5,914 research outputs found
Inflations of ideal triangulations
Starting with an ideal triangulation of the interior of a compact 3-manifold
M with boundary, no component of which is a 2-sphere, we provide a
construction, called an inflation of the ideal triangulation, to obtain a
strongly related triangulations of M itself. Besides a step-by-step algorithm
for such a construction, we provide examples of an inflation of the
two-tetrahedra ideal triangulation of the complement of the figure-eight knot
in the 3-sphere, giving a minimal triangulation, having ten tetrahedra, of the
figure-eight knot exterior. As another example, we provide an inflation of the
one-tetrahedron Gieseking manifold giving a minimal triangulation, having seven
tetrahedra, of a nonorientable compact 3-manifold with Klein bottle boundary.
Several applications of inflations are discussed.Comment: 48 pages, 45 figure
Euler characteristic and quadrilaterals of normal surfaces
Let be a compact 3-manifold with a triangulation . We give an
inequality relating the Euler characteristic of a surface normally embedded
in with the number of normal quadrilaterals in . This gives a relation
between a topological invariant of the surface and a quantity derived from its
combinatorial description. Secondly, we obtain an inequality relating the
number of normal triangles and normal quadrilaterals of , that depends on
the maximum number of tetrahedrons that share a vertex in .Comment: 7 pages, 1 figur
On the unsteady behavior of turbulence models
Periodically forced turbulence is used as a test case to evaluate the
predictions of two-equation and multiple-scale turbulence models in unsteady
flows. The limitations of the two-equation model are shown to originate in the
basic assumption of spectral equilibrium. A multiple-scale model based on a
picture of stepwise energy cascade overcomes some of these limitations, but the
absence of nonlocal interactions proves to lead to poor predictions of the time
variation of the dissipation rate. A new multiple-scale model that includes
nonlocal interactions is proposed and shown to reproduce the main features of
the frequency response correctly
Studies of iron impurities in YxPr1-xBa2Cu3O7-delta
Pr is the only rare earth which, when substituted for Y in YBa2Cu3O7, significantly alters the superconducting transition temperature T(sub c) without changing the crystal structure. For YxPr1-xBa2Cu3O7-delta with delta approx. equal to 0, T(sub c) is reduced rapidly as x is increased, reaching zero for x about 0.5. For x above 0.5 the compound is antiferromagnetic with a Neel temperature that increases with increasing x, rising to above room temperature for x near 1. A similar behavior is observed when the oxygen deficit delta is increased from zero to 1 with x=0. For the case of Pr substitution, the drop in T(sub c) is believed due to magnetic interactions. For the case of varying delta with x=0, the drop can be attributed to a combination of magnetic interactions, band filling, and changes in crystal structure. To study these effects, the Mossbauer effect of 57 Fe atoms substituted for the Cu atoms has been observed as a function of delta, x, and temperature. The observed spectra are all well described by a two quadrupole-split pairs, a central singlet, and a six-line magnetic hyperfine field pattern. For several Pr compositions both delta and temperature were varied, and the results support the hypothesis that a magnetic interaction exists between the Fe in the Cu lattice and the substitutional Pr atoms
Phase transition in nanomagnetite
Recently, the application of nanosized magnetite particles became an area of growing interest for
their potential practical applications. Nanosized magnetite samples of 36 and 9 nm sizes were
synthesized. Special care was taken on the right stoichiometry of the magnetite particles. Mössbauer
spectroscopy measurements were made in 4.2–300 K temperature range. The temperature
dependence of the intensities of the spectral components indicated size dependent transition taking
place in a broad temperature range. For nanosized samples, the hyperfine interaction values and their
relative intensities changed above the Verwey transition temperature value of bulk megnetite. The
continuous transition indicated the formation of dendritelike granular assemblies formed during the
preparation of the samples
Dynamic multilateral markets
We study dynamic multilateral markets, in which players' payoffs result from intra-coalitional bargaining. The latter is modeled as the ultimatum game with exogenous (time-invariant) recognition probabilities and unanimity acceptance rule. Players in agreeing coalitions leave the market and are replaced by their replicas, which keeps the pool of market participants constant over time. In this infinite game, we establish payoff uniqueness of stationary equilibria and the emergence of endogenous cooperation structures when traders experience some degree of (heterogeneous) bargaining frictions. When we focus on market games with different player types, we derive, under mild conditions, an explicit formula for each type's equilibrium payoff as the market frictions vanish
Generating multimedia presentations: from plain text to screenplay
In many Natural Language Generation (NLG) applications, the output is limited to plain text – i.e., a string of words with punctuation and paragraph breaks, but no indications for layout, or pictures, or dialogue. In several projects, we have begun to explore NLG applications in which these extra media are brought into play. This paper gives an informal account of what we have learned. For coherence, we focus on the domain of patient information leaflets, and follow an example in which the same content is expressed first in plain text, then in formatted text, then in text with pictures, and finally in a dialogue script that can be performed by two animated agents. We show how the same meaning can be mapped to realisation patterns in different media, and how the expanded options for expressing meaning are related to the perceived style and tone of the presentation. Throughout, we stress that the extra media are not simple added to plain text, but integrated with it: thus the use of formatting, or pictures, or dialogue, may require radical rewording of the text itself
Static and dynamic properties of large polymer melts in equilibrium
We present a detailed study of the static and dynamic behavior of long
semiflexible polymer chains in a melt. Starting from previously obtained fully
equilibrated high molecular weight polymer melts [{\it Zhang et al.} ACS Macro
Lett. 3, 198 (2014)] we investigate their static and dynamic scaling behavior
as predicted by theory. We find that for semiflexible chains in a melt, results
of the mean square internal distance, the probability distributions of the
end-to-end distance, and the chain structure factor are well described by
theoretical predictions for ideal chains. We examine the motion of monomers and
chains by molecular dynamics simulations using the ESPResSo++ package. The
scaling predictions of the mean squared displacement of inner monomers, center
of mass, and relations between them based on the Rouse and the reptation theory
are verified, and related characteristic relaxation times are determined.
Finally we give evidence that the entanglement length as determined
by a primitive path analysis (PPA) predicts a plateau modulus,
, consistent with stresses obtained from the
Green-Kubo relation. These comprehensively characterized equilibrium
structures, which offer a good compromise between flexibility, small ,
computational efficiency, and small deviations from ideality provide ideal
starting states for future non-equilibrium studies.Comment: 13 pages, 10 figures, to be published in J. Chem. Phys. (2016
Universality of the Gunn effect: self-sustained oscillations mediated by solitary waves
The Gunn effect consists of time-periodic oscillations of the current flowing
through an external purely resistive circuit mediated by solitary wave dynamics
of the electric field on an attached appropriate semiconductor. By means of a
new asymptotic analysis, it is argued that Gunn-like behavior occurs in
specific classes of model equations. As an illustration, an example related to
the constrained Cahn-Allen equation is analyzed.Comment: 4 pages,3 Post-Script figure
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