12,767 research outputs found
Memoryless Thermodynamics? A Reply
We reply to arXiv:1508.00203 `Comment on "Identifying Functional
Thermodynamics in Autonomous Maxwellian Ratchets" (arXiv:1507.01537v2)'.Comment: 4 pages; http://csc.ucdavis.edu/~cmg/compmech/pubs/MerhavReply.ht
Correlation-powered Information Engines and the Thermodynamics of Self-Correction
Information engines can use structured environments as a resource to generate
work by randomizing ordered inputs and leveraging the increased Shannon entropy
to transfer energy from a thermal reservoir to a work reservoir. We give a
broadly applicable expression for the work production of an information engine,
generally modeled as a memoryful channel that communicates inputs to outputs as
it interacts with an evolving environment. The expression establishes that an
information engine must have more than one memory state in order to leverage
input environment correlations. To emphasize this functioning, we designed an
information engine powered solely by temporal correlations and not by
statistical biases, as employed by previous engines. Key to this is the
engine's ability to synchronize---the engine automatically returns to a desired
dynamical phase when thrown into an unwanted, dissipative phase by corruptions
in the input---that is, by unanticipated environmental fluctuations. This
self-correcting mechanism is robust up to a critical level of corruption,
beyond which the system fails to act as an engine. We give explicit analytical
expressions for both work and critical corruption level and summarize engine
performance via a thermodynamic-function phase diagram over engine control
parameters. The results reveal a new thermodynamic mechanism based on
nonergodicity that underlies error correction as it operates to support
resilient engineered and biological systems.Comment: 22 pages, 13 figures;
http://csc.ucdavis.edu/~cmg/compmech/pubs/tos.ht
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
Above and Beyond the Landauer Bound: Thermodynamics of Modularity
Information processing typically occurs via the composition of modular units,
such as universal logic gates. The benefit of modular information processing,
in contrast to globally integrated information processing, is that complex
global computations are more easily and flexibly implemented via a series of
simpler, localized information processing operations which only control and
change local degrees of freedom. We show that, despite these benefits, there
are unavoidable thermodynamic costs to modularity---costs that arise directly
from the operation of localized processing and that go beyond Landauer's
dissipation bound for erasing information. Integrated computations can achieve
Landauer's bound, however, when they globally coordinate the control of all of
an information reservoir's degrees of freedom. Unfortunately, global
correlations among the information-bearing degrees of freedom are easily lost
by modular implementations. This is costly since such correlations are a
thermodynamic fuel. We quantify the minimum irretrievable dissipation of
modular computations in terms of the difference between the change in global
nonequilibrium free energy, which captures these global correlations, and the
local (marginal) change in nonequilibrium free energy, which bounds modular
work production. This modularity dissipation is proportional to the amount of
additional work required to perform the computational task modularly. It has
immediate consequences for physically embedded transducers, known as
information ratchets. We show how to circumvent modularity dissipation by
designing internal ratchet states that capture the global correlations and
patterns in the ratchet's information reservoir. Designed in this way,
information ratchets match the optimum thermodynamic efficiency of globally
integrated computations.Comment: 17 pages, 9 figures;
http://csc.ucdavis.edu/~cmg/compmech/pubs/idolip.ht
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