2,120 research outputs found
Is your EPL attractive? Classification of publications through download statistics
Here we consider the download statistics of EPL publications. We find that
papers in the journal are characterised by fast accumulations of downloads
during the first couple of months after publication, followed by slower rates
thereafter, behaviour which can be represented by a model with predictive
power. We also find that individual papers can be classified in various ways,
allowing us to compare categories for open-access and non-open-access papers.
For example, for the latter publications, which comprise the bulk of EPL
papers, a small proportion (2%) display intense bursts of download activity,
possibly following an extended period of less remarkable behaviour. About 18%
have an especially high degree of attractiveness over and above what is typical
for the journal. One can also classify the ageing of attractiveness by
examining download half-lives. Approximately 18% have strong interest
initially, waning in time. A further 20% exhibit "delayed recognition" with
relatively late spurs in download activity. Although open-access papers enjoy
more downloads on average, the proportions falling into each category are
similar.Comment: 6 pages, 8 figures, accepted for publication in EP
The 13 November 1984 occultation of BD +08 deg 0471 by (1) Ceres
The 13 November 1984 occultation of BD +08 deg 0471 was discovered during a photographic search carried out with the 0.5 meter Carnegie Double Astrograph at Lick Observatory and the Lowell Observatory PDS microdensitometer. Such a search was stimulated by the curious fact that few favorably located occultations of AGK3 or SAO catalog starts by Ceres will occur during the 1980s. The occultation on 13 November, however, is a particularly good event. The star is 1000 cubic M in V, yielding a predicted drop at occultation of about 10%. Such a drop can be detected by small telescopes equipped with photoelectric photometers, but is too small to be seen visually. The track was predicted to cross the Caribbean, Florida, southern Texas, and Mexico. Based on this prediction, preparations were made to observe the event in Mexico using four portable occultation data systems
Investigating interaction-induced chaos using time-dependent density functional theory
Systems whose underlying classical dynamics are chaotic exhibit signatures of
the chaos in their quantum mechanics. We investigate the possibility of using
time-dependent density functional theory (TDDFT) to study the case when chaos
is induced by electron-interaction alone. Nearest-neighbour level-spacing
statistics are in principle exactly and directly accessible from TDDFT. We
discuss how the TDDFT linear response procedure can reveal the mechanism of
chaos induced by electron-interaction alone. A simple model of a two-electron
quantum dot highlights the necessity to go beyond the adiabatic approximation
in TDDFT.Comment: 8 pages, 4 figure
Long-term Tracking in the Wild: A Benchmark
We introduce the OxUvA dataset and benchmark for evaluating single-object
tracking algorithms. Benchmarks have enabled great strides in the field of
object tracking by defining standardized evaluations on large sets of diverse
videos. However, these works have focused exclusively on sequences that are
just tens of seconds in length and in which the target is always visible.
Consequently, most researchers have designed methods tailored to this
"short-term" scenario, which is poorly representative of practitioners' needs.
Aiming to address this disparity, we compile a long-term, large-scale tracking
dataset of sequences with average length greater than two minutes and with
frequent target object disappearance. The OxUvA dataset is much larger than the
object tracking datasets of recent years: it comprises 366 sequences spanning
14 hours of video. We assess the performance of several algorithms, considering
both the ability to locate the target and to determine whether it is present or
absent. Our goal is to offer the community a large and diverse benchmark to
enable the design and evaluation of tracking methods ready to be used "in the
wild". The project website is http://oxuva.netComment: To appear at ECCV 201
Electronic Control of Spin Alignment in pi-Conjugated Molecular Magnets
Intramolecular spin alignment in pi-conjugated molecules is studied
theoretically in a model of a Peierls-Hubbard chain coupled with two localized
spins. By means of the exact diagonalization technique, we demonstrate that a
spin singlet (S=0) to quartet (S=3/2) transition can be induced by electronic
doping, depending on the chain length, the positions of the localized spins,
and the sign of the electron-spin coupling. The calculated results provides a
theoretical basis for understanding the mechanism of spin alignment recently
observed in a diradical donor molecule.Comment: 4 pages, 4 figures, Physical Review Letters (in press
Quantifying the connectivity of a network: The network correlation function method
Networks are useful for describing systems of interacting objects, where the
nodes represent the objects and the edges represent the interactions between
them. The applications include chemical and metabolic systems, food webs as
well as social networks. Lately, it was found that many of these networks
display some common topological features, such as high clustering, small
average path length (small world networks) and a power-law degree distribution
(scale free networks). The topological features of a network are commonly
related to the network's functionality. However, the topology alone does not
account for the nature of the interactions in the network and their strength.
Here we introduce a method for evaluating the correlations between pairs of
nodes in the network. These correlations depend both on the topology and on the
functionality of the network. A network with high connectivity displays strong
correlations between its interacting nodes and thus features small-world
functionality. We quantify the correlations between all pairs of nodes in the
network, and express them as matrix elements in the correlation matrix. From
this information one can plot the correlation function for the network and to
extract the correlation length. The connectivity of a network is then defined
as the ratio between this correlation length and the average path length of the
network. Using this method we distinguish between a topological small world and
a functional small world, where the latter is characterized by long range
correlations and high connectivity. Clearly, networks which share the same
topology, may have different connectivities, based on the nature and strength
of their interactions. The method is demonstrated on metabolic networks, but
can be readily generalized to other types of networks.Comment: 10 figure
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The performance realities of massively parallel processors: A case study
This paper presents the results of an architectural comparison of SIMD massive parallelism, as implemented in the Thinking Machines Corp. CM-2 computer, and vector or concurrent-vector processing, as implemented in the Cray Research Inc. Y-MP/8. The comparison is based primarily upon three application codes that represent Los Alamos production computing. Tests were run by porting optimized CM Fortran codes to the Y-MP, so that the same level of optimization was obtained on both machines. The results for fully-configured systems, using measured data rather than scaled data from smaller configurations, show that the Y-MP/8 is faster than the 64k CM-2 for all three codes. A simple model that accounts for the relative characteristic computational speeds of the two machines, and reduction in overall CM-2 performance due to communication or SIMD conditional execution, is included. The model predicts the performance of two codes well, but fails for the third code, because the proportion of communications in this code is very high. Other factors, such as memory bandwidth and compiler effects, are also discussed. Finally, the paper attempts to show the equivalence of the CM-2 and Y-MP programming models, and also comments on selected future massively parallel processor designs
Topological interactions in systems of mutually interlinked polymer rings
The topological interaction arising in interlinked polymeric rings such as
DNA catenanes is considered. More specifically, the free energy for a pair of
linked random walk rings is derived where the distance between two segments
each of which is part of a different ring is kept constant. The topology
conservation is imposed by the Gauss invariant. A previous approach (M.Otto,
T.A. Vilgis, Phys.Rev.Lett. {\bf 80}, 881 (1998)) to the problem is refined in
several ways. It is confirmed, that asymptotically, i.e. for large
where is average size of single random walk ring, the effective
topological interaction (free energy) scales .Comment: 16 pages, 3 figur
Efficient Triangle Counting in Large Graphs via Degree-based Vertex Partitioning
The number of triangles is a computationally expensive graph statistic which
is frequently used in complex network analysis (e.g., transitivity ratio), in
various random graph models (e.g., exponential random graph model) and in
important real world applications such as spam detection, uncovering of the
hidden thematic structure of the Web and link recommendation. Counting
triangles in graphs with millions and billions of edges requires algorithms
which run fast, use small amount of space, provide accurate estimates of the
number of triangles and preferably are parallelizable.
In this paper we present an efficient triangle counting algorithm which can
be adapted to the semistreaming model. The key idea of our algorithm is to
combine the sampling algorithm of Tsourakakis et al. and the partitioning of
the set of vertices into a high degree and a low degree subset respectively as
in the Alon, Yuster and Zwick work treating each set appropriately. We obtain a
running time
and an approximation (multiplicative error), where is the number
of vertices, the number of edges and the maximum number of
triangles an edge is contained.
Furthermore, we show how this algorithm can be adapted to the semistreaming
model with space usage and a constant number of passes (three) over the graph
stream. We apply our methods in various networks with several millions of edges
and we obtain excellent results. Finally, we propose a random projection based
method for triangle counting and provide a sufficient condition to obtain an
estimate with low variance.Comment: 1) 12 pages 2) To appear in the 7th Workshop on Algorithms and Models
for the Web Graph (WAW 2010
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