Classes de symétrie des solides piézoélectriquesSymmetry classes of piezoelectric solids

We apply here the harmonic and Cartan decomposition techniques to piezoelectric material symmetries classification. We show in particular that we shall reduce from 19 to 17 the number of symmetry classes corresponding to the piezoelectric phenomenon. To cite this article: G. Geymonat, T. Weller, C. R. Acad. Sci. Paris, Ser. I 335 (2002) 847–852.     

Synthesis and Characterization of Star‐Shaped Diblock Poly(ε‐caprolactone)/Poly(ethylene oxide) Copolymers

Summary: Star‐shaped hydroxy‐terminated poly(ε‐caprolactone)s (ssPCL), with arms of different lengths, were obtained by ring‐opening polymerization (ROP) of ε‐caprolactone initiated by pentaerythritol, and were condensed with α‐methyl‐ω‐(3‐carboxypropionyloxy)‐poly(ethylene oxide)s ( = 550–5 000) to afford four‐armed PCL‐PEO star diblock copolymers (ssPCL‐PEO). The polymers were characterized by ¹H and ¹³C NMR spectroscopy and size‐exclusion chromatography (SEC). The melting behavior of ssPCLs was studied by differential scanning calorimetry (DSC). X‐ray diffraction and DSC techniques were used to investigate the crystalline phases of ssPCL‐PEOs.

The part of the synthesis of four‐armed star‐shaped diblock poly(ε‐caprolactone)‐poly(ethylene oxide) copolymers as described.     

Increased Entropic Brain Dynamics during DeepDream-Induced Altered Perceptual Phenomenology

In recent years, the use of psychedelic drugs to study brain dynamics has flourished due to the unique opportunity they offer to investigate the neural mechanisms of conscious perception. Unfortunately, there are many difficulties to conduct experiments on pharmacologically-induced hallucinations, especially regarding ethical and legal issues. In addition, it is difficult to isolate the neural effects of psychedelic states from other physiological effects elicited by the drug ingestion. Here, we used the DeepDream algorithm to create visual stimuli that mimic the perception of hallucinatory states. Participants were first exposed to a regular video, followed by its modified version, while recording electroencephalography (EEG). Results showed that the frontal region’s activity was characterized by a higher entropy and lower complexity during the modified video, with respect to the regular one, at different time scales. Moreover, we found an increased undirected connectivity and a greater level of entropy in functional connectivity networks elicited by the modified video. These findings suggest that DeepDream and psychedelic drugs induced similar altered brain patterns and demonstrate the potential of adopting this method to study altered perceptual phenomenology in neuroimaging research.     

Bis(di‐2‐pyridyl sulfide‐κ2N,N′)(4‐methylpyrimidin‐2‐yl 2‐pyridylmethyl sulfide‐κ2N,S)ruthenium(II) bis(hexafluorophosphate) acetonitrile solvate

The crystal structure of the title compound, [Ru(C₁₀H₈N₂S)₂(C₁₁H₁₁N₃S)](PF₆)₂·C₂H₃N, is composed of a bivalent octa­hedral Ru^II complex, two PF₆⁻ anions and an acetonitrile solvent mol­ecule. Two PF₆⁻ units are found on a crystallographic binary axis, therefore contributing just one half each to the asymmetric unit cell. The structure displays a peculiar stereochemistry of the cation. Three bidentate ligands around the Ru centre, together with the coordination of the non‐symmetric S atom, mean that these two atoms are chiral. This would lead to four stereoisomers, but only an enantiomeric pair was found in the analyzed sample.     

Genesis of the multiscale approach for materials with microstructure

This paper presents an overview of the origin of multiscale approaches in mechanics. While the pioneer molecular models of linear elastic bodies by Navier, Cauchy and Poisson were contradicted by experiments, the phenomenological energetic approach by Green still seems suitable for simple materials only. Voigt’s molecular model, here reinterpreted in the light of contemporary mechanics, reconciled the two approaches providing a conceptual guideline for developing constitutive models based on a direct link between continuum and discrete solid mechanics. Such a theoretical background proves to be especially suitable for new complex materials. An example referred to masonry-like materials is given.     

A New Look at Relativity Transformations

A free system, considered to be a comparisonsystem, allows for the notion of objective existence andinertial frame. Transformations connecting inertialframes are shown to be either Lorentz or generalizedGalilei.