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Friedrich A.,Goethe University Frankfurt | Winkler B.,Goethe University Frankfurt | Juarez-Arellano E.A.,University of Papaloapan | Bayarjargal L.,Goethe University Frankfurt
Materials | Year: 2011

Transition metal nitrides, carbides and borides have a high potential for industrial applications as they not only have a high melting point but are generally harder and less compressible than the pure metals. Here we summarize recent advances in the synthesis of binary transition metal nitrides, carbides and borides focusing on the reaction of the elements at extreme conditions generated within the laser-heated diamond anvil cell. The current knowledge of their structures and high-pressure properties like high-(p; T) stability, compressibility and hardness is described as obtained from experiments. © 2011 by the authors. Source

Ramirez-Hernandez A.,University of Papaloapan | Martinez-Richa A.,University of Guanajuato
Journal of Applied Polymer Science | Year: 2010

The aim of this work is the kinetic and thermodynamic study (by differential scanning calorimetry (DSC) and proton nuclear magnetic resonance (1H-NMR)) of the polymerization of ε-caprolactone initiated by ammonium decamolybdate. By means of isothermal kinetics, enthalpies of reaction in the range 150-160°C, as well as constant rates of polymerization (using an nth-order kinetics function model), were determined. From an Arrhenius plot, activation energy (Ea - 85.3 kJ/mol) and preexponential factor (A - 1.78 x 108 min-1) were estimated. Using dynamic methods, crystallization and melting temperatures for the polymer obtained in situ were derived. Kinetic data for polymerization (obtained by 1H-NMR) were fitted to 13 different model reaction functions. It was found that power law equations represent better the conversion versus time plots for this system. On the basis of experimental facts, a coordination- insertion mechanism involving molybdenum(V) species is proposed. © 2009 Wiley Periodicals, Inc. Source

Pena-Castro J.M.,University of California at Riverside | Pena-Castro J.M.,University of Papaloapan | Van Zanten M.,University Utrecht | Van Zanten M.,Max Planck Institute for Plant Breeding Research | And 5 more authors.
Plant Journal | Year: 2011

Submergence of plant organs perturbs homeostasis by limiting diffusion of oxygen, carbon dioxide and ethylene. In rice (Oryza sativa L.), the haplotype at the multigenic SUBMERGENCE1 (SUB1) locus determines whether plants survive prolonged submergence. SUB1 encodes two or three transcription factors of the group VII ethylene response factor family: SUB1A, SUB1B and SUB1C. The presence of SUB1A-1 and its strong submergence-triggered ethylene-mediated induction confers submergence tolerance through a quiescence survival strategy that inhibits gibberellin (GA)-induced carbohydrate consumption and elongation growth. SUB1C is invariably present and acts downstream of the enhancement of GA responsiveness during submergence. In this study, heterologous ectopic expression of rice SUB1A and SUB1C in Arabidopsis thaliana was used to explore conserved mechanisms of action associated with these genes using developmental, physiological and molecular metrics. As in rice transgenic plants that ectopically express SUB1A-1, Arabidopsis transgenic plants that constitutively express SUB1A displayed GA insensitivity and abscisic acid hypersensitivity. Ectopic SUB1C expression had more limited effects on development, stress responses and the transcriptome. Observation of a delayed flowering phenotype in lines over-expressing SUB1A led to the finding that inhibition of floral initiation is a component of the quiescence survival strategy in rice. Together, these analyses demonstrate conserved as well as specific roles for group VII ethylene response factors in integration of abiotic responses with development. © 2011 Blackwell Publishing Ltd. Source

Cabrera-Amado A.,University of Papaloapan | Silva-Navarro G.,CINVESTAV
International Conference on Noise and Vibration Engineering 2012, ISMA 2012, including USD 2012: International Conference on Uncertainty in Structure Dynamics | Year: 2012

In this work a journal bearing based on two Magneto-Rheological (MR) dampers is used for the unbalance response compensation in a rotor-bearing system. The endogenous disturbance due to the unbalance disk of the rotor cause high vibration levels. This problem is addressed by applying a semiactive control scheme called Positive Position Feedback (PPF) control. To apply this control technique is necessary to measure one of the radial displacements at the MR suspension (proximitors) and for control design and physical implementations we used the so-called Choi-Lee-Park polynomial model to describe the experimental dynamics of both MR dampers, which are able to describe the nonlinear and hysteresis behavior. For analysis and control synthesis is employed a rotor-bearing model using finite element methods, by which one considers a flexible shaft, one rigid disk, two non-isotropic supports, one traditional journal bearing and a MR suspension. An industrial PID speed controller is used for rotor speed regulation, which is based on a sufficiently fast tuning, enabling a proper speed profile to pass over the second critical speeds (run-up or coast-down). The setup consists of one steel shaft between a rigid support and a MR suspension with two MR dampers mounted on four compression springs, to measure the angular speed of the motor is used an optical encoder and the radial displacements are measured by non-contact sensors (proximitors). The unbalance control scheme is integrated into a PC with an I/O acquisition card and a Matlab/Simulink flexible platform. In summary, the overall unbalance response in the rotor-bearing system is reduced up to 58% with respect to the open-loop response, which is validated with numerical and experimental results in a physical platform designed and constructed to prove the efficiency and robust of the proposed semiactive control scheme. © (2012) by the Katholieke Universiteit Leuven Department of Mechanical Engineering All rights reserved. Source

Fuentes-Azcatl R.,Metropolitan Autonomous University | Mendoza N.,University of Papaloapan | Alejandre J.,Metropolitan Autonomous University
Physica A: Statistical Mechanics and its Applications | Year: 2015

In a recent work, Fuentes and Alejandre (2014) found that for TIP4P models there is a dipole moment of minimum density at 240 K and that the Lennard-Jones parameters can be adjusted to match the experimental dielectric constant at 300 K and the temperature of maximum density, respectively. The same procedure is used in this work to re-parameterize the simple point charge (SPC) model keeping the original geometry. The new model fails to reproduce the experimental self-diffusion coefficient and shear viscosity but improves the results at different temperatures and pressures of dielectric constant, isothermal compressibility, thermal expansion coefficient, surface tension, coexisting densities at the liquid-vapor interface, equation of state of ice Ih and equation of state of liquids at high pressures. A second model that reproduces the dielectric constant, self-diffusion coefficient and shear viscosity is proposed but the temperature of maximum density is 250 K, compared with the experimental value of 277 K. Both models improve the SPC/E results for almost all properties. The TIP3P model was also analyzed but the liquid density at 240 K always increases and a minimum in the dipole moment was not found. It is not possible to adjust for that model the charge distribution and short range interaction parameters to reproduce at the same time the target properties. © 2014 Elsevier B.V. Source

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