High-speed InGaAsP/InP multiple quantum well, 1.55 mu m singlemode modulator

1.55 mu m single mode ridge waveguide modulators based on electroabsorption in InGaAsP/InP multiple quantum wells (MQW) are reported. A 10 dB extinction ratio was obtained by applying a 2 V drive voltage to a 100 mu m long device with a 3 dB on-state loss. The 3 dB cutoff frequency is 12.5 GHz.<>     

The effect of benzenesulfonamide plasticizers on the glass transition temperature of an amorphous aliphatic polyamide

The plasticizing effect of benzenesulfonamides (BSAs) on an amorphous aliphatic polyamide (AAPA) has been studied using dynamic mechanical analysis of copper‐supported spin‐coated mixtures. It follows that N‐(n‐butyl)BSA (BBSA), an amorphous liquid hydrogen bonding BSA, is fully miscible with AAPA because their mixtures are characterized by a single glass transition (T_g) throughout the compositional range. The T_g–composition dependence, however, is not linear because experimental results suggest a 20 K fall in T_g occurring around 0.65 BBSA units per amide unit, which coincides with the system shifting from a polymer‐like to a liquid‐like glass‐forming material. When considering a crystallizable hydrogen‐bonding plasticizer such as ethylBSA (EBSA), AAPA/EBSA mixtures become fully crystalline at a 1.3 EBSA unit per amide group. Nevertheless, melting point depression together with the single T_g observed throughout the compositional range on quenched (and therefore amorphous) samples confirms the miscibility of AAPA chains with the plasticizer. N,N‐DialkylBSAs, which lack the sulfonamide proton and therefore the possibility of hydrogen bonding with amide groups, quickly phase separate from AAPA, the glass transition of the latter staying mainly unaffected apart from a small (9 K) decrease at 10–15 mol% plasticizer. © 2001 Society of Chemical Industry     

Highly stable DNA triplexes formed with cationic phosphoramidate pyrimidine alpha-oligonucleotides

The ability of cationic phosphoramidate pyrimidine alpha-oligonucleotides (ONs) to form triplexes with DNA duplexes was investigated by UV melting experiments, circular dichroism spectroscopy and gel mobility shift experiments. Replacement of the phosphodiester linkages in alpha-ONs with positively charged phosphoramidate linkages results in more efficient triplex formation, the triplex stability increasing with the number of positive charges. At a neutral pH and in the absence of magnesium ions, it was found that a fully cationic phosphoramidate alpha-TFO (triplex-forming oligonucleotide) forms a highly stable triplex that melts at a higher temperature than the duplex target. No hysteresis between the annealing and melting curves was noticed; this indicates fast association. Moreover, the recognition of a DNA duplex with a cationic alpha-TFO through Hoogsteen base pairing is highly sequence-specific. To the best of our knowledge, this is the first report of stable triplexes in the pyrimidine motif formed by cationic alpha-oligonucleotides and duplex targets.     

Solid-state NMR for the study of membrane systems: the use of anisotropic interactions

The use of solid-state nuclear magnetic resonance (NMR) as a tool to determine the structure of membrane molecules is reviewed with a particular emphasis on techniques that provide information on orientation or order. Experiments reported here have been performed in membranes, rather than in micelles or organic solvents. Several ways to prepare and handle the samples are discussed, like sample orientation and magic-angle spinning (MAS). Results concerning lipids, membrane peptides and proteins are included, as well as a discussion regarding the potential of such methods and their pitfalls.     

Electrical,rheological properties and morphologies of biphasic blends filled with carbon nanotubes in one of the two phases

The present study compares two biphasic blends constituted by immiscible thermoplastics: polypropylene (PP)/polycaprolactone (PCL) and polyamide 12 (PA12)/PCL, both filled with carbon nanotubes (CNT). The experimentations, led with the aim to point up the differences between the two blends, were carried out on the rod formed samples (diameter 1.5 mm) just after extrusion or pelletization. During this process, CNT are first introduced in PCL and then mixed with PP or PA12. These two blends can comprise different kinds of morphologies depending on components weight fractions. The electrical conductivity is affected by the blend morphology on one hand and by the localization of CNT on the other hand. Even with a similar mixing sequence, CNT localization is different between the two blends. CNT migration from PCL to PA12 was highlighted in the PA12/PCL blend, in comparison with the PP/PCL blend where CNT stay in PCL.. Different experimental techniques such as selective phase extraction, microscopy analyses (SEM and TEM), rheology measurements and interfacial energy calculations based on surface tension measurements, can explain the different behaviours of each blend. A correlation between the observed morphology and the wetting coefficient calculated with experimental measurements of surface tensions allowed to predict CNT localization.     

Electro-oxidation of hydrolysed poly-oxymethylene-dimethylether on PtRu supported catalysts

Poly-oxymethylene-dimethylether (CH₃-O-(CH₂-O)_n-CH₃ (n = 3), abbreviated as POMM₃), which has no toxicity and a very low vapour pressure, unlike methanol, was investigated as a possible liquid fuel for a direct oxidation-type fuel cell. The electrocatalytic activity towards the oxidation of methanol, formaldehyde and a fully hydrolysed form of POMM₃ in 0.1 mol dm⁻³ HClO₄ solution was examined from 30 °C to 90 °C by using a channel flow cell system at three different types of PtRu catalysts, dispersed on high surface area supports, i.e., carbon black, antimony-doped tin oxide (Sb-SnO₂), and the latter mixed with a certain fraction of acetylene black (AB) to improve the electronic conductivity. The PtRu/Sb-SnO₂ + AB catalyst exhibited the best electrocatalytic activity and thermal stability towards the fully hydrolysed POMM₃ and formaldehyde oxidations, for which the mass activity was about ten times higher than that for methanol.