检索结果-内蒙古大学图书馆

Intermittent electron density and temperature fluctuations and associated fluxes in the Alcator C-Mod scrape-off layer

引用

PLASMA PHYSICS AND CONTROLLED FUSION 2018年第6期60卷

作者： Kube, R. Garcia, O. E. Theodorsen, A. Brunner, D. Kuang, A. Q. LaBombard, B. Terry, J. L. UiT Arctic Univ Norway Dept Phys & Technol NO-9037 Tromso Norway MIT Plasma Sci & Fus Ctr Cambridge MA 02139 USA

The Alcator C-Mod mirror Langmuir probe system has been used to sample data time series of fluctuating plasma parameters in the outboard mid-plane far scrape-off layer. We present a statistical analysis of one second long time series of electron density, temperature, radial electric drift velocity and the corresponding particle and electron heat fluxes. These are sampled during stationary plasma conditions in an ohmically heated, lower single null diverted discharge. The electron density and temperature are strongly correlated and feature fluctuation statistics similar to the ion saturation current. Both electron density and temperature time series are dominated by intermittent, large-amplitude burst with an exponential distribution of both burst amplitudes and waiting times between them. The characteristic time scale of the large-amplitude bursts is approximately 15 mu s. Large-amplitude velocity fluctuations feature a slightly faster characteristic time scale and appear at a faster rate than electron density and temperature fluctuations. Describing these time series as a superposition of uncorrelated exponential pulses, we find that probability distribution functions, power spectral densities as well as auto-correlation functions of the data time series agree well with predictions from the stochastic model. The electron particle and heat fluxes present large-amplitude fluctuations. For this low-density plasma, the radial electron heat flux is dominated by convection, that is, correlations of fluctuations in the electron density and radial velocity. Hot and dense blobs contribute only a minute fraction of the total fluctuation driven heat flux.

关键词： scrape-off layer turbulent transport blobs intermittency

来源：评论

学校读者我要写书评

暂无评论

Segmentation and Classification of Acute Lymphoblastic Leukemia Cells Tooled with Digital Image Processing and ML Techniques

Segmentation and Classification of Acute Lymphoblastic Leuke...

引用

International Conference on Intelligent Computing and Control Systems

作者： D. Umamaheswari S. Geetha Department of Computer Science Vidyasagar College of Arts and Science Udumalpet Tamil Nadu India Department of Computer Science Government Arts College Udumalpet Tamil Nadu India

ISBN: (纸本)9781538628430;9781538628423

Medical science has been contributing its active role in fighting vigorously against the life ceasing diseases. The algorithm is proposed by investigating the existing segmentation algorithms in the field of leukemia research for the sake of supporting hematopathologists to recognize Acute Lymphocytic Leukemia (ALL) by analyzing the blood cell images. There are four levels of separating and classifying benign and malignant white blood cells (WBC). They are, preprocessing, segmentation, extraction of features and classification. As a preliminary task of image analysis, segmentation is done with morphological operators and Otsu's thresholding. Then utilization of nucleus features with supervised KNN classifier gains the classification accuracy of 95.96%, 95.92% of sensitivity and 96% of specificity.

关键词： Acute lymphoblastic leukemia Morphological operators Otsu's thresholding Segmentation KNN classifier blobs WBC

来源：评论

学校读者我要写书评

暂无评论

On the propagation of blobs in the magnetotail: MHD simulations

引用

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 2013年第9期118卷 5497-5505页

作者： Birn, J. Nakamura, R. Hesse, M. Space Sci Inst Boulder CO 80301 USA Los Alamos Natl Lab Los Alamos NM USA Austrian Acad Sci Space Res Inst A-8010 Graz Austria NASA Goddard Space Flight Ctr Greenbelt MD 20771 USA

Using three-dimensional magnetohydrodynamic (MHD) simulations of the magnetotail, we investigate the fate of entropy-enhanced localized magnetic flux tubes (blobs). Such flux tubes may be the result of a slippage process that also generates entropy-depleted flux tubes (bubbles) or of a rapid localized energy increase, for instance, from wave absorption. We confirm the expectation that the entropy enhancement leads to a tailward motion and that the speed and distance traveled into the tail increase with the entropy enhancement, even though the blobs tend to break up into pieces. The vorticity on the outside of the blobs twists the magnetic field and generates field-aligned currents predominantly of region-2 sense (earthward on the dusk side and tailward on the dawn side), which might provide a possibility for remote identification from the ground. The breakup, however, leads to more turbulent flow patterns, associated with opposite vorticity and the generation of region-1 sense field-aligned currents of lower intensity but approximately equal integrated magnitude.

关键词： blobs entropy enhancement magnetotail dynamics

来源：评论

学校读者我要写书评

暂无评论

Edge and divertor plasma: detachment, stability, and plasma-wall interactions

引用

NUCLEAR FUSION 2017年第10期57卷

作者： Krasheninnikov, S. I. Kukushkin, A. S. Lee, Wonjae Phsenov, A. A. Smirnov, R. D. Smolyakov, A. I. Stepanenko, A. A. Zhang, Yanzeng Univ Calif San Diego La Jolla CA 92093 USA Kurchatov Inst Kurchatov Sq 1 Moscow 123182 Russia NRNU MEPhI Kashirskoje Av 31 Moscow 115409 Russia Univ Saskatchewan 116 Sci Pl Saskatoon SK S7N 5E2 Canada

The paper presents an overview of the results of studies on a wide range of the edge plasma related issues. The rollover of the plasma flux to the target during progressing detachment process is shown to be caused by the increase of the impurity radiation loss and volumetric plasma recombination, whereas the ion-neutral friction, although important for establishing the necessary edge plasma conditions, does not contribute per se to the rollover of the plasma flux to the target. The processes limiting the power loss by impurity radiation are discussed and a simple estimate of this limit is obtained. Different mechanisms of meso-scale thermal instabilities driven by impurity radiation and resulting in self-sustained oscillations in the edge plasma are identified. An impact of sheared magnetic field on the dynamics of the blobs and ELM filaments playing an important role in the edge and SOL plasma transport is discussed. Trapping of He, which is an intrinsic impurity for the fusion plasmas, in the plasma-facing tungsten material is considered. A newly developed model, accounting for the generation of additional He traps caused by He bubble growth, fits all the available experimental data on the layer of nano-bubbles observed in W under irradiation by low energy He plasma.

关键词： edge plasma divertor detachment current convective instability blobs He nano-bubbles

来源：评论

学校读者我要写书评

暂无评论

Pedestal and edge electrostatic turbulence characteristics from an XGC1 gyrokinetic simulation

引用

PLASMA PHYSICS AND CONTROLLED FUSION 2017年第10期59卷

作者： Churchill, R. M. Chang, C. S. Ku, S. Dominski, J. Princeton Plasma Phys Lab 100 Stellarator Rd Princeton NJ 08540 USA

Understanding the multi-scale neoclassical and turbulence physics in the edge region (pedestal + scrape-off layer (SOL)) is required in order to reliably predict performance in future fusion devices. We explore turbulent characteristics in the edge region from a multi-scale neoclassical and turbulent XGC1 gyrokinetic simulation in a DIII-D like tokamak geometry, here excluding neutrals and collisions. For an H-mode type plasma with steep pedestal, it is found that the electron density fluctuations increase towards the separatrix, and stay high well into the SOL, reaching a maximum value of dne delta n(e/)(n) over bar (e) similar to 0.18. blobs are observed, born around the magnetic separatrix surface and propagate radially outward with velocities generally less than 1 km s(-1). Strong poloidal motion of the blobs is also present, near 20 km s(-1), consistent with E x B rotation. The electron density fluctuations show a negative skewness in the closed field-line pedestal region, consistent with the presence of `holes', followed by a transition to strong positive skewness across the separatrix and into the SOL. These simulations indicate that not only neoclassical phenomena, but also turbulence, including the blob-generation mechanism, can remain important in the steep H-mode pedestal and SOL. Qualitative comparisons will be made to experimental observations.

关键词： pedestal turbulence blobs

来源：评论

学校读者我要写书评

暂无评论

Data storage in Big Data Context: A Survey 3

Data storage in Big Data Context: A Survey

引用

3rd International Conference on Systems of Collaboration (SysCo)

作者： ELomari, A. Maizate, A. Hassouni, L. Univ Hassan 2 RITM ESTC CED ENSEM Km 7Eljadida StBP 8012 Oasis Casablanca Morocco

ISBN: (纸本)9781509049264

As data volumes to be processed in all domains;scientific, professional, social ...etc., are increasing at a high speed, their management and storage raises more and more challenges. The emergence of highly scalable infrastructures has contributed to the evolution of storage management technologies. However, numerous problems have emerged such as consistency and availability of data, scalability of environments or yet the competitive access to data. The objective of this paper is to review, discuss and compare the main characteristics of some major technological orientations existing on the market, such as Google File System (GFS) and IBM General Parallel File System (GPFS) or yet on the open source systems such as Hadoop Distributed File System (HDFS), blobseer and Andrew File System (AFS), in order to understand the needs and constraints that led to these orientations. For each case, we will discuss a set of major problems of big data storage management, and how they were addressed in order to provide the best storage services.

关键词： Big Data Data Storage blobs HDFS GFS AFS GPFS blobseer

来源：评论

学校读者我要写书评

暂无评论

Engineering estimates of impurity fluxes on the ITER port plugs

引用

NUCLEAR FUSION 2016年第10期56卷

作者： Kotov, Vladislav Forschungszentrum Julich Inst Energie & Klimaforsch Plasmaphys Partner Trilateral Euregio Cluster TEC D-52425 Julich Germany

Predictions of impurity fluxes are required for design analysis of the ITER optical diagnostics. In the present paper a simplified model is proposed for calculation of the neutral impurity fluxes on the recessed surfaces which are not in direct contact with plasma. The method is based on the Monte-Carlo simulation of the neutral particles transport in prescribed and fixed plasma background. The plasma parameters are projected from experimental observations, scalings and ITER modelling results. blobs are approximated as stationary hot species. Results of 2D simulations with toroidally uniform wall and of the '2.5D model' are presented. In this latter the 3D geometry of ports is implemented, but details of the incident ion flux distribution on the first wall panels are neglected. The calculated worst case gross deposition rate of Be in the middle of the port plug faces reaches almost 0.1 nm s(-1). At the same time, the obtained Be erosion to deposition ratio at those locations is always larger than 5, indicating high probability of net erosion conditions there.

关键词： ITER first wall port-plug blobs erosion impurity deposition

来源：评论

学校读者我要写书评

暂无评论

The structure and poloidal dynamics of blob filaments in TJ-K

引用

PLASMA PHYSICS AND CONTROLLED FUSION 2016年第4期58卷

作者： Garland, S. Fuchert, G. Ramisch, M. Hirth, T. Univ Stuttgart Inst Interfacial Proc Engn & Plasma Technol D-70569 Stuttgart Germany Max Planck Inst Plasma Phys Boltzmannstr 2 D-85748 Garching Germany

Relatively dense, field-aligned, filament-like structures (blobs) have been observed to propagate radially and poloidally through the scrape-off layer (SOL) in magnetically confined fusion plasmas, and contribute significantly to SOL transport. A detailed understanding of blob structure and dynamics, and their dependence on magnetic field geometry, is important in magnetic confinement physics for the prediction of heat loads on reactor wall facing components, as well as for understanding plasma confinement and neutral particle recycling. Experimentally deduced centre of mass poloidal blob velocity components, obtained using the conditional averaging technique, have been compared to an analytical blob model which has been simplified to express blob velocity in terms of the magnetic field curvature vector. Background flows are not incorporated into the analytical model, and must be added in to obtain good agreement with the experimental data. In addition, the 3D structure of blobs in TJ-K has been investigated using the conditional average of density fluctuations in two toroidally separated poloidal planes. blobs are observed to be aligned to a flux tube near to the last closed flux surface, in the blob birth region. However at positions further along the blob trajectory, the structures do not deform according to the magnetic shear, rather they remain rigid, and retain their original form.

关键词： plasma physics magnetic confinement stellarator blobs filaments

来源：评论

学校读者我要写书评

暂无评论

Non-diffusive transport of suprathermal ions by intermittent turbulent structures

引用

PLASMA PHYSICS AND CONTROLLED FUSION 2016年第1期58卷

作者： Furno, I. Bovet, A. Fasoli, A. Gauthey, C. Gustafson, K. Ricci, P. van Milligen, B. Ph Ecole Polytech Fed Lausanne SPC CH-1015 Lausanne Switzerland CIEMAT Lab Nacl Fus E-28040 Madrid Spain

We report on recent experimental, numerical and theoretical investigations of suprathermal ion transport and turbulent plasma dynamics in TORPEX. TORPEX is a toroidal device in which field-aligned blobs are intermittently generated and propagate across a confining magnetic field. Suprathermal ions are locally injected using a miniaturized source and detected using gridded energy analyzers. We show evidence for subdiffusive and superdiffusive transport of suprathermal ions, using an unprecedented combination of uniquely resolved three-dimensional measurements and first-principles numerical simulation. We present time-resolved measurements of suprathermal ion current fluctuations, which exhibit a clear causality relation with blobs, as revealed by a transfer entropy method for the superdiffusive case. This link is further investigated by using a conditional sampling technique, which allows resolving the cross-field dynamics of both blobs and the suprathermal ion beam, revealing that suprathermal ions experiencing superdiffusive transport are associated with bursty displacement events, resulting in highly intermittent time traces. This work links observations usually inaccessible in fusion devices and astrophysical plasmas, namely energy resolved three-dimensional time-averaged measurements, with Eulerian time-resolved measurements, which are often the only accessible measurements in such systems.

关键词： TORPEX turbulence blobs suprathermal ions

来源：评论

学校读者我要写书评

暂无评论

Fluctuation statistics in the scrape-off layer of Alcator C-Mod

引用

PLASMA PHYSICS AND CONTROLLED FUSION 2016年第5期58卷

作者： Kube, R. Theodorsen, A. Garcia, O. E. LaBombard, B. Terry, J. L. UiT Arctic Univ Norway Dept Phys & Technol N-9037 Tromso Norway MIT Plasma Sci & Fus Ctr 77 Massachusetts Ave Cambridge MA 02139 USA

We study long time series of the ion saturation current and floating potential, sampled by Langmuir probes dwelled in the outboard mid-plane scrape-off layer and embedded in the lower divertor baffle of Alcator C-Mod. A series of ohmically heated L-mode plasma discharges is investigated with line-averaged plasma density ranging from (n) over bar (e)/n(G) = 0.15 to 0.42, where n(G) is the Greenwald density. All ion saturation current time series that are sampled in the far scrape-off layer are characterized by large-amplitude burst events. Coefficients of skewness and excess kurtosis of the time series obey a quadratic relationship and their histograms coincide partially upon proper normalization. Histograms of the ion saturation current time series are found to agree well with a prediction of a stochastic model for the particle density fluctuations in scrape-off layer plasmas. The distribution of the waiting times between successive large-amplitude burst events and of the burst amplitudes are approximately described by exponential distributions. The average waiting time and burst amplitude are found to vary weakly with the line-averaged plasma density. Conditional averaging reveals that the radial blob velocity, estimated from floating potential measurements, increases with the normalized burst amplitude in the outboard midplane scrape-off layer. For low density discharges, the conditionally averaged waveform of the floating potential associated with large amplitude bursts at the divertor probes has a dipolar shape. In detached divertor conditions the average waveform is random, indicating electrical disconnection of blobs from the sheaths at the divertor targets.

关键词： turbulence scrape-off layer blobs

来源：评论

学校读者我要写书评

暂无评论

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案：

请选择收藏分类：

通借通还

建议与咨询 留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案： 新增检索档案 确定 取消

请选择收藏分类： 新增自定义分类 确定 取消

通借通还

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

请选择保存的检索档案：

请选择收藏分类：