High temperature oxidation resistance of (Ti,Ta)(C,N)-based cermets

Cermets based on titanium–tantalum carbonitride were oxidized in static air between 800 °C and 1100 °C for 48 h. The thermogravimetric and microstructural study showed an outstanding reduction in the oxidation of more than 90% when the Ta content was increased. In cermets with low Ta content, the formation of a thin CoO/Co3O4 outer layer tends to disappear by reacting with the underlying rutile phase, which emerges at the surface. However, in cermets with higher Ta content, the formation of an external titanate layer, observed even at a low temperature, appears to prevent the oxygen diffusion and the oxidation progressionPeer reviewe

Kinetics of high-temperature oxidation of (Ti,Ta)(CN)-based cermets

The kinetics of the high-temperature oxidation of titanium–tantalum carbonitride-based cermets with different Ti/Ta ratios was studied. Isothermal oxidation tests were conducted under static air for 48 h at temperatures between 700 °C and 1200 °C. The oxidation satisfied the parabolic kinetics, characteristic of the existence of a protective oxide layer. The apparent activation energy suggests the rate-controlling process during oxidation is the simultaneous inward and outward diffusion of oxygen and titanium, respectively, through the formed protective layer, consisting mainly of a rutile phase. A higher Ta(V) content in the rutile decreased the oxygen diffusivity due to the reduction of oxygen vacancy concentration.Peer reviewe

Room temperature mechanosynthesis of the La 1-xSr xMnO 3±δ (0≤x≤1) system and microstructural study

Monophase nanocrystalline powders belonging to the La 1-xSr xMnO 3±δ system (0≤x≤1) with a perovskite structure have been obtained by mechanochemistry synthesis using a planetary ball milling equipment from La 2O 3, SrO, and Mn 2O 3 mixtures. The solid state reaction was complete after one hour of milling treatment. For all the compositional range, the diffraction domain was very small and the structure appeared as a pseudo cubic perovskite. After annealing at 1100 °C under static air, the symmetry evolution due to the La substitution by Sr was analyzed by X-ray and electron diffraction. Samples with x=0, 0.25, 0.5, and 0.75 were assigned to R-3c space group (1 6 7) in the rhombohedral system and perovskite structure. However, the symmetry of the last term of the system (x=1), SrMnO 3±δ sample, changed to P6 3/mmc space group (1 9 4) in the hexagonal system. The terms with x=0.8, 0.85, and 0.9 presented mainly rhombohedral symmetry. © 2012 Elsevier Inc.Peer Reviewe

Inverse core-rim microstructure in (Ti,Ta)(C,N)-based cermets developed by a mechanically induced self-sustaining reaction

Cermets with a nominal composition (Ti 0.8Ta 0.2C 0.5N 0.5- 20 wt.% Co) were synthesised by a mechanically induced self-sustaining reaction (MSR) process from stoichiometric elemental powder blends. The MSR allowed the production of a complex (Ti,Ta)(C,N) solid solution, which was the raw material used for the sintering process. The pressureless sintering process was performed at temperatures between 1400 °C and 1600 °C in an inert atmosphere. The microstructural characterisation showed a complex microstructure composed of a ceramic phase with an unusual inverse core-rim structure and a Ti-Ta-Co intermetallic phase that acted as the binder. © 2011 Elsevier Ltd. All rights reserved.Peer Reviewe

Nonexistence of self-similar singularities for the 3D incompressible Euler equations

We prove that there exists no self-similar finite time blowing up solution to the 3D incompressible Euler equations. By similar method we also show nonexistence of self-similar blowing up solutions to the divergence-free transport equation in $\Bbb R^n$. This result has direct applications to the density dependent Euler equations, the Boussinesq system, and the quasi-geostrophic equations, for which we also show nonexistence of self-similar blowing up solutions.Comment: This version refines the previous one by relaxing the condition of compact support for the vorticit

Boltzmann Entropy, the Holographic Bound and Newtonian Cosmology

[EN] The holographic principle sets an upper bound on the total (Boltzmann) entropy content of the Universe at around 10123kB (kB being Boltzmann¿s constant). In this work we point out the existence of a remarkable duality between nonrelativistic quantum mechanics on the one hand, and Newtonian cosmology on the other. Specifically, nonrelativistic quantum mechanics has a quantum probability fluid that exactly mimics the behaviour of the cosmological fluid, the latter considered in the Newtonian approximation. One proves that the equations governing the cosmological fluid (the Euler equation and the continuity equation) become the very equations that govern the quantum probability fluid after applying the Madelung transformation to the Schroedinger wavefunction. Under the assumption that gravitational equipotential surfaces can be identified with isoentropic surfaces, this model allows for a simple computation of the gravitational entropy of a Newtonian Universe.This research was supported by grant no. ENE2015-71333-R (Spain).Fernández De Córdoba, P.; Isidro, J. (2018). Boltzmann Entropy, the Holographic Bound and Newtonian Cosmology. Proceedings. 2(4):155-159. https://doi.org/10.3390/ecea-4-050081551592

Hyperbolic space in the Newtonian limit: The cosmological constant

[EN] In this paper, the cosmological constant and the Boltzmann entropy of a Newtonian Universe filled with a perfect fluid are computed, under the assumption that spatial sections are copies of 3-dimensional hyperbolic space.This research was supported by Grant No. RTI2018-102256-B-I00 (Spain).Castro-Palacio, JC.; Fernández De Córdoba, P.; Gallego Torromé, R.; Isidro, J. (2022). Hyperbolic space in the Newtonian limit: The cosmological constant. International Journal of Modern Physics D. 31(09):2250072-1-2250072-11. https://doi.org/10.1142/S02182718225007292250072-12250072-11310

CONTROL ÓPTIMO PARA EL CONTROL DE TEMPERATURA EN EL CULTIVO DE TOMATE EN INVERNADERO BASADO EN UN SISTEMA DINÁMICO.

ResumenUn control óptimo para regular la temperatura al interior de un invernadero se puede obtener a partir del modelo matemático integrado del cultivo y del invernadero. El modelo en consideración es exclusivo de la sierra norte del estado de Puebla, México; pues los parámetros necesarios se determinaron durante un periodo de cosecha de 80 días en la época de invierno. El modelo considera cinco estados: relativo con el cultivo consideramos el número de nodos, la masa seca del dosel y la masa seca de la raíz; relativo con el invernadero consideramos, la temperatura al interior del invernadero y la humedad relativa.Para aplicar la teoría de control óptimo, seleccionamos un costo funcional con el fin de aumentar el beneficio del agricultor, significa que el agricultor además de aumentar potencialmente la producción del cultivo obtendrá un ahorro en los gastos de consumo de energía.Construimos el algoritmo que da solución al problema de control óptimo y realizamos la simulación en un periodo de 80 días.Palabra(s) Clave: Control óptimo, Modelo dinámico integrado, Sistema de calefacción, Variables auxiliares, Variables de estado. OPTIMUM CONTROL FOR TEMPERATURE CONTROL IN GREENHOUSE TOMATO CULTIVATION BASED ON A DYNAMIC SYSTEMAbstractAn optimal control to regulate the temperature inside of a greenhouse can be obtained from a mathematical model, where such mathematical model integrates the dynamic model of the crop (tomato crop) and the greenhouse. This paper considers the dynamic model exclusive from northern mountain range of Puebla, Mexico. This means that all parameters were determined from a harvest throughout a period of 80 days in the winter season. The dynamic model considered 5 state variables, three of them are relative from the crop, they are the number of nodes (plant development), the biomass dry canopy, and the biomass dry root. The last 2 variables state are linked to the greenhouse, these are the temperature inside of the greenhouse and the relative humidity. Applying the optimal control theory with a proposal criterion of optimization, admissible trajectories for the variables state were obtained; such trajectories maximize the benefit of the crop, thereby the farmers and harvest improves the crop production, and reduce the energy consumption. An algorithm was built, which gives a solution for the optimal control and simulates a harvest throughout a period of 80 days.Keywords: Auxiliary states, Heating system, Integrated Dynamic Model, Optimal control, Variable state

Quantum Dynamics on the Worldvolume from Classical su(n) Cohomology

A key symmetry of classical p-branes is invariance under worldvolume diffeomorphisms. Under the assumption that the worldvolume, at fixed values of the time, is a compact, quantisable Kähler manifold, we prove that the Lie algebra of volume-preserving diffeomorphisms of the worldvolume can be approximated by su(n), for n → ∞. We also prove, under the same assumptions regarding the worldvolume at fixed time, that classical Nambu brackets on the worldvolume are quantised by the multibrackets corresponding to cocycles in the cohomology of the Lie algebra su(n)

Análisis de los factores genéticos y ambientales con influencia en la circunferencia escrotal en el vacuno de carne de Raza Retinta

De los caracteres del vacuno de carne, los relacionados con la eficiencia reproductiva han sido considerados de una importancia fundamental. Dentro de éstos, cabe destacar la CE, parámetro correlacionado positivamente con las características cualitativas y cuantitativas del semen, asl como asociado a parámetros reproductivos en hembras (precocidad sexual y fertilidad). En este trabaja se ha estudiado la CE desde distintos aspectos como los factores ambientales que le influyen, su evolución a lo largo del tiempo, el cálculo del parámetro genético de la heredabilidad y las relaciones con otras variables como el peso vivo del animal. Para ello, se realizaron 1.020 mediciones en 281 animales pertenencientes a 20 ganaderías del núcleo de Control del plan de mejora de esta raza. la media obtenida para la circunferencia escrotal fue de 30,66 ± 0, 166 (CV. = 17,3%)y 34,38 ± 0, 140 (C.V.= 9, 1%) para an ima les de un año de edad, y la heredabilidad estimada para este carácter de 0,36. El peso vivo, y en segundo lugar la edad, fueron las dos variables con mayor influencia en la circunferencia escrotal en esta raza. Otros factores ambientales a tener en cuenta en los análisis genéticos de esta variable son la ganadería y año -estación de medida-, cuyo efecto se ha mostrado altamente significativo. Así si bien la curva de crecimiento de la CE que mejor se ajusta al intervalo de crecimiento analizado fue la logistítica 2, a efectos prácticos de tipificac ión al año, consideramos que la curva polinómica de segundo grado da un ajuste equivalente, permitienndo una mayor simplificación de los cálculos necesarios para su aplicación en un plan de mejora