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Nomenclatura Unesco > (22) Física > (2204) Física de los fluidos
(2204.01) Coloides (2204.02) Dispersiones
(2204.03) Flujo de fluidos (2204.04) Mecánica de fluidos
(2204.05) Gases (2204.06) Fenómenos de alta presión
(2204.07) Ionización (2204.08) Líquidos
(2204.09) Dinámica de fluidos manéticos (Magnetofluidodinamica) (2204.10) Física de plasmas
(2204.11) Fluidos cuánticos (2204.99) Otras (especificar)

Mostrando recursos 1 - 20 de 128

1. Nonintegrable interaction of ion acoustic and electromagnetic waves in a plasma - Rizzato, Felipe Barbedo; Lopes, Sergio Roberto; Chian, Abraham Chian-Long
In this paper we reexamine the one-dimensional interaction of electromagnetic and ion acoustic waves in a plasma. Our model is similar to one solved by Rao et al. [Phys. Fluids 26, 2488 (1983)] under a number of analytical approximations. Here we perform a numerical investigation to examine the stability of the model. We find that for slightly overdense plasmas, the propagation of stable solitary modes can occur in an adiabatic regime where the ion acoustic electric-field potential is enslaved to the electromagnetic field of a laser. However, if the laser intensity or plasma density increases or the laser frequency decreases,...

2. Quasilinear evolution of cyclotron maser instability - Yoon, Peter H.; Ziebell, Luiz Fernando
A quasilinear analysis of the relativistic electron cyclotron maser instability is presented. A background plasma is assumed to support the wave motion, while the instability is driven by a tenuous population of energetic electrons possessing a loss-cone feature. The analysis makes use of an efBcient moment method. In this approach, evolution equations for the moments of particle distribution function are derived from the particle kinetic equation. Then, a self-similar model of the loss-cone electron distribution function is imposed. Simultaneously, the wave kinetic equation is solved. The resulting fully self-consistent set of equations that governs the evolution of the particles and...

3. Self-consistent chaos and Arnold diffusion in a cyclotron-maser wave-particle system - Pakter, Renato; Couto, Flavia de Oliveira; Rizzato, Felipe Barbedo
In this work, we search for the presence of chaos in a self-consistent model for the cyclotronresonance maser accelerator. Two characteristic regimes are identified. If the initial action variable of the accelerating particles is small, rapid phase bunching occurs and the particle population is condensed into a single macroparticle in phase space. As a result, this low-dimensional state is predominantly regular. For larger energies, on the other hand, there is no macroparticle formation. The system is high dimensional, and chaos is found. Arnold difFusion appears to occur in these chaotic states.

4. Low-dimensional phase-locked states in the zakharov equations - Oliveira, Glaucius Iahnke de; Oliveira, Luiz Paulo Luna de; Rizzato, Felipe Barbedo
In this paper we identify phase-locked states among the solutions of the Zakharov equations. Locked states appear as resonant island chains in the appropriate Poincaré plots, with the relevant surface of section obtained by projecting out the full dynamical set on a subspace defined in terms of a pair of center-manifold variables. This pair allows an accurate canonical description of the system immediately after an inverse pitchfork bifurcation destabilizes an initial homogeneous steady state. If one is very close to the bifurcation point, nonlinear saturation of the initial instability is provided by quasistatic integrable ion-acoustic fluctuations, but as one proceeds...

5. Chaotic dynamics induced by space-charge waves in cyclotron resonance accelerators - Pakter, Renato; Caldas, Ibere Luiz; Couto, Flavia de Oliveira; Caetano, Tiberio Silva; Rizzato, Felipe Barbedo
In this work, we analyze the effects produced by the inclusion of space-charge waves in a Hamiltonian model for a cyclotron resonant accelerator. We find that space charges impose limits on acceleration and that these limits appear as bounding curves on the appropriate stroboscopic phase spaces. In addition, space charges create nonlinearly locked states which undergo not only the period doubling bifurcations preceding chaos, but saddle-node inverse bifurcations as well.

6. Mapas não monotônicos e bifurcações a eles associadas em aceleradores a laser - Caetano, Tiberio Silva; Couto, Flavia de Oliveira; Corso, Gilberto Luiz; Pakter, Renato; Brunnet, Leonardo Gregory; Rizzato, Felipe Barbedo

7. Geração de caos em um acelerador Cyclotron através de ondas eletrostáticas - Caetano, Tiberio Silva; Couto, Flavia de Oliveira; Rizzato, Felipe Barbedo; Pakter, Renato; Caldas, Ibere Luiz

8. Resonant islands without separatrix chaos - Corso, Gilberto Luiz; Rizzato, Felipe Barbedo
An alternative type of Hamiltonian nonlinear resonant island is analyzed. In the usual case where the resonant island is pendulumlike, chains bifurcated out of the central elliptic point undergo infinite cascades of period-doubling bifurcations as they approach the island boundary. In the present case we find that those chains undergo either period doubling or inverse saddle-node bifurcations, depending on the strength of perturbing terms. In the saddle-node case we show that just after a reconnection process, external chains cross the island boundary to collapse against the bifurcated internal chains.

9. Influence of wave dispersion on the self-consistent dynamics of cyclotron-laser-type systems - Pakter, Renato; Schneider, Ruth de Souza; Rizzato, Felipe Barbedo
In this work, we make use of a Hamiltonian formalism to analyze the wave-particle dynamical interaction that takes place in cyclotronic systems. It is shown that the usual model of test particles moving in externally given wave 6elds is good only when the amplitude of the radiation is large enough; otherwise, wave dynamics must be considered and the dynamics mentioned undergoes some considerable changes. In this regard, the appearance of new Axed points and the saturation of the autoresonance process are both analyzed as functions of the dispersion relation of the laser field.

10. Disperson relation and the dielectric tensor for magnetized plasmas with inhomogeneous magnetic field - Gaelzer, Rudi; Schneider, Ruth de Souza; Ziebell, Luiz Fernando
We investigate the dispersion relation for a magnetized plasma with weak magnetic field gradients perpendicular to the ambient magnetic field. An explicit expression for the effective dielectric tensor is derived, incorporating the relevant contributions due to the inhomogeneity, which include corrections to all orders in the small parameter e, where e= [(1/Bo)(dBo/dz)]. It is shown that this effective dielectric tensor satisfies the required symmetry conditions and is the tensor which should be utilized in the dispersion relation, in order to describe correctly wave-particle interactions in media with inhomogeneous magnetic field. The case of high frequency oscillations propagating perpendicularly to the...

11. Construcciones didácticas con materiales de fácil acceso, para la comprensión de teorías y leyes físicas en la mecánica de fluidos - Durán Basto, Jorge Mauricio
En este trabajo se evaluó en los estudiantes de grado decimo de la institución educativa Jorge Villamil ortega, el grado de asimilación y comprensión del mundo de la mecánica de fluidos; sus conceptos, relaciones, principios y leyes físicas; implementando la pedagogía por proyectos mediante construcciones didácticas con materiales de fácil acceso y/o caseros. Para lo cual, se trabajó con dos grupos, un grupo control (clase magistral) y un grupo experimental (receptores de la estrategia). El grupo experimental además de recibir como el grupo control clases magistrales; implemento proyectos de aula, en los cuales diseñó, construyó y expuso conceptualmente el funcionamiento...

12. Estudio numérico y experimental de flujo Rayleigh-Bénard en cavidades cúbicas para régimen transitorio y turbulento - Valencia Merizalde, Leonardo
El presente trabajo estudia la convección Rayleigh-Bénard en cavidades cúbicas sin inclinación con respecto a la horizontal y calentadas por debajo para números de Rayleigh tanto dentro del estado estacionario como dentro del régimen turbulento.Inicialmente se estudian los efectos que tiene la variación de las propiedades físicas con la temperatura sobre la estructura de flujo, el mecanismo de transporte y la transferencia de calor para dos números de Rayleigh bajos (Ra=104 y Ra=5×104) en los que el flujo es laminar y estacionario y para un Rayleigh dentro del régimen turbulento (Ra=107). Para este estudio numérico se utilizó agua como fluido...

13. Transporte no pasivo de compuestos orgánicos volátiles en la zona no saturada. - Silva Rojas, Orlando
La forma más habitual de modelar el transporte de solutos en la zona no saturada es considerar que se comportan de manera pasiva y utilizar la solución del movimiento de las fases fluidas como información de entrada. La presencia de algunas sustancias químicas puede afectar a las propiedades físicas de los fluidos, originando así procesos de transporte no pasivos. El objetivo principal de esta tesis ha sido formular un modelo detallado que describa el transporte no pasivo en la zona no saturada y en condiciones isotérmicas de compuestos orgánicos volátiles solubles en agua. El modelo propuesto incluye las dependencias de...

14. Numerical simulation of multi-fluid flows with the Particle Finite Element Method - De Mier Torrecilla, Monica
La presencia simultánea de múltiples fluidos con diferentes propiedades ocurre en numerosos problemas medioambientales, procesos industriales y situaciones de la vida diaria. Algunos ejemplos son la interacción fluido-combustible en la extracción mejorada de petróleo, mezcla de polímeros, emulsiones en productos alimentarios, formación de gotas de lluvia en nubes, inyección en motores de combustión o reactores de columna de burbujas. A pesar de que los flujos de multi-fluidos son muy frecuentes, todavía suponen un reto tanto desde el punto de vista teórico como computacional. En el caso de fluidos inmiscibles, la dinámica de la interfase entre fluidos juega un papel determinante....

15. Simulación de plasmas de dispositivos de fusión por confinamiento magnético tipo tokamak y stellarator. Validación experimental y aplicación al estudio del Heliac Flexible TJ-II - Fontanet Saez, Joan
En el estudio de la fusión por confinamiento magnético es crucial conocer con detalle las condiciones físicas del plasma confinado. En este sentido los códigos de simulación son una herramienta muy útil para interpretar las propiedades del plasma. A lo largo de esta tesis se ha estudiado las propiedades del plasma de tokamaks y stellarators y se ha contribuido al desarrollo del código de transporte PRETOR, creado en el JET. Estos estudios se han realizado dentro de la colaboración existente entre el DFEN de la UPC y el Laboratorio Nacional de Fusión del CIEMAT.El código PRETOR permite simular la variación...

16. Three-dimensional simulation of pollutant dispersion in coastal waters - Mestres Ridge, Marc
Traditionally, the sea has been considered as the ultimate sink of most pollutions, due to its huge volume and assimilating capacities, and the coastal waters, because of their intermediate position between deep seas and human activities, has been acting as a buffer zone. However, during the past years, the interest in environmental issues in general, and in the conservation of the water quality in coastal regions, in particular, has steadily increased. For coastal waters, this growing interest can be related to the increase in population and industrial activity along rivers and on coastal areas, which poses an important threat on...

17. Expansão livre de um gás de esferas rígidas - Oliveira, Clesio Ismerio de; Goedert, Joao

18. Aplicação da teoria da bifurcação na dinâmica do pêndulo gravitacional composto - Lemos, Felipe X.G. de; Rizzato, Felipe Barbedo

19. Emissivity and growth of auroral kilometric radiation in source regions with perpendicular gradients - Cavalcanti, Claudio Jose de Holanda; Schneider, Ruth de Souza; Ziebell, Luiz Fernando
Emission and propagation of the auroral kilometric radiation in the auroral zones of the Earth are investigated with the use of the transfer equation for the intensity of the wave along the trajectory, which is obtained with the formulation of the geometríc optics. The cyclotron emissivity and the components of the dielectric tensor are evaluated using the locally homogeneous plasma approximation, taking into account thermal effects and con­ sidering both the energetic and the background electron populations. For frequencies in the vicinity of the electron cyclotron frequency we consider a range of values of the parallel wave number which result...

20. Professores de hoje, alunos de ontem... : (dificuldades com alguns conceitos-chave sobre fluidos) - Axt, Rolando
O texto trata de dificuldades conceituais que alunos e professores de Ciências e de Física apresentam na área da mecânica dos fluídos e sugere uma estratégia de ensino baseada em experimentos muitos fáceis de realizar como forma de ajudar os alunos a superar tais dificuldades.

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