Energetics and stability of vacancies in carbon nanotubes

In this work we present ab initio calculations of the formation energies and stability of different types of multi-vacancies in carbon nanotubes. We demonstrate that, as in the case of graphene, the reconstruction of the defects has drastic effects on the energetics of the tubes. In particular, the formation of pentagons eliminates the dangling bonds thus lowering the formation energy. This competition leads to vacancies having an even number of carbon atoms removed to be more stable. Finally the appearance of magic numbers indicating more stable defects can be represented by a model for the formation energies that is based on the number of dangling bonds of the unreconstructed system, the pentagons and the relaxation of the final form of the defect formed after the relaxation.     

Microorganism screening for limonene bioconversion and correlation with RAPD markers

The use of microorganisms for biotransformations of monoterpenes has stimulated the biotechnological market. Aiming at the highest efficiency in the process of strains screening, the application of molecular biology techniques have been proposed. Based on these aspects, the objective of this work was to select different strains able to convert limonene using fermentative process and random amplified polymorphic DNA (RAPD) markers. The results obtained in the fermentative screening, from 17 strains tested, pointed out that four microorganisms were able to convert limonene into oxygenated derivatives. The RAPD study showed a polymorphism of 96.02% and a similarity from 16.02 to 51.51%. Based on this it was possible to observe a high genetic diversity, even among strains of same species, concluding that the RAPD was not able to correlate the genetic characteristics of the microorganism with the results obtained from the biotransformation process.     

Two decades of high temperature gas chromatography (1983–2003): what's next?

The evolution of the concept of High Temperature High Resolution Gas Chromatography (HT-HRGC) is presented together with examples highlighting its potentialities. The range of molecular weight and number of functional groups present in the molecules eluting at higher temperature, far exceeds (Kovats Indices of 120) the usual HRGC range for analytes (Kovats Indices of 40–45). With usual column lengths and film thickness, this will already extend the range of analytes by 400 Da. Short, thin film columns would acme another 500 Da to the molecular weight window traditionally dealt with by HRGC.This range (700–1500 Da) can be surpassed by molecules presenting peculiar structures, the ceiling being 5000 Da. It is currently tackled only for peptides, oligosaccharides and a few polymers, by conventional analytical techniques. However, higher molecular weight analogues of all other organic species and yet unknown carbon skeletons have been neglected because this range was only poorly accessible to usual analytical techniques dealing with complex mistures.     

Decay of solutions for 2D Navier–Stokes equations posed on Lipschitz and smooth bounded and unbounded domains

Initial–boundary value problems for 2D Navier–Stokes equations posed on bounded and unbounded rectangles as well as on bounded and unbounded smooth domains were considered. The existence and uniqueness of regular global solutions in bounded rectangles and bounded smooth domains as well as exponential decay of solutions on bounded and unbounded domains were established.     

Extended squaraine dyes with large two-photon absorption cross-sections

Extended bis(donor)-substituted squaraine chromophores exhibit very high two-photon cross-sections (as high as 33 000 GM) in the near-IR; these can be attributed to the combination of large transition dipoles with small detuning energies. The modulus of the third-order nonlinear optical susceptibility at 1.3 mum has been found to be 7.0 x 10-11 esu for one of these chromophores.     

Continuous biotreatment of copper-concentrated solutions by biosorption with Sargassum sp.

Seaweed Sargassum sp. biomass proved to be useful for the recovery of ionic copper from highly concentrated solutions simulating effluents from semiconductor production. In the case of solutions containing copper in the form of chloride, sulfate, and nitrate salts, the best pH for the recovery of copper was 4.5. It was observed that copper biosorption from copper nitrate solutions was higher than the recovery of copper from copper chloride or copper sulfate solutions. The continuous system used was constituted of four column reactors filled with the biomass of Sargassum sp. and showed high operational stability. The biomass of Sargassum sp. in the reactors was gradually saturated from the bottom to the top of each column reactor. The biomass of Sargassum sp. in the first column saturated first, followed by a gradual saturation of the remaining columns owing to preconcentration performed by the biomass in the first column. The biomass of Sargassum in the bioreactors completely biosorbed the ionic copper contained in 63 L of copper sulfate solution, 72 L of copper chloride solution, and 72 L of copper nitrate solution, all the solutions containing copper at 500 mg/L. Effluents produced after biosorption presented copper concentrations < 0.5 mg/L.     

Exact partial wave expansion of optical beams with respect to an arbitrary origin

Using an analytical expression for an integral involving Bessel and Legendre functions, we succeed in obtaining the partial wave decomposition of a general optical beam at an arbitrary location relative to the origin. We also showed that solid angle integration will eliminate the radial dependence of the expansion coefficients. The beam shape coefficients obtained are given by an exact expression in terms of single or double integrals. These integrals can be evaluated numerically on a short time scale. We present the results for the case of a linear-polarized Gaussian beam.