10,829 research outputs found
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
Near-Field Directionality Beyond the Dipole Approximation: Electric Quadrupole and Higher-Order Multipole Angular Spectra
Within the context of spin-related optical phenomena, the near-field
directionality is generally understood from the quantum spin Hall effect of
light, according to which the transverse spin of surface or guided modes is
locked to the propagation direction. So far, most previous works have been
focused on the spin properties of circularly polarized dipolar sources.
However, in near-field optics, higher-order multipole sources (e.g.,
quadrupole, octupole, and so on) might become relevant, so a more in-depth
formulation would be highly valuable. Building on the angular spectrum
representation, we provide a general, analytical, and ready-to-use treatment in
order to address the near-field directionality of any multipole field,
particularizing to the electric quadrupole case. Besides underpinning and
upgrading the current framework on spin-dependent directionality, our results
may open up new perspectives for engineering light-matter coupling at the
nanoscale.Comment: 7 pages, 2 figures. Supplemental Material (19 pages). Supplemental
tools (calculator of angular spectra and animation) available at
https://doi.org/10.5281/zenodo.267790
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
Is Gastronomy A Relevant Factor for Sustainable Tourism? An Empirical Analysis of Spain Country Brand
Tourism has become a fundamental industry for the economic growth of many countries. Due to this, there is growing competitiveness among the different destinations to attract as many tourists as possible. As a result, disciplines such as marketing have developed tools to differentiate some destinations from others and concepts such as place branding and country brand have emerged. One of the key factors forming the country brand is gastronomy, as food tourism is one way to reduce
the growing problem of sustainability in tourism, as it impacts different aspects of the countryâs environment. However, there is a great lack of scientific works that relate both variables. In this paper, we propose to establish that, in the case of Spain, touristsâ perception of Spanish gastronomy is a key element of its country brand. To do that, this study relies on the use of Partial Least Squares Structural Equations Modeling (PLS-SEM) using a 496 cases data set
Disorder-Induced First Order Transition and Curie Temperature Lowering in Ferromagnatic Manganites
We study the effect that size disorder in the cations surrounding manganese
ions has on the magnetic properties of manganites. This disorder is mimic with
a proper distribution of spatially disordered Manganese energies. Both, the
Curie temperature and the order of the transition are strongly affected by
disorder. For moderate disorder the Curie temperature decreases linearly with
the the variance of the distribution of the manganese site energies, and for a
disorder comparable to that present in real materials the transition becomes
first order. Our results provide a theoretical framework to understand disorder
effects on the magnetic behavior of manganites.Comment: 4 pages, three figures include
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