120 research outputs found
A systematic comparison of supervised classifiers
Pattern recognition techniques have been employed in a myriad of industrial,
medical, commercial and academic applications. To tackle such a diversity of
data, many techniques have been devised. However, despite the long tradition of
pattern recognition research, there is no technique that yields the best
classification in all scenarios. Therefore, the consideration of as many as
possible techniques presents itself as an fundamental practice in applications
aiming at high accuracy. Typical works comparing methods either emphasize the
performance of a given algorithm in validation tests or systematically compare
various algorithms, assuming that the practical use of these methods is done by
experts. In many occasions, however, researchers have to deal with their
practical classification tasks without an in-depth knowledge about the
underlying mechanisms behind parameters. Actually, the adequate choice of
classifiers and parameters alike in such practical circumstances constitutes a
long-standing problem and is the subject of the current paper. We carried out a
study on the performance of nine well-known classifiers implemented by the Weka
framework and compared the dependence of the accuracy with their configuration
parameter configurations. The analysis of performance with default parameters
revealed that the k-nearest neighbors method exceeds by a large margin the
other methods when high dimensional datasets are considered. When other
configuration of parameters were allowed, we found that it is possible to
improve the quality of SVM in more than 20% even if parameters are set
randomly. Taken together, the investigation conducted in this paper suggests
that, apart from the SVM implementation, Weka's default configuration of
parameters provides an performance close the one achieved with the optimal
configuration
Accelerating networks
Evolving out-of-equilibrium networks have been under intense scrutiny
recently. In many real-world settings the number of links added per new node is
not constant but depends on the time at which the node is introduced in the
system. This simple idea gives rise to the concept of accelerating networks,
for which we review an existing definition and -- after finding it somewhat
constrictive -- offer a new definition. The new definition provided here views
network acceleration as a time dependent property of a given system, as opposed
to being a property of the specific algorithm applied to grow the network. The
defnition also covers both unweighted and weighted networks. As time-stamped
network data becomes increasingly available, the proposed measures may be
easily carried out on empirical datasets. As a simple case study we apply the
concepts to study the evolution of three different instances of Wikipedia,
namely, those in English, German, and Japanese, and find that the networks
undergo different acceleration regimes in their evolution.Comment: 12 pages, 8 figure
Fast Community Identification by Hierarchical Growth
A new method for community identification is proposed which is founded on the
analysis of successive neighborhoods, reached through hierarchical growth from
a starting vertex, and on the definition of communities as a subgraph whose
number of inner connections is larger than outer connections. In order to
determine the precision and speed of the method, it is compared with one of the
most popular community identification approaches, namely Girvan and Newman's
algorithm. Although the hierarchical growth method is not as precise as Girvan
and Newman's method, it is potentially faster than most community finding
algorithms.Comment: 6 pages, 5 figure
Structural constraints in complex networks
We present a link rewiring mechanism to produce surrogates of a network where
both the degree distribution and the rich--club connectivity are preserved. We
consider three real networks, the AS--Internet, the protein interaction and the
scientific collaboration. We show that for a given degree distribution, the
rich--club connectivity is sensitive to the degree--degree correlation, and on
the other hand the degree--degree correlation is constrained by the rich--club
connectivity. In particular, in the case of the Internet, the assortative
coefficient is always negative and a minor change in its value can reverse the
network's rich--club structure completely; while fixing the degree distribution
and the rich--club connectivity restricts the assortative coefficient to such a
narrow range, that a reasonable model of the Internet can be produced by
considering mainly the degree distribution and the rich--club connectivity. We
also comment on the suitability of using the maximal random network as a null
model to assess the rich--club connectivity in real networks.Comment: To appear in New Journal of Physics (www.njp.org
Analysis of microbial populations in Rusitec fermenters fed diets of variable composition
Trabajo presentado al : Joint Annual Meeting. ADSA-ASAS. Orlando Florida (USA), julio, 2015. T485Fermenters are widely used to study ruminal fermentation, but
infonnation on microbial populations developing in fermenters over
the incubation period is limited. Four Rusitec fermenters were fed
2 diets representative of those administered to dairy sheep (DAI;
50:50 alfalfa hay:concentrate) and fattening lambs (FAT; 15:85 barley
straw:concentrate) in a crossover design with 2 14-d incubation periods to assess the evolution of the microbial populations. There were 4
fermenters per diet. The fermenters received daily 30 g of diet DM and
samples from liquid (LIQ) and solid (SOL) digesta were taken on d 3,
8 and 14, and stored frozen at-80ÂȘC until DNA extraction. Concentrations ofbacterial and protozoal DNA and relative abundance offungi
and methanogenic archaea to total bacteria! DNA concentration were
detennined by real time PCR using previously validated primers and
DNA from bacteria and protozoa isolated from sheep rumen as standards. Data were analyzed as a mixed model with repeated measnres
using the PROC MlXED of SAS. The model included diet, incubation
nm, time, and diet x tin1e as fixed effects, and fermenter as a random
effect. Diet x sampling time interactions (P > 0.05) were detected for
bacteria! and protozoal DNA concentrations in both digesta phases. The
bacteria! DNA concentrations in SOL did not change (P = 0.002) over
the incubation period, whereas concentrations in LIQ increased (P <
0.001) by 1.5 and 1.8 times for DAI and FAT diets by the end ofthe
incubation, respectively. Protozoal DNA concentrations on d 14 were
37.8 and 8.0 times lower (P < 0.001; means across diets) than those on
d 3 for SOL and LIQ phases, respectively. Relative abundance offungi
decreased (P < 0.05) with time in both phases, and that ofmethanogenic archaea remain unchanged in LIQ and increased (P = 0.021) in
SOL. Concentration of bacteria! and protozoal DNA and the relative
abundance of methanogenic archaea were greater in the fermenters fed
the DAI diet (P < 0.05) compared with FAT diet. The results show that
microbial populations in Rusitec fermenters are affected by the incubated
diet and change over the incubation periodPeer reviewe
Can the evolution of music be analyzed in a quantitative manner?
We propose a methodology to study music development by applying multivariate
statistics on composers characteristics. Seven representative composers were
considered in terms of eight main musical features. Grades were assigned to
each characteristic and their correlations were analyzed. A bootstrap method
was applied to simulate hundreds of artificial composers influenced by the
seven representatives chosen. Afterwards we quantify non-numeric relations like
dialectics, opposition and innovation. Composers differences on style and
technique were represented as geometrical distances in the feature space,
making it possible to quantify, for example, how much Bach and Stockhausen
differ from other composers or how much Beethoven influenced Brahms. In
addition, we compared the results with a prior investigation on philosophy.
Opposition, strong on philosophy, was not remarkable on music. Supporting an
observation already considered by music theorists, strong influences were
identified between composers by the quantification of dialectics, implying
inheritance and suggesting a stronger master-disciple evolution when compared
to the philosophy analysis.Comment: 8 pages, 6 figures, added references for sections 1 and 4.C, better
mathematical description on section 2. New values and interpretation, now
considering a bootstrap metho
Human Computer Interactions in Next-Generation of Aircraft Smart Navigation Management Systems: Task Analysis and Architecture under an Agent-Oriented Methodological Approach
The limited efficiency of current air traffic systems will require a next-generation of Smart Air Traffic System (SATS) that relies on current technological advances. This challenge means a transition toward a new navigation and air-traffic procedures paradigm, where pilots and air traffic controllers perform and coordinate their activities according to new roles and technological supports. The design of new Human-Computer Interactions (HCI) for performing these activities is a key element of SATS. However efforts for developing such tools need to be inspired on a parallel characterization of hypothetical air traffic scenarios compatible with current ones. This paper is focused on airborne HCI into SATS where cockpit inputs came from aircraft navigation systems, surrounding traffic situation, controllers' indications, etc. So the HCI is intended to enhance situation awareness and decision-making through pilot cockpit. This work approach considers SATS as a system distributed on a large-scale with uncertainty in a dynamic environment. Therefore, a multi-agent systems based approach is well suited for modeling such an environment. We demonstrate that current methodologies for designing multi-agent systems are a useful tool to characterize HCI. We specifically illustrate how the selected methodological approach provides enough guidelines to obtain a cockpit HCI design that complies with future SATS specifications.This work was supported in part by Projects MINECO TEC2011-28626-C02-01/02, by program CENIT-ATLANTIDA (cofinanced by Indra and Boeing R&TE), and by ULPGC Precompetitive Research Project (ULPGC Own Program).Publicad
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