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An experimental method for the determination of kinetic data for liquid-phase reactions under linear rise of temperature is explained for the depolymerization of trioxane. Integral kinetic analysis of the data is performed in order to determine the kinetic model and the kinetic parameters. Experiments have been carried out at different heating rates between 0.5 and 2 deg/min, leading to similar kinetic parameters. The obtained results are in agreement with the kinetic model and parameters obtained from isothermal kinetic analysis. The programmedtemperature method seems to be a useful tool for a quick determination of kinetic models, avoiding experimental work.

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Abstract  

The characterization of samples of painted plasters obtained from the archaeological site of Xochicalco, in Central Mexico, is presented. Elemental concentrations of the painted layers were obtained by using proton induced X-ray emission (PIXE). The main crystalline structures of the samples are identified with the help of X-ray diffraction (XRD), while the microstructure is studied by scanning electron microscopy (SEM). The information resulting from the application of these three techniques is used to achieve more accurate values for the elemental concentrations. Additional data regarding organic components of the paintings was obtained through Fourier transform infrared spectrometry (FTIR). Although the latter results only provided reliable data on inorganic components, they help to clarify the results from XRD and confirm those of SEM.

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The aim of the present study was to evaluate the presence of lymphocytes and granulocytes in different stages of embryonic development and on the first posthatching day. The lymphocytes present in the bursa of Fabricius and thymus were evaluated by histological analysis of the yolk sac, bursa of Fabricius, thymus, liver and bone marrow of 100 chicken embryos divided into groups and treated with: (I) Marek’s disease vaccine as viral antigen, (II) Marek’s disease vaccine plus lymphokines, (III) lymphokines, and (IV) vaccine diluent. Group V was not treated. Samples were taken on days 14, 17 and 20 of incubation and on the first posthatching day. An increase in the number of epithelial matrix as precursors of lymphoid follicles was observed in the bursa of Fabricius of embryos inoculated with lymphokines compared to embryos in all the other groups (p < 0.05). In addition, a higher amount of granulocytes was found in the yolk sac and liver of embryos inoculated with lymphokines than in the embryos of all other groups (p < 0.05). In the bone marrow, no significant difference was observed among the treated groups concerning the amount of granulocytes. The results suggest that administration of antigens or protein molecules at an early stage of embryonic development increases the presence of granulocytes in the liver and granulopoiesis in the yolk sac, and also increases the number of epithelial matrixs in the bursa of Fabricius.

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Estudios sobre Rubiáceas Mexicanas, VII.

Tres espécies nuevas del Arachnothryx Planch. (Rondeletieae) de Oaxaca y Tabasco

Acta Botanica Hungarica
Authors: A. Borhidi, M. de los A. Guadarrama, G. Ortiz G., and C. Jiménez

Three new species of the genus Arachnothryx (Rubiaceae) are described from Oaxaca y Tabasco states of Mexico.

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Abstract  

Enthalpies of mixing and heat capacities of the systems formed of alkyl acetates (ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate and isobutyl acetate) with olive oil were measured at 298.15 K. The mixing of acetates with the oil was strongly endothermic, and the highest measured enthalpies per mole of mixture were 2000 J mol-1 for ethyl acetate at an acetate mole fraction of 0.6. The heat capacities of the mixtures were calculated too and values were decreasing as the mole fraction of acetate increases and varied from 296 to 3929 J K-1 mol-1.

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Summary Non-isothermal thermogravimetric data were used to evaluate the Arrhenius parameters (activation energy and the pre-exponential factor) of the combustion of two carbonaceous materials, selected as diesel soot surrogates. The paper reports on the application of model-free isoconversional methods (Flynn-Wall-Ozawa and Kissinger methods) for evaluating the activation energy of the combustion process. On the other hand, by means of the compensation relation between E and lnA, which was established by the model-dependent Coats-Redfern method, the value of the pre-exponential factor was estimated from the known value of the model-independent activation energy.

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Abstract  

The Intercomparison Studies Program (ISP) at the Oak Ridge National Laboratory (ORNL, Oak Ridge, TN, USA) provides natural-matrix urine quality-assurance/quality-control (QA/QC) samples to radiobioassay analysis laboratories. In 2003, a single laboratory (Los Alamos National Laboratory LANL, Los Alamos NM USA) requested a change in the test-samples provided previously by the ISP. The change was requested to evaluate measurement performance for analyses conducted using thermal-ionization mass spectrometry (TIMS). Radionuclides included 239Pu at two activity levels (75–150 μBq·sample−1 and 1200–1600 μBq·sample−1) and 238Pu (3700–7400 μBq·sample−1). In addition, 240Pu was added to the samples so that the 239+240Pu specific activity was 3700–7400 μBq·sample−1. In this paper, the results of testing during the period May, 2003 through September, 2005 are presented and discussed.

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Journal of Radioanalytical and Nuclear Chemistry
Authors: Hector Vega-Carrillo, M. Martinez-Blanco, Victor Hernandez-Davila, and Jose Ortiz-Rodriguez

Abstract  

Artificial neural networks have been applied to unfold the neutron spectra and to calculate the effective dose, the ambient equivalent dose, and the personal dose equivalent for 252Cf, 241Am–Be, and 239Pu–Be neutron sources. The count rates that these neutron sources produce in a Bonner Sphere Spectrometer with a 6LiI(Eu) were utilized as input in both artificial neural networks. Spectra and the ambient dose equivalent were also obtained with BUNKIUT code and the UTA4 response matrix. With both procedures spectra and ambient dose equivalent agrees in less than 10%. The Artificial neural network technology is an alternative procedure to unfold neutron spectra and to perform neutron dosimetry.

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