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Cauich-Cupul J.I.,Research Center Cientifica Of Yucatan | Perez-Pacheco E.,Technological Institute of Merida | Valadez-Gonzalez A.,Research Center Cientifica Of Yucatan | Herrera-Franco P.J.,Research Center Cientifica Of Yucatan
Journal of Materials Science | Year: 2011

Carbon fiber/epoxy material in the form of a single fiber unidirectional composite was subjected to controlled humidity environments. Moisture uptake in polymer composites has significant effects on the mechanical properties of the matrix as well as on the final performance of the composite material. Diminishing of the mechanical properties of the matrix is attributed to a decrease of its glass transition temperature (Tg). The quality of the fiber-matrix interphase was assessed using the single fiber fragmentation test and the fiber-fragment length, considered as an indicator of interfacial quality. In o der to measure the fiber fragment lengths and indentify failure mechanism at the interface optical observation and acoustic emission technique were used. The speed of propagation of an acoustic wave in the material was also determined. A comparison is made of interfacial shear strength values determined by acoustic emission and optical techniques. Excellent agreement between the two techniques was obtained. By means of a micromechanical model, it was possible to determine from the fragmentation lengths a measure of the interfacial shear strength between the fiber and the matrix. The role of moisture uptake swelling of the matrix on the residual stresses is considered to be important when considering the effect deterioration of interfacial shear properties. Both the contribution of the radial stresses and the mechanical component of fiber- matrix adhesion are seen to decrease rapidly for higher moisture contents in the matrix and/or interface. © Springer Science+Business Media, LLC 2011.

Aguilar C.A.,Autonomous University of Carmen | Montalvo C.,Autonomous University of Carmen | Rodriguez L.,Technological Institute of Merida | Ceron J.G.,Autonomous University of Carmen | Ceron R.M.,Autonomous University of Carmen
International Journal of Environmental Science and Technology | Year: 2012

Levels of barium, cadmium, chromium, copper, mercury and vanadium were determined by plasma emission spectroscopy in sediments and oysters (Crassostrea virginica) in the Palizada, Chumpán and Candelaria rivers, which flow into the Términos Lagoon, state of Campeche, Mexico. The relation between the condition index of the oyster and the detected elements were determined as well. Significant relations were observed between copper (r = -0.825, p < 0.05) and chromium (r = -0.787, p < 0.05), which indicates the oysters' affectation by ingesting both elements; concurrently, the results confirm that oysters present high tolerance to heavy metals. The average concentration of cadmium (2.05 μg/g), chromium (1. 82 μg/g) and copper (115. 55 μg/g) in rainy-season climate exceeded the limits for marine mollusks regarding different health standards. It was found that the rainy season, the sediment characteristics and organic matter content have a great influence on the transport and availability of heavy metals. © 2012 The Author(s).

Estrella-Gomez N.E.,Research Center Cientifica Of Yucatan | Sauri-Duch E.,Technological Institute of Merida | Zapata-Perez O.,CINVESTAV | Santamaria J.M.,Research Center Cientifica Of Yucatan
Environmental and Experimental Botany | Year: 2012

The relationship between accumulation of Pb2+ and changes in GSH biosynthesis was analyzed in both leaves and roots of the Pb2+-hyperaccumulator aquatic fern Salvinia minima, after exposure to 40μM Pb(NO3)2. Lead accumulation in both tissues increased the accumulation of GSH, increased the enzymatic activity of glutathione synthase (GS), and caused changes in the expression levels of SmGS genes in both tissues. The damage caused by Pb on plant performance, was evaluated by the changes in the content of pigments, particularly on the carotenoids content. Lead accumulation caused more damage in roots than in leaves as indicated by the decrease on their carotenoids content. It is interesting that in leaves, the concentration of GSH, the activity of GS and the expression levels of SmGS gene were all higher than in roots. These results, together with our previous finding that roots accumulated more phytochelatins than did leaves of S. minima plants exposed to similar concentrations of lead (Estrella et al., 2009), suggest that the Pb-hyperaccumulator aquatic fern, S. minima, displays a coordinated and differential response to Pb2+ at leaves and roots, where GSH may play an important role in protecting leaves from the detrimental effects of lead, perhaps by counteracting the effect of free radicals. © 2011 Elsevier B.V.

Rivera J.M.,University of Veracruz | Rincon S.,Technological Institute of Merida | Farfan N.,University of the Basque Country | Santillan R.,Research Center y
Journal of Organometallic Chemistry | Year: 2011

Nine new boronates, six of them chiral, with five-six-membered ring heterobicycles were prepared by reaction of the Schiff bases and phenyl boronic acid. The boronates were fully characterized by spectroscopic techniques, NMR 1H, 13C, 11B, Infrared spectroscopy, mass spectrometry and elemental analysis. The reaction showed high diasteroselectivity, only in the case of compound 4c, containing a methyl substituent in the aliphatic moiety, the induction is low giving a 2:1 mixture of two diatereoisomers. The results showed that the preferred stereochemistry in the heterocycles is that where all substituents in the five membered ring and the phenyl group attached to boron atom are on the same side. © 2011 Elsevier B.V. All rights reserved.

Ruiz J.C.R.,Technological Institute of Merida | Ancona D.A.B.,Autonomous University of Yucatan | Campos M.R.S.,Autonomous University of Yucatan
Nutricion Hospitalaria | Year: 2014

As the last century saw a decline in the burden of nutritional deficiency and infectious disease, the global burden of chronic disease, cardiovascular disease (CVD) in particular, is increasing. CVD is the leading cause of death in the developed countries. Significant research efforts on the prevention and treatment of this disease have identified elevated plasma cholesterol as a primary risk factor for CVD. Although CVD progresses with hypercholesterolemia, it seems possibility to delay and prevent its development through improvement of diet. Recent findings demonstrate that protein concentrates, protein hydrolysates, and peptides derived from vegetables may promote a significant decrease in blood cholesterol concentration. This reduction in cholesterol and lipid levels by protein, protein hydrolysates, and peptides can be the result of dietary changes, reduced cholesterol biosynthesis, changes in bile acid synthesis, and reduced absorption of lipid cholesterol and bile acid. Combination drug/diet therapies may reduce the number of drug prescriptions, the progressive rise in "optimal" drug dosage and costs associated with pharmaceutical management of disease. These bioactive vegetable proteins, hydrolysates and peptides may be used in formulation of functional foods, nutraceuticals, and natural drugs because of their health benefit effects suggesting their use as an alternative in treatment of various dyslipidemias, and a potential agent for reducing cardiovascular diseases risk factors.

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