2,613 research outputs found
KCrF_3: Electronic Structure, Magnetic and Orbital Ordering from First Principles
The electronic, magnetic and orbital structures of KCrF_3 are determined in
all its recently identified crystallographic phases (cubic, tetragonal, and
monoclinic) with a set of {\it ab initio} LSDA and LSDA+U calculations. The
high-temperature undistorted cubic phase is metallic within the LSDA, but at
the LSDA+U level it is a Mott insulator with a gap of 1.72 eV. The tetragonal
and monoclinic phases of KCrF_3 exhibit cooperative Jahn-Teller distortions
concomitant with staggered 3x^2-r^2/3y^2-r^2 orbital order. We find that the
energy gain due to the Jahn-Teller distortion is 82/104 meV per chromium ion in
the tetragonal/monoclinic phase, respectively. These phases show A-type
magnetic ordering and have a bandgap of 2.48 eV. In this Mott insulating state
KCrF_3 has a substantial conduction bandwidth of 2.1 eV, leading to the
possibility for the kinetic energy of charge carriers in electron- or
hole-doped derivatives of KCrF_3 to overcome the polaron localization at low
temperatures, in analogy with the situation encountered in the colossal
magnetoresistive manganites.Comment: 7 pages, 11 figure
Decentralized Implementation of Flood Resilience Measures – A Blessing or a Curse? Lessons from the Thames Estuary 2100 Plan and the Royal Docks Regeneration
This article presents a case study on the implementation of the Thames Estuary 2100 Plan in the Royal Docks, a regeneration project in the East of London. On paper, the Thames Estuary 2100 Plan advances the shift from traditional flood control to flood resilience, because of its long-term horizon, estuary-wide approach, and emphasis on floodplain management. In practice, however, we identify three frictions between vision and reality: a lack of local ownership of the plan, a lack of clear guidance for floodplain management, and limited capacities with local authority. These frictions suggest an ongoing ‘public-public divide’ in decentralized governance
Between adaptability and the urge to control: making long-term water policies in the Netherlands
Triggered by recent flood catastrophes and increasing concerns about climate change, scientists as well as policy makers increasingly call for making long-term water policies to enable a transformation towards flood resilience. A key question is how to make these long-term policies adaptive so that they are able to deal with uncertainties and changing circumstances. The paper proposes three conditions for making long-term water policies adaptive, which are then used to evaluate a new Dutch water policy approach called ‘Adaptive Delta Management’. Analysing this national policy approach and its translation to the Rotterdam region reveals that Dutch policymakers are torn between adaptability and the urge to control. Reflecting on this dilemma, the paper suggests a stronger focus on monitoring and learning to strengthen the adaptability of long-term water policies. Moreover, increasing the adaptive capacity of society also requires a stronger engagement with local stakeholders including citizens and businesses
Enhanced Loop-weakened Belief Propagation Algorithm for Performance Enhanced Polar Code Decoders
A polar code decoder based on the belief propagation algorithm is desirable because of the potentially low latency and its suitability for parallel execution on multicore and SIMD processors. However, current state-of-the-art algorithms require many iterations to achieve comparable bit and frame error rate compared to successive cancellation algorithms. Also, the current state-of-the-art belief propagation algorithms have a high computational complexity compared to successive cancellation. In this paper we present an enhanced belief propagation algorithm, in which parts of the computations are altered to reduce the negative effect of the short cycles in the polar code factor graph. Our proposed algorithm has a gain of approx+0.4mathbf{dB} in both frame and bit error rate compared to successive cancellation and a gain of approx+0.16mathbf{dB} and approx+0.13mathbf{dB} at a frame and bit error rate of 10-3 respectively, compared to belief propagation. Also, the maximum number of iterations of our algorithm is reduce to 0.6cdot I_{max}. As a result, the latency is up to approx 11 times lower compared to successive cancellation and up to approx 1.8 times lower compared to the current state-of-the-art belief propagation polar code algorithm. Furthermore, the reduction in the maximum iteration count results in a lower power consumption after implementation.</p
Computational Complexity Reduced Belief Propagation Algorithm for Polar Code Decoders
The belief propagation algorithm is desirable for a polar code based decoder, because of the potentially low latency and the ability of integration in digital signal processing units or other multi-core processor systems to parallelize the computations. Although belief propagation polar code decoder algorithms have the ability for a highly parallelized imple-mentation, the algorithms require many iterations to achieve a comparable frame error rate and bit error rate with respect to a successive cancellation polar code algorithm. The iterative nature of the belief propagation algorithms also result in a higher computational complexity, i.e. O(IN(2log_{2} N-1)) compared to the computational complexity O(Nlog_{2}N) of the successive cancellation decoder algorithm. In this paper we propose several simplifications for a simplified belief propagation algorithm for polar code decoders, where the arithmetic complexity of the nodes is reduced. The proposed belief propagation algorithm shows preliminary results of a net reduction of the arithmetic complexity of ≈ 13%. This reduction is a result of the reduced number of arithmetic operations, i.e., additions, compares, and multiplications, without a lost in error-correcting performance.</p
Polarization Suppression and Nonmonotonic Local Two-Body Correlations in the Two-Component Bose Gas in One Dimension
We study the interplay of quantum statistics, strong interactions and finite
temperatures in the two-component (spinor) Bose gas with repulsive
delta-function interactions in one dimension. Using the Thermodynamic Bethe
Ansatz, we obtain the equation of state, population densities and local density
correlation numerically as a function of all physical parameters (interaction,
temperature and chemical potentials), quantifying the full crossover between
low-temperature ferromagnetic and high-temperature unpolarized regimes. In
contrast to the single-component, Lieb-Liniger gas, nonmonotonic behaviour of
the local density correlation as a function of temperature is observed.Comment: 4 pages, 6 figure
Orbital excitations in LaMnO
We study the recently observed orbital excitations, orbitons, and treat
electron-electron correlations and lattice dynamics on equal footing. It is
shown that the orbiton energy and dispersion are determined by both
correlations and lattice-vibrations. The electron-phonon coupling causes
satellite structures in the orbiton spectral function and the elementary
excitations of the system are mixed modes with both orbital and phonon
character. It is proposed that the satellite structures observed in recent
Raman-scattering experiments on LaMnO are actually orbiton derived
satellites in the phonon spectral function, caused by the phonon-orbiton
interaction.Comment: 4 pages, 3 figures embedde
Orbital order in classical models of transition-metal compounds
We study the classical 120-degree and related orbital models. These are the
classical limits of quantum models which describe the interactions among
orbitals of transition-metal compounds. We demonstrate that at low temperatures
these models exhibit a long-range order which arises via an "order by disorder"
mechanism. This strongly indicates that there is orbital ordering in the
quantum version of these models, notwithstanding recent rigorous results on the
absence of spin order in these systems.Comment: 7 pages, 1 eps fi
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