Statistical properties of turbidity, oxygen and pH fluctuations in the Seine river estuary (France)

We consider here, the fluctuations of turbidity, oxygen and pH time series recorded from the MAREL system (Ifremer, France), which is based on the deployment of data buoys equipped with water analysis capabilities in an automated mode. We perform a spectral analysis (from 10 min to years) of these time series, and we estimate their probability density functions. Oxygen, turbidity and pH are important quantities for ecosystem studies and physics-biology couplings, and their fluctuations reveal the possible influence of environmental factors such as tides and turbulence. Turbidity variability is highly complex and does not appear to be directly coupled to turbulence, since no clear range is visible. On the other hand, oxygen percentage of saturation and pH data show remarkably nice scaling ranges, indicating an important coupling with turbulence, but also biological or chemical activity, since the statistics differ markedly from passive scalars. Several possible sources of this variability are discussed.     

Synthesis of triblock copolymers from glycolysed poly(ethylene terephthalate) by living radical polymerization

Valorization of poly(ethylene terephthalate) (PET) waste has been achieved using glycolysis. The resulting diols were employed for the synthesis of triblock copolymers by atom transfer radical polymerization using copper (I) bromide and (1,1,4,7,10,10)‐hexamethyltriethylenetetramine as catalyst system. Macroinitiator was obtained after depolymerization of PET waste followed by functionalization of the obtained glycolysate with 2‐bromoisobutyrate bromide. Polymerization of styrene (S) and glycidyl methacrylate (GMA) has been achieved leading to PS‐b‐PETG‐b‐PS and (PS‐stat‐PGMA)‐b‐PETG‐b‐(PS‐stat‐PGMA) triblock copolymers. Best results were obtained at 100 °C. At this temperature, termination reaction were negligible and the measured number‐average molar mass of the product increased linearly with monomer conversion in agreement with the theoretical M_n with low polydispersity products achieved. Polymers were also characterized by ¹H NMR. This work presents a original valorization of PET waste as (PS‐stat‐PGMA)‐b‐PETG‐b‐(PS‐stat‐PGMA) copolymer could be used as heat curable coatings. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 433–443, 2008     

Reeb foliation in the optimal control problem with phase constraints

An optimal control problem with two phase constraints and a two-dimensional control is considered. We prove that its optimal trajectories have a countable number of points of contact with the phase constraint bound on a finite time interval. The optimal synthesis of the problem after applying the quotient mapping by the action of the scale group has a complicated topological structure and, in some neighborhood of singular extremals, it is the Reeb foliation.     

Glasses and glass-ceramics in the oxyfluoride ternary system Pb(PO3)2-WO3-PbF2

Glasses were prepared by the melt-quenching method in the ternary system Pb(PO₃)₂-WO₃-PbF₂ and doped with Er³⁺ in order to prepare luminescent transparent glass-ceramics. This work focused on thermal and structural characterization of tungsten lead-phosphate glasses and crystallization study for preparing transparent glass-ceramics. Thermal properties such as thermal stability and crystallization behavior upon heating were investigated by DSC in function of PbF₂ content. For low PbF₂ concentrations, only one crystallization peak due to Pb₃(PO₄)₂ is observed whereas samples containing more than 15% of PbF₂ present another exothermic event at lower temperatures related with precipitation of PbF₂, Pb₂P₂O₇ and Pb₂OF₂. Structural investigations by Raman spectroscopy suggest that PbF₂ modifies the tungsten-phosphate network through the formation of P―F and P―O―Pb bonds but the average network connectivity remains almost constant. A crystallization study has been performed by DSC to investigate the dominant crystallization mechanisms in these glasses and it has been established that Pb₃(PO₄)₂ is nucleated on the surface whereas PbF₂, Pb₂P₂O₇ and Pb₂OF₂ crystallize dominantly from the glassy bulk. Transparent glass-ceramics containing nanosized PbF₂ crystallites were also prepared by suitable heat-treatment on the glass sample containing 20% of PbF₂ and Raman microscopy of these glass-ceramics supports the crystallization mechanisms determined by DSC.     

Correlative atomic scale characterisation of secondary carbides in M50 bearing steel

Correlative atom probe tomography (APT) and transmission electron microscopy (TEM) are used to characterise the microstructure and chemistry of carbide precipitation in M50 bearing steel. This is a prerequisite in establishing relationships between the microstructure and hydrogen embrittlement (HE) resistance. Secondary carbides are the focus of this study, as they play a major role in improving HE-resistance. Secondary carbides are observed in APT, with compositions close to M₄C_3, M₂C and M₃C. Correlative TEM measured orientation relationships between the martensite matrix and carbides, enabling the confirmation of M₃C cementite precipitates in the corresponding APT reconstruction. Additionally, other precipitates observed in TEM were correlated to the M₂C carbides in APT data. The M₄C₃ carbides are found to have a significantly lower volume fraction than the M₂C carbides.     

New Fluorinated Rhodamines for Optical Microscopy and Nanoscopy

New photostable rhodamine dyes represented by the compounds 1 a – r and 3 – 5 are proposed as efficient fluorescent markers with unique combination of structural features. Unlike rhodamines with monoalkylated nitrogen atoms, N′,N‐bis(2,2,2‐trifluoroethyl) derivatives 1 e , 1 i , 1 j , 3 ‐H and 5 were found to undergo sulfonation of the xanthene fragment at the positions 4′ and 5′. Two fluorine atoms were introduced into the positions 2′ and 7′ of the 3′,6′‐diaminoxanthene fragment in compounds 1 a – d , 1 i – l and 1 m – r . The new rhodamine dyes may be excited with λ=488 or 514 nm light; most of them emit light at λ=512–554 nm (compounds 1 q and 1r at λ=576 and 589 nm in methanol, respectively) and have high fluorescence quantum yields in solution (up to 98 %), relatively long excited‐state lifetimes (>3 ns) and are resistant against photobleaching, especially at high laser intensities, as is usually applied in confocal microscopy. Sulfonation of the xanthene fragment with 30 % SO₃ in H₂SO₄ is compatible with the secondary amide bond (rhodamine‐CON(Me)CH₂CH₂COOH) formed with MeNHCH₂CH₂COOCH₃ to providing the sterically unhindered carboxylic group required for further (bio)conjugation reactions. After creating the amino reactive sites, the modified derivatives may be used as fluorescent markers and labels for (bio)molecules in optical microscopy and nanoscopy with very‐high light intensities. Further, the new rhodamine dyes are able to pass the plasma membrane of living cells, introducing them as potential labels for recent live‐cell‐tag approaches. We exemplify the excellent performance of the fluorinated rhodamines in optical microscopy by fluorescence correlation spectroscopy (FCS) and stimulated emission depletion (STED) nanoscopy experiments.     

Study of interaction between tiagabine HCl and 2-HPβCD: investigation of inclusion process

Tiagabine (TGB) is an antiepileptic agent enhancing the activity of GABA at neuronal and glial region. It has recently been shown that enhancement of TGB chemical stability was improved by complexation with 2-hydroxypropyl-beta-cyclodextrin (2-HPβCD). The aim of this project is to explain the improvement of the chemical stability of complexed TGB by studying the inclusion properties and factors affecting the complexation selectivity between 2-HPβCD and TGB. Analysis of the interaction between 2-HPβCD and TGB and the effect of 2-HPβCD on TGB solubility was performed by phase solubility method described by Higuchi and Connors; the complexation was followed by characterization using DSC, FTIR and NMR spectroscopy. In aqueous media, the analysis of NMR proton shift change continuous variation method (Job’s plot) and the NMR diffusion-ordered spectroscopy (DOSY) measurements clearly show that TGB form 1:1 inclusion complex with 2-HPβCD with an association constant (K _a) of 3396 M^?1. More detailed information about the inclusion mode and the geometry of the complex was obtained by the analysis of 2D NMR NOESY experiment and molecular modelling calculations. The inclusion process indicates that A-ring, C₁₀–C₁₁ double bond and the half of the B-ring of TGB molecule were located inside the cavity while the nipecotic acid part of TGB (Ring C) was exposed towards the outside of the 2-HPβCD cavity. These results suggest that the inclusion of the C₁₀–C₁₁ double bond in the 2-HPβCD cavity may possibly the reason of improvement of TGB chemical stability.     

Interchromophore interactions and energy transfer in covalently bound porphyrin-chlorine heterodimer

Energetis of interchromophore interactions in a covalently bound prophyrin-chlorine heterodimer (Por-O-Chl) is investigated at temperatures from 77 to 293 K in solvents with differing polarity (toluene, tetrahydrofurane, and diethyl ether: petroleum ester: isopropanole=5∶5∶2 mixture). We substantiate the conclusion that the strong quenching of fluoresence and phosphorescence of the porphyrin fragments in both stable isomers of the Por-O-Chl heterodimer is induced not by the photoinduced charge transfer but rather by efficient processes of singlet-singlet (probability F^SS=1.3·10¹¹ to 6.8°10¹⁰ sec⁻¹) and triplet-triplet (probability F^TT≥10⁸ sec⁻¹) radiationless electronic excitation transfer. It is shown that the S−S transfer takes place without quantum losses from the thermodynamically equilibrated S₁ state of the donor, and its dynamics and main regularities at temperatures from 77 to 293 K are described by the inductive resonance theory without any additional asssumptions. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 1, pp. 75–82, January–February, 1998.