applied physics Applied physics is the application of physics to solve scientific or engineering problems. It is usually considered to be a bridge or a connection between physics and engineering. "Applied" is distinguished from "pure" by a subtle combination ...

, the concept of controlling self-organized criticality refers to the control of processes by which a

self-organized Self-organization, also called spontaneous order in the social sciences, is a process where some form of overall order arises from local interactions between parts of an initially disordered system. The process can be spontaneous when suffic ...

system dissipates

energy In physics, energy (from Ancient Greek: ἐνέργεια, ''enérgeia'', “activity”) is the quantitative property that is transferred to a body or to a physical system, recognizable in the performance of work and in the form of ...

. The objective of the control is to reduce the probability of occurrence of and size of

energy dissipation In thermodynamics, dissipation is the result of an irreversible process that takes place in homogeneous thermodynamic systems. In a dissipative process, energy (internal, bulk flow kinetic, or system potential) transforms from an initial form to ...

bursts, often called ''avalanches'', of self-organized systems. Dissipation of energy in a self-organized critical system into a lower energy state can be costly for society, since it depends on avalanches of all sizes usually following a kind of

power law In statistics, a power law is a functional relationship between two quantities, where a relative change in one quantity results in a proportional relative change in the other quantity, independent of the initial size of those quantities: one q ...

distribution and large avalanches can be damaging and disruptive.

Schemes

Several strategies have been proposed to deal with the issue of controlling self-organized criticality: #''The design of controlled avalanches.'' Daniel O. Cajueiro and Roberto F. S. Andrade show that if well-formulated small and medium avalanches are exogenously triggered in the system, the energy of the system is released in a way that large avalanches are rarer. #'' The modification of the degree of interdependence of the network where the avalanche spreads.''

Charles D. Brummitt Charles is a masculine given name predominantly found in English and French speaking countries. It is from the French form ''Charles'' of the Proto-Germanic name (in runic alphabet) or ''*karilaz'' (in Latin alphabet), whose meaning was " ...

, Raissa M. D'Souza and

E. A. Leicht E is the fifth letter of the Latin alphabet. E or e may also refer to: Commerce and transportation * €, the symbol for the euro, the European Union's standard currency unit * ℮, the estimated sign, an EU symbol indicating that the weigh ...

show that the dynamics of self-organized critical systems on

complex network In the context of network theory, a complex network is a graph (network) with non-trivial topological features—features that do not occur in simple networks such as lattices or random graphs but often occur in networks representing real ...

s depend on connectivity of the complex network. They find that while some connectivity is beneficial (since it suppresses the largest cascades in the system), too much connectivity gives space for the development of very large cascades and increases the size of capacity of the system. #'' The modification of the deposition process of the self-organized system.'' Pierre-Andre Noel, Charles D. Brummitt and Raissa M. D'Souza show that it is possible to control the self-organized system by modifying the natural deposition process of the self-organized system adjusting the place where the avalanche starts. #'' Dynamically modifying the local thresholds of cascading failures.'' In a model of an electric transmission network, Heiko Hoffmann and David W. Payton demonstrated that either randomly upgrading lines (sort of like preventive maintenance) or upgrading broken lines to a random breakage threshold suppresses self-organized criticality. Apparently, these strategies undermine the self-organization of large critical clusters. Here, a critical cluster is a collection of transmission lines that are near the failure threshold and that collapse entirely if triggered.

Applications

There are several events that arise in nature or society where these ideas of control may help to avoid them: #

Flood A flood is an overflow of water ( or rarely other fluids) that submerges land that is usually dry. In the sense of "flowing water", the word may also be applied to the inflow of the tide. Floods are an area of study of the discipline hydrol ...

caused by systems of dams and reservoirs or interconnected valleys. # Snow avalanches that take place in snow hills. # Forest fires in areas susceptible to a lightning bolt or a match lighting. # Cascades of load shedding that take place in power grids (a type of

power outage A power outage (also called a powercut, a power out, a power failure, a power blackout, a power loss, or a blackout) is the loss of the electrical power network supply to an end user. There are many causes of power failures in an electricity ...

). The OPA model is used to study different techniques for criticality control. #

Cascading failure A cascading failure is a failure in a system of interconnected parts in which the failure of one or few parts leads to the failure of other parts, growing progressively as a result of positive feedback. This can occur when a single part fails, in ...

in the internet switching fabric. #

Ischemic cascade The ischemic (ischaemic) cascade is a series of biochemical reactions that are initiated in the brain and other aerobic tissues after seconds to minutes of ischemia (inadequate blood supply). This is typically secondary to stroke, injury, or cardi ...

s, a series of biochemical reactions releasing toxins during moments of inadequate blood supply. #

Systemic risk In finance, systemic risk is the risk of collapse of an entire financial system or entire market, as opposed to the risk associated with any one individual entity, group or component of a system, that can be contained therein without harming the ...

in financial systems. # Excursions in nuclear energy systems. #

Earthquake An earthquake (also known as a quake, tremor or temblor) is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth's lithosphere that creates seismic waves. Earthquakes can range in intensity, fr ...

s and

induced seismicity Induced seismicity is typically minor earthquakes and tremors that are caused by human activity that alters the stresses and strains on Earth's crust. Most induced seismicity is of a low magnitude. A few sites regularly have larger quakes, such a ...

. The failure cascades in electrical transmission and financial sectors occur because economic forces cause these systems to operate near a critical point, where avalanches of indeterminate size become possible.

References

{{reflist Applied and interdisciplinary physics Control theory Chaos theory Self-organization Critical phenomena

Schemes

Applications

See also

References