Chiral luminescent compounds as a perspective for cholesteric liquid crystal lasers

We present the synthesis and characterization of fluorene based materials for mirror less laser applications. Mirror less lasing is obtained from a cholesteric liquid crystals mixture, that acts as a resonator, doped with a photoluminescent dye, that acts as an active medium. We propose to use fluorene based compounds to combine two necessary properties to achieve laser emission: chirality and luminescence. Two different compounds, a trimer and an oligomer are synthesized. The trimer and the oligomer are both prepared with chiral moieties and, in addition, they are liquid crystalline compatible. More, oligofluorenes are good blue emitters and the emission quantum yield is around 0.8 in the violet–blue range. These fluorene based compounds are used in cholesteric liquid crystals mixtures as luminescent chiral dopants and a fine tuning of the laser emission is obtained. The dependence of lasing efficiency on concentration and the handedness of chiral luminescent dopants are investigated.     

Synergistic profiles of chain‐breaking antioxidants with phosphites and hindered amine light stabilizers in styrene–ethylene–butadiene–styrene (SEBS) block copolymer

The photostabilization of poly(styrene‐b‐ethylene‐co‐butylene‐b‐styrene) (SEBS) by phosphite/p‐hydroxybenzoate antioxidants and hindered phenol/hindered amine light stabilizers (HALS) was studied by using a variety of spectroscopic methods, including FTIR, UV, and luminescence spectroscopy coupled with crosslinking and hydroperoxide analysis. The results were compared with those obtained for hindered phenols and their combinations with phosphite antioxidants. All the stabilizing packages stabilized the SEBS in terms of the inhibition of discoloration and the formation of hydroperoxides, acetophenone, and oxidation products, as well as chain scission and disaggregation of the styrene units. Although phosphite/p‐hydroxybenzoate combinations appeared to reduce the formation of oxidation products, they did not show any remarkable enhancement in long‐term stabilization with respect to phenolic/phosphite antioxidants. On the other hand, strong synergistic profiles were found with the HALS. Mobility and diffusion impediments in the polymeric material appeared to play an important role in the stabilizing activity of the HALS. J. VINYL. ADDIT. TECHNOL. 12:8–13, 2006. © 2006 Society of Plastics Engineers     

NUMERICAL SIMPLIFICATION METHOD FOR STATE-SPACE MODELS OF THERMAL SYSTEMS

A numerical method is presented to simplify state-space models of thermal systems, based on appropriate projection of the thermal field. The proposed coordinate system to express the equations of the original model highlights privileged directions. It allows us to obtain a simplified model where an approximation of the thermal field is given by a projection on a particular reduced basis. Illustrative examples are presented.     

PdCu membrane integration and lifetime in the production of hydrogen from methane

PdCu membranes prepared by sequential electroless plating were integrated into a hydrogen production and purification process. Hydrogen was produced from methane through catalytic partial oxidation and wet catalytic partial oxidation with Ni-based catalysts. Membrane permeance was measured with thermal cycles in an inert and hydrogen atmosphere at 673 and 773 K. Permeability was 1.98·10⁻³ mol/(smPa^0.5) at 673 K and 2.62·10⁻³ mol/(smPa^0.5) at 773 K. The optimum sweep gas flow required in the membrane module when operating with hydrogen-containing mixtures was selected. Peak hydrogen recovery was obtained using 15–20% of the feed to the module as sweep gas flow. Membranes were then placed downstream of the hydrogen production reactor. The CO and H₂O percentages fed to the membrane module did not have a major impact on membrane behavior. Around 60–67% of the hydrogen fed to the membrane module was separated, regardless of its composition.     

The molecular characterization of new types of Saccharomyces cerevisiae × S. kudriavzevii hybrid yeasts unveils a high genetic diversity

New double‐ and triple‐hybrid Saccharomyces yeasts were characterized using PCR‐restriction fragment length polymorphism of 35 nuclear genes, located on different chromosome arms, and the sequencing of one nuclear and one mitochondrial gene. Most of these new hybrids were originally isolated from fermentations; however, two of them correspond to clinical and dietary supplement isolates. This is the first time that the presence of double‐hybrid S. cerevisiae × S. kudriavzevii in non‐fermentative substrates has been reported and investigated. Phylogenetic analysis of the MET6 nuclear gene confirmed the double or triple parental origin of the new hybrids. Restriction analysis of gene regions in these hybrids revealed a high diversity of genome types. From these molecular characterizations, a reduction of the S. kudriavzevii fraction of the hybrid genomes is observed in most hybrids. Mitochondrial inheritance in hybrids was deduced from the analysis of mitochondrial COX2 gene sequences, which showed that most hybrids received the mitochondrial genome from the S. kudriavzevii parent. However, two strains inherited a S. cerevisiae COX2, being the first report of S. cerevisiae × S. kudriavzevii hybrids with S. cerevisiae mitochondrial genomes. These two strains are those showing a higher S. kudriavzevii nuclear genome reduction, especially in the wine hybrid AMH. This may be due to the release of selective pressures acting on the other hybrids to maintain kudriavzevii mitochondria‐interacting genes. Copyright © 2011 John Wiley & Sons, Ltd.     

Hydrogen production from methane and natural gas steam reforming in conventional and microreactor reaction systems

Ni-based (over MgO and Al₂O₃) and noble metal-based (Pd and Pt over Al₂O₃) catalysts were prepared by wet impregnation method and thereafter impregnated in microreactors. The catalytic activity was measured at several temperatures, atmospheric pressure and different steam to carbon, S/C, ratios. These conditions were the same for conventional, fixed bed reactor system, and microreactors. Weight hourly space velocity, WHSV, was maintained equal in order to compare the activity results from both reaction systems. For microreactor systems, similar activities of Ni-based catalyst were measured in the steam methane reforming (SMR) activity tests, but not in the case of natural gas steam reforming tests. When noble metal-based catalysts were used in the conventional reaction system no significant activity was measured but all catalysts showed some activity when they were tested in the microreactor systems. The analysis by SEM and TEM revealed a carbon-free surface for Ni-based catalyst as well as carbon filaments growth in case of noble metal-based catalysts.     

Unambiguous characterization of gunshot residue particles using scanning laser ablation and inductively coupled plasma-mass spectrometry

A new method based on scanning laser ablation and inductively coupled plasma-mass spectrometry (LA-ICPMS) for the detection and identification of gunshot residue (GSR) particles from firearms discharges has been developed. Tape lifts were used to collect inorganic residues from skin surfaces. The laser ablation pattern and ICPMS conditions were optimized for the detection of metals present in GSR, such as (121)Sb, (137)Ba, and (208)Pb. Other isotopes ((27)Al, (29)Si, (31)P, (33)S, (35)Cl, (39)K, (44)Ca, (57)Fe, (60)Ni, (63)Cu, (66)Zn, and (118)Sn) were monitored during the ICPMS analyses to obtain additional information to possibly classify the GSR particles as either characteristic of GSR or consistent with GSR. In experiments with real samples, different firearms, calibers, and ammunitions were used. The performed method evaluation confirms that the developed methodology can be used as an alternative to the standard scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) technique, with the significant advantage of drastically reducing the analysis time to less than 66 min.