Turbulence Modulation by Slender Fibers

In this paper, we numerically investigate the turbulence modulation produced by long flexible fibres in channel flow. The simulations are based on an Euler–Lagrangian approach, where fibres are modelled as chains of constrained, sub-Kolmogorov rods. A novel algorithm is deployed to make the resolution of dispersed systems of constraint equations, which represent the fibres, compatible with a state-of-the-art, Graphics Processing Units-accelerated flow-solver for direct numerical simulations in the two-way coupling regime on High Performance Computing architectures. Two-way coupling is accounted for using the Exact Regularized Point Particle method, which allows to calculate the disturbance generated by the fibers on the flow considering progressively refined grids, down to a quasi-viscous length-scale. The bending stiffness of the fibers is also modelled, while collisions are neglected. Results of fluid velocity statistics for friction Reynolds number of the flow (Formula presented.) and fibers with Stokes number (Formula presented.) = 0.01 (nearly tracers) and 10 (inertial) are presented, with special regard to turbulence modulation and its dependence on fiber inertia and volume fraction (equal to (Formula presented.) · (Formula presented.) and (Formula presented.) · (Formula presented.)). The non-Newtonian stresses determined by the carried phase are also displayed, determined by long and slender fibers with fixed aspect ratio (Formula presented.), which extend up to the inertial range of the turbulent flow

The Renormalization of Non-Commutative Field Theories in the Limit of Large Non-Commutativity

We show that renormalized non-commutative scalar field theories do not reduce to their planar sector in the limit of large non-commutativity. This follows from the fact that the RG equation of the Wilson-Polchinski type which describes the genus zero sector of non-commutative field theories couples generic planar amplitudes with non-planar amplitudes at exceptional values of the external momenta. We prove that the renormalization problem can be consistently restricted to this set of amplitudes. In the resulting renormalized theory non-planar divergences are treated as UV divergences requiring appropriate non-local counterterms. In 4 dimensions the model turns out to have one more relevant (non-planar) coupling than its commutative counterpart. This non-planar coupling is ``evanescent'': although in the massive (but not in the massless) case its contribution to planar amplitudes vanishes when the floating cut-off equals the renormalization scale, this coupling is needed to make the Wilsonian effective action UV finite at all values of the floating cut-off.Comment: 35 pages, 8 figures; typos correcte

The black hole behind the cut

We study the analytic structure of the heavy-heavy-light-light holographic correlators in the supergravity approximation of the AdS3 × S 3/CFT2 duality. As an explicit example, we derive the correlator where the heavy operator is a classical microstate of the 5D supersymmetric black hole and its dual geometry interpolates as a function of a continuous parameter between global AdS3 and the extremal BTZ black hole. The simplest perturbation of this interpolating geometry by a light field is described by the Heun equation and we exploit the relation of its connection coefficients to the Liouville CFT to analytically compute the correlator in the two limits, focusing in particular on the black hole regime. In this limit we find that the real poles of the correlator become dense and can be approximated by a cut. We show that, when the charges of the heavy state are in the black hole regime, the discontinuity across the cut has complex poles corresponding to the quasi-normal modes of BTZ. This behaviour is qualitatively similar to what is expected for the large central charge limit of a typical black hole microstate

3D Point Cloud Reconstruction from Single Plenoptic Image

Novel plenoptic cameras sample the light field crossing the main camera lens. The information available in a plenoptic image must be processed, in order to create the depth map of the scene from a single camera shot. In this paper a novel algorithm, for the reconstruction of 3D point cloud of the scene from a single plenoptic image, taken with a consumer plenoptic camera, is proposed. Experimental analysis is conducted on several test images, and results are compared with state of the art methodologies. The results are very promising, as the quality of the 3D point cloud from plenoptic image, is comparable with the quality obtained with current non-plenoptic methodologies, that necessitate more than one image

Physical States at the Tachyonic Vacuum of Open String Field Theory

We illustrate a method for computing the number of physical states of open string theory at the stable tachyonic vacuum in level truncation approximation. The method is based on the analysis of the gauge-fixed open string field theory quadratic action that includes Fadeev-Popov ghost string fields. Computations up to level 9 in the scalar sector are consistent with Sen's conjecture about the absence of physical open string states at the tachyonic vacuum. We also derive a long exact cohomology sequence that relates relative and absolute cohomologies of the BRS operator at the non-perturbative vacuum. We use this exact result in conjunction with our numerical findings to conclude that the higher ghost number non-perturbative BRS cohomologies are non-empty.Comment: 43 pages, 16 eps figures, LaTe

Aumento da sustentabilidade da produção de raças suínas locais através do uso de rótulos de qualidade - Estudo de caso e desenvolvimento de uma marca comercial no projecto TREASURE

The interest for traditional genetic resources, here comprised local pig breeds, has been increased in the last decades. Yet, at the time being, majority of local pig breeds still need to be supported with subsidies to ensure their conservation. However, the best strategy is if breeds could reach self-sustainability which is possible by an efficient marketing strategy of their products. The majority of studied breeds in project TREASURE are untapped, so the ambition is to develop an “umbrella” collective trademark that would gather together all breeds and that would create added values for their products. Major socio-economic aspects related to the implementation of the collective trademark include rights, responsibilities and expected added value for end-users. Based on the results obtained by an internal survey conducted in TREASURE, we have identified the main features of the collaborative trademark: 1) it should attract end-users such as farmers, breeders associations and meat processors; 2) it should be developed and promoted by an operational committee of end-users, under the coordination and supervision of TREASURE Consortium; 3) it should emphasize local pig genetic resources as the key common point, considering also production systems and nutrition; 4) it should explore possible collaboration or conflict with existing EU protected products (PDO, PGI, TSG) in order to optimally promote local products. An overview of intellectual property rights (IPR) in the context of pork value chains existing in the European Union is presented and prospects for TREASURE trademark analysed

The Wilson-Polchinski Renormalization Group Equation in the Planar Limit

We derive the Wilson-Polchinski RG equation in the planar limit. We explain that the equation necessarily involves also non-planar amplitudes with sphere topology, which represent multi-trace contributions to the effective action. The resulting RG equation turns out to be of the Hamilton-Jacobi type since loop effects manifest themselves through terms which are linear in first order derivatives of the effective action with respect to the sources. We briefly outline applications to renormalization of non-commutative field theories, matrix models with external sources and holography.Comment: 22 pages, Latex, 3 eps figure

The Spectrum of Open String Field Theory at the Stable Tachyonic Vacuum

We present a level (10,30) numerical computation of the spectrum of quadratic fluctuations of Open String Field Theory around the tachyonic vacuum, both in the scalar and in the vector sector. Our results are consistent with Sen's conjecture about gauge-triviality of the small excitations. The computation is sufficiently accurate to provide robust evidence for the absence of the photon from the open string spectrum. We also observe that ghost string field propagators develop double poles. We show that this requires non-empty BRST cohomologies at non-standard ghost numbers. We comment about the relations of our results with recent work on the same subject.Comment: 33 pages, 10 figure