57,253 research outputs found
A comparative evaluation of interactive segmentation algorithms
In this paper we present a comparative evaluation of four popular interactive segmentation algorithms. The evaluation was carried out as a series of user-experiments, in which participants were tasked with extracting 100 objects from a common dataset: 25 with each algorithm, constrained within a time limit of 2 min for each object. To facilitate the experiments, a âscribble-drivenâ segmentation tool was developed to enable interactive image segmentation by simply marking areas of foreground and background with the mouse. As the participants refined and improved their respective segmentations, the corresponding updated segmentation mask was stored along with the elapsed time. We then collected and evaluated each recorded mask against a manually segmented ground truth, thus allowing us to gauge segmentation accuracy over time. Two benchmarks were used for the evaluation: the well-known Jaccard index for measuring object accuracy, and a new fuzzy metric, proposed in this paper, designed for measuring boundary accuracy. Analysis of the experimental results demonstrates the effectiveness of the suggested measures and provides valuable insights into the performance and characteristics of the evaluated algorithms
On the accuracy of language trees
Historical linguistics aims at inferring the most likely language
phylogenetic tree starting from information concerning the evolutionary
relatedness of languages. The available information are typically lists of
homologous (lexical, phonological, syntactic) features or characters for many
different languages.
From this perspective the reconstruction of language trees is an example of
inverse problems: starting from present, incomplete and often noisy,
information, one aims at inferring the most likely past evolutionary history. A
fundamental issue in inverse problems is the evaluation of the inference made.
A standard way of dealing with this question is to generate data with
artificial models in order to have full access to the evolutionary process one
is going to infer. This procedure presents an intrinsic limitation: when
dealing with real data sets, one typically does not know which model of
evolution is the most suitable for them. A possible way out is to compare
algorithmic inference with expert classifications. This is the point of view we
take here by conducting a thorough survey of the accuracy of reconstruction
methods as compared with the Ethnologue expert classifications. We focus in
particular on state-of-the-art distance-based methods for phylogeny
reconstruction using worldwide linguistic databases.
In order to assess the accuracy of the inferred trees we introduce and
characterize two generalizations of standard definitions of distances between
trees. Based on these scores we quantify the relative performances of the
distance-based algorithms considered. Further we quantify how the completeness
and the coverage of the available databases affect the accuracy of the
reconstruction. Finally we draw some conclusions about where the accuracy of
the reconstructions in historical linguistics stands and about the leading
directions to improve it.Comment: 36 pages, 14 figure
Orthogonal Multiple Access with Correlated Sources: Feasible Region and Pragmatic Schemes
In this paper, we consider orthogonal multiple access coding schemes, where
correlated sources are encoded in a distributed fashion and transmitted,
through additive white Gaussian noise (AWGN) channels, to an access point (AP).
At the AP, component decoders, associated with the source encoders, iteratively
exchange soft information by taking into account the source correlation. The
first goal of this paper is to investigate the ultimate achievable performance
limits in terms of a multi-dimensional feasible region in the space of channel
parameters, deriving insights on the impact of the number of sources. The
second goal is the design of pragmatic schemes, where the sources use
"off-the-shelf" channel codes. In order to analyze the performance of given
coding schemes, we propose an extrinsic information transfer (EXIT)-based
approach, which allows to determine the corresponding multi-dimensional
feasible regions. On the basis of the proposed analytical framework, the
performance of pragmatic coded schemes, based on serially concatenated
convolutional codes (SCCCs), is discussed
Interactions between financial and environmental networks in OECD countries
We analyse a multiplex of networks between OECD countries during the decade
2002-2010, which consists of five financial layers, given by foreign direct
investment, equity securities, short-term, long-term and total debt securities,
and five environmental layers, given by emissions of N O x, P M 10 SO 2, CO 2
equivalent and the water footprint associated with international trade. We
present a new measure of cross-layer correlations between flows in different
layers based on reciprocity. For the assessment of results, we implement a null
model for this measure based on the exponential random graph theory. We find
that short-term financial flows are more correlated with environmental flows
than long-term investments. Moreover, the correlations between reverse
financial and environmental flows (i.e. flows of different layers going in
opposite directions) are generally stronger than correlations between synergic
flows (flows going in the same direction). This suggests a trade-off between
financial and environmental layers, where, more financialised countries display
higher correlations between outgoing financial flows and incoming environmental
flows from lower financialised countries, which could have important policy
implications. Five countries are identified as hubs in this finance-environment
multiplex: The United States, France, Germany, Belgium-Luxembourg and the
United Kingdom.Comment: Supplementary Information provide
Asteroid flux towards circumprimary habitable zones in binary star systems: I. Statistical Overview
So far, multiple stellar systems harbor more than 130 extra solar planets.
Dynamical simulations show that the outcome of planetary formation process can
lead to various planetary architecture (i.e. location, size, mass and water
content) when the star system is single or double. In the late phase of
planetary formation, when embryo-sized objects dominate the inner region of the
system, asteroids are also present and can provide additional material for
objects inside the habitable zone (hereafter HZ). In this study, we make a
comparison of several binary star systems and their efficiency to move icy
asteroids from beyond the snow-line into orbits crossing the HZ. We modeled a
belt of 10000 asteroids (remnants from the late phase of planetary formation
process) beyond the snow-line. The planetesimals are placed randomly around the
primary star and move under the gravitational influence of the two stars and a
gas giant. As the planetesimals do not interact with each other, we divided the
belt into 100 subrings which were separately integrated. In this statistical
study, several double star configurations with a G-type star as primary are
investigated. Our results show that small bodies also participate in bearing a
non-negligible amount of water to the HZ. The proximity of a companion moving
on an eccentric orbit increases the flux of asteroids to the HZ, which could
result into a more efficient water transport on a short timescale, causing a
heavy bombardment. In contrast to asteroids moving under the gravitational
perturbations of one G-type star and a gas giant, we show that the presence of
a companion star can not only favor a faster depletion of our disk of
planetesimals but can also bring 4 -- 5 times more water into the whole HZ.Comment: Accepted for publication in A&
Modeling the International-Trade Network: A Gravity Approach
This paper investigates whether the gravity model (GM) can explain the
statistical properties of the International Trade Network (ITN). We fit data on
international-trade flows with a GM specification using alternative fitting
techniques and we employ GM estimates to build a weighted predicted ITN, whose
topological properties are compared to observed ones. Furthermore, we propose
an estimation strategy to predict the binary ITN with a GM. We find that the GM
successfully replicates the weighted-network structure of the ITN, only if one
fixes its binary architecture equal to the observed one. Conversely, the GM
performs very badly when asked to predict the presence of a link, or the level
of the trade flow it carries, whenever the binary structure must be
simultaneously estimated
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