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Ciudad Sahagun, Mexico

Juarez-Santillan L.F.,Autonomous University of the State of Hidalgo | Lucho-Constantino C.A.,Polytechnic University of Pachuca | Vazquez-Rodriguez G.A.,Autonomous University of the State of Hidalgo | Ceron-Ubilla N.M.,Autonomous University of the State of Hidalgo | Beltran-Hernandez R.I.,Autonomous University of the State of Hidalgo
Bioresource Technology

Soil, sediments, water and plant samples from the mining zone of Molango were collected and analyzed and Mn-tolerant and Mn-accumulator plants were identified. Soil and sediments presented moderately alkaline and reducing conditions, a normal electrical conductivity, a sandy texture and medium-to-high cation exchange capacities. These properties favored the presence of Mn2+, which is the form most easily assimilated by plants, and the total Mn concentration (11,637-106,104 mg kg-1 dried weight, DW) was at phytotoxic level. Water was also an important Mn source. Equisetum hyemale and Telypteris kunthii survived in the presence of such Mn concentrations using an exclusion strategy, while Cnidoscolus multilobus, Platanus mexicana, Solanum diversifolium, Asclepius curassavica L. and Pluchea sympitifolia employed an accumulation strategy. These plants could be useful to re-vegetate and stabilize Mn tailings in order to decrease the erosion effects. © 2010 Elsevier Ltd. All rights reserved. Source

Vera E.E.,Polytechnic University of Pachuca | Vite M.,Tribology Group | Lewis R.,University of Sheffield | Gallardo E.A.,Tribology Group | Laguna-Camacho J.R.,University of Veracruz

In this study, the performance of the coatings TiN, CrN and WC/C applied on steel substrates that were subjected to sliding wear was analyzed. These materials normally exhibit an efficient performance in applications such as coatings of cutting tools, stamping processes, forming and plastic injection tooling where the contact and sliding conditions are severe. Due to this fact, this research was conducted to characterize the materials in relation to the wear process. The sliding wear test was performed using a reciprocating wear test machine. All tests were conducted in dry conditions with a room temperature between 20. °C and 23. °C and 45% to 50% relative humidity. A sliding velocity of 0.08 m/s and 2 mm amplitude were used. The applied loads were 11.76. N (Po = 1.74. GPa) and 7.84. N (1.52. GPa), respectively. Optical microscopy and scanning electron microscopy (SEM) were used to observe and analyze the wear mechanisms. Additionally, the variation of the friction coefficient versus the number of cycles was obtained. This was used to determine with a higher precision the time (presented as number of cycles) where the coating presented the initial signs of wear damage. In addition, energy dispersive X-ray analysis (EDS) was performed to obtain the chemical composition of the materials and hardness tests on the wear tracks were also carried out. It was possible to know the wear life of these coatings and possible causes of life variations. The load was an important factor in the variation of the wear life results, although other factors such as surface roughness and coating thickness were also significant. © 2011 Elsevier B.V. Source

Campos-Silva I.,National Polytechnic Institute of Mexico | Bravo-Barcenas D.,National Polytechnic Institute of Mexico | Meneses-Amador A.,National Polytechnic Institute of Mexico | Ortiz-Dominguez M.,Polytechnic University of Pachuca | And 3 more authors.
Surface and Coatings Technology

In this study, new data about the growth kinetics and indentation properties of cobalt boride layers formed on the surface of the ASTM F-75 biomedical alloy were estimated. The boron diffusion at the surface of the biomedical alloy was conducted using a powder-pack boriding process at temperatures of 1223-1273K with different exposure times for each temperature. Two mathematical approaches were proposed to determine the boron diffusion coefficients of the CoB and Co2B layers in the range of boriding temperatures, in which the experimental results of the kinetics of the cobalt boride layers were compared with those estimated using diffusion models.Finally, the mechanical characterization of the cobalt boride layers was evaluated by indentation techniques with applied loads of 0.98. N and 50. mN, respectively. According to the nanoindentation tests, a maximum hardness value (30. GPa) and a maximum Young's modulus (380. GPa) were obtained near the surface region (5. μm) of the borided cobalt alloy. © 2013 Elsevier B.V. Source

Ordaz P.,Polytechnic University of Pachuca | Poznyak A.,National Polytechnic Institute of Mexico
IMA Journal of Mathematical Control and Information

This paper presents the development of an adaptive state estimator and an output controller based on the attractive ellipsoid method (AEM) for a class of uncertain non-linear systems (quasi-Lipschitz with external perturbations). The proposed method guarantees that, under a specific persistent excitation condition, the controlled system trajectories converge to an ellipsoid having a smaller trace of the corresponding inverse ellipsoidal matrix comparing to classical AEM without adaptation. An underactuated vertical double pendulum is considered as an experimental illustrative example of the suggested approach. © The authors 2014. Published by Oxford University Press on behalf of the Institute of Mathematics and its Applications. All rights reserved. Source

Juarez-Perez E.J.,CSIC - Institute of Materials Science | Vinas C.,CSIC - Institute of Materials Science | Teixidor F.,CSIC - Institute of Materials Science | Santillan R.,CINVESTAV | And 4 more authors.

Fluorescent Fréchet-type poly(aryl ether) dendrimers that incorporate the 1, 3, 5-triphenylbenzene as core molecule and 3, 6, 9, or 12 terminal allyl ether groups have been prepared in very good yield by following the Frechet convergent approach. Regiospecific hydrosylilation reactions on the allyl ether functions with the cobaltabisdicarbollide derivative Cs[1, 1'-μ-SiMeH-3, 3'-Co(l, 2-C2B9H10) 2] lead to different generations of Féchet-type polyanionic metallodendrimers decorated with 3, 6, and 9 cobaltabisdicarbollide units. Starting dendrimers exhibit photoluminescence properties at room temperature under ultraviolet irradiation; nevertheless, after functionalization with cobaltabisdicarbollide derivatives, the fluorescence properties are quenched. Products are fully characterized by FTIR, NMR, and UV-vis spectroscopies. For metallodendrimers, the UV-vis absorptions have been a good tool for estimating the experimental number of cobaltabisdicarbollide units peripherally attached to the dendrimeric structure and consequently to corroborate the unified character of the dendrimers. Because of the anionic character of these compounds and the boron-rich content, we actually focus our research on biocompatibility studies and potential applications. © 2009 American Chemical Society. Source

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