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Granular surface flows are common in industrial practice and natural systems, however, theoretical description of such flows is at present incomplete. Two prototype systems involving surface flow are compared: heap formation by pouring at a point and rotating cylinders. Continuum models for analysis of these flows are reviewed, and experimental results for… (More)

We investigate the relationship between structure and robustness in the metabolic networks of Escherichia coli, Methanosarcina barkeri, Staphylococcus aureus, and Saccharomyces cerevisiae, using a cascading failure model based on a topological flux balance criterion. We find that, compared to appropriate null models, the metabolic networks are exceptionally… (More)

- L A N Amaral, J M Ottino
- 2003

We briefly describe the toolkit used for studying complex systems: nonlinear dynamics, statistical physics, and network theory. We place particular emphasis on network theory—the topic of this special issue—and its importance in augmenting the framework for the quantitative study of complex systems. In order to illustrate the main issues, we briefly review… (More)

- J M Ottino
- Nature
- 2004

Scientific breakthroughs occur at the edges of disciplines. Often ideas originating in one field find successful applications in other fields, sometimes leading to revolutionary shifts. Complexity is regarded by many to be such an example. Complex systems can be identified by what they do — display organization without a central organizing principle… (More)

- J. M. Ottino
- 2002

1. INTRODUCTION 1.1 Setting The establishment of a paradigm for mixing of fluids can substantially affect the development of various branches of physical sciences and technology. Mixing is intimately connected with turbulence, Earth and natural sciences, and various branches of engineering. However, in spite of its universality, there have been surprisingly… (More)

The diierence between the complicated and the complex is not just quantitative; it is also qualitative. Complexity requires both an augmentation of the conceptual framework and new tools. In this manuscript we describe the challenges faced when studying complex systems and describe how scientists from many diierent areas have responded to these challenges.… (More)

Mixing of granular solids is invariably accompanied by segregation, however, the fundamentals of the process are not well understood. We analyze density and size segregation in a chute flow of cohesionless spherical particles by means of computations and theory based on the transport equations for a mixture of nearly elastic particles. Computations for… (More)

Granular flow in a rotating tumbler is of theoretical and industrial significance. However, in spite of its relative simplicity, little is known about the dynamics of the top flowing layer. Here we present an experimental study of the velocity field within the fluidized layer of monodisperse particles in a quasi-2D ͑two-dimensional͒ rotating tumbler in the… (More)

We consider the impact of the effective gravitational acceleration g{eff} on gravity-driven granular shear flow utilizing a tumbler of radius R rotating at angular velocity omega when g{eff} is varied up to 25 times the gravitational level on Earth in a large centrifuge. The Froude number Fr=omega{2}R/g{eff} is shown to be the proper scaling to characterize… (More)

We investigate the effect of nanoscale variations in the surface roughness of individual particles on macroscale granular flow characteristics. Experiments were conducted in circular rotating tumblers with smooth and rough 2 and 3 mm steel particles. The smooth beads had a rms surface roughness of approximately 30 to 60 nm; rough beads had a surface… (More)