Carbon xerogel supported noble metal catalysts for fine chemical applications

Carbon xerogels are mesoporous materials obtained upon pyrolysis of the dried gels resulting from polycondensation of resorcinol and formaldehyde. Treatment with nitric acid under severe conditions introduces high amounts of oxygen containing functional groups onto the surface of the material, leading however to the collapse of its porous structure. The resulting material is then used to support 1 wt.% Pt, Ir and Ru monometallic catalysts by wet impregnation using organometallic precursors. The catalysts are characterized by N₂ adsorption–desorption isotherms at 77 K, temperature programmed desorption coupled with mass spectrometry, scanning and transmission electron microscopy, and H₂ chemisorption. The liquid-phase selective hydrogenation of cinnamaldehyde to cinnamyl alcohol is used in order to assess the catalytic performance of the prepared materials. Pt and Ru catalysts are initially very selective towards the hydrogenation of the olefinic double bond, while Ir is mostly selective towards the carbonyl group. After a thermal post-reduction treatment at 973 K, selectivity towards cinnamyl alcohol is significantly improved regardless of the metal nature. The Pt catalyst exhibits the best behavior, a complete shift in C=C to C=O hydrogenation being detected. The improvement in selectivity is rationalized in terms of both an increase in metal particle size and a modification in the surface chemistry of the catalyst after the post-reduction treatment.     

Photophysical study of a conjugated-non-conjugated PPV-type electroluminescent copolymer

This paper reports the photo- and electroluminescence studies of emitting species of one of the first reported blue emitters, the conjugated-non-conjugated multi-block copolymer, poly[1,8-octanedioxy-2,6-dimethoxy-1,4-phenylene-1,2-ethenylene-1,4-phenylene-1,2-ethenylene-3,5-dimethoxy-1,4-phenylene]. Because the conjugation length of the emissive center is very well defined (two and half phenylene-vinylene units) the differences found between the fluorescence profile of the fluorophore in solution, at several concentrations and that in the solid state allowed us to conclude that in solid the emission comes from associated forms, such as ground-state dimers and/or excimers. Time-resolved fluorescence in a nanosecond time scale recorded at ?_em=24,096 cm⁻¹ showed a monoexponential decay of 1.5 ns, which is compatible with rigid forms of stilbene derivatives.     

A simple technique for identifying a linearized model for a didactic magnetic levitation system

A simple technique for obtaining the parameters of a linearized model for a didactic magnetic levitation system is introduced. The proposed procedure only involves basic concepts of dynamic systems and is suitable for use in undergraduate control experiments. The project and validation of a digital lead compensator based on the linearized model are also presented.     

Within stem variation of Maritime Pine timber mechanichal properties

Within-stem variation of mechanical properties of Maritime pine timber (Pinus pinaster Ait.) as function of tree class quality and location of the specimens on the stem (percentage of stem height, distance to pith and orientation) is discussed. The results show a strong and consistent effect of the distance to pith on all mechanical properties studied. A trend for the decrease of mechanical properties along the stem (from butt to top) was detected probably due to the growing presence of juvenile wood caused by tree taper and vicinity to crown. Juvenile wood thus seems to play a decisive role on the within-stem variation of mechanical properties. A clear increase on bending strength (55%), modulus of elasticity parallel to grain (99%), compression strength parallel to grain (44%) and tension strength perpendicular to grain (27%) for distance to pith from 10% to 90% of the trunk radius was observed at all tree height levels studied. Orientation (north or south location on the stem) appears to be negligible.

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Variation der mechanischen Eigenschaften im Stammholz von maritimer Kiefer (Pinus pinaster Ait.)

Zusammenfassung In der vorliegenden Arbeit werden Schwankungen mechanischer Eigenschaften im Stammholz von maritimer Kiefer (Pinus pinaster Ait.) als Funktion von Baumklassenqualität und Ort der Probenentnahme auf dem Stamm (Prozent der Stammhöhe, Entfernung zur Markröhre und Faserorientierung) diskutiert. Die Ergebnisse zeigen einen gleichbleibend starken Einfluss des Abstands zur Markröhre auf alle untersuchten mechanischen Eigenschaften. Festgestellt wurde eine Tendenz zur Abnahme der mechanischen Eigenschaften entlang des Stammes von unten nach oben, was vermutlich auf die Zunahme des Anteils von Juvenilholz bei gleichzeitiger Stammverjüngung in Richtung Baumkrone zurückzuführen ist. So scheint Juvenilholz eine entscheidende Rolle bei Schwankungen mechanischer Eigenschaften in Stammholz zu spielen. Eine klare Zunahme des Einflusses auf die Biegefestigkeit (55%), auf den E-Modul parallel zur Faser (99%), auf die Längsdruck - (44%) und Zugfestigkeit (27%) senkrecht zur Faser bei Entfernung zur Markröhre von 10–90% des Baumumfanges wurde auf allen Ebenen der Stammhöhe festgestellt. Die Faserrichtung (Nord- oder Südorientierung) scheint keine Rolle zu spielen.

     

On the Development of Analogue Sampled-Data Signal Processing

This paper provides a historical perspective on thedevelopment of analogue sampled-data signal processing circuitsand systems. The evolution, role and current trends in the developmentof analogue sampled-data signal processing systems is surveyed.Firstly, the evolution of integrated circuit based techniques,culminating in the ubiquitous switched-capacitor technique istraced. Then the role that analogue sampled-data systems playwithin the context of a general information processing environmentis examined and the required characteristics are identified.Trends in silicon integrated circuit processing technology aresummarised and their impact on sampled analogue circuits areidentified. Finally, the application of analogue current-modetechniques, and in particular switched-currents, to overcomesome of the limitations of previous voltage based approaches,is discussed.     

Functional in-circuit characterisation of ΣΔ modulators

A method for the in-circuit functional testing of ΣΔ modulators is described which can be built in large integrated circuits or systems-on-chip. It allows for measuring gain and phase, as well as total harmonic distortion and signal to noise and harmonic distortion ratio parameters. This method can be built in-circuit using existing computational resources, such as digital signal processors or (re)configurable logic, which can therefore be used to implement both mission and test operations. Both simulation and experimental results were obtained which are in close agreement with those expected from the theory.     

Removal of phenols from aqueous solutions by emulsion liquid membranes

The present study deals with the extraction of phenols from aqueous solutions by using the emulsion liquid membranes technique. Besides phenol, two derivatives of phenol, i.e., tyrosol (2-(4-hydroxyphenyl)ethanol) and p-coumaric acid (4-hydroxycinnamic acid), which are typical components of the effluents produced in olive oil plants, were selected as the target solutes. The effect of the composition of the organic phase on the removal of solutes was examined. The influence of pH of feed phase on the extraction of tyrosol and p-coumaric was tested for the membrane with Cyanex 923 as an extractant. The use of 2% Cyanex 923 allowed obtaining a very high extraction of phenols (97-99%) in 5-6 min of contact time for either single solute solutions or for their mixtures. The removal efficiency of phenol and p-coumaric acid attained equivalent values by using the system with 2% isodecanol, but the removal rate of tyrosol was found greatly reduced. The extraction of tyrosol and p-coumaric acid from their binary mixture was also analysed for different operating conditions like the volume ratio of feed phase to stripping phase (sodium hydroxide), the temperature and the initial concentration of solute in the feed phase.     

Increasing mouse embryonic fibroblast cells adhesion on superhydrophilic vertically aligned carbon nanotube films

We have analyzed the adhesion of mouse embryonic fibroblasts (MEFs) genetically modified by green fluorescence protein (GFP) gene cultured on vertically-aligned carbon nanotubes (VACNTs) after 6 days. The VACNTs films grown on Ti were obtained by microwave plasma chemical vapor deposition process using Fe catalyst and submitted to an oxygen plasma treatment, for 2 min, at 400 V and 80 mTorr, to convert them to superhydrophilic. Cellular adhesion and morphology were analyzed by scanning electron, fluorescence microscopy, and thermodynamics analysis. Characterizations of superhydrophilic VACNTs films were evaluated by contact angle and X-Ray Photoelectron Spectroscopy. Differences of crowd adhered cells, as well as their spreading on superhydrophilic VACNTs scaffolds, were evaluated using focal adhesion analysis. This study was the first to demonstrate, in real time, that the wettability of VACNTs scaffolds might have enhanced and differential adherence patterns to the MEF-GFP on VACNTs substrates.