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 científicos disponíveis, seja por meio da coleta feita por diferentes senso- res, como por modelos matemáticos que geram inúmeras saídas 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