14,592 research outputs found
High Performance P3M N-body code: CUBEP3M
This paper presents CUBEP3M, a publicly-available high performance
cosmological N-body code and describes many utilities and extensions that have
been added to the standard package. These include a memory-light runtime SO
halo finder, a non-Gaussian initial conditions generator, and a system of
unique particle identification. CUBEP3M is fast, its accuracy is tuneable to
optimize speed or memory, and has been run on more than 27,000 cores, achieving
within a factor of two of ideal weak scaling even at this problem size. The
code can be run in an extra-lean mode where the peak memory imprint for large
runs is as low as 37 bytes per particles, which is almost two times leaner than
other widely used N-body codes. However, load imbalances can increase this
requirement by a factor of two, such that fast configurations with all the
utilities enabled and load imbalances factored in require between 70 and 120
bytes per particles. CUBEP3M is well designed to study large scales
cosmological systems, where imbalances are not too large and adaptive
time-stepping not essential. It has already been used for a broad number of
science applications that require either large samples of non-linear
realizations or very large dark matter N-body simulations, including
cosmological reionization, halo formation, baryonic acoustic oscillations, weak
lensing or non-Gaussian statistics. We discuss the structure, the accuracy,
known systematic effects and the scaling performance of the code and its
utilities, when applicable.Comment: 20 pages, 17 figures, added halo profiles, updated to match MNRAS
accepted versio
Quantum information and physics: Some future directions
I consider some promising future directions for quantum information theory that could influence the development of 21st century physics. Advances in the theory of the distinguishability of superoperators may lead to new strategies for improving the precision of quantum-limited measurements. A better grasp of the properties of multi-partite quantum entanglement may lead to deeper understanding of strongly-coupled dynamics in quantum many-body systems, quantum field theory, and quantum gravity
The Growth of Red Sequence Galaxies in a Cosmological Hydrodynamic Simulation
We examine the cosmic growth of the red sequence in a cosmological
hydrodynamic simulation that includes a heuristic prescription for quenching
star formation that yields a realistic passive galaxy population today. In this
prescription, halos dominated by hot gas are continually heated to prevent
their coronae from fueling new star formation. Hot coronae primarily form in
halos above \sim10^12 M\odot, so that galaxies with stellar masses \sim10^10.5
M\odot are the first to be quenched and move onto the red sequence at z > 2.
The red sequence is concurrently populated at low masses by satellite galaxies
in large halos that are starved of new fuel, resulting in a dip in passive
galaxy number densities around \sim10^10 M\odot. Stellar mass growth continues
for galaxies even after joining the red sequence, primarily through minor
mergers with a typical mass ratio \sim1:5. For the most massive systems, the
size growth implied by the distribution of merger mass ratios is typically
\sim2\times the corresponding mass growth, consistent with observations. This
model reproduces mass-density and colour-density trends in the local universe,
with essentially no evolution to z = 1, with the hint that such relations may
be washed out by z \sim 2. Simulated galaxies are increasingly likely to be red
at high masses or high local overdensities. In our model, the presence of
surrounding hot gas drives the trends with both mass and environment.Comment: 15 pages, 8 figures. MNRAS accepte
Fractals in the Nervous System: conceptual Implications for Theoretical Neuroscience
This essay is presented with two principal objectives in mind: first, to
document the prevalence of fractals at all levels of the nervous system, giving
credence to the notion of their functional relevance; and second, to draw
attention to the as yet still unresolved issues of the detailed relationships
among power law scaling, self-similarity, and self-organized criticality. As
regards criticality, I will document that it has become a pivotal reference
point in Neurodynamics. Furthermore, I will emphasize the not yet fully
appreciated significance of allometric control processes. For dynamic fractals,
I will assemble reasons for attributing to them the capacity to adapt task
execution to contextual changes across a range of scales. The final Section
consists of general reflections on the implications of the reviewed data, and
identifies what appear to be issues of fundamental importance for future
research in the rapidly evolving topic of this review
R\'enyi entanglement entropies in quantum dimer models : from criticality to topological order
Thanks to Pfaffian techniques, we study the R\'enyi entanglement entropies
and the entanglement spectrum of large subsystems for two-dimensional
Rokhsar-Kivelson wave functions constructed from a dimer model on the
triangular lattice. By including a fugacity on some suitable bonds, one
interpolates between the triangular lattice (t=1) and the square lattice (t=0).
The wave function is known to be a massive topological liquid for
whereas it is a gapless critical state at t=0. We mainly consider two
geometries for the subsystem: that of a semi-infinite cylinder, and the
disk-like setup proposed by Kitaev and Preskill [Phys. Rev. Lett. 96, 110404
(2006)]. In the cylinder case, the entropies contain an extensive term --
proportional to the length of the boundary -- and a universal sub-leading
constant . Fitting these cylinder data (up to a perimeter of L=32
sites) provides with a very high numerical accuracy ( at t=1 and
at ). In the topological liquid phase we find
, independent of the fugacity and the R\'enyi parameter
. At t=0 we recover a previously known result,
for . In the disk-like geometry --
designed to get rid of the boundary contributions -- we find an entropy in the whole massive phase whatever , in agreement with
the result of Flammia {\it et al.} [Phys. Rev. Lett. 103, 261601 (2009)]. Some
results for the gapless limit are discussed.Comment: 33 pages, 17 figures, minor correction
Laughlin-like states in bosonic and fermionic atomic synthetic ladders
The combination of interactions and static gauge fields plays a pivotal role
in our understanding of strongly-correlated quantum matter. Cold atomic gases
endowed with a synthetic dimension are emerging as an ideal platform to
experimentally address this interplay in quasi-one-dimensional systems. A
fundamental question is whether these setups can give access to pristine
two-dimensional phenomena, such as the fractional quantum Hall effect, and how.
We show that unambiguous signatures of bosonic and fermionic Laughlin-like
states can be observed and characterized in synthetic ladders. We theoretically
diagnose these Laughlin-like states focusing on the chiral current flowing in
the ladder, on the central charge of the low-energy theory, and on the
properties of the entanglement entropy. Remarkably, Laughlin-like states are
separated from conventional liquids by Lifschitz-type transitions,
characterized by sharp discontinuities in the current profiles, which we
address using extensive simulations based on matrix-product states. Our work
provides a qualitative and quantitative guideline towards the observability and
understanding of strongly-correlated states of matter in synthetic ladders. In
particular, we unveil how state-of-the-art experimental settings constitute an
ideal starting point to progressively tackle two-dimensional strongly
interacting systems from a ladder viewpoint, opening a new perspective for the
observation of non-Abelian states of matter.Comment: 19 pages, 17 figures. Updated version after publication in Phys. Rev.
Semiclassical Prediction of Large Spectral Fluctuations in Interacting Kicked Spin Chains
While plenty of results have been obtained for single-particle quantum
systems with chaotic dynamics through a semiclassical theory, much less is
known about quantum chaos in the many-body setting. We contribute to recent
efforts to make a semiclassical analysis of many-body systems feasible. This is
nontrivial due to both the enormous density of states and the exponential
proliferation of periodic orbits with the number of particles. As a model
system we study kicked interacting spin chains employing semiclassical methods
supplemented by a newly developed duality approach. We show that for this model
the line between integrability and chaos becomes blurred. Due to the
interaction structure the system features (non-isolated) manifolds of periodic
orbits possessing highly correlated, collective dynamics. As with the invariant
tori in integrable systems, their presence lead to significantly enhanced
spectral fluctuations, which by order of magnitude lie in-between integrable
and chaotic cases.Comment: 42 pages, 19 figure
Recommended from our members
On the formulation of hereditary cohesive-zone models
This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.The thesis presents novel formulations of hereditary cohesive zone models able to
capture rate-dependent crack propagation along a defined interface. The formulations
rely on the assumption that the measured fracture energy is the sum of an intrinsic fracture energy, related to the rupture of primary bonds at the atomic or molecular level, and an additional dissipation caused by any irreversible mechanisms present in the material and occurring simultaneously to fracture. The first contribution can be accounted for by introducing damage-type internal variables, which are to be driven by a rateindependent evolution law in order to be coherent with the definition as intrinsic energy. It is then proposed that the additional dissipation can be satisfactorily characterised
by the same continuum-type material constitutive law obeyed by the interface material considered as a continuum: it is postulated that the dimensional reduction whereby a three-dimensional thin layer is idealized as a surface does not qualitatively alter the functional description of the free energy.
The specific application considered is mode-I crack propagation along a rubber interface.
After focusing on viscoelasticity as a suitable candidate to reproduce rubber’s
behaviour, firstly the most common relaxation function, namely a single exponential term, is considerd after which the attention is turned to the use of fractional calculus and the related fractional integral kernel.
A comparison with experimental results is presented. A shortcoming of the proposed
approach is then noted, in that certain features of experimentally measured responses
(i.e.the non-monotonicity of the critical energy-release rate with respect to crack speed) will be shown to be out of reach for the described modelling paradigm. A novel micromechanical formulation is then sketched in an attempt to qualitatively understand
the phenomenon. An additional interface damaging mode is introduced, physically inspired by the desire to reproduce the formation of fibrils in a neighbourhood of the crack tip. Fibril formation is then driven by a variational argument applied to the whole of the interface, yielding its non-local character. Upon the introduction of an anisotropic fracture energy, motivated by experimental considerations, it is noted how the model can predict a non-monotonic energy-release rate vs crack speed behaviour, at least for a simple loading mode.Dunlop Oil & Marine Ltd and EPSR
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