78 research outputs found
Fundamental Bounds on First Passage Time Fluctuations for Currents
Current is a characteristic feature of nonequilibrium systems. In stochastic
systems, these currents exhibit fluctuations constrained by the rate of
dissipation in accordance with the recently discovered thermodynamic
uncertainty relation. Here, we derive a conjugate uncertainty relationship for
the first passage time to accumulate a fixed net current. More generally, we
use the tools of large-deviation theory to simply connect current fluctuations
and first passage time fluctuations in the limit of long times and large
currents. With this connection, previously discovered symmetries and bounds on
the large-deviation function for currents are readily transferred to first
passage times.Comment: 7 pages including S
Proof of the Finite-Time Thermodynamic Uncertainty Relation for Steady-State Currents
The thermodynamic uncertainty relation offers a universal energetic
constraint on the relative magnitude of current fluctuations in nonequilibrium
steady states. However, it has only been derived for long observation times.
Here, we prove a recently conjectured finite-time thermodynamic uncertainty
relation for steady-state current fluctuations. Our proof is based on a
quadratic bound to the large deviation rate function for currents in the limit
of a large ensemble of many copies.Comment: 3 page
Universal thermodynamic bounds on nonequilibrium response with biochemical applications
Diverse physical systems are characterized by their response to small
perturbations. Near thermodynamic equilibrium, the fluctuation-dissipation
theorem provides a powerful theoretical and experimental tool to determine the
nature of response by observing spontaneous equilibrium fluctuations. In this
spirit, we derive here a collection of equalities and inequalities valid
arbitrarily far from equilibrium that constrain the response of nonequilibrium
steady states in terms of the strength of nonequilibrium driving. Our work
opens new avenues for characterizing nonequilibrium response. As illustrations,
we show how our results rationalize the energetic requirements of two common
biochemical motifs.Comment: 21 pages, 15 figure
Efficiency and Large Deviations in Time-Asymmetric Stochastic Heat Engines
In a stochastic heat engine driven by a cyclic non-equilibrium protocol,
fluctuations in work and heat give rise to a fluctuating efficiency. Using
computer simulations and tools from large deviation theory, we have examined
these fluctuations in detail for a model two-state engine. We find in general
that the form of efficiency probability distributions is similar to those
described by Verley et al. [2014 Nat Comm, 5 4721], in particular featuring a
local minimum in the long-time limit. In contrast to the time-symmetric engine
protocols studied previously, however, this minimum need not occur at the value
characteristic of a reversible Carnot engine. Furthermore, while the local
minimum may reside at the global minimum of a large deviation rate function, it
does not generally correspond to the least likely efficiency measured over
finite time. We introduce a general approximation for the finite-time
efficiency distribution, , based on large deviation statistics of work
and heat, that remains very accurate even when deviates significantly
from its large deviation form.Comment: 10 pages, 3 figure
Thermodynamic uncertainty relation for Langevin dynamics by scaling time
The thermodynamic uncertainty relation (TUR) quantifies a relationship
between current fluctuations and dissipation in out-of-equilibrium overdamped
Langevin dynamics, making it a natural counterpart of the
fluctuation-dissipation theorem in equilibrium statistical mechanics. For
underdamped Langevin dynamics, the situation is known to be more complicated,
with dynamical activity also playing a role in limiting the magnitude of
current fluctuations. Progress on those underdamped TUR-like bounds has largely
come from applications of the information-theoretic Cram\'er-Rao inequality.
Here, we present an alternative perspective by employing large deviation
theory. The approach offers a general, unified treatment of TUR-like bounds for
both overdamped and underdamped Langevin dynamics built upon current
fluctuations achieved by scaling time. The bounds we derive following this
approach are similar to known results but with differences we discuss and
rationalize.Comment: 6 pages, 3 figure
Near-optimal protocols in complex nonequilibrium transformations
The development of sophisticated experimental means to control nanoscale
systems has motivated efforts to design driving protocols which minimize the
energy dissipated to the environment. Computational models are a crucial tool
in this practical challenge. We describe a general method for sampling an
ensemble of finite-time, nonequilibrium protocols biased towards a low average
dissipation. We show that this scheme can be carried out very efficiently in
several limiting cases. As an application, we sample the ensemble of
low-dissipation protocols that invert the magnetization of a 2D Ising model and
explore how the diversity of the protocols varies in response to constraints on
the average dissipation. In this example, we find that there is a large set of
protocols with average dissipation close to the optimal value, which we argue
is a general phenomenon.Comment: 6 pages and 3 figures plus 4 pages and 5 figures of supplemental
materia
Combinatorial synthesis and high-throughput photopotential and photocurrent screening of mixed-metal oxides for photoelectrochemical water splitting
A high-throughput method has been developed using a commercial piezoelectric inkjet printer for synthesis and characterization of mixed-metal oxide photoelectrode materials for water splitting. The printer was used to deposit metal nitrate solutions onto a conductive glass substrate. The deposited metal nitrate solutions were then pyrolyzed to yield mixed-metal oxides that contained up to eight distinct metals. The stoichiometry of the metal oxides was controlled quantitatively, allowing for the creation of vast libraries of novel materials. Automated methods were developed to measure the open-circuit potentials (Eoc), short-circuit photocurrent densities (Jsc), and current density vs. applied potential (J–E) behavior under visible light irradiation. The high-throughput measurement of Eoc is particularly significant because open-circuit potential measurements allow the interfacial energetics to be probed regardless of whether the band edges of the materials of concern are above, close to, or below the values needed to sustain water electrolysis under standard conditions. The Eoc measurements allow high-throughput compilation of a suite of data that can be associated with the composition of the various materials in the library, to thereby aid in the development of additional screens and to form a basis for development of theoretical guidance in the prediction of additional potentially promising photoelectrode compositions
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