136,939 research outputs found
An analytic model for a cooperative ballistic deposition in one dimension
We formulate a model for a cooperative ballistic deposition (CBD) process
whereby the incoming particles are correlated with the ones already adsorbed
via attractive force. The strength of the correlation is controlled by a
tunable parameter that interpolates the classical car parking problem at
, the ballistic deposition at and the CBD model at . The
effects of the correlation in the CBD model are as follows. The jamming
coverage increases with the strength of attraction due to an ever
increasing tendency of cluster formation. The system almost reaches the closest
packing structure as but never forms a percolating cluster which
is typical to 1D system. In the large regime, the mean cluster size
increases as . Furthermore, the asymptotic approach towards the
closest packing is purely algebraic both with as and with as where .Comment: 9 pages (in Revtex4), 9 eps figures; Submitted to publicatio
Catalogue of 55-80 MeV solar proton events extending through solar cycles 23 and 24
We present a new catalogue of solar energetic particle events near the Earth,
covering solar cycle 23 and the majority of solar cycle 24 (1996-2016), based
on the 55-80 MeV proton intensity data gathered by the SOHO/ERNE experiment. In
addition to ERNE proton and heavy ion observations, data from the ACE/EPAM
(near-relativistic electrons), SOHO/EPHIN (relativistic electrons), SOHO/LASCO
(coronal mass ejections, CMEs), and GOES soft X-ray experiments are also
considered and the associations between the particle and CME/X-ray events
deduced to obtain a better understanding of each event. A total of 176 SEP
events have been identified as having occurred during the time period of
interest; their onset and solar release times have been estimated using both
velocity dispersion analysis (VDA) and time-shifting analysis (TSA) for
protons, as well as TSA for near-relativistic electrons. Additionally, a brief
statistical analysis has been performed on the VDA and TSA results, as well as
the X-rays and CMEs associated with the proton/electron events, both to test
the viability of the VDA and to investigate possible differences between the
two solar cycles. We find, in confirmation of a number of previous studies,
that VDA results for protons that yield an apparent path length of 1 AU < s <~
3 AU seem to be useful, but those outside this range are probably unreliable,
as evidenced by the anticorrelation between apparent path length and release
time estimated from the X-ray activity. It also appears that even the
first-arriving energetic protons apparently undergo significant pitch angle
scattering in the interplanetary medium, with the resulting apparent path
length being on average about twice the length of the spiral magnetic field.
The analysis indicates an increase in high-energy SEP events originating from
the far eastern solar hemisphere; e.g., such an event...Comment: 33 pages, 12 figures (2 with multiple image files), 1 appendix as an
external PDF file. Article is in the accepted manuscript/referee (single
column) forma
Crustal structure of the Borderland-Continent Transition Zone of southern California adjacent to Los Angeles
We use data from the onshore-offshore component of Los Angeles Region Seismic Experiment (LARSE) to model the broad-scale features of the midcrust to upper mantle beneath a north-south transect that spans the continental borderland in the Los Angeles, California, region. We have developed an analysis method for wide-angle seismic data that consists primarily of refractions, lacks near-offset recordings, and contains wide gaps in coverage. Although the data restrict the analysis to the modeling of broad-scale structure, the technique allows one to explore the limits of the data and determine the resolving power of the data set. The resulting composite velocity model constrains the crustal thickness and location and width of the continent-Borderland transition zone. We find that the mid to lower crust layer velocities of the Inner Borderland are slightly lower than the corresponding layers in the average southern California crust model, while the upper mantle velocity is significantly higher. The data require the Moho to deepen significantly to the north. We constrain the transition zone to initiate between the offshore slope and the southwest Los Angeles Basin. If the Inner Borderland crust is 22 km thick, then the transition zone is constrained to initiate within a 2 km wide region beneath the southwest Los Angeles Basin, and have a width of 20–25 km. The strong, coherent, and continuous Pn phase suggests the Moho is coherent and laterally continuous beneath the Inner Borderland and transition zone. The Inner California Borderland seems to be modified and thickened oceanic crust, with the oceanic upper mantle intact beneath it
Automated detection of filaments in the large scale structure of the universe
We present a new method to identify large scale filaments and apply it to a
cosmological simulation. Using positions of haloes above a given mass as node
tracers, we look for filaments between them using the positions and masses of
all the remaining dark-matter haloes. In order to detect a filament, the first
step consists in the construction of a backbone linking two nodes, which is
given by a skeleton-like path connecting the highest local dark matter (DM)
density traced by non-node haloes. The filament quality is defined by a density
and gap parameters characterising its skeleton, and filament members are
selected by their binding energy in the plane perpendicular to the filament.
This membership condition is associated to characteristic orbital times;
however if one assumes a fixed orbital timescale for all the filaments, the
resulting filament properties show only marginal changes, indicating that the
use of dynamical information is not critical for the method. We test the method
in the simulation using massive haloes(h) as
filament nodes. The main properties of the resulting high-quality filaments
(which corresponds to of the detected filaments) are, i) their
lengths cover a wide range of values of up to hMpc, but are mostly
concentrated below 50hMpc; ii) their distribution of thickness peaks at
hMpc and increases slightly with the filament length; iii) their
nodes are connected on average to filaments for nodes; this number increases with the node mass to filaments for nodes.Comment: 17 pages, 13 figures, MNRAS Accepte
Random walks on temporal networks
Many natural and artificial networks evolve in time. Nodes and connections
appear and disappear at various timescales, and their dynamics has profound
consequences for any processes in which they are involved. The first empirical
analysis of the temporal patterns characterizing dynamic networks are still
recent, so that many questions remain open. Here, we study how random walks, as
paradigm of dynamical processes, unfold on temporally evolving networks. To
this aim, we use empirical dynamical networks of contacts between individuals,
and characterize the fundamental quantities that impact any general process
taking place upon them. Furthermore, we introduce different randomizing
strategies that allow us to single out the role of the different properties of
the empirical networks. We show that the random walk exploration is slower on
temporal networks than it is on the aggregate projected network, even when the
time is properly rescaled. In particular, we point out that a fundamental role
is played by the temporal correlations between consecutive contacts present in
the data. Finally, we address the consequences of the intrinsically limited
duration of many real world dynamical networks. Considering the fundamental
prototypical role of the random walk process, we believe that these results
could help to shed light on the behavior of more complex dynamics on temporally
evolving networks.Comment: 14 pages, 13 figure
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