Methane preconcentration in a microtrap using multiwalled carbon nanotubes as sorbents

The GC monitoring of green house gases is a challenging task because the concentration of organic species such as methane are relatively low (ppm to ppb) and their analysis requires some level of preconcentration. Since methane is highly volatile, it is not easily retained on conventional sorbents. In this paper we present multiwalled carbon nanotubes (MWNTs) as an effective sorbent for a microtrap designed for methane preconcentration. Its performance was compared to other commercially available carbon based sorbents, and it was found to be the most effective sorbent in terms of breakthrough volume and enthalpy of adsorption.     

Search for anomalous interaction mean free paths of charge, 2≦Z≦18 projectile fragments in emulsions exposed to 1.8 A GeV40Ar ions

⁴⁰Ar-emulsion interactions are studied, to investigate the question of anomalons, in twoG- 5 emulsion stacks. In about 4600 primary interactions, projectile fragments of Z≧2 for all generations have been followed until they interact or leave the stack. After careful estimation of charges of these fragments, variation of their mean free paths is studied as a function of distance from the preceding interaction. Generation effect,N _h dependence and production angle effect are investigated. In addition multi-chain events are analysed separately. Our results do not show anomalons at the 6% level and are consistent with non-occurrence of anomalons. However, this experiment is not sensitive enough to rule out anomalons (with a mfp of the order of 2 to 3 cm) produced at about 1% (or less) level.     

Thermal hysteresis of some important physical properties of nanoparticles

Gold nanoparticles show thermal hysteresis with properties such as surface plasmon absorption, conductivity, and zeta potential. The direction of the incremental change in plasmon peak position and its extinction depend on the nature of surface conjugation. The thermal profile of a surface plasmon resonance spectrum for nanoparticles may serve as a signature for the associated small molecule or macromolecule on which it is seeded. The thermal responses of zeta potential and conductivity profile are found to be independent of the surface conjugation with the later being subjected to a phase transition phenomenon as revealed by a temperature criticality.     

Ion-exchange separation of metal ions with thiosulphate

Summary In a cationic column of Amberlite IR-120 with thiosulphate as the eluting agent it has been possible to separate metal ions from several two to five component mixtures.

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Zusammenfassung Mischungen von 2–5 Metallionen konnten durch Ionenaustausch-chromatographie an Amberlite IR-120 mit Thiosulfat als Eluierungsmittel getrennt werden.

     

H2-release from alcohols,diols, and compounds with amino functionality promoted by titanium(II) sandwich complex, [Cp2Ti]: a theoretical approach

Structural Chemistry - The role of Ti(II) sandwich complex, [Cp2Ti], generated by the combination of [Cp2TiCl2] and two equivalents of nBuLi, in situ, in toluene has been investigated theoretically...     

Study of the Release Mechanism of Terminalia chebula Extract from Nanoporous Silica Gel

Sol/gel-derived silica gel was prepared at room temperature from tetraethyl orthosilicate precursor. The extracts of Terminalia chebula (Haritoki) were entrapped into the porous silica gel. Fourier transform infrared analysis revealed the proper adsorption of herbal values in the nanopores of the silica gel. Porosity was estimated by transmission electron microscope studies. The release kinetics of the extract in both 0.1 N HCl, pH 1.2, and Phosphate-buffer saline (PBS), pH 7.2, were determined using UV–Vis spectroscopy. Different dissolution models were applied to release data in order to evaluate the release mechanisms and kinetics. Biphasic release patterns were found in every formulation for both the buffer systems. The kinetics followed a zero-order equation for first 4 h and a Higuchi expression in a subsequent timeline in the case of 0.1 N HCl. In the case of PBS, the formulations showed best linearity with a first-order equation followed by Higuchi’s model. The sustained release of the extract predominantly followed diffusion and super case II transport mechanism. The release value was always above the minimum inhibitory concentration.     

Composites of poly(ε‐caprolactone) and Mo6S3I6 Nanowires

Composites of poly(ε‐caprolactone) (PCL) and molybdenum sulfur iodine (MoSI) nanowires were prepared using twin‐screw extrusion. Extensive microscopic examination of the composites revealed the nanowires were well dispersed in the PCL matrix, although bundles of Mo₆S₃I₆ ropes were evident at higher loadings. Secondary electron imaging (SEI) showed the nanowires had formed an extensive network throughout the PCL matrix, resulting in increased electrical conductivity of PCL, by eight orders of magnitude, and an electrical percolation threshold of 6.5 × 10^?3 vol%. Thermal analysis (DSC), WAXD, and hot stage polarized optical microscopy (HSPOM) experiments revealed Mo₆S₃I₆ addition altered PCL crystallization kinetics, nucleation density, and crystalline content. A greater number of smaller spherulites were formed via heterogeneous nucleation. The onset of thermal decomposition (TGA) of PCL decreased by 70°C, a consequence of the thermal degradation of Mo₆S₃I₆ to MoO₃, which in turn accelerates the formation of volatile gases during the first stage of PCL decomposition. Copyright © 2010 John Wiley & Sons, Ltd.     

Multiscale spatial Monte Carlo simulations: multigriding, computational singular perturbation, and hierarchical stochastic closures

Monte Carlo (MC) simulation of most spatially distributed systems is plagued by several problems, namely, execution of one process at a time, large separation of time scales of various processes, and large length scales. Recently, a coarse-grained Monte Carlo (CGMC) method was introduced that can capture large length scales at reasonable computational times. An inherent assumption in this CGMC method revolves around a mean-field closure invoked in each coarse cell that is inaccurate for short-ranged interactions. Two new approaches are explored to improve upon this closure. The first employs the local quasichemical approximation, which is applicable to first nearest-neighbor interactions. The second, termed multiscale CGMC method, employs singular perturbation ideas on multiple grids to capture the entire cluster probability distribution function via short microscopic MC simulations on small, fine-grid lattices by taking advantage of the time scale separation of multiple processes. Computational strategies for coupling the fast process at small length scales (fine grid) with the slow processes at large length scales (coarse grid) are discussed. Finally, the binomial tau-leap method is combined with the multiscale CGMC method to execute multiple processes over the entire lattice and provide additional computational acceleration. Numerical simulations demonstrate that in the presence of fast diffusion and slow adsorption and desorption processes the two new approaches provide more accurate solutions in comparison to the previously introduced CGMC method.