain.