1,720,975 research outputs found
The scaling equation of state of the 3-D O(4) universality class RID G-1270-2010
No full textWe determine the scaling equation of state of the three-dimensional O(4) universality class, which is relevant for the finite-temperature transition of quantum chromodynamics with two light flavors. We first consider the small-field expansion of the effective potential (Helmholtz free energy). Then, we apply a systematic approximation scheme based on polynomial parametric representations that are valid in the whole critical regime, satisfy the correct analytic properties (Griffiths' analyticity), take into account the Goldstone singularities at the coexistence curve, and match the small-field expansion of the effective potential. From the approximate representations of the equation of state, we obtain estimates of several universal amplitude ratios
Strong-disorder paramagnetic-ferromagnetic fixed point in the square-lattice +- J Ising model
Full text linkWe consider the random-bond +- J Ising model on a square lattice as a
function of the temperature T and of the disorder parameter p (p=1 corresponds
to the pure Ising model). We investigate the critical behavior along the
paramagnetic-ferromagnetic transition line at low temperatures, below the
temperature of the multicritical Nishimori point at T*= 0.9527(1),
p*=0.89083(3). We present finite-size scaling analyses of Monte Carlo results
at two temperature values, T=0.645 and T=0.5. The results show that the
paramagnetic-ferromagnetic transition line is reentrant for T<T*, that the
transitions are continuous and controlled by a strong-disorder fixed point with
critical exponents nu=1.50(4) and eta=0.128(8), and beta = 0.095(5). This fixed
point is definitely different from the Ising fixed point controlling the
paramagnetic-ferromagnetic transitions for T>T*. Our results for the critical
exponents are consistent with the hyperscaling relation 2 beta/nu - eta = d - 2
= 0
Universal dependence on disorder of two-dimensional randomly diluted and random-bond +/- J Ising models
No full textCritical behavior of the three-dimensional +/- J Ising model at the paramagnetic-ferromagnetic transition line
No full textThe scaling equation of state of the three-dimensional O(N) universality class: N >= 4
No full textWe determine the critical equation of state of the three-dimensional O(N)
universality class, for N=4, 5, 6, 32, 64. The N=4 is relevant for the chiral
phase transition in QCD with two flavors, the N=5 model is relevant for the
SO(5) theory of high-T_c superconductivity, while the N=6 model is relevant for
the chiral phase transition in two-color QCD with two flavors. We first
consider the small-field expansion of the effective potential (Helmholtz free
energy). Then, we apply a systematic approximation scheme based on polynomial
parametric representations that are valid in the whole critical regime, satisfy
the correct analytic properties (Griffiths' analyticity), take into account the
Goldstone singularities at the coexistence curve, and match the small-field
expansion of the effective potential. From the approximate representations of
the equation of state, we obtain estimates of universal amplitude ratios. We
also compare our approximate solutions with those obtained in the large-N
expansion, up to order 1/N, finding good agreement for N \gtrsim 32
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Critical behavior of the random-anisotropy model in the strong-anisotropy limit
No full textWe investigate the nature of the critical behavior of the random-anisotropy
Heisenberg model (RAM), which describes a magnetic system with random uniaxial
single-site anisotropy, such as some amorphous alloys of rare earths and
transition metals. In particular, we consider the strong-anisotropy limit
(SRAM), in which the Hamiltonian can be rewritten as the one of an Ising
spin-glass model with correlated bond disorder. We perform Monte Carlo
simulations of the SRAM on simple cubic L^3 lattices, up to L=30, measuring
correlation functions of the replica-replica overlap, which is the order
parameter at a glass transition. The corresponding results show critical
behavior and finite-size scaling. They provide evidence of a finite-temperature
continuous transition with critical exponents and
. These results are close to the corresponding estimates that
have been obtained in the usual Ising spin-glass model with uncorrelated bond
disorder, suggesting that the two models belong to the same universality class.
We also determine the leading correction-to-scaling exponent finding
Critical and multicritical behavior of the +- J Ising model in two and three dimensions
No full textWe report our Monte Carlo results on the critical and multicritical behavior
of the +- J Ising model [with a random-exchange probability P(J_{xy}) = p
\delta(J_{xy} - J) + (1-p) \delta(J_{xy} + J)], in two and three dimensions. We
study the transition line between the paramagnetic and ferromagnetic phase,
which extends from p=1 to a multicritical (Nishimori) point. By a finite-size
scaling analysis, we provide strong numerical evidence that in three dimensions
the critical behavior along this line belongs to the same universality class as
that of the critical transition in the randomly dilute Ising model. In two
dimensions we confirm that the critical behavior is controlled by the pure
Ising fixed point and that disorder is marginally irrelevant, giving rise to
universal logarithmic corrections. In both two and three dimensions, we also
determine the location of the multicritical Nishimori point, as well as the
renormalization-group dimensions of the operators that control the
renormalization-group flow close to it
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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