Hydrostatic equilibrium preservation in MHD numerical simulation with stratified atmospheres: Explicit Godunov-type schemes with MUSCL reconstruction

Many astrophysical processes involving plasma flows are produced in the context of a gravitationally stratified atmosphere in hydrostatic equilibrium, in which strong gradients can exist with gas properties that vary in small regions by several orders of magnitude. The standard Godunov-type schemes with polynomial reconstruction used to numerically solve these problems fail to preserve the hydrostatic equilibrium owing to the appearance of spurious fluxes generated by the numerical unbalance between gravitational forces and pressure gradients. Aims. The aim of this work is to present local hydrostatic reconstruction techniques that can be implemented in existing codes with Godunov-type methods to obtain well-balanced schemes that numerically satisfy the hydrostatic equilibrium for various conditions. Methods. The proposed numerical scheme is based on the Godunov method with second order MUSCL-type reconstruction, as is extensively used in astrophysical applications. The difference between the scheme and the standard formulations is only given by calculating the pressure and density Riemann states on each intercell face and by computing the gravitational source term on each cell. Results. The local hydrostatic reconstruction scheme is implemented in the FLASH code to verify the well-balanced property for hydrostatic equilibrium with constant or linearly variable temperature and constant or variable gravity. In addition, the behavior of the scheme for hydrostatic equilibrium with arbitrary temperature distributions is also analyzed together with the ability to propagate low-amplitude waves and to capture shock waves. Conclusions. The scheme is demonstrated to be robust and relatively simple to implement in existing codes. This approach produces good results in hydrostatic equilibrium preservation, satisfying the well-balanced property for the preset conditions and strongly reducing the spurious fluxes for extreme configurations.Fil: Krause, Gustavo Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Estudios Avanzados en Ingeniería y Tecnología. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto de Estudios Avanzados en Ingeniería y Tecnología; Argentin

Type-I intermittency with discontinuous reinjection probability density in a truncation model of the derivative nonlinear Schrödinger equation

In previous papers, the type-I intermittent phenomenon with continuous reinjection probability density (RPD) has been extensively studied. However, in this paper type-I intermittency considering discontinuous RPD function in one-dimensional maps is analyzed. To carry out the present study the analytic approximation presented by del Río and Elaskar (Int. J. Bifurc. Chaos 20:1185-1191, 2010) and Elaskar et al. (Physica A. 390:2759-2768, 2011) is extended to consider discontinuous RPD functions. The results of this analysis show that the characteristic relation only depends on the position of the lower bound of reinjection (LBR), therefore for the LBR below the tangent point the relation {Mathematical expression}, where {Mathematical expression} is the control parameter, remains robust regardless the form of the RPD, although the average of the laminar phases {Mathematical expression} can change. Finally, the study of discontinuous RPD for type-I intermittency which occurs in a three-wave truncation model for the derivative nonlinear Schrodinger equation is presented. In all tests the theoretical results properly verify the numerical dat

The Art of writing with light: memory, photography and fiction

Este trabajo intenta comparar tres textos filosóficos sobre fotografía: On photography (1977), escrito por Susan Sontag, La chambre claire (1980), escrito por Roland Barthes, y Für eine Philosophie der Fotografie (1983), escrito por Vilém Flusser. La comparación nos permite estudiar el proceso de representación, simulación y alienación, desde el comienzo de la fotografía como arte

Are CMEs capable of producing Moreton waves? A case study: The 2006 December 6 event

Considering the chromosphere and a stratified corona, we examine, by performing 2D compressible magnetohydrodynamics simulations, the capability of a coronal mass ejection (CME) scenario to drive a Moreton wave. We find that given a typical flux rope (FR) magnetic configuration, in initial pseudo-equilibrium, the larger the magnetic field and the lighter (and hotter) the FR, the larger the amplitude and the speed of the chromospheric disturbance, which eventually becomes aMoreton wave.We present arguments to explain why Moreton waves are much rarer than CME occurrences. In the frame of the present model, we explicitly exclude the action of flares that could be associated with the CME. Analysing the Mach number, we find that only fast magnetosonic shock waves will be able to produce Moreton events. In these cases an overexpansion of the FR is always present and it is the main factor responsible for the Moreton generation. Finally, we show that this scenario can account for the Moreton wave of the 2006 December 6 event (Francile et al. 2013).Fil: Krause, Gustavo Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Estudios Avanzados En Ingeniería y Tecnología. Universidad Nacional de Córdoba. Facultad de Ciencias exactas Físicas y Naturales. Instituto de Estudios Avanzados En Ingeniería y Tecnología; ArgentinaFil: Cécere, Mariana Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; ArgentinaFil: Zurbriggen, Ernesto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; ArgentinaFil: Costa, Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; ArgentinaFil: Francile, Carlos Natale. Universidad Nacional de San Juan. Facultad de Ciencias Exactas Físicas y Naturales. Departamento de Informática. Observatorio Astronómico Félix Aguilar; ArgentinaFil: Elaskar, Sergio Amado. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Estudios Avanzados En Ingeniería y Tecnología. Universidad Nacional de Córdoba. Facultad de Ciencias exactas Físicas y Naturales. Instituto de Estudios Avanzados En Ingeniería y Tecnología; Argentin

Influence of Coronal Holes on CME Deflections: Numerical study

The understanding of the causes that produce the deflection of coronal mass ejections (CMEs) is essential for the space weather forecast. We study the effects on CME trajectories produced by the different properties of a coronal hole (CH), close to the ejection area. We perform ideal magnetohydrodynamics simulations emulating the early rising of the CME in the presence of a CH. We find that, the stronger the magnetic field and the wider the CH area, the larger the CME deflection. The deflection reduces as the CH moves away from the ejection region. To quantify the deflection we propose a dimensionless parameter that depends on the CH properties. We show that a minimum magnetic energy region, responsible for the deflection, is associated with the presence of the CH near the CME. We establish a relationship between the CH properties, the location of the minimum magnetic region, and the CME deflection.Fil: Sahade, Abril. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; ArgentinaFil: Cécere, Mariana Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; ArgentinaFil: Krause, Gustavo Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Estudios Avanzados en Ingeniería y Tecnología. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto de Estudios Avanzados en Ingeniería y Tecnología; Argentin

Solución mediante métodos espectrales de la ecuación derivada no lineal de Schrödinger (DNLS)

Maestría en Ciencias De La Ingeniería - Mención AeroespacialLa manera convencial de estudiar el comportamiento de un plasma es mediante las ecuaciones de la Magnetohidrodinámica (MHD), pero cuando los fenómenos en estudio involucran frecuencias del orden de la frecuencia de ciclotrón iónica, es necesario incluir el efecto de considerar un valor finito para esta frecuencia. Este efecto es normalmente referido como efecto Hall, y su influencia puede observarse explícitamente en la ecuación de inducción magnética de las MHD. En el modelo “MHD-Hall” resultante, los modos de propagación de ondas se acoplan y el sistema es dispersivo, pero para propagación paralela (o casi paralela) al campo magnético ambiente ocurre la degeneración de los modos, el modo de Alfvén se desacopla de los modos magnetosónicos y las ondas son circularmente polarizadas pudiendo describirse mediante la Ecuación Derivada No Lineal de Schrödinger (DNLS). En el presente trabajo, dicha ecuación se soluciona numéricamente utilizando métodos espectrales para la resolución de las derivadas espaciales y un esquema de Runge-Kutta de cuarto orden para la integración en el tiempo. En primer lugar se considera la ecuación DNLS sin efectos difusivos manteniendo los términos no lineal y dispersivo, con condición inicial de una onda para verificar el cumplimiento de las condiciones analíticas de estabilidad modular, además de determinar el tiempo en el cual se produce la inestabilidad y la forma de la evolución posterior. En segundo término se analiza el caso con condición inicial de tres ondas cerca de resonancia con el objetivo de evaluar la transferencia de energía entre los diferentes modos y la influencia de los distintos parámetros que intervienen en la simulación. Finalmente se incorporan los efectos difusivos al caso de tres ondas iniciales, con una onda excitada y las restantes amortiguadas, tomando distintos valores de difusión para evaluar una serie de atractores hallados numéricamente y comparar los resultados con aquellos obtenidos mediante técnicas de truncamiento a tres ondas.Fil: Krause, Gustavo J. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; Argentina.Fil: Krause, Gustavo J. Fuerza Aérea Argentina. Universidad de la Defensa Nacional. Centro Regional Universitario Córdoba IUA; Argentina.

O funcionário fascinado

Reflexão filosófica sobre o sujeito no final do século. A transformação do sujeito em funcionário fascinado. A necessidade da ironia.Palavras-chave: Fenomenologia; sujeito; Vilém Flusser

Influência das relações DQQ/N e So/Xo na atividade de microorganismos desnitrificantes

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico. Programa de Pós-Graduação em Engenharia Química.As atividades industriais e agro-industriais do Estado de Santa Catarina tem colaborado intensamente para a redução da qualidade da água dos mananciais existentes naquela região. A suinocultura é um dos setores que mais vem contribuindo para a deteriorização do meio ambiente na mesma Dentre os problemas ambientais causados pelo lançamento dos dejetos de suínos nos corpos receptores, pode-se citar a eutrofização e a contaminação por produtos nocivos como nitrito e nitrato que oferecem riscos carcinogênicos ao homem. O nitrogênio pode ser removido por meio de processos biológicos ou físico-químicos. Dentre as alternativas, os processos biológicos são os que oferecem custos relativamente baixos, quando comparados com os processos físico-químicos. Entre os processos biológicos para a remoção de nitrogênio o processo usualmente mais adotado é o de nitrificação/desnitrificação. O processo de desnitrificação heterotrófica consiste da redução do nitrato a nitrogênio gasoso e a concomitante oxidação de compostos orgânicos, eliminando-se desta forma o impacto ambiental gerado por estes compostos. Para uma eficiente aplicação deste processo, devem ser observadas as relações estequiométricas entre doador e aceptor de elétrons, para que não ocorra a formação de compostos intermediários ou de produtos indesejáveis. As principais condições ambientais a serem atendidas são: temperatura, pH do meio, fonte de carbono com adequada relação C/N, baixa concentração de substâncias tóxicas e ausência de oxigênio no meio. Neste contexto, este trabalho teve como por objetivo avaliar alguns fatores que interferem na atividade dos microrganismos desnitrificantes e assim procurar indicar condições mais adequadas para o estabelecimento de uma metodologia para testes cinéticos de desnitrificação. Como variáveis para o estudo, avaliou-se a influencia da relação DQO/N e das relações S0/X0 no sistema. A faixa em que a relação DQO/N apresentou melhores resultados, foi entre 3 e 5 mgO2/mgN-NO3-, obtendo-se uma velocidade de remoção inicial específica de nitrato máxima de 83 mg N-NO3-/gSST.h. A faixa onde as relações S0/X0 apresentaram valores mais satisfatórios foi de 0,54 S0/X0 0,74 gN/gSST, apresentando uma eficiência média de remoção de nitrato de 95%. A concentração inicial de substrato (S0), demonstrou que altas concentrações de nitrato no meio ocasionam em uma maior quantidade de nitrito intermediário, possivelmente pela inibição das enzimas nitrito redutase, comprometendo o processo de desnitrificação. The industrial and agro industrial activities of Santa Catarina's State have deeply collaborated for the reduction of water quality of the existed water sources in that region. The swine production is one of the sectors which most is contributing for the damage of the environment in the same area. Among the environment problems cased by lancing swines objects on the receptors bodies, it can be cited the eutrofization and the contaminations by harmful products like nitrite e nitrate which offer carcinogenic risks to the man. The nitrogen can be removed by biological or physic-chemical process. Among the alternatives, the biological process is those who offer low cost relatively, when compared with physic-chemical process. Between the biological processes for the nitrogen removal the process most used is the nitrification/ denitrification. The heterotrophic denitrification process consists of the nitrate reduction to nitrogen gas and the concomitant oxidation of the organic composition, eliminating of this form the environment impact generated by this composition. For an efficient application of this process, it must be observed the stechiometric relations between electron donor and acceptor, to avoid formation of intermediary compositions or undesirable products. The principal ambient conditions to be attended are: temperature, the pH media, and carbon source with the appropriate relation C/N, low concentration of toxic substances and oxygen absence on the media. In this context, this work has as an objective to evaluate some factors that intervene on the activity of the denitrificants microorganisms and with that look for better conditions for the establishment of a methodology for this kinetic's denitrification tests. As variables for the study, it was evaluated the influence of relation DQO/N and the system relations S0/X0. The band which the relation DQO/N presented better results was between 3 and 5 mgO2/mgN-NO3-, obtained maximal specifics initial removal velocity of nitrate of the 83 mgN-NO3-/gSST.h. The band where the relations S0/X0 presented more satisfactory values was 0,54< S0/X0< 0,74 gN/gSST, presenting a mean efficiency of nitrate removal of the 95%. The initial substrate concentration (S0), demonstrated that high concentrations of nitrate on the no media causes a grater amount of intermediary nitrite, possibly for the inhibition of the nitrite redutase enzymes, compromising the denitrification process

Modelizacion numerica de cargas de viento sobre un tanque de almacenamiento de combustible

National audienceOne of the structural problems detected on oil storage tanks is wind-induced buckling failure. Accurate estimation of wind loads is important for the evaluation of structural integrity of these facilities. In this context, a numerical study is presented, employing the Reynolds Averaging Navier Stokes (RANS) methodology for the prediction of wind-induced pressure loads over a cylindrical storage tank. Mean pressure distributions obtained through RANS turbulence models, are compared with atmospheric boundary layer wind tunnel experimental measurements for a tank with both closed planar and conical roof shapes. Different aspect ratios and Reynolds numbers representative of the conditions present in oil storage tanks exposed to the atmosphere are considered. Details regarding both the employed numerical methodology and the computer implementation are discussed and presented. Finally, the conclusions obtained based on the present numerical study are introduced.Uno de los problemas estructurales detectados en tanques de almacenamiento de combustible es la falla por pandeo debido a cargas de viento. La adecuada estimación de estas cargas es importante para la evaluación de la integridad estructural de los mismos. En este contexto, se presenta un estudio numérico empleando la metodología Reynolds Averaging Navier Stokes (RANS) para la predicción de cargas de presión producida por el flujo de viento atmosférico sobre un tanque de almacenamiento ci-líndrico. Distribuciones de presión media obtenidas empleando distintos modelos de turbulencia RANS, son comparadas con las mediciones relevadas en un túnel de viento de capa límite atmosférica para un tanque con techo cerrado de forma plana y techo cónico de 25 grados. Diferentes relaciones de aspecto y números de Reynolds representativos de las condiciones presentes en tanques de almacenamiento de combustible expuestos a la atmósfera son considerados. Detalles sobre la metodología numérica em-pleada y aspectos de la implementación computacional son discutidos y presentados. Finalmente, se introducen las conclusiones obtenidas a partir del presente análisis numérico

Origin of the highest energy cosmic rays observed

Introducing a simple Galactic wind model patterned after the solar wind we show that back-tracing the orbits of the highest energy cosmic events suggests that they may all come from the Virgo cluster, and so probably from the active radio galaxy M87. This confirms a long standing expectation. Those powerful radio galaxies that have their relativistic jets stuck in the interstellar medium of the host galaxy, such as 3C147, will then enable us to derive limits on the production of any new kind of particle, expected in some extensions of the standard model in particle physics. New data from HIRES will be crucial in testing the model proposed here.Comment: At TAUP99, the 6th international workshop on topics in Astroparticle Physics and Underground Physics, College de France, Eds. J. Dumarchez, M. Froissart, D. Vignaud, (Sep 1999