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Papers by CR saber

os vegetales mínimamente procesados son definidos como cualquier fruta u hortaliza que ha sido al... more os vegetales mínimamente procesados son definidos como cualquier fruta u hortaliza que ha sido alterada físicamente a partir de su forma original, pero que mantiene su estado fresco (IFPA, 2002). El verdadero reto

Mikrochimica Acta, 2011

A new solid-phase extraction sorbent was used for the preconcentration of Pb(II) and Cr(III) ions... more A new solid-phase extraction sorbent was used for the preconcentration of Pb(II) and Cr(III) ions prior to their determination by flame atomic absorption spectrometry. It was prepared by immobilization of 2,4-dinitrophenylhydrazine on nano-alumina coated with sodium dodecyl sulfate. The sorbent was characterized by scanning electron microscopy, N2 adsorption and Fourier transform infrared spectrometry, and used for preconcentration and separation of Pb(II) and Cr(III) from aqueous solutions. The ions on the sorbent were eluted with a mixture of nitric acid and methanol. The effects of sample pH, flow rates of samples and eluent, type of eluent, breakthrough volume and potentially interfering ions were studied. Linearity is maintained between 1.2 and 350 μg L-1 of Pb(II), and between 2.4 and 520 μg L-1 of Cr(III) for an 800-mL sample. The detection limit (3 s, N = 10) for Pb(II) and Cr(III) ions is 0.43 and 0.55 μg L-1, respectively, and the maximum preconcentration factor is 267. The method was successfully applied to the evaluation of these trace and toxic metals in various water, food, industrial effluent and urine samples. Figure Recovery percentage of Pb(II) and Cr(III) ions at different solution volumes.

We present a survey of some of the most updated results on the dynamics of periodic and almost pe... more We present a survey of some of the most updated results on the dynamics of periodic and almost periodic difference equations.

Page 1. A Novel Color Space Creating method Applied to Skin Color Detection Seyyed Meysam Hossein... more Page 1. A Novel Color Space Creating method Applied to Skin Color Detection Seyyed Meysam Hosseini , Hasan Farsi , Saber Amjadi Engineering Department, Birjand University, Birjand, Iran Meysamhosseini@yahoo.ca,HFarsi@birjand.ac.ir,Amjadisa@yahoo.com ...

We show that for a k-periodic difference equation, if a periodic orbit of period r is globally as... more We show that for a k-periodic difference equation, if a periodic orbit of period r is globally asymptotically stable (GAS), then r must be a divisor of k. Moreover, if r divides k we construct a non-autonomous dynamical system having minimum period k and which has a GAS periodic orbit with minimum period r. Our method uses the technique of skew-product dynamical systems. Our methods are then applied to prove two conjectures of J. Cushing and S. Henson concerning a non-autonomous Beverton-Holt equation which arises in the study of the response of a population to a periodically fluctuating environmental force such as seasonal fluctuations in carrying capacity or demographic parameters like birth or death rates. We give an equality linking the average population with the growth rates and carrying capacities (in the 2-periodic case) which shows that out-of-phase oscillations in these quantities always have a deleterious effect on the average population. We give an example where in-phase oscillations cause the opposite to occur.

Elaydi and Yakubu showed that a globally asymptotically stable(GAS) periodic orbit in an autonomo... more Elaydi and Yakubu showed that a globally asymptotically stable(GAS) periodic orbit in an autonomous difference equation must in fact be a fixed point whenever the phase space is connected. In this paper we extend this result to periodic nonautonomous difference equations via the concept of skew-product dynamical systems. We show that for a k-periodic difference equation, if a periodic orbit of period r is GAS, then r must be a divisor of k. In particular sub-harmonic, or long periodic, oscillations cannot occur. Moreover, if r divides k we construct a non-autonomous dynamical system having minimum period k and which has a GAS periodic orbit with minimum period r. Our methods are then applied to prove two conjectures of J. Cushing and S. Henson concerning a non-autonomous Beverton-Holt equation which arises in the study of the response of a population to a periodically fluctuating environmental force such as seasonal fluctuations in carrying capacity or demographic parameters like birth or death rates. We show that the periodic fluctuations in the carrying capacity always have a deleterious effect on the average population, thus answering in the affirmative the second of the conjectures.

Biology and Fertility of Soils, 2000

The effect of long-term waste water irrigation (up to 80 years) on soil organic matter, soil mic... more The effect of long-term waste water irrigation (up to 80 years) on soil organic matter, soil microbial biomass and its activities was studied in two agricultural soils (Vertisols and Leptosols) irrigated for 25, 65 and 80 years respectively at Irrigation District 03 in the Valley of Mezquital near Mexico City. In the Vertisols, where larger amounts of water have been applied than in the Leptosols, total organic C (TOC) contents increased 2.5-fold after 80 years of irrigation. In the Leptosols, however, the degradability of the organic matter tended to increase with irrigation time. It appears that soil organic matter accumulation was not due to pollutants nor did microbial biomass:TOC ratios and qCO2 values indicate a pollutant effect. Increases in soil microbial biomass C and activities were presumably due to the larger application of organic matter. However, changes in soil microbial communities occurred, as denitrification capacities increased greatly and adenylate energy charge (AEC) ratios were reduced after long-term irrigation. These changes were supposed to be due to the addition of surfactants, especially alkylbenzene sulfonates (effect on denitrification capacity) and the addition of sodium and salts (effect on AEC) through waste water irrigation. Heavy metals contained in the sewage do not appear to be affecting soil processes yet, due to their low availability. Detrimental effects on soil microbial communities can be expected, however, from further increases in pollutant concentrations due to prolonged application of untreated waste water or an increase in mobility due to higher mineralization rates.

This paper makes a discourse analysis of the Civic Ordinance of Barcelona, adopted by the City Ha... more This paper makes a discourse analysis of the Civic Ordinance of Barcelona, adopted by the City Hall of Barcelona-Spain in January of 2006, in order to typify and manage behaviour in the public spaces of the city. The textual corpus we used for this analysis is the Ordinance project in its two versions. The Discourse Analysis methodology used in this study has been proposed by different authors in this field (Martín ). Results point to the emergence of two kinds of discourses inside the text, as well as MARÍA GISELA ESCOBAR Y LILIANA VARGAS MONROY Univ. Psychol. Bogotá (Colombia), 6 (3): 601-611, septiembre-diciembre de 2007

Mikrochimica Acta, 2011

Biology and Fertility of Soils, 2000