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  • Author or Editor: E. Ortega x
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Abstract  

We compute the maximal symmetric ring of quotients of infinite dimensional path algebras that can be approximated by finite dimensional path algebras.

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Wheat ( Triticum aestivum L.) grain production in the Central Highlands of Mexico occurs under rainfed conditions. Traditionally this crop has been planted by conventional means in solid stands combined with heavy tillage and lack of ground cover. These practices have been leading to soil erosion in the sloping lands, frequent drought stress, and water logging after occasional heavy rainstorms in the low lands. To ameliorate those constrains, farmers have started to replace the traditional planting system by the planting system on narrow raised beds. However, information on N management and varieties is needed. This 5-yr study was conducted from 1999 to 2003 to test a set of eight wheat genotypes using a raised-bed system to evaluate their performance as affected by N fertilizer management. Three N rates (40, 70 and 100 kg N ha −1 ) were applied at planting, at the end of tillering-early jointing, and split at planting and at the end of tillering-early jointing. Treatments included an unfertilized check plot. Results indicated that the optimum N fertilizer rate for wheat grain production varies from 0 to 40 kg N ha −1 ) depending upon the variety. Nitrogen timing practices had no effect on grain yield but on N use efficiency (NUE). The split application of 40 kg N ha −1 increased the NUE. Higher N rates reduced the NUE irrespective of the N timing practice. According to the differential performance among varieties, this study showed that the planting system on narrow raised beds is a variety-specific technology. The relative grain yield, stability, and NUE, indicated that Tlaxcala F2000, Nahuatl F2000 and Romoga F96 are the most adequate varieties for the planting system on narrow raised beds in the Central Highlands of Mexico.

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Acta Alimentaria
Authors: S. Aguilar-Rosas, M. Ballinas-Casarrubias, L. Elias-Ogaz, O. Martin-Belloso, and E. Ortega-Rivas

Pasteurisation of apple juice by a high temperature-short time treatment (HTST) at 90 °C for 30 s was compared with a high-voltage pulsed electric field treatment (PEF). The PEF treatment was carried out using a laboratory unit set with a bipolar pulse (4 μs wide), an intensity of 35 kV cm−1, and a frequency of 1200 pulses per second (pps). Enzyme inactivation and colour changes of the treated juices were compared, using a non-treated sample as control. Enzyme residual activities of pectinmethylesterase (PME) and polyphenoloxidase (PPO), as well as the chroma index for colour, showed statistical difference between treatments. No statistical significant difference was observed for the hue colour index. PEF could be considered a feasible alternative for producing pasteurised and stable apple juice.

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Journal of Radioanalytical and Nuclear Chemistry
Authors: F. Abel, G. Amsel, E. d'Artemare, M. Bruneaux, C. Cohen, B. Maurel, C. Ortega, S. Rigo, J. Siejka, M. Croset, and D. Dieumegard

Abstract  

Techniques are described which combine the use of nuclear reactions and of backscattering to obtain analytical results which would be difficult or impossible to reach using one of these methods only. The principles of stoichiometry determination by plateau height analysis are developed both for backscattering and for narrow resonances of nuclear reactions. Examples of applications are given to the determination of the composition of various thin films of aluminium and silicon oxides, silicon nitrides and calcium fluorides. The analysis of samples smaller than the beam, using backscattered particle monitoring, is presented.

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