739 research outputs found
Maxwell demon in Granular gas: a new kind of bifurcation? The hypercritical bifurcation
This paper starts with the investigation of the behaviour of a set of two
subsystems which are able to exchange some internal quantity according to a
given flux function. It is found that this sytem exhibit a bifurcation when the
flux passes through a maximum and that its kind (super-critical/sub-critical)
depends on the dissymmetry of the flux function near the maximum. It is also
found a new kind of bifurcation when the flux function is symmetric: we call it
hypercritical bifurcation because it generates much stronger fluctuations than
the super-critical one. The effect of a white noise is then investigated. We
show that an experimental set-up, leading to the Maxwell demon in granular gas,
displays all these kinds of bifurcation, just by changing the parameters of
excitation. It means that this system is much less simple as it was thought.Comment: 19 pages, 10 figure
Impact of Resonant Magnetic Perturbations on Zonal Modes, Drift-Wave Turbulence and the L-H Transition Threshold
We study the effects of Resonant Magnetic Perturbations (RMPs) on turbulence,
flows and confinement in the framework of resistive drift-wave turbulence. This
work was motivated, in parts, by experiments reported at the IAEA 2010
conference [Y. Xu {\it et al}, Nucl. Fusion \textbf{51}, 062030] which showed a
decrease of long-range correlations during the application of RMPs. We derive
and apply a zero-dimensional predator-prey model coupling the Drift-Wave Zonal
Mode system [M. Leconte and P.H. Diamond, Phys. Plasmas \textbf{19}, 055903] to
the evolution of mean quantities. This model has both density gradient drive
and RMP amplitude as control parameters and predicts a novel type of transport
bifurcation in the presence of RMPs. This model allows a description of the
full L-H transition evolution with RMPs, including the mean sheared flow
evolution. The key results are: i) The L-I and I-H power thresholds \emph{both}
increase with RMP amplitude |\bx|, the relative increase of the L-I threshold
scales as \Delta P_{\rm LI} \propto |\bx|^2 \nu_*^{-2} \gyro^{-2}, where
is edge collisionality and \gyro is the sound gyroradius. ii) RMPs
are predicted to \emph{decrease} the hysteresis between the forward and
back-transition. iii) Taking into account the mean density evolution, the
density profile - sustained by the particle source - has an increased turbulent
diffusion compared with the reference case without RMPs which provides one
possible explanation for the \emph{density pump-out} effect.Comment: 30 pages, IAEA-based articl
Soft Cache Hits and the Impact of Alternative Content Recommendations on Mobile Edge Caching
Caching popular content at the edge of future mobile networks has been widely
considered in order to alleviate the impact of the data tsunami on both the
access and backhaul networks. A number of interesting techniques have been
proposed, including femto-caching and "delayed" or opportunistic cache access.
Nevertheless, the majority of these approaches suffer from the rather limited
storage capacity of the edge caches, compared to the tremendous and rapidly
increasing size of the Internet content catalog. We propose to depart from the
assumption of hard cache misses, common in most existing works, and consider
"soft" cache misses, where if the original content is not available, an
alternative content that is locally cached can be recommended. Given that
Internet content consumption is increasingly entertainment-oriented, we believe
that a related content could often lead to complete or at least partial user
satisfaction, without the need to retrieve the original content over expensive
links. In this paper, we formulate the problem of optimal edge caching with
soft cache hits, in the context of delayed access, and analyze the expected
gains. We then show using synthetic and real datasets of related video contents
that promising caching gains could be achieved in practice
Lake and River Ice Investigations in Northern Manitoba Using Airborne SAR Imagery
Multichannel airborne SAR data were collected over northern Manitoba in April 1989 and January 1990. During the week of the SAR flights, several reconnaissance helicopter flights were undertaken, and ground calibration sites were visited to collect ice, snow, and water data. A total of six SAR image passes were flown in April 1989 and seven in January 1990, in order to collect a data set with numerous incidence angle, frequency, polarization, and look direction combinations. The data have been qualitatively assessed, with specific emphasis on C-band horizontally polarized imagery - the proposed SAR configuration for Radarsat. Results of the analysis have shown that airborne SAR can be used to identify various freshwater ice features, such as juxtaposition ice, refrozen slush, river ice runs, and lake ice. Open water leads were also successfully identified. A careful interpretation of the airborne SAR imagery in conjunction with the ground truth data has shown that the unusually bright returns characterizing the Burntwood River and the west portion of Split Lake were caused by a layer of refrozen slush that was generated during the initial formation of the ice cover. Although the results reported here focused exclusively on a qualitative analysis of C-HH data, preliminary analysis of the digital data suggests that changes in frequency and polarization produce measurable differences and can be used to develop classification algorithms for freshwater ice.Key words: synthetic aperture radar, fresh water iceMots clés: radar à antenne synthétique, glace d’eau douc
Fast-thermal coupled cores in ZPR revisited physical specificities and potentialities for ZEPHYR
International audienceThe development of fast reactor GEN-IV technology at an industrial scale would need asignificant improvement of nuclear data and related uncertainties. For this purpose,fast/thermal coupled configurations performed in MINERVE during the 1970âs have beenrecently revisited. The encouraging results obtained have led to further optimizations in orderto prepare experimental programs in the future ZEPHYR facility to be built in Cadarache.This paper describes the concept of fast/thermal coupled core and its use in the improvementof fast-spectrum nuclear data thanks to integral experiments. An optimized configuration ispresented with several variations in order to widen the possibilities of measurement so as toseparate reactivity effects due to absorption and scattering reactions
Control of Transport-barrier relaxations by Resonant Magnetic Perturbations
Transport-barrier relaxation oscillations in the presence of resonant
magnetic perturbations are investigated using three-dimensional global fluid
turbulence simulations from first principles at the edge of a tokamak. It is
shown that resonant magnetic perturbations have a stabilizing effect on these
relaxation oscillations and that this effect is due mainly to a modification of
the pressure profile linked to the presence of both residual residual magnetic
island chains and a stochastic layer.Comment: 4 page
Power transformer under short-circuit fault conditions: A multiphysics approach
Transformersâ windings experience mechanical loads from electromagnetic forces due to the currents they carry.
During normal operation, the resulting stresses and strains have minor influence, therefore they do not represent the significant risk to the devicesâ integrity.
However, transformers can suffer from high sudden short-circuit currents that are several times higher than those during the normal operation. These short-circuit currents are a significant threat, not only from an electrical but also from the structural integrity point of view. In this paper, coupled electromagnetic and structural mechanics simulations are carried out to evaluate short-circuit fault risks in a comprehensive and accurate way
Power transformer under short-circuit fault conditions: A multiphysics approach
Transformersâ windings experience mechanical loads from electromagnetic forces due to the currents they carry.
During normal operation, the resulting stresses and strains have minor influence, therefore they do not represent the significant risk to the devicesâ integrity.
However, transformers can suffer from high sudden short-circuit currents that are several times higher than those during the normal operation. These short-circuit currents are a significant threat, not only from an electrical but also from the structural integrity point of view. In this paper, coupled electromagnetic and structural mechanics simulations are carried out to evaluate short-circuit fault risks in a comprehensive and accurate way
Le matériau sol-chaux comme une matériau résistant à l'érosion pour les ouvrages hydrauliques : état de l'art et projet de R&D français DigueElite
International audienceThe treatment of silty and clayey soils with lime (calcium oxide or hydroxide) is a technique widely used for soils improvement and stabilization for construction of roads, highways, railways, platforms. However, the principles of lime treatment for hydraulic earthen structures remains barely applied or even forgotten (European case). If existing testimonials (levees, dams, mainly in US and Australia) are evidences that show effectiveness and durability of lime-treated structures, there was a necessity to evaluate a series of unknown characteristics and relevant properties of lime-treated soils for an application in hydraulic context, through laboratory studies and full-scale experiments
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