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El caos y el umbral de irreversibilidad en las suspensiones cortadas
D J Pine1, J P Gollub, J F Brady
1Department of Chemical Engineering and KITP, University of California, Santa Barbara, California 93106-5080, USA. pine@nyu.edu
Nature
|December 16, 2005
Resumen
Los investigadores observaron experimentalmente cómo falla la reversibilidad del tiempo en suspensiones lentamente cortadas. Un umbral de deformación dependiente de la concentración hace que las configuraciones de partículas se vuelvan impredecibles, asemejándose a caminatas aleatorias anisotrópicas.
Área de la Ciencia:
- Física estadística de las estadísticas.
- Física de la materia blanda Física de la materia blanda
- Los sistemas de no equilibrio no están en equilibrio.
Sus antecedentes:
- Las ecuaciones de movimiento reversibles en el tiempo pueden conducir a un comportamiento irreversible en sistemas de muchos cuerpos.
- Esta transición es fundamental, pero experimentalmente no se observa en muchos sistemas.
- El flujo de fluidos de bajo número de Reynolds, como los fluidos y suspensiones newtonianas cortadas, es típicamente reversible en el tiempo.
Objetivo del estudio:
- Para demostrar experimentalmente el fracaso de la reversibilidad del tiempo en las suspensiones lentamente cortadas.
- Identificar las condiciones y los mecanismos que conducen a un comportamiento irreversible en estos sistemas.
- Conectar la irreversibilidad observada con los conceptos de caos y previsibilidad.
Principales métodos:
- Corte experimental de suspensiones de partículas en varias concentraciones.
- Medición de desplazamientos y configuraciones de partículas en múltiples ciclos de cizallamiento.
- Simulaciones numéricas para modelar las interacciones de partículas y la dinámica caótica.
- Cálculo de los exponentes de Lyapunov para cuantificar el comportamiento caótico.
Principales resultados:
- Se identificó un umbral de deformación dependiente de la concentración, más allá del cual falla la reversibilidad en el tiempo.
- Los desplazamientos de partículas después del ciclismo siguieron las estadísticas de caminata aleatoria anisotrópica.
- Se observó un crecimiento pronunciado en el exponente de Lyapunov en la tensión umbral.
- Los resultados experimentales fueron consistentes con las simulaciones numéricas.
Conclusiones:
- El estudio proporciona la primera observación experimental de la falla de la reversibilidad del tiempo en las suspensiones cortadas.
- La tensión umbral está relacionada con el inicio de las interacciones de partículas caóticas.
- Este trabajo une la comprensión del caos, la reversibilidad y la previsibilidad en los sistemas de materia blanda.
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