391 research outputs found
Statistical analysis and modeling of intermittent transport events in the tokamak SOL
The turbulence observed in the scrape-off-layer of a tokamak is often
characterized by intermittent events of bursty nature, a feature which raises
concerns about the prediction of heat loads on the physical boundaries of the
device. It appears thus necessary to delve into the statistical properties of
turbulent physical fields such as density, electrostatic potential and
temperature, focusing on the mathematical expression of tails of the
probability distribution functions. The method followed here is to generate
statistical information from time-traces of the plasma density stemming from
Braginskii-type fluid simulations, and check this against a first-principles
theoretical model. The analysis of the numerical simulations indicates that the
probability distribution function of the intermittent process contains strong
exponential tails, as predicted by the analytical theory.Comment: 16 pages, 8 figure
A novel method for validating multi-classifiers. A case study for ICF-based health status classification
In this paper, we propose a novel method for the validation of a multi-classification model according to the intended use and aim of a device for health status classification and the clinical needs of the practitioners involved
Properties of convective cells generated in magnetized toroidal plasmas
Convective cells for turbulence control, generated by means of biased electrodes, are investigated in the simple magnetized toroidal plasmas of TORPEX. A two-dimensional array of 24 electrodes is installed on a metal limiter to test different biasing schemes. This allows influencing significantly both radial and vertical blob velocities. It is shown that these changes agree quantitatively with the flows deduced from the time averaged potential perturbations induced by the biasing. Detailed measurements along and across the magnetic field provide a rather clear picture of the effect of biasing on time averaged profiles. The biased electrodes produce perturbations of the plasma potential and density profiles that are fairly uniform along the magnetic field. Background flows influence the location where potential variations are induced. The magnitude of the achievable potential variations in the plasma is strongly limited by cross-field currents and saturates at large bias voltages once the electrodes draw electron saturation current. A quantitative discussion on the origin of cross-field currents is presented, considering contributions related with diamagnetic drifts, ion inertia, collisions with neutrals, and viscosity. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4740056
ZipNet-GAN: Inferring Fine-grained Mobile Traffic Patterns via a Generative Adversarial Neural Network
Large-scale mobile traffic analytics is becoming essential to digital
infrastructure provisioning, public transportation, events planning, and other
domains. Monitoring city-wide mobile traffic is however a complex and costly
process that relies on dedicated probes. Some of these probes have limited
precision or coverage, others gather tens of gigabytes of logs daily, which
independently offer limited insights. Extracting fine-grained patterns involves
expensive spatial aggregation of measurements, storage, and post-processing. In
this paper, we propose a mobile traffic super-resolution technique that
overcomes these problems by inferring narrowly localised traffic consumption
from coarse measurements. We draw inspiration from image processing and design
a deep-learning architecture tailored to mobile networking, which combines
Zipper Network (ZipNet) and Generative Adversarial neural Network (GAN) models.
This enables to uniquely capture spatio-temporal relations between traffic
volume snapshots routinely monitored over broad coverage areas
(`low-resolution') and the corresponding consumption at 0.05 km level
(`high-resolution') usually obtained after intensive computation. Experiments
we conduct with a real-world data set demonstrate that the proposed
ZipNet(-GAN) infers traffic consumption with remarkable accuracy and up to
100 higher granularity as compared to standard probing, while
outperforming existing data interpolation techniques. To our knowledge, this is
the first time super-resolution concepts are applied to large-scale mobile
traffic analysis and our solution is the first to infer fine-grained urban
traffic patterns from coarse aggregates.Comment: To appear ACM CoNEXT 201
Methodology for turbulence code validation: Quantification of simulation-experiment agreement and application to the TORPEX experiment
A methodology for plasma turbulence code validation is discussed, focusing on quantitative assessment of the agreement between experiments and simulations. The present work extends the analysis carried out in a previous paper [P. Ricci et al., Phys. Plasmas 16, 055703 (2009)] where the validation observables were introduced. Here, it is discussed how to quantify the agreement between experiments and simulations with respect to each observable, how to define a metric to evaluate this agreement globally, and-finally-how to assess the quality of a validation procedure. The methodology is then applied to the simulation of the basic plasma physics experiment TORPEX [A. Fasoli et al., Phys. Plasmas 13, 055902 (2006)], considering both two-dimensional and three-dimensional simulation models. [doi: 10.1063/1.3559436
Approaching the investigation of plasma turbulence through a rigorous verification and validation procedure: A practical examplea)
In the present work, a Verification and Validation procedure is presented and applied showing, through a practical example, how it can contribute to advancing our physics understanding of plasma turbulence. Bridging the gap between plasma physics and other scientific domains, in particular, the computational fluid dynamics community, a rigorous methodology for the verification of a plasma simulation code is presented, based on the method of manufactured solutions. This methodology assesses that the model equations are correctly solved, within the order of accuracy of the numerical scheme. The technique to carry out a solution verification is described to provide a rigorous estimate of the uncertainty affecting the numerical results. A methodology for plasma turbulence code validation is also discussed, focusing on quantitative assessment of the agreement between experiments and simulations. The Verification and Validation methodology is then applied to the study of plasma turbulence in the basic plasma physics experiment TORPEX [Fasoli et al., Phys. Plasmas 13, 055902 (2006)], considering both two-dimensional and three-dimensional simulations carried out with the GBS code [Ricci et al., Plasma Phys. Controlled Fusion 54, 124047 (2012)]. The validation procedure allows progress in the understanding of the turbulent dynamics in TORPEX, by pinpointing the presence of a turbulent regime transition, due to the competition between the resistive and ideal interchange instabilities
Studying the impact of ocean eddies on the ecosystem of the Prince Edward Islands: DEIMEC ll
The Dynamics of Eddy Impacts on Marionâs Ecosystem Study (DEIMEC) programme was begun in 2002 with the aim of understanding the importance of the oceanic, upstream environment to the ecosystem of the Prince Edward Islands. This island group consists of two small volcanic islands and provides many opportunities for studying ecological and evolutionary processes, for monitoring ecological changes in relation to global climate change and for conserving a unique component of the planetâs biological diversity
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