2,908 research outputs found
Generic transient memory formation in disordered systems with noise
Out-of-equilibrium disordered systems may form memories of external driving
in a remarkable fashion. The system "remembers" multiple values from a series
of training inputs yet "forgets" nearly all of them at long times despite the
inputs being continually repeated. Here, learning and forgetting are
inseparable aspects of a single process. The memory loss may be prevented by
the addition of noise. We identify a class of systems with this behavior,
giving as an example a model of non-brownian suspensions under cyclic shear.Comment: 4 pages, 3 figure
Multiple transient memories in sheared suspensions: robustness, structure, and routes to plasticity
Multiple transient memories, originally discovered in charge-density-wave
conductors, are a remarkable and initially counterintuitive example of how a
system can store information about its driving. In this class of memories, a
system can learn multiple driving inputs, nearly all of which are eventually
forgotten despite their continual input. If sufficient noise is present, the
system regains plasticity so that it can continue to learn new memories
indefinitely. Recently, Keim & Nagel showed how multiple transient memories
could be generalized to a generic driven disordered system with noise, giving
as an example simulations of a simple model of a sheared non-Brownian
suspension. Here, we further explore simulation models of suspensions under
cyclic shear, focussing on three main themes: robustness, structure, and
overdriving. We show that multiple transient memories are a robust feature
independent of many details of the model. The steady-state spatial distribution
of the particles is sensitive to the driving algorithm; nonetheless, the memory
formation is independent of such a change in particle correlations. Finally, we
demonstrate that overdriving provides another means for controlling memory
formation and retention
Multiple transient memories in experiments on sheared non-Brownian suspensions
A system with multiple transient memories can remember a set of inputs but
subsequently forgets almost all of them, even as they are continually applied.
If noise is added, the system can store all memories indefinitely. The
phenomenon has recently been predicted for cyclically sheared non-Brownian
suspensions. Here we present experiments on such suspensions, finding behavior
consistent with multiple transient memories and showing how memories can be
stabilized by noise.Comment: 5 pages, 4 figure
FAIR, POSTFAIR, AND NOFAIR: A COMPARISON OF CROPPING ALTERNATIVES FOR THE SOUTHERN GREAT PLAINS
The Federal Agriculture Improvement and Reform Act of 1996 was promoted as legislation that would enable and encourage farmers to base planting decisions on market incentives rather than commodity programs. Data from a designed experiment are used to compare the economics of three cropping systems for alternative commodity programs.Crop Production/Industries,
Breakup of Air Bubbles in Water: Memory and Breakdown of Cylindrical Symmetry
Using high-speed video, we have studied air bubbles detaching from an
underwater nozzle. As a bubble distorts, it forms a thin neck which develops a
singular shape as it pinches off. As in other singularities, the minimum neck
radius scales with the time until breakup. However, because the air-water
interfacial tension does not drive breakup, even small initial cylindrical
asymmetries are preserved throughout the collapse. This novel, non-universal
singularity retains a memory of the nozzle shape, size and tilt angle. In the
last stages, the air appears to tear instead of pinch.Comment: Submitted to Phys. Rev. Lett. 4 pages, 4 figures. Revised for
resubmissio
Fluid Elasticity Can Enable Propulsion at Low Reynolds Number
Conventionally, a microscopic particle that performs a reciprocal stroke
cannot move through its environment. This is because at small scales, the
response of simple Newtonian fluids is purely viscous and flows are
time-reversible. We show that by contrast, fluid elasticity enables propulsion
by reciprocal forcing that is otherwise impossible. We present experiments on
rigid objects actuated reciprocally in viscous fluids, demonstrating for the
first time a purely elastic propulsion set by the object's shape and boundary
conditions. We describe two different artificial "swimmers" that experimentally
realize this principle.Comment: 5 pages, 4 figure
Memory formation in matter
Memory formation in matter is a theme of broad intellectual relevance; it
sits at the interdisciplinary crossroads of physics, biology, chemistry, and
computer science. Memory connotes the ability to encode, access, and erase
signatures of past history in the state of a system. Once the system has
completely relaxed to thermal equilibrium, it is no longer able to recall
aspects of its evolution. Memory of initial conditions or previous training
protocols will be lost. Thus many forms of memory are intrinsically tied to
far-from-equilibrium behavior and to transient response to a perturbation. This
general behavior arises in diverse contexts in condensed matter physics and
materials: phase change memory, shape memory, echoes, memory effects in
glasses, return-point memory in disordered magnets, as well as related contexts
in computer science. Yet, as opposed to the situation in biology, there is
currently no common categorization and description of the memory behavior that
appears to be prevalent throughout condensed-matter systems. Here we focus on
material memories. We will describe the basic phenomenology of a few of the
known behaviors that can be understood as constituting a memory. We hope that
this will be a guide towards developing the unifying conceptual underpinnings
for a broad understanding of memory effects that appear in materials
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