Julio Puerta

Three and four generalized Lorentzian approximations for the Voigt line shape.

Three and four generalized Lorentzians in two variables have been obtained to approximate the Voigt function by using the asymptotical Padé method. The accuracy has been greatly improved with respect to the one and two generalized Lorentzian approximations reported in a previous paper. Furthermore, the four Lorentzian function is always positive for all values of the normalized collision width and line separation. This approximation gives an accuracy for most of the values of better than 0.0001, and in the worst region the absolute error is ~0.001. In the limits of low and high pressure adequate limit functions are obtained. A four generalized Lorentzian gives a reliable and easily calculable approximation to the Voigt function for most of the experimental needs.

Generalized Lorentzian approximations for the Voigt line shape

The object of the work reported in this paper was to find a simple and easy to calculate approximation to the Voigt function using the Padé method. To do this we calculated the multipole approximation to the complex function as the error function or as the plasma dispersion function. This generalized Lorentzian approximation can be used instead of the exact function in experiments that do not require great accuracy.

Experimental verification of the grid effects in a velocity analyzer with variable geometry

A velocity analyzer with adjustable interelectrodic distances is described here. Several experiments have been performed in a double plasma machine with this analyzer of variable geometry in order to investigate the effects of the discontinuous structure of the grids. The measured displacements of the characteristic curve for different interelectrodic distances show excellent agreement with the theoretical predictions due to the depletion of the discriminating potential in the holes of the grid, as is shown in our recent theoretical analysis using a Schwarz–Christoffel transformation. The influence of the grid structure on the temperature determined from the characteristic curve is also investigated and the correlation experiment theory is qualitatively correct.

Synthesis of carbon nanotubes by laser ablation in graphite substrate of industrial arc electrodes

In this work, an inexpensive and simple technique for the synthesis of carbon nanotubes (CNTs) by using graphite as the target for IR laser radiation is presented. This graphite material is obtained from the recycled graphite electrode core of an electric arc furnace. The experiment was carried out in a reaction chamber in an argon atmosphere at a low pressure. For laser ablation, a Lumonics TEA CO2 laser beam (7 J; 0.05–50 μs pulse length) was used in multimode operation. Products were collected on free mica sheets. The substrates were characterized by scanning electron microscopy (SEM) and the products were characterized (collected as powder) by transmission electron microscopy (TEM). They showed significant amounts of high-quality dense filaments (CNTs) that were morphologically not aligned.

Generalized Lorentzian approximations for the Voigt line shape: errata.

Pablo Martin and Julio Puerta Universidad Simon Bolivar, Departamento Fisica, Apdo. 80659, Caracas 1081, Venezuela. Received 19 March 1981. 0003-6935/81/152601-01

Effects of the magnetic field over the nanometric growth morphology on the material synthesis in a liquid spray thermal plasma reactor

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Catalytic Chemical Vapor Deposition Synthesis of Carbon Aerogels of High-Surface Area and Porosity

It is possible that the magnetic field affect the growth morphology of the materials at nanometric scale while there are synthesized. In this work is developed a thermal plasma reactor in fluidized bed assisted by magnetic mirror for material synthesis using a liquid spray. An aluminum solution is carrier in the plasma reactor with a without magnetic external magnetic field applied. We found from the characterization of material synthesized that: Aluminum nanowire and alumina nanofiber are generated when the external magnetic mirror is applied to the thermal plasma reactor.

Banana orbits in elliptic tokamaks with hole currents

In this work carbon aerogels were synthesized by catalytic chemical vapor deposition method (CCVD). Ferrocene were employed as a source both of catalytic material (Fe) and of carbon. Gaseous hydrogen and argon were used as reductant and carrier gas, respectively. The products of reaction were collected over alumina. The morphology and textural properties of the soot produced in the reaction chamber were investigated using Scanning Electron Microscopy, High-Resolution Transmission Electron Microscopy, X-ray photoelectron spectroscopy, and N2 physisorption (BET and BHJ methods). After the evaluation of the porous structure of the synthesized products, 780 ± 20 m2/g of and 0.55 ± 0.02 cm3/g of were found. The presence of iron carbide and the partial oxidation of carbon nanostructures were revealed by XPS.

Modifying the growth morphology of aluminum crystals by magnetic mirror in a thermal plasma reactor

Ware Pinch is a consequence of breaking of up-down symmetry due to the inductive electric field. This symmetry breaking happens, though up-down symmetry for magnetic surface is assumed. In previous work Ware Pinch and banana orbits were studied for tokamak magnetic surface with ellipticity and triangularity, but up-down symmetry. Hole currents appear in large tokamaks and their influence in Ware Pinch and banana orbits are now considered here for tokamaks magnetic surfaces with ellipticity and triangularity.

Preliminary results of eigenvalue and eigenvector treatment for kink instabilities in tokamaks

Effect of magnetic fields on growth morphology of aluminum crystals was studied in a fluidized bed thermal plasma reactor assisted by magnetic mirrors. Aluminum crystals were precipitated in the reactor using aluminum powder or aluminum-graphite mixture as precursors. The absent of magnetic field was also studied for comparison. Products were characterized by scanning electron microscopy (SEM) and X-ray Diffraction (XRD). Results indicated that, regardless the precursor used, it was observed the presence of aluminum nanowires when the external magnetic mirror was applied, suggesting that magnetic fields are able to modify growth morphology at nanoscale.