5,459 research outputs found
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), copaÃba ( 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 municÃpio de Nova Ipixuna. No inventário foram encontrados 1.512 indivÃduos 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 indivÃduos/ha ± um desvio padrão, respectivamente) o que sugere seu manejo para a exploração sustentável de produtos florestais não-madeireiros. Uxi e copaÃba apresentaram baixas densidades (0,41±1,06 e 0,29±0,59 indivÃduos/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
- …