3,705 research outputs found
Identifying Functional Thermodynamics in Autonomous Maxwellian Ratchets
We introduce a family of Maxwellian Demons for which correlations among
information bearing degrees of freedom can be calculated exactly and in compact
analytical form. This allows one to precisely determine Demon functional
thermodynamic operating regimes, when previous methods either misclassify or
simply fail due to approximations they invoke. This reveals that these Demons
are more functional than previous candidates. They too behave either as
engines, lifting a mass against gravity by extracting energy from a single heat
reservoir, or as Landauer erasers, consuming external work to remove
information from a sequence of binary symbols by decreasing their individual
uncertainty. Going beyond these, our Demon exhibits a new functionality that
erases bits not by simply decreasing individual-symbol uncertainty, but by
increasing inter-bit correlations (that is, by adding temporal order) while
increasing single-symbol uncertainty. In all cases, but especially in the new
erasure regime, exactly accounting for informational correlations leads to
tight bounds on Demon performance, expressed as a refined Second Law of
Thermodynamics that relies on the Kolmogorov-Sinai entropy for dynamical
processes and not on changes purely in system configurational entropy, as
previously employed. We rigorously derive the refined Second Law under minimal
assumptions and so it applies quite broadly---for Demons with and without
memory and input sequences that are correlated or not. We note that general
Maxwellian Demons readily violate previously proposed, alternative such bounds,
while the current bound still holds.Comment: 13 pages, 9 figures,
http://csc.ucdavis.edu/~cmg/compmech/pubs/mrd.ht
MIHash: Online Hashing with Mutual Information
Learning-based hashing methods are widely used for nearest neighbor
retrieval, and recently, online hashing methods have demonstrated good
performance-complexity trade-offs by learning hash functions from streaming
data. In this paper, we first address a key challenge for online hashing: the
binary codes for indexed data must be recomputed to keep pace with updates to
the hash functions. We propose an efficient quality measure for hash functions,
based on an information-theoretic quantity, mutual information, and use it
successfully as a criterion to eliminate unnecessary hash table updates. Next,
we also show how to optimize the mutual information objective using stochastic
gradient descent. We thus develop a novel hashing method, MIHash, that can be
used in both online and batch settings. Experiments on image retrieval
benchmarks (including a 2.5M image dataset) confirm the effectiveness of our
formulation, both in reducing hash table recomputations and in learning
high-quality hash functions.Comment: International Conference on Computer Vision (ICCV), 201
An autonomous and reversible Maxwell's demon
Building on a model introduced by Mandal and Jarzynski [Proc. Natl. Acad.
Sci. U. S. A., {\bf 109}, (2012) 11641], we present a simple version of an
autonomous reversible Maxwell's demon. By changing the entropy of a tape
consisting of a sequence of bits passing through the demon, the demon can lift
a mass using the coupling to a heat bath. Our model becomes reversible by
allowing the tape to move in both directions. In this thermodynamically
consistent model, total entropy production consists of three terms one of which
recovers the irreversible limit studied by MJ. Our demon allows an
interpretation in terms of an enzyme transporting and transforming molecules
between compartments. Moreover, both genuine equilibrium and a linear response
regime with corresponding Onsager coefficients are well defined. Efficiency and
efficiency at maximum power are calculated. In linear response, the latter is
shown to be bounded by 1/2 if the demon operates as a machine and by 1/3 if it
is operated as an eraser.Comment: 6 pages, 3 figure
Thermodynamic costs of information processing in sensory adaption
Biological sensory systems react to changes in their surroundings. They are
characterized by fast response and slow adaptation to varying environmental
cues. Insofar as sensory adaptive systems map environmental changes to changes
of their internal degrees of freedom, they can be regarded as computational
devices manipulating information. Landauer established that information is
ultimately physical, and its manipulation subject to the entropic and energetic
bounds of thermodynamics. Thus the fundamental costs of biological sensory
adaptation can be elucidated by tracking how the information the system has
about its environment is altered. These bounds are particularly relevant for
small organisms, which unlike everyday computers operate at very low energies.
In this paper, we establish a general framework for the thermodynamics of
information processing in sensing. With it, we quantify how during sensory
adaptation information about the past is erased, while information about the
present is gathered. This process produces entropy larger than the amount of
old information erased and has an energetic cost bounded by the amount of new
information written to memory. We apply these principles to the E. coli's
chemotaxis pathway during binary ligand concentration changes. In this regime,
we quantify the amount of information stored by each methyl group and show that
receptors consume energy in the range of the information-theoretic minimum. Our
work provides a basis for further inquiries into more complex phenomena, such
as gradient sensing and frequency response.Comment: 17 pages, 6 figure
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