221,309 research outputs found
Laplacian growth as one-dimensional turbulence
A new model of Laplacian stochastic growth is formulated using conformal
mappings. The model describes two growth regimes, stable and turbulent,
separated by a sharp phase transition. The first few Fourier components of the
mapping define the web, an envelope of the cluster. The web is used to study
the transition and the dynamics of large-scale features of the cluster
characterized by evolution from macro- to micro-scales. Also, we derive scaling
laws for the cluster size.Comment: 4 pages, RevTex, 4 figure
Topology and Evolution of Technology Innovation Networks
The web of relations linking technological innovation can be fairly described
in terms of patent citations. The resulting patent citation network provides a
picture of the large-scale organization of innovations and its time evolution.
Here we study the patterns of change of patents registered by the US Patent and
Trademark Office (USPTO). We show that the scaling behavior exhibited by this
network is consistent with a preferential attachment mechanism together with a
Weibull-shaped aging term. Such attachment kernel is shared by scientific
citation networks, thus indicating an universal type of mechanism linking ideas
and designs and their evolution. The implications for evolutionary theory of
innovation are discussed.Comment: 6 pages, 5 figures, submitted to Physical Review
Opinion formation driven by PageRank node influence on directed networks
We study a two states opinion formation model driven by PageRank node
influence and report an extensive numerical study on how PageRank affects
collective opinion formations in large-scale empirical directed networks. In
our model the opinion of a node can be updated by the sum of its neighbor
nodes' opinions weighted by the node influence of the neighbor nodes at each
step. We consider PageRank probability and its sublinear power as node
influence measures and investigate evolution of opinion under various
conditions. First, we observe that all networks reach steady state opinion
after a certain relaxation time. This time scale is decreasing with the
heterogeneity of node influence in the networks. Second, we find that our model
shows consensus and non-consensus behavior in steady state depending on types
of networks: Web graph, citation network of physics articles, and LiveJournal
social network show non-consensus behavior while Wikipedia article network
shows consensus behavior. Third, we find that a more heterogeneous influence
distribution leads to a more uniform opinion state in the cases of Web graph,
Wikipedia, and Livejournal. However, the opposite behavior is observed in the
citation network. Finally we identify that a small number of influential nodes
can impose their own opinion on significant fraction of other nodes in all
considered networks. Our study shows that the effects of heterogeneity of node
influence on opinion formation can be significant and suggests further
investigations on the interplay between node influence and collective opinion
in networks.Comment: 10 pages, 6 figures. Published in Physica A 436, 707-715 (2015
Using the Topology of Large Scale Structure to constrain Dark Energy
The use of standard rulers, such as the scale of the Baryonic Acoustic
oscillations (BAO), has become one of the more powerful techniques employed in
cosmology to probe the entity driving the accelerating expansion of the
Universe. In this paper, the topology of large scale structure (LSS) is used as
one such standard ruler to study this mysterious `dark energy'. By following
the redshift evolution of the clustering of luminous red galaxies (LRGs) as
measured by their 3D topology (counting structures in the cosmic web), we can
chart the expansion rate and extract information about the equation of state of
dark energy. Using the technique first introduced in (Park & Kim, 2009), we
evaluate the constraints that can be achieved using 3D topology measurements
from next-generation LSS surveys such as the Baryonic Oscillation Spectroscopic
Survey (BOSS). In conjunction with the information that will be available from
the Planck satellite, we find a single topology measurement on 3 different
scales is capable of constraining a single dark energy parameter to within 5%
and 10% when dynamics are permitted. This offers an alternative use of the data
available from redshift surveys and serves as a cross-check for BAO studies.Comment: 8 pages, 5 figures, 2 tables, Submitted to MNRAS, updated
acknowledgement
Quenching in Cosmic Sheets: Tracing the Impact of Large Scale Structure Collapse on the Evolution of Dwarf Galaxies
Dwarf galaxies are thought to quench primarily due to environmental processes
most typically occurring in galaxy groups and clusters or around single,
massive galaxies. However, at earlier epochs, (), the collapse of
large scale structure (forming Zel'dovich sheets and subsequently filaments of
the cosmic web) can produce volume-filling accretion shocks which elevate large
swaths of the intergalactic medium (IGM) in these structures to a hot (
K) phase. We study the impact of such an event on the evolution of central
dwarf galaxies () in the field using a spatially large,
high resolution cosmological zoom simulation which covers the cosmic web
environment between two protoclusters. We find that the shock-heated sheet acts
as an environmental quencher much like clusters and filaments at lower
redshift, creating a population of quenched, central dwarf galaxies. Even
massive dwarfs which do not quench are affected by the shock, with reductions
to their sSFR and gas accretion. This process can potentially explain the
presence of isolated quenched dwarf galaxies, and represents an avenue of
pre-processing, via which quenched satellites of bound systems quench before
infall.Comment: 15 pages, 10 figures. Submitted to MNRA
Evolution of cosmic filaments in the MTNG simulation
We present a study of the evolution of cosmic filaments across redshift with
emphasis on some important properties: filament lengths, growth rates, and
radial profiles of galaxy densities. Following an observation-driven approach,
we build cosmic filament catalogues at z=0,1,2,3 and 4 from the galaxy
distributions of the large hydro-dynamical run of the MilleniumTNG project. We
employ the extensively used DisPerSE cosmic web finder code, for which we
provide a user-friendly guide, including the details of a physics-driven
calibration procedure, with the hope of helping future users. We perform the
first statistical measurements of the evolution of connectivity in a
large-scale simulation, finding that the connectivity of cosmic nodes (defined
as the number of filaments attached) globally decreases from early to late
times. The study of cosmic filaments in proper coordinates reveals that
filaments grow in length and radial extent, as expected from large-scale
structures in an expanding Universe. But the most interesting results arise
once the Hubble flow is factored out. We find remarkably stable comoving
filament length functions and over-density profiles, showing only little
evolution of the total population of filaments in the past ~12.25 Gyrs.
However, by tracking the spatial evolution of individual structures, we
demonstrate that filaments of different lengths actually follow different
evolutionary paths. While short filaments preferentially contract, long
filaments expand along their longitudinal direction with growth rates that are
the highest in the early, matter dominated Universe. Filament diversity at
fixed redshift is also shown by the different (~) density values
between the shortest and longest filaments. Our results hint that cosmic
filaments can be used as additional probes for dark energy, but further
theoretical work is still needed.Comment: 17 pages, submitted to Astronomy & Astrophysics, comments welcome
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