Converging spherical and cylindrical shocks with zero temperature gradient in the rear flow field

Résumé Nous avons étudié les ondes de choc sphériques et cylindriques convergentes près du centre (ou de l'axe) de l'implosion, lorsque celles-ci sont devenues intenses et que l'écoulement qui les suit est devenu «semblable à lui-même», ayant «oublié» les conditions initiales. Un tel écoulement devient probablement isotherme à cause de l'échange thermique intense par conduction ou par rayonnement. Nous avons donc étudié un écoulement isotherme à un moment donné, plutôt que l'écoulement adiabatique habituellement supposé (Guderley, 1942). Les deux genres d'écoulement sont comparés. Nous avons calculé l'exposant de la loi de la propagation des ondes de choc par la règle caractéristique de Whitham (1958) pour des valeurs différentes de =c _p/c _v; nous l'avons comparé avec l'exposant exact obtenu par l'intégration numérique des équations de similarité. Les deux valeurs ne concordent pas aussi bien que lorsque l'on admet que l'écoulement qui suit l'onde de choc est adiabatique.     

EXCITED STATE INTERACTIONS OF 7-AZAINDOLE WITH ALCOHOL AND WATER

Abstract— The fluorescence spectrum of 7-azaindole in alcohol is composed of two fluorescence bands. Effects of pH, temperature and solvent deuteration on the fluorescence spectra and quantum yields of 7-azaindole and other model compounds in ethanol and in water are reported. The long wavelength band arises from a tautomeric species formed in an adiabatic photoreaction involving double proton transfer between one molecule of 7-azaindole and one molecule of alcohol.
The fluorescence spectrum of 7-azaindole in water is composed of only one band, but the emission is weak and shows a large solvent isotope effect. The possibility of a double proton transfer reaction between 7-azaindole and water is discussed.     

Voltammetric oxidation of anthraquinones in acetonitrile and nitromethane

The voltammetric oxidation of seven anthraquinones to the singly-charged radical cations has been investigated in acetonitrile and nitromethane. The voltammetric waves can be used for the quantitative determination of anthraquinones. Benzoquinones, naphthaquinones and phenanthraquinones are not oxidized in these solvents.     

Heavy Vacuum Gas Oil Upregulates the Rhamnosyltransferases and Quorum Sensing Cascades of Rhamnolipids Biosynthesis in Pseudomonas sp. AK6U

We followed a comparative approach to investigate how heavy vacuum gas oil (HVGO) affects the expression of genes involved in biosurfactants biosynthesis and the composition of the rhamnolipid congeners in Pseudomonas sp. AK6U. HVGO stimulated biosurfactants production as indicated by the lower surface tension (26 mN/m) and higher yield (7.8 g/L) compared to a glucose culture (49.7 mN/m, 0.305 g/L). Quantitative real-time PCR showed that the biosurfactants production genes rhlA and rhlB were strongly upregulated in the HVGO culture during the early and late exponential growth phases. To the contrary, the rhamnose biosynthesis genes algC, rmlA and rmlC were downregulated in the HVGO culture. Genes of the quorum sensing systems which regulate biosurfactants biosynthesis exhibited a hierarchical expression profile. The lasI gene was strongly upregulated (20-fold) in the HVGO culture during the early log phase, whereas both rhlI and pqsE were upregulated during the late log phase. Rhamnolipid congener analysis using high-performance liquid chromatography-mass spectrometry revealed a much higher proportion (up to 69%) of the high-molecularweight homologue Rha–Rha–C₁₀–C₁₀ in the HVGO culture. The results shed light on the temporal and carbon source-mediated shifts in rhamonlipids’ composition and regulation of biosynthesis which can be potentially exploited to produce different rhamnolipid formulations tailored for specific applications.     

Green synthesis of new thiouracilodepsipeptides in ionic liquid: One‐pot four‐component reaction of isocyanides

Thiouracil‐containing depsipeptides were produced via one‐pot four‐component condensation/Passerini tandem reaction of thiouracil, 2‐chloroacetic acid derivatives, ketones, and isocyanides in ionic liquid as green reaction media in high yields.     

Palladium‐Mediated Cleavage of Proteins with Thiazolidine‐Modified Backbone in Live Cells

Chemical protein synthesis and biorthogonal modification chemistries allow production of unique proteins for a range of biological studies. Bond‐forming reactions for site‐selective protein labeling are commonly used in these endeavors. Selective bond‐cleavage reactions, however, are much less explored and still pose a great challenge. In addition, most of studies with modified proteins prepared by either total synthesis or semisynthesis have been applied mainly for in vitro experiments with very limited extension to live cells. Reported here is an approach for studying uniquely modified proteins containing a traceless cell delivery unit and palladium‐based cleavable element for chemical activation, and monitoring the effect of these proteins in live cells. This approach is demonstrated for the synthesis of a caged ubiquitin‐aldehyde, which was decaged for the inhibition of deubiquitinases in live cells.     

Reactive intermediates in the reaction of hydrazinecarbothioamides with 2-(bis(methylthio)methylene)malononitrile and ethyl 2-cyano-3,3-bis(methylthio)acrylate

Research on Chemical Intermediates - The reaction of N-substituted hydrazinecarbothioamides with both 2-(bis(methylthio)methylene)malononitrile and ethyl 2-cyano-3,3-bis(methylthio)acrylate...     

Electrospun EGNPs reinforced precursor carbon nanofibril composites by using RSM

Response surface methodology (RSM),based on five‐level, four variable Box‐Benkhen technique was investigated for modeling the average fiber diameter of electrospun polyacrylonitrile (PAN) nanofibers. The four important electrospinning parameters were studied including applied voltage (kV), Berry's number, deposition distance from nozzle to collector (cm), and spinning angle (? in degree). The measured fiber diameters were in a good agreement with the predicted results by using RSM technique. High‐regression coefficient between the variables and the response (R² = 87.74%) indicates excellent evaluation of experimental data by second‐order polynomial regression model. The optimum PAN average fiber diameters of 208 and 37‐nm standard deviation were collected at 19 kV, Berry's number = 10, 25^° spinning angle, and 16‐cm deposition distance. The PAN/N,N‐dimethylformamide (DMF) polymer solution with the optimum weight concentration (10 wt.%) was selected to study the effect of dispersing exfoliated graphite nanoplatelets (EGNPs) in PAN/DMF solution on the electrospun EGNP/PAN fibril composite diameter. Five different EGNPs weight concentrations (2, 4, 6, 8, and 10 wt.%) were dispersed in the optimized PAN/DMF polymer solution. Morphology of EGNPs/PAN fibril composites and its distribution were investigated by scanning electron microscopy (SEM) to show the minimum fiber diameter for the above‐mentioned 5 wt. % of EGNPs. A minimum fibril composite diameter of 182 nm was obtained at 10 wt.% of EGNPs. Morphological characteristics of electrospun fibers and their distribution were tested by Raman spectroscopy, SEM, differential light scattering, and high‐resolution transmission electron microscopy.