42 research outputs found
The influence of Ga-irradiation on the transport properties of mesoscopic conducting thin films
We studied the influence of 30keV Ga-ions -- commonly used in focused ion
beam (FIB) devices -- on the transport properties of thin crystalline graphite
flake, LaCaMnO and Co thin films. The changes of the
electrical resistance were measured in-situ during irradiation and also the
temperature and magnetic field dependence before and after irradiation. Our
results show that the transport properties of these materials strongly change
at Ga fluences much below those used for patterning and ion beam induced
deposition (IBID), limiting seriously the use of FIB when the intrinsic
properties of the materials of interest are of importance. We present a method
that can be used to protect the sample as well as to produce selectively
irradiation-induced changes.Comment: 14 pages, 11 figures, will be published in Nanotechnology 201
Strong interconversion of non-polar phonons and Josephson plasma oscillations induced by equilibrium Josephson currents in high T_c superconductors
We analyze consequences of dynamical modulations of Josephson current by
non-polar lattice mode in the Josephson junction barrier. In the high
junctions, the effect of such modulations can be anomalously strong due to the
proximity of the insulating barrier to the superconducting state. Accordingly,
the interconversion of sound (as well as other non-polar phonons) and the
Josephson plasma oscillations mediated by stationary Josephson currents, which
may be present in the junction due to various reasons, becomes possible. We
suggest that this effect can be employed for imaging of the stationary
Josephson currents. Estimates of the effect are given.Comment: 11 RevTeX pages, no figure
An alternative application to the portuguese agro-industrial residue : wheat straw
The effects of alkaline treatments of the wheat straw with sodium hydroxide were investigated. The optimal condition for extraction of hemicelluloses was found to be with 0.50 mol/l sodium hydroxide at 55 °C for 2 h. This resulted in the release of 17.3% of hemicellulose (% dry starting material), corresponding to the dissolution of 49.3% of the original hemicellulose. The yields were determined by gravimetric analysis and expressed as a proportion of the starting material. Chemical composition and physico-chemical properties of the samples of hemicelluloses were elucidated by a combination of sugar analyses, Fourier transform infrared (FTIR), and thermal analysis. The results showed that the treatments were very effective on the extraction of hemicelluloses from wheat straw and that the extraction intensity (expressed in terms of alkali concentration) had a great influence on the yield and chemical features of the hemicelluloses. The FTIR analysis revealed typical signal pattern for the hemicellulosic fraction in the 1,200–1,000 cm−1 region. Bands between 1,166 and 1,000 cm−1 are typical of xylans.Conselho Nacional de
Desenvolvimento CientÃfico e Tecnológico (CNPq)Fundação de Amparo a Pesquisa do Estado de São Paulo/Brazil (FAPESP)Fundação para a Ciência e a Tecnologia (FCT) - SFRH/BPD/26156/2005, SFRH/BPD/26108/200
Cellulosic films obtained from the treatment of sugarcane bagasse fibers with N -methylmorpholine- N -oxide (NMMO)
Ethanol/water organosolv pulping was used to obtain sugarcane bagasse pulp
that was bleached with sodium chlorite. This bleached pulp was used to obtain cellulosic
films that were further evaluated by Fourier transform infrared (FTIR) spectroscopy,
thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). A good film
formation was observed when temperature of 74 °C and baths of distilled water were used,
which after FTIR, TGA, and SEM analysis indicated no significant difference between the
reaction times. The results showed this to be an interesting and promising process,
combining the prerequisites for a more efficient utilization of agro-industrial residues.Fundação de Amparo à Pesquisa
do Estado de São Paulo (FAPESP), (CNPq), and Coordenação de Aperfeiçoamento de Pessoal de NÃvel Superior (CAPES), Brazil; Fundação para a Ciência e a Tecnologia (FCT) and CEMU