6,346 research outputs found
Soap films as two-dimensional fluids: Diffusion and flow fields
We observe tracer particles diffusing in soap films to measure the
two-dimensional (2D) viscous properties of the films. We make soap films with a
variety of water-glycerol mixtures and of differing thicknesses. The
single-particle diffusivity relates closely to parameters of the film (such as
thickness ) for thin films, but the relation breaks down for thicker films.
Notably, the diffusivity is faster than expected for thicker films, with the
transition at using the tracer particle diameter . This
indicates a transition from purely 2D diffusion to diffusion that is more
three-dimensional. Additionally, we measure larger length scale flow fields
from correlated particle motions and find good agreement with what is expected
from theory of 2D fluids for all our films, thin and thick. We measure the
effective 2D viscosity of a soap film using single-particle diffusivity
measurements in thin films, and using the two-particle correlation measurements
in all films
On palimpsests in neural memory: an information theory viewpoint
The finite capacity of neural memory and the
reconsolidation phenomenon suggest it is important to be able
to update stored information as in a palimpsest, where new
information overwrites old information. Moreover, changing
information in memory is metabolically costly. In this paper, we
suggest that information-theoretic approaches may inform the
fundamental limits in constructing such a memory system. In
particular, we define malleable coding, that considers not only
representation length but also ease of representation update,
thereby encouraging some form of recycling to convert an old
codeword into a new one. Malleability cost is the difficulty of
synchronizing compressed versions, and malleable codes are of
particular interest when representing information and modifying
the representation are both expensive. We examine the tradeoff
between compression efficiency and malleability cost, under a
malleability metric defined with respect to a string edit distance.
This introduces a metric topology to the compressed domain. We
characterize the exact set of achievable rates and malleability as
the solution of a subgraph isomorphism problem. This is all done
within the optimization approach to biology framework.Accepted manuscrip
- …