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Characterization of the blob generation region and blobby transport in a stellarator

PLASMA PHYSICS AND CONTROLLED FUSION 2016年第5期58卷

作者： Fuchert, G. Birkenmeier, G. Ramisch, M. Stroth, U. Max Planck Inst Plasma Phys Boltzmannstr 2 D-85748 Garching Germany Tech Univ Munich Phys Dept E28 James Franck Str 1 D-85748 Garching Germany Univ Stuttgart Inst Grenzflachenverfahrenstech & Plasmatechnol D-70569 Stuttgart Germany

Filaments of increased pressure ('blobs') in the scrape-off layer of toroidally confined magnetized plasmas are studied in the context of fusion research due to their relevance for confinement and wall safety. Analytical models in simple toroidal magnetic field geometries have proven useful to get a quantitative understanding of blob dynamics in tokamaks. However, their direct applicability to the more complicated stellarator geometry is far less studied. The experiments presented here show that in the stellarator TJ-K blobs are field-aligned structures occurring in scrape-off layer regions of negative mean normal curvature, which is in agreement with common blob models. Furthermore, it is shown that in TJ-K, in accordance with findings from tokamaks, blobs account for a significant fraction of the turbulent scrape-off layer transport of the order of several tens of percent.

关键词： stellarator scrape-off layer blobs turbulent transport

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Towards a quantitative prediction of the blob detection rate

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PLASMA PHYSICS AND CONTROLLED FUSION 2016年第5期58卷

作者： Fuchert, G. Carralero, D. Manz, P. Stroth, U. Wolfrum, E. Max Planck Inst Plasma Phys Boltzmannstr 2 D-85748 Garching Germany Tech Univ Munich Phy Dept E28 James Franck Str 1 D-85748 Garching Germany

To estimate the particle and energy flux to the plasma facing components of a future fusion power plant, the transport carried by filaments of increased pressure, called blobs, is of critical importance. To understand this transport the rate of the filaments has to be known. The novel approach presented here allows the prediction of both the blob generation and detection rates based on background plasma parameters only. The prediction is in a good overall agreement with recent experiments in ASDEX Upgrade.

关键词： plasma turbulence scrape-off layer blobs tokamak

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On the statistics and features of turbulent structures in RFX-mod

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PLASMA PHYSICS AND CONTROLLED FUSION 2016年第4期58卷

作者： Vianello, N. Spolaore, M. Agostini, M. Cavazzana, R. De Masi, G. Martines, E. Momo, B. Scarin, P. Spagnolo, S. Zuin, M. Ecole Polytech Fed Lausanne Swiss Plasma Ctr CH-1015 Lausanne Switzerland Univ Padua Consorzio RFX CNR ENEA Ist Nazl Fis NuclAcciaierie Venete SpA Corso Stati Uniti 4 I-35127 Padua Italy

An extensive statistical characterization of the electromagnetic turbulence in the edge region of RFX-mod, operated as a tokamak and as a Reversed Field Pinch, is presented. Striking similarity are observed on the intermittent character of the electrostatic turbulence between the two configurations whereas the difference between magnetic turbulence is likely to be imputed to the different beta value of the two configurations. blobs are characterized in terms of their spatial structure, the associated enstrophy and energy and the mechanism of energy and enstrophy transfer between intermittent fluctuation at different scales is addressed.

关键词： blobs turbulence tokamak reversed field pinch

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Blob dynamics in the TORPEX experiment: a multi-code validation

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PLASMA PHYSICS AND CONTROLLED FUSION 2016年第4期58卷

作者： Riva, F. Colin, C. Denis, J. Easy, L. Furno, I. Madsen, J. Militello, F. Naulin, V. Nielsen, A. H. Olsen, J. M. B. Omotani, J. T. Rasmussen, J. J. Ricci, P. Serre, E. Tamain, P. Theiler, C. Ecole Polytech Fed Lausanne Swiss Plasma Ctr SPC CH-1015 Lausanne Switzerland Aix Marseille Univ CNRS Cent Marseille UMR 7340 M2P2 F-13451 Marseille France CEA IRFM F-13108 St Paul Les Durance France Univ York Dept Phys York YO10 5DD N Yorkshire England Culham Sci Ctr CCFE Abingdon OX14 3DB Oxon England Tech Univ Denmark Deparment Phys DK-2800 Lyngby Denmark

Three-dimensional and two-dimensional seeded blob simulations are performed with five different fluid models, all based on the drift-reduced Braginskii equations, and the numerical results are compared among themselves and validated against experimental measurements provided by the TORPEX device ( Fasoli et al 2006 Phys. Plasmas 13 055902). The five models are implemented in four simulation codes, typically used to simulate the plasma dynamics in the tokamak scrape-off layer, namely BOUT++ (Dudson et al 2009 Comput. Phys. Commun. 180 1467), GBS (Ricci et al 2012 Plasma Phys. Control. Fusion 54 124047), HESEL (Nielsen et al 2015 Phys. Lett. A 379 3097), and TOKAM3X (Tamain et al 2014 Contrib. Plasma Phys. 54 555). Three blobs with different velocities and different stability properties are simulated. The differences observed among the simulation results and the different levels of agreement with experimental measurements are investigated, increasing our confidence in our simulation tools and shedding light on the blob dynamics. The comparisons demonstrate that the radial blob dynamics observed in the three-dimensional simulations is in good agreement with experimental measurements and that, in the present experimental scenario, the two-dimensional model derived under the assumption of k(vertical bar vertical bar) = 0 is able to recover the blob dynamics observed in the three-dimensional simulations. Moreover, it is found that an accurate measurement of the blob temperature is important to perform reliable seeded blob simulations.

关键词： blobs turbulence code validation

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Blob dynamics in TORPEX poloidal null configurations

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PLASMA PHYSICS AND CONTROLLED FUSION 2016年第12期58卷

作者： Shanahan, B. W. Dudson, B. D. Univ York York Plasma Inst Dept Phys York YO10 5DD N Yorkshire England

3D blob dynamics are simulated in X-point magnetic configurations in the TORPEX device via a non-field-aligned coordinate system, using an isothermal model which evolves density, vorticity, parallel velocity and parallel current density. By modifying the parallel gradient operator to include perpendicular perturbations from poloidal field coils, numerical singularities associated with field aligned coordinates are avoided. A comparison with a previously developed analytical model (Avino 2016 Phys. Rev. Lett. 116 105001) is performed and an agreement is found with minimal modification. Experimental comparison determines that the null region can cause an acceleration of filaments due to increasing connection length, but this acceleration is small relative to other effects, which we quantify. Experimental measurements (Avino 2016 Phys. Rev. Lett. 116 105001) are reproduced, and the dominant acceleration mechanism is identified as that of a developing dipole in a moving background. Contributions from increasing connection length close to the null point are a small correction.

关键词： blobs filaments turbulence X-point BOUT plus TORPEX

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Contrasting effects of strabismic amblyopia on metabolic activity in superficial and deep layers of striate cortex

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JOURNAL OF NEUROPHYSIOLOGY 2015年第9期113卷 3337-3344页

作者： Adams, Daniel L. Economides, John R. Horton, Jonathan C. Univ Calif San Francisco Beckman Vis Ctr San Francisco CA 94143 USA Univ Trento Ctr Mind Brain Sci Trento Italy

To probe the mechanism of visual suppression, we have raised macaques with strabismus by disinserting the medial rectus muscle in each eye at 1 mo of age. Typically, this operation produces a comitant, alternating exotropia with normal acuity in each eye. Here we describe an unusual occurrence: the development of severe amblyopia in one eye of a monkey after induction of exotropia. Shortly after surgery, the animal demonstrated a strong fixation preference for the left eye, with apparent suppression of the right eye. Later, behavioral testing showed inability to track or to saccade to targets with the right eye. With the left eye occluded, the animal demonstrated no visually guided behavior. Optokinetic nystagmus was absent in the right eye. Metabolic activity in striate cortex was assessed by processing the tissue for cytochrome oxidase (CO). Amblyopia caused loss of CO in one eye's rows of patches, presumably those serving the blind eye. Layers 4A and 4B showed columns of reduced CO, in register with pale rows of patches in layer 2/3. Layers 4C, 5, and 6 also showed columns of CO activity, but remarkably, comparison with more superficial layers showed a reversal in contrast. In other words, pale CO staining in layers 2/3, 4A, and 4B was aligned with dark CO staining in layers 4C, 5, and 6. No experimental intervention or deprivation paradigm has been reported previously to produce opposite effects on metabolic activity in layers 2/3, 4A, and 4B vs. layers 4C, 5, and 6 within a given eye's columns.

关键词： exotropia suppression cytochrome oxidase strabismus stereopsis ocular dominance column blobs

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Qualitative and Quantitative Evaluation of Blob-Based Time-of-Flight PET Image Reconstruction in Hybrid Brain PET/MR Imaging

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MOLECULAR IMAGING AND BIOLOGY 2015年第5期17卷 704-713页

作者： Leemans, Eva L. Kotasidis, Fotis Wissmeyer, Michael Garibotto, Valentina Zaidi, Habib Univ Hosp Geneva Div Nucl Med & Mol Imaging CH-1211 Geneva 4 Switzerland Univ Twente Tech Med NL-7522 NB Enschede Netherlands Univ Geneva Geneva Neurosci Ctr CH-1205 Geneva Switzerland Univ Groningen Univ Med Ctr Groningen Dept Nucl Med & Mol Imaging NL-9700 RB Groningen Netherlands

Many neurological diseases affect small structures in the brain and, as such, reliable visual evaluation and accurate quantification are required. Recent technological developments made the clinical use of hybrid positron emission tomography/magnetic resonance (PET/MR) systems possible, providing both functional and anatomical information in a single imaging session. Nevertheless, there is a trade-off between spatial resolution and image quality (contrast and noise), which is dictated mainly by the chosen acquisition and reconstruction protocols. Image reconstruction algorithms using spherical symmetric basis functions (blobs) for image representation have a number of additional parameters that impact both the qualitative and quantitative image characteristics. Hence, a detailed investigation of the blob-based reconstruction characteristics using different parameters is needed to achieve optimal reconstruction results. This work evaluated the impact of a range of blob parameters on image quality and quantitative accuracy of brain PET images acquired on the Ingenuity Time-of-Flight (TOF) PET/MR system. Two different phantoms were used to simulate brain imaging applications. Image contrast and noise characteristics were assessed using an image quality phantom. Quantitative performance in a clinical setting was investigated using the Hoffman 3D brain phantom at various count levels. Furthermore, the visual quality of four clinical studies was scored blindly by two experienced physicians to qualitatively evaluate the influence of different reconstruction protocols, hereby providing indications on parameters producing the best image quality. Quantitative evaluation using the image quality phantom showed that larger basis function radii result in lower contrast recovery (similar to 2 %) and lower variance levels (similar to 15 %). The brain phantom and clinical studies confirmed these observations since lower contrast was seen between anatomical structures. High and low c

关键词： PET/MRI Image reconstruction blobs Visual quality Contrast Noise

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Basis Functions in Image Reconstruction From Projections: A Tutorial Introduction

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SENSING AND IMAGING 2015年第1期16卷 1-21页

作者： Herman, Gabor T. CUNY Grad Ctr Dept Comp Sci New York NY 10016 USA

The series expansion approaches to image reconstruction from projections assume that the object to be reconstructed can be represented as a linear combination of fixed basis functions and the task of the reconstruction algorithm is to estimate the coefficients in such a linear combination based on the measured projection data. It is demonstrated that using spherically symmetric basis functions (blobs), instead of ones based on the more traditional pixels, yields superior reconstructions of medically relevant objects. The demonstration uses simulated computerized tomography projection data of head cross-sections and the series expansion method ART for the reconstruction. In addition to showing the results of one anecdotal example, the relative efficacy of using pixel and blob basis functions in image reconstruction from projections is also evaluated using a statistical hypothesis testing based task oriented comparison methodology. The superiority of the efficacy of blob basis functions over that of pixel basis function is found to be statistically significant.

关键词： Image reconstruction Computerized tomography Pixels blobs Image representation

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Multi-Touch Helpdesk Management System with Communication Enable 5

Multi-Touch Helpdesk Management System with Communication En...

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2015 Fifth International Conference on Communication Systems and Network Technologies (CSNT)

作者： Khanam, Deeba Dhankhar, Sunil Swami Keshwanand Inst Technol Dept Comp Sci & Engn Jaipur Rajasthan India

ISBN: (纸本)9781479917976

The research in this paper focused on the development of a general purpose helpdesk system on a multi-touch panel for a collage or an institution. This system is implemented on Multi-touch technology under NUI (Natural User Interface). The developed helpdesk system would be able to help the guest and in-campus persons without any kind of special training, just by touching the surface or with usual hand gestures. Communication Feature makes the helpdesk communicable enable via both Wireless or network communication model and more powerful. The application would be implemented on a table-top surface which would support multi-touch technology. Making of such system in cost effective manner is the major task to be done. Dealing with hardware and software components and description of protocols used are illustrated in this document.

关键词： Touch blobs surface computing Helpdesk.NUI HCI GSM

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Events Detection Using a Video-Surveillance Ontology and a Rule-Based Approach 13

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13th European Conference on Computer Vision (ECCV)

作者： Tani, Mohammed Yassine Kazi Lablack, Adel Ghomari, Abdelghani Bilasco, Ioan Marius Univ ES Senia RIIR Lab Oran Algeria Univ Lille 1 Lab Informat Fondamentale Lille Lille France

ISBN: (纸本)9783319161815;9783319161808

In this paper, we propose the use of a Video-surveillance Ontology and a rule-based approach to detect an event. The scene is described using the concepts presented in the ontology. Then, the blobs are extracted from the video stream and are represented using the bounding boxes that enclose them. Finally, a set of rules have been proposed and have been applied to videos selected from PETS 2012 challenge that contain multiple objects events (e.g. Group walking, Group splitting, etc.).

关键词： Ontology Video surveillance blobs Rules

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