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

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

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

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

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

Characterization of phenolic composition in tropical wines of altitude in the Northeast of Brazil.

The objective of this study was to evaluate the phenolic composition of red wines made from grapes cultivated in tropical region of altitude at 1,100 meters, in the Northeast of Brazil

Characterization of phenolic composition in tropical wines of altitude in the Northeast of Brazil.

The objective of this study was to evaluate the phenolic composition of red wines made from grapes cultivated in tropical region of altitude at 1,100 meters, in the Northeast of Brazil.BIO Web of Conferences, v. 7, p. 02014, 2016

Estrutura populacional de espécies de interesse florestal não-madeireiro no Sudeste do Pará, Brasil.

O trabalho descreve a estrutura populacional de cinco espécies com potencial para a exploração sustentável de produtos florestais não-madeireiros na região Sudeste do estado do Pará, Brasil. As espécies, naturalmente comuns na região foram: castanha-do-pará ( Bertholletia excelsa Bonpl. - Lecythidaceae), andiroba ( Carapa guianensis Aubl. - Meliaceae), copaíba ( Copaifera sp. - Fabaceae), uxi ( Endopleura uchi [Huber] Cuatrec. - Humiriaceae) e cupuaçu ( Theobroma grandiflorum [Willd. ex Spreng.] K. Schum. - Sterculiaceae). As cinco espécies foram estudadas em 17 parcelas de um hectare (20m x 500m) num assentamento agroextrativista no município de Nova Ipixuna. No inventário foram encontrados 1.512 indivíduos em 109 morfoespécies com DAP?25cm onde se calculou a densidade, área basal e o volume estimado. Castanha-do-pará, andiroba e cupuaçu mostraram altas densidades (2,53±1,37; 2,76±2,17 e 2,12±1,90 indivíduos/ha ± um desvio padrão, respectivamente) o que sugere seu manejo para a exploração sustentável de produtos florestais não-madeireiros. Uxi e copaíba apresentaram baixas densidades (0,41±1,06 e 0,29±0,59 indivíduos/ha, respectivamente), o que não permite sugerir uma forma de manejo economicamente viável. Quanto à distribuição diamétrica, apenas andiroba apresentou uma distribuição em forma de J-reverso