45,421 research outputs found
Probing equilibrium glass flow up to exapoise viscosities
Glasses are out-of-equilibrium systems aging under the crystallization
threat. During ordinary glass formation, the atomic diffusion slows down
rendering its experimental investigation impractically long, to the extent that
a timescale divergence is taken for granted by many. We circumvent here these
limitations, taking advantage of a wide family of glasses rapidly obtained by
physical vapor deposition directly into the solid state, endowed with different
"ages" rivaling those reached by standard cooling and waiting for millennia.
Isothermally probing the mechanical response of each of these glasses, we infer
a correspondence with viscosity along the equilibrium line, up to exapoise
values. We find a dependence of the elastic modulus on the glass age, which,
traced back to temperature steepness index of the viscosity, tears down one of
the cornerstones of several glass transition theories: the dynamical
divergence. Critically, our results suggest that the conventional wisdom
picture of a glass ceasing to flow at finite temperature could be wrong.Comment: 4 figures and 1 supplementary figur
Considerations on bubble fragmentation models
n this paper we describe the restrictions that the probability density function (p.d.f.) of the size of particles resulting from the rupture of a drop or bubble must satisfy. Using conservation of volume, we show that when a particle of diameter, D0, breaks into exactly two fragments of sizes D and D2 = (D30âD3)1/3 respectively, the resulting p.d.f., f(D; D0), must satisfy a symmetry relation given by D22 f(D; D0) = D2 f(D2; D0), which does not depend on the nature of the underlying fragmentation process. In general, for an arbitrary number of resulting particles, m(D0), we determine that the daughter p.d.f. should satisfy the conservation of volume condition given by m(D0) â«0D0 (D/D0)3 f(D; D0) dD = 1. A detailed analysis of some contemporary fragmentation models shows that they may not exhibit the required conservation of volume condition if they are not adequately formulated. Furthermore, we also analyse several models proposed in the literature for the breakup frequency of drops or bubbles based on different principles, g(Ï”, D0). Although, most of the models are formulated in terms of the particle size D0 and the dissipation rate of turbulent kinetic energy, Ï”, and apparently provide different results, we show here that they are nearly identical when expressed in dimensionless form in terms of the Weber number, g*(Wet) = g(Ï”, D0) D2/30 Ï”â1/3, with Wet ~ Ï Ï”2/3 D05/3/Ï, where Ï is the density of the continuous phase and Ï the surface tension
Formation of corner waves in the wake of a partially submerged bluff body
We study theoretically and numerically the downstream flow near the corner of a bluff body partially submerged at a deadrise depth Îh into a uniform stream of velocity U, in the presence of gravity, g. When the Froude number, Fr=U/âgÎh, is large, a three-dimensional steady plunging wave, which is referred to as a corner wave, forms near the corner, developing downstream in a similar way to a two-dimensional plunging wave evolving in time. We have performed an asymptotic analysis of the flow near this corner to describe the wave's initial evolution and to clarify the physical mechanism that leads to its formation. Using the two-dimensions-plus-time approximation, the problem reduces to one similar to dam-break flow with a wet bed in front of the dam. The analysis shows that, at leading order, the problem admits a self-similar formulation when the size of the wave is small compared with the height difference Îh. The essential feature of the self-similar solution is the formation of a mushroom-shaped jet from which two smaller lateral jets stem. However, numerical simulations show that this self-similar solution is questionable from the physical point of view, as the two lateral jets plunge onto the free surface, leading to a self-intersecting flow. The physical mechanism leading to the formation of the mushroom-shaped structure is discussed
Automatic assessment of creativity in heuristic problem-solving based on query diversity
IndexaciĂłn: Web of Science; Scopus.Research, development and innovation are the pillars on which companies rely to offer new products and services capable of attracting consumer demand. This is why creative problem-solving emerges as one of the most relevant skills of the 21st century. Fortunately, there are many creativity training programs that have proven effective. However, many of these programs and methods base on a previous measurement of creativity and require experienced reviewers, they consume time for being manual, and they are far from everyday activities. In this study, we propose a model to estimate the creative quality of users' solutions dealing with heuristic problems, based on the automatic analysis of query patterns issued during the information search to solve the problem. This model has been able to predict the creative quality of solutions produced by 226 users, reaching a sensitivity of 78.43%. Likewise, the level of agreement among reviewers in relation to the creative characteristics is evaluated through two rubrics, and thereby, observing the difficulties of the manual evaluation: subjectivity and effort. The proposed model could be used to foster prompt detection of non-creative solutions and it could be implemented in diverse industrial processes that can range from the recruitment of talent to the evaluation of performance in R&D&I processes.https://www.revistadyna.com/search/automatic-assessment-of-creativity-in-heuristic-problem-solving-based-on-query-diversit
Pion's valence-quark GPD and its extension beyond DGLAP region
We briefly report on a recent computation, with the help of a fruitful
algebraic model, sketching the pion valence dressed-quark generalized parton
distribution and, very preliminary, discuss on a possible avenue to get
reliable results in both Dokshitzer-Gribov-Lipatov-Altarelli-Parisi (DGLAP) and
Efremov-Radyushkin-Brodsky-Lepage (ERBL) kinematial regions.Comment: 6 pages, 4 figures, contribution to 21st International conference on
Few-Body Problem
A brief comment on the similarities of the IR solutions for the ghost propagator DSE in Landau and Coulomb gauges
This brief note is devoted to reconcile the conclusions from a recent
analysis of the IR solutions for the ghost propagator Dyson-Schwinger equations
in Coulomb gauge with previous studies in Landau gauge.Comment: 4 pages, 1 figur
A generalization of the cumulant expansion. Application to a scale-invariant probabilistic model
As well known, cumulant expansion is an alternative way to moment expansion
to fully characterize probability distributions provided all the moments exist.
If this is not the case, the so called escort mean values (or q-moments) have
been proposed to characterize probability densities with divergent moments [C.
Tsallis et al, J. Math. Phys 50, 043303 (2009)]. We introduce here a new
mathematical object, namely the q-cumulants, which, in analogy to the
cumulants, provide an alternative characterization to that of the q-moments for
the probability densities. We illustrate this new scheme on a recently proposed
family of scale-invariant discrete probabilistic models [A. Rodriguez et al, J.
Stat. Mech. (2008) P09006; R. Hanel et al, Eur. Phys. J. B 72, 263268 (2009)]
having q-Gaussians as limiting probability distributions
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