507 research outputs found
Near-equilibrium measurements of nonequilibrium free energy
A central endeavor of thermodynamics is the measurement of free energy
changes. Regrettably, although we can measure the free energy of a system in
thermodynamic equilibrium, typically all we can say about the free energy of a
non-equilibrium ensemble is that it is larger than that of the same system at
equilibrium. Herein, we derive a formally exact expression for the probability
distribution of a driven system, which involves path ensemble averages of the
work over trajectories of the time-reversed system. From this we find a simple
near-equilibrium approximation for the free energy in terms of an excess mean
time-reversed work, which can be experimentally measured on real systems. With
analysis and computer simulation, we demonstrate the accuracy of our
approximations for several simple models.Comment: 5 pages, 3 figure
On the Solution of a Computable General Equilibrium Model
Many of today's most significant socioeconomic problems, such as slower economic growth, the decline of some established industries, and shifts in patterns of foreign trade, are international or transnational in nature. But these problems manifest themselves in a variety of ways; both the intensities and the perceptions of the problems differ from one country to another, so that intercountry comparative analyses of recent historical developments are necessary. Through these analyses we attempt to identify the underlying processes of economic structural change and formulate useful hypotheses concerning future developments. The understanding of these processes and future prospects provides the focus for IIASA's project on Comparative Analysis of Economic Structure and Growth.
Our research concentrates primarily on the empirical analysis of interregional and intertemporal economic structural change, on the sources of and constraints on economic growth, on problems of adaptation to sudden changes, and especially on problems arising from changing patterns of international trade, resource availability, and technology. The project relies on IIASA's accumulated expertise in related fields and, in particular, on the data bases and systems of models that have been developed in the recent past.
This paper is concerned with the solution algorithm of a nonlinear multisectoral model. The model has been developed at IIASA and falls into the class of so called computable general equilibrium models. The economic theoretical properties of the model, as well as some results of simulations based on it, have been reported elsewhere
Stochastic control in microscopic nonequilibrium systems
Quantifying energy flows at nanometer scales promises to guide future
research in a variety of disciplines, from microscopic control and
manipulation, to autonomously operating molecular machines. A general
understanding of the thermodynamic costs of nonequilibrium processes would
illuminate the design principles for efficient microscopic machines.
Considerable effort has gone into finding and classifying the deterministic
control protocols that drive a system rapidly between states at minimum
energetic cost. But for autonomous microscopic systems, driving processes are
themselves stochastic. Here we generalize a linear-response framework to
incorporate such protocol variability, deriving a lower bound on the work that
is realized at finite protocol duration, far from the quasistatic limit. Our
findings are confirmed in model systems. This theory provides a thermodynamic
rationale for rapid operation, independent of functional incentives.Comment: 11 pages, 4 figure
Neutrino pair synchrotron radiation from relativistic electrons in strong magnetic fields
The emissivity for the neutrino pair synchrotron radiation in strong magnetic
fields has been calculated both analytically and numerically for high densities
and moderate temperatures, as can be found in neutron stars. Under these
conditions, the electrons are relativistic and degenerate. We give here our
results in terms of an universal function of a single variable. For two
different regimes of the electron gas we present a simplified calculation and
compare our results to those of Kaminker et al. Agreement is found for the
classical region, where many Landau levels contribute to the emissivity , but
some differences arise in the quantum regime. One finds that the emissivity for
neutrino pair synchrotron radiation is competitive, and can be dominant, with
other neutrino processes for magnetic fields of the order .This indicates the relevance of this process for some astrophysical
scenarios, such as neutron stars and supernovae.Comment: 19 pages, AAS latex, 6 figures on a separate file. Accepted for
publication in Ap.
Optimal Control of the F-ATPase Molecular Motor
F-ATPase is a rotary molecular motor that \emph{in vivo} is subject to
strong nonequilibrium driving forces. There is great interest in understanding
the operational principles governing its high efficiency of free-energy
transduction. Here we use a near-equilibrium framework to design a non-trivial
control protocol to minimize dissipation in rotating F to synthesize ATP.
We find that the designed protocol requires much less work than a naive
(constant-velocity) protocol across a wide range of protocol durations. Our
analysis points to a possible mechanism for energetically efficient driving of
F \emph{in vivo} and provides insight into free-energy transduction for a
broader class of biomolecular and synthetic machines.Comment: 7 pages + SI, Minor revisio
Thermodynamic metrics and optimal paths
A fundamental problem in modern thermodynamics is how a molecular-scale
machine performs useful work, while operating away from thermal equilibrium
without excessive dissipation. To this end, we derive a friction tensor that
induces a Riemannian manifold on the space of thermodynamic states. Within the
linear-response regime, this metric structure controls the dissipation of
finite-time transformations, and bestows optimal protocols with many useful
properties. We discuss the connection to the existing thermodynamic length
formalism, and demonstrate the utility of this metric by solving for optimal
control parameter protocols in a simple nonequilibrium model.Comment: 5 page
Hidden energy flows in strongly coupled nonequilibrium systems
Quantifying the flow of energy within and through fluctuating nanoscale
systems poses a significant challenge to understanding microscopic biological
machines. A common approach involves coarse-graining, which allows a simplified
description of such systems. This has the side effect of inducing so-called
hidden contributions (due to sub-resolution dynamics) that complicate the
resulting thermodynamics. Here we develop a thermodynamically consistent theory
describing the nonequilibrium excess power internal to autonomous systems, and
introduce a phenomenological framework to quantify the hidden excess power
associated with their operation. We confirm our theoretical predictions in
numerical simulations of a minimal model for both a molecular transport motor
and a rotary motor.Comment: 14 pages, 3 figure
The thermodynamics of prediction
A system responding to a stochastic driving signal can be interpreted as
computing, by means of its dynamics, an implicit model of the environmental
variables. The system's state retains information about past environmental
fluctuations, and a fraction of this information is predictive of future ones.
The remaining nonpredictive information reflects model complexity that does not
improve predictive power, and thus represents the ineffectiveness of the model.
We expose the fundamental equivalence between this model inefficiency and
thermodynamic inefficiency, measured by dissipation. Our results hold
arbitrarily far from thermodynamic equilibrium and are applicable to a wide
range of systems, including biomolecular machines. They highlight a profound
connection between the effective use of information and efficient thermodynamic
operation: any system constructed to keep memory about its environment and to
operate with maximal energetic efficiency has to be predictive.Comment: 5 pages, 1 figur
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