luis camacho - Academia.edu (original) (raw)

Papers by luis camacho

Journal of Electroanalytical Chemistry and Interfacial Electrochemistry, 1990

At concentrations above 2 X10-4 M and acid pH values, cefazohn and ce£metazole yield reduction wa... more At concentrations above 2 X10-4 M and acid pH values, cefazohn and ce£metazole yield reduction waves in which the current varies exponentially with the potential throughout and the diffusion plateau is reached abruptly. On the basis of consideration of the reduction product, this behaviour is assumed to be governed by an irreversible electron transfer and the adsorption of the products, which is negligible compared with that of the reactants. We have used a mass transfer equation based on the diffusion-layer approximation and assumed that the molecules are adsorbed immediately once they have reached the electrode surface by diffusion .

Revista De Filosofia De La Universidad De Costa Rica, 2005

Por simetria entendemos continuidad en la aplicacion de principios filosoficos a diferentes asunt... more Por simetria entendemos continuidad en la aplicacion de principios filosoficos a diferentes asuntos y similitud en la solucion a problemas diferentes tratados en un sistema filosofico. Por asimetria entendemos la interrupcion de tal continuidad y la introduccion de soluciones que no encajan con el resto. La posicion de Popper sobre la diferencia entre verificacion y refutacion se toma como el ejemplo principal: mientras que - segun el - no puede haber verificacion de hipotesis y teorias cientificas, estas pueden ser falsadas cuando las consecuencias esperadas no ocurren. El sistema Luis Camacho Simetrias y asimetrias en Leibniz filosofico de Leibniz muestra un alto grado de simetria, pero su pretension de que vivimos en el mejor de los mundos posibles es asimetrica con su idea de que hay un numero infinito de mundos posibles, muchos de los cuales tendrian que diferir entre si unicamente por detalles irrelevantes.

Revista De Filosofia De La Universidad De Costa Rica, 2013

Sobre el argumento ontológico Resumen: se intenta replicar aquí a quienes acusan de incapacidad d... more Sobre el argumento ontológico Resumen: se intenta replicar aquí a quienes acusan de incapacidad de entender a los que rechazan el argumento ontológico.

This work reports (P, r, T, xi) measurements in the compressed fluid phase for the ternary system... more This work reports (P, r, T, xi) measurements in the compressed fluid phase for the ternary system carbon dioxide – heptane – dodecane in the (313 to 363) K temperature range and at pressures up to 25 MPa. The obtained data were measured by means of a static-synthetic method based apparatus which couples a feeding cell with an Anton Paar vibrating tube densimeter reported in previous papers. Measurements were performed with an estimated uncertainty, to be less than ±0.01 MPa for pressure, ±0.03 K for temperature and ±0.001 for . Obtained data were correlated with the five-parameter Modified Toscani Swarcz equation to represent the behavior of this mixture. Derived thermodynamic properties (isobaric expansivity, isothermal compressibility, thermal pressure coefficient and internal pressure) were also calculated by using the parameters of the equation above mentioned. PrT properties for this ternary system have not been reported in open literature before this work. Experimental data ob...

El desarrollo de variedad de soya para el trópico caliente hace necesario conocer las característ... more El desarrollo de variedad de soya para el trópico caliente hace necesario conocer las características fisiológicas de la planta asociadas con la producción de semilla. 60 cm-;. JO cms.

Coherent Light Microscopy, 2010

In this chapter, we present a new method capable of recovery of the quantitative phase informatio... more In this chapter, we present a new method capable of recovery of the quantitative phase information of microscopic samples. Essentially, a spatial light modulator (SLM) and digital image processing are the basics to extract the sample's phase distribution. The SLM produces a set of misfocused images of the input sample at the CCD plane by displaying a set of lenses with different power at the SLM device. The recorded images are then numerically processed to retrieve phase information. Computations are based on the wave propagation equation and lead to a complex amplitude image containing information of both amplitude and phase distributions of the input sample diffracted wave front. The proposed configuration becomes a non-interferometric architecture (conventional transmission imaging mode) where no moving elements are included. Experimental results are provided in comparison with conventional digital holographic microscopy.

2005 IEEE Antennas and Propagation Society International Symposium

... Luis M. Camacho* and Saibun Tjuatja Wave Scattering Research Center, Department of Electrical... more ... Luis M. Camacho* and Saibun Tjuatja Wave Scattering Research Center, Department of Electrical Engineering University ofTexas at Arlington UTA Box 19016, Arlington, TX, 76019-0016, USA luis.camachogieee.org ... 8, pp. 623-630, August 1975. [6] DM Sullivan, "A simplified ...

Journal of Electroanalytical Chemistry and Interfacial Electrochemistry, 1985

The it -E relations have been analyzed in differential pulse polarography (DPP) for processes in ... more The it -E relations have been analyzed in differential pulse polarography (DPP) for processes in which a very fast dimerization preceded by a reversible electron transfer takes place. The peak half-width and the variations of parameters such as Ep with t and the reactant concentration have been studied. These parameters can be related to those obtained by dc polarography for the same process. The results obtained have been experimentally verified in the dimerization process of l-(p-methoxy-phenyl)-hepten-1-one-3 (MHO) in methanol.

2012 IEEE International Geoscience and Remote Sensing Symposium, 2012

A numerical approach to model the microwave emission from soil with vegetation cover is developed... more A numerical approach to model the microwave emission from soil with vegetation cover is developed. The vegetation cover is represented as an irregular layer on top of a homogeneous half space representing the soil. The phase matrix of the layer components as well as the emission characteristics have been estimated using the Finite-Difference Time-Domain (FDTD) Method. The phase matrix was then integrated into a layer model that accounts for the scattering between the layer and soil, using the radiative transfer theory. The effects of interface roughness on emission are incorporated into the model through the surface phase matrices, which are computed using the Integral Equation Model (IEM). The validity of the phase matrices computation is tested against theoretical models. The microwave emission model predictions are compared to field measurements, showing a good agreement.

IGARSS 2008 - 2008 IEEE International Geoscience and Remote Sensing Symposium, 2008

A 3D-FDTD algorithm is developed and used to compute the emissivity of finite-size and arbitrary-... more A 3D-FDTD algorithm is developed and used to compute the emissivity of finite-size and arbitrary-shape objects. Under thermal equilibrium, the emissivity of an object is the same as its absorptivity. The absorptivity is a function of both the scattering cross section and the absorption cross section of the object; in this study, these cross sections were computed using the FDTD approach. Emissivity values for spherical, cylindrical and landmine-like objects as function of observation angle, polarization and permittivity are generated and presented in this paper.

2010 IEEE International Geoscience and Remote Sensing Symposium, 2010

SPIE Proceedings, 2011

ABSTRACT

The Journal of Physical Chemistry B, 2000

Infrared transmission and reflection-absorption spectroscopies were used to determine the orienta... more Infrared transmission and reflection-absorption spectroscopies were used to determine the orientation of Langmuir-Blodgett (LB) mixed films consisting of a phospholipid (DMPA) and a viologen (TMV) in a ratio of TMV:DMPA) 1:2. For comparison, the orientation of a DMPA monolayer was also studied. No important changes were observed for the organization of the DMPA monolayer when the TMV molecules were incorporated. The alkyl chains of both compounds adopted a hexagonal configuration where these alkyl tails were fully extended with all-trans conformation and an average tilt angle with respect to the support close to 20°. Further information about the hydrated CO groups and the orientation of the phospholipid headgroups was obtained from the CO stretching vibration mode and from the 1300-1000 cm-1 spectrum region, respectively. Finally, the average tilt angle for the plane of the bipyridyl group with respect to the substrate surface was estimated close to 10°from UV-visible absorption spectroscopy with plane polarized light (s and p) under different angles of incidence. Moreover, the bipyridyl group was located encapsulated between the headgroups of the phospholipid and the solid surface.

PLoS ONE, 2010

There are strong evidences that Mycobacterium tuberculosis survives in a non-replicating state in... more There are strong evidences that Mycobacterium tuberculosis survives in a non-replicating state in the absence of oxygen in closed lesions and granuloma in vivo. In addition, M. tuberculosis is acid-resistant, allowing mycobacteria to survive in acidic, inflamed lesions. The ability of M. tuberculosis to resist to acid was recently shown to contribute to the bacillus virulence although the mechanisms involved have yet to be deciphered. In this study, we report that M. tuberculosis resistance to acid is oxygen-dependent; whereas aerobic mycobacteria were resistant to a mild acid challenge (pH 5.5) as previously reported, we found microaerophilic and hypoxic mycobacteria to be more sensitive to acid. In hypoxic conditions, mild-acidity promoted the dissipation of the protonmotive force, rapid ATP depletion and cell death. Exogenous nitrate, the most effective alternate terminal electron acceptor after molecular oxygen, protected hypoxic mycobacteria from acid stress. Nitrate-mediated resistance to acidity was not observed for a respiratory nitrate reductase NarGH knockout mutant strain. Furthermore, we found that nitrate respiration was equally important in protecting hypoxic non-replicating mycobacteria from radical nitrogen species toxicity. Overall, these data shed light on a new role for nitrate respiration in protecting M. tuberculosis from acidity and reactive nitrogen species, two environmental stresses likely encountered by the pathogen during the course of infection.

Optics Express, 2010

A new method for recovery the quantitative phase information of microscopic samples is presented.... more A new method for recovery the quantitative phase information of microscopic samples is presented. It is based on a spatial light modulator (SLM) and digital image processing as key elements to extract the sample's phase distribution. By displaying a set of lenses with different focal power, the SLM produces a set of defocused images of the input sample at the CCD plane. Such recorded images are then numerically processed to retrieve phase information. This iterative process is based on the wave propagation equation and leads on a complex amplitude image containing information of both amplitude and phase distributions of the input sample diffracted wave front. The proposed configuration is a non-interferometric architecture (conventional transmission imaging mode) where no moving elements are included. Experimental results perfectly correlate with the results obtained by conventional digital holographic microscopy (DHM).

Materials Science and Engineering: C, 2006

The properties of 4-methylbenzenethiol capped gold nanoparticles have been investigated at the ai... more The properties of 4-methylbenzenethiol capped gold nanoparticles have been investigated at the air-water interface. Langmuir isotherms and compression cycles show that a stable monolayer is formed on the water surface. In situ UV-visible spectroscopy confirms that the plasmon absorption band is present which is characteristic of small metallic particles. The monolayer was imaged using real time Brewster Angle Microscopy (BAM). Above surface pressures of 5 mN m À 1 the monolayer was virtually homogeneous. During decompression, the monolayer fractured into rod-like structures. These rods were initially orientated parallel to the movable barriers containing the monolayer and as the area was increased, their orientation randomized. During subsequent compressions the rods recombined to recreate a homogeneous monolayer.

Langmuir, 2012

The design of new molecules with directed interactions to functional molecules as complementary b... more The design of new molecules with directed interactions to functional molecules as complementary building blocks is one of the main goals of supramolecular chemistry. A new p-tert-butylcalix[6]arene monosubstituted derivative bearing only one alkyl chain with an acid group (C6A3C) has been synthesized. The C6A3C has been successfully used for building Langmuir monolayers at the air−water interface. The C6A3C molecule adopts a flatlike orientation with respect to the air−water interface. The molecular structure gives the molecule amphiphilic character, while allowing the control of both the dissociation degree and the molecular conformation at the air−water interface. The C63AC has been combined with pristine fullerene (C60) to form the supramolecular complex C6A3C:C60 in 2:1 molar ratio (CFC). The CFC complex retains the ability of C6A3C to form Langmuir monolayers at the air/water interface. The interfacial molecular arrangement of the CFC complex has been convincingly described by in situ UV− vis reflection spectroscopy and synchrotron X-ray reflectivity measurements. Computer simulations complement the experimental data, confirming a perpendicular orientation of the calixarene units of CFC with respect to the air−water interface. This orientation is stabilized by the formation of intermolecular H-bonds. The interfacial monolayer of the CFC supramolecular complex is proposed as a useful model for the well-defined self-assembly of recognition and functional building blocks.

Langmuir, 2013

The formation of well-defined supramolecular structures in the nanoscopic scale is a fundamental ... more The formation of well-defined supramolecular structures in the nanoscopic scale is a fundamental step in nanotechnology. The fine control of the layer-by-layer growth of the supramolecular assemblies at interfaces is most desirable. The collapse of a mixed monolayer composed of two surfactants in equimolar ratio: the organic dye N-10-dodecyl acridine (DAO) and stearic acid (SA) is analyzed herein. The collapse process of the DAO:SA mixed monolayer has been monitored using surface pressuremolecular area (π-A), surface potential isotherms, UV-visible reflection spectroscopy, Polarization-Modulated Infrared Reflection-Absorption Spectroscopy (PM-IRRAS), Brewster Angle Microscopy (BAM), and synchrotron-based in situ X-ray Reflectivity (XRR) measurements. The collapse of the DAO:SA mixed monolayer leads to an ordered trilayer. The growth of anisotropic 2D domains of micrometric size is observed during the formation of the trilayer, relating to the ordering of the acridine polar headgroups. The trilayer is organized with the first and third monolayers displaying the polar headgroups pointing to the aqueous subphase, whereas the intermediate layer display the polar headgroups pointing to the air. The trilayer is stabilized by the strong self-aggregation acridine dye group of the DAO molecule. The controlled transition from a monolayer to a trilayer described herein is proposed as a model for further interfacial supramolecular structures of tunable thickness comprising organic dyes.

Journal of Phytopathology, 2000

... 1990; Allen, 1995; Rusuku et al., 1997). During the Sep-tember-December season of 1990. sever... more ... 1990; Allen, 1995; Rusuku et al., 1997). During the Sep-tember-December season of 1990. severe Fusarium wilt us сорусыскяптяcentercodtsiatonsiii: 0931 - 1785/00/4801 0039 S 15.00/0 Page 2. 40 Bl'rlk iiARA and Camacho Fig. ] Prefectures of Rwanda. ...