A manera de estudio comparativo, en este artículo se propone un paralelo formal entre la física de Aristóteles y la física de Einstein. La finalidad no es la del rigor histórico. Se trata más bien de un ejercicio de análisis conceptual. En este sentido, se discute la posible similitud entre la forma del mundo según Aristóteles y la forma (geometría global) del universo según Einstein. Se estudia también la relación entre cinemática, dinámica y gravitación en sus respectivas teorías de movimiento. Finalmente se compara la ontología del espacio aristotélico con la ontología del espacio-tiempo relativista.

PALABRAS CLAVE: Aristóteles, Einstein, dinámica, cosmología, gravitación

REVISTA Ideas y Valores Vol. 142 Páginas 140-160

ISSN: 0120-0062

Este artículo elabora un repaso histórico de la emergencia de la termodinámica, de los abordajes historiográficos que ha recibido esta ciencia y de su relación con los debates cosmológicos y religiosos de finales del siglo XIX. El desarrollo conceptual que desembocará en la formulación de la conservación de la energía y en el concepto de entropía es abordado en la primera parte del presente trabajo. La segunda parte dibuja, brevemente, el panorama historiográfico de la termodinámica, llamando la atención sobre los variados significados históricos que tuvieron los conceptos de la energía y la entropía y sobre su influencia en el mundo social y cultural de la época. Un aspecto puntual de la interacción entre termodinámica y sociedad será analizado en la última parte del artículo, al explorar la forma como las leyes de la termodinámica estuvieron informadas por cuestiones teológicas y cómo a su vez estas leyes articularon discursos tanto materialistas y naturalistas como de apología cristiana.

PALABRAS CLAVE: termodinámica, energía, entropía, historiografía, cosmología, ciencia y religión.

REVISTA Revista de la Academia Colombiana de Ciencias Exactas, Físicas y Naturales: Historia y Filosofía de la Ciencia Vol. 34 Páginas 37-52

ISSN: 0370-3908

Predicting the population dynamics of insects in natural conditions is essential for their management or preservation, and temperature-dependent development models contribute to achieving this. In this research the effects of temperature and soil moisture content on egg development and hatching of Clavipalpus ursinus (Blanchard) were evaluated. The eggs were exposed to seven temperature treatments with averages of 7.2, 13.0, 15.5, 19.7, 20.6, 22.0 and 25.3°C, in combination with three soil moisture contents of 40%, 60% and 80%. A linear and two non-linear (Lactin and Briere) models were evaluated in order to determine the thermal requirements of this developmental stage. Temperature affected significantly the time of development and egg hatching, while no significant effect was observed for moisture content. Thermal requirements were set as: 7.2°C for lower developmental threshold, 20.6°C for optimum developmental threshold, 25.3°C for maximum temperature and 344.83 degree-days for the thermal constant. The linear model described satisfactorily egg development at intermediate temperatures; nevertheless, a slightly better fit of the observed data was obtained with the Lactin model. Egg development took place inside a narrow range of temperatures. Consequently, an increment of soil temperature could generate a negative impact on the population size of this species or changes in its biological parameters.

PALABRAS CLAVE: egg development, pests, soil moisture, thermal requirements

REVISTA: Insect Science Vol.19  Páginas 657-665

ISSN: 1744-7917

The input–output balance methodology has been applied to characterize the energy balance of agricultural systems. This study proposes to extend this methodology with the inclusion of multivariate analysis to reveal particular patterns in the energy use of a system. The objective was to demonstrate the usefulness of multivariate exploratory techniques to analyze the variability found in a farming system and, establish efficiency categories that can be used to improve the energy balance of the system. To this purpose an input–output analysis was applied to the major greenhouse tomato production area in Colombia. Individual energy profiles were built and the k-means clustering method was applied to the production factors. On average, the production system in the study zone consumes 141.8 GJ ha−1 to produce 96.4 GJ ha−1, resulting in an energy efficiency of 0.68. With the k-means clustering analysis, three clusters of farmers were identified with energy efficiencies of 0.54, 0.67 and 0.78. The most energy efficient cluster grouped 56.3% of the farmers. It is possible to optimize the production system by improving the management practices of those with the lowest energy use efficiencies. Multivariate analysis techniques demonstrated to be a complementary pathway to improve the energy efficiency of a system.

PALABRAS CLAVE: Energy use, Regional analysis, Greenhouse tomato, k-means clustering, Colombia

REVISTA: Energy  Vol. 47 Páginas 465-470

ISSN: 0360-5442

The input–output balance methodology has been applied to characterize the energy balance of agricultural systems. This study proposes to extend this methodology with the inclusion of multivariate analysis to reveal particular patterns in the energy use of a system. The objective was to demonstrate the usefulness of multivariate exploratory techniques to analyze the variability found in a farming system and, establish efficiency categories that can be used to improve the energy balance of the system. To this purpose an input–output analysis was applied to the major greenhouse tomato production area in Colombia. Individual energy profiles were built and the k-means clustering method was applied to the production factors. On average, the production system in the study zone consumes 141.8 GJ ha−1 to produce 96.4 GJ ha−1, resulting in an energy efficiency of 0.68. With the k-means clustering analysis, three clusters of farmers were identified with energy efficiencies of 0.54, 0.67 and 0.78. The most energy efficient cluster grouped 56.3% of the farmers. It is possible to optimize the production system by improving the management practices of those with the lowest energy use efficiencies. Multivariate analysis techniques demonstrated to be a complementary pathway to improve the energy efficiency of a system.

PALABRAS CLAVE: Energy use, Regional analysis, Greenhouse tomato, k-means clustering, Colombia

REVISTA: Energy  Vol. 47 Páginas 465-470

ISSN: 0360-5442

The presence of 17 pesticide residues was determined in just-picked tomatoes coming from open field and greenhouse farms in Colombia. Pesticide residues were quantified through a multiresidue method using ultra performance liquid chromatograph coupled to mass spectrometer. The results give no clear indication about which farming system is producing the most contaminated tomatoes. While the share of open field samples violating the maximum residue limits (MRLs) was higher, the presence of more than one pesticide per sample was detected in a higher number of greenhouse samples. Results showed that all positive samples for acephate exceeded the recommended MRL, indicating indiscriminate use of this insecticide. In both farming systems, the pre-harvest intervals are not respected due to the management practices applied and the continuous ripening of the fruit, once the harvest starts. The results of the present study confirm the need for a monitoring program, actually inexistent, focused in the food commodities consumed locally.

PALABRAS CLAVE: Colombia, Tomato, Pesticide residues, Faming systems

REVISTA: Food Control  Vol.30 Páginas 400-403

ISSN: 0956-7135

This work presents the validation results of a simple, fast and low-cost sample preparation method for the determination of pesticide residues in soil by ultrafast liquid chromatography coupled to electrospray ionization mass spectrometry. The method uses acetonitrile ultrasound-assisted extraction, centrifugation and evaporation step, without further cleanup. Recovery studies were performed for two soil blanks, presenting results in the range of 70-110% with relative standard deviation lower than 20%. The correlation coefficients for analytical calibration curves were higher than 0.99. Pesticide residues were detected in soils in the range of 1-62 ng g-1, depending on the compound. The uncertainty of the method was estimated from different addition-recovery experiments and calculations from certificates. The extraction process was identified as the main source of uncertainty, and the expanded uncertainties for each pesticide, using a coverage factor of two, were between 8.4 and 33%. The proposed method was applied to the determination of pesticides in real samples.

PALABRAS CLAVE: pesticide, mass spectrometry, liquid chromatography, soil

REVISTA: Journal of the Brazilian Chemical Society

ISSN: 0103-5053

Worldwide, the presence of pesticide residues in vegetables has been extensively characterized. In Colombia, tomato is among the most consumed horticultural commodities; however, the presence of pesticide residues in tomato has not been determined. Through an extensive sampling in Bogota, we assessed the presence of 24 pesticides in fresh tomatoes. Only one sample containing carbendazim exceeded the Maximum Residue Limit. At least one pesticide was detected in 70.5% of the samples and the most detected were pyrimethanil, carbendazim, dimethomorph and acephate. The results showed that tomato consumption in Bogota does not represent a risk to human health. Nevertheless, a monitoring program must be established to control the contamination of staple foods, such as tomato.

PALABRAS CLAVE: Pesticide residues, Maximum residue limit, Risk

REVISTA: Food Control Vol. 35 Páginas 213-217

ISSN: 0956-7135

A comparative study on acid and hydrothermal methods as ways to reduce interlamellar charge has been carried out on a vermiculite. This study showed that the application of the hydrothermal treatment as a previous step to pillaring the vermiculites, reported here for the first time, is a new route to obtain the porous material with a particular interest as heterogeneous catalysts, starting from mineral clays with a high density of charge. Modified clays have been characterized by atomic absorption, emission spectrograph, X-ray diffraction, cation-exchange capacity, total acidity, infrared spectroscopy (DRIFT), and nitrogen adsorption. The results have shown that all solids have been structurally modified. However, acid and hydrothermal methods showed different behavior. For the vermiculite, the hydrothermal treatment did not produce major differences in terms of the crystalline structure, whereas the acid method caused severe structural damage. The catalytic properties have been tested over Pt-impregnated samples (1%) using the hydroisomerization of heptane. Important catalytic activity was established for all solids with high selectivity regarding the isomer products.

REVISTA: Journal of Physical Chemistry. B Vol. 109(40) Páginas 19026-19033

ISSN: 1520-6106

A series of vermiculites pillared with mixed precursors of Al–Zr, Al–Hf and Al–Ce were obtained from natural vermiculite subjected to a process of negative harge reduction through hydrothermal treatment. The catalytic activity of the solids evaluated in the decane hydroconversion, was superior to that of recognized pillared clays and comparable to those of very active catalysts such as zeolites USY. The distributions of profiles of the reaction products suggest that the porosity/pore architecture of the pillared vermiculites should be similar to that of ultrastable Y zeolites.

PALABRAS CLAVE: Vermiculite, Pillared vermiculite, Decane hydroconversion.

REVISTA: Applied Catalysis A: Gen  Vol. 345 Páginas112-118

ISSN: 0926-860X