7,232 research outputs found
Two novel evolutionary formulations of the graph coloring problem
We introduce two novel evolutionary formulations of the problem of coloring
the nodes of a graph. The first formulation is based on the relationship that
exists between a graph's chromatic number and its acyclic orientations. It
views such orientations as individuals and evolves them with the aid of
evolutionary operators that are very heavily based on the structure of the
graph and its acyclic orientations. The second formulation, unlike the first
one, does not tackle one graph at a time, but rather aims at evolving a
`program' to color all graphs belonging to a class whose members all have the
same number of nodes and other common attributes. The heuristics that result
from these formulations have been tested on some of the Second DIMACS
Implementation Challenge benchmark graphs, and have been found to be
competitive when compared to the several other heuristics that have also been
tested on those graphs.Comment: To appear in Journal of Combinatorial Optimizatio
Time-Reversal Symmetry Breaking and Decoherence in Chaotic Dirac Billiards
In this work, we perform a statistical study on Dirac Billiards in the
extreme quantum limit (a single open channel on the leads). Our numerical
analysis uses a large ensemble of random matrices and demonstrates the
preponderant role of dephasing mechanisms in such chaotic billiards. Physical
implementations of these billiards range from quantum dots of graphene to
topological insulators structures. We show, in particular, that the role of
finite crossover fields between the universal symmetries quickly leaves the
conductance to the asymptotic limit of unitary ensembles. Furthermore, we show
that the dephasing mechanisms strikingly lead Dirac billiards from the extreme
quantum regime to the semiclassical Gaussian regime
Generation of higher derivatives operators and electromagnetic wave propagation in a Lorentz-violation scenario
We study the perturbative generation of higher-derivative operators as
corrections to the photon effective action, which are originated from a Lorentz
violation background. Such corrections are obtained, at one-loop order, through
the proper-time method, using the zeta function regularization. We focus over
the lowest order corrections and investigate their influence in the propagation
of electromagnetic waves through the vacuum, in the presence of a strong,
constant magnetic field. This is a setting of experimental relevance, since it
bases active efforts to measure non linear electromagnetic effects. After
surprising cancellations of Lorentz violating corrections to the Maxwell's
equation, we show that no effects of the kind of Lorentz violation we consider
can be detected in such a context.Comment: v2: 13 pages, no figures, section IV considerably rewritten, main
results unchanged and are now obtained in a simpler way. To appear in PL
Some Extended Classes of Distributions: Characterizations and Properties
Based on a simple relationship between two truncated moments and certain functions of the th order statistic, we characterize some extended classes of distributions recently proposed in the statistical literature, videlicet Beta-G, Gamma-G, Kumaraswamy-G and McDonald-G. Several properties of these extended classes and some special cases are discussed. We compare these classes in terms of goodness-of-fit criteria using some baseline distributions by means of two real data sets
Efficient Computation of Multiple Density-Based Clustering Hierarchies
HDBSCAN*, a state-of-the-art density-based hierarchical clustering method,
produces a hierarchical organization of clusters in a dataset w.r.t. a
parameter mpts. While the performance of HDBSCAN* is robust w.r.t. mpts in the
sense that a small change in mpts typically leads to only a small or no change
in the clustering structure, choosing a "good" mpts value can be challenging:
depending on the data distribution, a high or low value for mpts may be more
appropriate, and certain data clusters may reveal themselves at different
values of mpts. To explore results for a range of mpts values, however, one has
to run HDBSCAN* for each value in the range independently, which is
computationally inefficient. In this paper, we propose an efficient approach to
compute all HDBSCAN* hierarchies for a range of mpts values by replacing the
graph used by HDBSCAN* with a much smaller graph that is guaranteed to contain
the required information. An extensive experimental evaluation shows that with
our approach one can obtain over one hundred hierarchies for the computational
cost equivalent to running HDBSCAN* about 2 times.Comment: A short version of this paper appears at IEEE ICDM 2017. Corrected
typos. Revised abstrac
Leadership and turnover intentions in a public hospital: The mediating effect of organisational commitment and moderating effect by activity department
This research aimed to study the effect of leadership (transformational and transactional) on turnover intentions and whether this relationship is mediated by organisational commitment and moderated by the department of activity. To this end, it was hypothesized that: (1) leadership has a negative and significant association with turnover intentions; (2) leadership has a positive and significant association with affective organisational commitment; (3) organisational commitment has a negative and significant association with turnover intentions; (4) organisational commitment has a mediating effect on the relationship between leadership and turnover intentions; (5) the department to which the employee belongs has a moderating effect on the relationship between leadership and organisational turnover intentions. The sample consists of 477 participants working at the Hospital Professor Doutor Fernando Fonseca (HFF) in Portugal, performing their functions in several departments. This is a quantitative, correlational, and cross-sectional study. The results indicate that transformational leadership has a negative and significant effect on turnover intentions and a positive and significant effect on affective and normative commitment. Transactional leadership negatively and significantly affects all three components of organisational commitment. Affective and normative commitment has a negative and significant effect on turnover intentions. Calculative commitment has a positive and significant effect on turnover intentions. Affective commitment and calculative commitment have a partial mediating effect on the relationship between transformational leadership and organisational turnover intentions. The department to which the employee belongs does not have a moderating effect on the relationship between leadership and turnover intentions. It has been proven that leadership plays an extremely important role in the smooth running of this hospiinfo:eu-repo/semantics/publishedVersio
Lógica fuzzy aplicada à gerência de distribuição de carga em um grid de computadores.
Os avanços tecnológicos têm levado a um aumento no volume de dados cientÃficos disponÃveis, seja por meio da coleta feita por diferentes senso- res, como por modelos matemáticos que geram inúmeras saÃdas distintas. Especialmente nas pesquisas em mudanças climáticas, os especialistas têm que lidar com esse grande volume de dados, o que extrapola a capacidade do ser humano de cálculo e análise. Desta forma, o apoio computacional se torna fundamental para alavancar as pesquisas em diferentes áreas. Em busca de uma solução economicamente viável e ecologicamente correta para este problema, e que ainda pudesse ser compartilhada por diversos projetos na empresa, a equipe do projeto SCAF adotou a computação em grade
On the dual equivalence between self-dual and Maxwell-Chern-Simons models with Lorentz symmetry breaking
In this paper, we use gauge embedding procedure and master action approach to
establish the equivalence between the self-dual and Maxwell-Chern-Simons models
with Lorentz symmetry breaking. As a result, new kinds of Lorentz-breaking
terms arise.Comment: 14 pages, minor corrections, version accepted to Physical Review
Elementos estruturadores da quÃmica orgânica implÃcitos na argumentação de professor e alunos de graduação
Mullins (2008) propõe que o bom desempenho em tópicos de QuÃmica Orgânica seria consequência do domÃnio adequado de elementos fundamentais quais sejam, eletronegatividade, ligação covalente polar, efeito estérico, efeito indutivo, ressonância e aromaticidade pois teriam valor instrumental na resolução de tarefas. O presente trabalho tem como foco investigar como estes elementos estruturantes estão presentes na argumentação desenvolvida por alunos e professores de graduação sob a luz da psicologia cognitiva. Como resultado propomos a estereoquÃmica como mais um elemento estruturador ao modelo de Mullins
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