A unified treatment of the equation of state of hard linear bodies

An unified treatment of the equation of state of convex (spherocylinders) and non-convex (dumbells) hard bodies is presented. Comparison of our results with simulation shows very good agreement for diatomics and excellent for triatomics.     

Capillary Rise in Porous Media

Capillary rise experiments were performed in columns filled with glass beads and Berea sandstones, using visual methods to register the advance of the water front. For the glass bead filled columns, early time data are well fitted by the Washburn equation. However, in the experiments, the advancing front exceeded the predicted equilibrium height. For large times, an algebraic behavior of the velocity of the front is observed (T. Delker et al., Phys. Rev. Lett. 76, 2902 (1996)). A model for studying the capillary pressure evolution in a regular assembly of spheres is proposed and developed. It is based on a quasi-static advance of the meniscus with a piston-like motion and allows us to estimate the hydraulic equilibrium height, with values very close to those obtained by fitting early time data to a Washburn equation. The change of regime is explained as a transition in the mechanism of advance of the meniscus. On the other hand, only the Washburn regime was observed for the sandstones. The front velocity was fitted to an algebraical form with an exponent close to 0.5, a value expected from the asymptotic limit of the Washburn equation. Copyright 2001 Academic Press.     

Investigation of the quantitative properties of the quadrupole orthogonal acceleration time-of-flight mass spectrometer with electrospray ionisation using 3,4-methylenedioxymethamphetamine

This paper describes the investigation of the potential of a quadrupole orthogonal acceleration time-of-flight mass spectrometer (Q-TOF) equipped with an atmospheric pressure ionisation interface for quantitative measurements of small molecules separated by reversed phase liquid chromatography. To this end, the detection limits and linear dynamic range in particular were studied in an LC/MS/MS experiment using 3,4-methylenedioxymethamphetamine standards and 3,4-methylenedioxyethylamphetamine for internal standardisation. In a second phase, the experiment was repeated with real biological extracts (whole blood, serum, and vitreous humour). A calibration for 3,4-methylenedioxymethamphetamine and its metabolite 3,4-methylenedioxyamphetamine was prepared in each of these matrices again using 3,4-methylenedioxyethylamphetamine as internal standard. The resulting quantitative data were compared with those obtained by liquid chromatography with fluorescence detection for the same extracts. The Q-TOF results revealed excellent sensitivity and a linear dynamic range of nearly four decades (2-10 000 pg on-column, r(2) = 0.9998, 1/x weighting). Furthermore, all the calibration curves prepared in biological material were superimposable, LC/MS/MS and LC-fluorescence, and the quantitative results for actual samples compared very favourably. It was concluded that the Q-TOF achieves a linear dynamic range for quantitative LC/MS/MS work exceeding that of fluorescence detection and at much better absolute sensitivity. Copyright 1999 John Wiley & Sons, Ltd.     

M?ssbauer study of carbon coated iron magnetic nanoparticles produced by simultaneous reduction/pyrolysis

Magnetic iron nanoparticles immersed in a carbon matrix were produced by a combined process of controlled dispersion of Fe^3?+? ions in sucrose, thermal decomposition with simultaneous reduction of iron cores and the formation of the porous carbonaceous matrix. The materials were prepared with iron contents of 1, 4 and 8 in %wt in sucrose and heated at 400, 600 and 800°. The samples were analyzed by XRD, Mössbauer spectroscopy, magnetization measurements, TG, SEM and TEM. The materials prepared at 400° are composed essentially of Fe₃O₄ particles and carbon, while treatments at higher temperatures, e.g. 600 and 800° produced as main phases Fe⁰ and Fe₃C. The Mössbauer spectra of samples heated at 400° showed two sextets characteristic of a magnetite phase and other contributions compatible with Fe^3?+? and Fe^2?+? phases in a carbonaceous matrix. Samples treated at temperatures above 600° showed the presence of metallic iron with concentrations between 16?C43%. The samples heated at 800° produced higher amounts of Fe₃C (between 20% and 58%). SEM showed for the iron 8% sample treated at 600?C800°C particle sizes smaller than 50 nm. Due to the presence of Fe⁰ particles in the carbonaceous porous matrix the materials have great potential for application as magnetic adsorbents.     

Microcalorimetric study on the growth and metabolism of <Emphasis Type="Italic">Pseudomonas aeruginosa</Emphasis>

Microcalorimetry is an experimental technique which allows us to precisely measure the energy released as a consequence of any transformation process. All organisms produce heat as a consequence of metabolism. The rate of heat production is an adequate measurement of metabolic activity of organisms and their constituent parts, cells and sub-cellular levels. Microorganisms produce small amounts of heat, in the order of 1–3 pW per cell. Despite the low quantity of heat produced by bacteria, their exponential replication in culture medium allows their detection using microcalorimetry. This study is a microcalorimetric study of the growth and metabolism of the bacterium Pseudomonas aeruginosa, using the heat liberated as a consequence of bacterial metabolism. With this aim, we used a Calvet microcalorimeter, inside which two Teflon screw-capped stainless steel cells were located (sample and reference). Experiments were carried out at final concentrations of 10⁶, 10⁵, 10³ and 10 CFU/mL, and a constant temperature of 309.65 K was maintained within the microcalorimeter. Recording the difference in calorific potential over time we obtained P. aeruginosa’s growth curves. The shape of these curves is characteristic and has a single phase. Thus, the heat flow curves were mathematically studied to calculate the growth constant and generation time of this bacterium.     

Effect of the AL-MCM-41 catalyst on the catalytic pyrolysis of atmospheric petroleum residue (ATR)

Thermogravimetry (TG) was used in this study to evaluate thermal and catalytic pyrolysis of Atmospheric Petroleum Residue (ATR) which can be found in the state of Rio Grande do Norte/Brazil, after a process of atmospheric distillation of petroleum. The utilized sample in the process of catalytic pyrolysis was Al-MCM-41, a mesoporous material. The procedures for obtaining the thermogravimetric curves were performed in a thermobalance with heating rates of 5, 10, and 20 °C min⁻¹. From TG, the activation energy was determined using the Flynn–Wall kinetic method, which decreased from 161 kJ mol⁻¹, for the pure ATR, to 71 kJ mol⁻¹, in the presence of the Al-MCM-41, showing the efficiency of the catalyst in the pyrolysis of Atmospheric Petroleum Residue.     

Ion pair-based dispersive liquid-liquid microextraction for gold determination at ppb level in solid samples after ultrasound-assisted extraction and in waters by electrothermal-atomic absorption spectrometry

A new methodology was developed for the determination of ultratrace levels of gold in water samples, soils and river sediments. Dispersive liquid-liquid microextraction was used to preconcentrate the ion pair formed between AuCl₄⁻ and [CH₃(CH₂)₃]₄N⁺ in a microliter-range volume of chlorobenzene using acetone as disperser solvent. When solid samples were analyzed, the method consisted of a combination of ultrasound-assisted extraction and dispersive liquid-liquid microextraction with final detection by electrothermal-atomic absorption spectrometry. Since an HCl medium was required for the formation of the AuCl₄⁻ complex, HCl together with HNO₃ was used as extractants for ultrasound-assisted extraction. After optimization, the enrichment factor obtained was 220 for water samples. Moreover, the extraction efficiency was around 96%. The repeatability, expressed as relative standard deviation ranged from 3.6% to 9.7%. The instrumental detection limit was 8.4 ng L⁻¹, whereas the procedural detection limits were 42 ng L⁻¹ for water samples and 1.5 ng g⁻¹ for environmental solid samples.