763 research outputs found
Press forming a 0/90 cross-ply advanced thermoplastic composite using the double-dome benchmark geometry
A pre-consolidated thermoplastic advanced composite cross-ply sheet comprised of two uniaxial plies orientated at 0/90° has been thermoformed using tooling based on the double-dome bench-mark geometry. Mitigation of wrinkling was achieved using springs to apply tension to the forming sheet rather than using a friction-based blank-holder. The shear angle across the surface of the formed geometry has been measured and compared with data collected previously from experiments on woven engineering fabrics. The shear behaviour of the material has been characterised as a function of rate and temperature using the picture frame shear test technique. Multi-scale modelling predictions of the material’s shear behaviour have been incorporated in finite element forming predictions; the latter are compared against the experimental results
Consequences of the H-Theorem from Nonlinear Fokker-Planck Equations
A general type of nonlinear Fokker-Planck equation is derived directly from a
master equation, by introducing generalized transition rates. The H-theorem is
demonstrated for systems that follow those classes of nonlinear Fokker-Planck
equations, in the presence of an external potential. For that, a relation
involving terms of Fokker-Planck equations and general entropic forms is
proposed. It is shown that, at equilibrium, this relation is equivalent to the
maximum-entropy principle. Families of Fokker-Planck equations may be related
to a single type of entropy, and so, the correspondence between well-known
entropic forms and their associated Fokker-Planck equations is explored. It is
shown that the Boltzmann-Gibbs entropy, apart from its connection with the
standard -- linear Fokker-Planck equation -- may be also related to a family of
nonlinear Fokker-Planck equations.Comment: 19 pages, no figure
Chaos edges of -logistic maps: Connection between the relaxation and sensitivity entropic indices
Chaos thresholds of the -logistic maps are numerically analysed at accumulation points of cycles 2, 3
and 5. We verify that the nonextensive -generalization of a Pesin-like
identity is preserved through averaging over the entire phase space. More
precisely, we computationally verify , where the entropy (), the sensitivity to the initial
conditions , and
(). The entropic index
depend on
both and the cycle. We also study the relaxation that occurs if we start
with an ensemble of initial conditions homogeneously occupying the entire phase
space. The associated Lebesgue measure asymptotically decreases as
(). These results led to (i) the first
illustration of the connection (conjectured by one of us) between sensitivity
and relaxation entropic indices, namely , where the positive numbers depend on the
cycle; (ii) an unexpected and new scaling, namely ( for , and for ).Comment: 5 pages, 5 figure
Influence of Refractory Periods in the Hopfield model
We study both analytically and numerically the effects of including
refractory periods in the Hopfield model for associative memory. These periods
are introduced in the dynamics of the network as thresholds that depend on the
state of the neuron at the previous time. Both the retrieval properties and the
dynamical behaviour are analyzed.Comment: Revtex, 7 pages, 7 figure
Quantum group invariant, nonextensive quantum statistical mechanics
We study the consequences of introducing quantum group invariance in the
formalism of nonextensive quantum statistical mechanics.
We find that the corresponding thermodynamical system is equivalent to a
Bose-Einstein gas in the Boltzmann-Gibbs formalism with a higher critical
temperature than the standard Bose-Einstein case.Comment: Revtex file, 6 pages, one figure. The original article has been
expanded to include some additional comments, one figure and a discussion
regarding the critical temperature. One reference adde
Construction of coherent states for physical algebraic systems
We construct a general state which is an eigenvector of the annihilation
operator of the Generalized Heisenberg Algebra. We show for several systems,
which are characterized by different energy spectra, that this general state
satisfies the minimal set of conditions required to obtain Klauder's minimal
coherent states.Comment: 15 pages, 3 figure
On a generalised model for time-dependent variance with long-term memory
The ARCH process (R. F. Engle, 1982) constitutes a paradigmatic generator of
stochastic time series with time-dependent variance like it appears on a wide
broad of systems besides economics in which ARCH was born. Although the ARCH
process captures the so-called "volatility clustering" and the asymptotic
power-law probability density distribution of the random variable, it is not
capable to reproduce further statistical properties of many of these time
series such as: the strong persistence of the instantaneous variance
characterised by large values of the Hurst exponent (H > 0.8), and asymptotic
power-law decay of the absolute values self-correlation function. By means of
considering an effective return obtained from a correlation of past returns
that has a q-exponential form we are able to fix the limitations of the
original model. Moreover, this improvement can be obtained through the correct
choice of a sole additional parameter, . The assessment of its validity
and usefulness is made by mimicking daily fluctuations of SP500 financial
index.Comment: 6 pages, 4 figure
Correlation functions in the factorization approach of nonextensive quantum statistics
We study the long range behavior of a gas whose partition function depends on
a parameter q and it has been claimed to be a good approximation to the
partition function proposed in the formulation of nonextensive statistical
mechanics. We compare our results, at large temperatures and at the critical
point, with the case of Boltzmann-Gibbs thermodynamics for the case of a
Bose-Einstein gas. In particular, we find that for all temperatures the long
range correlations in a Bose gas decrease when the value of q departs from the
standard value q=1.Comment: revtex file, 10 pages, two eps style figures, packaged as a single
tar.gz fil
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