708 research outputs found
On the role of the QB protein of PS II in photoinhibition
AbstractPreillumination of spinach thylakoid membranes under strictly anaerobic conditions (i.e. in the presence of glucose oxidase) and in the absence of an electron acceptor inactivates specifically photosystem (PS) II. Inhibition can be complete within 3 min depending on the glucose oxidase concentration and light intensity. Artificial donor or acceptor systems do not restore PS II. Atrazine binding affinity is not diminished. No degradation of peptide subunits is observed. Trypsinized PS II preparations, in which the QB-binding site has been destroyed, can also be inactivated by light. It is concluded that photoinhibition of thylakoid membranes under anaerobic conditions inactivates the reaction center of PS II. This photoinactivation does not depend on the degradation of a peptide subunit. Not only the QB site but also a modified (trypsinized) QA site can induce photoinhibition
Optimizing the ensemble for equilibration in broad-histogram Monte Carlo simulations
We present an adaptive algorithm which optimizes the statistical-mechanical
ensemble in a generalized broad-histogram Monte Carlo simulation to maximize
the system's rate of round trips in total energy. The scaling of the mean
round-trip time from the ground state to the maximum entropy state for this
local-update method is found to be O([N log N]^2) for both the ferromagnetic
and the fully frustrated 2D Ising model with N spins. Our new algorithm thereby
substantially outperforms flat-histogram methods such as the Wang-Landau
algorithm.Comment: 6 pages, 5 figure
Chiral spin liquid and emergent anyons in a Kagome lattice Mott insulator
Topological phases in frustrated quantum spin systems have fascinated
researchers for decades. One of the earliest proposals for such a phase was the
chiral spin liquid put forward by Kalmeyer and Laughlin in 1987 as the bosonic
analogue of the fractional quantum Hall effect. Elusive for many years, recent
times have finally seen a number of models that realize this phase. However,
these models are somewhat artificial and unlikely to be found in realistic
materials. Here, we take an important step towards the goal of finding a chiral
spin liquid in nature by examining a physically motivated model for a Mott
insulator on the Kagome lattice with broken time-reversal symmetry. We first
provide a theoretical justification for the emergent chiral spin liquid phase
in terms of a network model perspective. We then present an unambiguous
numerical identification and characterization of the universal topological
properties of the phase, including ground state degeneracy, edge physics, and
anyonic bulk excitations, by using a variety of powerful numerical probes,
including the entanglement spectrum and modular transformations.Comment: 9 pages, 9 figures; partially supersedes arXiv:1303.696
Strong-disorder renormalization for interacting non-Abelian anyon systems in two dimensions
We consider the effect of quenched spatial disorder on systems of
interacting, pinned non-Abelian anyons as might arise in disordered Hall
samples at filling fractions \nu=5/2 or \nu=12/5. In one spatial dimension,
such disordered anyon models have previously been shown to exhibit a hierarchy
of infinite randomness phases. Here, we address systems in two spatial
dimensions and report on the behavior of Ising and Fibonacci anyons under the
numerical strong-disorder renormalization group (SDRG). In order to manage the
topology-dependent interactions generated during the flow, we introduce a
planar approximation to the SDRG treatment. We characterize this planar
approximation by studying the flow of disordered hard-core bosons and the
transverse field Ising model, where it successfully reproduces the known
infinite randomness critical point with exponent \psi ~ 0.43. Our main
conclusion for disordered anyon models in two spatial dimensions is that
systems of Ising anyons as well as systems of Fibonacci anyons do not realize
infinite randomness phases, but flow back to weaker disorder under the
numerical SDRG treatment.Comment: 12 pages, 12 figures, 1 tabl
Photosynthesis by isolated chloroplasts XII. Inhibitors of Co2 assimilation in a reconstituted chloroplast system
Photosynthesis by isolated chloroplasts XI. Co2 assimilation in a reconstituted chloroplast system
Photosynthesis by isolated chloroplasts X. Dependence of carbon dioxide assimilation on the photochemical reactions of chloroplasts
Two-dimensional quantum liquids from interacting non-Abelian anyons
A set of localized, non-Abelian anyons - such as vortices in a p_x + i p_y
superconductor or quasiholes in certain quantum Hall states - gives rise to a
macroscopic degeneracy. Such a degeneracy is split in the presence of
interactions between the anyons. Here we show that in two spatial dimensions
this splitting selects a unique collective state as ground state of the
interacting many-body system. This collective state can be a novel gapped
quantum liquid nucleated inside the original parent liquid (of which the anyons
are excitations). This physics is of relevance for any quantum Hall plateau
realizing a non-Abelian quantum Hall state when moving off the center of the
plateau.Comment: 5 pages, 6 figure
Dynamics of the Wang-Landau algorithm and complexity of rare events for the three-dimensional bimodal Ising spin glass
We investigate the performance of flat-histogram methods based on a
multicanonical ensemble and the Wang-Landau algorithm for the three-dimensional
+/- J spin glass by measuring round-trip times in the energy range between the
zero-temperature ground state and the state of highest energy. Strong
sample-to-sample variations are found for fixed system size and the
distribution of round-trip times follows a fat-tailed Frechet extremal value
distribution. Rare events in the fat tails of these distributions corresponding
to extremely slowly equilibrating spin glass realizations dominate the
calculations of statistical averages. While the typical round-trip time scales
exponential as expected for this NP-hard problem, we find that the average
round-trip time is no longer well-defined for systems with N >= 8^3 spins. We
relate the round-trip times for multicanonical sampling to intrinsic properties
of the energy landscape and compare with the numerical effort needed by the
genetic Cluster-Exact Approximation to calculate the exact ground state
energies. For systems with N >= 8^3 spins the simulation of these rare events
becomes increasingly hard. For N >= 14^3 there are samples where the
Wang-Landau algorithm fails to find the true ground state within reasonable
simulation times. We expect similar behavior for other algorithms based on
multicanonical sampling.Comment: 9 pages, 12 figure
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