Heat conduction across molecular junctions between nanoparticles

We investigate the problem of heat conduction across molecular junctions connecting two nanoparticles, both in vacuum and in a liquid environment, using classical molecular dynamics simulations. In vacuum, the well-known result of a length independent conductance is recovered; its precise value, however, is found to depend sensitively on the overlap between the vibrational spectrum of the junction and the density of states of the nanoparticles that act as thermal contacts. In a liquid environment, the conductance is constant up to a crossover length, above which a standard Fourier regime is recovered.     

Fitting models to correlated data III: A comparison between residual analysis and other methods

Applications of the χ² test, the F test, the Durbin-Watson d test, and the f (or Sign) test, to examples of correlated data treatment, show important drawbacks with the d test and (apparently) with the f test. An analytical approach based on residual analysis suggests an improvement in their use that leads to better results at lowest order; it also points out a distinction between goodness-of-fit tests, as the f test, and goodness-of-modeling tests, as the χ² and F tests. The residual analysis method is applied to the same examples; it looks faster, simpler, and often more accurate than the classical ones.     

Self-organized structures in a superorganism: do ants “behave” like molecules?

While the striking structures (e.g. nest architecture, trail networks) of insect societies may seem familiar to many of us, the understanding of pattern formation still constitutes a challenging problem. Over the last two decades, self-organization has dramatically changed our view on how collective decision-making and structures may emerge out of a population of ant workers having each their own individuality as well as a limited access to information. A variety of collective behaviour spontaneously outcome from multiple interactions between nestmates, even when there is no directing influence imposed by an external template, a pacemaker or a leader. By focussing this review on foraging structures, we show that ant societies display some properties which are usually considered in physico-chemical systems, as typical signatures of self-organization. We detail the key role played by feed-back loops, fluctuations, number of interacting units and sensitivity to environmental factors in the emergence of a structured collective behaviour. Nonetheless, going beyond simple analogies with non-living self-organized patterns, we stress on the specificities of social structures made of complex living units of which the biological features have been selected throughout the evolution depending on their adaptive value. In particular, we consider the ability of each ant individual to process information about environmental and social parameters, to accordingly tune its interactions with nestmates and ultimately to determine the final pattern emerging at the collective level. We emphasize on the parsimony and simplicity of behavioural rules at the individual level which allow an efficient processing of information, energy and matter within the whole colony.     

Fast characterization of foodstuff by headspace mass spectrometry (HS-MS)

The field of the rapid characterization of products by HS-MS is reviewed. The general principle of HS-MS systems consists of introducing volatile components present in the HS of a sample without prior chromatographic separation into the ionization chamber of a mass spectrometer. The spectrum resulting from simultaneous ionization and fragmentation of the mixture of molecules introduced constitutes a “fingerprint” that is characteristic of the product being analyzed. Exploitation of this spectral information allows one determine the composition of the sample.     

A new preparation of samarium dibromide and its use in stoichiometric and catalytic pinacol coupling reactions

A new convenient preparation of samarium dibromide in THF is reported. Pinacol coupling reactions using SmBr₂ in catalytic amounts together with mischmetall as a coreductant have been performed with a variety of carbonyl compounds.     

Reactions of ketene acetals—IX: The synthesis of naphthoquinones from benzoquinones

Halogenobenzoquinones react with ketene acetals and give benzofurans, but in the presence of acetic acid, naphthoquinones are produced in variable yields. Some aspects of the reaction have been studied and the method has been applied to the synthesis of useful intermediates and of derivatives of some naturally occurring naphthoquinones such as tri-O-methylflaviolin 20 and tetra-O-methylspinochrome B23. Benzoquinones also react with conjugated ketene acetals without acid catalysis, providing convenient syntheses of ramentaceone 43, O-methylstypandrone 45 and 1,3,6,8-tetramethoxyanthraquinone 34.     

Retrodienic reactions XVI - flash thermolytic generation of reactive functional allenes

Butadienal 1, propadienol 2 and propadienamine 3 are synthesized by flash vacuum thermolysis of their anthracenic Diels-Alder adducts and characterized at low temperature.     

Apurinic DNA reactivity: Modelisation of apurinic DNA breakage with phenylhydrazine and formation of a pyrazole adduct

We have elucidated the exact mechanism of apurinic oligodeoxynucleotide d(Tp[AP]pT) cleavage by phenylhydrazine and shown that the final isolated product is in fact a 3-substituted derivative of 1-phenyl-pyrazole.     

Structure of absintholide a new guaianolide dimer of Artemisia absinthium L.

Absintholide $\text{1}$ is a new guaianolide dimer whose structure and stereochemistry has been elucidated on the basis of high resolution n.m.r.