Modelamiento y simulación de susceptibilidad magnética AC en manganitas La2/3Ca1/3MnO3

In this study, a model for obtaining the AC magnetic susceptibility of La2/3Ca1/3MnO3 manganites was proposed. The samples were composed of a combination of Mn4+ and Mn3+ ions that influence the material stoichiometry. The model is based on the Hamiltonian, including the Heisenberg interaction and the Zeeman effect. For determining AC susceptibility, a time-dependent external magnetic field h(t) was applied to the sample. Several mathematical tools, such as Fourier transforms, were required for performing the simulations. The study was conducted for various angular frequencies and temperatures. The simulations were obtained using a graphic interface that allowed the online monitoring of the results. According to the results, the AC susceptibility decreases not only with the temperature, but also with the frequencyEn este trabajo se propone un modelo para obtener la susceptibilidad magnética AC de manganitas La2/3Ca1/3MnO3 . Las muestras están compuestas por una combinación de iones Mn4+ y Mn3+ que influencian la estequiometría del material. El modelo se basa en un Hamiltoniano que incluye interacción Heisenberg y efecto Zeeman. Para determinar la susceptibilidad AC, se aplica un campo magnético externo dependiente del tiempo h(t) a la muestra. Para llevar a cabo las simulaciones se requirieron algunas herramientas matemáticas, tales como transformadas de Fourier. El estudio fue llevado a cabo para diversas frecuencias angulares y temperaturas. Las simulaciones se obtuvieron empleando una interfaz gráfica que permitió el monitoreo en línea de los resultados. De acuerdo con dichos resultados, la susceptibilidad AC disminuye no solo con la temperatura, sino también con la frecuenci

Graphic user interface for monte carlo simulation of ferromagnetic/antiferromagnetic manganite bilayers

Las manganitas han sido ampliamente estudiadas debido a sus propiedades importantes tales como magnetorresistencia colosal y polarización de intercambio, que son fenómenos importantes empleados en diversas aplicaciones tecnológicas. Por esta razón, en este trabajo se presenta el estudio del efecto de la polarización de intercambio (exchange bias) para el caso de bicapas de La2/3Ca1/3MnO3/La1/3Ca2/3MnO3. Este estudio se llevó a cabo empleando el método de Monte Carlo junto con el algoritmo de Metropolis. Con el fin de que este estudio sea más fácil, se construyó una interface gráfica para hacer más amigable la interacción con el usuario. La interface permite el control de parámetros como el espesor de la película, la temperatura, el campo magnético el número de pasos de Monte Carlo y los parámetros de intercambio. Los resultados obtenidos reflejaron la influencia de todos estos parámetros sobre el Exchange bias y el campo coercitivo.The manganites have been widely studied because of their important properties as colossal magnetoresistance and exchange bias that are important phenomena used in many technological applications. For this reason, in this work, a study of the exchange bias effect present in La2/3Ca1/3MnO3/La1/3Ca2/3MnO3. This study was carried out by using the Monte Carlo method and the Metropolis Algorithm. In order to make easy this study, a graphic user interface was built alloying a friendly interaction. The interface permits to control the thickness of Ferromagnetic and Antiferromagnetic layer, temperatures the magnetic field, the number of Monte Carlo steps and the exchange parameters. Results obtained reflected the influence of all of these parameters on the exchange bias and coercive fields

A Discontinuous Adaptive Sliding-Mode Observer for a Class of Uncertain Nonlinear Systems ⋆

International audienceIn this paper the problem of simultaneous state and parameter estimation is studied for a class of uncertain nonlinear systems. A discontinuous adaptive sliding-mode observer is proposed based on a discontinuous nonlinear parameter estimation algorithm. It is shown that such an algorithm provides a rate of convergence faster than exponential. Then, the proposed discontinuous parameter estimation algorithm is included in the structure of a sliding-mode state observer providing an ultimate bound for the full estimation error. Some simulation results illustrate the feasibility of the proposed adaptive sliding-mode observer

Stability Analysis for Impulsive Systems: 2D Vector Lyapunov Function Approach

This paper contributes to the stability analysis for impulsive dynamical systems based on a vector Lyapunov function and its divergence operator. The new method relies on a 2D time domain representation. The result is illustrated for the exponential stability of linear impulsive systems based on LMIs. The obtained results provide some notions of minimum and maximum dwell-time. Some examples illustrate the feasibility of the proposed approach

Multi-level data fusion strategies for modeling three-way electrophoresis capillary and fluorescence arrays enhancing geographical and grape variety classification of wines

Capillary electrophoresis with diode array detection (CE-DAD) and multidimensional fluorescence spectroscopy (EEM) second-order data were fused and chemometrically processed for geographical and grape variety classification of wines. Multi-levels data fusion strategies on three-way data were evaluated and compared revealing their advantages/disadvantages in the classification context. Straightforward approaches based on a series of data preprocessing and feature extraction steps were developed for each studied level. Partial least square discriminant analysis (PLS-DA) and its multi-way extension (NPLS-DA) were applied to CE-DAD, EEM and fused data matrices structured as two-way and three-way arrays, respectively. Classification results achieved on each model were evaluated through global indices such as average sensitivity non-error rate and average precision. Different degrees of improvement were observed comparing the fused matrix results with those obtained using a single one, clear benefits have been demonstrated when level of data fusion increases, achieving with the high-level strategy the best classification results.Fil: Ríos Reina, Rocío. Universidad de Sevilla; EspañaFil: Azcarate, Silvana Mariela. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Ciencias de la Tierra y Ambientales de La Pampa. Universidad Nacional de La Pampa. Facultad de Ciencias Exactas y Naturales. Instituto de Ciencias de la Tierra y Ambientales de La Pampa; ArgentinaFil: Camiña, José Manuel. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Ciencias de la Tierra y Ambientales de La Pampa. Universidad Nacional de La Pampa. Facultad de Ciencias Exactas y Naturales. Instituto de Ciencias de la Tierra y Ambientales de La Pampa; ArgentinaFil: Goicoechea, Hector Casimiro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; Argentina. Universidad Nacional del Litoral. Facultad de Bioquímica y Ciencias Biológicas. Laboratorio de Desarrollo Analítico y Quimiometría; Argentin

Comparison of fracture toughness values of normal and high strength concrete determined by three point bend and modified disk-shaped compact tension specimens

The modified disk shaped compact tension test is a configuration derived from standard compact tension test that is used for measuring fracture mechanical properties of primarily metallic materials. The compact tension configuration is commonly used for measurement fracture mechanical properties as e.g. fracture toughness, Young’s modulus, work of fracture etc. The modified compact tension tests imply significant modifications of the specimen morphology in order to avoid premature failure. The modified compact tension test is not proper for quasi-brittle materials due to its complicated shape (steel-concrete interface), but it is easily extracted from drill core and we do not need large amount of material for obtaining fracture properties as we need for e.g. three- or four- point bend test. Since it is a new test method, a wide range of tests is needed to be done before it can be applied. In the paper the selected outputs of the experiments performed on normal and high strength concrete will be processed and the values of fracture mechanical parameters will be discussed

Adaptive Estimation for Uncertain Nonlinear Systems: A Sliding-Mode Observer Approach

International audienceThis paper deals with the problem of adaptive estimation, i.e. the simultaneous estimation of the state and parameters, for a class of uncertain nonlinear systems. A nonlinear adaptive sliding-mode observer is proposed based on a nonlinear parameter estimation algorithm. The nonlinear parameter estimation algorithm provides a rate of convergence faster than exponential while the sliding-mode observer ensures ultimate boundness for the state estimation error attenuating the effects of the external disturbances. Linear matrix inequalities (LMIs) are provided for the synthesis of the adaptive observer and some simulation results show the feasibility of the proposed approach

Uso do Modelo Auto-regressivo de Duração Condicional para predizer a queda do dólar no mercado cambiário colombiano

The fundamental objective of the Autoregressive Conditional Duration (ACD) model is the modeling of time series with non-equidistant periods. Given the leptokurtic nature of TRM returns and the durations behavior associated with them, a Rayleigh Distribution with transmutation is used, which allows approaching in an adjusted form to a heavy tail distribution, coherent with this stylized fact in returns. It is concluded that the time elapsed between dollar falls, on average, is between 3 and 6 days..El objetivo fundamental del modelo autorregresivo de duración condicional (ADC) es elmodelamiento de series de tiempo con periodos no equidistantes. Dada la naturaleza leptocúrtica de los retornos de la tasa representativa del mercado (TRM) y el comportamiento de las duraciones asociado a estos, se usó una distribución de Rayleigh con transmutación, que permite aproximar de forma ajustada a una distribución de colas pesadas, coherente con este hecho estilizado en los retornos. Se concluye que el tiempo transcurrido entre caídas del dólar, en promedio, se encuentra entre 3 y 6 días.O objetivo fundamental do modelo Auto-regressivo de Duração Condicional (ADC) é o modelamento de séries de tempo com períodos não equidistantes. Dada a natureza leptocúrtica dos retornos da trm e o comportamento das durações associados a estes, se usou uma Distribuição de Rayleigh com transmutação, que permite se aproximar de forma ajustada, a uma distribuição de colas pesadas, coerente com este facto estilizado nos retornos. Se conclui que, o tempo transcorrido entre quedas do dólar, em média, encontra-se entre 3 e 6 dias

1,1′-[(2-Phenyl-2,3-dihydro-1H-benz­imidazole-1,3-di­yl)bis­(methyl­ene)]bis­(1H-benzotriazole)

The imidazole ring in the title compound, C27H22N8, adopts a slight envelope conformation with the C atom carrying the phenyl ring being the flap atom. The phenyl ring is almost perpendicular to the mean plane of the imidazole ring [dihedral angle = 88.90 (7)°]. The (1H-benzotriazol-1-yl)methyl groups bound to the imidazole ring are positioned on the same side of the imidazole ring. The dihedral angle between these benzotriazolyl rings is 17.71 (5)°. The crystal packing is stabilized by a C—H⋯π inter­action, which connects the mol­ecules into zigzag chains running along the b axis