5,210 research outputs found
Composition law of cardinal order permutations
In this paper the theorems that determine composition laws for both cardinal
ordering permutations and their inverses are proven. So, the relative positions
of points in a hs-periodic orbit become completely known as well as in which
order those points are visited. No matter how a hs-periodic orbit emerges, be
it through a period doubling cascade (s=2^n) of the h-periodic orbit, or as a
primary window (like the saddle-node bifurcation cascade with h=2^n), or as a
secondary window (the birth of a periodic window inside the h-periodic
one). Certainly, period doubling cascade orbits are particular cases with h=2
and s=2^n. Both composition laws are also shown in algorithmic way for their
easy use
Discretization-related issues in the KPZ equation: Consistency, Galilean-invariance violation, and fluctuation--dissipation relation
In order to perform numerical simulations of the KPZ equation, in any
dimensionality, a spatial discretization scheme must be prescribed. The known
fact that the KPZ equation can be obtained as a result of a Hopf--Cole
transformation applied to a diffusion equation (with \emph{multiplicative}
noise) is shown here to strongly restrict the arbitrariness in the choice of
spatial discretization schemes. On one hand, the discretization prescriptions
for the Laplacian and the nonlinear (KPZ) term cannot be independently chosen.
On the other hand, since the discretization is an operation performed on
\emph{space} and the Hopf--Cole transformation is \emph{local} both in space
and time, the former should be the same regardless of the field to which it is
applied. It is shown that whereas some discretization schemes pass both
consistency tests, known examples in the literature do not. The requirement of
consistency for the discretization of Lyapunov functionals is argued to be a
natural and safe starting point in choosing spatial discretization schemes. We
also analyze the relation between real-space and pseudo-spectral discrete
representations. In addition we discuss the relevance of the Galilean
invariance violation in these consistent discretization schemes, and the
alleged conflict of standard discretization with the fluctuation--dissipation
theorem, peculiar of 1D.Comment: RevTex, 23pgs, 2 figures, submitted to Phys. Rev.
Ordering and finite-size effects in the dynamics of one-dimensional transient patterns
We introduce and analyze a general one-dimensional model for the description
of transient patterns which occur in the evolution between two spatially
homogeneous states. This phenomenon occurs, for example, during the
Freedericksz transition in nematic liquid crystals.The dynamics leads to the
emergence of finite domains which are locally periodic and independent of each
other. This picture is substantiated by a finite-size scaling law for the
structure factor. The mechanism of evolution towards the final homogeneous
state is by local roll destruction and associated reduction of local
wavenumber. The scaling law breaks down for systems of size comparable to the
size of the locally periodic domains. For systems of this size or smaller, an
apparent nonlinear selection of a global wavelength holds, giving rise to long
lived periodic configurations which do not occur for large systems. We also
make explicit the unsuitability of a description of transient pattern dynamics
in terms of a few Fourier mode amplitudes, even for small systems with a few
linearly unstable modes.Comment: 18 pages (REVTEX) + 10 postscript figures appende
Nuevos datos sobre la sucesión del "CXG" (Grupo das Beiras) : evidencia sedimentaria del origen glacioderivado de las facies conglomeráticas de la FM. del Cabeço das Popas, en la región de Monfortinho (Portugal Central)
La presencia de "dropstones" en las facies finas laminadas que se intercalan entre los orto y paraconglomerados característicos de la Fm. del Cabeço das opas
(CXG: Grupo das Beiras), prueba su origen glacioderivado. La edad véndica media-superior considerada para esta Fm. permite postular la existencia de
episodios glaciares postvarangerienses en el Macizo Hespérico
Viscoelastic behavior of a polyester resin concrete reinforced with nonmetallic bars under bending loads
This paper deals with the study of a highly durable polyester polymer concrete reinforced with glass fibre reinforced polymer rebars. The paper describes the properties of this specific concrete, which were tested using different experimental techniques such as porosimetry, scanning electron microscopy and petrography. Likewise, characterisation in a macro-scale was carried out to define the mechanical properties of the material (modulus of elasticity, stress-strain curve, ultimate strength and bond). Based on the latter properties, the paper presents a relatively simple method to estimate the ultimate bearing capacity of beams under bending load. The calculation method has been verified by testing beams and full-scale elements. At the end, and due to the viscoelastic nature of the polymer, several considerations will be made in order identify safety factors dependent on the loads nature: permanent loads (deferred deformations) and live loads.Peer ReviewedPostprint (author’s final draft
A systematic review of Twitter’s hashtags in public health: an example of a globally adopted standard
The objective is to find evidence and make recommendations on the use of Twitter in public health,particularly through
the study of hashtags(#). This systematic review shows the use of Twitter in different areas of public health: epidemiological surveillance, health promotion, health protection and disease prevention. Articles on this subject published in indexed journals with impact factor show the importance of conversations to engage the attention of Twitter users by using citations (@ user) and retweets(RT); however, not much importance seems to be given to the use of hashtags(#), which are often assimilated to the concept of keywords. Although tracking recurring hashtagsshould be less expensive than computing Twitter content, the potential of hashtaggeddata has not been properly exploited or recognized over the past years, probably due to the lack of efficient tools
Novel effects of strains in graphene and other two dimensional materials
The analysis of the electronic properties of strained or lattice deformed
graphene combines ideas from classical condensed matter physics, soft matter,
and geometrical aspects of quantum field theory (QFT) in curved spaces. Recent
theoretical and experimental work shows the influence of strains in many
properties of graphene not considered before, such as electronic transport,
spin-orbit coupling, the formation of Moir\'e patterns, optics, ... There is
also significant evidence of anharmonic effects, which can modify the
structural properties of graphene. These phenomena are not restricted to
graphene, and they are being intensively studied in other two dimensional
materials, such as the metallic dichalcogenides. We review here recent
developments related to the role of strains in the structural and electronic
properties of graphene and other two dimensional compounds.Comment: 75 pages, 15 figures, review articl
Product shape change by internal stresses
The design of a product component may require complex processing steps such as metal forming followed by a thermal treatment. The thermal treatment may improve the functional performance of the material itself, but may result in rather unwanted changes in the shape of the product. Here it is shown that Finite Element modeling of the various processes can assist in the design of a robust and accurate production process. The modeling approach presented allows a coupling between various complex material models, in such a way that full cold forming and thermal treatment processes are calculated. This coupling of material models is key for the design and concerns the novelty of the proposed approach. Cold forming by deep drawing is calculated whereby planar anisotropy is implemented. The thermal hardening treatment consists of three contributions: creep, thermal expansion and phase transformation. All models are based on experimental data, acquired from tensile and dilatometer tests, and are implemented into the material model either directly or by a simple fit. It is shown that the effects of a complete forming and heat treatment of a cup could be successfully calculated. The predicted cup shape change was compared to experiments, and shows excellent agreement.This research was carried out under the project number T63.3.12480 in the framework of the research program of the Materials innovation institute M2i, Delft, the Netherlands; and has been part of Press Perfect project, RFSR-CT-2012-00021 funded by the Research Fund for Coal & Steel.Peer Reviewe
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