23,864 research outputs found
Exploration of Reaction Pathways and Chemical Transformation Networks
For the investigation of chemical reaction networks, the identification of
all relevant intermediates and elementary reactions is mandatory. Many
algorithmic approaches exist that perform explorations efficiently and
automatedly. These approaches differ in their application range, the level of
completeness of the exploration, as well as the amount of heuristics and human
intervention required. Here, we describe and compare the different approaches
based on these criteria. Future directions leveraging the strengths of chemical
heuristics, human interaction, and physical rigor are discussed.Comment: 48 pages, 4 figure
Geometric Universality of Currents
We discuss a non-equilibrium statistical system on a graph or network.
Identical particles are injected, interact with each other, traverse, and leave
the graph in a stochastic manner described in terms of Poisson rates, possibly
dependent on time and instantaneous occupation numbers at the nodes of the
graph. We show that under the assumption of constancy of the relative rates,
the system demonstrates a profound statistical symmetry, resulting in geometric
universality of the statistics of the particle currents. This phenomenon
applies broadly to many man-made and natural open stochastic systems, such as
queuing of packages over the internet, transport of electrons and
quasi-particles in mesoscopic systems, and chains of reactions in bio-chemical
networks. We illustrate the utility of our general approach using two enabling
examples from the two latter disciplines.Comment: 15 pages, 5 figure
Ultracold Chemistry and its Reaction Kinetics
We study the reaction kinetics of chemical processes occurring in the
ultracold regime and systematically investigate their dynamics. Quantum
entanglement is found to play a key role in driving an ultracold reaction
towards a dynamical equilibrium. In case of multiple concurrent reactions
Hamiltonian chaos dominates the phase space dynamics in the mean field
approximation.Comment: 15 pages, 5 figure
Dissipation in noisy chemical networks: The role of deficiency
We study the effect of intrinsic noise on the thermodynamic balance of
complex chemical networks subtending cellular metabolism and gene regulation. A
topological network property called deficiency, known to determine the
possibility of complex behavior such as multistability and oscillations, is
shown to also characterize the entropic balance. In particular, only when
deficiency is zero does the average stochastic dissipation rate equal that of
the corresponding deterministic model, where correlations are disregarded. In
fact, dissipation can be reduced by the effect of noise, as occurs in a toy
model of metabolism that we employ to illustrate our findings. This phenomenon
highlights that there is a close interplay between deficiency and the
activation of new dissipative pathways at low molecule numbers.Comment: 10 Pages, 6 figure
Symmetry and the thermodynamics of currents in open quantum systems
Symmetry is a powerful concept in physics, and its recent application to
understand nonequilibrium behavior is providing deep insights and
groundbreaking exact results. Here we show how to harness symmetry to control
transport and statistics in open quantum systems. Such control is enabled by a
first-order-type dynamic phase transition in current statistics and the
associated coexistence of different transport channels (or nonequilibrium
steady states) classified by symmetry. Microreversibility then ensues, via the
Gallavotti-Cohen fluctuation theorem, a twin dynamic phase transition for rare
current fluctuations. Interestingly, the symmetry present in the initial state
is spontaneously broken at the fluctuating level, where the quantum system
selects the symmetry sector that maximally facilitates a given fluctuation. We
illustrate these results in a qubit network model motivated by the problem of
coherent energy harvesting in photosynthetic complexes, and introduce the
concept of a symmetry-controlled quantum thermal switch, suggesting
symmetry-based design strategies for quantum devices with controllable
transport properties.Comment: 12 pages, 6 figure
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