3,234 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
Modeling the input history of programs for improved instruction-memory performance
When a program is loaded into memory for execution, the relative position of
its basic blocks is crucial, since loading basic blocks that are unlikely to be
executed first places them high in the instruction-memory hierarchy only to be
dislodged as the execution goes on. In this paper we study the use of Bayesian
networks as models of the input history of a program. The main point is the
creation of a probabilistic model that persists as the program is run on
different inputs and at each new input refines its own parameters in order to
reflect the program's input history more accurately. As the model is thus
tuned, it causes basic blocks to be reordered so that, upon arrival of the next
input for execution, loading the basic blocks into memory automatically takes
into account the input history of the program. We report on extensive
experiments, whose results demonstrate the efficacy of the overall approach in
progressively lowering the execution times of a program on identical inputs
placed randomly in a sequence of varied inputs. We provide results on selected
SPEC CINT2000 programs and also evaluate our approach as compared to the gcc
level-3 optimization and to Pettis-Hansen reordering
Non-Hermitian Hamiltonians of Lie algebraic type
We analyse a class of non-Hermitian Hamiltonians, which can be expressed
bilinearly in terms of generators of a sl(2,R)-Lie algebra or their isomorphic
su(1,1)-counterparts. The Hamlitonians are prototypes for solvable models of
Lie algebraic type. Demanding a real spectrum and the existence of a well
defined metric, we systematically investigate the constraints these
requirements impose on the coupling constants of the model and the parameters
in the metric operator. We compute isospectral Hermitian counterparts for some
of the original non-Hermitian Hamiltonian. Alternatively we employ a
generalized Bogoliubov transformation, which allows to compute explicitly real
energy eigenvalue spectra for these type of Hamiltonians, together with their
eigenstates. We compare the two approaches.Comment: 27 page
Sorgo para pastejo/corte e cobertura do solo no período de outono/inverno (safrinha) em Mato Grosso do Sul.
Em Mato Grosso do Sul, as principais culturas utilizadas para cobertura de solo na safrinha são o milheto, a aveia e o nabo (Hernani et al., 1995; Machado, 2003). Para pastejo, também são utilizadas essas espécies, com exceção do nabo. Devido ao risco de geadas, as espécies adaptadas ao clima frio, como a aveia e o nabo, são mais utilizadas na região sul do Estado. Na região norte, o milheto e o sorgo são mais produtivos no período de outono, porque o clima, apesar de seco, é quente, favorecendo as espécies tropicais. Em regiões com esta condição, o sorgo é muito utilizado para a produção de grãos, sendo recente sua utilização para a produção de palha e forragem. Pela sua tolerância a déficit hídrico e a baixas temperaturas, a cultura vem ganhando importância econômica no Estado. Este estudo teve como objetivo selecionar genótipos de sorgo para pastejo na safra de outono/inverno, em sucessão a soja.bitstream/item/38771/1/BP-200416.pd
Aspectos fenológicos de Hibiscus sabdariff L. (Malvaceae).
A espécie Hibiscus sabdariffa L., pertencente à família Malvaceae, popularmente conhecida como vinagreira possui inúmeras propriedades terapêuticas já comprovadas cientificamente como antioxidante, antiescorbútico, diurético, anti-hipertensivo, antirreumático e antimicrobiano. O trabalho teve como objetivo caracterizar aspectos da fenologia de H. sabdariffa cultivada no horto de plantas medicinais da Embrapa Amazônia Oriental durante o período de 2010 a 2011. Foram observados diariamente cinco indivíduos organizados para demonstração mensal a partir de registro de presença ou ausência da fenofase. Os dados registrados mostraram que no ano de 2010 ocorreu floração em seis meses, sendo em fevereiro registrada a maior frequência com 14 dias. Já no ano de 2011 a floração ocorreu somente em três meses a maior frequência foi observada em setembro com 21 dias e a menor no mês de outubro com 18 dias. Não houve ocorrência de frutificação para os dois anos
Loop variables in the geometry of a rotating black string
In this paper we analyze in the Wilson loop context the parallel transport of
vectors and spinors around a closed loop in the background space-time of a
rotating black string in order to classify its global properties. We also
examine particular closed orbits in this space-time and verify the Mandelstam
relations.Comment: 14 pages, iopart styl
Metric operators for non-Hermitian quadratic su(2) Hamiltonians
A class of non-Hermitian quadratic su(2) Hamiltonians having an anti-linear
symmetry is constructed. This is achieved by analysing the possible symmetries
of such systems in terms of automorphisms of the algebra. In fact, different
realisations for this type of symmetry are obtained, including the natural
occurrence of charge conjugation together with parity and time reversal. Once
specified the underlying anti-linear symmetry of the Hamiltonian, the former,
if unbroken, leads to a purely real spectrum and the latter can be mapped to a
Hermitian counterpart by, amongst other possibilities, a similarity
transformation. Here, Lie-algebraic methods which were used to investigate the
generalised Swanson Hamiltonian are employed to identify the class of quadratic
Hamiltonians that allow for such a mapping to the Hermitian counterpart.
Whereas for the linear su(2) system every Hamiltonian of this type can be
mapped to a Hermitian counterpart by a transformation which is itself an
exponential of a linear combination of su(2) generators, the situation is more
complicated for quadratic Hamiltonians. Therefore, the possibility of more
elaborate similarity transformations, including quadratic exponents, is also
explored in detail. The existence of finite dimensional representations for the
su(2) Hamiltonian, as opposed to the su(1,1) studied before, allows for
comparison with explicit diagonalisation results for finite matrices. Finally,
the similarity transformations constructed are compared with the analogue of
Swanson's method for exact diagonalsation of the problem, establishing a simple
relation between both approaches.Comment: 25 pages, 6 figure
A spin chain model with non-Hermitian interaction: the Ising quantum spin chain in an imaginary field
We investigate a lattice version of the Yang-Lee model which is characterized by a non-Hermitian quantum spin chain Hamiltonian. We propose a new way to implement PT-symmetry on the lattice, which serves to guarantee the reality of the spectrum in certain regions of values of the coupling constants. In that region of unbroken PT-symmetry we construct a Dyson map, a metric operator and find the Hermitian counterpart of the Hamiltonian for small values of the number of sites, both exactly and perturbatively. Besides the standard perturbation theory about the Hermitian part of the Hamiltonian, we also carry out an expansion in the second coupling constant of the model. Our constructions turns out to be unique with the sole assumption that the Dyson map is Hermitian. Finally we compute the magnetization of the chain in the z and x direction
Práticas de controle de ferrugem da videira por fontes de resitência avaliadas em casa-de-vegetação.
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