1,059 research outputs found
Fractal Weyl law for Linux Kernel Architecture
We study the properties of spectrum and eigenstates of the Google matrix of a
directed network formed by the procedure calls in the Linux Kernel. Our results
obtained for various versions of the Linux Kernel show that the spectrum is
characterized by the fractal Weyl law established recently for systems of
quantum chaotic scattering and the Perron-Frobenius operators of dynamical
maps. The fractal Weyl exponent is found to be that
corresponds to the fractal dimension of the network . The
eigenmodes of the Google matrix of Linux Kernel are localized on certain
principal nodes. We argue that the fractal Weyl law should be generic for
directed networks with the fractal dimension .Comment: RevTex 6 pages, 7 figs, linked to arXiv:1003.5455[cs.SE]. Research at
http://www.quantware.ups-tlse.fr/, Improved version, changed forma
Resting vs. active: a meta-analysis of the intra- and inter-specific associations between minimum, sustained, and maximum metabolic rates in vertebrates
Variation in aerobic capacity has far reaching consequences for the physiology, ecology, and evolution of vertebrates. Whether at rest or active, animals are constrained to operate within the energetic bounds determined by their minimum (minMR) and sustained or maximum metabolic rates (upperMR). MinMR and upperMR can differ considerably among individuals and species but are often presumed to be mechanistically linked to one another. Specifically, minMR is thought to reflect the idling cost of the machinery needed to support upperMR. However, previous analyses based on limited datasets have come to conflicting conclusions regarding the generality and strength of their association.
Here we conduct the first comprehensive assessment of their relationship, based on a large number of published estimates of both the intra-specific (n = 176) and inter-specific (n = 41) phenotypic correlations between minMR and upperMR, estimated as either exercise-induced maximum metabolic rate (VO2max), cold-induced summit metabolic rate (Msum), or daily energy expenditure (DEE).
Our meta-analysis shows that there is a general positive association between minMR and upperMR that is shared among vertebrate taxonomic classes. However, there was stronger evidence for intra-specific correlations between minMR and Msum and between minMR and DEE than there was for a correlation between minMR and VO2max across different taxa. As expected, inter-specific correlation estimates were consistently higher than intra-specific estimates across all traits and vertebrate classes.
An interesting exception to this general trend was observed in mammals, which contrast with birds and exhibit no correlation between minMR and Msum. We speculate that this is due to the evolution and recruitment of brown fat as a thermogenic tissue, which illustrates how some species and lineages might circumvent this seemingly general association.
We conclude that, in spite of some variability across taxa and traits, the contention that minMR and upperMR are positively correlated generally holds true both within and across vertebrate species. Ecological and comparative studies should therefore take into consideration the possibility that variation in any one of these traits might partly reflect correlated responses to selection on other metabolic parameters
Magnetic Field Effect for Two Electrons in a Two Dimensional Random Potential
We study the problem of two particles with Coulomb repulsion in a
two-dimensional disordered potential in the presence of a magnetic field. For
the regime, when without interaction all states are well localized, it is shown
that above a critical excitation energy electron pairs become delocalized by
interaction. The transition between the localized and delocalized regimes goes
in the same way as the metal-insulator transition at the mobility edge in the
three dimensional Anderson model with broken time reversal symmetry.Comment: revtex, 7 pages, 6 figure
Low energy transition in spectral statistics of 2D interactingfermions
We study the level spacing statistics and eigenstate properties of
spinless fermions with Coulomb interaction on a two dimensional lattice at
constant filling factor and various disorder strength. In the limit of large
lattice size, undergoes a transition from the Poisson to the
Wigner-Dyson distribution at a critical total energy independent of the number
of fermions. This implies the emergence of quantum ergodicity induced by
interaction and delocalization in the Hilbert space at zero temperature.Comment: revtex, 5 pages, 4 figures; new data for eigenfunctions are adde
Ground state properties of the 2D disordered Hubbard model
We study the ground state of the two-dimensional (2D) disordered Hubbard
model by means of the projector quantum Monte Carlo (PQMC) method. This
approach allows us to investigate the ground state properties of this model for
lattice sizes up to , at quarter filling, for a broad range of
interaction and disorder strengths. Our results show that the ground state of
this system of spin-1/2 fermions remains localised in the presence of the
short-ranged Hubbard interaction.Comment: 7 pages, 9 figure
Sparsity without the Complexity: Loss Localisation using Tree Measurements
We study network loss tomography based on observing average loss rates over a
set of paths forming a tree -- a severely underdetermined linear problem for
the unknown link loss probabilities. We examine in detail the role of sparsity
as a regularising principle, pointing out that the problem is technically
distinct from others in the compressed sensing literature. While sparsity has
been applied in the context of tomography, key questions regarding uniqueness
and recovery remain unanswered. Our work exploits the tree structure of path
measurements to derive sufficient conditions for sparse solutions to be unique
and the condition that minimization recovers the true underlying
solution. We present a fast single-pass linear algorithm for
minimization and prove that a minimum solution is both unique and
sparsest for tree topologies. By considering the placement of lossy links
within trees, we show that sparse solutions remain unique more often than is
commonly supposed. We prove similar results for a noisy version of the problem
Effect of Pnictogen Height on Spin Waves in Iron Pnictides
We use inelastic neutron scattering to study spin waves in the antiferromagnetic ordered phase of iron pnictide NaFeAs throughout the Brillouin zone. Comparing with the well-studied AFe2As2 (A=Ca, Sr, Ba) family, spin waves in NaFeAs have considerably lower zone boundary energies and more isotropic effective in-plane magnetic exchange couplings. These results are consistent with calculations from a combined density functional theory and dynamical mean field theory and provide strong evidence that pnictogen height controls the strength of electron-electron correlations and consequently the effective bandwidth of magnetic excitations
Quantum Computing of Quantum Chaos in the Kicked Rotator Model
We investigate a quantum algorithm which simulates efficiently the quantum
kicked rotator model, a system which displays rich physical properties, and
enables to study problems of quantum chaos, atomic physics and localization of
electrons in solids. The effects of errors in gate operations are tested on
this algorithm in numerical simulations with up to 20 qubits. In this way
various physical quantities are investigated. Some of them, such as second
moment of probability distribution and tunneling transitions through invariant
curves are shown to be particularly sensitive to errors. However,
investigations of the fidelity and Wigner and Husimi distributions show that
these physical quantities are robust in presence of imperfections. This implies
that the algorithm can simulate the dynamics of quantum chaos in presence of a
moderate amount of noise.Comment: research at Quantware MIPS Center http://www.quantware.ups-tlse.fr,
revtex 11 pages, 13 figs, 2 figs and discussion adde
Dynamical localization simulated on a few qubits quantum computer
We show that a quantum computer operating with a small number of qubits can
simulate the dynamical localization of classical chaos in a system described by
the quantum sawtooth map model. The dynamics of the system is computed
efficiently up to a time , and then the localization length
can be obtained with accuracy by means of order computer runs,
followed by coarse grained projective measurements on the computational basis.
We also show that in the presence of static imperfections a reliable
computation of the localization length is possible without error correction up
to an imperfection threshold which drops polynomially with the number of
qubits.Comment: 8 pages, 8 figure
Particlization in hybrid models
In hybrid models, which combine hydrodynamical and transport approaches to
describe different stages of heavy-ion collisions, conversion of fluid to
individual particles, particlization, is a non-trivial technical problem. We
describe in detail how to find the particlization hypersurface in a 3+1
dimensional model, and how to sample the particle distributions evaluated using
the Cooper-Frye procedure to create an ensemble of particles as an initial
state for the transport stage. We also discuss the role and magnitude of the
negative contributions in the Cooper-Frye procedure.Comment: 18 pages, 28 figures, EPJA: Topical issue on "Relativistic Hydro- and
Thermodynamics"; version accepted for publication, typos and error in Eq.(1)
corrected, the purpose of sampling and change from UrQMD to fluid clarified,
added discussion why attempts to cancel negative contributions of Cooper-Frye
are not applicable her
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