6,651 research outputs found
Trailing Edge Noise Reduction by Passive and Active Flow Controls
This paper presents the results on the use of porous metal foams (passive control) and dielectric barrier surface plasma actuations (active control) for the reduction of vortex shedding tonal noises from the nonflat plate type trailing edge serration in a NACA0012 airfoil previously discussed in Chong et al. (AIAA J. Vol. 51, 2013, pp. 2665-2677). The use of porous metal foams to fill the interstices between adjacent members of the sawtooth can almost completely suppress the vortex shedding tonal noise, whilst the serration effect on the broadband noise reduction is retained. This concept will promote the nonflat plate type serrated trailing edge to become a genuine alternative to the conventional flat plate type serrated trailing edge, which is known to have drawbacks in the structural stability, aerodynamic performances and implementation issues. For the plasma actuators, configuration which produces electric wind in a tangential direction is found to be not very effective in suppressing the vortices emanated from the serration blunt root. On the other hand, for the plasma configuration which produces electric wind in a vertical direction, good level of vortex shedding tonal noise reduction has been demonstrated. However, the self noise produced by the plasma actuators negates the noise benefits on the tonal noise reduction. This characteristic illustrates the need to further develop the plasma actuators in a two pronged approach. First is to increase the electric wind speed, thereby allowing the plasma actuators to be used in a higher free jet velocity which naturally produces a larger level of jet noise. Second, the self noise radiated by the plasma actuators should be reduced
Au cœur ténébreux d’une éco-randonnée littéraire entre la Laponie et la Tasmanie : Oiseau de Malheur de Johanna Sinisalo
This article seeks to shed light on the ecological issues underlying the Finnish author Johanna Sinisalo\u27s novel Linnunaivot / Oiseau de malheur (translated into English as Birdbrain) published in Finland in 2008, translated into several languages. After a brief overview of her other main novels, also marked by environmental issues and preoccupations, the essay focuses on the topical places of this Nordic eco-novel, more particularly on its narrative structure, presented in the form of a hiking tour rooted in the landscape and culture of Finland, yet pursued in such a way as to tackle a number of ecological issues since Australia and Tasmania. The alternating narration between two (human) narrators is enriched by the presence of a third one, a trickster bird whose mediation at once complicates and facilitates the understanding of this eco-tale which resonates with two 19th-century intertexts, Joseph Conrad\u27s The Heart of Darkness, and Edgar Allan Poe\u27s poem « The Raven »
Global High-resolution Land-use Change Projections: A Bayesian Multinomial Logit Downscaling Approach Incorporating Model Uncertainty and Spatial Effects
Using econometric models to estimate land-use change has a long tradition in scientific literature. Recent contributions show the importance of including spatial information and of using a multinomial framework to take into account the interdependencies between the land-use classes. Few studies, however, agree on the relevant determinants of land-use change and there are no contributions so far comparing determinants on a global scale. Using multiple 5 arc minute resolution datasets of land-use change between 2000 and 2010 and taking into account the transitions between forest, cropland, grassland and all other land covers, we estimate a Bayesian multinomial logit model, using the efficient PĂłlya-Gamma sampling procedure introduced by Polson et al. (2013). To identify and measure the determinants of land-use change and the strength of spatial separation, our model implements Bayesian model selection through stochastic search variable selection (SSVS) priors and spatial information via Gaussian Process (GP) priors.
Our results indicate that spatial proximity is of central importance in land-use change, in all regions except the pacific islands. We also show that infrastructure policy, proxied by mean time to market, seems to have a significant impact on deforestation throughout most regions.
In a second step we use aggregate, supra national land-use change results from the partial equilibrium agricultural model GLOBIOM as a framework for projecting our model in ten-year intervals up to 2100 on a spatially explicit scale along multiple shared socioeconomic pathways
Radiative lepton flavor violating decays in the Randall Sundrum background with localized leptons
We study the radiative lepton flavor violating l_i -> l_j\gamma decays in the
two Higgs doublet model, respecting the Randall Sundrum scenario and estimate
the contributions of the KK modes of left (right) handed charged lepton
doublets (singlets) on the branching ratios. We observe that the branching
ratios are sensitive to the contributions of the charged lepton KK modes.Comment: 23 pages, 10 figures, 2 table
Force indeterminacy in the jammed state of hard disks
Granular packings of hard discs are investigated by means of contact dynamics
which is an appropriate technique to explore the allowed force-realizations in
the space of contact forces. Configurations are generated for given values of
the friction coefficient, and then an ensemble of equilibrium forces is found
for fixed contacts. We study the force fluctuations within this ensemble. In
the limit of zero friction the fluctuations vanish in accordance with the
isostaticity of the packing. The magnitude of the fluctuations has a
non-monotonous friction dependence. The increase for small friction can be
attributed to the opening of the angle of the Coulomb cone, while the decrease
as friction increases is due to the reduction of connectivity of the
contact-network, leading to local, independent clusters of indeterminacy. We
discuss the relevance of indeterminacy to packings of deformable particles and
to the mechanical response properties.Comment: 4 pages, 3 figures. Minor changes, journal reference adde
Review of the Theoretical Heavy-ion Physics
In this contribution we briefly give an overview of the theoretical models used to describe experimental data from heavy-ion collisions from
The Breakdown of Kinetic Theory in Granular Shear Flows
We examine two basic assumptions of kinetic theory-- binary collisions and
molecular chaos-- using numerical simulations of sheared granular materials. We
investigate a wide range of densities and restitution coefficients and
demonstrate that kinetic theory breaks down at large density and small
restitution coefficients. In the regimes where kinetic theory fails, there is
an associated emergence of clusters of spatially correlated grains
Neutrinos in flat extra dimension: towards a realistic scenario
We consider the simple extension of the Standard Model in which an additional
right handed neutrino propagates along a flat extra dimension, while the
Standard Model fields are confined on a 3-brane. The fifth dimension is
orbifold compactified. In this scenario, the neutrino mass can be
naturally suppressed. By studying systematically the fundamental parameter
space, we show that the strong phenomenological constraints on mixing angles
between active and sterile neutrinos (especially those derived from the SNO
experiment data) do not conflict with the possibility of generating a realistic
neutrino mass spectrum. As a second step, we explore the possibility of a
successful leptogenesis through the decays of the Kaluza-Klein excitations of
the right handed neutrino.Comment: 16 pages, 2 ps figure
Quark-lepton mass unification at TeV scales
A scenario combining a model of early (TeV) unification of quarks and leptons
with the physics of large extra dimensions provides a natural mechanism linking
quark and lepton masses at TeV scale. This has been dubbed as early
quark-lepton mass unification by one of us (PQH) in one of the two models of
early quark-lepton unification, which are consistent with data, namely SU(4)_PS
\otimes SU(2)_L \otimes SU(2)_R \otimes SU(2)_H. In particular, it focused on
the issue of naturally light Dirac neutrino. The present paper will focus on
similar issues in the other model, namely SU(4)_PS \otimes SU(3)_L \otimes
SU(3)_H.Comment: Accepted for publication in PRD: The new version is in agreement with
the accepted manuscrip
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