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Multi-walled carbon nanotubes (MWCNTs) are successfully processed in the form of thin films (buckypapers), and their morphology and electrical behaviour are characterized. The MWCNTs are synthesized by the floating catalyst chemical vapour deposition process. The effects of a sequence of treatments applied for MWCNTs purification on the buckypapers electrical behaviour are also examined. Nanocomposite thin films constituted of pristine and purified MWCNTs and Pd nanoparticles are prepared in order to evaluate their viability as H 2 sensors at room temperature. For this purpose, the electrical resistance of the nanocomposite films in atmospheres with different H 2 concentrations, is determined. Scanning electron microscopy (SEM) images show that the buckypapers and the nanocomposite films are 2D structures constituted by randomly oriented MWCNTs. The buckypapers present a semiconductor-like electrical behaviour as determined by the standard four point method. Room temperature resistivity values of around 10 -3 Ω m are assessed. Nanocomposite films show different electrical behaviour depending on the purification treatment applied to the MWCNTs employed. Furthermore, the electrical resistance of the nanocomposite films is found to increase when the measurements are performed in H 2 atmosphere. Values of H 2 sensitivity at room temperature of the nanocomposite films up to 2.15% are determined for H 2 average concentration higher than 350 ppm with short recovery time. Fil: Zilli, Dario Adrian. Universidad de Buenos Aires. Programa de Investigación y Desarrollo de Fuentes Alternativas de Materias Primas y Energía; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Bonelli, Pablo Ricardo. Universidad de Buenos Aires. Programa de Investigación y Desarrollo de Fuentes Alternativas de Materias Primas y Energía; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Cukierman, Ana Lea. Universidad de Buenos Aires. Programa de Investigación y Desarrollo de Fuentes Alternativas de Materias Primas y Energía; Argentina. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

We present micro-calorimetric specific heat measurements on different multiwall carbon nanotubes of large outer diameter, as a function of temperature in the range 10–120 K. A clear anomaly at 60 K with the shape of a peak is present in two of the samples, and both the height and the characteristic temperature of the peak are independent of magnetic field and do not exhibit thermal hysteresis, discarding magnetic degrees of freedom related to Fe seeds or contributions from adsorbed gases. These features suggest that the anomaly may be caused by a structural change. As the anomaly is also unaffected by induced intertube disorder, it may be related with a melting of orientational dislocations of individual tubes within multiwall nanotubes, an effect that was theoretically predicted to occur in carbon nanotubes and represents a distinctive feature of asymmetric molecular systems.

Transmission electron microscopy of arrays of multi-walled carbon nanotubes reveals the presence of numerous Y-junctions. The diameter distributions of the samples are found to be bimodal, with one mode corresponding to the branches and the other mode to the trunk of the Y-junctions. The analysis of the micrographs shows that the junctions form via the merger of metal particles during the tip-growth of the

Epoxy composites based on aligned chemical vapor deposition–grown multiwall carbon nanotubes (MWCNTs), containing trapped iron nanoparticles, with weight fractions ranging from 0.03 to 1 wt%, were produced following a well-known processing way. Electrical and mechanical properties as well as their densities were measured. The results are compared with previous studies investigating the magnetic percolation behavior in the same samples of composites. A percolation threshold at 0.4 wt% of MWCNTs was determined by the electrical property and it agrees with the threshold observed in the magnetic properties. A hop in the porosity and a depression of the bulk mechanical properties were also found at the threshold value. These results point out that there is an efficiency threshold related to the sonication stage of the fabrication process and the weight fraction of MWCNTs, and after this threshold, the initial nanotubes pans were not separated into individual MWCNTs or into small ropes. An optimized sonication stage is proposed and the improvement in the dispersion of the filler is shown. POLYM. COMPOS., 28:612–617, 2007. © 2007 Society of Plastics Engineers

Drug loaded buckypapers based on different types of carbon nanotubes (CNTs) were prepared and characterized in order to evaluate their potentialities for the design of novel transdermal drug delivery systems. Lab-synthesized CNTs as well as commercial samples were employed. Clonidine hydrochloride was used as model drug, and the influence of composition of the drug loaded buckypapers and processing variables on in vitro release profiles was investigated. To examine the influence of the drug nature the evaluation was further extended to buckypapers prepared with flurbiprofen and one type of CNTs, their selection being based on the results obtained with the former drug. Scanning electronic microscopy images indicated that the model drugs were finely dispersed on the CNTs. Differential scanning calorimetry, and X-ray diffraction pointed to an amorphous state of both drugs in the buckypapers. A higher degree of CNT-drug superficial interactions resulted in a slower release of the drug. These interactions were in turn affected by the type of CNTs employed (single wall or multiwall CNTs), their functionalization with hydroxyl or carboxyl groups, the chemical structure of the drug, and the CNT:drug mass ratio. Furthermore, the application of a second layer of drug free CNTs on the loaded buckypaper, led to decelerate the drug release and to reduce the burst effect. Fil: Schwengber, Alex. Universidad de Buenos Aires. Programa de Investigación y Desarrollo de Fuentes Alternativas de Materias Primas y Energía; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Prado, Héctor Juan. Universidad de Buenos Aires. Programa de Investigación y Desarrollo de Fuentes Alternativas de Materias Primas y Energía; Argentina. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Zilli, Dario Adrian. Universidad de Buenos Aires. Programa de Investigación y Desarrollo de Fuentes Alternativas de Materias Primas y Energía; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Bonelli, Pablo Ricardo. Universidad de Buenos Aires. Programa de Investigación y Desarrollo de Fuentes Alternativas de Materias Primas y Energía; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Cukierman, Ana Lea. Universidad de Buenos Aires. Programa de Investigación y Desarrollo de Fuentes Alternativas de Materias Primas y Energía; Argentina. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

The adsorption characteristics of self-oriented multi-walled carbon nanotube (MWCNT) arrays are examined from N2 (−196 °C) adsorption measurements. The arrays were synthesized in a laboratory by in situ chemical vapour deposition of iron or cobalt phthalocyanines at 880 and 950 °C, under otherwise constant conditions, in an attempt to obtain different morphological structures. For both precursors, increasing the temperature leads to MWCNT arrays with lower Brunauer–Emmett–Teller (BET) surface area and total pore volume, though the effect is more pronounced for those arising from the iron-based compound. Despite this, precursor yields of individual nanotubes of larger diameter, higher BET area and total pore volume characterize the resulting arrays compared to those arising from cobalt phthalocyanine for the same temperatures. As evidenced by SEM and TEM images, the arrays synthesized from iron phthalocyanine at 880 °C show better vertical alignment and denser structures than those obtained from this compound at 950 °C, and also from cobalt phthalocyanine at both temperatures. Further ultrasonication of the arrays produced from the iron compound brings about a significant reduction in their adsorption capacity, attributable to the pronounced disarrangement of the resulting structures. The present results demonstrate that the alignment of MWCNT arrays plays a crucial role in their N2 adsorption characteristics.

Epoxy matrix composites have been prepared using as filler different weight fractions (0.03–1 wt%) of CVD grown multi-walled carbon nanotubes (MWCNTs) containing trapped iron nanoparticles. Magnetic characterization performed at room temperature with magnetic field between K19 and 19 kG shows that the nanocomposites are weakly ferromagnetic at room temperature. An abrupt variation in the dependence of both the coercivity field, BC, and remanent magnetization, MR, with the weight fraction of MWCNTs, f, was found for fZ 0.4%. Results suggest the formation of MWCNTs agglomerates for increasing weight concentrations, in accordance with SEM micrographs. q 2005 Elsevier Ltd. All rights reserved.

We report on high-speed eclipse photometry of the dwarf nova V2051 Oph while it was in a low brightness state, at B ~ 16.2 mag. In comparison to the average IUE spectra, the ultraviolet continuum and emission lines appear reduced by factors of, respectively, ~4 and ~5. Flickering activity is mostly suppressed and the lightcurve shows the eclipse of a compact white dwarf at disc centre which contributes ~60 per cent of the total light at 3900--4300 A. We use measurements of contact phases in the eclipse lightcurve to derive the binary geometry and to estimate masses and relevant dimensions. We find a mass ratio of q= 0.19+/-0.03 and an inclination of i= 83+/-2 degrees. The masses of the component stars are M_1 = 0.78+/-0.06 M_dot and M_2 = 0.15+/-0.03 M_dot. Our photometric model predicts K_1 = 83+/-12 km/s and K_2= 435+/-11 km/s. The predicted value of K_1 is in accordance with the velocity amplitude obtained from the emission lines after a correction for asymmetric line emission in the disc is made (Watts et al. 1986). The secondary of V2051 Oph is significantly more massive than the secondaries of the other ultra-short period dwarf novae. V2051 Oph is probably a relatively young system, whose secondary star had not enough time to evolve out of thermal equilibrium., Comment: 16 pages, 7 postscript figures, coded using MNRAS latex style. To appear in Monthly Notices of the Royal Astronomical Society. Revised version with changes in section 4.3. For related papers and files see ftp://fsc01.fsc.ufsc.br/pub/bap and http://www.fsc.ufsc.br/~astro

Data warehouse implementation is assumed to be a very knowledge-demanding, expensive and long-lasting process. As such it requires senior management sponsorship, involvement of experts, a big budget and probably years of development time. Presented Outpatient Health Care Statistics Data Warehouse implementation research provides ample evidence against the infallibility of the above statements. New, inexpensive, but powerful technology, which provides outstanding platform for On-Line Analytical Processing (OLAP), has emerged recently. Presumably, it will be the basis for the estimated future growth of data warehouse market, both in the medical and in other business fields. Methods and tools for building, maintaining and exploiting data warehouses are also briefly discussed in the paper.