Temporal cleaning of a high-energy fiber-based ultrafast laser using cross-polarized wave generation

We report the use of cross-polarized wave generation to perform both pulse shortening and temporal cleaning of a high-energy ytterbium-doped fiber-based femtosecond laser system. The nonlinear processes allow both a highly efficient nonlinear conversion of 20% and a large compression ratio of 3.5, with inherently improved coherent and incoherent contrasts. This results in the generation of 37 μJ, 115 fs pulses at a repetition rate of 100 kHz with high temporal quality.     

Novel diblock copolymer‐grafted multiwalled carbon nanotubes via a combination of living and controlled/living surface polymerizations

Diels–Alder cycloaddition reactions were used to functionalize multiwalled carbon nanotubes (MWNTs) with 1‐benzocylcobutene‐1′‐phenylethylene (BCB‐PE) or 4‐hydroxyethylbenzocyclobutene (BCB‐EO). The covalent functionalization of the nanotubes with these initiator precursors was verified by FTIR and thermogravimetric analysis (TGA). After appropriate transformations/additions, the functionalized MWNTs were used for surface initiated anionic and ring opening polymerizations of ethylene oxide and ε‐caprolactone (ε‐CL), respectively. The OH‐end groups were transformed to isopropylbromide groups by reaction with 2‐bromoisobutyryl bromide, for subsequent atom transfer radical polymerization of styrene or 2‐dimethylaminoethyl methacrylate to afford the final diblock copolymers. ¹H NMR, differential scanning calorimetry (DSC), TGA, and transmission electron microscopy (TEM) were used for the characterization of the nanocomposite materials. TEM images showed the presence of a polymer layer around the MWNTs as well as the dissociation of MWNT bundles. Consequently, this general methodology, employing combinations of different polymerization techniques, increases the diversity of diblocks that can be grafted from MWNTs. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1104–1112, 2010     

State diagrams of arabinoxylan-water binaries

Since Arabinoxylans are natural polysaccharides that seem promising candidates as cryostabilizers, the state diagram (i.e. the representation in the temperature-composition plan of the macroscopic phases) of their aqueous solutions seemed worth determining.

Two lots of purified water extractable arabinoxylans (WEA) of different molecular mass (56 and 410 kDa labeled as LMW-AX and HMW-AX, respectively) were used to prepare aqueous solutions of various composition. These were cooled below their freezing point and annealed for 2 h at a suitable temperature before a DSC 5°C min⁻¹ heating run aimed at determining their primary glass transition temperature, T_g′, and the onset of ice fusion. Once the corresponding composition, C_g′, was assessed, the main curves of the corresponding state diagram were drawn.

As expected, the T_g′ value drawn for HMW-AX was higher (−17°C) than for LMW-AX (−35°C). The C_g′ was instead found close to 75% w/w for both HMW-AX and LMW-AX. The fictitiousness of this coincidence could be easily recognized by expressing the solute concentration in molar fraction, X: it was then possible to verify that, as expected, X_g′ for LMW-AX was one order of magnitude larger than for HLW-AX.     

High-performance liquid chromatography of glutathione conjugates

Summary An ion-exchange high-performance liquid chromatographic method is described for the quantitative assay of glutathione (GSH) conjugates derived from endogenous electrophilic substances as well as xenobiotics. GSH (reduced and oxidized forms) and GSH conjugates were condensated with o-phthaldialdehyde to highly fluorescent derivatives and monitored at 338 nm excitation and 450 nm emission wavelengths after separation by ion-exchange HPLC on a 60-5NH₂ Polygosil analytical column. The detection limit was 2 pmol for the GSH conjugate of cholesterol epoxide and 6 pmol for the GSH conjugate of oleic acid epoxide. This method allows sensitive determination of all GSH conjugates independent of the chromatographic and spectrophotometric properties of the electrophilic substrates. Using this method we could show for the first time that the endogenous compound oleic acid epoxide is a specific substrate for the cytosolic rat liver GSH S-transferase. The method is applied to the determination of GSH S-transferase activity towards oleic acid epoxide and cholesterol epoxide.     

Exact parametric analytic solutions of the elastica ODEs for bars including effects of the transverse deformation

We succeed in constructing exact parametric analytic solutions for the non-linear ordinary differential equations governing the elastica response of a cantilever due to a generalized end loading by taking into account the effects of transverse deformation. Application to the case of the eccentric buckling of a cantilever by taking into account the above influences is developed.     

Transient gas flow simulation using an Adaptive Method of LinesSimulation d'écoulements dans un gazoduc par la méthode adaptative de lignes

Designing natural gas pipelines to safely and efficiently handle unsteady flows, requires knowledge of pressure drop, flowrate and temperature distribution throughout the system. The accurate prediction of these parameters is essential in order to achieve optimum cumulative deliverability, and safe and reliable operation. An Adaptive Method of Lines algorithm is formulated for the solution of Euler system of equations, which fully simulates slow and fast transients. Two test cases present the improvement of the numerical solution from grid adaptation. Good results are obtained both for slow and fast transients simulations proving that the suggested numerical procedure is appropriate for such predictions. To cite this article: E. Tentis et al., C. R. Mecanique 331 (2003).     

Metal oxidation states in biological water splitting

A central question in biological water splitting concerns the oxidation states of the manganese ions that comprise the oxygen-evolving complex of photosystem II. Understanding the nature and order of oxidation events that occur during the catalytic cycle of five S_i states (i = 0–4) is of fundamental importance both for the natural system and for artificial water oxidation catalysts. Despite the widespread adoption of the so-called “high-valent scheme”—where, for example, the Mn oxidation states in the S₂ state are assigned as III, IV, IV, IV—the competing “low-valent scheme” that differs by a total of two metal unpaired electrons (i.e. III, III, III, IV in the S₂ state) is favored by several recent studies for the biological catalyst. The question of the correct oxidation state assignment is addressed here by a detailed computational comparison of the two schemes using a common structural platform and theoretical approach. Models based on crystallographic constraints were constructed for all conceivable oxidation state assignments in the four (semi)stable S states of the oxygen evolving complex, sampling various protonation levels and patterns to ensure comprehensive coverage. The models are evaluated with respect to their geometric, energetic, electronic, and spectroscopic properties against available experimental EXAFS, XFEL-XRD, EPR, ENDOR and Mn K pre-edge XANES data. New 2.5 K ⁵⁵Mn ENDOR data of the S₂ state are also reported. Our results conclusively show that the entire S state phenomenology can only be accommodated within the high-valent scheme by adopting a single motif and protonation pattern that progresses smoothly from S₀ (III, III, III, IV) to S₃ (IV, IV, IV, IV), satisfying all experimental constraints and reproducing all observables. By contrast, it was impossible to construct a consistent cycle based on the low-valent scheme for all S states. Instead, the low-valent models developed here may provide new insight into the over-reduced S states and the states involved in the assembly of the catalytically active water oxidizing cluster.