2,343 research outputs found
Intermittency and scaling laws for wall bounded turbulence
Well defined scaling laws clearly appear in wall bounded turbulence, even
very close to the wall, where a distinct violation of the refined Kolmogorov
similarity hypothesis (RKSH) occurs together with the simultaneous persistence
of scaling laws. A new form of RKSH for the wall region is here proposed in
terms of the structure functions of order two which, in physical terms,
confirms the prevailing role of the momentum transfer towards the wall in the
near wall dynamics.Comment: 10 pages, 5 figure
Scaling properties in the production range of shear dominated flows
Recent developments in turbulence are focused on the effect of large scale
anisotropy on the small scale statistics of velocity increments. According to
Kolmogorov, isotropy is recovered in the large Reynolds number limit as the
scale is reduced and, in the so-called inertial range, universal features
-namely the scaling exponents of structure functions - emerge clearly. However
this picture is violated in a number of cases, typically in the high shear
region of wall bounded flows. The common opinion ascribes this effect to the
contamination of the inertial range by the larger anisotropic scales, i.e. the
residual anisotropy is assumed as a weak perturbation of an otherwise isotropic
dynamics. In this case, given the rotational invariance of the Navier-Stokes
equations, the isotropic component of the structure functions keeps the same
exponents of isotropic turbulence. This kind of reasoning fails when the
anisotropic effects are strong as in the production range of shear dominated
flows. This regime is analyzed here by means of both numerical and experimental
data for a homogeneous shear flow. A well defined scaling behavior is found to
exist, with exponents which differ substantially from those of classical
isotropic turbulence. Contrary to what predicted by the perturbation approach,
such a deep alteration concerns the isotropic sector itself. The general
validity of these results is discussed in the context of turbulence near solid
walls, where more appropriate closure models for the coarse grained
Navier-Stokes equations would be advisable.Comment: 4 pages, 4 figure
Comment on “Faraday waves in a Hele–Shawcell” [Phys. Fluids 30, 042106 (2018)]
Comment on “Faraday waves in a Hele-Shaw cell” [Phys Fluids 30, 042106 (2018).We propose improved dimensionless variables and scaling law to describe the height ofFaraday waves in a vertically vibrating Hele-Shaw cell. In comparison with those suggestedby Li et al., the influence of the liquid depth d on the wave height H is disregarded, andthe critical acceleration Fc, at which the Faraday instability is triggered, is now taken intoaccount. We support our approach with results from an additional set of experimental data,that includes the measurement of Fc, and encompasses the parameter range studied by Liet al.Fil: Boschan, A.. Universidad de Buenos Aires. Facultad de IngenierĂa. Departamento de FĂsica. Grupo de Medios Porosos; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; ArgentinaFil: Noseda, M.. Universidad de Buenos Aires. Facultad de IngenierĂa. Departamento de FĂsica. Grupo de Medios Porosos; ArgentinaFil: Aguirre, Maria Alejandra. Universidad de Buenos Aires. Facultad de IngenierĂa. Departamento de FĂsica. Grupo de Medios Porosos; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; ArgentinaFil: Piva, M.. Universidad de Buenos Aires. Facultad de IngenierĂa. Departamento de FĂsica. Grupo de Medios Porosos; Argentin
Possible unconventional superconductivity in substituted BaFeAs revealed by magnetic pair-breaking studies
The possible existence of a sign-changing gap symmetry in
BaFeAs-derived superconductors (SC) has been an exciting topic of
research in the last few years. To further investigate this subject we combine
Electron Spin Resonance (ESR) and pressure-dependent transport measurements to
investigate magnetic pair-breaking effects on BaFeAs (
Mn, Co, Cu, and Ni) single crystals. An ESR signal, indicative of the presence
of localized magnetic moments, is observed only for Cu and Mn compounds,
which display very low SC transition temperature () and no SC,
respectively. From the ESR analysis assuming the absence of bottleneck effects,
the microscopic parameters are extracted to show that this reduction of
cannot be accounted by the Abrikosov-Gorkov pair-breaking expression for a
sign-preserving gap function. Our results reveal an unconventional spin- and
pressure-dependent pair-breaking effect and impose strong constraints on the
pairing symmetry of these materials
Preliminary studies on the effect of Oidium tuckeri on the phenolic composition of grapes and wines
Research NoteA study of the influence of Oidium tuckeri on anthocyanins and the hydroxycinnamic tartaric esters of grapes and red wines was carried out during the 1993 harvest. After infection the level of anthocyanins in the skins of berries and in wines was lower than in healthy grapes and their wines. It is of particular interest that two bisubstituted anthocyanins reacted less sensitive to the pathogen. Wines from infected grapes contained more hydroxycinnamic tartaric esters
A vision-based fully automated approach to robust image cropping detection
The definition of valid and robust methodologies for assessing the authenticity of digital information is nowadays critical to contrast social manipulation through the media. A key research topic in multimedia forensics is the development of methods for detecting tampered content in large image collections without any human intervention. This paper introduces AMARCORD (Automatic Manhattan-scene AsymmetRically CrOpped imageRy Detector), a fully automated detector for exposing evidences of asymmetrical image cropping on Manhattan-World scenes. The proposed solution estimates and exploits the camera principal point, i.e., a physical feature extracted directly from the image content that is quite insensitive to image processing operations, such as compression and resizing, typical of social media platforms. Robust computer vision techniques are employed throughout, so as to cope with large sources of noise in the data and improve detection performance. The method leverages a novel metric based on robust statistics, and is also capable to decide autonomously whether the image at hand is tractable or not. The results of an extensive experimental evaluation covering several cropping scenarios demonstrate the effectiveness and robustness of our approac
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