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Alfonso-Orjuela J.E.,National University of Colombia | Alfonso-Orjuela J.E.,Centro Internacional Of Fisica Cif | Andrade-Zambrano D.F.,Grupo de materiales con Aplicaciones Tecnologicas GMAT | Andrade-Zambrano D.F.,National University of Colombia | Arroyo-Osorio J.M.,National University of Colombia
Revista Mexicana de Fisica | Year: 2011

To study the effect of multiline laser processing in the optical response of silicon, a set of p-type single-crystalline silicon wafers with 0.01 to 0.02 Ωm resistivity, 525 μm thickness, and [111] orientation, was irradiated with a multiline Nd:YAG pulsed laser (1064, 532 and 355 nm) applying energies from 310 to 3100 J. A group of those surfaces was produced using argon gas blowing, while other group was manufactured in free atmosphere. Using confocal microscopy, it was observed that the gas-protected samples shown surface periodic structures in the form of ripples with an average pitch of 547 nm. Trough diffuse reflectance tests it was determined that proportionally to the energy supplied in the laser processing, these surfaces reflect between 10% and 30% in the UV region and between 60% and 80% in the IR region. On the other hand, the free atmosphere-made surfaces presented structures and diffraction properties characteristic of porous silicon (PS). The refractive index of the surfaces with periodic structures was calculated based on the diffuse reflectance measures while that of PS surfaces was calculated using the surface voids fraction (pores) determined with the confocal microscope image analysis software. Source

Urbina A.,El Rosario University | Urbina A.,National University of Colombia | Godoy-Silva R.,National University of Colombia | Hoyos M.,CNRS Physics Laboratory | And 2 more authors.
Journal of Chromatography B: Analytical Technologies in the Biomedical and Life Sciences | Year: 2016

Though blood bank processing traditionally employs centrifugation, new separation techniques may be appealing for large scale processes. Split-flow fractionation (SPLITT) is a family of techniques that separates in absence of labelling and uses very low flow rates and force fields, and is therefore expected to minimize cell damage. However, the hydrodynamic stress and possible consequent damaging effects of SPLITT fractionation have not been yet examined. The aim of this study was to investigate the hydrodynamic damage of SPLITT fractionation to human red blood cells, and to compare these effects with those induced by centrifugation. Peripheral whole blood samples were collected from healthy volunteers. Samples were diluted in a buffered saline solution, and were exposed to SPLITT fractionation (flow rates 1-10 ml/min) or centrifugation (100-1500 g) for 10 min. Cell viability, shape, diameter, mean corpuscular hemoglobin, and membrane potential were measured. Under the operating conditions employed, both SPLITT and centrifugation maintained cell viability above 98%, but resulted in significant sublethal damage, including echinocyte formation, decreased cell diameter, decreased mean corpuscular hemoglobin, and membrane hyperpolarization which was inhibited by EGTA. Wall shear stress and maximum energy dissipation rate showed significant correlation with lethal and sublethal damage. Our data do not support the assumption that SPLITT fractionation induces very low shear stress and is innocuous to cell function. Some changes in SPLITT channel design are suggested to minimize cell damage. Measurement of membrane potential and cell diameter could provide a new, reliable and convenient basis for evaluation of hydrodynamic effects on different cell models, allowing identification of optimal operating conditions on different scales. © 2016 Elsevier B.V. Source

This work is framed within a geothermal research project cofinanced by ISAGEN and COLCIENCIAS called "Modeling Subsurface Structure Resistive From Surveys Magnetotelluric In Geothermal Areas Of Colombia, Case Nevado Del Ruiz" In which through a cooperative agreement between the Universidad Autónoma de México (UNAM) the Servicio Geológico Colombiano (SGC) and the Centro Internacional de Física (CIF) has been acquired magnetotelluric information composed of 105 soundings located to west of the Nevado del Ruiz. This paper illustrates the application of a methodology for processing and modeling based on 58 soundings associated with five (5) profiles. The selection of the profiles was performed using criteria such as high density of stations, proximity to a well drilled in the area and the possibility of crossing some of the surface geological structures most relevant. In the data field processing, the SSMT2000 and MTEDITOR software were used, both from the Phoenix Geophysics House, which are programmed in the basic processing algorithms such as transformation to the frequency domain programmed, the cross spectra and auto spectra, and magnetotelluric transfer function; thus is possible to obtain as a first result the MT (magnetotelluric) soundings values e xpressed in apparent resistivities and phases for each frequency. For the modeling state we used the winGlink software from the Geosystem house. As a first approximation 1D inversion were made. The invariant curve of the impedance tensor with Bostick algorithm (Bostick Transform), with Occam algorithm and additionally with the model resistivities discrete layers were used. After an analysis of the dimensionality is passed to the 2D inversion. The procedure consisted of rotating the impedances tensor to the main axes (as a first approximation) for profiles oriented NW (MT 1 and MT 2) and SW (MT 3) and rotate the tensor in EW direction for profiles oriented NS (MT 4 and MT 5), selection made from regional strike directionality found. For the 2 models, two electromagnetic modes (TE and TM) simultaneously in the inversion process were used. Finally, electrical resistivity models were obtained along five magnetotelluric profiles where we can observe that 2D models are more accurated due to the high complexity of the area (as best approach to information present in soundings). Source

Escobar-Paramo P.,Centro Internacional Of Fisica Cif | Gougat-Barbera C.,Montpellier University | Hochberg M.E.,Montpellier University
Evolutionary Applications | Year: 2012

The use of bacteriophages against pathogenic bacteria in health care and in the food industry is now being advocated as an alternative to the use of antibiotics. But what is the evolutionary response for a bacterial population if both antibiotics and phages are used in combination? We employ an experimental evolution approach to address these questions and exposed Pseudomonas fluorescens SBW25 and a related hypermutator strain (mutS-) to the action of the antibiotic rifampicin and the lytic bacteriophage SBW25φ{symbol}2. We then compared the densities, growth rates, and the mutations at the rpoB locus leading to rifampicin resistance of the evolved bacterial populations. We observed that the evolutionary response of populations under different treatments varied depending on the order in which the antimicrobials were added and whether the bacterium was a hypermutator. We found that wild-type rifampicin-resistant populations involved in biofilm formation often reverted to rifampicin sensitivity when stresses were added sequentially. In contrast, when the mortality agents were added simultaneously, phage populations frequently went extinct and the bacteria evolved antibiotic resistance. However, populations of the hypermutator mutS- converged to a single genotype at the rpoB locus. Future investigation on other bacteria and using different antibiotics and bacteriophage are needed to evaluate the generality of our findings. provided the original work is properly cited and is not used for commercial purposes. © 2012 Blackwell Publishing Ltd. Source

Alfonso J.E.,National University of Colombia | Alfonso J.E.,Centro Internacional Of Fisica Cif | Olaya J.J.,National University of Colombia | Bedoya-Hincapie C.M.,National University of Colombia | And 2 more authors.
Materials | Year: 2014

The aim of this work is to assess the evolution of the structural and optical properties of BixTiyOz films grown by rf magnetron sputtering upon post-deposition annealing treatments in order to obtain good quality films with large grain size, low defect density and high refractive index similar to that of single crystals. Films with thickness in the range of 220-250 nm have been successfully grown. After annealing treatment at 600 °C the films show excellent transparency and full crystallization. It is shown that to achieve larger crystallite sizes, up to 17 nm, it is better to carry the annealing under dry air than under oxygen atmosphere, probably because the nucleation rate is reduced. The refractive index of the films is similar under both atmospheres and it is very high (n =2.5 at 589 nm). However it is still slightly lower than that of the single crystal value due to the polycrystalline morphology of the thin films. © 2014 by the authors. Source

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