740 research outputs found
Topological phases and criticality in low-dimensional systems with disorder and interactions
In this work criticality arsing due to topological phase transitions in systems with disorder and interaction is investigated
Autotuning and Self-Adaptability in Concurrency Libraries
Autotuning is an established technique for optimizing the performance of
parallel applications. However, programmers must prepare applications for
autotuning, which is tedious and error prone coding work. We demonstrate how
applications become ready for autotuning with few or no modifications by
extending Threading Building Blocks (TBB), a library for parallel programming,
with autotuning. The extended TBB library optimizes all application-independent
tuning parameters fully automatically. We compare manual effort, autotuning
overhead and performance gains on 17 examples. While some examples benefit only
slightly, others speed up by 28% over standard TBB.Comment: Presented at 1st Workshop on Resource Awareness and Adaptivity in
Multi-Core Computing (Racing 2014) (arXiv:1405.2281
Extended critical phase in quasiperiodic quantum Hall systems
We consider the effects of quasiperiodic spatial modulation on the quantum
Hall plateau transition, by analyzing the Chalker-Coddington network model for
the integer quantum Hall transition with quasiperiodically modulated link
phases. In the conventional case (uncorrelated random phases), there is a
critical point separating topologically distinct integer quantum Hall
insulators. Surprisingly, the quasiperiodic version of the model supports an
extended critical phase for some angles of modulation. We characterize this
critical phase and the transitions between critical and insulating phases. For
quasiperiodic potentials with two incommensurate wavelengths, the transitions
we find are in a different universality class from the random transition. Upon
adding more wavelengths they undergo a crossover to the uncorrelated random
case. We expect our results to be relevant to the quantum Hall phases of
twisted bilayer graphene or other Moir\'e systems with large unit cells.Comment: 11 pages, 9 figure
Spectrum-Wide Quantum Criticality at the Surface of Class AIII Topological Phases: An “Energy Stack” of Integer Quantum Hall Plateau Transitions
In the absence of spin-orbit coupling, the conventional dogma of Anderson localization asserts that all states localize in two dimensions, with a glaring exception: the quantum Hall plateau transition (QHPT). In that case, the localization length diverges and interference-induced quantum-critical spatial fluctuations appear at all length scales. Normally, QHPT states occur only at isolated energies; accessing them therefore requires fine-tuning of the electron density or magnetic field. In this paper we show that QHPT states can be realized throughout an energy continuum, i.e., as an “energy stack” of critical states wherein each state in the stack exhibits QHPT phenomenology. The stacking occurs without fine-tuning at the surface of a class AIII topological phase, where it is protected by U(1) and (anomalous) chiral or time-reversal symmetries. Spectrum-wide criticality is diagnosed by comparing numerics to universal results for the longitudinal Landauer conductance and wave function multifractality at the QHPT. Results are obtained from an effective 2D surface field theory and from a bulk 3D lattice model. We demonstrate that the stacking of quantum-critical QHPT states is a robust phenomenon that occurs for AIII topological phases with both odd and even winding numbers. The latter conclusion may have important implications for the still poorly understood logarithmic conformal field theory believed to describe the QHPT
Interfacial energy during the emulsification of water-in-heavy crude oil emulsions
The aim of this study was to investigate the interfacial energy involved in the production of water-in-oil (W/O) emulsions composed of water and a Brazilian heavy crude oil. For such purpose an experimental set-up was developed to measure the different energy terms involved in the emulsification process. W/O emulsions containing different water volume fractions (0.1, 0.25 and 0.4) were prepared in a batch calorimeter by using a high-shear rotating homogenizer at two distinct rotation speeds (14000 and 22000 rpm). The results showed that the energy dissipated as heat represented around 80% of the energy transferred to the emulsion, while around 20% contributed to the internal energy. Only a very small fraction of the energy (0.02 - 0.06%) was stored in the water-oil interface. The results demonstrated that the high energy dissipation contributes to the kinetic stability of the W/O emulsions321127137CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQCOORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESThe authors are grateful to PETROBRAS S.A. and FINEP, Brazil, for the financial support to this study. We also acknowledge the grants conceded by CAPES and CNPq, Brazi
Stability of topologically protected slow light against disorder
Slowing down light in on-chip photonic devices strongly enhances light-matter
interaction, but typically also leads to increased backscattering and
small-bandwidth operation. It was shown re- cently that, if one modifies the
edge termination of a photonic Chern insulator such that the edge mode wraps
many times around the Brillouin zone, light can be slowed to arbitrarily low
group velocity over a large bandwidth, without being subject to backscattering.
Here we study the robust- ness of these in-gap slow light modes against
fabrication disorder, finding that disorder on scales significantly larger than
the minigaps between edge bands is tolerable. We identify the mechanism for
wavepacket breakup as disorder-induced velocity renormalization and calculate
the associated breakup time.Comment: 5 pages, 5 figure
Generalized multifractality at metal-insulator transitions and in metallic phases of 2D disordered systems
We study generalized multifractality characterizing fluctuations and
correlations of eigenstates in disordered systems of symmetry classes AII, D,
and DIII. Both metallic phases and Andersonlocalization transitions are
considered. By using the non-linear sigma-model approach, we construct
pure-scaling eigenfunction observables. The construction is verified by
numerical simulations of appropriate microscopic models, which also yield
numerical values of the corresponding exponents. In the metallic phases, the
numerically obtained exponents satisfy Weyl symmetry relations as well as
generalized parabolicity (proportionality to eigenvalues of the quadratic
Casimir operator). At the same time, the generalized parabolicity is strongly
violated at critical points of metal-insulator transitions, signalling
violation of local conformal invariance. Moreover, in classes D and DIII, even
the Weyl symmetry breaks down at critical points of metal-insulator
transitions. This last feature is related with a peculiarity of the sigma-model
manifolds in these symmetry classes: they consist of two disjoint components.
Domain walls associated with these additional degrees of freedom are crucial
for ensuring Anderson localization and, at the same time, lead to the violation
of the Weyl symmetry.Comment: 36 pages, 14 figure
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