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Oliva-Aviles A.I.,Research Center Estudios Avanzados | Aviles F.,Research Center Cientifica Of Yucatan | Sosa V.,Research Center Estudios Avanzados
Carbon | Year: 2011

Aligned multi-walled carbon nanotube (MWCNT)/polymer composite films are prepared by solution casting in the presence of an alternating electric field. Application of 7 kV/m at a frequency of 60 Hz to the polymer composite melt induces MWCNT alignment in the direction of the applied field, which is maintained after polymer crystallization. The electrical conductivity and piezoresistive response of electric-field-aligned and randomly oriented 0.1-0.75 wt% MWCNT/polysulfone films are evaluated. Electrical conductivity is 3-5 orders of magnitude higher for composites with electric-field-aligned MWCNTs than for randomly oriented composites. MWCNT alignment inside the polymer matrix also increases the film piezoresistive sensitivity, enhancing the strain sensing capabilities of the composite film. © 2011 Elsevier Ltd. All rights reserved.

Medina-Elizalde M.,UK National Oceanography Center | Medina-Elizalde M.,Research Center Cientifica Of Yucatan | Medina-Elizalde M.,University of Massachusetts Amherst
Earth and Planetary Science Letters | Year: 2013

I present a quality-controlled compilation of sea-level data from U-Th dated corals, encompassing 30 studies of 13 locations around the world. The compilation contains relative sea level (RSL) data from each location based on both conventional and open-system U-Th ages. I have applied a commonly used age quality control criterion based on the initial 234U/238U activity ratios of corals in order to select reliable ages and to reconstruct sea level histories for the last 150,000yr. This analysis reveals scatter of RSL estimates among coeval coral benchmarks both within individual locations and between locations, particularly during Marine Isotope Stage (MIS) 5a and the glacial inception following the last interglacial. The character of data scatter during these time intervals imply that uncertainties still exist regarding tectonics, glacio-isostacy, U-series dating, and/or coral position. To elucidate robust underlying patterns, with confidence limits, I performed a Monte Carlo-style statistical analysis of the compiled coral data considering appropriate age and sea-level uncertainties. By its nature, such an analysis has the tendency to smooth/obscure millennial-scale (and finer) details that may be important in individual datasets, and favour the major underlying patterns that are supported by all datasets. This statistical analysis is thus functional to illustrate major trends that are statistically robust ('what we know'), trends that are suggested but still are supported by few data ('what we might know, subject to addition of more supporting data and improved corrections'), and which patterns/data are clear outliers ('unlikely to be realistic given the rest of the global data and possibly needing further adjustments'). Prior to the last glacial maximum and with the possible exception of the 130-120ka period, available coral data generally have insufficient temporal resolution and unexplained scatter, which hinders identification of a well-defined pattern with usefully narrow confidence limits. This analysis thus provides a framework that objectively identifies critical targets for new data collection, improved corrections, and integration of coral data with independent, stratigraphically continuous methods of sea-level reconstruction. © 2012 Elsevier B.V.

Zozulya V.V.,Research Center Cientifica Of Yucatan
Archive of Applied Mechanics | Year: 2013

A high-order theory for functionally graded axially symmetric cylindrical shell based on expansion of the axially symmetric equations of elasticity for functionally graded materials into Legendre polynomials series has been developed. The axially symmetric equations of elasticity have been expanded into Legendre polynomials series in terms of a thickness coordinate. In the same way, functions that describe functionally graded relations has been also expanded. Thereby, all equations of elasticity including Hook's law have been transformed to corresponding equations for coefficients of Legendre polynomials expansion. Then system of differential equations in terms of displacements and boundary conditions for the coefficients of Legendre polynomials expansion coefficients has been obtained. Cases of the first and second approximations have been considered in more details. For obtained boundary-value problems' solution, a finite element has been used and numerical calculations have been done with COMSOL MULTIPHYSICS and MATLAB. © 2012 Springer-Verlag.

De-la-Pena C.,Research Center Cientifica Of Yucatan | Loyola-Vargas V.M.,Research Center Cientifica Of Yucatan
Plant Physiology | Year: 2014

Microbes and plants have evolved biochemical mechanisms to communicate with each other. The molecules responsible for such communication are secreted during beneficial or harmful interactions. Hundreds of these molecules secreted into the rhizosphere have been identified, and their functions are being studied in order to understand the mechanisms of interaction and communication among the different members of the rhizosphere community. The importance of root and microbe secretion to the underground habitat in improving crop productivity is increasingly recognized, with the discovery and characterization of new secreting compounds found in the rhizosphere. Different omic approaches, such as genomics, transcriptomics, proteomics, and metabolomics, have expanded our understanding of the first signals between microbes and plants. In this review, we highlight the more recent discoveries related to molecules secreted into the rhizosphere and how they affect plant productivity, either negatively or positively. In addition, we include a survey of novel approaches to studying the rhizosphere and emerging opportunities to direct future studies. © 2014 American Society of Plant Biologists. All rights reserved.

Hernandez-Perez A.,Research Center Cientifica Of Yucatan | Aviles F.,Research Center Cientifica Of Yucatan
Computational Materials Science | Year: 2010

This work investigates the influence of the interphase on the effective properties of carbon nanotube (CNT) composites using finite element analysis and elasticity solutions for representative volume elements. The influence of interphase thickness and gradient in elastic modulus on the elastic properties and stress distribution of the composite is examined, in order to shed some light on experimental parameters that are difficult to measure. It is found that the thickness of the interphase strongly influences the elastic properties and stress distribution of the composite, especially for matrices with low elastic modulus. Modeling results also suggests that the interphase thickness in CNT nanocomposites should be at least of the order of the CNT thickness and that the interphase modulus may follow an exponential gradient. © 2009 Elsevier B.V. All rights reserved.

Ramirez M. I.M.,Research Center Cientifica Of Yucatan | Jimenez Nah C.F.,Research Center Cientifica Of Yucatan
Phytotaxa | Year: 2012

A new species of Hechtia, H. pueblensis, from the Mexican State of Puebla, is described and illustrated. The new taxon is well documented with illustrations and photographs of staminate and pistillate flowers, as well as fruits. It shares its small-sized rosette and usually simple panicles with H. lyman-smithii (from a nearby geographical region in Oaxaca) and with H. fragilis (from Puebla and Oaxaca). © 2012 Magnolia Press.

Zozulya V.V.,Research Center Cientifica Of Yucatan | Zhang Ch.,University of Siegen
International Journal of Mechanical Sciences | Year: 2012

In this paper a high order theory for functionally graded (FG) axisymmetric cylindrical shells based on the expansion of the axisymmetric equations of elasticity for functionally graded materials (FGMs) into Fourier series in terms of Legendres polynomials is presented. Starting from the axisymmetric equations of elasticity, the stress and strain tensors, the displacement, traction and body force vectors are expanded into Fourier series in terms of Legendres polynomials in the thickness coordinate. In the same way the material parameters that describe the functionally graded material properties are also expanded into Fourier series. All equations of the linear elasticity including Hookes law are transformed into the corresponding equations for the Fourier series expansion coefficients. Then a system of differential equations in terms of the displacements and the boundary conditions for the Fourier series expansion coefficients is obtained. In particular the first and second order approximations of the exact shell theory are considered in more details. The obtained boundary-value problems are solved by the finite element method (FEM) with COMSOL Multiphysics and MATLAB software. Numerical results are presented and discussed. © 2012 Elsevier Ltd.

Chavarria-Hernandez J.C.,Research Center Cientifica Of Yucatan | Pacheco-Catalan D.E.,Research Center Cientifica Of Yucatan
Fuel | Year: 2014

Three correlations are proposed to predict the kinematic viscosity of fatty acid methyl esters (FAMEs) in a wide temperature range. One correlation is derived for saturated species from C6:0 to C24:0 while two complementary correlations are used for unsaturated species, from C14:1 to C22:1, including C18:2 and C18:3. The correlation for saturated FAMEs was derived from 247 viscosity experimental points taken from the literature, giving an average absolute deviation (AAD) of 1.33%. In the case of unsaturated species, 154 experimental data points reported in the literature were considered, obtaining an AAD of 2.88%. The predictive capacity of the proposed correlations was tested by calculating the viscosity of 31 pure biodiesels (193 data points) and four binary biodiesel blends (150 data points) whose compositions and viscosities at different temperatures were gathered from the literature. A global AAD of 5.33% was obtained for pure biodiesels while the global AAD for biodiesel blends was 7.58%. These results were compared to the AADs obtained for other different six models previously reported in the literature and applied to the same data bank. The comparison showed that the lowest AADs for both data sets (pure biodiesel and biodiesel blends) were obtained with the correlations of this work. © 2014 Elsevier Ltd. All rights reserved.

Aviles F.,Research Center Cientifica Of Yucatan | Aguilar-Montero M.,Research Center Cientifica Of Yucatan
Composite Structures | Year: 2010

Sandwich specimens composed of E-glass/polyester face sheets bonded to a PVC foam core were exposed to high moisture (95% RH) and immersed in sea-water for extended periods of time. Degradation of mechanical properties of the face sheets, foam core and face/core interface were progressively evaluated using flexural testing of the laminates, through-thickness tension of the foam core and interfacial sandwich DCB fracture testing. Testing reveals substantial flexural stiffness and strength reductions for the laminated composites, and only minor reduction in the tensile stiffness and strength of the foam. Degradation of the interfacial face/core fracture toughness is weak for specimens subjected to elevated moisture and more pronounced for sandwich specimens immersed in sea-water. After 30 days of exposure to high moisture, foam damage is visible in the form of cracks and pits on the cell walls. Optical examinations of expansional strains show that moisture absorbed by the foam penetrates only about to 2-3 mm from the core free surface for the 95% RH condition, while penetrates deeply for the immersed condition. © 2009 Elsevier Ltd. All rights reserved.

Research Center En Quimica Aplicada, Instituto Nacional de Investigaciones Nucleares and Research Center Cientifica Of Yucatan | Date: 2013-07-03

A method for obtaining sweet gas, synthetic gas, and sulphur from natural gas. The method includes the steps of removing impurities from the natural gas for obtaining pre-treated natural gas; sweetening the pre-treated natural gas through a separation using a plurality of membranes for obtaining sweet gas and acid gases; ionizing the acid gases to dissociate them into sulphur and synthetic gas with remnants of acid gases; and neutralizing the synthetic gas with remnants of acid gases for generating sweet gas. Likewise, a system is presented on how to implement the method.

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