Synchronized flutter of two slender flags

The interactions and synchronization of two parallel and slender flags in a uniform axial flow are studied in the present paper by generalizing Lighthill's Elongated Body Theory (EBT) and Lighthill's Large Amplitude Elongated Body Theory (LAEBT) to account for the hydrodynamic coupling between flags. The proposed method consists in two successive steps, namely the reconstruction of the flow created by a flapping flag within the LAEBT framework and the computation of the fluid force generated by this nonuniform flow on the second flag. In the limit of slender flags in close proximity, we show that the effect of the wakes have little influence on the long time coupled-dynamics and can be neglected in the modeling. This provides a simplified framework extending LAEBT to the coupled dynamics of two flags. Using this simplified model, both linear and large amplitude results are reported to explore the selection of the flapping regime as well as the dynamical properties of two side-by-side slender flags. Hydrodynamic coupling of the two flags is observed to destabilize the flags for most parameters, and to induce a long-term synchronization of the flags, either in-phase or out-of-phase.Comment: 14 pages, 10 figures, to appear in J. Fluid Mec

Electro-hydrodynamic synchronization of piezoelectric flags

Hydrodynamic coupling of flexible flags in axial flows may profoundly influence their flapping dynamics, in particular driving their synchronization. This work investigates the effect of such coupling on the harvesting efficiency of coupled piezoelectric flags, that convert their periodic deformation into an electrical current. Considering two flags connected to a single output circuit, we investigate using numerical simulations the relative importance of hydrodynamic coupling to electrodynamic coupling of the flags through the output circuit due to the inverse piezoelectric effect. It is shown that electrodynamic coupling is dominant beyond a critical distance, and induces a synchronization of the flags' motion resulting in enhanced energy harvesting performance. We further show that this electrodynamic coupling can be strengthened using resonant harvesting circuits.Comment: 14 pages, 10 figures, to appear in J. Fluids Struc

Field evidence of social influence in the expression of political preferences: the case of secessionist flags in Barcelona

Different models of social influence have explored the dynamics of social contagion, imitation, and diffusion of different types of traits, opinions, and conducts. However, few behavioral data indicating social influence dynamics have been obtained from direct observation in `natural' social contexts. The present research provides that kind of evidence in the case of the public expression of political preferences in the city of Barcelona, where thousands of citizens supporting the secession of Catalonia from Spain have placed a Catalan flag in their balconies. We present two different studies. 1) In July 2013 we registered the number of flags in 26% of the the city. We find that there is a large dispersion in the density of flags in districts with similar density of pro-independence voters. However, we find that the density of flags tends to be fostered in those electoral district where there is a clear majority of pro-independence vote, while it is inhibited in the opposite cases. 2) During 17 days around Catalonia's 2013 National Holiday we observed the position at balcony resolution of the flags displayed in the facades of 82 blocks. We compare the clustering of flags on the facades observed each day to equivalent random distributions and find that successive hangings of flags are not independent events but that a local influence mechanism is favoring their clustering. We also find that except for the National Holiday day the density of flags tends to be fostered in those facades where there is a clear majority of pro-independence vote.Comment: 27 pages, 13 figures, 2 table

Spherical multiple flags

For a reductive group G, the products of projective rational varieties homogeneous under G that are spherical for G have been classified by Stembridge. We consider the B-orbit closures in these spherical varieties and prove that under some mild restrictions they are normal, Cohen-Macaulay and have a rational resolution.Comment: 16 page

Classic and mirabolic Robinson-Schensted-Knuth correspondence for partial flags

In this paper we first generalize to the case of partial flags a result proved both by Spaltenstein and by Steinberg that relates the relative position of two complete flags and the irreducible components of the flag variety in which they lie, using the Robinson-Schensted-Knuth correspondence. Then we use this result to generalize the mirabolic Robinson-Schensted-Knuth correspondence defined by Travkin, to the case of two partial flags and a line.Comment: 27 pages, slightly rewritten to combine two papers into one and clarify some section

'Red flags of corruption'in world bank projects : an analysis of infrastructure contracts

"Red flags"are indicators of potential issues regarding governance failure, collusion or corruption in projects. While some specific red flags can be powerful indicators of issues to be addressed, the hypothesis of this paper is that many proposed red flags are potentially too ubiquitous and randomly distributed to be useful as indicators of significant governance failure. The paper examines project documentation from a small sample of World Bank water and sanitation projects in an attempt to collect data on the presence or absence of 13 commonly accepted red flags. This paper finds that: (i) almost every contract reviewed raised at least one of 13 red flags analyzed; (ii) potentially tainted contracts did not exhibit notably more red flags than control contracts; and (iii) the occurrence of multiple red flags in the same contract was rare enough to suggest that joint occurrence was largely by chance, not as a result of a strongly causal inter-relationship between flags. The ubiquity and apparent randomness of these red flags suggests that their roll-out as a monitoring tool requires additional thought as to interpretation, context and use. The paper examines an alternate tool for uncovering potential problem projects -- supplier concentration. Across a very small sample, there does appear to be a relationship between such concentration and potential problem projects.Post Conflict Reconstruction,Debt Markets,Government Procurement,Investment and Investment Climate,Literature&Folklore