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 Δh into a uniform stream of velocity U, in the presence of gravity, g. When the Froude number, Fr=U/√gΔh, 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 Δh. 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

Discourse Markers and Modal Expressions in Speakers with and without Asperger Syndrome: A Pragmatic-Perceptive Approach

From a theoretical point of view, this paper offers a new framework for the analysis of discourse markers: a pragmatic-perceptive model that emphasizes the point of the communication process in which such particles become more relevant. Furthermore, this approach tries to give an account of the modal expressions (attenuators and intensifiers) that speakers use in oral speech. The quotients of absolute and relative frequency with regard to the use of textual, interactive and enunciative markers - focused on the message, the addressee and the addresser respectively - are compared in two samples of 20 subjects with typical development and other 20 with Asperger syndrome. The general results of this research suggest that these latter speakers display a suitable command of textual markers, whereas they overexploit the enunciative ones in conversation

Polydispersity Effects in the Dynamics and Stability of Bubbling Flows

The occurrence of swarms of small bubbles in a variety of industrial systems enhances their performance. However, the effects that size polydispersity may produce on the stability of kinematic waves, the gain factor, mean bubble velocity, kinematic and dynamic wave velocities is, to our knowledge, not yet well established. We found that size polydispersity enhances the stability of a bubble column by a factor of about 23% as a function of frequency and for a particular type of bubble column. In this way our model predicts effects that might be verified experimentally but this, however, remain to be assessed. Our results reinforce the point of view advocated in this work in the sense that a description of a bubble column based on the concept of randomness of a bubble cloud and average properties of the fluid motion, may be a useful approach that has not been exploited in engineering systems.Comment: 11 pages, 2 figures, presented at the 3rd NEXT-SigmaPhi International Conference, 13-18 August, 2005, Kolymbari, Cret

On the Randi\'{c} index and conditional parameters of a graph

The aim of this paper is to study some parameters of simple graphs related with the degree of the vertices. So, our main tool is the $n\times n$ matrix ${\cal A}$ whose ($i,j$)-entry is $$a_{ij}= \left\lbrace \begin{array}{ll} \frac{1}{\sqrt{\delta_i\delta_j}} & {\rm if }\quad v_i\sim v_j ; \\ 0 & {\rm otherwise,} \end{array} \right.$$ where $\delta_i$ denotes the degree of the vertex $v_i$. We study the Randi\'{c} index and some interesting particular cases of conditional excess, conditional Wiener index, and conditional diameter. In particular, using the matrix ${\cal A}$ or its eigenvalues, we obtain tight bounds on the studied parameters.Comment: arXiv admin note: text overlap with arXiv:math/060243

Downlink beamforming for cellular mobile communications

A new technique for downlink transmission beamformer design in cellular mobile communications systems using an antenna array at the base station is presented. The method is based on estimation of an underlying spatial distribution associated with each source's spatial downlink channel. The algorithm isPeer ReviewedPostprint (published version

On the impact of exchange rate regimes on tourism

The main objective of this paper is to analyze the effect of the exchange rate arrangements on international tourism. The ambiguity of literature about the effect of exchange rate volatility contrasts with the magnitude of the impact of a common currency on trade. On the basis of a gravity equation we estimate a moderate effect of a currency union on tourism of almost 12%. Furthermore, we estimate a gravity equation for international trade, obtaining that the common currency effect on trade is reduced when tourism is introduced as a regressor. This suggests that tourism flows may contribute to explain the excessive magnitude of the estimated effect of a common currency on trade in this literature. Finally, we analyze the impact of several de facto exchange rate arrangements on tourism, finding that less flexible exchange rates promotes tourism flows.Tourism, Exchange Rate Regime, Common Currency