Avalanches in a magnetic froth.Avalanches in a magnetic froth Thin films of synthetic garnet garnet, name applied to a group of isomorphic minerals crystallizing in the cubic system. They are used chiefly as gems and as abrasives (as in garnet paper). , an iron-oxide compound, have long played an important role as magnetic bubble memories magnetic bubble memory n. A memory that stores data in the form of bubbles, or circular areas, on a thin film of magnetic silicate. No longer used in most computers, magnetic bubble memory is similar to RAM but does not lose the stored information when , in which bits of digital data are stored as compact, circular regions, or domains, magnetized in the opposite direction of the thin magnetic film through which they move. The magnetic garnet films also prove useful for studying the evolution of magnetization patterns, says Kenneth L. Babcock of the University of California, Santa Barbara History The predecessor to UCSB, Santa Barbara State College, focused on teacher training, industrial arts, home economics, and foreign languages. Intense lobbying by an interest group in the City of Santa Barbara led by Thomas Storke and Pearl Chase persuaded the State . Babcock, working with Robert M. Westervelt of Harvard University Harvard University, mainly at Cambridge, Mass., including Harvard College, the oldest American college. Harvard College Harvard College, originally for men, was founded in 1636 with a grant from the General Court of the Massachusetts Bay Colony. , investigated the behavior of thin-film magnetic domains having a disordered cellular pattern resembling a two-dimensional soap froth. They discovered that under the influence of an increasing external magnetic field, magnetized "cells" having fewer than six sides tend to contract and sometimes collapse, while other cells grow to fill the vacated space. That behavior bears a striking resemblance to the evolution of soap froths over time (SN: 7/29/89, p.72). The researchers have also observed a dramatic "melting" transition, in which a front sweeps through an orderly lattice of magnetized cells, leaving behind a disordered magnetic froth. "These transitions are analogous to the melting of solids induced by changing the pressure while holding the temperature fixed," Babcock says. Magnetic avalanches can also produce striking patterns, the researchers say. In such avalanches, the elimination of a given cell caused by a small increase in the external magnetic field alters the local pattern sufficiently to trigger the collapse of neighboring neigh·bor n. 1. One who lives near or next to another. 2. A person, place, or thing adjacent to or located near another. 3. A fellow human. 4. Used as a form of familiar address. v. cells, producing a wave of destruction. The researchers find that for certain ranges of external magnetic-field strengths, the magnetic froth shifts into a barely stable state readily susceptible to additional avalanches, even for very small increases in the external magnetic field. In other words Adv. 1. in other words - otherwise stated; "in other words, we are broke" put differently , the magnetic froth apparently organizes itself into a precarious state prone to avalanches. That type of behavior seems to meet the requirements of self-organized criticality In physics, self-organized criticality (SOC) is a property of (classes of) dynamical systems which have a critical point as an attractor. Their macroscopic behaviour thus displays the spatial and/or temporal scale-invariance characteristic of the critical point of a phase , a recently introduced theoretical notion proposed as the source of erratic behavior in a variety of computer models and physical systems (SN: 7/15/89, p.40). |
|
||||||||||||||||||
Printer friendly
Cite/link
Email
Feedback
Reader Opinion