Synthesis of a new N-containing hexahelicene

A new helically chiral hexacyclic system, containing one pyridine unit, was prepared through a four-step synthesis involving palladium promoted Mizoroki-Heck couplings and classical oxidative photodehydrocyclisation.     

The Synthesis and Characterization of a New Cobalt Dimethylphenylpiperazinium Cyclotetraphosphate Hexahydrate,Co[C12 H19 N2]2 P4 O12.6 H2 O

Cobalt dimethylphenylpiperazinium cyclotetraphosphate hexahydrate, Co[C₁₂H₁₉N₂]₂P₄O₁₂.6H₂O, was synthesized by a reaction between cyclotetraphosphoric acid H₄P₄O₁₂, cobalt carbonate, and 1-(2,4-dimethylphenylpiperazine). It crystallizes in the triclinic system, space group P, with the following unit cell parameters: a = 7.336(1), b = 8.413(1), c = 14.926(2) Å, α = 87.46(1), β = 83.13(1), γ = 82.98(1)°, V = 907.3(2) ų, and Z = 1. The atomic arrangement can be described as layers containing P₄O₁₂ rings a and Co(H₂O)₆ octahedra spreading in the (001) planes between which are located the dimethylphenylpiperazinium groups via H-bonds. The synthesis and characterization by X-ray diffraction, IR absorption, and thermal analysis are described.     

Synthesis and X‐Ray Analysis of a New [6]Helicene

A new disubstituted hexahelicene derivative 3 bearing methoxy functions at positions 3 and 14 has been prepared in racemic form through a Heck reaction followed by photocyclodehydrogenation. Suitable crystals of rac‐3 were analyzed by X‐ray crystallography and showed similar geometry to the structure of hexahelicene itself. Deprotection of 3 using boron tribromide led to 3,14‐dihydroxyhexahelicene 4 in quantitative yield. The complexation of transition metal atoms seemed to be quite possible by these two bidentate hexahelicene derivatives.     

Speech enhancement in dual-microphone mobile phones using Kalman filter

In this paper, a dual-microphone speech enhancement algorithm for the mobile phones is proposed. The adopted method exploits the coherence function algorithm and the Kalman filter. This algorithm has a simple implementation that does not need a prediction of interfering signals statistics. In addition, this algorithm can be used in small devices with so closely distance between the two microphones. Moreover, the use of such algorithm allows reducing multiple noise sources at many azimuths positions. Finally, the new algorithm proves its performances referring to the perceptual evaluation of speech quality and the time domain waveforms.     

Répartitio n simulta née de S( n) et $$ S( n+1)$$ S( n+1) da ns les progressio ns arithmétiques

If \(q\ge 2\) is an integer, we denote by \(S_q(n)\) the sum of the digits in base q of the positive integer n and by \(v_q(n)\) its q-adic valuation. The goal of this work is to study exponential sums of the form \(\displaystyle \sum \nolimits _{n\le x}\exp \big (2i\pi \big (\frac{l}{m} S_q(n)+\frac{k}{m'}S_q(n+1)+\theta n\big )\big )\) in order to prove some statistical properties of integers n for which \(S_q(n)\) and \(S_q(n+1)\) belong to given arithmetic progressions. This extends the results obtained by Gelfond in 1968 and those obtained by Mauduit–Sárközy in 1996.     

Synchronized analysis of an unsteady laminar flow downstream of a circular cylinder centred between two parallel walls using PIV and mass transfer probes

Experiments are carried out in the wake of a cylinder of d _c  = 10 mm diameter placed symmetrically between two parallel walls with a blockage ratio r = 1/3 and a Reynolds number varying between 75 ≤ Re ≤ 277. Particle image velocimetry is exerted to obtain the instantaneous velocity components in the cylinder wake. A snapshot proper orthogonal decomposition (POD) is also applied to these PIV results in order to extract the dominant modes through the implementation of an inhomogeneous filtering of these different snapshots, apart from an interpolation to estimate the wall shear rate at the lower wall downstream the cylinder. Mass transfer circular probes are placed at the lower wall downstream this obstacle so as to further determine the time evolution of the wall shear rate, by bringing the inverse method to bear on the convective-diffusion equation. Comparisons between the two synchronized techniques demonstrate that electrochemical method can give more accurate information about the coherent structures present in the flow and about the interaction of the von Kármán vortices with the walls of the tunnel as well. The comparison between the two measurement techniques in the flow regions concerns the spatiotemporal evolutions of the wall shear rate obtained from PIV measurements and the wall shear rate using mass transfer probes. Discrepancy between the PIV measurements and the electrochemical ones near the wall, where the secondary vortices P ₁′ are generated at wall, are caused by a PIV bias and a limitations of the singular mass transfer probes.     

Monitoring Conformational Changes in an Enzyme Conversion Inhibitor Using Pure Shift Exchange NMR Spectroscopy

We report the acquisition of 2D NMR EXSY spectra with ultrahigh resolution, which allows for probing the slow conformational exchange process in a pharmaceutical compound. The resolution enhancement is achieved by implementing interferogram based PSYCHE homonuclear decoupling to generate a pure shift proton spectrum along the direct domain of the resulting data. The performance of this pure shift EXSY pulse sequence is compared to the standard experiment recorded under identical conditions. It is found that although being less sensitive and requiring a longer acquisition time, the quality of pure shift spectra allows for extracting exchange rates values that are coherent with the ones determined by standard approach, on a temperature range that demonstrates the robustness of the chosen homonuclear decoupling method. The resolution enhancement provided by the simplification of proton line shape allows for probing a higher number of proton sites whose analysis would have been biased using a standard method. These results open the way to a thorough and accurate study of chemical exchange processes based on a multi-site analysis of 2D pure shift EXSY spectra     

Etude de la chute de pression singulière dans les élargissements brusques en écoulement monophasique turbulent

Résumé On étude théoriquement et expérimentalement les effets de frottement pariétal et de distribution de vitesse moyenne et fluctuante sur le coefficient de chute de pression singulière dans un élargissement brusque en écoulement monophasique turbulent. Les résultats expérimentaux ont permis d'une part de tester la limite de validité de cette approche, et d'autre part de mieux preciser l'organisation de l'écoulement pariétal au voisinage de l'élargissement.

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The theoretical and experimental study deals with the effects of wall shear stress and distribution of mean and fluctuating velocity on the coefficient of singular pressure loss in a sudden enlargement for a turbulent single phase flow. The experimental results allowed to verify the limit of validity of the present model, and specify the wall flow organization near the abrupt enlargement.

     

Circularly Polarized Fluorescent Helicene-Boranils: Synthesis,Photophysical and Chiroptical Properties

Mono- and di-boranil-substituted helicenes were prepared by BF₂-borylation of the corresponding anils, readily synthesized by condensation of 2-amino- and 2,15-diamino-helicenes with 4-(diethylamino)salicylaldehyde. After enantiomeric resolution using HPLC, their chiroptical properties including circularly polarized fluorescence in solution and in PMMA films were investigated and rationalized with the help of NMR, X-ray and quantum-chemical calculations.